Post-Traumatic Hypotension and Muffled Heart Sounds
A 3-year-old male neutered Boxer (25 kg) is brought to the emergency service after being hit by a car 45 minutes ago. He is recumbent but responsive, with HR 180, weak femoral pulses, pale mucous membranes, RR 40, and SpO2 94% on room air. Thoracic auscultation reveals muffled heart sounds on the left and increased respiratory effort. PCV 35%, TS 6.0 g/dL, lactate 6.0 mmol/L. FAST scan shows no free abdominal fluid. A 20 mL/kg crystalloid bolus is being considered.
1. Calculate the crystalloid bolus volume and explain the immediate priorities.
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The bolus volume is 25 kg x 20 mL/kg = 500 mL. Give it over about 15-20 minutes while monitoring HR, pulse quality, mucous membrane color, mentation, and lactate. However, the muffled heart sounds and increased respiratory effort suggest pleural space or pericardial disease, so the dog may have obstructive shock rather than simple hypovolemia. Start the bolus cautiously while preparing for thoracic ultrasound and thoracocentesis. Do not give repeated large boluses without reassessing, because over-resuscitation can worsen respiratory compromise.
2. What do the muffled heart sounds and respiratory pattern suggest, and how would you confirm?
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Muffled heart sounds plus increased respiratory effort after trauma suggest pleural effusion, hemothorax, pneumothorax, diaphragmatic hernia, or pericardial effusion. Confirm with thoracic ultrasound, which is rapid and can be done at the bedside; radiographs can help if the dog is stable enough. If pleural or pericardial fluid/air is identified and the dog is unstable, perform thoracocentesis or pericardiocentesis as indicated. These conditions can cause obstructive shock and will not be fixed by crystalloids alone.
3. After the 500-mL bolus, HR is 190, MAP is 50 mmHg, and respiratory effort is worse. What should you do next?
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Stop further crystalloid boluses and reassess for pleural space or pericardial disease. Worsening respiratory effort with persistent hypotension suggests obstructive shock or fluid overload, not simple dehydration. Perform thoracic ultrasound and thoracocentesis if indicated. Provide analgesia and oxygen, and consider a colloid at 3-5 mL/kg or blood products if hemothorax is the cause. Recheck lactate, PCV/TS, and blood pressure frequently, and avoid giving more large crystalloid boluses until the cause of shock is addressed.