Using Nomograms to Reduce Harm from Clinical Calculations

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.