Using Nomograms to Reduce Harm from Clinical Calculations

Abstract

Abstract-Handheld calculators and computer spreadsheets are ubiquitous and taken for granted. However in hospitals, errors in routine calculations frequently occur -for instance after making an unnoticed typing slip, such as omitting a decimal point in a drug dose calculation -and can result in patient harm. This paper is concerned with dependable calculation, and examines user tasks and technologies for safer calculations in the clinical environment. We demonstrate significant differences in complexity, speed and accuracy between alternative methods of performing calculations.The recent raised awareness of latent coding errors in applications designed to perfom medical dosage calculations has resulted in the introduction of national regulations that require all medical apps to meet similar standards of safety and reliability as other items of medical equipment. This paper provides evidence that general purpose calculators are also unnecessarily hazardous in the clinical environment, and should be subject to similar regulation. This paper contributes to the current debate about the use of computer systems to improve healthcare, and argues that "the latest IT" does not automatically confer benefit: its effectiveness should be empirically evaluated like any other medical intervention.The combination of simple reliable low technology graphical calculation aids and high technology computers with touch screen interfaces offers potential for improvement in patient safety; however further development and stringent evaluation are required before deployment in safety critical environments.

Using Graphical Representations to Support the Calculation of Infusion Parameters

“…[7]) and confirming that rerepresenting calculation problems can improve performance (e.g. [10]). Although the effect of representation on answer accuracy was not significant, there was a trend toward superior accuracy in graphical problems.…”

“…Hence there is an opportunity to see whether modifications to environmental artefacts might facilitate accurate calculations. Previous work [10] has experimented with nomograms -one dimensional slide rule-like representations -to make such calculations easier. Empirical results indicate that these representations can significantly reduce the number of errors made in calculation tasks.…”

Visualizing Magnitude

“…Here we focus our review on a few recent studies that have evaluated different forms of graphical number representations designed to support number entry in the context of medical infusion pump programming Thimbleby & Williams, 2013;Tu et al, 2014). Thimbleby and Williams (2013) studied nomograms to facilitate calculations on infusion pump parameters, such as medication volume and rate of infusion. As can be seen in Figure 1a, a nomogram consists of a number of scales, with one scale per infusion pump parameter.…”

A nomogram for calculating the maximum dose of local anaesthetic

“…aviation nomogram). The currently recommended ‘buddy’ system in medicine, where two users perform calculations independently using the same method, is not a sufficient safeguard to prevent catastrophic drug dosage errors .…”