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CARDIOVASCULAR ANESTHESIA

Agreements Between the Prothrombin Times of Blood Treated In Vitro with Heparinase During Cardiopulmonary Bypass (CPB) and Blood Sampled After CPB and Systemic Protamine

Anthony M.-H. Ho, MSc, MD, FRCPC, FCCP^*, Anna Lee, MPH, PhD^*, Elizabeth Ling, MSc, MD, FRCPC, Alan Daly, CCP, Kevin Teoh, MD, FRCSC, and Theodore E. Warkentin, MD, FRCPC^||

*Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Hong Kong, People’s Republic of China; and Departments of Anaesthesia, Clinical Perfusion, Surgery, and ||Medicine, Hamilton Health Sciences Corporation, McMaster University, Hamilton, Ontario, Canada

Address correspondence and reprint requests to Dr. Anthony Ho, Department of Anaesthesia and Intensive Care, Prince of Wales Hospital, Shatin, NT, Hong Kong SAR, PRC. Address e-mail to hoamh{at}hotmail.com

The prothrombin time (PT) is useful for identifying coagulation factor deficits after cardiopulmonary bypass (CPB). However, long processing times and the need for fresh frozen plasma (FFP) to be thawed cause delays in factor replacement. We hypothesized that, by treating with heparinase, blood sampled toward the end of CPB can provide PT results that help to determine the requirement for FFP after CPB. Laboratory delays can be eliminated with point-of-care monitors. We studied 158 adults undergoing nonemergent cardiac surgery. Blood taken before separation from CPB was mixed with heparinase, and PT was measured in the laboratory with a HemoTec timer. Agreements between these results and laboratory measurements of blood taken after systemic protamine were compared by using Bland and Altman plots with the threshold of ±1.0 s. We found that the laboratory PT measurements during CPB versus after CPB were compara-ble, but the limits of agreement exceeded these thresholds. Similarly, there was unsatisfactory agreement between the HemoTec and laboratory PT results measured before, during, and after CPB. For each PT measured during CPB, the corresponding confidence interval for the postprotamine PT was calculated. During CPB, a laboratory PT of 16 s or 18 s suggests a 83% or 93% probability of not requiring or potentially requiring, respectively, FFP after CPB. We conclude that the majority of PT measurements obtained from blood taken before weaning from CPB and treated in vitro with heparinase was associated with a high probability of whether or not FFP would be needed after CPB.

IMPLICATIONS: Coagulation dysfunction after cardiopulmonary bypass may contribute to bleeding. Obtaining coagulation tests and fresh frozen plasma requires time and delays treatment in patients who need fresh frozen plasma. We have devised a technique to provide early estimation of postbypass coagulation status.

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