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British Journal of Anaesthesia
BJA

Frequency of surgical treatment and related hospital procedures in the UK: a national ecological study using hospital episode statistics

      Abstract

      Background

      Despite evidence of high activity, the number of surgical procedures performed in UK hospitals, their cost and subsequent mortality remain unclear.

      Methods

      Time-trend ecological study using hospital episode data from England, Scotland, Wales and Northern Ireland. The primary outcome was the number of in-hospital procedures, grouped using three increasingly specific categories of surgery. Secondary outcomes were all-cause mortality, length of hospital stay and healthcare costs according to standard National Health Service tariffs.

      Results

      Between April 1, 2009 and March 31, 2014, 39 631 801 surgical patient episodes were recorded. There was an annual average of 7 926 360 procedures (inclusive category), 5 104 165 procedures (intermediate category) and 1 526 421 procedures (restrictive category). This equates to 12 537, 8073 and 2414 procedures per 100 000 population per year, respectively. On average there were 85 181 deaths (1.1%) within 30 days of a procedure each year, rising to 178 040 deaths (2.3%) after 90 days. Approximately 62.8% of all procedures were day cases. Median length of stay for in-patient procedures was 1.7 (1.3–2.0) days. The total cost of surgery over the 5 yr period was £54.6 billion ($104.4 billion), representing an average annual cost of £10.9 billion (inclusive), £9.5 billion (intermediate) and £5.6 billion (restrictive). For each category, the number of procedures increased each year, while mortality decreased. One-third of all mortalities in national death registers occurred within 90 days of a procedure (inclusive category).

      Conclusions

      The number of surgical procedures in the UK varies widely according to definition. The number of procedures is slowly increasing whilst the number of deaths is decreasing.
      Editor's key points
      • Cost and other indicators of efficiency of healthcare are needed to better inform health policy and clinician decision-making
      • Definitions of ‘surgery’ and anaesthetic episodes vary widely; these greatly affect the denominator of any estimates of healthcare efficiency.
      • In the UK, as with most western countries, approximately one in ten people undergo a surgical procedure each year.
      • On average, postoperative mortality is decreasing each year.
      Despite advances in pharmacological therapies, the worldwide use of surgical treatments is thought to be increasing.
      • Weiser TG
      • Haynes AB
      • Molina G
      • et al.
      Estimate of the global volume of surgery in 2012: an assessment supporting improved health outcomes.
      • Weiser TG
      • Regenbogen SE
      • Thompson KD
      • et al.
      An estimation of the global volume of surgery: a modelling strategy based on available data.
      Due to the large volumes of activity, patient outcomes after surgery are a growing public health concern and an important focus of health research and policy.
      • Findlay GP
      • Goodwin APL
      • Protopapa K
      • Smith NCE
      • Mason M
      A review of the perioperative care of surgical patients. A report by the National Confidential Enquiry into Patient Outcome and Death.
      GlobalSurg Collaborative
      Mortality of emergency abdominal surgery in high-, middle- and low-income countries.
      • Khuri SF
      • Henderson WG
      • DePalma RG
      • et al.
      Determinants of long-term survival after major surgery and the adverse effect of postoperative complications.
      • World Health Organisation
      • Pearse RM
      • Harrison DA
      • James P
      • et al.
      Identification and characterisation of the high-risk surgical population in the United Kingdom.
      • Pearse RM
      • Moreno RP
      • Bauer P
      • et al.
      Mortality after surgery in Europe: a 7 day cohort study.
      However, initiatives to improve the quality of surgical care and subsequent patient outcomes have been hampered by the paucity of reliable audit data. Compared with diseases such as cancer and myocardial infarction, few countries regularly collate data describing the total number of surgical procedures, the associated mortality or healthcare costs. This limited understanding represents a key barrier to improving the safety and effectiveness of surgical treatments, and the planning of future service requirements.
      Crude global estimates suggest 312 million major surgical procedures were performed in 2012, an increase of one-third over eight years.
      • Weiser TG
      • Haynes AB
      • Molina G
      • et al.
      Estimate of the global volume of surgery in 2012: an assessment supporting improved health outcomes.
      However, these worldwide statistics may not be accurate at the individual country level. In England, published estimates of the total volume of surgery using healthcare registry data vary almost 10-fold from 1.6 to 11 million procedures each year.
      • Pearse RM
      • Harrison DA
      • James P
      • et al.
      Identification and characterisation of the high-risk surgical population in the United Kingdom.
      • Hospital Episode Statistics Analysis
      • Health and Social Care Information Centre
      Hospital Episode Statistics, Admitted patient Care 2013-2014.
      Meanwhile, the results of a prospective national census suggest 3 million anaesthetics are administered every year for surgery.
      • Cook TM
      • Woodall N
      • Frerk C
      • Fourth National Audit P
      Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia.
      Importantly, without consensus on the overall denominator of surgical procedures performed, postoperative mortality rates and healthcare costs remain impossible to calculate. This uncertainty is primarily due to wide variations in the definition of surgery used, making comparison difficult. A number of high volume procedures may be categorized very differently. Important examples include pacemaker insertion, endoscopy and interventional radiology procedures.
      There is a need for accurate data describing surgical activity, outcomes and cost in order to facilitate healthcare research, policy and delivery. We used National Health Service (NHS) registry data to estimate the annual number of surgical procedures in the UK. We used three alternative categorizations of surgery to demonstrate the effect of different definitions on estimates of surgical volume. Our secondary aims were to describe the all-cause mortality, length of hospital stay and healthcare costs associated with surgical treatments in each category, and the effect of alternative categorizations of surgery on these measures.

      Methods

       Study design

      This was a time-trend ecological study using summary national-level hospital episode data for the NHS in England, Scotland, Wales and Northern Ireland. Data from England, Wales and Scotland were available between April 1, 2009 and March 31, 2014. Data for Northern Ireland were available for the period April 1, 2012 to March 31, 2014. Full datasets were obtained for England and Wales. Length of stay data were not available for Scotland and mortality data were not available for Northern Ireland (Supplementary Table S1). The study was subject to institutional review, and was sponsored by Queen Mary University of London. Research ethics approval was not required as the study did not involve analysis of individual patient data.
      • National Research Ethics Service, Health Research Authority
      Does my project require review by a Research Ethics Committee?.

       Data sources

      Public bodies in each of the UK nations generate annual anonymous national summary data for utilization of hospital services, including the number of hospital procedures, which are publically available on their web sites. All episodes in these summary data are either: NHS funded and provided; NHS funded and privately provided; or privately funded and NHS provided. NHS Digital (formerly the Health and Social Care Information Centre) for England, NHS Wales Information Service for Wales and the Information Services Division Scotland for Scotland are able to link patient-level data to Office for National Statistics (ONS) records on request and subsequently provide anonymous national-level summary mortality data grouped by hospital procedure. The Department of Health, Social Services and Public Safety for Northern Ireland is unable to provide ONS-linked mortality data. The median length of hospital stay for each episode of hospital care associated with a procedure was only available for England, Wales and Northern Ireland.
      Hospital procedures are identified by staff at respective hospitals who assign an Office of Population Censuses and Surveys version 4 (OPCS4) code prior to entering the procedure into the dataset. Two very similar versions of OPCS4 codes (v4.6, 2009–11 and v4.7, 2011–4), were manually checked for compatibility and transcription errors prior to analysis. Data were managed using Microsoft Excel (Seattle, WA, USA).

       Categories of surgery

      All OPCS4 codes for hospital procedures were reviewed. We removed codes that were clearly not surgical in nature (e.g. radiotherapy, diagnostic imaging or oxygen therapy), and stratified the remaining codes according to three increasingly strict categories. The first ‘inclusive’ category comprised procedures that might be considered surgery, including minor surgery, interventional radiology procedures and diagnostic endoscopies, but excluding non-invasive diagnostic procedures (e.g. diagnostic imaging). The second ‘intermediate’ category included procedures routinely undertaken in an operating theatre and/or under general or regional anaesthesia. The third ‘restrictive’ category included major procedures that due to duration or complexity may often result in tissue injury. Three investigators (T.E.F.A., A.J.F., T.D.D.) independently reviewed all the OPCS4 codes and categorized them according to each category. Where unanimous agreement was not reached, a second round of independent review was carried out. Where agreement was not reached after two rounds, each code was discussed and referred to the senior investigator (R.M.P.) for final decision on inclusion.

       Number of surgical procedures

      We calculated the total number of procedures occurring in each country over the 5 yr period by summing the number of all procedures included in the respective categories. As data were not available for Northern Ireland before 2012, we imputed the number of procedures in Northern Ireland for the years 2009–11 using data from 2012 to 2013 to provide estimates of the total frequency and cost of surgery for the UK overall.

       Mortality

      We calculated the total number of deaths within 30, 60 and 90 days after procedures for each category in England, Scotland and Wales. We presented deaths as a proportion of procedures and as a proportion of total national deaths.

       Length of hospital stay and day-case procedures

      The national summary data tables include median hospital length of stay for each OPSC4 code, calculated by subtracting the date of admission from the date of discharge. This excludes admissions with zero days length of stay (i.e. day-case procedures). The total number of day-case admissions for each OPCS4 code is also listed. We calculated the total median hospital length of stay and summarized the total number of day-case admissions for each category of surgery.

       Cost

      To estimate the total cost of hospital procedures, we applied the NHS Payment by Results (PbR) tariff to the estimates of the number of procedures. As tariff is indexed using Healthcare Resource Groups (HRG), OPCS4 codes were matched to HRG, first by taking the commonest (mode) HRG for a given OPCS4 code and then by the most appropriate HRG where a modal match was not possible (A.J.F.). Matching was independently checked by a second investigator (T.E.F.A.). HRG groups without complication codes were selected to provide a conservative estimate of cost. We multiplied the tariff for each HRG by the number of hospital episodes to estimate the hospital cost of procedures, presented in Pounds Sterling (£) and US Dollars ($) according to the Bank of England conversion rate on March 31, 2014.

       Statistical analysis

      We used SPSS version 22 (IBM, New York, NY, USA) to analyse the data. Categorical variables were presented as frequency (%). Continuous variables were presented as mean (SD) for normally distributed data and median [inter-quartile range (IQR)] for non-normally distributed data. Length of hospital stay, which does not follow a normal distribution, was presented as median (IQR).
      • Abbott TE
      • Vaid N
      • Ip D
      • et al.
      A single-centre observational cohort study of admission National Early Warning Score (NEWS).
      Missing data were handled by list-wise deletion.

       Sensitivity analyses

      Firstly, in order to contextualize our categories of surgery, we repeated our analysis by categorizing our dataset using an alternative classification of surgery.
      • British United Provident Association
      BUPA Schedule of Procedures.
      We matched OPCS4 codes into the following categories: minor, intermediate, major, major plus, and complex major using previously published methods.
      • British United Provident Association
      BUPA Schedule of Procedures.
      • Gillies M
      • Harrison EM
      • Pearse RM
      • et al.
      Intensive care utilisation and outcomes after high-risk surgery in Scotland: a population based cohort study.
      We repeated the calculation of number of procedures, mortality, length of hospital stay and cost according to this alternative classification. Secondly, in order to evaluate the effect of missing mortality data for Northern Ireland, we estimated the annual total number of post-procedure deaths for the whole UK, including Northern Ireland. We multiplied the average annual procedure mortality for England, Scotland and Wales by the number of procedures for the whole UK (including Northern Ireland). As procedure frequency in Northern Ireland was not available before April 1, 2012, this analysis was restricted to the period April 1, 2012–March 31, 2014 and the mean calculated to estimate the annual number of deaths. Thirdly, to account for possible information bias due to retrospective application of the March 31, 2014 currency exchange rate in the cost analysis, we recalculated the conversions using the Bank of England exchange rates on March 31 each year.

      Results

      There were 1306 OPCS4 codes for hospital procedures. We included 1179 codes in the inclusive category of surgery, 1047 codes in the intermediate category and 553 codes in the restrictive category (Supplementary data, Fig. S1 and Tables S2–S5). There was a high rate of reviewer agreement, and only 2.9% (82/2779) were referred for review by a senior author (R.M.P.) for arbitration on inclusion. OPCS4 codes are made up of three characters and we provide these in parentheses following the name of the code below.

       Number of surgical procedures

      There were 39 631 801 (inclusive category) individual patient episodes associated with surgical procedures in the UK between April 1, 2009 and March 31, 2014. This represents an average of 7 926 360 (inclusive category), 5 104 165 (intermediate), 1 526 421 (restrictive) procedures per year, or 12 537, 8073 and 2414 respective procedures per 100 000 population per year. We present the frequency of hospital procedures performed in the UK per 100 000 population in the Supplementary data, Table S6. The total number of all procedures increased by 5.3% over the 5 yr period (inclusive category), by 4.2% using the intermediate category and by 6.5% using the restrictive category (Table 1). We present the 10 most common procedures over the 5 yr study period for each category in Table 2. Four of the most common procedures in the inclusive category were endoscopic, accounting for 7.8 million procedures (19.7%) over five years.
      Table 1Frequency of hospital procedures in the UK between April 1, 2009 and March 31, 2014. The number of procedures per year stratified by financial year and country for three categories of surgery: ‘inclusive’, ‘intermediate’ and ‘restrictive’. Data regarding the number of procedures were not available in Northern Ireland before April 1, 2012, so values for 2013–2 were used to estimate annual UK totals from 2009 to 2012. Numbers in parentheses are imputed
      Year2014–132013–122012–112011–102010–09Total
      England
          Inclusive7 025 9746 915 3806 845 2026 755 3166 597 89734 139 769
          Intermediate4 540 3714 418 7924 376 9824 402 1954 315 15822 053 498
          Restrictive1 366 8681 338 3581 276 6861 304 2411 267 0006 553 153
      Wales
          Inclusive339 946337 663336 665332 601348 3411 695 216
          Intermediate211 175211 368214 645210 883223 9621 072 033
          Restrictive64 22265 41166 67564 22067 606328 134
      Scotland
          Inclusive554 259551 953551 946552 589563 5482 774 295
          Intermediate366 659362 901358 595360 851368 2141 817 220
          Restrictive116 485115 704116 178117 646117 154583 167
      Northern Ireland
          Inclusive205 745204 194(204 194)(204 194)(204 194)1 022 521
          Intermediate116 470115 401(115 401)(115 401)(115 401)578 074
          Restrictive33 90333 437(33 437)(33 437)(33 437)167 651
      Total for England, Scotland and Wales
          Inclusive7 920 1797 804 9967 733 8137 640 5067 509 78638 609 280
          Intermediate5 118 2054 993 0614 950 2224 973 9294 907 33424 942 751
          Restrictive1 547 5751 519 4731 459 5391 486 1071 451 7607 464 454
      Total for UK
          Inclusive8 125 9248 009 1907 938 0077 844 7007 713 98039 631 801
          Intermediate5 234 6755 108 4625 065 6235 089 3305 022 73525 520 825
          Restrictive1 581 4781 552 9101 492 9761 519 5441 485 1977 632 105
      Table 2The 10 most frequent procedures included in each category (inclusive, intermediate, restrictive) over five years. Procedure code, total frequency shown and proportion of total volume over five years (%) are shown in parentheses
      RankInclusiveIntermediateRestrictive
      1Diagnostic upper gastrointestinal endoscopy (G45; 3 273 173; 8.3%)Prosthesis of lens (C75; 1 906 986; 7.5%)Cholecystectomy (J18; 409 612; 5.4%)
      2Prosthesis of lens (C75; 1 906 986; 4.8%)Excision of skin lesion (S06; 1 076 599; 4.2%)Total knee replacement with cement (W40; 390 309; 5.1%)
      3Diagnostic colonoscopy (H22; 1 835 537; 4.6%)Surgical removal of tooth (F09; 592 073; 2.3%)Spinal operations (V54; 287 629; 3.8%)
      4Diagnostic cystoscopy (M45; 1 510 160; 3.8%)Vitreous body procedures (C79; 514 780; 1.0%)Open reduction of fracture with extra-medullary fixation (W20; 261 500; 3.4%)
      5Diagnostic sigmoidoscopy (H25; 1 180 286; 3.0%)Caesarean section (R18; 505 495; 2.0%)Closed reduction of fracture with internal fixation (W24; 251 509; 3.3%)
      6Excision of skin lesion (S06; 1 076 599; 2.7%)Therapeutic endoscopy of semilunar cartilage (W82; 422 891; 1.7%)Excision of breast tissue (B28; 239 148; 3.1%)
      7Therapeutic colonoscopy (H20; 621 916; 1.6%)Cholecystectomy (J18; 409 612; 1.6%)Internal fixation of bone (W28; 213 096; 2.8%)
      8Surgical removal of tooth (F09; 592 073; 1.5%)Inguinal hernia repair (T20; 392 462; 1.5%)Emergency appendicectomy (H01; 210 691; 2.8%)
      9Joint aspiration (W90; 540 218; 1.4%)Angioplasty with stent insertion (K75; 391 724; 1.5%)Total hip replacement with cement (W37; 193 739; 2.5%)
      10Vitreous body procedures (C79; 514 780; 1.3%)Total knee replacement with cement (W40; 390 309; 1.5%)Hysterectomy (Q07; 184 072; 2.4%)

       Mortality

      Over five years, the mean 30-, 60- and 90-day post-procedure mortality rates in England, Scotland and Wales were: 425 904/38 609 280 (1.1%), 684 657/38 609 280 (1.8%) and 890 201/38 609 280 (2.3%) (inclusive category). Within 30 days after surgery, 1.1% of patients died according to the inclusive category, 1.0% according to the intermediate category and 1.5% died according to the restrictive category (Table 3). There was a consistent decrease in 30 day postoperative mortality (restrictive category), from 1.7% in 2009–10 to 1.3% in 2013–4 (Table 3). Similarly, the 90 day mortality rate decreased from 3.1% in 2009–10 to 2.5% in 2013–4 (Table 3 and Fig. 2). We present the 10 procedures with the highest crude 30 day mortality rate over five years for each category in the Supplementary data, Table S7. The procedure category with the highest mortality rate was pericardial procedures (L18), which carries a 34.1% risk of death within 30 days of surgery. The mortality rate associated with laparotomy (T30) was 19.0%. There were 169 procedure categories with a mortality rate ≥5%, representing 213 111 deaths over five years. As a proportion of national deaths, mortality within 90 days of a hospital procedure accounted for 32.3% (inclusive), 18.3% (intermediate) and 7.7% (restrictive) of deaths over five years (Table 4).
      Table 3Aggregate post-procedure mortality in England, Scotland and Wales between April 1, 2009 and March 31, 2014. The combined number of in-hospital and out of hospital deaths following hospital procedures in England, Scotland and Wales per financial year with crude (unadjusted) mortality rates as a proportion of the total number of procedures, stratified according to three categories of surgery. Data are presented as n (%) for 30, 60 and 90 day mortality, with a total across the 5 yr study period. Mortality data were not available for Northern Ireland
      Year2014–132013–122012–112011–102010–09Total
      30 day mortality, n (%)
          Inclusive82 979 (1.05)85 522 (1.10)85 357 (1.10)85 944 (1.12)86 102 (1.15)425 904 (1.10)
          Intermediate49 356 (0.96)51 208 (1.03)50 999 (1.03)51 966 (1.04)51 457 (1.05)254 986 (1.02)
          Restrictive20 408 (1.32)22 021 (1.45)22 331 (1.53)23 403 (1.57)23 897 (1.65)112 060 (1.50)
      60 day mortality n (%)
          Inclusive133 900 (1.69)137 749 (1.76)137 264 (1.77)137 793 (1.80)137 951 (1.84)684 657 (1.77)
          Intermediate76 639 (1.50)79 146 (1.59)78 491 (1.59)79 272 (1.59)78 483 (1.60)392 031 (1.57)
          Restrictive30 758 (1.99)33 113 (2.18)33 233 (2.28)34 615 (2.33)35 326 (2.43)167 045 (2.24)
      90 day mortality n (%)
          Inclusive174 620 (2.20)179 465 (2.30)178 378 (2.31)178 794 (2.34)178 944 (2.38)890 201 (2.31)
          Intermediate99 195 (1.94)101 940 (2.04)100 759 (2.04)101 148 (2.03)100 356 (2.05)503 398 (2.02)
          Restrictive39 222 (2.53)41 871 (2.76)41 942 (2.87)43 426 (2.92)44 443 (3.06)210 904 (2.83)
      Figure thumbnail gr2
      Fig 2Crude 90 day post-procedure mortality for England, Scotland and Wales during the period April 1, 2009–March 31, 2014, stratified by inclusive, intermediate and restrictive categories of surgery and shown in % on the left axis. Procedure frequency using the inclusive category shown on the right axis in multiples of 1 000 000 procedures. It is unclear whether the observed reduction in mortality rates between 2009 and 2014 reflect improvements in perioperative care or are an artefact of the increasing frequency of procedures.
      Table 4Post-procedure mortality as a proportion of National deaths. The combined number of in-hospital and out of hospital deaths following hospital procedures in England, Scotland and Wales per financial year as a proportion of the total number of deaths nationally (%), stratified according to three categories of surgery. Data are presented as n (%) for 30-day, 60-day and 90-day mortality are presented separately, with a total across the five-year study period. Mortality data were not available for Northern Ireland
      2014–20132013–20122012–20112011–20102010–2009Total
      National deaths555 663561 490554 268538 028547 2092 756 658
      Within 30 days after surgery, n (%)
          Inclusive82 979 (14.93)85 522 (15.23)85 357 (15.40)85 944 (15.97)86 102 (15.73)425 904 (15.45)
          Intermediate49 356 (9.12)51 208 (9.12)50 999 (9.20)51 966 (9.66)51 457 (9.40)254 986 (9.25)
          Restrictive20 408 (3.92)22 021 (3.92)22 331 (4.03)23 403 (4.35)23 897 (4.37)112 060 (4.07)
      Within 60 days after surgery n (%)
          Inclusive133 900 (24.10)137 749 (24.53)137 264 (24.76)137 793 (25.61)137 951 (25.21)684 657 (24.84)
          Intermediate76 639 (13.79)79 146 (14.10)78 491 (14.16)79 272 (14.73)78 483 (14.34)392 031 (14.22)
          Restrictive30 758 (5.54)33 113 (5.90)33 233 (6.00)34 615 (6.43)35 326 (6.46)167 045 (6.06)
      Within 90 days after surgery n (%)
          Inclusive174 620 (31.43)179 465 (31.96)178 378 (32.18)178 794 (33.23)178 944 (32.70)890 201 (32.29)
          Intermediate99 195 (17.85)101 940 (18.16)100 759 (18.18)101 148 (18.80)100 356 (18.34)503 398 (18.26)
          Restrictive39 222 (7.06)41 871 (7.46)41 942 (7.57)43 426 (8.07)44 443 (8.12)210 904 (7.65)

       Length of hospital stay and day-case procedures

      For the period April 1, 2012–March 31, 2014 median length of stay in England, Wales and Northern Ireland was 1.7 (IQR 1.3–2.0) days (inclusive category), 1.7 (IQR 1.3–2.0) days (intermediate) and 3.8 (IQR 3.6–4.0) days (restrictive). This excluded procedures with length of stay stated as zero days (i.e. day cases), which accounted for 4 688 661 (62.8%) (inclusive), 2 538 242 (52.8%) (intermediate) and 394 025 (27.2%) (restrictive) procedures per year. Median length of stay in England and Wales (restrictive) reduced from 5.0 (IQR 2.0–8.3) days in 2009–10 to 4.00 (IQR 2.0–7.8) days in 2013–4 (20.0%). We present the five procedures with the highest median length of stay for each category in the Supplementary data, Table S8. Open heart assistance procedures (K54) had the longest length of stay [42.0 (40.0–43.0) days] in the restrictive category.
      Figure thumbnail gr1
      Fig 1Flow diagram showing Office of Population Censuses and Surveys version 4 (OPCS4) codes included in each category of surgery (inclusive, intermediate or restrictive).

       Cost of surgery

      The estimated total cost of hospital procedures in the UK over five years was £54 631 317 163 ($104 389 947 396), representing an average annual cost of £10 926 263 433 (inclusive), £9 508 213 884 (intermediate) and £5 550 530 996 (restrictive). We present the five procedures attracting the largest aggregate payments over five years, and the number of procedures performed in the Supplementary data, Table S9. Orthopaedic procedures, including spinal surgery (V54), total knee (W40) replacement, and open (W20, W19) and closed (W24) reduction of fractures accounted for £8 785 890 035/54 631 317 163 (16.1%) of the total cost of surgery. The estimated total cost of procedures in the inclusive category in 2009–10 was £10 471 024 463 ($15 848 942 627) compared wth £11 056 095 814 ($18 424 983 674) for 2013–4. This represents a 5.6% increase over five years.

       Sensitivity analysis

      We matched OPCS4 codes to British United Provident Association (BUPA) codes using a previously published method.
      • Gillies M
      • Harrison EM
      • Pearse RM
      • et al.
      Intensive care utilisation and outcomes after high-risk surgery in Scotland: a population based cohort study.
      We were unable to match 371 codes. There were 171 minor procedure codes, 219 intermediate, 272 major, 108 major plus and 159 complex major. We applied BUPA codes to the national NHS dataset. Using this classification there were a total of 7 520 256 procedures and 85 419 (1.2%) deaths within 30 days of a procedure per year. The average median length of stay was 2.8 days and average total cost was £9 800 407 961 per year (Table 5). When we applied the average 30 day post-procedure mortality rate for England, Scotland and Wales to the average UK frequency estimate, the mean annual number of deaths was 86 231 (inclusive), 51 305 (intermediate) and 21 710 (restrictive). When we repeated the currency conversions using the Bank of England exchange for each financial year, the results were similar.
      Table 5Summary of hospital procedure frequency, mortality (%), median length of hospital stay (days) and cost to National Health Service (NHS) providers (£) stratified by British United Provident Association (BUPA) procedure severity grading. Office of Population Censuses and Surveys version 4 (OPCS4) codes were matched to BUPA codes. Frequency and cost were presented as total over five years and average annual total for the UK. Deaths within 30 days of surgery presented as total over five years with average percentage mortality for England, Scotland and Wales. Length of stay presented as annual median for England, Wales and Northern Ireland
      BUPA gradingFrequency (total)Frequency (annual)Total deaths (%)Median length of stayCost (total) £Cost (annual) £
      Minor11 414 356.02 282 871185 907 (1.7)1.06 297 244 6741 259 448 935
      Intermediate14 045 849.02 809 170128 529 (0.9)1.012 298 560 4622 459 712 092
      Major8 909 387.01 781 87768 008 (0.8)2.015 213 166 6523 042 633 330
      Major plus2 041 560.0408 31220 225 (1.0)3.010 207 671 6962 041 534 339
      Complex major1 190 126.0238 02524 428 (2.1)7.04 985 396 319997 079 264
      Total37 601 278.07 520 256427 097 (1.2)49 002 039 8039 800 407 961

      Discussion

      The principal finding of this study was that surgery accounts for more than 39 million individual patient episodes in the UK over five years and the annual number of procedures is increasing year on year. The number of procedures is dependent on the definition used, ranging from 7.9 million per year for the most inclusive category to 1.5 million per year for the most restrictive. This is less than the largest previous estimates of national surgical volume.
      • Hospital Episode Statistics Analysis
      • Health and Social Care Information Centre
      Hospital Episode Statistics, Admitted patient Care 2013-2014.
      Equivalent to one-in-10 members of the UK population undergo a surgical procedure every year, and equivalent to one-third of all UK deaths occur within the three months following a hospital procedure. Post-procedure mortality rates appear to be decreasing year on year; however, this still represents almost nine-hundred-thousand deaths over five years. We are unable to say whether these deaths are attributable to surgery or if they are preventable because these data represent all-cause mortality. However, it raises questions about whether there are opportunities to intervene in the perioperative care pathway to further patient benefit, and to what degree life expectancy influences the decision of doctors and patients to proceed with invasive procedures. Given the high procedure volume, total annual cost of surgery (£11 billion) accounts for a substantial portion (9.4%) of the total NHS budget (£117 billion for 2013–4).

      Information Services Division Scotland. Scottish health Service Costs—Year ended 31 March 2014. 2015.

      NHS Wales. NHS Expenditure by Budget Category and Year 2013-2014. 2015.

      Legistlation.gov.uk Budget Act (Northern Ireland) 2014. 2014.

      • NHS England
      This estimate does not include spending on associated outpatient appointments, investigations or treatment for post-procedure complications.
      This is the first investigation, of which we are aware, to estimate the total number of surgical procedures across all four nations of the UK. Our findings are consistent with previous reports, which suggest that between 1.6 and 11 million procedures are performed in England each year.
      • Pearse RM
      • Harrison DA
      • James P
      • et al.
      Identification and characterisation of the high-risk surgical population in the United Kingdom.
      • Hospital Episode Statistics Analysis
      • Health and Social Care Information Centre
      Hospital Episode Statistics, Admitted patient Care 2013-2014.
      However, these studies were probably targeted at different patient populations (e.g. the estimate of 1.6 million procedures was likely focused on major surgery according to our restrictive category).
      • Pearse RM
      • Harrison DA
      • James P
      • et al.
      Identification and characterisation of the high-risk surgical population in the United Kingdom.
      Three million general anaesthetics were administered during the National Audit Project-4 (NAP-4) audit of airway management and this would account for around two-thirds of the intermediate category, which included procedures typically performed under regional or general anaesthesia.
      • Cook TM
      • Woodall N
      • Frerk C
      • Fourth National Audit P
      Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia.
      Similarly, accepted global estimates of the frequency of surgery suggest that in high-income countries over 11 000 procedures are performed annually per 100 000 head of population.
      • Weiser TG
      • Haynes AB
      • Molina G
      • et al.
      Estimate of the global volume of surgery in 2012: an assessment supporting improved health outcomes.
      • Weiser TG
      • Regenbogen SE
      • Thompson KD
      • et al.
      An estimation of the global volume of surgery: a modelling strategy based on available data.
      When considered in the context of our data, many procedures included in these estimates may not be considered as surgery by many clinicians. The term ‘surgery’ may mean very different things to different stakeholders, such as clinicians, researchers, policy makers and patients. The absence of a standard vocabulary is unhelpful and promotes confusion. There may be international differences in what is considered ‘surgery’ (e.g. in some countries, regional analgesia for non-instrumental delivery during childbirth would be considered a surgical procedure whereas in other countries it would not). We did not include non-instrumental delivery in any category. Our estimates of procedural mortality are consistent with previous estimates (0.5–4.0%) and are likely to be among the most accurate estimates of postoperative mortality in the UK.
      • Pearse RM
      • Harrison DA
      • James P
      • et al.
      Identification and characterisation of the high-risk surgical population in the United Kingdom.
      • Pearse RM
      • Moreno RP
      • Bauer P
      • et al.
      Mortality after surgery in Europe: a 7 day cohort study.
      • Abbott TE
      • Ackland GL
      • Archbold RA
      • et al.
      Preoperative heart rate and myocardial injury after non-cardiac surgery: results of a predefined secondary analysis of the VISION study.
      • Vascular Events In Noncardiac Surgery Patients Cohort Evaluation Study I
      • Devereaux PJ
      • Chan MT
      • et al.
      Association between postoperative troponin levels and 30-day mortality among patients undergoing noncardiac surgery.
      • International Surgical Outcomes Study group
      Global patient outcomes after elective surgery: Prospective cohort study in 27 low, middle and high income countries.
      The mortality rate for laparotomies was 19%, which is consistent with other observations for this patient group.
      • Al-Temimi MH
      • Griffee M
      • Enniss TM
      • et al.
      When is death inevitable after emergency laparotomy? Analysis of the American College of Surgeons National Surgical Quality Improvement Program database.
      • Saunders DI
      • Murray D
      • Pichel AC
      • Varley S
      • Peden CJ
      • Network UKEL
      Variations in mortality after emergency laparotomy: the first report of the UK Emergency Laparotomy Network.
      • Symons NR
      • Moorthy K
      • Almoudaris AM
      • et al.
      Mortality in high-risk emergency general surgical admissions.
      • Vester-Andersen M
      • Lundstrom LH
      • Moller MH
      • et al.
      Mortality and postoperative care pathways after emergency gastrointestinal surgery in 2904 patients: a population-based cohort study.

      NELA project team. First patient report of the National Emergency Laparotomy Audit RCoA London, 2015.

      We identified a consistent decreasing trend in mortality rates over five years. However, it is unclear whether this represents a true reduction in mortality, because of improved patient care and perioperative risk assessment, or whether this is a statistical artefact of an increased number of low-risk procedures (denominator).
      • James S
      • Jhanji S
      • Smith A
      • O'brien G
      • Fitzgibbon M
      • Pearse RM
      Comparison of the prognostic accuracy of scoring systems, cardiopulmonary exercise testing, and plasma biomarkers: a single-centre observational pilot study.
      • Wijeysundera DN
      • Pearse RM
      • Shulman MA
      • et al.
      Measurement of Exercise Tolerance before Surgery (METS) study: a protocol for an international multicentre prospective cohort study of cardiopulmonary exercise testing prior to major non-cardiac surgery.
      The magnitude of the difference between 30 day and 90 day mortality rates is striking, suggesting much greater emphasis should be placed on 90 day postoperative mortality as a clinical outcome measure. The median length of hospital stay (restrictive category) was 3.8 days, with a reducing trend over five years. We were unable to investigate the influence of complications on hospital length of stay in this study.
      This study has several strengths. We used summary data for all hospital procedures undertaken by NHS providers across the UK. Therefore, our results represent the majority of surgery undertaken nationally over the 5 yr period of interest, which makes these data generalizable to the entire UK population. In contrast to previous reports using similar source data, we adopted three transparent consensus categories of surgery to reflect the variety of opinions regarding what constitutes surgery. Our categories of surgery are available in the Supplementary data (Tables S2–S5) and we hope others will expand on this work. The mortality data were generated through linkage to the ONS death register. Therefore, the mortality rates represent all deaths in the UK within the allotted time period, not just in-hospital mortality, which has been a key limitation of previous epidemiological studies.
      • Pearse RM
      • Moreno RP
      • Bauer P
      • et al.
      Mortality after surgery in Europe: a 7 day cohort study.
      • Vascular Events In Noncardiac Surgery Patients Cohort Evaluation Study I
      • Devereaux PJ
      • Chan MT
      • et al.
      Association between postoperative troponin levels and 30-day mortality among patients undergoing noncardiac surgery.
      This study also has several limitations. This was an ecological study using group-level data. We were not able to undertake patient-level multivariable statistical modelling or risk adjustment.
      • Fowler AJ
      • Ahmad T
      • Phull MK
      • Allard S
      • Gillies MA
      • Pearse RM
      Meta-analysis of the association between preoperative anaemia and mortality after surgery.
      • Prowle JR
      • Kam EP
      • Ahmad T
      • Smith NC
      • Protopapa K
      • Pearse RM
      Preoperative renal dysfunction and mortality after non-cardiac surgery.
      Hospital episode data rely on clinicians and coders at each hospital to record details about individual patient admissions. The accuracy and completeness of data coding, as well as clinical care, is likely to vary between hospitals and between individuals at each hospital, which may introduce information bias.
      • Gillies MA
      • Power GS
      • Harrison DA
      • et al.
      Regional variation in critical care provision and outcome after high-risk surgery.
      • Ozdemir BA
      • Sinha S
      • Karthikesalingam A
      • et al.
      Mortality of emergency general surgical patients and associations with hospital structures and processes.
      There is a possibility that a patient who had multiple admissions for procedures and died may be double counted in the mortality estimate. Where multiple procedures occur in one admission, the hospital episode is coded according to the predominant procedure, so this analysis may underestimate the total number of procedures. The source data represent all hospital procedures provided or funded through the NHS, but does not include procedures provided and paid for privately. We approached private providers in order to estimate the volume of private surgery in the UK, but this was unsuccessful. We prospectively created three categories of surgery and categorized OPCS4 codes by consensus. This is inherently subjective and not all clinicians or researchers will agree with our interpretation. Restrictions regarding public availability of hospital episode data in Northern Ireland mean that the primary analysis did not include data from Northern Ireland before 2012 and the mortality analysis did not include deaths in Northern Ireland. However, we do not believe this has a significant effect on the generalizability of the results to the UK population. Cost data were generated by linking OPCS4 codes to the commonest (modal) HRG code for that procedure and multiplying these by the PbR tariff. Standard methodology for health economic analysis uses PbR tariff.
      • Pearse RM
      • Abbott TE
      • Haslop R
      • et al.
      The Prevention of Respiratory Insufficiency after Surgical Management (PRISM) Trial. Report of the protocol for a pragmatic randomized controlled trial of CPAP to prevent respiratory complications and improve survival following major abdominal surgery.
      However, tariff represents the payment to the provider (hospital), which is not necessarily the same as the actual cost.
      • Abbott T
      • White SM
      • Pandit JJ
      Factors affecting the profitability of surgical procedures under ‘Payment by Results’.
      Payments to hospitals can be increased through the use of postoperative complications codes and through national or local adjustment of tariff.
      • Abbott TE
      • Pearse RM
      Saving money: an ideal driver for improved perioperative care?.
      We did not attempt to attribute an excess cost to patients with complications codes, and our approach therefore provides a conservative estimate of income to hospitals for care provided. Finally, we presented the mortality data as crude (unadjusted) incidence rates because we did not have access to mortality data stratified by age in order to perform age standardization. As it was not our intention to make comparisons between countries, or make inferences regarding exposures that might influence postoperative mortality, we do not think this influences our interpretation.

      Conclusions

      A very large number of hospital procedures are performed in the UK every year, representing a significant proportion of NHS activity, expenditure and mortality. However, the total number of procedures is sensitive to the definition of surgery used. Universal and clinically relevant definitions of surgery are required for coordinated research, healthcare policy and planning. Further research is needed to better understand the population undergoing major surgery, who are the primary focus of perioperative medicine, and procedures undertaken in the last year of life.

      Authors' contributions

      Developed the analysis plan: T.E.F.A., A.J.F., M.A.G., R.M.P.
      Extracted the data: T.E.F.A., A.J.F., T.D.D.
      T.E.F.A. performed the data analysis with input from A.J.F., R.M.P.
      The manuscript was drafted by T.E.F.A., A.J.F., R.M.P., and revised following critical review by all authors.

      Declaration of interest

      E.M.H. has served on an advisory board for GSK. R.M.P. holds research grants, and has given lectures and/or performed consultancy work for GSK, Nestle Health Sciences, BBraun, Medtronic and Edwards Lifesciences, and is a member of the Associate editorial board of the British Journal of Anaesthesia; there are no other relationships or activities that could appear to have influenced the submitted work. All other authors declare no conflict of interests.

      Funding

      T.E.F.A. is supported by a Medical Research Council and British Journal of Anaesthesia clinical research training fellowship (grant reference MR/M017974/1), and R.M.P. is supported by an NIHR research professorship. T.D.D. is funded by the Welsh Clinical Academic Training (WCAT) Fellowship. M.A.G. is a Chief Scientist Office (Scotland) NHS Research Scheme Clinician.

      Patient and public involvement

      This article addresses several key research areas identified in the recent James Lind Alliance Priority Setting Partnership for perioperative medicine, in which patients played an active role. The research proposal was reviewed by the Patient, Public and Carer Involvement group at the Royal College of Anaesthetists Health Services Research Centre, which provided feedback during both development and design phases.

      Supplementary Material

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