How to Induce and Maintain Anesthesia - Veterinary Guide PDF

How to induce and maintain anaesthesia CP3.14 Supporting the animal Pamela Murison1 2022-23 2 Year ILO(s) Therapeutics and management CP3024 a Formulate an analgesic, sedative or anaesthetic plan for a veterinary patient, demonstrating an understanding of the underpinning principles, including...

How to induce and maintain anaesthesia CP3.14 Supporting the animal Pamela Murison1 2022-23 2 Year ILO(s) Therapeutics and management CP3024 a Formulate an analgesic, sedative or anaesthetic plan for a veterinary patient, demonstrating an understanding of the underpinning principles, including pharmacology & the safe use of anaesthetic equipment. 3 Lecture ILOs After this lecture you should be able to  Compare different techniques for induction and maintenance of anaesthesia  Discuss reasons for and complications associated with endotracheal intubation and other airways  Select patient appropriate induction and maintenance drugs and techniques for anaesthesia 4 Outline    Options for induction/maintenance Options for airway Case examples 5 Induction    IM IV Inhalation 6 Induction  IM e.g. feral cat – Often ketamine based IV – Most common Inhalation – Some exotics, small mammals (e.g. rodent) – Cats, dogs, foals occasionally – Sevoflurane less aversive, fast onset –   7 Factors affecting choices    Access to vein Temperament of animal Speed of induction required 8 Factors influencing induction  Speed of injection – – –  Too fast? Too slow? How does premedication alter? Hypoalbuminaemia 9 Co-induction    More than one agent Minimise doses Minimise cardiovascular effects  Midazolam? – –  Fentanyl? –  Often give small dose propofol (or alfax) first  0.2-0.3 mg/kg Beware excitation 1-2 mcg/kg Ketamine? – 0.5 mg/kg 10 Maintenance   Inhalation – Volatile agent e.g. isoflurane +/- nitrous oxide – Delivered via anaesthetic machine, breathing system – Most common (UK) Injectable anaesthetics – Top up IM (not ideal) – Intravenous top-up or infusion  Can be expensive  Can depress ventilation 11 Supplementing anaesthesia/analgesia  Fentanyl – –  Ketamine – –  1-5 mcg/kg bolus 2-10 mcg/kg/hour 0.25-0.5 mg/kg bolus 0.3-0.6 mg/kg/hr Lidocaine – – 1 mg/kg bolus 1.5-3 mg/kg/hr 12 Options for airway management    Mask Supraglottic airway Endotracheal intubation 13 Airway management  Mask – – – – Risk leak of gases Difficult to hold in place Does not protect against aspiration Useful very small patients 14 Supraglottic airway  Laryngeal mask – – – – – – Intermediate between mask/ETT Sit over larynx, does not enter trachea Better seal but not perfect Easily dislodged Popular in rabbits V-gel, anatomically designed 15 Endotracheal intubation  Insertion of an endotracheal tube into the trachea – Orally – Nasally – Alternatives? 16 Types of endotracheal tube 17 Benefits to tracheal intubation    Allows a patent airway – Relaxation of tissues Allows the anaesthetist to support ventilation Protects against aspiration of material – Regurgitation, haemorrhage, saliva etc 18 Methods of endotracheal intubation     Blind Manually assisted Laryngoscope guided (Bronchoscope guided) 19 Laryngoscope   Handle Blade – – Different shapes Different sizes  Light  Not just a torch! 21 Dogs • Think of bevel angle when inserting • Don’t twist ON cords • Rotation after pass through cords may help 22 Cats    Laryngospasm Desensitise using lidocaine spray Minimal touch on cords 23 Horses  Oral  Nasal 24 Is the tube in the trachea?      Visual confirmation Condensation in transparent tubes Breathing system bag movement Palpation of tube Capnography – These are useful!   [Pressing chest] [Cotton wool in front of tube –moving?] – These are not useful! 25 After intubation   Secure the tube Inflate the cuff – – Just enough to stop a leak e.g. when breath given 26 Should you always intubate?  Horses/cats – – – Maintain airway well Evidence in cats may increase anaesthetic risk So for short procedures/healthy animals not nec to intubate  Dogs – – – Easy to intubate (usually) Airway may be affected by the anatomy Regurgitation more likely in some dogs 27 Should you always intubate?  Pigs/rabbits – – – Difficult to intubate May cause trauma Can maintain airway quite well by mask  Ruminants – – High regurgitation risk Intubation very important if GA 28 Length of ETT   Not past the point of the shoulder Can enter 1 bronchus 29 Risks/complications       Laryngospasm Trauma/swelling (post-op) Endobronchial intubation Kinking ETT Obsruction with secretions etc Obstruction of bevelled end   Tracheal stenosis (rare) Tracheal rupture (rare) 30 Before induction: Good practice  Place an IV line  Pre-oxygenate – – If possible If not stressful 31 Example 1      Image: D Flaherty  2 yo healthy Labrador Ovariohysterectomy Acepromazine + methadone IM Placed IV line Induction? Maintenance? 32 Example 2: 7 yo GSD, ruptured splenic mass     Image: D Flaherty Poor pulses Pale Methadone premedication Induction? 33 Bulldog airway surgery   Low dose alpha-2 + methadone premedication What are concerns/aims with this case? 34 Bulldog     May have difficult airway Pre-oxygenation important Risk of regurgitation? Aim for fast recovery 35 Bulldog     May have difficult airway Pre-oxygenation important Risk of regurgitation? Aim for fast recovery 36   Risk of regurgitation? Supporting ventilation 37 Risk of regurgitation?      Rapid induction In sternal recumbency Until tube cuffed If regurgitates, head down (drain) Have suction ready IPPV Intermittent positive pressure ventilation 38   Anaesthetics depress ventilation Pathophysiology may require ventilation (e.g. diaphragmatic rupture)  Squeeze bag- gently Look for chest rise  Ventilators- automate  – – – 10-15 mL/kg Vt Us 10-12 cmH2O pressure dog (higher horse) Rate species dependent 39     Often more than one way Think about pros and cons to technique Think about pathophysiology Not just drug choices 40 Further reading:   BSAVA Manual of canine and feline anaesthesia – Chapters 14 and 15 – Airway management- pages 56-59 For other species, Veterinary Anaesthesia (Hall, Clarke and Trim) will have useful information