Cardiovascular

Question 1

What would be the anticoagulant optometrist for bypass in a patient who developed HIT?

Answer 1

If surgery involving cardiopulmonary bypass is contemplated, waiting until antibody titers become undetectable is the best choice.

For emergency operations, various strategies for anticoagulation exist that include direct thrombin inhibitors, bivalirudin, and lepirudin. Other options are use of danaparoid (factor Xa inhibitor) or use of unfractionated heparin plus a drug to prevent thrombosis such as tirofi- ban (glycoprotein IIb/IIIa inhibitor), or epoprostenol (prostacyclin [PGI2]).

There is also the option of performing plasma phoresis to remove antiplatelet antibodies if time allows

Question 2

Oxygen consumption (Vo2) is measured in a 70-kg subject on a treadmill at 2500 mL per minute. This corresponds to what METs?

Answer 2

One MET is equal to the amount of energy expended during 1 minute at rest, which is roughly 3.5 mL of oxygen per kilogram of body weight per minute (3.5 mL/kg/min).

For a 70-kg (150 lb) person, one MET would equal 250 mL O2 per minute. So 2500 mL would correspond to 10 METs (Barash: Clinical Anesthesia, ed 7, p 591).

Question 3

What parameters can reflect LV filling pressure?

Answer 3

The Frank-Starling curve relates left ventricular filling pressure to left ventricular work.

Left ventricu- lar end-diastolic volume,
left ventricular end-diastolic pressure,
left atrial pressure,
PA occlusion pressure,
and, in some instances, central venous pressure can reflect left ventricular filling pressure.

Question 4

What would be the most explanation for rise in PA pressure during Bypass?

Answer 4

During cardiopulmonary bypass, it is common for a PA catheter to migrate distally 3 to 5 cm into the PA. In fact, PA catheter migration during cardiopulmonary bypass is so common that with- drawing the catheter 3 to 5 cm before the initiation of cardiopulmonary bypass may be routinely indicated.

Distal catheter migration into a wedge position is often detected by noting an increase in the measured PA pressure. PA catheter migration during cardiopulmonary bypass has been implicated in cases of PA rupture. Although catheter migration is the most likely explanation for a rise in PA pressure during cardiopulmonary bypass, the anesthesiologist must also consider inad- equate ventricular venting as a potential cause of increasing PA pressures during cardiopulmonary bypass, particularly if the PA pressure does not decline after withdrawal of the PA catheter from a presumed wedge position. Ventricular distention during cardiopulmonary bypass is detrimental because it can increase myocardial oxygen demand at a time when there is no coronary blood flow. Malposition of the aortic cannula may result in unilateral facial blanching. Malposition of the venous cannula may result in facial or scleral edema or may manifest as poor blood return to the cardiopulmonary bypass circuit (Barash: Clinical Anesthesia, ed 7, p 1095).