Introduction to Veterinary Anaesthesia 2024 PDF

INTRODUCTION TO VETERINARY ANAESTHESIA Hanna Machin Dip ACVAA, Dip SIAV, MVetMed, MRCVS Lecturer in Veterinary Anaesthesia Online learning 3010, 2024  ANAESTHESIA & ANALGESIA TEACHING IN THE 3010 MODULE: VETERINARY MEDICINE 1...

INTRODUCTION TO VETERINARY ANAESTHESIA Hanna Machin Dip ACVAA, Dip SIAV, MVetMed, MRCVS Lecturer in Veterinary Anaesthesia Online learning 3010, 2024  ANAESTHESIA & ANALGESIA TEACHING IN THE 3010 MODULE: VETERINARY MEDICINE 1 Practical 2: Lectures: Anaesthetic machine check Premedication & sedation Breathing system safety Injectable anaesthetic agents Endotracheal intubation dog and cat Inhalational agents Monitoring in Veterinary Anaesthesia Monitoring & patient instrumentation Common complications & accidents in Veterinary Anaesthesia Practical 4: Fluid therapy Intravenous cannulation Pain Management (2h) Online learning: Introduction Anaesthetic Equipment ECG interpretation Capnography waveforms interpretation Fluid therapy & CRI calculations LEARNING OBJECTIVES Be able to: Define the terms general anaesthesia, local anaesthesia, analgesia Describe the components of general anaesthesia Describe the stages of anaesthesia Explain the process of anaesthesia including patient preparation and immediate post- anaesthetic care SOME DEFINITIONS… ANAESTHESIA: from Greek “ an- aesthesia”: lack of feeling/ sensation GENERAL ANAESTHESIA: state of unconsciousness produced by drugs administration, characterized by controlled, reversible depression of the Central Nervous System (CNS) and perception SOME DEFINITIONS… ANALGESIA: absence of pain in response to stimulation which would normally be painful NOCICEPTION: (under general anaesthesia): process of encoding noxious stimuli (transduction, transmission, modulation of nociceptive stimuli) LOCAL ANAESTHESIA (ANALGESIA): loss of pain sensation in a circumscribed body area REGIONAL ANAESTHESIA (ANALGESIA): insensibility to pain in a larger (but limited) body area usually defined by the innervation pattern of affected nerves THE TRIAD OF GENERAL ANAESTHESIA BALANCED ANAESTHESIA: simultaneous use of multiple drugs & technique to produce a state of general anaesthesia THE IDEAL ANAESTHETIC AGENT Rapid onset Safe following extravascular injection Rapid recovery No toxic effects High lipid solubility No histamine release Does not accumulate with prolonged infusion No hypersensitivity reactions Analgesic at sub-anaesthetic concentrations Water-soluble formulation No (or Minimal) cardiovascular depression No (or Minimal) respiratory depression Long shelf-life at room temperature No emetic effects No pain on injection No excitation No emergence phenomena Does not interact with other agents THE ANAESTHESIA TIMELINE S TA B I L I S E P R E - E X I S T I N G C O N D I T I O N S Medical management (e.g. diabetes, hyperthyroidism) Fluid Therapy (i.e. treat hypovolaemia & dehydration) Analgesia Anxiolysis Oxygen supplementation Surgical procedures (e.g., thoracocentesis, tracheostomy, pericardial drainage..) C H R O N I C M E D I C AT I O N S & A N T I - A N X I E T Y M E D I C AT I O N S Consider also anti-anxiety/ sedative medication(s) if stressed/anxious/aggressive patients (i.e. TRAZODONE, GABAPENTIN…) → to be administered ~2h before transport +/- the night before Image from: Grubb T, Sager J, Gaynor JS, Montgomery E, Parker JA, Shafford H, Tearney C. 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2020 Mar/Apr;56(2):59-82. doi: 10.5326/JAAHA-MS-7055. PMID: 32078360 FASTING GUIDELINES To help ↓gastro-oesophageal reflux (GOR) & aspiration pneumonia, ↓ stomach size No clear consensus within the literature Species differences ~ 6 hours fasting (dogs & cats) Reduce fasting times for diabetic, neonatal, geriatric patients Image from: Grubb T, Sager J, Gaynor JS, Montgomery E, Parker JA, Shafford H, Tearney C. 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2020 Mar/Apr;56(2):59-82. doi: 10.5326/JAAHA-MS- 7055. PMID: 32078360 AMERICAN SOCIETY OF ANESTHESIOLOGISTS (ASA) P H Y S I C A L S TAT U S C L A S S I F I C AT I O N S Y S T E M ANAESTHETIC RISK ↑ ASA status = ↑risks E Q U I P M E N T P R E PA R AT I O N Check:  O2 supply  Scavanging system  Anaesthetic machine(s)  Breathing system  Endotracheal tubes (ET tubes)  Intubation tools (laryngoscope)  Monitoring equipment  Rewarming devices  Emergency drugs  …. P R E M E D I C AT I O N Intravascular (IV), Intramuscular (IM) or subcutaneous (SC) Careful monitoring throughout Give adequate time for drugs to work Calm & quiet environment If sedation level insufficient: add more drug/use ≠ drugs More on this on premedication and sedation lecture! IM administration: Neck muscles Epaxial muscles Semimembranosus/semitendinosus Quadriceps IV CANULA PLACEMENT Administration of fluids and medications (peri-anaesthetic period) Blood sample collection Emergencies Patient welfare Aseptic technique required! Image from: Image from: Intravenous catheter placement // WVS Academy https://books.lib.uoguelph.ca/vetm3430/chapter/1- 3-medication-techniques/  P R E - OX YG E N AT I O N Administration of high fraction of inspired oxygen (FIO2) before induction by: Facemask Flow-by Oxygen cage/tent  For All patients: Images from: Veterinary Anesthetic and Monitoring Equipment, edited by Kristen G. Cooley, and Rebecca A. Johnson, John Wiley & Sons, Incorporated, 2018. Especially if difficult ventilation/intubation is expected ↑body 02 stores → delay onset of Hb desatura on during apnoea →Hypoxaemia Might not be tolerated Can cause stress & anxiety B E F O R E S TA R T I N G... Crush box Emergency drugs CPR cheat sheet CPR algorithm INDUCTION OF ANAESTHESIA  Endotracheal Tubes (ET tubes) tubes of different sizes  Laryngoscope  Tie  Syringe to inflate ET Tube cuff  Helper/mouth-gag  Induction agent of choice  Local anaesthetic  Lube  Swab to hold tongue  HOW TO CHOOSE THE CORRECT ET TUBE SIZE? Choose at least 3 X ET tubes: the size you think it will fit, one above, one below For brachycephalic breeds have huge selection available ≠ formulas & tables (careful with overweight patients) Image from: 3.5 - https://www.theveterinarynurse.com/content/practical/endotra cheal-intubation-of-the-dog-and-cat/ Image from: ASNA_Endotracheal_Tube_Size_Chart (aspcapro.org) E N D OT R A C H E A L I N T U B AT I O N Images from: https://www.theveterinarynurse.com/Review/article/how-to-manage-a-difficult-airway E N D OT R A C H E A L I N T U B AT I O N Measure ET tube length before insertion (thoracic inlet) Keep head elevated until airways are secured Secure ET tube Connect to breathing system with O2 Check that ET Tube is in the trachea: - Check for condensation on the ET tube - Connect to capnograph & breathing system - Give a breath if patient is not breathing Check ET Tube cuff +/- inflation Image from: https://kidocs.org/2013/11/much-hot-gas-etco2-non-anaesthetists/ Image from: https://derangedphysiology.com S EC U R I N G T H E A I R WAY S Under inflation of ET Tube cuff: Change of capnograph trace Lower ET CO2 values Risk of aspiration pneumonia Leak of anaesthetic agents: - Pollution - Safety of personnel Image from: https://www.vetfolio.com/learn/article/capnography-in-dogs S EC U R I N G T H E A I R WAY S ET tube Cuff inflation: If over inflation: risk of tracheal ischemic necrosis Recommended safe ET tube cuff pressure range: 20–30 cmH2O Methods of measuring cuff pressure: Minimum occlusive volume technique Syringe devices (Tru-Cuff , AG Cuffill syringe) Image from: https://www.researchgate.net/figure/Diagram- Image from: representing-potential-mechanism-for-tracheal-mucosal- https://aneskey.com/trac perfusion-injury-secondary_fig2_51874813 heal-tubes-tracheostomy- tubes-and-airways/ AFTER INDUCTION “ The ABCD MNEMONIC ” AIRWAY BREATHING CIRCULATION & CUFF DRUGS/DEPTH of ANAESTHESIA EQUIPMENT/EYES FORMS Image from:Measuring clinical parameters | Veterian Key MONITORING Continuous Recording Which monitoring device gives us more info?  S TA G E S O F A N A E S T H E S I A Species differences Stage of voluntary movement Stage I Stage of involuntary movement or delirium Stage of surgical anaesthesia Adequate plane of anaesthesia Extreme CNS depression Recovery MAINTENANCE OF ANAESTHESIA Administration of INHALATIONAL AGENT and/or INJECTABLE AGENTS and /or additional drugs (i.e., alpha 2 agonists/opioids, ketamine, lidocaine) and O2 More info on the induction & maintenance lecture RECOVERY CHECKLIST E X T U B AT I O N Keep patient in sternal (if possible) ET tube cuff deflation Keep monitoring Dog: swallowing, head/limb movement (i.e., brachy exception) Cat: ear flick, strong medial palpebral reflex (before swallowing): laryngospasm risk +/- sedation if required RECOVERY… Critical phase: ↑ risk morbidity & mortality → con nuous monitoring important RECOVERY Starts when maintenance agents is discontinued & patient start to regain consciousness Calm & warm environment Monitoring Patient warming Fluid therapy Eye lube Express bladder Adequate padding Pain scoring & analgesia +/- Sedation RECOVERY Delay: Excessive anaesthetic depth/drug administered Drugs with long duration of action Prolonged anaesthesia Comorbidities (hepatic, renal disease) Hypothermia Hypoglycaemia (diabetic, paediatric, exotic…) Poor circulation (hypotension, haemorrhage) Hypoxaemia EMERGENCE DELIRIUM State of stress, unease, anxiety, characterized by vocalization, panting, restlessness, uncoordinated thrashing Patient may not be mentally appropriate ≠ causes: Hypoxaemia? Pain? Recent opioid administration? → if not pain related…Sedation Alpha 2 agonists, Acepromazine, Propofol (0.5-1 mg/kg IV slowly) Have ET tube, laryngoscope, tie available to re- intubate if necessary HANDOVER REFERENCES T H A N K Y O U F O R Y O U R AT T E N T I O N. ANY QUESTIONS?