NAVLE Emergency Medicine | Shock Types, GDV, Urethral Obstruction, Addison's

Emergency questions on the NAVLE reward knowing which intervention comes first, which drugs are contraindicated, and the species-specific differences in shock presentation. GDV, urethral obstruction in cats, and Addisonian crisis are the most frequently tested conditions.

Shock Classification and Treatment

Type	Mechanism	Signs	Treatment
Hypovolemic	Blood/fluid loss	Tachycardia, pale MM, weak pulses	IV crystalloids 10–20 mL/kg bolus; pRBC if PCV <20%
Distributive (septic)	Vasodilation, maldistribution	Early: brick-red MM, bounding pulses; Late: pale MM (cats go directly to late)	Aggressive IV fluids + broad-spectrum antibiotics + vasopressors
Cardiogenic	Pump failure	Dyspnea, pulmonary edema, muffled sounds	Dobutamine/pimobendan; diuretics; NO aggressive fluids
Obstructive	Physical obstruction (tamponade, pneumothorax)	Beck's triad: muffled heart sounds, JVD, hypotension	Pericardiocentesis (tamponade); chest tube (tension pneumothorax)

Gastric Dilatation-Volvulus (GDV)

Large, deep-chested breeds (Great Dane #1, Standard Poodle, German Shepherd, Weimaraner). Gastric volvulus 270–360° → gastric ischemia + shock + death within hours. Signs: unproductive retching, tympanic abdominal distension, hypersalivation, cardiovascular shock.

Priority order (this is tested):

IV catheter + fluid resuscitation FIRST—before any decompression
ECG monitoring (ventricular arrhythmias—VT common post-GDV)
Gastric decompression (trocarization or orogastric tube)
Emergency surgery: gastric repositioning + prophylactic gastropexy

VT management: lidocaine 2 mg/kg IV bolus; CRI 50–80 μg/kg/min. Gastric necrosis (black tissue at surgery) = resection; mortality 30–50% with necrosis.

NAVLE PearlIn GDV, IV access and fluid resuscitation come BEFORE gastric decompression. A horse in cardiovascular shock will die during NG tube passage without IV access. Always stabilize cardiovascular function first. This is the most common order-of-operations trap in GDV questions.

Feline Urethral Obstruction

Male cats (anatomically narrow urethra). Causes: urethral plug, urolithiasis, urethral spasm. Life-threatening complication: hyperkalemia → bradycardia, tall peaked T waves, widened QRS → cardiac arrest.

Acute management: calcium gluconate 0.5 mL/kg IV slowly (cardioprotective—does NOT lower K+, just stabilizes cardiac membrane), then regular insulin + dextrose (lowers K+ into cells), IV fluids (0.9% NaCl dilutes K+), then unblock urethra. Post-obstruction: aggressive IV fluid support for post-obstructive diuresis (massive loss of fluids and electrolytes).

Anaphylaxis

IgE-mediated; mast cell degranulation; causes: vaccines, bee stings, penicillin, NSAIDs. Species differences in shock organ: Dogs = LIVER (hepatic venous system → bloody diarrhea, vomiting, acute collapse). Cats = RESPIRATORY (bronchospasm, laryngeal edema). Horses = respiratory + cutaneous.

Treatment: Epinephrine 0.01 mg/kg IM (vastus lateralis) is FIRST LINE. Then diphenhydramine 1–2 mg/kg IM/slow IV, dexamethasone 0.2 mg/kg IV, IV fluids. Never use epinephrine IV bolus (ventricular fibrillation risk).

Hypoadrenocorticism (Addisonian Crisis)

Classic electrolytes: hyponatremia + hyperkalemia; Na:K ratio <27 (normal >27). Bradycardia from hyperkalemia, weakness, vomiting, collapse. Diagnosis: ACTH stimulation test (pre- and post-cortisol both low, flat response). Resting cortisol <1 μg/dL—highly supportive.

Treatment: 0.9% NaCl IV (corrects both hyponatremia AND dilutes hyperkalemia), dexamethasone (does NOT interfere with cortisol assay unlike prednisone), DOCP long-term mineralocorticoid replacement, prednisone long-term glucocorticoid.

Classic NAVLE TrapIn Addisonian crisis, use DEXAMETHASONE acutely—NOT prednisolone. Prednisolone cross-reacts with cortisol assays and will interfere with ACTH stimulation test results if given before the test. Dexamethasone does NOT cross-react. Give dex first, run the ACTH stimulation test, then switch to prednisone for long-term management.

Acute Hemorrhagic Diarrhea Syndrome (AHDS / HGE)

Small breed dogs (Mini Schnauzer, Yorkshire Terrier, Mini Poodle). Clostridium perfringens Type A delta toxin. Hallmark: dramatically elevated PCV (>60%) with NORMAL total protein—hemoconcentration from plasma loss, not true polycythemia. Explosive bloody diarrhea ("raspberry jam"), vomiting. Treatment: aggressive IV fluid replacement, antiemetics; excellent prognosis.

NAVLE Emergency Medicine: Shock, GDV, Urethral Obstruction, and Critical Care