Norepinephrine Infusion During Cardiopulmonary Bypass

Rationale

1.1. Vasoplegia and cardiac surgery:

Vasoplegia Syndrome (VS), prevailing in about 20% of cardiac surgical procedures (1), is defined as low mean arterial pressure (MAP) with normal or high cardiac indices and which is resistant to treatment with the commonly used vasopressors. (2,3) Vasoplegia might occur either during or after the cardiopulmonary bypass periods or during the postoperative period during the intensive care unit (ICU) stay. (3) Many factors have been found to be related to the increased Vasoplegia during the cardiopulmonary bypass period such as left ventricular ejection fraction more than 40%, male patients, elderly patients, higher body mass index, long cardiopulmonary bypass time, hypotension upon the start of cardiopulmonary bypass, perioperative use of angiotensin-converting enzyme inhibitors (ACE) and presence of infective endocarditis. (4,5)

1.2. Effects of Cardiopulmonary bypass (CPB) on Post cardiotomy Vasoplegia.

Cardiopulmonary bypass itself may intensify the effects of vasoplegia due to hemodilution which decreases the blood viscosity, so, reducing the overall peripheral vascular resistance. Moreover, the interaction of blood with the tubing of the cardiopulmonary bypass machine results in the release of inflammatory mediators which play an important role in reducing the peripheral resistance and aggravating the hypotension. Although compensatory and auto-regulatory mechanisms play an important role in maintaining adequate tissue perfusion, hypotension during the cardiopulmonary bypass period may result in poor outcomes as postoperative stroke (4) especially if the mean arterial pressure is below 65 mmHg. (6)

1.3. Hyperlactatemia after cardiac surgery

Lactate was used as a marker for adequate tissue perfusion since the mid-1800s. Although the literature has illustrated the undesirable effects of high lactate levels, however, the cause, the prevention as well as treatment measures of hyperlactatemia remain obscure. Additionally, lactic acidosis or hyperlactatemia might occur in cases of refractory vasoplegia. A rise in lactate levels is common during cardiac surgery and is well known for its deleterious and its association with poor patients' outcomes. (7)

Owing to its detrimental effects, measures to reduce the effects and treat vasoplegia were used. Firstly, excluding any equipment or mechanical failure such as the arterial line monitor, adjusting the bypass flows for higher cardiac index (CI>2.2), confirming the proper cannula position and ruling out any aortic dissection.

Secondly, adjusting some physiological parameters is of great value as checking hematocrit level for excessive hemodilution, adjusting the anesthetics with severe vasodilatory properties, excluding the possibility of a drug reaction or anaphylaxis and temperature management during hypothermic bypass.

Thirdly, the use of conventional vasopressor agents as phenylephrine, norepinephrine, and vasopressin. Finally, the use of some off-label agents as vitamin C, hydroxocobalamin, angiotensin 2, methylene blue and prostaglandin inhibitors. (8)

1.4. Why this clinical trial?

The use of norepinephrine during CPB has its own potential benefits. It is not clear if the use of continuous norepinephrine infusion during CPB would be effective and safe in lessening the postoperative hyperlactatemia and development of vasoplegia after cardiac surgery.

The here proposed randomized controlled clinical trial will test the use of continuous norepinephrine infusion during CPB with respect to the efficacy and safety to reduce the postoperative rise in blood lactate level.

Inclusion criteria

• American Society of Anesthesiologists (ASA) physical status between ІІІ and ІV
• Scheduled for any type of elective cardiac surgery using CPB
• General anesthesia provided in an endotracheally intubated patient.

Exclusion criteria

• Decline consent to participate.
• Emergency surgery.
• Ejection fraction (EF%) less than 35%.
• Scheduled for re-do surgery.
• Scheduled for emergency surgery.
• Preoperative ventilator or circulatory support.
• Body mass index (BMI) greater than 40 Kg/m2.
• History of alcohol abuse.
• History of drug abuse.
• Pregnancy.
• Consent for another interventional study during anaesthesia
• No written informed consent.