19. A 72-year-old man presented with sudden onset of severe central abdominal pain for 4 hours. The pain is disproportionate to the minimal abdominal tenderness on examination. His serum lactate is elevated. His blood pressure was 130/85 and pulse rate was 96 bpm, which is irregular. Which is the most appropriate investigation to confirm the diagnosis? A. X-ray-Chest erect B. Abdominal ultrasonography C. Contrast-enhanced CT angiography of the abdomen D. Urgent Colonoscopy E. Diagnostic laparoscopy
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The answer is confirmed. Here is the full explanation:
Answer: C. Contrast-enhanced CT Angiography of the Abdomen
Why This is Acute Mesenteric Ischemia (AMI)
This clinical scenario contains the classic triad of AMI:
| Feature | Significance |
|---|---|
| Severe central abdominal pain out of proportion to tenderness | Hallmark sign of AMI |
| Irregular pulse (atrial fibrillation) | Source of cardioembolic clot to the SMA |
| Elevated serum lactate | Tissue hypoperfusion / bowel ischemia |
| Elderly patient (72 y/o) | Higher risk group |
| 4-hour onset | Acute presentation - bowel infarction may begin within 6 hours |
The irregular pulse strongly suggests atrial fibrillation, making this most likely an arterial embolus to the superior mesenteric artery (SMA) - the most common cause of AMI, responsible for >50% of cases. The embolic source is usually a cardiac thrombus from the left atrium or ventricle. - Schwartz's Principles of Surgery, 11th Ed.
Why CT Angiography is the Investigation of Choice
CT angiography is the study of choice for diagnosing acute mesenteric ischemia. It:
- Directly visualises the mesenteric vasculature and identifies arterial occlusion, stenosis, or embolus
- Distinguishes the cause (embolism vs. thrombosis vs. nonocclusive ischemia) - critical for treatment planning
- Identifies ischemic bowel changes (wall thickening, pneumatosis intestinalis, portal vein gas)
- Excludes other causes of acute abdominal pain
- Frameworks for Internal Medicine: "CT angiography is the study of choice for diagnosing acute mesenteric ischemia. It provides information about the underlying cause (eg, thrombosis vs embolism) as well as location, which is helpful for procedural planning."
Why the Other Options are Incorrect
A. X-ray Chest erect - Erect chest X-ray is used to detect free gas under the diaphragm (perforation). It cannot diagnose AMI and shows only nonspecific findings in early disease. Not appropriate here.
B. Abdominal ultrasonography - Ultrasound has limited utility in AMI due to bowel gas interference. It cannot reliably visualise mesenteric vessel occlusion and would waste precious time.
D. Urgent Colonoscopy - Colonoscopy is used for ischemic colitis (large bowel ischemia), not acute mesenteric (small bowel) ischemia. This patient has central abdominal pain suggesting small bowel/SMA territory involvement. Colonoscopy would be dangerous and unhelpful here.
E. Diagnostic laparoscopy - This may be used if imaging is equivocal or for therapeutic purposes, but it is an invasive procedure and is NOT the first-line investigation for confirming the diagnosis. CT angiography comes first.
Key Teaching Point
Time is bowel in AMI. Intestinal mucosal sloughing begins within 3 hours and full-thickness infarction occurs by 6 hours. CT angiography must be obtained urgently, and once confirmed, treatment (surgical or endovascular revascularisation + anticoagulation) should begin immediately. Mortality is up to 80% if diagnosis is delayed.
The correct answer is C.
A 35 year old lab technician presented following sodium hydroxide splash injury to left eye and washed 5 min with tap water. Patient complains of photophobia and blurring of vision. He is brought to the emergency department.What is the most appropriate next step of management, A. Apply pressure B. Apply artificial tear C. Irrigate with normal saline D. Apply topical antibiotics E. Apply topical steroids
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Excellent - the textbook source is definitive. Here is the complete answer:
Answer: C. Irrigate with Normal Saline
The Clinical Scenario
This is an alkali (NaOH) chemical burn to the eye - one of the most serious ocular emergencies. Sodium hydroxide is a strong base. The patient received only 5 minutes of tap water irrigation at the scene, which is far from sufficient. On arrival to the ED, the most important and immediate next step is to continue copious irrigation with normal saline.
Why Immediate Irrigation is the Priority
Alkali burns are more dangerous than acid burns because of liquefactive necrosis - alkalis penetrate deeply and rapidly through the corneal stroma and into the anterior chamber, damaging the lens, trabecular meshwork, and ciliary body. The damage continues as long as the chemical remains in contact with ocular tissue.
"Copious irrigation is crucial to minimize duration of contact with the chemical and to normalize the pH in the conjunctival sac as soon as possible. The speed and efficacy of irrigation is the most important prognostic factor following chemical injury."
- Kanski's Clinical Ophthalmology, 10th Edition
Protocol for ED Irrigation
- Instil topical anaesthetic first (e.g. proxymetacaine/oxybuprocaine) - this dramatically improves patient comfort and cooperation for irrigation
- Use a lid speculum to keep the eye open
- Irrigate with sterile normal saline or Ringer's lactate for 15-30 minutes continuously (or until the conjunctival pH is neutral - pH 7.0-7.4)
- Double-evert the upper eyelid to check the superior fornix for retained particulate matter - remove any particles found
- Measure conjunctival pH after irrigation; if still abnormal, repeat irrigation
- After pH is normalised, perform slit-lamp examination and grade the injury (Roper-Hall or Dua classification)
- Urgent ophthalmology consultation
Tap water is acceptable if nothing else is available to avoid delay, but sterile buffered saline is preferred - it is the standard in the ED setting. - Kanski's Clinical Ophthalmology
Why the Other Options are Wrong
| Option | Why Incorrect |
|---|---|
| A. Apply pressure | Absolutely contraindicated - would drive chemical deeper into ocular tissue |
| B. Artificial tears | Volume is grossly insufficient; does not dilute/neutralise alkali adequately |
| D. Topical antibiotics | Important later to prevent infection, but NOT before pH is neutralised |
| E. Topical steroids | Used in subsequent management to reduce inflammation, but NOT the first step |
Key Teaching Point
In ocular chemical burns, "dilute and irrigate" takes absolute priority over everything else - over history-taking, over examination, over any drops or treatment. This is true even if some irrigation has already occurred at the scene. 5 minutes of home tap water is completely inadequate for a strong alkali splash. The ED must continue copious irrigation immediately.
The correct answer is C.
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