NR 507 Week 4 Hemorrhagic Shock Compensation Case Example

A Normal Blood Pressure That Was Not Reassuring: A 23-Year-Old With a Splenic Laceration, Read as One Short Insult and a Long Defense, From Baroreceptor Reflex to the Ceiling of Compensation

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College of Nursing, Chamberlain University

NR 507: Advanced Pathophysiology

Instructor Name

Month Day, Year

A Normal Blood Pressure That Was Not Reassuring: A 23-Year-Old With a Splenic Laceration, Read as One Short Insult and a Long Defense, From Baroreceptor Reflex to the Ceiling of Compensation

The Case

Mr. R., 23, a healthy bicycle mechanic, went over his handlebars on a mountain bike trail and struck his left upper abdomen. He rode home, felt lightheaded and came to the emergency department 90 minutes after the fall. He was anxious and pale, with cool hands, a capillary refill of 3 seconds and pain in his left upper abdomen radiating to the tip of his left shoulder. Heart rate was 118, blood pressure 118/82 mm Hg, respiratory rate 24 and oxygen saturation 98% on room air. Initial laboratory values showed hemoglobin 13.6 g/dL, lactate 3.1 mmol/L, glucose 168 mg/dL and white cell count 15,200/µL. After a bladder catheter was placed, his urine output over the first hour was 20 mL. Computed tomography showed a splenic laceration with hemoperitoneum. Four hours later, after 1 liter of crystalloid, his hemoglobin was 10.9 g/dL.

Almost every abnormal number in this chart is the body defending itself. This paper treats the injury briefly and spends its length on the defense, because the defense is what fills the chart and what, at the moment he arrived, was hiding how much blood he had lost.

The Insult, Kept Short

The spleen is a highly vascular organ, and a laceration bleeds into the peritoneal cavity, where the blood is concealed. Blood irritating the underside of the diaphragm is referred along the phrenic nerve to the shoulder, which explains the pain at the tip of his left shoulder. The primary fault is simple: loss of circulating blood volume. Everything else follows from the body's attempts to keep blood flowing to the brain and heart despite that loss (Gutierrez et al., 2004).

Fast Responses, Second by Second

The baroreceptor reflex. As blood volume falls, venous return and stroke volume fall, and stretch receptors in the walls of the carotid arteries and the aortic arch sense less distension and fire less often. Within seconds, the brainstem reduces vagal tone and increases sympathetic output. The heart rate rises, which is his rate of 118, to maintain cardiac output as stroke volume falls.

Arteriolar and venous constriction. Sympathetic activity constricts arterioles in the skin, gut and kidneys, raising systemic vascular resistance, and constricts veins, moving blood from those reservoirs back toward the heart. Constriction in the skin explains his pallor, cool hands and slow capillary refill. The raised resistance holds up the diastolic pressure, 82 mm Hg, while the smaller stroke volume lowers the systolic rise, so the pulse pressure narrows to 36 mm Hg. A narrow pulse pressure with a normal systolic value is a sign of compensation, not of safety.

Adrenal medulla. Circulating epinephrine adds to the heart rate and constriction, raises glucose by stimulating glycogen breakdown, which is his glucose of 168 mg/dL, and releases white cells marginated along vessel walls into the circulating pool, which is part of his count of 15,200. His anxiety has the same source.

Breathing. His respiratory rate of 24 reflects sympathetic drive and early metabolic acidosis, as tissues with reduced flow shift toward anaerobic metabolism.

Slow Responses, Over Hours and Days

Transcapillary refill. When arterioles constrict and capillary hydrostatic pressure falls, the balance of forces across capillary walls shifts, and fluid moves from the interstitial space into the blood. Over hours, this restores part of the plasma volume. Because the fluid carries no red cells, it dilutes the remaining blood, which is why his hemoglobin was 13.6 g/dL on arrival, before refill and resuscitation had diluted it, and 10.9 g/dL four hours later. The first hemoglobin described the concentration of what was left, not how much had been lost.

Hormonal retention of salt and water. Reduced renal perfusion activates the renin-angiotensin-aldosterone system. Angiotensin II constricts vessels and, with aldosterone, drives sodium and water retention. Antidiuretic hormone, released in response to the fall in volume, concentrates the urine. Together, these produce his low urine output of 20 mL in the first hour.

Red cell replacement. Lower oxygen delivery to the kidney increases erythropoietin production, but new red cells take days to appear. If he recovers without transfusion, a rise in reticulocytes would be expected within several days.

What the Defense Costs

Compensation redistributes blood; it does not create any. The flow preserved for the brain and heart is taken from the skin, gut and kidneys, and those tissues pay for it. His lactate of 3.1 mmol/L shows tissue where oxygen delivery has fallen below need, and his low urine output shows kidneys receiving less blood, a risk for acute kidney injury if the state continues. The gut, sensitive to prolonged constriction, is at risk of ischemic injury that can later allow bacteria and toxins to cross its lining. Each defense buys time and charges interest.

The Ceiling

The most dangerous feature of this case is that his defenses were working well. A young, healthy person can maintain a normal systolic pressure until a large share of the blood volume is lost, commonly estimated at around 30%, because heart rate and resistance have so much room to rise. Once that reserve is used, blood pressure falls quickly rather than gradually, because there is no further compensation to call on (Gutierrez et al., 2004). A clinician who waited for hypotension would be waiting for the ceiling.

Trauma teaching makes the same point with a classification. The Advanced Trauma Life Support course grades hemorrhage by the estimated share of blood volume lost and places a fall in blood pressure in the class of loss above about 30%, while the classes below it are marked by rising heart rate, narrowing pulse pressure and changes in mental state and urine output with blood pressure preserved (American College of Surgeons Committee on Trauma, 2018). Mr. R.'s findings, a heart rate over 100, a narrow pulse pressure, anxiety and a urine output well below normal with a normal systolic pressure, sit in the upper part of the compensated range. The classification is a teaching approximation, and individual patients do not follow it exactly, but it gives a name to the danger: the next increment of loss is the one that shows up as hypotension.

Mr. R. was near that point. His heart rate, narrow pulse pressure, lactate and urine output together suggested a moderate loss held in check by compensation. The case is a reminder that in hemorrhage, a normal blood pressure in a young person is information about the strength of the defense, not about the size of the bleed.

References

American College of Surgeons Committee on Trauma. (2018). Advanced trauma life support: Student course manual (10th ed.). American College of Surgeons.

Gutierrez, G., Reines, H. D., & Wulf-Gutierrez, M. E. (2004). Clinical review: Hemorrhagic shock. Critical Care, 8(5), 373-381. https://doi.org/10.1186/cc2851