General Anesthesia

Definition of anesthesia

Insensitivity to pain or painful stimuli(no response), achieved via general or regional techniques.

Three components of anesthesia

Amnesia(volatine anesthetic>sleep and dont remember) , Akinesia(muscle relaxants-dont move), Analgesia(opiods- limited pain)

MAC definition

Minimum alveolar concentration at which 50% of patients are akinetic. MAC 1.3=99% akinetic

Factors increasing MAC

Acute amphetamine use, cocaine, chronic alcohol use, young age, hyperthermia, red hair.

Factors decreasing MAC

Propofol, etomidate, barbiturates, benzos, ketamine, opioids, α2 agonists, acute alcohol, local anesthetics, hypothermia, hypercarbia, pregnancy, advanced age.

Inhaled anesthetics examples

Isoflurane, Sevoflurane, Desflurane, Nitrous oxide.

Blood solubility effect

Lower solubility → faster induction/recovery.

Lipid solubility effect

Higher solubility → higher potency (1/MAC).

IV anesthetics used for induction

Propofol, Etomidate, Ketamine, Benzodiazepines, Barbiturates.

Propofol mechanism

Potentiates GABA-A chloride currents.

Propofol key effects

Hypnosis, ↓Cerebral metabolic rate of O2, ↓CBF, ↓ICP, profound vasodilation, respiratory depression, antiemetic.

Etomidate key effects

Minimal hemodynamic change; adrenal suppression; no analgesia.

Ketamine mechanism

NMDA receptor antagonist.

Ketamine key effects

Cerebral vasodilator(inc CBF and Cerebral Metabolic Rate of O2) , Profound Analgesia, dissociation, ↑BP/HR/CO, bronchodilation, emergence reactions.

Benzodiazepine key effects

Sedation, anxiolysis, anterograde amnesia, anticonvulsant.

Barbiturate key effects

CNS depression, ↓CMRO2, ↓CBF, apnea, modest hypotension.

Methohexital

Barbituate, activates epileptic foci(stimulatory) and is used in ECT

Neuromuscular blocker classes and examples

Depolarizing (succinylcholine) and non-depolarizing (rocuronium, vecuronium, cisatracurium).

Succinylcholine contraindications

Burns, trauma, immobility, denervation injuries(ex: Stroke, spinal cord injury), muscular dystrophy, hyperkalemia risk.

Succinylcholine side effects

Bradycardia, arrhythmias, hyperkalemia, myalgia, ↑ICP, ↑IOP, malignant hyperthermia.

Malignant hyperthermia triggers

Volatile anesthetics + succinylcholine.

Malignant hyperthermia treatment

Stop triggers, give IV dantrolene, correct acidosis/hyperkalemia.

Reversal of Ach non-depolarizers

Neostigmine + glycopyrrolate OR Sugammadex (for roc/vec).

Sugammadex mechanism

Encapsulates rocuronium/vecuronium, removing them from NMJ.

Miller vs MAC Airway blade

MiLLer=straight L’s and MAC is curved like C

RSI definition

Rapid induction + succinylcholine; no mask ventilation; used for full stomach or aspiration risk.

Reasons NOT to use RSI

Contraindication to succinylcholine (hyperkalemia, MH, ↑ICP).

Airway assessment predictors

Oral Aperture/Interincisor gap(less than 3cm inc risk to inability to open mouth) Mallampati classification, thyromental distance(shortened=decreased space to dispalce tongue), cervical ROM, BMI(>30 is difficult airway)

Mallampati I,II,III, IV

I: Full visibility of soft palate, fauces, tonsillar pillars and uvula.

II: Visible soft palate, fauces and uvula

BAD:

III: Only soft palate and base of uvula visible

IV: Soft palate is not visible; only Hard palate

Mallampati IV

Only hard palate visible; highest difficulty risk.

IV Anesthetics Summary