What is the clinical use of inhaled anesthetics?
volatile liquids that can be aerosolized in special vaporizer systems
What is balanced anesthesia?
combining 2 anesthetics
What are 2 ways to complete balanced anesthesia?
IV (induction) and inhaled (maintenance) or volatile anesthetics (induction) and IV (maintenance)
What are common inhaled anesthetics?
nitrous oxide, desflurane, sevoflurane, isoflurane, enflurane, halothane, methoxyflurane
What are common IV anesthetics?
barbiturates (thiopental and methohexital), benzodiazepines (midazolam and diazepam), opioid analgesics (morphine, fentanyl, sufentanil, alfentanil, remifentanil), propofol, ketamine, droperidol, etomidate, dexmedetomidine
What is Stage I of anesthesia (stage of analgesia)?
analgesia without amnesia initially, later analgesia with amnesia
What is Stage II of anesthesia (stage of excitement)?
pt appears delirious and may vocalize, respirations are irregular with vomiting possible (rapidly increase concentration to get over this stage), ends with re-establishment of regular breathing
What is Stage III of anesthesia (stage of surgical anesthesia)?
regular respirations and extends to complete cessation of respirations with changes in eye movements, reflexes, and pupil changes
What is Stage IV of anesthesia (stage of medullary depression)?
severe depression of CNS from vasomotor center and respiratory center (pt dies without full circulatory and respiratory support)
What is uptake and distribution of inhales anesthetics?
transfer of the anesthetic from alveolar air to the blood anf from the blood to the brain
What does uptake and distribution of inhaled anesthetics depend on?
solubility properties of anesthesia, anesthetic concentration of inspired air, pulmonary ventilation, pulmonary blood flow, and arteriovenous concentration gradient
What is one of the most important properties influencing the transfer of anesthetic from lungs to blood?
solubility properties of anesthesia
What are relatively insoluble in blood?
desflurane and nitrous oxide
What are highly soluble in blood?
halthane and isoflurane
Is there an inverse or direct relationship between blood solubility of an anesthetic to the rate of rise of tension in arterial blood?
What does anesthetic concentration in inspired air do?
direct effects on max tension in alveoli and rate of tension increase in arterial blood
What is the rate of rise of anesthetic gas tension in arterial blood dependent on?
rate and depth of ventilation
What does hyperventilation do to anesthesia?
increases the speed of induction
What does an increase in pulmonary blood flow (increased CO) do to anesthetics?
increases blood carrying capacity and decreases rate of rise in anesthetic tension in blood
What do patients in circulatory shock do to anesthetics?
decrease CO and increased ventilation will accelerate induction of anesthesia
What contains more drug venous or arterial blood?
What tissues accumulate anesthetics easily?
those that are highly vascularized
What determines the times it takes to recover from taking anesthetics?
rate of elimination from brain
What is the major route of elimination of anesthetics?
lungs into expired air
Do age and duration of anesthesia effect anesthesia gas tension?
Is anesthesia that is insoluble in blood/brain eliminated faster or slower?
What is the basic pharmacodynamics of inhales anesthetics?
depress spontaneous and evoke activity of neurons in brain through interactions and modification of ligand-gated ion channels
What is the primary target of general anesthetics?
GABA A Cl- channel
what do inhaled anesthetics, barbiturates, benzodiazepine, etomidate, and propofol facilitate?
activation of GABA A receptor (increase Cl- ion flux)
What is the primary target of ketamine?
antagonism of action of glutamic acid on NMDA receptor
What are the other targets of inhaled anesthetics?
hyperpolarization of cell membrane and decrease duration of opening of nicotinic receptor-activated cation channels
What is MAC?
minimal alveloar anesthetic concentration = median concentration that results in imobility in 50% pts when exposed to a noxious stimulus
What is the blood:gas partition coefficient, percent metabolism, and MAC of isoflurane?
1.40, <2%, 1.40
What is the blood:gas partition coefficient, percent metabolism, and MAC of halothane?
2.30, >40%, 0.75
What is the blood:gas partition coefficient, percent metabolism, and MAC of methoxyflurane?
12, >70%, 0.16
What is the blood:gas partition coefficient, percent metabolism, and MAC of nitrous oxide?
0.47, none, >100
What is the blood:gas partition coefficient, percent metabolism, and MAC of desflurane?
0.42, <0.05%, 6-7
What are the 4 chronic toxic effects of inhaled anesthetics?
hepatotoxicity, nephrotoxicity, malignant hyperthermia, and chronic toxcitiy
What causes hepatotoxicity?
halothane: reactive metabolites or an immune mediated response
What causes nephrotoxicity?
metabolism of metoxyflurane by renal β-lyase (only in methoflurane)
What is malignant hyperthermia?
AD genetic disorder of skeletal muscle characterized by tachycardia, HTN, muscle rigidity, hyperthermia, hyperkalemia, acid-base disturbance with acidosis
How do you Tx malignant hyperthermia?
dantrolene (Ca2+ release blocker
What are 4 disorders involved with chronic toxicity?
mutagenicity, carcinogenicity, effects on reproductive organs, and hematotoxicity
Are inhaled anesthtetics normaly mutagenic?
Who are at risk for carcinogenicity?
operating room personnel
What are the effects on reproductive organs from inhaled anesthetics?
higher rate of miscarriages (in OR personnel) and increased rate of abortions in pregnant women who undergo surgery
What inhaled anesthetic causes megaloblastic anemia?
What are the indications for IV anesthetics?
do not require vaporizing equipment, faster onset, rapid recovery, lack analgesic properties
What are the 2 IV barbiturates?
thiopental and methohexital
What are the effects of thiopental?
rapidly crosses BBB, rapid loss of consciousness (only brief), potent respiratory depressant (transient apnea), cerebral blood flow decreased
Who is thiopental indicated for?
pts with cerebral swelling
What are adverse effects of thiopental?
reduces hepatic blood flow and GFR, can worsen porphyria
What are the effects of methohexital?
central excitatory actvity (useful in neurosurgery) and choice for pts getting ECT
Why is methohexital preferred for quick ambulatory surgeries?
What are the effects of benzodiazepines?
sedation, anxiolysis, and amnesia (control agigitation); slower onset of CNS effects;
What are adverse effects of benzodiazepines?
deep sedation leading to prolonged recovery time with possible anterograde amnesia
What Tx can be given to decrease recovery time after using benzodiazepines?
What are the effects of opioid analgesics?
general anesthesia in pts undergoing CT or other major surgery
What are adverse effects of opioid analgesics?
awareness during anesthesia, unpleasant post-operative recall, chest wall rigidity, impaired ventilation, post-op respiratory depression, post-op morbidity, vent. Support, GI/bladder complications, mortality after CT surgery
What are the effects of propofol?
rapid recovery, ambulate sooner, feel better, induction and maintenance of anesthesia, component of balance anesthesia, used for outpatient procedures and long term sedation in crtically ill patients
Is propofol the best drug of choice for children?
no can lead to acidosis
What are the adverse effects of propofol?
apnea and pain at injection site
What are the effects of etomidate?
used for induction in pts with limited CV reserve (elderly), minimum CV and respiratory depression, HR unchanged, low incidence of apnea, rapid recovery, no analgesic effects
Since etomidate has no analgesic effects, what do you coadminister with?
What are the adverse effects of etomidate?
increased incidence of pain at injection site and may cause adrenocortical suppression
What are the effects of ketamine?
dissociative anesthesia, rapid distribution, highly abusive, CV stimulation (increases HR, BP, CO), inhibits NE reuptake, increases cerebral blood flow and oxygen consumption, reduces respiratory rate
When do you use ketamine?
poor risk elderly pts, high risk pts in cardiogenic or septic shock, and children undergoing painful procedures
What is the MOA of ketamine?
antagonism of the action of glutamic acid NMDA receptors
Who uses conscious sedation?
Why would you use conscious sedation?
alleviation of anxiety and pain in combination with an altered level of consciousness associated with use of smaller doses
What is the patient able to do in conscious sedation?
airway patent and responsible to verbal commands
What IV anesthetics are used in conscious sedation?
diazepam, midazolam, propofol, opioid analgesics (meperidine, fentanyl), and antagonist drugs (flumazenil and naloxone)
When is conscious sedation in ICU?
pt under severe stress and requiring mecahnical ventilation
What do you combine when using conscious sedation in ICU?
sedative-hypnotic drugs or low doses of IV anesthetics, NMJ blocks, and dexmedetomidine