Patient Safety Tip of the Week
December 8, 2015
Danger of Inaccurate Weights in Stroke Care
In our September
2015 What's New in the Patient Safety World column “Stroke:
Doing Less Well Than You Think?” we noted an issue related to the dosing of
tPA in acute stroke. That related to the timing of
the initial dose and beginning of infusion of tPA and what to do if there is an interruption in the
infusion.
But another issue related
to the tPA dose is the
weight of the patient. Often, in the urgency to administer thrombolytic therapy
in a timely fashion, staff do not formally weigh the patient on a scale. They
either ask the patient how much they weigh or they estimate the patient’s
weight themselves. It turns out that estimating a patient’s weight frequently
results in erroneous weights being used in the dose calculation (Barrow
2015). Clinicians underestimated
mean difference weight by 1.13 kg between estimated and actual weight but
disparities were most likely at the upper and lower extremes of weight. So some
patients will be underdosed, others overdosed. Though
80% of patients received a tPA
dose within the acceptable range, 11.5% were underdosed
and 8.1% overdosed.
When they looked at
improvement in NIHSS scores, those patients who received a dose in the
acceptable range had the greatest improvement. But those in the “underdosed” range (corresponding to the heaviest patients)
had less improvement than those in the “overdosed” range. That heavier, underdosed population accounted for about a third of all
their stroke patients.
The authors conclude
that beds capable of weighing patients should be mandated in emergency rooms
for patients with acute stroke.
Of course, errors
related to inaccurate weights are not unique to tPA or other thrombolytic therapies. They may occur
with any medication that is dosed based upon patient weight. The impact of
inaccurate estimations of patient weight on anticoagulation with low molecular
weight heparins (LMWH’s) has been discussed several times (NPSA 2010; dos
Reis Macedo 2011). In the latter study of enoxaparin dosing in an ED population, it was
found that when weight estimation was used to determine the enoxaparin dosage
25% of the patients were inadequately anticoagulated during the initial crucial
phase of treatment.
In our August 2,
2011 Patient Safety Tip of the Week “Hazards
of e-Prescribing” we highlighted several studies and examples of erroneous
doses due to confusion about patient weights. ISMP Canada reported a
case in which a chemotherapy agent was given in excessive dosage after the
height and weight on a computerized order entry system were transposed (ISMP
Canada 2010). They discussed several factors that contributed to the
problem and had several excellent suggestions on ways to avoid this type of
error. ISMP (US) reprinted this in August 2010 (ISMP
2010). ISMP and ECRI had co-authored an article on the importance of
accurate patient weights in a 2009
PPSA Safety Advisory. That article mentioned several cases in which weights
were incorrectly entered into computerized systems, confusing pounds with
kilograms, resulting in overdosing or underdosing.
The PPSA article notes that the weight issue is so important because most of
the drugs that have weight-based dosing are hi-alert drugs.
Patient self-reported weights appear to correlate better
with actual weights. Finardi and colleagues found a
negligible small mean difference between self-reported and measured weights in
high risk elderly ED patients (Finardi 2012).
Neither old age nor acute disease status impaired the strong correlation of
reported and measured weight. Therefore, those authors conclude that self-reported
weight can be used as approximation for real body weight in elderly ED patients
presenting with non-specific complaints.
In the setting of acute stroke a patient may be unable to
communicate what they weigh. When we discuss patient safety with our patients
or laypersons we tell them they should record their weight (and keep it
up-to-date) on their list of medications that they should keep with them at all
possible times. Tools like the Patient
Med List from the Massachusetts Coalition for the Prevention of Medical Errors
include a place at the top of the list for patients to record their weight and
height.
And don’t forget the other setting where inaccurate weights
become problematic – the patient who has been hospitalized for a long time.
We’ve seen some patients who have been hospitalized for several weeks,
typically with multiple complications, who have lost considerable amounts of
weight. Unfortunately, clinicians often use the weight recorded on admission
(or “locked” into a field in the EMR that is used for weight-based
calculations) to calculate a medication dose rather than using the current
weight. This can often lead to overdosing of such patients.
The key lesson: always use the actual current weight if you
are doing a weight-based calculation for a drug dosage, particularly for a
high-alert medication.
Some of our previous columns on improving stroke care:
March 2012 “Helicopter
Transport and Stroke”
November 6,
2012 “Using
LEAN to Improve Stroke Care”
March 18, 2014 “Systems
Approach Improving Stroke Care”
June 17, 2014 “SO2S
Confirms Routine O2 of No Benefit in Stroke”
September 23, 2014 “Stroke
Thrombolysis: Need to Focus on Imaging-to-Needle Time”
January 27, 2015 “The
Golden Hour for Stroke Thrombolysis”
May 12, 2015 “More
on Delays for In-Hospital Stroke”
June 2015 “Too
Much of a Good Thing? Very Early Mobilization in Stroke”
September 2015 “Stroke:
Doing Less Well Than You Think?”
References:
Barrow T, Khan MS, Halse O, et al.
Estimating Weight of Patients With Acute Stroke When
Dosing for Thrombolysis. Stroke 2015; Published ahead of print November 10,
2015
http://stroke.ahajournals.org/content/early/2015/11/09/STROKEAHA.115.011436
NPSA (National Patient Safety Agency - UK). Reducing treatment
dose errors with low molecular weight heparins. July 30, 2010
http://www.nrls.npsa.nhs.uk/resources/?entryid45=75208
dos Reis Macedo
LG, de Oliveira L, Pintão MC, et al. Error in body
weight estimation leads to inadequate parenteral anticoagulation. Am J Emerg Med 2011; 29(6): 613-617
http://www.ajemjournal.com/article/S0735-6757%2810%2900008-2/abstract
ISMP
Canada. Vulnerabilities of Electronic Prescribing Systems: Height and Weight
Mix-up Leads to an Incident with Panitumumab. ISMP
Canada Safety Bulletin 2010; 10(5): 1-3 July 31, 2010
http://www.ismp-canada.org/download/safetyBulletins/ISMPCSB2010-05-ElectronicPrescribingSystems.pdf
ISMP. Electronic prescribing vulnerabilities: Height and
weight mix-up leads to dosing error. ISMP Medication Safety Alert! Acute Care
Edition 2010; August 26, 2010
http://www.ismp.org/Newsletters/acutecare/articles/20100826.asp
PPSA (Pennsylvania Patient Safety Authority), ECRI, ISMP.
Medication errors: significance of accurate weights. Pennsylvania
Patient Safety Advisory 2009; 6(1): 10-15 www.patientsafetyauthority.org/ADVISORIES/AdvisoryLibrary/2009/Mar6(1)/Pages/10.aspx
Finardi P, Nickel CH, Koller MT, Bingisser R. Accuracy
of self-reported weight in a high risk geriatric population in the emergency
department. Swiss Med Wkly 2012; 142: w13585
http://www.smw.ch/content/smw-2012-13585/
Massachusetts Coalition for the Prevention of Medical Errors. Patient Med List.
http://www.macoalition.org/Initiatives/docs/PatientMedCard%20-%20Final%20Word%2010.19.06.doc
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