Surgery Lab 4: Anesthetic Emergencies and Cardiopulmonary Resuscitation

CPR vs. CPCR and Species Differences

• Definitions and Core Terminology:

  • Cardiopulmonary Resuscitation (CPR): A foundational emergency procedure utilized across human and veterinary medicine designed to address and treat cardiopulmonary arrest (CPA).

  • Cardiopulmonary Cerebral Resuscitation (CPCR): An expanded clinical designation emphasizing that resuscitation must accomplish more than restoring cardiac activity; the fundamental preservation and restoration of cerebral perfusion and brain function are paramount.

• Comparative Resuscitation: Humans vs. Animals:

  • Resuscitation protocols, procedural physical interventions, and pharmacologic algorithms employed in veterinary species are frequently extrapolated directly from human emergency medicine standards.

  • Fundamental physiological, pathological, and prognostic variations distinguish animal resuscitation from human protocols across four key domains:

  • Etiology of CPA: The primary pathological events triggering cardiopulmonary arrest differ markedly between human patients and veterinary species.

  • Response to Physical Resuscitation: Animals display differing physical biomechanics and physiological responses to external chest compressions and manual ventilatory techniques.

  • Response to Resuscitative Pharmacology: Emergency cardiovascular and neurovascular drugs yield divergent metabolic and hemodynamic outcomes in veterinary species.

  • Prognosis for Functional Survival: Veterinary clinical populations exhibit divergent survival statistics and reduced rates of return to normal baseline neurologic and systemic function compared to humans.

• Unique Veterinary Arrest Complications:

  • Resuscitated veterinary patients experience a high incidence of secondary rearrest following initial return of spontaneous circulation (ROSC).

  • Severe post-arrest complications frequently prompt humane euthanasia decisions in veterinary clinical practice.

  • Veterinary patients exhibit minimal responsiveness to electrical defibrillation compared to human arrest patients due to differing underlying etiologies of CPA.

Resuscitation Prognosis and Ethical Considerations

• Comparative Survival Metrics:

  • Human Patients:

  • Initial successful resuscitation rate: up to $40\text{--}60\%$

  • Final survival to hospital discharge: approximately $17\%$

  • Canine Patients:

  • Initial successful resuscitation rate: $13\%$

  • Final survival to hospital discharge: $4.1\%$

  • Feline Patients:

  • Initial successful resuscitation rate: $15.6\%$

  • Final survival to hospital discharge: $9.6\%$

• Ethical Resuscitation Deliberations:

  • Clinical appropriateness must be evaluated before or during resuscitation based on individual patient circumstances.

  • Resuscitative interventions prompt significant ethical scrutiny regarding whether to perform CPR on terminally ill patients.

  • Resuscitative viability must consider whether interventions will result in intractable, ongoing quality-of-life deficits.

Tiers of Resuscitative Intervention: BLS vs. ALS

• Basic Life Support (BLS):

  • Constitutes the foundational baseline of resuscitation, encompassing:

  • Airway management

  • Breathing and ventilatory support

  • Circulatory support via chest compressions

  • Basic emergency drug delivery

  • Standard capability across virtually all veterinary clinical practices and hospital settings.

• Advanced Life Support (ALS):

  • Encompasses all components of Basic Life Support combined with advanced critical interventions:

  • Advanced cardiovascular pharmacology

  • Continuous electrocardiographic (ECG) monitoring

  • Electrical defibrillation when indicated by underlying rhythm analysis

  • Internal cardiac massage (internal chest compressions), performed selectively under specific anatomical indications

  • Typically established in dedicated critical care facilities and emergency centers, though many general practices retain the capacity to deliver substantial ALS components.

• The CABD Algorithmic Sequence:

  • Clinical assessment and intervention follow a prioritized progression:

  • C — Circulation: Assessed and addressed first.

  • A — Airway: Cleared and secured.

  • B — Breathing: Ventilatory support initiated.

  • D — Drugs: Pharmacological support administered.

Circulation (C): Assessment, Positioning, and Compression Mechanics

• Primary Circulatory Assessment:

  • Rapid assessment of circulatory function precedes all other interventions via:

  • Auscultation of cardiac fields

  • Palpation of central and peripheral pulses

  • Inspection of mucous membrane (MM) color

  • Assessment of capillary refill time (CRT)

  • Critical Safety Rule: Never initiate or deliver chest compressions when the heart is actively beating.

• Patient Positioning for Compressions:

  • Primary Recumbency: Right lateral recumbency.

  • Alternative Recumbency: Dorsal recumbency.

  • Anatomical Target: Intercostal spaces 5 through 6 ($5^{\text{th}}\text{--}6^{\text{th}}$ intercostal space).

• Hand Placement Mechanics by Patient Size:

  • Small Patients (Felines and Small Canines):

  • Direct the fingers underneath the ventral chest wall.

  • Position the thumb along the dorsal aspect of the chest.

  • Deliver chest compressions by directly squeezing the thorax between the thumb and opposing fingers.

  • Medium-Sized Patients:

  • Place one hand flat underneath the chest for stabilization.

  • Position the heel of the opposing hand directly over the cardiac field on the upper thoracic wall to deliver downward compressions.

  • Large Patients:

  • Place a firm bolster (such as a book or sandbag) beneath the dependent thorax to prevent dissipation of force.

  • Interlock the fingers of both hands directly over the widest portion of the chest.

  • Maintain locked, rigid arms at the elbows.

  • Pivot and rock from the hips, utilizing upper body mass rather than arm musculature to execute compressions.

• Compression Rate, Depth, and Physiological Goals:

  • Compression Frequency: Baseline delivery is $100\,\text{compressions/minute}$ (equivalent to approximately $2\,\text{compressions/second}$).

  • Smaller patients require faster compression rates.

  • Larger patients require comparatively slower compression rates.

  • Displacement Depth: Depress the thoracic cage by approximately $\frac{1}{3}$ of its total width.

  • Physiological Objectives of Compressions:

  • Induce rapid shifts in intrathoracic pressure.

  • Maximize systemic venous return to the right atrium.

  • Optimize forward stroke volume and cardiac output.

• Operational Priorities and Simultaneous Techniques:

  • Chest compressions represent the single most vital component of CPCR.

  • Passive air movement into and out of the pulmonary parenchyma occurs naturally alongside chest displacement.

  • Solo Rescuer Management: Concentrate exclusively on uninterrupted chest compressions; do not stop compressions to provide breaths.

  • Multi-Rescuer Management: Deliver simultaneous ventilations concurrently with ongoing chest compressions.

  • Interposed Abdominal Compressions: Compressing the abdomen alternately with thoracic compressions augments venous return returning from the caudal circulation.

Assessing Compression Efficacy and Resuscitation Monitoring

• Physical Palpation Monitoring:

  • Lingual Pulse: Direct palpation of the lingual artery to verify perfusion to cranial structures.

  • Digital Pulse: Palpation of distal extremities to evaluate terminal peripheral microvascular flow.

  • Femoral Pulse: Rapidly palpated at the onset of CPR to confirm whether chest compressions are generating forward hemodynamic flow.

  • Expected Physical Finding: Rescuers must palpate a distinct peripheral pulse synchronized with each external compression cycle.

• Instrument-Based Hemodynamic Monitoring:

  • Doppler Flowmetry:

  • Position the crystal probe directly over the cornea/eyeball or beneath the tongue over the lingual artery.

  • Effective compressions produce an audible, rhythmic systolic flow signal.

  • Pulse Oximetry ($\text{SpO}_2$):

  • Clip the sensor probe to the lingual mucosa.

  • Hemodynamically effective compressions correlate with measurable upward trajectories in oxygen saturation ($\text{SpO}_2$).

  • Capnography ($\text{PaCO}_2$ / End-Tidal $\text{CO}_2$):

  • Real-time pulmonary blood flow and functional cardiac output correlate with gas exchange.

  • Successful compressions generate progressive increases in partial pressure of carbon dioxide ($\text{PaCO}_2$).

Timing Cycles, Corrective Actions, and Internal Cardiac Compressions

• Compression Timing Cycles:

  • Maintain uninterrupted compressions for uninterrupted cycles of approximately $3\,\text{minutes}$.

  • Pause briefly at the completion of each $3\text{-minute}$ cycle to check for persistent spontaneous cardiac pulses.

  • If a spontaneous pulse is absent, immediately resume external compressions.

  • Immediate Cessation Criteria: Terminate compressions instantly if the patient exhibits:

  • Purposeful consciousness or voluntary movement

  • Independent, spontaneous breathing efforts

  • Palpable pulse or auscultated heartbeat independent of external compressions

• Troubleshooting Ineffective Compressions:

  • When compressions fail to yield palpable pulses, Doppler signals, or rising capnography values, systematically alter:

  • Patient recumbency and thoracic angle

  • Exact positioning of hands over the thoracic wall

  • Force and physical depth of compressions

  • Rescuer fatigue (rotate the person delivering compressions)

  • Consideration of internal compressions

• Internal Cardiac Compressions (Open-Chest CPR):

  • Generally avoided in routine resuscitation due to a severe decline in long-term functional recovery for patients who already carry a grave prognosis.

  • Specific anatomical and clinical indications where open-chest compressions may be considered:

  • Patients exceeding $20\,\text{kg}$ in body mass

  • Severe pneumothorax

  • Pleural effusion

  • Pericardial effusion or cardiac tamponade

  • Penetrating thoracic trauma

  • Severe thoracic wall trauma or flail chest

  • Hemoperitoneum

  • Diaphragmatic hernia

Airway (A): Assessment, Clearing, and Securing Techniques

• Airway Evaluation and Decontamination:

  • The initial priority requires inspecting the oral cavity and pharynx to ensure complete patency.

  • Clear all foreign objects, mucosal fluids, and vomitus using mechanical scoop-and-drain techniques.

• Comparative Modalities of Airway Access:

  • Mouth-to-Snout Ventilation:

  • Most accessible baseline technique for acute trauma in field settings (e.g., structure fires, vehicular trauma/Hit-by-Car [HBC]).

  • Primary drawbacks involve personal safety, hygiene, and operator reluctance when managing unfamiliar animals.

  • Face Mask Delivery:

  • Readily applicable non-invasive bridge, but fails to isolate or deliver gas volume directly into the lower respiratory tract.

  • Endotracheal (ET) Intubation:

  • The gold standard for securing the airway in veterinary resuscitation.

  • Requires a cuffed endotracheal tube.

  • Critical technical check: Confirm placement within the tracheal lumen, which can prove technically challenging in entirely apneic patients.

  • Emergency Tracheostomy:

  • Indicated when oral mass lesions, physical obstructions, or foreign bodies preclude oral intubation.

  • Surgical procedure performed by the veterinarian (DVM) requiring extensive post-procedural nursing and airway management.

  • Transtracheal Catheterization:

  • Less invasive surgical alternative to formal tracheostomy.

  • Facilitates the administration of high fractions of oxygen, though volumetric flow remains limited by narrow catheter luminal diameters.

Breathing (B): Oxygenation, Ventilation Parameters, and Acupuncture Stimulation

• Ventilatory Support Parameters:

  • Resuscitative gas source: Provide $100\%\,\text{O}_2$.

  • Target rate: Administer $1\,\text{breath every } 6\,\text{seconds}$, establishing a baseline frequency of approximately $10\,\text{breaths/minute}$.

  • Delivered tidal volume ($\text{V}_T$): Maintain delivery within $10\text{--}15\,\text{mL/kg}$.

  • Peak Inspiratory Pressure Limits: Prevent pulmonary barotrauma and overinflation:

  • Canine Limit: Do not exceed $20\,\text{cmH}_2\text{O}$

  • Feline Limit: Do not exceed $15\,\text{cmH}_2\text{O}$

• Equipment Setup and Safety Checks:

  • Ambu Bags: Self-filling resuscitation bags deliver ambient air unless plumbed directly to an oxygen tank or anesthetic circuit to provide $100\%\,\text{O}_2$.

  • Anesthetic Machine Setup:

  • When using an anesthetic circuit for manual ventilation, the rebreathing bag empties and refills progressively; an Ambu bag attached to oxygen can resolve filling delays.

  • Vaporizer: Confirm the anesthetic vaporizer is completely turned OFF to avoid delivering inhalant to an unstable patient.

  • Carbon Dioxide Absorbent: Ensure the soda lime canister is chemically active and not exhausted.

• Acupuncture Respiratory Stimulation (GV 26):

  • Equipment: $25\text{-gauge}$ hypodermic needle.

  • Anatomical Site: Nasal philtrum midline, positioned midway between the ventral margin of the nares and the margin of the upper lip.

  • Application: Advance the needle directly until making firm contact with underlying premaxillary bone; rotate and twist the needle continuously.

  • Intended Outcomes: Triggers sympathetic reflex pathways stimulating intrinsic pulmonary respiration and chronotropic/inotropic cardiac drive.

• Discontinuation Criteria for Ventilatory Support:

  • Do not terminate ventilation simply because a spontaneous heartbeat or pulse returns.

  • Continue manual ventilations until mucosal color remains fully pink and regular spontaneous breathing resumes.

  • Gradually step down to intermittent manual bagging throughout post-arrest recovery.

Drugs (D): Administration Routes and Anatomical Prioritization

• Institutional Preparedness:

  • Dosing protocols in emergency medicine evolve continually; reference current veterinary emergency formularies.

  • Post pre-calculated emergency dosage charts in critical procedural zones throughout the hospital.

• Administration Routes in Descending Order of Priority:

  • 1. Intravenous (IV) — Central Vein (Preferred Route):

  • Provides rapid delivery directly into core central circulation.

  • Cannulation of the external jugular vein utilizing large-bore vascular catheters.

  • 2. Intratracheal (IT):

  • Utilized when vascular access is not established.

  • Dosing Adjustment: Double ($2\times$) standard IV dosages to account for incomplete pulmonary absorption.

  • Dilution: Dilute the calculated drug volume with $3\text{--}5\,\text{mL}$ of sterile saline.

  • Administration: Deliver the solution deep into the lower bronchial tree through the ET tube using a red rubber feeding tube or urinary catheter.

  • 3. Intravenous (IV) — Peripheral Vein:

  • Common access point during anesthesia, though transit times to the central circulation are delayed compared to central routes.

  • Placing an additional peripheral catheter assists with rapid fluid resuscitation.

  • 4. Intraosseous (IO):

  • Rapid non-collapsible vascular access indicated for neonates, pediatric patients, avian patients, and exotic species.

  • Anatomical entry sites: Trochanteric fossa of the femur, proximal greater tubercle of the humerus, tibial crest.

  • 5. Intralingual:

  • Sublingual injection into the lingual vascular bed provides rapid uptake near cerebral venous drainage.

  • 6. Intracardiac (Contraindicated):

  • Not recommended due to severe clinical risks: pulmonary parenchymal laceration, direct myocardial laceration, coronary vessel disruption, and refractory tension pneumothorax.

Emergency Pharmacology: Core Resuscitative Agents and Vasopressors

• Vasopressin:

  • Physiology: Endogenous non-adrenergic peptide (antidiuretic hormone) produced in the hypothalamus and stored/secreted by the posterior pituitary; regulates systemic free water reabsorption.

  • Resuscitative Profile:

  • Induces peripheral arterial vasoconstriction independent of adrenergic receptors, making it effective during severe metabolic acidemia.

  • Preserves cerebral tissue oxygenation, restores coronary perfusion pressure, improves initial ROSC rates, and supports post-arrest neurologic recovery.

  • Human clinical trials demonstrate survival rates equivalent to epinephrine.

  • Clinical Indications: Asystole, pulseless electrical activity (PEA), ventricular tachycardia.

  • Dosage Regimen:

  • Bolus dose: $0.4\text{--}0.8\,\text{U/kg}$

  • Constant Rate Infusion (CRI): $0.01\text{--}0.04\,\text{U/kg/min}$

• Epinephrine:

  • Physiology: Mixed $\alpha$- and $\beta$-adrenergic receptor agonist stimulating sympathetic cardiovascular pathways.

  • Hemodynamic Effects: $\alpha_1$-mediated peripheral vasoconstriction routes cardiac output to core coronary and cerebral beds within seconds of administration.

  • Administration Interval: Administer repeat doses every $3\text{--}5\,\text{minutes}$.

  • Dosage Protocol: Protocols feature low-dose or high-dose options; start at the low-dose tier, reserving high-dose escalations for refractory arrest.

• Dopamine:

  • Physiology: Inotropic catecholamine that increases myocardial contractile force and chronotropic speed.

  • Clinical Utility: Acts as an active cardiac stimulant indicated for hemodynamic failure when the heart maintains intrinsic electrical rhythm.

  • Administration: Requires continuous administration through a controlled, slow intravenous infusion.

Secondary Pharmacologic Agents, Buffers, and Reversals

• Atropine:

  • Anticholinergic (parasympatholytic) that blocks muscarinic receptors to resolve severe bradycardia.

  • Onset of clinical action occurs over several minutes.

  • Alternative Agent: Glycopyrrolate, which carries a lower risk of precipitating post-administration tachyarrhythmias.

• Lidocaine NEAT:

  • Formulated strictly as lidocaine hydrochloride without epinephrine additive.

  • Epinephrine must not be co-administered in this setting to avoid unnecessary myocardial stimulation.

  • Administered as an antiarrhythmic to suppress ventricular tachycardia and prevent ventricular fibrillation (VF).

  • Increases the electrical threshold required to achieve successful defibrillation.

• Doxapram:

  • Analeptic central respiratory stimulant.

  • Increases myocardial oxygen consumption ($\text{MVO}_2$), which may worsen ischemic myocardial injury.

  • Clinical availability in veterinary medicine is currently limited within Canada.

• Corticosteroids:

  • Clinical Status: No longer indicated for routine CPR; prospective controlled studies fail to show survival benefit.

  • Historical Indications: Membrane stabilization, lactic acid clearance, and attenuation of endotoxic shock.

  • Major Risk: Induces rapid peripheral vascular collapse and hypotension if administered without concurrent intravenous volume expansion.

  • Formulations Historically Encountered: Prednisolone sodium succinate, dexamethasone.

• Sodium Bicarbonate:

  • Alkalinizing agent indicated for pre-existing metabolic acidosis and hyperkalemia.

  • Clinical guidelines advise confirming metabolic acid-base status on blood gas analysis prior to administration.

  • Alternatively, avoid empiric use until arrest durations surpass $10\,\text{minutes}$, when severe intracellular and extracellular acidosis has developed.

• Calcium Gluconate:

  • Not indicated for routine cardiopulmonary arrest.

  • Reserved for arrest precipitated by severe documented hypocalcemia, life-threatening hyperkalemia, or calcium channel blocker toxicosis.

Fluid Therapy Protocols in Cardiopulmonary Arrest

• Traditional Shock Fluid Rates:

  • Historical full-shock fluid resuscitation guidelines:

  • Canines: Up to $90\,\text{mL/kg/h}$ for the initial hour maximum

  • Felines: Up to $45\,\text{mL/kg/h}$ for the initial hour maximum

  • Complications associated with traditional rates include:

  • Rapid dilution of clotting factors and red blood cell mass (hemodilution)

  • Systemic fluid overload and pulmonary edema

  • Escalation of intracranial pressure (ICP)

• Updated Shock Fluid Resuscitation Rates:

  • Resuscitation protocols utilize fractional aliquots, administering $\frac{1}{4}$ of the traditional shock rate over a $15\text{-minute}$ window, followed by formal patient re-evaluation:

  • Canines: Administer $22\,\text{mL/kg/h}$, delivered in $15\text{-minute}$ bolus increments as clinically indicated

  • Felines: Administer $11\,\text{mL/kg/h}$, delivered in $15\text{-minute}$ bolus increments as clinically indicated

• Fluid Types and Prescriptions:

  • First-Line Fluids: Balanced isotonic crystalloids.

  • Adjunctive Solutions: Synthetic colloids or hypertonic saline ($7\text{--}7.5\%\,\text{NaCl}$) depending on intravascular volume needs.

  • Dextrose Contraindication: Avoid dextrose infusions during CPR unless hypoglycemia is confirmed via glucometry.

  • Oxygen Carriers: Consider hemoglobin-based oxygen carriers (Oxyglobin) when available.

Defibrillation: Indications, Mechanics, and Energy Delivery

• Etiological Variations in Defibrillation:

  • Electrical defibrillation serves as an immediate first-line intervention in human CPR, where ventricular fibrillation (VF) represents the most common arrest rhythm.

  • In veterinary medicine, VF occurs infrequently in dogs and is rare in cats; as a result, routine defibrillation is less commonly indicated.

  • Automated External Defibrillators (AEDs) algorithmically analyze cardiac rhythms to identify shockable waveforms and deliver titrated shocks.

• Defibrillation Technique and Clinical Precautions:

  • Position the patient in dorsal recumbency or lateral recumbency.

  • Shave thoracic hair coats over electrode contact zones when time permits.

  • Apply generous quantities of conductive electrode gel to the paddle interfaces.

  • Critical Safety Warning: Never use alcohol during defibrillation due to electrical arcing and fire risk.

• Defibrillation Energy Dosing:

  • External Paddles:

  • Initial external shock energy dose: Deliver $3\text{--}5\,\text{J/kg}$

  • Refractory rhythms: Increase the energy dose by $50\%$

  • Internal Paddles:

  • Indicated during open-chest CPR with direct epicardial paddle placement

  • Internal energy dose: Deliver $0.5\text{--}1\,\text{J/kg}$