Pre-operative Evaluation of Autonomic Functions

Core Autonomic Function Tests

The European Society of Cardiology recommends cardiovagal function tests, including heart rate variability during deep breathing, active orthostatism, and Valsalva maneuver, to assess parasympathetic function in patients with suspected autonomic dysfunction 2, 3
The American Heart Association suggests that tests should be performed with continuous beat-to-beat blood pressure and ECG monitoring in a quiet environment with temperature controlled between 21-23°C 3, 1
Patients should fast for 3 hours before testing and avoid nicotine, caffeine, theine, or taurine-containing drinks on the day of examination to ensure accurate results 3, 1
Test results should be interpreted according to age-specific reference values due to physiological reduction in heart rate variability with aging, as recommended by the American College of Cardiology 2, 1

The American Diabetes Association recommends testing for Type 1 diabetic patients with disease duration ≥5 years and all Type 2 diabetic patients, especially those with microangiopathic complications 2, 4
Patients with symptoms suggesting orthostatic or post-prandial hypotension or episodes of serious unfelt hypoglycemia should undergo testing, as suggested by the European Society of Anaesthesiology 5, 6
Patients with known neurodegenerative diseases, Parkinsonism, or peripheral neuropathies benefit from pre-operative autonomic evaluation, according to the American Academy of Neurology 1
Patients with prolonged QTc interval (>440 ms) on ECG should undergo autonomic testing, as recommended by the American Heart Association 4

Cardiac autonomic neuropathy (CAN) is associated with increased risk of perioperative hemodynamic instability and vasopressor requirements, as reported by the American Society of Anesthesiologists 2
Preoperative decrease in respiratory heart rate variability (respiratory sinus arrhythmia) predicts perioperative hemodynamic instability, according to the European Society of Anaesthesiology 2
Both general and regional anesthesia significantly affect sympathetic tone, with greater effects in patients with pre-existing autonomic dysfunction, as noted by the American Society of Anesthesiologists 2

If CAN is detected, ambulatory blood pressure monitoring should be performed to identify nocturnal non-dipping patterns, as recommended by the European Society of Cardiology 2, 4
QT interval should be measured on standard ECG; if prolonged, 24-hour ECG monitoring is indicated to detect paroxysmal ventricular rhythm disorders, according to the American Heart Association 2, 4

Drugs that may induce orthostatic hypotension should be avoided in patients with detected CAN, as recommended by the American Society of Anesthesiologists 2, 4
Perioperative vasopressor requirements correlate with the degree of dysautonomia, requiring careful titration, according to the European Society of Anaesthesiology 2
Patients with CAN have increased risk of myocardial infarction (which may be painless), increased cardiovascular events, and sudden death, as reported by the American Heart Association 4

Avoid testing during acute illness, stressful conditions, fever, infection, or dehydration, as recommended by the American College of Cardiology 1
Testing should not be performed during hypoglycemia or marked hyperglycemia, according to the American Diabetes Association 1
No single autonomic function test provides comprehensive assessment; different clinical questions require different test batteries, as noted by the European Society of Cardiology 3, 1