General Anesthetics Flashcards
Components of Anesthetic State
Amnesia
Unconsciousness
Analgesia
Immobility in response to noxious stimuli
Define MAC
Minimal alveolar concentration –> Measured by concentration of anesthetic in the end-tidal expired air (correlates well with concentration at the site of action – brain)
Molecular Targets of Anesthetics
GABA(A) receptors
NMDA receptors
Other membrane associate proteins
Stages of General Anesthesia
- Pre-medicatoin
- Induction
- Maintenance
Parenterally administered Anesthetic
Barbiturate
Activates GABA(A) receptors; used to induce anesthesia; 1/2 life = 12 hours (hangover)
Sodium Thiopental
SE of Sodium Thiopental
CNS depression (decrease O2 demand, decrease BF, decrease intracranial P); CV vasodilator; Respiratory depression
Most commonly used anesthetic in the US; GABA(A) mechanism; Used to induce and maintain anesthesia; anti-emetic; Half-life in body: 3.5 hrs (less hangover)
Propofol
SE of Propofol
Pain on injection; Can cause initial excitation on induction; CNS effects; CV Effects more severe reduction in BP than thiopental and depression of myocardial contractility; Respiratory: more depression than Thiopental
Used to induce anesthesia in patients at risk for hypotension
Etomidate
SE of Etomidate
Pain on injection, myoclonus; N/V; Suppression of adrenocortical response to stress – only used to induce anesthesia in patients with hemodynamic problems
Also CNS SE; CV: less than thiopental; Respiratory: less than thiopental
Produces dissociative anesthesia; NMDA receptor antagonist; No effect on respiration
Ketamine
SE of Ketamine
Nystagmus, salivation, lacrimation, increase muscle tone and spontaneous movement;
Increased intracranial pressure d/t increased cerebral blood flow;
Emergence delirium; Hypertension (sympathomimentic)
What populations is Ketamine useful for?
Patients with bronchospasm; Children undergoing short, painful procedures
Short acting benzodiazepine; GABA(A) activator; Used for conscious sedation, anxiolysis, amnesia during short procedures; Used preoperatively to decrease anxiety
Midazolam
How does Midazolam differ from Sodium Thiopental?
Slower induction and longer duration; Metabolized by hydroxylation to active metabolite
SE of Midazolam
Respiratory depression and arrest (IV); Use with caution in patients with NM disease, Parkinson’s, Bipolar; CV effects similar to Thiopental
What does it mean if a anesthetic has a low blood:gas PC?
- Need high amounts in inspired air
- Induction is quick (equilibrium is reached quickly)
- Recovery will be quick (drug moves out of blood into gas readily)
What does it mean if a anesthetic has a high blood:gas PC?
- Need less in inspired air
2. Induction and recovery are slow (equilibria is reached slowly)
What does it mean if an anesthetic has a high fat:blood PC?
Half-life will be long (hang over) d/t slow release into blood; enough gets into brain to make the patient feel sleepy
What are some factors that affect induction with a gaseous anesthetic?
- Anesthetic concentration in the inspired air
- Pulmonary Ventilation
- Pulmonary BF
- Arteriovenous concentration gradient
When is anesthesia achieved with gaseous anesthetics?
Anesthesia is achieved when the brain partial pressure is equal to MAC
How does elimination of the gas occur?
Reverse of induction: gas moves from blood into inspired air
Rate of elimination is dependent upon the blood:gas partition coefficient (lowest eliminated fastest)
Gas needs to get into the blood to be eliminated
Moderate blood:gas PC; Excreted unchanged in expired air
Isoflurane
What is Isoflurane used for?
Can be used to induce and maintain; but mostly for maintenance
SE of Isoflurane
Airway irritant, coughing, decreases tidal volume and increases respiratory rate; CV: myocardial depression, decreases BP, arrythmias, cerebral vessel vasodilation
Very low solubility in blood; induction and recovery are rapid; Excreted unchanged in expired air
Desflurane
What are the clinical uses of Desflurane?
Outpatient surgeries/maintenance; Skeletal muscle relaxation
SE of Desflurane
CV; Respiratory: worse irritant, can produce bronchospasm
Very low blood: gas partition coefficient; 5% of administered does is metabolized to fluoride ion in the liver; Degraded to compound A by absorbents
Sevoflurane
What are the clinical uses of Sevoflurane?
Very popular; Inpatient and outpatient, can be used to induce and maintain in children and adults; NOT a respiratory irritant
Very insoluble in blood, rapidly equilibrates; Uptake from air results in increased concentration of other anesthetics; Useful for induction
Nitrous Oxide
Why do you patients need to breathe 100% O2 during emergence when given N2O?
N2O can dilute oxygen
What are some clinical uses of N2O?
Weak anesthetic; Good for sedation and analgesia; Used together with other inhaled anesthetics to reduce dose needed
What is N2O CI for?
Pneumothorax
