Monitoring in Veterinary Anaesthesia (PDF) 4th October 2024

MONITORING IN VETERINARY ANAESTHESIA Hanna Machin Dip ACVAA, Dip SIAV, MVetMed, MRCVS Lecturer in Veterinary Anaesthesia at the University of Surrey 4th October 2024 OBJECTIVES Explain the importance of t...

MONITORING IN VETERINARY ANAESTHESIA Hanna Machin Dip ACVAA, Dip SIAV, MVetMed, MRCVS Lecturer in Veterinary Anaesthesia at the University of Surrey 4th October 2024 OBJECTIVES Explain the importance of the monitoring of the anaesthetised patient Describe the use and interpretation of physical examination findings in the assessment the anaesthetised patient Identify the clinical signs used to assess anaesthetic depth Describe the use and interpretation of electronic equipment in the physiological monitoring of the anaesthetised patient, specifically electrocardiography, pulse oximetry, capnography and arterial pressure measurement Discuss the potential sources of error associated with the various physiological monitors and their influence on the interpretation of global patient status Understand the importance of the anaesthetic record as a legal document AIM OF MONITORING Maintain adequate depth of anaesthesia Assess adequacy of analgesia Maintain function of different body systems as physiologically normal as possible Identify changes/issues Evaluate response to treatment Safety of patients & staff Legal purposes HOW? Complete patient overview The 5 Human senses Monitoring equipment Anaesthetic record Image from: https://cpaexamcoach.com/use- your-five-human-senses-for-cpa-exam-success ANAESTHETIC RECORD Legal document Must be filled in its entirety Recording at least q 5’ (but monitor continuously) Any important event occurred should be recorded! Source of info for future anaesthetics  MONITORING OF THE CENTRAL NERVOUS SYSTEM HOW DO WE MONITOR? Species differences Eye position & movement, palpebral reflex, lacrimation, nystagmus Jaw tone Laryngeal & pharyngeal reflexes Physiological parameters (Heart Rate, Respiratory Rate, Blood Pressure…) Anal tone? Pedal reflex Righting Reflex Evaluate trends  MONITORING OF THE CENTRAL NERVOUS SYSTEM To assure adequate anaesthetic level Often inconsistent signs Species differences (i.e. Horses, Ruminants) Drugs effects (i.e. Ketamine) Aim during anaesthesia: stage III, plane 2 Image from: Clarke, Trimm and Hall (2014) Veterinary Anaesthesia (Eleventh Edition), Saunders E X A M P L E S O F A N A E S T H E T I C P L A N E S ( D O G S & C AT S ) Eyes central position Eyes central position Eyes rotated No palpebral reflex Palpebral reflex + (ventromedial position) No jaw tone Mild/ strong jaw tone + palpebral reflex → no No movement palpebral reflex Possible movements RR & HR usually decrease Relaxed jaw tone LIGHT PLANE SURGICAL PLANE DEEP PLANE LIGHT PLANE OF ANAESTHESIA M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M Respiratory Rate (RR) & Rhythm Capnography Pulse Oximetry Mucous Membrane Colour Tidal Volume Blood Gas Analysis M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M RESPIRATORY RATE (RR) & RHYTHM Observe: Chest movements Reservoir bag movements RR on monitor (Capnography) Auscultation Change in respiratory rate & pattern → change in the depth of anaesthesia ↑ RR: light plane of anaesthesia, nociception/pain, hyperthermia, hypercapnia.. ↓ RR: deep plane of anaesthesia, hypothermia Apnoea: rapid administration of drugs, overdose of anaesthetic, breath holding (light plane of anaesthesia) M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M CAPNOMETRY Breath by breath analysis of Expired CO2 (End-tidal CO2- ET CO2) RR FiCO2 (inspired CO2 levels) CAPNOGRAPHY Graphical representation of CAPNOMETRY throughout the respiratory cycle Image from: https://kidocs.org/2013/11/much-hot-gas- etco2-non-anaesthetists/ M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M END EXPIRATION CAPNOGRAPHY Waveform: Pressure vs time plot Expressed as % or partial pressure (mmHg) Normal ET CO2 values: 35 - 45 mmHg PHASE Hypocapnia: < 35 mmHg, hypercapnia > 45 mmHg  Non-invasive, continuous EXPIRATION INSPIRATION  Early issue detection NORMAL capnograph trace Image from: https://www.nuemblog.com/blog/capnography M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M CAPNOGRAPHY Image from: ikolaus Gravenstein, Michael B. Jaffe. Capnography, Anesthesia Equipment (Third Edition),W.B. Saunders,2021, Pages 239-252 M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M CAPNOGRAPHY Estimates arterial CO2 (PaCO2, Partial pressure of CO2 in the arterial blood) Ventilation/perfusion mismatch PaCO2 ] ALVEOLAR DEAD SPACE Image from: https://airwayjedi.com/2017/01/06/ventilation-perfusion- mismatch/ M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M CAPNOGRAPHY/CAPNOMETRY Gives info on: METABOLISM CARDIAC OUTPUT → CPR ALVEOLAR VENTILATION ANAESTHETIC EQUIPMENT RESPIRATORY RHYTHM M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M SIDESTREAM vs MAINSTREAM capnography Image from: Marshall, M A. “Capnography in Dogs.” Compendium on Continuing Education for The Practicing Veterinarian 26 (2004): 761-777.  M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M METABOLISM CAPNOGRAPHY PULMONARY PERFUSION ALVEOLAR VENTILATION TECHNICAL ERRORS ↓ Hypothermia ↓ Cardiac output Hyperventilation Disconnection ETCO2 Hypothyroidism Hypotension Asthma Sampling leaks or blockage Drugs/anaesthetic depth Hypovolemia Apnoea ET tube obstruction Pulmonary embolism ET tube cuff deflated Cardiac pulmonary Ventilatory settings: arrest hyperventilation ↑ Fever ↑ Cardiac Output Hypoventilation Exhausted CO2 absorber ETCO2 Hyperthermia ↑ Blood pressure Rebreathing Inadequate fresh gas flow Malignant hyperthermia Faulty valves Seizures Ventilatory settings: Hyperthyroidism hypoventilation Image from: Marshall, M A. “Capnography in Dogs.” Compendium on Continuing Education for The Practicing Veterinarian 26 (2004): 761-777. M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M PULSE-OXIMETRY Use recommended in ≠ studies AAHA guidelines on monitoring Decreases odds of anaesthetic death in cats (Broadbelt at al. 2007)  Early problem recognition (especially with capnography) M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M SPO2 value PULSE-OXIMETRY Pulse rate Measure the degree of saturation of Haemoglobin (Hb) with O2 Calculates the amount of Oxy-Hb as a % of Total Hb Normal range 98-100% Pulse waveform Hypoxaemia if Sp02 < 90- 95% Easy to use, non-invasive Continuous measurements Detects hypoxaemia earlier than human eye Can be positioned on tongue, ears, prepuce, vulva, lips, toe web, skin flap… Audible signal for each pulse with ≠ pitch A B R I E F R E C A P... 98-99% of O2 in blood is carried in RBCs in combination with Hb (SaO2) 1-2% O2 dissolved in plasma (PaO2) O2 saturation: % of Hb molecules saturated with O2 Image from: https://stock.adobe.com/uk/images/oxygen-transport-oxygen-binds-to- hemoglobin-and-is-released-by-red-blood-cells-gas-exchange-mechanism/565825079 One Hb molecule carries maximum 4 X O2 molecules (fully saturated with O2) Image from: Thomas C., Lamb A. Physiology of Haemoglobin Continuing Education in Anaesthesia, Critical Care & Pain | Volume 12 Number 5 2012 A BRIEF RECAP… BOHR effect: O2 - HEMOGLOBIN DISSOCIATION CURVE O2 released into ssues with High CO2, ↓ PH ( ssue & organs) O2 is bound to Hb in ssues with ↓ CO2, ↑PH (lungs) HALDANE effect: De-O2 Hb greater ability to carry CO2 O2-Hb less able to carry CO2 O2 of blood in the lungs displace CO2 from Hb Normal range 98-99% Hypoxaemia if Sp02 < 90- 95% (PaO2 < 60mmHg) Image from: https://partone.litfl.com/oxygen_storage.html  A B R I E F R E C A P... O2 - HEMOGLOBIN DISSOCIATION CURVE Reluctance O2 unloads > to release easily O2 from Hb Image from: https://x.com/silmerrillon/status/1269260948990119943/photo/1 M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M HOW PULSE-OXIMETRY WORKS PULSE PLETHYSMOGRAPHY to detect pulse waveform INFRARED SPECTROSCOPY to detect absorption of light (red & infrared) by tissue under probe 02-Hb absorbs > INFRARED light De-02-Hb absorbs > RED light Only measured from arterial blood (pulsatile) Images from: How equipment works.com M O N I TO R I N G T H E R E S P I R ATO R Y S Y S T E M PULSE-OXIMETRY If quality of signal is poor calculation of Hb saturation might be wrong: “SEE PLETH BEFORE O2” Interference Movement Hypoperfusion & peripheral vasoconstriction Species related inaccuracies Pigmentation (Sp02 overestimation) Carboxyhaemoglobin/ Methaemoglobin Image from: https://ccforum.biomedcentral.com/articles/10.1186/cc341  M O N I TO R I N G T H E R E S P I R ATO R Y & CARDIOVASCULAR SYSTEM PULSE-OXIMETRY (PLETHYSMOGRAPH) Additional info on: Vascular tone Perfusion Fluid responsiveness Pulse deficits/variation during arrhythmias Image from: https://corom.org/embrace-the-full- power-of-your-spo2/ Image from: Mohanty, Pankaj. (2014). Early detection and management of critically sick newborn in neonatal intensive care unit using perfusion index and pleth variability index in advanced pulseoximetry. Indian journal of child health. 1. 158-159. MONITORING THE CARDIOVASCULAR SYSTEM Monitor tissue O2 delivery Maintain cardiac output & SaO2 Heart Rate (HR) & Rhythm Blood Pressure Image from: Mathis, A. (2016), Practical guide to monitoring anaesthetised small animal patients. In Practice, 38: 363- Mucous Membrane Colour 372. https://doi.org/10.1136/inp.i3947 Peripheral Pulses Palpation (rate, quality, synchronicity with heart beats) Pulse Oximeter Capnography/Capnometry MONITORING THE CARDIOVASCULAR SYSTEM HEART RATE & RHYTHM PALPATION of the APEX BEAT AUSCULTATION (stethoscope, oesophageal stethoscope) ECG  Graphic representation of changes of electrical activity on the heart measured at the surface of the skin  Monitor HR & rhythm  Electrolytes disturbances  Myocardial hypoxia AMPLITUDE (mV) Not a measure of contractility TIME (sec) Careful about artifacts Image from: https://www.bhf.org.uk/informationsupport/tests/ecg MONITORING THE CARDIOVASCULAR SYSTEM ECG LEFT DEPOLARISATION BUNDLE VENTRICLES BRANCH REPOLARISATION ATRIAL DEPOLARISATION VENTRICLES RIGHT BUNDLE BRANCH Image from: Beyrami Enanlou, Hamed & Lotfivand, Nasser. (2017). Shannon’s Energy Based Algorithm in ECG Signal Processing. Computational and Mathematical Methods in Medicine. 2017. 1-16. 10.1155/2017/8081361 MONITORING THE CARDIOVASCULAR SYSTEM ECG 3 LEADS (+, - & ground lead) usually positioned on BOTH arms and LEFT LEG Paws, axilla + inguinal region, ears… Adhesive patches, crocodile clips… +/- gel ≠ trace appereance depending on leads placement (relatively to the heart) Most common: lead II (right shoulder, left leg) To look at the electricity of the heart from a 360 degree angle  EINTHOVEN’s TRIANGLE MONITORING THE CARDIOVASCULAR SYSTEM HOW to DESCRIBE an ECG  Look at the HEART RATE: Is it FAST or SLOW for this SPECIES & BREED?  Is RHYTHM regular or irregular? Look at R-R intervals Are P waves and QRS complex regular?  Is there a P wave in front of every QRS?  Is there a QRS following every P wave?  Are QRS normal (tall & narrow) or abnormal (wide & bizzarre) MONITORING THE CARDIOVASCULAR SYSTEM BLOOD PRESSURE MEASUREMENT Pressure = Force of blood flow/Area (arterial wall) Blood Pressure = Cardiac Output X Systemic Vascular Resistance Stroke Volume X HR Preload, Afterload, Contractility MONITORING THE CARDIOVASCULAR SYSTEM BLOOD PRESSURE MEASUREMENT ≠ Values for ≠ species & breeds Systolic Mean Diastolic SAP MAP DAP < 50 mmHg >150 mmHg > 100mmHg > 90 mmHg Blood pressure values under anaesthesia Image from: Canine and Feline Anesthesia and Co- Existing Disease, First Edition. Edited by Lindsey B.C. Snyder and Rebecca A. Johnson. © 2015. MONITORING THE CARDIOVASCULAR SYSTEM WHY DO WE CARE ABOUT MAP? Indirect indicator of Tissue perfusion Anaesthetic drugs depress autoregulatory mechanisms Start treatment if MAP< 70 mmHg & SAP