ANESTHESIA

Evaluating preanesthetic patients

Anesthesia for non-anesthesiologists

Turn the gas off—we’re done! Recovery from anesthesia

Mandatory preanesthetic evaluation:Helping to avoid anesthetic nightmares

IN THE REAL WORLD

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Anesthesia is an extremely com-mon procedure in veterinarypractice; nonetheless, it carries a

risk of morbidity and mortality. A pre-anesthetic evaluation helps practition-ers anticipate potential adverse eventsand proceed with the best course ofaction: address any abnormalities inadvance, refer the patient to a facilityequipped for high-risk patients, or evencancel the anesthetic procedure. A sys-tematic approach helps practitionersestablish baseline data and completelyassess risk factors.1

Patients undergoing anesthetic pro-cedures are subject to a number ofpotential risks, including hypotension,dysrhythmias, hypoxemia, and evendeath.1 To ensure that each patientreceives a complete diagnostic workupwith attention to all potential vari-ables, a systematic approach is best.Consistency eliminates confusion thatmay occur in busy hospitals withmultiple doctors using different pro-tocols, and it also promotes the estab-lishment of best practices. A standard-ized, systematic approach can alsoincrease clients’ respect when they seea procedure in place to ensure thesafety of their pets.

The most important goal of the pre-anesthetic examination is an accurateassessment of the patient’s health status.The evaluation answers three questions:

1. Is the patient in the best possiblecondition to undergo anesthesia?

2. Should the patient’s condition beimproved before the anestheticprocedure?

3. Does the patient’s health statusor concurrent medication influ-ence the anesthetic event, andshould the procedure therefore

be delayed or even canceled?The preanesthetic evaluation may

reveal reasons to delay, cancel, orreschedule a procedure until thepatient’s condition is optimal. In addi-tion to providing time for a patient’scondition to stabilize or improve, adelay also allows the practitioner timeto conduct additional testing to obtainmore information on the patient’shealth or, if necessary, to find a teamthat is better equipped to manage high-risk patients during anesthesia.

The importance of collecting base-line data should not be underestimat-ed. Charting trends over time is one ofthe best ways to facilitate early diagno-sis and treatment of disease, and inmany cases collecting the preoperativeblood sample may be the only oppor-tunity to obtain baseline clinical patho-logic data on a patient.

Evaluation and preparationA complete preanesthetic evaluationshould consider the medical history,physical examination findings, andlaboratory data. Because the patient’shealth status and disease history arecritical factors in determining theappropriate anesthetic protocol, evalu-ation involves more than performing abattery of tests. It requires using allavailable information to determine thesafest anesthesia method—or whetheranesthesia is appropriate.

Age, sex, and breed are highly im-portant elements to consider. Differentbreeds and sexes are predisposed todifferent conditions, such as dilatedcardiomyopathy in cocker spaniels andimmune-mediated disease in femaledogs. A thorough medical history is

likewise essential because it may revealprevious disease and anesthetic com-plications, concurrent medications,and other circumstances (such as arecent meal) that may affect the proce-dure. The veterinary team also needsto document preventive care treat-ments such as vaccinations, deworm-ing, parasite control, dental care, anddisease screening tests. If deficienciesin preventive care exist, they should becorrected before any elective proce-dures are performed.

All participating team membersshould be informed of every procedurebeing performed on the patient, alongwith any medical history that couldlead to an anesthetic complication.This ensures that the entire team hasreceived the same information, whichminimizes the chance of miscommuni-cation during the procedure.

EVALUATING PREANESTHETIC PATIENTS

Karen Faunt, DVM, MS, DACVIM (Small Animal)

Preanestheticassessment goals

The objectives of a preanestheticmedical assessment are to:

• decrease morbidity and mortalityduring and after surgery

• determine a patient’s healthstatus to minimize the risk ofadverse events

• increase the quality of care whiledecreasing cost

• promote a systematic andproblem-oriented approach tothe anesthetic procedure

• help earn clients’ trust byensuring their pets’ safety andwell-being

• provide baseline test results forfuture healthcare.

Cover photo of the Olathe Animal Hospital in Olathe, KS taken by Mark McDonald.

Evaluate: • history and drug therapy• bleeding disorders• hyper- and hypothermia• previous anesthesia problems• pre-existing organ compromise

Fractious pet: Goal is to immobilize, obtainblood sample, place intravenous catheter,and perform examination and patient evalua-tion immediately. Immobilizing agent shouldserve as premedication or induction agent.

Patient

Weight

Complete physical examina-tion, internal organ screen,CBC with differential

1.Capillaryrefill time

<2 sec = normal;proceed with exam.

2. Mucous

membrane color• Pink = normal; pro-

ceed with exam.• Abnormal color:

Evaluate hematocritand hemoglobin; ifnormal, proceedwith exam.

3. Heart auscultationIf normal, proceedwith exam.

4.Lung auscultation

5. Temperature

Evaluate femoralpulse rate andheart rate ratio• Ratio >0.95 = normal;

proceed with exam.• Ratio <0.95 = abnor-

mal; evaluate ECGand go to cardiacprotocol.

Evaluate pulse quality• If firm and steady,

proceed.• If abnormal, evaluate

ECG and go to car-diac protocol.

Murmur present

Young petsConsider congenitalheart problem orphysiologic murmur.

Mature petsSuspect acquiredcardiac disease.Evaluate cardiacfunction and pro-ceed to cardiacprotocol.

Perform exercisetolerance test.**Physiologic murmurshould resolve.

If ejection or systolicmurmur is present, con-sider stenosis or othercongenital cardiac ab-normality. Refer unlessemergency. If emergency,cautiously proceed witha cardiac protocol.

• Normal air move-ment: Proceed withexamination.

• Abnormal (nomovement,noncomplaint,dry/moist rates):Postpone if possi-ble and make diag-nosis; otherwisego to pulmonaryprotocol.

Proceed withexamination.

Proceed with pulmonaryprotocol.

Hypothermia(<99 F)Give warm 2.5%dextrose in 0.45%NaCl intravenouslyand warm pet. If noimprovement, post-pone anesthesia andlook for other cause.

Hyperthermia(>103 F)Check WBC count.If elevated, postponeanesthesia (if possi-ble). Otherwise, giveintravenous 0.9%NaCl and intra-venous cefazolinonly. Proceed toappropriate protocol.

Giant and other high-risk breedsGive acepromazine (0.025 mg/lb [maximum of1.5 mg] subcutaneously), butorphanol (0.1 to0.2 mg/lb [maximum of 5 mg] subcutaneously),and intravenous Normosol. If temperature doesnot change, postpone anesthesia and evaluatefor and treat underlying disease. If temperatureis normal, go to healthy pet protocol but do notuse additional premedications.

Abnormal heart rate values (awake patient)• Small dog: <100, >140• Medium dog: <80, >140• Large dog: <60, >100• Cat: <120, >160If the heart rate is less than above, perform ECG and go to car-diac protocol. With normal ECG, give an intramuscular injectionof glycopyrrolate 0.005 mg/lb (maximum of 0.4 mg) with premed-ications. If heart rate is greater than above and no glycopyrrolateor atropine has been given, evaluate ECG, go to cardiac proto-col and rule out reasons for tachycardia (pain, anxiety, shock).

Is the petobese?

Figure 1: Canine and Feline Anesthesia Physical Examination*

No

Yes

**Exercise tolerance testPerform ECG and immediately walk dog vigorouslyfor 10 minutes. Recheck ECG. Normal = heart rateincrease is less than 25% of pre-walk heart rateand returns to normal within five minutes.

*All protocols referenced in Figure 1 can be found in Novak W. Anesthesia for the Pet Practitioner. Portland, Ore: Banfield, 2003.

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ANESTHESIA IN THE REAL WORLD

Physical examinationPatients should also receive a thoroughphysical examination as part of thepreanesthetic evaluation. Findingsshould be recorded in the patient’smedical record. A detailed evaluationof the cardiovascular, pulmonary, andcentral nervous systems is vital becauseall anesthetic drugs depress cardiovas-cular and pulmonary function. Theliver and kidneys also require specificassessment because of their role inmetabolizing and eliminating anes-

thetic drugs. Any abnormal examina-tion findings should be resolved beforeanesthesia. The anesthetic protocolmay need to be adjusted to ensure thepatient’s safety.

Our hospitals use a five-stepapproach in conjunction with a physi-cal examination before any anestheticprocedure to assess major organ func-tion and the patient’s overall health(Figure 1):

1. Monitor capillary refill time,femoral pulse-to-heart-rate ratio,

pulse quality, and heart rate.These parameters are key to evalu-ating perfusion, and adequateperfusion is vital to a successfulanesthetic outcome.

2. Evaluate mucous membrane colorfor evidence of anemia, hyperemia(sepsis, hyperthermia, or poly-cythemia), icterus, or cyanosis.

3. Auscultate the heart. In youngpatients, a murmur may indicatea congenital heart abnormality,which can pose a considerable risk

Figure 2: Preanesthetic Blood Work Evaluation

Hct, Hgb, RBC count Platelets, clotting problems

WBC count MCV, MCH, MCHC**

• If Hct <25% and/or Hgb <10 g/dl, postponeor transfuse before surgery.

• If Hct >40% (cat) or >45%(dog),* see prerenal azotemia protocol.

• If other abnormalitiespresent, use appropriateprotocol. Give diphenhy-dramine at 1 mg/lb intra-muscularly (maximumdose 50 mg) 30 minutesbefore transfusion and donot use acepromazine premedication. Look forunderlying cause.

Confirm platelet abnormalityor clotting problem byreviewing blood smear andchecking BMBT and ACT.• Platelet count <125,000/µl

or von Willebrand’sdisease or other clottingdisorder present:Postpone or transfuse(use fresh frozen plasmaor fresh whole bloodbefore surgery).

• Platelet count <20,000/µl:Rule out blood parasites;postpone all electiveprocedures until plateletcount is normalized.

• WBC <4,000/µl: Reviewblood smear.

• If neutrophilia with leftshift present, postponesurgery and make diag-nosis. Otherwise seeabdominal protocol.

• If values are abnormal,check pet with pulseoximetry.

• If MCV low, check bileacids.

• Postpone surgery ifpossible. Select liverprotocol if suspectportosystemic shunt.

BUN/Creatinine

• Low: Check bile acids.Use liver protocol.

• High: See next step.

Check urinalysis.• Urine specific gravity

>1.020 (dog) and >1.030(cat): Rehydrate. Addressunderlying cause beforeproceeding. Considerprerenal azotemia.

• Urine specific gravity<1.020 (dog) and <1.030 (cat): Check other urinalysis parame-ters. Consider renaldisease and proceed to renal protocol.

*Pets living in higher elevations and some breeds such as greyhounds may have naturally occurring hematocrit elevations.**Normal adult vs. pediatric values will vary.

Source: Novak W. Anesthesia for the Pet Practitioner. Portland, Ore: Banfield, 2003.

• Elevated BUN andcreatinine: Palpatebladder. If obstructed,do urinalysis by cysto-centesis and proceed topostrenal protocol.

• BUN elevated and nor-mal creatinine: Considergastrointestinal bleeding.

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EVALUATING PREANESTHETIC PATIENTS

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ANESTHESIA IN THE REAL WORLD

of an adverse anesthetic event.Such patients should be consid-ered high-risk and undergo anes-thetic procedures only at a prac-tice equipped to address thesespecial needs. In adults, it is im-portant to know if abnormalitiesrepresent a new finding or whe-ther there is evidence of diseaseprogression or heart failure. Ifany complications exist, a cardiacworkup should be completedbefore anesthesia, if possible.

4. Auscultate the entire lung field toensure normal sounds, airflow,oxygenation, and ventilation.

5. Evaluate the patient for hypo- orhyperthermia. Both are important,and their cause must be identifiedand corrected before anesthesia.

This approach allows accurate evalu-ation of the patient’s condition andhelps detect abnormal findings. Whenproblems are recognized, an appropri-ate anesthetic protocol provides guide-lines for proceeding.

Laboratory dataIn order to evaluate the patient’s cur-rent health status, a complete bloodcount (CBC) and serum chemistry pro-file (including electrolytes) should beperformed during the 48 hours beforegeneral anesthesia. Laboratory data areespecially important in apparentlyhealthy patients to ensure that potentialproblems are uncovered. Depending onthe results, additional diagnostics maybe needed. Because sick patients’ condi-tion and laboratory values can change

Calcium ALT/Bilirubin/ALP Albumin/Total protein

• If elevated, look for renaldisease or neoplasia(lymphoma, perianaladenocarcinoma).Consider Addison’sdisease.

• If low, check albumin.• Proceed to cardiac

workup and performECG. If normal, proceedwith anesthesia.

Recheck new bloodsample in a few hours.If lipemia persists, evaluatediet and check for hypo-thyroidism, diabetes melli-tus, pancreatitis, andprimary hyperlipidemia.

• If elevated, evaluate forliver disease. If totalbilirubin <2.0 mg/dl,check bile acids andevaluate electrolytes.Consider radiographsand ultrasound.

• If electrolytes abnormal,treat as cardiac case.

• If liver disease present,avoid using aceproma-zine and proceed to liver protocol.

• If total protein <3.5 g/dl,look for cause.

• Give plasma if possible(administer diphen-hydramine at 1 mg/lb[maximum dose 50 mg]intramuscularly beforeinfusion; wait 30minutes).

• Remove acepromazinefrom premedication. If noother abnormalities, usehealthy pet protocol.

Potassium Glucose

• If high or low (suspectedor documented), verifysample value.

• Look for cause (checkrenal function and urinarytract for urethral blockageor ruptured bladder).

• Proceed to cardiac proto-col (perform ECG).

• If <100 mg/dl, look forcause. Start 2.5%dextrose in 0.45% NaClintravenously. Go tohealthy pet protocol.

• If >200 mg/dl, do serumfructosamine test andpostpone anesthesia.

• If serum fructosaminetest is elevated, usediabetic protocol tostabilize pet.

Lipemia

See lipemia protocol.

in just a few hours, the CBC and serumchemistry profile for these patientsshould be collected and evaluated justbefore the anesthetic procedure. Using asystematic diagnostic approach (Figure2, page 4) helps doctors appropriatelyand thoroughly address aberrant find-ings before anesthesia and thereby placethe patient in the best possible condi-tion to undergo the procedure.

Many compromised patients have

electrolyte abnormalities. Dependingon the underlying cause, abnormalitiesmay or may not be clinically significant.Again, abnormalities should be ad-dressed before anesthesia.

Lipemic blood samples may be seenif the patient has recently eaten or hasan underlying condition such as hypo-thyroidism, diabetes mellitus, pancre-atitis, or primary hyperlipidemia, andlipemia may interfere with some serum

chemistry profile results. If lipemia isdiscovered, a new blood sample shouldbe drawn after a few hours. If the sec-ond sample is also lipemic, furtherevaluation may be warranted. However,if anesthesia cannot be delayed, ananesthesia protocol without propofolis preferred because propofol can beassociated with seizure activity in gross-ly lipemic human patients.

This approach to evaluating pre-anesthetic patients helps determine thebest anesthesia protocol for the pet.Once premedications are administered,it is essential to reevaluate major organsystems using the five-step approachpreviously discussed; drugs can haveprofound effects on cardiovascular andpulmonary systems before induction.This reevaluation may change the pre-ferred anesthetic protocol or promptpostponement of anesthesia until fur-ther assessment can be performed.

ConclusionWhen preanesthetic evaluation revealsabnormalities, it is the practitioner’sresponsibility to appropriately addresseach one before proceeding. But whatexactly does this mean? There is nosimple answer; it depends on the situa-tion and the abnormality.

Ideally, the practitioner decideswhether further diagnostics or support-ive care is necessary. How long toadminister supportive care before theanesthetic procedure (minutes, hours,days, or weeks) is based on the practi-tioner’s assessment. In emergency situa-tions, the patient may be stabilized foronly a short time—as when there isonly enough time to administer shockfluids to optimize perfusion. On theother hand, elective procedures may bedelayed until the abnormalities areresolved or stabilized.

In all cases, the practitioner’s goal isto place the patient in the best condi-tion possible before the anesthetic pro-cedure or to decide that anesthesia isnot in the patient’s best interest. Thepatient’s condition on recovery shouldalways be as good as or better than itwas before anesthesia.

References1. Gaynor JS, Dunlop CI, Wagner AE, et al.

Complications and mortality associated withanesthesia in dogs and cats. J Am Anim HospAssoc 1999;35:13-17.

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EVALUATING PREANESTHETIC PATIENTS

Value of preanesthetic testing

All patients on wellness plans at Banfield, The Pet Hospital, are evaluated once ortwice annually with a CBC, serum chemistry analysis, and urinalysis. All patients arealso tested before anesthesia and during diagnostic evaluations, when indicated.

During the five-year period from January 2001 to December 2005, Banfield,The Pet Hospital practitioners performed approximately 700,000 anestheticprocedures that were accompanied by preanesthetic laboratory assessment inconjunction with a complete medical history and physical examination. Approxi-mately 65% of Pets had at least one value that was technically outside of thenormal range. However, only 17.5% of these Pets had one or more clinically rele-vant abnormal value(s). Banfield’s practice standards call for a careful review of allcase data for these Pets before deciding whether to proceed with anesthesia,repeat the blood work, or cancel the procedure.

A similar review of Banfield’s data published in the Banfield journal showedthat an overwhelming majority (99.9%) of the procedures were performed withoutdelay while others were postponed (0.1%). In some cases of apparently healthypets being admitted for elective surgery, preanesthetic testing led to the cancella-tion of surgery because of elevated BUN or creatinine levels (more than 1,300cases), anemia (more than 100 cases) or elevated hepatic enzyme activities.Conditions uncovered during preanesthetic screening include renal disease,anemia, pyometra, neoplasia, hepatopathy, and cardiac disease.

Frequency of top 10 clinically relevant abnormal laboratory results: Preanesthetic screens

FelineParameter Criterion for abnormality Percent*Platelets <150 or >550 x 103/µl 5.07%WBC <4 or >20 x 103/µl 4.89%Bilirubin >1 mg/dl 4.77%ALT >120 IU/L 4.11%MCV <35 or >50 fl 2.99%MCHC <25% or >38% 1.92%Creatinine >3 mg/dl 1.43%BUN <10 or >40 mg/dl 1.36%ALP >250 mg/dl 0.85%Globulin >5 g/dl (kittten) 0.84%

and >6 g/dl (adult)

CanineParameter Criterion for abnormality Percent*BUN <5 or >30 mg/dl 2.71%Bilirubin >1.5 mg/dl 2.65%MCHC <30% or >40% 2.51%Platelets <150 or >550 x 103/µl 2.10%ALP >400 mg/dl 1.92%MCV <55 or >75 fl 1.67%WBC <4 or >20 x 103/µl 1.40%ALT >200 IU/L (puppy) 1.32%

and >400 IU/L (adult) Globulin >5 g/dl 0.89%Creatinine >2 mg/dl 0.71%

* Note: Percent of Pets with blood values outside Banfield’s normal range.

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In any discussion of the basic princi-ples of successful anesthesia in gen-eral practice, two assumptions are in

order. The first is that practitioners arealready anesthetizing patients successful-ly on a routine basis and therefore havea good understanding of and comfortlevel with anesthetic drugs and combi-nations. The second is that these practi-tioners are looking for simple ways toimprove their existing protocols ratherthan desiring to make extensive changesor use completely new drugs. This articlewill make some simple recommenda-tions to answer a question these practi-tioners may be asking: “What can I doto make anesthesia safer?”

Don’t treat all patients alikeIn a busy practice it is easy to use stan-dard anesthesia and analgesia protocolsthat treat all patients alike. While it isimperative to perform a complete pre-operative evaluation and physical exam-ination on each patient, it is importantto treat all abnormalities detected indi-vidually. If you find a problem, youmust then ask yourself, “Does this pro-cedure really have to be done today?”Clients do have expectations aboutwhen a procedure will occur, but whenyou explain to them that you have theiranimal’s safety in mind, they will usuallyagree to further diagnostics so that theanimal can be safely anesthetized.

It is also wise to pay attention to that“little voice in your head” telling you thatsomething is not right with a patient. Weoften ignore that voice when we are in ahurry, often with bad results. Anesthesiais one of the areas where you can’t affordto be in a hurry but must always bethorough and attentive to detail.

If you have detected an abnormalityin the patient—for instance an abnormallab result or a slight heart murmur—how do you handle it? It may simply bea matter of deleting a drug (such as ace-promazine) from your usual regimen or

decreasing the dosage used. Let thepatient’s condition dictate the amountto give rather than always giving thesame dosage; this goes for premedica-tions and induction drugs as well asthe amount of inhalant used (i.e., thevaporizer setting).

The benefit of oxygenAs veterinarians we recognize the bene-fit of maintaining patients on oxygenwith inhalant anesthesia, but we oftenforget that preoxygenation can makeinduction safer by preventing the desat-uration that can occur immediately afterinduction. Use of a mask or flow-byoxygen (i.e., from anesthetic tubingplaced in front of the animal’s nose) forthree to five minutes before induction isindicated for any geriatric or sick pa-tient without cardiopulmonary reserves.Oxygen after extubation also increasespatient safety, especially if the patient isshivering (which increases metabolicrequirements) or has underlying cardiacdisease. Upper airway muscle relaxationseems to considerably impair breathingin some pets, especially brachycephalicdogs and cats. You can’t just extubatethem and walk away; they need to havesome flow-by oxygen until they areawake enough and able to maintain sat-uration. Respiratory depression causedby residual anesthetic drugs can be fatal;the patient may breathe well when stim-ulated, but when you leave it alone andit relaxes, hypoventilation recurs.

Premedication and induction: Are fewer drugs safer?Anesthesia induction is probably themost dangerous time for the patientbecause of the changes taking place inthe cardiopulmonary and central nerv-ous systems. Many veterinarians there-fore think that avoiding any premed-icants and masking with only one drugis safer than using multiple drugs.

However, this may not be the case; theamount of cardiopulmonary depressionproduced by high percentages of isoflu-rane or sevoflurane (which is requiredfor induction with no premedications)may overwhelm the patient. A morebalanced approach, such as using somepremedications or injectable drugs forintubation and to decrease the percentinhalant needed for maintenance, maybe smoother and safer. Wrestling with abig, healthy dog—or even a small, appre-hensive dog or cat—can cause the releaseof catecholamines, which can triggerarrhythmias or cardiovascular collapse.

Another way to make induction saferis to monitor the patient closely throughthis period. Consider attaching electro-cardiograph (ECG) leads and a bloodpressure cuff before induction. Not allpatients will tolerate this, but many will,especially if they have been premedicat-ed. If a problem occurs during induc-tion, you will see it immediately.

Maintenance: How much to use?Currently used inhalants such as isoflu-rane and sevoflurane allow rapid con-trol of the anesthetic plane, which helpsmake anesthesia safer. It is important,however, to understand that patients’inhalant requirements vary widely; forexample, the vaporizer setting shouldbe decreased with hypothermia, con-current illness, and other drugs. Thepatient must be closely monitored andthe vaporizer adjusted based on theindividual patient; guidelines aboutsetting the vaporizer at X percent forX minutes are just that: guidelines.

Some patients may not tolerate in-halants well, and the percent used mustbe kept very low: less than 1 minimumalveolar concentration (MAC) for theinhalant (1 MAC = 1.3% isoflurane and2.3% sevoflurane). In these cases analge-sia must be provided by giving otherdrugs, such as opioids, intermittently or

ANESTHESIA FORNON-ANESTHESIOLOGISTS

Nora S. Matthews, DVM, DACVA

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as a constant-rate infusion (CRI). Pre-loading the patient with intravenousfluids and using inotropic agents intra-operatively may also be necessary.

Some practitioners may be comfort-able with these more advanced tech-niques, but if not, they should referthese patients to a boarded anesthesiol-ogist for more advanced management.At Texas A&M, we have had patientsreferred for routine surgical proceduresbecause the anesthetic management ofthe case was not routine.

Monitoring: How much is enough?The purpose of monitoring is to alertthe anesthetist to problems before theybecome serious (i.e., before cardiacarrest occurs). This requires great vigi-lance as well as accurate interpretationof monitor readings. There are certain-ly anesthetists who can maintain andmonitor patients with no equipment,but in today’s litigious society, I wouldnot recommend this approach or con-sider it a reasonable standard of care. Itis also possible for a patient to be fullymonitored with a pulse oximeter, ECG,and blood pressure monitor and stillsuffer an anesthetic death. However,the well-monitored patient generallystands a better chance of not only surviv-ing under anesthesia, but of recoveringrapidly and feeling better postopera-tively. Monitoring heart and respiratoryrate, heart rhythm and depth of respi-ration, mucous membrane color, andcapillary refill time are basics. Bloodpressure is tremendously helpful inassessing depth of anesthesia, guidingfluid therapy, and allowing the use ofinotropic drugs such as dobutamine.In cases of anesthetic arrest, bloodpressure usually declines or is low for aperiod of time before the arrest occurs,therefore giving the practitioner awarning and time to react to the prob-lem. Since accurate, noninvasive bloodpressure monitors are now relativelyinexpensive, it seems logical to encour-age their use. Maintenance of adequateblood pressure (i.e., systolic blood pres-sure >90 mm of Hg and mean bloodpressure >60 mm of Hg) indicatesgood tissue perfusion and adequaterenal perfusion, which helps preventpostoperative renal failure. If practi-tioners are determined to improve their

standard of anesthesia, blood pressuremonitoring is the place to start.

Pulse oximeters and capnographs(which measure expired CO

2) can be

helpful in evaluating patient oxygena-tion, peripheral perfusion (SpO

2), and

ventilation (PaCO2), and I encourage

the use of these monitors as well.However, it is outside the scope of thisarticle to describe the indications andshortcomings of both, and many goodreferences exist.1

Disaster preparednessOf course, it doesn’t help to monitorthe patient if you aren’t prepared totreat the problems you encounter. It’sessential to have emergency drugsreadily available (and to check themfrequently for expiration dates) alongwith appropriately sized syringes andneedles. Dosing charts should be easyto read and allow rapid drug prepara-tion (e.g., they should be set up in 5-kgintervals rather than mg/kg, whichrequires calculation). Emergency drugcharts can be laminated and posted inall locations where they might beneeded. Another good option is to usean emergency drug calculator pro-gram, such as the one from the Colo-rado State University emergency andcritical care website (www.csuvets.colostate.edu), and to print an emer-gency drug sheet for each patient—orat least each high-risk patient.

Does fluid administrationhelp for routine anestheticprocedures?In my opinion, yes. Many if not mostpatients are dehydrated when they are

hospitalized and after food and waterhave been withheld for a number ofhours. Intravenous fluids have theadvantage of requiring an intravenouscatheter (which is a safety factor initself), and they rapidly expand the vas-cular space, which helps improve tissueand renal perfusion. Especially whennonsteroidal anti-inflammatory drugs(NSAIDs) are used perioperatively, fluidsmay help prevent renal compromise.Crystalloids, such as lactated Ringer’ssolution, can be given at 10 ml/kg/hrunless the patient cannot tolerate thisfluid volume (e.g., the patient with car-diac disease that is prone to pulmonaryedema). Since crystalloids don’t remainin the intravascular space very long, useof a colloid such as hetastarch, blood, orplasma may be required for patients thatare anemic, hypoproteinemic, or notresponding to treatment of hypovolemiawith crystalloids alone.

There is evidence in people thatpatients given fluids during short proce-dures feel better and experience lessnausea and headaches than those whodon’t get fluids.2 Unfortunately, we can’task our patients about this, but it seemslikely that it would be true for them aswell. Subcutaneous fluids are better thannone if this is the only route available.

Take-home thoughtsIn summary, I think it is possible toimprove anesthetic management ofpatients without radically changingprotocols and procedures by payingclose attention to important basics.Make sure you have evaluated thepatient thoroughly before anesthesia,tailor the anesthetic protocol for thatparticular patient, and be prepared forexpected and unexpected problems.Careful monitoring and patientsupport (attention to oxygenation,fluid therapy, patient comfort, andsupport of body temperature duringand after anesthesia) are key ingredi-ents in safe anesthesia.

References1. Hartsfield SM. Equipment and monitor-

ing. In: Tranquilli WJ, Thurmon JC, Benson GJ,eds. Essentials of small animal anesthesia andanalgesia. Philadelphia, Pa: Lippincott Williamsand Wilkins, 1999.

2. Maharaj CH, Kallam SR, Malik A, et al.Preoperative intravenous fluid therapy decreas-es postoperative nausea and pain in high riskpatients. Anesth Analg 2005;100:675-682.

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“The purpose of monitoringis to alert theanesthetist to problemsbefore theybecome serious.”

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Did you know that most adverseevents associated with anesthesiaoccur during recovery? That’s

right; of the three anesthetic periods—induction, maintenance, and recovery—the recovery period is often the mostcritical. Why? Many factors can play arole: the unrecognized residual effects ofanesthetic agents, the termination ofoxygen and fluid support, and, perhapsmost importantly, a lack of monitoringor personnel.

In anesthetized people, one studyfound a 26% overall complication ratewhen intraoperative and postoperativecomplications were combined. Of the26%, only 3% occurred intraopera-tively and 23% occurred in recovery.1

Contrary to what might be expected,these complications did not occurprimarily in severely compromisedpatients but in patients only mildly tomoderately compromised (AmericanSociety of Anesthesiologists classifica-tion ASA II to ASA III—Table 1).1

Unfortunately, without a thoroughphysical examination and appropriatechemistry and ancillary tests (e.g., anelectrocardiogram or thoracic radi-ographs) before induction, mild dis-ease that might change an ASA Ipatient to an ASA II or III can be easilyoverlooked. This oversight can putpatients at extreme risk for postanes-thetic complications.

The most common complications inanesthetized people include respiratorycompromise (15.2%), cardiovascularabnormalities (12.3%), and excessivepain (7.2%).2 Respiratory complicationsinclude general respiratory depression,upper airway dysfunction, apnea, andhypoxemia-hypercarbia, while cardio-vascular complications include hypo-tension and arrhythmias. One veteri-nary study from a major referral centerreported an overall anesthetic compli-cation rate of 12% in dogs and 10.5%in cats, with respiratory and cardiovas-

cular complications most common.3 Ina Canadian study, the most commoncauses of anesthetic complications indogs and cats were respiratory and car-diovascular dysfunction, and complica-tions occurred in both the maintenanceand recovery phases of anesthesia.4 Anda British study of anesthetic risk insmall animals found that 25% of allfatalities occurred postoperatively.5

Since mammals are affected similarly byanesthetic drugs, it is not surprisingthat postanesthetic complications inveterinary patients are similar to thosein people.

In addition, hypothermia should beconsidered in veterinary patients. Be-cause of the rapid heat loss associatedwith a small body mass and large bodysurface area, veterinary patients oftenbecome hypothermic under anesthesia.Hypothermia can cause a wide array ofside effects and should be preventedwhen possible.

Optimally, postoperative complica-tions can be minimized by thoroughpreoperative assessment and stabiliza-tion and appropriate intraoperativemanagement and support. However,attentive monitoring and support wellinto the recovery period is imperativefor a successful anesthetic outcome.Although young, healthy patients mayrecover rapidly with a minimumamount of support required, aged andcompromised patients may recoverslowly and require an extended moni-toring period (Table 2). Regardless ofthe duration, patients should be moni-tored until they are fully recovered fromanesthesia. After anesthesia, sleep fromsedatives and analgesics is acceptable,but residual anesthesia is not. The dif-ference is that patients still anesthetizedare not rousable when stimulated, whilepatients that are sleeping comfortablydue to analgesia and light sedation arerousable with stimulation.

TURN THE GAS OFF—WE’RE DONE!RECOVERY FROM ANESTHESIA

Tamara Grubb, DVM, MS, DACVA

Uniontown, Wash.

Table 1: American Society of Anesthesiologists classification of patients undergoing anesthesia

ASA I: A normal, healthy patientASA II: A patient with mild systemic disease (compensated cardiac disease,

mild fever)ASA III: A patient with severe systemic disease (moderate dehydration,

anemia, cachexia, hypovolemia)ASA IV: A patient with severe systemic disease that is life-threateningASA V: A patient not expected to live

Table 2: Monitoring recommendations for the recovery period

Heart rate and rhythmPulse strength Mucous membrane color and capillary refill timeRespiratory rate, rhythm, and depth (using thoracic excursions as a guide)Core body temperatureECGBlood pressure (e.g., using oscillometric or Doppler methods)Pulse oximetry (if possible)End-tidal CO

2or arterial blood gases (in select cases)

Urinary output (in select cases)Blood glucose and serum electrolytes (in select cases)

Respiratory complicationsAll anesthetic agents cause some degreeof dose-dependent respiratory depres-sion (both depression of respiratoryrate and tidal volume), and this depres-sion is not eliminated when the vapor-izer is turned off. Instead, residualdepression lasts well into the recoveryperiod and, when unrecognized, is oneof the major contributors to postanes-thetic morbidity and mortality. Fur-thermore, both upper and lower airwaydysfunction occur in recovery, andeither condition can lead to hypoxemiaand hypercarbia.

Upper airway complications includelaryngeal dysfunction, paralysis, edema,and collapse of the soft palate or othertissues into the airway. Brachycephalicpatients and patients who have sufferedtraumatic intubation are likely to expe-rience postoperative upper airway dys-function. All patients should be leftintubated until they are swallowingvigorously, and patients with suspectedupper airway dysfunction shouldremain intubated until they will nolonger tolerate the endotracheal tube.Patients should not be excessively stim-ulated for extubation. Excessive stimu-lation may rouse the patient enough toallow extubation but not enough toensure adequate ventilation. Lower air-way dysfunction includes atelectasis andventilation-perfusion mismatch, both ofwhich can contribute to impaired venti-latory function. Airway disease, age, and

anesthesia of long duration all con-tribute to lower airway dysfunction.

In order to prevent respiratory com-plications, patients should be closelymonitored during recovery. Respiratoryrate and volume (as judged by thoracicexcursions) and mucous membranecolor should be assessed routinely. Aspeople transition from 100% oxygenduring anesthesia to 21% oxygen afteranesthesia, hemoglobin in the redblood cells (RBCs) rapidly desaturates,6

and we can assume that the same phe-nomenon also occurs in veterinarypatients. Pulse oximetery may be usefulduring recovery to detect RBC desatu-ration, and supplemental oxygenshould be provided if desaturation isexpected or suspected. Oxygen can bedelivered through the endotracheal tubeor through a nasal cannula if thepatient is already extubated.

Cardiovascular complicationsHypotension and arrhythmias are anes-thetic complications that can occur inboth human and veterinary patients.Hypertension may also occur in people,but it is rarely a problem in veterinarymedicine unless linked to a specificcause (e.g., pain or a hypertensive dis-ease, such as hyperthyroidism). Mostanesthetic agents, including inhalantagents, cause a dose-dependent decreasein systemic arterial blood pressurethrough a variety of mechanisms

(Table 3). As with anesthetic-inducedrespiratory depression, anesthetic-induced cardiovascular depression isnot eliminated when the vaporizer isturned off; instead, function improvesover time. In veterinary medicine,blood pressure is not routinely meas-ured in the recovery period, so we areunsure of the incidence of hypotensionin dogs recovering from anesthesia.However, since most of the commonlyused anesthetic drugs cause hypoten-sion, we should expect residual hypo-tension to occur in our patients duringthe recovery period.

Arrhythmias may occur secondary toa whole array of anesthesia-related fac-tors, including the arrhythmogeniceffects of the drugs themselves, hypoxia,and hypercarbia. As with hypotension,cardiac arrhythmias may occur moreoften than we recognize. In a study ofhealthy dogs anesthetized with eitherisoflurane or propofol, arrhythmiasoccurred in the first 24 hours after anes-thesia in 56 out of 60 dogs, althoughthe overall number of arrhythmias perpatient was low.7

To detect cardiovascular complica-tions, both blood pressure and electro-cardiogram (ECG) monitoring shouldcontinue well into the recovery periodwhenever possible. Intravenous fluidtherapy should be continued in hypo-volemic and hypotensive patients, andpositive inotropic agents such asdopamine or dobutamine should be

10

RECOVERY FROM ANESTHESIA

Table 3: Cardiovascular effects of commonly used anesthetic drugs

Cardiovascular component affected Drug(s) Effect

Heart rate Ketamine, tiletamine Increased rate

Propofol, alpha-2 agonists Decreased rate

Contractility Inhalant anesthetic agents, Decreased contractilitypropofol, thiobarbiturates

Ketamine, tiletamine Indirect increase in contractility(direct decrease in contractility)

Preload Acepromazine, isoflurane, Vasodilators = decreased preload sevoflurane (decreased cardiac return)

Afterload Alpha-2 agonists, halothane, Vacoconstriction = increased afterloadketamine, tiletamine

Relaxation Ketamine, halothane Impaired relaxation

11

ANESTHESIA IN THE REAL WORLD

available for patients in which hypoten-sion persists despite appropriate fluidtherapy. Specific antiarrhythmic thera-py should also be available to treatarrhythmias that develop. Drugs usedto treat hypotension and arrhythmiashave been reviewed elsewhere.8

Uncontrolled pain, stress,and excitementUncontrolled pain in recovery is aproblem in both veterinary and humanpatients.9-11 Unfortunately, uncontrolledpain can become a pathology in itself,producing such adverse effects astachycardia, hypertension, tachypnea,gastric ulcerations, ileus, decreasedrenal function, catabolism, alteredhemostasis, and impaired woundhealing.12 Furthermore, pain can cause

excitement as the patient regains con-sciousness, resulting in a turbulentrecovery.13 In fact, it can be difficult todifferentiate the effects of pain from“emergence delirium” caused by theanesthetic drugs themselves. Fortu-nately, differentiation really isn’t neces-sary since excitement, regardless of thecause, is not appropriate in the recoveryperiod. Excitement with subsequentphysiologic stress can lead to respirato-ry and hemodynamic compromise, andall forms of stress should be treated.14-15

Drugs that provide both sedationand analgesia should be considered.Options in this category include opi-oids and alpha-2 agonists. Opioids areoften the first choice because of theiranalgesic potency. However, if opioidtherapy is already being used and the

patient remains painful, alpha-2 ago-nists should be considered. These drugsaugment the analgesia provided byopioids and decrease the anesthesia-induced stress response. Alpha-2 ago-nists are often used in human medicineto control excitement and pain follow-ing recovery from anesthesia.15 If painpersists after initial treatment, otherpossible analgesic protocols includelocal anesthetic blockade and constantrate infusions. See the drug recommen-dations and dosages in Table 4.

Appropriate use of analgesic drugsin the preoperative and intraoperativeperiod will decrease pain in recovery;16

however, breakthrough pain oftenoccurs. Thus, regardless of the use ofpreemptive or intraoperative analge-sia, pain should still be anticipated,

Table 4: Analgesic drug dosages commonly used during anesthetic recovery*

Drug Class Dosage Comments

Morphine Opioid, full agonist 0.25 to 2.0 mg/kg IM, SQ in dogs; Potent opioid, may cause0.1 to 0.3 mg/kg IM, SQ in cats excitement in cats

Morphine Opioid, full agonist 0.05 to 0.2 mg/kg/hr in dogs Run as constant (use sedation in cats) rate infusion (CRI)

Hydromorphone Opioid, full agonist 0.05 to 0.2 mg/kg IM, SQ, IV Potent opioid, may causein dogs and cats hyperthermia in cats

Hydromorphone Opioid, full agonist 0.05 to 0.1 mg/kg/hr in dogs; Run as CRI 0.01 to 0.05 mg/kg/hr in cats

Fentanyl Opioid, full agonist 5 to 20 µg/kg/hr in dogs Potent opioid, short duration,and cats run as CRI

Buprenorphine Opioid, partial agonist 0.01 to 0.03 mg/kg IM, SQ, IV in Long-lasting analgesia,dogs and cats; buccally in cats minimal sedation

Butorphanol Opioid, 0.2 to 0.4 mg/kg IM, SQ, IV Short-lasting analgesia,agonist-antagonist in dogs and cats mild sedation

Medetomidine Alpha-2 agonist 1 to 5 µg/kg IV, IM, SQ in Moderate analgesia,dogs and cats moderate sedation

Ketamine NMDA-receptor 2 to 10 µg/kg/min in dogs Run as CRI with aantagonist and cats true analgesic agent

Lidocaine Local anesthetic agent 2 to 4 mg/kg local block in May need to sedate dogs and cats patient to perform block

Lidocaine Local anesthetic agent 25 µg/kg/min Run as CRI

Bupiviacaine Local anesthetic agent 1 to 2 mg/kg local block in May need to sedate patientdogs and cats to perform block. Do not give IV.

Carprofen, NSAIDs See individual drug Other NSAIDs are not FDA-approvedderacoxib recommendations for surgical pain in dogs

*Not all of the drugs or dosages referenced are approved by the FDA. Please check drug labels or www.fda.gov/cvm for more information on individual drugs.

and all patients should be assessed forpain in recovery.

HypothermiaHypothermia develops rapidly inpatients under anesthesia, and the causeof the drop in body temperature is mul-tifactorial. Some contributing factorsinclude direct suppression of thermo-regulatory activity of the hypothalamusby general anesthesia; anesthesia-induced vasodilation, which redistrib-utes warm blood from the body’s coreto the skin where heat is released; evap-oration of surgical scrub solutions fromthe body surface; equilibration of corebody temperature with ambient temper-ature through open body cavities; deliv-ery of cold anesthetic gases to the largesurface area of the alveoli; and conduc-tion of heat to the metal table.

Hypothermia causes a variety ofcomplications, including clotting dys-function, increased risk of infection, tis-sue hypoxia, acidosis, abnormal electri-cal conduction in the heart, and myo-cardial ischemia.17 Hypothermia alsocauses cerebral effects that decrease thepatient’s anesthetic needs. Unfortunate-ly, the decreased anesthetic need is notalways recognized and anesthesia deliv-ery is not changed, resulting in an anes-thetic overdose. Although shivering inrecovery may increase the body temper-ature, the intensive muscle movementsassociated with shivering cause discom-

fort and increase oxygen consumptionby as much as 200%.18 In fact, in humanmedicine, one area of research focus isprevention of shivering in the postopera-tive period. Finally—and importantly—hypothermia is the main cause ofprolonged recovery in small animalpatients. Listed in Table 5 are some ofthe problems that arise as core bodytemperature decreases.19

Prevention of hypothermia should bethe goal for all patients, and activerewarming should begin immediatelyonce hypothermia has occurred. Forcedair blankets have been shown to be themost effective means of rewarming.20

Increasing ambient temperature alsocontributes significantly to warming.This can involve everything from heat-ing an entire room to creating a warmedarea around the patient using hot waterbottles or sand bags with a blanketcovering the patient and the warmingdevices. As always, insulation should beplaced between heated items and thepatients so that the skin is not burned.

SummaryUnfortunately, the importance of theanesthetic recovery period is often over-looked even though most unexpectedanesthetic deaths occur during recovery.Common complications include hypo-ventilation, hypotension, hypothermia,and excessive pain. For a successfulanesthetic outcome, appropriate moni-

toring and patient support must occurwell into the recovery period.

References1. Tarrac SE. A description of intraoperative

and postanesthesia complication rates. J PerianesNursing 2006;21(2):88-96.

2. Mayson KV, Beestra JE, Choi PT. The inci-dence of postoperative complications in thePACU. Can J Anesth 2005;52(S1):A62.

3. Gaynor JS, Dunlop CI, Wagner AE, et al.Complications and mortality associated withanesthesia in dogs and cats. J Am Anim HospAssoc 1999;35:13-17.

4. Dyson DH, Maxie GM, Schnurr D.Morbidity and mortality associated with anes-thetic management in small animal veterinarypractice in Ontario. J Am Anim Hosp Assoc1998;34:325-335.

5. Clarke KW, Hall LW. A survey of anaesthe-sia in small animal practice. J Assoc Vet Anaesthe-siol 1990;17:4-10.

6. Daley MD, Norman PH, Colmenares ME,et al. Hypoxaemia in adults in the post-anaesthe-sia care unit. Can J Anaesth 1991;38(6):740-746.

7. Buhl K, Kersten U, Kramer S, et al.Incidence of post-anaesthetic arrhythmias indogs. J Small Anim Pract 2005;46(3):131-138.

8. Laste NJ. Cardiovascular pharmacothera-py. Hemodynamic drugs and antiarrhythmicagents. Vet Clin Nort Am Small Anim Pract 2001;31(6):1231-1252.

9. Hellyer PW. Treatment of pain in dogs andcats. J Am Vet Med Assoc 2002;221(2):212-215.

10. Kehlet H, Dahl JB. Anaesthesia, surgery,and challenges in postoperative recovery. Lancet2003;362(9399):1921-1928.

11. Skinner HB. Multimodal acute painmanagement. Am J Orthop 2004;33(5S):5-9.

12. Middleton C. Understanding the physio-logical effects of unrelieved pain. Nurs Times2003;99(37):28-31.

13. Vaurio LE, Sands LP, Wang Y, et al.Postoperative delirium: The importance of painand pain management. Anesth Analg 2006;102:1267-1273.

14. Manworren RC, Paulos CL, Pop R.Treating children for acute agitation in thePACU: differentiating pain and emergence deliri-um. J Perianesth Nurs 2004;19(3):183-193.

15. Pandharipande P, Ely EW, Maze M.Alpha-2 agonists: can they modify the outcomesin the Postanesthesia Care Unit? Curr DrugTargets 2005;6(7):749-754.

16. Lascelles BD, Cripps PJ, Jones A, et al.Efficacy and kinetics of carprofen, administeredpreoperatively or postoperatively, for the preven-tion of pain in dogs undergoing ovariohysterec-tomy. Vet Surg 1998;27(6):568-582.

17. Noble KA. Chill can kill. J PerianesNursing 2006;21(3):204-207.

18. Sessler DI. Temperature disturbances.In: Gregory GA, ed. Pediatric anesthesia, 4th ed.Philadelphia, Pa: Churchill Livingstone, 2002;53-69.

19. Haskins SC. Operating room emergen-cies. In, Slatter D., ed. Small animal surgery, 3rdedition. Philadelphia: Saunders, 2003;2521-2532.

20. Good KK, Verble JA, Secrest J, et al.Postoperative hypothermia—the chilling conse-quences. AORN J 2006;83(5):1055-1066.

12

RECOVERY FROM ANESTHESIA

Table 5: Effects of hypothermia

Some of the problems that can arise when an animal’s core body temperaturedecreases are as follows:*

• >96 F—no adverse effects from hypothermia. Shivering and nonshiveringthermogenesis increase in conscious patients.

• 90 to 94 F—cerebral depression with reduced anesthetic requirements,prolonged anesthetic recovery. Shivering is impaired in conscious patients.Note: Animals often get this cold during anesthesia. Anesthetic gas deliveryshould be decreased, but this is often overlooked.

• 82 to 86 F—marked cerebral depression with little or no anesthetic required.Atrial arrhythmias occur; shivering is nonexistent in conscious patients.

• 77 to 80 F—cold-induced ECG changes (prolonged P-R interval, widenedQRS) and increased myocardial automaticity occur. Oxygen delivery is usual-ly inadequate (due to extreme vasoconstriction) and lactic acidosis occurs,normal reflexes and pain responses are absent, blood viscosity is increased,and microcirculatory sludging occurs.

• 72 to 74 F—spontaneous ventilation ceases, ventricular fibrillation and coag-ulation disorders occur.

• <68 F—asystole and ECG silence occur.

* Haskins SC. Operating room emergencies. In: Slatter D, ed. Small animal surgery, 3rdedition. Philadelphia: Saunders, 2003;2521-2532.

13

While statistically rare,adverse anesthetic eventscan be disastrous in veteri-

nary practice. Many variables canaffect the outcome of an anestheticprocedure, including individualpatient characteristics, the anestheticagents being used, the anesthetist incharge, and the procedure beingperformed. Veterinary patients pose a greater anesthetic challenge thantheir human counterparts because ofweight and breed variables, clients’monetary limitations, and often theabsence of a comprehensive anesthet-ic history. A thorough preanestheticevaluation aids in the identificationof pre-existing conditions, whichimproves anesthetic safety and alsoprovides invaluable baseline data forfuture diagnostic use. Beyond thenumerous medical benefits, offering acomprehensive preanesthetic evalua-tion that includes diagnostic testingcan protect your practice from liabili-ty issues and help to prevent anes-thetic nightmares.

Improved preanestheticpatient care A comprehensive preanesthetic evalua-tion that includes laboratory profilingallows for a thorough evaluation oforgan systems, including the hemato-poietic, renal, hepatic, and endocrinesystems. Proper interpretation fre-quently involves assessing individualtest results in relation to others—forexample, evaluating calcium levels inlight of albumin levels or amylaselevels with regard to renal function.Hematology is a critical part of thepreanesthetic evaluation because ithelps identify anemia, polycythemia,leukopenia, leukocytosis, and throm-bocytopenia, all of which may con-tribute to adverse anesthetic events.1

Pre-existing renal or hepatic disease

may interfere with anesthetic metabo-lism and excretion, especially in anes-thetics requiring biotransformation forelimination. Undetected hypoglycemiamay result in serious cerebral dysfunc-tion and death. Electrolyte abnormali-ties such as hyperkalemia may predis-pose the patient to life-threateningcardiac arrhythmias.

A policy of mandatory preanestheticevaluation and testing helps eliminateclient confusion because no additionalforms or signatures are required. Italso communicates a consistent mes-sage that the practice believes this kindof evaluation is critical. Moreover,

mandatory preanesthetic evaluationcreates a simplified workflow in the vet-erinary hospital, from the front office totechnicians to veterinarians. A standard-ized policy eliminates confusion andprocedural variation, which minimizestechnical and billing errors. Mandatorypreanesthetic evaluation including diag-nostic testing is becoming the standardof care in our profession.

It is still crucial that the veterinary

team educate clients about the risks ofanesthesia and the surgical procedure,as well as the safety benefits of thor-ough patient evaluation, testing, andmonitoring. Remind clients that thereis no such thing as a “routine” surgeryand that every precaution will betaken to ensure their pet’s safety.During discharge, review the preanes-thetic blood work with the client andemphasize the importance and med-ical significance of normal findings.Sharing the test results not only addsvalue but also emphasizes your hospi-tal’s high level of care and commit-ment to its clients and patients.Encourage clients to maintain petrecords, including blood work, whichcan later serve as important baselinedata should their pet become ill.Emphasize that your practice and theclient are partners in caring for pets.

Risk vs. benefit The cost of preanesthetic evaluation andtesting must be weighed against thebenefits. In a recent preanesthetic-profiling study of approximately 700,000patients, 65% of patients had at least onevalue that was outside the normal range.However, only 17.5% of these patientshad one or more clinically relevantabnormal value(s).2 (See Value of pre-anesthetic testing, page 6, for more infor-mation on this study and the relativeincidence of various preanesthetic abnor-malities.) Preanesthetic testing included acomplete blood count (CBC) and a 12-test serum chemistry profile. Electrolyteswere not part of the preanesthetic pro-tocol, which undoubtedly would haveincreased the percentage of patients withresults deviating from the referencerange. Not every abnormality signifi-cantly affects anesthesia or surgery; how-ever, factors such as hematocrit, plateletcount, and creatinine can significantlyaffect patient recovery and survival.

MANDATORY PREANESTHETICEVALUATION: HELPING TO AVOIDANESTHETIC NIGHTMARES

Fred Metzger, DVM, DABVP

“Mandatorypreanestheticevaluationincludingdiagnostictesting isbecoming thestandard of care in ourprofession.”

The following case illustrates thevalue of preanesthetic testing.

A case of mandatory evaluation Ruca, a 6-month-old chocolateLabrador retriever, was presented atMetzger Animal Hospital for a routineovariohysterectomy. The client wasinformed that preanesthetic diagnostic

testing would be performed and wasincluded in the cost of the procedure.Unfortunately, the results revealedevidence of kidney failure (see Patientcase history). The blood work wasrepeated and an abdominal ultrasoundwas performed, which confirmed thepresence of kidney abnormalities thatwere likely congenital. The patient’sprognosis was poor to grave.

The client was devastated, but she ex-pressed appreciation that the conditionhad been diagnosed. She was able to takeRuca home and make her as comfortableas possible in her remaining weeks.

Summary Ruca’s case emphasizes the value ofpreanesthetic evaluation and testing—anesthesia could have resulted in many

14

MANDATORY PREANESTHETIC EVALUATION

History of preanestheticevaluation atMetzger AnimalHospital

Hematology profileRBC 5.73 M/µL (5.50 to 8.50) HCT 35.7% Low (37.0 to 55.0)HGB 11.9 g/dL Low (12.0 to 18.0) MCV 70 fL (60 to 77) MCH 24.2 pg (19.5 to 26.0)MCHC 33.3 g/dL (32 to 36) WBC 11.4 K/µL (5.70 to 16.30) Neutrophil 8.40 K/µL (3.00 to 11.50) Band 0.0 K/µL (0.00 to 0.30) Lymphocyte 1.80 K/µL (1.00 to 4.80) Monocyte 1.20 K/µL (0.15 to 1.35) Eosinophil 0.0 K/µL (0.10 to 1.25) Platelets 333 K/µL (164 to 510)

Erythron: Mild nonregenerative anemia (normocytic, normochromic,and lack of reticulocytosis) Leukon: Normal Thrombon: Normal

Patient case history

Patient name: Ruca Patient data: 6-month-old femalechocolate Labrador retriever Presenting reason: Routine ovario-hysterectomy History: Normal, active puppy Physical examination findings:Patient is alert with normal temper-ature, and auscultation of the chestreveals no murmurs or abnormallung sounds. Plan: Preanesthetic blood work andurinalysis before surgery

For more information about Ruca’s case, visit the website created by Ruca’s owner, Mel Fox: www.personal.psu.edu/users/m/k/mkr127/tribute.htm

Preanesthetic profiling of young patients was a new concept in the 1980sand became more com-mon in the late 1990s. To overcome compliancechallenges, doctors atMetzger Animal Hospitaldeveloped a client con-sent form for preanesthet-ic testing in 1996. Clientswould choose from amongthree health screeningoptions based on theirpet’s age and healthstatus and then sign theform, which resulted incompliance of approxi-mately 65% to 70%.

In 1997, complianceincreased to more than80% after the hospitalstarted mailing the formto the client’s homebefore the scheduledsurgery. In 1998, doctorsinstituted mandatorypreanesthetic testing forall surgical and dentalprocedures. Tests includea complete blood count,serum chemistry profilewith electrolytes, urinaly-sis, and, for patients over 7 years of age, total T

4testing. Advan-

tages include a morecomprehensive testingprotocol, less client con-fusion, and better teammember efficiency.

Case Study

complications, including death. If Rucahad survived surgery only to presentwith renal failure several days later, theowner (and perhaps the veterinarian)might have speculated that the surgicalprocedure resulted in renal failure. Illfeelings and even legal action arepotential consequences of not per-forming a thorough preanestheticevaluation that includes diagnostic

testing—or at least offering this serviceto every client. While anesthetic com-plications are rare and significantpreanesthetic testing abnormalitiesuncommon, when they do arise theycan be deadly. Remember, statistics areirrelevant to a grieving pet owner. Thebenefits of a thorough preanestheticevaluation and testing program arenumerous, and each veterinary hospi-

tal must develop and implement a pro-gram that is suited to their needs.

References1. Rebar AH, Metzger FL. Hematology in

practice. In: Rebar AH, MacWilliams PS,Feldman BF, et al, eds. A guide to hematologyin dogs and cats. Jackson, Wyo: Teton NewMedia, 2002;5-8.

2. Lewis HB. Healthy pets benefit fromblood work. Banfield 2006;2(1):18-20.

15

ANESTHESIA IN THE REAL WORLD

Chemistry profile

BUN 90 mg/dL High (7 to 27) Creatinine 5.9 mg/dL High (0.4 to 1.8) Phosphorus 7.3 mg/dL High (2.1 to 6.3) Calcium 11.0 mg/dL (8.2 to 12.4) Sodium 154 mmol/L (141 to 156) Potassium 4.7 mmol/L (4.0 to 5.6) Chloride 112 mmol/L (105 to 115) Total protein 6.3 g/dL (5.1 to 7.8) Albumin 2.9 g/dL (2.5 to 3.6) Globulin 3.4 g/dL (2.8 to 4.5) ALT 58 U/L (5 to 60) ALP 133 U/L (10 to 150) Total billirubin 0.2 mg/dL (0.0 to 0.4) Cholesterol 148 mg/dL (112 to 328) Amylase 1300 U/L (500 to 1500) Glucose 81 mg/dL (60 to 125)

Urinalysis Urine chemistries: 1+ protein Negative for glucose, ketones, billirubin Urine SG: 1.018 Sediment: Unremarkable

Interpretation Azotemia, hyperphosphatemia, non-concentrated urine specific gravity, andnonregenerative anemia indicate renalfailure (most likely chronic because ofthe unremarkable history and nonregen-erative anemia).

Additional testing Urine protein creatinine ratio: 0.9(normal <0.5) Urine culture and sensitivity: No growth Leptospirosis titer: Negative SNAP 3 Dx: Negative Basal cortisol: Normal Ultrasound evaluation: Decreased renalsize and abnormal architecture

Presumptive diagnosisRenal failure (congenital) Note: A necropsy was performed, which

confirmed chronic renal failure(renal dysplasia).

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