Pharmacology · General Anesthesia

Organ-Specific Effects of Inhalational Anesthetics

Pulmonary, hepatic, renal, skeletal muscle, and obstetrical pharmacology

Malignant hyperthermia is placed first and given the most real estate because it is the only inhalational anesthetic adverse effect that kills in the operating room without warning. The table works through it systematically: genetics, triggers, mechanism, earliest sign, and treatment in order — the order you need them in an emergency.
The earliest sign is rising end-tidal carbon dioxide, not fever. The infographic makes that explicit because acting on the early metabolic signal is what saves lives; waiting for hyperthermia is what does not.
The hepatotoxicity table is a rank order built on one variable: what fraction of each agent undergoes hepatic metabolism to trifluoroacetylated proteins. Halothane leads by an order of magnitude. Sevoflurane metabolizes substantially but through a different pathway and does not generate the neoantigen that triggers immune hepatitis.
The pulmonary and obstetrical cards share a common thread — both involve situations where a volatile agent's normal effects become hazards at higher doses. Bronchodilation is beneficial; airway irritation with desflurane is not. Uterine relaxation is useful for specific obstetrical procedures; at concentrations above 1.5 minimum alveolar concentration during delivery it causes hemorrhage.
The renal summary in the rule box closes the organ survey. It is brief because the clinical bottom line is simple: fluoride-related nephrotoxicity from sevoflurane has not been demonstrated in humans despite elevated serum levels, and compound A from low-flow delivery remains a theoretical concern.

Malignant Hyperthermia — High Yield

Pharmacogenetic Crisis

Malignant Hyperthermia: Mechanism, Presentation, Treatment

Component	Key Facts
Genetics	Ryanodine receptor type 1 (RYR1) gene mutation — gain-of-function; autosomal dominant; sarcoplasmic reticulum calcium release channel is pathologically sensitive to triggers
Triggers	ALL volatile halogenated agents (halothane, isoflurane, sevoflurane, desflurane, enflurane) + succinylcholine. Nitrous oxide is NOT a trigger.
Mechanism	Uncontrolled calcium release from sarcoplasmic reticulum → sustained skeletal muscle contracture → massive hypermetabolism → heat, CO2, lactic acid, rhabdomyolysis, hyperkalemia
Earliest sign	Rapidly rising end-tidal CO2 unexplained by ventilation changes. Act on this — do not wait for fever (hyperthermia is a late sign).
Other signs	Tachycardia, masseter spasm, generalized muscle rigidity, hyperthermia (>40–41°C), metabolic acidosis, cardiovascular collapse
Treatment	1. Stop trigger — discontinue all volatile agents, flush circuit with 100% O2, switch to total intravenous anesthesia. 2. Dantrolene 2.5 mg/kg IV (repeat q5 min as needed). 3. Active cooling, bicarbonate, treat hyperkalemia, fluids for myoglobinuria.
Dantrolene mechanism	Binds ryanodine receptor type 1 → stabilizes sarcoplasmic reticulum calcium channel in closed state → stops uncontrolled calcium release
Prevention	Total intravenous anesthesia (propofol + opioids + nondepolarizing agents). Nitrous oxide permitted. Dantrolene must be immediately available in every operating room.

Hepatotoxicity — Trifluoroacetylation Rank Order

Comparative Risk

Volatile Agent Hepatotoxic Risk by Metabolic Fraction

Agent	Hepatic Metabolism	Risk Level
Halothane	~20% (highest)	Highest — immune hepatitis ~1:35,000; fatal on re-exposure
Enflurane	~2–5%	Very low — cross-reactive hepatitis possible
Isoflurane	~0.2%	Very low — rare case reports with prior halothane exposure
Sevoflurane	~3–5% (different pathway — hexafluoroisopropanol, not trifluoroacetyl)	Minimal — does not generate trifluoroacetylated proteins
Desflurane	<0.02% (lowest)	Negligible — preferred in patients with prior halothane hepatitis

Pulmonary and Obstetrical Effects

Pulmonary

Key Effects

All agents: dose-dependent respiratory depression; hypercapnia under spontaneous ventilation; controlled ventilation is standard
Bronchodilation: all volatile agents; sevoflurane and halothane most potent; avoid desflurane in reactive airways
Hypoxic pulmonary vasoconstriction inhibition: all volatile agents; worsens oxygenation during one-lung ventilation; propofol does not inhibit — preferred for thoracic total intravenous anesthesia

Obstetrical

Key Effects

Uterine relaxation: all volatile agents; dose-dependent; risk of atony and hemorrhage at concentrations above 1.5 minimum alveolar concentration
Cesarean section: keep volatile agent at or below 0.5–0.75 minimum alveolar concentration; administer oxytocin after delivery
Placental transfer: all volatile agents cross freely; fetal drug accumulation is a function of induction-to-delivery interval
Nitrous oxide in labor: 50% concentration provides analgesia via N-methyl-D-aspartate antagonism; minimal uterine relaxation
Deliberate uterine relaxation: volatile agents or intravenous nitroglycerin for retained placenta, uterine inversion

Renal: All volatile agents transiently reduce glomerular filtration rate (hemodynamic). Fluoride-induced nephrotoxicity risk: enflurane (subclinical at standard doses) > sevoflurane (systemic fluoride elevated but intrarenal metabolism minimal — no clinically significant nephrotoxicity demonstrated). Compound A from sevoflurane at low flow: nephrotoxic in rats, not demonstrated in humans.

Suggested References

Author / Organization	Title	Source
Katzung BG, ed.	Basic and Clinical Pharmacology. 15th ed.	McGraw-Hill; 2021
Brunton LL, Knollmann BC, eds.	Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed.	McGraw-Hill; 2023
Miller RD, ed.	Miller's Anesthesia, 8th ed. Chapters 27, 77	Philadelphia: Elsevier; 2015
Enkin M, et al.	A Guide to Effective Care in Pregnancy and Childbirth, 3rd ed.	Oxford: Oxford University Press; 2000
Dahan A, et al.	Sex-related differences in the influence of morphine on ventilatory control in humans	Anesthesiology. 1998;88(4):903–913
Goff MJ, et al.	Absence of bronchodilation during desflurane anesthesia: a comparison to sevoflurane and thiopental	Anesthesiology. 2000;93(2):404–408
Kenna JG, et al.	Halothane hepatitis in children	Br Med J (Clin Res Ed). 1987;294(6581):1209–1211
Njoku D, et al.	Biotransformation of halothane, enflurane, isoflurane, and desflurane to trifluoroacetylated liver proteins	Anesth Analg. 1997;84(1):173–178
Wulf H, et al.	Neuromuscular blocking effects of rocuronium during desflurane, isoflurane, and sevoflurane anesthesia	Can J Anaesth. 1998;45(6):526–532
Rosenberg H, et al.	Malignant hyperthermia: a review	Orphanet J Rare Dis. 2015;10:93
Kharasch ED	Sevoflurane and renal toxicity	Curr Opin Anaesthesiol. 1998;11(4):377–381
Flood P, Rathmell JP, Shafer SL, eds.	Stoelting's Pharmacology and Physiology in Anesthetic Practice, 5th ed.	Philadelphia: Wolters Kluwer; 2015
Stoelting RK, Hillier SC	Pharmacology and Physiology in Anesthetic Practice, 4th ed.	Philadelphia: Lippincott Williams & Wilkins; 2006
Mhyre JM, Healy D	The unanticipated difficult intubation in obstetrics	Anesth Analg. 2011;112(3):648–652
Mushambi MC, et al.	Obstetric Anesthetists' Association and Difficult Airway Society guidelines for the management of difficult and failed tracheal intubation in obstetrics	Anaesthesia. 2015;70(11):1286–1306