Acute Respiratory Distress Syndrome and Prone Positioning

The pathogenesis of ARDS typically is described in 3 phases: (1) exudative, (2) proliferative, and (3) fibrotic. The exudative phase is the initial response to the lung injury. In this phase, damage occurs to both the endothelial and epithelial walls of the alveoli. The resulting increased capillary permeability leads to impaired fluid drainage from the alveolar space and increased protein-rich fluid inside the alveoli, leading to further alveolar damage and the release of pro-inflammatory cytokines.^4,7  Neutrophils and macrophages then are recruited by the lungs and toxic mediators are released, resulting in further cell damage, inflammation, and pulmonary edema. Intrapulmonary shunting increases, leading to severe hypoxemia.^4,7 

During the proliferative phase, the patient’s lung begins its repair processes; the epithelial integrity is reestablished, the alveolar fluid is reabsorbed, and the alveolar structure and function is restored. The fibrotic phase, which may not occur in all patients, is due to inadequate or delayed epithelialization and the formation of interstitial and alveolar fibrosis. This phase can lead to increased ventilator days and mortality.⁴ 

Much of the current ARDS research focuses on mechanical ventilation as a supportive strategy that also prevents injuries caused by the ventilator (ventilator-induced lung injuries [VILI]), which include volutrauma from alveolar overdistention and atelectrauma from alveolar nonheterogeneous recruitment and derecruitment.⁷  The 2017 clinical practice guidelines from the American Thoracic Society, the European Society of Intensive Care Medicine, and the Society of Critical Care Medicine recommend evidence-based treatment strategies for adult patients with ARDS.¹³  Supportive strategies to limit lung damage are known as lung-protective ventilation and include low tidal volume and inspiratory pressure, positive end-expiratory pressure (PEEP), lung recruitment maneuvers (LRMs), extracorporeal membrane oxygenation (ECMO), and high-frequency oscillatory (HFO) ventilation.

The use of low tidal volume strategies (4-8 mL/kg of predicted body weight combined with limited inspiratory pressure or plateau pressure < 30 cm H₂O) reduce mortality of patients with ARDS by preventing volutrauma and barotrauma.^13,14  Alveolar pressure can be estimated during an inspiratory pause by measuring plateau pressure; during that inspiratory pause, flow is at zero and the plateau pressure should reflect inspiratory alveolar pressure.

Positive end-expiratory pressure has been a treatment strategy for patients with ARDS for more than 50 years. Positive end-expiratory pressure reflects the pressure in the alveoli at end expiration; an increased PEEP may improve alveolar recruitment and reduce the effects of atelectrauma. Patients with moderate to severe ARDS and larger amounts of potentially recruitable lung benefit the greatest from high PEEP (Table 2).¹⁵  High PEEP should not be used for all patients with ARDS because of the lack of mortality benefit and risk of alveolar injury, increased shunt, and dead space, along with the hemodynamic effects of increased pulmonary vascular resistance.^13,16 

An LRM consists of a brief application of high (30-40 cm H₂O) continuous positive airway pressure, incremental PEEP increases at a constant driving pressure, or a high driving pressure.^13,17  The physiologic benefits of an LRM include decreased VILI and decreased mortality. The LRM, however, may lead to hemodynamic instability and barotrauma. Lung recruitment maneuvers done in conjunction with a higher PEEP strategy makes it difficult to isolate the direct benefits of the LRM. The guidelines suggest caution using LRM in patients who have concurrent hypovolemia or shock.¹³ 

The use of ECMO for severe refractory ARDS has increased since 2009.¹⁸  Extracorporeal membrane oxygenation uses a mechanical artificial lung to provide oxygenation and removal of carbon dioxide. This strategy may allow recovery from the primary lung injury and minimize VILI.^18–20  The patient’s respiratory system may contribute to ventilation during ECMO. Because of the complexity of ECMO and limited availability of centers that provide this treatment, the amount of literature is limited. The guidelines suggest that additional research is needed on whether to recommend the use of ECMO for managing ARDS.¹³  Several studies including a large international randomized controlled trial are in process.^8,18–20 

High-frequency oscillatory ventilation delivers very small tidal volumes at higher mean airway pressures with a rapid oscillatory respiratory rate of up to 900 breaths per minute.²¹  This ventilator strategy has not been shown to be beneficial in adult patients with ARDS; in contrast, studies have shown patients are significantly harmed with routine HFO use.^13,21,22  Although not recommended for routine use, HFO ventilation is an adjunctive rescue mode for refractory hypoxemia.²³ 

Prone positioning has been used as a treatment modality for patients with ARDS for more than 40 years. One of the first mentions of prone positioning was made in 1974 by Froese and Bryan.²⁴  In that same year, Bryan²⁵  noted that the supine position—despite various ventilation modes and increased end-expiratory pressure—left the dependent areas of the lungs without adequate ventilation. Bryan believed that placing the patient in the prone position improved expansion of dependent areas of the lung and that this position should be used as a strategy in the treatment of ARDS.²⁵  In 1976, Piehl and Brown²⁶  used the terminology of extreme position to review the positive effects of prone positioning, including an increase in oxygenation and pulmonary hygiene. Because of the dramatic positive results in some patients in the study, placement in the prone position was used as a rescue mode after other ventilator strategies proved unsuccessful.²⁶ 

The physiologic mechanism for the change and the resulting improvement in patients’ oxygenation while in the prone position led to further investigations.^27–30  With the patient in the prone position, the once dependent (dorsal) lung fields were well ventilated and perfusion was improved with a decrease in intrapulmonary shunting.²⁷  Researchers believed this change was due to recruitment of the well-perfused dorsal lung that overshadowed the derecruitment of the ventral lung fields.^27,28  Additionally, researchers noted that patients treated with mechanical ventilation and placed in the prone position had decreases in lung strain; this effect was due to the more even distribution of inflation and ventilation throughout the dorsal lung fields, minimizing the occurrence of VILI.^29,30 

Early randomized controlled studies showed improvement in oxygenation that helped build the case for the prone position; however, these studies did not demonstrate reduced mortality.^31–33  The Proning Severe ARDS Patients (PROSEVA) trial in 2013, however, demonstrated a significant decrease in mortality of patients with ARDS and established the methodology for a longer prone position (16 hours) before returning to supine position.³⁴  A subsequent meta-analysis pooled results from 8 randomized controlled trials, with a subgroup analysis showing that patients with severe ARDS had a mortality benefit when prone positioning was used for a minimum of 12 hours per day.³⁵  The use of prone positioning for more than 12 hours per day in patients with severe ARDS is strongly recommended in the 2017 clinical practice guidelines.¹³ 

In early considerations for placing patients in the prone position, clinicians were concerned about logistics.²⁵  The prone position was used for patients with severe ARDS but often as a late rescue strategy due to a lack of clinicians’ expertise with performance of the procedure, concern with complications, and uncertainty regarding the evidence.¹⁹  Multiple techniques have been used to place patients in the prone position; all techniques focus on patient safety while also easing the physical burden on clinicians performing the procedure.^26–29 

Manual prone positioning is the first methodology described in the literature.^32,33,36  This technique is still used today as researchers work to improve safety and ease of performing manual prone positioning.³⁶  Assistive turning devices have been designed specifically to assist with manually positioning the patient in the correct prone position or to assist with repositioning.^37–39  Specialty beds that mechanically rotate the patient into the correct position are also used.^37,39,40 

Challenges with all the prone positioning techniques include a lack of knowledge and familiarity of the procedure, the number of staff members needed to safely place critically ill patients in the prone position, prevention of complications from the turning procedure, and the ability to maintain the patient in the position for the recommended length of time. Complications of prone positioning that also occur with supine positioning include, but are not limited to, tube dislodgement (endotracheal, chest, central access, and urinary catheters), hemodynamic compromise, eye injuries, and pressure injuries.^34,39 

When placing a patient in the prone position, the clinicians must pay attention to devices being used to care for the patient, such as airway management and other invasive lines. In preparation for and maintenance during prone positioning, the clinician must thoroughly assess the patient and provide care that mitigates some of the known complications.³⁸ 

With the recognized benefits of using the prone position in patients with ARDS, emphasis is being placed on having a well-trained team that follows a streamlined process to produce the desired effects of and minimize potential complications of prone positioning. What follows is a description of how we updated our procedures and guidelines in our health care system.

Within the 2 hospitals in our 1100-bed health care system, prone positioning is being used as a lung-protective strategy for patients with ARDS because of the recent research noting reduced mortality with the maneuver.^13,34,35  The health care system had previously developed a nurse-driven guideline for prone positioning. However, with our increased and earlier use of prone positioning, the gaps and opportunities for improvement were highlighted.

Our original 2010 guideline was outdated and lacked interdisciplinary input. In this outdated guideline, the physician determined if a patient required prone positioning and the nursing team would develop a plan for when repositioning could happen, leaving physicians out of the process. In general, the medical team was unfamiliar with the guideline and processes. The prone positioning plan was based on the number of staff required to place a patient in the prone position, also taking into account the availability of the respiratory therapist and the time taken to gather supplies and wait for delivery of protective devices. Across the ICUs there was a lack of standardization and communication regarding the prone positioning procedure, including when the procedure would occur, which varied depending on day of the week and time of day.

Our health care system’s critical care stakeholders, recognizing the need to create best practice within like units and across all ICUs, invited an interdisciplinary team led by a pulmonary critical care intensivist and critical care clinical nurse specialists to discuss prone positioning in the institution. Team members included providers (physicians, physician assistants, and nurse practitioners), clinical nurses, respiratory care providers, physical therapists, and wound ostomy continence nurses. The team’s goal was 2-fold: to review the latest evidence for using prone positioning including methodology, equipment, and staffing, and to create a new guideline. Initial dialogue focused on gaps in current practice and current evidence as well as knowledge deficits of all stakeholders regarding the prone positioning process. The clinical nurse specialist played a key role as content expert in the early phase of the guideline development, educating the team on current practice and collecting input from team members.

As part of planning of the new protocol, many efforts were made to ensure that all team members in all adult ICUs had an opportunity to communicate their needs related to prone positioning. The guideline was reviewed by all stakeholders and their feedback was incorporated in the final guideline, particularly feedback related to inclusion and exclusion criteria for cardiovascular surgery and neurosurgical patients. Because each stakeholder had an active role in the development of the new process, the completed guideline became the Inaugural Interprofessional Clinical Practice Guideline.

The interdisciplinary guideline, adapted from the stepwise process introduced by Guérin et al³⁴  in 2013, was implemented in the system in 2014 and revised in 2018 (Table 3). A key feature included in the guideline was the interdisciplinary component, which ensures that all team members are involved in the procedure from planning to procedure and recovery.

Within the guidelines, inclusion and exclusion criteria for placing a patient in prone positioning have been based on a review of the literature and have become the standard of care for all ICUs in the system (Table 4).^28,34,41  We also included in the guidelines that 16 hours was the recommended length for a patient to be in the prone position. Team members can now plan maintenance interventions and prepare for the return to the supine position at the 16th hour. The updated procedures in the guidelines have improved teamwork and efficiency, changing the process from a purely nursing one to one that is interdisciplinary.

The guidelines require a team huddle, which is led by the nurse caring for the patient, before the prone positioning procedure. This short meeting reinforces communication of procedures, orders, and other care requirements needed before placing the patient in the prone position and the time needed to perform those tasks. One important procedural step that we added to our guidelines is the use of the side-lying position in the middle of turning the patient. The side-lying position allows the team to pause, assess the patient and the initial response to the position change, and change the monitor leads from the ventral to dorsal chest. While a patient is in the prone position, nurses must be vigilant in monitoring the patient’s vital signs and response to medications.³⁸  Therefore, in our health care system, the clinical nurse is a key member of the team coordinating the care of patients prior to placement in the prone position and while in the position. The nurse assesses any changes that may occur due to the prone position.

During the implementation of the guideline, several strategies were used to meet education needs of the staff, including face-to-face education sessions, a video of the entire process developed by the ICU team, a quick reference sheet for the step-by-step process, and web-based education that provided details for each discipline. After implementation of the new guideline, simulation sessions have been conducted to maintain competence and incorporate unit-based champions who can guide the staff through the process in real-time.

Over time, the number of patients placed in the prone position has increased in our health care system. In 2016, members of the team implemented data collection through electronic medical records. Before that time, no direct means had been available to capture data related to prone positioning. In 2017, the first full year of data collection, 48 patients with ARDS had been placed in the prone position across the 5 adult ICUs in the system, with most cases occurring in the 2 medical ICUs. Comparison of the first 6 months of calendar years 2017 and 2018 revealed that 28 patients were placed in the prone position during that time in 2017, compared with 33 in 2018.

The team continues working to expand the information gathered through the process to evaluate the care of patients with ARDS as well as the proning procedure itself. Nurses at our health care system have acknowledged and appreciated the interdisciplinary focus on the prone positioning and the stepwise process and have found that the guidelines help in minimizing previous anxieties that often accompanied the prone order.

The advanced practice nurse (APN) is well positioned as a leader in the development of a prone positioning guideline and in the guiding and reinforcing of the process with all disciplines once use of prone positioning is initiated for patients with ARDS. The APN can facilitate the communication of the plan, ensure proper orders are written, and mentor the clinical nurse in the role of team leader for planning and caring for the patient in the prone position. Additionally, the APN can ensure that team members are prepared for adverse events that may occur related to placing a patient in the prone position.

Acute respiratory distress syndrome continues to be a frequent diagnosis in ICUs. Even with the many treatment modalities used over the last 50 years, more research still is needed for improved outcomes. Recent research efforts have focused on preventive measures to mitigate or minimize the long-term detrimental effects of ARDS on both patients and their families. Early recognition and treatment should continue to be a focused strategy, along with research into preventing complications related to the disease and treatment modalities. Using the prone position as an effective therapy to reduce mortality for patients with ARDS is recommended for moderate to severe cases and for those who meet inclusion criteria. Critical care clinicians are encouraged to explore the use of prone positioning as an early treatment option. We highly encourage establishing a prone-positioning guideline, including interdisciplinary involvement throughout the procedure, and providing staff training to achieve the best results for patients.