Study design
A retrospective review of 2 sequential cohorts of patients who underwent primary THA or TKA under a single surgeon between January 2013 and December 2017 was performed. Universal screening for iron deficiency of all patients irrespective of Hb level was introduced as part of the pre-operative protocol from January 2015. Prior to this only patients found to be anaemic, defined as Hb level less than 12g/dL, were investigated with iron studies and this formed the comparator control group for the study. Between the 2 sequential groups of patients, no other change in patient management or surgical technique was introduced and the surgical time was comparable. Data was collected by review of the hospital records and surgeon’s electronic patient files. Ethics approval for the study was obtained by hospital Research and Ethics Committee.
Demographics of the two study populations are shown in Table 1. The iron studies comprised serum iron, serum ferritin, serum transferrin, serum total iron binding capacity (TIBC), and serum transferrin saturation (TSAT). Patients with studies indicating iron deficiency were referred to a haematologist, who investigated the cause and administered intravenous iron infusion as appropriate pre surgery. Iron transfusions comprised a single dose of 500-1000mg intravenous Ferritin carboxy maltose, administered in a day stay unit, given a minimum 4 weeks before surgery. The primary outcome measure of the study is blood transfusion rate between the 2 cohorts. Secondary outcome measures such as pre and post-operative Hb levels, per operative blood loss, and rates of iron transfusion were also collected. Data in the universal iron screening cohort, regarding patients who were diagnosed to have incidental malignancies on further investigation, was also collected.
Table 1
Comparison of cohorts pre and post universal screening
|
2013–2015
(Pre universal screening group)
|
2015–2017
(Universal screening group)
|
P-value
|
Number
|
420
|
514
|
|
Age - mean (SD)
|
71.1 (9.26)
|
71.7 (9.51)
|
0.3324
|
Gender (M:F)
|
200:220
|
239:275
|
0.9805
|
Side (Right:Left)
|
195:225
|
271:243
|
0.0484
|
THA:TKA
|
220:200
|
296:218
|
0.9151
|
BMI – mean (SD)
|
30.12 (5.60)
|
29.56 (5.67)
|
0.1317
|
Haemoglobin (pre op) – mean (SD)
|
134.97gm/dl (12.33)
|
138.33gm/dl (12.91)
|
0.0001
|
Iron deficiency anaemia
|
105 (25%)
|
180 (35%)
|
0.7829
|
Iron infusion rate
|
21 (5%)
|
71 (13.8%)
|
< 0.0001
|
Blood Transfusion rate
|
20 (4.8%)
|
15 (2.9%)
|
0.0886
|
All THA were performed through an anterolateral approach in the lateral position. Uncemented acetabular and femoral components were used, with no drain. All TKA were performed using computer navigation without tourniquet, using cemented components and routine patella resurfacing. A subcutaneous suction drains outside the joint cavity was used in TKA, with the drain removed within 24 hours after surgery. Intra-operative cell salvage was used in all cases with autologous re-infusion if sufficient blood was salvaged. After implantation of components, topical tranexamic acid (3gm diluted in 20 ml N/saline) was instilled for 5 minutes to the surgical site prior to final lavage and closure.
Patients were ambulated on the day of surgery. Venous thromboembolism prophylaxis comprised of enoxaparin 40mg daily, commenced 4 hours post-operatively until discharge from hospital. Patients were discharged on aspirin for 6 weeks post-operatively. For patients on warfarin pre-operatively, this was continued during the peri-operative period. Warfarin dose was adjusted leading to surgery, aiming for an International Normalization Ratio (INR) of 2 on the day of surgery. The warfarin was restarted the night of surgery, with bridging enoxaparin if the INR fell below 2.
Data collected included demographics, body mass index (BMI), preoperative haemoglobin (Early Hb), iron parameters (Serum iron, Total Iron binding capacity, Serum Transferrin and Serum Ferritin), Haemoglobin post iron transfusion (Late Hb) and post operatively (Post-op Hb), perioperative blood loss, type of anesthesia, ASA grade and type of anticoagulation, total blood loss, blood collected by cell salvage and Hb change between pre-operative and day 2 post-operative. Anaemia in our study is defined as Hb less than 13g/dL in males and less than 12g/dL in females. The transfusion trigger post-operatively was Hb less than 8g/dL or symptomatic anaemia with Hb less than 10g/dL and co-existing co-morbidities
Statistical methods
Descriptive statistics for iron variables were presented for all data and by iron transfusion (performed or not performed), depending on the distribution of the data with mean and standard deviation presented for normally distributed variables. Independent t-tests were performed to compare continuous iron variables between the two cohorts.
Bivariate binary logistic regressions were performed for the outcome: blood transfusion versus demographic and blood-related predictors. A multivariable model was performed including previous iron transfusion and variables with P value < 0.2 on bivariate regression.
Bivariate linear regressions were performed for the outcomes: blood loss, RBC collected and HB drop (in separate models) versus demographic and blood-related predictors. A multivariable model was performed including previous iron transfusion and variables with P value < 0.2 on bivariate regression. Assumptions of a linear model were checked by inspection of histograms and scatter `plots of residuals and predicted values.
A cross tabulation was performed for Iron deficiency anaemia versus general anemia, with associated Chi-Square P value.