Isoflurane is a profound respiratory depressant, this effect being accentuated by narcotic premedication or concurrent use of other respiratory depressants.
Isoflurane causes an increase in cerebral blood flow at deeper levels of anaesthesia (1.5%) and this may give rise to an increase in cerebral spinal fluid pressure. Where appropriate, this can be prevented or reversed by hyperventilating the patient before or during anaesthesia. As with other halogenated anaesthetics, isoflurane must be used with caution in patients with increased intracranial pressure. In such cases, hyperventilation may be necessary.
As with all halogenated anaesthetics, repeat anaesthesia within a short period of time should be approached with caution since the risk of hepatotoxicity is not fully understood. There is insufficient experience of use in repeated anaesthesia to make a definite recommendation in this regard.
Isoflurane has been reported to interact with dry carbon dioxide adsorbents during closed-circuit anaesthesia to form carbon monoxide. Inhalation of carbon monoxide may lead to formation of significant levels of carboxyhaemoglobin in exposed patients. Carboxyhaemoglobin is toxic even in low concentrations and is not easily detected by standard anaesthesia monitors eg, pulse oximeters. Direct measurement of carboxyhaemoglobin should be carried out in the event that a patient on closed-circuit anaesthesia with an implicated agent develops oxygen desaturation which does not respond to the usual therapeutic measures. All necessary precautions should be taken to ensure that carbon dioxide adsorbents are not allowed to dry out.
Caution should be exercised when administering isoflurane to patients with preexisting liver disease.
Isoflurane is a powerful systemic and coronary arterial dilator. The effect on systemic arterial pressure is easily controlled in the normal healthy patient and has been used specifically as a means of inducing hypotension. However, the phenomenon of "coronary steal" means that isoflurane should be used with caution in patients with coronary artery disease. In particular, patients with subendocardial ischaemia might be anticipated to be more susceptible.
Salivation and tracheo-bronchial secretions may be stimulated in children but pharyngeal and laryngeal reflexes are quickly diminished.
Because levels of anaesthesia can be altered easily and quickly with isoflurane, only vaporisers which produce a predictable concentration with a good degree of accuracy should be used. The degree of hypotension and ventilatory depression may provide some indication as to the level of anaesthesia. The level of anaesthesia may be changed quickly with isoflurane. Heart rhythm remains stable but spontaneous breathing should be monitored closely and supported where necessary.
It is recommended that vapour from isoflurane and other inhalational agents are efficiently extracted from the area of use.
Isoflurane should only be administered by, or in the presence of, anaesthetists with the appropriate anaesthesia and resuscitation equipment.
Use of inhaled anaesthetic agents has been associated with very rare increases in serum potassium levels that have resulted in cardiac arrhythmias and death in children during the postoperative period. The condition has been described in patients with latent as well as overt neuromuscular disease particularly Duchenne muscular dystrophy. Use of suxamethonium has been associated with most, but not all of these cases. These patients showed evidence of muscle damage with increased serum creatinine kinase concentration and myoglobinuria. These patients did not have classical signs of malignant hyperthermia eg, muscle rigidity, rapid increase in body temperature or increased oxygen uptake and carbon dioxide production. Prompt and vigorous treatment for hyperkalemia and arrhythmias is recommended. Subsequent evaluation for latent neuromuscular disease is indicated.
Effects on the Ability to Drive or Operate Machinery: As with all general inhalation anaesthetics, it is advisable to allow 24 hrs to elapse before driving or operating machinery.
Use in pregnancy & lactation: Reproduction studies have been carried out on rats and rabbits after repeated exposure to isoflurane at anaesthetic concentrations. In both species, there was no effect on fertility, pregnancy or delivery. The viability of the offspring was unaffected.
The correlation between animal study results and human reactions is not known and insufficient data are present for humans and animals to estimate the risk of teratogenicity in children of women who receive isoflurane anaesthesia during pregnancy. Isoflurane is not recommended during the 1st trimester of pregnancy.
All anaesthetics should be avoided during pregnancy if possible. Unavoidable anaesthesia with isoflurane should be undertaken using due caution. There is an increasing volume of information on the use of isoflurane in pregnancy and obstetrics anaesthesia and use in operative obstetrical interventions eg, caesarean section is established.
A suitable level of anaesthesia for caesarean section can be maintained with 0.5-0.75% isoflurane in oxygen/nitrous oxide. Increased blood loss has been observed, comparable with other volatile anaesthetics (eg, halothane), in patients undergoing uterine curettage or other gynaecological surgical procedures.
Should isoflurane be administered during lactation, lactation is to be interrupted after the anaesthesia. Lactation can be restarted after the drug has been discharged from the circulation.