Page 494 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

364 PART 3: Cardiovascular Disorders

Sodium nitroprusside is a potent venous and arterial vasodilator with intervention for maximal survival. Relative contraindications to sur-
very short onset of action (1-2 minutes) and half-life (2 minutes) that gery include severe organ dysfunction such as diffuse CAD, end-stage
is very effective for acute blood pressure control. It is usually started at chronic obstructive pulmonary disease, old age (for those over age 80
0.25 µg/kg/min and titrated up to 3 µg/kg/min but doses as high as 10 µg/ the risk rises markedly, perhaps as high as 80%), moribund patient,
57
kg/min have been used. Nitroprusside may increase dP/dT through paraplegia, and stroke. Whether an acute stroke represents a contraindi-
max
a sympathetic reflex from its peripheral vasodilatory effects when used cation to surgery is controversial. Stroke does represent an independent
alone. Therefore, it should be used in combination with a β-blocker and negative influence on survival. Surgery may make the neurologic deficit
started after a reduction in heart rate (usually <80 bpm) is accomplished. worse due to intraoperative bleeding from heparinization, embolization,
It is typically used for initial BP control (24-48 hours) due to potential for or reperfusion injury when the occluded carotid is reopened. Without
thiocyanate toxicity with longer use and at doses greater than 3 µg/kg/ surgery, however, these patients have a near uniformly fatal prognosis.
min. It requires continuous monitoring of blood pressure via arterial line. It has been shown that the presence of the stroke does not increase the
Nicardipine is a calcium channel blocking agent with a rapid onset risk of mortality with surgery. Shumway group found 85% of survivors
58
(5-10 minutes). It is readily titratable and may be preferable to nitroprus- to be improved or unchanged neurologically, and suggested that there is
side due to lack of toxicity. no way to predict neurologic outcome from the preoperative neurologic
β-Blockers are the cornerstone therapy for blood pressure control in status. Stroke is therefore only a relative contraindication to surgery, and
acute aortic dissection but should be used with caution or avoided only deeply comatose or moribund patients should be refused definitive
in certain clinical settings. β-Blockade without concomitant α-blockade surgical repair.
in cocaine users is generally contraindicated due to risk of worsening Aortic branch complications in type A dissections are best managed
arterial vasoconstriction and hypertension caused by unopposed α stim- by surgically restoring flow to the true lumen by definitive repair of
ulation. Labetalol is generally considered safer due to α- and β-blocking the dissection and postoperative assessment for persistent ischemia.
29
properties although verapamil is preferred in this setting which, in com- Less than 10% of patients will require further procedures for persistent
bination with nitroglycerine, is very effective to reverse vasoconstriction ischemia after definitive repair of the dissection. Rarely, organ hypo-
caused by acute cocaine exposure. Benzodiazepines are used as first- perfusion may continue, necessitating emergent fenestration (creating
55
line treatment for the cocaine intoxicated patients while phentolamine communication between the true and false lumina) of the abdominal
can be used as a second-line agent for refractory cases. In patients with aorta, ideally by an interventional radiologist with cutting balloons. 11
56
severe asthma, a selective β -blocker such as metoprolol or esmolol, or Type B dissection management has changed significantly in recent
1
a calcium channel blocker (CCB) such as verapamil or diltiazem should years. Uncomplicated type B dissections are best managed by intensive
be used. CCB should be avoided in patients with heart failure due to medical treatment of blood pressure and long-term surveillance for
severe left ventricular systolic dysfunction while β-blockers should be the development of complications. Endostenting has recently been
59
used with caution in such patients. Angiotensin-converting-enzyme approved by the FDA for use in aneurysms and dissections of the
inhibitors (ACEI) are usually reserved for chronic treatment. However, descending aorta in both the acute and chronic phases. Aortic stent-graft
they can be very useful acutely if a renal artery is compromised by the placement allows for occlusion of the intimal entry tear by implantation
dissection flap, causing excessive renin release. The agent of choice is of a membrane-covered (Dacron), self-expanding (usually nitinol) stent
intravenous enalaprilat (usual dose 0.625-1.25 mg every 6 hours). (Fig. 42-13) to initiate progressive thrombus formation within the false
Hypotension in a patient with suspected or proven aortic dissection lumen and resultant aortic remodeling. The limited number of studies
4
should be investigated and treated promptly. Life-threatening compli- thus far, including the INSTEAD and STABLE trials, show an initial
61
60
cations such as cardiac tamponade or aortic rupture as well the pos- successful placement rate of the stent of approximately 90%. The trials
sibility of pseudohypotension caused by blood pressure measurement demonstrate improved aortic remodeling and obliteration of the false
in an extremity affected by the dissection flap should be evaluated. lumen, which should reduce the long-term risk of aneurysm develop-
Persistent hypotension after volume resuscitation is generally treated ment. However, as of yet, endostenting has not been shown to improve
with vasoactive drugs with little or no cardiac effects (phenylephrine long-term survival over medical therapy. Placement of the endostent in
or norepinephrine) while dopamine or dobutamine should generally
be avoided. Phenylephrine (a pure α -agonist) is the preferred vasoac-
1
tive drug followed by norepinephrine, which is mainly α -agonist with
1
some β -activity. Central venous pressure via central line or complete
1
hemodynamic monitoring via pulmonary arterial line may be helpful in
patients with hypotension especially if congestive heart failure is present.
■ CHRONIC MANAGEMENT
Once blood pressure and heart rate are controlled, intravenous drugs are
gradually transitioned to oral agents. Long-term blood pressure control
is extremely important for both types of dissection, whether repaired or
managed conservatively, since many patients with repaired dissections
(surgical or endovascular) may develop new aneurysms or pseudoaneu-
rysms, recurrent dissection, or rupture. β-Blockers remain the corner-
stone of chronic treatment but other agents such as ACEI, aldosterone
receptor-blockers, or calcium channel-blockers can be used depending
on the clinical situation.
■ DEFINITIVE MANAGEMENT

Acute aortic dissections, especially type A, are extremely dangerous
lesions that may become complicated with rupture and death at any
moment. Investigations should be performed expeditiously to deter-
mine the dissection type and the presence of aortic branch complica- FIGURE 42-13. Conformable GORE®TAG® Thoracic Endoprosthesis for stenting of type B
tions. Patients with type A dissections should be offered urgent surgical dissections. (Used with permission of W. L. Gore & Associates, Inc., Flagstaff, AZ.)

section03.indd 364 1/23/2015 2:08:31 PM