Recommendations to Weigh Patients and Document Metric Weights to Ensure Accurate Medication Dosing (adopted October 25, 2018)

Accurate patient information (e.g., age, allergies, laboratory results) helps practitioners select appropriate medications, doses, and routes of administration.1 One vital piece of patient information, the patient’s weight, is especially important because it is used to calculate the appropriate dose of a medication (e.g., mg/kg, mcg/ kg, mg/m2). A prescribed or dispensed medication dose can differ significantly from the appropriate dose because of a missing or inaccurate patient weight.

Oncology, elderly, pediatric, and neonatal patients are at greater risk for adverse drug events because they are more vulnerable to the effects of an error and their weight may change frequently over short periods of time.2 Formulas such as the Cockcroft-Gault, which is used to estimate creatinine clearance to aid in the dosing of medications, and the Harris-Benedict formula, which is used to calculate basal metabolic rate, rely on accurate patient weights. Also, both height and weight are needed to use nomograms to determine body surface area and body mass index.

In the United States, most patients are weighed in pounds. But weighing and documenting patients’ weights in pounds introduces the need to convert the weight into kilograms, an error-prone process,2 to conduct weight-based and other dosing. Another risk when measuring the patient’s weight in pounds is failing to convert the weight into kilograms but recording that weight in kilograms (e.g., a weight of 220 lb. documented as 220 kg instead of 100 kg), resulting in greater than two-fold dosing errors. Adding to the complexity, there are various types of and terms used for patient weights used in healthcare such as ideal body weights, “dry” body weights and adjusted body weights.

Practitioners face a number of barriers to obtain an actual, accurate patient weight. One such barrier can occur at the beginning of the patient encounter. There are times when a patient arrives at a hospital and may not be weighed; for example, if a patient is admitted for an emergency or is not ambulant2. Care units may not be provided with appropriate scales to weigh patients, such as bed or wheelchair scales. When healthcare practitioners cannot or do not obtain the patient’s actual weight, they estimate the patient’s weights, which according to published studies is not accurate.3-7

The intent of this statement is to raise awareness of the safe practices associated with obtaining and documenting a patient’s weight across the continuum. Organizations affected by this statement will need to address the processes associated with obtaining and documenting patient weights and determining the appropriate type of weight to use when dosing medications.

Recommendations

  1. Weigh and document the metric weight of each patient as soon as possible on admission and during each outpatient or emergency department encounter.1,8
  2. Weigh patients at risk for weight changes such as neonates and oncology more frequently and according to policy.
  3. Avoid the use of a stated, estimated, or historical weight. Do not rely on a patient’s stated weight, a healthcare provider’s estimated weight, or a documented weight from a previous encounter.1,8
  4. Measure and document patient weights in metric units only.1,8,9 Document the date the weight was measured.
  5. Have appropriate metric scales (e.g., standing scales, chair scales, beds/stretchers with scales, builtin floor scales) available in all areas where patients are admitted or encountered. If scales can measure in both pounds and metric units (i.e., kg, g), modify the scale to lock out the ability to weigh in pounds.1,8,9
  6. When purchasing or replacing scales, buy scales that measure in, or can be locked to measure in, metric units only.8
  7. Implement automated decision support (CDS) rules to alert practitioners to significant changes in patient weight (e.g., a 10% or greater change for patients younger than 1 year).
  8. For patients under 18 years of age, implement CDS to rules compare entered weight with expected weight (e.g., based on growth  charts) and alert practitioners to unexpected discrepancies.9
  9. Ensure that printed material, information system screens, medication device screens (e.g., infusion pumps), and order sets list or prompt for the patient’s weight in metric units only.1,8
  10. Implement a policy defining the frequency at which patients are routinely weighed throughout an admission and as necessary when the patient’s condition changes.9
  11. Use, maintain (e.g., calibrate), and test scales according to manufacturer guidelines.1
  12. Charts are available near all scales to facilitate conversion of patient weights from kilograms (or grams) to pounds, so patients or caregivers can be provided the weight in pounds, if requested.8

References

  1. Bailey BR, Gaunt MJ, Grissinger M. Update on medication errors associated with incorrect patient weights. Pa Patient Saf Advis. 2016 Jun;13(2):50-57. Accessed September 15, 2017. http://patientsafety.pa.gov/ADVISORIES/Pages/201606_50.aspx
  2. Pennsylvania Patient Safety Authority. Medication errors: significance of accurate patient weights. Pa Patient Saf Advis. 2009 Mar;6(1):10-5. Accessed September 15, 2017. http://patientsafety.pa.gov/ADVISORIES/Pages/200903_10.aspx
  3. Bloomfield R, Steel E, MacLennan G, et al: Accuracy of weight and height estimation in an intensive care unit: Implications for clinical practice and research. Crit Care Med. 2006 Aug;34(8):2153–7.
  4. Uesugi T, Okada N, Sakai K, et al. Accuracy of visual estimation of body height and weight in supine paediatric patients. Paediatr Anaesth. 2002 Jul;12(6):489–94.
  5. Coe TR, Halkes M, Houghton K, et al. The accuracy of visual estimation of weight and height in preoperative supine patients. Anaesthesia. 1999 Jun;54(6):582–6.
  6. Hall WL, Larkin GL, Trujillo MJ, et al. Errors in weight estimation in the emergency department: comparing performances by providers and patients. J Emerg Med. 2004 Oct;27(3):219–4.
  7. Kahn CA, Oman JA, Rudkin SE, et al. Can ED staff accurately estimate the weight of adult patients? Am J Emerg Med. 2007 Mar;25(3):307-12.
  8. Institute for Safe Medication Practices. ISMP 2016-2017 Targeted Medication Safety Best Practices for Hospitals. 2016. Accessed September 15, 2017. http://www.ismp.org/tools/bestpractices/default.aspx
  9. Emergency Nurses Association. Position statement: weighing patients in kilogram. 2016 Sep. Accessed September 15, 2017. https://www.ena.org/docs/default-source/resource-library/practiceresources/position-statements/weighingallpatientsinkilograms.pdf

Actions/Decisions are those of the Council as a whole and may not reflect the views/positions of individual member organizations.

© 2017 National Coordinating Council for Medication Error Reporting and Prevention. All Rights Reserved. *Permission is hereby granted to reproduce information contained herein provided that such reproduction shall not modify the text andshall include the copyright notice appearing on the pages from which it was copied.

Adopted: 
October 25, 2018