General inhalation anaesthetic for use in induction and maintenance.
Isoflurane 250 ml
Isoflurane with oxygen or with an oxygen/nitrous oxide mixture may be used for induction, but more usually a short-acting barbiturate or other intravenous induction agent is administered followed by inhalation of the isoflurane mixture.
It is recommended that induction with isoflurane be initiated at a concentration of 0.5%. Concentrations of 1.5 to 3.0% usually produce surgical anesthesia in 7 to 10 minutes.
Surgical levels of anesthesia may be maintained with 1.0-2.5% isoflurane in oxygen/nitrous oxide mixtures. An additional 0.5-1.0% isoflurane may be required when given with oxygen alone.
Arterial pressure levels during maintenance tend to be inversely related to alveolar isoflurane concentrations in the absence of other complicating factors. Excessive falls in blood pressure may be due to depth of anesthesia and, in these circumstances, should be corrected by reducing the inspired isoflurane concentration.
Induced hypotension can be achieved by artificially ventilating patients with isoflurane 2.5-4.0%. Pre-treatment with clonidine significantly decreases the isoflurane requirement for maintaining induced hypotension.
It is recommended that isoflurane should be vaporized using a flow through vaporizer specifically calibrated for the agent, though non-calibrated vaporizers may be used, particularly with low-flow or closed systems, in conjunction with equipment capable of monitoring inspired or expired concentrations.