General anesthetics Flashcards
Inhalation anesthetics
Maintenance
Nitrous oxide
Halothane (PROTOTYPE)
Sevoflurane
Isoflurane
Desflurane
Continuously inhaled. Requires monitoring, special equipment, and ENDOTRACHEAL intubation
Recovery = exhalation
Narrow therapeutic index (2-4)
ETHER bonds
Mechanism: reversibly interact with hydrophobic sites of specific membrane proteins (signal transduction pathways). evidence: chiral anesthetics.
Targets: GABA-A, glycine receptor activity.
Inhibit glutamate, nicotinic, 5-HT3 receptors.
Voltage gated ion channels (Na+, K+): inhibit AP propagation
GPCRs
Equilibrium: exhaled = inhaled
Uptake affected by: BLOOD SOLUBILITY, ALVEOLAR BLOOD FLOW, PARTIAL PRESSURE
Intravenous anesthetics
Induction Methohexital (barbituate) Etomidate (non-barb) Propofol (non-barb) Ketamine (non-barb) Single IV dose Requires monitoring. No special equipment. Rapid onset Depth/duration not as well controlled --metabolism, renal clearance
Nitrous Oxide
Inhalation Higher partial pressure = less soluble. Low gamma (partition) Faster inducion HIGH MAC (needs a lot to do work) Low potency. Cannot produce anesthesia by itself.
Halothane
Inhalation
Prototype
Low partial pressure = high solubility = bigger blood compartment
MAC = .77
Sevoflurane
Inhalation
Induction in kids
MAC = 2.0
Isoflurane
Inhalation
MAC = 1.15
Desflurane
Inhalation
Lowest partition (gamma)
Fastest induction
High MAC (6.00)
Methohexital
Intravenous
Barbituate
Etomidate
Intravenous
Non-barbituate
Propofol
Intravenous
Non-barbituate
Ketamine
Intravenous
Non-barbituate
General anesthesia
Reversible CNS depression
Lose response to external stimuli
Permit surgical/noxious procedures
Dissociative sedation
Trance-like cataleptic state
Analgesia (ketamine) and amnesia
Retain airway reflexes and CV stability
Ideal general anesthetics
Anesthesia Analgesia/anxiolytic Amnesia Muscle relaxation Inhibit reflex responses to trauma Rapid Little/no systemic toxicity No anesthetic agents have all of these. Need adjuncts.
Stages of anesthesia
- Conscious, but drowsy. Variable analgesia.
- Excitement and delirium. Unconscious. Reflex to pain. Irregular respiration. RECOVERY from inhalation anesthesia.
- Surgical anesthesia
- Medullary depression. Death.
Induction –> Maintenance –> Emergence
CV effects during anesthesia
Decreased mean arterial pressure Systemic vasodilation Myocardial suppression Blunted baroreceptor reflex Reduced sympathetic tone
Respiratory effects during anesthesia
Reduced/eliminated ventilatory drive
Assisted ventilation needed
Lost gag/cough reflex
Reduced LES tone (endotracheal intubation)
Temperature effects during anesthesia
Hypothermia (<36C)
effects during anesthesia (during/after emergence)
N/v (stimulation of chemoreceptor zone) (treat: 5-HT3 antagonists)
return of sympathetic tone (tachy, HTN)
Shivering (tx: meperidine)
Partial pressure of inhaled anesthetics
% of total atmospheric pressure
Index of the molecule to leave liquid phase into gaseous phase
More water soluble = lower partial pressure
Increased PP: likes to stay in blood
Ex. High PP: NO. Low PP: halothane.
Blood solubility of inhaled anesthetics
Blood:gas partition coefficient
Gamma = [blood] / [gas]
LOW BLOOD SOLUBILITY = MORE RAPID INDUCTION
–counter-intuitive
“Second gas” effect
Bulk uptake of an agent can “pull” more agent into lung
Low solubility agents with high partial pressures (ex NO)
Deliver second gas with NO, the second gas will be delivered faster
Only good for first breath
Tissue solubility
Lipid content and rate of perfusion
Brain is highly lipophilic. 3x the flow of other tissues
Pulmonary ventilation rate
Maintains alveolar tension. Hastens induction.
Important for high blood solubility.
Potency of inhalation anesthetics
Minimum concentration required to induce anesthesia.
Minimum Alveolar Concentration (MAC)
1 MAC = partial pressure that prevents movement in 50% of adults in response to pain
NOT RELATED TO INDUCTION RATE
1.3 MAC is ED95 (usual for surgery)
Additive when co administered
