Aortic Dissection

Pathophysiology: An aortic dissection results from an intimal tear creating a subintimal hematoma within the wall of the aorta. The hematoma may begin as a tear in the intima of the aorta or with rupture of the vasa vasorum within the aortic media. Passage of blood into the media, creates a false channel. This channel is contained externally by the outer media and adventitial layers of aorta. With each cardiac contraction, the dissected channel can extend proximally or distally.

Risk factors: Trauma to the aorta (deceleration injuries in MVA, iatrogenic as instrumentation - cardiac cath, IABP). Non-traumatic systemic HTN, atherosclerosis, CTD with cystic medial degeneration (Marfan and Ehlers-Danlos syndromes), pregnancy, cocaine use, syphilis, congenital CVD (bicuspid aortic valve, aortic coarctation, Ebstein's anomaly). About half of all aortic dissections in women under 40 years of age occur during pregnancy.

Classification:

Stanford Type A (proximal)

Stanford Type B (distal)

Ligamentum arteriosum is the point of reference

Debakey type I: ascending aorta, arch of aorta, descending aorta - Stanford types A & B.

Debakey type II: descending aorta

Debakey type IIIa: descending aorta above diaphragm

Debakey type IIIb: descending aorta below diaphgram.

Acute aorta dissection: < 2 weeks

Chronic aorta dissection: > 2 weeks.

Clinical features: Severe CP, abrupt onset, "tearing", "ripping" sensation, knife like, radiating from anterior chest to back, ripping between the shoulder blades. Almost peaks in severity immediately, after onset. Pt. may have cardiovascular collapse at onset of symptoms. Hypotension/hypertension. Differential BP in both arms. Stroke, paraplegia. MI. Murmur of AI, pericardial rub, cardiac tamponade, loss of peripheral pulses.

Complications: Cardiac tamponade from hemopericardium is the most common cause of death, aortic regurgitation, myocardial infarction, stroke, intrapleural rupture (mostly in the left side), branch artery compromise. The latter may involve brachiocephalic vessels, causing stroke or discrepancy in upper extremity blood pressures, the intercostal vessels causing paraplegia (spinal cord infarction), mesenteric or renal vessels compromising blood flow to the bowel or kidneys, or iliofemoral vessels reducing distal blood flow to the legs.

Diagnostics:

    • TEE has become the gold standard for identifying intimal flaps, evidence of tamponade, and aortic insufficiency.

    • CTA

Admit Orders

    • Admit: ICU

    • Attendee: Dr.

    • Dx: Aortic Dissection - type A

    • Condition: guarded

    • Code Status: Full resuscitation

    • Consult: Cardiothoracic surgery, cardiology

    • Vitals, cardiac telemetry, neurocheck.

    • Activities: bed rest, bedside commode

    • Allergies:

    • Nursing: O2 at 2 L/min or more via NC. Keep sPO2 >92%

    • Diet: NPO except meds

    • IV fluids: heplock (flush qshift)

    • Labs: CBC, electrolytes, BUN, Cr, PT, aPTT, INR, troponin q8h, CPK-MB q6h, ECG, CXR (PA and Lat), TEE or 2-D echo, CT with IV contrast, stool guaiac.

Treatment:

    • Type A dissection: Surgery. Resuspension or replacement of the aortic valve, resection of the intimal tear, and interposition graft replacement to reapproximate the aortic wall. Bioglue can be used to improve tissue integrity, as also the use of teflon felts. If the aortic root is destroyed and cannot be reconstructed, a Bentall procedure (valved conduit) is performed. Repair is usually performed during a period of deep hypothermic circulatory arrest. If the tear extends down into the descending aortia (Debakey type I), an initial repair via a median sternotomy leaving an elephant trunk for repair of the descending aorta.

    • Type B dissection: Uncomplicated type B dissections are treated medically. Surgery for complicated dissections (patient's complaining of persistent pain, uncontrollable HTN, evidence of aneurysmal expansion or rupture, or visceral, renal, or lower extremity vascular compromise). Chronic type B dissections should be operated upon when they reach 6 - 6.5 cm in diameter. Endovascular stenting has become more common in the management of type B dissections.

Preoperative considerations:

    • Goal SBP about 110 mm Hg, HR: 60 - 70/min.

    • Pulse check. Complete neurological exam. Neurochecks

    • Labetalol, 10-20 mg IV x 2 min, then infuse 1-2 mg/min to desired effect and stop infusion. Max cumulative dose is 300 mg. OR

    • Start with Esmolol, 500 mcg/kg IV bolus and f/up with 50 mcg/kg/min. Increase infusion by 25 mcg/kg/min every 5 min until HR 60-80/min. Max dose rate is 200 mcg/kg/min. OR

    • Metoprolol, 5 mg IV q5 min.

    • Add Nitroprusside. Start at 0.2 mcg/kg/min and titrate upward to desired effect to keep SBP 100 - 120 mmHg.