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Journal of Neuroscience Nursing:
doi: 10.1097/JNN.0b013e3181ecafd4
Article

Effect of Body Position on Cerebral Oxygenation and Physiologic Parameters in Patients With Acute Neurological Conditions

Ledwith, Mary B.; Bloom, Stephanie; Maloney-Wilensky, Eileen; Coyle, Bernadette; Polomano, Rosemary C.; Le Roux, Peter D.

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Author Information

Stephanie Bloom, MSN ACNP, is an ICU nurse practitioner in the Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA.

Eileen Maloney-Wilensky, CRNP MSN, is the director of Neurosurgery Clinical Research and Midlevel Provider Program in the Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA.

Bernadette Coyle, RN, is a clinical nurse in the Department of Nursing, Hospital of the University of Pennsylvania, Philadelphia, PA.

Rosemary C. Polomano, PhD RN, is an associate professor for Pain Practice at the University of Pennsylvania School of Nursing and an associate professor of Anesthesiology and Critical Care at the University of Pennsylvania, Philadelphia, PA.

Peter D. Le Roux, MD, is an associate professor in the Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA.

Questions or comments about this article may be directed to Mary B. Ledwith, RN, at ledwithm@uphs.upenn.edu. She is a nurse manager in the Neuro Intensive Care Unit, Hospital of the University of Pennsylvania, Philadelphia, PA.

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Abstract

How body position influences brain tissue oxygen (PbtO2) and intracranial pressure (ICP) in critically ill neurosurgical patients remains poorly defined. In a prospective observational repeated measures study, we examined the effects of 12 different body positions on neurodynamic and hemodynamic outcomes. Thirty-three consecutive patients (mean ± SD, age = 48.3 ± 16.6 years; 22 men), admitted after traumatic brain injury, subarachnoid hemorrhage, or craniotomy for tumor, were evaluated in a neurocritical care unit at a level 1 academic trauma center. Patients were eligible if the admission score in the Glasgow Coma Scale was ≤8 and they had a Licox CMP Monitoring System (Integra Neurosciences, Plainsboro, NJ). Patients were exposed to all 12 positions in random order. Changes from baseline to the 15-minute postposition assessment mean change scores showed a downward trend for PbtO2 for all positions with statistically significant decreases observed for supine head of bed (HOB) elevated 30° and 45° (p < .01) and right and left lateral positioning HOB 30° (p < .05). ICP decreased with supine HOB 45° (p < .01) and knee elevation, HOB 30o and 45° (p < .05), and increased (p < .05) with right and left lateral HOB 15o. Hemodynamic parameters were similar in the various positions. Positioning practices can positively or negatively affect PbtO2 and ICP and fluctuate with considerable variability among patients. Nurses must consider potential effects of turning, evaluate changes with positioning on the basis of monitoring feedback from multimodality devices, and make independent clinical judgments about optimal positions to maintain or improve cerebral oxygenation.

Traumatic brain injury (TBI) affects approximately 1.4 million people in the United States annually; 235,000 of these cases are serious enough to require hospital care and intensive care unit (ICU) care. About 50,000 TBI patients die each year (Langlois, Rutland-Brown, & Thomas, 2004). Virtually, no TBI is without consequence, and it is estimated that 2% of the U.S. population currently live with TBI-related disabilities (Thurman, Alverson, Dunn, Guerrero, & Sniezek, 1999). Although less frequent, aneurysmal subarachnoid hemorrhage (SAH) can be more devastating with long-lasting neurological impairments. Each year, approximately 30,000 people, most between 40 and 60 years of age, suffer aneurysmal SAH in the United States; 60% die or are disabled. In addition, approximately half the patients who appear to experience a favorable outcome suffer from significant neuropsychological and cognitive deficits (LeRoux & Winn, 2004).

Not all neuron damage occurs at the time of injury or aneurysm rupture, and much of the poor outcomes observed after TBI or SAH are associated with delayed cerebral injury that develops while the patient receives ICU care. This concept of secondary neuronal injury and its prevention is central to modern TBI and SAH critical care management. In particular, secondary cerebral insults such as hypotension, hypoxia, and increased intracranial pressure (ICP) or reduced cerebral perfusion pressure (CPP) among others have been demonstrated in multiple studies to adversely affect patient outcomes (Iacono, 2000; Meixensberger et al., 2003; Phillips, 2003; Rao, 2007; Sullivan, 2000). Consequently, the foundation of care in severely brain-injured patients is to monitor and control ICP, CPP, and mean arterial pressure (MAP) and to manage fluctuations that may lead to further brain injury. The goal of this care is to maintain adequate cerebral blood flow (CBF) and ultimately delivery of oxygen and glucose to brain cells (Albano, Comandante, & Nolan, 2005; Littlejohns & Bader, 2005).

Several variables influence ICP, CPP, or MAP after brain injury, among them is body positioning. Multisystem and extracranial pathophysiological processes that occur after brain injury can render severe SAH and TBI patients vulnerable to random body position changes (Yanko & Mitcho, 2001). However, the exact effects of body position, a critical component of basic nursing care in the ICU, on intracranial physiology after brain injury are not well defined. For example, the guidelines for the management of severe head injury jointly published by the American Association of Neurological Surgeons and the Brain Trauma Foundation (2007) do not include specific recommendations for optimal patient positioning practices after severe brain injury (Bratton et al., 2007). Similarly, guidelines on care of SAH patients are unclear about optimal patient position (Bederson et al., 2009; Mayberg et al., 1994).

Current positioning practices in neurocritical care units are largely based on studies that suggest head of bed (HOB) elevation may reduce ICP. However, there is no consensus on the degree of elevation for best practice. Although 30° of head elevation is believed to be associated with improvements in ICP and CPP (Phillips, 2003; Winkelman, 2000), other studies have not found the most beneficial backrest position for ICP and CPP (March, Mitchell, Grady, & Winn, 1990). Other studies show that head rotation and head and neck flexion may increase ICP, decrease jugular venous outflow, and alter CBF (Albano et al., 2005; Wong, 2000). Turning and repositioning also may be associated with transient increases in ICP and subsequent changes in cerebral and cardiovascular variables (Price, Collins, & Gallagher, 2003). These various studies form the basis for current care of the brain-injured patients, that is, head elevation, avoidance of head rotation and head flexion, and cautious repositioning. In a literature review on positioning for diverse patient populations, Sullivan (2000) suggests that caution should be used with side-lying positions and HOB elevation no greater than 45° should be used for TBI patients.

Several investigators have challenged this traditional notion of head elevation after SAH or TBI, in large part because of potential effects from cerebral autoregulation. The goal of ICP reduction is to improve CPP and so CBF. Rosner and Coley (1986), in a study of 18 patients with TBI with intracranial hypertension, suggested that ICP reductions during head elevation were accompanied by CPP reductions. In a subsequent study of 34 patients with TBI and intracranial hypertension, these investigators suggested that the head-flat position was associated with reduced morbidity and mortality (Rosner & Daughton, 1990). Blissitt (2006) studied 20 patients with aneurismal SAH and examined transcranial doppler velocities when the bed position was moved in sequence 0o-20o-45o-0o and demonstrated in general that head elevation did not cause harmful changes in CBF in SAH patients. In 2004, Fan conducted a systematic review to evaluate existing evidence for the effects of head or body position on ICP and CPP. Eleven articles were reviewed; 9 concluded that a 30° head elevation decreased ICP compared with a flat position. A significant change in CPP was not observed in 5 of these 9 studies. However, several of these studies included few patients, so Fan was not able to make definitive conclusions and instead recommended that future research was necessary to investigate the effects of patient position to explore the combination of head elevation and lateral side-lying positions in different neurological and neurosurgical patients.

The goal of ICP and CPP control is to deliver adequate CBF and oxygen to the brain and to avoid cerebral ischemia. Brain tissue oxygen (PbtO2) now can be monitored with the devices approved by the Food and Drug Administration. A PbtO2 monitor appears to discriminate between normal oxygenation, threatened ischemia, and critical ischemia when ICP and CPP, among other variables, vary (Scheufler, Lehnert, Rohrborn, Nadstawek, & Thees, 2004). Brain oxygen values between 20 and 40 mmHg are regarded as normal, whereas reductions (<15 mmHg) are associated with cerebral ischemia. In addition, poor patient outcome after TBI is associated with the number, duration, and intensity of cerebral hypoxic episodes (PbtO2 <15 mmHg) and any PbtO2 values <5 mmHg (Valadka, Gopinath, Contant, Uzura, & Robertson, 1998; van den Brink et al., 2000). Decreases in PbtO2 also are not benign and are associated with independent chemical markers of brain ischemia (Hlatky, Valadka, & Robertson, 2005), whereas increases in MAP to elevate CPP can improve PbtO2 in ischemic areas of the brain (Stocchetti et al., 1998). A brain oxygen monitor, therefore, may be a useful tool to examine how body position influences intracranial physiology after brain injury.

Few studies have examined the effects of patient positioning on PbtO2. Meixensberger et al. (1997) reported that head elevation of 30° produced a decrease in ICP without risk to the regional cerebral microcirculation, as measured by PbtO2 after severe brain injury. Similarly, Ng, Lim, and Wong (2006), who studied 38 patients with severe TBI, found that routine nursing care with patient positioning at 30° for head elevation within 24 hours of trauma significantly decreased ICP. Although there was a downward trend for CPP, this did not adversely affect brain oxygenation. We therefore undertook this study to examine the effects of patient positioning, including a combination of head elevation and side lying on PbtO2 ICP, CPP, and MAP after severe brain injury. We hypothesized that no single position is optimal in improving neurodymanic parameters for all severely brain-injured patients.

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Clinical Material and Methods

Study Design

A quasi-experimental, prospective repeated measures design with control over the intervention was used to investigate the effects of positioning on PbtO2 in severely brain-injured patients. The University of Pennsylvania institutional review board approved the study as part of a larger study of the "Brain Oxygen Monitoring Outcome Study." Waiver of informed consent was granted for this study because it involved the collection of data in the course of clinical care and monitoring. All research procedures were in accordance and compliance with the Health Insurance Portability and Accountability Act regulations and the institution's policies and guidelines for protection of human subjects.

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Patient Sample

Patients diagnosed with severe SAH or TBI admitted to the neuro-ICU at the Hospital of the University of Pennsylvania, a university-affiliated level 1 trauma center, and who underwent PbtO2 monitoring were part of this study. Severe SAH or TBI was defined by an admission postresuscitation score of ≤8 in the Glasgow Coma Scale (GCS) or if they subsequently deteriorated to a GCS ≤8. Each patient underwent the Licox CMP PbtO2 and ICP monitoring (Integra Neurosciences, Plainsboro NJ) and hemodynamic monitoring. At the time of evaluation, all patients were neurologically and physiologically stable (i.e., normal ICP, heart rate, blood pressure, and arterial oxygen saturation [SaO2]).

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Body and Head Position

Each subject served as their own control and was placed in each of the 12 predetermined body positions at 2-hour intervals. Random order of assignments to head and body position was delivered using a random numbers table to ensure that the sequence of positioning was different for each subject and to control for the potential influences of order of treatment effects. The 12 study positions were supine, supine with knee bent, left lateral position, and right lateral position, and in each of these positions, the HOB then was elevated to 15°, 30°, or 45°. To standardize the degree of head, lateral turns, and knee elevation, commercially available products were used for all of these positions. Lateral head rotation, neck flexion, and head hyperextension was avoided in each position. The HOB elevation was consistently measured with the use of a protractor (Johnson Magnetic Angle locator no. 700). A commercially available foam wedge (body wedge, model no. 920406; Alimed Inc., Dedham, MA) was used to consistently measure and maintain lateral positions. Knee elevation also was consistently measured and maintained with a commercially available foam wedge (knee elevation model no. 9-235; Alimed Inc.). To allow for adequate stabilization of brain and hemodynamic parameters after turning, subjects remained in each of the study positions for 15 minutes before postpositioning measurements were obtained. No therapeutic interventions were initiated during position changes to limit the confounding influence of treatments.

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Intracranial Monitors

ICP, brain temperature, and PbtO2 were continuously monitored before and after each position using commercially available products (Licox CMP; Integra Neuroscience). Cerebral perfusion pressure was calculated (CPP = MAP − ICP). Intracranial monitors (ICP, brain temperature, and PbtO2) were inserted at the bedside in the neuro-ICU through a burr hole into the frontal lobe and secured with a triple-lumen bolt. The monitors were placed into the white matter that appeared normal on the head CT scan and on the side of maximal pathology. Follow-up head CT scans were performed in all patients within 24 hours of insertion to confirm correct placement of the various monitors, for example, not in a contusion or infarct. Probe function and stability were confirmed by an appropriate PbtO2 increase after an oxygen challenge (FiO2 1.0 for 5 minutes). To allow for probe equilibration, patients were not studied until at least 6 hours after PbtO2 monitor insertion.

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Physiological Measurements and Data Collection

The following systemic parameters were continuously measured before and after each position: (a) heart rate using a 12-lead electrocardiogram of the Hewlett Packard Component Monitoring System (Revision C; Hewlett Packard, Palo Alto, CA); (b) systolic, diastolic, and mean arterial blood pressure by radial artery catheter connected to an external transducer for standard fluid-filled column hemodynamic monitoring (the transducer was placed at the phlebostatic axis, interface through the parameter module of the Hewlett Packard Component Monitoring System, Revision C); and (c) systemic arterial oxygen saturation (SaO2) by Plethysmograph Module of the Hewlett Packard monitor. Physiologic parameters and data obtained from intracranial monitors were recorded using a bedside monitor (Component Monitoring System M1046-9090C; Hewlett Packard). In addition, these physiologic variables and fractional concentration of inspired oxygen (FiO2) and central venous pressure were recorded every 15 minutes on the ICU flow sheet. All patients on mechanical ventilators routinely have daily PaO2 measurements. More frequent PaO2 readings were obtained if a change in a patient's clinical status was observed. In addition, serum hemoglobin and hematocrit levels were measured daily on all patients.

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Statistical Analysis

Each position was considered a separate event, and subjects served as their own controls. Data are expressed as mean ± SD or as a median, where the data are not normally distributed. The differences between preposition (baseline immediately before position change) and postposition (15 minutes after position change) measurements for PbtO2, ICP, and CCP were examined using either the Student's t test or the Wilcoxon signed-rank test for paired data depending on distribution of the data. A p value of less than .05 was considered statistically significant. All analyses were performed using the Statistical Package for the Social Sciences for Windows (Version 1.5; SPSS Inc., Chicago, IL).

A power analysis performed a priori indicated that 33 patients would yield sufficient statistical power of .80 to detect a treatment effect with body positioning on PbtO2 with sigma = 1, medium treatment effect size = .5, and alpha = .05, two-tailed.

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Results

Patient Characteristics

Thirty-three patients, including 11 women and 22 men (mean age = 48.3 ± 16.6 years), were included in this study. Of these, eleven patients had SAH, 11 had closed head injury, 4 had acute traumatic subdural hematomas, 2 had gunshot wounds to the head, 2 had intraparenchymal hemorrhage, and 2 were in a coma after craniotomies for tumor. All patients had a GCS score ≤8 before the start of the study. On admission, 11 patients had a GCS score ≥8 but deteriorated shortly after that to a GCS score ≤8. One subject was eliminated from the study because the Licox monitor was found on follow-up CT scan to be incorrectly placed in gray matter, hence causing an artificial increase in PbtO2. Three patients did not complete all 12 positions. Thirty patients with complete data were included in the final analysis.

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Baseline Values

At the start of the study, mean ICP, CPP, and PbtO2 was 10 ± 6.15, 90.88 ± 16.58, and 37.6 ± 13.61, respectively, in all patients.

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Brain Tissue Oxygen

Table 1 lists the mean ± SD PbtO2 values for all patients at baseline before the position change and 15 minutes after each position turn. A significant change was observed in four positions: (a) supine with HOB 30° (decrease), (b) supine with HOB 45° (decrease), (c) left lateral with HOB 30° (decrease), and (d) right lateral with HOB 30° (decrease).

Table 1
Table 1
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ICP and Cerebral Perfusion Pressure

The ICP and the CPP before and after each position turn and mean differences are illustrated in Table 2. Four positions led to a significant change in ICP: (a) supine with HOB 45° (decrease), (b) left lateral with HOB 15° (increase), (c) right lateral with HOB 15° (increase), and (d) knee elevation with HOB (decrease). Only one position had a significant effect on CPP-left lateral with HOB 30° (decrease).

Table 2
Table 2
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Discussion

Patient body and head position may potentially influence intracranial hemodynamics after severe brain injury. Normally, constant CBF is maintained by an intact cerebral autoregulation system, but when the brain is injured, compensatory mechanisms for sustaining CBF may be affected. Factors that can override or affect these protective mechanisms are elevated ICP in excess of 40 mmHg, mean blood pressures that exceed 60 to 150 mmHg, local or diffuse injury from ischemia, or inflammation. A critical component of neurointensive nursing care is identifying the most optimal body position that augments adequate CBF while controlling ICP, CPP, and PbtO2 (Hickey, 2003).

Optimal positions have not been clearly defined for the severely brain-injured patient. Our results suggest that there is no single position that reliably increases brain oxygen, decreases ICP, and increases CPP. This emphasizes the role of multimodality monitoring and close observation with any change in position both initially and while patients remain in a particular position. The findings also suggest that the lateral position may be the most detrimental to PbtO2, ICP, and CCP, especially when the HOB is not elevated. With both the right and the left lateral positions, trends for adverse effects on ICP, CPP, and brain oxygen were observed, suggesting that the lateral position should be used with caution and patients should be closely monitored when in this position.

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Body Position and Neurocritical Care

The patient population in critical care units is diverse, and so careful consideration on how body position influences their care is warranted. However, the effect of body position on patient outcome in brain-injured patients is only beginning to be elucidated. For example, Wojner et al. (2002) observed in 11 patients with acute ischemic stroke that this patient population may benefit from lower HOB positions, specifically a flat position to promote increased blood flow to ischemic brain tissue. Studies of TBI patients suggest that HOB elevation is preferable (Phillips, 2003; Winkelman, 2000), although a flat position is thought by some to improve ICP and CPP (Rosner & Coley 1986). These differences may depend on autoregulation among other factors. Recommendations for body position and turning of trauma patients including those with TBI are summarized (Christie, 2008; Sullivan, 2000). However, there are no universally accepted guidelines, and it remains unclear if body position alters outcome. Our data suggest that there may be no single optimal position. This is consistent with the heterogeneity of TBI and the concept of "targeted" care in which care is individualized to the specific patient and his or her pathology.

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The Lateral Position in the ICU

Turning and positioning patients, including in the lateral position, are necessary and well accepted in ICUs. In neurocritical care, position may have an important influence on intracranial hemodynamics, and in this study, we observed that the lateral position may have the most adverse affect on intracranial physiology. However, there are other important considerations, in particular, skin and lung function, when deciding about a lateral position. A catabolic state after injury and a decrease in blood flow can result in ischemia of the skin and subcutaneous tissues. Inadequate repositioning of the patient can increase the risk of pressure ulcers (Griffiths & Gallimore, 2005). Consequently, turning patients laterally to relieve pressure from the boney prominences may help alleviate pressure wounds. Marklew (2006) reviewed the literature on lateral body position for patients with unilateral lung disease, lateral positions for patients with healthy lungs and bilateral lung disease, and prone position and continuous rotational therapy and its effects on lung function. For patients with normal lungs capacity, change in position did not significantly increase gas exchange. Sitting up and getting into a chair may improve oxygenation. Patients on bed rest with bilateral lung injury or healthy lungs may benefit from right lateral positioning because the right lung is larger and more vascular than the left and may improve lung capacity and perfusion. Marklew concluded that it is essential for nurses to understand how body position can alter patient's oxygenation. Our data show that severely brain-injured patients in the lateral position should be carefully monitored. Alternatively, patients should be managed with mattresses designed to reduce the risk of pressure sores and receive very close attention to pulmonary care and toilette.

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Intracranial Hemodynamics

Severely brain-injured patients admitted to an ICU are often complex. Immediately after their initial injury, they may have decreased brain oxygen, hypoxia, hypotension, or increased ICP among other secondary cerebral insults. The primary focus of management for these patients is the control of ICP and CPP to prevent secondary injury. Today, multimodality devices are used to assist with this management because monitoring ICP and CPP alone does not always reflect brain oxygen or metabolism adequately. Our data demonstrate that there was no single position that consistently improved ICP, CPP, or brain oxygen. This suggests that there may not be a single optimal position to manage all patients with severe brain injury. Instead, we believe that the use of multimodality devices can best help determine the optimal position for an individual patient and so help decrease secondary injury. In the absence of monitoring, HOB elevation to 30° augmented with slight knee elevation may be the best default position for ICP and CPP control.

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Study Limitations

The study has several potential limitations. First, although the data showed statistical significance in some positions, the sample size is small. The findings therefore should be considered preliminary but can provide important point estimates to calculate the adequacy of sample sizes in future studies. Second, patients with several different pathologies were examined. This may introduce bias. However, all patients were in coma at the time of evaluation (i.e., GCS ≤ 8). Third, all patients in the study were physiologically stable before the study and throughout the position changes. We did not feel it appropriate to subject unstable patients to random position changes. Nevertheless, we cannot conclude whether the same findings would apply to patients who were not physiologically stable or had increased ICP. Fourth, the study and the position changes occurred over a study period often greater than 24 hours. This may influence our results in two ways: multiple nurses recorded the data or there was a change in physiologic variables over time. However, because the same team of ICU nurses provided care to the patients in a protocol-driven manner and information and education were provided to the bedside nurse during the study, we think data entry is unlikely to play a significant role. Moreover, we do not know if changes in CBF that may occur over time influenced our results. Fifth, the challenges were administered in a consecutive manner, and so one position may have influenced the next. Because the choice of position was random, we believe that this is unlikely to affect our results. In addition, we chose not to examine the prone position. The physiological effects of this position are varied, and although it may improve oxygenation in patients with acute respiratory distress syndrome (Reinprecht et al., 2003), it also may increase ICP in some neurosurgical patients (Nekludov, Bellander, & Mure, 2006). Despite these potential limitations, the data are compelling and suggest that there is no one optimal position for all severely brain-injured patients and that among various positions, the lateral position may have the most potential for harm.

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Conclusion

In this prospective clinical study, we subjected 30 patients to 12 random body and head positions while they underwent multimodality intracranial monitoring. Our data suggest that there is no single optimal body position and that the lateral position should be used with caution.

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Acknowledgments

This work was supported, in part, by research grants from the Mary Elisabeth Groff Surgical and Medical Research Trust (PDLR), the Integra Foundation (PDLR), and the Integra Neuroscience (PDLR). The authors thank the Neuro ICU nurses at the University of Pennsylvania for their support; without their help, the study would not have been possible.

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© 2010 American Association of Neuroscience Nurses

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