British Journal of Anaesthesia, Vol 82, Issue 6 847-851, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
J. Canet, J. Sanchis, P. Vila, A. Zegri, C. Llubia and F. Vidal
We have analysed the ventilatory response to sustained inspiratory
resistive loads in 14 patients, while awake and during halothane (n = 7) or
isoflurane (n = 7) anaesthesia. Patients breathed halothane or isoflurane
in oxygen at 1.2 minimum alveolar concentration (MAC). Inspiratory
resistances of 0, 12 and 37 cm H2O litre-1 s were applied. Tidal volume
(VT) was maintained with the greater loads. At the greatest resistance, a
significant reduction in minute ventilation occurred in both awake (-18.9%)
and anaesthetized states, with both halothane (-10.4%) and isoflurane
(-14.5%). Ventilatory frequency decreased significantly from mean 14.6 (SD
4.7) to 12.5 (4.3) bpm in the awake state and during anaesthesia, with
increasing inspiratory resistance (29.5 (3.6) to 23.7 (7.2) bpm and 25.8
(3.3) to 23.4 (4.0) bpm, respectively, for halothane and isoflurane)
because inspiratory time (TI) was significantly longer (P < 0.01).
End-tidal PCO2 increased by 0.3 kPa, on average, from baseline to the
highest level of resistance (P < 0.01). Inspiratory occlusion pressure
at 100 ms increased significantly with increased loading in all situations
(P < 0.001). We found a similar pattern of ventilatory adaptation to
sustained inspiratory flow resistive loads both in awake and anaesthetized
states. VT was maintained at increased loads because of an increase in
inspiratory neuromuscular output and inspiratory duration.
CLINICAL INVESTIGATIONS
Ventilatory compensation for inspiratory resistive loads during anaesthesia with halothane or isoflurane
Servei d'Anestesiologia i Reanimacio, Hospital Universitari Germans Trias i Pujol, Badalona 08916, Barcelona, Spain; Departament de Pneumologia, Hospital de Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain
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