NAVLE Emergency and Critical Care Guide: Shock, Fluids and CPR

Emergency and critical care questions on the NAVLE test whether you can recognize a dying patient and do the right first thing: which shock, which fluid, which drug, which rhythm, which antidote. The numbers matter more here than in most areas, because CPR rates, potassium limits and antidote timing are exact. This guide sets out the high-yield emergencies across small and large animals, with the figures verified against the Merck Veterinary Manual and the "gotcha" that separates the correct answer from the reasonable-sounding one. Where a figure could not be verified, it has been left out rather than guessed.

Why Emergency Medicine Is Worth Studying Separately

Emergencies cut across the species blocks: a blocked cat, a dog with GDV, a surgical colic, a bloated cow and a foal with failure of passive transfer all test the same skill of triage, stabilize, then treat the cause. Learn the shared framework once and you answer emergency questions in every block. For the exam format, see the complete NAVLE guide.

Shock: Recognition and Treatment

The Four Categories

Stages and Species Differences

• Early decompensatory (dogs): Pale membranes, prolonged CRT, weak pulses, tachycardia, dull mentation.
• Cats: Merck describes the feline shock picture as gray mucous membranes, slow CRT, weak pulses, hypothermia and a normal or low heart rate. A hypothermic, bradycardic cat is in shock; rewarm it while resuscitating because cold cats respond poorly to fluids.
• Targets: Merck's perfusion end points include a CRT of 1 to 2 seconds, systolic blood pressure above 90 mm Hg, mean arterial pressure of 60 to 80 mm Hg for small-volume resuscitation or 80 to 90 mm Hg as the supranormal target for large-volume resuscitation, and SpO2 above 90%. Normal heart rates are roughly 60 to 120 in dogs and 150 to 220 in cats. Rising lactate means poor perfusion; falling lactate with treatment is the reassuring trend.

Fluid Therapy

• Fluid types: Balanced isotonic crystalloids are the default; most of a bolus leaves the vessels within an hour. Saline suits hyperkalemia, hypercalcemia and hypochloremic alkalosis. Hypertonic saline gives brief small-volume expansion (large dogs, horses, head trauma). Hydroxyethyl starch is used cautiously: Merck advises against it in patients with pre-existing azotemia, and coagulation effects appear at high daily doses; plasma is the colloid when factors or albumin are needed. Dextrose 5% is free water, never a resuscitation fluid.
• Shock doses: The whole-blood volume that fluid boluses are built from is about 80 to 90 mL/kg in dogs and 40 to 60 mL/kg in cats. Merck describes a large-volume approach in dogs of 20 to 50 mL/kg of balanced crystalloid given rapidly in aliquots with reassessment, and a small-volume approach of 10 to 15 mL/kg in dogs and 5 to 10 mL/kg in cats, with colloid boluses of about 5 mL/kg in dogs and 2 to 5 mL/kg in cats. The tested principle is to give crystalloids in aliquots and reassess, and to be far more conservative in cats and in cardiogenic shock.
• Dehydration deficit: Percent dehydration times body weight in kilograms gives the deficit in liters (Merck's example: a 12 kg dog that is 8% dehydrated has lost 0.96 L), replaced over 4 to 12 hours together with maintenance and ongoing losses.
• Maintenance: Merck's formula for dogs and cats of 2 to 70 kg is 30 times body weight in kilograms plus 70 mL per 24 hours, with allometric formulas for animals outside that range.
• Potassium: Never exceed 0.5 mEq/kg/hour IV. Merck's sliding scale for KCl added to a liter of maintenance fluid: serum potassium below 2.0 mEq/L add 80 mEq; 2.1 to 2.5 add 60; 2.6 to 3.0 add 40; 3.1 to 3.5 add 25 to 30; 3.6 to 5.0 add 20; above 5.0 add none. DKA and post-obstruction patients need close potassium monitoring.

Fluid rules that answer most questions: crystalloid boluses in quarter aliquots and reassess; cats get less; potassium never faster than 0.5 mEq/kg per hour; deficit equals percent dehydration times kilograms, in liters; nothing by bolus into a failing heart.

Cardiopulmonary Resuscitation (RECOVER)

• Compressions: 100 to 120 per minute regardless of size, depth one third to one half of chest width in lateral recumbency, full recoil, in uninterrupted 2-minute cycles with a change of compressor at each cycle. Round-chested dogs over the widest part of the thorax; keel-chested dogs and cats over the heart.
• Ventilation: Intubate in lateral recumbency without stopping compressions; 10 breaths per minute (one every 6 seconds), tidal volume about 10 mL/kg, one-second inspiration. Avoid hyperventilation.
• Rhythm check: Brief pauses (under 10 seconds) only between 2-minute cycles, with ECG and end-tidal CO2 (a rising ETCO2 is the best indicator of effective compressions and return of spontaneous circulation).
• Drugs for non-shockable rhythms (asystole, pulseless electrical activity): Low-dose epinephrine 0.01 mg/kg IV every 3 to 5 minutes (every other cycle); high-dose epinephrine is no longer recommended. Vasopressin 0.8 U/kg IV is an alternative. Atropine 0.04 to 0.05 mg/kg IV (Merck's table gives 0.05) as a single early dose, especially for vagally mediated arrests.
• Shockable rhythms (ventricular fibrillation, pulseless ventricular tachycardia): Defibrillate as soon as it is recognized; Merck lists 4 to 6 J/kg for external monophasic and 2 to 4 J/kg for external biphasic defibrillators, then resume compressions immediately for a full 2-minute cycle before reassessing. Do not give epinephrine as the first response to VF.
• Reversal agents: Naloxone 0.04 mg/kg for opioids, flumazenil 0.01 mg/kg for benzodiazepines, atipamezole 0.1 mg/kg for alpha-2 agonists (all IV, from Merck's CPR table).

Gastric Dilatation-Volvulus

• Signalment: Large, deep-chested breeds (Great Dane, German Shepherd, Setters, Weimaraner, Standard Poodle); older dogs; single large meals and a relative with GDV raise risk.
• Signs: Non-productive retching, hypersalivation, restlessness, tympanic distended cranial abdomen, tachycardia, weak pulses and collapse from obstructive and hypovolemic shock; splenic congestion accompanies the twist.
• Diagnosis: Right lateral radiograph: the pylorus displaced dorsally and cranially with a soft-tissue shelf compartmentalizing the stomach (the double bubble or reverse C sign). Avoid ventrodorsal positioning in a dyspneic dog.
• Stabilize: Two large-bore cephalic catheters (caudal venous return is obstructed), crystalloids at shock rates in aliquots, oxygen, then decompress by orogastric tube or trocar. Watch for ventricular arrhythmias. Merck notes preoperative lactate above 6 mmol/L is associated with gastric necrosis.
• Surgery: Derotate, resect necrotic wall, splenectomy if thrombosed, and always perform a gastropexy; without it recurrence is extremely high. Merck cites mortality of roughly 20 to 45% in treated dogs.

Urethral Obstruction and Hyperkalemia

• Signs: Straining without producing urine, vocalizing, a large firm painful bladder, then vomiting, bradycardia, hypothermia and collapse as hyperkalemia and postrenal azotemia develop.
• Emergency order: ECG and potassium first, IV fluids, treat life-threatening hyperkalemia, then relieve the obstruction under sedation, place an indwelling catheter, and match the post-obstructive diuresis; the patient swings from hyperkalemia to hypokalemia within a day.
• Hyperkalemia treatment (Merck figures): 10% calcium gluconate 0.5 to 1.5 mL/kg slowly IV over 15 to 30 minutes with ECG monitoring protects the heart within minutes but does not lower potassium. Regular insulin 0.25 to 0.5 U/kg IV with 50% dextrose 0.5 to 1 mL/kg diluted (then dextrose in the fluids for 2 to 6 hours to prevent hypoglycemia) drives potassium into cells; dextrose alone also works more slowly. Bicarbonate for acidosis; decompressive cystocentesis if the catheter cannot pass promptly.
• Gotcha: ECG changes progress from tall tented T waves through flattened P waves and prolonged PR to wide QRS, atrial standstill and sinus arrest. Bradycardia in a sick cat is a potassium question until proven otherwise. The same algorithm answers Addisonian crisis, uroabdomen and anuric renal failure questions.

Diabetic Ketoacidosis

• Diagnosis: Hyperglycemia, glucosuria, ketones (beta-hydroxybutyrate is missed by nitroprusside dipsticks), metabolic acidosis, and usually a concurrent disease (pancreatitis, infection, Cushing's, diestrus).
• Treatment order: Fluids first for hours before insulin, replace potassium and phosphorus (both fall sharply once insulin starts; severe hypophosphatemia causes hemolysis), then regular insulin. Merck describes a constant-rate infusion made by adding regular insulin (2.2 U/kg for dogs or 1.1 U/kg for cats) to 250 mL of 0.9% saline, adjusted hourly to blood glucose, adding dextrose to the fluids as glucose falls; or an intermittent IM regular insulin protocol. Blood glucose should not fall faster than 50 to 100 mg/dL per hour to avoid cerebral edema. Bicarbonate is reserved for severe acidosis that does not respond to fluids.
• Gotcha: Regular (short-acting) insulin by IV constant-rate infusion or IM injection is the standard DKA protocol; Merck notes that glargine SC then IM protocols are supported in cats and that IM lispro has been used. Long-acting insulins are started once the patient is rehydrated and eating. A DKA patient with a normal potassium on admission is actually potassium-depleted and will crash when insulin starts.