Br. J. Surg. 1991, Vol. 78, March, 356-360
G. P. Copeland, D. Jones and M. Walters Department of Surgery, Broadgreen Hospital, Thomas Drive, Liverpool L 14 3LB, UK Correspondence to: Mr G . P. Copeland
POSSUM: a scoring system for surgical audit POSSUM, a Physiological and Operative Severity Score f o r the enumeration of Mortality and morbidity, is described. This system has been devised f r o m both a retrospective and prospective analysis and the present paper attempts to validate it prospectively. Logistic regression analysis yielded statistically sign ficant equations f o r both mortality and morbidity ( P < 0.001). When displayed graphically zones of increasing morbidity and mortality rates could be defined which could be of value in surgical audit. The scoring system produced assessments f o r morbidity and mortality rates which did not significantly differ f r o m observed rates.
While data regarding the access of patients to care and outcome (presented as overall mortality and morbidity rates) are relatively easy to derive, ‘quality of care’ has proved a more elusive determinant. In most hospitals, quality of care is assessed by discussion of individual cases or by review of series of patients undergoing particular types of surgical procedure. Comparisons between different surgeons, units, hospitals and regions are bedevilled by differences in patient presentation, general fitness of the local populace and the nature of the surgery undertaken. The Royal College of Surgeons of England has defined audit as the ‘systematic appraisal of the implementation and outcome of any process in the context of prescribed targets and standards”. The difficulty in this definition rests in the interpretation of prescribed targets and standards, and it infers that outcome for individuals and series of patients can be predicted. In this context morbidity is probably as important as mortality, certainly when discussing quality of care. Perhaps of parallel importance in audit is the discussion of individuals in whom death or complications could have been expected, but did not occur. Thus audit should include discussion of ‘surgical success’, in addition to mortality and morbidity rates, if it is to be educational. The ideal scoring system for surgical audit purposes should assess mortality and morbidity and should allow audit retrieval of the surgical success. It should be quick and easy to use and should be applicable to all general surgical procedures in both the emergency and elective setting. It should be of use in all types of hospital and should provide educational information. Finally it should be possible to integrate the scoring system into pre-existing audit programmes with the minimum of disruption. There are many scoring systems that predict the risk of mortality with varying degrees of accuracy. However, morbidity is almost universally ignored. Many scores have been devised which are ideally suited to special types of surgical procedure or to assessing particular types of complication. Some scores are ideal for assessing the risk of mortality and to a lesser extent morbidity in particular groups of surgical patients, such as those with c a r d i o v a ~ c u l a rand ~ ~ ~gastrointestinalL8 disease, or for assessing the risk of developing particular complication^^^^^. Others are of use in particular surgical settings, such as patients requiring intensive care””’. Probably the best known and most widely used scoring system is APACHE I1 which is ideal for the intensive care patient but requires 24 h of observation and weighting tables for individual disease states”. Whereas such a score can be applied to the majority of general surgical patients it only assesses the risk of mortality. Theoretically the smaller the number of variables the easier the scoring system. Indeed some systems have reduced the number of variables to two (age and lymphocyte count 1 3 ) but this reduction clearly has disadvantages if one factor is not available. Other scoring systems have reduced variables by multifactorial analysis and
have derived complex mathematical equations to assess the risk of mortality, but few surgeons carry calculators in everyday practice. We identified the need for a simple scoring system that could be used across the general surgical spectrum, whose main use would be in surgical audit. Our present system has been in development over the past 2 years. Initially 62 individual factors (48 preoperative factors and 14 operative and postoperative factors) were assessed by a multivariate discriminant retrospective analysis over a 6-month period, to reduce the number of variables. Of these, 35 factors were assessed prospectively for a further 6 months to produce the present scoring system. In this later prospective analysis all variables were subjected to multivariate discriminant analysis and, using this linear discriminant t e c h n i q ~ e ’ multivariate ~, discriminant function coefficients were obtained for each set of variables. Only significant independent factors were included in the final score design. The multivariate discriminant function coefficients of those remaining factors were divided by a constant and rounded to the nearest whole number to derive a point value on an exponential score (1, 2, 4, 8) for the variable. Thus a 12-factor, four-grade, physiological score was developed. Any decrease in score variables below this level resulted in a loss of predictive ability for mortality or morbidity. While this preoperative physiological score yields a statistically predictive risk of morbidity and mortality for the patients overall, there were intergroup differences depending on the nature of the surgical procedure. Logistic regression analysis of all data enabled a six-factor, surgical, operative severity score to be evolved which compensated for the type of surgical procedure. In the present prospective study we have applied this dual scoring system to all patients admitted during a 6-month period, equivalent to our periods of previous study. During this period the present POSSUM (Physiological and Operative Severity Score for the enumeration of Mortality and morbidity) system has been assessed.
Patients and methods During the 6 months from August 1988 to February 1989 all patients admitted for inpatient surgery were scored using the POSSUM system at Walton Hospital, Liverpool. In all, 1440 patients underwent elective or emergency surgery during this period and required inpatient care for at least 24 h after operation. Patients undergoing surgery for trauma (12 patients) and those in whom no outpatient review at 6 weeks was available (56 patients) were excluded. Thus 1372 prospectively scored patients were available for study. All patients were scored before operation (using the physiological score) and at discharge (using the operative severity score). The physiological score reflects the indices at the time of surgery rather than at the time of admission. All patients had blood samples taken for determination of urea and electrolyte levels, haemoglobin concentration
-
0007-1 323/91/03035546
0 1991 Butterworth-Heinemann Ltd
355
Surgical audit: G. P. Copeland et al.
Table 1 Physiological score (to be scored at the time ofsurgery) Score 1
Age (years) Cardiac signs
2
No failure
Diuretic, digoxin, antianginal Peripheral oedema; warfarin therapy or hypertensive therapy Borderline cardiomegaly
No dyspnoea
Dyspnoea on exertion
Chest radiograph Respiratory history
Glasgow coma score Haemoglobin (Silo0 ml) White cell count ( x 10'*/1) Urea (mmol/l) Sodium (mmol/l) Potassium (mmol/l) Electrocardiogram
< 89
101-120
2 121
81-100 a 9
15
12-14
9-1 1
13-16
11.5-12'9 16.1-1 7.0
10.0-11.4 17.1- 18.0
410
10.1-20.0 3.140
2 I36
< 39
68 69.9 2 18.1
220.1 6 3.0
7.6-1 0.0
10.1-1 5.0
131-135
126130
2 15.1
< I25 < 2.8 > 6.0
2'9-3.1 5.4-5.9
3.2-3.4 5.1-5.3
3.5-5.0
-
9e99
50-80
< 7.5
Dyspnoea at rest (rate > 30/min) Fibrosis or consolidation
2 171
131-170 10&109
110-130
Raised jugular venous pressure Cardiom ega1y
Limiting dyspnoea (one flight) Moderate COAD
Mild COAD
Chest radiograph Blood pregsure (systolic) (mmHg) Pulse (beats/min)
271
61-70
6 60
8
4
Atrial fibrillation (rate 6&90)
Normal
Any other abnormal rhythm or 2 5 ectopics/min Q waves or ST/T wave changes
COAD, chronic obstructive airways disease
Table 2 Operative severity score. (Definitions of surgical procedures with regard to severity are guidelines; not all procedures are listed and the closest should be selected) Score
1
2
4
Operative severity*
Minor
Moderate
Major
Multiple procedures Total blood loss (ml)
1 < 100
101-500
501-999
Peritoneal soiling
None
Minor (serous fluid)
Local pus
Presence of malignancy
None
Primary only
Nodal metastases
Distant metastases
Mode of surgery
Elective
Emergency resuscitation of > 2 h possiblet Operation < 24 h after admission
Emergency (immediate surgery < 2 h needed)
8 Major +
2
>2
2 1000 Free bowel content, pus or blood
* Surgery of moderate severity includes appendicectomy, cholecystectomy, mastectomy, transurethral resection of prostate; major surgery includes any laparotomy, bowel resection, cholecystectomy with choledochotomy, peripheral vascular procedure or major amputation; major + surgery includes any aortic procedure, abdominoperineal resection, pancreatic or liver resection, oesophagogastrectomy; indicates that resuscitation is possible even if this period is not actually utilized and white cell count, and all had electrocardiography performed. A chest radiograph was obtained in 69.7 per cent of patients. Scores were awarded according to Tables I and 2. Complications were recorded on a separate sheet (Table 3 ) . For the purposes of study the following definitions were used: Wound haemorrhage: local haematoma requiring evacuation Deep haemorrhage: postoperative bleeding requiring re-exploration Chest infection: production of purulent sputum with positive bacteriological cultures, with or without chest radiography changes or pyrexia, or consolidation seen on chest radiograph Woundinfection: wound cellulitis or the discharge ofpurulent exudate Urinary infection: the presence of z lo5 bacteria/ml with the presence of white cells in the urine, in previously clear urine Deep infection: the presence of an intra-abdominal collection confirmed clinically or radiologically
356
Septicaemia: positive blood culture Pyrexia of unknown origin: any temperature above 37°C for more than 24 h occurring after the original pyrexia following surgery (if present) had settled, for which no obvious cause could be found Wound dehiscence: superficial or deep wound breakdown Deep venous thrombosis and pulmonary embolus: when suspected, confirmed radiologically by venography or ventilation/perfusion scanning, or diagnosed at post mortem Cardiac failure: symptoms or signs of left ventricular or congestive cardiac failure which required an alteration from preoperative therapeutic measures Impaired renal function: arbitrarily defined as an increase in blood urea of > 5 mmol/l from preoperative levels Hypotension: a fall in systolic blood pressure below 90 mmHg for more than 2 h as determined by sphygmomanometry or arterial pressure transducer measurement
Br. J. Surg., Vol. 78, No. 3, March 1991
Surgical audit: G. P. Copeland e t al.
Table 3 Information to be included on a complications record sheet ~
~~~
.~ ~~
~~~
Name Hospital no. Diagnosis Operation Date of admission Date of operation Date of discharge Surgeon Anaesthetist Outcome* Haemorrhage Wound Deep Other Infection? Chest Wound Urinary tract Deep Septicaemia Pyrexia of unknown origin Other Wound dehiscence Superficial Deep Anastomotic leak Thrombosis Deep vein thrombosis Pulmonary embolus Other Cerebrovascular accident Myocardial infarct Cardiac failure Impaired renal function (urea increase > 5 mmol/l from preoperative level) Hypotension (
0.2
0.2
0.4
0.6
0.8
1 .o
1-specificity (false positive rate)
Figure 6 Receiver operating characteristic curve,for morbidity
Br. J. Surg.. Vol. 78, No. 3, March 1991
Surgical audit: G. P. Copeland et al.
Table 7 Predicied versus observed rates for mortality and morbidity* Observed rate (YO) Predicted risk (YO)
Mortality
Morbidity
85 75 65 55 45 35 25
86.5 78.3 67-7 56.4 46.0 38.5 29.3
84.3 75.7 67.3 56.9 47.5 37.4 26.4
*There was good correlation between observed and predicted rates for morbidity and mortality (P
G. P. Copeland, D. Jones and M. Walters Department of Surgery, Broadgreen Hospital, Thomas Drive, Liverpool L 14 3LB, UK Correspondence to: Mr G . P. Copeland
POSSUM: a scoring system for surgical audit POSSUM, a Physiological and Operative Severity Score f o r the enumeration of Mortality and morbidity, is described. This system has been devised f r o m both a retrospective and prospective analysis and the present paper attempts to validate it prospectively. Logistic regression analysis yielded statistically sign ficant equations f o r both mortality and morbidity ( P < 0.001). When displayed graphically zones of increasing morbidity and mortality rates could be defined which could be of value in surgical audit. The scoring system produced assessments f o r morbidity and mortality rates which did not significantly differ f r o m observed rates.
While data regarding the access of patients to care and outcome (presented as overall mortality and morbidity rates) are relatively easy to derive, ‘quality of care’ has proved a more elusive determinant. In most hospitals, quality of care is assessed by discussion of individual cases or by review of series of patients undergoing particular types of surgical procedure. Comparisons between different surgeons, units, hospitals and regions are bedevilled by differences in patient presentation, general fitness of the local populace and the nature of the surgery undertaken. The Royal College of Surgeons of England has defined audit as the ‘systematic appraisal of the implementation and outcome of any process in the context of prescribed targets and standards”. The difficulty in this definition rests in the interpretation of prescribed targets and standards, and it infers that outcome for individuals and series of patients can be predicted. In this context morbidity is probably as important as mortality, certainly when discussing quality of care. Perhaps of parallel importance in audit is the discussion of individuals in whom death or complications could have been expected, but did not occur. Thus audit should include discussion of ‘surgical success’, in addition to mortality and morbidity rates, if it is to be educational. The ideal scoring system for surgical audit purposes should assess mortality and morbidity and should allow audit retrieval of the surgical success. It should be quick and easy to use and should be applicable to all general surgical procedures in both the emergency and elective setting. It should be of use in all types of hospital and should provide educational information. Finally it should be possible to integrate the scoring system into pre-existing audit programmes with the minimum of disruption. There are many scoring systems that predict the risk of mortality with varying degrees of accuracy. However, morbidity is almost universally ignored. Many scores have been devised which are ideally suited to special types of surgical procedure or to assessing particular types of complication. Some scores are ideal for assessing the risk of mortality and to a lesser extent morbidity in particular groups of surgical patients, such as those with c a r d i o v a ~ c u l a rand ~ ~ ~gastrointestinalL8 disease, or for assessing the risk of developing particular complication^^^^^. Others are of use in particular surgical settings, such as patients requiring intensive care””’. Probably the best known and most widely used scoring system is APACHE I1 which is ideal for the intensive care patient but requires 24 h of observation and weighting tables for individual disease states”. Whereas such a score can be applied to the majority of general surgical patients it only assesses the risk of mortality. Theoretically the smaller the number of variables the easier the scoring system. Indeed some systems have reduced the number of variables to two (age and lymphocyte count 1 3 ) but this reduction clearly has disadvantages if one factor is not available. Other scoring systems have reduced variables by multifactorial analysis and
have derived complex mathematical equations to assess the risk of mortality, but few surgeons carry calculators in everyday practice. We identified the need for a simple scoring system that could be used across the general surgical spectrum, whose main use would be in surgical audit. Our present system has been in development over the past 2 years. Initially 62 individual factors (48 preoperative factors and 14 operative and postoperative factors) were assessed by a multivariate discriminant retrospective analysis over a 6-month period, to reduce the number of variables. Of these, 35 factors were assessed prospectively for a further 6 months to produce the present scoring system. In this later prospective analysis all variables were subjected to multivariate discriminant analysis and, using this linear discriminant t e c h n i q ~ e ’ multivariate ~, discriminant function coefficients were obtained for each set of variables. Only significant independent factors were included in the final score design. The multivariate discriminant function coefficients of those remaining factors were divided by a constant and rounded to the nearest whole number to derive a point value on an exponential score (1, 2, 4, 8) for the variable. Thus a 12-factor, four-grade, physiological score was developed. Any decrease in score variables below this level resulted in a loss of predictive ability for mortality or morbidity. While this preoperative physiological score yields a statistically predictive risk of morbidity and mortality for the patients overall, there were intergroup differences depending on the nature of the surgical procedure. Logistic regression analysis of all data enabled a six-factor, surgical, operative severity score to be evolved which compensated for the type of surgical procedure. In the present prospective study we have applied this dual scoring system to all patients admitted during a 6-month period, equivalent to our periods of previous study. During this period the present POSSUM (Physiological and Operative Severity Score for the enumeration of Mortality and morbidity) system has been assessed.
Patients and methods During the 6 months from August 1988 to February 1989 all patients admitted for inpatient surgery were scored using the POSSUM system at Walton Hospital, Liverpool. In all, 1440 patients underwent elective or emergency surgery during this period and required inpatient care for at least 24 h after operation. Patients undergoing surgery for trauma (12 patients) and those in whom no outpatient review at 6 weeks was available (56 patients) were excluded. Thus 1372 prospectively scored patients were available for study. All patients were scored before operation (using the physiological score) and at discharge (using the operative severity score). The physiological score reflects the indices at the time of surgery rather than at the time of admission. All patients had blood samples taken for determination of urea and electrolyte levels, haemoglobin concentration
-
0007-1 323/91/03035546
0 1991 Butterworth-Heinemann Ltd
355
Surgical audit: G. P. Copeland et al.
Table 1 Physiological score (to be scored at the time ofsurgery) Score 1
Age (years) Cardiac signs
2
No failure
Diuretic, digoxin, antianginal Peripheral oedema; warfarin therapy or hypertensive therapy Borderline cardiomegaly
No dyspnoea
Dyspnoea on exertion
Chest radiograph Respiratory history
Glasgow coma score Haemoglobin (Silo0 ml) White cell count ( x 10'*/1) Urea (mmol/l) Sodium (mmol/l) Potassium (mmol/l) Electrocardiogram
< 89
101-120
2 121
81-100 a 9
15
12-14
9-1 1
13-16
11.5-12'9 16.1-1 7.0
10.0-11.4 17.1- 18.0
410
10.1-20.0 3.140
2 I36
< 39
68 69.9 2 18.1
220.1 6 3.0
7.6-1 0.0
10.1-1 5.0
131-135
126130
2 15.1
< I25 < 2.8 > 6.0
2'9-3.1 5.4-5.9
3.2-3.4 5.1-5.3
3.5-5.0
-
9e99
50-80
< 7.5
Dyspnoea at rest (rate > 30/min) Fibrosis or consolidation
2 171
131-170 10&109
110-130
Raised jugular venous pressure Cardiom ega1y
Limiting dyspnoea (one flight) Moderate COAD
Mild COAD
Chest radiograph Blood pregsure (systolic) (mmHg) Pulse (beats/min)
271
61-70
6 60
8
4
Atrial fibrillation (rate 6&90)
Normal
Any other abnormal rhythm or 2 5 ectopics/min Q waves or ST/T wave changes
COAD, chronic obstructive airways disease
Table 2 Operative severity score. (Definitions of surgical procedures with regard to severity are guidelines; not all procedures are listed and the closest should be selected) Score
1
2
4
Operative severity*
Minor
Moderate
Major
Multiple procedures Total blood loss (ml)
1 < 100
101-500
501-999
Peritoneal soiling
None
Minor (serous fluid)
Local pus
Presence of malignancy
None
Primary only
Nodal metastases
Distant metastases
Mode of surgery
Elective
Emergency resuscitation of > 2 h possiblet Operation < 24 h after admission
Emergency (immediate surgery < 2 h needed)
8 Major +
2
>2
2 1000 Free bowel content, pus or blood
* Surgery of moderate severity includes appendicectomy, cholecystectomy, mastectomy, transurethral resection of prostate; major surgery includes any laparotomy, bowel resection, cholecystectomy with choledochotomy, peripheral vascular procedure or major amputation; major + surgery includes any aortic procedure, abdominoperineal resection, pancreatic or liver resection, oesophagogastrectomy; indicates that resuscitation is possible even if this period is not actually utilized and white cell count, and all had electrocardiography performed. A chest radiograph was obtained in 69.7 per cent of patients. Scores were awarded according to Tables I and 2. Complications were recorded on a separate sheet (Table 3 ) . For the purposes of study the following definitions were used: Wound haemorrhage: local haematoma requiring evacuation Deep haemorrhage: postoperative bleeding requiring re-exploration Chest infection: production of purulent sputum with positive bacteriological cultures, with or without chest radiography changes or pyrexia, or consolidation seen on chest radiograph Woundinfection: wound cellulitis or the discharge ofpurulent exudate Urinary infection: the presence of z lo5 bacteria/ml with the presence of white cells in the urine, in previously clear urine Deep infection: the presence of an intra-abdominal collection confirmed clinically or radiologically
356
Septicaemia: positive blood culture Pyrexia of unknown origin: any temperature above 37°C for more than 24 h occurring after the original pyrexia following surgery (if present) had settled, for which no obvious cause could be found Wound dehiscence: superficial or deep wound breakdown Deep venous thrombosis and pulmonary embolus: when suspected, confirmed radiologically by venography or ventilation/perfusion scanning, or diagnosed at post mortem Cardiac failure: symptoms or signs of left ventricular or congestive cardiac failure which required an alteration from preoperative therapeutic measures Impaired renal function: arbitrarily defined as an increase in blood urea of > 5 mmol/l from preoperative levels Hypotension: a fall in systolic blood pressure below 90 mmHg for more than 2 h as determined by sphygmomanometry or arterial pressure transducer measurement
Br. J. Surg., Vol. 78, No. 3, March 1991
Surgical audit: G. P. Copeland e t al.
Table 3 Information to be included on a complications record sheet ~
~~~
.~ ~~
~~~
Name Hospital no. Diagnosis Operation Date of admission Date of operation Date of discharge Surgeon Anaesthetist Outcome* Haemorrhage Wound Deep Other Infection? Chest Wound Urinary tract Deep Septicaemia Pyrexia of unknown origin Other Wound dehiscence Superficial Deep Anastomotic leak Thrombosis Deep vein thrombosis Pulmonary embolus Other Cerebrovascular accident Myocardial infarct Cardiac failure Impaired renal function (urea increase > 5 mmol/l from preoperative level) Hypotension (
0.2
0.2
0.4
0.6
0.8
1 .o
1-specificity (false positive rate)
Figure 6 Receiver operating characteristic curve,for morbidity
Br. J. Surg.. Vol. 78, No. 3, March 1991
Surgical audit: G. P. Copeland et al.
Table 7 Predicied versus observed rates for mortality and morbidity* Observed rate (YO) Predicted risk (YO)
Mortality
Morbidity
85 75 65 55 45 35 25
86.5 78.3 67-7 56.4 46.0 38.5 29.3
84.3 75.7 67.3 56.9 47.5 37.4 26.4
*There was good correlation between observed and predicted rates for morbidity and mortality (P
