Recent papers discussed include two large, multicentre, highpositive end-expiratory pressure trials in acute lung injury and reflects upon the usefulness of such trial designs. Further papers considered include the emerging story of β 2 -agonists for pulmonary oedema, highlights the newly described, iatrogenic demon, of ventilator-induced diaphragm injury, promotes the addition of B-type natriuretic peptide testing to the prediction of extubation success, and muses again over the oxygen debate.
Emerging clarity in setting positive end-expiratory pressure?Minimising ventilator-induced lung injury while providing optimal respiratory support remains challenging. Limiting tidal volumes to 6 ml/kg (predicted body weight) has been widely adopted, in theory at least, but numerous other debates remain -perhaps most contentiously -regarding positive end-expiratory pressure (PEEP). Two large trials investigating the optimal ventilatory approach to patients with acute lung injury have recently been published.In the first, a combined Canadian, Australian and Saudi Arabian multicentre study, 983 patients were randomised to a 6 ml/kg (predicted body weight) tidal volume with either established ARDSnet PEEP settings or a 'high PEEP strategy with recruitment manoeuvres' [1]. Of note, plateau pressures in the lower PEEP group were limited to 30 cmH 2 O whilst those in the high-PEEP group were limited to 40 cmH 2 O. The protocol produced a significantly higher average PEEP in the experimental group, with consequently higher plateau pressures. There was no difference between the two groups with regard to the 28-day mortality, ventilator days, intensive care unit days or days of hospitalisation. There was a significant reduction in the high-PEEP group in the incidence of refractory hypoxaemia and the use of rescue therapies. In short, the high-PEEP strategy did no harm -and may have done some good, in terms of improvements in short-term physiology -but these results did not translate into statistically significant outcome improvements, although there was a trend suggesting that a significantly larger trial might produce such an outcome.The second study, a French multicentre randomised control trial, investigated 767 patients with acute lung injury [2]. The patients were randomised to either a minimal distension strategy (intrinsic plus extrinsic PEEP 5 to 9 cmH 2 O) or a recruitment strategy, in which the PEEP was maximised and plateau pressures were maintained between 28 and 30 cmH 2 O. A detailed ventilatory protocol including weaning was employed. Patients were recruited, on average, 24 hours after initiation of mechanical ventilation. The recruitment group received significantly higher PEEP and plateau pressures. There was no difference in 28-day or 60-day mortality. There was a significant reduction in ventilator-free days, organ-failure-free days and the need for adjunctive therapies in the recruitment group. In short, two large studies asking similar questions with significantly different, detailed, protocols reach t...
