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Emergency and Acute Medicine – Acetaminophen (APAP) Poisoning
Overview and Pathophysiology
Acetaminophen is widely available as a single-agent analgesic, in combination with opioid medications, and as an ingredient in more than 200 over-the-counter cold and flu products. It is among the most common causes of both intentional and accidental poisoning and is the leading cause of acute liver failure requiring transplantation in the United States.
After ingestion, most acetaminophen is safely metabolized, but a small fraction is converted by the cytochrome P-450 system into N-acetyl-p-benzoquinoneimine (NAPQI), a highly toxic metabolite. Under normal conditions, NAPQI is neutralized by glutathione. In overdose, glutathione stores are rapidly depleted, allowing NAPQI to accumulate and cause hepatocellular injury. N-acetylcysteine (NAC) restores glutathione levels and prevents or limits liver damage. Patients with malnutrition are at higher risk because of reduced baseline glutathione reserves.
Pharmacokinetics and Toxic Thresholds
The normal acetaminophen half-life is approximately 2.5–4 hours but becomes prolonged in overdose, often exceeding 4 hours and indicating hepatic dysfunction. An acute ingestion greater than 150 mg/kg is potentially toxic. At 4 hours after ingestion, a serum acetaminophen level of 140 μg/mL or higher suggests toxicity, while therapeutic levels range from 5–20 μg/mL. The Rumack–Matthew nomogram is used to guide treatment decisions following a single, acute ingestion.
Clinical Course and Symptoms
Toxicity typically progresses through four stages.
Phase I (0.5–24 hours): Nausea, vomiting, and malaise may occur, particularly with large ingestions, though symptoms can be mild or absent early.
Phase II (24–72 hours): Gastrointestinal symptoms may improve, but liver injury evolves. Patients develop right upper quadrant pain, rising transaminases, prolonged PT/INR, elevated bilirubin, and sometimes oliguria.
Phase III (72–96 hours): This is the most critical period. Liver enzyme abnormalities peak, hepatic encephalopathy may appear, and worsening coagulopathy or renal failure signals a high likelihood of requiring liver transplantation.
Phase IV (96 hours to 10 days): Patients either recover with gradual hepatic regeneration or progress to fulminant liver failure.
Essential Evaluation
A careful history must identify all acetaminophen-containing products ingested and the timing of ingestion. A serum acetaminophen level should be obtained at 4 hours post-ingestion or immediately upon presentation if more than 4 hours have elapsed. The Rumack–Matthew nomogram applies only to single, acute ingestions and should not be used for chronic or delayed presentations. Early consultation with a poison center or toxicologist is strongly recommended.
Diagnostic Testing
Laboratory evaluation includes serum acetaminophen concentration, electrolytes, blood urea nitrogen, creatinine, glucose, liver enzymes (AST typically rises first), bilirubin, and PT/INR. Severe toxicity may result in AST/ALT levels exceeding 10,000 IU/L. A pregnancy test and toxicology screen should be obtained when appropriate.
Differential Diagnosis
Acetaminophen toxicity should always be considered as a co-ingestant in overdose. Other causes of acute liver injury include viral hepatitis, Reye syndrome, Amanita mushroom poisoning, herbal or dietary supplement toxicity, and other hepatotoxic drugs.
Initial Stabilization
Management begins with airway, breathing, and circulation assessment. Supplemental oxygen should be provided as needed. In patients with altered mental status, empiric administration of naloxone, thiamine, and dextrose (or bedside glucose testing) is appropriate.
Emergency Department Management
Supportive care includes intravenous fluids and antiemetics. A single dose of activated charcoal should be administered if the patient presents soon after ingestion.
N-acetylcysteine (NAC) is the cornerstone of therapy and is nearly 100% effective at preventing hepatotoxicity if started within 8 hours of acute overdose.
NAC Administration Options
Oral NAC has an unpleasant taste and odor and should be diluted to improve tolerability; antiemetics are often required. Vomited doses within one hour should be repeated, and persistent vomiting necessitates nasogastric or intravenous administration.
Intravenous NAC is given as a 21-hour infusion protocol. Oral NAC may be administered intravenously if the IV formulation is unavailable, with toxicology guidance.
Pregnancy Considerations
NAC is not teratogenic and crosses the placenta. Treating the mother effectively protects the fetus, particularly after 14 weeks’ gestation when fetal metabolism can produce toxic metabolites.
Disposition and Follow-Up
Admission is required for patients with hepatotoxic acetaminophen levels, abnormal liver tests, chronic ingestion with liver injury, or suicide attempts requiring psychiatric care.
Asymptomatic patients with non-toxic ingestions who do not require NAC may be discharged with counseling. Early hepatology or transplant consultation is warranted when significant liver injury is present. Patients with intentional overdose require psychiatric evaluation, while those with accidental poisoning need poison-prevention counseling.
Clinical Pearls and Pitfalls
Always consider occult acetaminophen exposure in patients presenting after opioid overdose or with unexplained liver injury. The Rumack–Matthew nomogram should not be used for chronic ingestion or late presentation. NAC should not be stopped until acetaminophen levels are undetectable and clinical and laboratory evidence of hepatotoxicity has improved or resolved.
Overview and Pathophysiology
Acetaminophen is widely available as a single-agent analgesic, in combination with opioid medications, and as an ingredient in more than 200 over-the-counter cold and flu products. It is among the most common causes of both intentional and accidental poisoning and is the leading cause of acute liver failure requiring transplantation in the United States.
After ingestion, most acetaminophen is safely metabolized, but a small fraction is converted by the cytochrome P-450 system into N-acetyl-p-benzoquinoneimine (NAPQI), a highly toxic metabolite. Under normal conditions, NAPQI is neutralized by glutathione. In overdose, glutathione stores are rapidly depleted, allowing NAPQI to accumulate and cause hepatocellular injury. N-acetylcysteine (NAC) restores glutathione levels and prevents or limits liver damage. Patients with malnutrition are at higher risk because of reduced baseline glutathione reserves.
Pharmacokinetics and Toxic Thresholds
The normal acetaminophen half-life is approximately 2.5–4 hours but becomes prolonged in overdose, often exceeding 4 hours and indicating hepatic dysfunction. An acute ingestion greater than 150 mg/kg is potentially toxic. At 4 hours after ingestion, a serum acetaminophen level of 140 μg/mL or higher suggests toxicity, while therapeutic levels range from 5–20 μg/mL. The Rumack–Matthew nomogram is used to guide treatment decisions following a single, acute ingestion.
Clinical Course and Symptoms
Toxicity typically progresses through four stages.
Phase I (0.5–24 hours): Nausea, vomiting, and malaise may occur, particularly with large ingestions, though symptoms can be mild or absent early.
Phase II (24–72 hours): Gastrointestinal symptoms may improve, but liver injury evolves. Patients develop right upper quadrant pain, rising transaminases, prolonged PT/INR, elevated bilirubin, and sometimes oliguria.
Phase III (72–96 hours): This is the most critical period. Liver enzyme abnormalities peak, hepatic encephalopathy may appear, and worsening coagulopathy or renal failure signals a high likelihood of requiring liver transplantation.
Phase IV (96 hours to 10 days): Patients either recover with gradual hepatic regeneration or progress to fulminant liver failure.
Essential Evaluation
A careful history must identify all acetaminophen-containing products ingested and the timing of ingestion. A serum acetaminophen level should be obtained at 4 hours post-ingestion or immediately upon presentation if more than 4 hours have elapsed. The Rumack–Matthew nomogram applies only to single, acute ingestions and should not be used for chronic or delayed presentations. Early consultation with a poison center or toxicologist is strongly recommended.
Diagnostic Testing
Laboratory evaluation includes serum acetaminophen concentration, electrolytes, blood urea nitrogen, creatinine, glucose, liver enzymes (AST typically rises first), bilirubin, and PT/INR. Severe toxicity may result in AST/ALT levels exceeding 10,000 IU/L. A pregnancy test and toxicology screen should be obtained when appropriate.
Differential Diagnosis
Acetaminophen toxicity should always be considered as a co-ingestant in overdose. Other causes of acute liver injury include viral hepatitis, Reye syndrome, Amanita mushroom poisoning, herbal or dietary supplement toxicity, and other hepatotoxic drugs.
Initial Stabilization
Management begins with airway, breathing, and circulation assessment. Supplemental oxygen should be provided as needed. In patients with altered mental status, empiric administration of naloxone, thiamine, and dextrose (or bedside glucose testing) is appropriate.
Emergency Department Management
Supportive care includes intravenous fluids and antiemetics. A single dose of activated charcoal should be administered if the patient presents soon after ingestion.
N-acetylcysteine (NAC) is the cornerstone of therapy and is nearly 100% effective at preventing hepatotoxicity if started within 8 hours of acute overdose.
- If the acetaminophen level cannot be obtained within 8 hours and toxicity is suspected, NAC should be started empirically and stopped if levels prove non-toxic.
- For presentations ≥8 hours after ingestion, NAC should be started immediately while awaiting laboratory confirmation.
- For late (>24 hours) or chronic ingestions, NAC is indicated if ingestion exceeds 150 mg/kg, symptoms are present, or liver tests are abnormal. Therapy may be discontinued once acetaminophen is undetectable and liver enzymes remain normal.
NAC Administration Options
Oral NAC has an unpleasant taste and odor and should be diluted to improve tolerability; antiemetics are often required. Vomited doses within one hour should be repeated, and persistent vomiting necessitates nasogastric or intravenous administration.
Intravenous NAC is given as a 21-hour infusion protocol. Oral NAC may be administered intravenously if the IV formulation is unavailable, with toxicology guidance.
Pregnancy Considerations
NAC is not teratogenic and crosses the placenta. Treating the mother effectively protects the fetus, particularly after 14 weeks’ gestation when fetal metabolism can produce toxic metabolites.
Disposition and Follow-Up
Admission is required for patients with hepatotoxic acetaminophen levels, abnormal liver tests, chronic ingestion with liver injury, or suicide attempts requiring psychiatric care.
Asymptomatic patients with non-toxic ingestions who do not require NAC may be discharged with counseling. Early hepatology or transplant consultation is warranted when significant liver injury is present. Patients with intentional overdose require psychiatric evaluation, while those with accidental poisoning need poison-prevention counseling.
Clinical Pearls and Pitfalls
Always consider occult acetaminophen exposure in patients presenting after opioid overdose or with unexplained liver injury. The Rumack–Matthew nomogram should not be used for chronic ingestion or late presentation. NAC should not be stopped until acetaminophen levels are undetectable and clinical and laboratory evidence of hepatotoxicity has improved or resolved.
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Diagnostic Test – Darkfield Microscopy
1. What is this?
Darkfield microscopy is the most accurate diagnostic test for primary syphilis.
It allows direct visualization of Treponema pallidum, the causative organism, from an active lesion.
2. How is it done?
- A scraping or swab is obtained from a syphilitic chancre
- The specimen is placed on a glass slide
- The slide is examined using darkfield illumination
- Motile spirochetes can be seen directly if T. pallidum is present
3. When do you select darkfield microscopy?
Choose darkfield microscopy when:
- The clinical scenario suggests primary syphilis
- The question asks for the most accurate diagnostic test
- There is a painless genital ulcer (chancre)
- In primary syphilis, RPR and VDRL have a false-negative rate of ~25%
- Darkfield microscopy is more sensitive than RPR or VDRL in this stage
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Emergency and Acute Medicine – Penetrating Abdominal Trauma
Overview and Mechanism of Injury
Penetrating abdominal trauma results from injury caused by knives, gunshots, or other foreign objects breaching the abdominal wall. Damage to solid organs most often leads to significant hemorrhage, whereas hollow viscus injuries may cause leakage of bowel contents with subsequent peritonitis and sepsis. Injuries are frequently complex, and combined thoracic and abdominal involvement occurs in approximately one-quarter of cases.
Etiology and Injury Patterns
Penetrating trauma carries a high risk of intra-abdominal injury. Approximately 80% of gunshot wounds and 20–30% of stab wounds result in significant abdominal pathology. Commonly injured structures include the liver, small bowel, stomach, colon, major vascular structures, retroperitoneum, and mesentery or omentum. Less frequently affected organs include the spleen, diaphragm, kidneys, pancreas, duodenum, and biliary system.
Clinical Presentation
Patients present with an obvious penetrating wound and may range from having localized pain to overt peritoneal signs and hemodynamic instability. High-velocity projectiles can cause extensive tissue destruction through direct injury, secondary missiles (bone or bullet fragments), and temporary cavitation. Exit wounds may be larger than entrance wounds, but small or inconspicuous entry and exit sites can mask severe internal injury.
Clinicians must remember the full anatomic boundaries of the abdomen, which extend from the nipples anteriorly and the inferior scapular tips posteriorly down to the inferior gluteal folds.
Initial Evaluation and Essential Workup
Gunshot wounds to the abdomen are generally assumed to have caused intra-abdominal injury and are typically managed with operative exploration.
For stab wounds to the anterior abdomen, local wound exploration is essential. If the anterior fascia is violated, further evaluation with diagnostic peritoneal lavage or bedside ultrasonography is indicated.
Diagnostic laparoscopy is particularly useful for identifying diaphragmatic injuries and selected liver or splenic lacerations and may help avoid unnecessary laparotomy in stable patients.
CT imaging is valuable for evaluating suspected retroperitoneal injuries in stable patients but is unreliable for detecting hollow viscus or diaphragmatic injuries.
Diagnostic peritoneal lavage remains useful in select cases. A red blood cell count of 10,000/mm³ or greater is an indication for laparotomy. Patients with lower counts should be closely observed for 8–24 hours for evolving peritoneal signs.
Diagnostic Tests and Interpretation
Laboratory evaluation includes serial hemoglobin or hematocrit measurements to assess ongoing blood loss, urinalysis to screen for genitourinary injury, arterial blood gas analysis to evaluate hypovolemia, and blood typing with cross-matching for patients with suspected significant injury.
Imaging studies may include plain radiographs with external markers to localize foreign bodies, identify fractures, or detect free air. Intravenous pyelography may be used when renal injury is suspected. Focused abdominal sonography for trauma (FAST) can rapidly identify intraperitoneal fluid, while CT with intravenous contrast is reserved for stable patients in experienced centers.
Differential Diagnosis
Upper abdominal penetrating wounds may involve intrathoracic structures, while lower thoracic injuries can extend into the abdominal cavity. Both possibilities should always be considered during evaluation.
Prehospital Management
Fluid resuscitation should be carefully titrated to clinical response. Military antishock trousers are not recommended. Open wounds should be covered with sterile dressings, and eviscerated bowel should be protected with moist sterile dressings. Impaled objects must be stabilized in place and never removed in the field.
Initial Stabilization and Therapy
Management begins with high-flow oxygen and placement of two large-bore intravenous lines for crystalloid infusion. If there is no response after 2 liters of crystalloid, transfusion of packed red blood cells is indicated, using O-negative blood initially if the patient is unstable. Type-specific and cross-matched blood should be administered as soon as available.
Pediatric Considerations
Children in hypovolemic shock should receive crystalloid boluses of 20 mL/kg. Severe shock requires transfusion of packed red blood cells at 1 mL/kg. Diagnostic peritoneal lavage is relatively contraindicated in children younger than 8 years.
Emergency Department Procedures
A nasogastric tube should be placed to reduce aspiration risk and decompress the stomach prior to diagnostic peritoneal lavage. This may also relieve respiratory distress caused by diaphragmatic injury with herniation of abdominal contents.
A Foley catheter should be inserted after excluding urethral injury to assist in detecting genitourinary trauma and monitoring urine output. Tetanus prophylaxis should be administered when indicated.
Medications
Broad-spectrum intravenous antibiotics with gram-negative and anaerobic coverage are required due to the high risk of contamination. Acceptable regimens include second-generation cephalosporins, beta-lactam/beta-lactamase inhibitor combinations, or combination therapy with aminoglycosides and anaerobic agents. Tetanus toxoid and tetanus immunoglobulin should be given as appropriate.
Disposition and Follow-Up
Patients requiring operative intervention must be admitted. Those with negative diagnostic studies should be observed for at least 8 hours with serial abdominal examinations and repeated hematocrit measurements.
Patients with stab wounds that do not penetrate the fascia may be discharged after a period of observation in the emergency department.
Clinical Pearls and Pitfalls
Permissive hypotension is increasingly supported during resuscitation to limit bleeding. Overaggressive crystalloid administration should be avoided. Complete exposure of the patient is essential to avoid missed injuries. Routine spinal immobilization is unnecessary unless there is clear evidence of spinal cord injury.
Overview and Mechanism of Injury
Penetrating abdominal trauma results from injury caused by knives, gunshots, or other foreign objects breaching the abdominal wall. Damage to solid organs most often leads to significant hemorrhage, whereas hollow viscus injuries may cause leakage of bowel contents with subsequent peritonitis and sepsis. Injuries are frequently complex, and combined thoracic and abdominal involvement occurs in approximately one-quarter of cases.
Etiology and Injury Patterns
Penetrating trauma carries a high risk of intra-abdominal injury. Approximately 80% of gunshot wounds and 20–30% of stab wounds result in significant abdominal pathology. Commonly injured structures include the liver, small bowel, stomach, colon, major vascular structures, retroperitoneum, and mesentery or omentum. Less frequently affected organs include the spleen, diaphragm, kidneys, pancreas, duodenum, and biliary system.
Clinical Presentation
Patients present with an obvious penetrating wound and may range from having localized pain to overt peritoneal signs and hemodynamic instability. High-velocity projectiles can cause extensive tissue destruction through direct injury, secondary missiles (bone or bullet fragments), and temporary cavitation. Exit wounds may be larger than entrance wounds, but small or inconspicuous entry and exit sites can mask severe internal injury.
Clinicians must remember the full anatomic boundaries of the abdomen, which extend from the nipples anteriorly and the inferior scapular tips posteriorly down to the inferior gluteal folds.
Initial Evaluation and Essential Workup
Gunshot wounds to the abdomen are generally assumed to have caused intra-abdominal injury and are typically managed with operative exploration.
For stab wounds to the anterior abdomen, local wound exploration is essential. If the anterior fascia is violated, further evaluation with diagnostic peritoneal lavage or bedside ultrasonography is indicated.
Diagnostic laparoscopy is particularly useful for identifying diaphragmatic injuries and selected liver or splenic lacerations and may help avoid unnecessary laparotomy in stable patients.
CT imaging is valuable for evaluating suspected retroperitoneal injuries in stable patients but is unreliable for detecting hollow viscus or diaphragmatic injuries.
Diagnostic peritoneal lavage remains useful in select cases. A red blood cell count of 10,000/mm³ or greater is an indication for laparotomy. Patients with lower counts should be closely observed for 8–24 hours for evolving peritoneal signs.
Diagnostic Tests and Interpretation
Laboratory evaluation includes serial hemoglobin or hematocrit measurements to assess ongoing blood loss, urinalysis to screen for genitourinary injury, arterial blood gas analysis to evaluate hypovolemia, and blood typing with cross-matching for patients with suspected significant injury.
Imaging studies may include plain radiographs with external markers to localize foreign bodies, identify fractures, or detect free air. Intravenous pyelography may be used when renal injury is suspected. Focused abdominal sonography for trauma (FAST) can rapidly identify intraperitoneal fluid, while CT with intravenous contrast is reserved for stable patients in experienced centers.
Differential Diagnosis
Upper abdominal penetrating wounds may involve intrathoracic structures, while lower thoracic injuries can extend into the abdominal cavity. Both possibilities should always be considered during evaluation.
Prehospital Management
Fluid resuscitation should be carefully titrated to clinical response. Military antishock trousers are not recommended. Open wounds should be covered with sterile dressings, and eviscerated bowel should be protected with moist sterile dressings. Impaled objects must be stabilized in place and never removed in the field.
Initial Stabilization and Therapy
Management begins with high-flow oxygen and placement of two large-bore intravenous lines for crystalloid infusion. If there is no response after 2 liters of crystalloid, transfusion of packed red blood cells is indicated, using O-negative blood initially if the patient is unstable. Type-specific and cross-matched blood should be administered as soon as available.
Pediatric Considerations
Children in hypovolemic shock should receive crystalloid boluses of 20 mL/kg. Severe shock requires transfusion of packed red blood cells at 1 mL/kg. Diagnostic peritoneal lavage is relatively contraindicated in children younger than 8 years.
Emergency Department Procedures
A nasogastric tube should be placed to reduce aspiration risk and decompress the stomach prior to diagnostic peritoneal lavage. This may also relieve respiratory distress caused by diaphragmatic injury with herniation of abdominal contents.
A Foley catheter should be inserted after excluding urethral injury to assist in detecting genitourinary trauma and monitoring urine output. Tetanus prophylaxis should be administered when indicated.
Medications
Broad-spectrum intravenous antibiotics with gram-negative and anaerobic coverage are required due to the high risk of contamination. Acceptable regimens include second-generation cephalosporins, beta-lactam/beta-lactamase inhibitor combinations, or combination therapy with aminoglycosides and anaerobic agents. Tetanus toxoid and tetanus immunoglobulin should be given as appropriate.
Disposition and Follow-Up
Patients requiring operative intervention must be admitted. Those with negative diagnostic studies should be observed for at least 8 hours with serial abdominal examinations and repeated hematocrit measurements.
Patients with stab wounds that do not penetrate the fascia may be discharged after a period of observation in the emergency department.
Clinical Pearls and Pitfalls
Permissive hypotension is increasingly supported during resuscitation to limit bleeding. Overaggressive crystalloid administration should be avoided. Complete exposure of the patient is essential to avoid missed injuries. Routine spinal immobilization is unnecessary unless there is clear evidence of spinal cord injury.
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Diagnostic Test – Indium-Labeled Leukocyte Scan
1. How does this test work?
The indium-labeled leukocyte scan is a nuclear medicine study used to detect occult infection or evaluate fever of unknown origin (FUO).
Mechanism:
- A sample of the patient’s blood is drawn.
- White blood cells (leukocytes) are isolated and tagged with radioactive indium.
- The labeled blood is re-injected into the patient.
- The indium-tagged leukocytes migrate and localize to areas of active infection or inflammation.
- Nuclear imaging detects areas of increased uptake, identifying the site of infection.
2. When is an indium scan the right text?
Answer indium-labeled leukocyte scan when you see:
- Occult infection or fever of unknown origin
- Routine studies are negative, such as:
- Blood cultures
- Chest X-ray
- Urinalysis
- Suspicion of infection that is difficult to localize
- Situations where gallium scans are inaccurate, particularly:
- Intra-abdominal infections
3. What is the most accurate test?
- A biopsy of the suspected site of infection is more accurate than an indium-labeled leukocyte scan.
- The indium scan is best used as a localizing tool, guiding further definitive testing.
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Diagnostic Test – Herpes Simplex PCR
1. What is this?
Herpes simplex PCR is a molecular diagnostic test performed on cerebrospinal fluid (CSF).
It detects HSV DNA and is the single most accurate diagnostic test for herpes simplex encephalitis.
2. When is this the correct choice?
Select HSV PCR of the CSF when the clinical scenario includes:
- Fever
- Headache
- Altered mental status or confusion
- Symptom duration less than 2 weeks
Key test-taking point:
- CSF HSV PCR is more accurate than:
- EEG
- Head CT
- Brain MRI
- Even brain biopsy
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Diagnostic Test – Gallium Scanning
1. How does this test work?
Gallium scanning is a nuclear medicine imaging study used to detect infection and certain malignancies.
Mechanism:
2. When is a gallium scan the appropriate choice?
Choose a gallium scan when the clinical picture includes:
1. How does this test work?
Gallium scanning is a nuclear medicine imaging study used to detect infection and certain malignancies.
Mechanism:
- Gallium localizes to areas with:
- Increased white blood cell activity
- Increased iron metabolism
- It is transported in the blood bound to transferrin
- Areas of inflammation, infection, or malignancy show increased gallium uptake
2. When is a gallium scan the appropriate choice?
Choose a gallium scan when the clinical picture includes:
- Persistent fever without localizing symptoms
- Negative initial evaluation, including:
- Blood cultures
- Chest X-ray
- Urinalysis
- Fever of unknown origin (FUO)
- Lymphoma
- Occult abscesses
- A biopsy is the most definitive test following an abnormal gallium scan
- Malignancy → requires histologic confirmation
- Infection → requires culture confirmation
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Diagnostic Test – Legionella Urine Antigen
1. What is this?
The Legionella urine antigen test detects antigen from Legionella pneumophila in the urine. It is a rapid, noninvasive test and is considered the best initial test to make a specific diagnosis of Legionella pneumonia.
2. What is the best test?
Choose Legionella urine antigen when the clinical scenario shows:
1. What is this?
The Legionella urine antigen test detects antigen from Legionella pneumophila in the urine. It is a rapid, noninvasive test and is considered the best initial test to make a specific diagnosis of Legionella pneumonia.
2. What is the best test?
- The urine antigen test has ~100% specificity for Legionella pneumophila serogroup 1.
- However, only 70–80% of Legionella infections are caused by serogroup 1.
- Therefore, the definitive diagnostic test is:
- Sputum culture or tracheal aspirate culture on buffered charcoal yeast extract (BCYE) agar.
Choose Legionella urine antigen when the clinical scenario shows:
- Pneumonia in a nursing home resident or recent hospitalization
- High fever
- Confusion
- Diarrhea
- Hyponatremia
- Possible lab abnormalities:
- ↑ Creatine phosphokinase (CPK)
- ↑ Liver function tests
- ↑ Creatinine
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Emergency and Acute Medicine – Evaluation and Management of Abdominal Pain
Overview and Pain Mechanisms
Abdominal pain originates from several distinct physiologic processes. Parietal pain occurs when the peritoneum becomes inflamed by irritating substances. It is conveyed through somatic nerves, intensifies with movement or changes in abdominal wall tension, and is typically sharp, well defined, and associated with rebound tenderness and involuntary guarding.
In contrast, visceral pain arises from internal organs and is transmitted through autonomic afferent pathways. This pain is often vague and poorly localized, reflecting embryologic origin rather than precise anatomy. Pain from foregut organs is perceived in the epigastrium, midgut pain around the umbilicus, and hindgut pain in the suprapubic region. It commonly results from distention of hollow organs, stretching of organ capsules, or smooth muscle spasm, and may be constant or colicky.
As inflammation progresses and involves the parietal peritoneum, localized tenderness develops. Ischemic pain, frequently due to vascular emergencies, is characteristically severe and diffuse. Referred pain is experienced at a site distant from the affected organ because of shared neural pathways. Abdominal wall pain is usually persistent and aching, often accompanied by muscle spasm and involvement of nearby muscle groups.
Causes of Abdominal Pain
Etiologies are broad and include peritoneal irritation from gastric acid, fecal contamination, pus, blood, bile, or pancreatic enzymes. Obstructive processes may affect the small or large bowel, gallbladder, ureters, or kidneys, and may be complicated by ischemia of intestinal, renal, or splenic tissue. Inflammatory conditions include appendicitis, inflammatory bowel disease, cholecystitis, hepatitis, peptic ulcer disease, pancreatitis, pelvic inflammatory disease, and pyelonephritis. Additional considerations include abdominal wall pathology and referred pain from extra-abdominal sources such as intrathoracic disease.
Clinical Assessment: History and Symptoms
A thorough history is critical. Important features include the onset, timing, duration, and progression of pain; its initial and current location; radiation; and quality (sharp, dull, cramping). Clinicians should assess aggravating and relieving factors and associated symptoms such as anorexia, nausea, vomiting (including bilious or coffee-ground material), malaise, syncope, respiratory complaints, changes in bowel habits or stool color, hematuria, urinary symptoms, trauma, gynecologic or obstetric history, recent surgery, family history of vascular disease, alcohol intake, and medication use, particularly NSAIDs or aspirin.
Physical Examination Findings
General examination may reveal fever, tachycardia, tachypnea, hypotension, jaundice, or abnormal peripheral pulses. Abdominal evaluation should include inspection for distension, auscultation for altered bowel sounds, and palpation for masses or tenderness. Signs of peritoneal irritation such as guarding and rebound tenderness are key. Specific maneuvers—including Rovsing, psoas, obturator, McBurney point tenderness, Murphy sign, and Carnett sign—help localize pathology. Rectal and pelvic examinations may identify tenderness, masses, cervical motion tenderness, or occult blood. Genitourinary assessment includes evaluation for flank pain, dysuria, costovertebral angle tenderness, testicular pain, and suprapubic tenderness. Skin findings such as jaundice, ecchymosis, rashes, or vesicular lesions may provide diagnostic clues.
Initial Workup
Pregnancy testing is mandatory in women of reproductive age. In many cases, ultrasonography serves as the first-line imaging study, with CT scanning reserved for situations in which ultrasound is nondiagnostic or when more detailed evaluation is required.
Investigations and Interpretation
Laboratory studies typically include a complete blood count, serum electrolytes, renal function tests, glucose, inflammatory markers, liver function tests, lactic acid, serum lipase, urinalysis, stool studies when indicated, and pregnancy testing.
Imaging is guided by clinical suspicion and may include ECG for possible cardiac causes, abdominal radiographs, upright chest radiograph to assess for free air, ultrasonography for biliary disease, hydronephrosis, free fluid, aneurysm, or torsion, and CT scanning tailored to suspected pathology. CT angiography is essential when mesenteric ischemia or abdominal aortic aneurysm is suspected. MRI may be considered when radiation exposure or contrast nephrotoxicity is a concern.
Differential Diagnosis
Abdominal pain encompasses a wide differential including gastrointestinal, vascular, genitourinary, gynecologic, metabolic, infectious, and referred causes. Examples include bowel obstruction, appendicitis, cholecystitis, pancreatitis, diverticulitis, ectopic pregnancy, ovarian torsion, renal colic, ischemic bowel, myocardial infarction, pneumonia, abdominal wall disorders, and herpes zoster. Pediatric considerations vary by age and include intussusception, volvulus, incarcerated hernia, Meckel diverticulitis, and sickle cell crisis.
Management in the Emergency Department
Initial management focuses on stabilization and symptom control. This includes bowel rest, nasogastric decompression when indicated, intravenous fluids, correction of electrolyte abnormalities, and antiemetics. Adequate analgesia should be provided promptly and not delayed. Blood typing and cross-matching are required in unstable patients, and early surgical consultation is crucial when a surgical cause is suspected.
Pharmacologic Therapy
Pain control commonly involves opioids such as fentanyl or morphine. Nausea and vomiting are treated with antiemetics including ondansetron, prochlorperazine, or promethazine.
Disposition and Follow-Up
Hospital admission is indicated for patients with suspected surgical pathology, peritoneal signs, inability to tolerate oral intake, uncontrolled pain, serious medical causes such as myocardial infarction or diabetic ketoacidosis, or the need for intravenous antibiotics.
Discharge may be appropriate when serious pathology has been excluded, pain is well controlled, oral intake is tolerated, and the patient can comply with clear return instructions.
Discharge Advice and Safety Netting
Patients should be advised to return immediately for worsening or persistent pain, ongoing vomiting, blood in vomitus or stool, jaundice, fever or chills, or lack of improvement within 8–12 hours.
Clinical Pearls
Older adults often present atypically and are at higher risk for life-threatening conditions. Constipation should not be diagnosed solely by the absence of stool in the rectum. When vomiting precedes the onset of abdominal pain, a surgical cause is less likely.
Overview and Pain Mechanisms
Abdominal pain originates from several distinct physiologic processes. Parietal pain occurs when the peritoneum becomes inflamed by irritating substances. It is conveyed through somatic nerves, intensifies with movement or changes in abdominal wall tension, and is typically sharp, well defined, and associated with rebound tenderness and involuntary guarding.
In contrast, visceral pain arises from internal organs and is transmitted through autonomic afferent pathways. This pain is often vague and poorly localized, reflecting embryologic origin rather than precise anatomy. Pain from foregut organs is perceived in the epigastrium, midgut pain around the umbilicus, and hindgut pain in the suprapubic region. It commonly results from distention of hollow organs, stretching of organ capsules, or smooth muscle spasm, and may be constant or colicky.
As inflammation progresses and involves the parietal peritoneum, localized tenderness develops. Ischemic pain, frequently due to vascular emergencies, is characteristically severe and diffuse. Referred pain is experienced at a site distant from the affected organ because of shared neural pathways. Abdominal wall pain is usually persistent and aching, often accompanied by muscle spasm and involvement of nearby muscle groups.
Causes of Abdominal Pain
Etiologies are broad and include peritoneal irritation from gastric acid, fecal contamination, pus, blood, bile, or pancreatic enzymes. Obstructive processes may affect the small or large bowel, gallbladder, ureters, or kidneys, and may be complicated by ischemia of intestinal, renal, or splenic tissue. Inflammatory conditions include appendicitis, inflammatory bowel disease, cholecystitis, hepatitis, peptic ulcer disease, pancreatitis, pelvic inflammatory disease, and pyelonephritis. Additional considerations include abdominal wall pathology and referred pain from extra-abdominal sources such as intrathoracic disease.
Clinical Assessment: History and Symptoms
A thorough history is critical. Important features include the onset, timing, duration, and progression of pain; its initial and current location; radiation; and quality (sharp, dull, cramping). Clinicians should assess aggravating and relieving factors and associated symptoms such as anorexia, nausea, vomiting (including bilious or coffee-ground material), malaise, syncope, respiratory complaints, changes in bowel habits or stool color, hematuria, urinary symptoms, trauma, gynecologic or obstetric history, recent surgery, family history of vascular disease, alcohol intake, and medication use, particularly NSAIDs or aspirin.
Physical Examination Findings
General examination may reveal fever, tachycardia, tachypnea, hypotension, jaundice, or abnormal peripheral pulses. Abdominal evaluation should include inspection for distension, auscultation for altered bowel sounds, and palpation for masses or tenderness. Signs of peritoneal irritation such as guarding and rebound tenderness are key. Specific maneuvers—including Rovsing, psoas, obturator, McBurney point tenderness, Murphy sign, and Carnett sign—help localize pathology. Rectal and pelvic examinations may identify tenderness, masses, cervical motion tenderness, or occult blood. Genitourinary assessment includes evaluation for flank pain, dysuria, costovertebral angle tenderness, testicular pain, and suprapubic tenderness. Skin findings such as jaundice, ecchymosis, rashes, or vesicular lesions may provide diagnostic clues.
Initial Workup
Pregnancy testing is mandatory in women of reproductive age. In many cases, ultrasonography serves as the first-line imaging study, with CT scanning reserved for situations in which ultrasound is nondiagnostic or when more detailed evaluation is required.
Investigations and Interpretation
Laboratory studies typically include a complete blood count, serum electrolytes, renal function tests, glucose, inflammatory markers, liver function tests, lactic acid, serum lipase, urinalysis, stool studies when indicated, and pregnancy testing.
Imaging is guided by clinical suspicion and may include ECG for possible cardiac causes, abdominal radiographs, upright chest radiograph to assess for free air, ultrasonography for biliary disease, hydronephrosis, free fluid, aneurysm, or torsion, and CT scanning tailored to suspected pathology. CT angiography is essential when mesenteric ischemia or abdominal aortic aneurysm is suspected. MRI may be considered when radiation exposure or contrast nephrotoxicity is a concern.
Differential Diagnosis
Abdominal pain encompasses a wide differential including gastrointestinal, vascular, genitourinary, gynecologic, metabolic, infectious, and referred causes. Examples include bowel obstruction, appendicitis, cholecystitis, pancreatitis, diverticulitis, ectopic pregnancy, ovarian torsion, renal colic, ischemic bowel, myocardial infarction, pneumonia, abdominal wall disorders, and herpes zoster. Pediatric considerations vary by age and include intussusception, volvulus, incarcerated hernia, Meckel diverticulitis, and sickle cell crisis.
Management in the Emergency Department
Initial management focuses on stabilization and symptom control. This includes bowel rest, nasogastric decompression when indicated, intravenous fluids, correction of electrolyte abnormalities, and antiemetics. Adequate analgesia should be provided promptly and not delayed. Blood typing and cross-matching are required in unstable patients, and early surgical consultation is crucial when a surgical cause is suspected.
Pharmacologic Therapy
Pain control commonly involves opioids such as fentanyl or morphine. Nausea and vomiting are treated with antiemetics including ondansetron, prochlorperazine, or promethazine.
Disposition and Follow-Up
Hospital admission is indicated for patients with suspected surgical pathology, peritoneal signs, inability to tolerate oral intake, uncontrolled pain, serious medical causes such as myocardial infarction or diabetic ketoacidosis, or the need for intravenous antibiotics.
Discharge may be appropriate when serious pathology has been excluded, pain is well controlled, oral intake is tolerated, and the patient can comply with clear return instructions.
Discharge Advice and Safety Netting
Patients should be advised to return immediately for worsening or persistent pain, ongoing vomiting, blood in vomitus or stool, jaundice, fever or chills, or lack of improvement within 8–12 hours.
Clinical Pearls
Older adults often present atypically and are at higher risk for life-threatening conditions. Constipation should not be diagnosed solely by the absence of stool in the rectum. When vomiting precedes the onset of abdominal pain, a surgical cause is less likely.
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Diagnostic Test – Monospot Test
1. What is this?
The Monospot test is the best initial screening test used to diagnose infectious mononucleosis (IM).
It detects heterophile antibodies, which are characteristically produced during infection with Epstein–Barr virus (EBV).
2. When do you answer Monospot test?
Answer Monospot test when the clinical vignette describes:
- Sore throat
- Fever
- Lymphadenopathy (especially posterior cervical)
- Malaise and fatigue
- Splenomegaly (present in ~50% of patients)
- Exudative pharyngitis (may be present)
- Rash occurs in ~15% of cases normally
- Rash in ~90% of patients if ampicillin or amoxicillin is given
3. What is the most accurate test?
- The most accurate test in the acute phase is:
- IgM antibody to EBV viral capsid antigen (VCA)
- EBV nuclear antigen (EBNA) antibodies appear later, usually 3–4 weeks after infection, and are not useful for acute diagnosis
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Emergency and Acute Medicine – Blunt Abdominal Trauma
Overview and Mechanism of Injury
Blunt abdominal trauma results from a sudden transfer of force or pressure to the abdomen. Injury to solid organs most commonly presents with hemorrhage, whereas damage to hollow viscus organs leads to bleeding and peritonitis due to leakage of bowel contents. The clinical impact depends on the magnitude of force, organs involved, and associated injuries.
Etiology and Patterns of Injury
Motor vehicle collisions account for approximately 60% of blunt abdominal trauma cases. Solid organs are injured more often than hollow organs. The spleen is the most frequently affected organ, followed by the liver, intestines, retroperitoneal structures, and kidneys. Less commonly involved structures include the mesentery, pancreas, diaphragm, urinary bladder, urethra, and major vascular structures.
Pediatric Considerations
Children often appear to tolerate blunt trauma better due to the increased elasticity of their tissues. However, because the liver and spleen extend beyond the protective rib cage in children, these organs are more exposed and vulnerable to injury. As a result, significant intra-abdominal injury may occur despite minimal external signs.
Clinical Presentation
Symptoms range widely from mild abdominal discomfort to overt peritoneal irritation and hypovolemic shock. Patients may report nausea or vomiting. Labored breathing can occur due to diaphragmatic irritation or upper abdominal injury. Left shoulder pain during inspiration (Kehr sign) suggests diaphragmatic irritation from intra-abdominal bleeding. Hollow viscus injuries, particularly small-bowel trauma, may present in a delayed fashion.
Initial Evaluation and Essential Workup
Management begins with rapid assessment and stabilization of airway, breathing, and circulation (ABCs). The primary goal is to identify patients who require urgent operative intervention.
A careful abdominal examination should assess for tenderness, distension, guarding, and signs of peritoneal irritation, while recognizing that injuries to the retroperitoneum or intrathoracic abdomen may not be detected by palpation alone. The anatomical boundaries of the abdomen extend from the diaphragm superiorly to the intragluteal folds inferiorly and include the entire circumferential torso.
The skin should be inspected for abrasions or ecchymoses, including the back, which requires rolling the patient. Seatbelt or lap-belt marks are particularly concerning for significant intra-abdominal injury. Bowel sounds may be diminished or absent, although this is a late finding.
A Foley catheter may be placed to monitor urine output if there is no blood at the urethral meatus, no perineal hematoma, and a normal prostate examination. Pelvic radiographs are useful when pelvic fracture or gross hematuria suggests genitourinary injury, prompting further evaluation with specialized imaging when indicated.
Imaging and Diagnostic Modalities
CT scanning is the most valuable tool for evaluating solid organ injury, retroperitoneal structures, and determining the need for surgery, provided the patient is hemodynamically stable enough for transport.
Focused Assessment with Sonography for Trauma (FAST) is a rapid, noninvasive bedside test used to detect free intraperitoneal fluid. While efficient, it is operator dependent.
Diagnostic peritoneal lavage (DPL) is primarily reserved for unstable patients and is especially helpful in identifying injuries within the intrathoracic abdomen, pelvis, or true abdominal cavity. A positive study includes gross blood, elevated red or white blood cell counts, or the presence of bile, feces, or food particles.
Laboratory Evaluation
Initial hemoglobin and hematocrit levels may be normal due to acute isovolemic blood loss. Blood typing and screening are essential, with cross-matching of packed red blood cells for unstable patients. Urinalysis should be performed to detect hematuria, and microscopic hematuria in the setting of shock warrants genitourinary evaluation. Arterial blood gas analysis may reveal a base deficit, indicating hypovolemia and guiding resuscitation efforts.
Differential Diagnosis
Pain from lower thoracic injuries may mimic abdominal pathology and should always be considered in the evaluation of blunt trauma patients.
Prehospital Management
Fluid resuscitation should be titrated to clinical response, with a target systolic blood pressure of 90–100 mm Hg. Normal vital signs do not exclude significant intra-abdominal injury.
Emergency Department Stabilization and Treatment
Initial stabilization focuses on securing the airway, providing high-flow oxygen, and establishing two large-bore intravenous lines for crystalloid infusion. If there is no response after 2 liters of crystalloid, packed red blood cells should be administered. In cases of profound shock, immediate transfusion with O-negative blood may be lifesaving.
A nasogastric tube may be placed to decompress the stomach, reduce distention, and lower aspiration risk, and may improve respiratory distress caused by diaphragmatic herniation of the stomach.
Medications
Tetanus prophylaxis should be administered in patients with open wounds, using tetanus toxoid and tetanus immunoglobulin when indicated. Broad-spectrum intravenous antibiotics with aerobic and anaerobic coverage, such as a second-generation cephalosporin, are recommended when contamination or hollow viscus injury is suspected.
Pediatric Resuscitation Considerations
In children with shock, crystalloid boluses are given at 20 mL/kg, and packed red blood cells are administered at 1 mL/kg when needed.
Disposition and Follow-Up
Admission is indicated for postoperative patients, those with equivocal findings on FAST, CT, or DPL, and for most blunt abdominal trauma cases requiring observation and serial abdominal examinations.
Patients in whom intra-abdominal injury is suspected should not be discharged without an adequate period of observation, even if initial imaging and examination are negative.
Clinical Pearls and Pitfalls
Do not delay blood transfusion in patients with clinical shock despite a normal hematocrit. Avoid excessive crystalloid resuscitation. Always obtain a pregnancy test in females of childbearing age. Unstable patients should never be transported to CT for diagnostic imaging.
Overview and Mechanism of Injury
Blunt abdominal trauma results from a sudden transfer of force or pressure to the abdomen. Injury to solid organs most commonly presents with hemorrhage, whereas damage to hollow viscus organs leads to bleeding and peritonitis due to leakage of bowel contents. The clinical impact depends on the magnitude of force, organs involved, and associated injuries.
Etiology and Patterns of Injury
Motor vehicle collisions account for approximately 60% of blunt abdominal trauma cases. Solid organs are injured more often than hollow organs. The spleen is the most frequently affected organ, followed by the liver, intestines, retroperitoneal structures, and kidneys. Less commonly involved structures include the mesentery, pancreas, diaphragm, urinary bladder, urethra, and major vascular structures.
Pediatric Considerations
Children often appear to tolerate blunt trauma better due to the increased elasticity of their tissues. However, because the liver and spleen extend beyond the protective rib cage in children, these organs are more exposed and vulnerable to injury. As a result, significant intra-abdominal injury may occur despite minimal external signs.
Clinical Presentation
Symptoms range widely from mild abdominal discomfort to overt peritoneal irritation and hypovolemic shock. Patients may report nausea or vomiting. Labored breathing can occur due to diaphragmatic irritation or upper abdominal injury. Left shoulder pain during inspiration (Kehr sign) suggests diaphragmatic irritation from intra-abdominal bleeding. Hollow viscus injuries, particularly small-bowel trauma, may present in a delayed fashion.
Initial Evaluation and Essential Workup
Management begins with rapid assessment and stabilization of airway, breathing, and circulation (ABCs). The primary goal is to identify patients who require urgent operative intervention.
A careful abdominal examination should assess for tenderness, distension, guarding, and signs of peritoneal irritation, while recognizing that injuries to the retroperitoneum or intrathoracic abdomen may not be detected by palpation alone. The anatomical boundaries of the abdomen extend from the diaphragm superiorly to the intragluteal folds inferiorly and include the entire circumferential torso.
The skin should be inspected for abrasions or ecchymoses, including the back, which requires rolling the patient. Seatbelt or lap-belt marks are particularly concerning for significant intra-abdominal injury. Bowel sounds may be diminished or absent, although this is a late finding.
A Foley catheter may be placed to monitor urine output if there is no blood at the urethral meatus, no perineal hematoma, and a normal prostate examination. Pelvic radiographs are useful when pelvic fracture or gross hematuria suggests genitourinary injury, prompting further evaluation with specialized imaging when indicated.
Imaging and Diagnostic Modalities
CT scanning is the most valuable tool for evaluating solid organ injury, retroperitoneal structures, and determining the need for surgery, provided the patient is hemodynamically stable enough for transport.
Focused Assessment with Sonography for Trauma (FAST) is a rapid, noninvasive bedside test used to detect free intraperitoneal fluid. While efficient, it is operator dependent.
Diagnostic peritoneal lavage (DPL) is primarily reserved for unstable patients and is especially helpful in identifying injuries within the intrathoracic abdomen, pelvis, or true abdominal cavity. A positive study includes gross blood, elevated red or white blood cell counts, or the presence of bile, feces, or food particles.
Laboratory Evaluation
Initial hemoglobin and hematocrit levels may be normal due to acute isovolemic blood loss. Blood typing and screening are essential, with cross-matching of packed red blood cells for unstable patients. Urinalysis should be performed to detect hematuria, and microscopic hematuria in the setting of shock warrants genitourinary evaluation. Arterial blood gas analysis may reveal a base deficit, indicating hypovolemia and guiding resuscitation efforts.
Differential Diagnosis
Pain from lower thoracic injuries may mimic abdominal pathology and should always be considered in the evaluation of blunt trauma patients.
Prehospital Management
Fluid resuscitation should be titrated to clinical response, with a target systolic blood pressure of 90–100 mm Hg. Normal vital signs do not exclude significant intra-abdominal injury.
Emergency Department Stabilization and Treatment
Initial stabilization focuses on securing the airway, providing high-flow oxygen, and establishing two large-bore intravenous lines for crystalloid infusion. If there is no response after 2 liters of crystalloid, packed red blood cells should be administered. In cases of profound shock, immediate transfusion with O-negative blood may be lifesaving.
A nasogastric tube may be placed to decompress the stomach, reduce distention, and lower aspiration risk, and may improve respiratory distress caused by diaphragmatic herniation of the stomach.
Medications
Tetanus prophylaxis should be administered in patients with open wounds, using tetanus toxoid and tetanus immunoglobulin when indicated. Broad-spectrum intravenous antibiotics with aerobic and anaerobic coverage, such as a second-generation cephalosporin, are recommended when contamination or hollow viscus injury is suspected.
Pediatric Resuscitation Considerations
In children with shock, crystalloid boluses are given at 20 mL/kg, and packed red blood cells are administered at 1 mL/kg when needed.
Disposition and Follow-Up
Admission is indicated for postoperative patients, those with equivocal findings on FAST, CT, or DPL, and for most blunt abdominal trauma cases requiring observation and serial abdominal examinations.
Patients in whom intra-abdominal injury is suspected should not be discharged without an adequate period of observation, even if initial imaging and examination are negative.
Clinical Pearls and Pitfalls
Do not delay blood transfusion in patients with clinical shock despite a normal hematocrit. Avoid excessive crystalloid resuscitation. Always obtain a pregnancy test in females of childbearing age. Unstable patients should never be transported to CT for diagnostic imaging.
