Timely access to neurocritical care is crucial for the survival of patients with nontraumatic intracerebral hemorrhage, and that frequently means transporting them by helicopter emergency medical services. HEMS expands timely access to neurosurgical care for patients with ICH and mitigates the clinical deterioration that is common early in the patient's clinical course, but emergency physicians and HEMS teams must still coordinate care to mitigate risks for secondary injury.
Nontraumatic ICH is the second most common cause of stroke and has a 30-day mortality of approximately 40 percent. (Circulation 2018;137:e67; http://bit.ly/2RNGwBR; Am J Emerg Med 2011;29:391; http://bit.ly/2TRucgZ.) Only one-third of the U.S. population lives within 90 minutes of a neurocritical care unit by ground, making HEMS essential for them to receive definitive neurosurgical care. (Neurocrit Care 2012;16:232; http://bit.ly/2RA8Kkc.)
ICH sometimes encompasses subarachnoid hemorrhage, but here we focus on nontraumatic intraparenchymal and intraventricular hemorrhage. The early clinical phase of ICH is especially high-risk because intracranial pressure rises further in response to the mass effects from hematoma expansion, edema, inflammatory effects, and herniation. (Lancet Neurol 2012;11:101.) Neurologic deterioration commonly occurs in the prehospital period, and is associated with worse neurologic outcome and higher mortality. (Crit Care Med 2008;36:172; Acad Emerg Med 2012;19:133; http://bit.ly/2TRAcXb.) Neurogenic pulmonary edema also occurs in up to 35 percent of patients, and others can experience a stress-induced cardiomyopathy. (Anesth Analg 2013;116:855.)
Coordinating ICH Care
Stabilizing care includes close monitoring, supportive care, and preventing hematoma expansion and secondary brain injury. (Crit Care 2016;20:272; http://bit.ly/2TLMX5w.) These are HEMS' goals as they mitigate the physiologic stressors of flight such as worsening hypoxia, barometric change, vibration, noise, g-force, and temperature change. (U.S. Air Force. Jan. 9, 2017; http://bit.ly/2TSRC5B; U.S. Airforce Research Laboratory. http://bit.ly/2TRASf3.)
Appreciating that clinical deterioration is expected, it's crucial that bedside handovers relay the injury severity, baseline neurologic exam, and anticipated clinical course so HEMS can intervene quickly when conditions change. A structured handover enhances a shared mental model and promotes safety during this critical transition period. (Pediatr Crit Care Med 2018;19:e72; Emerg Med Australas 2013;25:393; http://bit.ly/2TTI1vI.)
If intubation is required, it's preferable to intubate before transport with a neuroprotective rapid sequence induction approach that minimizes sympathetic stimulation, ICP spikes, hypotension, and hypoxia, all of which can cause secondary injury and worsen clinical outcome. Emergency physicians can help the HEMS team improve cerebral venous outflow and reduce ICP by elevating the head of the bed, loosening overly restrictive endotracheal tube ties and cervical collars, and placing an orogastric tube for gastric decompression at altitude. (J Cereb Blood Flow Metab 2016;36:1338; http://bit.ly/2DfsdxT; Neurosurgery 2004;54:593.)
Higher post-intubation sedation and analgesia requirements may be needed to prevent discomfort and ICP spikes given the stimulation and stress of transport. This needs to be balanced with adequate hemodynamic resuscitation to maintain normal blood pressure and cerebral perfusion. (Neurol Clin 2008;26:521; http://bit.ly/2DenJqU; Stroke 2015;46:2032; http://bit.ly/2TRZAvY.) If neuromuscular blockade is required, it's preferable to coordinate dose timing so that a full neurologic exam is possible at the receiving facility.
Hypoxia prevention is critical during ascent in an unpressurized helicopter. Hypobaric hypoxia is expected as the barometric pressure drops, resulting in a lower partial pressure of oxygen (PO2). The PO2 will drop approximately 5 mm Hg for every 1,000 feet in altitude. Ascending from sea level to 3,000 feet, for example, the barometric pressure will drop from 760 mm Hg to 681 mm Hg, corresponding to a drop in the partial pressure of inspired oxygen from 150 to 133 mm Hg and in arterial oxygen partial pressure (PaO2) from 100 to 85 mm Hg. (Respiration 2010;80:161; http://bit.ly/2TOfU0O.)
If the barometric pressure is known at the beginning and at maximum altitude, an oxygen correction formula can be used (%FiO2 x BP1 / BP2 = %FiO2 required for altitude) to determine the required FiO2 to maintain an equivalent PO2. If FiO2 requirements are high at sea level, maintaining an equivalent PaO2 at higher altitudes may not be possible. (U.S. Air Force. Jan. 9, 2017; http://bit.ly/2TSRC5B.) Patients with concomitant pulmonary and cardiac disease are at increased risk of hypoxemia at altitude and require optimization of their oxygenation before transport to prevent end-organ dysfunction and secondary brain injury. (Ann Am Thorac Soc 2014;11:1614; http://bit.ly/2TXsXx5.)
Emergency physicians can also initiate blood pressure management and coagulopathy reversal to limit hematoma growth and ICP, and those can be continued in flight. (Crit Care 2016;20:272; http://bit.ly/2TLMX5w.) AHA guidelines state that acutely lowering blood pressure to 140 mm Hg for ICH patients presenting with a systolic blood pressure of 150-220 mm Hg is safe (Class I, Level A) and can be effective for improving functional outcome (Class IIa, Level B), though these were published before the results of the ATACH-2 trial, which suggested that a systolic goal of <160 mm Hg is typically adequate. (Stroke 2015;46:2032; http://bit.ly/2TRZAvY; N Engl J Med 2016;375:1033; http://bit.ly/2TSK1nG.)
Coagulopathy reversal strategies have been well described, and may prevent further clinical deterioration. (Crit Care 2016;20:272; http://bit.ly/2TLMX5w; Neurosurgery 2017;81:240). Availability of thawed plasma and prothrombin complex concentrate is increasingly common for HEMS in high-resource settings, which can reduce intervention times further. (Emerg Med J 2014;31:109.) Seizures and rising ICP increase the risk of secondary brain injury, and hyperosmolar therapy can help reduce vasogenic edema and ICP in the herniating patient. In flight, therapy will be guided by signs of rising ICP and herniation (i.e., ipsilateral pupillary dilation, hypertension, and bradycardia). (Neurocrit Care 2015;23 Suppl 2:S76; http://bit.ly/2TW59tw.)
Seizures are common after ICH, yet the association with clinical outcome remains unclear. (Lancet Neurol 2012;11:720; http://bit.ly/2TRFNN4; Lancet Neurol 2012;11:101.) A rapidly expanding space-occupying lesion, focal ischemia, and blood breakdown products contribute to seizures in ICH. (Lancet Neurol 2012;11:101.) Prophylactic anticonvulsants are not recommended, but anticipating and treating clinical seizures in flight may attenuate the detrimental effects on ICP and prevent secondary injury. (Stroke 2015;46:2032; http://bit.ly/2TRZAvY.)
Dr. Johnson is an assistant professor of emergency medicine and pulmonary, critical care, and sleep medicine (adjunct) at the University of Washington in Seattle, WA. He cares for patients in the emergency department and medical intensive care unit and on the neurocritical care service at Harborview Medical Center. He receives research funding from the National Institutes of Health and Medic One Foundation, and serves as the associate program director for the University of Washington's Critical Care Medicine Fellowship. Follow him on Twitter at @NickJohnsonMD. Mr. Danielson is a nurse practitioner and flight nurse. He specializes in emergency and critical care at Airlift Northwest. Follow him on Twitter @Kyl_Dan.