Use of a target-controlled infusion system for propofol does not improve subjective assessment of anaesthetic depth by inexperienced anaesthesiologists.

BACKGROUND AND OBJECTIVES: Target-controlled infusion, via the calculated effect compartment concentrations, may help anaesthesiologists to titrate anaesthetic depth and to shorten recovery from anaesthesia. METHODS: In this prospective, randomized clinical study, we compared the performance of six inexperienced anaesthesiologists with <1 yr of training when using target- or manually controlled infusion of propofol, combined with manual dosing of fentanyl. Ninety-two premedicated ASA I-III patients undergoing minor elective urological or gynaecological surgery were assigned to the manual- or target-controlled infusion group. Bispectral index was recorded in a blinded manner. Subjective assessment of anaesthetic depth on a 10 point numerical scale (1 = very deep anaesthesia, 10 = awake) was asked at regular intervals and the correlation with the blinded bispectral index was analysed using the prediction probability, PK. The propofol concentration profile was calculated post hoc. RESULTS: Propofol administration was similar in both groups with no significant difference for the administered amount and concentrations of propofol. Recovery times were also not different. In both groups, a large percentage of the bispectral index data points recorded during surgery showed bispectral index values below the recommended value of 40, but in the target-controlled infusion group there were significantly less bispectral index values above the recommended upper limit of 60 (2.5% vs. 5.1%). CONCLUSIONS: A target-controlled infusion system does not help inexperienced anaesthesiologists to assess anaesthetic depth or to shorten recovery times, but may reduce episodes of overly light anaesthesia and thus help to prevent awareness.

[The performance of respirator alarms during simulated critical events in CMV/IPPV artificial respiration]. / Alarmverhalten von Respiratoren bei definiert auslösbaren Störfällen unter CMV/IPPV-Beatmung.

Alarm systems of ventilators enhance detection of possible critical events during artificial ventilation. Due to their significance, in some countries the alarm detection of ventilators is regulated by federal law. Up to now, no recommendations for the adjustment of alarm limits exist and only a few detailed investigations of the accuracy of alarm detection are available. METHODS. The response of four commercially available ventilators (Servoventilator 900C, Siemens, Inc.; Bennett 7200a, Hoyer, Inc.; Veolar, Hamilton, Inc.; EVITA, Dräger, Inc.) to critical events during artificial ventilation of a test lung were evaluated. We measured the alarm time (the time between event creation and alarm response) of ten different simulated critical events including disconnection, differentisized leaks, failure of the gas supply, and obstruction at different places in the artificial airway. DISCUSSION. All respirators were able to recognise severe critical situations such as hose disconnection, failure of gas supply, and total airway obstruction within a short time (< 15 s). The recognition of small airway leaks was more difficult for the ventilators even when the alarm thresholds were close. The alarm detection of the EVITA (software 10.0 or less) under conditions of partial airway obstruction may be a source of risk for the patient as the machine continued supplying inspiration with pressure-limited ventilation even when the pressure threshold was reached.