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Hemodynamic management
SOP » Anaesthesia protocol » Hemodynamic management
Last modified on Tue 15 Jul 2014

The first major challenge during OPCAB surgery exists in managing the cardiovascular changes that occur with dislocation of the heart during exposition of the site of anastomosis. This event is often associated with kinking of systemic and pulmonary veins so that preload decreases acutely and cardiac performance drops suddenly if no appropriate precautions are taken. Surgical manipulation of the heart will also provoke arrhythmias and mechanical compression of the heart (mostly the right ventricle).

The second major challenge is in preventing the consequences of acute myocardial ischemia during coronary artery occlusion. The severity of myocardial ischemia and reperfusion will is related to the use of an intracoronary shunt. The decision to place an intracoronary shunt depends on surgical factors such as the luminal size of the coronary artery.

Cardiovascular stability

Certain goals (more are less arbitrarily chosen) should be aimed during the entire procedure. For our institution we favor the following hemodynamic conditions

  • Heart rate between 60-70bpm sinus rhythm
  • Systolic arterial blood pressure > 85mm Hg
  • Diastolic arterial blood pressure >50mm Hg
  • Central venous pressure > 5 mm Hg
  • PcWP 10 > < 18 mm Hg
  • Cardiac index > 2 L / m²
  • Normoxia – normocarbia and normothermia

The treatment of hemodynamic changes is based on an understanding of the pathophysiology involved. The principles are summarized below :

PRELOAD

Decreases due to obstructed Inferior and superior caval and Pulmonary venous return

  • Preserve systemic and pulmonary venous return by elevation of the legs
  • Trendelenburg position (may compromise SVC return)
  • Administer Colloids to a Central venous pressure > 5-8 mmHg

Obstruction of RV outflow tract due to compression also decreases LV preload (serial ventricular interdependence)

  • Communicate with surgeon /reposition heart

AFTERLOAD

As blood pressure falls with manipulation of the heart the coronary perfusion becomes compromised. Pharmacological increase of afterload may improve collateral perfusion. The decision to increase afterload depends on the preexisting ventricular function.
In severely depressed ventricles low doses of inotropics are being administered together with vasopressors.
In normal or near normal ventricular function we administer neosynephrine bolus per 50 µg IV.
Further arguments to use alpha 1 agonists are :

  • They decrease venous capacitance (improve preload)
  • They have a pharmacological preconditioning effect (G-protein coupled)

RATE - RYTHM

A rigid control of sinus rhythm in OPCAB surgery is demanding for the surgeon and is of primary importance. Sinus tachycardia, Ventricular extrasystoles and atrial fibrillation occur frequently.

  • Potassium blood levels should be above 4 mmol/l
  • We administer magnesium sulfate 25 mg/kg in almost all patients as a prevention

Other drugs that are being considered (but not routinely used) in order of importance :

  • Xylocaine 1 mg / kg
  • Diltiazem 0,25 mg /kg
  • Esmolol 300µg/kg/min
  • Propafenone 1 mg / kg
  • Lanoxin 7,5 µg/kg

A right coronary artery bypass is often associated with bradycardia - AV junctional rhythm, so the decision to place atrial pacing leads should be considered.

Tachycardia is often first sign of ischemia and if nitroglycerin is not already infusing, a nitroglycerin infusion is then should be started and is most often continued throughout the procedure.

CONTRACTILITY

As myocardial consumption is directly related to the inotropic state, positive inotropic stimulation is avoided.
In the post grafting period positive inotropic drugs are rarely used but occasionally serve to treat myocardial stunning.

With routine CPB-supported CABG surgery, most surgeons use cardioplegia to temporarily protect the heart from ischemia during grafting. In OPCAB surgery, the grafting (and obligatory ischemia) takes place while the heart is expected to continue its normal function. All variables that determine myocardial oxygen demand should therefore be controlled and myocardial oxygen supply should be maximized through collateral supply if present.

In practice the following methods are usually used at our institute :

  • Intracoronary shunts are placed routinely
  • Isosorbide dinitrate is used to treat increased wall tension during ischemia.
  • Heart rate is maintained below 80 bpm (this is usually achieved with the above described anesthetic technique and the continuation of beta-blockade until the morning of surgery. If tachycardia is present prior to induction, beta-blockade is increased (metoprolol IV).
  • Transfusion trigger is hemoglobin 9 g/dl.