Anesthesia Monitoring Conduction - Lecture 4

• To keep the patient safe, it's important to monitor patients under anesthesia.
• Anesthetic monitoring includes indicators of circulation and electrocardiography per chapter 6.
• Monitoring a patient under anesthesia involves understanding why and how it's done.
• Understanding of the concepts and devices for monitoring circulation, cardiac impulses, and electrocardiography (ECG) is important.

Vital Signs Groupings

• Monitoring circulation involves assessing heart rate and rhythm, pulse strength, capillary refill time (CRT), mucous membrane color, blood pressure, and cardiac sounds/impulses/conduction.
• Oxygenation assessment includes mucous membrane color, CRT, hemoglobin saturation, inspired oxygen, and arterial blood oxygen.
• Ventilation monitoring includes respiratory rate and depth, breath sounds, end-expired carbon dioxide levels, arterial carbon dioxide, and blood pH.

Instruments to Monitor Circulation and Heart Rate/Rhythm

• Esophageal stethoscope amplifies heart sounds.
• Electrocardiography graphically represents the electrical activity of the heart and is used to detect arrhythmias.
• CRT/MM assesses circulation.
• Peripheral pulse and pulse quality indicates circulation.
• Echocardiography is used to monitor circulation.

Cardiac Auscultation

• Listen on the left, right, & sternal (& trachea) to distinguish sounds & breathing.
• Palpate the pulse while obtaining heart rate from cardiac auscultation.
• Listen for at least a minute for abnormal sounds like whooshes/murmurs, clicks, or abnormal patterns.
• Heart rates can be more difficult to hear in anesthetized patients, so patience is important.
• Locate the apical pulse to find the loudest sounds, typically at the 5th and 6th ribs, where you feel the heartbeat through the chest.
• Reduced cardiac contraction strength, often due to drugs, can affect auscultation.
• Cardiac auscultation is performed using ABCD locations.
• Auscultation along the ventral aspects, including the sternum and trachea, can be helpful.
• The best location to obtain a heart rate is on the left side at the 5th or 6th rib, or at the point of the elbow.

Common Cardiovascular Circulation Problems

• Cardiac Arrhythmias
• Cardiac Murmurs
• Hypotension: low blood pressure
• Hemorrhage: excessive bleeding
• Hypoxemia: low blood oxygen
• Respiratory Arrest: cessation of breathing
• Cardiac Arrest: cessation of heart function

Indicators of Circulation: Heart Rhythm

• Heart rhythm, along with heart rate, should be assessed.
• Cardiac arrhythmias occur commonly in anesthetized animals and vary in significance.

Causes of Arrhythmias

• Hypoxemia: low blood oxygen
• Hypercapnea: high blood carbon dioxide
• Hypotension: low blood pressure
• Hypo/Hyperthermia: abnormal body temperature
• Electrolyte abnormalities (potassium and magnesium)
• Oculo-cardiac reflex
• Disease states or conditions
• Drugs
• Inadequate anesthesia/analgesia

Part 3: Impulses/Conduction Cascade

• Electrical impulses flow from the base-to-apex of the heart's anatomy.
• Resting heart cell state is negatively charged on the inside, called "polarized" and impermeable to positive ions.
• Electrical impulses are generated by specialized cardiac cells automatically.

Depolarization, Repolarization & Refractory Period

• When a heart cell is stimulated by electricity, that cell becomes permeable and allows positive ions in.
• Sodium rushes into the cell (depolarization), causing the cell to have positive cells inside, leading to contraction.
• After contraction, the cell returns to its negative state (repolarization).
• Repolarization occurs when the cell is more permeable to potassium ions which leave the cell, causing it to be negatively charged again, leading to muscle relaxation.
• A cell cannot "fire" (depolarize/contract) until it is in its resting state, a period called the refractory period.
• A shortened refractory period can lead to continuous "firing" (fibrillation).
• The depolarization and repolarization process creates the electrical activity of the heart, which can be represented as the PQRST waveform on an ECG.

Electrocardiography (ECG or EKG)

• ECG records electrical activity about the heart rhythm in real time.
• Electrodes are attached to the limbs, thorax, and/or other areas to detect electrical impulses produced by a beating heart.
• Cardiac electrical impulses (action potentials) originating from the SA node are recorded as voltage against time.
• An ECG produces the P QRS T waveform.
• One heartbeat = one ventricular contraction.
• The ECG trace (graph) provides heart rate calculated from complexes. Irregular rate or rhythm can affect accuracy.
• ECGs can read up to 12 leads.
• Each of the 12 leads provides different views of the heart as a 2D structure from 12 different angles, even though the heart itself is a 3D structure.

Einthoven's Triangle

• A 3-limb lead setup with 3 electrodes placed on the animal.
• Enables a useful ECG tracing.
• This triangle is an imaginary formation of three limb leads used in electrocardiography.
• A single "lead" is generated from the communication of two electrodes.
• Lead I compares the right "arm" to the left "arm". The right forelimb (-ve) to the left forelimb (+ve)
• Lead II compares the right "arm" to the left "leg". The right forelimb (-ve) to the left hindlimb (+ve). "Lead II" to set the machine to.
• Lead III compares the left "arm" to the left "leg". The left forelimb (-ve) to the left hindlimb (+ve).
• Type A conduction means current flows from base to apex, so the electrode must be placed from various angles for capturing the electrical sign.
• Lead II is used in small animals to provide the tallest R wave because of the electrode's distance apart.
• Small animals, like dogs, cats, avians, and other exotics, all have type A conduction.

Electrode Placement

• Smoke (black) goes over fire (red)
• WHITE ON RIGHT - rhymes with "right upper quadrant - forelimb/'arm.'"
• LL for LEFT LEG - alliteration leads to "Red on left hindleg."
• This is like reading a book or newspaper with hands (upper) and feet at the bottom.
• For a 4 electrode set up, the patient is in right lateral recumbency. The ground is on the bottom and/or top. Also, white is black upper quadrant on top, and red balls are on top of the green tree.
• If using a 5 lead setup, a brown electrode goes on the apex of the heart

Electrodes

• While 3-electrode setups (black, white, & red) are common in the lab, 4 electrode setups have a green electrode, in addition to black, white, & red.
• Atraumatic (crocodile) flat clips (upper right) are preferable when anesthetized to alligator clips
• Red dots with snap clips are best for patient comfort; it may be a good idea to shave the hair. Either electrode requires gel or alcohol to work.

ECG Tech Tips

• In addition to snaps/patches (red dots) and clips, needles placed SQ can be utilized for very small patients with the clips attached to them
• Complete an ECG under normal & varying conditions
• Aim for a steady & artifact free baseline.
• Know the machine and ECG settings (speed, sensitivity, size, lead #...).
• Ensure all connections are tight on each electrode and cord.
• Ensure wires are not twisted, bent, or touching other electrical equipment.
• Ground your equipment to reduce interference.
• Coil cords loosely, keep dry, and clean.
• Understanding what a normal P QRS T complex looks like is important for troubleshooting.

ECG Setting Reminders

• Use sizing ("gain") to completely fit the ECG parameters on the screen.
• Set ECG to Lead II.
• Okay to change leads to look at other "views" to troubleshoot
• The anesthetist must know what a normal P QRS T complex looks like, how to troubleshoot lead placement or troubleshoot machine settings, and alert RVT/DVM if needed.
• ECGs can be complex, and requires you to have a good foundation
• For anesthesia monitoring patient body position does not matter; electrode placement & leads matter.
• Electrodes must contact skin and use electrode (ECG gel) paste, saline, or alcohol, although anesthesia gel is ideal
• Shave hair should red dots be placed on a pad for proper skin contact.

Textbook Reminders

• Review how to place electrodes, how it print an ECG strip from an ECG)
• Note how to determine heart rate from ECG strip.
• Review how to interpret ECGs.

Normal Sinus Rhythm

• P wave indicates Atrial muscle depolarization or atria's contractions.
• QRS indicates Ventricular muscle depolarization or ventricles contracting.
• T Wave indicates Ventricular muscle repolarization or ventricles relaxing. It can be assumed that Artial repolarization does occur.

ECG Components

• P-R interval refers tot he electrical impulse passing through the atrioventricular (AV) node.
• Q wave refers to an electrical impulse that passes from impulses pass through the AV ode via the left bundle branch.
• R wave refers to The His-Purkinje fiber fully activated.
• S wave refers to the basilar parts of of ventricular depolarization.
• S-T segment refers to complex returns to baseline.
• T waved refers to the depolarization of the the last contractions.

Speed and Amplitude

• Speed is the horizontal axis (x) and adjustable durations to 50mm/s or 25mm/s.
• Amplitude is the vertical axis (y) and adjustable sensitivity/voltage mV.
• Set machine to Lead II in small animals to yield the maximum electrical sign.

ECG Questions

• What is the heart rate and normal limits?
• Are there P waves? Is there a P wave for every QRS wave? Is there a QRS wave for every P wave?
• What is the QRS Morphology? Is it wide and or bazar? Is the R wave tall and narrow?
• Are the P-R intervals' in duration and the same? Is it continuous or discontinuous?
• Are the R-R intervals' same? Is it Regular or irregular?
• The goal is to explore the relationships and arrangements of the waveform

ECG: Sinus Arrhythmia

• Sinus Arrythmia includes heart rate coordinated with respiration
• HR slows down during expiration with increased inspiration
• Sinus Arrythmia is normal in in dogs, horses, and cattle and abnormal in cats
• Be patient during the breathing pattern

Differentiate Sinus Arrythmia

• Sinus Arrythmia that can have can increase with inpiration.
• SA would have a rhythmic increase in rate during breath in.
• It is impossible to determine that pattern without an machine

Sinus Bradycardia

• Abnormally low heart rate
• Common with drugs that contain reversal agents or anticholinergics
• Common during anesthesia: excessive anesthetic depth and drug reactions

Sinus Tachycardia

• Sinus Tachycardia's are abnormally fast.
• Check for Inadequate Anesthetic depths, drug reactions or from surgical stimulation.

Key Points

• Proper electrodes must be be placed with a clean wire.
• Machines should generally be placed with a Lead II setting
• Gels should be replaced over time.
• Monitoring equipment generates HR, RR, and tidal volume helping the anesthetist accurately to assesses patient status.
• Effective monitoring indicates memorization with levels when veterinarians should be noted.

These questions cover essential parameters and techniques for monitoring a patient's ventilation and cardiac function. Topics include auscultation, heart rhythm assessment, and interpreting physiological data during anesthesia. It also covers troubleshooting discrepancies in oxygen saturation and the effects of anesthetic drugs on cardiac function.