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April 1, 2013 Volume 77, Number 4
How Can Anesthesiologists Impact Traumatic Brain Injury Outcomes? Monica S. Vavilala, M.D.


Public Health Burden of Traumatic Brain Injury (TBI)
Anesthesiologists frequently provide care for TBI patients during their most vulnerable periods in the emergency room, operating room and intensive care unit. This is because globally, including in the United States, TBI is a leading cause of death and disability. Approximately 1.7 million people sustain TBI each year in the United States, accounting for 275,000 hospitalizations and 52,000 deaths.1 TBI is a contributing factor in approximately one-third of all injury deaths, and the highest incidence is in children 0 to 4 years, adolescents aged 15 to 19 years, and elderly adults > 65 years, with males being more affected in all age groups. Falls are the most common cause of TBI, and elderly patients receiving anticoagulants are at risk of intracranial hemorrhage and significant morbidity, even with ground-level falls. Whereas patients with severe TBI [GCS (Glasgow Coma Score) ≤ 8] have the highest morbidity and mortality, mild (GCS, 13-15) and moderate (GCS 9- 12) TBI patients are also at risk of significant long-term disability and account for a greater percentage of the public health burden because of their larger numbers.

The Importance of Second Insult Prevention and Brain Trauma Foundation (BTF) Guidelines
The primary injury to the brain is caused by the initial mechanical impact with parenchymal and vascular injuries such as diffuse axonal injury, cerebral contusions and microvascular hemorrhages. Primary injury is largely irreversible and untreatable. Immediately after the primary injury, inflammatory processes ensue, releasing excitotoxic neurotransmitters and free radicals that may cause cerebral edema and increased intracranial pressure (ICP) with resultant cerebral ischemia. Macrovascular injuries may result in extradural, subdural and intracerebral hemorrhages that may also cause cerebral edema, reduced cerebral perfusion pressure and ischemia. These second injuries contribute to the progression of TBI, worsen outcomes and are thought to be largely preventable.

Current 2007 BTF Guidelines
(https://www.braintrauma.org/pdf/protected/Guidelines_Management_2007w_bookmarks.pdf2 provide the best evidence-based treatment recommendations for select acute care management strategies of the hospitalized severe TBI patient and are largely aimed at preventing second insults/injuries. Because of the lack of Class I evidence to support all guidelines indicators, many of these guidelines are consensus-based with supportive, but less rigorous, evidence-based studies. However, a study by the Centers for Disease Control estimated that stricter adherence to the BTF guidelines could reduce mortality by >3,600 deaths annually, save $262 million in annual medical costs and $43 million in annual rehabilitation costs, with $62 billion savings in lifetime societal costs.3 There are no intraoperative guidelines for the anesthetic care of the TBI patient.

Despite longstanding recognition that single episodes of hypoxia and hypotension are associated with in-hospital mortality, prevalence estimates of in-hospital hypoxia and hypotension in TBI patients currently range from 25 percent and 50 percent, respectively, even after adjusting for injury severity. The most important secondary insults continue to be hypotension (systolic blood pressure [SBP] < 90 mm Hg or CPP < 50mmHg in adults and SBP < 5th percentile for age or CPP < 40mmHg in children) and hypoxemia (PaO2 < 60 mm Hg). Other commonly occurring secondary insults include hypoglycemia (glucose < 60-70mg/dL), hyperglycemia (glucose >200mg/dL), hypercarbia (PaCO2 >45mmHg), hypocarbia (PaCO2 < 35mmhg) and increased ICP (ICP >20mmHg). These patients are critically ill, often with associated hemodynamic instability and acute lung injuries, making 100 percent adherence to the BTF guidelines impractical. However, better dissemination of the BTF guidelines throughout the pre- and in-hospital acute care settings (e.g., emergency responders in the field, emergency departments, operating rooms and intensive care units) with more aggressive and prompt interventions may reduce second insults and improve neurologic outcomes for TBI patients.

Anesthetic Care for TBI Patients
Anesthesiologists may encounter TBI patients in a number of clinical care settings such as airway management in the emergency department, anesthesia for operations for associated traumatic orthopedic, intrathoracic or intra-abdominal injuries, during emergency decompressive craniotomies with or without evacuation of hemorrhage, or in the intensive care unit. The major goals of intraoperative anesthetic care are aimed at minimizing second insults, optimizing cerebral perfusion and operative conditions, and facilitating early decompression. Numerous factors completely or partially under the control of anesthesiologists may impact outcomes for the TBI patient (Table 1). It is unclear whether or not the BTF guidelines apply to the same degree during general anesthesia and yet, as Table 1 shows, there is a large gap in knowledge as to the effect of anesthesia care on outcomes in TBI. The few small studies do, however, suggest that in both adults and children, intraoperative second insults are common and may be associated with poor outcomes. The differential effects of anesthetic agents on outcome of TBI have not been demonstrated in humans. Details of the anesthetic techniques suitable for patients with TBI are presented in a recent review.4 Consistent with optimizing cerebral physiology, a balanced anesthetic technique with < 1 MAC volatile anesthetic agent, intermittent opioid use and muscle relaxation is preferred. Consistent with the goal of timely resuscitation, two large-bore intravenous lines should be available and delays in surgical care should not occur due to central venous line placement. Invasive arterial cannulation is desired for blood sampling and blood pressure monitoring.

In a recent New England Journal of Medicine article, Chesnut et al. reported no outcome benefits with ICP monitoring in severe TBI, but this study was conducted in the developing world. Additionally, intraoperative data were not specifically evaluated. Moreover, patients undergoing extracranial surgery early in their hospitalization but who have severe TBI may represent a subset of TBI patients who would benefit from intraoperative ICP monitoring. Postoperative head CT scans are common to exclude new or worsening TBI, but future changes in reimbursement and concerns for radiation exposure may give pause to routine repeat head CT scans. Finally, the availability of intraoperative and ICU bedside CT scanners reduces transport-related risks for those TBI patients who do require repeat head CT imaging.

How Can Anesthesiologists Contribute to Advances in TBI Outcomes?
Anesthesiologists can improve TBI outcomes by providing high-quality TBI anesthesia care via educational and outreach efforts, via advocacy and injury prevention efforts, and through research. The need for education in TBI was recently demonstrated in a recent ASA survey presented by McCunn et al., which showed that despite guidelines suggesting otherwise, the majority of respondents routinely maintained CPP >70mmHg and that hyperventilation in the absence of cerebral herniation was common practice in TBI. Anesthesiologists can become involved with pre-hospital TBI care and local quality improvement efforts and affiliate with local injury prevention centers to decrease the burden of TBI. The role of anesthesiologists in TBI research is well recognized, and anesthesiologists have continued to make significant contributions to the understanding of TBI pathophysiology, anesthetic impact and treatment options in TBI. These inroads have facilitated anesthesia care decisions based on scientific discovery. However, much of this knowledge comes from experimental studies, and decades of trials based on these findings have not yet resulted in a proven therapy in TBI. The need for combination therapy aimed at different therapeutic targets coupled with the need for human studies suggests that anesthesiologists presently have an opportunity to make contributions to high-quality clinical TBI research that will ultimately inform best anesthesia care practice. Recently, the Society for Neuroscience in Anesthesiology and Critical Care contributed to the development of intraoperative data elements in the NINDS Common Data Elements project www.commondataelements.ninds.nih.gov, and these data elements can be used to collect clinical data across multiple sites in a standardized manner in clinical research.

Summary
Injuries and TBI are major public health concerns. Anesthesia care may impact TBI outcomes, but the data from the intraoperative period are grossly lacking, and yet the perioperative period is a potentially important one where TBI outcomes may be improved. There are a number of ways anesthesiologists can make a difference in the outcomes of patients with TBI, including our roles in clinical care, education, advocacy, injury prevention and research.



Monica S. Vavilala, M.D. is Professor of Anesthesiology and Pain Medicine, Associate Director, Harborview Injury Prevention and Research Center, University of Washington, Seattle.

References
1. Faul M, Xu L, Wald MM, Coronado VG. Traumatic Brain Injury in the United States: Emergency Department Visits, Hospitalizations, and Deaths. Atlanta (GA): Centers for Disease Control and Prevention, National Center for Injury Prevention and Control; 2010.
2. Bratton SL, Chestnut RM, Ghajar J, et al.; Brain Trauma Foundation; American Association of Neurological Surgeons; Congress of Neurological Surgeons; Joint Section on Neurotrauma and Critical Care, AANS/CNS. Guidelines for the management of severe traumatic brain injury. I. Blood pressure and oxygenation. J Neurotrauma. 2007;24(suppl 1): S7-S13 .
3. Faul M, Wald MM, Rutland-Brown W, Sullivent EE, Sattin RW. Using a cost-benefit analysis to estimate outcomes of a clinical treatment guideline: testing theBrain Trauma Foundation guidelines for the treatment of severe traumatic brain injury. J Trauma. 2007;63(6): 1271-1278.
4. Sharma D, Vavilala MS. Perioperative management of adult traumatic brain injury. Anesthesiol Clin. 2012;30(2):333-346.