Monitoring Anesthetic Depth Spring 2025 PDF

MONITORING ANESTHETIC DEPTH DR. LISA EBNER CVM 746 LECTURE OBJECTIVES 1. Recognize the signs associated with the different planes of anesthesia 2. Describe how a patient in a surgical plane of anesthesia looks 3. List any factors that may affect your monitoring of patient depth ...

MONITORING ANESTHETIC DEPTH DR. LISA EBNER CVM 746 LECTURE OBJECTIVES 1. Recognize the signs associated with the different planes of anesthesia 2. Describe how a patient in a surgical plane of anesthesia looks 3. List any factors that may affect your monitoring of patient depth  WHAT IS GENERAL ANESTHESIA? varietyof aspects involved f 1. Both the loss of consciousness and sensation 2. Should include muscle relaxation, analgesia, suppression areflexia of stress response and hypnosis absenseofpain 3. Reversible process 4. May be produced with 1 drug or a combination of drugs ❖Remember that drugs or techniques that adequately Balanced induce anesthesia in one species and for one Anesthesia procedure may not work in another species! hypnosis analgesia  CLASSICAL STAGES AND PLANES OF ANESTHESIA Anesthetic level Reaction to Palpebral Eye and pupil reflex Jaw tone HR RR surgical reflex stimulation Stage I + + Normal to dilated Normal to Normal to Normal to Stage II + + tense Stage III N to N to Plane 1 ± + Third eyelid elevated N to N to Plane 2 - - Plane 3 Abdominal slow, Plane 4 - - shallow Stage IV Apnea Cardiac arrest  STAGE I Defined as the time from the start of administration of induction drugs until loss of consciousness Stage of voluntary movement Able to initially turn or lift head without support Some analgesia present can appearrough wo premeds Progressive ataxia → lateral recumbency If patient is excited (i.e. little premed effect)→ struggling, breath holding, increased heart rate and pupil dilation due to epinephrine release, defecation, urination, salivation Most variable stage!  STAGE II Patient may display the following: struggling or exaggerated reaction increased or irregular respiratory to stimuli pattern; breath holding vomiting or regurgitation can Increased heart rate; arrhythmias due occur; salivation (esp. ruminants to catecholamine release and cats) active palpebral reflexes Laryngospasm (esp. cats and pigs) tight anal sphincter tone Dilated pupils; nystagmus (common jaw tone present in horses) May vocalize ❖Can be characterized as stage of delirium and involuntary movement and lasts from loss of consciousness to onset of regular breathing pattern  STAGE III perfged Stage of surgical anesthesia due to level of unconsciousness with progressive depression of reflexes, muscle relaxation and slow, regular breathing pattern Vomiting (by Plane 1) and swallowing (by Plane 2) reflexes abolished Loss of jaw tone  STAGE III, PLANE I May also be called a “light” plane of anesthesia Persists until eyeball movement stops Minimally invasive/painful procedures (ex. biopsy, wound closure)  STAGE III, PLANE II May also be called a “medium” plane of anesthesia Most surgical procedures performed at this plane (“light plane of surgical anesthesia”) Characterized by progressive intercostal paralysis Respiration and heart rate have stabilized Sluggish palpebral reflex Strong corneal reflex Adequate muscle relaxation and analgesia Abolished laryngeal reflexes  STAGE III, PLANE III May also be called “deep” plane of anesthesia or “deep plane of surgical anesthesia” Toodeep Decrease in heart rate Slow, shallow abdominal breathing pattern (“diaphragmatic respiration”) No jaw tone No reaction to surgical stimulation, profound muscle relaxation No palpebral reflex, weak corneal reflex Pupil progressively dilated and central  STAGE III, PLANE IV Pupils dilated Hypotension progressing to shock Slow CRT Slow, irregular respirations Lack of muscle tone No anal sphincter tone  STAGE IV Anesthetic overdose Extreme CNS depression→ anesthetic overdose Pale to white mm, CRT ≥ 3 seconds Respiratory arrest followed by cardiac arrest Central, widely dilated pupils Absent ocular reflexes Flaccid muscle tone o Death unless swift intervention  SUMMARY OF WHAT YOU SHOULD BE CHECKING TO MONITOR DEPTH Check the following ocular signs – quite variable among species! Palpebral reflex ❖These reflexes can Feye Eye position Lacrimation movestoventralposition be species, drug and Nystagmus patient dependent! Corneal reflex II I ❖No clear division Why should Jaw tone exists between you place lubrication Anal reflex relaxed stages! ointment in the eyes? Pedal reflex; tail pinch, ear pinch or ear-flick reflex Overall muscle tone or degree of patient relaxation Lossof palpebralrefl soeyesdryup pron to Eger  WHAT IS THE GOAL FOR A SURGICAL ANESTHESIA PLANE? Relaxed jaw tone…is it easy to open with 2 fingers? Mild to no palpebral reflex Ventral medial eye rotation Relaxed anal tone Smooth, regular respiratory pattern Normal heart rate m No swallowing, coughing, vomiting or laryngospasm  SPECIES SPECIFIC SIGNS TO LOOK FOR From: Lumb & Jones’ 4th ed. page 16 Horses will lacrimate in light stages of anesthesia. Eyes stay central instead of ventral medial eye rotation. Nystagmus in Stage II. EEEist Corneal reflex persists into deeper anesthesia plane. Cats may go into laryngospasm and/or may retain cough, swallow, and vomiting reflex until they reach a deeper plane of anesthesia. opposite Cattle have consistent, reliable eyeball rotation. What about sheep and goats? scleraperfect SPECIES SPECIFIC SIGNS Rodents Observe feet, ears, muzzle for pallor or cyanosis Pedal reflex pinching toe Poultry Examine comb and/or wattle for pallor Vent reflex Rabbits Can use the color of light reflected from the eye to determine circulation status ARE THERE ANY FACTORS THAT MAKE MONITORING DEPTH DIFFICULT? Drugs - mostcommon Ketamine – typical eye signs not produced still blink swallow laryngealreflexes Propofol – no analgesia; apnea Oxygenation adequacy CO2 retention Physical status OTHER METHODS TO MEASURE DEPTH Anesthetic gas analyzer Useful piece of equipment, but not commonly available in general practice Used to perform minimum alveolar concentration (MAC) studies in many species measuresgascoming out of P'slungs  GOT ANYTHING ELSE UP YOUR SLEEVE? Bispectral Index (BIS) Tate om ain 60 adequateunder anesthesia wakingup Ʃ mainlyused in research or humanmed From: avmajournals.avma.org BIS MONITORING IN RESEARCH  WHAT ABOUT RECOVERY? Progresses in reverse order 7 Every species and patient will recovery differently Treat post-op pain if suspected YhEior r pth.ie1 Stage II can be a difficult time due to delirium/dysphoria, especially in equine patients Horses are often sedated with an alpha2 agonist going into inhalant anesthesia recovery and stimulation is minimized (quiet, dark room) preventthemfrominjuringthemselves How long should patients be closely monitored in recovery? manually w temf.GE Fa'g R IF YOU NEED A GOOD CHUCKLE TODAY… https://www.youtube.com/watch?v=lRwb8Kp4zWU https://www.youtube.com/watch?v=Bx6KD7PWKfs  RESOURCES Handbook of Veterinary Anesthesia. 5th ed. Chapters 9 (pages 163-165) and 14 (pages 260-262). BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. 2nd ed. Chapter 7: pages 61-64. Lumb and Jones’ Veterinary Anesthesia and Analgesia. 5th ed. Chapter 4 (pages 86-89)