Patient-specific Risk Factors

“Never treat a stranger.” Identification of patient-specific risk factors is predicated on data obtained from the physical evaluation.1 Past and present illnesses; major hospitalizations; review of organ systems; family history; social history; history of drug allergies and other adverse drug effects; medications, vitamins and other dietary supplements (including special diets) currently taken by the patient must be considered in determining perioperative risk.

Since the stress-response is mediated primarily by the sympathoadrenal system, the history should also seek to determine the patient’s functional capacity (FC).13 FC relates to a person’s functional reserve, which correlates well with maximum oxygen uptake during treadmill testing and is expressed in metabolic equivalents (METs). One MET equals the resting or basal oxygen requirement (i.e., 3.5 ml of O2 per kg per minute) of a 40–year-old, 70-kg man.

A validated method to determine FC, predicated on a person’s ability to perform a spectrum of common daily activities, is presented in Box C.14-16 FC is classified as excellent (>10 METs), good (7 METs to 10 METs), moderate (6 METs to 4 METs), or poor (<4 METs). The inability of a person to climb two flights of stairs or to run a short distance indicates poor functional capacity (<4 METs). When functional capacity is low, the risk of a medical emergency is high.13

Box C. Estimated Energy Requirement for a Spectrum of Common Daily Activities.13-15

1 MET



<4 METs
Can you…
  • Take care of yourself?
  • Eat, get dressed, or use the toilet?
  • Walk indoor around the house?
  • Walk 100 m on level ground at 3 to 5 km per hour
≥4 METs



>10 METs
Can you…
  • Climb two flights of stairs or walk uphill, or run a short distance?
  • Do heavy work around the house like scrubbing floors or lifting or moving heavy furniture?
  • Participate in strenuous sports like swimming, singles tennis, football, basketball, or skiing?

For example, a person with no evidence of coronary artery disease (CAD), but who reports a history of sedentary lifestyle and has poor FC may benefit from a preoperative evaluation. Conversely, a patient considered high risk because of a history of CAD who is asymptomatic and runs 30 minutes daily may need no further cardiovascular testing before proceeding with planned dental procedures, i.e., when functional capacity is high, the risk of a medical emergency is low.

Physical examination is also part of risk assessment.1,13 A patient’s mental state and general appearance, e.g., cyanosis, pallor, diaphoresis, shortness of breath, tightness and/or pain in the chest with minimal activity, tremor, anxiety, and peripheral edema are signs and symptoms that provide invaluable clues regarding the patient’s overall health status. Critically, the physical examination must also include a determination of the patient’s baseline vital signs Box D.1,13

Box D. Vital Signs.1

Blood pressure
  • Normal: <120/80 mm Hg
  • Prehypertension: 120-139/80-89 mm Hg
  • Abnormal; <90/50 or ≥140-90 mm Hg
Pulse rate and rhythm
  • Normal – adult: 60-100 beats/min.
  • Normal – child: 90-120 beats/min.
  • Normal – aged: 70-89 beats/min.
  • Abnormal: <90/50 or ≥140-90 mm Hg
Rate of respiration
  • Normal – adult: 16-20 breaths/min.
  • Normal – child: 24-28 breaths/min.
  • Abnormal: rates <10 or >20 breaths/min.
Body temperature
  • Normal: ≈37°C (orally)
  • Maximum circadian variation: ≈0.6°C
  • Fever: ≥37.8°C (orally)

Predicated on patient-specific risk factors identified during the physical evaluation, the American Society of Anesthesiology (ASA) Physical Status (PS) Classification system provides a practical method to quantify perioperative risk for patients undergoing surgical (and by extension dental) procedures (Box E).17,18 The rate of perioperative complications in medicine correlates closely to the ASA PS classification and ranges from 0.4/1000 for ASA PS I to 9.6/1000 for ASA PS IV.19

Box E. Modified ASA Physical Status Classification.16,17

Physical Status Risk of Major Medical Event
ASA PS I
  • Normal healthy patient
    • No limitation on physical activity
      • Excellent functional capacity
        • >10 METs
  • Remote risk
    • No organic, physiologic, or psychiatric problems
      • Excludes the very young and the very old
ASA PS II
  • Patient with well-controlled mild systemic disease affecting one organ system
    • No substantive functional limitations
      • Good functional capacity
        • 7 to 10 METs
  • Minimal risk
    • Well-controlled hypertension (HTN); diabetes mellitus (DM); respiratory problems, i.e., asthma or chronic obstructive pulmonary disease (COPD); seizure disorder
    • Mild obesity (BMI 30-39)
    • Pregnancy
ASA PS III
  • Patient with one or more moderate-to-severe systemic disease
    • Substantive functional limitation (but not incapacitating)
      • Moderate functional capacity
        • 4 to 6 METs
  • No immediate risk
    • Poorly controlled DM or HTN
    • Asymptomatic congestive heart failure (CHF)
    • Stable angina
    • History of (>3 months) myocardial infarction, cerebrovascular accident (CVA), transient ischemic attack (TIA), or coronary artery stents
    • Morbid obesity (BMI ≥40)
    • End stage renal disease (ESRD), patient undergoing regularly scheduled dialysis
    • Respiratory problems with intermittent symptoms (asthma, COPD)
ASA PS IV
  • Patient has at least one severe systemic disease that is poorly controlled or at end-stage that is a constants threat to life
    • Substantive functional limitation (incapacitating)
      • Poor functional capacity
        • <4 METs
  • Possible risk
    • History of recent (<3 months) of MI, CVA, TIA
    • Unstable angina
    • Severe valve dysfunction
    • Symptomatic COPD
    • Symptomatic CHF
    • Hepato-renal failure
    • ESRD, patient not undergoing regularly scheduled dialysis
ASA PS V
  • Moribund patients, not expected to survive 24 hours without medical or surgical intervention
    • No residual functional reserve
  • Imminent risk
    • Multi-organ failure