No diversion in Western Massachusetts.

Background: Massachusetts (MA) instituted a moratorium on ambulance diversion ("No Diversion") on January 1, 2009.

Study Objectives: Determine whether No Diversion was associated with changes in Emergency Department (ED) throughput measures.

Design: Comparison of three 3-month periods. Period 1: 1 year prior (January-March 2008); Period 2: 3 months prior (October-December 2008); Period 3: 3 months after (January-March 2009).

Setting: Seven EDs in Western MA; two - including the only Level I Trauma Center - were "high" diversion (≥562 h/year) and 5 were "low" diversion (≤260 h/year). For "all," "high" diversion and "low" diversion ED groups, we compared mean monthly throughput measures, including: 1) total volume, 2) number of admissions, 3) number of elopements, 4) length of stay for all, admitted and discharged patients. Mean absolute and percent changes were estimated using mixed-effects regression analysis. Linear mixed models were run for "all," "high" and "low" diversion EDs comparing means of changes between periods. Results are presented as mean change per month in number and percent, and 95% confidence intervals were calculated. We specified that a clinically significant effect of No Diversion had to meet two criteria: 1) there was a consistent difference in the means for both the Period 1 vs. Period 3 comparison and the Period 2 vs. Period 3 comparison, and 2) both comparisons had to achieve statistical significance at p ≤ 0.01.

Results: According to pre-determined criteria, no clinically significant changes were found in any ED group in mean monthly volume, admissions, elopements, or length-of-stay for any patient disposition group.

Conclusion: No Diversion was not associated with significant changes in throughput measures in "all," "high" diversion and "low" diversion EDs.