Introduction

Post-operative hemoglobin (Hb) determination after total knee arthroplasty (TKA) is considered essential to determine whether autologous blood transfusion (ABT) is indicated. However, the usefulness of this procedure has not been formally validated when modern blood saving procedures are used.
The primary objective of the study was to determine whether this assay performed the first post-operative day provided clinically useful information for the possible indication of ABT when modern blood saving procedures were used. The hypothesis tested was that there was a significant relationship between the Hb level on the first post-operative day and the necessity of post-operative ABT.

Materials And Methods

All patients operated on for elective TKA between October 2016 and October 2017 were eligible. 101 cases were selected.
Hb levels were systematically collected on the first post-operative day, and subsequently if required. The possible existence of clinical signs suggestive of anemia (asthenia, syncope, thirst, sweating, pallor, cooling of the extremities, increased respiration and pulse rate, decreased blood pressure) was noted. The need for post-operative ABT, its motivation and timing was noted. The length of hospitalization was noted, as well as the patient's discharge mode (at home or in a rehabilitation center).
The primary criterion was the need for post-operative ABT. The relationship with the Hb level on the first post-operative day was analyzed by a Fisher exact test; the sensitivity, specificity, predictive and negative values of a Hb level on the first post-operative day of less than 10 g/dl on the need for ABT were calculated; the ROC curve was constructed and the area under the curve was calculated. All statistical tests were performed at the 5% threshold.

Results

Five patients (5%) received ABT during the early post-operative phase: two in view of the Hb level on the first post-operative day, and three later. The mean Hb level on the first post-operative day was 11.7 ± 1.3 g/dl (range, 7.0 to 17.1 g/dl). The mean Hb loss was 2.2 ± 1.1 g/dl. Ninety-five patients (94%) had Hb levels on the first post-operative day greater than 10 g/dl; one was transfused immediately and three later. Six patients (6%) had Hb levels on the first post-operative day of less than 10 g/dl (7.0 to 9.9 g/dl); only one was transfused immediately.

There was no significant relationship between post-operative ABT and Hb level on the first post-operative day. The sensitivity of the Hb level on the first postoperative day to predict ABT was 20%, the specificity 95%, the positive predictive value 17% and the negative predictive value 96%. The analysis of the ROC curve does not find a relevant threshold (Figure 2), with an area under the curve of 0.329.

Discussion

The systematic determination of Hb on the first post-operative day after TKA does not seem to be a useful factor in the management of the patient when a modern blood saving protocol is followed, including normalization of pre-operative Hb and use of tranexamic acid. No more relevant decision-making factor for this time frame emerged from this study.