Adverse Physiologic Effects of Lateral Steep Position in Acute Respiratory Failure
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: Two of 12 ventilated patients were unable to tolerate 30 minutes in the Roto Rest bed's 62-degree lateral position. Respiratory system compliance fell in the others, resulting in a decrease in delivered tidal volume.
Source: Schellongowski P, et al. Intensive Care Med. 2007:Jan 25; [Epub ahead of print].
In this study, investigators from the combined medical-surgical ICU at Vienna General Hospital in Austria determined the physiologic effects of lateral rotation therapy in 12 consecutive patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS). The patients were hemodynamically stable and being managed with pressure-control ventilation during the initial 96 hours of ALI or ARDS. Primary diagnoses associated with ALI or ARDS were pneumonia in 11 patients and near-drowning in 1 patient; their PaO2/FIO2 ratios ranged from 72 to 169 mm Hg (median, 128) on FIO2 0.45-1.00 (median, 0.70) and PEEP 6-15 cm H2O (median, 10).
The study was carried out in two parts. First, measurements were made with the patients in the supine position as well as in the right and left lateral maximum-rotation (62-degree) positions during the usual 4-min cycle of the Roto Rest continuous rotation therapy bed, with the order of the positions randomized. In the second phase, carried out 1 hr later, rotation was stopped and measurements carried out after 10 min supine and after 10-, 20-, and 30 min in the full-right or full-left lateral position, after which this protocol was repeated in the alternate position. Measurements made at every step in each of the 2 study phases included arterial blood pressure, cardiac index, arterial and mixed-venous blood gases, arterial oxygen saturation, pulmonary shunt fraction, tidal volume, peak inspiratory pressure, positive end-expiratory pressure, and static compliance. The study was to be stopped if sustained hypotension developed necessitating initiation of or increase in vasopressor therapy, or desaturation by pulse oximetry to 87% or less.
The study had to be aborted in 2 patients because of acute hemodynamic and respiratory deterioration. Among the 10 patients who completed the protocol, marked inter-individual changes in oxygenation occurred in relation to body position, but these were not predictable and the overall mean values were not significantly different. In both phases of the study, there were no significant mean changes in PaO2/FIO2 ratio, pulmonary shunt fraction, mean arterial pressure, or cardiac index in the various positions studied. However, in both phases of the study, static respiratory system compliance and delivered tidal volume were lower in both lateral steep positions than supine (p < 0.01), including at all 3 time points in Phase 2. Arterial PCO2 was significantly higher in the lateral steep positions (p < 0.01).
Commentary
Continuous lateral rotation therapy, also marketed as kinetic or oscillation therapy, was initially developed for mobilization of stroke patients and to prevent skin breakdown and pneumonia in high-risk, critically ill patients. However, the Roto Rest bed and its variations, provided by several companies, have become widely used beyond those circumstances in the management of patients with acute respiratory failure. Studies have shown that, in critically-ill patients at high risk for developing ventilator-associated pneumonia, the incidence of this complication is reduced with vigorously-applied continuous rotation therapy, although mortality, costs, and other outcomes are not different.1 The use of the Roto Rest and various other (less well studied) beds has expanded in some centers to many patients on ventilators beyond those judged at highest risk for complications as included in the existing studies.
The present study by Schellongowski and colleagues sounds a cautionary note for the current widespread enthusiasm for continuous lateral rotation therapy for mechanically ventilated patients. It shows that static respiratory system compliance is reduced in the maximum lateral positions achieved by this bed, and that some patients experience deterioration in hemodynamics and oxygenation when held in these positions for more than 10 minutes. Further, it demonstrates that these adverse effects may be difficult to predict in individual patients.
The decreased tidal volumes observed with the lateral steep position in comparison with the supine position were from about 650 mL to about 530 mL, with corresponding mean arterial PCO2 values of around 45 and 49 mm Hg, respectively. These are not clinically serious changes, and in part they reflect the use of pressure-control ventilation, in which changes in compliance produce changes in delivered tidal volume rather than in airway pressures. Most likely, if the patients in this study had been managed with volume assist-control as in the ARDS Network protocol for managing ALI/ARDS,2 these changes would not have been observed.
One practical point is suggested by the findings of this study. When patients are being managed with continuous lateral rotation therapy, assessment of gas exchange and respiratory system mechanics in response to changes in ventilator settings (or for routine monitoring) should be made with the patient always in the same position, preferably supine.
References
- Hess DR. Patient positioning and ventilator-associated pneumonia. Respir Care. 2005:Jul;50(7):892-898.
- The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301-1308.
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