Severe Hypotension at the Initiation of Cardiopulmonary Bypass: Is it Avoidable?

Hemodilution, hypothermia, and non-physiological circulation mechanics resulting from extracorporeal circulation (ECC) cause transient decrease in mean arterial pressure (MAP) which is also called phenomenon A. We investigated the effects of the amount and ingredient of the priming solution on phenomenon A. Twenty-four patients were equally allocated into three groups with respect to ECC priming solution amount and ingredient. Priming sol ution consisted, of 25 ml/kg lactated Ringer (crystalloid) in group I , of 15 ml/kg Jactated Ringer in group 2, and of 15 ml/kg HES %6 (colloid) in group 3. Phenomenon A s was defined as a decrease of the mean arterial pressure below 40 mmHg for at least 4 minutes after the initiation of ECC in spite of a blood flow of 2.5 l/m 2• Measurements w ere obtained at T ı (completion of cannulation), T2 (first minute of ECC) and at T3 (fifth minute of ECC). There were five patients -with phenomenon A in group I (62.5%), two in group 2 (25%), and one in group 3 (12.5%). We did not observe any correlation between MAP, blood cell count, epinephrine and norepinephrine levels in the three groups. W e think hemodilution (as the cause of phenomenon A) must have other causes. We conclude that hemodilution is one of the main causes of phenomenon A, but the exact mechanism is not known yet. We think that using less priming solution and choosing colloidal fluids may well decrease the ineidence of phenomenon A.