Hemocue as a guide for intraoperative blood transfusion

Background and purpose: Surgical procedures are associated with blood loss. Quantification of the lost blood during surgery helps guide appropriate replacement to maintain homeostasis. The decision to transfuse blood intraoperatively is very commonly based on visual estimates which may be inaccurate or laboratory hemoglobin levels which have a longer waiting time for results. Hemoglobin estimation of lost blood using HemoCue has been done but, we could not locate any study which has measured patient’s hemoglobin level with HemoCue and correlated it with the target hemoglobin when visual estimated surgical blood loss is equal to maximum allowable blood loss [MABL].

Aim: To determine the ability of HemoCue as a guide for intraoperative blood transfusion

**Objectives:**To determine the mean difference, upper and lower limits of agreement in following at the time of MABL:

Primary objective:

1.Estimated blood loss with HemoCue hemoglobin and average visual blood loss.

Secondary objectives:

1**.** Estimated blood loss with laboratory hemoglobin and average visual blood loss. 2. Estimated blood loss with HemoCue hemoglobin and laboratory hemoglobin. 3. Upper and lower limits of agreement with hemoglobin measured with HemoCue and laboratory analyser. Methods: This Prospective cross-sectional study will be conducted after obtaining approval from Institutional Ethics Committee-Human Research between April 2024 to August 2025. Consenting patients who fulfil the inclusion criteria will be explained about the study procedure and 3 ml of patient’s venous blood samples will be collected in an EDTA vial and transported to the laboratory for Hb assessment (Hblab1). On the day of surgery, anaesthesia will be induced. Careful intraoperative fluid therapy will be given till the blood loss is below maximum allowable blood loss. Two experienced anaesthesiologists (one consultant and one Senior Resident) will independently assess the visual blood loss (VBL) during the procedure. An average of the two values will be taken as the average visual blood loss (VBLAV). Once the VBLAV ≥MABL, another 3 ml venous blood sample will be withdrawn. One drop will be used for hemoglobin assessment with HemoCue (HbH) and the rest of it will be transported in EDTA vial for Hb estimation in the laboratory (HbLab2). If by the end of surgical procedure, MABL is not reached, the patient will be excluded from the study.

Sample size: There are no studies which have estimated blood loss by measuring HemoCue hemoglobin of patient’s blood in the intraoperative period. However, in the study by Zajak et al. HemoCue was used to estimate blood loss by measuring Hemoglobin of suction blood. Assuming that all the lost blood was collected in this study in the suction bottle and thus, the estimated blood loss in suction blood is equal to actual total blood loss, we have calculated the sample size from this study. Considering the mean blood loss of 251 [109-411] ml with the HemoCue and visually estimated blood loss of 300 [200-500] ml as per the study by Zajak et al, to estimate this difference in blood loss at α=5% and power=80%, a sample of 50 patients is required. To account for loss to follow up in 25% patients (due to non-achieving of MABL by the end of surgery), a sample of 63 patients is required. Statistical analysis: Data will be entered in a spreadsheet. Analysis will be done in SPSS version 20.0. Paired t-test will be used to compare the blood loss by different methods as these are being applied in the same patient. Bland Altmann analysis to calculate the mean difference between two methods and the upper and lower limits of agreement will be applied. A p-value <0.05 will be taken as significant.