Free Prone positioning in acute respiratory distress syndrome
Kristy Gibson Nurse, Kent Hospital intensive care unit, Warwick, Rhode Island, United States
Marlene Dufault Nurse, professor, College of Nursing, University of Rhode Island, Newport Hospital, Newport, Rhode Island, United States
Kathy Bergeron Clinical nurse specialist, emergency department, intensive care unit stroke team co-ordinator, Newport Hospital life saving skills classes co-ordinator, Newport Hospital, Newport, Rhode Island, United States
Acute respiratory distress syndrome (ARDS) is a condition with a high morbidity and mortality rate, and treatment is often long and costly. Prone positioning is a rarely used intervention for patients with this syndrome, although research suggests it may be effective. A literature search was undertaken to examine the effects of prone positioning on oxygenation, morbidity and mortality in patients with ARDS. It revealed that prone positioning, when used with low tidal volume ventilation over an extended period, may reduce mortality rates in selected patients with severe ARDS. The selection of patients with severe ARDS for prone positioning should be done on a case-by-case basis to maximise benefits and minimise complications. Further research is required on the use of prone positioning in patients with severe ARDS to support or disclaim the therapy’s use in practice, and to compare confounding variables such as ideal prone duration and mechanical versus manual pronation.
Nursing Standard. 29, 50, 34-39. doi: 10.7748/ns.29.50.34.e9261Correspondence
All articles are subject to external double-blind peer review and checked for plagiarism using automated software.
Received: 25 June 2014
Accepted: 05 February 2015
Published: 12 August 2015
ACUTE RESPIRATORY DISTRESS syndrome (ARDS) is seen periodically in intensive care units, with an incidence of approximately 5% in mechanically ventilated patients, and a mortality rate of around 40% (Walkey et al 2012). Treatment is often long and costly and is primarily supportive (Morrell 2010, Longo et al 2012). Studies suggest that prone positioning in ventilated patients with ARDS may improve impaired gas exchange. However, prone positioning (also referred to as prone therapy) is used typically as a last resort because of lack of knowledge and/or disinclination of the clinician to use it (Morrell 2010). Exploration of prone positioning may help to support or disclaim its use in practice, potentially improving patient outcomes. The aim of this literature review is therefore to examine the effect of prone positioning on oxygenation and outcomes, to guide best practice.
A full understanding of the pathophysiology of ARDS remains elusive (Hudack 2012). ARDS results usually from sudden direct or indirect lung damage that triggers a systemic inflammatory response syndrome. Signs and symptoms include rapid onset, severe dyspnoea, diffuse bilateral pulmonary infiltrates and sudden hypoxaemia, resulting in non-cardiogenic respiratory failure within approximately one week of insult (Longo et al 2012, Parrillo and Dellinger 2014). The leading cause of death in patients with ARDS is multiple organ failure, however the pathophysiologic link between multiple organ failure and ARDS is not understood fully (Pierrakos et al 2012). There are several pathways involved; therefore, there is no single biomarker to predict outcomes for the syndrome (Pierrakos et al 2012).
At a molecular level, after the initial insult, there is a loss of the lung’s alveolar capillary barrier to macromolecules, resulting in accumulation of protein-rich plasma, leading to pulmonary oedema, microvascular occlusion and pulmonary vascular damage (Longo et al 2012, Pierrakos et al 2012). The lungs become stiff and less compliant. Blood shunts inside the pulmonary space, unable to oxygenate circulating erythrocytes, and the resulting hypoxia leads to pulmonary hypertension. Atelectasis ensues in dependent regions of the lung. Severe hypoxaemia and hypercapnia develop, resulting in tachypnoea and increased work of breathing, producing respiratory fatigue and respiratory failure (Longo et al 2012). As the syndrome progresses, the patient may improve or deteriorate. The pulmonary oedema resolves and the initiation of lung repair begins. However, lung injury may progress to fibrosis, progressive vascular occlusion, pulmonary hypertension, large bullae and pulmonary dead space. There is an increase in morbidity and mortality at this time as a result of the emphysema-like changes that make oxygenation progressively difficult in the stiff, non-compliant lungs (Hudack 2012, Longo et al 2012, Pierrakos et al 2012). Patients that progress to this point require continuing support with oxygenation and respiration (Longo et al 2012).
Current treatment regimens are primarily supportive. They include endotracheal intubation and ventilator support at low tidal volumes to prevent ventilator-associated lung injury; high positive end expiratory pressure levels to prevent alveolar collapse; appropriate nutritional sustenance; and treatment of other failing organs (Morrell 2010, Longo et al 2012). Fluids are monitored and managed to minimise pulmonary oedema. Transfer of certain patients with ARDS for treatment at an extracorporeal membrane oxygenation centre has been reported to improve outcomes (Williams 2013). Other support includes prophylaxis, prompt diagnosis and treatment of complications (Longo et al 2012).
Use of prone positioning
Prone positioning involves placing the patient with his or her ventral side down and dorsal side up. It was used first in patients with ARDS experiencing severe hypoxaemia by healthcare providers in 1976 with results that suggested improved oxygenation (Parrillo and Dellinger 2014). Studies subsequently replicated these results, showing that prone positioning improves oxygenation in approximately 60-70% of this population (Gattinoni et al 2001). The benefits of prone positioning include increased chest wall elasticity; alveoli recruitment of the posterior lung units; increased end expiratory lung volume; decreased compression of lung tissue from dependent regions such as pleural effusions, the heart and the abdomen; and facilitation of secretion drainage (Kopterides et al 2009, Robak et al 2011, Pierrakos et al 2012). Ventilator-associated injury may be prevented or delayed when prone positioning is used because there is an optimised ventilation-perfusion ratio, resulting in more homogeneous ventilation and distribution of lung stress and strain (Taccone et al 2009, Pierrakos et al 2012, Guérin et al 2013).
Complications and contraindications
Before considering prone therapy for a patient, the potential for complications should be investigated. Complications that have occurred include device displacement, venous access loss, vomiting, haemodynamic instability and new or worsening pressure ulcers (Kopterides et al 2009, Taccone et al 2009). These adverse events may be related to an increased amount of time in a prone position (Taccone et al 2009). Assessment of the risks and benefits are essential before attempting prone therapy.
Prone therapy should be selected for patients on a case-by-case basis to ensure patient safety. Contraindications include severe haemodynamic instability; life-threatening arrhythmia; evidence of elevated intracranial, intraocular or intra-abdominal pressures; seizure; multiple trauma; facial, chest, spine or pelvic fractures; tracheotomy less than 24 hours old; recent cardiothoracic surgery; left ventricular failure; pregnancy in the second or third trimester; open abdominal wound, though it may be possible if an abdominal binder is used, and surgical advice may be required; inguinal or abdominal soft tissue infection; intestinal ischaemia; and patients previously demonstrating poor tolerance of prone positioning (Gattinoni et al 2001, Murray and Patterson 2002, Robak et al 2011). Prone positioning therapy may not be tolerated or could worsen the condition of these patients.
A literature search was undertaken using Cumulative Index to Nursing and Allied Health Literature (CINAHL) and Medline search engines with the following keywords: ‘prone position’, ‘acute respiratory distress syndrome’ and ‘ARDS’. The goal of the search strategy was to include recent unbiased peer-reviewed clinical studies and meta-analyses aimed at examining oxygenation, morbidity and mortality related to ARDS and prone therapy published between January 2001 and June 2014. By unbiased, it is meant the articles do not favour certain ideas without considering other ideas. Inclusion criteria included peer-reviewed studies of adult patients with ARDS who were prone positioned. A total of 31 hits were found in CINAHL and 29 hits in Medline with free full text. Studies involving children and animals were excluded since the physiological make-up of these populations may differ somewhat to the exact population being studied.
The strength of empirical evidence in the articles was graded from level I to VII, based on guidelines adapted from Melnyk and Fineout-Overholt (2011):
▶ Level I = systematic reviews and meta-analyses of randomised controlled trials (RCTs).
▶ Level II = one or more RCTs.
▶ Level III = controlled trials without randomisation.
▶ Level IV = case-control or cohort studies.
▶ Level V = systematic reviews of descriptive and qualitative studies.
▶ Level VI = single descriptive or qualitative studies.
▶ Level VII = expert opinion.
Studies greater than level III strength were excluded. Table 1 summarises chronologically the findings of the literature review.
Studies of prone positioning
In a multicentre, randomised trial, supine positioning was compared with prone positioning for six or more hours daily for ten days (Gattinoni et al 2001). Adult mechanically ventilated patients experiencing acute lung injury (ALI) or ARDS without evidence of cardiogenic pulmonary oedema, cerebral oedema, intracranial hypertension or conditions contraindicating prone positioning were included. Oxygenation improved significantly with prone therapy, improving oxygenation in more than 70% of instances with 69.9% of the effect occurring during the first hour of being placed in the prone position. However, mortality rates did not differ significantly, suggesting that the oxygenation improvement may have been transient or that the patients were not placed in the prone position for a long enough period. There was no increase in complications in the experimental group (Gattinoni et al 2001).
In a multicentre, unblinded RCT of 342 ventilated adults with moderate-to-severe ARDS from 25 intensive care units in Italy and Spain, patients were either positioned supine or prone for approximately 20 hours per day (Taccone et al 2009). Prone positioning was enabled using an automated pronating bed in 20 of the 25 units. Results did not suggest that prone positioning affected patients with ARDS significantly. However, there was a clinically significant (statistically non-significant), approximately 10% decrease in mortality rates of patients with severe hypoxaemia, suggesting that prone positioning may be beneficial only to patients with severe ARDS. The experimental group experienced more complications such as pressure ulcers, greater requirement for sedation, device displacement, vomiting, loss of venous access and haemodynamic instability. The authors attributed these complications to the length of time spent in the prone position (Taccone et al 2009).
In a meta-analysis, the effects of prone positioning on adult patients in hypoxic respiratory failure, including patients with ARDS and ALI, were analysed focusing only on RCTs (Kopterides et al 2009). Four studies with 662 patients in prone position for a mean of ten hours and 609 that were left supine were included. Oxygenation improved with pronation, but there were no statistically significant differences in overall mortality, length of stay, duration of mechanical ventilation, pneumothorax and ventilator-associated pneumonia. However, the mortality rate was lower in the most severely ill patients who were ventilated in the prone position. Complications included more new or worsening pressure ulcers in prone patients, compared with supine patients (Kopterides et al 2009).
The results of four clinical trials from 2001 to 2009 involving adult ventilated patients with acute hypoxaemic respiratory failure or ARDS were reviewed in a meta-analysis (Gattinoni et al 2010). Although overall survival rates did not improve, prone positioning did improve gas exchange and improved survival rates in patients who were severely hypoxaemic. This may be a result of having the physiological prerequisites to make pronation effective (Gattinoni et al 2010).
Seven RCTs from 2001 to 2009 were examined by Abroug et al (2011). Mortality was calculated in the overall included studies as well as in two subgroups: patients with ALI or hypoxaemia, and patients with ARDS. Effect of prone therapy duration and major adverse airway complications were assessed. This meta-analysis suggested that long intervals (17-24 hours per day) of prone therapy may decrease significantly the mortality of patients with ARDS only. Prone therapy was not associated with an increase in major airways complications (Abroug et al 2011).
In a prospective RCT, the short-term effects of oxygenation in prone and semi-recumbent positions were studied in 20 adults with ARDS who were not receiving extracorporeal gas exchange (Robak et al 2011). The control group received four hours of prone positioning. The experimental group was placed in the prone position in a low-airloss bed system manually for two hours and then placed in the prone-upright position using the bed. Hourly lung compliance and blood gases were measured. There were no statistically significant changes in lung compliance. Results revealed that 70% of patients had improved oxygenation in the prone position and 85% had improved oxygenation with prone-upright positioning. Three non-responders with ARDS responded following prone-upright positioning. Better effects were seen in patients with more severe ARDS. It is speculated that the caudal shift of the diaphragm in the prone-upright position may lead to redistribution of ventilation and perfusion, optimising the ventilation-perfusion ratio. The study was limited by the low sample size and short duration. However, results suggest the potential of the upright prone position to help improve oxygenation in patients with ARDS (Robak et al 2011).
In a multicentre, prospective RCT, mortality in 466 adult mechanically ventilated patients recently diagnosed with severe ARDS was examined. The experimental group underwent prone positioning for at least 16 hours daily (Guérin et al 2013). Prone positioning was stopped after 28 days, when oxygenation improved or when complications occurred. Results were compared with the control group of supine patients, and the mortality rate for the experimental group was lower than for the control group. Complications did not differ significantly, except for an increased rate of cardiac arrest in the control group. These results suggest that long prone sessions with patients with severe ARDS may significantly decrease mortality rate (Guérin et al 2013).
In a meta-analysis by Beitler et al (2014), seven trials from 2001 to 2013 including 2,119 patients with ARDS were evaluated to determine the correlation of mortality with prone positioning. The meta-analysis revealed that prone positioning was not significantly correlated with risk of death. However, when stratified by tidal volume ventilation, a significant decrease in death occurred in those placed in the prone position with low tidal volume ventilation, compared with prone patients receiving high tidal volume ventilation. This suggests that the use of prone positioning in patients with ARDS with recommended low tidal volume ventilation may decrease mortality rates (Beitler et al 2014).
Discussion and implications for practice
Confounding variables involved duration of prone therapy, use of mechanical prone beds and experience of and education on prone therapy for staff. Optimal duration of prone therapy is a confounding variable. While longer periods of prone therapy may increase oxygenation, the risk of complications may increase. There is no agreement on how long a patient should be placed in the prone position. However, research suggests that the longer a patient is given prone therapy the greater the benefits (Abroug et al 2011).
Ventilation strategy is a confounding variable that may have altered previous research studies. Over time, the use of low tidal volume ventilation has become more mainstream for this population. The meta-analysis by Beitler et al (2014) suggests that the mortality rate is significantly lower in prone patients with ARDS with low tidal volume ventilation versus similar patients with high tidal volume ventilation.
A limitation is the lack of clarity regarding what types of bed were used in most studies. In the study by Taccone et al (2009), 20 of 25 centres that participated in the study used automated pronating beds. There is no mention of how many patients experienced pronation via the automated pronating bed versus standard manual manipulation in a hospital bed. In the study by Robak et al (2011), a low-airloss bed system was used, and the patients were placed manually in the prone position. In the study by Guérin et al (2013), only standard intensive care unit beds were used. The effectiveness of mechanical beds versus manual pronation should be questioned, and whether this may have altered results. Otherwise, no conclusion can be made in regard to mechanical bed versus manual positioning.
Lack of experience of and education on prone therapy for staff is a limitation and may cause disinclination to use the therapy. It may also increase complications. The technical aspects of prone positioning are not simple. A co-ordinated team effort is required to help prevent adverse events related to repositioning (Guérin et al 2013). Further, it can be physically challenging for all involved to place the patient into the prone position. Collaboration with nurses, physicians and respiratory therapists is necessary to manoeuvre the patient into position successfully and increase the benefit of therapy for the patient (Murray and Patterson 2002). Strict observation of the effects of positioning is necessary because individual response may vary (Robak et al 2011). Some studies found increased complications such as increased requirement for sedation, device displacement, vomiting, loss of venous access, haemodynamic instability and pressure ulcers with prone positioning (Kopterides et al 2009, Taccone et al 2009). However, patients in other studies did not experience an increase in complications (Abroug et al 2011). It is possible that such complications may be avoided with training and collaboration among clinicians before use of prone therapy.
Prone positioning relieves severe hypoxia and prevents ventilator-induced lung injury by decreasing over-inflation of the lung, promoting alveolar recruitment and homogenising the distribution of stress and strain on the lung (Guérin et al 2013). When prone positioning is used generally in patients who are hypoxaemic, there is no mortality benefit (Kopterides et al 2009, Taccone et al 2009, Gattinoni et al 2010, Abroug et al 2011). However, when long intervals of prone positioning are used early with recommended low tidal volume ventilation in patients with severe ARDS, there appears to be a decreased rate of mortality in this population (Morrell 2010, Abroug et al 2011, Beitler et al 2014). This could be related to the physiological lung conditions required for pronation to work.
There does not appear to be benefit to patients with ALI or mild-to-moderate ARDS. Oxygenation may improve, but the results are transient and appear not to reduce the mortality rate in this population (Kopterides et al 2009, Gattinoni et al 2010, Abroug et al 2011). Therefore, prone positioning may expose patients with less severe ARDS to unnecessary complications (Gattinoni et al 2010).
Further research on prone therapy is required in patients with severe ARDS to support or disclaim the use in practice, and to compare confounding variables such as ideal prone therapy duration and mechanical versus manual pronation.
ARDS is a condition with a high morbidity and mortality rate, and treatment is primarily supportive. Based on the evidence reviewed, prone therapy improves oxygenation in patients with ARDS. Prone positioning, when used with low tidal volume ventilation and over an extended period, may improve mortality in selected patients with severe ARDS. Selection of patients with severe ARDS for prone therapy, withholding contraindications, should be done on a case-by-case basis to maximise benefits and minimise complications. Collaborative effort and education is required to limit complications of prone therapy.
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