Comprehensive Study Guide for Veterinary Anesthesia (VETT 2209)

Core Terminology in Veterinary Anesthesia

• Anesthesia: Defined as an absolute absence of sensation. This absence can affect the entire body or be localized to a specific, isolated region of the body.
• General Anesthesia (GA): A state of unconsciousness and insensibility to painful stimuli.     - It provides a controlled environment necessary for surgery or other painful procedures.     - It ensures the patient does not move during the procedure.     - It is often referred to as a state of "controlled death."
• Induction: The specific process or phase that transitions a patient from a state of consciousness into a state of general anesthesia.
• Maintenance of Anesthesia: The ongoing process of keeping a patient under general anesthesia until the surgical or diagnostic procedure is complete and the recovery phase begins.
• Local Anesthesia: A loss of sensation in a specific, localized region of the body without a loss of consciousness.
• Premedication: The administration of one or more pharmacological agents prior to the induction of general anesthesia. This process provides numerous clinical benefits for the patient and the surgical team.
• Sedation: A pharmacological state characterized by calmness or drowsiness.
• Neuroleptanalgesia: A state of profound sedation and analgesia. This is achieved by the combined administration of an opioid and a tranquilizer. It is commonly utilized for minor medical or diagnostic procedures.

Statistical Volatility and Risk Management

• Anesthesia-Related Mortality Statistics: A $2008$ study published in the Journal of Veterinary Anesthesia and Analgesia investigated the risks associated with anesthesia and sedation-related deaths. The findings established the following risk ratios:     - Healthy Dogs: $1$ in $1849$     - Sick Dogs: $1$ in $75$     - Healthy Cats: $1$ in $895$     - Sick Cats: $1$ in $71$
• Risk Reduction Factors: The primary factors identified for reducing anesthesia-related deaths include:     - Diligent patient monitoring.     - Following a standardized checklist to prevent human error and equipment oversight.
• Expert Perspective: The American Veterinary Medical Association (AVMA) emphasizes the philosophy that "there are no safe anesthetic agents; there are only safe anesthetists."

Pre-Anesthetic Patient Preparation and Evaluation

• Primary Objective: To identify any factors that may compromise the health of the patient and to notify the veterinarian before anesthesia begins.
• The Evaluation Process: Before any anesthetic episode, a thorough preparation must occur, which includes:     - Obtaining a comprehensive patient history from the owner.     - Performing a thorough physical examination.     - Conducting diagnostic testing centered on critical systems: the nervous system, the cardiovascular system, and the pulmonary system.
• Goal of Evaluation: To uncover hidden abnormalities that might impair the patient’s physiological ability to compensate while under anesthesia, which could lead to intraoperative or postoperative complications.
• Clinical Findings to Report to the Veterinarian:     - Hydration Status: Dehydration.     - Body Condition: Obesity or cachexia (severe weight loss/wasting).     - Neurological State: Changes in consciousness or other signs of neurological disease such as seizures, ataxia, or abnormal pupillary responses.     - Perfusion: Pale mucous membranes ($\text{mm}$) or a prolonged capillary refill time ($\text{CRT}$).     - Mucous Membrane Color: Any abnormalities such as icteric (yellow), pale, or injected (brick red) colors.     - Cardiac Function: Abnormal heart rate ($\text{HR}$), abnormal rhythm, or the presence of a heart murmur.     - Pulse Quality: Weak or irregular pulses.     - Respiratory Function: Increased respiratory rate or effort; abnormal lung sounds such as crackles or wheezes.     - Thermoregulation: Marked hypothermia or hyperthermia.

Clinical Considerations: Elective vs. Emergency Procedures

• Elective Procedures:     - Requirements include pre-anesthetic blood work.     - Addressing any underlying health concerns identified during screening.     - Selecting a specific anesthetic protocol tailored to the individual patient’s needs.
• Emergency Surgery:     - Requires a clinical judgment call: weighing the risks of anesthesia against the time required for stabilization.     - Examples of emergency cases include Gastric Dilatation-Volvulus ($\text{GDV}$) or a bleeding splenic tumor.

Fasting Protocols and Pathophysiological Rationale

• Pathophysiology Under Anesthesia:     - The swallow reflex is significantly weakened.     - The lower esophageal sphincter tone decreases.     - Many premedications and anesthetic agents induce nausea.
• Complications of Improper Fasting: The combination of the above factors can lead to the reflux of stomach contents into the esophagus and pharynx. This creates a risk for:     - Aspiration pneumonia.     - Esophagitis.     - Esophageal stricture.
• Fasting Recommendations by Species:     - Dogs and Cats: Food withheld for $8-12 \, \text{hours}$; Water withheld for $2-4 \, \text{hours}$.     - Horses: Food withheld for $8-12 \, \text{hours}$; Water withheld for $0-2 \, \text{hours}$.     - Cattle: Food withheld for $24-48 \, \text{hours}$; Water withheld for $8-12 \, \text{hours}$.     - Small Ruminants: Food withheld for $12-18 \, \text{hours}$; Water withheld for $8-12 \, \text{hours}$.     - Neonates/Pediatrics: No withholding of food or water.
• Pediatric Note: Young animals are not fasted because they are at a high risk for hypoglycemia. Their glucose levels must be monitored throughout the procedure.
• Administrative Duties: When admitting a patient, the veterinary technician must confirm with the owner if the patient was fasted. It is helpful for receptionists to call owners the night before to remind them of fasting requirements.

Pre-Anesthetic Patient Stabilization

• Requirement: Any abnormalities identified during the initial evaluation must be treated or corrected before the induction of anesthesia.
• Conditions to Correct: Dehydration, anemia, cardiac arrhythmias, respiratory compromise, major organ failure, and acid-base disturbances.
• Stabilization Methods: Administration of antibiotics, analgesics, intravenous ($\text{IV}$) fluids, blood transfusions, or oxygen therapy as prescribed by the veterinarian.
• Role of the Registered Veterinary Technician (RVT):     - Calculating precise drug dosages.     - Placing intravenous ($\text{IV}$) catheters.     - Setting up intravenous ($\text{IV}$) fluids at appropriate flow rates.     - Administering drugs, blood products, or oxygen as required.

American Society of Anesthesiologists (ASA) Physical Status Classification

• Purpose: A system developed by the American Society of Anesthesiologists to provide a subjective rating of a patient's condition based on historical, physical, and laboratory findings.
• The Scale: Five distinct classes to guide the anesthetist in appropriate management. Any emergency procedure is appended with the letter "E" (e.g., $ASA \, IIE$).
• ASA Risk Classification Breakdown:     - Class I (Minimal Risk): A normal, healthy animal with no underlying disease.     - Class II (Slight Risk): Minor disease is present; animal has slight to mild systemic disturbances but is able to compensate. Examples: Neonate, geriatric, or obese patients.     - Class III (Moderate Risk): Obvious systemic disease or disturbances are present with mild clinical signs. Examples: Anaemia, moderate dehydration, fever, low-grade heart murmur, or cardiac disease.     - Class IV (High Risk): The animal is significantly compromised by pre-existing systemic disease of a severe nature. Examples: Severe dehydration, shock, uraemia, toxaemia, high fever, uncompensated heart disease, uncompensated diabetes, pulmonary disease, or emaciation.

Species-Specific Considerations: Bovine Anesthesia

• Recumbency Risks: Prolonged recumbency in cattle creates a risk for myopathies and neuropathies. Proper positioning and protective padding are vital.
• Ruminal Bloat: In recumbency, the esophageal opening becomes submerged in ruminal contents. This prevents naturally occurring eructation, leading to gas accumulation (bloat). The severity depends on the rate of fermentation and the duration of gas accumulation.
• Respiratory Compromise: The sheer weight of the abdominal viscera and its massive contents prevents the diaphragm from moving freely during inspiration. This results in shallow ventilation and reduced gas exchange.
• Aspiration: Regurgitation and subsequent aspiration are serious complications in cattle.
• Food Safety: As cattle are food animals for human consumption, the anesthetist must always consider drug withdrawal times and chemical residues.