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Approach to the Critical Patient
Immediate priorities
Initial stabilization and triage
Airway patency and aspiration risk
Active vomiting with altered mental status
Ongoing hematemesis
Breathing and oxygenation
SpO2 target 92% or higher
Respiratory fatigue from severe metabolic acidosis
Circulation and perfusion
Shock index concern
Capillary refill delay
Point-of-care glucose
Hypoglycemia risk with poor intake
Hyperglycemia as alternative diagnosis
Risk stratification
High-risk features
Hemodynamic instability
SBP under 90 mmHg adult
Age-adjusted hypotension pediatric
Severe dehydration
Lethargy or altered mental status
Anuria or minimal urine output
Invasive bacterial diarrhea concern
Bloody diarrhea
Severe abdominal pain
Severe systemic illness
Sepsis criteria
Immunocompromised state
Infection control
Isolation and precautions
Contact precautions for suspected infectious diarrhea
Norovirus outbreak setting
Diapered or incontinent patients
Soap-and-water hand hygiene triggers
Suspected norovirus
Suspected Clostridioides difficile
Initial resuscitation
Fluid and symptom control pathway
Oral rehydration trial if stable
Small frequent sips
Early antiemetic to enable ORS
IV fluids if unable to tolerate PO or shock
Isotonic crystalloid bolus strategy
Reassessment after each bolus
Early diagnostic decision points
Testing thresholds
No routine labs for mild self-limited illness
Short duration
No red flags
Escalate testing for severe or high-risk illness
Significant dehydration
Blood in stool
Consultation triggers
Escalation and specialty involvement
Surgery trigger
Peritoneal signs
Concern for appendicitis or obstruction
ICU trigger
Persistent shock after fluids
Severe acidosis with end-organ dysfunction
History
Core symptom pattern
Symptom characterization
Diarrhea profile
Watery volume and frequency
Blood or mucus
Vomiting profile
Frequency and bilious content
Inability to keep fluids down
Timeline
Onset time and peak severity
Duration over 7 days
Exposure and epidemiology
Exposure risks
Sick contacts
Household cluster
Daycare or school exposure
Food exposures
Undercooked poultry or eggs
Unpasteurized dairy or juice
Water exposures
Untreated well or stream water
Recent swimming in lakes or pools
Travel exposures
Recent international travel
Cruise ship exposure
High-risk history
Complicating factors
Dehydration indicators
Dizziness or syncope
Oliguria
Medication and healthcare exposures
Recent antibiotics within 8 weeks
Recent hospitalization or long-term care exposure
Comorbidities
Chronic kidney disease
Inflammatory bowel disease
Immunocompromise
Transplant
Chemotherapy
Focused differentials in history
Alternative diagnosis clues
Predominant localized abdominal pain
RLQ pain
Severe constant pain out of proportion
Genitourinary symptoms
Dysuria
Flank pain
Neurologic or toxin concern
Neurologic symptoms after fish ingestion
Severe symptoms within 6 hours of meal
Physical Exam
Vital signs and perfusion
Severity assessment
Vital signs trend
Fever pattern
Tachycardia
Perfusion markers
Capillary refill time
Peripheral temperature
Orthostasis when safe
Postural tachycardia
Postural hypotension
Hydration assessment
Dehydration findings
General appearance
Lethargy or irritability
Weak cry or poor interaction pediatric
Mucous membranes and tears
Dry mucosa
Reduced tears pediatric
Skin and eyes
Decreased skin turgor
Sunken eyes pediatric
Urine output surrogate
Dry diaper over 6 to 8 hours infant
Minimal urine adult
Abdominal and systemic exam
Abdomen and complications
Abdominal tenderness pattern
Diffuse mild tenderness
Localized guarding
Peritoneal signs
Rebound
Rigidity
Extraintestinal findings
Rash suggesting viral syndrome
Arthritis suggesting reactive process
Differential Diagnosis
Primary gastroenteritis categories
Infectious gastroenteritis
Viral gastroenteritis
Norovirus infection
Rotavirus infection pediatric
Bacterial gastroenteritis
Campylobacter enteritis
Salmonella gastroenteritis
Protozoal gastroenteritis
Giardia infection
Cryptosporidiosis
Life-threatening mimics
High-risk alternate diagnoses
Surgical abdomen
Appendicitis ICD-10 K35
Bowel obstruction ICD-10 K56
Severe systemic infection
Sepsis ICD-10 A41.9
Meningitis ICD-10 G03.9 in infants with vomiting
Vascular and ischemic
Mesenteric ischemia ICD-10 K55.9
Aortic catastrophe with abdominal pain
Important specific entities
Targeted infectious considerations
Inflammatory dysentery
Shigellosis ICD-10 A03
Entamoeba histolytica colitis ICD-10 A06.0
Shiga toxin producing E. coli
STEC enteritis ICD-10 A04.3
Hemolytic uremic syndrome ICD-10 D59.3 risk
Clostridioides difficile infection
CDI ICD-10 A04.7
Fulminant colitis risk
Noninfectious diarrhea
Noninfectious causes
Inflammatory bowel disease flare
Ulcerative colitis ICD-10 K51
Crohn disease ICD-10 K50
Medication-related diarrhea
Metformin effect
Magnesium-containing laxatives
Endocrine and metabolic
Thyrotoxicosis ICD-10 E05.90
Adrenal crisis ICD-10 E27.2
Laboratory Tests
Core labs for severity and complications
Baseline assessment for moderate to severe illness
Basic metabolic panel
Sodium and potassium derangements
Hypokalemia with vomiting and diarrhea
Hypernatremia pediatric dehydration
Creatinine for AKI
Prerenal azotemia pattern
CKD baseline comparison
Serum glucose
Hypoglycemia pediatric risk
Hyperglycemia alternative diagnosis
Venous blood gas if severe
Metabolic acidosis assessment
Bicarbonate level estimate
Lactate if shock
Infection and inflammatory evaluation
Labs when systemic illness or invasive diarrhea concern
Complete blood count
Leukocytosis support for bacterial or stress response
Hemoglobin and platelets baseline for HUS risk
Blood cultures triggers
High fever and toxicity
Immunocompromised or suspected enteric fever
Stool studies
Stool testing indications
Multiplex stool PCR panel
Severe illness
Public health or outbreak setting
Stool culture with susceptibilities
Dysentery
Immunocompromised host
Shiga toxin assay
Bloody diarrhea
HUS concern
Clostridioides difficile testing
3 or more unformed stools in 24 hours with risk factors
Recent antibiotics or healthcare exposure
Ova and parasites
Diarrhea over 14 days
Travel or daycare exposure
Pitfalls and interpretation
Common limitations
Mild viral gastroenteritis
Normal labs do not exclude dehydration
Fever absence does not exclude bacterial disease
Stool PCR overdiagnosis
Detection without causation
Clinical correlation requirement
Diagnostic Tests
Scoring Systems
Severity scoring and bedside tools
Clinical Dehydration Scale pediatric
General appearance component
Eyes and mucous membranes component
Tears component
Association with dehydration severity and ORS failure risk
Gorelick dehydration scale pediatric
Physical signs count approach
Application in ED triage
Sepsis screening framework
qSOFA adult limitations in ED
Pediatric sepsis recognition based on age-adjusted vitals
MRI
MRI role in vomiting and diarrhea presentations
Alternative diagnosis evaluation
Inflammatory bowel disease complications
Pregnancy appendicitis pathway
Limited role in uncomplicated gastroenteritis
Time and availability constraints
Motion artifact with active vomiting
CT
CT abdomen pelvis indications
Surgical abdomen concern
Localized peritonitis
Obstruction symptoms
Severe abdominal pain disproportionate
Mesenteric ischemia concern
Toxic megacolon concern
Complicated colitis concern
Severe CDI
IBD flare with systemic toxicity
Ultrasound (or US)
Ultrasound applications
Appendicitis assessment
RLQ pain with vomiting
Pediatric first-line imaging
Biliary pathology assessment
RUQ pain with vomiting
Gallbladder wall and stones
POCUS volume status adjunct
IVC assessment limitations
Lung ultrasound for alternative diagnosis in dyspnea
Disposition
Discharge criteria
Safe discharge features
Stable vital signs
No persistent tachycardia after rehydration
Afebrile or improving fever pattern
Oral intake adequacy
Tolerating ORS or fluids after antiemetic
No intractable vomiting
No high-risk features
No bloody diarrhea with systemic toxicity
No severe abdominal tenderness
Reliable follow-up and return ability
Caregiver understanding pediatric
Access to re-evaluation
Admission criteria
Inpatient indications
Severe dehydration
Ongoing large volume losses
AKI or significant electrolyte abnormality
Persistent inability to tolerate oral fluids
Failed ORS despite antiemetic
Recurrent ED visits
Invasive infection concern
Bacteremia risk group
Severe dysentery
Social and safety concerns
Frailty or poor supports
Unsafe home situation
ICU criteria
Critical care indications
Shock requiring vasoactive support
Persistent hypotension after adequate fluids
Rising lactate with organ dysfunction
Fulminant colitis concern
Toxic megacolon features
Severe CDI with ileus
Treatment
Rehydration strategy
Fluid replacement and targets
Oral rehydration solution
Early initiation for mild to moderate dehydration
Frequent small volumes
Continued feeding pediatric
ORS composition principle
Glucose-sodium cotransport mechanism
Avoid high-sugar drinks worsening diarrhea
IV isotonic crystalloids
Adult bolus approach
0.9% sodium chloride 1 L IV
Repeat 500 mL to 1 L based on response
Reassessment after each bolus
Ringer lactate 1 L IV
Repeat 500 mL to 1 L based on response
Preference in significant acidosis consideration
Pediatric bolus approach
0.9% sodium chloride 20 mL/kg IV
Repeat up to 60 mL/kg with reassessment
Escalate for shock physiology
Ringer lactate 20 mL/kg IV
Repeat up to 60 mL/kg with reassessment
Monitor for ongoing losses
Antiemetics
Vomiting control to enable hydration
Ondansetron oral
Adult 4 mg PO
Repeat 4 mg PO once after 8 hours if needed
QT prolongation risk in susceptible patients
Pediatric 0.15 mg/kg PO
Maximum 8 mg PO
Single-dose strategy for ORS success
Ondansetron IV
Adult 4 mg IV
Repeat 4 mg IV once after 8 hours if needed
ECG consideration with risk factors
Pediatric 0.15 mg/kg IV
Maximum 8 mg IV
Prefer oral when possible
Antidiarrheals and adjuncts
Symptom control and safety
Loperamide
Adult 4 mg PO once
2 mg PO after each loose stool
Maximum 16 mg per day
Avoid loperamide triggers
Bloody diarrhea
Suspected inflammatory colitis or CDI
Bismuth subsalicylate adult
524 mg PO every 30 to 60 minutes as needed
Maximum 8 doses per day
Salicylate contraindications
Avoid in pediatrics
Reye syndrome risk
Viral illness in children
Probiotics
Limited benefit in acute infectious diarrhea
Modest duration reduction in some studies
Avoid in severe immunocompromise
Empiric antibiotics
When antibiotics help
Indications for empiric therapy
Moderate to severe travelers diarrhea
Frequent stools with functional impairment
Fever or blood in stool
Dysentery with systemic symptoms
High fever
Severe tenesmus
Suspected cholera with severe dehydration
Profuse rice-water diarrhea
Outbreak or endemic exposure
Avoid antibiotics triggers
Suspected STEC infection
Bloody diarrhea with minimal fever
HUS risk
Mild noninvasive watery diarrhea
Self-limited course
Supportive care preferred
Adult empiric regimens
Azithromycin
1 g PO single dose
Preferred for dysentery and South Asia travel
Macrolide resistance local variation
500 mg PO daily for 3 days
Alternative to single dose
Nausea risk with 1 g dose
Ciprofloxacin
750 mg PO single dose
Avoid with high fluoroquinolone resistance regions
Tendinopathy and QT risk
500 mg PO twice daily for 3 days
Alternative regimen
Avoid in pregnancy when possible
Rifaximin
200 mg PO three times daily for 3 days
Noninvasive travelers diarrhea only
Avoid with fever or blood in stool
Pediatric empiric regimens
Azithromycin
10 mg/kg PO daily for 3 days
Maximum 500 mg per day
Preferred for travelers diarrhea dysentery concern
20 mg/kg PO single dose
Maximum 1 g
Consider in selected settings
Targeted antimicrobial therapy
Common pathogen-directed therapy
Shigella suspected or confirmed
Azithromycin adult 500 mg PO daily for 3 days
Local resistance patterns consideration
Public health notification in outbreaks
Ceftriaxone adult 2 g IV daily
Severe illness or unable to take PO
Typical duration 3 to 5 days
Campylobacter severe disease
Azithromycin adult 500 mg PO daily for 3 days
Greatest benefit early in disease course
Fluoroquinolone resistance common in some regions
Azithromycin pediatric 10 mg/kg PO daily for 3 days
Maximum 500 mg per day
Consider with dysentery or high fever
Nontyphoidal Salmonella high-risk host
Ciprofloxacin adult 500 mg PO twice daily
Typical duration 3 to 7 days
Bacteremia risk groups only
Ceftriaxone adult 2 g IV daily
Severe infection or bacteremia
Typical duration 7 to 14 days for bacteremia
Clostridioides difficile management
CDI treatment pathway
Nonsevere initial episode
Fidaxomicin 200 mg PO twice daily for 10 days
Preferred when available per major guidelines
Lower recurrence compared with vancomycin in trials
Vancomycin 125 mg PO four times daily for 10 days
Alternative first-line
Avoid antimotility agents
Severe or fulminant CDI concern
Vancomycin 500 mg PO or NG four times daily
Add rectal vancomycin if ileus
Early surgical consultation for toxic megacolon concern
Metronidazole 500 mg IV every 8 hours
Adjunct in fulminant disease
Not preferred as monotherapy for initial nonsevere disease
Special Populations
Pregnancy
Pregnancy-specific considerations
Maternal and fetal risks
Lower threshold for IV fluids with persistent vomiting
Fetal monitoring consideration in viable gestation with severe illness
Medication safety
Ondansetron risk-benefit individualized
Avoid tetracyclines when possible
Antibiotic selection
Azithromycin preferred for travelers diarrhea when needed
Avoid fluoroquinolones when alternatives exist
Geriatric
Older adult considerations
Higher complication risk
AKI with modest volume loss
Delirium with dehydration
Medication risks
QT prolongation interactions
Diuretic and ACE inhibitor effect on volume status
Disposition threshold
Lower threshold for observation
Home support assessment
Pediatrics
Pediatric considerations
Dehydration recognition
Weight change when available
Capillary refill and mental status emphasis
Feeding guidance
Continue breastfeeding
Early return to age-appropriate diet after rehydration
Red flags
Bilious vomiting
Bloody stool in young infant
Background
Epidemiology
Burden and common etiologies
Viral predominance in community gastroenteritis
Norovirus as common cause of outbreaks
Rotavirus reduced in vaccinated populations
Bacterial patterns
Campylobacter common in poultry exposure
Salmonella associated with eggs poultry reptiles
Seasonality and settings
Winter vomiting illness pattern for norovirus
Daycare and long-term care outbreaks
Pathophysiology
Mechanisms of diarrhea and vomiting
Secretory diarrhea physiology
Increased chloride secretion and water loss
Minimal fecal leukocytes
Inflammatory diarrhea physiology
Mucosal invasion and cytokine response
Blood and fecal leukocytes
Dehydration and electrolyte loss
Hypokalemia from stool losses
Metabolic acidosis from bicarbonate loss
Therapeutic Considerations
Rationale for key therapies
Oral rehydration effectiveness
Glucose-sodium cotransport intact in most diarrheas
Reduced need for IV fluids in mild to moderate dehydration
Antibiotic stewardship
Limited benefit in most noninvasive gastroenteritis
Harm potential with STEC and HUS risk
Antiemetic use
Improved ORS success with single-dose ondansetron pediatric
QT risk management in susceptible patients
Patient Discharge Instructions
Copy discharge instructions
Home care and return precautions
Hydration plan
Oral rehydration solution preferred
Small frequent sips after vomiting
Diet guidance
Resume regular diet as tolerated
Avoid high-sugar drinks and alcohol
Contagion reduction
Hand hygiene with soap and water if vomiting illness
Avoid food preparation for others while symptomatic
Return to ED immediately
Blood in stool
Severe or worsening abdominal pain
Signs of dehydration
Confusion or fainting
Persistent vomiting with inability to keep fluids down
Fever with worsening condition
Follow-up timing
Primary care follow-up if symptoms over 3 days without improvement
Earlier follow-up for infants older adults pregnancy immunocompromise
References
Clinical guidelines and evidence sources
Major guideline sources
IDSA Clinical Practice Guidelines for Infectious Diarrhea
Stool testing indications and pathogen-specific management framework
High-risk host considerations
ACG Clinical Guideline for Acute Infectious Diarrhea in Adults
Empiric antibiotic criteria and travelers diarrhea approach
Supportive care and antimotility cautions
CDC guidance for norovirus and foodborne illness
Outbreak control and isolation considerations
Hand hygiene recommendations
SHEA IDSA Clostridioides difficile guidelines
Fidaxomicin and vancomycin first-line recommendations
Fulminant CDI management pathway
Evidence levels and recommendation framing
Recommendation grading conventions
IDSA strong versus conditional recommendations based on evidence certainty
Stewardship emphasis for empiric antibiotics
Testing escalation for severe or high-risk illness
Class I IIa IIb convention for supportive care in critical illness contexts
Class I isotonic crystalloid for hypovolemic shock
Class IIa antiemetic to enable oral rehydration in selected patients
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.