- The study of the relationship between a drug’s
dose, tissue concentration, and elapsed time is called pharmacokinetics
(how a body affects a drug). The study of drug action, including
toxic responses, is called pharmacodynamics (how a drug affects
- The greater the uptake of anesthetic agent, the
greater the difference between inspired and alveolar concentrations,
and the slower the rate of induction.
- Three factors affect anesthetic uptake: solubility
in the blood, alveolar blood flow, and the difference in partial
pressure between alveolar gas and venous blood.
- Low-output states predispose patients to overdosage
with soluble agents, as the rate of rise in alveolar concentrations
will be markedly increased.
- Many of the factors that speed induction also
speed recovery: elimination of rebreathing, high fresh gas flows,
low anesthetic-circuit volume, low absorption by the anesthetic
circuit, decreased solubility, high cerebral blood flow, and increased
- General anesthesia is an altered physiological
state characterized by reversible loss of consciousness, analgesia
of the entire body, amnesia, and some degree of muscle relaxation.
- The unitary hypothesis proposes that all inhalation
agents share a common mechanism of action at the molecular level.
This is supported by the observation that the anesthetic potency
of inhalation agents correlates directly with their lipid solubility
- The minimum alveolar concentration (MAC) is the
alveolar concentration of an inhaled anesthetic that prevents movement
in 50% of patients in response to a standardized stimulus
(eg, surgical incision).
- Prolonged exposure to anesthetic concentrations
of nitrous oxide can result in bone marrow depression (megaloblastic
anemia) and even neurological deficiencies (peripheral neuropathies and
- Halothane hepatitis is extremely rare (1 per
35,000 cases). Patients exposed to multiple halothane anesthetics
at short intervals, middle-aged obese women, and persons with a
familial predisposition to halothane toxicity or a personal history
of toxicity are considered to be at increased risk.
- Isoflurane dilates coronary arteries, but is
not nearly as potent a dilator as nitroglycerin or adenosine. Dilation
of normal coronary arteries could theoretically divert blood away
from fixed stenotic lesions. There have been conflicting reports
about whether the coronary steal syndrome causes regional myocardial
ischemia during episodes of tachycardia or drops in perfusion pressure.
- The low solubility of desflurane in blood and
body tissues causes a very rapid washin and washout of anesthetic.
- Rapid increases in desflurane concentration
lead to transient but sometimes worrisome elevations in heart rate,
blood pressure, and catecholamine levels that are more pronounced
than occur with isoflurane, particularly in patients with cardiovascular
- Nonpungency and rapid increases in alveolar
anesthetic concentration make sevoflurane an excellent choice for
smooth and rapid inhalation inductions in pediatric and adult patients.
Nitrous oxide, chloroform, and ether were the first universally
accepted general anesthetics. Ethyl chloride, ethylene, and cyclopropane
were also used; the latter was particularly popular because of the
fast induction associated with its use. Recovery from cyclopropane
was notable; because of its rapidity of effect and the fact that
it did not result in delirium, patients were more clear ...