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Safety in practice

How to reduce dose errors for heparin

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A Rapid Response Report by the National Patient Safety Agency outlines how errors associated with calculating doses of low molecular weight heparin can be reduced  

Why do we need to improve practice?

Low molecular weight heparins (LMWHs) are used in the prevention and treatment of venous thromboembolism (VTE) and treatment of acute coronary syndromes. They are administered using intravenous or subcutaneous injection and are considered the treatment of choice. They are seen as effective, with a low risk of heparin-induced thrombocytopaenia. Potentially, patients can be discharged home with LMWH thus shortening their hospital stay.

When used for the prevention of VTE, a standard dosing regimen is used. When treating a thromboembolic event the dose is dependent on the weight of the patient. Treatment dose regimens also depend on the clinical indication for therapy. Underdosing or overdosing can lead to serious consequences for the patient.

Between 1 January 2005 and 1 September 2009 the National Patient Safety Agency received 2,716 reports relating to errors with LMWH.

Dosing errors with LMWHs can occur if the prescribed treatment dose is not calculated using the patient’s current body weight. Reports indicate some patients are not weighed prior to dosing, weight is estimated, recorded inaccurately or doses based on weight are miscalculated.  Inappropriate prescribing, failure to consider certain vulnerable groups (eg limited renal function) or incorrect duration of treatment was also evident.

The types of incidents include:

  • Patient prescribed and administered a 50% overdose of a LMWH requiring ICU for respiratory support.
  • Patient’s weight estimated rather than actual weight. This resulted in an underdose of a LMWH.
  • Patient with renal impairment was prescribed 100mg twice a day instead of 55 mg once a day, an almost four times overdose.

In July 2010, in response to these reports which included one death and three cases of severe harm,  the NPSA issued a Rapid Response Report  on reducing treatment dose errors when using low molecular weight heparins.

Frances Wood, clinical reviewer, NPSA

Five ways to make practice safer in your hospital

1     Ensure you are using an accurate patient weight 

Accurate patient weight should be obtained and recorded at first contact with primary or secondary care and throughout treatment. Reasons for not obtaining weight should be clearly documented.

2      Do not estimate weight

It is often inaccurate and can lead to incorrect dosing. The range of weighing equipment available should prevent the need for estimation in all but the most exceptional circumstances.

3      Check your equipment

Your weighing device should meet the requirements for clinical weighing scales. For information click here.

4      Consider patient mobility

Many patients in primary and secondary care cannot stand on a set of scales. Weighing equipment should be suitable and available for the intended patient group.  Lack of equipment should be highlighted using local risk assessment processes.

5      Use dose calculation tools

These should be readily available to healthcare practitioners at the time of prescribing and administering LMWHs.


What should my trust be doing?

The NPSA Rapid Response Report identified key actions to make practice safer. The NPSA has asked your organisation to:

Ensure that a patient’s weight is used as the basis for calculating the required treatment dose of LMWH. The weight must be accurately recorded in kilograms in the inpatient medication chart (when in use) and clinical record. Patients should be weighed at the start of therapy and, where applicable, during treatment.

Consider renal function when prescribing treatment doses of LMWHs. The renal function test should not delay initiation of the first dose but every effort must be made to base subsequent dosing on these results.

Provide dose calculation tools for a range of body weights, specific clinical indications and LMWH products, and that consideration is given to rationalising the range of LMWH products used in the organisation.

Ensure that essential information such as dose, weight, renal function, indication and duration of treatment is communicated at transfers of care (eg. by discharge letters) and used to ensure that future doses are safe.

Guarantee that dosing checks based on patient information are made by healthcare professionals who review, dispense or administer LMWHs when this information is readily available to them.

Demonstrate system improvements through the collection and review of data, such as incident reports, clinical pharmacy interventions, audit or other relevant outcome measures.


Did you know?

  • An observational study in 2007 looking at 10,687 patients identified that almost half the patients treated with enoxaparin did not receive a recommended dose.
  • Older people living in the community with unavailable weight data appear to be more likely to have a high risk of mortality and hospitalisation.
  • For patients with mobility problems, scales are available for hoists and stand aids. Wheelchair, bed and trolley weighing devices also exist.
  • A number of trusts have implemented strategies that include the use of practical dosing calculation tools to reduce calculation errors with LMWHs. These have been incorporated in medication charts, policies, posters and other readily available formats.
  • You can share ideas or interventions successfully implemented by visiting the discussion thread titled Reducing treatment dose errors with LMWH on the Patient Safety First medication safety forum


Every reported incident counts

Following the announcement of the abolition of the NPSA, it remains important for all NHS organisations across England and Wales to continue reporting patient safety incidents through the National Reporting and Learning System. Trends in safety incidents can then be identified and acted upon as early as possible.  This aspect of our work will continue within the new proposed structure of the NHS Commissioning Board. Please keep reporting to ensure safer care.

  • Find the Rapid Response Report and supporting information on the NPSA website by clicking here

How to use the Rapid Response Report to Change Practice

Lisa Jones, ward manager, medical admissions unit, Glan Clwyd Hospital, Betsi Cadwaladr University Health Board believes nurses have a key role to play in helping to reduce heparin treatment dose errors. 

‘There can be many reasons for prescribing low molecular weight heparin. Mainly, it is either prophylactic or for the treatment of ACS (acute coronary syndrome) or thromboses such as pulmonary embolism (PE) or deep vein thrombosis (DVT).

‘Used prophylactically, there is a standard dose but even then, there is risk attached, and factors such as the patient’s renal function need to be considered, so a good patient history is crucial.

‘But when used for the treatment of clot-related conditions, the dose is weight-related, so if you simply guess or estimate the weight of the patient you are at risk of underdosing or overdosing, both which have serious implications.

‘We have found the most important factor in reducing dose error is making sure staff have equipment readily available to hand that allows them to weigh patients.

‘We used to have just one set of scales for the unit; we now have one for each bay, some which you stand on and some which patients can sit on. The trust is also looking into purchasing bariatric scales, and in A&E there are now scales that weigh patients who are on a trolley or in a wheelchair.

‘We hold regular thromboprophylactic study days, linked closely with drug companies, to build up and refresh the staff’s knowledge. To improve risk assessment, we also currently have a staff nurse dedicated to thromboprophalaxis, education and risk assessment.

‘Our principal pharmacist Uttam Chouhan [corr] has developed a desktop icon available to doctors which enables them to input factors such as a patient’s blood results, age and renal function, which tells them what dose to prescribe. The battle we do have is ensuring that nurses have the time and provision to weigh patients and to encourage doctors to use the desktop icon with every patient.

‘Nurses who are more experienced and have been on the thromboprophylactic course are more aware of the dangers of incorrect prescribing and are more likely to pull doctors up on that. The challenge, on an acute unit with junior doctors on rotation, is keeping that level of knowledge and awareness constant.

‘Our trust was formerly three different trusts. Now we have joined together, the same drug chart is used across a larger patient population and we are standardising procedures.

‘We also have good pharmacy support which is crucial. The pharmacists carry out a thorough drug history and go through the ‘take home’ medication with each patient so there is less room for errors. But there are still other things we want to develop such as an e-discharge script.

‘The importance of getting a correct patient weight when prescribing heparin can be easily underestimated without improving staff knowledge on the issue. The publication of the RRR has been extremely helpful in highlighting this.’

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