Clinical validation of electromyography and acceleromyography as sensors for muscle relaxation.

BACKGROUND AND OBJECTIVE: The aim of this study was to determine which of two clinically applied methods, electromyography or acceleromyography, was less affected by external disturbances, had a higher sensitivity and which would provide the better input signal for closed loop control of muscle relaxation. METHODS: In 14 adult patients, anaesthesia was induced with intravenous opioids and propofol. The response of the thumb to ulnar nerve stimulation was recorded on the same arm. Mivacurium was used for neuromuscular blockade. Under stable conditions of relaxation, the infusion-rate was decreased and the effects of turning the hand were investigated. RESULTS: Electromyography and acceleromyography both reflected the change of the infusion rate (P = 0.015 and P < 0.001, respectively). Electromyography was significantly less affected by the hand-turn (P = 0.008) than acceleromyography. While zero counts were detected with acceleromyography, electromyography could still detect at least one count in 51.1%. CONCLUSIONS: Electromyography is more reliable for use in daily practice as it is less influenced by external disturbances than acceleromyography.

Model-based control of neuromuscular block using mivacurium: design and clinical verification.

BACKGROUND: Short-acting agents for neuromuscular block (NMB) require frequent dosing adjustments for individual patient's needs. In this study, we verified a new closed-loop controller for mivacurium dosing in clinical trials. METHODS: Fifteen patients were studied. T1% measured with electromyography was used as input signal for the model-based controller. After induction of propofol/opiate anaesthesia, stabilization of baseline electromyography signal was awaited and a bolus of 0.3 mg kg-1 mivacurium was then administered to facilitate endotracheal intubation. Closed-loop infusion was started thereafter, targeting a neuromuscular block of 90%. Setpoint deviation, the number of manual interventions and surgeon's complaints were recorded. Drug use and its variability between and within patients were evaluated. RESULTS: Median time of closed-loop control for the 11 patients included in the data processing was 135 [89-336] min (median [range]). Four patients had to be excluded because of sensor problems. Mean absolute deviation from setpoint was 1.8 +/- 0.9 T1%. Neither manual interventions nor complaints from the surgeons were recorded. Mean necessary mivacurium infusion rate was 7.0 +/- 2.2 microg kg-1 min-1. Intrapatient variability of mean infusion rates over 30-min interval showed high differences up to a factor of 1.8 between highest and lowest requirement in the same patient. CONCLUSIONS: Neuromuscular block can precisely be controlled with mivacurium using our model-based controller. The amount of mivacurium needed to maintain T1% at defined constant levels differed largely between and within patients. Closed-loop control seems therefore advantageous to automatically maintain neuromuscular block at constant levels.

Model-based control of mechanical ventilation: design and clinical validation.

BACKGROUND: We developed a model-based control system using end-tidal carbon dioxide fraction (FE'(CO(2))) to adjust a ventilator during clinical anaesthesia. METHODS: We studied 16 ASA I-II patients (mean age 38 (range 20-59) yr; weight 67 (54-87) kg) during i.v. anaesthesia for elective surgery. After periods of normal ventilation the patients were either hyper- or hypoventilated to assess precision and dynamic behaviour of the control system. These data were compared with a previous group where a fuzzy-logic controller had been used. Responses to different clinical events (invalid carbon dioxide measurement, limb tourniquet release, tube cuff leak, exhaustion of carbon dioxide absorbent, simulation of pulmonary embolism) were also noted. RESULTS: The model-based controller correctly maintained the setpoint. No significant difference was found for the static performance between the two controllers. The dynamic response of the model-based controller was more rapid (P<0.05). The mean rise time after a setpoint increase of 1 vol% was 313 (sd 90) s and 142 (17) s for fuzzy-logic and model-based control, respectively, and after a 1 vol% decrease was 355 (127) s and 177 (36) s, respectively. The new model-based controller had a consistent response to clinical artefacts. CONCLUSION: A model-based FE'(CO(2)) controller can be used in a clinical setting. It reacts appropriately to artefacts, and has a better dynamic response to setpoint changes than a previously described fuzzy-logic controller.

Operating room management and strategies in Switzerland: results of a survey.

BACKGROUND AND OBJECTIVE: Operating room management structures and interrelationships both within the operating suite and with other departments in the hospital can be very complex. Several different professional and support groups are represented that often have infrastructures of their own that may compete or conflict with the management hierarchy in the operating room. Today, there is often little actual management of the operating suite as an entity. We surveyed current operating room management in Switzerland. METHODS: A questionnaire was sent to the chief anaesthesiologists of all public hospitals in Switzerland. It asked for information about the structure, organization and management of operating rooms as well as respondents' opinions and expectations about management. Derived from both the literature and the results of the survey, a 'stages of excellence' model of best practice was developed. RESULTS: The overall response rate was 70%. Most anaesthesiologists were unsatisfied with current management policies and structures in their operating rooms. Of the hospitals questioned, 40% did not have an information system at all for the operating rooms. The remaining 60% had an information system that allowed rough scheduling in 71%, but only a few had more sophisticated systems that enabled dynamic scheduling (19%), user-defined conflict checking (5%), administration of a subsequent patient transfer station (postanaesthesia care units, intensive medical care, intensive care units) (10%) or other more advanced uses. All hospitals questioned offered some type of ambulatory surgery in a 'hospital-integrated' manner (i.e. use of the same operating room for both in- and outpatient surgery), but none had implemented a more efficient system where outpatient surgery was performed in separate facilities. CONCLUSIONS: Current management of the operating room in Switzerland is far from best-practice standards.

Model-based automatic feedback control versus human control of end-tidal isoflurane concentration using low-flow anaesthesia.

We studied the clinical use of an automatic feedback control system to adjust the end-tidal anaesthetic concentration with a low-flow method. The end-tidal controller uses two input signals (the end-tidal and inspiratory concentrations) to control the isoflurane concentration in the fresh gas flow, using a model-based algorithm. We studied 22 ASA I-III patients during elective surgery lasting more than 2 h. The anaesthetist was asked to make four step changes of the target end-tidal concentration (+0.3, +0.6, -0.3, -0.6 vol%), either manually (Group A) or by setting the target value for the feedback controller (Group B), and then the control was changed and the step changes were repeated, in a crossover design. Eighty step changes with each control method were compared in terms of response time, maximal overshoot and stability. The automatic control system was more accurate and stable than the human controller for step increases and step decreases, with less overshoot/undershoot and greater stability [e.g. maximal overshoot 14.7 (SD 3.7)% and 18 (8.1)% respectively for +0.6 vol% step changes, and 19.8 (3.7)% and 30.7 (13.2)% respectively for +0.3 vol% step changes]. However, the automatic control system showed a faster response time than the manual method only with large increasing steps (e.g. 149 (32) s and 205 (57) s respectively for +0.6 vol% step changes) and was not different from manual control for decreasing steps. Automatic control of the end-tidal isoflurane concentration can be better than human control in a clinical setting, and this task could be done automatically.

Resistance, reverse flow and opening pressure of unidirectional valves.

Based on a new preliminary standard of the 'Comité Européen de Normalisation', the following unidirectional valves were tested with regard to resistance, opening pressure, reverse flow and dislocation: the Dräger inspiratory and expiratory valves, the Engström inspiratory valve, the Ohmeda valve, the Siemens Ventilator 710 inspiratory and expiratory valves, the Siemens Ventilator 900C unidirectional valve of the absorber and the Megamed 700 inspiratory and expiratory valves of the circle system 219 (Megamed 700 CS 219). The following valves fulfilled all Comité Européen de Normalisation requirements: Dräger inspiratory and expiratory valves, Siemens 900 absorber valve and Megamed 700 CS 219 inspiratory valve. The Siemens 710 valve and the Megamed 700 CS 219 expiratory valve did not meet the requirements for flow resistance. The Ohmeda and Siemens 710 valves and the Engström inspiratory valve did not fulfil the Comité Européen de Normalisation requirements for reverse flow. In addition, the Engström inspiratory valve did not comply with the dislocation test. The requirements for the opening pressure were met by all the valves tested. Valves with the disc in a horizontal position achieved better results than those with the disc in a vertical position. These measurements, showing the differences in the performance of various types of valves confirm the feasibility of the standards proposal.