Isoflurane

Cardiovascular

Although atrial dysrhythmias have been reported in 3.9% of patients and ventricular dysrhythmias in 2.5% [ ], the dysrhythmogenicity of isoflurane is less pronounced than that of halothane [ ]. Indeed, the incidence of dysrhythmias due to catecholamines in cardiovascular anesthesia and during oral surgery is reduced by using isoflurane rather than the other agents.

The most controversial adverse effect of isoflurane is its potential to cause coronary steal in patients with critical stenosis in the coronary circulation. Most recent work suggests that the risk of myocardial ischemia is not increased, as long as the hemodynamics, especially heart rate, are well controlled [ ]. However, there are still isolated reports, suggesting that the issue is not settled. In some cases isoflurane has caused a specific coronary steal even with good hemodynamic control [ ].

Isoflurane can cause marked hypertension during induction of anesthesia. Of 26 patients who were anesthetized with 0.5% isoflurane in oxygen, increased to 4% in 2 minutes, nine had increases in systolic blood pressure by more than 10 mmHg (mean 26) [ ]. Tracheal intubation markedly increased the blood pressure in all patients, but there was a negative correlation between the isoflurane-induced increase and that induced by intubation. Tracheal intubation produced a larger increase in blood pressure in the isoflurane-induced hypertensive patients.

Respiratory

Marked respiratory depression has been documented in children [ ] and coughing associated with nausea and vomiting occurs in about 10% of subjects [ ].

Like halothane, isoflurane is useful in cases of life-threatening acute severe asthma refractory to drug therapy.

• An 11-year-old girl with acute asthma, severe CO ₂ narcosis, and ventricular fibrillation induced by hypoxemia was successfully treated with isoflurane in oxygen for 14 hours. Her recovery may have been due to bronchodilatation and the treatment that was possible because of the low dysrhythmogenic effect of isoflurane [ ].

Nervous system

Seizures are uncommon with isoflurane, but reports continue to appear.

Psychological

Memory function and its relation to depth of hypnotic state has been prospectively evaluated in anesthetized and non-anesthetized subjects, using the Bispectral Index during general anesthesia and an auditory word stem completion test and process dissociation procedure after anesthesia [ ]. Isoflurane was used in 47 patients and propofol in one. There was evidence of memory for words presented during light anesthesia (Bispectral Index score 61–80) and adequate anesthesia (score 41–60) but not during deep anesthesia (score 21–40). The process dissociation procedure showed a significant implicit memory contribution but not reliable explicit memory contribution. Memory performance was better in non-anesthetized subjects than in anesthetized patients, with a higher contribution from explicit memory and a comparable contribution from implicit memory. The authors concluded that during general anesthesia for elective surgery, implicit memory persists, even in adequate hypnotic states, to a comparable degree as in non-anesthetized subjects.

Endocrine

The effects of anesthesia for more than 10 hours with either isoflurane or sevoflurane on hormone secretion have been studied in 20 patients [ ]. Adrenaline and noradrenaline concentrations increased continuously during and after surgery in the isoflurane group whereas they increased only after surgery in the sevoflurane group; both concentrations were higher in the isoflurane group during anesthesia. Cortisol increased continuously but adrenocorticotropic hormone increased only during surgery. Antidiuretic hormone increased during surgery and the isoflurane group had significantly higher values than the sevoflurane group. Glucose increased both during and after surgery but insulin increased only after surgery; glucagon fell during surgery in both groups.

Metabolism

The effects of anesthesia with sevoflurane (0.5, 1.0, and 1.5 MAC) and isoflurane (0.5, 1.0, and 1.5 MAC) on glucose tolerance have been studied in a randomized study in 30 patients [ ]. The insulinogenic index (change in concentration of immunoreactive insulin/change in glucose concentration), the acute insulin response, and the rates of glucose disappearance were significantly lower in all anesthesia groups than in the control group. However, there were no differences among the six anesthesia groups.