In the context of the acute lung injury (ALI)/Acute Respiratory Distress Syndrome (ARDS), it has been shown that dependent portions of the lung undergo the most alveolar collapse.1 Supine positioning is primarily responsible for this increased atelectasis.2 The dorsal lung fields comprise over 50% of the lung tissue, which results in a significant decrease in functional alveoli, and, therefore, a reduction in functional residual capacity. Clinicians began seeking ways to optimize the dorsal lung field's efficacy, and decrease the dependent alveolar collapse. An effective means of achieving this goal is intermittent prone positioning (IPP).
In the mechanically ventilated patient, ventilation: perfusion (V:Q) ratios are drastically different than the spontaneously breathing individual. When patients breathe spontaneously their ventilation distribution is relatively homogeneous.3 However, during mechanical ventilation with positive pressure, gas travels the "path of least resistance" to the ventral portion of the lung, in the supine patient.
In animals, it has been found that there is a more homogeneous distribution of ventilation when patients are placed in the prone position versus supine.1 The increase in homogeneity is attributed to the repositioning of the pressure from the intrathoracic organs (heart and lung), leading to an alteration in pleural pressures.1 Increased homogeneity in ventilation leads to an increased utilization of functional alveoli and therefore improved gas exchange and oxygenation.
The heart is responsible for compressing 7% to 42% of the left lung and 11% to 16% of the right lung in the supine position.1 This compression is relieved when the patient is placed in the prone position. Another source of lung compression is the abdomen. In the supine position, gravity is pushing down on the abdominal contents causing them to displace the diaphragm upward into the chest wall (Figure 1).4 This displacement and pressure weakens the diaphragmatic excursion and therefore reduces lung expansion. When a patient is placed in the prone position, the abdominal contents remain uncompressed, and the diaphragm is able to contract, allowing normal lung expansion.
In the supine position, patients are able to produce more ventral chest wall movement owing to the freedom of the ventral rib cage; however, this causes the dorsal portion of the chest wall to have little or no impact in chest wall movement.5 Since ventilation follows chest wall movement, increased ventral wall movement would lead to preferential ventral ventilation. When the patient is placed in the prone position, the ventral mobility is decreased, and therefore chest wall movement becomes more synchronyous between the ventral and dorsal regions, leading to increased homogeneity in ventilation.
NURSING ROLES AND RESPONSIBILITIES IN THE CARE OF THE PRONE PATIENT
Barriers to Implementing IPP
The benefits of prone positioning have been reported since 1973;6 however, in some ICU's this modality of care often remains a last resort or impossible task. Many clinicians are aware of the improved oxygenation that accompanies prone positioning; however, there remains a lack of clinical data that shows that IPP improves mortality. This lack of data has prevented the widespread use of this treatment.
Nurses have an extremely important role in the care of the prone positioned patient. This responsibility begins prior to the initiation of the therapy. The staff nurse holds the power in many institutions to initiate IPP. On the "flip side" the nurses' fears of proning a patient can eliminate the option of this modality altogether. As Offner et al7 points out, reluctance is also related to the misconception of the complexity of the maneuver and risk of life-threatening complications. The limited knowledge of relative versus absolute contraindications is a primary barrier in initiating IPP. It is the nurses' responsibility to understand these contraindications thoroughly.
Another barrier in the use of prone positioning in the trauma patient is the lack of consensus on the optimal time and duration of prone positioning, and parameters for measuring success.8 In the past, studies have focused a great deal on the efficacy of prone positioning and adjuncts to prone positioning; however, limited research has been performed on the details of the procedure (ie, timing, duration, and measurement parameters).
Initiation of IPP
Nurses are important advocates in initiating advanced therapies for their patients. Nurses who understand the physiologic and evidence base of IPP earn trust from the team that the procedure will be performed appropriately; leading to an increase in the utilization of such techniques.
On the basis of relevant studies, the triggers for initiation of IPP include the following: (a) Evidence of ALI/ARDS (defined as: acute bilateral infiltrates on chest x-ray, severe hypoxemia, no evidence of left atrial hypertension).9 (b) PaO2/FiO2 ratio (P:F) <200, (c) Positive End-Expiratory Pressure (PEEP) >8 cm H2O.9 These are not the only triggers for the implementation of IPP (Table 1), and do not take the place of clinical judgment and physical assessment.
Continuation of IPP
As a member of the team who are at the beside 24/7, nursing staff have the unique ability to evaluate trends in patient response on a minute to minute, hour to hour and day to day basis. Continuous bedside monitoring of SvO2, patient agitation, hemodynamic parameters, and abdominal compartment pressures, allow the staff to understand the patient's response to proning, and better anticipate patient needs.
Several schedules have been proposed for the supine to prone ratio. Michaels et al used a 6 hours prone, 6 hours supine or 8 hours prone and 4 hours supine approach to optimize the patient's ventilation.10 The variation in proning schedule is grossly regulated by the nursing staff. They are able to assess the patient tolerance and progress weaning ventilator support in a given position. This will key them in to understanding when that patient will tolerate changing positions. The nursing staff also plays an important role in ensuring that the needs of the patient are met whereas the patient is in any given position. Schedules can be designed to balance nursing workload, patient safety, as well as improvement in lung function with decreased atelectasis.10 Michaels' schedule (6 hours prone/6 hours supine, or 8 hours prone/4 hours supine) appeared to be successful in satisfying patients and clinical staff, and is an excellent beginning schedule until patient response can be judged.
Cessation of IPP
Premature discontinuation of IPP can quickly reverse its positive effects; therefore, the cessation of prone positioning needs to be carefully considered and involve all of the critical care team. However, the nursing staff, as the team members that best know patient response and needs, have an integral role in this evaluation. As shown in Table 1, criteria for cessation have not been well defined. Each patient needs to be evaluated individually on the basis of his or her response to the procedure. Some patients progress rapidly, and therefore do not need to continue IPP for extended periods of time; however, other patients (ie, patients with multiple comorbities, underlying lung pathology, or patients in severe ARDS) may require IPP for much longer. Criteria for beginning discussion of cessation of IPP suggested in several studies includes: FiO2 <=.40, PEEP <=8 cm H2O, P:F >=250-300.11,12
Complications of Proning
Complications related to proning are dependent on the patient population. In trauma patients, the following complications are more frequently identified, however, all are preventable. With proper education and a confident group of practitioners the risk can be dramatically diminished.
* Complication: Pressure necrosis, particularly in the face and sacrum.7
* Prevention: Utilization of pressure relieving devices on the face rest, frequent head turns, wound nurse consult when patient initiated into IPP.
* Complication: Wound dehiscence.7
* Prevention: Splinting wounds prior to turning to prevent pulling on sutures, staples or wound bed.
* Complication: Hemodynamic instability (ie, Severe hypotension and bradycardia associated with fluid shift and intrathoracic pressure changes).
* Prevention: Continue adequate fluid resuscitation especially prior to turning; anticipate need for vasopressors, or inotropes during turning and fluid shifts.
* Complication: Accidental discontinuation of vascular and endotracheal access.14,15
* Prevention: Adequate staffing during turning procedure, assess the quality of securing devices prior to every turn, perform a "time out" prior to turning to assess vascular, endotracheal, and bladder devices.
* Complication: Contractures of shoulder and hip.9
* Prevention: Consult physical therapy as soon as IPP is initiated; continue to perform passive range of motion when patient is in supine position.
* Complication: Nerve injury, such as brachial plexus injury.
* Prevention: Change head and arm positions every 2 hours, consult physical therapy as soon as IPP is initiated.
NURSING RESPONSIBILITY
As discussed, there are barriers to the initiation, continuation, and cessation of prone positioning; however, with education of evidenced based guidelines, nurses can overcome these barriers to provide a better standard of care. Critical care nurses can transition IPP from a "last ditch effort" to a standard of care for the trauma patient with ARDS. To facilitate this transition, nurses can use the F.L.I.P. approach.
* F- Find the Current Policies at Your Institution. Understanding your current policies gives a starting point for expanding on them, developing new ones, or simply reeducating your unit.
* L- Learn the Literature. Continuously review the literature in relation to the specific patient population (ie, traumatic brain injury, multitrauma, pediatric, etc).
* I- Initiate a Protocol for Your Institution. Work with the multidisciplinary team at your institution to develop a standard of care, including an evidenced based algorithmic approach for the critical aspects of IPP (evaluation of the patient in a timely manner, initiation within 24 to 48 hours of onset of ALI/ARDS, continuation with constant reevaluation, and cessation after certain criteria has been met).
* P- Be a Patient Advocate. Develop an ongoing evaluation process for your new guidelines to assess efficacy, complications, and opportunity for improvements. Also, it is important to share your experiences with other units and health professionals.
CONCLUSION
Nursing staff play a vital role in the care of their patients and the betterment of patient outcomes. When caring for a trauma patient with ARDS, nurses are responsible for seeking out modalities of care that may benefit the patient, while causing the least harm. Equipping nursing staff with the proper education and resources necessary to carry out advanced respiratory skills, such as IPP, will lead to sooner initiation, more consistent continuation, timely cessation of care, and decreased pulmonary related mortality.13
REFERENCES