Surgery and Perioperative Risk Calculators

ASA classification grades overall health from I to VI: ASA I = healthy; ASA II = mild systemic disease (e.g., well-controlled hypertension, BMI 30–40, social smoker); ASA III = severe systemic disease (e.g., poorly controlled DM, COPD, morbid obesity, active hepatitis, alcohol dependence); ASA IV = life-threatening disease (e.g., recent MI/stroke, LVEF <25%, sepsis); ASA V = moribund, not expected to survive without surgery; ASA VI = brain-dead organ donor. ASA III–IV patients warrant heightened pre-operative optimization and intra-operative vigilance.

The Revised Cardiac Risk Index predicts major adverse cardiac events (MACE) after non-cardiac surgery. Six risk factors score 1 point each: high-risk surgery, ischemic heart disease, congestive heart failure, cerebrovascular disease, insulin-dependent diabetes, and pre-operative creatinine >2.0 mg/dL. RCRI 0: <1% MACE risk; RCRI 1: ~1%; RCRI 2: ~2.4%; RCRI ≥3: ≥5.4%. ACC/AHA guidelines recommend RCRI before elective non-cardiac surgery in patients with known or suspected cardiac disease.

The Mallampati score assesses oropharyngeal visibility with mouth open and tongue protruded, without phonation: Class I = soft palate, uvula, fauces, pillars visible; Class II = soft palate, uvula, fauces visible; Class III = soft palate and base of uvula visible; Class IV = only hard palate visible. Class III–IV predicts difficult laryngoscopy (sensitivity ~35%, specificity ~90%). Mallampati should be combined with other predictors — thyromental distance, mouth opening, neck mobility, and jaw protrusion — for a complete airway assessment.

The Caprini score stratifies VTE risk in surgical patients using weighted risk factors. Score 0–1 = very low risk (early ambulation only); 2 = low risk (pneumatic compression); 3–4 = moderate risk (low molecular weight heparin + compression); ≥5 = high risk (LMWH + compression, extended prophylaxis up to 28 days in abdominal/pelvic cancer surgery). The Caprini model is most validated in general, plastic, and abdominal surgery. For orthopedic surgery, specialty-specific guidelines take precedence.

Mean arterial pressure (MAP = [SBP + 2×DBP] ÷ 3) is the key perfusion pressure target during surgery. For most patients, MAP ≥65 mmHg is required to maintain organ perfusion. In patients with chronic hypertension, cerebrovascular disease, or renal impairment, a higher MAP target (≥75–80 mmHg) may be needed. Intra-operative hypotension (MAP <65 for >3–5 minutes) is independently associated with acute kidney injury, myocardial injury, and 30-day mortality.

Body surface area is used to dose chemotherapy agents administered perioperatively, certain anticoagulants, and some anesthetic agents in obese patients. The Mosteller formula (BSA = √[height(cm) × weight(kg) ÷ 3600]) is preferred for its simplicity. For obese patients, lean body weight or adjusted body weight may be more appropriate than actual weight to avoid drug toxicity. Always cross-reference specific drug monographs for dosing guidance in extremes of body size.