### Description

The mortality risk for patients undergoing anaesthesia and surgery can be estimated from clinical status and nature of operative intervention using logistic regression.

 Parameter Finding Odds if Present Odds if Absent age >= 70 years 9.03 1 50 - 69 years 4.26 1 congestive heart failure 3.016 1 renal failure serum creatinine >= 3.39 mg/dL 7.39 1 abdominal surgery 9.87 1 emergency surgery 5.31 1 constant 0.00029 N/A

where:

• The serum creatinine conversion factor to µmol/L is 88.4

• Emergency surgery indicates a non-elective procedure.

• Odds = EXP(beta coefficient), with the beta coefficient determined by logistic regression. Thus the constant for the equation is -8.1456.

s =

= odds (constant) * odds (age) * odds (CHF) * odds (renal failure) * odds (abdominal surgery) * odds (emergency surgery)

probability of hospital mortality =

= (s / (1 + s))

Note: In the paper text, the equation for probability of mortality is

probability of hospital mortality =

= (EXP (s)) / (1 + (EXP (s)))

However, the represented tabular data matches the other equation exactly but deviates from the exponential form significantly, as demonstrated in the spreadsheet.

Other pre-existing conditions associated with increased mortality:

(1) hypotension ( systolic blood pressure < 90 mm Hg): mortality rate during emergency surgery (major and minor) similar to that seen with congestive heart failure, but elective major surgery mortality rate low (possibly since few elective procedures would be done in a hypotensive patient)

(2) history of previous myocardial infarction:

(2a) patients with MI less than 1 year before surgery had serious risk during emergency surgery (major and minor) and an increased risk during elective major surgery, often from perioperative re-infarction;

(2b) patients with an MI a year or more before surgery had an increased mortality rate during emergency major surgery, but not if surgery elective

(2c) patients with angina pectoris did not have an increased risk of dying

(3) chronic obstructive lung disease: increased risk seen with major emergency surgery and to a lesser extent with major elective surgery

(4) diabetes mellitus: increased risk seen with major elective surgery and to a lesser extent with major emergency surgery

(5) cancer: increased risk seen with major emergency surgery and to a lesser extent with major elective surgery

Intra-operative and post-operative conditions associated with increased mortality:

(1) post-operative myocardial infarction

(2) other cardiopulmonary complications: these had a lower mortality rate if they occurred intra-operatively rather than post-operatively

Limitations:

• mortality rate will likely improve over time with new therapeutic modalities, so that the probabilities given by the equation may become worse case