Concept: Waiting Times for Surgery

Background

Waiting times were first defined as the time between the date of a patient's last pre-operative visit to the surgeon and the date of the surgery (DeCoster et al., 1998). This measure of surgical waiting time was developed because, except for cardiac surgery, there was no centralized surgery registry in Manitoba. And, in using administrative data (routinely collected computerized hospital discharge abstracts and medical services/physician claims) to estimate the wait for surgery, we had no field indicating when the patient and the physician made a decision to proceed with surgery.

This method assumes that the patient is referred to a surgeon for a particular problem, that the surgeon and patient decide to proceed with surgery (beginning of wait), after which any problems that arise are handled by the patient's family physician, and the patient doesn't see the surgeon again until the date of the surgery (end of wait): in short, that there is usually only one pre-operative visit to the surgeon. This method was similar to one used by the Nova Scotia Department of Health (1996).


• This method isn't suitable for procedures for chronic conditions (e.g. total joint replacement, hysterectomy for benign disease) that might involve a number of pre-surgical visits to the surgeon.
  
• This method estimates waiting times only for patients who had the procedure; persons who were going to have the surgery but did not - because they left the province, died, changed their minds or were still waiting - were not in the data.

Procedures Investigated

De Coster et al. (1998) examined eleven procedures : eight core elective surgical procedures (cholecystectomy, hernia repair, excision of breast lesions, varicose vein repair, carpal tunnel release, trans-urethral prostatectomy, tonsillectomy, carotid endarterectomy), cataract surgery, and two coronary procedures: coronary artery bypass surgery (CABS) and coronary angioplasty (PTCA).


• For cataract surgery, if the visit closest to surgery was for ultrasound measurement only, the previous visit was used as the marker.
  
• For CABS, the presence of an angiogram was used in addition to a pre-op visit to the surgeon as a marker for when the waiting time began.
  
• PTCA is not a surgical procedure so there is no pre-op visit to a surgeon; therefore angiography was used as the marker for waiting time for PTCA.

Notes

• Only procedures that were the primary reason for hospitalization (indicated by the procedure code being in the first position) were included.
• Urgent and emergent cases, and patients whose visit to the surgeon was less than three days pre-op were excluded, except for coronary procedures, in which urgent/emergent as well as elective/day procedures were analyzed.
• Diagnostic codes, procedure codes, and physician tariffs are available from MCHP.
• Waiting times were estimated for each year from 92/93 to 96/97, except for the coronary procedures (90/91 to 96/97 were used). The waiting time for each year was compared to the overall median for five or seven years.
• Waits according to age (< 65 yrs/65+yrs), gender, region of residence (grouped into Winnipeg, West, South, Mid-North, Far North), and neighbourhood income quintile were also analyzed.
• As of March 2000, the analyses were being updated with two more years (97/98 & 98/99) of data.

Calculating Average Waiting Times: Median vs. Mean

Both median waiting times (the mid-point, the length of time half the people over a given time period had to wait for surgery) and mean waiting times (see Confidence Interval of Median and Statistical Analysis of Mean Waiting Times concepts) were used.


• The median, unlike the mean, is not influenced by outliers (i.e. unusually short or long waiting times).
• 95% confidence intervals were calculated for all comparisons, with adjustment for multiple comparisons
• Programming code for calculating confidence intervals for the median is available.
• One limitation of median analyses was that it doesn't allow adjustments for other factors in making comparisons.
• Mean analysis resolves this problem and is statistically more powerful and sensitive.

In order to deal with the problem of outliers, Tukey's robust outlier detection method was used to separate a few extremely unusual waiting times.


• The interquartile range (IQR) was calculated first.
  
• Outliers were identified as waiting times which were longer than 3 times the IQR + the 75th percentile or shorter than the 25th percentile - [3*IQR]. Outliers were excluded from all mean analyses thereby assuring a robust comparison of the mean waiting times, uninfluenced by a few extreme values.

Based on the analysis of medians and substantive considerations, a decision was made to take mean waiting times of longer than three days as a clinically significant characteristic; no average waiting times less than this were tested for statistical significance. (see DeCoster et al (1998) , page 71).

Cataract Surgery

During the period of this study, cataract surgery in Manitoba was available in only the cities of Brandon and Winnipeg.


• Both cities had private clinics as well as public hospitals performing the procedure.
  
• In both cases, the surgeon's fee was paid by Manitoba Health; however private clinics charged a "facility" fee of about 1,000 dollars which was not covered by Manitoba Health.
  
• Waiting times were shorter for cataract surgery done in a private clinic compared to in the public hospital.
  
• When cataract patients were categorized according to where their surgeon practiced - those who operated publicly only vs. those who operated both publicly and privately - the waiting time picture was different.

  Note: no surgeons only operated privately

• Patients who had cataract surgery in a public hospital by a surgeon who operated publicly had to wait from 7 to 10 weeks.
  
• However, if the surgeon operated both privately and publicly their public hospital patients waited from 14 to 23 weeks. Meanwhile their private clinic patients had to wait, on average, about 4 weeks.

Note : the surgeons who operated both publicly and privately performed over 50% of the cataract surgery provided in the public sector; it is possible that the longer waits for public sector surgery reflected the limits of available resources.