The sedation of patients requiring prolonged mechanical ventilation in the Intensive Therapy Unit : the role of Isoflurane

Isoflurane is a volatile anaesthetic agent which is little metabolised and allows rapid recovery. Previous experience in patients requiring less than 24 h of sedation suggests that isoflurane may be a satisfactory sedative agent in the intensive therapy unit (ITU) (Kong 1989). This project was set up to investigate the efficacy and safety of isoflurane to sedate critically ill patients for more than 24 h. The electroencephalogram (EEG) was recorded continuously in an attempt to find an objective measure of level of sedation. Isoflurane was compared with midazolam for sedation of ventilated patients in the ITU in a randomised controlled trial on sixty patients. Patients either received 0.1-0.6% isoflurane in an air-oxygen mixture or a continuous intravenous infusion of midazolam 0.01-0.20 mg/kg/h. Sedation was assessed initially and hourly thereafter on a six-point clinical scale. The EEG was recorded throughout sedation. The trial sedative was stopped when the patient was judged ready for weaning from ventilatory support, and the time to full recovery was assessed. Various physiological and biochemical assessments were made during and after the period of sedation to assess the safety of prolonged isoflurane administration. Isoflurane and midazolam produced satisfactory sedation during the period of sedation but the patients given isoflurane recovered significantly more quickly with a more rapid return to consciousness and an earlier endotracheal extubation. It was not possible to correlate a single measure of the EEG with the clinical sedation score and the difficulties associated with this type of data collection are discussed. The plasma concentration of inorganic fluoride in those patients given isoflurane did rise, although no clinical or statistical deterioration in renal function was observed. There was no difference between the two groups in any of the physiological or biochemical observations made. Isoflurane is a suitable agent to sedate mechanically ventilated patients in the ITU. No side effects have so far been detected even when it is administered for a prolonged period in critically ill patients.