Analysing Deviation-From-Target Data: Applying the Correct Force in Sellick's Maneuver.

The problem of comparing the deviation from a target of two or more treatments or procedures arises now and again in medicine. Practitioners usually carry out a t-test on a loss function such as absolute error. We have adapted and developed statistical methods to give a normative methodology for deviation-from-target problems and exemplify them by evaluating the performance of a tactile feedback device. Parametric and nonparametric analyses are compared and contrasted. We recommend nonparametric methods for inference about loss functions such as absolute error, with a permutation test for testing the hypothesis that the two methods perform identically, and the nonparametric bootstrap for deriving standard errors and confidence intervals on loss function ratios. We develop a new permutation test that can be used when the practitioner is unwilling to decide which loss function should be used. We recommend parametric analysis when more insight into how one method is superior is desired, or there are covariates, and discuss the complications. The results for our example are that the tactile sensing device reduces an upward bias in applied force, and more importantly reduces the spread (variance) of the applied force. It performs significantly better than manual force application.

A cricoid cartilage compression device for the accurate and reproducible application of cricoid pressure.

We describe the development and laboratory assessment of a refined prototype tactile feedback device for the safe and accurate application of cricoid pressure. We recruited 20 operating department practitioners and compared their performance of cricoid pressure on a training simulator using both the device and a manual unaided technique. The device significantly reduced the spread of the applied force: average (SE) root mean squared error decreased from 8.23 (0.48) N to 5.23 (0.32) N (p < 0.001). The average (SE) upwards bias in applied force also decreased, from 2.30 (0.74) N to 0.88 (0.48) N (p < 0.01). Most importantly, the percentage of force applications that deviated from target by more than 10 N decreased from 18% to 7% (p < 0.01). The device requires no prior training, is cheap to manufacture, is single-use and requires no power to operate, whilst ensuring that the correct force is always consistently applied.