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Obtaining an accurate body weight measurement in adults and children in primary and secondary care settings (not babies)

Introduction

  • In an adult body weight should be recorded as part of the malnutrition screening process on admission for hospital in-patients, out-patients, people in care homes, and people attending GP surgeries
  • Body weight should be repeated weekly for in-patients and when there is clinical concern for others, or on home visits if weight is relevant to purpose of visit, i.e. person receiving nutritional support or weight management review
  • An accurate body weight is required to:
    • assess and monitor fluid and nutritional status
    • calculate safe doses of medication and clinical therapies
    • calculate nutritional and fluid requirements so appropriate nutrition support plans can be devised
    • establish and monitor fluid and nutritional status, and to calculate safe doses of medication
    • when selecting supportive equipment such as pressure relieving beds, chairs, and mattresses

Background/evidence

  • Weighing equipment are important diagnostic and monitoring tools
  • A lack of consistent weight recordings in conjunction with the use of inaccurate or inappropriate weighing equipment hinders optimal care leading to potential errors in diagnosis, treatment, or medication dosage
  • The Local Authorities Coordinators of Regulatory Services (LOCARS) and the Department of Health recommend that:
    • class III weighing scales should be used in healthcare premises:
      • where greater accuracy is required (e.g. when weight is used to calculate medication doses or therapy or patients are being monitored for fluid retention)
      • for the calculation of weight for medication and ongoing treatment or monitoring
      • scales may be standing, sitting, hoist, wheelchair, or bed scales according to patient need
    • Class IV (less accurate domestic type scales) should only be used for monitoring/recording an individual's weight:
      • where weight is not required to calculate treatments or therapies
      • in GP consulting rooms, nursing or residential homes, and home visits
      • where there is no risk the scale will be used to weigh someone under the age of 18
  • Maximum scale intervals:
    • maximum scale interval for adults is 0.5 kg and for children it is 0.2 kg
  • Training and responsibilities:
    • basic training in the use of weighing equipment should be given to all healthcare professionals involved in weighing individuals
    • if the healthcare professional does not feel competent undertaking and recording body weight additional training should be sought
    • if the role of weighing is delegated to non-registered staff the Registered Nurse maintains accountability to ensure the non-registered staff are trained and competent in obtaining accurate weight measurements
  • Changes in body weight:
    • short term changes in body weight, e.g. >0.25 kg per day, are likely to reflect changes in hydration rather than actual body weight
    • if recorded body weight is not as expected then the person should be re-weighed
  • Using proxy measurements:
    • if it is not possible to weigh a patient a proxy measure of weight such as mid upper arm circumference may be used using the appropriate measurement tool and calculations
  • Equipment needed to obtain body weight:
    • appropriate weighing scales placed on a flat even surface
    • cleaning equipment, as per local policy, to clean scales after use
    • weight conversion chart (to inform the person of their weight in stones/pounds if they prefer)

Procedure for weighing an individual

  • Prior to use check:
    • the calibration date is still valid
    • scales have sufficient battery power to weigh the person (if appropriate)
    • for any signs of damage
  • Position the scales for easy access, and to ensure privacy and dignity
  • Place weighing equipment on a firm, solid surface or on the appropriate hoist equipment
  • Apply brakes to scales (if appropriate)
  • Ensure that no part of the scales is leaning against a fixed object (e.g. a wall)
  • If using:
    • stand on scales:
      • adjust the legs to ensure scales are level
      • check spirit level if present
    • wheelchair weighing scales:
      • weigh wheelchair
      • weigh individual in the wheelchair
      • calculate the individual's weight
    • hoist scales:
      • ensure scales are compatible with the type of hoist being used
      • ensure hoist slings are compatible and of an appropriate size for the person
  • If unsure check manufacturers guidance
  • Explain the procedure to the person being weighed
  • Where the person has capacity to consent verbal agreement should be obtained
  • Where the person does not have capacity, a risk assessment should be undertaken and decision regarding safe weight measurement made in the person's best interest
  • The individual should be weighed:
    • wearing light indoor clothing (in community or out-patient settings)
    • night wear/hospital gowns (in hospital wards)
  • Request the person remove shoes and outdoor garments as appropriate
  • If weighing patients with stoma or catheter bags ensure they are emptied before weighing
  • If weighing children they should be weighed wearing only a dry nappy or pants
  • Where this is not possible or in older children the amount and type of clothing should be recorded
  • Ensure that the weighing equipment records zero before the person is positioned on it or the hoist sling is attached
  • If the weighing equipment does not show zero reset them before placing the patient onto them
  • Following a risk assessment provide the appropriate level of assistance if the person cannot get on to the weighing equipment independently
  • The person should remain still as possible while being weighed
  • Monitor to ensure that:
    • clothing is not touching any fixed part of the scales or surroundings
    • body weight is not supported on an object, e.g. a walking stick or wall, and the person does not have their feet placed on the floor (when using sitting scales) or on any part of the hoist
  • Once the scales register a weight, record the reading on the scales and document in the appropriate documentation or nutrition screening tool
  • Where necessary, or if requested, use a weight conversion chart to inform the person of their weight
  • If possible check with the person and previous medical records that the weight reflects their expected weight and is similar to previous weights recorded
  • If the weight is not as expected then the person should be re-weighed
  • Also consider deliberate weight loss and fluid balance
  • Once accurate weight is recorded assist the person to move away from weighing scales
  • Ensure they are dressed appropriately and comfortable at end of procedure
  • Routine cleaning of scales should be undertaken, in accordance with the manufacturer's instructions and local policy, after every patient use
  • Return scales to storage position
  • Record weight in kilograms (kg) in the appropriate noting system, including growth chart, screening tool, or medication chart (as appropriate)
  • Record time of day patient was weighed and what clothing was worn
  • Repeat weight should be recorded on the same scale, at the same time of day after urinating (if possible)
  • Where weight is recorded as part of nutrition screening tool use it to calculate body mass index (BMI) and percentage body loss

full guideline available from…
http://www.nnng.org.uk/wp-content/uploads/2017/02/Accurate-Body-Weight-Measurement-GPG-Final-draft-Feb17.pdf 

National Nurses Nutrition Group. Obtaining an accurate body weight measurement in adults and children in primary and secondary care settings (not babies). Updated February 2017.
First included: December 2015, updated November 2017.