Respiration/VentilationProne positioning in hypoxemic respiratory failure: Meta-analysis of randomized controlled trials
Introduction
The acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are common and fatal diseases that represent a major public health problem [1]. Even though ARDS-associated mortality has been shown to be decreasing over the last 2 decades [2], it still remains higher than 30% [1], [3]. A recently published review of the studies reporting epidemiologic data on ARDS and ALI estimated their incidence to be approximately 20 to 75 cases per 100 000 person-years [4]. Another study [5] showed that among patients requiring mechanical ventilation for more than 24 hours, 5 patients have hypoxemic respiratory failure (HRF) for every one who is actually diagnosed with ARDS/ALI. This leaves a large, yet poorly characterized group of patients who contribute to the rising cost of healthcare.
Despite recent advances in the elucidation of the mechanisms of ALI and promising results from animal models, all pharmacologic approaches in the treatment of ARDS have been proven ineffective [6], with glucocorticoids representing the most recently proven unsuccessful intervention [7]. Thus, the only therapy so far showing a clear survival benefit (9% absolute decrease in mortality) remains the lung-protective ventilation strategy in which low tidal volume mechanical ventilation of 6 mL/kg is applied instead of the traditionally used tidal volume of greater than 10 mL/kg [8].
Prone positioning was initially shown to improve oxygenation in mechanically ventilated patients with hypoxemic acute respiratory failure more than 30 years ago [9], [10]. Over the last few years, numerous studies have shown that ventilation in the prone position improves oxygenation, sometimes dramatically, in approximately 70% of the patients [11]. Even though most clinical experience with the prone positioning has been derived from mechanically ventilated patients with ARDS/ALI, oxygenation improvement has been shown in a number of respiratory illnesses, such as hydrostatic/cardiogenic pulmonary edema [12], chronic obstructive pulmonary disease [13], [14], and postoperative hypoxemia [15]. Prone positioning has even been used in awake nonintubated patients with HRF to avoid mechanical ventilation [16]. The beneficial effects of prone positioning on gas exchange seem to stem from the recruitment of posterior atelectatic lung units [17] and increase of the end-expiratory lung volume [18], improvement of respiratory mechanics [18], [19], decrease of ventilation-perfusion mismatch [20], decrease of lungs' compression by the heart [21], attenuation of ventilator-induced lung injury (VILI) [22], [23], and facilitation of secretions, drainage [13].
Despite the undisputed improvement in oxygenation and lung mechanics attained by prone ventilation, normalizing physiologic variables in acute illness and applying physiologically sound treatments may not be sufficient [8], [24] and may even be harmful [25]. Although prone positioning is frequently used in the management of adult patients with HRF, it constantly sparks emotional responses and debates among critical care specialists [26], because the intensive care community is in equipoise regarding its actual clinical benefits. Although there have been reviews in the literature on this issue, they are mostly narrative [11], [27]. Thus, we decided to systematically review, assess, and synthesize the available evidence from studies that compared prone with supine positioning in terms of mortality and other important clinical outcomes among adult patients with HRF.
Section snippets
Methods
This article was prepared in accordance with the QUOROM statement [28].
Search results and trial characteristics
In Fig. 1, we present a flow diagram describing in detail the selection process applied to identify the pool of RCTs included in the meta-analysis. We identified 53 published clinical trials including patients with HRF that were treated in the prone position. From these, 10 trials were excluded because of inappropriate study design, that is, they were retrospective, not controlled, or not randomized clinical trials (1, 5, and 4 trials, respectively). In addition, 3 studies were excluded because
Discussion
The purpose of our study was to compare the effect of prone and supine mechanical ventilation on mortality and other relevant secondary clinical outcomes among patients with HRF, irrespective of changes in gas exchange and lung mechanics. Our main finding is that the evidence from randomized controlled trials does not support any benefit in mortality from the implementation of prone positioning ventilation in the broad group of hypoxemic patients. However, there is evidence that prone
Conclusions
The available evidence does not support a beneficiary effect of prone positioning on mortality among the broad group of patients with HRF, but a positive mortality effect in patients with severe ARDS cannot be excluded. In addition, our data show that ventilation in the prone position may lower the incidence of VAP at the expense of an increased incidence of pressure sores and, probably, complications related to the position of the ETT.
It is conceivable that negative trial results cannot deter
References (56)
- et al.
Pharmacological therapy for acute respiratory distress syndrome
Mayo Clin Proc
(2006) - et al.
Influence of positioning on ventilation-perfusion relationships in severe adult respiratory distress syndrome
Chest
(1994) - et al.
Improving the quality of reports of meta-analyses of randomised controlled trials: the QUOROM statement. Quality of Reporting of Meta-analyses
Lancet
(1999) - et al.
Does quality of reports of randomised trials affect estimates of intervention efficacy reported in meta-analyses?
Lancet
(1998) - et al.
Assessing the quality of reports of randomized clinical trials: is blinding necessary?
Control Clin Trials
(1996) - et al.
Meta-analysis in clinical trials
Control Clin Trials
(1986) Evidence-based medicine in the ICU: important advances and limitations
Chest
(2004)- et al.
Pediatric Prone Positioning Study Group. Clinical trial design-effect of prone positioning on clinical outcomes in infants and children with acute respiratory distress syndrome
J Crit Care
(2006) - et al.
Epidemiology of acute lung injury
Curr Opin Crit Care
(2005) - et al.
Improved survival of patients with acute respiratory distress syndrome (ARDS): 1983-1993
JAMA
(1995)