Situation: A 48-year-old woman weighing 60 kg returns to the surgical ward after an open abdominal operation under general anesthesia. She has an indwelling urinary catheter and a wound drain. Her preoperative blood pressure was 126/80 mmHg and her heart rate was 80/min. Her daughter stays with her as a watcher. The nurse reviews her blood pressure (BP), heart rate (HR), respiratory rate (RR), and urine output for her first 3 hours on the ward: Hour 1: BP 122/80 mmHg, HR 88/min, RR 18/min, urine 50 mL Hour 2: BP 116/84 mmHg, HR 104/min, RR 20/min, urine 32 mL Hour 3: BP 108/84 mmHg, HR 118/min, RR 24/min, urine 16 mL She is restless and rates her incisional pain 7/10; morphine 2 mg intravenous was given 1 hour ago, and she is awake and easy to talk to. Her skin is cool, the dressing is dry, and the drain holds 30 mL of serosanguineous fluid. The catheter tubing flushes freely. Which problem should the nurse suspect?

The systolic pressure is still above 100 mmHg, but the pulse pressure is narrowing (42, then 32, then 24 mmHg), the heart rate keeps rising, urine output has fallen below 0.5 mL/kg/h (30 mL/h for her 60 kg), and her skin is cool: this is compensated hypovolemic shock. Pain explains restlessness and tachycardia but not a falling pressure with oliguria, and a dry dressing with little drain output does not exclude bleeding inside the abdomen.

Clinical picture: early compensated hypovolemic shock

This patient is showing a progressive pattern of hemodynamic deterioration that points to internal hemorrhage rather than pain, opioid effect, or catheter obstruction. The key is to look at the trend across the three hours, not any single value.

Why the vital signs tell the story

Her systolic blood pressure remains above 100 mmHg, which can falsely reassure an examiner. However, the pulse pressure is steadily narrowing: 42 mmHg at hour 1, 32 mmHg at hour 2, and 24 mmHg at hour 3. A falling pulse pressure reflects rising systemic vascular resistance as the body tries to preserve perfusion to vital organs while intravascular volume is being lost. At the same time, the heart rate climbs from 88 to 118/min, and the respiratory rate rises from 18 to 24/min. Tachycardia plus narrowing pulse pressure plus tachypnea is the classic bedside signature of compensated hypovolemic shock.

Urine output: the earliest renal signal

For a 60 kg adult, the minimum acceptable urine output is 0.5 mL/kg/h, or 30 mL/h. Her hourly output falls from 50 mL to 32 mL to 16 mL. Oliguria that worsens in parallel with tachycardia and narrowing pulse pressure indicates that renal perfusion is being sacrificed as part of the compensatory response to blood loss. This is not a catheter problem because the tubing flushes freely and urine is still draining.

Why the other options do not fit

Option	Why it is less likely
Obstructed urinary catheter	An obstruction would cause bladder distention, discomfort, and absent or minimal drainage. Here the catheter flushes freely and urine is still being produced, just in decreasing amounts. The falling output reflects reduced renal perfusion, not a mechanical blockage.
Opioid-related hypotension	Morphine can lower blood pressure through vasodilation and reduced sympathetic tone, but it would not typically cause a progressive rise in heart rate with narrowing pulse pressure and oliguria over three hours. The vital sign trend is more consistent with volume loss than with a drug effect.
Uncontrolled incisional pain	Pain explains restlessness and tachycardia, and her pain score of 7/10 is significant. However, pain does not cause a falling pulse pressure, cool skin, and progressive oliguria. Pain-driven tachycardia is usually accompanied by an elevated or normal blood pressure, not a narrowing pulse pressure.

The trap: a dry dressing and low drain output

Key point! A dry dressing and only 30 mL of serosanguineous fluid in the drain do not rule out bleeding. After open abdominal surgery, blood can collect in the peritoneal cavity or retroperitoneal space without appearing on the dressing or in the drain. Postoperative intra-abdominal hemorrhage may be concealed, and the first clues are hemodynamic rather than visible blood loss. The cool skin is a sign of peripheral vasoconstriction, another compensatory mechanism that shunts blood away from the skin to preserve core perfusion.

Applying the shock index

The shock index is calculated as heart rate divided by systolic blood pressure. In this patient, it rises from 0.72 (88/122) to 0.90 (104/116) to 1.09 (118/108). A shock index above 0.9 is considered abnormal and suggests early hemodynamic instability even when the systolic pressure is still within an acceptable range. This simple bedside calculation reinforces the suspicion of ongoing blood loss and the need for prompt surgical team notification, serial hemoglobin checks, and preparation for volume resuscitation or return to the operating room.

Watch out! Do not wait for hypotension to diagnose hemorrhagic shock. By the time systolic blood pressure falls below 90 mmHg, the patient has already lost a substantial portion of circulating volume and may be entering decompensated shock. The narrowing pulse pressure, rising heart rate, falling urine output, and cool skin are the early warning signs that must trigger immediate action.