Short-term effects of prone position in critically ill patients with acute respiratory distress syndrome

Clinical guidelines for the use of the prone position in acute respiratory distress syndrome

The mortality associated with acute respiratory distress syndrome (ARDS) remains high. It has been suggested that use of the prone position may improve survival. However, approaches to the use of the position are often haphazard. The development of clinical guidelines indicating the need for the prone position in ARDS and the process by which the manoeuvre may be performed were thought to be important for two reasons. Primarily, we sought to improve oxygenation through the use of the prone position whilst promoting patient safety. Secondly, we wished to standardize our approach to the use of the prone position and make recommendations for practice so that its use was no longer seen as a last resort in the management of ARDS. The process associated with the development of clinical guidelines is first described. This is followed by presentation of the clinical guidelines. Included in these are the criteria and discussion which indicate consideration of the prone position, potential exclusion criteria, pre-turn considerations, the turning technique, monitoring the effectiveness of the prone position, passive movements and limb positioning and, finally, documentation of the problems associated with use of the prone position. The paper concludes with discussion concerning the potential for future research in this area.

4A randomized trial of prolonged prone positioning in children with acute respiratory failure

STUDY OBJECTIVE

To compare the effect of the prone position (PP) vs supine position (SP) on oxygenation in children with acute respiratory failure (ARF).

DESIGN

Prospective, randomized controlled trial.

SETTING

A 36-bed pediatric critical-care unit in a tertiary-care, university-based children's hospital.

PATIENTS

Ten children (mean [SD] age, 5 +/- 3.6 years) with ARF with a baseline oxygenation index (OI) of 22 +/- 8.5.

INTERVENTIONS

Following a period of stabilization in the SP, baseline data were collected and patients were randomized to one of two groups in a two-crossover study design: group 1, supine/prone sequence; group 2, prone/supine sequence. Each position was maintained for 12 h. Lung mechanics and acute response to inhaled nitric oxide were examined in each position.

MEASUREMENTS AND MAIN RESULTS

OI was significantly better in the PP compared to the SP over the 12-h period (analysis of variance, p = 0.0016). When patients were prone, a significant improvement in OI was detected (7.9 +/- 5.3; p = 0.002); this improvement occurred early (within 2 h in 9 of 10 patients) and was sustained over the 12-h study period. Static respiratory system compliance and resistance were not significantly affected by the position change. Inhaled nitric oxide had no effect on oxygenation in either position. Urine output increased while prone, resulting in a significantly improved fluid balance (+ 6.6 +/- 15.2 mL/kg/12 h in PP vs + 18.9 +/- 13.6 mL/kg/12 h in SP; p = 0.041). No serious adverse effects were detected in the PP.

CONCLUSION

In children with ARF, oxygenation is significantly superior in the PP than in the SP. This improvement occurs early, remains sustained for a 12-h period, and is independent of changes in lung mechanics.

Prone positioning for acute respiratory distress syndrome in the surgical intensive care unit: who, when, and how long?

BACKGROUND

We evaluated the effects of prone positioning (PP) on surgery and trauma patients with acute respiratory distress syndrome (ARDS).

METHODS

Patients with ARDS were studied. Exclusion criteria were contraindications to PP. Patients were evaluated in the supine position and after being turned to the PP. After 6 hours, patients were returned to the supine position for 3 hours. One hour after each position change, arterial and mixed venous blood was drawn and analyzed for blood gases and pH, and hemodynamics were measured.

RESULTS

Over 20 months, 27 patients met the criteria, and 20 of the patients were entered into the study. On day 1, 18 of 20 patients (90%) responded with an increase in PaO(2) during PP. On day 2, 16 of 17 patients (94%) responded; on day 3, 15 of 16 patients responded (94%); on day 4, 11 of 13 patients responded (85%); on day 5, 8 of 8 patients responded (100%); and on day 6, 4 of 5 patients responded (80%). Pao(2)/Fio(2) and Qs/Qt were significantly improved (P<.05) during PP. There were 91 periods of PP, lasting 10.3+/-1.2 hours. Of 91 changes to PP, 78 changes (86%) resulted in an improvement in Pao(2)/Fio(2) of more than 20%.

CONCLUSIONS

PP improves oxygenation in ARDS for 6 days with few complications.

Thirty years of clinical trials in acute respiratory distress syndrome

OBJECTIVE

To systematically review clinical trials in acute respiratory distress syndrome (ARDS).

DATA SOURCES

Computerized bibliographic search of published research and citation review of relevant articles.

STUDY SELECTION

All clinical trials of therapies for ARDS were reviewed. Therapies that have been compared in prospective, randomized trials were the focus of this analysis.

DATA EXTRACTION

Data on population, interventions, and outcomes were obtained by review. Studies were graded for quality of scientific evidence.

MAIN RESULTS

Lung protective ventilator strategy is supported by improved outcome in a single large, prospective trial and a second smaller trial. Other therapies for ARDS, including noninvasive positive pressure ventilation, inverse ratio ventilation, fluid restriction, inhaled nitric oxide, almitrine, prostacyclin, liquid ventilation, surfactant, and immune-modulating therapies, cannot be recommended at this time. Results of small trials using corticosteroids in late ARDS support the need for confirmatory large clinical trials.

CONCLUSIONS

Lung protective ventilator strategy is the first therapy found to improve outcome in ARDS. Trials of prone ventilation and fluid restriction in ARDS and corticosteroids in late ARDS support the need for large, prospective, randomized trials.

Acute respiratory distress syndrome: resource use and outcomes in 1985 and 1995, trends in mortality and comorbidities

PURPOSE

The purpose of this study was to compare resource consumption and mortality between (ARDS) patients with adult respiratory distress syndrome treated at our center in 1985 (45 patients) and those treated in 1995.

MATERIALS AND METHODS

This was a retrospective observational study, considering trauma and nontrauma ARDS separately. We recorded severity index scores (APACHE III), infectious complications and multiorgan failure, intensive care unit (ICU) resource consumption (TISS 28), length of stay, time on mechanical ventilation, and ICU mortality.

RESULTS

We found no variation in overall ARDS mortality and no reduction in mortality in the ARDS trauma group (43.5% in 1985 vs. 38.5% in 1995, not significant) but a significant increase in mortality among nontrauma septic ARDS patients (68.2% vs. 82.9%, P < .001), largely attributable to the new comorbidities of human immunodeficiency virus (HIV) infection and hematologic malignancy. TISS-28 showed an overall reduction over this time period (49.7 +/- 6.6 vs. 38.3 +/- 9.7, P < .001), due to fewer monitoring measures, particularly a lower use of pulmonary artery catheter. There were no overall changes in length of stay or days on mechanical ventilation between 1985 and 1995, but these variables did increase among the trauma subgroup.

CONCLUSION

In our setting, mortality remained constant from 1985 to 1995 among ARDS trauma patients but not among nontrauma ARDS patients because of the new case-mix of the latter population, which now includes HIV and other immunodepressed patients.

Prone ventilation

Considerable clinical experience confirms that oxygenation can be improved in many patients with ARDS by employing prone ventilation. The improvement occurs because, in the prone position, the lung fits into the thorax such that lung distention is more uniform and compressive forces extant in the supine position, which serve to cause dorsal airspace collapse, are reduced. Whether these changes translate into improved clinical outcomes has yet to be determined, but prone ventilation has the potential of reducing oxygen toxicity and limiting ventilator-induced lung injury.

Hemodynamic and gas exchange response to inhaled nitric oxide and prone positioning in acute respiratory distress syndrome patients

OBJECTIVE

To analyze the single effect and the interaction of prone position and inhaled nitric oxide (iNO) on lung function and hemodynamic variables.

DESIGN

2 x 2 factorial trial.

SETTING

Department of intensive care medicine at a university hospital.

PATIENTS

Fourteen patients on volume-controlled mechanical ventilation for acute respiratory distress syndrome (ARDS).

INTERVENTION

Four experimental conditions, each one characterized by the patient's position (supine or prone) with iNO or without iNO.

MEASUREMENTS AND RESULTS

Hemodynamic and gas exchange data were collected for each experimental condition. PaO2 was increased both by positioning (p < .01) and iNO (p < .01); iNO caused also a reduction in venous admixture (p < .01), pulmonary artery pressure (p < .01), and pulmonary vascular resistance index (p < .05). We could not demonstrate any significant interaction between the two treatments. The average effect of prone positioning was the same both with and without iNO, whereas the average effect of iNO was the same in both the prone and the supine position.

CONCLUSION

In the studied acute respiratory distress syndrome patients the average effects of iNO and positioning on oxygenation were additive and no interaction could be shown. A strategy including both treatments could warrant the best improvement in oxygenation, and should take into account the individual response to each treatment and the possible combination of the two.

Respiratory failure. Conventional and high-tech support

Although significant progress has been made in the treatment of patients with acute lung failure in the critical care setting, the mortality rate from acute lung injury and ARDS is unacceptably high, given the numbers of patients treated for these syndromes each year. The improved understanding of the pathophysiology of respiratory failure from basic science and clinical research is reflected in improved survival rates over the years. Advances in the mechanical ventilator (through microprocessor technology); biosurface technology; liquid ventilation; and, in some cases, returning to so-called "antiquated" practices of patient care (e.g., prone positioning) seem to have had an impact nonetheless. As refinement continues to occur in these areas, morbidity and mortality from lung failure will have a lesser impact on patients as physicians treat the consequences of organ failure in the ICU.

Acute lung injury and acute respiratory distress syndrome in sepsis and septic shock

Sepsis remains the leading cause of ARDS, and ARDS is still an often fatal condition. With our expanding knowledge of the pathobiologic mechanisms and the relationship between these two entities, early recognition, treatment, and prevention of sepsis may prevent or hasten recovery from ARDS. Understanding the biologic markers involved in the complex inflammatory response of sepsis and acute lung injury offers the possibility of future investigations to target treatment based on these mediators.

Effect of the prone position on patients with hydrostatic pulmonary edema compared with patients with acute respiratory distress syndrome and pulmonary fibrosis

This study examined the effect of the prone position on mechanically ventilated patients with hydrostatic pulmonary edema (HPE). Eight patients with acute HPE and mechanically ventilated in the prone position (Group 1) were studied. Six patients with acute HPE and mechanically ventilated in the supine position (Group 2), 20 patients with ARDS (Group 3), and 5 patients with pulmonary fibrosis (PF) (Group 4) served as control patients. Patients with HPE, who after being mechanically ventilated for at least 6 h needed an FI(O(2)) >/= 0.6 to achieve an Sa(O(2)) of approximately 90%, and did not respond to recruitment maneuvers, were turned to the prone position. Parameters of oxygenation, lung mechanics, and hemodynamics were determined in both the supine and prone positions. All patients with HPE exhibited improvement of oxygenation when they were placed in the prone position. The Pa(O(2))/FI(O(2)) ratio increased from 72 +/- 16 in the supine position to 208 +/- 61 after 6 h in the prone position (p < 0.001); the rise in Pa(O(2)) was persistent, without detrimental effect on hemodynamics. Fifteen of 20 patients with ARDS (75%) improved oxygenation when in the prone position. The Pa(O(2))/FI(O(2)) ratio increased from 83 +/- 14 in the supine position to 189 +/- 34 after 6 h in the prone position (p < 0.001). In contrast, 5 of 20 patients with ARDS (25%) and none of the patients with PF responded favorably to prone positioning. Patients with HPE and early ARDS responded better to prone positioning than did patients with late ARDS and PF. Patients with HPE and ventilated in the supine position had a lower Pa(O(2))/FI(O(2)) ratio and the duration of mechanical ventilation was longer compared with that of patients in the prone position. Our results show that the prone position may be a useful maneuver in treating patients with severe hypoxemia due to pulmonary edema. The presence of pulmonary edema, as in early ARDS and HPE predicts a beneficial effect of the prone position on gas exchange. In contrast, the presence of fibrosis, as in late ARDS and pulmonary fibrosis, predisposes to nonresponsiveness to prone positioning.

Intermittent prone positioning in the treatment of severe and moderate posttraumatic lung injury

OBJECTIVE

Severe posttraumatic lung injury is characterized by impairment of gas exchange and pulmonary densities. The influence of intermittent prone positioning on pulmonary gas exchange and parenchymal densities was investigated prospectively in patients with pulmonary injury after multiple trauma with blunt chest trauma.

SETTING

A six-bed trauma intensive care unit in a university hospital.

DESIGN

Prospective, descriptive study.

PATIENTS

Twenty-two consecutive patients with pulmonary injury after multiple trauma with blunt chest trauma and acute lung injury (n = 11) or severe acute respiratory distress syndrome (ARDS) (n = 11) according to the definitions of the consensus conference on ARDS.

INTERVENTIONS

Pulmonary densities were calculated planimetrically from computed tomographic scans of the chest before the first and after the last cycle of prone positioning. Indications for prone positioning were a) mechanical ventilation with FIO2 >0.5 at positive end-expiratory pressure >10 cm H2O for >24 hrs; or b) pulmonary densities in two or more quadrants being constant or increasing within 48 hrs. Arterial blood gas analysis was performed every 2 hrs. Intrapulmonary right-to-left shunt (Qs/Qt) and alveolar-arterial PO2 difference were calculated 2 hrs after the beginning and end of every prone and supine cycle, respectively. Patients were ventilated in the prone position for 8 hrs each day.

MEASUREMENTS AND MAIN RESULTS

Every single posture change from the supine to the prone position resulted in a significant average increase in the oxygenation index of 28+/-8 torr (3.7+/-1.1 kPa) (p<.0001). There was a significant improvement in oxygenation (4.3+/-0.8 torr [0.57+/-0.11 kPa]) with time between two consecutive measurements in the prone as well as the supine position (p<.0001). Alveolar-arterial PO2 difference and Qs/Qt showed a significant decrease of 25+/-7 torr (3.3+/-0.9 kPa) and 1.1+/-0.46%, respectively, for every cycle of prone positioning. Statistical analysis revealed no significant alteration of gas exchange within every prone and supine cycle. Total static lung compliance improved significantly over time (p<.001). However, ventilation of patients in the prone position demonstrated a mean decrease in compliance of 2.1+/-0.72 mL/cm H2O. The response to prone positioning was similar in patients with ARDS and acute lung injury and revealed no significant difference. In both groups, the course of the oxygenation index and Qs/Qt over time was almost parallel. Posture changes were continued for 9.0+/-1.1 days. The oxygenation index showed an overall increase of 129+/-20 torr (17.2+/-2.7 kPa) from baseline supine at the end of prone positioning (p<.0001). Pulmonary densities were reduced significantly from 31.1+/-2.5% to 3.8+/-0.81%, Qs/Qt was reduced from 24.9+/-1.5% to 11.7+/-0.32%, and FIO2 was reduced from 0.43+/-0.04 to 0.26+/-0.02 (p<.01). Gas exchange improved in all patients, and no patient died immediately as a result of respiratory failure.

CONCLUSION

Repeated prone positioning recruits collapsed lung tissue and improves gas exchange in trauma patients with blunt chest trauma and severe ARDS as well as in trauma patients with acute lung injury.

Use of the prone position in the management of acute respiratory distress syndrome

The positioning of patients is usually within the domain of nursing practice, whether this is to achieve increased comfort or as a therapeutic intervention to avoid the occurrence of pressure sores. The use of the prone position to improve oxygenation, in the acute respiratory distress syndrome, has become increasingly popular in intensive care over the past decade (Thomas 1997). A systematic review was, therefore, undertaken to ascertain if the prone position did, in fact, improve oxygenation, leading to decreased mortality, or if the effects were merely transitory. Review findings indicate that use of the prone position does improve oxygenation, as measured by PaO2/FiO2 indices, and appears to reduce mortality. However, caution should be taken in applying these results to practice. First, the studies available for review demonstrated various methodological flaws. It is also apparent that untoward incidences associated with the prone position have yet to be investigated systematically.

Prone ventilation--it's time

Prone positioning to improve oxygenation in acute lung injury was first reported over 20 years ago. Although this and several subsequent studies have shown that prone positioning improved oxygenation in the majority of patients, it has failed to become common practice in intensive care units. This paper reviews the mechanism by which prone positioning improves oxygenation and the clinical studies of its use to date.

Effects of the prone position on gas exchange and hemodynamics in severe acute respiratory distress syndrome

OBJECTIVES

To address the following issues regarding the use of prone position ventilation in patients with severe acute respiratory distress syndrome (ARDS): a) response rate; b) magnitude and duration of improved oxygenation in responders during a 12-hr trial and the consequences of returning to the supine position; c) effects of the prone position on gas exchange and hemodynamics; d) consequences of oxygenation in nonresponders; and e) effects of repeated prone position trials.

DESIGN

Prospective, nonrandomized interventional study.

SETTING

Medical intensive care unit, university tertiary care center.

PATIENTS

Nineteen consecutive, mechanically ventilated patients (age 45+/-20 yrs, mean+/-SD) with ARDS and severe hypoxemia, defined as PaO2/FiO2 of < or = 150 with FiO2 of > or = 0.6 persisting for < or =24 hrs, and a pulmonary artery occlusion pressure of <18 mm Hg.

INTERVENTIONS

Patients were turned prone for 2 hrs. Nonresponders were returned supine, but responders were maintained prone for 12 hrs before being returned to the supine position. The procedure was repeated on a daily basis in all patients, until inclusion criteria were no longer met or the patients died.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic, blood gas, and gas exchange measurements were performed at the following time points: a) baseline supine; b) after 30 mins prone; and c) after 120 mins prone. Additional measurements for nonresponders were taken after 30 mins supine. For responders, additional measurements were taken after 12 hrs prone and 30 mins supine. Patients were considered responders if an increase in PaO2 of > or = 10 torr (> or =1.3 kPa), or increase in the PaO2/FiO2 ratio of >20 occurred within 120 mins. Eleven (57%) patients responded to the prone position. There was no difference in initial baseline parameters between responders and nonresponders. After 30 mins, the prone position in responders increased PaO2 and decreased calculated venous admixture (Qva/Qt). This improvement was the maximal obtained, and was maintained throughout the 12-hr prone period. After 12 hrs prone, mean FiO2 had been lowered from 0.85+/-0.16 to 0.66+/-0.18 (p < .05). Thirty minutes after the patients were returned supine, PaO2, PaO2/FiO2, and Qva/Qt were not different from 12-hr prone values, and were improved in comparison with baseline supine values. There was no worsening of gas exchange or hemodynamics in nonresponders. After the initial trial, a total of 28 additional episodes of prone position ventilation were performed in nine of the 19 patients. Of the 24 additional episodes in the responders, there was a response in 17 (71%) of 24 episodes. In the four additional episodes in nonresponders, there was a response in only one (25%) of four episodes. Response was accompanied by the same beneficial effects on gas exchange and Qva/Qt and absence of effect on hemodynamics as in the initial trial. There was no worsening in gas exchange or hemodynamics in nonresponder trials.

CONCLUSIONS

Based on the data from this study, the prone position can improve oxygenation in severely hypoxemic ARDS patients without deleterious effects on hemodynamics. This beneficial effect does not immediately disappear on return to the supine position. In our patients, an absence of response to this technique was not accompanied by worsening hypoxemia or hemodynamic instability. Repeated daily trials in the prone position should be considered in the management of ARDS patients with severe hypoxemia.