Estudiante

Critical Care

December 2004 Vol 8 No 6

Putensen and Wrigge

Review

Clinical review: Biphasic positive airway pressure and airway pressure release ventilation
Christian Putensen1 and Hermann Wrigge2
for Anesthesiology and Intensive Care Medicine, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany 2Assistant Professor for Anesthesiology andIntensive Care Medicine, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany
1Professor

Corresponding author: Christian Putensen, putensen@uni-bonn.de

Published online: 2 August 2004 This article is online at http://ccforum.com/content/8/6/492 © 2004 BioMed Central Ltd

Critical Care 2004, 8:492-497 (DOI 10.1186/cc2919)

Abstract
This reviewfocuses on mechanical ventilation strategies that allow unsupported spontaneous breathing activity in any phase of the ventilatory cycle. By allowing patients with the acute respiratory distress syndrome to breathe spontaneously, one can expect improvements in gas exchange and systemic blood flow, based on findings from both experimental and clinical trials. In addition, by increasingend-expiratory lung volume, as occurs when using biphasic positive airway pressure or airway pressure release ventilation, recruitment of collapsed or consolidated lung is likely to occur, especially in juxtadiaphragmatic lung legions. Traditional approaches to mechanical ventilatory support of patients with acute respiratory distress syndrome require adaptation of the patient to the mechanical ventilatorusing heavy sedation and even muscle relaxation. Recent investigations have questioned the utility of sedation, muscle paralysis and mechanical control of ventilation. Furthermore, evidence exists that lowering sedation levels will decrease the duration of mechanical ventilatory support, length of stay in the intensive care unit, and overall costs of hospitalization. Based on currently availabledata, we suggest considering the use of techniques of mechanical ventilatory support that maintain, rather than suppress, spontaneous ventilatory effort, especially in patients with severe pulmonary dysfunction.
Keywords acute respiratory distress syndrome, airway pressure release ventilation, biphasic positive airway pressure, mechanical ventilation

Introduction
Partial ventilatory supportis commonly used, not only to wean patients from mechanical ventilation but also to provide stable ventilatory assistance to a desired degree. Conventional partial ventilatory support modalities either provide ventilatory assistance to every inspiratory effort and modulate the tidal volume (VT) of the patient (e.g. pressure support ventilation [PSV] [1] and pressure assisted ventilation [2]) ormodulate minute ventilation by periodically adding mechanical insufflations to unsupported spontaneous breathing (e.g. intermittent mandatory ventilation [IMV] [3]). In contrast, biphasic positive airway pressure (BiPAP) [4] and airway

pressure release ventilation (APRV) [5] allow unrestricted spontaneous breathing in any phase of the mechanical cycle.

The principles of airway pressurerelease ventilation and biphasic positive airway pressure
APRV and BiPAP ventilate by time-cycled switching between two pressure levels in a high flow or demand valve continuous positive airway pressure (CPAP) circuit, and therefore they allow unrestricted spontaneous breathing in any phase of the mechanical ventilator cycle [4,5]. The degree of ventilatory support is determined by the durationof

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APRV = airway pressure release ventilation; ARDS = acute respiratory distress syndrome; ATC = automatic tube compensation; BiPAP = biphasic positive airway pressure; CMV = controlled mechanical ventilation; CPAP = continuous positive airway pressure; CT = computed tomography; DO2 = oxygen delivery; IMV = intermittent mandatory ventilation; PSV = pressure support ventilation; VA/Q =...