An unresponsive 42-year-old woman arrives at your ED via ambulance after a heroin overdose. She is bradypneic with an SpO2 of 80% on room air, so she's endotracheally intubated and mechanically ventilated, which seems to stabilize her. She's admitted to your ICU for further medical management.
On arrival to your unit, the patient's arterial blood gas (ABG) results are: pH, 7.52; PaCO2, 25 mm Hg; PaO2, 75 mm Hg; HCO3-, 22 mEq/L; and SaO2, 88%. Ventilator settings were optimized, the fraction of inspired oxygen (FiO2) was 1.0, and ventilator strategies minimized alveolar overdistension and maximized alveolar recruitment. However, the patient's ABGs demonstrate refractory hypoxemia, worsening respiratory alkalosis, and a widened A-a gradient (the difference between alveolar and arterial concentration of oxygen). The intensivist on call believes that the patient has acute respiratory distress syndrome (ARDS) and prescribes prone positioning.
This article reviews prone positioning and how it can benefit the patient with ARDS. Although prone positioning has been in the literature for some time, it's not common in ICUs, so you may not be familiar with it.1 Before we look at the therapy, let's briefly review ARDS.
What is ARDS?
ARDS is a complex syndrome, and its complete etiology isn't fully understood. However, ARDS usually starts with a massive insult to the lung. Many times this insult isn't respiratory in nature, for example, trauma, radiation, or sepsis.1 Our hypothetical patient's ARDS was precipitated by a heroin overdose, which researchers believe triggers a massive, systemic inflammatory response that results in acute lung injury.
In the lungs, inflammatory mediators such as interleukins can damage the alveolar epithelial and endothelial capillary membrane and degrade the basement membrane. Damage to these tissues lets protein-rich plasma leak into the alveolar space, leading to pulmonary edema. As this fluid further damages the alveoli, surfactant production is decreased, leading to atelectasis and hypoxemia.2 Therefore, ARDS is characterized by a combination of atelectasis, decreased surfactant, protein-rich pulmonary edema, and interstitial inflammation, especially in dependent areas.
A hallmark of ARDS is that the pulmonary edema isn't cardiac in nature, and many young patients with ARDS don't have a significant cardiac history. Pulmonary edema causes the lungs to eventually become stiff and noncompliant, making optimal ventilation even harder to achieve. This fluid in the alveoli causes another hallmark characteristic of ARDS, the inability to improve arterial oxygenation with an increase of delivered FiO2.
The American-European Consensus Conference defines ARDS as acute onset of the following:
* bilateral infiltrates on chest X-ray, consistent with pulmonary edema
* no clinical evidence of left atrial hypertension with a pulmonary artery occlusion pressure of 18 mm Hg or less
* PaO2/FiO2 ratio of 200 mm Hg or less regardless of positive end-expiratory pressure (PEEP) level.3
Despite much research on ARDS, the traditional therapy remains mechanical ventilation to address refractory hypoxemia. Other important aspects of managing ARDS include:
* identifying and treating the underlying cause.
* using low tidal volumes to reduce volutrauma, as mechanical ventilation can overexpand aerated alveoli.4 These overexpanded alveoli lose their elastic recoil; compress adjacent blood vessels, reducing blood flow; and trap air, preventing oxygen from entering the circulation.
* limiting PEEP as much as possible because high levels of positive pressure can cause barotrauma, damaging alveolar capillary membranes.4 High PEEP can lead to alveolar rupture and can cause increased permeability of alveolar walls, leading to a further increase in pulmonary edema.
* allowing permissive hypercapnia. Low tidal volume ventilation raises the patient's PaCO2 level and may result in hypercapnia. Letting hypercapnia and respiratory acidosis develop gradually in patients with ARDS can limit ventilator-induced lung injury, and studies have shown that patients can tolerate moderate permissive hypercapnia for long periods of time.4
* using prone positioning.5
What is prone positioning?
In prone positioning, patients with ARDS are placed on their abdomens for a portion of the day. The concept has been advocated in the literature since 1974 as a way to expand the dependent lung areas.6 In theory, expanding dependent lung areas opens collapsed alveoli, increasing ventilation capacity and improving oxygenation.
Work of breathing can also be reduced with prone positioning because it reduces the pressure on the lungs from the cardiac structures and abdominal organs. Reducing work of breathing saves vital energy that the patient can use for healing and recovery.
A generally simple, safe, and noninvasive technique, prone positioning may help improve oxygenation while preventing further pulmonary injury caused by high PEEP, volutrauma, and oxygen toxicity.7 Oxygen toxicity, or exposure to prolonged or high concentrations of oxygen, can damage the alveolar epithelium, inactivate surfactant, and lead to increased intra-alveolar edema, all of which contribute to increased pulmonary fibrosis.8
Does prone positioning work?
Many studies have found that prone positioning improves oxygenation in patients with ARDS. Gattinoni's landmark study included 304 patients with acute lung injury or ARDS; patients in the study group were proned for 6 or more hours a day for 10 days.9 Although no significant differences in mortality were demonstrated at the end of the 10-day study period, at the time of ICU discharge, or at 6 months, the researchers did find that the use of the prone position improved oxygenation in more than 70% of the instances in which it was used.9 A small study of 12 mechanically ventilated patients with ARDS found that PaO2 values increased 60% to 80% in patients who were proned, compared to those who weren't.10 A study of 61 patients with acute lung injury and ARDS (44 patients were positioned supine, 13 placed prone, and 4 patients who were initially placed supine were changed to prone positioning) found that prone kinetic therapy (use of a bed that turns continuously and slowly more than 40 degrees along its longitudinal axis) resulted in greater improvement in PaO2/FiO2 ratios, reduced pulmonary-related mortality, fewer ventilator days, and shorter hospital length of stay than supine kinetic therapy.11
Prone positioning also improves postural drainage, so that more secretions can be suctioned from the patient, improving ventilation.
Prone positioning requires more diligent care by the ICU nurse. A specific set of skills is needed to care for the patient in the prone position: recognizing when prone positioning may be beneficial, being able to communicate with the patient's family about the therapy, and maintenance of invasive lines and tubes so they don't become dislodged. You'll also assess the patient's skin regularly and intervene to prevent skin breakdown in vulnerable areas during prone positioning. The nursing literature gives excellent guidance in this area.
* When to prone. Seaton-Mills advocates that patient positioning falls under the nursing domain in patient care, and states that critical care nurses should be proactive with turning patients with ARDS.12 However, in many facilities, a prescription is needed for prone positioning. Starting a prone position regime early for patients with ARDS, based on the physiologic markers discussed earlier, offers the greatest potential for a beneficial outcome.
Determine if the risks of prone positioning are outweighed by the patient's need for improved oxygenation (see Some contraindications to proning). Bedside nurses who understand the mechanisms of ARDS are in a good position to help initiate prone positioning appropriately.5
* Manual or mechanical turning? Once the decision has been made to place a patient in prone position, the next task is actually turning the patient. This article provides a brief overview of the proning process; consult appropriate resources for a full description. A team approach is best to keep mechanically ventilated patients safe. A respiratory therapist or the most experienced nurse of the team performing this maneuver should be in charge of the patient's head, ensuring the security of the endotracheal (ET) tube and I.V. lines during the move.12 This person can then direct the rest of the team.
Using the bottom sheet, two nurses should position the patient near them at the edge of the bed. If the patient is to be rolled on his right side, his right arm should be placed under his right hip. When the ET tube and I.V. lines are secured, the team can slowly roll the patient into the prone position. The patient can then be placed in a swimmer's pose.2 The patient's head should be turned toward the ventilator, never face down.
Carefully place limbs, keeping in mind the goal of preventing extension and contraction of shoulders or elbows. Pillows can be strategically placed to provide additional support to the pelvis, shoulder, and face.1
An alternative to manually turning the patient is to use a specialized mechanical bed, which can rotate 360 degrees. Advantages to mechanical beds include eliminating the risk of injury to the nursing staff and saving nursing time in busy ICUs. Once the patient is properly secured in the bed, one nurse can care for and reposition the patient for the entire shift.
If the patient's clinical condition deteriorates and a code is called, a mechanical bed can return the patient to a supine position in a fraction of the time it would take to manually reposition the patient for CPR or other lifesaving procedures. Many of these beds also deflate as soon as they are in supine position, creating an automatic backboard for chest compressions. Finally, the pads in these beds are usually designed to provide the strategic support needed by the patient to prevent edema and skin breakdown.
* Other issues. Patients should be adequately sedated while in the prone position, and may need more sedation than what was administered when the patient was in a supine position. Nutrition is another area of concern. Many mechanically ventilated patients receive enteral nutrition, and being in the prone position could increase the risk of aspiration. One solution is for patients to receive higher amounts of feeding, if tolerated, while they're supine, to ensure adequate nutritional intake over a 24-hour period.11 My facility administers bolus enteral feedings while the patient is supine.
Monitor for potential complications of proning. Consult with the facility's wound ostomy and continence nurse as indicated.5
Provide emotional and educational support for the patient's family. Tell them ahead of time that they may not be able to see the patient's face while the patient is in the prone position. Warn them about the possibility of facial edema, which can be quite unsettling.12
One facility's experience
The ICU of a community hospital near Pittsburgh, Pa., holds 11 patients, many of whom are receiving mechanical ventilation. From December 2005 until January 2007, prone positioning was used on 6 patients with ARDS. The regimen prescribed by the pulmonologist/intensivist consisted of placing the patient in the prone position for 2 hours at a time, for a total of 6 to 8 hours per day. Average length of prone positioning therapy was 5.5 days. The improvement in their oxygenation rates (measured as the PaO2/FiO2 ratio) is shown in Proning: A small sample.
Based on the literature and the positive benefits witnessed, the facility decided to use prone positioning when appropriate for patients with ARDS. To help critical care nurses feel more comfortable with using prone positioning, the facility has taken these steps:
* Having educated resource personnel available. The unit occasionally uses a specialized bed for proning. When this bed is used, a sales representative from the company accompanies the bed to the unit, shows the staff how to set up the bed, how to properly place the patient in the bed, and how to operate the bed in order to achieve the desired results. The representative also instructs the staff about patient safety issues related to using this type of bed.
* Having the ICU clinician act as liaison. The ICU clinician offers knowledge and assistance to our staff nurses, as well as acting as a liaison between the healthcare providers and staff, and relaying questions and concerns.
* Developing staff education materials. The facility is working on a self-learning packet on prone positioning for ICU staff nurses. The packet will contain much of the evidence-based research on the benefits of prone positioning for patients with ARDS, as well as information on how to safely care for these type of patients. The packet also will include information on the signs that indicate patient improvement and contraindications to therapy.
By understanding prone positioning, we can give patients with ARDS the best possible evidence-based care.
Some contraindications to proning
* facial or pelvic fractures
* burns or open wounds on ventral body surface
* life-threatening dysrhythmias
* conditions associated with spinal instability
* multiple trauma
* conditions associated with increased intracranial pressure
* abdominal trauma or surgery
* acute bleeding