Objective and quantitative analysis of daytime sleepiness in physicians after night duties

Work place studies often have the disadvantage of lacking objective data less prone to subject bias. The aim of this study was to contribute objective data to the discussion about safety aspects of night shifts in physicians. For this purpose we applied the Pupillographic Sleepiness Test (PST).

The PST allows recording and analyses of pupillary sleepiness-related oscillations in darkness for 11 min in the sitting subject. The parameter of evaluation is the Pupillary Unrest Index (PUI; mm/min). For statistical analysis the natural logarithm of this parameter is used (lnPUI). Thirty-four physicians were examined by the PST and subjective scales during the first half of the day. Data taken during a day work period (D) were compared to those taken directly after night duty (N) by a Wilcoxon signed rank test.

Night duty caused a mean sleep reduction of 3 h (Difference N-D: median 3 h, minimum 0 h, maximum 7 h, p < 0.001). Time since the last sleep period was about equal in both conditions (Difference N-D: median -0.25 h, min. -4 h, max. 20 h, p = 0.2). The lnPUI was larger after night duty (Difference N-D: median 0.19, min. -0.71, max. 1.29, p = 0.03). The increase of physiologically measured sleepiness correlated significantly with changes in subjective measures (PUI/SSS, Spearman Rho 0.41, p = 0.02; PUI/VAS, Spearman Rho 0.38, p = 0.02).

Despite a mean sleep duration of 4 h, considerable sleepiness in physicians after nights on duty was found, implying lower safety levels for both patients (if physicians remaining on duty) and physicians while commuting home.