Hidden blood loss and its influential factors after total hip arthroplasty

Patients

A total of 322 patients (including 99 males and 223 females) with a complete history of disease and an average age of 71 (35-94) years were recruited in this study. The diagnosis of patients included FNF (65.5%), OA (8.1%), ANFH (10.9%), RA (7.1%), and DDH (8.4%). All the patients underwent primary THA surgery which was performed by one same orthopedic surgeon at Changzhou No.2 People’s Hospital of Nanjing Medical University from January 2008 to June 2014. Patients who underwent previous operations on the hip were excluded. All enrolled patients had no history of hematological diseases which could affect severely blood coagulation. Variables such as gender, age, height, weight, BMI, length of incision, pre-operative and post-operative hematocrit (HCT), intra-operative blood loss, post-operative drain blood volume, transfusion blood volume, and reinfusion volume of drained blood were recorded.

This study was reviewed and approved by the Ethics Committee of Changzhou No.2 People’s Hospital. And informed consent was received from all patients.

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Intra-operative treatment

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The surgery was performed under general anesthesia or continuous epidural anesthesia. All the patients received a standard operating procedure via the posterior-lateral incision. Length of incision was within a range of 10 to 15 cm. The prosthetic types of implants were divided into cemented and uncemented. The intra-operative blood loss was calculated by weighing the used compresses and recording the amount of blood in the suction bottle and the filtrated drainage blood which was recycled and transfused to patients by self-blood transfusion equipment during operation.

Post-operative treatment

The drainage tube was removed 48 h after operation, and the drainage volume was recorded as the post-operative blood loss. During the post-operative period, hemostatic such as tranexamic acid was not used and low molecular weight heparin (LMWH) was routinely injected to prevent deep venous thrombosis. Qiong Danshen injection triazine (a kind of Chinese medicine) or cinepazide was used to improve microcirculation and facilitate recovery of patients. After removal of drainage tube, patients were requested to take an x-ray in order to examine the location of the prosthesis and encouraged to walk with a walking aid.

Calculation of HBL

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The patient’s blood volume (PBV) was calculated by Gross formula: PBV = k1× h3 + k2 × w + k3, (h, height (m); w, weight (kg); for male, k1 = 0.3669, k2 = 0.03219, and k3 = 0.6041; for female k1 = 0.3561, k2 = 0.03308, and k3 = 0.1833) [21]. The total perioperative blood loss was calculated by multiplying PBV by the change of HCT, and HBL was further calculated. The perioperative blood loss was the sum of intra-operative blood loss, post-operative drainage volume, transfusion volume, and HBL.

Statistical analysis

Multiple and stepwise regression analysis was performed to evaluate the influential factors of HBL using fourteen independent variables, including seven qualitative variables (age, BMI, PT, blood transfusion volume, operation time, length of incision, and change of HCT between pre-operation and post-operation) and seven quantitative variables (sex, hypertension, anesthesia method, prosthetic type, anticoagulants, hemorheologic agent, and diagnosis). In the quantitative variables, male, hypertension, general anesthesia, uncemented prosthesis, nonuse of LMWH, nonuse of hemorheologic agent, and FNF diagnosis were set as “0”, others were converted into dummy variables. A positive coefficient indicates a positive influence on the dependent variable (HBL), whereas a negative coefficient indicates a negative influence. All independent variables were incorporated into the model using the method of “Enter”. All statistical analyses were performed by SPSS for Windows Ver.18.0 (SPSS Inc. IL, USA), and differences at a level of P < 0.05 were identified statistically significant.

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