Intraoperative assessment of the Lawrence 3000 Doppler Cardiac Output Monitor.

Transoesophageal Doppler cardiac output measurement was evaluated against the thermodilution method in eleven patients undergoing elective cardiac surgery. A total of 106 pairs of Doppler and thermodilution values were obtained. Cardiac output was measured over a range of 2.3 l.min-1. to 11.51 l.min-1. The mean difference between the Doppler and thermodilution measures was -1.0 l.min-1 (thermodilution minus Doppler). Standard deviction was 1.8 l.min-1. This is a significant difference. It is concluded that these techniques do not agree when measuring cardiac outputs.

Hypoxaemia during postoperative recovery using continuous pulse oximetry.

Continuous pulse oximetry monitoring was used to determine the incidence of hypoxaemia (arterial oxygen saturation less than or equal to 90%) occurring in the first hour of postoperative recovery. Of 107 patients studied, hypoxaemia was recorded in 80%. Twenty-eight (26%) of these patients had saturations below 80%. The average frequency (i.e., the number of desaturations per patient) and the total duration of these desaturations was 7.7 desaturations and 182 seconds respectively. Intermittent measurements taken preoperatively and at 5 and 30 minutes postoperatively revealed hypoxaemia in 2%, 4% and 6% of patients respectively. In 39 patients who received oxygen therapy throughout the monitoring period, 64% experienced hypoxaemia within the first 15 minutes of recovery as opposed to only 18% in the final 15 minutes monitoring period. Of the factors assessed, only patients with a body mass index greater than 25 had an increased risk of hypoxaemia (P less than 0.01). Four patients required active intervention and ventilatory assistance. We conclude that postoperative hypoxaemia is a particularly common occurrence even in patients otherwise considered healthy. Hence, pulse oximetry should be employed routinely during recovery. Where possible, monitoring should be performed continuously for at least 45 minutes.

Neurological monitoring during anaesthesia and surgery.

The ability to monitor the electrical activity of the central nervous system and to record responses to stimulation allows for a more immediate assessment of the functional integrity of the nervous system during anaesthesia than do conventional techniques. These monitoring methods, however, have been slow to find acceptance in clinical practice. The reasons include the difficulty with standardization and reproducibility of results from such monitoring techniques as the electroencephalogram (EEG) and evoked potentials, along with the level of expertise necessary for accurate interpretation of the voluminous data collected. Anaesthetic agents along with variations in physiological parameters can markedly alter the recordings not to mention the influence of diathermy, other electrical devices, muscle activity and artifact. Because of these inherent difficulties, most anaesthetists still rely on optimising such physiological parameters as arterial, venous and intracranial pressures, oxygen and carbon dioxide tensions, to ensure the functional integrity of the nervous system. This brief review explores the potential areas of application of electrophysiologic monitoring in surgery and anaesthesia.

Alfentanil for short duration laparoscopic procedures.

Alfentanil in low dosage (8 micrograms kg-1) as an analgesic agent for short duration surgery was evaluated. Forty-one women undergoing laparoscopy received double-blind either alfentanil 8 micrograms kg-1 or normal saline at induction, and all received thiopentone, alcuronium, enflurane, nitrous oxide and oxygen. The fall in mean arterial pressure (MAP) with induction was similar between groups. The MAP following intubation with alfentanil was unchanged, while with normal saline a mean rise of 23 (SD 15.2) mmHg occurred (P less than 0.001). The pulse rate following intubation showed a smaller rise (P less than 0.001) with alfentanil of 26 (SD 14.6) beats min-1, than the normal saline group of 46 (SD 13.3) beats min-1. Alfentanil was found to be a safe and effective analgesic agent in short duration surgery, by reducing sympathetic responses to intubation without cardiovascular depression or compromise of postoperative recovery.