Anesthesia Review

1. Anesthesia Review Vic V. Vernenkar, D.O. St. Barnabas Hospital Dept. of Surgery

2. The Anesthesiologist

3. 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.

4. ASA Classification

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

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

12. 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.

14. 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.

15. 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.

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

17. 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.

18. 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!

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

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

22. 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!

23. 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.

24. 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.

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

27. 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.

28. 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.

29. LMA

30. 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.

31. 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.

32. 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.

33. Inhalation Anesthetic Agents

34. Volatile Agents • Halothane • Isoflurane • Sevoflurane • Desflurane

35. 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.

36. 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.

37. 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.

38. 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.

39. Spinal

40. 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.

41. Epidural