Introduction

Isoflurane is among the many anesthetic agents discovered by Ross C. Terrell in 1965. It was approved for medical use in the United States in 1979. Isoflurane, along with sevoflurane, is a widely used halogenated ether used as an anesthetic agent. Isoflurane is a clear, colorless stable liquid with a mildly pungent, musty odor. Isoflurane has the advantage of favorable blood gas distribution, low blood solubility, and rapid and smooth recovery.

Pharmacodynamics

Isoflurane alters tissue excitability by decreasing the extent of gap junction-mediated cell-cell coupling and altering channel activity; This results in the induction of muscle relaxation and reduction of pain sensitivity. Isoflurane allows rapid induction and recovery from anesthesia. Despite its mild pungent smell, isoflurane does not stimulate tracheobronchial secretions and excessive salivation. The anesthetic agent is a profound respiratory depressant.

Isoflurane decreases blood pressure in a dose-dependent manner. Anesthetization with isoflurane maintains a stable heart rhythm. Cardiac output is maintained, under controlled ventilation and normal PaCO_2, compensating for stroke reduction. Isoflurane, in certain animals, can produce coronary vasodilation at the arteriolar level.

Isoflurane has a dose-dependent effect on central nervous system depression. The agent does produce convulsive activity. Isoflurane does not prevent cerebral edema or an increase in intracranial pressure following traumatic brain injury. Further, the need for muscle relaxants decreases at increased concentrations of isoflurane.

Pharmacokinetics

Isoflurane has a blood gas coefficient of 1.4 which is less than other potent inhaled anesthetics. The rapid rise in alveolar concentration towards inspired concentration can be observed with isoflurane due to its low blood solubility. The mild pungency of the agent can provoke breath-holding or coughing which can affect the rate at which inspired concentration can be increased. However, this effect can be minimized by premedication or nitrous oxide or by using an intravenous agent for induction.

Isoflurane’s low solubility enhances its elimination. The duration of the anesthesia affects the rate of recovery. The rapid elimination allows quick reversal of circulatory, respiratory and neuromuscular depression.

Strengths & Limitations

Advantages

• Produces rapid induction and recovery from anesthesia
• The depth of anesthesia can be easily and rapidly altered
• Non-explosive and non-flammable
• Non-irritant

Disadvantages

• Produces moderate respiratory depression
• Produces moderate cardiovascular depression
• Pungent odor

References

Burns WB, Eger EI 2^nd (2011). Ross C. Terrell, PhD, an anesthetic pioneer. Anesth Analg. 113(2):387-9. doi: 10.1213/ANE.0b013e3182222b8a.

Eger EI 2^nd (1981). Isoflurane: a review. Anesthesiology. 55(5):559-76.

Eger EI 2^nd (1984). The pharmacology of isoflurane. Br J Anaesth. 56 Suppl 1:71S-99S.