Safer treatment doses for low molecular weight heparins: summary of a safety report from the National Patient Safety Agency

Observational data from Australia suggest that only a quarter of hospital patients taking renally excreted medicines had been weighed. 6 Another observational study from Canada showed inaccurate patient weights used for enoxaparin dosing. 7 Health professionals' visual estimates of patient weight have been shown to be unreliable 8 and less accurate than weight information given by patients or carers, or calculation by tools using approximations such as knee height or mid-arm circumference. 9 National guidance in England now requires all NHS organisations to have accurate weighing equipment. 10 This summary is based on a safety report (known as a rapid response report or RRR) on reducing treatment dose errors with low molecular weight heparins, issued by the National Patient Safety Agency (NPSA) in June 2010 (NPSA/2010/RRR013, www.nrls.npsa.nhs.uk/heparin ). Always weigh patients and record weight (in kg only) on admission or before starting therapy and during treatment Use appropriate weighing equipment, 10 including hoists and under-bed weighing systems for those who are bedbound or who cannot stand Patients who are morbidly obese (body mass index >40) will need special equipment and may need monitoring of anti-Xa level because they are at increased risk of bleeding Prescribe according to clinical indication, using practical dose calculation tools (see examples at www.nrls.npsa.nhs.uk/heparininfo ) Know and record your patient's renal function, as low molecular weight heparins pose particular risks to patients with renal impairment-ideally before prescribing, but don't delay first dose until you get renal function tests Always record the patient's weight, renal function, clinical indication (treatment for deep vein thrombosis, pulmonary embolism, myocardial infarction, or unstable coronary artery disease), and duration of treatment when prescribing.