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 anaesthetic, isoflurane must be used with caution in patients with increased intracranial pressure. 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 which 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 tracheobronchial secretions may be stimulated in children but pharyngeal and laryngeal reflexes are quickly diminished. 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.
Effects on the Ability to Drive or Operate Machinery: As with all anaesthetics, it is advisable to allow 24 hrs to elapse before driving or operating machinery.