Anesthesia is one of three domains tied at 13% of the VTNE — around 26 questions. The domain covers the full anesthetic event from patient assessment to recovery: ASA status, premedication, induction, the anesthesia machine, monitoring parameters, and complication management. Anesthetic errors carry life-threatening consequences in practice, so the VTNE tests this domain rigorously.
13% of the VTNE — approximately 26 questions. Allocate roughly 13% of your total study hours here to mirror the exam's weighting.
Build a mental flowchart of the anesthetic event: pre-anesthetic assessment → premedication → induction → maintenance → monitoring loop → recovery. Know each drug category's mechanism, typical agents, and reversal agents. Then study the anesthesia machine components so you can troubleshoot a scenario question (e.g., rising end-tidal CO2 = rebreathing problem).
Pre-anesthetic Assessment & ASA Status
ASA Physical Status: I (normal healthy), II (mild systemic disease), III (moderate disease, some functional impairment), IV (severe disease, life-threatening), V (moribund, not expected to survive 24 hr without surgery). Grade before every procedure. Higher ASA = increased anesthetic risk, more intensive monitoring required.
Patient History & Exam
History: prior anesthetic reactions, current medications, last food/water (fasting: dogs 8–12 hr, cats 6–8 hr solids; water allowed until premedication). Exam: cardiovascular auscultation, thoracic percussion, mucous membrane color and CRT, hydration, neurologic status. Flag concerns: arrhythmia, murmur, dyspnea, significant dehydration.
Premedication & Anticholinergics
Goals: reduce anxiety, reduce induction drug requirements, provide pre-emptive analgesia. Common premeds: acepromazine (sedation, anti-emetic; contraindicated in seizure-prone, hypotensive, or brachycephalic patients), dexmedetomidine (sedation + analgesia, reversible with atipamezole), butorphanol, buprenorphine. Anticholinergics (atropine, glycopyrrolate): used to prevent vagal bradycardia, increase HR and secretion management.
Induction Agents (Propofol, Ketamine, Etomidate)
Propofol: smooth induction, rapid recovery, no analgesia, causes apnea at high doses — have airway equipment ready. Ketamine: dissociative, provides analgesia and maintains airway reflexes, increases HR and BP — use with care in cardiac disease. Etomidate: minimal cardiovascular effects, preferred for critical/cardiac patients. Alfaxalone: similar to propofol profile, gaining use.
Anesthesia Machine Components
Flow meter (controls O2/N2O flow rate in L/min). Vaporizer (delivers precise volatile agent concentration — isoflurane or sevoflurane). Pressure manometer (measures circuit pressure). CO2 absorbent canister (contains soda lime or Baralyme — changes color when exhausted: Soda Sorb changes purple to white). Pop-off valve: open during spontaneous ventilation; close during manual IPPV. Reservoir bag: 60 mL/kg body weight.
Vaporizers & Troubleshooting
Variable bypass vaporizers: isoflurane (1.28–2.5% MAC), sevoflurane (2.36–3.7% MAC in dogs). Never fill one agent into the wrong vaporizer. Dial settings are in % inspired concentration. If patient too light: deepen plane, increase vaporizer setting. If too deep: decrease vaporizer, consider pain as a stimulus issue. Vaporizer must be level during use.
Breathing Circuits & CO2 Absorption
Rebreathing (circle system): used in patients > 3 kg; conserves heat/moisture; requires CO2 absorber. Non-rebreathing (Bain, Mapleson D): used in patients < 3 kg or where minimal dead space needed; requires high fresh gas flows (150–200 mL/kg/min). Exhausted CO2 absorber: ETCO2 rises without clinical explanation — replace granules.
Ventilation Modes
Spontaneous ventilation: patient breathes on own. Assisted ventilation: tech squeezes bag to supplement patient breath. Controlled ventilation: IPPV — set rate and tidal volume (10–15 mL/kg), target ETCO2 35–45 mmHg. Hyperventilation lowers CO2, causing vasoconstriction and reduced perfusion — avoid.
Monitoring (ETCO2, SpO2, ECG, Temp)
SpO2 (pulse oximetry): normal ≥ 95% — < 90% = hypoxemia, action required. ETCO2 (capnography): normal 35–45 mmHg; rising = hypoventilation or rebreathing; falling = hyperventilation or reduced cardiac output. ECG: normal sinus rhythm; identify common arrhythmias (2nd degree AV block under anesthesia is common). Temperature: hypothermia common — use warming devices.
Recovery Management
Place in quiet, warm area in sternal recumbency. Monitor every 5 minutes. Extubate when swallowing reflex returns. Oxygen supplementation until fully recovered. Assess pain; administer analgesics per protocol. Document recovery time and any complications. Do not leave unattended until ambulatory.
Complications & Emergencies
Apnea: stimulate patient, assist ventilation with O2. Bradycardia: identify cause (vagal reflex, drug effect, hypothermia); atropine if < 40 bpm in dogs. Hypotension (MAP < 60): reduce anesthetic depth, IV fluid bolus, consider vasopressors. Cardiac arrest: CPR per RECOVER guidelines (BLS: 100 compressions/min, 30:2 ratio).
Local & Regional Techniques
Dental blocks (infraorbital, mandibular alveolar), line blocks (incision infiltration), ring blocks (digits), epidural (morphine ± local anesthetic for caudal procedures), intra-articular injection. Lidocaine: fast onset, 1–2 hr duration. Bupivacaine: slow onset, 4–6 hr duration — never IV in cats (fatal cardiotoxicity).
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Frequently Asked Questions
What is the ASA classification system used in veterinary anesthesia?
The ASA Physical Status scale (I–V) grades patient anesthetic risk. ASA I: healthy, no disease. ASA II: mild systemic disease, no functional impairment. ASA III: moderate disease with functional impairment. ASA IV: severe life-threatening disease. ASA V: moribund (not expected to survive). An "E" suffix denotes emergency procedures.
What does a rising ETCO2 during anesthesia indicate?
Rising end-tidal CO2 (ETCO2) during anesthesia most commonly indicates hypoventilation (patient not breathing adequately), or a failing CO2 absorber canister in the circle system causing rebreathing of exhaled CO2. Assist ventilation if due to hypoventilation; replace soda lime if absorber is the cause.
Why is bupivacaine contraindicated intravenously in cats?
Intravenous bupivacaine causes severe, potentially fatal cardiotoxicity in cats due to species-specific sensitivity. Bupivacaine blocks cardiac sodium channels with greater affinity and slower dissociation than lidocaine, leading to arrhythmias and cardiac arrest. It is used only for local infiltration or nerve blocks at correct doses.
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