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Abstract & Commentary
Synopsis: In a small study of patients with ARDS, prone positioning was compared with continuous rotation treatment, and a similar improvement in oxygenation was seen.
Source: Staudinger T, et al. Comparison of prone positioning and continuous rotation of patients with adult respiratory distress syndrome: Results of a pilot study. 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 compared the effect of this therapy to prone positioning 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 requiring increases in current therapy during rotation. The bed was designed to rotate continuously from one lateral position to the other, reaching a 124° angle every 4 minutes with a 15 second pause at the maximum rotation. Supine positioning was performed daily 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 < 200 mm Hg, low pulmonary artery wedge pressure, and an appropriate clinical setting. All patients were monitored with pulmonary artery catheters and arterial lines. They were sedated and ventilated with pressure control mode, small tidal volumes (6-8 mL/kg), FIO2 0.60 or less, and positive end-expiratory pressure (PEEP) up to 20 cm H2O to keep SaO2 > 91%. Nitric oxide (NO) was used in all patients prior to entry into the study. Patients were begun at 1 ppm NO and, if the patient was a "responder," increased until the maximum effect on oxygen saturation was obtained. All patients were started on NO during the study, although as oxygenation improved, NO was weaned. Hemodynamic and gas exchange variables were obtained hourly.
Twenty-six patients were entered into the study—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 number of NO responders (75% vs 79%), APACHE II Scores, Murray Lung Injury Score (mean = 3), average NO dose (20 ppm), ventilatory parameters, or blood gases on entry. Intrapulmonary shunt and oxygenation ratio were the same in both groups over the first 72 hours. There was no difference in the number of patients improving 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 2 patients in the rotation group. There were no complications related to the therapy (lines or tubes lost) in either group. There was no difference in mortality (59% vs 64%) or time to resolution of ARDS in survivors (5 days).
Comment by Charles G. Durbin, Jr., MD
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 is hindered by the fact that even prone positioning has not been shown to improve patient survival, despite its ability to improve oxygenation. Nitric oxide as 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 (limiting the tidal volume probably improves survival), it is difficult not to believe that a therapy that improves oxygenation and allows reduction in inspired oxygen concentration isn’t valuable.
This is a dilemma of clinical medicine: improvement in short-term or surrogate measures of "improvement" are so 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 the findings of this study constitute an interesting observation, this therapy is unlikely to improve patient survival.