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SHOCK (Slides) - Vega 2025
M Laura Vega
Created on January 14, 2024
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Small Animal Emergency Medicine 2025 Laura Vega DVM, MS, DACVECC
Shock
Lesson objectives
Differentiate the underlying pathophysiological mechanisms of the major types of shock
Identify the clinical signs that allow for a rapid diagnosis of shock in small animals
Develop an appropriate initial treatment plan for shock in small animal patients
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Severe imbalance between oxygen supply and demand, leading to inadequate cellular energy production
Shock is...
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Oxygen delivery
Oxygen consumption
Severe imbalance between oxygen supply and demand, leading to inadequate cellular energy production
Shock is...
https://copd.net/clinical/home-oxygen-benefits
SaO2: oxygen saturationPaO2: arterial partial pressure of oxygen
Sympathetic vs parasympathetic nervous systems
Contractility
Afterload
Preload
Heart rate x Stroke volume
(1.34 x Hemoglobin x SaO2) + (0.003 x PaO2)
Oxygen delivery
Cardiac output
Arterial content of O2
- Na+/K+ - ATPase dysfunction
- Cellular necrosis and apoptosis
- Acidemia
- Endothelial dysfunction
- Activation of inflammatory and coagulation cascades
- Multiorgan dysfunction syndrome
- Death
https://www.brainkart.com/article/Conditions-Precipitating-Shock_31724/
Consequences of shock
https://www.oeveo.com/media/blog/358-no-more-shocks-puppy-proofing-your-cables-with-oeveo.html
Functional classification of shock
Cardiogenic
Obstructive
Distributive
Hypovolemic
Metabolic
Hypoxic
Circulatory
Types of shock
Decreased cardiac output
Decreased preload
- Hemorrhage
- Internal or external
- Severe dehydration
- Gastrointestinal
- Renal
- Third space fluid loss
- Severe burns
Decreased intravascular volume
Hypovolemic
"relative hypovolemia"
Decreased systemic vascular resistance +/- Preload +/- Contractility
- Anaphylactic shock: histamine-induced vasodilation
- Septic shock: cytokine-mediated endothelial dysfunction
- Neurogenic shock
- Pheochromocytoma or extreme fear
Maldistribution of fluid from changes in vascular tone and increased vascular permeability
Distributive
Decreased diastolic filling and preload
Decreased cardiac output
- Gastric-dilatation-volvulus
- Obstruction of vena cava
- Tension pneumothorax
- Cardiac tamponade from pericardial effusion
- Positive pressure ventilation
Compression of heart or great vessel that interferes with venous return
Obstructive
"Primary" decrease in cardiac output
- Systolic failure (e.g. dilated cardiomyopathy)
- Diastolic failure (e.g. hyperthrophic cardiomyopathy)
- Atrioventricular valve degeneration or defects
- Brady- or tachy-arrhythmias
Decrease in forward flow from the heart due to "pump failure"
Cardiogenic
Decreased tissue oxygen delivery
Decreased arterial oxygen content
Deranged cellular metabolism leading to inappropriate O2 tissue use
- Severe hypoglycemia
- Mitochondrial dysfunction
- Severe pulmonary disease
- Anemia
- Dyshemoglobinemias
Metabolic
Hypoxic
Compensatory mechanisms
⇧Renal water reabsorption
- Antidiuretic hormone
Peripheral vasoconstriction Renal Na+ reabsorption
Angiotensin II
⇧Respiratory rate and tidal volume
- RAAS activation
- Chemoreceptors
⇧Heart rate⇧Cardiac contractility Peripheral vasoconstriction
- Baroreceptor reflex
Compensatory mechanisms
- Clinical diagnosis
- One abnormality can be enough
- Compensatory vs decompensated shock
- Blood pressure?
Heart rate* Pulse quality Mucous membrane color Capillary refill time Peripheral temperature Mentation
PERFUSION PARAMETERS
Clinical manifestations
Characterized by initial vasodilation instead of vasoconstriction"hyperdynamic phase"
TachycardiaCRT < 1 secondRed to injected MMElevated temperatureBounding pulses
Anaphylactic & septic shock
https://todaysveterinarypractice.com/emergency-medicine-critical-care/systemic-inflammatory-response-syndrome-sepsis-part-1-recognition-diagnosis/
Unpredictable heart rate changesRarely manifest signs of vasodilatory shock Lungs = "shock organ"
Mucous membranes?Capillary refill time?Bradycardia*Hypothermia*
Cats ≠ Small dogs
Drastically different treatmentLook for clues to try attempt to diagnose
Signalment Heart murmurRespiratory distressCoughing (dogs)Jugular venous distension AscitesPleural or pericardial effusionPulmonary crackles Arrhythmias Syncope
Cardiogenic shock
- Head to tail examination - what is the cause?
- Point-of-care tests: PCV/TS, blood glucose, lactate, blood pressure, ECG, POCUS, acid-base and electrolyte panel
- Once more stable CBC/Chem/UA, chest x-rays, abdominal x-rays or ultasound, echocardiogram, fluid analysis, bacterial cultures, etc.
Further diagnostics
1. Flow-by oxygen2. Obtain IV access 3. IV fluid bolus resuscitation
Where to start ?
Restore O2 delivery to tissues as soon as possible
Goal =
Treatment
NOT if cardiogenic
1. Flow-by oxygen2. Obtain IV access 3. IV fluid bolus resuscitation
Where to start ?
Restore O2 delivery to tissues as soon as possible
Goal =
Treatment
Consider benefits vs risks in each patient
Immediate reassessment following bolus is key!
Hypertonic salineSynthetic vs natural colloids Whole blood vs component therapy
Additional options
Isotonic crystalloids 5-20ml/kg IV over 10-20 minutes Repeat as needed up to 90ml/kg in dogs or 66ml/kg in cats
Mainstay therapy
- Vasopressors (epinephrine)
- Anti-histamines
Anaphylactic
- Vasopressors (norepinephrine)
- Broad-spectrum antibiotics
Septic
Obstructive
Tap it!
Distributive
- Gastric trocarization
- Thoracocentesis
- Pericardiocentesis
- Congestive heart failure? Diuretics (furosemide), O2 therapy, +/- thoracocentesis
- Systolic dysfunction? Positive inotropes (dobutamine, pimobendan)
- Treat life-threatening arrhythmias? Lidocaine vs atropine, vs others
Correct underlying diseaseDepends on etiology O2 therapyNO IV fluids*Minimize stress
Cardiogenic
Clinical reassessment every 5 to 10 minutes or after every therapeutic intervention during stabilizationOnce normal perfusion parameters ⇒ successful resuscitation, can de-escalate monitoring and therapy
Resuscitation endpoints
Reassessment: static mentation, pulse quality, MM and CRT. Updated TPR: T 97.4, P 160, R 50.
Initial treatments: oxgen cage 40%, IV catheter placement, 0.2mg/kg butorphanol, 10ml/kg Lactated Ringer's IV over 40 minutes.
Clinical exam findings: quiet (previously reported to be spicy), T 97.8, P 150, R 48, MM pale pink tacky, CRT unable to determine, delayed skin tent, sunken eyes, weak pulses, III/VI parasternal systolic heart murmur (history of heart murmur on record), and some increased respiratory effort.
Spot the mistake!
Pearl, a 16 year old FS DSH, presented to the ER for anorexia, lethargy, and rapid breathing.