Anesthesia Review

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Anesthesia Review

• Vic V. Vernenkar, D.O.
• St. Barnabas Hospital
• Dept. of Surgery

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The Anesthesiologist
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Initial Assessment

• ASA classification is part of the physical
  examination of the patient.
• Is graded classes 1-6 in order of increasing risk
  of mortality.

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ASA Classification
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Monitoring

• Noninvasive BP monitoring with appropriate cuff
  size.
• Invasive BP monitoring (A-line) for elective
  hypotension, anticipation of wide variations in
  BP, need for frequent blood sampling.
• Common sites are femoral and radial sites.
• Dont use Brachial artery.

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Monitoring

• EKG for detection of dysrhythmias, myocardial
  ischemia, electrolyte abnormalities.
• Leads V2 and V5 together detect 95 of
  intraoperative ischemia, allowing for early
  intervention.
• Pulse oximetry estimates level of oxygen binding
  by hemoglobin
• SaO2 of 70, 80, and 90 correlates to PaO2 of
  40, 50, 60.

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Monitoring

• Temperature- Axilla, esophagus, pharynx, bladder.
• Urine output- a measure of end-organ perfusion
  Foley for all cases over 2 hrs,to decompress
  bladder (lap procedures).
• Swan-Ganz- for LVEDP, CO, SVR.
• Capnography- confirms adequacy of ventilation,
  ETT placement, estimates PaCO2.
• Unexpected rise in CO2 Malignant hyperthermia.

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Induction of Anesthesia

• IV or mask induction of general anesthesia.
• Combination of agents based on patient
  characteristics, and procedure.
• Includes an amnestic, analgesic, hypnotic, muscle
  relaxant, and a volatile agent.
• Rapid sequence induction.

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Rapid Sequence Induction

• Pre-oxygenate with 100 allows de-nitrogenation
  of patients FRV, extra time.
• Indications include recent oral intake, GERD,
  delayed emptying, pregnancy, bowel obstruction.
• Lidocaine, Atropine, Etomidate, Rocuronium (when
  Succinylcholine is contraindicated), Versed.

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Analgesic Agents

• In boluses at induction and before incision, then
  maintenance as needed.
• Additional doses based upon sympathetic response
  to pain, like increased HR, BP.
• Fentanyl, a synthetic narcotic, onset 2min, peak
  5min. Metabolized by liver.
• Gag is blunted, minimal cardiac depression, can
  induce respiratory arrest.
• 40 times potency of morphine, no cross allergy
  though.

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Analgesics

• Morphine- 5min onset, peak at 20min.
• Metabolites cleared by kidney
• Histamine release with hypotension possible.
• Ketamine- PCP analog, intense analgesia, amnesia,
  dissociative anesthesia.

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Analgesics

• Ketamine increases HR, BP, bronchodilator,
  maintains spontaneous ventilation. Increased CBF.
• Illusions, dysphoria.
• Not a respiratory depressant, can be sole
  anesthetic agent.
• One of several induction agents, good for
  children, contraindicated in head injury.

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Sedative-Hypnotic Agents

• Sodium thiopental, a barbiturate, induces
  unconsciousness within 30 seconds without
  analgesia.
• Excellent anticonvulsant.
• After single dose drug redistribution into muscle
  may result in rapid awakening.

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Sedative-Hypnotic Agents

• Side effects hypotension (in hypovolemia),heart
  failure, beta blockade, resp. arrest, decreases
  CBF, metabolic rate.
• Propafol, fast acting, no hangover (great for
  outpatients) antipyretic, antiemetic.
• Rapid metabolism by liver.
• Side effects hypotension, blunting of airway
  reflexes helping in intubation, resp. arrest.

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Sedative-Hypnotic Agents

• Used for maintaining anesthesia, sedation in ICU.
• 1.1kCal/mL!
• Etomidate, fast acting, minimal hypotension,
  great for induction.

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Sedative-Hypnotic Agents

• Rapid metabolism by liver, avoid continuous
  infusions as can cause adrenocortical
  suppression.
• Can cause myoclonus.
• Benzodiazapines, provide anxiolysis, hypnosis,
  amnesia, anticonvulsant, skeletal muscle relaxant
  properties.

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Sedative-Hypnotic Agents

• No analgesic properties here.
• Versed most common, short acting, liver metab, so
  watch it.crosses placenta.
• Ativan long acting.
• Flumazenil is a benzodiazapine
  antagonistassociated with seizures!

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Muscle Relaxants

• Used to facilitate intubation.
• During abdominal surgery.
• When movement can be devastating.
• Paralyzed but still feel and remember everything!
• No analgesia, hypnosis, or amnesia.
• Diaphragm last to go down, first to recover.
• Neck Muscles first to go down, last to recover.

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Muscle Relaxants

• Depolarizing and non-depolarizing.
• Depolarizing agents cause an initial transient
  muscle fiber activation before relaxation occurs.

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Muscle Relaxants(Depolarizing)

• Succinylcholine, provides rapid depolarizing
  blockade. Mimics acetylcholine, 30 seconds, short
  duration 5-10 min.
• Rapidly metabolized by plasma pseudocholinesterase
  .
• The only one!

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Muscle Relaxants(Depolarizing)

• 1in 3000 homozygous for trait where it is
  abnormalprolonged paralysis.
• Increase in serum potassium.cardiac arrest in
  some.
• Contraindicated in stroke, burns, trauma,
  myopathy,bedridden, renal failure.
• Malignant hyperthermia rare complication of
  succinylcholine.An autosomal dominant disorder of
  skeletal muscle calcium metabolism.

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Malignant Hyperthermia

• Combo of volatile anesthetic plus succs.
• First Sign is Increased end-tidal CO2.
• Acidosis, muscle spasm.
• Hypertension, arrhythmias.
• Hypoxemia, hyperkalemia
• Tachycardia, pyrexia.
• Myoglobinuria.
• Tx IV Dantrolene 10mg/kg, cool, D/c volatile
  agent.

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Non-Depolarizing

• Rocuronium
• Pancuronium
• Vecuronium
• Atracurium
• Mivacurium
• All inhibit acetylcholine at NMJ.
• No fasciculation, or increase in potassium.

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Non-Depolarizing

• Rocuronium, fast, used when succs
  contraindicated.
• Pancuronium, inexpensive, used for prolonged
  paralysis, tachy, prolonged in renal.
• Mivacurium dependent on pseudocholinesterase.
• All potentiated by hypokalemia, calcemia,
  hypermagnesemia.
• Monitored by peripheral nerve stimulation.
• To reverse, use Neostigmine (blocks acetyl
  cholinesterase) plus anticholinergic agent (to
  counteract brady) at end of surgery.

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Airway

• Mask ventilation used at time of induction.
• Can be sole means of airway in patients with
  minimal risk of aspiration.
• Ventilation also facilitated by oral or nasal
  airway (tongue, awake patient).
• LMA lodges in hypopharynx superior to larynx
  preventing soft tissue obstruction of airway.
  Contraindicated in aspirators, paralyzed, need
  for controlled ventilation.

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LMA
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Airway

• Endotracheal Intubation allows for vent support,
  oxygenation, relative protection of airway.
• Confirm position by checking bilateral chest
  rising, condensation in ETT, End-tidal CO2,
  bilateral breath sounds.
• Fiberoptic laryngoscopy in difficult intubations.

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Inhalation Anesthetic

• After induction anesthesia is maintained with a
  volatile anesthetic.
• Provides hypnosis, amnesia, some degree of
  analgesia and muscle relaxation.
• Differ in blood solubility, potency, side effect
  profiles.

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Inhalation Anesthetic

• Minimum Alveolar Conc. (MAC) is the smallest
  concentration at which 50 of patients will not
  move in response to surgical incision.
• Solubility of agents correlates with speed of
  induction, so insoluble agents provide quickest
  onset.

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Inhalation Anesthetic Agents
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Volatile Agents

• Halothane
• Isoflurane
• Sevoflurane
• Desflurane

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Side Effects of Volatile Agents

• Hypotension via cardiac depression (halothane) or
  vasodilitation.
• Arrythmogenic (halothane) potentiated by
  epinephrine.
• Isoflurane least cardiac depressant, most
  coronary artery dilation.

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Side Effects of Volatile Agents

• Rapid, shallow breathing resulting in decreased
  minute ventilation, bronchodilation.
• Blunts hypoxic drive
• Impair cerebral auto regulation, or ability of
  brain to maintain cerebral blood flow over a wide
  range of BPs.
• Isoflurane used in ICP patients
• Halothane rarely causes Hepatitis.

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Nitrous Oxide

• Not potent, requires large inhalation
  concentrations.
• Insoluble in blood
• Minimal cardiac depression, BP changes little. No
  muscle relaxant properties like volatile agents.
• Not bronchodilator, increases PVR.
• May expand air cavities by diffusing in faster
  than diffuses out.ba-boom. Avoid in PTX, SBO,
  middle ear occlusion.

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Regional Anesthesia

• Spinal Anesthesia, L3-L4 interspace. Free flow of
  CSF confirms subarachnoid placement where local
  is injected.
• Anesthesia occurs in minutes, lasting up to 2 hrs
  depending on agent and dose.
• Level of sympathetic block higher than sensory
  block, this in turn above level of motor block.
• Sympathetic block results in hypotension.
• High spinal results in respiratory depression.
• Motor recovers before sensory.

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Spinal
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Regional Anesthesia

• In Epidural anesthesia, a catheter is placed in
  epidural space allowing for continuous infusion
  to relieve postoperative pain.
• Final level of sensory blockade depends on volume
  injected not dose.
• Onset slower than spinal.

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Epidural
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