Prone Positioning in Acute Respiratory Distress Syndrome

A review of the potential benefits and uses of prone positioning in patients with acute respiratory distress syndrome

By Jane Guttendorf, DNP, CRNP, ACNP-BC, CCRN

Assistant Professor, Acute & Tertiary Care, University of Pittsburgh, School of Nursing

Managing acute respiratory distress syndrome (ARDS) with prone positioning has been identified as far back as 1976 with noted improvements in oxygenation but no associated mortality benefit.1 In 2001, Gattinoni et al again demonstrated improved oxygenation in patients with acute lung injury or ARDS who were proned for an average of seven hours/day over 10 days.2 There was improved PaO2 and PaO2/FiO2 (P/F) ratio, but mortality was not significantly different: 21% in the prone group and 25% in the supine group.2 However, this study enrolled subjects prior to the widespread adoption of the Berlin definition for ARDS and when the usual delivered tidal volume (TV) was 10 mL/kg ideal body weight (IBW). Continued advances in mechanical ventilation strategies for ARDS, including low TV ventilation (6 mL/kg based on IBW), use of neuromuscular blockade, and ARDSNet FiO2 and positive end expiratory pressure (PEEP) titration tables, prompted a renewed interest in proning.

A 2013 study by Guerin et al (PROSEVA) documented improved outcomes in addition to improved oxygenation in patients with severe ARDS as identified by the American-European Consensus Conference criteria (P/F ratio < 150 mmHg on at least 60% FiO2 and 5 cm H2O of PEEP).3 This was an unblinded, randomized controlled trial (RCT) that enrolled 466 subjects from 26 intensive care units (ICUs) in France and one in Spain, assigning patients to either a prone or supine group. Patients were ventilated with a low TV strategy (6 mL/kg IBW), FiO2 of at least 60%, and PEEP ≥ 5 cm H2O, targeting a plateau pressure of ≤ 30 cm H2O, and pH of 7.20 to 7.45. Key points of this trial compared with earlier ones were that patients were enrolled early (within 36 hours of intubation and initiation of mechanical ventilation), had severe ARDS, and were proned for at least 16 hours daily until day 28. Mortality at day 28 was significantly lower in the prone group (16%) than in the supine group (32.8%) (P < 0.001), and this difference persisted out to 90 days.3

Since publication of the PROSEVA trial, there have been at least four systematic reviews of prone positioning in ARDS. In a 2015 Cochrane review including 2,165 participants in 10 studies, there was a trend toward improved (but not significantly different) mortality with proning.4 However, in a subgroup analysis, three groups consistently saw favorable results with prone ventilation: those recruited within 48 hours of meeting entry criteria (relative risk [RR] 0.75; 95% confidence interval [CI], 0.59-94), those treated with proning for 16 or more hours per day (RR 0.77; 95% CI, 0.61-0.99), and patients with severe hypoxemia at enrollment (RR 0.77; 95% CI, 0.65-0.92).4 Similarly, Munshi et al reviewed eight RCTs that included 2,129 patients.5 There was no difference in mortality between prone and supine patients (RR 0.84; 95% CI, 0.68-1.04), but again, subgroup analyses found reduced mortality in patients with longer duration of proning (12 hours or more) (RR 0.74; 95% CI, 0.56-0.99) and for patients with moderate to severe ARDS (RR 0.74; 95% CI, 0.56-0.99). P/F ratio was significantly higher for all patients in the prone group at day 4.5

Dalmedico et al reviewed seven studies published between 2014 and 2016.6 Combined use of a protective ventilation strategy and proning between 16-20 hours/day in patients with severe ARDS (P/F ratio < 150 mmHg) was associated with a significant reduction in mortality in at least four of the seven trials.6 In another systematic review of therapeutic strategies in association with lung protective ventilation in moderate to severe ARDS patients, the addition of prone positioning was associated with significantly lower 28-day mortality (RR 0.69; 95% CI, 0.48-0.99).7

PHYSIOLOGIC BENEFITS OF PRONING IN IMPROVING GAS EXCHANGE

Pulmonary blood flow is preferentially distributed to the dependent lung fields (dorsal and basal lung segments), and perfusion remains relatively constant in these areas during both supine and prone ventilation. Prone ventilation is more sensitive to changes in pressure gradients and is affected by lung and chest wall compliance, intra-abdominal pressure, and displacement from the heart and lungs within the chest cavity.8 ARDS is known to heterogeneously affect alveoli, producing severe capillary leak, and often affecting dependent alveoli to a greater extent than more ventral ones. Mechanical ventilation in the supine position often promotes better ventilation of the more ventral alveoli since the anterior chest is more readily able to expand (i.e., is more compliant). Subsequently, these alveoli can overinflate, leading to ventilator-induced lung injury (VILI).8,9 Prone positioning in ARDS allows for better ventilation of the more dependent alveoli, while improving ventilation-perfusion matching as the dependent portions continue to receive a preferential amount of blood flow.8-10 In some patients, clearance of carbon dioxide (CO2) may improve with proning, and some patients experience improvement in cardiac output.10 Right ventricular function may improve as well because of a decrease in pulmonary vascular resistance associated with improved alveolar recruitment.10

WHO BENEFITS FROM PRONING?

As noted earlier, the ARDS patients most likely to benefit from trials of prone positioning include those who have severe ARDS (P/F ratio < 100 mmHg to 150 mmHg), are early in the course of disease, and are on at least a moderate amount of PEEP (5 cmH2O to 10 cmH2O). Adding proning to high PEEP strategies can help mitigate the adverse effects of PEEP in that ventilation is better directed to the dependent alveoli, thus lessening VILI.11 The proning trial should continue for at least 16 hours/day, and patients often benefit from repeated days of prone therapy.

A recent prevalence study that included 735 ARDS patients from 141 ICUs in 20 countries evaluating the use of prone positioning in ARDS patients demonstrated that proning likely still is under-utilized.12 The prevalence of ARDS was between 8.9% and 13.3%. At least one proning session was completed in 13.7% of patients, and the rate of proning significantly differed among mild, moderate, and severe ARDS patients (5.9%, 10.3%, and 32.9%, respectively).12,13

More recently, data are emerging to support the use of prone positioning for patients with ARDS due to COVID-19. In one small single-center report, prolonged trials of proning (up to 36 hours) were useful in improving P/F ratio in patients failing a traditional 16-hour prone trial.14 Oxygenation improved significantly during ventilation in the prone position, and the P/F ratio in the supine position after a prolonged prone trial was significantly higher than before proning (P = 0.034).14

Another area of current study is the use of proning in awake, spontaneously breathing COVID-19 patients with respiratory failure outside of the ICU in an attempt to prevent escalation to intubation and mechanical ventilation.15-19 In one study, 50 patients with mild to moderate ARDS from COVID-19 requiring oxygen therapy outside of the ICU were treated with a protocol of prone positioning three times per day for 30-60 minutes alternating with supine positioning. Prone positioning was associated with significant increases in oxygenation during proning and after returning to the supine position as well. At 45-day follow-up, there were two deaths, seven patients required ICU admission, and 41 patients had been discharged from the hospital.18 Case reports also are beginning to appear, documenting the use of awake proning in conjunction with standard supplemental oxygen and as an adjunct to high-flow nasal cannula and even noninvasive ventilation.20-23

CONTRAINDICATIONS TO PRONE POSITIONING

There are few absolute contraindications to proning, but patients with facial fractures, unstable spinal or pelvic fractures, or increased intracranial pressure should avoid proning. An open chest or abdomen can be a contraindication, although if the open abdomen is well supported with the use of an abdominal binder, these patients may be successfully proned after consultation with the surgical team. Women in the third trimester of pregnancy may not tolerate proning and should be evaluated on a case-by-case basis. Obesity is not a contraindication to proning; in fact, morbidly obese patients may experience significant benefit from proning. However, obese patients may have increasing intra-abdominal hypertension in the prone position, which may lead to renal or hepatic dysfunction.11 Veno-venous extracorporeal membrane oxygenation (ECMO) patients can be successfully proned with careful attention to adequate drainage and cannula positioning (offloading pressure on the cannula itself).

PRONING PRIMER: PLAN, PREPARE, PRACTICE

It is important for clinical teams to develop a protocol for proning patients, review procedures, prepare equipment/supplies, and have a coordinated effort. (See Table 1.) Educating patients and family members about expectations is important. Most centers are doing manual proning of patients in the standard ICU bed, but there are lift devices and proning beds available. Coordinate care such that activities like bathing, dressing changes, diagnostic testing, and off-unit travel for scans and procedures are provided while the patient is supine. If there are many patients to prone (e.g., in the setting of a COVID surge), consider a “unit schedule” since each patient will require about four to five staff members to assist with the turn. For planned (non-emergent) proning, we try to time the turn to prone in late afternoon to early evening so that the patient will remain proned for the remainder of the night; the patients then will be returned to the supine position in the early to mid-morning.

Table 1: Procedure for Proning the Intensive Care Unit Patient

Preparation for Proning

  • Evaluate need for additional sedation and/or neuromuscular blocker.
  • Prevent pressure injuries: pad the face (forehead, cheeks, chin, and endotracheal tube holder).
  • Pad bony prominences (shoulders, hips, knees, feet) and chest, sternum, abdomen, genitalia.
  • Secure invasive lines, endotracheal tube, ECMO cannulas, chest tubes.
  • Keep emergency drugs at bedside.
  • Assign one nurse to monitor hemodynamics, with ready access to infusion pumps for titration of pressors or fluid bolus as needed.

Supine to Prone Turn

  • Cocoon or sandwich the patient in a sheet.
  • Pull patient to the edge of the bed with lateral/horizontal movement.
  • Tuck the dependent arm down next to the body.
  • Roll patient up on one side onto the tucked arm (lateral or side-lying position).
  • Place new electrodes for ECG monitoring on patient’s back and remove old ones from the anterior chest and limbs (place new electrodes for each turn).
  • Complete the turn from side-lying to prone.
  • Position the head, neck, limbs once in prone position.
  • Position arms in swimmer’s position.
  • Place pillows, wedges, rolls, and pressure-relief devices as needed.
  • Verify that tubes are patent and not kinked, particularly the endotracheal tube, chest tubes, ECMO cannulas, dialysis catheter.

Prone to Supine Turn

  • Secure the airway, invasive lines, and all tubes.
  • Lift to remove pillows, rolls, wedges.
  • Cocoon or sandwich the patient in a sheet.
  • Pull patient to the edge of the bed with lateral/horizontal movement.
  • Tuck the dependent arm down next to body.
  • Roll patient up on one side (lateral or side-lying position).
  • Place new electrodes for ECG monitoring on anterior chest and limbs and remove old ones from the back and posterior limbs.
  • Complete the turn from side-lying to supine.
  • Position head, neck, and limbs properly.

ECMO = extracorporeal membrane oxygenation; ECG = electrocardiogram

A coordinated team effort is critically important. The leader is at the head of the bed and is responsible for managing the airway, securing the endotracheal tube during the turn, and coordinating the team’s actions. Participants may include nurses, respiratory therapists, perfusionists, physicians, advanced practice providers, and patient care technicians. Some centers have established dedicated proning teams and may include assistance from physical therapists and rehabilitation personnel.

Plan ahead for potential emergency complications that may occur during the prone trial, such as hemodynamic instability, desaturation, agitation/moving, bleeding, tracheal secretions, or arrest. Have emergency medications, such as intravenous fluids and vasopressors, available, particularly for the first proning session until it is clear how each patient will respond. Consider developing a procedure for early return to the supine position in the event of an emergency. Cardiopulmonary resuscitation can be provided in the prone position, as can cardioversion and defibrillation, until enough people have assembled to safely return the patient to a supine position.24-26

Resources for education and training exist. The New England Journal of Medicine website (nejm.org) has “how to” videos associated with the PROSEVA trial publication (https://www.nejm.org/doi/full/10.1056/NEJMoa1214103).3 Consider developing a checklist for proning to ensure patient safety.27,28

COMPLICATIONS OF PRONING

Immediate complications of proning include hemodynamic instability, arrhythmias, cardiac arrest, worsened hypoxemia, accidental extubation, or unintentional line removal. It is helpful to have a supraglottic device readily available in the event the airway needs to be secured immediately. A videolaryngoscope can be very helpful if the patient must be intubated while proned. There are case reports of ultrasound-guided IJ line insertions in the prone position if a line needs to be placed emergently.29

More delayed complications nearly all relate to pressure injury. The most common complication is facial pressure injury from the endotracheal tube stabilizing device as well as pressure on bony parts of the forehead, cheeks, and chin, and over the bridge of the nose.30 Proper positioning of the arm and shoulder (see Table 1) will help avoid brachial plexus injury or peripheral nerve root compression.31,32 There is a case report of lower cranial nerve (CN) dysfunction (CN IX-XII) associated with significant dysphagia in the recovery period, along with tongue deviation, trapezius and sternocleidomastoid weakness that was thought to be the result of pressure on the face and possible neck hyperextension during prone positioning.33 Other serious pressure complications can involve the eye and include increased intraocular pressure, edema of sclera, and corneal injury. An increase in intraocular pressure can be sight-threatening and needs close surveillance.34 Lubrication of the eye can help to reduce the risks of corneal ulceration and exposure keratopathy.

Edematous scrotum and genitalia may predispose to pressure injury, breakdown, and, in one case report, was thought to be responsible for the development of Fournier’s gangrene, which required surgical debridement.35 Other complications may include vomiting or reflux of gastric contents while in the prone position. This may be lessened by placing the bed in reverse Trendelenburg position. Increased intra-abdominal pressure may make it difficult for patients to tolerate gastric feedings, so smaller volume feedings may be indicated.

SUMMARY

The benefits of prone positioning as an adjunctive therapy for severe ARDS patients are clearly outlined with regard to improved oxygenation, with more recent reports demonstrating a survival benefit. However, there are risks associated with the process of turning as well as with known pressure-related injuries. Careful assessment for complications is an important component of daily care. Meticulous attention to positioning of limbs, padding of pressure points, and the use of pillows, wedges, and foams to offload pressure are useful mitigation strategies.

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