As isoflurane has a mild pungency, inhalation should usually be preceded by the use of a short acting barbiturate, or other intravenous induction agent, to prevent coughing. Salivation and coughing may be troublesome in small children induced with isoflurane. Alternatively, isoflurane with oxygen or with an oxygen/nitrous oxide mixture may be administered. It is recommended that the induction with isoflurane be initiated at a concentration of 0.5%. Concentration of 1.5-3.0% usually produce surgical anaesthesia in 7-10 minutes. Blood pressure decreases during induction but this may be compensated by surgical stimulation.
Adequate anaesthesia for surgery may be sustained with an inspired isoflurane concentration of 1.0% to 2.5% in an oxygen/ 70% nitrous oxide mixture. Additional inspired isoflurane (0.5% to 1.0%) will be required with lower nitrous oxide levels, or when isoflurane is given with oxygen alone or with with air/oxygen mixtures. Blood pressure decreases during maintenance anaesthesia in relation to depth of anaesthesia. That is, blood pressure is inversely related to the isoflurane concentration. Provided there are no other complicating factors this is probably due to peripheral vasodilatation. Cardiac rhythm remain stable. Excessive falls in blood pressure may be due to the depth of anaesthesia and in such circumstances can 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.