Inhaled Anaesthetics - Fluorinated Agents, Inert Agents and Therapeutic Gases MCQs

Ans. C. Helium Helium can be used to replace nitrogen, as the carrier gas for oxygen (Helium) to reduce the work of breathing.

Malignant hyperthermia is a contraindication for the use of Inhalational agents and succinylcholine Pseudocholinesterase deficiency can cause prolongation of action of Succinylcholine leading to delayed recovery from the muscle relaxant and scoline apnea Reference: FRCA in a box, page no 188

Enflurane is the most epileptogenic inhalational anaesthetic especially in the presence of cerebral injury and hypocapnia So enflurane is contraindicated in patients with a Known history of seizures Cerebrovascular disease In head injuries as seizure activity can increase the cerebral metabolism manifold Besides enflurane increases cerebrospinal fluid secretion and decreases its absorption which is deleterious in those with poor intracranial compliance Seizures have been associated with the use of sevoflurane in high concentrations, especially in the paediatric population. Epileptogenic Potential : Enflurane >>> Sevoflurane Reference : Drugs in Anaesthesia and Intensive Care, Edward Scarth, Susan Smith 5th edition

Potency is inversely proportional to MAC i.e. agents with high MAC will have low MAC. N 2 O has the highest MAC, hence it is least potent. Methoxyflurane has the lowest MAC, hence it is the most potent. The potency of inhalational anesthetic agents is measured inversely by their Minimum Alveolar Concentration (MAC) . Potency is inversely proportional to MAC (lower MAC = higher potency). Methoxyflurane has the lowest MAC among these agents, making it the most potent. Nitrous Oxide (N 2 O) has the highest MAC , making it the least potent. Sequence Explanation: Methoxyflurane: Most potent (lowest MAC). Halothane: Next most potent after Methoxyflurane. Isoflurane: Less potent than Halothane. N 2 O: Least potent (highest MAC). Key Takeaway: The potency of anesthetic agents follows the sequence Methoxyflurane > Halothane > Isoflurane > N 2 O , as determined by their MAC values.

All fluorinated inhalational agents (including halothane ) can cause uterine relaxation Traditionally, Halothane is a as to possess maximum uterine relaxant property Reference : Drugs in Anaesthesia and Intensive Care, Edward Scarth, Susan Smith 5th edition

The phenomenon by which the rise in the alveolar partial pressure of nitrous oxide is disproportionately rapid when it is administered in high concentrations is known as concentration effect. The phenomenon by which the speed of onset of inhalational anaesthetic agents is increased when they are administered along with N 2 O as a carrier gas. The combined action of two drugs is greater than would be expected from a purely additive, and thus called the second gas effect . Reference: Physics, Pharmacology and Physiology for Anesthetists, Matthew E. Cross, second edition, pg 149-150.

MAC is reduced by: other depressant drugs (e.g., opioids, sedatives, other inhalational agents). CNS depletion of catecholamines, e.g., by α-methyldopa, reserpine. hypoxaemia/hypotension. pregnancy, possibly due to increased progesterone extremes of age. MAC is increased in: children. hyperthermia. hyperthyroidism. chronic alcoholism. chronic alcoholism. It is unaffected by duration of anesthesia, sex, acidemia/ alkalemia, hypercapnia or hypocapnia. Reference: FRCA A to Z, edition 5, page no 381

Isoflurane is the agent of choice in cirrhosis The cirrhotic liver has compromised portal venous blood flow and hence it is essential to preserve hepatic arterial blood flow Though isoflurane may reduce hepatic blood flow, hepatic oxygen supply is better maintained Another alternative to isoflurane is Sevoflurane which decreases portal vein blood flow, but increases hepatic artery blood flow , so that the total hepatic blood flow and oxygen delivery are better maintained Reference : Drugs in Anaesthesia and Intensive Care, Edward Scarth, Susan Smith 5th edition