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Positioning of Patients with Severe Traumatic Brain Injury: Research-Based Practice.

Abstract: Traumatic brain injuries (TBIs) are the most common disabling injuries in the United States, accounting for 44% of all deaths due to trauma. Once inflicted, primary cerebral injury is immutable and irreversible. Consequently, initial critical care of TBI patients focuses on prevention of secondary cerebral injury through the treatment of intracranial hypertension, systemic resuscitation, and multisystem stabilization. Relationships exist between therapeutic positioning, multisystemic stability, and prevention of secondary cerebral injury in severe TBI. A critical review and synthesis of current research literature on multisystem responses to positioning led to development of clinical recommendations based on currently available evidence and generated best practices for positioning patients with severe TBI.

Traumatic brain injuries (TBIs) are the most common disabling injuries in the United States, accounting for 44% of all deaths due to trauma. Classified as unintentional injuries, approximately 500,000 new TBI cases occur annually.[1,26] Once inflicted, primary cerebral injury resulting from TBI is immutable and irreversible.[1] Consequently, initial critical care of TBI patients focuses on prevention of secondary cerebral injury through the treatment of intracranial hypertension, systemic resuscitation, and multisystem stabilization.

Secondary cerebral injury most frequently results from cerebral edema and systemic insults such as hypoxia, hypercarbia, hypotension, impaired oxygen delivery; and acidosis.[1,5] Recent studies indicate that early episodes of hypotension and hypoxia significantly increase morbidity and mortality in TBI patients.[8]

Critically ill TBI patients experience considerable risk for secondary cerebral injury due to simultaneously occurring multisystem challenges, including cardiovascular vulnerability, autonomic dysfunction, fluid and electrolyte alterations, acute mechanical ventilation dependency, associated pulmonary pathology, and cerebrovascular compromise.[1] This complex integration of multisystem physiologic processes renders TBI patients most vulnerable to random body position changes.

This article describes the relationship between therapeutic positioning, multisystem stability, and prevention of secondary cerebral injury in severe TBI. Current research literature on multisystem responses to positioning is reviewed and synthesized; clinical recommendations based on currently available evidence are developed; and research implications for generating best practices for positioning patients with severe TBI are explored.

Position-Related Physiologic Responses

Description of position-related physiologic responses demonstrates the dynamic relationship between body position and multisystem stability in the critically ill patient. This highlights the role of therapeutic positioning in preventing secondary cerebral injury in patients with TBI.

Plasma Volume Responses

It has been proposed that changes in backrest elevation and lateral side-lying positions alter plasma volume and cardiac filling pressures, resulting in cardiovascular and hemodynamic responses in a variety of critically ill patients.[27] Patients with known alterations in autonomic function have diminished or impaired responses to changes in plasma volume and, consequently, to changes in position.[18] Negative sodium and potassium balances, reduced plasma volume, increased urine output, and decreased levels of plasma catecholamines also have been observed in early bedrest periods (2-10 days), creating further vulnerability during positioning for critically ill patients.[9,22]

Ventilation-Perfusion Responses

Some body positions may also preferentially promote optimal matching of ventilation and perfusion, particularly in mechanically ventilated patients.[16] Lateral positioning of mechanically ventilated patients results in the preferential delivery of a smaller proportion of inspired volume and a higher proportion of pulmonary blood flow to the dependent lung due to gravitational effects.[30] Unilateral lung pathology also leads to a ventilation/perfusion mismatch between the lungs, which may be further influenced by lateral positioning.[62]

Cerebral Responses

Varying degrees of head elevation and lateral sidelying positions also have been associated with changes in jugular venous outflow, intracranial pressure, cerebral perfusion pressure, and cerebral tissue oxygenation.[20,42] Head elevation is generally presumed to be associated with enhanced jugular venous outflow and decreased intracranial pressure. However, the relationship between head elevation and cerebral perfusion pressure and cerebral tissue oxygenation is less clearly understood. Lateral side-lying positions also may have variable effects on cerebral dynamics.

Therapeutic Positioning

Because patients with severe TBI are at risk for experiencing varied physiologic responses to position changes, implementation of scientifically based positioning practices may prove extremely beneficial in preventing further multisystem instability and associated secondary cerebral injury in this population. Clinical adaptations of research-based positioning interventions aimed at achieving or maintaining multisystem stability may be expected to reduce both the rate of acute secondary cerebral injury and that of associated secondary systemic disabilities in TBI.

Positioning is one of the most frequently performed nursing activities in critical care, often providing a central pivotal focus for planning other nursing activities.[16,20] Currently, the concept of therapeutic positioning is emerging in trauma and critical care with the adaptation of research-based positioning strategies designed to enhance or promote physiologic stability and tolerance of nursing and medical treatments.[16,20] Research findings in trauma literature suggest that positioning may be related to multisystem consequences including altered hemodynamics, impaired gas exchange, changes in cerebral tissue perfusion, and increases in intracranial pressure.[20]

Review of Current Research in Positioning

Numerous researchers have investigated the influence of positioning on the physiologic responses of selected body systems in a variety of critically ill patient populations including postoperative cardiac surgery, surgical intensive care, multitrauma, and severe TBI. Critical review of current research investigating multiple physiologic responses to positioning interventions provides direction for developing research-based positioning practices for patients with severe TBI.

Cardiovascular Research in Positioning

Research generated in the cardiovascular arena has investigated the relationship between body position, pulmonary artery pressure measurements, and cardiac output. Current cardiovascular research demonstrates no statistically or clinically significant differences in pulmonary artery pressure measurements and cardiac output during 0, 20, 30, 45, and 60 degrees of backrest elevation.[10,11,12,14,24,35,36,71,74,75] Inclusion of patients with elevated filling pressures, use of mechanical ventilation, and vasoactive drugs did not alter these findings.[10,12,14,35,71]

The phlebostatic axis has been empirically demonstrated as a valid anatomic reference point for the right atrium, while both the phlebostatic axis and midanterior-posterior diameter have been found to be valid reference points for the left atrium in supine backrest positions.[32,33,73] Current research findings are inconclusive, however, regarding empirical determination of valid reference points for coronary atria and reliability of pulmonary artery pressure measurements in lateral side-lying positions.[7,16,23,31,33,50]

Statistically significant differences in cardiac output measurements were demonstrated between right and left lateral and supine positions.[15,69] Emerson and Banasik further demonstrated statistically significant differences in central venous pressure in lateral side-lying as compared to supine positions.[17]

Clinical recommendations for therapeutic positioning based on current cardiovascular research are listed in Table 1. In considering these recommendations for the critical care of severe TBI patients, it must be recognized that original research studies were conducted in cardiovascular patient populations. Adaptations of these cardiovascular-based positioning strategies in the TBI population require further investigation.

Table 1. Positioning Recommendations Based on Cardiovascular Research

1. Consider position of 0 through 60 degrees of supine backrest elevation, Pulmonary artery pressures and cardiac output remain stable during 0 through 60 degrees of backrest elevation.

2. Phlebostatic axis is a valid anatomic reference point for both the right and left atria in supine backrest positions.

3. Use caution when assuming lateral side-lying positions. Differences in cardiac output and central venous pressure occur during assumption of right and left side-lying positions.

Pulmonary Research in Positioning

Additional researchers have investigated the relationship between body position, oxygenation, and gas exchange. Studies evaluating the relationship between backrest elevation and gas exchange among different patient populations have yielded conflicting results. Partial pressure of arterial oxygen (Pa[O.sub.2]) seems to decrease in the sitting position immediately after surgical procedures, but this change may diminish over time.[13,41,59] Findings from additional studies, however, contradict these results.[25,43]

Other studies have demonstrated no statistically significant differences in mixed venous oxygen saturation during 0, 20, 30, 40, and 45 degrees of backrest elevation in mechanically ventilated postoperative cardiac surgical patients.[14,49]

Additional investigators have studied the relationship between lateral side-lying positions and oxygenation in samples of postoperative cardiac surgery patients and those with unilateral lung disease. In patients with unilateral lung disease, research findings have consistently demonstrated that ventilation/perfusion matching is improved when the unaffected lung is dependent, otherwise known as the "good lung down" hypothesis.[29,54,55,61,66,76]

In several samples of mechanically ventilated postoperative cardiac surgical patients, Banasik and colleagues have shown significant reductions in Pa[O.sub.2] values in left lateral side-lying positions.[2,3] Others have reported decreases in mixed venous oxygen saturation immediately after lateral positioning of postoperative cardiac surgical patients and other critically ill patients, with return to baseline values within 5 minutes.[48,52,64,67,72] These findings remained consistent with inclusion of mechanically ventilated patients as subjects.[52]

Clinical recommendations for therapeutic positioning based on current pulmonary research are listed in Table 2. In considering these recommendations for the critical care of TBI patients, it must again be noted that original research studies were conducted in cardiopulmonary patient populations. Adaptations of these pulmonary-based positioning strategies in the TBI population also require further study.

Table 2. Positioning Recommendations Based on Pulmonary Research

1. Use caution when assuming sitting positions in postoperative patients. Pa[O.sub.2] may decrease in the sitting position immediately following surgical procedures. This change diminishes over time.

2. Assume lateral side-lying positions with caution. Pa[O.sub.2] may be significantly reduced in the left lateral side-lying position in mechanically ventilated postoperative patients. Mixed venous oxygen saturation decreases immediately after lateral positioning but returns to baseline within 5 minutes.

3. Consider positions of 0 through 45 degrees of supine backrest elevation. Mixed venous oxygen saturation remains constant during 0 through 45 degrees of backrest elevation.

4. Consider "good lung down" position (if possible) in patients with unilateral lung disease. In the presence of unilateral lung disease, ventilation/perfusion matching is improved when the unaffected lung is dependent.

Neurologic Research in Positioning

Critical review of neuroscience literature provides further direction for determining best practices for positioning patients with severe TBI. Investigators have demonstrated that head elevation decreases intracranial pressure.[21,34,37,39,47,51,53,56] Others have demonstrated that head rotation and head and neck flexion are associated with increased intracranial pressure, decreased jugular venous outflow, and localized changes in cerebral blood flow.[4,21,28,38,44,45,47,63,70]

Additional studies have indicated that turning and repositioning are related to at least transient increases in intracranial pressure with associated changes in selected cerebrovascular and cardiovascular variables.[4,38,45,46,51,63,65,68] Guided by these research findings, clinical practice has generally adapted various degrees of head elevation, avoidance of head rotation and head flexion, and cautious repositioning as standardized treatments in the care of TBI patients.

During recent years, however, several researchers have challenged this traditional clinical practice and have included the measurement of additional cerebrovascular variables in their investigations. Rosner and Coley demonstrated that intracranial pressure reductions were accompanied by cerebral perfusion pressure reductions during head elevation in a study of 18 patients with varying degrees of intracranial hypertension.[57] These investigators proposed that 0 degrees of head elevation maximizes cerebral perfusion pressure and may reduce the severity and frequency of intracranial pressure wave occurrence. Rosner and Daughton, in a subsequent study of 34 TBI patients with intracranial hypertension, reported that 0 degrees of head elevation was associated with reduced morbidity and mortality.[58]

In a further conflicting study, Feldman et al. studied 22 TBI patients and concluded that head elevation of 30 degrees significantly reduced intracranial pressure without significantly changing cerebral perfusion pressure, cerebral blood flow, cerebral metabolic rate of oxygen consumption, arteriovenous difference of lactate, or cerebrovascular resistance.[19]

March, Mitchell, Grady, and Winn also examined the relationship between four backrest and head elevation positions and intracranial pressure, cerebral perfusion pressure, and transcranial doppler measurement of cerebral blood flow velocities in four subjects.[40] After conducting nonparametric statistical analysis of study results, the investigators proposed that backrest and head elevation positions should be assigned after analysis of individual patient responses in intracranial pressure, cerebral perfusion pressure, and cerebral blood flow to varying positions.

Schneider, Helden, Franke, Lanksch, and Unterberg also studied four head elevation positions in 25 comatose patients with reduced cerebral compliance.[60] These researchers concluded that head elevation significantly reduced intracranial pressure with no statistically significant changes in cerebral perfusion pressure and jugular venous oxygen saturation. These investigators noted, however, that individual responses of cerebral perfusion pressure to changes in head position were quite unpredictable. After considering both individual and group responses, Schneider et al. also recommended implementing individualized approaches to head elevation.[60]

Although all these research efforts have been aimed at providing empirically based guidance on positioning practices in TBI, they have yielded somewhat inconclusive, occasionally conflicting findings, restricting broader evidence-based clinical applications. Despite these limitations, clinical practice has incorporated various adaptations of head elevation and positioning in standardized TBI care. Clinical recommendations for therapeutic positioning based on current neurologic research are listed in Table 3.

Table 3. Positioning Recommendations Based on Neurologic Research

1. Consider using head elevation of up to 30 degrees to decrease intracranial pressure. Head elevation of up to 30 degrees significantly reduces intracranial pressure without significantly changing cerebral blood flow, cerebral metabolic rate of oxygen consumption, or cerebrovascular resistance.

2. Monitor cerebral perfusion pressure cautiously during assumption of head elevation position. Head elevation, while reducing intracranial pressure, may also decrease cerebral perfusion pressure.

3. Avoid head rotation and neck flexion. Head rotation and neck flexion are associated with increased intracranial pressure, decreased jugular venous outflow, and localized changes in cerebral blood flow.

4. Turn and reposition patients with caution. These maneuvers contribute to transient increases in intracranial pressure with associated changes in cerebrovascular parameters.

In considering these recommendations for the critical care of the TBI population, it must be pointed out that neurologic investigations have generally been limited to exclusive consideration of cerebral responses to positioning. It is now known that multisystem responses, particularly cardiovascular and pulmonary responses, may influence development of secondary cerebral injury and ultimately outcome in severe TBI.[8] Therefore, clinical practice recommendations for TBI patients can no longer be restricted to research based on unilateral system responses to body position but must consider multisystem positioning responses.

Current Practice Recommendations

Current research-based recommendations for positioning practices in severe TBI may be presented based on an assimilation of positioning research concerning multiple physiologic systems. Table 4 lists these current multisystem-focused positioning recommendations.

Table 4. Positioning Recommendations Based on Assimilation of Multisystem-Focused Research

1. Cautiously consider lateral side-lying positions in patients with unstable cardiovascular status. Differences in cardiac output and central venous pressure occur during assumption of right and left lateral side-lying positions.

2. Cautiously consider lateral side-lying positions in patients with unstable pulmonary status. Pa[O.sub.2] may be significantly reduced after assumption of left lateral side-lying position. Mixed venous oxygen saturation may decrease immediately after lateral positioning with a return to baseline within 5 minutes.

3. Turn and reposition patients with caution since these maneuvers are associated with at least transient increases in intracranial pressure and associated changes in cerebrovascular parameters.

4. In the presence of unilateral lung disease, position patient (if possible) with the "good lung down." In the presence of unilateral lung disease, ventilation/perfusion matching is improved when the unaffected lung is dependent.

5. Head elevation of up to 30 degrees, in the supine backrest position, may reduce intracranial pressure without significantly changing hemodynamic parameters (pulmonary artery pressure, cardiac output), systemic oxygenation parameters (mixed venous oxygen saturation), or cerebral dynamics parameters (cerebral blood flow, cerebral metabolic rate of oxygen consumption, and cerebrovascular resistance).

6. Avoid head rotation and neck flexion, which are associated with increased intracranial pressure, decreased jugular venous outflow, and localized changes in cerebral blood flow.

7. Backrest and head elevation positions should be assigned after careful consideration of individual patient responses, including intracranial pressure, cerebral perfusion, cerebral bloodflow, cardiovascular and hemodynamic parameters, and systemic oxygenation.

Note, however, that these recommendations are cautiously preliminary because no single research study has yet simultaneously investigated comprehensive multisystem responses to positioning in severe TBI patients. Although these initial recommendations are admittedly introductory, it must also be recognized that practice must proceed with the best available evidence while new investigations are still ongoing. Consideration of currently available research at least provides the best available empirical basis for current practice while new evidence is being generated.

Research Implications

I am currently conducting further research into simultaneous multisystem responses to therapeutic positioning in severe TBI. My hope is that conclusions from this ongoing study will lead to determination of best practice(s) for positioning TBI patients from a comprehensive multisystemic physiologic perspective. By simultaneously measuring multiple cerebral, hemodynamic, and systemic oxygenation variables in a sample large enough to detect statistically and clinically meaningful responses, this study will validate earlier research as well as generate new direction for establishing empirically based and clinically applicable multisystem-focused positioning strategies for TBI patients.

Results of this study will guide the determination of best practice(s) for positioning TBI patients with optimization of multisystem parameters. Subsequent intervention studies investigating the clinical application of these research-based positioning strategies are expected to demonstrate improved physiological, functional, cognitive, perceptual (i.e., quality of life), and financial outcomes of TBI patients by reducing the incidence of secondary cerebral injury and associated secondary systemic disabilities.

Summary

Review of current positioning research has provided a template of best available evidence from which preliminary recommendations may guide present practice in therapeutic positioning of patients with severe TBI. Ongoing and future studies may generate further direction for conclusive empirically based determination of best practices for positioning. Translation of research-based positioning interventions, as integral components of independent and interdependent nursing practice, may ultimately be utilized in managing the symptoms and preventing disability associated with TBI, thereby limiting the biobehavioral burden of this illness.

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Questions or comments about this article may be directed to: Jacqueline Sullivan, PhD RN CNRN CCRN, Thomas Jefferson University Hospital, 1900 Gibbon Building, 111 S. 11th Street, Philadelpia, PA 19107. She is a clinician researcher and clinical assistant professor of neuroscience and critical care nursing.

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Date:Aug 1, 2000
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