Abstract
Purpose
Unbiased prediction of case durations is an integral part of matching operating room (OR) staffing to workload. Monitoring systematic bias in surgeons’ scheduled case durations can identify those services with estimates sufficiently inaccurate that statistical analysis of historical data may be useful in preference to the surgeons’ estimates. We describe a method to monitor surgical services’ average bias in scheduled case durations.
Methods
Actual case duration, predicted (scheduled) case duration, and service were obtained for all 58,291 cases during 39 four-week periods at an academic hospital. For each four-week period, a ratio was computed for each service. The numerator for each service equalled the sum of the differences in minutes between actual case duration and scheduled case duration. The denominator equalled the sum in hours of the actual durations of all of the service’s cases. The ratio was multiplied by eight hours to yield the number of minutes of underestimated case duration per eight hours of OR time during the four-week period.
Results
The ratios followed a normal distribution for each service. Using the Student’s t distribution, the 95% lower confidence bounds for the average underestimate of case duration ranged from three to 65 min per eight hours of used OR time.
Conclusions
To reduce over-utilized OR time, we recommend monitoring each service’s 95% lower confidence bound of the bias in scheduled case durations. For services consistently underestimating their case durations, schedule their cases using statistical estimates of case durations based on their historical data, and disregard their own estimates.
Résumé
Objectif
La prédiction non biaisée de la durée des cas fait partie de ľattribution du personnel à la salle ďopération (SO). La mesure du biais systématique de la durée des opérations réglées peut indiquer les services dont les estimations sont suffisamment imprécises pour qu’une analyse statistique des données historiques soit plus utile que les prédictions des chirurgiens. Nous décrivons une méthode pour mesurer le biais moyen de la durée des opérations réglées.
Méthode
La durée réelle, la durée prévue des cas réglés et le service ont été obtenus à partir des 58 291 cas vus pendant 39 périodes de quatre semaines dans un hôpital universitaire. Pour chaque période, un ratio a été calculé. Le numérateur pour chaque service égalait la somme des différences en minutes entre la durée réelle et prévue. Le dénominateur égalait la somme en heures des durées réelles de tous les cas du service. Le ratio a été multiplié par huit heures pour avoir le nombre de minutes sous-estimées par huit heures de temps de SO pendant la période.
Résultats
Les ratios présentaient une distribution normale pour chaque service. Selon la distribution t de Student, la valeur la plus faible de ľintervalle de confiance de 95 % pour la moyenne estimée de la durée des cas allait de trois à 65 min par 8 h ďusage du temps de SO.
Conclusion
Pour réduire le dépassement de temps de SO, nous recommandons le monitorage de la valeur inférieure de ľintervalle de confiance de 95 % du biais dans la durée des cas réglés pour chaque service. Si la sous-estimation est régulière il vaut mieux utiliser des prédictions statistiques de la durée fondées sur les données historiques plutôt que des estimés personnels.
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Dexter, F., Macario, A., Epstein, R.H. et al. Validity and usefulness of a method to monitor surgical services’ average bias in scheduled case durations. Can J Anesth 52, 935–939 (2005). https://doi.org/10.1007/BF03022054
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DOI: https://doi.org/10.1007/BF03022054