Chapter 26: General Anesthesia, Monitored Anesthetic Care, and Sedation
Guedel classically described four stages of anesthesia for inhalation anesthetics. Which of the following findings occurs only in the stage of “surgical anesthesia”?
(A) unconsciousness and amnesia
(C) no movement except respiration
(D) increased muscular movement
(E) hypertension and tachycardia
The answer is C. Although Guedel's four stages and signs of anesthesia are mostly of historic interest, it is still frequently referenced:
Stage 1: awake to unconscious, analgesia increases
Stage 2: “excitement” stage to onset of automatic breathing, sympathetic activity (hypertension, tachycardia), purposeless movements, irregular respiration
Stage 3: “surgical anesthesia,” regular breathing, stable heart rate and blood pressure, no movement except respiration
Stage 4: anesthetic overdose, from cessation of respiration and collapse of circulation to death
Refs: Hewer CL. The stages and signs of general anaesthesia. Br Med J.1937;2(3996):274–276.
Urban BW, Bleckwenn M. Concepts and correlations relevant to general anaesthesia. Br J Anaesth. 2002;89(1):3–16.
During a preoperative consultation, a patient expresses concern about anesthetic awareness for their upcoming surgery. A discussion of risk factors for anesthetic awareness ensues. Which of the following situations has the lowest likelihood of anesthetic awareness?
(C) maintenance of anesthesia with a BIS number of 60
(D) maintenance of anesthesia with end-tidal anesthetic gas concentration >0.5 MAC
(E) maintenance of anesthesia with nitrous oxide (N2O)
The answer is C. Evidence suggests a maintenance anesthetic using a BIS-guided technique with the BIS titrated to 40 to 60 is effective at preventing awareness (as is an end-tidal anesthetic gas concentration >0.7 MAC). Anesthetic awareness can occur with:
low anesthetic delivery: error or interruption of delivery; use of only N2O for maintenance anesthesia
patients with low cardiovascular reserve: pregnancy, hypovolemia, or cardiac failure (caesarean section, cardiac surgery, emergency surgery, trauma surgery)
patients with high anesthetic requirement: tolerance to sedative medications (chronic alcohol, benzodiazepine, or opioid use)
Ref: Miller RD. Miller's Anesthesia, 8th ed. Philadelphia, PA: Elsevier; 2015.
Sevoflurane is used to perform an inhalation induction on a pediatric patient. Which of the following side effects is most likely?