NACCT Platform Abstracts 2012 - The American Academy of Clinical ...

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Variability of limb circumference measurements in a simulation of Crotalid envenomated patients
Kirk L Cumpston 1 , Penny S Reynolds 1 , Marie Knorr 1 , Trevor Slone 1 , Paul E Stromberg 1 , Brandon K Wills 1
1 Virginia Commonwealth University Health System, Richmond VA USA
Objectives: Documenting the progression of edema resulting from Crotalid envenomation requires measurements of limb
circumference. It is assumed that measurements are accurate and can influence decision-making for antivenin administration
when cases are managed through poison center telephone consultation. We conducted a study designed to assess the
variability between individual observers and repeatability of measurements of limb circumference in healthy, non-envenomated
volunteers.
Methods: Two healthy volunteers acted as simulated snakebite patients. Two bite sites on the wrist and ankle were indicated
by an indelible marker. Nurse participants received verbal instructions of the case scenario and instructed to measure limb
circumference at the bite site, 10cm distal, and 10cm proximal to the bite site. Nurses repeated the procedure after 4-5 hours
on the same patient. We used both variance components (mixed model ANOVA) and Bland-Altman analyses to estimate
repeatability and reproducibility. Repeatability is the variation resulting from duplicated measurements taken on the same part
by the same observer; reproducibility is the observer-to-observer variability. Clinically-relevant limits of agreement were
estimated as 2 cm.
Results: A total of 450 observations were made by 34 observers on two simulated patients. Estimated reproducibility was
1.7 cm and repeatability was 3.1 cm. Limits of agreement range from Bland-Altman analysis was 5 cm.
Conclusions: Reproducibility (observer-to-observer variation) was within a priori guideline limits. However repeatability
(measurements obtained by the same nurse at the same site at two separate time periods) was poor. Three participants
showed significantly large deviations (> 3 SD) between replicate measurements. Limitations of the study include use of
simulated non-envenomated patients and a small possibly non-representative patient sample. Potential strategies to increase
accuracy and precision should include greater standardization in measurement procedures and duplicate measurements per
sampling period. Otherwise, our data suggest that an increase of > 5 cm in limb circumference may be required to indicate
clinically-significant edema.