Chapter 8: Anesthesia Flashcards
Inhalational agents: effects
- Blunt hypoxic drive
- Caused unconsciousness, amnesia, some analgesia
- Most have myocardial depression, increase CBF, decrease RBF
MAC (minimum alveolar concentration)
Smallest concentration of inhalation agent at which 50% of patients will not move with incision
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
Manifestations of halothane hepatitis
Fever, eosinophilia, jaundice, increased LFTs
Sevoflurane
Fast, less laryngospasm and less pungent; good for mask induction
Isoflurane
Good for neurosurgery (lowers brain oxygen consumption; no increase in ICP)
Enflurane
Can cause seizures
Sodium thiopental
- (Barbiturate) fast acting
- Side effects: decrease CBF and metabolic rate, decrease blood pressure
Propofol
- Very rapid distribution and on/off; amnesia; sedative
- Not an analgesic
- Metabolized in liver and by plasma cholinesterase’s
- Side effects: hypotension, respiratory depression
Ketamine
Dissociation of thalamic / limbic systems; places patient in a cataleptic state (amnesia, analgesia).
- No respiratory depression
- Contraindicated in patients with head injury
- Good for children
Side effects: hallucinations, cathetcholamine release (increase CO2, tachycardia), increased airway secretions and increased cerebral blood flow
Etomidate
Fewer hemodynamic changes; fast acting
- Continuous infusions can lead to adrenocortical suppression
When is RSI indicated?
- Recent oral intake
- GERD
- Delayed gastric emptying
- Pregnancy
- Bowel obstruction
Last muscle to go down and first muscle to recover from paralytics
Diaphragm
First to go down and last to recover from paralytics
Neck muscles and face
Malignant hyperthermia: pathophysiology
- Caused by a defect in calcium metabolism
- Calcium released from sarcoplasmic reticulum causes muscle excitation: contraction syndrome
Malignant hyperthermia: signs
Increased end-tidal CO2…
then fever, tachycardia, rigidity, acidosis, hyperkalemia
Malignant hyperthermia: treatment
dantrolene (10mg/kg) inhibits calcium release and decouples excitation; cooling blankets, HCO3, glucose, supportive care
When do you NOT use succinylcholine?
Severe burns. Neurologic injury. Neuromuscular disorders. Spinal cord injury. Massive trauma. Acute renal failure.
Complications of succinylcholine
- Malignant hyperthermia
- Hyperkalemia
- Open-angle glaucoma
- Atypical pseudocholinesterases
Nondepolarizing agents: mechanism
- Inhibits neuromuscular junction by competing with acetylcholine
- Can get prolongation of these agents with myasthenia gravis
Cis-atracurium
Non-depolarizer
- Undergoes Hoffman degradation
- Can be used in liver and renal failure
- Histamine release
Rocuronium
Non-depolarizer: Fast, intermediate duration; hepatic metabolism
Pancuronium
Non-depolarizer:
- Slow acting, long-lasting; renal metabolism
- Most common side effect: tachycardia
Neostigmine, Edrophonium: mechanism
Blocks acetylcholinesterase, increasing acetylcholine
Should be with neostigmine or edrophonium to counteract effects of generalized acetylcholine overdose
Atropine or glycopyrrolate
Local anesthestics: mechanism
Work by increasing action potential threshold, preventing Na influx.
- Can use 0.5 cc/kg of 1% lidocaine.
Why are infected tissues difficult to anesthetize with local anesthetics?
Secondary to acidosis.
Length of action of local anesthetics: greatest to least
Bupivacaine > lidocaine > procaine
Side effects of local anesthetics
Tremors
Seizures
Tinnitus
Arrhythmias (CNS symptoms occur before cardiac)
What does addition of epinephrine to local anesthetics allow?
Allows higher doses to be used, stays locally
When do you not use epinephrine with local anesthetics?
Arrhythmias, unstable angina, uncontrolled hypertension, poor collaterals (penis and ear), uteroplacental insufficiency
Two different genres of local anesthetics
Amides (all have “i” in first part of their name)
Esters
Allergic reactions: amides vs esters
Esters: increased allergic reactions due to PABA analogue
Metabolism: opioids
Metabolized by the liver and excreted via kidney
What can narcotics cause precipitate in patients on MAOIs?
Hyperpyrexic coma
Morphine: effects
Analgesia, euphoria, respiratory depression, miosis, constipation, histamine release (causes hypotension), decreased cough
Demerol: effects
Analgesia, euphoria, respiratory depression, miosis, tremors, fasciculations, convulsions
Does demerol cause histamine release?
NO.
Why avoid demerol in patients with renal failure?
Can cause seizures (buildup of normeperidine analogues)
Fentanyl
Fast acting; 80x strength of morphine (does not cross-react in patients with morphine allergy); no histamine release
Benzodiazepines: effects
Anticonvulsant.
Amnesic.
Anxiolytic.
Respiratory depression.
Benzodiazepines: metabolized in
Liver
Versed (midazolam)
Benzo:
- Short acting
- Contraindicated in pregnancy
- Crosses placenta
Valium (Diazepam)
Benzo:
- Intermediate acting
Ativan (lorazepam)
Benzo:
- Long acting
Flumazenil
- Competitive inhibitor
- May cause seizures and arrhythmias
- Contraindicated in patients with elevated ICP or status epilepticus
Epidural anesthesia
Allows analgesia by sympathetic denervation.
Vasodilation.
Epidural with morphine can cause…
Can cause respiratory depression
Epidural with lidocaine can cause…
Decreased heart rate and blood pressure
How can motor function be spared with epidural?
Dilute concentrations
Tx: acute hypotension / bradycardia with epidural
Turn epidural flow down.
Fluids.
Phenylephrine.
Atropine
Epidural level: affect cardiac accelerator nerves
T1-5
Contraindications: epidural
Hypertrophic cardiomyopathy.
Cyanotic heart disease.
Why h-cmp and cyanotic heart disease contraindications to epidural anesthesia?
Sympathetic denervation causes decreased after load, which worsens these conditions
Spinal anesthesia
Injection into subarachnoid space, spread determined by baricity and patient position
Contraindications: spinal
Hypertrophic cardiomyopathy.
Cyanotic heart disease.
Tx: Spinal headache
Rest. Fluids. Caffeine. Analgesics. Blood patch to site if it persists > 24 hours.
Headache is worse sitting up.
Associated with most postop hospital mortality
- Pre-op renal failure
2. CHF
May have no pain or EKG changes. Can have hypotension, arrhythmias, increased filling pressures, oliguria, bradycardia.
Postop MI
Considered high risk surgery
Most aortic, major vascular, peripheral vascular surgery
Risk: carotid endarterectomy (CEA)
Considered moderate risk surgery
Biggest risk factors for post MI
Age > 70. DM. Previous MI. CHF. Unstable angina.
MC PACU complication
nausea and vomiting.
