Anesthesia Review

Vic V. Vernenkar, D.O.

St. Barnabas Hospital

Dept. of Surgery

The Anesthesiologist

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.

ASA Classification

Class 1 Healthy

Class 2 Mild systemic disease, no func limitations

Class 3 Moderate to severe systemic disease, functional limitations

Class 4 Severe systemic disease, constantly life threatening, functionally incapacitating

Class 5 Not expected to survive with or without surgery 24h

Class 6 Organ Donor

Class E Emergency

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.

Don’t use Brachial artery.

MonitoringEKG 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 hemoglobinSaO2 of 70%, 80%, and 90% correlates to PaO2 of 40, 50, 60.

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.

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.

Rapid Sequence Induction

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

Analgesic AgentsIn 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.

Analgesics

Morphine- 5min onset, peak at 20min.

Metabolites cleared by kidney

Histamine release with hypotension possible.

Ketamine- PCP analog, intense analgesia, amnesia, dissociative anesthesia.

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.

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.

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.

Sedative-Hypnotic Agents

Used for maintaining anesthesia, sedation in ICU.

1.1kCal/mL!

Etomidate, fast acting, minimal hypotension, great for induction.

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.

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 antagonist…associated with seizures!

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.

Muscle Relaxants

Depolarizing and non-depolarizing.

Depolarizing agents cause an initial transient muscle fiber activation before relaxation occurs.

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!

Muscle Relaxants(Depolarizing)1in 3000 homozygous for trait where it is abnormal…prolonged 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.

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

Non-Depolarizing

Rocuronium

Pancuronium

Vecuronium

Atracurium

Mivacurium

All inhibit acetylcholine at NMJ.

No fasciculation, or increase in potassium.

Non-DepolarizingRocuronium, 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.

AirwayMask 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.

LMA

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.

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.

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.

Inhalation Anesthetic Agents

Volatile Agents

Halothane

Isoflurane

Sevoflurane

Desflurane

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.

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.

Nitrous OxideNot potent, requires large inhalation concentrations.Insoluble in bloodMinimal 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.

Regional AnesthesiaSpinal 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.

Spinal

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.

Epidural