Care for the Patient with Aortic Dissection
Thus far, this has not come up in the fellowship exam, except as a question regarding diagnostic modalities: Question 13 from the second paper of 2010. LITFL have an excellent summary of this topic, in succinct point form and complete with recent references.
As the diagnostic steps have already been covered elsewhere, this section will focus on the potential complications and management strategies. The canonical source for this information would have to be the most recent iteration of the ACCF/AHA Guidelines for Diagnosis and Management of Patients With Thoracic Aortic Disease.
Aortic Dissection, in brief
The Stanford classification divides dissections into Type A (involving the ascending aorta) and Type B (the rest). The point of separation is the left subclavian artery: any dissection distal to this point is Type B (B is for Boring). An "acute" dissection is one which has been around for less than 2 weeks.
Aortic dissection, intramural haematoma and penetrating atherosclerotic ulcer all form a spectrum of related disorders grouped as "acute aortic syndromes". Of these, aortic dissection is the more common.
I paraphrase Table 9 from the ACCF/AHA guidelines:
- Weight lifting
- Deceleration or torsional injury
- Coarctation of the aorta
- Marfan syndrome
- Ehlers-Danlos syndrome
- Bicuspid aortic valve (including prior aortic valve replacement)
- Inflammatory vasculitis ("Aortitis")
- Polycystic kidney disease
- Chronic corticosteroids
- Infections involving the aortic wall
Complications of aortic dissection
- About 40% die immediately. They are underidentified, as few are subjected to autopsy.
- About 1% die per hour thereafter.
- About 5-20% will die shortly after their definitive surgery.
- Cardiac failure due to aortic regurgitation
- Cardiac failure due to cardiac tamponade
- Myocardial ischemia or infarction
- Ischemic stroke
- Paraplegia due to spinal ischemia
- Aortopulmonary fistula with hemorrhage
- Mesenteric ischemia
- Renal ischemia
- Limb ischemia
Idiosyncrasies of ICU management
Mandatory mechanical ventilation
This, ironically, is not mandatory. However, if the dissection flap is especially fragile, one would want to avoid any sort of Valsalva-like scenario, where the patient coughs, and then turns pale and dies instantly. To avoid this, one may wish to consider the following strategies:
- Sedation with opiates
- Minimal suctioning
- Neuromuscular blockade
- Total controlled ventilation
Control of blood pressure
Aortic wall stress is affected by the velocity of ventricular contraction (dP/dt), the rate of ventricular contraction, and blood pressure. One's blood pressure is what one dissects one's intima with. Oh's Manual recommends a systolic BP target of 100-110 mmHg, or a MAP of 55-65 mmHg (pp. 1033).
Beta-blockade is the standard of care, as beta blockers decrease the force of cardiac contraction and therefore reduce the velocity of the aortic jet. Labetalol or esmolol are described by the AHA document as "excellent" choice. Various vasodilators (eg. sodium nitroprusside) can also be used, provided beta-blockade is firmly in place (one does not wish to see any reflex tachycardia).