Principles of Ophthalmic anesthesia, various drugs and their implications, surgeries and their concerns, MAC

Moderator : DR RENU Presenter: DR SHAKTHI

RAHUL

www.anaesthesia.co.in anaesthesia.co.in@gmail.com

Principles of ophthalmic Anesthesia• Safety• Smooth induction• Akinesia• Profound analgesia• Avoidance or obtundation of oculomedulary reflex• Control of intraocular pressure • Awareness of drug interactions• Smooth emergence

Oculo cardiac reflexFirst described by Bernard Aschner and Guiseppe Dagnini – 1908 •Incidence up to 70-79% in ped. Ophthalmology (Allen et al. Eye,1998 )

•Triggered by traction of extra ocular muscles , pressure on globe, intra orbital or retrobulbar injections

Pathway

……..• Manifestations : Bradycardia : AV block :Ventricular bigeminy :Ventricular tachycardia (Alexender JP: Br J Ophth 1975 )

• Significant OCR –related bradycardia = 10-20 % decrease in resting heart rate , sustained for 5 secs or longer

…… Risk factors• Hypercarbia and hypoxemia• Inappropriate anesthetic depth• Surgery

Prevention• Avoid Hypercarbia and hypoxemia• Avoid Inappropriate anesthetic depth• Regional blocks• Topical lignocaine/ prilocaine/ proparacaine• Intravenous atropine/ glycopyrrolate ?

Treatment : Release of stimulus : Increasing depth of anesthesia : Ventilatory status : Local anesthetics : Atropine/ glycopyrrolate

When to start the surgery again ? Effect of repeated manipulation ?

Intra ocular pressure• IOP is determined by

– External pressure

– Venous congestion

– Changes in intraocular volume

• Normal IOP 12-20 mm of Hg, abnormal above 22 mmHg

• Newborn 9.5 mmHg, approximate adult pressure by 5

yrs of age

• Open globe IOP – atmospheric pressure

The effect of cardiac and respiratory variables on intraocular pressure (IOP)

Variable Effect on IOP

Central venous pressureIncreaseDecrease

¯¯¯

Arterial blood pressureIncreaseDecrease

¯

PaCO2

Increase (hypoventilation)Decrease (hyperventilation)

¯¯

PaO2

IncreaseDecrease

0

The effect of anesthetic agents on intraocular pressure (IOP)

Drugs Effect on IOPInhaled anesthetics Volatile agents Nitrous oxide

↓↓

↓

Intravenous anestheticsBarbituratesBenzodiazepinesKetamineOpioids

Etomidate

↓↓↓↓

?↓↓

Muscle relaxantsDepolarizers (Succinylcholine)Nondepolarizers

↑↑ 0/↓

Strategies to prevent increases in intraocular pressure (IOP)

• Avoid direct pressure on the globe– Patch eye with Fox shield

– No retrobulbar or peribulbar injections

– Careful face mask technique

• Avoid increases in central venous pressure– Prevent coughing during induction and intubation

– Ensure a deep level of anesthesia and relaxation prior to laryngoscopy

– Avoid head-down position

– Deep extubation

HOW SUCCINYL CHOLINE INCREASES IOP

Mechanism : Tonic contraction of extra ocular muscle : Dilation of choroidal vasculature : Relaxation of orbital smooth muscle Calobrisi BL, Int anesthesiol Clin28:83,1990

IOP ↑ in 1-2 min, peak 3 min, returns to normal after 4-6 min, ↑ up to 10-20 mmhg

Numerous methods for blunting Sx induced rise in IOP tried, results not consistent/ reliable

Oculo respiratory Reflex

• Afferent : Trigeminal nerve • Efferent : Pneumotaxic centers of the pons Medullary respiratory centers • Stimulus : pressure on the extra ocular muscles• Response : tachypnea or respiratory arrest ( Johnson and

Frost , 1994 )

• Reflex not inhibited by atropine or glycopyrrolate

Postoperative nausea and vomiting• Avg incidence in age above 3 yrs is above 30%

(Rose and Watcha, BJA1999 )

• Untreated children after strabismus sx : 40-88% (Lerman,CJA1995 )

• Risk low below the age of 2 yrs

Risk factorsEberhart 2004 Surgery greater than 30 min, Age > 3 Strabismus surgery Previous history in patient/family

• Other factors : gender, anesthetic technique, intraoperative opioids , inadequate pain control, gastric distension, skill of anesthesiologist ( Patel and Rice, 1991;Weinstein et al ,1994; Duncan,1995 )

• Oral fluid intake and early ambulation before discharge

(ASA task force 2002 , Williams et al ,anesthesiology,2002)

Intraoperative prophylaxisConsensus Guidelines for Managing PONV

Anaesthesia Analgesia 2003; 97: 62-71.

Prophylaxis

• Clonidine premedication• Avoiding opioid analgesics• Dexamethasone ( 0.15 – 1mg/kg )• 5 HT-3 antagonist ( Ondansetron, Granisetron)• Metoclopramide ( 100-250µg/kg)• Droperidol (10µg/kg )D.pptx

• Withholding oral intake postoperatively• Hydration

• Transdermal scopolamine: 1.5mg 1hr prior to surgery (Anaes. Analg. 2007;104:92-96 )

Nonpharmacological• Acupuncture, acupressure and acupoint stimulation at

P6 (Lee et al. Anes & Analg88:1362,1999)

• Early positive results with Korean pressure point K 9 (BJA 2005;95:77-81.)

Post operative apnea• Occurs more commonly in infants with prev h/o

apnea ( Liu et al.,Anesthesiology59:506,1983) , younger than 42 to 44 weeks PC ( Malviya S, Anes & Anal.85:1207,1997), anemia

• Although risk persist up to the age of 60 wks PC Kurth et al, Anesthesiology75:22-26,1991

Cote et al study ( 1987 -1993)

CONCLUSION• Apnea strongly and inversely correlated both with gestational

age and post conceptional age• An ass. risk factor was continuing episodes of apnea at home• SGA seemed to be some what protected from apnea

compared with those with normal or LGA infants• Anemia( hematocrit < 30) was a significant risk factor even

beyond 43 wks post conceptional age• Relationships of postoperative apnea with h/o NEC, neonatal

apnea, RDS, BPD or operative use of opioids could not be determined

• Probability of apnea in non anemic, decrease with post conceptual and postnatal age but is not less than 5% until postconceptional age of 48 wks and not less than 1 % until postconceptional age of 56 wks

• Should be monitored for al least 12 hrs postoperatively (Kurth et al. Anesthesiology66:483,1987) / 18-24 hrs (Liu et al .Anesthesiology59:506,1983

• Role of caffeine

Premedication

• Aims : To allay separation anxiety• Most commonly used drugs : Phenargan Diazepam Midazolam Clonidine Ketamine Triclofos

…………

• Phenargan : Oral 1 mg/kg • Chloral hydrate : Oral 30-50 mg/kg : Rectal 30-50 mg/kg , max – 1 gm• Triclofos : Oral 25-30 mg/kg up to 1 gm

• Topical local analgesia: EMLA cream takes 90min to be fully active

MEDICATION ROUTE DOSE ( mg/kg) TIME TO

ONSET( min )ELIMINATION TI/2 ( HR)

Midazolam Oral

Intranasal

Rectal

0.25 – 1.0

0.2 - 0.3

0.3 – 1.0

10

<10

10

2

2 -3

2 -3

Ketamine Oral

Intranasal

Rectal

3.0 – 6.0

3.0 – 5.0

5.0 – 6.0

10

< 10

20 -30

2 – 3

3

3

Clonidine Oral 0.002 – 0.004 45 8 – 12

Strabismus surgery

• Prevalence: app. 3% population (Vivian, 2000)

• Technique : recession or resection• Incidence increased with CNS dysfunction,

oculomotor nerve trauma, sensory abnormality (cataract or refractive aberrations),various

syndromes: Marfan syndrome, Down syndrome ,Homocystenuria, Goldenhar’s syndrome, Moebius syndrome, Stickler syndrome, Cri du chat syndrome, Apert’s syndrome )

• Concerns : Forced duction test : OCR : OER : Malignant hyperthermia : Ass. disease • General anesthesia : ETT/ LMA• Spontaneous/ controlled ventilation :controlled

ventilation preferred (Blanc et al 1988)

Forced duction test : helpful in differentiating between a paretic muscle and a restrictive force preventing ocular motion

• Succinylcholine contraindicated in less than 20 mins of testing

• NDMR preferred

Malignant hyperthermia

• One in 20,000 – 50,000 anesthetics, depending on drugs and location

• One in 2,000 – 3,000 based on genetic testing• Rare in Infants• Incidence decrease after 50 yrs

Triggering Agents for MH

• Trigger agents– Halothane– Sevoflurane– Isoflurane– Desflurane

- Succinylcholine

• Non-trigger agents– Opioids– Non-depolarizing

muscle relaxants– Ketamine– Propofol– Anxiolytics– Nitrous oxide

Signs of MH

• Specific– Tachycardia– Tachypnea– Acidosis– Hyperkalemia

• Non-specific -Muscle rigidity– Increased CO2

production– Rhabdomyolysis– Marked temperature

elevation

Symptomatic Treatment of MH• Cooling Surface (ice, cooling blanket)• Central Intravenous iced saline• Nasogastric and rectal lavage • Intra-abdominal lavage • Cardiac bypass • Sodium Bicarbonate for metabolic acidosis • Management of hyperkalemia - insulin/glucose

Diuretics - mannitol, lasix• Dantrolene

Postoperative pain

• Ass. with moderate pain Mainstay NSAIDS• Acetaminophen : Rectal sup. 30-40 mg/kg loading

dose, subsequent dose 20 mg/kg, interval 6-8hrs, 2 hrs required for peak plasma concentration

: Oral 10-15 mg/kg every 4 hrs• Ibuprofen : 6-10 mg/kg , 6 hrly• Ketarolac : IM 0.75mg/kg, IV 0.5 mg/kg 6-8 hrly• Declofenac: 1- 1.5 mg sup. Repeated every 8 hrs

Retinopathy of prematurity

• Abnormal proliferation of undifferentiated primitive mesenchymal cells in the retina

• Ass. With low birth weight, prematurity, neonatal high oxygen exposure, recurrent apnea

• Incidence : 70% of extremely LBW (Moore, 2000)

• Retinal tears and detachment may occur sec to contraction of the vitreous humour

• Anes. Goals: PaO2 around 70 mmHg : SpO2 90- 95% : Prolonged exposure to high PaO2 to be

avoided until PC 44 weeks. : Avoiding freq fluctuations in FiO2

Vitroretinal surgery• Most commonly secondary to ROP, trauma and

vitreous degeneration sec to some syndrome (Acute intermittent porphyria, Cystinosis, Homocystenuria, Hurler’s

syndrome, Marfan syndrome, Stickler’s syndrome )

• Small amenable to laser therapies or cryopexy more sig. require sx. treatment

• Concerns : Akinesia : Proper control of IOP( mannitol, acetozolamide)

:OCR :Silicone oil / long acting inert gases

………

• Intravitreal injection of gases: SF6, C3F8

• N2O rapidly enters from the gas bubble and increase the size of gas bubble

• N2O should be discontinued at least 20 mins before

• If pt require anesthesia again N2O should be avoided

for 5 days for air injection, 10 days for SF6 injection, 30 days for perfluropropane

• Avoidance of air travel

Glaucoma• Prevalence , 1: 10,000 live birth• Congenital abnormality , inherited as AR, M>F• 10% ass. With systemic illness• Diagnosis : tonometry, corneal examination,

fundoscopy and gonioscopy• Corrective procedures: Goniotomy, trabeculotomy,

trabeculectomy and cyclocryotherapy

• Concerns : Stable IOP Akinesia Post operative pain PONV

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