INHALATIONAL INDUCTION AGENTS

  MAC – minimum alveolar concentration = smallest concentration of inhalational agent at which 50% of patients will not move with incision

•  Small MAC → more lipid soluble = more potent

•  Speed of induction is inversely proportional to solubility

•  Nitrous oxide is fastest but has high MAC (low potency)

  Inhalational agents cause unconsciousness, amnesia, and some analgesia (pain relief)

  Blunt hypoxic drive

  Most have some myocardial depression, ↑ cerebral blood flow, and ↓ renal blood flow

  Nitrous oxide (NO₂) – fast, minimal myocardial depression; tremors at induction

  Halothane – slow onset/offset, highest degree of cardiac depression and arrhythmias; least pungent, which is good for children

•  Halothane hepatitis – fever, eosinophilia, jaundice, ↑ LFTs

  Sevoflurane – fast, less laryngospasm and less pungent; good for mask induction

  Isoflurane – good for neurosurgery (lowers brain O₂ consumption; no increase in ICP)

  Enflurane – can cause seizures

INTRAVENOUS INDUCTION AGENTS

  Sodium thiopental (barbiturate) – fast acting

•  Side effects: ↓ cerebral blood flow and metabolic rate, ↓ blood pressure

  Propofol – very rapid distribution and on/off; amnesia; sedative

•  Side effects: hypotension, respiratory depression

•  Not an analgesic

•  Do not use in patients with egg allergy

•  Metabolized in liver and by plasma cholinesterases

  Ketamine – dissociation of thalamic/limbic systems; places patient in a cataleptic state (amnesia, analgesia)

•  No respiratory depression

•  Side effects: hallucinations, catecholamine release (↑ CO₂, tachycardia), ↑ airway secretions, and ↑ cerebral blood flow

•  Contraindicated in patients with head injury

•  Good for children

  Etomidate – fewer hemodynamic changes; fast acting

•  Continuous infusions can lead to adrenocortical suppression

  Rapid sequence intubation – can be indicated for recent oral intake, GERD, delayed gastric emptying, pregnancy, bowel obstruction (pre-oxygenate, etomidate, succinylcholine typical sequence)

MUSCLE RELAXANTS (PARALYTICS)

  Diaphragm – last muscle to go down and 1st muscle to recover from paralytics

  Neck muscles and face – 1st to go down and last to recover from paralytics

  Depolarizing agents – only one is succinylcholine; depolarizes neuromuscular junction

  Succinylcholine – fast, short acting; causes fasciculations, ↑ ICP; many side effects →

•  Malignant hyperthermia

•  Caused by a defect in calcium metabolism

•  Calcium released from sarcoplasmic reticulum causes muscle excitation – contraction syndrome

•  Side effects: 1st sign is ↑ end-tidal CO₂, then fever, tachycardia, rigidity, acidosis, hyperkalemia

•  Tx: dantrolene (10 mg/kg) inhibits Ca release and decouples excitation complex; cooling blankets, HCO₃, glucose, supportive care

•  Hyperkalemia – depolarization releases K

•  Do not use in patients with severe burns, neurologic injury, neuromuscular disorders, spinal cord injury, massive trauma, or acute renal failure

•  Open-angle glaucoma can become closed-angle glaucoma

•  Atypical pseudocholinesterases – cause prolonged paralysis (Asians)

  Nondepolarizing agents

•  Inhibit neuromuscular junction by competing with acetylcholine

•  Can get prolongation of these agents with myasthenia gravis

•  Cis-atracurium – undergoes Hoffman degradation

•  Can be used in liver and renal failure

•  Histamine release

•  Rocuronium – fast, intermediate duration; hepatic metabolism

•  Pancuronium – slow acting, long-lasting; renal metabolism

•  Most common side effect – tachycardia

•  Reversing drugs for nondepolarizing agents

•  Neostigmine – blocks acetylcholinesterase, increasing acetylcholine

•  Edrophonium – blocks acetylcholinesterase, increasing acetylcholine

•  Atropine or glycopyrrolate should be given with neostigmine or edrophonium to counteract effects of generalized acetylcholine overdose

LOCAL ANESTHETICS

  Work by increasing action potential threshold, preventing Na influx

  Can use 0.5 cc/kg of 1% lidocaine

  Infected tissues are hard to anesthetize secondary to acidosis

  Length of action – bupivacaine > lidocaine > procaine

  Side effects: tremors, seizures, tinnitus, arrhythmias (CNS symptoms occur before cardiac)

  Epinephrine allows higher doses to be used, stays locally

•  No epinephrine with arrhythmias, unstable angina, uncontrolled hypertension, poor collaterals (penis and ear), uteroplacental insufficiency

  Amides (all have an “i” in first part of the name) – lidocaine, bupivacaine, mepivacaine; rarely cause allergic reactions

  Esters – tetracaine, procaine, cocaine; ↑ allergic reactions due to PABA analogue

NARCOTICS (OPIOIDS)

  Morphine, fentanyl, Demerol, codeine

  Act on mu-opioid receptors

  Profound analgesia, respiratory depression (↓ CO₂ drive), no cardiac effects, blunt sympathetic response

  Metabolized by the liver and excreted via kidney

  Overdose of narcotics – Tx: Narcan (works for all)

  Avoid use of narcotics in patients on MAOIs → can cause hyperpyrexic coma

  Morphine – analgesia, euphoria, respiratory depression, miosis, constipation, histamine release (causes hypotension), ↓ cough

  Demerol – analgesia, euphoria, respiratory depression, miosis, tremors, fasciculations, convulsions

•  No histamine release

•  Can cause seizures (buildup of normeperidine analogues) – avoid in patients with renal failure and be careful with total amount given for other patients

  Methadone – simulates morphine, less euphoria

  Fentanyl – fast acting; 80× strength of morphine (does not cross-react in patients with morphine allergy); no histamine release

  Sufentanil and remifentanil – very fast-acting narcotics with short half-lives

  Most potent narcotic – sufentanil

BENZODIAZEPINES

  Anticonvulsant, amnesic, anxiolytic, respiratory depression; not analgesic; liver metabolism

  Versed (midazolam) – short acting; contraindicated in pregnancy, crosses placenta

  Valium (diazepam) – intermediate acting

  Ativan (lorazepam) – long acting

  Overdose of these drugs – Tx: flumazenil (competitive inhibitor; may cause seizures and arrhythmias; contraindicated in patients with elevated ICP or status epilepticus)

EPIDURAL AND SPINAL ANESTHESIA

  Epidural anesthesia – allows analgesia by sympathetic denervation; vasodilation

•  Morphine in epidural can cause respiratory depression

•  Lidocaine in epidural can cause decreased heart rate and blood pressure

•  Dilute concentrations allow sparing of motor function

•  Tx for acute hypotension and bradycardia: turn epidural down; fluids, phenylephrine, atropine

•  T-5 epidural can affect cardiac accelerator nerves

•  Epidural contraindicated with hypertrophic cardiomyopathy or cyanotic heart disease → sympathetic denervation causes decreased afterload, which worsens these conditions

  Spinal anesthesia – injection into subarachnoid space, spread determined by baricity and patient position

•  Neurologic blockade is above motor blockade

•  Spinal contraindicated with hypertrophic cardiomyopathy, cyanotic heart disease

  Caudal block – through sacrum, good for pediatric hernias and perianal surgery

  Epidural and spinal complications – hypotension, headache, urinary retention (need urinary catheter in these patients), abscess/hematoma formation, respiratory depression (with high spinal)

  Spinal headaches – caused by CSF leak after spinal/epidural; headache gets worse sitting up; Tx: rest, fluids, caffeine, analgesics; blood patch to site if it persists > 24 hours.

PERIOPERATIVE COMPLICATIONS

  Pre-op renal failure (#1) and CHF – associated with most postop hospital mortality

  Postop MI – may have no pain or EKG changes; can have hypotension, arrhythmias, ↑ filling pressures, oliguria, bradycardia

  Patients who need cardiology workup pre-op – angina, previous MI, shortness of breath, CHF, walks < 2 blocks due to shortness of breath or chest pain, FEV₁ < 70% predicted, severe valvular disease, PVCs > 5/min, high grade heart block, age > 70, DM, renal insufficiency, patients undergoing major vascular surgery (peripheral and aortic)

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