Nausea and Vomiting

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Core Mechanism: Emesis is a complex, vagally-mediated reflex coordinated by the "vomiting center" located in the medulla oblongata. It receives afferent input from four primary sources:

1. Chemoreceptor Trigger Zone (CTZ): Located outside the blood-brain barrier in the area postrema. It directly detects circulating systemic toxins, drugs (e.g., aspirin, digoxin, acetaminophen), and metabolic derangements (e.g., uremia, diabetic ketoacidosis).
2. Vestibular System: Mediates motion sickness and labyrinthitis via histamine (H1) and muscarinic (M1) receptors.
3. Central Nervous System (CNS): Cortical pathways respond to elevated intracranial pressure (ICP), CNS tumors, meningitis, and psychiatric triggers (anxiety).
4. Peripheral Visceral Afferents: Vagal and sympathetic nerves in the GI tract, peritoneum, and biliary tree sense distention, inflammation, or ischemia (e.g., bowel obstruction, peritonitis, biliary colic).

• The Mechanical Event: Stimulation of the vomiting center triggers the somatic and autonomic sequence: retrograde peristalsis, glottic closure, diaphragmatic contraction, and forceful expulsion of gastric contents.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Assess ABCs, particularly airway protection against aspiration. Assess for clinical signs of cardiovascular compromise or severe (>15%) dehydration. Place the patient on a continuous monitor and establish IV access.
• First-Line Interventions:
• Keep the patient strictly NPO initially.
• Initiate IV hydration; the sources specifically recommend utilizing D5LR (5% Dextrose in Lactated Ringer's) if starvation ketosis is present or if treating hyperemesis gravidarum.
• Administer an Antiemetic. (External clinical knowledge: Ondansetron 4-8 mg IV/PO or Metoclopramide 10 mg IV are standard first-line agents).
• Administer Analgesics concurrently if abdominal pain is present.
• Essential Monitoring: Order serial examinations, strictly monitor intake and output, and frequently reassess vital signs and ability to tolerate oral fluids.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

Nausea and vomiting are notoriously non-specific; you must actively hunt for systemic, toxicologic, and surgical catastrophes.

• "Can't-Miss" Mimics & Causes:
• Surgical Abdomen/Ischemia: Bowel obstruction, ischemic bowel, acute appendicitis, gonadal torsion.
• Metabolic/Endocrine Crises: Diabetic Ketoacidosis (DKA), adrenal insufficiency, uremia.
• Neurologic Catastrophes: Raised intracranial pressure, intracranial hemorrhage, meningitis.
• Cardiopulmonary: Myocardial infarction (particularly inferior wall) and pulmonary embolism.
• Toxicologic: Acetaminophen, aspirin, digoxin toxicity, or carbon monoxide poisoning.
• Prioritized Diagnostic Workup:
• Labs: CBC, comprehensive metabolic panel (to evaluate for severe electrolyte abnormalities and uremia), and a pregnancy test for females of childbearing age. Check specific tox screens (e.g., salicylate, acetaminophen, digoxin levels) if overdose is suspected.
• Imaging: CT Abdomen/Pelvis is the gold standard if an obstruction, ileus, or surgical abdomen is suspected. POCUS (Ultrasound) is the gold standard for suspected cholecystitis or biliary colic.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• 12-Lead ECG: Look explicitly for new ST/T wave changes, bundle branch blocks, significant arrhythmias, or a prolonged QTc (>500 ms). Ischemia can present primarily with nausea, and many antiemetics (like ondansetron or droperidol) further prolong the QT interval.
• POCUS (Gallbladder): To rule in cholecystitis as the cause of vomiting, look for a sonographic Murphy's sign, pericholecystic fluid, gallbladder wall thickening >4 mm, or a dilated common bile duct.
• Plain Radiographs / CT: Evaluate for free intra-abdominal air (perforation) or dilated loops of bowel with air-fluid levels confirming a mechanical obstruction.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

Emergency Department Clinical Decision Unit (CDU) / Observation protocols dictate strict cutoffs for who can be observed versus who requires formal admission:

• Mandatory Admission/Exclusion Criteria: Patients must be excluded from short-term observation if they exhibit:
• Unstable Vital Signs: HR > 110 bpm, SBP < 100 mmHg, RR > 22, or pO2 < 94%.
• High-Risk Status: Immunocompromised patients (T-cells < 200, active chemotherapy, transplants) or pregnant patients with complications.
• Surgical/Critical Pathology: Any signs of bowel obstruction (even partial), cholecystitis, a surgical abdomen (rigidity, rebound, free air), DKA, or sepsis.
• Disposition to Home: Discharge is only appropriate when the patient has acceptable vital signs, resolution of symptoms, and the demonstrated ability to tolerate oral fluids without vomiting.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Cognitive Trap (Anchoring on the GI Tract): Assuming nausea and vomiting strictly represent "gastroenteritis." Critical Action: You must actively remember that abdominal pain and vomiting may be secondary to urological, respiratory, cardiovascular, or gynecological disorders.
• Cognitive Trap (Misinterpreting the Timeline): Failing to establish the exact sequence of symptom onset. Critical Action: Always ask whether the pain or the vomiting came first. Vomiting that follows the onset of abdominal pain strongly implies a surgical cause (e.g., appendicitis), whereas vomiting preceding the pain is often non-surgical.
• Critical Action (Triage Recognition): Never send a patient home or to an unmonitored observation unit if the underlying cause is not amenable to short-term treatment (e.g., bowel ischemia, DTs, DKA, sepsis).

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzwords:
• "Vomiting that follows the onset of abdominal pain" = Surgical abdomen (e.g., appendicitis).
• "Severe (>15%) dehydration or unremitting emesis" = Requires D5LR to prevent/treat starvation ketosis.
• Classic Distractor: A test question features a 65-year-old diabetic female complaining of "nausea, vomiting, and indigestion" after eating. The options will include ordering an abdominal ultrasound or prescribing a proton pump inhibitor. Correction: This is a classic atypical presentation for acute coronary syndrome. The correct first step is to obtain a 12-lead ECG to rule out an inferior myocardial infarction.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The History Pivot: "I will take a detailed history, specifically focusing on the timeline. Because the patient's vomiting followed the onset of their abdominal pain, I am highly suspicious of a surgical etiology like appendicitis or obstruction, rather than simple gastroenteritis. I will also review their old notes for previous surgeries that might cause adhesions."
• The Systemic Sweep: "Because nausea and vomiting are highly non-specific, my physical exam will not just focus on the abdomen. I will explicitly rule out urological, respiratory, cardiovascular, and gynecological etiologies, including a pelvic exam and a 12-lead ECG to rule out atypical ACS."
• The Disposition Plan: "The patient's vital signs are currently stable. I will initiate NPO status, provide IV D5LR hydration to address potential starvation ketosis, and administer antiemetics and analgesia. If they fail PO challenge, demonstrate severe electrolyte abnormalities, or exhibit surgical signs like rebound tenderness, I will admit them; otherwise, I will discharge them once they tolerate oral fluids with strict return precautions."