SHOCK (Slides) - Vega 2025

Shock

Small Animal Emergency Medicine 2025 Laura Vega DVM, MS, DACVECC

Lesson objectives

Identify the clinical signs that allow for a rapid diagnosis of shock in small animals

Differentiate the underlying pathophysiological mechanisms of the major types of shock

Develop an appropriate initial treatment plan for shock in small animal patients

Shock is...

Severe imbalance between oxygen supply and demand, leading to inadequate cellular energy production

https://www.ebay.com/itm/354121059614

Shock is...

Oxygen delivery

Severe imbalance between oxygen supply and demand, leading to inadequate cellular energy production

Oxygen consumption

https://www.ebay.com/itm/354121059614

Oxygen delivery

https://copd.net/clinical/home-oxygen-benefits

Arterial content of O2

Cardiac output

Heart rate x Stroke volume

(1.34 x Hemoglobin x SaO2) + (0.003 x PaO2)

SaO2: oxygen saturationPaO2: arterial partial pressure of oxygen

Sympathetic vs parasympathetic nervous systems

Afterload

Preload

Contractility

Consequences of shock

• 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/

Functional classification of shock

https://www.oeveo.com/media/blog/358-no-more-shocks-puppy-proofing-your-cables-with-oeveo.html

Hypovolemic

Circulatory

Distributive

Types of shock

Hypoxic

Obstructive

Cardiogenic

Metabolic

Hypovolemic

Decreased intravascular volume

• Hemorrhage
• Internal or external

• Severe dehydration
• Gastrointestinal
• Renal
• Third space fluid loss
• Severe burns

Decreased preload

Decreased cardiac output

Distributive

Maldistribution of fluid from changes in vascular tone and increased vascular permeability

• Anaphylactic shock: histamine-induced vasodilation
• Septic shock: cytokine-mediated endothelial dysfunction
• Neurogenic shock
• Pheochromocytoma or extreme fear

"relative hypovolemia"

Decreased systemic vascular resistance +/- Preload +/- Contractility

Obstructive

• 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

Decreased diastolic filling and preload

Decreased cardiac output

Cardiogenic

• 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"

"Primary" decrease in cardiac output

Hypoxic

• Severe pulmonary disease
• Anemia
• Dyshemoglobinemias

Decreased arterial oxygen content

Decreased tissue oxygen delivery

Metabolic

• Severe hypoglycemia

• Mitochondrial dysfunction

Deranged cellular metabolism leading to inappropriate O2 tissue use

Compensatory mechanisms

Compensatory mechanisms

⇧Heart rate⇧Cardiac contractility Peripheral vasoconstriction

• Baroreceptor reflex

• Chemoreceptors

⇧Respiratory rate and tidal volume

Peripheral vasoconstriction Renal Na+ reabsorption

• RAAS activation

Angiotensin II

• Antidiuretic hormone

⇧Renal water reabsorption

Clinical manifestations

• Clinical diagnosis
• One abnormality can be enough
• Compensatory vs decompensated shock
• Blood pressure?

PERFUSION PARAMETERS

Heart rate* Pulse quality Mucous membrane color Capillary refill time Peripheral temperature Mentation

TachycardiaCRT < 1 secondRed to injected MMElevated temperatureBounding pulses

Anaphylactic & septic shock

Characterized by initial vasodilation instead of vasoconstriction"hyperdynamic phase"

https://todaysveterinarypractice.com/emergency-medicine-critical-care/systemic-inflammatory-response-syndrome-sepsis-part-1-recognition-diagnosis/

Mucous membranes?Capillary refill time?Bradycardia*Hypothermia*

Cats ≠ Small dogs

Unpredictable heart rate changesRarely manifest signs of vasodilatory shock Lungs = "shock organ"

Signalment Heart murmurRespiratory distressCoughing (dogs)Jugular venous distension AscitesPleural or pericardial effusionPulmonary crackles Arrhythmias Syncope

Cardiogenic shock

Drastically different treatmentLook for clues to try attempt to diagnose

Further diagnostics

• 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.

Treatment

Restore O2 delivery to tissues as soon as possible

Goal =

Where to start ?

1. Flow-by oxygen2. Obtain IV access 3. IV fluid bolus resuscitation

Treatment

Restore O2 delivery to tissues as soon as possible

Goal =

Where to start ?

1. Flow-by oxygen2. Obtain IV access 3. IV fluid bolus resuscitation

NOT if cardiogenic

Mainstay therapy

Additional options

Hypertonic salineSynthetic vs natural colloids Whole blood vs component therapy

Isotonic crystalloids 5-20ml/kg IV over 10-20 minutes Repeat as needed up to 90ml/kg in dogs or 66ml/kg in cats

Consider benefits vs risks in each patient

Immediate reassessment following bolus is key!

Distributive

Septic

Obstructive

• Vasopressors (norepinephrine)

• Broad-spectrum antibiotics

• Gastric trocarization
• Thoracocentesis
• Pericardiocentesis

Anaphylactic

• Vasopressors (epinephrine)

• Anti-histamines

Tap it!

Cardiogenic

• 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

Resuscitation endpoints

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

Spot the mistake!

Pearl, a 16 year old FS DSH, presented to the ER for anorexia, lethargy, and rapid breathing.

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.

Initial treatments: oxgen cage 40%, IV catheter placement, 0.2mg/kg butorphanol, 10ml/kg Lactated Ringer's IV over 40 minutes.

Reassessment: static mentation, pulse quality, MM and CRT. Updated TPR: T 97.4, P 160, R 50.