General Anesthetics- Inhaled

Question 1

Halothane

Answer 1

1. Inhaled Anesthetic Agent - prototype drug
2. Very potent, very soluble
3. Side Effects:
   - Respiratory depression
   - vasodilation: blood pressure dec (proportional to the depth of anesthesia), reduces renal function and urine flow
   - depresses the myocardium and dec. cardiac output
   - sensitization to catecholamines may cause arrhythmia’s
   - uterine relaxation (may prolong delivery)
   - Hepatic necrosis: more common after repeated administrations, 2-5 days post surgery, hepatitis
   - Miscarriage
   - immune response
4. Halothane with Succinylcholine may trigger Malignant hyperthermia (tx with dantrolene)
5. NONE

Question 2

Enflurane

Answer 2

1. Inhaled Anesthetic
2. Less potent than halothane, but less blood soluble- more rapid induction, allows smooth adjustment to the depth of anesthesia
3. Side Effects:
   - Depresses respiration as concentration inc.
   - high concentration may produce CNS stimulation and seizures (CI in pts with seizures)
   - Nausea, vomiting, shivering postoperatively
   - Uterine relaxation
   - Produces fluoride during metabolism- may cause irreversible damage to the kidney
   - muscle relaxation and analgesia
4. Drug interactions: potentiate non-depolarizing neuromuscular blocking agents
5. NONE

Question 3

Isoflurane

Answer 3

1. Inhaled anesthetic
2. Less potent than halothane, less drug soluble, used commonly because of LOW TOXICITY, pungent odor so not commonly used for induction, rapid emergence (occurs more rapidly than halothane or enflurance) easy to rapidly adjust depth of anesthesia, useful in neurosurgery
3. Side Effects:
   - Decreased BP, respiration, and inc HR porportional to the depth of anesthesia (inc. HR may be prevented with opioid use)
   - Vasodilation- dec. BP (add nitrous oxide to reduce vasodilation)
   - dilates cerebral vasculature, inc cerebral blood flow and intracranial pressure, reduces cerebral o2 consumption
   - coronary steal phenomenon: vasodilation in small coronary arteries diverts blood flow from ischemic to non-ischemia areas: high risk for MI pts
   - No significant myocardial depression or catecholamine sensitization
   - Muscle relaxation
   - high concentrations produce uterine relaxation
4. potentiates non-depolarizing NM blockers
5. NO RENAL OR HEPATIC TOXICITY

Question 4

Sevoflurance

Answer 4

1. Inhaled anesthestic
2. less potent than halothane, similar solubility to Nitrous exide- very insoluble, induction and emergence are rapid, depth of anesthesia easily controlled
   - least airway irritation of any inhaled agent (can be used for induction)
3. Side Effects:
   - inc. cerebral blood flow, inc in intracranial pressure ( minimized by hyperventilating agent)
   - relaxation of skeletal muscle
4. NONE
5. OTHER:
   - widely used in children- because not irritating
   - cardiac and resp. depression are minimal
   - renal toxicity and hepatic toxicity very rare
   - safest drug for pts. with cardiovascular disease
   (rapid effect, least irritating, safest in CV disease)

Question 5

Desflurane

Answer 5

1. Inhaled anesthetic
2. Not very potent, very insoluble, very rapid emergence and induction (outpt surgery), pungent odor, irritates airwayrs (so not used for induction), easy to control depth of anesthesia
3. Side Effects:
   - Blood pressure dec due to vasodilation
   - vasodilation of cerebral vessel- inc intracranial pressure (hyperventilating agent to dec)
   - HR inc
   - profound ventilatory depression
   - Some muscle relaxation and potentiation of NM junction blockade
4. NONE
5. No liver or kidney toxicity

Question 6

Metabolism of Halothane

Answer 6

• unchanged and exhaled during anesthesia
• remainder metabolized by the p450 system
• Metabolism produces bromine and chlorine - produces toxic metabolites - causes immune response and hepatitis
• repeated exposure may induce hepatic enzymes- inc. the metabolism of halothane and the production of the toxic metabolites

Question 7

Metabolism of Sevoflurane and Enflurane

Answer 7

Inhaled anesthetic

• metabolized to release fluroide ions (which may cause kidney damage- although rare)
• Degradation of sevoflurane by CO2 absorbants in machines leads to production of haloalkane, compound A- causes kidney toxicity in rats= uncommon as long as machine is working properly

Question 8

Nitrous Oxide

Answer 8

1. Inhales Anesthetic
2. low potency, low solubility in blood- rapid onset of action, Probably works by blocking NDMA receptors,
3. Side Effects
   - produces a feeling of relaxation, body warmth, and tingling, numbness, auditory sensations, and euphoria
   - Good analgesia but not used for anesthesia
   - Diffusion hypoxia with anesthesia termination
   - No depression of Heart
   - Attenuates
4. Drug interactions:
   - Used as an adjuvant with other drugs to inc rate of induction
   - attenuates hypotension when combined with other anesthetics
   - prevents some autonomic responses to pain during gen. anesthetia
   - Little respiratory depression- but may produce hypoxia in COPD pts.
   - No NM blockade
5. Other:
   - Used in dentistry
   - No renal or hepatic toxicity
6. Adverse Effects
   - Trapped Gas effect
   - Causes euphoria- drug of abuse
   - Chronic low level exposure causes peripheral neuropathy
   - With prolonged exposure- methionine synthase is inactivated- interfere with DNA synthesis and dec. production of leukocytes and RBC (Megaloblastic Anemia)
   - Bone marrow depression if gas use for 3 days
   - Do not use for at least 3 months after eye surgeries that use intra-ocular gas - irreversible blindness