Estimating the duration of common elective operations: implications for operating list management

Transcription

1 doi: /j x Estimating the duration of common elective operations: implications for operating list management J. J. Pandit 1 and A. Carey 2 1 Consultant 2 Medical student, Nuffield Department of Anaesthetics, John Radcliffe Hospital, Oxford OX3 9DU, UK Summary Over-running operating lists are known to be a common cause of cancellation of operations on the day of surgery. We investigated whether lists were overbooked because surgeons were optimistic in their estimates of the time that operations would take to complete. We used a questionnaire to assess the estimates of total operation time of 22 surgeons, 35 anaesthetists and 16 senior nursing staff for 31 common, general surgical and urological procedures. The response rate was 66%. We found no difference between the estimates of these three groups of staff, or between these estimates and times obtained from theatre computer records (p = 0.722). We then applied the average of the surgeons estimates prospectively to 50 consecutive published surgical lists. Surgical estimates were very accurate in predicting the actual duration of the list (r 2 = 0.61; p < 0.001), but were poor at booking the list to within its scheduled duration: 50% of lists were predictably overbooked, 50% over-ran their scheduled time, and 34% of lists suffered a cancellation. We suggest that using the estimates of operating times to plan lists would reduce the incidence of predictable over-runs and cancellations.... Correspondence to: J. J. Pandit jaideep.pandit@physiol.ox.ac.uk Accepted: 25 May 2006 Between 10% and 40% of booked elective operations may be cancelled before surgery takes place [1 8]. The reasons include cancellation by the patient, cancellation for poorly optimised medical conditions, or cancellations due to poor organisation [3, 4, 7, 8]. We previously concluded that a nurse-led pre-assessment system to optimise patients medically was effective in approximately halving the number of cancellations [3]. The most common cause of the remaining cancellations was lack of theatre time (i.e. over-running operating lists). The Audit Commission has estimated that in about 5% of hospitals in the UK, the majority of operating lists were consistently over-running [4]. An operating list may over-run because of delayed starts, slow turnover, unanticipated surgical anaesthetic problems or staff shortages. Many of these are difficult to quantify. However, one relatively easily measured factor is the possibility that some operating lists are predictably over-booked. In North America, the provision of surgical-anaesthetic services is virtually unlimited in time because of the way in which health care is financed. Theatres are often utilised for as long as needed for operations and cancellations due to over-running are rare. Instead, over-runs add to overall costs, which can pose different but equally important problems for the hospital [9 14]. In contrast, in the UK, each surgical team is offered a dedicated operating room for a predetermined length of time. Usually, 4 h is a single session (or contractually a programmed activity [15, 16]). Thus a half-day list is usually 4 h; a full-day list is 8 h (lunch breaks or rests are excluded from these times). Over-booking occurs when the expected duration of all the listed operations combined is anticipated to exceed these allocated times. Surgical lists are most commonly currently booked by surgical teams and our initial prejudice was that surgeons were optimistic about the times taken for operations. We planned to obtain estimates (using a questionnaire) from surgeons for times taken for common operations and compare these estimates with those of other staff groups (i.e. anaesthetists and theatre nursing staff). A second aim of the study was to compare these subjective estimates with more objective data obtained from the theatre computer. Finally, we wished to apply these time 768 Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland

2 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations estimates to actual published operating lists, to assess whether the total duration of the surgical list (and hence any patient cancellations) could be predicted. Methods This study was conducted at our large teaching hospital. We have previously provided an outline of work done by our hospital elsewhere [3]. In brief, it consists of four separate surgical sites: neurosurgery, ophthalmology and plastic surgery are located at the Radcliffe Infirmary; gynaecology is based at the Women s Centre; elective general surgery, renal transplant surgery and urology are based at the Churchill; and emergency and elective general surgery, paediatric and cardiac surgery are located at the John Radcliffe. This study was based at the last two sites. Questionnaires We sent a questionnaire to 22 consultant surgeons, 35 consultant anaesthetists and 16 senior theatre nursing staff (grades F and above). The questionnaire simply asked respondents to note (in minutes) the total operating time for some selected operations. In a short preamble to the questionnaire, we emphasised that total operating time included time for anaesthetic induction (including any epidurals, local anaesthetic blocks or invasive monitoring which might be normal for the procedure), time for patient positioning, and time to take the patient from the operating room to the recovery area (or intensive care unit if this was routine for any operation). Respondents were also reminded that our centre was a teaching hospital and the duration of some operations might be influenced by the need to train. We did not ask respondents to break down the total operating time estimate into component parts (e.g. anaesthesia, positioning, surgery, etc.). Recipients did not know the purpose of this study, nor that other staff groups were also being canvassed. We asked about 21 common operations in general surgery and 10 in urology. Surgeons were asked only questions relating to their own subspecialist field but anaesthetists and theatre nursing staff were asked about all 31 operations. Terminology used in the analysis The duration of an operation was the time from the start of anaesthesia to the arrival of the patient in the recovery area. The actual duration of a list was the time from the start of anaesthesia in the first patient on the list to the arrival of the last patient in the recovery area (minus any known breaks or interruptions, if any, for rest or lunch). The scheduled duration of a list was the time available for the list. Lists were either scheduled for a half day (4 h) or a full day (8 h). A list over-run was when the actual duration of the list exceeded its scheduled duration by (arbitrarily) more than 20 min. A list under-run was when the actual duration of the list was less than its scheduled duration by (arbitrarily) more than 20 min. An over-booked list was one in which the sum of surgeons average estimates for the duration of individual operations on that list exceeded the scheduled duration of the list by (arbitrarily) more than 20 min. An under-booked list was one in which the sum of surgeons average estimates for the duration of individual operations on that list was smaller than the scheduled duration of the list by (arbitrarily) more than 20 min. Data retrieval from theatre computer records During a 3-month data collection period (September November 2004), we retrieved data from the theatre computer (the hospital s own Theatre Information Management System, TIMS) for the same 31 operations as examined in the questionnaires. The time of arrival of patient in anaesthetic room to time of arrival of patient in recovery room was taken to represent the duration of operation. We did not retrieve or store any patient or staff identifying factors. Any case for which the relevant data was missing from TIMS was not included in our analysis. Data analysis For each operation, we averaged the times from the questionnaires to yield group means for each of the three staff groups (surgeons, anaesthetists, theatre staff), and one mean for TIMS. We subjected this averaged data to an analysis of variance (ANOVA, SPSS for Windows version 11.2, Chicago, IL): the response was duration of operation, and there were two factors: operation (a fixed factor, with 31 levels, one for each operation) and group (a random factor, with four levels, one for each staff group and TIMS). A value of p < 0.05 was taken as statistically significant. Finally, we averaged the group means and the TIMS mean to yield an overall combined estimate of the duration of each operation. Analysis of published surgical lists We used data from 50 consecutive surgical lists (25 lists in the period September November 2004 and 25 lists in the period July September 2005); with patient and staff identifiers removed. We used data only from those lists that contained solely the operations featured in our Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland 769

3 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Anaesthesia, 2006, 61, pages questionnaire (lists containing any operation not examined had to be excluded). We recorded the actual start time and end times for each list to obtain the actual duration of each list. We noted whether the list was scheduled for a half-day (4 h) or a full day (8 h). We also recorded any patient cancellations from the list. We used these data to address the following questions: Do surgeons over-book (or under-book) lists? Using confidence interval analysis [17], we compared the estimated duration of the list calculated using surgeons estimates for individual operations, with the scheduled time for the list; Are surgeons accurate in predicting the actual duration of an operating list? Using confidence interval analysis [17], we compared the estimated duration of the list calculated using surgeons estimates for individual operations with the actual duration of the list; How many lists over-run (or under-run)? Using confidence interval analysis [17], we compared the actual duration of the operating list with the scheduled time available for the list; What is the cancellation rate? We expressed cancellations both as (a) the number of lists suffering a cancellation, and (b) the number of patients cancelled as a proportion of the number booked for surgery. Results Questionnaire estimates and the computer records We obtained responses from 19 of 22 surgeons (86%) asked, 21 of 35 anaesthetists (60%) and eight of 16 nurses (50%), making an overall response rate of 66%. Tables 1 4 show the estimated time for each of the 31 operations provided by each of the three staff groups and by TIMS. Generally, staff groups agreed on estimated times, and this was also in broad agreement with TIMS. For some operations (e.g. laparoscopic cholecystectomy), surgeons were a little more optimistic in their estimates as compared with other staff groups. In contrast, for other operations (e.g. anterior resection, total cystectomy and percutaneous nephrolithotomy), surgeons offered much higher estimates than their colleagues. When subjected to analysis of variance, the data showed that operation significantly influenced the response (p = 0.001), confirming as expected that different operations yield different estimates for their duration. However, staff group did not significantly influence the response (p = 0.722), suggesting that, overall, the estimates of the three staff groups were similar. Analysis of published surgical lists Do surgeons over-book (or under-book) operating lists? There were 19 lists of scheduled duration 240 min. Of these, 10 (50%) were significantly (i.e. by greater than 20 min) over-booked. Equally, seven (37%) were significantly under-booked. There were 31 lists of scheduled duration 480 min. Of these, 13 (42%) were significantly (i.e. by greater than 20 min) over-booked. Equally, 16 (52%) were significantly under-booked. In summary, the booking of both half-day or full-day lists to within their scheduled duration using the surgeons own estimates of list duration was generally poor (Fig. 1). Approximately 50% of lists were predictably over-booked. Table 1 General surgery: varicose vein, cholecystectomy and hernia operations. The data are mean time in min (SD), then on the next line median [range]; n = number of respondents. The combined estimate is the mean of all the four previous columns (SD). Operation Questionnaire estimates Surgeons Anaesthetists Theatre Staff TIMS estimates Combined estimate Unilateral varicose veins 72 (23) 87 (32) 113 (38) 72 (21) 86 (19) 75 [30 105] 90 [40 180] 120 [60 195] 70 [35 115] n = 15 n = 30 n = 16 n = 26 Laparoscopic cholecystectomy 63 (15) 87 (20) 105 (21) 88 (29) 86 (18) 60 [45 90] 90 [45 120] 105 [75 135] 85 [45 175] n = 7 n = 17 n = 7 n = 99 Repair of inguinal hernia 49 (13) 58 (20) 75 (23) 68 (26) 63 (11) 53 [25 60] 60 [30 120] 75 [45 120] 63 [26 155] n = 14 n = 19 n = 8 n = 137 Repair of umbilical hernia 44 (13) 58 (25) 66 (28) 62 (23) 58 (10) 45 [20 60] 55 [30 120] 55 [40 120] 55 [34 127] n = 14 n = 17 n = 8 n = 30 Repair of incisional hernia 94 (41) 66 (27) 83 (35) 95 (51) 85 (13) 90 [40 180] 60 [40 120] 75 [45 150] 75 [37 228] n = 13 n = 14 n = 8 n = Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland

4 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Table 2 General surgery: breast operations. The data are mean time in minutes (SD), then on the next line median [range]; n = number of respondents. The combined estimate is the mean of all the four previous columns (SD). Operation Questionnaire estimates Surgeons Anaesthetists Theatre Staff TIMS estimates Combined estimate Mastectomy (including axillary node dissection) 103 (25) 92 (20) 118 (37) 92 (21) 101 (12) 120 [65 120] 94 [60 120] 120 [75 180] 95 [45 125] n = 5 n = 14 n = 7 n = 25 Wide local excision of lesion of breast 57 (20) 55 (16) 84 (32) 69 (17) 66 (13) 45 [45 90] 46 [30 90] 60 [60 135] 65 [25 115] n = 5 n = 17 n = 7 n = 91 Excision biopsy of breast lesion after localisation 53 (10) 52 (13) 56 (31) 54 (26) 54 (2) 60 [40 60] 50 [30 83] 53 [30 120] 53 [27 95] n = 5 n = 16 n = 7 n = 5 Biopsy sampling of axillary lymph nodes 49 (10) 47 (14) 61 (14) 43 (4) 50 (8) 45 [40 60] 45 [25 60] 60 [25 90] 43 [40 45] n = 5 n = 13 n = 7 n = 2 Table 3 General surgery: gastro-intestinal operations. The data are mean time in minutes (SD), then on the next line median [range]; n = number of respondents. The combined estimate is the mean of all the four previous columns (SD). Operation Questionnaire estimates Surgeons Anaesthetists Theatre Staff TIMS estimates Combined estimate Total excision of colon and ileorectal anastomosis 174 (33) 166 (39) 150 (42) 207 (45) 174 (24) 180 [ ] 180 [90 210] 150 [ ] 207 [ ] n = 5 n = 11 n = 2 n = 14 Hemicolectomy 122 (31) 142 (44) 135 (64) 167 (34) 141 (19) 120 [90 180] 120 [90 253] 135 [90 180] 163 [ ] n = 8 n = 14 n = 2 n = 14 Sigmoid colectomy 135 (32) 128 (26) 150 (42) 182 (72) 149 (24) 150 [90 180] 120 [90 180] 150 [ ] 143 [ ] n = 8 n = 13 n = 2 n = 6 Colostomy (including revision) 73 (15) 92 (25) 90 (0) 119 (49) 94 (19) 68 [60 90] 90 [45 120] 90 [90 90] 125 [50 175] n = 6 n = 13 n = 2 n = 5 Abdominoperineal resection of rectum and anus 195 (53] 201 (66) 210 (42) 310 (71) 229 (54) 210 [90 240] 200 [90 300] 210 [ ] 310 [ ] n = 6 n = 14 n = 2 n = 2 Anterior resection 184 (32) 165 (51) 125 (23) 224 (64) 175 (41) 180 [ ] 165 [90 240] 120 [ ] 210 [ ] n = 7 n = 13 n = 3 n = 37 Reversal of Hartmann s procedure Transanal resection of rectal cancer 161 (32) 121 (45) 110 (35) 159 (35) 138 (26) 165 [ ] 120 [60 210] 90 [90 150] 167 [ ] n = 8 n = 12 n = 3 n = 6 71 (33) 74 (25) 65 (35) 60 (0) 68 (6) 60 [45 120] 68 [45 120] 65 [40 90] 60 [60 60] n = 4 n = 12 n = 2 n = 2 Haemorrhoidectomy 54 (9) 52 (19) 50 (9) 46 (12) 51 (3) 60 [40 60] 45 [30 90] 49 [40 60] 45 [25 70] n = 8 n = 15 n = 6 n = 23 Laying open of low anal fistula 40 (14) 42 (12) 42 (10) 50 (34) 44 (4) 45 [15 60] 43 [22 60] 40 [30 60] 43 [20 115] n = 7 n = 16 n = 6 n = 6 Drainage through perineal region (including ischiorectal abscess) Excision of pilonidal sinus and suture skin graft 34 (9) 51 (23) 55 (9) 39 (12) 45 (10) 30 [20 45] 45 [25 120] 60 [45 60] 37 [20 65] n = 7 n = 14 n = 3 n = (10) 60 (21) 58 (4) 36 (13) 51 (11) 50 [30 60] 60 [30 100] 60 [53 60] 31 [15 70] n = 9 n = 16 n = 3 n = 24 Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland 771

5 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Anaesthesia, 2006, 61, pages Table 4 Urology operations. The data are mean time in minutes (SD), then on the next line median [range]; n = number of respondents. The combined estimate is the mean of all the four previous columns (SD). Operation Questionnaire estimates Surgeons Anaesthetists Theatre Staff TIMS estimates Combined estimate Nephrectomy (including nephro-ureterectomy) 185 (11) 177 (33) 185 (25) 200 (62) 187 (9) 180 [ ] 180 [ ] 188 [ ] 214 [ ] n = 3 n = 10 n = 6 n = 15 Percutaneous nephrolithotomy (PCNL) 300 (170) 108 (36) 175 (52) 165 (14) 187 (81) 300 [ ] 120 [60 165] 180 [ ] 165 [ ] n = 2 n = 10 n = 6 n = 2 Uteroscopic extraction of calculus of ureter + laser 75 (21) 97 (32) 130 (36) 80 (20) 96 (25) 75 [60 90] 120 [45 120] 135 [90 180] 89 [45 95] n = 2 n = 9 n = 6 n = 6 Total cystectomy (with intestinal conduit) 450 (42) 309 (92) 350 (56) 365 (169) 369 (59) 450 [ ] 300 [ ] 360 [ ] 460 [ ] n = 2 n = 10 n = 6 n = 3 Check cystoscopy 25 (10) 30 (10) 39 (9) 37 (11) 33 (6) 30 [10 30] 30 [15 60] 40 [30 53] 35 [21 60] n = 4 n = 16 n = 7 n = 13 Endoscopic resection of lesion of bladder (TURBT) 43 (13) 43 (12) 66 (23) 51 (11) 51 (11) 42 [30 60] 45 [20 62] 60 [45 105] 39 [17 82] n = 4 n = 17 n = 7 n = 36 Dilation of urethra 25 (10) 27 (13) 40 (11) 25 (8) 29 (7) 30 [10 30] 30 [10 60] 38 [30 60] 23 [20 38] n = 4 n = 13 n = 7 n = 5 Endoscopic resection of prostate (TURP) 83 (19) 75 (27) 96 (29) 77 (29) 83 (9) 83 [60 105] 75 [30 120] 105 [45 120] 81 [30 175] n = 4 n = 15 n = 7 n = 32 Correction of hydrocoele 45 (12) 49 (10) 61 (14) 53 (13) 52 (7) 45 [30 60] 48 [30 60] 60 [45 90] 55 [35 65] n = 4 n = 12 n = 7 n = 5 Circumcision 31 (9) 46 (12) 55 (16) 51 (7) 46 (11) 30 [20 45] 45 [30 75] 45 [38 75] 50 [35 65] n = 4 n = 14 n = 7 n = 16 Are surgeons estimates accurate in predicting the actual duration of the list? Excluding the seven half-day lists which suffered cancellations, the mean actual duration of 12 lists scheduled for 240 min was 221 min (95% confidence interval min), which was not significantly different from the surgeons predicted mean estimate for the duration of these lists of 255 min (95% confidence interval min; p = 0.720). Excluding the 10 full-day lists which suffered cancellations, the mean actual duration of 21 lists scheduled for 480 min was 470 min (95% confidence interval min), which was not significantly different from the surgeons predicted mean estimate for the duration of these lists of 465 min (95% confidence interval min; p = 0.383). This reasonably good ability to predict actual list duration from estimates is shown graphically in Fig. 1: the overall correlation coefficient, r is 0.78 (r 2 = 0.61; p < 0.001). In total, 17 lists suffered a cancellation, of which 15 were predicted by surgical estimates to over-run their scheduled duration. In summary, surgeons estimates were reasonably accurate in predicting both the actual list duration and whether an over-run and subsequent cancellation was likely to occur. How many lists over-run (or under-run)? Of the 19 half-day lists, three over-ran by more than 20 min. In addition, however, seven lists finished on or before time only because they suffered a cancellation and would otherwise have over-run. Thus, a total of 10 lists (53%) were actually over-running; a proportion similar to that predicted to over-run (50%, see above). A total of seven lists (37%) under-ran by more than 20 min, and two (11%) finished within 20 min of the scheduled time. Of the 31 full-day lists, five over-ran by more than 20 min. In addition, however, 10 lists finished on or before time only because they suffered a cancellation and would otherwise have over-run. Thus a total of 15 lists (48%) were actually over-running; a proportion similar to that predicted to over-run (42%, see above). A total of nine lists (29%) under-ran by more than 20 min, and seven (23%) finished within 20 min of the scheduled time. 772 Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland

6 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Estimated list duration (min) Actual list duration (min) Figure 1 Estimated duration of list plotted against actual duration of list (lists on which a cancellation occurred are excluded). s, half-day (240 min) lists;, full-day (480 min) lists. Each point represents a single list. The diagonal line is the line of identity (i.e. the estimated duration matches the actual duration). The two squares represent the range of times within 20 min either side of the scheduled duration for each of the half-day and full-day lists (i.e. if surgeons estimates or combined estimates were good at planning the list to its scheduled duration, all points should fall within these boxes). What is the cancellation rate? Seven of 19 (37%) half-day lists suffered a cancellation, and 10 of 31 (32%) full-day lists suffered a cancellation, yielding a cancellation rate for all lists in this cohort of 34%. Of 165 originally patients booked for surgery in our data set, 23 (14%) were cancelled. Discussion Contrary to our expectations, surgeons are not more optimistic than anaesthetists or nurses in their estimates of the time needed for common operations. Furthermore, these subjective estimates are all in agreement with more objective data from the theatre computer. Predictable over-booking, rather than any unanticipated influence, appears to be the main factor underlying cancellation. Before we consider the impact of this data on the management of operating lists, it is important to consider some potential limitations and strengths of this study. The response rate to the questionnaires across all staff groups was good. However, for some specific operations, the number of responses was low, e.g. transanal resection of tumour (Table 3) and PCNL (Table 4), probably because only a few specialists regularly undertake these procedures. Similarly, very little data was extracted from TIMS for some operations, e.g. biopsy sampling axillary lymph nodes (Table 2), because by chance very few such procedures were recorded during our data collection period. However, low returns were not uniform across all staff groups. For example, PCNL yielded responses from the only two surgeons undertaking this procedure but 10 anaesthetic responses, which was acceptable (Table 4). We decided therefore to include all such data sets in our analysis, and also present a combined estimate, which averaged the estimates of all staff groups. Surgeons responses may have been so accurate because they guessed the purpose of this study and did not wish to be outliers, and this may have been a source of bias. However, we think this unlikely: there were still large differences between estimates of staff groups for some individual operations (e.g. PCNL and total cystectomy, Table 4). We might have used TIMS data alone and avoided the need for any subjective questionnaire estimates, but we regarded TIMS data only as pseudo-objective and prone to errors. We encountered missing data, implausible times and operations that did not match those on the published list. Our publication of the combined estimate (Tables 1 4) may have some value in adjusting for deficiencies of the two methods (questionnaire and computer), and also for the problem of low returns for some operations. A particular strength of our study was to emphasise the total duration of an operation. Some studies measure only the time from skin incision to application of a surgical dressing [18 20], which has less value in planning an operating list. Our definition of 20 min as a list over- or under-run is larger than that of Widdison [19] (10 min) and Durani et al. [20] (1 min), but is more useful as it resembles the duration of some short surgical procedures such as cystoscopy. We were careful to record data for published lists over two separate time periods over the year, to avoid potential problems related to fluctuations in case mix, staffing, or absences due to staff leave over the year [18]. Some factors may have led us to overestimate the duration of lists. Our simple sum of the estimates for individual operations should yield the list duration, but list duration can sometimes be shorter if, for example, one anaesthetist is present to induce anaesthesia, and another anaesthetist awakens or recovers the previous patient [21]. Other factors may have led us to overestimate the cancellations. Some cancellations may instead have occurred for other reasons (e.g. medical), but by chance on a list that was over-booked. Furthermore, patients may have been postponed for other reasons before arriving in hospital, but their name somehow appeared in error on Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland 773

7 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Anaesthesia, 2006, 61, pages the published operating list: our methodology would have recorded this as a cancellation. Our mathematical analysis is relatively simple, Previous studies have used sophisticated techniques such as upper prediction bound analysis [22], bin packing algorithms and fuzzy constraints [23], and L1 regression [18]. Such complex tools may have enabled us to analyse our data in more detail, but a strength of our approach is that it is intuitive, relevant and readily applied by others. Indeed, Dexter & Macario have argued that a simple average of the past 39 durations for an operation, combined with surgeons mean estimates for that operation, yields a good measure of future operating times [11]. Why lists are over-booked We can only speculate on the reasons why as many as 50% of lists are predictably over-booked. Surgeons may experience pressure from managers to reduce waiting lists by adding more patients to an already full list. Surgeons who book fewer patients on their lists (albeit appropriately) may fear criticism (e.g. not working hard ) from their clinical colleagues [24]. We assumed that all surgeons book their own lists: it may be that in some other hospitals, non-clinical managers are now more directly involved in planning surgical lists, and so managers estimates may be more relevant. If surgeons are asked about the average time for a certain operation in a questionnaire, they may respond quite accurately (in agreement with estimates of other staff groups). However, they may feel that they themselves always perform better than average, so are justified in booking more patients than the norm. Intentionally over-booking a list might cause the team as a whole to work harder and our data suggests that this may be the case: although 50% of lists are predictably over-booked, only 34% suffered a cancellation. However, this is a very high cost strategy: 14% of booked patients were cancelled, which is unacceptable. Finally, lists may be booked more randomly and less by design, than we might suppose. Surgeons may (subconsciously) know how long a given operation will take, but they then do not consciously use this knowledge to plan the list. Why lists are under-booked We were surprised to find that about a third of lists were apparently under-booked. This may simply be because surgeons are poor at planning a list, and this leads to both frequent over-booking and under-booking. Some lists may have been intentionally under-booked to accommodate planned absences for meetings, etc. We might then have expected parallel reductions in allocation of anaesthetic nursing staff, but this did not occur. Some patients may have been cancelled for surgical or medical reasons after they arrived in hospital, but before the list was published. Since we analysed only the published list, this would have given the appearance of under-booking. A final explanation for apparent under-booking is that surgeons may have felt some particular routine operations would actually turn out to be more complex, and so allowed themselves more time. Again, our study design would not have detected this. Comparison with previous work Much of the work examining the management of operating lists has come from North America [1, 9 14, 18, 21 24]; UK data is quite sparse. Barr et al. reported that 21% of lists over-ran and 33% under-ran [25]. More recently, an analysis of general surgical lists in a district general hospital found that 56% of lists over-ran and 70% under-ran [19]. Over-booking contributed to 42% of over-runs, and both over-runs and under-runs could be reliably predicted [19], as in our current study. In a very large US study examining cases retrospectively, Gordon et al. found that 31% of lists were predictably over-booked and 30% predictably under-booked [26]. One important shortcoming of these studies is that they did not publish actual times for durations of specific operations. Thus, although their conclusions are broadly similar to our own, further detailed comparison is limited. The Audit Commission s report on operating theatres emphasised utilisation rate, defined as the time for which a set of operating theatres is used, as a proportion of the time for which it is available (a target of 92.5% was proposed) [4]. This target can be quite readily achieved (simply by the mathematics of averaging) enabling some hospitals to report utilisation rates > 100% (indicating regular, systematic over-runs) [4]. This will not help reduce cancellations. As we have seen in our current study, an under-running list does not compensate for an over-running list: our crude utilisation rate was 93.8%, which seems superficially acceptable. In a North American study, Wright et al. [18] compared the ability to predict the end-time of a surgical list using surgeons own estimates with those using computer-based estimates. However, they did not examine over-runs or patient cancellations (these notions may not have been relevant to their US model). They concluded (as we have done) that surgeons estimates of the likely duration of a list were similar to (and indeed a little more accurate) than computer estimates. In addition, they found that some surgical operations appear inherently more variable than others. Laparoscopic surgery has a co-efficient of variation of 42%, compared with hernia 774 Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland

8 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Table 5 Comparison of published times from three other sources with our own study (data from Tables 1 4). Times in minutes. Widdison* [19] Kendall et al. [28] Centers for Medicare and Medicaid Services*, This study (Tables 1 4) Breast lumpectomy Inguinal hernia repair Laparoscopic cholecystectomy Lymph node biopsy Unilateral varicose veins Anterior resection Mastectomy Cystoscopy Hemicolectomy *Only surgical times; anaesthesia and recovery times excluded. These times were obtained from data contained at: repair, abdominal hysterectomy and transurethral prostatectomy which are all more predictable with a coefficient of variation of just 4%. This suggests that any system which uses estimates of operation time to plan lists might be more accurate for the latter group of operations than the former. While many studies analyse different methods of operating list management, very few papers report actual data for the duration of common operations. Abouleish et al. have also observed that very little publicly accessible data exists on surgical duration [27]. Table 5 shows that, for the few data we have been able to retrieve, different publications generally agree on the operation times [19, 28]. This in turn suggests that it might indeed be possible to generate (within limits) universal measures for many common operations and use these to plan lists. Implications of the study for clinical practice Anecdotally, a number of factors are cited as being responsible for over-running lists (e.g. late starts, staff absence, variations in speed of operating or administering anaesthesia) [4, 24]. Our data suggest that there is actually seldom a reason to invoke any of these factors: overbooking is the main problem. Dexter et al. reached the similar conclusion that issues such as case turnover times have negligible impact on theatre efficiency [9]. We might plausibly use the data in Tables 1 4 to plan and manage operating lists, and it would be important to assess if this will reduce cancellations. These operating time data are also potentially useful for costing the service; a factor which is becoming more important with the introduction of Payment- By-Results in the National Health Service [29]. In brief, this complex scheme requires hospitals to know the costs of delivering procedures, as they will be reimbursed according to a single reference cost. The largest proportion of any hospital cost is invariably in staff salary [9, 13, 14, 28] and, therefore, procedure duration directly influences cost. Our data might help in calculating some average costs. Our data also have potential implications for the management of waiting lists. Traditionally, waiting lists are described in terms of the number of patients waiting for surgery (and for how long). A more relevant method might be to focus instead on the total time required to conduct the operations for which patients are waiting. For example, our data suggest that 100 patients added per month to a waiting list for a hernia repair will need 10 days of surgical operating capacity for hernias per month for the waiting list to remain static. Finally, it will be important for others in different surgical centres to repeat our approach to assess whether the times we present in Tables 1 4 are representative, or if they are instead more typical of a teaching hospital. References 1 Lacqua MJ, Evans JT. Cancelled elective surgery: an evaluation. American Surgeon 1994; 60: Ivarson B, Kimbald PO, Sjöberg T, Larsson S. Patient reactions to cancelled or postponed heart operations. Journal of Nursing Management 2002; 10: Rai M, Pandit JJ. Day of surgery cancellations after nurse-led preassessment in an elective surgical centre: the first 2 years. Anaesthesia 2003; 58: Audit Commission. Operating Theatres. Review of National Findings. London: HMSO, Audit Commission. Waiting for Elective Admission. London: HMSO, House of Common Public Accounts Committee. The Use of Operating Theatres in Northern Ireland. Health and Personal Social Services. Seventh Report of Session London: HMSO, Schofield WN, Rubin G, Piza M et al. Cancellation of operations on the day of intended surgery at a major Australian referral hospital. Medical Journal of Australia 2005; 182: Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland 775

9 J. J. Pandit & A. Carey Æ Estimating duration of common elective operations Anaesthesia, 2006, 61, pages Cegan PC. The easiest cut: managing elective surgery in the public sector. Medical Journal of Australia 2005; 182: Dexter F, Abouleish A, Epstein RH, Whitten CW, Lubarsky DA. Use of operating room information system data to predict the impact of reducing turnover times on staffing costs. Anesthesia and Analgesia 2003; 97: Overdyk FJ, Harvey SC, Fishman RL et al. Successful strategies for improving operating room efficiency at academic institutions. Anesthesia and Analgesia 1996; 85: Dexter F, Macario A. Applications of information systems to operating room scheduling. Anesthesiology 1999; 91: Dexter F, Epstein RH, Marsh HM. Statistical analysis of weekday operating room anesthesia group staffing at nine independently managed surgical suites. Anesthesia and Analgesia 2001; 92: Strum DP, Vargas LG, May JH et al. Surgical suite utilization and capacity planning: a minimal cost analysis model. Journal of Medical Systems 1997; 21: Strum DP, Vargas LG, May JH. Surgical subspecialty block utilization and capacity planning: a minimal cost analysis model. Anesthesiology 1999; 90: Pandit JJ. The new consultant contract and anaesthesia: practical implications of the new terminology. A personal view. Anaesthesia News 2003; 195: British Medical Association. The New NHS Consultant Contract (England), August London: BMA, Altman DG, Machin D, Bryant TN, Gardner MJ. Statistics with Confidence, 2nd edn. Bristol: JW Arrowsmith, BMJ Books, Wright I, Kooperberg C, Bonar B, Bashein G. Statistical modeling to predict elective surgery time: comparison with a computer scheduling system and surgeon-provided estimates. Anesthesiology 1996; 85: Widdison AL. Can we predict when an operating list will finish? Annals of the Royal College of Surgeons (Suppl.) 1995; 77: Durani P, Seagrave M, Neumann L. The use of theatre time in elective orthopaedic surgery. Annals of the Royal College of Surgeons (Suppl.) 2005; 87: Abouleish AE, Hensley SL, Zornow MH, Prough DS. Inclusion of turnover time does not influence identification of surgical services that over- and underutilize allocated block time. Anesthesia and Analgesia 2003; 96: Dexter F, Traub RD, Lebowitz P. Scheduling a delay between different surgeons cases in the same operating room on the same day using upper prediction bounds for case durations. Anesthesia and Analgesia 2001; 92: Dexter F, Macario A, Traub R. Which algorithm for scheduling add-on elective cases maximizes operating room utilization?: Use of bin packing algorithms and fuzzy constraints in operating room management. Anesthesiology 1999; 91: Abouleish AE. Responding to You re inefficient work faster!. American Society of Anesthesiologists Newsletter 2003; 67: Barr A, McNeilly RH, Rogers S. Use of operating theatres. British Medical Journal 1982; 285: Gordon T, Paul S, Lyles A, Fountain J. Surgical unit time utilization review: resource utilization and management implications. Journal of Medical Systems 1988; 12: Abouleish AE, Dexter F, Whitten CW, Zavaleta J, Prough DS. Quantifying net staffing costs due to longer-than-average surgical case durations. Anesthesiology 2004; 100: Kendell J, Wildsmith JAW, Gray IG. Costing anaesthetic practice. An economic comparison of regional and general anaesthesia for varicose vein and inguinal hernia surgery. Anaesthesia 2000; 55: Audit Commission. Introducing Payment by Results. Getting the Balance Right for the NHS and Taxpayers. London: HMSO, Journal compilation Ó 2006 The Association of Anaesthetists of Great Britain and Ireland