Impact of postoperative weight loss on anticoagulant dosing after major lower limb amputation

Major lower limb amputation is often the final treatment for patients with chronic limb-threatening ischaemia. Postoperative weight loss is a common but under-recognised issue that may affect dosing accuracy for weight-dependent anticoagulants such as low molecular weight heparin (LMWH) and direct oral anticoagulants (DOACs). This study assessed the extent of postoperative weight change and the frequency of anticoagulant dose adjustment in routine practice.

A single-centre retrospective cohort study included patients who underwent above- or below-knee amputation between July 2022 and January 2023. Inclusion criteria were documented pre- and postoperative weights and inpatient prescription of LMWH or DOACs. LMWH was prescribed exclusively as dalteparin and DOAC therapy as edoxaban. Doses were reviewed against British National Formulary weight-based recommendations.

Of 39 patients, 17 met inclusion criteria (median age 69 years; 53% male). Procedures were divided evenly between emergency and elective. The mean postoperative weight loss was 7.5%±2.3% of preoperative body weight. Patients undergoing above-knee amputation lost more weight (mean 8.7kg) than those with below-knee amputation (mean 3.8kg). Two patients (11.8%) required dose adjustments - one on edoxaban after falling below 60kg, and one on dalteparin after dropping from 59.5kg to 55.5kg.

Major amputation is associated with clinically relevant postoperative weight loss, yet anticoagulant dose adjustments were uncommon. Routine postoperative weight monitoring and prompt review of weight-based therapy are recommended to improve dosing accuracy and reduce potential anticoagulation risk.