BJA Advance Access originally published online on February 24, 2006
British Journal of Anaesthesia 2006 96(4):522-532; doi:10.1093/bja/ael033
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The effect of bi-level positive airway pressure mechanical ventilation on gas exchange during general anaesthesia
1Department of Anaesthetics, University of Sydney and Royal Prince Alfred Hospital Sydney, NSW, Australia
2Department of Respiratory Medicine, University of Sydney and Royal Prince Alfred Hospital Sydney, NSW, Australia
*Corresponding author: Department of Anaesthetics, University of Sydney and Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW, Australia 2050. E-mail: bbaker{at}usyd.edu.au
Background. Atelectasis may occur and ventilation–perfusion mismatch may increase during general anaesthesia with neuromuscular paralysis and mechanical ventilation, though preservation of some intermittent muscle contraction might mitigate this process. There is still no ideal manoeuvre to minimize such mismatch or atelectasis. Bi-level positive airway pressure (BiPAP) ventilation adjusts to extra breaths and improves gas exchange during recovery of diaphragm function after neuromuscular paralysis. We hypothesize that BiPAP ventilation may limit the development of pulmonary shunt and may improve ventilation–perfusion mismatch when compared with standard IPPV, with or without PEEP when neuromuscular paralysis has been used during surgery.
Methods. Twenty ventilated patients either on BiPAP or IPPV with or without PEEP were studied randomly using the multiple inert gas elimination technique (MIGET) at 60 and 120 min after rocuronium at induction and after 60 min. Non-invasive cardiac output (NICO®) monitoring and plasma concentrations of rocuronium were measured. We compared the data of MIGET, gas exchange, haemodynamic variables and pulmonary mechanics measurements between the different ventilatory modes.
Results. Intrapulmonary shunt (blood flow to 
) did not increase at 60 min of anaesthesia in any of the different ventilation modes compared with the shunt value before anaesthesia. Log standard deviation of perfusion increased in IPPV, with and without PEEP groups, compared with the baseline (P<0.05) but did not increase in the BiPAP group. BiPAP ventilation generated a higher level of PaO2 than IPPV with or without PEEP (P<0.05).
Conclusion. BiPAP ventilation was beneficial in decreasing ventilation–perfusion mismatch and improving oxygenation when compared with conventional IPPV (with or without PEEP).
3Present address: Department of Anaesthesia, Guangzhou Medical College, Guangzhou, China