Updated: 10/14/2018

Inhaled Anesthetics

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Snapshot
  • A 25-year-old woman is on the operative table for an elective laparoscopic cholecystectomy. After administration of isoflurane and succinylcholine, the patient developed hypercarbia that is resistant to increasing the patient's minute ventilation. She also developed massester and generalized muscle rigidity. The patient is immediately treated with dantrolene and a malignant hyperthermia protocol is initiated. (Malignant hyperthermia)
Introduction
  • General anesthesia
    • is a central nervous system (CNS) depressive state that is reversible and provides
      • analgesia
      • sedation and decreased anxiety
      • amnesia and impaired consciousness
      • relaxation of skeletal muscle
      • prevention of reflexes
    • can be divided into
      • intravenous anesthesia
      • inhaled anesthesia
  • Inhaled anesthesia
    • primarily used for maintenance of anesthesia
    • potency
      • the index of potency is the inverse of the Minimum Alveolar Concentration (potency = 1/MAC)
        • MAC is the concentration of inhaled anesthetic needed to prevent movement in 50% of patients in response to a noxious stimuli (e.g., surgical incision)
        • for example, a high potency inhaled anesthetic has a low MAC
          • the more lipid soluble the inhaled anesthetic is, the more potent it is; thus, the lower the MAC
    • the goal of inhalation anesthesia is to maintain an optimal brain partial pressure (Pbr)
      • the movement of the anesthetic from one body compartment to the next is based on the drug partial pressure gradient
        • the inhaled anesthetic drug would move
          • from the alveolar partial pressure (Palv) → arterial partial pressure (Pa) → Pbr
            • eventually this steady state is achieved so that
              • Palv = Pa = Pbr
                • the speed of achieving this steady state is determined by a number of factors, such as
                  • blood solubility 
                  • alveolar wash-in
                    • replacing normal lung gases with the inhaled anesthetic
                  • cardiac output
                  • tissue type's effect on the anesthetic
            • blood solubility
              • this is determined by the blood/gas partition coefficient
                • this is the concentration ratio of the inhaled anesthetic in the blood phase to the gas phase when equilibrium is achieved
                  • anesthetics with low blood solubility
                    • equilibrium is achieved rapidly
                    • quickly saturates the blood
                    • results in a rapid induction and recovery
  • Examples
    • nitrous oxide
      • low blood solubility → low blood/gas partition coefficient → rapid induction/recovery 
      • low lipid solubility → low potency → high MAC
    • halothane and -fluranes
      • high blood solubility → high blood/gas partition coefficient → slow induction/recovery
      • high lipid solubility → high potency → low MAC
Medications
  • Medications
    • desflurane, enflurane, halothane, isoflurane, methoxyflurane, sevoflurane, and nitrous oxide
  • Mechanism of action
    • unknown
  • Side effects
    • myocardial depression (halogenated hydrocarbons are vagomimetic)
    • respiratory depression
    • ↑ cerebral blood flow, which in turn
      • ↓ cerebral metabolic demand
  • Adverse effects
    • cardiac arrhythmias
    • concentration-dependent hypotension
    • malignant hyperthermia 
      • clinical presentation
        • fever and severe muscle contractions after
          • administration of a volatile anesthetic or succinylcholine
      • pathogenesis
        • autosomal dominant with variable penetrance
        • mutation in the ryanodine receptor which
          • increases calcium release from the sarcoplasm reticulum
      • treatment
        • dantrolene
    • hepatotoxicity (halothane)
    • nephrothoxicity (methoxyflurane)
    • increased risk of seizure (enflurane)
    • expansion of trapped gas within a body cavity (nitrous oxide)
 

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Questions (5)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.NE.75) While on a teaching sabbatical in Uruguay, a pathologist examined the excised liver of an 18-year-old otherwise healthy female who passed away due to massive hepatic necrosis 5 days after she underwent general anesthesia to repair a fractured femur. Which of the following is a general anesthetic most likely responsible for her death? Review Topic

QID: 106847
1

Bupivacaine

5%

(4/73)

2

Lidocaine

5%

(4/73)

3

Midazolam

5%

(4/73)

4

Halothane

77%

(56/73)

5

Desflurane

5%

(4/73)

M1

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