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Synopsis: In a small study of patients with acute respiratory distress syndrome, prone positioning was compared with continuous rotation treatment, and a similar improvement in oxygenation was seen.
Source: Staudinger T, et al. Crit Care Med 2001; 29(1):51-56.
Prone positioning has been shown to be effective at improving oxygenation in some patients with severe acute respiratory distress syndrome (ARDS). The technical difficulties of this maneuver and difficulties with other interventions make a less complicated positional alternative attractive. Staudinger and colleagues used a specially designed kinetic bed to provide continuous rotation, and examined the effect of this therapy in a group of 26 patients with recently diagnosed (< 72 hours) ARDS. Patients were randomly assigned to receive prone positioning or the kinetic bed treatment. Exclusion criteria were pregnancy, malignant cardiac arrhythmias, recent (< 72 hours) thoracic or abdominal surgery, death during the first 24 hours following randomization, or severe hemodynamic instability requiring initiation of vasoactive therapy or increases in current infusion rates during rotation. The bed was designed to rotate continuously from one lateral position to the other, reaching a 124 degree angle, every 4 minutes, with a 15 second pause at the maximum rotation. Supine positioning was performed daily in such a fashion as to perform routine care procedures as briefly as possible (2-4 hours).
Patients were entered into the study based on the usual criteria for ARDS: diffuse pulmonary infiltrates, an oxygenation ratio (PaO2/FIO2) of less than 200, low wedge pressure, and the right clinical setting. All patients were monitored with pulmonary artery catheters and arterial lines. They were sedated and ventilated in the pressure control mode, using small tidal volumes (6-8 mL/kg), FIO2 0.6 or less, and PEEP up to 20 cm H2O in order to keep arterial saturation greater than 91%. Inhaled nitric oxide (iNO) was used in all patients prior to entry into the study, beginning at 1 ppm. If the patient was a responder to iNO, the dose was increased until the maximum effect on oxygen saturation was obtained. All patients were on iNO initially, but this therapy was weaned as oxygenation improved. Hemodynamic and gas exchange variables were obtained hourly.
Twenty-six patients were entered into the study, with 12 assigned to the prone treatment group and 14 to the rotation treatment group. There were no differences between the groups in age (52 vs 54), the proportion of iNO responders (75% vs 79%), initial APACHE II or Murray Lung Injury Scores, or the average iNO dose (20 ppm). Initial ventilatory parameters and blood gases on entry along with intrapulmonary shunt and oxygenation ratio over the first 72 hours were not different in the two groups. There was no difference in the number of patients who improved, or in the area under the curve for the above oxygenation measures, between the groups. No patients were excluded from the prone group for hemodynamic instability, while maximal rotation was temporarily reduced in two patients in the rotation group. There were no complications related to the therapy (such as lines or tubes lost) in either group. There was no difference in mortality (59% vs 64%), or in time to resolution of ARDS in survivors (5 days).
This is a preliminary study demonstrating equal efficacy of continuous rotation and prone positioning in improving measures of oxygenation in patients with severe ARDS. The convenience of such therapy would certainly justify adding it to the armamentarium against ARDS if it also improved survival.
Clinical application of the results of this study are hindered by the fact that even prone positioning has not been shown to improve patient survival, despite its ability to improve oxygenation. Nitric oxide, also used in this study, is another therapy that does not improve survival despite having a salutary effect on measures of oxygenation. Despite the recognition that few therapies have been shown to improve the outcome of ARDS (probably, limiting the tidal volume does improve survival), it is difficult not to believe that a therapy which improves oxygenation and allows reduction in inspired oxygen concentration isn’t valuable.
This is a dilemma of clinical medicine: improvements in short-term or surrogate measures of "improvement" are attractive when things appear desperate despite the lack of support of long-term improvement. We must resist embracing new expensive or dangerous therapies that do not have the scientific underpinnings of proven efficacy. While this study’s results are an interesting observation, this therapy is unlikely to improve patient survival.