Incidence

• Peak incidence in the 6th and 7th decades with the mean age of diagnosis at 63 years
• Males account for 65% of cases
• Circadian and seasonal patterns have been described with peak frequency between 8:00 AM and 9:00 AM and during winter months.
• 3.5 per 100,000 persons per year (US data)

Prevalence

Actual prevalence unknown since many patients (~20%) die prior to hospital presentation. Autopsy series report 1 acute aortic dissection for every 128 to 745 autopsies.

Neurologic complications are the main cause of disability among survivors.

• Acute dissection of the ascending aorta has a 30-day mortality rate of 20% with surgical repair and 50% with medical therapy alone.
• Death most often results from aortic rupture, cardiac tamponade, stroke, and visceral ischemia.

History

• 96% of acute aortic dissections are identified with the following prediction model:
  • Aortic pain with immediate onset, a tearing or ripping character, or both
  • Mediastinal widening, aortic widening, or both on chest radiography
  • Pulse differentials (absence of a proximal extremity or carotid pulse), blood pressure differentials (systolic pressure difference >20 mm Hg between arms), or both

Signs/Physical Exam

• Hypertension (69% of distal and 36% of proximal dissections)
• Hypotension, shock, or tamponade (27% of proximal dissections)
• Pulse or blood pressure differentials (20%)
• Focal neurologic deficits (12%)
• Murmur of aortic insufficiency (32%)
• Pleural effusion (left > right)
• Horner syndrome
• Superior vena cava syndrome

Labs/Studies

• Baseline and serial cardiac biomarkers, BUN/Cr, CBC with platelets, coagulation profile and TEG, if available
• ECG may be normal (~30%) or show nonspecific ST-T changes (40%), left ventricular hypertrophy (26%), ischemia (15%), or infarction (10%).
• Chest radiograph findings include mediastinal widening (61%), abnormal aortic contour (49%), pleural effusion (19%), displacement/calcification of aorta (14%). Normal findings are present in 12% of patients.
• CT angiography is quick, highly sensitive, and specific; 64-slice multidetector CT with cardiac gating may allow for simultaneous evaluation of pulmonary and coronary arteries.
• TEE is highly sensitive for ascending aortic dissection and allows rapid evaluation of hemodynamic instability (tamponade, coronary dissection, valvular regurgitation, tension hemothorax, etc.).
• MRI/MRA has high sensitivity and specificity, avoids radiation, and iodinated contrast; but is more time-consuming and contraindicated with metallic implants.
• Aortography: Previously the reference standard, this is performed less often and rarely as the initial study.

• Short-acting drugs permit rapid termination of effect, if desired, and should be considered.
• Morphine, beta-blockers, and vasodilating drugs can be used to control pain and blood pressure. Esmolol is ultra-short-acting and has organ-independent elimination (metabolized within red blood cells).
• Sodium nitroprusside may cause an increase in aortic dP/dt; it is generally added only after a negative inotrope is administered.
• Nicardipine may be preferred in patients intolerant of beta-antagonists and does not cause a reflex tachycardia.
• Enalaprilat may be useful in refractory hypertension due to renal artery compromise.
• Phenylephrine and norepinephrine are preferred pressors due to a relative lack of associated increase in aortic dP/dt.

• No superiority has been demonstrated with any given anesthetic technique.
• for open repair, GETA is typically employed, alone or in combination with epidural anesthesia; epidural placement may be precluded by hemodynamic instability.
• Evoked-potentials monitoring may influence technique (i.e., volatile anesthetic concentration, use of muscle relaxant).
• for endovascular repair, local, regional, and general techniques may be used.

• ECG with ST-segment analysis
• Temperature (central and peripheral sites if bypass is to be used)
• Foley catheter
• Arterial line: Right radial artery may be preferred if blood flow to the left subclavian artery is disrupted due to dissection or cross-clamp placement. Femoral artery insertion may permit monitoring of distal perfusion pressures.
• Central venous access may be appropriate for IV access and administration of vasoactive medications.
• Pulmonary artery catheterization can provide SvO₂, SVR, CO, PAP.
• TEE aids in diagnosis, anatomic localization, identification of complications, and characterization of valvular and ventricular function in real time.
• Lumbar drains and evoked-potentials may be placed for patients at risk for spinal cord ischemia.
• The potential for catastrophic hemorrhage necessitates appropriate vascular access, availability of blood products, rapid infuser system, and autologous red cell salvage.

• Slow, controlled titration of medications to the desired effect can help maintain hemodynamic stability. Hypertension and tachycardia increase shear stress and risk of rupture.
• Single-lumen ETT may be typically placed for a median sternotomy approach.
• Lung isolation with a double lumen tube or bronchial blocker aids in the exposure of the descending aorta and is preferred for procedures using the lateral thoracotomy approach.

• Thermoregulation: forced air and fluid warming systems are necessary due to significant heat loss with open procedures.
• Fluid management: Maintenance of intravascular volume may be challenging due to significant hemorrhage and evaporative losses; no specific colloid or crystalloid strategy has emerged as superior.
• Coagulation: Consumption and dilution of coagulation factors and platelets may be significant; replacement is guided by conventional coagulation studies as well as TEG, if available.
• Renal protection: Maintenance of renal blood flow and urine output is essential; IV mannitol and fenoldopam can be employed to reduce the risk of kidney injury.

• Ongoing cardiac or pulmonary instability, bleeding, hypothermia, or neurologic injury may necessitate continued mechanical ventilation; otherwise patients may be extubated at the conclusion of the procedure.
• Pain, hypertension, and tachycardia should be anticipated and addressed.