Q. Outline possible reasons for prolongation of paralysis imduced by an intravenous dose of 1 mg/kg of suxamethonium. Briefly indicate the consequences of such prolonged block. Overview 1 mg/kg is normal intubating dose of suxamethonium Therefore , phase 11 block is unlikely Thus the factors that may prolongation the effect of suxamethonium is the abnormalities in the metabolism of suxamethonium Suxamethonium is metabolised by pseudocholinesterase Therefore , the alteration in concentration and activity of the enzymes ----result-prolongation of effect of suxamethonium Acquired enzymes deficiency Overview Causes Liver disease Pregnancy Drugs interaction But However, the acquired enzymes defieciency is not often clinically significant causes Inherited enzymes defieciency Overview Overview dibucaine number, the percentage inhibition of plasma cholinesterase produced by a standard titre of dibucaine = 10-5 mmol/l Function the degree of inhibition of hydrolysis by dibucaine allow one to differentiate between normal patinet and patient with atypical pseudocholinesterase enzyme Implication if abnormalities are found, the entire family should be tested Mechanism Plasma of healthy that experienced prolonged response with suxamethonium contained abnormal enzymes The atypical enzyme able to hydrolysis the test substance but unable to hydrolyse suxamethonium Local anesthesia chichocaine ( dibucaine ) able to inhibit hydrolysis of benzocholine

Definition A test for differentiation of one of several forms of atypical pseudocholinesterases that are unable to inactivate succinylcholine at normal rates; based on the percentage of inhibition of the enzymes by dibucaine,

Result normal enzyme has a DN of at least 75 and higher, heterozygous atypical enzyme has a DN of 4070, homozygous atypical enzyme has a DN of less than 20 Pharmacodynamic drugs interaction Overview hypokalemia hypermagnesemia hypothermia ? Drugs ? Mechanism of interaction Clinical consequences 1. Continue ventilation 2. Closed observation 3. Monitoring of neuromuscular function 4. Possible treatment 5. Investigation of patients 6. Investigation for family 7. Implication for future anesthesia