Cortinez Luis I, Somma Jacques, Robertson Kerri M, Keifer John C, Wright David R, Hsu Yung-Wei, MacLeod David B, Moretti Eugene W
Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA.
Can J Anaesth. 2005 Apr;52(4):374-8. doi: 10.1007/BF03016279.
Excessive blood sampling, with its inherent risks, is of growing concern among clinicians. We performed this study to measure the changes in hematocrit (Hct) during a laboratory investigation where multiple blood samples are collected. The performance of a simple mathematical model, used in clinical practice to predict Hct changes, is evaluated.
Eight healthy male volunteers participated in this study. The equation Hct(f) = Hct(i)*(EBV-BL)/EBV is used to predict changes in Hct. Where Hct(f) and Hct(i) are, respectively, the final and initial Hct, EBV is the estimated blood volume and BL is the blood loss.
Thirty-five pharmacokinetic samples per subject were collected totalling 314 mL of BL. The Hct decreased from 44.2% +/- 2.2% to 39.9% +/- 2.5% (P = 0.001). On average, model predictions tended to have a discrete tendency to underestimate the Hct changes (-0.5% points of bias). While the predictions of the Hct were very accurate in 50% of the subjects, the discrepancy of the Hct predictions was clinically significant in the other 50% of the subjects.
Consistent with the model prediction, this study demonstrated a significant reduction in the Hct values in healthy subjects undergoing incremental phlebotomy. On average, the model successfully predicted the decrease in Hct. However, the inter- and intra-individual variabilities in the Hct changes are clinically significant. In clinical settings, which are not well controlled environments, the variability is likely to be greater and the clinical use of the model cannot replace the need to monitor the Hct.
过度采血及其固有风险日益引起临床医生的关注。我们开展本研究以测量在采集多份血样的实验室检查过程中血细胞比容（Hct）的变化。评估一种在临床实践中用于预测Hct变化的简单数学模型的性能。
8名健康男性志愿者参与了本研究。使用公式Hct(f) = Hct(i)*(EBV - BL)/EBV来预测Hct的变化。其中Hct(f)和Hct(i)分别为最终和初始Hct，EBV为估计血容量，BL为失血量。
每位受试者采集了35份药代动力学样本，共失血314 mL。Hct从44.2%±2.2%降至39.9%±2.5%（P = 0.001）。平均而言，模型预测往往有离散倾向，低估了Hct的变化（偏差为 - 0.5个百分点）。虽然50%的受试者中Hct的预测非常准确，但在另外50%的受试者中，Hct预测的差异具有临床意义。
与模型预测一致，本研究表明接受递增式静脉放血的健康受试者的Hct值显著降低。平均而言，该模型成功预测了Hct的降低。然而，Hct变化的个体间和个体内变异性具有临床意义。在控制不佳的临床环境中，变异性可能更大，该模型的临床应用无法取代监测Hct的需求。
