Case Review
Trenton Wray, MD, Elizabeth Powell, MD, William Hinckley, MD, and Peter V.R. Tilney, DO
A 55-Year-Old Man With an Aortic Dissection A 55-year-old man presented to a community hospital with a chief complaint of possible seizure and altered mental status. Emergency medical services (EMS) had found him as the sole occupant of his car, which had been pulled over to the side of the road with no sign or report of trauma. On EMS arrival, the patient was noted to be bradycardic into the 50s with a weak, thready radial pulse and unobtainable blood pressure. EMS arrived at the community hospital with the patient who was noted to be very drowsy, actively vomiting, mumbling incoherently, and was not spontaneously moving his left lower extremity. His initial vitals were as follows: heart rate of 60, blood pressure of 82/61, and oxygen saturation 98% room air; he was also afebrile. A secondary survey was performed, which showed no evidence of trauma, no chest wall tenderness, no cardiac murmurs, a tender abdomen, movement of both of his upper extremities, movement of his right lower extremity, and limited, prompted movement of his left lower extremity. Over the next several minutes, the patient became increasingly agitated with ongoing vomiting and confusion. Fluid resuscitation was initiated, and the patient was intubated. After this, a focused assessment with sonography in trauma examination was performed, which showed no evidence of cardiac effusion or hemoperitoneum. After the intubation was completed, a chest x-ray was performed, which showed a poorly defined aortic arch (Fig. 1).1 The patient, with ongoing resuscitation, was taken for a computed tomographic (CT) scan. A noncontrast head CT scan was noted to be negative. Because of his chest x-ray findings as well as his constellation of symptoms, which included neurologic deficit, altered mental status, vomiting, hypotension, and abdominal tenderness, CT scans of the chest, abdomen, and pelvis with intravenous contrast were performed. It showed a large, Stanford type A aortic dissection extending from the aortic root (Fig. 2) through the aortic arch (Figs. 3 and 4) and the descending aorta and involving the right iliac artery (Fig. 5). The dissection involved the celiac trunk and superior mesenteric artery but preserved the renal arteries. The patient was sedated aggressively with propofol and fentanyl. A position of comfort and synchrony with the ventilator were also strictly maintained. After initial fluid resuscitation, his blood pressure had increased to 139/70 with an ongoing heart rate of 61. Thus, a right-sided internal jugular central venous catheter was placed, and the patient was started on an esmolol drip for a goal heart rate of 60 and systolic blood pressure of 100 to 120. A local rotor wing critical care transport service was contacted for rapid transport to a facility capable of emergent surgical intervention. 184
On arrival to the tertiary care facility, the patient was immediately taken to the operating room where he underwent surgical repair with a 34-mm Hemashield graft (Atrium Medical Corporation, Hudson, NH) under circulatory arrest. He was subsequently transferred to the intensive care unit where he was extubated on postoperative day 0. His care was advanced over the next several days with excellent functional improvement but did have a residual left gaze preference with slight expressive aphasia. Thus, neurology was consulted and magnetic resonance imaging/magnetic resonance angiography was performed, which showed small, scattered areas of acute infarct. The patient underwent inpatient physical therapy and was discharged to an inpatient rehabilitation facility alert, oriented, and able to ambulate on hospital day 10.
Discussion The aorta is the body’s largest blood vessel, and all oxygenated blood must pass through the aorta in order to reach the systemic circulation. Anatomically, it travels from its root just beyond the left ventricle and ends at its bifurcation into the right and left common iliac arteries. Histologically, the aorta consists of 3 layers: the tunica intima, media, and adventitia. The innermost layer, the tunica intima, consists of a thin endothelial layer and is easily damaged. The middle layer, the tunica media, consists of elastic tissue. The outer layer, the tunica adventitia, consists of collagen fibers, sensory nerve fibers, and a network of small blood vessels supplying the aorta known as the vasa vasorum. The inner 2 layers do not have sensory innervation, so pain is primarily perceived from the adventitia and tends to follow the anatomic course of the portion of the aorta involved. In aortic dissection, the easily damaged intima is violated, which allows blood to enter the medial layer. Depending on the force and frequency of pulsatile blood against the dissection point, blood may dissect in this layer and create a “false lumen” between the tunica intima and the tunica adventitia. Depending on the location and extent of the dissection, a variety of signs, symptoms, and sequelae develop. Aortic dissections are the most common aortic emergency, occurring with an average incidence of 10,000 per year in the United States.1 They carry an in-hospital mortality of up to 58%2 and a mortality of 0.25% to 1% per hour for the first 48 hours.3 Rapid diagnosis and management with transport to definitive care are essential in the management of aortic dissection. Prehospital and transport medical crews should have an understanding of how to recognize and treat these complex patients. Air Medical Journal 33:5
Figure 1. A post-intubation chest X-ray was complete in the supine view. Note the poorly demarcated aortic knob as indicated by the red arrow.
Figure 2. Arrows indicating dissection involving the aortic root (top left) and the thoracic descending aorta (bottom right).
Figure 3. Coronal image of the thoracic aorta. The arrow indicates dissection at the aortic arch with loss of the lumen of the left internal carotid artery.
September-October 2014
Atraumatic aortic dissections have a bimodal age distribution. Younger patients will often have conditions that predispose them to an intimal tear in areas of the aorta that are vulnerable to sheer stress. Examples of this are collagen vascular disease (Marfan syndrome and Ehlers-Danlos syndrome), bicuspid aorta, aortic coarctation, and vasculitis.4 Furthermore, patients may report an activity inducing an acute elevation in blood pressure, such as cocaine use5 or recent history of intense resistance exercise.6 Before cardiac surgery is also associated with an increased risk.4 The largest group of those diagnosed with aortic dissection is composed of patients ⬎ 50 years old with chronic hypertension.1 Aortic dissection is classified using 2 different systems (Stanford and DeBakey), which help delineate treatment strategies. Stanford type A dissections involve the ascending aorta, although they may involve the arch and descending aorta as well. They are typically considered surgical emergencies because of the proximity of the false lumen to multiple structures essential for cardiac output. Stanford type B dissections are limited to the descending aorta (distal to the left subclavian artery) and are more often managed medically because of equal or higher mortality with surgical management.7 The less commonly used DeBakey system divides dissections into 3 categories. DeBakey type I dissections involve the ascending aorta, the arch, and the descending aorta. Type II involves the ascending aorta only. DeBakey type III dissections begin distal to the left subclavian artery but may dissect proximally and distally (type IIIa) or distally alone (type IIIb).2,8 For simplification, the Stanford classification system is more commonly used; type A dissections are those that involve the ascending aorta (and are therefore surgical emergencies), and type B dissections are those that do not. Depending on the location of the dissection, patients can present with a variety of symptoms, which, similar to many vascular events, begin abruptly.6 Often, signs and symptoms will follow the anatomic course of the aorta and localize to sites of impaired circulation (Fig. 6). Involvement of the aortic root may affect the pericardium, aortic valves, and the coronary arteries.19 This may result in syncope and hypotension caused by a number of different etiologies, including pericardial tamponade, severe aortic insufficiency, aortic rupture with massive hemothorax (because of dissection through the adventitia), bradyarrhythmia caused by occlusion of the coronary arteries, or sudden increase in vagal tone because of stimulation of aortic baroreceptors. Syncope is a presenting symptom in 9% to 14% of Stanford type A aortic dissections, and hypotension/shock is present on presentation in up to 27%.1,9 Both are associated with increased mortality.4,10 If the ascending aorta is involved, patients often present with chest pain radiating to the left shoulder and back as the dissection moves toward the arch. If the aortic arch is involved, patients may complain of pain in the jaw, neck, and upper back. Furthermore, involvement of the arch may result in obstruction of the carotid arteries, leading to acute stroke, Horner Syndrome, or altered mental status. If the descending 185
Figure 4. Transverse image. The arrow indicates dissection through the aortic arch.
Figure 5. The arrow indicates involvement of the right iliac artery.
Figure 6. Classification schemes for Aortic Dissection–Stanford and DeBakey. The Stanford system is more commonly used. Stanford Type A dissections are those that involve the ascending aorta and are managed surgically due to the potential for rapid development of lifethreatening complications. Stanford Type B dissections are all dissections that do not involve the ascending aorta. These may be managed surgically if severe complications develop but are more commonly managed medically. Reprinted from: Braverman AC. Aortic Dissection: Prompt diagnosis and emergency treatment are critical. Cleve Clin J Med 2011;78:685696. Copyright 2011 Cleveland Clinic Foundation. All rights reserved.
© 2011 Cleveland Clinic Foundation. Cleveland Clinic Journal of Medicine. 186
Air Medical Journal 33:5
Table 1. Beta Blockers Agent
Dose/Administration
Comments
Labetalol
Drip: 0.5-2.0 mg/min Intermittent: 20 mg IV slow push, then 20-80 mg every 10-20 minutes as needed
Contains some anti-alpha activity as well May be used as a single agent May be transitioned to by mouth as inpatient Longer half-life and duration of effect, less titratable Use with caution in patients at risk of hypotension or severe aortic regurgitation
Esmolol
Bolus: 500 g/kg/min Drip: 50-200 g/kg/min Must rebolus for each titration of drip
Rapidly cleared, more easily titratable B1 selective (may be preferable in COPD/asthma) No transition to oral therapy No anti-alpha activity with less antihypertensive properties
Intermittent: 5 mg IV every 5 min (up to 15 mg)
B1 selective Acceptable if labetalol or esmolol not accessible Intermittent bolus only
Metoprolol
COPD ⫽ chronic obstructive pulmonary disorder; IV, intravenous.
aorta is involved, abdominal pain, lower back pain, leg pain, acute renal failure (14%-16%), limb ischemia (9%), mesenteric ischemia (2%-5%), and/or lower extremity weakness (3%) may result.1,4,10 Patients may even present solely with neurologic symptoms, leading to diagnostic uncertainty (eg, misdiagnosis as a primary stroke) and ultimately delaying definitive care.3 In a few patients, fever (because of the presence of an inflammatory thrombus) may be the primary symptom present.1,3 Pulse deficit (with a pulse gradient from right to left) occurs in up to 30% to 50% of Stanford type A dissections, and this alone is associated with a high rate of complications.1,9 Recognizing pulse deficit in the prehospital setting may aid in the early diagnosis of this condition and speed management. When an aortic dissection is suspected, diagnostic imaging should be pursued as early as possible. A chest radiograph can be helpful in establishing a diagnosis but is normal in 12% to 37% of patients.1,6 The most common finding is a widened mediastinum or an abnormal aortic contour. Other findings that may be present include pleural effusion; hemothorax (if rupture has occurred); and deviation of the trachea, mainstem bronchi, or esophagus.11 Transthoracic echocardiography can be useful in diagnosing ascending aortic dissections and pericardial tamponade but should not be viewed as a definitive diagnostic test because of the lack of sensitivity.12,13 Transesophageal echocardiography has shown higher sensitivity than transthoracic echocardiography14 but is limited by the lack of rapid availability in the emergency department/prehospital setting. Furthermore, because the procedure can be uncomfortable, a rise in blood pressure may theoretically occur, which could worsen the condition. A contrasted CT scan is useful to confirm the diagnosis and determine the classification and extent of the dissection.11 Aortography is still considered the “gold standard.” However, because of its lack of usability in unstable patients and more readily available means of diagnosis, it is less commonly used. September-October 2014
CT imaging remains the most common diagnostic study used to diagnose aortic dissection.1,4 Treatment of acute aortic dissection is determined by the location, extent, and classification of the dissection and requires rapid involvement of specialized care. The patient’s airway, breathing, and circulation should be assessed and aggressively maintained. The patient should be carefully monitored throughout their emergency department course and transport. Furthermore, the medical transport crew should monitor closely for potential complications and take steps to prevent these from occurring. The initial medical management of aortic dissection is aimed at minimizing the rate of rise, force, and frequency of left ventricular contraction while maintaining cerebral perfusion. This involves lowering both the number of times the left ventricle contracts as well as the force of each contraction. Over half of patients are hypertensive because of pain, catecholamine surge, and/or activation of the renin-angiotensin system because of malperfusion of the kidneys.1 Less commonly, patients will present with hypotension and altered mental status. In this case, providers should first evaluate for pseudohypotension (most commonly caused by placement of the cuff on the left side in the presence of a false lumen). If the blood pressure measurements are accurate, volume resuscitation and cautious vasopressor support should be supplied in order to restore cerebral perfusion. It should be noted that mild, relative hypotension may be allowed so long as cerebral or coronary perfusion is not compromised. If the patient is not already hypotensive or bradycardic, steps should be taken to lower the heart rate to a goal of 60 to 80 and a systolic blood pressure of 100 to 120.7,16 The primary goal is to limit the beat-by-beat stress on the intima of the aorta. Although the mean arterial pressure (MAP) is a more appropriate target for blood pressure management in most situations, systolic blood pressure is a better target in the case of aortic dissection because it is a better measure of 187
Table 2. Calcium Channel Blockers Agent Dose/Administration Nicardipine20
Diltiazem
Clevidipine
Comments
Drip: 2.5-5 mg/h; increase by 2.5 mg/h every 15 minutes until target reached (max 15 mg/h)
Ideal afterload-reducing agent Minimal cardiac suppression Use primarily in combination with myocardial suppressant Beta blocker should be used first to prevent reflex tachycardia
Bolus: 10-20 mg IV slow push Drip: 5-15 mg/h
Myocardial depressant Do not use in combination with beta blocker May be of use in patients with contraindication to beta blocker
Drip: 1-2 mg/h is recommended for initiation. Titration to a max of 32 mg/h. Avoid in patients with soybean or egg allergies. Product is held in lipid infusion.
Ideal afterload reducing agent because of its high selectivity for vascular smooth muscle. It is ideal in promoting an overall decrease in systemic vascular resistance.
Dose/Administration
Comments
Drip: 0.3-0.5 g/kg/min and titrate to target (max 15 g/kg/min)
Rapidly titratable Use only in combination with beta blocker Beta blocker should be used first to prevent reflex tachycardia Use with caution in patients with renal or hepatic failure
IV ⫽ intravenous.
Table 3. Nitrates Agent Sodium nitroprusside
the pulsatile shear stress on the intima of the aorta. Automated noninvasive blood pressure cuffs are most often oscillatory measurements and, therefore, measure MAP directly and provide only estimates of systolic and diastolic blood pressure. Invasive blood pressure monitoring techniques (eg, arterial catheters) measure the systolic and diastolic pressures directly and provide a calculation for the MAP.17 Because of this, patients with acute aortic dissection should have an arterial catheter placed (ideally in the right arm) for the most accurate monitoring of systolic blood pressure and heart rate.16,17 Methods of lowering blood pressure should be aimed at 3 primary objectives. First, the catecholamine response to pain should be minimized using opiate pain medications when indicated. Second, steps should be taken to reduce activities that induce coughing, straining, or the Valsalva maneuver. Specifically, if the patient has been intubated, ensuring ventilator synchrony and proper placement of the endotracheal tube (not in contact with the carina) is essential. Third, medical therapy should aimed first at beta blockade and then at peripheral vasodilation. If the patient’s heart rate is above 60 and blood pressure is above 120, treatment should begin with titratable intravenous beta blockers. No particular beta blocker has been shown in the literature to be more effective than others. However, common practice is to begin with either labetalol or esmolol. Labetalol may be favored because it contains both anti-alpha and anti-beta activity, and intermittent bolusing can be used initially. However, it may be limited by its prolonged half-life. 188
Esmolol, a shorter-acting agent, is also commonly used and requires an initial bolus followed by a closely titrated drip. The goal heart rate should be 60 to 80 but should be targeted to as close to 60 as possible. Of note, beta blockers should be used with caution in acute cocaine toxicity.18 Once pain has been controlled, the patient appears comfortable, and the goal heart rate has been met with a beta blocker, a vasodilatory agent can be started. No particular agent has been shown to be better than another, but common practice is to use a calcium channel blocker. Nicardipine is preferred by these authors because of its primarily peripheral effect and short half-life. A relatively new dihydropyridine calcium channel blocker, clevidipine, has also been introduced to acutely reduce blood pressures in this population. It is easily titratable and has a very short half-life. It is prepared similarly to propofol in that it is in a lipid emulsion and thus is contraindicated to those patients with egg or soybean allergies. Sodium nitroprusside may also be used, but caution should be used in renal impairment, which is not uncommon in aortic dissection. It is important not to begin the vasodilatory agent until a beta blocker is in place because this may induce a reflex tachycardia, which may propagate the dissection. The goal systolic blood pressure is 100 to 1207; it is usually closer to 100 unless the patient has known, severe, pre-existing hypertension. Tables 1 to 3 provide a list of medications that may be used. Stanford type A (DeBakey I or II) dissection is a surgical emergency that requires rapid transport to surgical intervention to prevent catastrophic loss in cardiac output and/or neuAir Medical Journal 33:5
rologic compromise. Furthermore, severe Stanford type B (DeBakey III) at risk for rupture or high-risk malperfusion syndromes may also require emergent surgical evaluation.21 We present a relatively unusual case of a Stanford type A aortic dissection presenting with syncope, altered mental status, and hypotension. The prehospital and transport medical crews play a large role in the recognition, prevention of propagation/rupture, and delivery to definitive management for these patients.
References
EMS Fellow at the University of Cincinnati, attending physician at West Chester Hospital, and a flight physician with UC Health Air Care & Mobile Care. William Hinckley, MD, is an attending physician at the University of Cincinnati and a flight physician with UC Health Air Care & Mobile Care. Peter V.R. Tilney, DO, is a board-certified emergency physician at Central Maine Medical Center (CMMC) in Lewiston. He is also the medical director of LifeFlight of Maine and can be reached at [email protected]. 1067-9991X/$36.00 Copyright 2014 by Air Medical Journal Associates http://dx.doi.org/10.1016/j.amj.2014.06.006
1. Hagan, PG, Nienaber, CA, Isselbacher, EM, et al. The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA. 2000;283:897-903. 2. Daily PO, Trueblood HW, Stinson EB, et al. Management of acute aortic dissections. Ann Thorac Surg. 1970;10:237-247. 3. Harris KM, Strauss CE, Eagle KA, et al. Correlates of delayed recognition and treatment of acute type A aortic dissection: the International Registry of Acute Aortic Dissection (IRAD). Circulation. 2011;124:1911-1918. 4. Tsai TT, Nienaber CA, Eagle KA. Acute aortic syndromes. Circulation. 2005;112:3802. 5. Hsue PY, Salinas CL, Bolger AF, Benowitz NL, Waters DD. Acute aortic dissection related to crack cocaine. Circulation. 2002;105:1592. 6. Elefteriades JA, Hatzaras I, Tranquilli MA, et al. Weight lifting and rupture of silent aortic aneurysms. JAMA. 2003;290:2803. 7. Karmy-Jones R, Aldea G, Boyle EM Jr. The continuing evolution in the management of thoracic aortic dissection. Chest. 2000;117:1221-1223. 8. DeBakey ME, Beall AC, Cooley DA, et al. Dissecting aneurysms of the aorta. Surg Clin North Am. 1966;46:1045-1055. 9. Bussone E, Rampoldi V, Nienaber CA, et al. Usefulness of pulse deficit to predict inhospital complications and mortality in patients with acute type A aortic dissection. Am J Cardiol. 2002;89:851-855. 10. Mehta RH, Suzuki T, Hagan PG, et al. Predicting death in patients with acute aortic dissection. Circulation. 2002;105:200-206. 11. Hogg K, Teece S. The sensitivity of a normal chest radiograph in ruling out aortic dissection. Emerg Med J. 2004;21:199. 12. Erbel R, Alfonso F, Boileau C, et al. Diagnosis and management of aortic dissection. Eur Heart J. 2001;22:1642e81. 13. Nienaber C, Von Kodolitsch Y, Nicolas V, et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med. 1993;328:1-9. 14. Meredith E, Masani ND. Echocardiography in the emergency assessment of acute aortic syndromes. Eur J Echocardiogr 2009;10:31-39. 15. Braverman A. Aortic dissection: prompt diagnosis and emergency treatment are critical. Cleve Clin J Med. 2011;78:685-696. 16. Hiratzka L, Bakris G, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/ SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease. Circulation. 2010;121:e266-369. 17. Lakhal K, Macq C, Ehrmann S, Boulain T, Capdevila X. Noninvasive monitoring of blood pressure in the critically ill: reliability according to the cuff site (arm, thigh, or ankle). Crit Care Med. 2012;40:1207-1213. 18. Fareed F, Chan G, Hoffman R. Death temporally related to the use of a beta adrenergic receptor antagonist in cocaine associated myocardial infarction. J Med Toxicol. 2007;4:169-172. 19. Nallamothu BK, Mehta RH, Saint S, et al. Syncope in acute aortic dissection: diagnostic, prognostic, and clinical implications. Am J Med. 2002;113:468. 20. Kim K, Moon I, et al. Nicardipine hydrochloride injectable phase IV open-label clinical trial: study on the anti-hypertensive effect and safety of nicardipine for acute aortic dissection. J Intern Med Res. 2002;30:337-345. 21. Fattori R, Cao P, De Rango P, et al. Interdisciplinary expert consensus document on management of type B aortic dissection. J Am Coll Cardiol. 2013;61:1661-1678.
Trenton Wray, MD, is a fourth year emergency medicine resident at the University of Cincinnati and a flight physician with UC Health Air Care & Mobile Care. Elizabeth Powell, MD, is an September-October 2014
189
Trenton Wray, MD, Elizabeth Powell, MD, William Hinckley, MD, and Peter V.R. Tilney, DO
A 55-Year-Old Man With an Aortic Dissection A 55-year-old man presented to a community hospital with a chief complaint of possible seizure and altered mental status. Emergency medical services (EMS) had found him as the sole occupant of his car, which had been pulled over to the side of the road with no sign or report of trauma. On EMS arrival, the patient was noted to be bradycardic into the 50s with a weak, thready radial pulse and unobtainable blood pressure. EMS arrived at the community hospital with the patient who was noted to be very drowsy, actively vomiting, mumbling incoherently, and was not spontaneously moving his left lower extremity. His initial vitals were as follows: heart rate of 60, blood pressure of 82/61, and oxygen saturation 98% room air; he was also afebrile. A secondary survey was performed, which showed no evidence of trauma, no chest wall tenderness, no cardiac murmurs, a tender abdomen, movement of both of his upper extremities, movement of his right lower extremity, and limited, prompted movement of his left lower extremity. Over the next several minutes, the patient became increasingly agitated with ongoing vomiting and confusion. Fluid resuscitation was initiated, and the patient was intubated. After this, a focused assessment with sonography in trauma examination was performed, which showed no evidence of cardiac effusion or hemoperitoneum. After the intubation was completed, a chest x-ray was performed, which showed a poorly defined aortic arch (Fig. 1).1 The patient, with ongoing resuscitation, was taken for a computed tomographic (CT) scan. A noncontrast head CT scan was noted to be negative. Because of his chest x-ray findings as well as his constellation of symptoms, which included neurologic deficit, altered mental status, vomiting, hypotension, and abdominal tenderness, CT scans of the chest, abdomen, and pelvis with intravenous contrast were performed. It showed a large, Stanford type A aortic dissection extending from the aortic root (Fig. 2) through the aortic arch (Figs. 3 and 4) and the descending aorta and involving the right iliac artery (Fig. 5). The dissection involved the celiac trunk and superior mesenteric artery but preserved the renal arteries. The patient was sedated aggressively with propofol and fentanyl. A position of comfort and synchrony with the ventilator were also strictly maintained. After initial fluid resuscitation, his blood pressure had increased to 139/70 with an ongoing heart rate of 61. Thus, a right-sided internal jugular central venous catheter was placed, and the patient was started on an esmolol drip for a goal heart rate of 60 and systolic blood pressure of 100 to 120. A local rotor wing critical care transport service was contacted for rapid transport to a facility capable of emergent surgical intervention. 184
On arrival to the tertiary care facility, the patient was immediately taken to the operating room where he underwent surgical repair with a 34-mm Hemashield graft (Atrium Medical Corporation, Hudson, NH) under circulatory arrest. He was subsequently transferred to the intensive care unit where he was extubated on postoperative day 0. His care was advanced over the next several days with excellent functional improvement but did have a residual left gaze preference with slight expressive aphasia. Thus, neurology was consulted and magnetic resonance imaging/magnetic resonance angiography was performed, which showed small, scattered areas of acute infarct. The patient underwent inpatient physical therapy and was discharged to an inpatient rehabilitation facility alert, oriented, and able to ambulate on hospital day 10.
Discussion The aorta is the body’s largest blood vessel, and all oxygenated blood must pass through the aorta in order to reach the systemic circulation. Anatomically, it travels from its root just beyond the left ventricle and ends at its bifurcation into the right and left common iliac arteries. Histologically, the aorta consists of 3 layers: the tunica intima, media, and adventitia. The innermost layer, the tunica intima, consists of a thin endothelial layer and is easily damaged. The middle layer, the tunica media, consists of elastic tissue. The outer layer, the tunica adventitia, consists of collagen fibers, sensory nerve fibers, and a network of small blood vessels supplying the aorta known as the vasa vasorum. The inner 2 layers do not have sensory innervation, so pain is primarily perceived from the adventitia and tends to follow the anatomic course of the portion of the aorta involved. In aortic dissection, the easily damaged intima is violated, which allows blood to enter the medial layer. Depending on the force and frequency of pulsatile blood against the dissection point, blood may dissect in this layer and create a “false lumen” between the tunica intima and the tunica adventitia. Depending on the location and extent of the dissection, a variety of signs, symptoms, and sequelae develop. Aortic dissections are the most common aortic emergency, occurring with an average incidence of 10,000 per year in the United States.1 They carry an in-hospital mortality of up to 58%2 and a mortality of 0.25% to 1% per hour for the first 48 hours.3 Rapid diagnosis and management with transport to definitive care are essential in the management of aortic dissection. Prehospital and transport medical crews should have an understanding of how to recognize and treat these complex patients. Air Medical Journal 33:5
Figure 1. A post-intubation chest X-ray was complete in the supine view. Note the poorly demarcated aortic knob as indicated by the red arrow.
Figure 2. Arrows indicating dissection involving the aortic root (top left) and the thoracic descending aorta (bottom right).
Figure 3. Coronal image of the thoracic aorta. The arrow indicates dissection at the aortic arch with loss of the lumen of the left internal carotid artery.
September-October 2014
Atraumatic aortic dissections have a bimodal age distribution. Younger patients will often have conditions that predispose them to an intimal tear in areas of the aorta that are vulnerable to sheer stress. Examples of this are collagen vascular disease (Marfan syndrome and Ehlers-Danlos syndrome), bicuspid aorta, aortic coarctation, and vasculitis.4 Furthermore, patients may report an activity inducing an acute elevation in blood pressure, such as cocaine use5 or recent history of intense resistance exercise.6 Before cardiac surgery is also associated with an increased risk.4 The largest group of those diagnosed with aortic dissection is composed of patients ⬎ 50 years old with chronic hypertension.1 Aortic dissection is classified using 2 different systems (Stanford and DeBakey), which help delineate treatment strategies. Stanford type A dissections involve the ascending aorta, although they may involve the arch and descending aorta as well. They are typically considered surgical emergencies because of the proximity of the false lumen to multiple structures essential for cardiac output. Stanford type B dissections are limited to the descending aorta (distal to the left subclavian artery) and are more often managed medically because of equal or higher mortality with surgical management.7 The less commonly used DeBakey system divides dissections into 3 categories. DeBakey type I dissections involve the ascending aorta, the arch, and the descending aorta. Type II involves the ascending aorta only. DeBakey type III dissections begin distal to the left subclavian artery but may dissect proximally and distally (type IIIa) or distally alone (type IIIb).2,8 For simplification, the Stanford classification system is more commonly used; type A dissections are those that involve the ascending aorta (and are therefore surgical emergencies), and type B dissections are those that do not. Depending on the location of the dissection, patients can present with a variety of symptoms, which, similar to many vascular events, begin abruptly.6 Often, signs and symptoms will follow the anatomic course of the aorta and localize to sites of impaired circulation (Fig. 6). Involvement of the aortic root may affect the pericardium, aortic valves, and the coronary arteries.19 This may result in syncope and hypotension caused by a number of different etiologies, including pericardial tamponade, severe aortic insufficiency, aortic rupture with massive hemothorax (because of dissection through the adventitia), bradyarrhythmia caused by occlusion of the coronary arteries, or sudden increase in vagal tone because of stimulation of aortic baroreceptors. Syncope is a presenting symptom in 9% to 14% of Stanford type A aortic dissections, and hypotension/shock is present on presentation in up to 27%.1,9 Both are associated with increased mortality.4,10 If the ascending aorta is involved, patients often present with chest pain radiating to the left shoulder and back as the dissection moves toward the arch. If the aortic arch is involved, patients may complain of pain in the jaw, neck, and upper back. Furthermore, involvement of the arch may result in obstruction of the carotid arteries, leading to acute stroke, Horner Syndrome, or altered mental status. If the descending 185
Figure 4. Transverse image. The arrow indicates dissection through the aortic arch.
Figure 5. The arrow indicates involvement of the right iliac artery.
Figure 6. Classification schemes for Aortic Dissection–Stanford and DeBakey. The Stanford system is more commonly used. Stanford Type A dissections are those that involve the ascending aorta and are managed surgically due to the potential for rapid development of lifethreatening complications. Stanford Type B dissections are all dissections that do not involve the ascending aorta. These may be managed surgically if severe complications develop but are more commonly managed medically. Reprinted from: Braverman AC. Aortic Dissection: Prompt diagnosis and emergency treatment are critical. Cleve Clin J Med 2011;78:685696. Copyright 2011 Cleveland Clinic Foundation. All rights reserved.
© 2011 Cleveland Clinic Foundation. Cleveland Clinic Journal of Medicine. 186
Air Medical Journal 33:5
Table 1. Beta Blockers Agent
Dose/Administration
Comments
Labetalol
Drip: 0.5-2.0 mg/min Intermittent: 20 mg IV slow push, then 20-80 mg every 10-20 minutes as needed
Contains some anti-alpha activity as well May be used as a single agent May be transitioned to by mouth as inpatient Longer half-life and duration of effect, less titratable Use with caution in patients at risk of hypotension or severe aortic regurgitation
Esmolol
Bolus: 500 g/kg/min Drip: 50-200 g/kg/min Must rebolus for each titration of drip
Rapidly cleared, more easily titratable B1 selective (may be preferable in COPD/asthma) No transition to oral therapy No anti-alpha activity with less antihypertensive properties
Intermittent: 5 mg IV every 5 min (up to 15 mg)
B1 selective Acceptable if labetalol or esmolol not accessible Intermittent bolus only
Metoprolol
COPD ⫽ chronic obstructive pulmonary disorder; IV, intravenous.
aorta is involved, abdominal pain, lower back pain, leg pain, acute renal failure (14%-16%), limb ischemia (9%), mesenteric ischemia (2%-5%), and/or lower extremity weakness (3%) may result.1,4,10 Patients may even present solely with neurologic symptoms, leading to diagnostic uncertainty (eg, misdiagnosis as a primary stroke) and ultimately delaying definitive care.3 In a few patients, fever (because of the presence of an inflammatory thrombus) may be the primary symptom present.1,3 Pulse deficit (with a pulse gradient from right to left) occurs in up to 30% to 50% of Stanford type A dissections, and this alone is associated with a high rate of complications.1,9 Recognizing pulse deficit in the prehospital setting may aid in the early diagnosis of this condition and speed management. When an aortic dissection is suspected, diagnostic imaging should be pursued as early as possible. A chest radiograph can be helpful in establishing a diagnosis but is normal in 12% to 37% of patients.1,6 The most common finding is a widened mediastinum or an abnormal aortic contour. Other findings that may be present include pleural effusion; hemothorax (if rupture has occurred); and deviation of the trachea, mainstem bronchi, or esophagus.11 Transthoracic echocardiography can be useful in diagnosing ascending aortic dissections and pericardial tamponade but should not be viewed as a definitive diagnostic test because of the lack of sensitivity.12,13 Transesophageal echocardiography has shown higher sensitivity than transthoracic echocardiography14 but is limited by the lack of rapid availability in the emergency department/prehospital setting. Furthermore, because the procedure can be uncomfortable, a rise in blood pressure may theoretically occur, which could worsen the condition. A contrasted CT scan is useful to confirm the diagnosis and determine the classification and extent of the dissection.11 Aortography is still considered the “gold standard.” However, because of its lack of usability in unstable patients and more readily available means of diagnosis, it is less commonly used. September-October 2014
CT imaging remains the most common diagnostic study used to diagnose aortic dissection.1,4 Treatment of acute aortic dissection is determined by the location, extent, and classification of the dissection and requires rapid involvement of specialized care. The patient’s airway, breathing, and circulation should be assessed and aggressively maintained. The patient should be carefully monitored throughout their emergency department course and transport. Furthermore, the medical transport crew should monitor closely for potential complications and take steps to prevent these from occurring. The initial medical management of aortic dissection is aimed at minimizing the rate of rise, force, and frequency of left ventricular contraction while maintaining cerebral perfusion. This involves lowering both the number of times the left ventricle contracts as well as the force of each contraction. Over half of patients are hypertensive because of pain, catecholamine surge, and/or activation of the renin-angiotensin system because of malperfusion of the kidneys.1 Less commonly, patients will present with hypotension and altered mental status. In this case, providers should first evaluate for pseudohypotension (most commonly caused by placement of the cuff on the left side in the presence of a false lumen). If the blood pressure measurements are accurate, volume resuscitation and cautious vasopressor support should be supplied in order to restore cerebral perfusion. It should be noted that mild, relative hypotension may be allowed so long as cerebral or coronary perfusion is not compromised. If the patient is not already hypotensive or bradycardic, steps should be taken to lower the heart rate to a goal of 60 to 80 and a systolic blood pressure of 100 to 120.7,16 The primary goal is to limit the beat-by-beat stress on the intima of the aorta. Although the mean arterial pressure (MAP) is a more appropriate target for blood pressure management in most situations, systolic blood pressure is a better target in the case of aortic dissection because it is a better measure of 187
Table 2. Calcium Channel Blockers Agent Dose/Administration Nicardipine20
Diltiazem
Clevidipine
Comments
Drip: 2.5-5 mg/h; increase by 2.5 mg/h every 15 minutes until target reached (max 15 mg/h)
Ideal afterload-reducing agent Minimal cardiac suppression Use primarily in combination with myocardial suppressant Beta blocker should be used first to prevent reflex tachycardia
Bolus: 10-20 mg IV slow push Drip: 5-15 mg/h
Myocardial depressant Do not use in combination with beta blocker May be of use in patients with contraindication to beta blocker
Drip: 1-2 mg/h is recommended for initiation. Titration to a max of 32 mg/h. Avoid in patients with soybean or egg allergies. Product is held in lipid infusion.
Ideal afterload reducing agent because of its high selectivity for vascular smooth muscle. It is ideal in promoting an overall decrease in systemic vascular resistance.
Dose/Administration
Comments
Drip: 0.3-0.5 g/kg/min and titrate to target (max 15 g/kg/min)
Rapidly titratable Use only in combination with beta blocker Beta blocker should be used first to prevent reflex tachycardia Use with caution in patients with renal or hepatic failure
IV ⫽ intravenous.
Table 3. Nitrates Agent Sodium nitroprusside
the pulsatile shear stress on the intima of the aorta. Automated noninvasive blood pressure cuffs are most often oscillatory measurements and, therefore, measure MAP directly and provide only estimates of systolic and diastolic blood pressure. Invasive blood pressure monitoring techniques (eg, arterial catheters) measure the systolic and diastolic pressures directly and provide a calculation for the MAP.17 Because of this, patients with acute aortic dissection should have an arterial catheter placed (ideally in the right arm) for the most accurate monitoring of systolic blood pressure and heart rate.16,17 Methods of lowering blood pressure should be aimed at 3 primary objectives. First, the catecholamine response to pain should be minimized using opiate pain medications when indicated. Second, steps should be taken to reduce activities that induce coughing, straining, or the Valsalva maneuver. Specifically, if the patient has been intubated, ensuring ventilator synchrony and proper placement of the endotracheal tube (not in contact with the carina) is essential. Third, medical therapy should aimed first at beta blockade and then at peripheral vasodilation. If the patient’s heart rate is above 60 and blood pressure is above 120, treatment should begin with titratable intravenous beta blockers. No particular beta blocker has been shown in the literature to be more effective than others. However, common practice is to begin with either labetalol or esmolol. Labetalol may be favored because it contains both anti-alpha and anti-beta activity, and intermittent bolusing can be used initially. However, it may be limited by its prolonged half-life. 188
Esmolol, a shorter-acting agent, is also commonly used and requires an initial bolus followed by a closely titrated drip. The goal heart rate should be 60 to 80 but should be targeted to as close to 60 as possible. Of note, beta blockers should be used with caution in acute cocaine toxicity.18 Once pain has been controlled, the patient appears comfortable, and the goal heart rate has been met with a beta blocker, a vasodilatory agent can be started. No particular agent has been shown to be better than another, but common practice is to use a calcium channel blocker. Nicardipine is preferred by these authors because of its primarily peripheral effect and short half-life. A relatively new dihydropyridine calcium channel blocker, clevidipine, has also been introduced to acutely reduce blood pressures in this population. It is easily titratable and has a very short half-life. It is prepared similarly to propofol in that it is in a lipid emulsion and thus is contraindicated to those patients with egg or soybean allergies. Sodium nitroprusside may also be used, but caution should be used in renal impairment, which is not uncommon in aortic dissection. It is important not to begin the vasodilatory agent until a beta blocker is in place because this may induce a reflex tachycardia, which may propagate the dissection. The goal systolic blood pressure is 100 to 1207; it is usually closer to 100 unless the patient has known, severe, pre-existing hypertension. Tables 1 to 3 provide a list of medications that may be used. Stanford type A (DeBakey I or II) dissection is a surgical emergency that requires rapid transport to surgical intervention to prevent catastrophic loss in cardiac output and/or neuAir Medical Journal 33:5
rologic compromise. Furthermore, severe Stanford type B (DeBakey III) at risk for rupture or high-risk malperfusion syndromes may also require emergent surgical evaluation.21 We present a relatively unusual case of a Stanford type A aortic dissection presenting with syncope, altered mental status, and hypotension. The prehospital and transport medical crews play a large role in the recognition, prevention of propagation/rupture, and delivery to definitive management for these patients.
References
EMS Fellow at the University of Cincinnati, attending physician at West Chester Hospital, and a flight physician with UC Health Air Care & Mobile Care. William Hinckley, MD, is an attending physician at the University of Cincinnati and a flight physician with UC Health Air Care & Mobile Care. Peter V.R. Tilney, DO, is a board-certified emergency physician at Central Maine Medical Center (CMMC) in Lewiston. He is also the medical director of LifeFlight of Maine and can be reached at [email protected]. 1067-9991X/$36.00 Copyright 2014 by Air Medical Journal Associates http://dx.doi.org/10.1016/j.amj.2014.06.006
1. Hagan, PG, Nienaber, CA, Isselbacher, EM, et al. The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA. 2000;283:897-903. 2. Daily PO, Trueblood HW, Stinson EB, et al. Management of acute aortic dissections. Ann Thorac Surg. 1970;10:237-247. 3. Harris KM, Strauss CE, Eagle KA, et al. Correlates of delayed recognition and treatment of acute type A aortic dissection: the International Registry of Acute Aortic Dissection (IRAD). Circulation. 2011;124:1911-1918. 4. Tsai TT, Nienaber CA, Eagle KA. Acute aortic syndromes. Circulation. 2005;112:3802. 5. Hsue PY, Salinas CL, Bolger AF, Benowitz NL, Waters DD. Acute aortic dissection related to crack cocaine. Circulation. 2002;105:1592. 6. Elefteriades JA, Hatzaras I, Tranquilli MA, et al. Weight lifting and rupture of silent aortic aneurysms. JAMA. 2003;290:2803. 7. Karmy-Jones R, Aldea G, Boyle EM Jr. The continuing evolution in the management of thoracic aortic dissection. Chest. 2000;117:1221-1223. 8. DeBakey ME, Beall AC, Cooley DA, et al. Dissecting aneurysms of the aorta. Surg Clin North Am. 1966;46:1045-1055. 9. Bussone E, Rampoldi V, Nienaber CA, et al. Usefulness of pulse deficit to predict inhospital complications and mortality in patients with acute type A aortic dissection. Am J Cardiol. 2002;89:851-855. 10. Mehta RH, Suzuki T, Hagan PG, et al. Predicting death in patients with acute aortic dissection. Circulation. 2002;105:200-206. 11. Hogg K, Teece S. The sensitivity of a normal chest radiograph in ruling out aortic dissection. Emerg Med J. 2004;21:199. 12. Erbel R, Alfonso F, Boileau C, et al. Diagnosis and management of aortic dissection. Eur Heart J. 2001;22:1642e81. 13. Nienaber C, Von Kodolitsch Y, Nicolas V, et al. The diagnosis of thoracic aortic dissection by noninvasive imaging procedures. N Engl J Med. 1993;328:1-9. 14. Meredith E, Masani ND. Echocardiography in the emergency assessment of acute aortic syndromes. Eur J Echocardiogr 2009;10:31-39. 15. Braverman A. Aortic dissection: prompt diagnosis and emergency treatment are critical. Cleve Clin J Med. 2011;78:685-696. 16. Hiratzka L, Bakris G, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/ SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease. Circulation. 2010;121:e266-369. 17. Lakhal K, Macq C, Ehrmann S, Boulain T, Capdevila X. Noninvasive monitoring of blood pressure in the critically ill: reliability according to the cuff site (arm, thigh, or ankle). Crit Care Med. 2012;40:1207-1213. 18. Fareed F, Chan G, Hoffman R. Death temporally related to the use of a beta adrenergic receptor antagonist in cocaine associated myocardial infarction. J Med Toxicol. 2007;4:169-172. 19. Nallamothu BK, Mehta RH, Saint S, et al. Syncope in acute aortic dissection: diagnostic, prognostic, and clinical implications. Am J Med. 2002;113:468. 20. Kim K, Moon I, et al. Nicardipine hydrochloride injectable phase IV open-label clinical trial: study on the anti-hypertensive effect and safety of nicardipine for acute aortic dissection. J Intern Med Res. 2002;30:337-345. 21. Fattori R, Cao P, De Rango P, et al. Interdisciplinary expert consensus document on management of type B aortic dissection. J Am Coll Cardiol. 2013;61:1661-1678.
Trenton Wray, MD, is a fourth year emergency medicine resident at the University of Cincinnati and a flight physician with UC Health Air Care & Mobile Care. Elizabeth Powell, MD, is an September-October 2014
189
