General Anesthesia


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  • General Anesthesia

    1. 2. GENERAL ANESTHESIA Reading Assignment Chapter 2, pp 51-118 in VAAA
    2. 3. Definition of Anesthesia <ul><li>Simple: </li></ul><ul><ul><li>“ drug induced unconsciousness” </li></ul></ul><ul><li>Complete: </li></ul><ul><ul><li>A state of controlled and reversible unconsciousness achieved through injectable or inhaled drugs characterized by the absence of: </li></ul></ul><ul><ul><ul><li>Pain </li></ul></ul></ul><ul><ul><ul><li>Memory </li></ul></ul></ul><ul><ul><ul><li>Motor response </li></ul></ul></ul><ul><ul><ul><li>Reflexes </li></ul></ul></ul>
    3. 4. Components of General Anesthesia <ul><li>1) Preanethesia </li></ul><ul><ul><li>Minimum data base + patient status>>anesthetic protocol </li></ul></ul><ul><li>2)Induction – animal leaves state of consciousness </li></ul><ul><ul><li>Phases: </li></ul></ul><ul><ul><ul><li>Incoordination/ excitement </li></ul></ul></ul><ul><ul><ul><li>Progressive relaxation </li></ul></ul></ul><ul><ul><ul><li>Unconsciousness </li></ul></ul></ul><ul><ul><ul><li>Continues until maintenance level achieved </li></ul></ul></ul>
    4. 5. Components of General Anesthesia (cont) <ul><li>3) Maintenance – sufficient anesthesia administered to keep patient at appropriate depth of anesthesia </li></ul><ul><ul><li>Loss of protected reflexes </li></ul></ul><ul><ul><li> during this time </li></ul></ul><ul><ul><li>Surgical procedures performed </li></ul></ul><ul><li>CLOSE MONITORING IS ESSENTIAL </li></ul><ul><li>4) Recovery (reversal of induction)– begins when the conc. Of anesthethetic agent begins to decrease in CNS </li></ul><ul><li>Elimination: </li></ul><ul><li>Most injectable medications>>liver metabolism>>renal excretion (except ketamine in cats = direct to kidneys) </li></ul><ul><li>Inhalants – eliminated through lungs </li></ul>
    5. 6. SAFETY OF GENERAL ANESTHESIA <ul><li>“ General anesthesia is not without risk.” </li></ul><ul><li>“ Monitoring by a trained individual is the single most important factor in preventing serious anesthetic problems.” </li></ul><ul><li>Multiple precautionary steps minimize risk: </li></ul><ul><ul><li>Minimum database – consists of ? </li></ul></ul><ul><ul><li>Minimum dose – to effect (premeds,correct existing px) </li></ul></ul><ul><ul><li>Endotracheal tube </li></ul></ul><ul><ul><li>Fluid therapy </li></ul></ul>
    6. 7. CLASSICAL STAGES AND PLANES OF ANESTHESIA <ul><li>Animals pass through a series of anesthetic stages and planes, roughly correlated with changes in anesthetic depth. </li></ul><ul><li>Animals show a progressive loss of: pain perception>> motor coordination>>consciousness >>reflex responses>>muscle tone>>> cardiopulmonary function </li></ul><ul><li>THE “ART” OF ANESTHESIA </li></ul><ul><li>These stages and planes are not well defined in every animal. The technician monitoring anesthesia of the patient must evaluate as many variables and indicators as possible to determine the patient’s depth of anesthesia. The technician must ensure that the patient does not feel surgical pain but must avoid excessive anesthetic depth. </li></ul>
    7. 8. STAGE I <ul><li>Immediately after the administration of an inhalant or injectable agent </li></ul><ul><li>animal is conscious but disoriented, shows reduced sensitivity to pain </li></ul><ul><li>all reflexes are intact, animal is still awake, may struggle, urinate and/or defecate </li></ul><ul><li>IDEALLY SHORT = DANGEROUS </li></ul>
    8. 9. STAGE II <ul><li>loss of consciousness BUT involuntary excitement </li></ul><ul><li>all reflexes intact (exaggerated) </li></ul><ul><ul><li>yawning pupils dilated </li></ul></ul><ul><li>actions are not under conscious control </li></ul><ul><ul><li>unpleasant for the animal struggling animal may injure itself or staff </li></ul></ul><ul><li>potentially hazardous for the animal d/t release of epinephrine >>>> cardiac arrhythmias </li></ul><ul><li>Stage II ends when patient shows signs of muscle relaxation, decreased reflex activity and slower respirations. </li></ul><ul><li>IDEALLY SHORT = DANGEROUS </li></ul>
    9. 10. STAGE III (VAA table 2-1; p. 57) <ul><li>Subdivided into FOUR planes: </li></ul><ul><li>PLANE 1 “light” patient will not tolerate surgery </li></ul><ul><li>respiratory pattern becomes regular </li></ul><ul><li>eyeballs start to rotate ventrally </li></ul><ul><li>gagging and swallowing reflexes gone or heavily depressed </li></ul><ul><li>other reflexes present but less brisk </li></ul><ul><li>PLANE 2 “medium” suitable for most surgery </li></ul><ul><li>usually unconscious and immobile respirations regular but shallow (12 to 16) </li></ul><ul><li>relaxed skeletal muscles heart rate and blood pressure mildly decreased </li></ul><ul><li>palpebral reflex gone </li></ul><ul><li>eyes: sluggish papillary light response eyeballs central or rotated ventrally </li></ul><ul><li>pupils slightly dilated </li></ul><ul><li>PLANE 3 “deep” animal appears deeply anesthetized </li></ul><ul><li>significant depression of respiratory and cardiovascular functions </li></ul><ul><li>respiratory rate = less than 12 breaths per minute shallow respirations </li></ul><ul><li>heart rate is significantly reduced pulse strength is reduced </li></ul><ul><li>capillary refill time (CRT) is increased </li></ul><ul><li>eyes: poor pupillary light reflex eyeballs central pupils dilated </li></ul><ul><li>weak or absent reflexes marked skeletal muscle relaxation </li></ul><ul><li>PLANE 4 “too deep” </li></ul><ul><li>respiratory effort is primarily abdominal muscular in nature </li></ul><ul><li>further decrease in respiratory effort and effectiveness </li></ul><ul><li>eyes: fully dilated pupils no papillary light response dry eyes </li></ul><ul><li>no muscle tone dramatic drops in heart rates and blood pressure </li></ul><ul><li>pale mucous membranes prolonged CRT nearing death </li></ul>Entubation Surgical Anesthesia
    10. 11. STAGE IV DON’T GO HERE !! complete cessation of respiration circulatory collapse DEATH
    11. 12. INDUCTION TECHNIQUES AND AGENTS <ul><li>Injectable Anesthetic Agents </li></ul><ul><li>1. Intravenous Injection </li></ul><ul><li> one of the most common induction techniques </li></ul><ul><li>standard dose is calculated, drawn into syringe </li></ul><ul><li>injected as needed directly into vein “to effect” </li></ul><ul><ul><ul><ul><li>Through Stage I and II quickly to ? </li></ul></ul></ul></ul><ul><li>endotracheal intubation </li></ul><ul><li>constant infusion “to effect” --more complex </li></ul>
    12. 13. Induction (cont) <ul><li>2. Intramuscular Injection useful for animals that cannot be handled easily ie? </li></ul><ul><ul><li>usually requires a larger dose </li></ul></ul><ul><ul><li>cannot be given to effect </li></ul></ul><ul><ul><li>slower induction </li></ul></ul><ul><ul><li>lengthy recovery time </li></ul></ul><ul><li>Oral Administration of injectables </li></ul><ul><li>*feral in big carrier </li></ul><ul><li>an extra-label use -- not used routinely </li></ul><ul><li>beware of producing aspiration </li></ul><ul><li>avoid contact with eyes </li></ul><ul><ul><ul><li>NOT RECOMMENDED </li></ul></ul></ul>
    13. 14. Inhalation Agents <ul><li>Need to use rapid –acting inhalant agents </li></ul><ul><li>1. Mask Induction </li></ul><ul><ul><li>may be more suited for critical patients </li></ul></ul><ul><li>Cautions: Prevention </li></ul><ul><ul><li>anesthetic gas pollution of room use tight-fitting mask </li></ul></ul><ul><ul><li>risk of stressing patient use preanesthetic sedation </li></ul></ul><ul><ul><li>may be dangerous with animals with poor respiratory function </li></ul></ul><ul><ul><ul><ul><ul><li>Myth about masking </li></ul></ul></ul></ul></ul>
    14. 15. Inhalation Induction (cont) <ul><li>2. Anesthetic Chamber Induction </li></ul><ul><li>uses sturdy, see-through container </li></ul><ul><li>Cautions: small patients only </li></ul><ul><li> difficult to monitor patient </li></ul><ul><li> risk of vomiting/regurgitation hyperthermia </li></ul><ul><li> waste gas contamination of room + exposure of personnel </li></ul><ul><li>Another option for fractious cats </li></ul>
    15. 16. Intubation <ul><li>Position </li></ul><ul><ul><li>Sternal, extend neck, tongue out </li></ul></ul><ul><li>Visualize </li></ul><ul><ul><li>Soft palette may be in way </li></ul></ul><ul><ul><li>Epiglottis </li></ul></ul><ul><ul><li>Arytenoid cartilages </li></ul></ul><ul><li>Place </li></ul><ul><ul><li>Watch in in – between cartilages (where goes if to side or over?) </li></ul></ul><ul><ul><li>Timing (cats) </li></ul></ul><ul><li>Confirm </li></ul><ul><ul><li>Cough </li></ul></ul><ul><ul><li>Watch rebreathing bag </li></ul></ul><ul><ul><li>Condensation in tube </li></ul></ul><ul><ul><li>“ hair test” </li></ul></ul><ul><ul><li>Bag and observe </li></ul></ul><ul><li>Secure </li></ul>
    16. 17. GENERAL ANESTHESIA <ul><li>(CONTINUED) </li></ul>
    17. 18. MAINTENANCE OF ANESTHESIA <ul><li>Two important tasks: </li></ul><ul><li>1. monitor patient closely to ensure that vital signs remain within normal ranges </li></ul><ul><li>2. maintain patient at an appropriate level of anesthesia so no pain is felt </li></ul><ul><li>THE KEY TO EFFECTIVE AND SAFE ANESTHESIA . . . IS PATIENT MONITORING. </li></ul>
    18. 19. A. Monitoring Vital Signs <ul><li>Vital signs = those variables that indicate response of an animal’s homeostatic mechanisms to anesthesia </li></ul><ul><li>Rely on your own senses first and foremost, confirm with electronic devices </li></ul><ul><ul><li>“ Oh don’t listen to that thing” </li></ul></ul><ul><ul><li>ie pulse ox # can be low for several reasons? </li></ul></ul><ul><ul><li>Check more than one thing </li></ul></ul>
    19. 20. Monitoring Vitals (cont) <ul><li>1. Heart rate and rhythm </li></ul><ul><li>Normal minimal heart rates: dog=>? beats per minute cats=>? bpm </li></ul><ul><li>Lower heart rates may indicate excessive anesthetic depth </li></ul><ul><li>result of a depressant effect of anesthetic on heart rate and myocardial function </li></ul><ul><li>Cardiac rhythm can also be affected by anesthetic agents, esp. halothane, xylazine </li></ul><ul><li>Cardiac monitoring: direct palpation- where? </li></ul><ul><li>auscultation </li></ul><ul><li>esophageal stethoscope </li></ul><ul><li>cardiac monitor </li></ul><ul><li>NOTE: The presence of a beating heart does not necessarily imply adequate circulation </li></ul>
    20. 21. Monitoring Vitals (cont) <ul><li>2. Capillary refill time CRT </li></ul><ul><li>reflects perfusion of tissue with blood but not infallible </li></ul><ul><li>prolonged CRT indicates that tissues have reduced blood supply </li></ul><ul><li>due to: vasoconstriction, low blood pressure (what drugs?), shock, excessive anesthesia </li></ul>
    21. 22. Monitoring Vitals (cont) <ul><li>3. Mucous membrane color gingival, conjunctiva, tongue, vulva or prepuce </li></ul><ul><li>pale mm color = poor perfusion or ? </li></ul><ul><li>bluish discoloration = “cyanosis” = stagnant blood flow or lack of oxygen </li></ul><ul><li>Yellow can mean? </li></ul>
    22. 23. Monitoring Vitals (cont) <ul><li>4. Pulse strength subjective, palpate a major artery </li></ul><ul><li>reflects adequacy of blood circulation throughout the body </li></ul><ul><li>hypotension = weak, “thready” pulse </li></ul><ul><li>5. Blood loss estimated by counting used sponges </li></ul><ul><li>How much blood in a gauze pad? </li></ul><ul><li>if excessive, predisposes to shock </li></ul>
    23. 24. Monitoring Vitals (cont) <ul><li>6. Respiration rate and depth </li></ul><ul><li>monitor by observing animal’s chest or reservoir bag </li></ul><ul><li>monitor: respiratory rate depth of respiration (tidal volume) </li></ul><ul><li>at moderate depth of anesthesia, normal rate = _ ? _breaths per minute <6 and should be using IPPV? </li></ul><ul><li>“ atelectasis” = partial collapse of alveoli, “bag” or “sigh” animal every 5-10 minutes </li></ul><ul><ul><li>d/t decrease in tidal volume (25%) </li></ul></ul><ul><li>Hyperventilation and tachypnea </li></ul><ul><li>due to build-up of CO2, disease?,pain </li></ul><ul><li>Type of respiration: </li></ul><ul><li>thoracic or abdominal (when?) </li></ul>
    24. 25. Monitoring Vitals (cont) <ul><li>7. Thermoregulation </li></ul><ul><li>hypothermia = the most common anesthetic complication </li></ul><ul><li>MOST TEMP LOSS OCCURS WHEN? </li></ul><ul><li>contributing causes: </li></ul><ul><ul><li>ALCOHOL USE IN PREP </li></ul></ul><ul><ul><li>NO MUSCLE ACTIVITY </li></ul></ul><ul><ul><ul><li>DECREASED METABOLIC STATE (d/t drugs) </li></ul></ul></ul><ul><ul><li>OPEN BODY - Flush </li></ul></ul><ul><li>prevention: </li></ul><ul><ul><li>Check temp q 15min </li></ul></ul><ul><ul><li>Warm iv fluids </li></ul></ul><ul><ul><li>Circulating hot water blanket/ hot water bottles </li></ul></ul><ul><ul><li>Bair Hugger </li></ul></ul><ul><ul><li>NEVER electric blanket* </li></ul></ul>
    25. 26. B. Use of Instruments to Monitor Vital Signs <ul><li>1. Blood pressure </li></ul><ul><ul><ul><li>Systolic ventricles contract (highest) </li></ul></ul></ul><ul><ul><ul><li>Diastolic between contractions (lowest) </li></ul></ul></ul><ul><ul><ul><li>MAP - Average </li></ul></ul></ul><ul><li>2. Doppler blood pressure monitors </li></ul><ul><ul><ul><li>Manual cuff inflate/deflate uses sound </li></ul></ul></ul><ul><li>3. Oscillometer blood pressure monitors </li></ul><ul><ul><ul><li>Automatic ie Dynamap </li></ul></ul></ul>
    26. 27. Use of Instruments to Monitor Vital Signs (cont) <ul><li>4. Central venous pressure ( CVP ) </li></ul><ul><ul><ul><li>Catheter into jugular to anterior vena cava </li></ul></ul></ul><ul><li>5. Blood gases – arterial blood sample </li></ul><ul><li>a. Oxygen </li></ul><ul><ul><ul><ul><ul><li>Free molecule in plasma (PaO2) Blood Gas Analyzer </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Bound on hemoglobin (Sao2) Pulse Oximeter </li></ul></ul></ul></ul></ul><ul><li>b. Carbon dioxide (PaCO2) – blood gas analyzer </li></ul><ul><li>6. Capnography – monitors CO2 </li></ul>
    27. 28. 7) Electrocardiography <ul><li>Normal rythym </li></ul><ul><ul><li>P,QRS, T </li></ul></ul><ul><li>Tachycardia </li></ul><ul><ul><li>>200 cat </li></ul></ul><ul><ul><li>>170 dog </li></ul></ul><ul><li>Bradycardia </li></ul><ul><ul><li><60 dog </li></ul></ul><ul><ul><li><100 cat </li></ul></ul>
    28. 29. ECG Abnormalities <ul><li>Heart block </li></ul><ul><li>PVC </li></ul><ul><li>Fibrillation </li></ul><ul><li>Respiratory Arrythmia </li></ul><ul><ul><li>normal </li></ul></ul>
    29. 30. C. Reflexes and Other Indicators of Anesthetic Depth <ul><li>Reflex = </li></ul><ul><li>1. Reflex activity --diminishes w/ deeper anesthesia </li></ul><ul><li>2. Palpebral reflex -- blink </li></ul><ul><li>3. Swallowing reflex – indicator to pull e-tube </li></ul><ul><li>4. Pedal reflex – squeeze digit>>pulls leg back </li></ul><ul><li>5. Ear flick reflex – tickle inside of ear </li></ul><ul><li>6. Corneal reflex – corneal contact >> blink/retract </li></ul><ul><li>7. Laryngeal reflex – closes epiglottis </li></ul><ul><li>8. Muscle tone – jaw tone </li></ul><ul><li>9. Eye position and pupil size – I central II ventral III central </li></ul><ul><li>10. Salivary and lacrimal secretions – why we need lube </li></ul><ul><li>11. Heart and respiratory rates – reflexes discussed prev. </li></ul><ul><li>12. Response to surgical stimulation – pain response </li></ul><ul><ul><ul><ul><li>Increase HR and increase RR </li></ul></ul></ul></ul>
    30. 31. D. Judging Anesthetic Depth <ul><li>monitor as many variables as possible consider all the information </li></ul><ul><li>each animal is unique and has an individual response to increasing anesthetic depth </li></ul>
    31. 32. E. Recording Information during Anesthesia <ul><li>drug log </li></ul><ul><li>controlled substance log </li></ul><ul><li>patient’s record </li></ul><ul><ul><li>In anesthesia log </li></ul></ul>
    32. 33. RECOVERY FROM GENERAL ANESTHESIA <ul><li>Recovery period = the period between _ ? ___and _ ? ___ </li></ul><ul><li>Factors affecting length of recovery period: </li></ul><ul><li>1. length of anesthesia – direct relationship </li></ul><ul><li>2. condition of the patient -- disease </li></ul><ul><li>3. type of anesthetic given and route of administration </li></ul><ul><ul><li>SQ>IM>IV INJ>INHALANT </li></ul></ul><ul><li>4. patient’s temperature – inverse relationship </li></ul><ul><li>5. breed of the patient (ie sighthound w/ _ ? _) </li></ul><ul><li>Stages of Recovery </li></ul><ul><li>progresses back through the same anesthetic stages that occurred during induction </li></ul>
    33. 34. MONITORING <ul><li>recovery should take place in an area where animal can be monitored closely: </li></ul><ul><li>emergency kit oxygen monitoring equipment </li></ul><ul><li>check vital signs every 5 minutes: MM color, CRT, respiratory effort + temp q 15min until >98 </li></ul><ul><li>ADMINISTRATION OF OXYGEN </li></ul><ul><li>for 5 minutes after discontinuation of anesthetic agent: </li></ul><ul><li>keeps patient oxygenated </li></ul><ul><li>eliminates waste gases through scavenger system </li></ul><ul><li>allows periodic bagging >>>>>> reinflates collapsed alveoli </li></ul>
    34. 35. EXTUBATION <ul><li>remove when swallowing reflex returns </li></ul><ul><li>Exception: brachycephalic = delay extubation till can lift the head </li></ul><ul><li>remove the ET tube at the end of inspiration </li></ul><ul><li>if blood or fluid had accumulated in oral cavity, leave cuff of tube partially inflated </li></ul><ul><ul><li>as remove the tube >>>>> prevents these fluids from flowing down trachea </li></ul></ul><ul><li>STIMULATION OF THE PATIENT </li></ul><ul><li>may hasten recovery by gentle stimulation >>>>>>> reticular activating center </li></ul><ul><li>rubbing face, head and neck, moving the limbs </li></ul><ul><li>turn the patient over every 10 to 15 minutes (avoids ?) </li></ul>
    35. 36. REASSURING THE PATIENT <ul><li>quiet, calm, gentle handling, low light situation </li></ul><ul><li>minimize patient discomfort –blankets/padding, pain meds </li></ul><ul><li>POSTOPERATIVE ANALGESIA </li></ul><ul><li>before the animal experiences postoperative pain </li></ul><ul><ul><li>(more on these drugs in another lecture) </li></ul></ul><ul><li>NURSING CARE </li></ul><ul><li>application of supplemental heat if patient hypothermic </li></ul><ul><li>warm towels hot water bottles circulating warm water pads </li></ul><ul><li>remember NEVER electric heating pads </li></ul>
    36. 37. PREVENTING PATIENT SELF INJURY <ul><li>some patients will go through period of excitement a “stormy” recovery </li></ul><ul><ul><li>Padding to avoid head banging </li></ul></ul><ul><li>tranquilization and/or use of analgesic medications </li></ul><ul><li>never left alone on a table or in a cage with the door left open </li></ul>