Maintenance of anesthesia

1. Maintenance of anesthesia Kelly Shinkaruk, MD FRCPC HLT 123 October 17, 2009

2. Objectives • What is anesthesia? • Manual monitoring techniques • Inspection • Palpation • Auscultation • Evaluation and maintenance of anesthetic depth using • Non-invasive monitors • Invasive monitors • Nervous system monitors • Adjusting medications to maintain anesthetic

3. Objectives • What is anesthesia? • Manual monitoring techniques • Inspection • Palpation • Auscultation • Evaluation and maintenance of anesthetic depth using • Non-invasive monitors • Invasive monitors • Nervous system monitors • Adjusting medications to maintain anesthetic

4. What is anesthesia? • “…drug induced reversible depression of the central nervous system resulting in the loss of response to and perception of all external stimuli.” • Components of anesthesia • Unconsciousness • Amnesia • Analgesia • Immobility • Attenuation of autonomic response to noxious stimulation

5. Components of General Anesthesia

6. Components of General Anesthesia

7. Goals of Maintenance • Responsible for autonomic nervous system • Maintenance throughout case of • anesthesia • amnesia • analgesia • paralysis (if indicated) • In addition • Minimize negative effects of anesthetic • Fluid maintenance/balance/resuscitation • Cardiac output and end organ perfusion

8. Goals of Maintenance • Why use monitors? • Detect deficit or overdose of anesthetic agents and resolve the aberrancy • Early detection of adverse events • Prevention of periop critical events • Prior to advent of standard monitoring, anesthesia had very high morbidity and mortality • Now it’s very low 

9. CAS Monitors

10. CAS Monitors • Use monitors to help narrow your differential diagnosis • No single monitor can make a diagnosis, must verify one monitor with another!

11. Depth of Anesthesia • If monitored vitals change • Consider differential diagnosis • Simultaneously manage and diagnose • ABCs, verify result with another monitor • Inspect, palpate, auscultate • Make adjustments to medications as appropriate!!!

12. Objectives • What is anesthesia? • Manual monitoring techniques • Inspection • Palpation • Auscultation • Evaluation and maintenance of anesthetic depth using • Non-invasive monitors • Invasive monitors • Nervous system monitors • Adjusting medications to maintain anesthetic

13. Manual Monitoring Techniques • “The only indispensable monitor is the presence, at all times, of a physician or an anesthesia assistant, under the immediate supervision of an anesthesiologist, with appropriate training and experience.” • CAS guidelines 2008 • Provides valuable information about • Depth of anesthesia • Diagnosis of intraoperative complications

14. Manual Monitoring Techniques • Inspection (Adequate Lighting) • Historically, sole monitor • Initial information by observation • Inspect for alterations • Diaphoresis • Spontaneous movement • Respiratory rate and pattern esp. when spontaneous • Abnormal retractions or indrawing • Cyanosis • JVP • Skin colour and/or rash

15. Manual Monitoring Techniques • Palpation • Correlate information from inspection • Physical contact with patient • Palpate for • Tracheal position • Subcutaneous emphysema • Pulsus paradoxus • Heart rate, rhythm, contour

16. Manual Monitoring Techniques • Ausculation (Stethoscope!!!) • Respiratory system • Endotracheal tube placement/malposition • Wheezes/crackles • stridor/decreased air entry • Cardiovascular system • Murmurs/bruits • Changes in quality of heart sounds (S1, S2, decreased heart sounds)

17. Objectives • What is anesthesia? • Manual monitoring techniques • Inspection • Palpation • Auscultation • Evaluation and maintenance of anesthetic depth using • Non-invasive monitors • Invasive monitors • Nervous system monitors • Adjusting medications to maintain anesthetic

18. Non Invasive Monitors

19. Non Invasive Monitors • Pulse Oximetry • Simple, noninvasive, continuous • indirectly measures the oxygen saturation of a patient's blood • Detect and prevent hypoxemia • Affected by • dyshemoglobins, vital dyes, nail polish, ambient light, motion artifact, background noise/electrocautery

20. Non Invasive Monitors • Pulse Oximetry • When sats fall, differential diagnosis • Low FiO2 (relative or absolute) • Inadequate alveolar ventilation • V/Q mismatch • Excessive metabolic O2 demand • Low cardiac output • Treatment? • 100% O2 • Increase ventilation rate/Vt or change vent mode • Recruitment maneuvers

21. Non Invasive Monitors • Blood Pressure (via cuff) • Indicates adequacy of circulation • Minimum monitoring interval - 5min • Monitor location – upper arm, leg, forearm

22. Non Invasive Monitors • Blood pressure • Hypertension diagnosis? • Light anesthesia • Catecholamine release • Laryngoscopy • Surgical stimulation • Emergence from anesthesia • Administration of vasopressors • Treatment? • Deepen anesthetic • d/c vasopressors

23. Non Invasive Monitors • Blood Pressure • Hypotension differential diagnosis? • Is extensive… • Hypovolemia • Relative overdose of anesthetic agents • Treatment? • Initially, go through ABCs, inspect for evidence of bleeding, 100%O2, turn down anesthetic • Fluid bolus – NS/RL 500-1000mL • Vasopressor – Phenylephrine 100mcg or Ephedrine 2-10mg

24. Non Invasive Monitors • Electrocardiogram • Three or five leads • Continuous measurement of heart rate and rhythm • Questionable indicator of myocardial ischemia • Signs of light anesthesia • tachycardia • Might notice changes in rhythm • Vasovagal episodes • Tell surgeon to STOP!!! • Atropine 0.4mg or Ephedrine 5-10mg

25. Non Invasive Monitors • Expired Agents/Gases • The most important objective indicator of depth of anesthesia • Monitors the concentration of gas (volatile, CO2, O2) being expired from the patient • MAC (minimum alveolar concentration) = 50% of people will not move with surgical stimulus • Monitor end tidal concentration of agents

26. Non Invasive Monitors • Expired Agents/Gases • MAC is affected by many things • Intravenous medications – PPF, opioids, benzos • Pre-op medications – pregabalin, benzos • Age • Medical conditions/patient health • Hypo/hyperthermia

27. Non Invasive Monitors • Expired Agents/Gases • If low and patient appears light • Increase flow rate • Increase percent of volatile delivered from vaporizer • Make sure to monitor MAC as can increase rapidly! (and cause hypotension)

28. Non Invasive Monitors • Capnography • Insp/exp CO2 concentration • Vital monitor of physiology • Confirm ETT placement • Recognize ETT malposition/extubation/disconnection • Assess adequacy of ventilation/PaO2 • Aids diagnosis of PE, partial A/W obstruction, RAD/bronchospasm • Assess efficacy of CPR efforts

29. Non Invasive Monitors

30. Non Invasive Monitors • Capnography • If increased ETCO2 • Check CO2 absorber! • Increase minute ventilation (RR or Vt) • ?hypermetabolic process? • If decreased ETCO2 • Sudden vs slow • Decrease ventilation • Verify other signs of hypoperfusion

31. Non Invasive Monitors • Respiratory Function • Especially useful in spontaneously ventilating patient • Light patient • Hyperventilation - increased RR/Vt and hypocapnia • Breath holding • Bronchospasm/laryngospasm • Very deep patient • Hypoventilation – decreased RR/Vt and hypercapnia

32. Non Invasive Monitors • Increase in respiratory rate • Differential mainly light anesthetic and hypoventilation • Increase ventilation (RR or Vt) • Deepen anesthetic • Administer analgesic

33. Non Invasive Monitors • Ventilator Pressures • Early indication of light anesthetic and other problems! Always check: • Breathing circuit • ETT • Pulmonary compliance • Alarms for increased pressure • Coughing • Insufficient muscle paralysis • Bronchospasm • Obstruction/pt biting ETT

34. Non Invasive Monitors • Ventilatory Pressure elevated • Differential diagnosis • Manage and diagnose • Inspect patient and ETT – biting, blocked, disconnected (if low pressure alarm) • Take off machine and verify compliance • Auscultate breath sounds – ETT malposition • Treatment • Deepen anesthetic • Paralysis • Reposition/Suction/change ETT

35. Non Invasive Monitors • Temperature Monitoring • Can be monitored via bladder, distal esophagus, ear canal, trachea, nasopharynx, rectum • Attempts made to maintain temperature as close to normothermia as possible • Situations requiring temp monitoring • Long cases • Anticipated fluctuations in temperature • Bair hugger • Malignant hyperthermia patients

36. Invasive Monitors

37. Invasive Monitors • Arterial Line • Continuous blood pressure measurement • Placed in a peripheral artery • Radial • Brachial • Dorsalis pedis • Rarely femoral • Waveform gives information about intravascular status • Help with diagnosis of cardiac tamponade,etc

38. Invasive Monitors • Arterial line • Indications: induced hypotension, induced hypothermia, major cardiac/thoracic/vascular/neurosurgical procedures • Always keep BP cuff in place for verification of arterial BP • Used for frequent blood sampling esp. ABGs • Be aware that tracing can be damped/positional • Flattened waves might be artifactual • Verify with BP cuff

39. Invasive Monitors • Central Venous Pressure (CVP) • Estimates of right atrial/ventricular pressures • Serial measurements more useful than single value • monitor intravascular volume/fluid status • Renal failure patients • Difficult IV access • Anticipated need for vasopressor infusion/TPN/Hemodialysis • Massive transfusion

40. Invasive Monitors

41. Invasive Monitors • Pulmonary Artery Catheter (PAC) • Rarely indicated, TEE rapidly replacing • Inflation in pulmonary artery reflects left atrial filling pressure • Can calculate cardiac output • High risk of complications • PA rupture • PVCs/Vtach • Hemo/pneumothorax

42. Invasive Monitors

43. Invasive Monitors • Transesophageal Echo • Echo probe placed in esophagus during GA • Uses ultrasound technology • Assess cardiac function/filling/valves • Replacing PAC technology • Requires special equipment

44. Invasive Monitors

45. Invasive Monitors • Evaluation of • Native valve disease • Prosthetic heart valve function/dysfunction • Cardiac masses • The ICU patient with hemodynamic instability • Congenital heart disease • Thromboembolic risk in patient with atrial fibrillation and inadequate anticoagulation • Detection of • Aortic dissection • Complications of endocarditis • Potential etiologies of stroke • Adjunct to • Percutaneous cardiac procedures • Cardiac surgical procedures

46. Invasive Monitors • Heart valve repair • Most congenital heart surgery requiring cardiopulmonary bypass • Endocarditis, particularly with extensive disease or inadequate preoperative evaluation of disease extent • Ascending aortic dissection repair when aortic valve involvement unknown • Evaluation of life-threatening hemodynamic disturbances when ventricular function is unknown • Pericardial window procedures • Hypertrophic obstructive cardiomyopathy repair • Heart valve replacement • Removal of cardiac tumors • Increased risk of myocardial ischemia or hemodynamic disturbances • Intracardiacthrombectomy or pulmonary embolectomy • Suspected cardiac trauma or for detection of foreign bodies • Cardiac aneurysm repair • Thoracic aortic dissection repair without suspected aortic valve involvement • Evaluation of anastomotic sites during heart and/or lung transplantation • Monitoring placement and function of assist devices

47. Nervous System Monitors

48. Nervous System Monitors • Electroencephalogram (EEG) • Represents spontaneous electrical activity of the cerebral cortex • Measures amplitude and frequency of discharge • Four frequencies: beta, alpha, theta, delta

49. Nervous System Monitors • Electroencephalogram (EEG) • EEG may be used to detect intraop cerebral ischemia • Deep anesthesia and cerebral ischemia decrease or abolish normal alpha/beta; delta/theta predominate

50. Nervous System Monitors • Bispectral Index (BIS) • A variable derived from the EEG • Measure of the hypnotic effect of anesthetic • Gives a value between 0 and 100 • Decreasing numbers = deeper anesthetic • <60 appears to predict unconsciousness • Used in trauma, crash OB, cardiac, unstable patient with minimal reserve/anesthetic