A PROSPECTIVE STUDY OF PREDICTORS OF TRANSFUSION IN TKR

Abstract

Loss of blood is inevitable during knee replacement surgery, sometimes requiring transfusion. Allogenic blood leads to a risk of disease transmission and immunological reaction. There are various practices used. There is still a risk of bacterial transmission with stored blood and haemolytic transfusion reactions can still occur. Data was collected between 1998 and 2006. There was data on transfusion in 1532 patients undergoing primary knee replacements. There were 1375 unilateral TKRs and 157 bilateral TKRs. After reducing the bilateral cases to one record per patient, it was agreed to restrict the main analysis to 1532 patients. Data was collected prospectively at a pre-admission clinic 3 weeks prior to surgery. Haemoglobin was checked and body demographics including BMI were obtained. Each patient also had a knee score assessed. All patients received a LMWH pre-op until discharge. A tourniquet was used in each case and all patients had a medial para-patellar approach. No drains were used and operation details such as a lateral release were recorded. As per unit protocol, patients with a post-op haemoglobin less than 8.5g/dl were transfused as were symptomatic patients with haemoglobin between 8.5g/dl and 10g/dl. Each of the possible predictive factors was tested for significant association with transfusion using chi-squared or t-tests as appropriate. Multiple logistic regression was used to test for the independent predictive of factors after adjusting for one another. Results show that transfusion was more likely if the patient was older, female, short, light or thin. Among peri-operative factors, the chance of a transfusion was increased for bilateral patients, those with low knee scores and those with high ASA scores. Also patients undergoing a lateral release, those with low pre-op haemoglobin and those with a large post-op drop were more likely to be transfused. All the significant variables were entered into a forward stepwise multiple logistic regression. Transfusion was significantly more likely in those undergoing a bilateral procedure, with a low BMI, low pre-op haemoglobin and those with a large post-op drop (> 3g/dl). Allogenic transfusion is associated with immune-related reactions, from pyrexia to urticaria to haemolytic transfusion reactions, which can be life threatening. There is also the risk of viral pathogen transmission. Women were shown to be almost twice as likely to need transfusion. This has been shown in previous studies and is thought to be due to women having a lower weight and pre-op haemoglobin, both of which were shown to be significant independent factors in increasing the risk of transfusion. A pre-operative haemoglobin of less than 13g/dl, a BMI less than 25, and undergoing a bilateral procedure were shown to have an increased risk of transfusion. For patients falling into these categories, measures can be planned to try and reduce this risk.