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Special Article |

The POSSUM System of Surgical Audit FREE

Graham Paul Copeland, ChM
[+] Author Affiliations

From the Department of Surgery, Warrington Hospital, Warrington, England.


Arch Surg. 2002;137(1):15-19. doi:10.1001/archsurg.137.1.15.
Text Size: A A A
Published online

Surgical audit is not a new phenomenon. As early as 1750 BC, King Hammurabi of Babylon issued decrees for the punishment of negligent physicians, particularly surgeons. In such a decree discovered at Susa in Iran and inscribed on a 2-m-high black diorite stone, Hammurabi states that:

If a doctor inflicts a serious wound with his operation knife on a free man's slave and kills him, the doctor must replace the slave with another. If a doctor has treated a free man but caused a serious injury from which the man dies, or if he has opened an abscess and the man goes blind, the man is to cut off his hands.

Not surprisingly, internal medicine rather than surgery was popular at that time. Indeed, to many surgeons today, this edict still seems to be exacted in a sublimated way.

The outcome of surgical intervention, whether death or uncomplicated survival, complications, or long-term morbidity, is not solely dependent on the abilities of the surgeon in isolation. The patient's physiological status, the disease that requires surgical correction, the nature of the operation, and the preoperative and postoperative support services have a major effect on the ultimate outcome. It is evident to surgeons worldwide that raw mortality and morbidity rates do little to expound these differences, and that the use of such statistics is at best inaccurate and at worst dangerous. When taken to an extreme, mortality rates can achieve what appears to be a self-fulfilling prophecy. The unit that selects only low-risk cases achieves a low mortality rate and therefore attracts more patients, perhaps undeservedly, whereas the unit that cannot select only low-risk cases is left with a worsening case mix, and their performance as judged by mortality rate will appear to deteriorate still further over time.

With this in mind, during the 1980s a system was developed to allow for the first time an assessment of surgical quality that was risk adjusted for the patient's acute and chronic physiological status and for the nature of the operation. By using a process of multivariate discriminant analysis, a scoring system was developed that could accurately predict 30-day mortality and morbidity rates. The POSSUM audit system (Physiological and Operative Severity Score for the Enumeration of Mortality and Morbidity)1 was designed to be easy and rapid to use and to have wide application across the general surgical spectrum, both in the elective and emergency settings, and to be applicable in most health care systems.26

The POSSUM system is a 2-part scoring system that includes a physiological assessment and a measure of operative severity. The physiological part of the score includes 12 variables, each divided into 4 grades with an exponentially increasing score (1, 2, 4, and 8) (Figure 1). The physiological variables are those apparent at the time of surgery and include clinical symptoms and signs, results of simple biochemical and hematological investigations, and electrocardiographic changes. If a particular variable is not available, a score of 1 is allocated. Some variables may be assessed by means of clinical symptoms or signs or by means of changes on chest radiographic findings. The minimum score, therefore, is 12, with a maximum score of 88.

Place holder to copy figure label and caption
Figure 1.

Physiological and operative severity assessment for the POSSUM system (Physiological and Operative Severity Score for the Enumeration of Mortality and Morbidity). In some variables, signs may be assessed clinically and/or by changes in results on chest x-ray film (CXR). Ellipses indicate not applicable; JVP, jugular venous pressure; UTI, urinary tract infection; SOB, shortness of breath; PUO, pyrexia of unknown origin; COAD, chronic obstructive airway disease; Mod, moderate; BP, blood pressure; DVT, deep venous thrombosis; PE, pulmonary embolism; CVA, cerebrovascular accident; MI, myocardial infarction; Na, sodium; DOB, date of birth; K, potassium; Hb, hemoglobin; WCC, white blood cell count; ECG, electrocardiogram; and AF, atrial fibrillation.

Graphic Jump Location

The operative severity part of the score includes 6 variables, each divided into 4 grades with an exponentially increasing score (1, 2, 4, and 8) (Figure 1). The number of operations indicates the chronology of the procedure(s) within 30 days. Examples of surgical magnitude for general surgery are shown in Table 1.

Table Graphic Jump LocationTable 1. Examples of Magnitude for General Surgery*

Once these scores are known, it is possible to estimate the predicted risk for mortality and morbidity using the following equations (where R1 indicates mortality and R2, morbidity): and Although at first sight complex, a patient score can be obtained with practice in 90 seconds, and commercially available computer packages can be used to estimate risk instantly (even manual estimation takes only 60 seconds). We have recently validated an orthopedic POSSUM system that uses the same physiological assessment and predictive equations but has a modified operative severity score (Figure 2). Examples of operative magnitude for orthopedic surgery are shown in Table 2.

Place holder to copy figure label and caption
Figure 2.

Orthopedic score sheet for the POSSUM system. Abbreviations are defined in the legend to Figure 1.

Graphic Jump Location

Table Graphic Jump LocationTable 2. Examples of Operative Magnitude for Orthopedic Surgery

Individualized patient predictions allow assessment of a patient's risk for death or complication. They also allow a retrospective assessment as to whether a procedure was reasonable to attempt. However, as the operative severity score is not available until the operation has been undertaken, the POSSUM score cannot be used to prevent a patient from undergoing a potentially curative procedure. Although the POSSUM system was designed specifically not to be used as a "futility index," it is possible to select a combination of scores for which a more senior opinion must be sought before surgical intervention. As the POSSUM system uses a logistic model, predictions of less than 0% and greater than 100% are impossible. This model more closely approximates the clinical situation, in which we can never be certain that a patient will survive or die after surgery. Predictions beyond these extremes (<0% and >100%), however, are possible if linear models are used, and this is a major danger of the Portsmouth POSSUM adaptation.7 However, within the normal range, both a linear and a logistic model will yield similar results if the appropriate mathematical methods are used.8

Surgical procedures for patients with predictions of mortality exceeding 95% rarely result in a successful outcome. Whatever the findings of the audit of "surgical success," the patient with a high prediction of death or complication but for whom no such adverse outcome occurs often has more to teach us than our failures. In my own unit, such a success audit has identified groups of patients, in particular the high-risk patient with a perforated viscus, in whom more rapid resuscitation and surgery can produce better outcomes.9 This group of patients certainly does not benefit from prolonged attempts at resuscitation without rapid surgical intervention.

By using the predictions from individual patients, it is possible to extrapolate from groups of patients the likely number of adverse outcomes and thus obtain a risk-adjusted quality measure. This measure, the ratio of observed number of adverse outcomes to predicted number of adverse outcomes (O/E ratio), can be used to assess differences between surgeons and to observe changes over time. A ratio of 1.00 indicates average performance; greater than 1.00, performance worse than expected; and less than 1.00, performance better than expected.5 These definitions remain the mainstay of application of the O/E ratio in general surgery, although models have been designed recently that use the POSSUM system to assess risk-adjusted length of hospital stay for comparative purposes.10

Using the O/E ratio, we can assess overall surgeon performance across the whole range of general and orthopedic surgery. Examples of variability in mortality and morbidity rates, with their attendant O/E ratios, are shown for one unit in Table 3. This clearly demonstrates the danger of using raw mortality and morbidity rates for comparative audit. Not surprisingly, vascular surgeons have a higher mortality rate; gastroenterological surgeons, the highest morbidity rate; and urologic surgeons, the lowest mortality and morbidity rates. The POSSUM system has found wide application for such comparative purposes, having been used in a wide variety of surgical subspecialities ranging from vascular surgery3 to gastroenterology4 and coloproctology,11,12 and to more specialized areas such as bariatric surgery13 and lung resection.14 Examples of its use in orthopedic surgery are illustrated in Table 4. The POSSUM system has also been found to have wide application in greatly varying health care systems throughout the world (Table 5).

Table Graphic Jump LocationTable 3. Raw and Risk-Adjusted Outcome Measures for 12 Months in One Unit*

Table Graphic Jump LocationTable 4. Variability in Raw and Risk-Adjusted Outcome Data in Orthopedic Surgery During 12 Months*

Table Graphic Jump LocationTable 5. Examples of the Application of the POSSUM System Between Units in Countries With Varying Numbers of Patients per Annum and Variable Case Mix*

All predictions will have confidence limits dependent on the number of operations performed and on the number of adverse outcomes. Overreaction should be avoided, and the cause of deficiencies in quality should be carefully examined. In a published data set from my own unit, an apparent deficiency in one surgeon was due to a process change at ward level in anticoagulation prophylaxis administration.5 This was rapidly identified and corrected with minimal morbidity overall and without penalizing the surgeon inappropriately. Variation in outcome will occur over time, but if deteriorating O/E ratios can be identified early, remedial action can be taken. Early trend analysis for morbidity can identify early downturns in performance before this is replaced with mortality. Sudden death after surgery is a rare event, and death usually follows a series of antecedent complications. This fact is often forgotten by systems that assess death only as an end point, and is perhaps one of the major advantages of the POSSUM system over other audit scoring systems.6,15

The POSSUM system can assess differences between individual units and departments and allow comparison over time. Table 6 illustrates minor variations in O/E ratio over time in one surgeon's performance, but more major variation can also occur. Table 7 illustrates a downturn in performance within one unit, which on closer inquiry was associated with an increase in morbidity, in particular renal and respiratory complications. This appeared to correlate with a sudden local decrease in availability of intensive care unit beds and resulted in a need to transfer patients to neighboring hospitals. In the transferred group, the O/E ratio was 1.60; in the resident group, the O/E ratio was 0.98. Corrective action was rapidly taken, with a subsequent fall in O/E ratio to acceptable levels. Surgery and in particular resuscitative measures are never static over time. An increasing number of units in North America and Europe are identifying the benefits of preoperative and perioperative resuscitation in high-risk patients.1618 With a mortality risk between 20% to 80%,this group of patients has the most to gain from optimization. The POSSUM system can allow for changes over time in our medical treatment. If care should improve significantly, O/E ratios will fall worldwide and simple adjustments in the logistic regression equations can be made to continue to allow comparison over time. Unfortunately, no equation adjustment has been necessary during the past 10 years. At first glance, this may appear disappointing, but on closer review, the number of procedures being performed in the high-risk patient group has steadily increased during the past 3 years. In England, there has been a 30% increase in procedures in patients whose risk for death exceeds 20% and a 12% increase in procedures in patients whose risk exceeds 40.

Table Graphic Jump LocationTable 6. Variations in Annual Performance of One Surgeon During 6 Years*

Table Graphic Jump LocationTable 7. Effect of Intensive Care Unit Bed Availability on Risk-Adjusted Outcome of Operative Intervention in One Unit*

The POSSUM system, therefore, offers many differing facets. It allows a numerical prediction of mortality and morbidity for an individual patient. It allows comparative audit providing a method of adjustment of case mix. It allows comparison to be made over time and can be easily adjusted to radical changes in health care in the future. Only by using systems of this type will the comparative audit become a reality rather than a fantasy19,20 and, for the first time, will the public and the medical profession trust in outcome measures. Hammurabi's methods have been in operation for 4000 years; perhaps now is the time to change.

ARTICLE INFORMATION

Corresponding author and reprints: Graham Paul Copeland, ChM, Warrington Hospital, Lovely Lane, Warrington, Cheshire WA5 1QG, England.

Copeland  GPJones  DWalters  M POSSUM: a scoring system for surgical audit. Br J Surg. 1991;78355- 360
Link to Article
Jones  HJSde Cossart  L Risk scoring in surgical patients. Br J Surg. 1999;86149- 157
Link to Article
Copeland  GPJones  DWilcox  AHarris  PL Comparative vascular audit using the POSSUM scoring system. Ann R Coll Surg Engl. 1993;75175- 177
Sagar  PMHartley  MNMacFie  JTaylor  BACopeland  GP Comparison of individual surgeon's performance. Dis Colon Rectum. 1996;39654- 658
Link to Article
Copeland  GPSagar  PBrennan  J  et al.  Risk adjusted analysis of surgeon performance. Br J Surg. 1995;82408- 411
Link to Article
Copeland  GP Assessing the surgeon: 10 years experience with the POSSUM system. J Clin Excellence. 2000;2187- 190
Prytherch  DWhiteley  MSHiggins  BWeaver  PCProut  WGPowell  SJ POSSUM and Portsmouth POSSUM for predicting mortality. Br J Surg. 1998;851217- 1220
Link to Article
Wijesinghe  LDMahmood  TScott  DLABerridge  DCKent  PJKester  RC Comparison of POSSUM and the Portsmouth predictor equation for predicting death following vascular surgery. Br J Surg. 1998;85209- 212
Link to Article
McIlroy  BMiller  ACopeland  GPKiff  R Audit of emergency preoperative resuscitation. Br J Surg. 1994;811492- 1494
Link to Article
Copeland  GPBrett  MMcIlroy  BNathwami  DWard  J Predicting length of stay in general surgery. Health Trends. 1997;2915- 18
Tekkis  PPKocher  HMBentley  AJ  et al.  Operative mortality rates among surgeons: comparison of POSSUM and p-POSSUM scoring systems in gastrointestinal surgery. Dis Colon Rectum. 2000;431528- 1532
Link to Article
Wang  TKTu  HH Colorectal perforation with barium enema in the elderly: case analysis with the POSSUM scoring system. J Gastroenterol. 1998;33201- 205
Link to Article
Cajigas  JCEscalante  CFIngelmo  A Application of the POSSUM system in bariatric surgery. Obes Surg. 1999;9279- 281
Link to Article
Brunelli  AFianchini  AXiume  FGesuita  RMattei  ACarle  F Evaluation of the POSSUM scoring system in lung surgery. Thorac Cardiovasc Surg. 1998;46141- 146
Link to Article
Gotohda  NIwagaki  HItano  S Can POSSUM, a scoring system for perioperative surgical risk, predict postoperative clinical course? Acta Med Okayama. 1998;52325- 329
Shoemaker  WCAppel  PLKram  HBWaxman  KLee  T Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients. Chest. 1988;941176- 1186
Link to Article
Boyd  OGrounds  RMBennett  ED A randomized clinical trial of the effect of deliberate perioperative increase in oxygen delivery on mortality in high-risk surgical patients. JAMA. 1993;2702699- 2707
Link to Article
Wilson  JWoods  IFawcett  J  et al.  Reducing the risk of major elective surgery: randomised controlled trial of preoperative optimisation of oxygen delivery. BMJ. 1999;3181099- 1103
Link to Article
Copeland  GP Surgical scoring, risk assessment and the surgeon. J R Coll Surg Edinb. 1992;37145- 148
Copeland  GP Comparative audit: fact versus fantasy. Br J Surg. 1993;801424- 1425
Link to Article

Figures

Place holder to copy figure label and caption
Figure 1.

Physiological and operative severity assessment for the POSSUM system (Physiological and Operative Severity Score for the Enumeration of Mortality and Morbidity). In some variables, signs may be assessed clinically and/or by changes in results on chest x-ray film (CXR). Ellipses indicate not applicable; JVP, jugular venous pressure; UTI, urinary tract infection; SOB, shortness of breath; PUO, pyrexia of unknown origin; COAD, chronic obstructive airway disease; Mod, moderate; BP, blood pressure; DVT, deep venous thrombosis; PE, pulmonary embolism; CVA, cerebrovascular accident; MI, myocardial infarction; Na, sodium; DOB, date of birth; K, potassium; Hb, hemoglobin; WCC, white blood cell count; ECG, electrocardiogram; and AF, atrial fibrillation.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

Orthopedic score sheet for the POSSUM system. Abbreviations are defined in the legend to Figure 1.

Graphic Jump Location

Tables

Table Graphic Jump LocationTable 1. Examples of Magnitude for General Surgery*
Table Graphic Jump LocationTable 2. Examples of Operative Magnitude for Orthopedic Surgery
Table Graphic Jump LocationTable 3. Raw and Risk-Adjusted Outcome Measures for 12 Months in One Unit*
Table Graphic Jump LocationTable 4. Variability in Raw and Risk-Adjusted Outcome Data in Orthopedic Surgery During 12 Months*
Table Graphic Jump LocationTable 5. Examples of the Application of the POSSUM System Between Units in Countries With Varying Numbers of Patients per Annum and Variable Case Mix*
Table Graphic Jump LocationTable 6. Variations in Annual Performance of One Surgeon During 6 Years*
Table Graphic Jump LocationTable 7. Effect of Intensive Care Unit Bed Availability on Risk-Adjusted Outcome of Operative Intervention in One Unit*

References

Copeland  GPJones  DWalters  M POSSUM: a scoring system for surgical audit. Br J Surg. 1991;78355- 360
Link to Article
Jones  HJSde Cossart  L Risk scoring in surgical patients. Br J Surg. 1999;86149- 157
Link to Article
Copeland  GPJones  DWilcox  AHarris  PL Comparative vascular audit using the POSSUM scoring system. Ann R Coll Surg Engl. 1993;75175- 177
Sagar  PMHartley  MNMacFie  JTaylor  BACopeland  GP Comparison of individual surgeon's performance. Dis Colon Rectum. 1996;39654- 658
Link to Article
Copeland  GPSagar  PBrennan  J  et al.  Risk adjusted analysis of surgeon performance. Br J Surg. 1995;82408- 411
Link to Article
Copeland  GP Assessing the surgeon: 10 years experience with the POSSUM system. J Clin Excellence. 2000;2187- 190
Prytherch  DWhiteley  MSHiggins  BWeaver  PCProut  WGPowell  SJ POSSUM and Portsmouth POSSUM for predicting mortality. Br J Surg. 1998;851217- 1220
Link to Article
Wijesinghe  LDMahmood  TScott  DLABerridge  DCKent  PJKester  RC Comparison of POSSUM and the Portsmouth predictor equation for predicting death following vascular surgery. Br J Surg. 1998;85209- 212
Link to Article
McIlroy  BMiller  ACopeland  GPKiff  R Audit of emergency preoperative resuscitation. Br J Surg. 1994;811492- 1494
Link to Article
Copeland  GPBrett  MMcIlroy  BNathwami  DWard  J Predicting length of stay in general surgery. Health Trends. 1997;2915- 18
Tekkis  PPKocher  HMBentley  AJ  et al.  Operative mortality rates among surgeons: comparison of POSSUM and p-POSSUM scoring systems in gastrointestinal surgery. Dis Colon Rectum. 2000;431528- 1532
Link to Article
Wang  TKTu  HH Colorectal perforation with barium enema in the elderly: case analysis with the POSSUM scoring system. J Gastroenterol. 1998;33201- 205
Link to Article
Cajigas  JCEscalante  CFIngelmo  A Application of the POSSUM system in bariatric surgery. Obes Surg. 1999;9279- 281
Link to Article
Brunelli  AFianchini  AXiume  FGesuita  RMattei  ACarle  F Evaluation of the POSSUM scoring system in lung surgery. Thorac Cardiovasc Surg. 1998;46141- 146
Link to Article
Gotohda  NIwagaki  HItano  S Can POSSUM, a scoring system for perioperative surgical risk, predict postoperative clinical course? Acta Med Okayama. 1998;52325- 329
Shoemaker  WCAppel  PLKram  HBWaxman  KLee  T Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients. Chest. 1988;941176- 1186
Link to Article
Boyd  OGrounds  RMBennett  ED A randomized clinical trial of the effect of deliberate perioperative increase in oxygen delivery on mortality in high-risk surgical patients. JAMA. 1993;2702699- 2707
Link to Article
Wilson  JWoods  IFawcett  J  et al.  Reducing the risk of major elective surgery: randomised controlled trial of preoperative optimisation of oxygen delivery. BMJ. 1999;3181099- 1103
Link to Article
Copeland  GP Surgical scoring, risk assessment and the surgeon. J R Coll Surg Edinb. 1992;37145- 148
Copeland  GP Comparative audit: fact versus fantasy. Br J Surg. 1993;801424- 1425
Link to Article

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