Anesthesiology is the practice of autonomic nervous system (ANS) medicine (Grecu L. Autonomic nervous system: physiology and pharmacology. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds. Clinical Anesthesia. Philadelphia: Lippincott Williams & Wilkins; 2013: 362–407). Data recorded on the anesthesia record often reflect ANS function and homeostasis. Drugs used during anesthesia as well as painful stimulation and disease states frequently produce ANS-related side effects.