MAINTAINING ANESTHESIA

Involves both vital signs and reflexes

Can be done with or without machines

MONITORING

Tell us how well a patient is maintaining homeostasis through respiration & circulation◦ Often grouped according to whether they reflect

circulation, oxygenation, or ventilation◦ For example, values that reflect circulation are:

HR, heart rhythm, pulse strength, CRT, mucous membrane color, and blood pressure

◦ Values that reflect oxygenation are: mucous membrane color, hemoglobin saturation, measurement of arterial blood oxygen

◦ Values that reflect ventilation are: RR, respiratory depth, breath sounds, expired CO2 levels, measurement of arterial CO2

VITAL SIGNS

MONITORING WITHOUT INSTRUMENTATION

THE MOST IMPORTANT MONITORING TOOLS ARE YOUR HANDS, EYES, & EARS!

MACHINES WILL FAIL!

ONLY RELY ON MACHINES FOR VALUES THAT YOU CANNOT GET ON YOUR OWN(blood pressure, ECG, SPO2)

Anesthetic agents are expected to lower the heart rates of patients

While under anesthesia, the following heart rates are appropriate for dog:◦ Large dogs: 60 - 140 beats per minute◦ Small dogs: 70-160 beats per minute ◦ Notify the vet if heart rates are outside these ranges

While under anesthesia, the following heart rates are appropriate for cats:◦ 100-180 beats per minute

HEART RATE AND RHYTHM

AUSCULTATION

PALPATION

ESOPHAGEAL STETHOSCOPE

OPTIONS FOR CARDIAC MONITORING

ESOPHAGEAL STETHOSCOPE

An esophageal stethoscope is a thin, flexible tube that is attached to a regular stethoscope. Lubrication is applied to the end of the tube which is placed in the oral cavity and down the

esophagus until a heartbeat is heard.

This allows a person to listen to the heart on an animal that is draped in for a surgical procedure

The rate of the return to color for mucous membranes after the application of digital pressure compresses capillaries and blocks blood flow temporarily

Provides information about tissue perfusion

A normal CRT does not guarantee that the patient is normal, however a prolonged CRT (longer than 2 seconds) means that tissue perfusion is not adequate◦ Possibly due to vasoconstriction, hypotension,

hypothermia, heart failure, shock, or increased anesthetic depth

CAPILLARY REFILL TIME

IDEALLY, COLOR SHOULD BE PINK!◦ If gums are pigmented, look at the conjunctiva, or

the inner prepuce or vulva◦ If pale, there may be blood loss, anemia, or poor

perfusion CYANOSIS = purple or blue discoloration=

EMERGENCY! ICTERUS=yellow discoloration, may indicate

severe liver disease or hemolysis

MUCOUS MEMBRANE COLOR

Can be done at the lingual, femoral, metacarpal/metatarsal, and dorsal pedal arteries

Should be strong and match the heart beat Weak pulses may indicate hypotension

Causes: excessive anesthetic depth, cardiac insufficiency, excessive blood loss

PULSE STRENGTH

Excessive blood loss can cause complications such as shock

One soaked3x3 gauze = ~5-6 mL of blood

One soaked 4x4 gauze= ~10mL blood

The actual amount lost may be more due to clotting or pooling of blood

Healthy animal can tolerate ~ 13mL/kg blood loss during surgery

EVALUATING BLOOD LOSS

Intra-abdominal blood clot

Intra-abdominal blood pooling

Anesthetic agents are expected to reduce the tidal volume, which is the amount of air inhaled with each breath.

Can be evaluated by watching the patient’s chest or the reservoir bag on the anesthetic machine

Normal values while under anesthesia for dogs & cats: 8-20 bpm

RESPIRATION RATE AND DEPTH

Bagging the patient refers to the process of manual ventilation.

Gentle squeezing of the reservoir bag causes oxygen/anesthetic gas to be forced into the patient’s lungs◦Can be used to increase anestheticdepth. If an animal is waking up, manually forcing anesthetic gas into the lungs will cause it to fall asleep more rapidly◦Can be to increase respiratory rate. If the

respiratory rate is low, we can provide manual breaths ~q20 seconds to increase the rate

◦To reverse atelectasis. Atelectasis refers to the collapse of alveoli

RESPIRATION RATE AND DEPTH

RESPIRATORY RATE & DEPTH Hyperventilation=Increase in respiratory

depth Tachypnea = increase in respiratory rate Causes of hyperventilation and

tachypnea:◦ Increased CO2 in the blood◦ Underlying pulmonary disease◦ Surgical stimulation◦ Decrease in anesthetic depth (animal is too light)

RESPIRATORY RATE AND DEPTH

Normal breaths are smooth and regular, not gasping or labored

DO NOT FORGET TO USE YOUR STETHOSCOPE TO EVALUATE BREATH SOUNDS!◦ Should not hear crackles or wheezes

Hypothermia is the most common anesthetic problem◦ Begin prevention from the moment the animal is

induced. The greatest decrease in body temperature

is within the first 20 minutes of anesthesia.

THERMOREGULATION

The following can decrease body temperature:

◦ Shave and scrub of the surgical area◦ Inability of the animal to shiver to create body heat◦ Decreased metabolic rate◦ Exposure of the internal organs to the air◦ Anesthetic agents that cause vasodilation, and

increase the rate of heat loss◦ Pediatric and geriatric animals ◦ Room temperature

Check the patient’s temperature at least every 30 minutes if there is not an esophageal probe available. In between temp checks, feel the animal’s extremities

THERMOREGULATION

Several methods to avoid hypothermia:◦ Circulating warm water heating pad. Electric

heating pads may cause more burns. For all heating pads, put a towel between the heating pad and the patient

◦ IV fluid line warmer◦ Hot water bags/rice socks◦ Saran wrap/bubble wrap◦ Bair hugger◦ Warm towels◦ Heated surgery table◦ Baby booties on the paws

THERMOREGULATION

Fluid line warmer

Self-warming surgery table

Circulating warm waterheating pad

BairHuggers

Excessive efforts to warm a patient could cause thermal injuries.◦ Always place towels between the patient and the

heat source!

THERMOREGULATION

Some patients, usually cats, will become hyperthermic post-operatively. This is due to the effects of some drugs such as ketamine and opioids.◦ If the temp reaches 103.5˚ or higher, we should

begin cooling methods. Taking all blankets/towels out of the cage Putting a fan in front of the cage Wiping the patient down with a wet washcloth Applying alcohol to the footpads.

THERMOREGULATION

REFLEXES•Reflexes are involuntary reactions to a stimulus•It is also important to monitor reflexes, which will help you determine the stages and planes of anesthesia.

Palpebral Reflex

Touch the corner of the eyelids and the animal blinks.

The palpebral reflex is stimulated by tapping the skin at the medial canthus of the eye or by running the finger along the eyelashes. This disappears in light to medium plane of surgical anesthesia in small animals.

Simulation of the larynx will cause the animal to swallow. This is a mechanism to prevent accidental aspiration of fluids into the lungs. ◦ passing an endotracheal tube ◦ presence of secretions at the larynx.

Laryngeal (Swallowing) Reflex

Withdrawal Reflex Pull a limb gently, pinch the toe and the

animal will pull back the limb. The reflex is obtained by firm pressure of the interdigital skin in the dog and cat,

squeezing the claws together in cattle and swine and firm pressure on the pastern of horses. The reflex disappears late in phase

III and indicates deep anesthesia. When checking the reflex, the legs should be

held in extension. Probably more useful in monitoring laboratory animal patients and

birds.

Pupillary Reflex

Shine a light in the eye and the pupil constricts.

The pupillary responses under anesthesia are heavily influenced by pre-medication. Species

variations exist. There is also variability in response to different anesthetics. In general, in un-premedicated patients, the pupil is dilated in the early excitement phase and then becomes progressively constricted as surgical anesthesia occurs. With very deep surgical anesthesia the pupil begins to dilate again and with entry into

phase IV, with respiratory and cardiac arrest, the pupil is maximally dilated.

Corneal Reflex

Touch the cornea and the animal blinks. Be careful not to damage the cornea if this

reflex is tested.

The corneal reflex is obtained by gentle palpation of the lateral aspect of the

cornea. This causes reflex closure of the eyelids. The reflex disappears in the

deeper levels of phase III, plane II. This reflex is not always reliable in the dog, particularly if the eyeball is markedly

rotated.

EAR FLICK REFLEX

Pinnal reflex used in cats. Gently touch the hair on the inner surface of the ear and

watch the pinna twitch.

Don’t test too frequently or the reflex will be inaccurately lost.