Eliminating Blood Transfusions: What about Hypotensive Anesthesia?

Abstract

In Reply:—We appreciate the commitment of all with a particular interest in avoiding allogeneic blood transfusions. 1In the first letter, Drs. Teruya et al. show that a substantial deficiency of one coagulation factor may go undetected by standard preoperative activated partial thromboplastin time (aPTT) measurement. Indeed, the sensitivity of commercial aPTT kits to detect isolated coagulation factor deficiency may be extremely variable. 2In widely used aPTT kits, such as the Actin®FS (Dade Behring, Marburg, Germany), abnormal results are obtained at the following coagulation factors thresholds:F8 < 52%, F9 < 41%, F11 < 29%, and F12 < 30%, thus at significantly higher concentrations, as with the kits studied by Drs. Teruya et al. Nevertheless, knowing the coagulation factor sensitivity of the aPTT kit used at the local hospital is important.The rationale of transfusion algorithms guided by coagulation monitoring is not to predict high or low blood loss in an individual patient based on a preoperative coagulation test but to monitor blood coagulation throughout surgery. This enables one to detect a coagulation deficit early and to characterize its cause—low platelet number versus compromised platelet function versus low coagulation factors. In turn, this enables a specific treatment to avoid unnecessary blood loss and allogeneic blood transfusion caused by a significant coagulation deficit. Bedside coagulation monitoring, such as Thrombelastograph®analysis 3(Thrombelastograph®Coagulation Analyser; Haemoscope, Morton Grove, IL) or hemoSTATUS 4(Medtronic Blood Management, Parker, CO) may be particularly helpful because of the short turn-around time and high sensitivity.In the second letter, Drs. Klowden et al. suggest that controlled hypotension warranted more recognition as an anesthesia technique to reduce the need for allogeneic blood transfusions. To document efficacy, four book chapters from 1979–1996 are referenced. To our knowledge, there is only one prospective randomized study with defined transfusion criteria that has shown efficacy, 5and this study was discussed in our review article. 1Although hypotensive anesthesia seems safe at relatively high hemoglobin concentrations, efficacy has been challenged recently, 6and this is conceivable because of the fact that a majority of surgical bleeding is venous bleeding. By which mechanism should a lower arterial pressure thus reduce venous bleeding? At least to us, this is unclear. In contrast, low central venous pressure may reduce blood loss and transfusion requirement substantially in liver surgery. 7–9Therefore, anesthesia techniques do have an impact on surgical blood loss and transfusion requirements, but attention probably should focus more on central venous pressure than on arterial blood pressure.