POSSUM Scoring System for Surgical Audit

Components:

(1) physiologic score

(2) operative score

(3) tally of complications

(4) calculations of estimated morbidity and mortality rates from scores

 

Physiologic Score

 

The physiologic score is calculated before surgery.

 

Parameters:

(1) age

(2) cardiac signs

(3) respiratory history

(4) systolic blood pressure

(5) pulse in beats per minute

(6) Glasgow coma score

(7) hemoglobin

(8) white blood cell count

(9) urea

(10) sodium

(11) potassium

(12) electrocardiogram

 

Parameter	Finding	Points
age in years	<= 60 years	1
	61 - 70 years	2
	>= 71 years	4
cardiac signs	no failure	1
	diuretics, digoxin, antianginal therapy, antihypertensive therapy	2
	peripheral edema, warfarin therapy, borderline cardiomegaly on chest X-ray	4
	raised jugular venous pressure, cardiomegaly on chest X-ray	8
respiratory findings	no dyspnea	1
	dyspnea on exertion; mild evidence of COPD on chest X-ray	2
	limiting dyspnea after 1 flight of stairs; moderate COPD on chest X-ray	4
	dyspnea at rest; respiratory rate > 30 breaths per minute; fibrosis or consolidation on chest X-ray	8
systolic blood pressure	<= 89 mm Hg	8
	90 - 99 mm Hg	4
	100 - 109 mm Hg	2
	110 - 130 mm Hg	1
	131 - 170 mm Hg	2
	>= 171 mm Hg	4
pulse	<= 39 beats per minute	8
	40 - 49 beats per minute	2
	50 - 80 beats per minute	1
	81 - 100 beats per minute	2
	101 - 120 beats per minute	4
	>= 121 beats per minute	8
Glasgow coma score	15	1
	12 - 14	2
	9 - 11	4
	<= 8	8
hemoglobin	<= 9.9 g/dL	8
	10.0 - 11.4 g/dL	4
	11.5 - 12.9 g/dL	2
	13.0 - 16.0 g/dL	1
	16.1 - 17.0 g/dL	2
	17.1 - 18.0 g/dL	4
	>= 18.1 g/dL	8
white blood cell count	<= 3,000 per µL	4
	3,100 - 3,999 per µL	2
	4,000 - 10,000 per µL	1
	10,100 - 20,000 per µL	2
	>= 20,100 per µL	4
urea	<= 7.5 mmol/L	1
	7.6 - 10.0 mmol/L	2
	10.1 - 15.0 mmol/L	4
	>= 15.1 mmol/L	8
sodium	<= 125  mmol/L	8
	126 - 130 mmol/L	4
	131 - 135 mmol/L	2
	>= 136 mmol/L	1
potassium	<= 2.8 mmol/L	8
	2.9 - 3.1 mmol/L	4
	3.2 - 3.4 mmol/L	2
	3.5 - 5.0 mmol/L	1
	5.1 - 5.3 mmol/L	2
	5.4 - 5.9 mmol/L	4
	>= 6.0 mmol/L	8
electrocardiogram	normal	1
	atrial fibrillation with heart rate 60-90	4
	any other abnormal rhythm	8
	>= 5 ectopics per minute	8
	Q waves or ST-T wave changes	8

(from Table 1, page 356)

 

where:

• Table 1 on page 356 includes "chest radiograph" as an indented entry below both "cardiac signs" and "respiratory history". I have merged the radiograph findings with the clinical findings into one score; this corresponds to the 12 factors mentioned on page 355.An alternative approach would be to have as separate parameters. This would increase the number of parameters from 12 to 14, the minimum score from 12 to 14, and maximum score from 96 to 112.

 

Operative Score

 

The operative score is calculated at discharge.

 

Parameters:

(1) operative severity

(2) number of procedures done

(3) total blood loss

(4) peritoneal soiling

(5) presence of malignancy

(6) mode of surgery

 

Parameter	Finding	Points
operative severity	minor	1
	moderate	2
	major	4
	very major	8
number of procedures	1	1
	2	4
	> 2	8
total blood loss in mL	<= 100 mL	1
	101 - 500 mL	2
	501 - 999 mL	4
	>= 1,000 mL	8
peritoneal soiling	none	1
	minor (serous fluid without pus)	2
	local pus	4
	free bowel content, pus or blood	8
presence of malignancy	none	1
	primary only	2
	nodal metastases	4
	distant metastases	8
mode of surgery	elective	1
	emergency with resuscitation >= 2 hours	4
	operation < 24 hours after admission	4
	immediate surgery	8

(from Table 2, page 356)

 

where:

• Moderate severity procedures: appendectomy, cholecystectomy, mastectomy, transurethral resection of prostate

• Major severity procedures: laparotomy, bowel resection, cholecystectomy with choledochotomy, peripheral vascular procedure, major amputation

• Very major severity procedures: procedure involving aorta, abdominoperineal resection, pancreatic resection, hepatic resection, esophago-gastrectomy

• emergency surgery with resuscitation: I am assuming that this refers to pre-operative stabilization.

 

operative score =

= SUM(points for all 6 parameters)

 

Complications

 

Complications (defined pages 356-357):

(1) hemorrhage: wound, deep, other

(2) infection: chest, wound, urinary tract, deep, septicemia, fever of unknown origin, other

(3) wound dehiscence: superficial, deep

(4) anastomotic leak

(5) thrombosis: deep vein thrombosis, pulmonary embolus, other thrombosis, cerebrovascular accident, myocardial infarction

(6) cardiac failure

(7) impaired renal function ((urea post-operative) > (urea pre-operative) + (5 mmol/L))

(8) hypotension (systolic blood pressure < 90 mm Hg for 2 hours or more)

(9) respiratory failure

(10) any other complication

(11) death

 

Interpretation:

• minimum physiologic score: 12

• maximum physiologic score: 88

• minimum operative score: 6

• maximum operative score: 48

 

X =

= (0.16 * (physiologic score)) + (0.19 * (operative score)) - 5.91

 

Y =

= (0.13 * (physiologic score)) + (0.16 * (operative score)) - 7.04

 

probability of morbidity =

= 1 / (1 + EXP((-1) * (X)))

 

probability of mortality =

= 1 / (1 + EXP((-1) * (Y)))

 

where:

• The article uses the form: LN ((probability) / (1 - (probability))) = X

 

Performance:

• Whiteley et al (see the next section) felt that the POSSUM score performed badly when tested using a standard test for goodness of fit. This was associated with an overestimated probability of mortality, especially at lower scores. They developed the Portsmouth score that used the same data but modified the equation for calculating "Y".