Severe and morbid obesity (Class II -III) represents a challenge for successful knee surgery. There isn't consensus on what influence body mass index has on blood loss and on red blood cell (RBC) transfusion during total knee arthroplasty (TKA). The objective was to determine blood loss and transfusion needs in severe and morbid obese patients undertaking TKA.
We recorded retrospectively all patients undergoing TKA. Obesity was assessed according to WHO guidelines. Perioperative haemoglobin and treatments for its optimisation were recorded. Blood losses were estimated from specific formulae for lost red-cell mass and percentage of lost blood volume.
922 patients were included: 35.90% were obese Class I and 18.76% obese Class II - III. Estimated blood volume was 4390  ±  470 ml, 4736  ±  423 ml and 5030 ± 464 ml among non-obese, obese Class I and obese Class II-III, respectively (P < 0.001). The global estimated blood volume (EBV) lost was 1502  ±  680 ml without differences between the three groups. However, the percentage of lost blood volume was lower in obese Class II -III (29.65%) than in non-obese (33.55%) and obese Class I (30.97%) (P < 0.005). Transfusion rates were 12.7%, 12.1% and 6.4% for non-obese, obese Class I and Class II -III, respectively (P = 0.062). A negative transfusion risk was predicted for Class II -III patients.
Severely and morbidly obese patients did not show greater blood loss nor higher RBC transfusion needs after primary TKA than non-obese and obese Class I patients. This could be because obese Class II -III patients had higher EBV but similar RBC losses.