InfusionFox
Emergency · Workflow hub

Shock hub

Decision support for the four shock categories. The differential matters because the treatments contradict each other; the wrong call can kill the patient.

  • Don't bolus a cardiogenic patient. Aggressive fluids cause acute pulmonary edema. Listen to the chest, look at the pulses and jugular before fluids.
  • Don't start vasopressors before fluid resuscitation in distributive shock. Norepinephrine pushed into an empty tank causes ischemia without restoring perfusion.
  • Obstructive shock needs the obstruction relieved. No amount of fluids or pressors fixes tamponade or GDV. Drain it, decompress it, refer it.
  • Lactate trends matter more than single values. Persistent elevation despite resuscitation = inadequate response. Reassess.

First 5 minutes — universal workup

Regardless of suspected shock type:
  • IV access (or IO). Two catheters in critical patients.
  • Blood pressure: Doppler or oscillometric. Compensated shock can be normotensive.
  • Lactate, glucose, PCV/TS, electrolytes, BUN/creatinine: point-of-care if possible.
  • AFAST + TFAST: fastest way to differentiate. Free fluid, pericardial effusion, B-lines.
  • Continuous ECG: arrhythmia source vs consequence?
  • Focused history: trauma, cardiac disease, anaphylaxis trigger, GI losses, deep-chested breed.
  • Cardiopulmonary exam: pulses, jugular fill, MM/CRT, heart sounds, lung sounds.

Point-of-care ultrasound + clinical exam usually identifies the shock category within minutes.

The four shock categories

Hypovolemic

Mechanism: Loss of intravascular volume.

Hemorrhage (trauma, hemoabdomen, GI bleeding, coagulopathy), GI losses, severe dehydration, polyuric crisis.

HR
↑↑
Pulses
Weak, thready
CRT
Prolonged (>2 sec)
MM
Pale; white if hemorrhage
Extremities
Cool
AFAST
May show free fluid
PCV/TP
↓ if hemorrhage; ↑ if dehydration
Distributive

Mechanism: Loss of vasomotor tone → relative hypovolemia.

Sepsis, SIRS (pancreatitis, parvo), anaphylaxis, neurogenic, drug-induced.

HR
↑ (cats may not)
Pulses
Bounding early, weak late
CRT
Rapid early, prolonged late
MM
Injected early, grey late
Extremities
Warm early, cool late
Temp
Fever or hypothermia
Lactate
Often markedly elevated
Cardiogenic

Mechanism: Pump failure → inadequate cardiac output despite volume.

DCM, advanced MMVD, HCM (cats), tachy- or bradyarrhythmias. Cardiomyopathy may be undiagnosed.

HR
Variable
Pulses
Weak; may be irregular
Heart sounds
Murmur, gallop, arrhythmia
Jugular
Often distended
Lung sounds
Crackles (edema)
TFAST
B-lines, pleural effusion
CRT
Prolonged
Obstructive

Mechanism: Mechanical obstruction to flow.

Pericardial tamponade, GDV, tension pneumothorax, PTE, caval syndrome, severe pleural effusion.

HR
↑↑
Pulses
Weak; pulsus paradoxus possible
Heart sounds
Muffled (tamponade)
Jugular
Markedly distended
AFAST/TFAST
Pericardial effusion, GDV gas
Abdomen
Distended, tympanic if GDV

Type-specific treatment

  1. 1

    Hypovolemic shock

    Volume resuscitation is the answer. Dose-titrate; reassess after each bolus.

    Bolus (dog)15–30 mL/kg crystalloid IV over 15 min, reassess Bolus (cat)10–15 mL/kg IV over 15 min, reassess Crystalloid ceiling90 mL/kg dog · 60 mL/kg cat If hemorrhagicpRBC if PCV < 20% or active bleeding If still hypotensive past ceilingAdd norepinephrine

    Hemorrhage control runs in parallel. Permissive hypotension (target MAP 60–65) may be appropriate if active surgical bleeding can't yet be controlled; discuss with surgeon.

    Fluid therapy → Transfusion →
  2. 2

    Distributive shock

    Fluids first, then vasopressors. Source control is parallel and equally important. Anaphylaxis has its own protocol.

    Initial bolus15–30 mL/kg dog · 10–15 mL/kg cat IV ReassessBP, lactate, mentation, urine output Fluid-refractoryNorepinephrine 0.05–1 µg/kg/min Target MAP≥ 65 mmHg If septicBroad-spectrum antibiotics within 1 hr Source controlDrain abscess, remove infected tissue, debride

    Caution: over-resuscitation in distributive shock causes pulmonary edema and worsens outcomes. Once perfusion improves, switch from volume to vasopressors.

    Norepinephrine → Fluid therapy → Anaphylaxis →
  3. 3

    Cardiogenic shock

    Fluids are not the answer here. The pump is failing; volume floods the lungs. Treatment is rate/rhythm control, positive inotropy, and afterload reduction.

    OxygenFlow-by, mask, or oxygen cage Pulmonary edemaFurosemide 2 mg/kg IV, repeat q1h until improvement InotropyDobutamine 1–10 µg/kg/min (cat: caution > 5) ArrhythmiaTreat the rhythm (lidocaine for VT in dogs) Cautious fluids only ifConcurrent dehydration; 2–5 mL/kg increments ReferCardiology consult; many need echo

    If diagnosis is unclear (hypovolemic vs cardiogenic), a 5–10 mL/kg "fluid challenge" with continuous reassessment is safer than a 30 mL/kg bolus. Worsening tachypnea or crackles = stop fluids, treat as cardiogenic.

    Dobutamine → Lidocaine (VT, dogs) →
  4. 4

    Obstructive shock

    The mechanical obstruction must be relieved. Drugs are temporary holding patterns at best.

    Pericardial tamponadePericardiocentesis (right 4th–6th IC space) GDVTrocarization or orogastric tube; emergent surgery Tension pneumothoraxEmergent thoracocentesis Pleural effusionTherapeutic thoracocentesis PTEOxygen, anticoagulation, address cause Caval syndromeSurgical heartworm extraction

    Cautious volume support (5–10 mL/kg) often helps as a bridge to definitive intervention, particularly in tamponade. Do not delay the procedure to give fluids.

Lactate as a guide

Single most useful biomarker in shock. Reflects tissue hypoperfusion. Trends matter more than single values.
< 2.5 mmol/L
Normal
2.5–5
Mild hyperlactatemia
5–8
Moderate, concerning
> 8
Severe; high mortality association

Lactate clearance > 50% in 6 hr is associated with survival. Persistently elevated or rising lactate despite resuscitation = inadequate response. Reconsider the diagnosis (missed bleed, wrong shock category, GI translocation) and escalate.

Endpoints of resuscitation

Stop bolusing fluids and reassess strategy when:
  • HR normalized for species
  • MAP ≥ 65 mmHg, SBP ≥ 90, Doppler ≥ 90
  • Lactate trending down > 50% in 6 hr or normalized
  • Mentation improved
  • CRT < 2 sec, MM pink, extremities warm
  • Urine output ≥ 1 mL/kg/hr

If any of these is not improving despite reaching the volume ceiling, reconsider the diagnosis and escalate to vasopressor or other targeted therapy. Don't give a fifth and sixth bolus hoping it will work.

Sources

  • Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. Elsevier; 2023. Chapters on Hypovolemic, Distributive, Cardiogenic, and Obstructive Shock.
  • Boller EM, Otto CM. Septic shock. In Silverstein & Hopper, 3rd ed.
  • Hayes G, Mathews K, Doig G, et al. The acute patient physiologic and laboratory evaluation (APPLE) score. J Vet Intern Med 2010;24:1034–1047.
  • Conti-Patara A, de Araújo Caldeira J, de Mattos-Junior E, et al. Changes in tissue perfusion parameters in dogs with severe sepsis/septic shock in response to goal-directed hemodynamic optimization. J Vet Emerg Crit Care 2012;22:409–418.
  • Boag AK, Hughes D. Assessment and treatment of perfusion abnormalities in the emergency patient. Vet Clin North Am Small Anim Pract 2005;35:319–342.