General Anesthetics Flashcards
General anesthetics is divided into inhaled and IV anesthetics. What is the subdivision of inhaled anesthetics
Nitrous Oxide Halogenated Hydrocarbons: HEMIDS Fluranes Halothane Enflurane Methoxyflurane Isoflurane Desflurane Sevoflurane
what are the IV anesthetics and what are they used for
-used as adjuncts to inhaled anesthetics
Barbiturates Etomidate Ketoamine Opioids Propofol
what drug is usually used in the induction phase (phase from administration of anesthetic to development of surgical anesthesia)
IV Thiopental
what drug is used in the maintenance phase (phase where the patient is surgically anesthetized)
maintained with inhaled anesthetics
what are the stage of anesthesia with their signs
-Stage I: Analgesia. Amnesia.
-Stage II: Excitement. Delirium. Respiration is irregular. Vomiting. To avoid this
stage, thiopental is given IV before.
-Stage III: Surgical anesthesia. Unconsciousness.
-Stage IV: Medullary depression. No eye movement. Respiratory and cardiovascular
failure
most reliable indication that stage III has been reached (surgical anesthesia)
loss of eyelash reflex and establishment of respiratory pattern that is regular in rate and depth
mechanism of action of inhaled anesthetics
direct interactions with ligand gated ion channels
- GABA mediated inhibition at GABA-A receptors
- inhibition of nicotinic receptors
- interaction with glycine receptors
what is minimum alveolar concentration (MAC)
- standard of comparison for potency of general anesthesia
- % of alveolar gas mixture or partial pressure of anesthetic as a percentage of 760mmHg
- conc that results in immobility of 50% of patients when exposed to a noxious stimuli such as surgical incision (ED50)
things that decrease minimum alveolar concentration aka MAC
- opioid analgesics or sedative-hypnotics
- hypothermia
- hypothyroidism
- pregnancy
what increases MAC
anxiety
hyperthryoidism
SN: MAC is additive–> .7 MAC for isoflurane and .3 MAC for N20 = 1 MAC
relationship between MAC and liposolubility
as liposolubility (λ(oil:gas)) increases, MAC decreases because potency of anesthetic increases
relationship between blood solubility, rate of rise in tension of arterial blood, and onset of anesthesia
the higher the blood solubility ( λ(blood:gas) ) –> more molecules need to dissolve in blood –> arterial tension in blood increases slowly –> slower onset of anesthesia
high liposolubility is also associated with high blood solubility so more potent inhaled anesthetics have slower onset
relationship between ventilation, arterial tension, and blood solubility
- increase in pulmonary ventilation will cause only a slight increase in arterial tension if anesthetic has low blood solubility
- increase in pulmonary ventilation would cause a significant increase in arterial tension if anesthetic has high blood solubility
what are the CVS effects of inhaled anesthetics
- most depress cardiac contractility –> decreased mean arterial pressure
- Halothane and Enflurane cause myocardial depression via reduced cardiac output –> decreased mean arterial pressure
- Isoflurane, Desflurane, and Sevoflurane cause vasodilation –> decreased mean arterial pressure and have minimal effect on cardiac output
which inhaled anesthetics is best to give patient with myocardial dysfunction
the ones that have minimal effect on cardiac output –> Isoflurane, Desflurane, Sevoflurane
cardiac AE seen with use of halothane
it makes myocardium more sensitive to circulating catecholamines –> ventricular arrhythmias
which inhaled anesthetic is less suitable for patient with bronchospasm and why
Isoflurane and Desflurane because they are very pungent
which inhaled anesthetic is best to use for those with increased cerebral pressure due to brain tumor or injury and why?
Nitric oxide because it increases cerebral blood flow the least hence least increase in intracranial pressure
effect of halogenated hydrocarbon inhaled anesthetic on uterine smooth muscle
potent uterine relaxants
AE of inhaled anesthetics
Hepatotoxicity (Halothane)
Hematoxocity
Nephrotoxicity (Methoxyflurane)
Malignant Hyperthermia (esp with use of succinylcholine)
Megaloblastic Anemia (prolonged exposure to N2O causes decrease methionine synthase)
malignant hyperthermia is caused by what defect
defect in ryanodine receptor gene (RYR1) –> altered release of Ca
treatment of malignant hyperthermia
Dantrolene (prevents calcium release from sarcoplasmic reticulum
barbiturate most commonly used for induction of anesthesia
Thiopental
the other barbiturate is Methohexital
important effect of the barbiturates (name them)
thiopental and methohexital
- decreased intracranial pressure (good especially if cranial swelling)
- do not produced analgesia
important effects of using propofol and fospropofol
- post operative vomiting is unlikely
- no analgesia
- reduces intracranial pressure
AE of propofol
causes hypotension
type of patients that Etomidate is used on
those at risk for hypotension
important effect of etomidate
no analgesic
reduces intracranial pressure
AE of etomidate
nausea and vomiting
adrenocortical suppression
only IV anesthetic that has ability for analgesic properties and stimulation the cardiovascular system
Ketamine - dissociative anesthesia
good for geriatric patients and high risk patients in cardiogenic or septic shock because of cardiostimulatory properties
AE of Ketamine
- increases intracranial pressure
- emergence phenomena (post-op disorientation, sensory and perceptual illusions)
name the benzos given during surgery and their prupose
Diazepam, Lorazepam, Midazolam
for their anxiolytic and anterograde amnesic properties
what is used to achieve muscle relaxation during surgery
competitive neuromuscular blocker Pancuronium
Depolarizing blocker Succinylcholine
what is used to reverse the effect of competitive neuromuscular blockade
Neostigmine
used to prevent aspiration of stomach content
anti-emetic Ondansetron
prevents salivation and bronchial secretion and to protect heart from arrhythmias caused by inhalation agents and neuromuscular blockade
antimuscarinic - Scopolamine
