Advanced Anaesthetic Monitoring for Veterinary Practices

Advanced Anaesthetic Monitoring

• This lecture covers the topic of advanced anesthetic monitoring for veterinary practices.
• The lecture is part of a larger course on anesthesia, critical care, and surgical techniques (A6004C17).
• The date of the lecture is Tuesday, January 14th, 2025.

Learning Objectives

• Students will be able to evaluate the triage, assessment, monitoring, and care of critical patients.
• Students will be able to understand the role of a veterinary nurse in managing patients throughout a range of anesthetic and surgical procedures, from simple to complex cases.
• Advanced monitoring techniques in veterinary practice will be introduced.
• The techniques include blood gas analysis, blood pressure analysis, electrocardiography, and capnography.

Blood Gas Analysis (BGA)

• BGA measures several key parameters related to a patient's oxygenation, ventilation, and acid-base balance.
• Oxygenation (PO2): A key parameter of oxygenation.
• Ventilation (PCO2): A crucial parameter related to ventilation.
• Acid-base status (pH): Measures the acid-base balance within the blood.
• Additional parameters include electrolytes, blood glucose, blood lactate, ionized calcium, % oxygen saturation, base excess, and bicarbonate concentration.

Why Measure BGA?

• Aids in diagnosing, treating, and managing various disease processes.
• Helps identify metabolic or respiratory dysfunction.
• Can be used alone or in conjunction with other blood tests for comprehensive diagnostics.

Sample Collection and Processing

• Venous or Arterial Samples: Different methods of obtaining blood samples.
• Venous: Easier access, suitable for conscious patients, but can be painful. Aseptic technique is important. Often involves drawing from the jugular vein or a central venous line.
• Arterial: Often more challenging to access, especially when a patient is conscious. Requires strict aseptic technique and access to the artery or central arterial line. Local anesthesia might be needed for some patient types.
• Anaerobic Technique: Using airtight syringes to prevent air from entering the sample. Also possible to draw a sample directly from a central line, discarding the initial few drops of blood.
• Heparinised Syringe: Using lithium heparin-coated syringes to prevent blood clotting; analyzing the sample immediately is critical in this case.

BGA Machine

• EPOC BGA machine is a common tool in veterinary practice.
• Resources are available for the user, including instruction videos, product flyers, and user manuals.

Evaluation of Findings (Normal Ranges)

• PO₂: 5 x inspired oxygen percentage is a rough guide, severe is less than 60 mmHg. This value does not reflect oxygen content and requires HCT/Hg for more thorough analysis.
• PCO₂: 35-45 mmHg. Hypoventilation results from values greater than 45 mmHg. Hyperventilation is reflected by readings less than 35 mm Hg.
• pH: 7.35 - 7.45
• HCO₃⁻: 22-36 mmol/L
• Base Excess: -4 to +4 mmol/L
• Anion Gap: 12-25 mmol/L (dogs); 13-27 mmol/L (cats)

Oxygenation

• PO₂ correlates roughly with 5 times the inspired oxygen concentration (%).
• Critically low: below 60 mmHg
• Doesn't assess oxygen content; requires further tests to define it, such as HCT or Hg.
• Often used in combination with pulse oximetry.

Ventilation

• The gold standard for ventilation assessment is PaCO₂.
• PaCO₂ > 45 mmHg = Hypoventilation.
• PaCO₂ < 35 mmHg = Hyperventilation.

Blood Pressure (BP) Analysis

• Cardiovascular status: reflects tissue perfusion.
• Systolic arterial pressure (SAP): 90-120 mmHg (contraction).
• Diastolic arterial pressure (DAP): 55-90 mmHg (relaxation).
• Mean arterial pressure (MAP): 60-100 mmHg. MAP > 60 mmHg is crucial for adequate organ perfusion.

BP Methods

• Direct method: Measures blood pressure directly from an artery using an arterial catheter—considered the gold standard.
• The Dorsal pedal, Femoral, Coccygeal, or Auricular arteries are options for catheter placement.
• Blood pressure from the arterial catheter and tubing is measured by a specialized transducer connected to an ECG monitor.
• Indirect method: Measures blood pressure indirectly without direct artery access by using a physical cuff on the animal limb; less accurate than direct measurement. Includes Doppler and oscillometric methods; an example is a blood pressure cuff.

Hypotension

• MAP < 60 mmHg: Indicates low blood pressure.
• Potential causes: drugs (e.g., isoflurane), vasodilation, hypovolemia, lowered cardiac output, and more.
• Veterinary nurses: Monitor, provide information needed, and take suitable steps like reducing volatile agents, IVFT, or using positive inotropes.

Hypertension

• MAP > 100 mmHg: Elevated blood pressure.
• Causes include;
  • light surgical anesthesia
  • Pain
  • Medication (e.g., ketamine) or
  • underlying diseases.
• Actions to take:
  • Inform veterinary surgeon to change the anesthetic plane
  • Check the patient to reduce or resolve pain
  • Adjust meds as needed or correct the cause or underlying diseases.

Electrocardiography (ECG)

• ECG measures electrical activity in the heart.

ECG Pre-Lecture Tasks

• Review information about the heart's structure and function using the relevant pre-lecture materials.
• Analyze ECG traces by using the required instruction sheet..

ECG Basics

• Questions about electrocardiogram (ECG), including definitions, indications, and interpreting ECG traces. Questions cover the P wave, QRS complex, and T wave, indicating their respective functions.
• The role of the veterinary nurse in the process is explained as well.

ECG Interpretation Guides

• A step-by-step guide to help in interpreting electrocardiogram (ECG) readings.
• The various heart rates (regular/irregular, bradycardia, tachycardia etc) is defined.
• The roles of the P-wave, QRS complex, and T-wave are defined and explained as well.
• Samples of tracings are provided to understand the interpretations.

Heart Block (ECG)

• Includes definitions—first, second, and third-degree heart block.

Capnography

• Instructions to review capnography notes for tutorial completion.

Capnography Revision Questions

• Questions about the definition of related terms (capnometer, capnograph, capnogram)
• What carbon dioxide level defines normocapnia, hypercapnia, and hypocapnia?
• In practice, Veterinary nurses can compare and contrast side-stream and main stream carbon dioxide measurement techniques, including their use in veterinary anesthesia.
• Examine and interpret capnography waveforms and analyze potential causes for unusual waveforms, including conditions when a waveform is absent. Instructions to discuss placement and justification for proper capnograph placement.

Summary

• Nursing roles regarding monitoring during veterinary anesthesia—crucial procedures that include monitoring.
• Availability of diverse monitoring tools to veterinary nurses.
• Importance of interpreting information provided by monitoring machines.
• Monitoring equipment limitations; must supplement physical examination.

Tutorial

• The tutorial is a two‐hour session that involves critical revision of the topic.
• It covers review questions and case studies on advanced monitoring methods.

This quiz focuses on advanced anesthetic monitoring specifically for veterinary applications. Students will learn about crucial techniques such as blood gas analysis, electrocardiography, and the role of veterinary nurses in managing patients. It's part of a broader course covering anesthesia, critical care, and surgical procedures.