Development and validation of an instrument to predict prolonged length of stay in the postanesthesia care unit following ambulatory surgery

Samuel Rupp, Elena Ahrens, Maira I. Rudolph, Omid Azimaraghi, Maximilian S. Schaefer, Philipp Fassbender, Carina P. Himes, Preeti Anand, Parsa Mirhaji, Richard Smith, Jeffrey Freda, Matthias Eikermann, Karuna Wongtangman

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Purpose: We sought to develop and validate an Anticipated Surveillance Requirement Prediction Instrument (ASRI) for prediction of prolonged postanesthesia care unit length of stay (PACU-LOS, more than four hours) after ambulatory surgery. Methods: We analyzed hospital registry data from patients who received anesthesia care in ambulatory surgery centres (ASCs) of university-affiliated hospital networks in New York, USA (development and internal validation cohort [n = 183,711]) and Massachusetts, USA (validation cohort [n = 148,105]). We used stepwise backwards elimination to create ASRI. Results: The model showed discriminatory ability in the development, internal, and external validation cohorts with areas under the receiver operating characteristic curve of 0.82 (95% confidence interval [CI], 0.82 to 0.83), 0.82 (95% CI, 0.81 to 0.83), and 0.80 (95% CI, 0.79 to 0.80), respectively. In cases started in the afternoon, ASRI scores ≥ 43 had a total predicted risk for PACU stay past 8 p.m. of 32% (95% CI, 31.1 to 33.3) vs 8% (95% CI, 7.9 to 8.5) compared with low score values (P-for-interaction < 0.001), which translated to a higher direct PACU cost of care of USD 207 (95% CI, 194 to 2,019; model estimate, 1.68; 95% CI, 1.64 to 1.73; P < 0.001) The effects of using the ASRI score on PACU use efficiency were greater in a free-standing ASC with no limitations on PACU bed availability. Conclusion: We developed and validated a preoperative prediction tool for prolonged PACU-LOS after ambulatory surgery that can be used to guide scheduling in ambulatory surgery to optimize PACU use during normal work hours, particularly in settings without limitation of PACU bed availability.

Original languageEnglish (US)
Pages (from-to)1939-1949
Number of pages11
JournalCanadian Journal of Anesthesia
Issue number12
StatePublished - Dec 2023


  • ambulatory surgery
  • postoperative length of stay
  • prediction model

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine


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