The Trauma Dog with a Normal Blood Pressure
A 4-year-old female spayed Labrador retriever is hit by a car and brought in 30 minutes later. She is obtunded but responsive to pain, with a heart rate of 160/min, respiratory rate of 44/min, and weak, thready femoral pulses. Mucous membranes are pale pink with a CRT of 2 seconds. Systolic blood pressure by Doppler is 110 mmHg. You note a distended abdomen with a fluid wave, and FAST reveals free fluid in all four quadrants. PCV is 38%, total solids 5.0 g/dL, lactate 6.8 mmol/L. She has a fracture of the right femur and a suspected pelvic fracture. The blood pressure reading was taken while she was struggling.
1. Explain why a Doppler systolic of 110 mmHg does not exclude shock in this patient, and identify the findings that indicate decompensated shock.
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Doppler systolic pressure measures only the peak pressure and is poorly sensitive for compensated or early decompensated shock, especially in a struggling, tachycardic patient where sympathetic tone and movement artifact can inflate the reading. A single normal systolic value does not reflect perfusion. The findings that indicate decompensated shock here are: obtundation, tachycardia (160/min), thready pulses, prolonged CRT, lactate 6.8 mmol/L (marker of hypoperfusion and anaerobic metabolism), and free abdominal fluid with falling total solids (5.0 g/dL) suggesting hemorrhage. The combination of tachycardia, altered mentation, hyperlactatemia, and a fluid wave is consistent with hemorrhagic shock - likely from a splenic or hepatic injury or pelvic fracture bleeding. I would not rely on the blood pressure alone; I would reassess after calming the patient, use trends in lactate and mentation, and consider that the true perfusion pressure may be lower than the struggling reading suggests.
2. Describe your resuscitation strategy, including fluid type and volume, endpoints, and when you would consider blood products.
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Initial resuscitation: Two large-bore IV catheters; begin a balanced isotonic crystalloid bolus of 10–20 mL/kg over 15–20 minutes, reassessing after each bolus. In hemorrhagic shock, avoid over-resuscitation - target permissive hypotension (systolic ~90 mmHg or MAP ~60 mmHg) until hemorrhage is controlled, because aggressive crystalloid dilutes clotting factors and raises hydrostatic pressure, worsening bleeding. Endpoints: improved mentation, stronger pulses, CRT <2 seconds, lactate clearance, and urine output >0.5–1 mL/kg/hr.
Blood products: With free abdominal fluid and falling TS, transfusion is likely needed. If the PCV falls below ~25% or the patient remains unstable despite two crystalloid boluses, give packed red blood cells (10–20 mL/kg) or whole blood (20 mL/kg) if available. Fresh frozen plasma (10–15 mL/kg) if coagulopathy is suspected. Crossmatch if time permits; type-specific or universal donor otherwise.
Other: Analgesia (opioid), prevent hypothermia with active warming, and do not delay surgery - if hemorrhage is ongoing (e.g., splenic rupture), the definitive treatment is hemostasis, not more fluids. Recheck lactate and PCV/TS serially. Avoid hydroxyethyl starch.
3. The patient's PCV drops from 38% to 22% over 45 minutes while receiving crystalloids. What does this mean, and what is your next step?
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A falling PCV despite crystalloid resuscitation in a trauma patient with free abdominal fluid indicates ongoing hemorrhage - the crystalloid dilutes the remaining red cell mass while active bleeding continues to extravasate blood into the abdomen. The drop from 38% to 22% is clinically significant and signals that the patient is not achieving hemostasis. My next step is to transfuse (packed RBCs 10–20 mL/kg or whole blood 20 mL/kg) and expedite definitive hemorrhage control - surgical exploration or, if available, interventional hemostasis. I would stop large-volume crystalloid boluses, maintain permissive hypotension, and reassess the abdomen with repeat FAST. I would also check coagulation (PT/aPTT, fibrinogen) and platelet count, since dilutional and consumption coagulopathy can develop. If the patient arrests or becomes unstable, consider emergency thoracotomy or laparotomy per institutional capability. The key teaching point: a falling PCV during resuscitation is a surgical problem, not a fluid problem.