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Pre-operative medications

  • If the cardiac index is low ( < 2.0 to 2.2 L/min/m2) then the cause of the hypotension is inadequate flow or a “pump” problem.
  • Look at the cardiac rhythm. Absolute or relative bradycardias or tachycardias (commonly new atrial fibrillation) can lead to decreased C.O. and should be corrected.
  • Look at the CVP to assess preload. A patient with a low C.I. and a CVP that is “relatively” low should be given a fluid challenge. Although the CVP in normal individuals varies between 0 and 4 mmHg, patients immediately post-op cardiac surgery commonly have decreased cardiac compliance for multiple reasons. In fact the majority of uncomplicated patients have CVP’s in the 6 to 10 mmHg range. Remember, what you really are interested in is a volume measurement (preload= right or left end-diastolic volume), but what you are measuring are pressures (CVP or PCWP = Right or left ventricular end-diastolic pressures). Therefore if the compliance worsens (ventricle “stiffens”) the same or even a lesser volume can give a higher pressure. If you think the patient may be “preload responsive” (i.e., on the ascending portion of Starling’s curve so that an increase in preload will increase cardiac output), then give the patient a fluid bolus. The amount is usually between 250 and 500 cc but should be at least enough to raise the CVP by 3 to 4 mmHg. Both crystalloids (normal saline) and colloids (Pentaspan) can be given. Although there may be theoretical reasons to choose one over the other, there is no convincing clinical evidence that one is superior. If the CVP increased by 3-4 but the cardiac output did not increase, then the patient is on the flat portion of the Starling curve and is not pre-load responsive. The absence of respiratory variation on the CVP monitor tracing is also suggestive that the patient has an adequate preload and that further volume therapy is unlikely to increase cardiac output. Remember that PEEP can decrease preload by decreasing venous return.
  • High afterload. Secondary to vasoconstriction and hypertension.
  • Decreased contractility.This should be managed with inotropic agents while simultaneously looking for the cause.
    • Low pre-operative ejection fraction
    • Prolonged CPB time or cross-clamp times, difficulty with myocardial protection intra-op
    • Acute bypass graft occlusion (check the ECG)
    • Graft spasm (especially LIMA) – check the ECG for ST elevation
  • Tamponade .
  • Acute valvular regurgitation. A valve repair or replacement can rarely have acute dehiscence. Check for a new regurgitant murmur and new ‘v’ waves on the PCWP tracing in the case of a MVR.