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Pharmacokinetic Principles
Clinical overview
Physiology of inhaled anesthetics
Clinical
100
At equilibrium, the CNS partial pressure of inhaled anesthetics equals to?
At equilibrium, the CNS partial pressure of inhaled anesthetics equal their arterial partial pressure, which in turn equals their alveolar partial pressure if cardiopulmonary function is normal.
100
The most potent volatile anesthetic?
What is :Isoflurane is the most potent of the volatile anesthetics in clinical use,has great physical stability, and undergoes essentially no deterioration during storage for up to 5 years or on exposure to sunlight.
100
Age effect on MAC?
What is :MAC decreases with age and there are similarities between agents in the decline in MAC and age. Excluding data in patients <1 year of age (where MAC can be lower)
100
This inhaled anesthetic is the weakest trigger for MH and does not relax skeletal muscles?
All of the potent volatile anesthetics serve as triggers for malignant hyperthermia (MH) in genetically susceptible patients. In contrast, nitrous oxide is only a weak trigger for MH. The augmentation of caffeine-induced contractures by nitrous oxide is 1.3-fold, by isoflurane is 3-fold, and by halothane, 11-fold. Although desflurane is a weak trigger for MH, it has been associated with an unusual delayed onset of symptoms of MH in animals and humans.
200
Which of the inhaled anesthetics are true gases?
What is :Technically, of the inhaled anesthetics only nitrous oxide and xenon are true gases,while the so-called potent agents are the vapors of volatile liquids
200
Accumulation of this anesthetic can diminish hearing postoperatively?
What is :Accumulation of nitrous oxide in the middle ear can diminish hearing postoperatively and is relatively contraindicated for tympanoplasty because the increased pressure can dislodge a tympanic graft. Seventy-five percent nitrous oxide can expand a pneumo-thorax to double or triple its size in 10 and 30 minutes, respectively
200
The increase in CBF with increasing dose caused by the potent agents occurs despite decreases in CMR, how this phenomenon called?
This phenomenon has been called uncoupling, but from a mechanistic standpoint, true uncoupling of flow from metabolism may not occur. That is, as CMR is depressed by the volatile anesthetics, there still is a coupled decline in CBF opposed by a coincident direct vasodilatory effect on the cerebral blood vessels. The net effect on the cerebral vessels depends on the sum of indirect vasoconstricting and direct vasodilating influences
200
People who chronically abuse nitrous oxide likely to develop?
A sensory motor polyneuropathy that is often combined with signs of posterior lateral spinal cord degeneration has been described in humans who chronically inhale nitrous oxide for recreational use.. These effects have been attributed to reduced activity of the vitamin B12-dependent enzymes.
300
Recovery from anesthesia, like induction, depends on?
What is:Recovery from anesthesia, like induction, depends on anesthetic solubility, cardiac output, and minute ventilation. Solubility is the primary determinant of the rate of fall of FA
300
In extremely dry CO2 absorbers degrades to form carbon monoxide the most?
What is :In extremely dry CO2 absorbers, desflurane (and to a lesser extent isoflurane, enflurane, and sevoflurane) degrades to form carbon monoxide.
300
This anesthetic gas at 1 MAC results in minimal, if any, changes in steady-state heart rate?
In volunteers, sevoflurane up to about 1 MAC results in minimal, if any changes in steady-state heart rate while enflurane, isoflurane, and desflurane increase it 5 to 10% from baseline . Both desflurane and, to a lesser extent, isoflurane have been associated with transient and significant increases in heart rate during rapid increases in the inspired concentration of either anesthetic
300
The metabolism of this gas may result in injury to renal collecting tubules?
The metabolism of enflurane may result in a well-described injury to renal collecting tubules.The nephrotoxicity presents as a high-output renal insufficiency that is unresponsive to vasopressin and is characterized by dilute polyuria, dehydration, serum hypernatremia, hyperosmolality, elevated blood urea nitrogen, and creatinine
400
During recovery from anesthesia, washout of high concentrations of nitrous oxide can lower alveolar concentrations of oxygen and carbon dioxide, a phenomenon called?
What is :During recovery from anesthesia, washout of high concentrations of nitrous oxide can lower alveolar concentrations of oxygen and carbon dioxide,a phenomenon called diffusion hypoxia.
400
It is nonexplosive, nonpungent, and odorless, and thus can be inhaled with ease?
What is :Xenon is an inert gas. Difficult to obtain, and hence extremely expensive, it has received considerable interest in the last few years because it has many characteristics approaching those of an “ideal” inhaled anesthetic, although it can trigger malignant hyperthermia.
400
Effect of volatile anesthetics on ventilatory effects?
All volatile anesthetics decrease tidal volume and increase respiratory rate such that there are only minor effects on decreasing minute ventilation. The ventilatory effects are dose-dependent, with higher concentrations of volatile anesthetics resulting in greater decreases in tidal volume and greater increases in respiratory rate, with the exception of isoflurane, which does not increase respiratory rate above 1 MAC
400
This medication if not stopped 24-48 hrs prior to the surgery, it may abolish anesthetic preconditioning?
A preconditioning stimulus such as brief coronary occlusion and ischemia initiates a signaling cascade of intracellular events that reduces ischemia and reperfusion myocardial injury. Sulfonylurea oral hyperglycemic drugs close KATP channels, abolishing anesthetic preconditioning. They should be discontinued 24 to 48 hours prior to elective surgery in high-risk patients
500
Henry's Law states:
At constant temperature, the amount of a given gas dissolved in a given liquid is directly proportional to the partial pressure of the gas in contact with the liquid. Anesthetic gases in the lungs diffuse into blood until the partial pressures in the lungs and blood are equal.
500
The metabolism of Sevoflurane results in ?
The metabolism of sevoflurane results in inorganic fluoride; the increase in plasma fluoride after sevoflurane administration has not been associated with renal-concentrating defects.Unlike other potent volatile anesthetics, sevoflurane is not metabolized to trifluoroacetate; rather, it is metabolized to anacyl halide (hexafluoroisopropanol). This does not stimulate formation of antibodies.
500
Alveolar concentration of anesthetic that blunts adrenergic responses to noxious stimuli known as?
MAC-BAR and is approximately 50% higher than standard MAC. MAC awake?
500
What is the typical time to LOC with Sevoflurane?
The typical time to loss of consciousness is 60 seconds when delivering 8% Sevoflurane via mask. Laryngeal mask placement can be successfully achieved 2 minutes after administering 7% sevofluranevia the face mask.