HOW MUCH BLOOD IS REALLY LOST IN TOTAL KNEE AND HIP ARTHROPLASTY?

Abstract

In Total Knee Arthroplasty (TKA) and Total Hip Arthroplasty (THA) the total blood loss is composed of ‘visible’ blood loss from the surgical field and wound drainage, and blood loss into the tissues which is ‘hidden’. Blood management should be aimed at addressing the total blood loss.

56 TKAs and 46 THAs were prospectively studied. TKAs were performed with tourniquet. After tourniquet release, all drained blood was salvaged and significant volumes reinfused. No reinfusion was used for THAs.

The true total blood loss was calculated in the following way:

Patient Blood Volume (PBV) is: [1]

PBV = k1 x height3 + k2 x weight + k3

Therefore patient total Red Blood Cell volume (RBCv) is:

RBCv = PBV x Hct. (where Hct is Haematocrit)

Total RBCv loss = PBV x (Hct preop – Hct postop) + ml RBC transfused

The result is reconverted to Whole Blood volume.

Hidden Loss = Total Loss – Visible Loss.

In TKA, the mean total true blood loss was 1474ml. The mean hidden loss was 735ml. Therefore hidden loss is 50% of the total loss and the total true loss following TKA is twice the visible volume. In THA, the mean total true blood loss was 1629ml. The mean hidden loss was 343ml.

Thus hidden loss in THA is much smaller. (21%) Total loss is 1.3 times the visible loss. In the TKA group, comparing patients with large losses receiving reinfusion and those with small losses not receiving reinfusion, the proportion of total true loss which was hidden was the same, at 50%.

Patients with Body Mass Index (BMI) > 30 were compared with those with a BMI < 30 and no correlation was found between BMI and Hidden Loss.

Joint Replacement Surgery involves a ‘hidden’ blood loss which is not revealed and cannot be measured or reinfused in practice, but which should be taken into account when planning blood loss management. In TKA it is substantial. In THA it is much smaller and probably not of as much clinical concern. Hidden loss is no greater in the Obese patient.