Monitoring Vital Signs: Circulation, Oxygenation, Ventilation

Vital Signs Grouping

• Circulation encompasses heart rate, rhythm, pulse strength, CRT, MM, BP, cardiac sounds & impulses/conduction.
• Oxygenation includes MM, CRT, hemoglobin saturation, inspired oxygen, and arterial blood oxygen.
• Ventilation involves respiratory rate and depth, breath sounds, end-expired CO2, arterial CO2 levels, and blood pH.

Instruments to Monitor Circulation, Heart Rate & Rhythm

• Instruments include Esophageal Stethoscope and Electrocardiography (ECG).
• CRT/MM, Peripheral Pulse & Pulse Quality are also key components.
• Heart Rate measurement and Echocardiography (ultrasound of the heart) are important tools.

Cardiac Auscultation

• Listen to the left, right, sternal areas, and throat to monitor effectively.
• Pay attention to breathing patterns to distinguish sounds.
• Palpate the pulse while listening to correlate findings.
• Listen for at least one minute to identify any abnormal sounds.
• Heart rate may be harder to hear on anesthetized patients, so patience is required.
• Locate the apical pulse at the 5th/6th ribs for the loudest sounds, which can be reduced due to cardiac contraction strength.

Heart Rhythm

• Heart rhythm should be assessed along with heart rate for a comprehensive evaluation.
• Arrhythmias are common in anesthetized animals, varying in significance.
• The anesthetist must frequently assess the patient's heart rhythm during anesthetic procedures to ensure patient safety.

Causes of Arrhythmias

• Potential causes include hypoxemia and hypercapnia.
• Hypotension, hypo/hyperthermia, and electrolyte abnormalities (potassium & magnesium) are contributing factors.
• Oculo-cardiac reflex, diseases, and drugs/inadequate anesthesia/analgesia can also lead to arrhythmias.

Common Cardiovascular Circulation Issues

• Issues include cardiac arrhythmias and cardiac murmurs.
• Hypotension, Hemorrhage, Hypoxemia, Respiratory arrest, Cardiac arrest can all affect cardiovascular circulation.

A&P Review

• Impulses typically flow from the base to the apex of the heart (SA to Purkinje fibers).
• A resting heart cell is negatively charged inside ("polarized") and impermeable to positive ions.
• Electrical impulses result from the automaticity of specialized cardiac cells.
• An electrical zap causes changes in permeability for positive ion entry.

Depolarization and Repolarization

• Sodium rushes into the cell, causing it to have positive charges inside and out, leading to contraction (depolarization).
• After contraction and relaxation, cells return to their negative resting state.
• Repolarization occurs when the cell becomes permeable to potassium, which leaves the cell.
• The cell cannot depolarize/contract until it is in its resting state, during the refractory period.
• A shortened refractory period could cause the heart muscle to fire continuously, leading to fibrillation (an arrhythmia).
• Depolarization and repolarization processes generate the electrical activity, represented by PQRST waveforms on an ECG.

Electrocardiography (ECG)

• Records electrical activity related to heart rhythm in real time.
• Electrodes are attached to limbs, thorax, etc., to capture electrical impulses generated by the heart.
• Cardiac electrical impulses (action potentials) originating from the SA node are recorded as voltage against time.
• A PQRST waveform is produced, where one heart beat equals one ventricular contraction.
• Heart rate is calculated from the ECG trace based on the highest points of complexes.
• ECG's can use up to 12 leads to read the heart as a 2D structure from different angles.

ECG Views and Leads

• Each of the 12 leads provides a different perspective of the heart's electrical activity.
• Anesthesia often uses a 3-limb lead setup known as Einthoven's Triangle.
• One lead communicates between two electrodes, with Lead 1 comparing RL to LA and Lead 2 comparing RA to LL.
• Monitors commonly display Lead 2, which yields the largest complex and represents natural conduction.
• Small animals typically have "Type A" conduction, where current flows from base to apex.
• Electrodes are placed at various angles to “capture” the electrical signal.
• Lead II is often used in small animals because wider electrode spacing yields the tallest R wave.

Lead Placement and Clip Types

• Use "White on Right & Smoke over Fire" for lead placement.
• Crocodile clips (atraumatic) require gel or alcohol for contact.
• Alligator clips can cause skin trauma if left in place too long.
• Red dot stickers with snap clips are another option.
• For very small patients, needles placed subcutaneously can be used with attached clips.

ECG Settings

• Adjust the ECG module settings to ensure the graph is large but not off-screen.
• Set the module to Lead II initially.
• Changing leads is useful for troubleshooting.

Tech Tips for ECGs

• Learn to obtain the best ECG readings under normal conditions.
• Aim for a steady baseline, artifact-free tracing that can be interpreted accurately.
• Knowing your machine & ECG settings is crucial.
• Ground equipment to reduce interference.
• Ensure wires aren't twisted, bent, or touching other equipment.
• All connections must be tight on each electrode and cord.
• Coil cords loosely and keep them dry and clean.
• Understand the limitations of an ECG.

ECG Rhythm

• Know what a normal P QRS T Complex looks like and how to troubleshoot.
• Be able to appropriately place leads.
• Understand machine settings.
• You should alert RVT/DVM if needed.
• ECG interpretation can be complex, so start simple.
• Patient body position doesn't matter, but electrode placement and leads do.
• Electrodes must contact the skin using ECG gel, saline, or alcohol, and must all be placed on a paw pad

ECG Waveforms

• P Wave: This represents atrial muscles depolarizing (atrial contractions).
• QRS Complex: This represents ventricular muscles depolarizing (ventricular contractions).
• T Wave: This represents ventricular muscle repolarization (ventricles relaxing & refilling).
• Atrial repolarization occurs but is hidden in the QRS complex.

Sinus Arrhythmia and Tachycardia

• Sinus Tachycardia indicates an abnormally fast heart rate, often due to inadequate depth, drug reactions, or surgical stimulation.
• Causes include anticholinergics & cyclohexemides, inadequate anesthetic depth, pain, hypotension, blood loss & shock, low oxygen, or high carbon dioxide.

An overview of vital signs monitoring, including circulation, oxygenation, and ventilation. It highlights tools like ECG and echocardiography for assessing heart function. Proper cardiac auscultation techniques are emphasized for identifying abnormalities.