14.1 Preoperative Risk Assessment, Cardiovascular Risk Indices, and Fasting Guidelines

14.1 Preoperative Risk Assessment, Cardiovascular Risk Indices, and Fasting Guidelines

Preoperative evaluation is the clinical foundation of anaesthetic practice. It transitions anaesthesia from an acute intraoperative intervention into a comprehensive perioperative discipline designed to identify occult pathophysiology, quantify organ-specific reserve, optimize chronic medical conditions, formulate tailored anaesthetic plans, and obtain informed patient consent.

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1. Goals and Structure of Preoperative Evaluation

The fundamental goals of the preoperative consultation include:

1. Baseline Physiological Appraisal: Establishing baseline cardiopulmonary, renal, metabolic, and neurological status.
2. Identification of Undiagnosed Pathology: Detecting unsuspected aortic stenosis, severe pulmonary hypertension, obstructive sleep apnoea, or difficult airway anatomy.
3. Risk Stratification and Shared Decision-Making: Formulating objective quantitative risk estimates for major adverse cardiovascular, pulmonary, and mortality outcomes to guide informed consent.
4. Comorbidity Optimization: Initiating disease-modifying interventions (e.g., intravenous iron for anemia, smoking cessation, optimization of heart failure pharmacotherapy).
5. Formulating an Anaesthetic Strategy: Planning airway management techniques, invasive monitoring lines, regional anaesthetic blocks, and postoperative care disposition (day surgery, post-anaesthesia care unit, or high-dependency/intensive care unit).

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2. ASA Physical Status Classification System

Introduced in 1941 and revised in 2014 and 2020 by the American Society of Anesthesiologists, the ASA Physical Status (ASA-PS) classification system remains the most universally utilized clinical scale for grading a patient's overall physical condition.

                    [ ASA PHYSICAL STATUS CLASSIFICATION ]
                                      |
        +-----------------------------+-----------------------------+
        |                             |                             |
  [ ASA I - III ]               [ ASA IV - V ]                   [ ASA VI ]
(Low to Severe Disease)     (Life-Threatening / Moribund)   (Brain-Dead Organ Donor)
        |                             |                             |
   ASA I: Normal healthy       ASA IV: Constant threat        Declared brain-dead;
   ASA II: Mild systemic       ASA V: Moribund without op     organ procurement
   ASA III: Substantive limit

             * Append 'E' to ANY class for EMERGENCY surgery *

ASA Physical Status Categories

• ASA I: A normal healthy patient. Non-smoker, minimal or no alcohol consumption, excellent functional capacity.
• ASA II: A patient with mild systemic disease without substantive functional limitations. Examples: well-controlled hypertension, well-controlled type 2 diabetes mellitus, mild asthma, active cigarette smoker, social drinker, pregnancy, obesity ($30 < \text{BMI} < 40\text{ kg/m}^2$).
• ASA III: A patient with severe systemic disease that results in substantive functional limitations; one or more moderate-to-severe diseases. Examples: poorly controlled diabetes or hypertension, stable angina, history of myocardial infarction ($>3\text{ months}$ prior), chronic obstructive pulmonary disease (COPD), end-stage renal disease (ESRD) on scheduled hemodialysis, morbid obesity ($\text{BMI} \ge 40\text{ kg/m}^2$), implanted pacemaker, moderate reduction of ejection fraction.
• ASA IV: A patient with severe systemic disease that is a constant threat to life. Examples: recent myocardial infarction or stroke ($<3\text{ months}$ prior), unstable angina, ongoing cardiac ischemia, severe symptomatic valvular stenosis, severe reduction of ejection fraction, sepsis, acute renal failure, symptomatic heart failure.
• ASA V: A moribund patient who is not expected to survive without the operation. Examples: ruptured abdominal or thoracic aortic aneurysm, massive polytrauma with hemorrhagic shock, intracranial bleed with midline shift and mass effect, ischemic bowel with multiorgan failure.
• ASA VI: A declared brain-dead patient whose organs are being removed for donor purposes.
• Emergency Modifier ('E'): Appended to any class (e.g., ASA IIE, ASA IVE) when a delay in surgical treatment would significantly increase the threat to the patient's life or body part.

Mortality rises steeply with ASA class, but the ASA does not publish class-specific mortality figures; reported rates vary widely with the population and the operation.

Clinical Utility and Inherent Limitations

While ASA-PS exhibits a robust, statistically significant correlation with perioperative morbidity, intensive care admission, and 30-day mortality, it possesses two major limitations:

1. Moderate Inter-Rater Reliability: Multiple clinical audits demonstrate that anaesthetists frequently assign different ASA scores to the same patient (e.g., classifying a compensated diabetic smoker as ASA II versus ASA III).
2. Absence of Procedural Risk: The ASA-PS evaluates solely the patient's physiological state, ignoring surgical magnitude. An ASA I patient undergoing a complex Whipple pancreatoduodenectomy faces dramatically higher procedural morbidity than an ASA III patient undergoing cataract extraction under topical anaesthesia.

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3. Cardiovascular Risk Stratification: RCRI, METs, and ESC/ESAIC Guidelines

Cardiovascular complications—including acute myocardial infarction, acute pulmonary edema, ventricular fibrillation, and cardiac arrest—represent the primary causes of perioperative death in non-cardiac surgery.

The Revised Cardiac Risk Index (RCRI / Lee Index)

Developed by Lee and colleagues, the RCRI is the most widely validated and utilized risk-scoring tool for predicting Major Adverse Cardiac Events (MACE: myocardial infarction, pulmonary edema, ventricular fibrillation, complete heart block, or cardiac arrest) within 30 days of non-cardiac surgery.

The RCRI assesses 6 independent clinical predictors, each scoring 1 point:

1. High-Risk Surgery: Intraperitoneal, intrathoracic, or suprainguinal vascular surgery.
2. History of Ischemic Heart Disease: Prior myocardial infarction, positive exercise stress test, current complaint of angina pectoris, use of sublingual nitrate therapy, or ECG showing pathological Q waves.
3. History of Congestive Heart Failure: Prior clinical diagnosis of heart failure, history of paroxysmal nocturnal dyspnea, history of pulmonary edema, physical findings of bilateral rales, an $S_3$ gallop, or chest radiograph demonstrating pulmonary venous congestion.
4. History of Cerebrovascular Disease: Prior transient ischemic attack (TIA) or stroke.
5. Preoperative Treatment with Insulin: Diabetes mellitus managed with insulin therapy (diet- or oral-hypoglycemic-controlled diabetes does not score a point).
6. Preoperative Renal Impairment: Preoperative serum creatinine $>170\text{ }\mu\text{mol/L}$ ($>2.0\text{ mg/dL}$).

Note on Modern Rates: Contemporary cohorts report higher baseline MACE rates than Lee's 1999 study due to high-sensitivity cardiac troponin assays detecting subclinical myocardial injury after noncardiac surgery (MINS).

Functional Capacity Assessment (METs)

Functional capacity is a powerful independent predictor of perioperative cardiovascular and pulmonary outcomes. It is quantified in Metabolic Equivalents of Task (METs), where: $1\text{ MET} = 3.5\text{ mL } \text{O}_2/\text{kg/min}$ This represents the resting basal oxygen consumption of an average seated adult.

• Poor Functional Capacity ($<4\text{ METs}$): Inability to climb two flights of stairs, walk up a steep hill, or walk at $4\text{ km/h}$ on level ground. Associated with significantly higher postoperative cardiac events, pulmonary morbidity, and 30-day mortality.
• Moderate Functional Capacity ($4\text{--}10\text{ METs}$): Able to climb a flight of stairs without stopping, perform heavy housework (scrubbing floors, moving furniture), or walk on level ground at $6\text{ km/h}$.
• Excellent Functional Capacity ($>10\text{ METs}$): Participation in strenuous sports (swimming, singles tennis, running, cycling) or heavy manual labor. Patients with $>10\text{ METs}$ rarely experience perioperative cardiac complications even in the presence of stable coronary artery disease.

                          [ FUNCTIONAL CAPACITY IN METs ]
                                         |
         +-------------------------------+-------------------------------+
         |                               |                               |
   [ < 4 METs ]                   [ 4 - 10 METs ]                  [ > 10 METs ]
   (Poor Reserve)                (Moderate Reserve)             (Excellent Reserve)
         |                               |                               |
• Cannot climb 1-2 flights       • Climbs 1-2 flights of stairs   • Strenuous athletics
• Cannot walk up a hill          • Walks briskly on level ground  • Running, swimming
• High perioperative risk        • Heavy housework / scrubbing    • Negligible cardiac risk

ESC/ESAIC Perioperative Cardiovascular Guidelines

The 2022 European Society of Cardiology (ESC) guideline on non-cardiac surgery, endorsed by ESAIC, recommends a structured clinical pathway:

1. High-Sensitivity Cardiac Troponin (hs-cTnI / hs-cTnT): Recommended preoperatively and at 24 and 48 hours postoperatively in patients undergoing intermediate- or high-risk non-cardiac surgery who have known cardiovascular disease, cardiovascular risk factors (including age $\ge 65\text{ years}$), or symptoms suggestive of cardiovascular disease (Class I).
2. B-Type Natriuretic Peptides (BNP / NT-proBNP): Measurement should be considered (Class IIa) in the same high-risk population before intermediate- or high-risk surgery; the Canadian guideline uses age $\ge 65$ or RCRI $\ge 1$ as its trigger. Elevated preoperative NT-proBNP independently predicts 30-day mortality and MACE.
3. 12-Lead Electrocardiogram (ECG): Recommended in patients with known cardiovascular disease, symptoms, or undergoing intermediate- to high-risk surgery. Not routinely recommended in asymptomatic patients undergoing low-risk surgery.
4. Transthoracic Echocardiography (TTE): Indicated in patients with newly detected murmurs, unexplained dyspnea, suspected or known heart failure with clinical deterioration, or prior to high-risk surgery in patients with poor or unknown functional capacity. Routine TTE is not recommended in stable, asymptomatic individuals.
5. Non-Invasive Stress Imaging: Pharmacological (dobutamine or dipyridamole) stress echocardiography or myocardial perfusion scintigraphy is indicated only in patients with poor functional capacity ($<4\text{ METs}$) scheduled for high-risk non-cardiac surgery if the results would alter clinical management (e.g., prompting coronary revascularization prior to elective surgery).

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4. Pulmonary Risk Assessment: The ARISCAT Score

Postoperative Pulmonary Complications (PPCs)—including atelectasis, pneumonia, acute respiratory failure, and acute respiratory distress syndrome (ARDS)—occur with equal or greater frequency than cardiac complications and markedly prolong hospital length of stay.

The ARISCAT Score (Assess Respiratory Risk in Surgical Patients in Catalonia) evaluates 7 independent clinical risk factors for PPCs:

ARISCAT Risk Stratification

• Low Risk ($<26\text{ points}$): PPC risk $\approx 1.6\%$.
• Intermediate Risk ($26\text{--}44\text{ points}$): PPC risk $\approx 13.3\%$.
• High Risk ($\ge 45\text{ points}$): PPC risk $\approx 42.1\%$.

Clinical Significance: Notice that surgical site (upper abdominal or intrathoracic incision) and surgical duration ($>3\text{ hours}$) contribute enormous weight to the score due to diaphragmatic splinting, impaired functional residual capacity ($FRC$), and atelectasis formation.

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5. Preoperative Fasting Guidelines and Gastric POCUS

Pulmonary aspiration of gastric contents is a devastating anaesthetic complication, leading to chemical pneumonitis (Mendelson's syndrome), acute hypoxemic respiratory failure, and death. Fasting protocols minimize residual gastric volume while avoiding prolonged dehydration and ketosis.

European Preoperative Fasting Guidelines

Two European documents apply: the European Society of Anaesthesiology (ESA, now ESAIC) 2011 guideline for adults and children, and the ESAIC 2022 paediatric fasting guideline, which shortened the intervals for children.

            [ EUROPEAN FASTING INTERVALS FOR ELECTIVE SURGERY ]

  ADULTS (ESA 2011)
    Clear fluids ............ until 2 h before induction
    Solid food .............. until 6 h before induction

  CHILDREN (ESAIC 2022)
    Clear fluids ............ until 1 h before induction
    Breast milk ............. until 3 h before induction
    Formula / non-human milk  until 4 h before induction
    Solid food .............. until 6 h before induction

• Clear Fluids — 2 hours in adults, 1 hour in children: Water, pulp-free fruit juice, tea or coffee (the adult guideline accepts a small amount of milk, up to about one-fifth of the cup), and carbohydrate-rich preoperative drinks. Clear liquids leave the stomach exponentially with a half-time of roughly $15-20\text{ minutes}$, so little residual volume remains at the fasting limit.
• Breast Milk — 3 hours (ESAIC 2022 paediatric guideline): The older European and ASA recommendation was 4 hours.
• Formula and Non-Human Milk — 4 hours in infants and children (ESAIC 2022): Cow's milk curdles in gastric acid, so in adults it is treated like food.
• Solid Food — 6 hours: Applies to a light meal (e.g., toast and tea) in both adults and children.
• 8 Hours — Fried or Fatty Meals and Meat: This additional interval comes from the American Society of Anesthesiologists (ASA) 2017 practice guideline rather than the European guidelines; such meals empty more slowly.

Important Provisos: These guidelines apply strictly to elective patients without conditions causing delayed gastric emptying (e.g., gastroparesis, trauma, opioid administration, active labor, bowel obstruction, or acute pain).

Gastric Point-of-Care Ultrasound (POCUS)

Gastric POCUS has emerged as an objective bedside tool to evaluate gastric contents and aspiration risk when fasting status is ambiguous or delayed emptying is suspected.

• Scanning Technique: A curvilinear low-frequency transducer ($2-5\text{ MHz}$) is placed in the epigastrium in a sagittal or parasagittal plane. The gastric antrum is imaged between the left lobe of the liver anteriorly, the pancreas posteriorly, and the abdominal aorta or inferior vena cava.
• Anatomical Positions: Evaluated first in the supine position, and subsequently in the right lateral decubitus (RLD) position (which shifts gravity-dependent fluid into the antrum).

Perlas Qualitative Grading System

1. Grade 0 (Empty Stomach): The antrum appears completely collapsed with flat, opposing anterior and posterior walls (resembling a "bull's eye" or "target"). Antrum is empty in both supine and RLD positions. Indicates negligible gastric volume ($<0.4\text{ mL/kg}$); extremely low aspiration risk.
2. Grade 1 (Low-Volume Clear Fluid): The antrum appears empty or collapsed in the supine position, but clear hypoechoic fluid is visualized when the patient turns into the right lateral decubitus (RLD) position. Correlates with physiological baseline gastric secretions ($<1.5\text{ mL/kg}$); considered safe for elective induction in the vast majority of patients.
3. Grade 2 (High-Volume Clear Fluid): Clear hypoechoic fluid is readily visible distending the gastric antrum in both supine and RLD positions. Correlates with elevated gastric volume ($>1.5\text{ mL/kg}$); signifies high aspiration risk. Elective surgery should be postponed, or rapid sequence induction (RSI) employed.
4. Solid Contents (Any Position): Presence of hyperechoic particulate material with acoustic shadowing ("frosted glass" appearance). Indicates a full stomach regardless of position; elective procedures must be delayed.

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6. Perioperative Chronic Medication Management

Managing chronic pharmacotherapy requires balancing the risk of rebound physiological exacerbations against adverse anaesthetic drug interactions.