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Approach to the Critical Patient
Immediate stabilization
Resuscitation priorities
Airway risk
Altered mental status
Active emesis
Shock with poor perfusion
Breathing threats
Tachypnea with fatigue
Hypoxemia
Suspected aspiration
Circulation threats
Hypotension
Cool mottled extremities
Capillary refill > 3 seconds
If shock, escalate to resuscitation bay
Early ICU consult
Early surgery consult
Monitoring
Continuous ECG
Dysrhythmia triggers for electrolyte correction
Demand ischemia risk in sepsis
Pulse oximetry
SpO2 target 92-96%
Lower target acceptable in chronic hypercapnia
Noninvasive blood pressure cycling
If vasopressors, arterial line for titration (Class I, expert consensus)
If severe shock, invasive MAP targeting (Class I, expert consensus)
Core temperature
Hypothermia as late sepsis marker
Fever as early infection marker
Hemodynamic targets
MAP >= 65 mmHg (Class I, sepsis consensus)
Higher target if chronic hypertension with altered mentation
Lower target acceptable if bleeding risk and stable mentation
Urine output >= 0.5 mL/kg/hour
Foley catheter in shock or need for strict I and O
Avoid Foley if stable and no monitoring need
Lactate trend to clearance
Lactate >= 2 mmol/L as hypoperfusion marker
Lactate >= 4 mmol/L as high risk marker
Early time-critical actions
NPO status
Aspiration reduction
Operative readiness
Broad-spectrum antibiotics within 1 hour in septic shock (Class I, sepsis consensus)
Do not delay for imaging if unstable
Blood cultures before antibiotics if no delay
IV crystalloid bolus if hypotension or lactate >= 4 mmol/L (Class I, sepsis consensus)
30 mL/kg initial strategy as reference dose
Smaller boluses with frequent reassessment in heart failure
Early source control pathway (Class I, sepsis consensus)
Surgery consult at first suspicion
IR consult if abscess or contained leak suspected
Key concepts
Problem framing
Perforated viscus
Loss of GI tract integrity
Contamination of peritoneal or retroperitoneal space
Chemical peritonitis progressing to bacterial peritonitis
Time dependence
Early antibiotics improve outcomes in intra-abdominal sepsis
Delayed source control increases mortality in peritonitis
High-risk phenotypes
Generalized peritonitis
Rigid abdomen
Rebound tenderness
Guarding with severe pain
Sepsis or septic shock
Hypotension
Elevated lactate
Altered mentation
Contained perforation
Localized tenderness
Stable vitals
CT evidence of localized extraluminal air or fluid
Pitfalls
Common misses
Analgesia avoidance
Pain control does not mask peritonitis progression
Untreated pain worsens tachycardia and work of breathing
Normal initial imaging
Early perforation with minimal free air
Retroperitoneal perforation with subtle findings
Under-triage in older adults
Blunted fever and leukocytosis
Rapid decompensation risk
Delayed antibiotics in suspected perforation
Increased risk of sepsis progression
Worse source control window
History
Presentation patterns
Symptom profile
Sudden severe abdominal pain
Perforated peptic ulcer pattern
Pain onset to peak within minutes
Progressive abdominal pain over hours
Perforated appendicitis pattern
Perforated diverticulitis pattern
Pain with vomiting
Gastric outlet pathology
Small bowel pathology
Fever and rigors
Established peritonitis
Bacteremia risk
Timing and evolution
Time of onset
Sudden versus gradual
Worsening trajectory
Last oral intake
Aspiration risk
Operative planning
Recent antibiotics
Partially treated infection
Resistant organism risk
Localizing clues
Epigastric pain
Peptic ulcer disease
Gastric perforation
RUQ pain
Perforated cholecystitis
Duodenal perforation
LLQ pain
Diverticulitis with perforation
Colonic malignancy with perforation
Suprapubic pain
Sigmoid perforation
Pelvic abscess
Risk factors and triggers
Medication and exposures
NSAID use
Peptic ulcer disease risk
Perforation risk
Steroid use
Blunted peritoneal signs
Increased infection risk
Chemotherapy or neutropenia
Typhlitis risk
High mortality perforation risk
Alcohol use disorder
Gastritis and ulcer risk
Aspiration risk
Comorbidities
Known peptic ulcer disease
Prior GI bleed
Prior perforation
Diverticular disease
Prior diverticulitis episodes
Prior abscess or perforation
Inflammatory bowel disease
Toxic megacolon risk
Steroid immunosuppression
Atherosclerotic disease
Mesenteric ischemia risk
Ischemic perforation risk
Recent events
Recent endoscopy
Iatrogenic perforation risk
Instrumentation location
Recent abdominal surgery
Anastomotic leak risk
Abscess risk
Abdominal trauma
Hollow viscus injury risk
Delayed perforation risk
Red flags
High-acuity symptoms
Syncope or presyncope
Shock marker
Ongoing hemorrhage marker
Dyspnea
Sepsis physiology
Aspiration pneumonia risk
Confusion
Sepsis encephalopathy
Hypoperfusion marker
Severe generalized pain with immobility
Peritonitis marker
Operative abdomen marker
Physical Exam
General and hemodynamics
Global severity
Toxic appearance
Lethargy
Diaphoresis
Vital sign patterns
Tachycardia
Hypotension
Fever
Hypothermia
Perfusion and volume status
Mental status changes
Agitation
Somnolence
Skin findings
Cool clammy extremities
Mottling
Capillary refill
Delayed refill in shock
Normal refill does not exclude sepsis
Abdominal exam
Peritoneal signs
Guarding
Voluntary guarding
Involuntary rigidity
Rebound tenderness
Localized peritonitis
Generalized peritonitis
Percussion tenderness
Peritoneal irritation marker
Useful when palpation limited
Distension and bowel activity
Abdominal distension
Ileus marker
Obstruction marker
Bowel sounds
Hypoactive in ileus
High-pitched in obstruction
Hernia and scars
Incarcerated hernia
Strangulation risk
Perforation risk
Recent incision findings
Tenderness near incision
Drain output concern for leak
Extra-abdominal clues
Respiratory
Basilar crackles
Aspiration risk
Sepsis-related lung injury
Pleural irritation
Referred pain patterns
Free air under diaphragm association
Rectal exam
Occult blood
Malignancy concern
Ischemia concern
Mass
Obstructing lesion concern
Perforation proximal to obstruction concern
Pelvic and genitourinary
Testicular exam in males
Torsion mimic
Epididymitis mimic
Pelvic tenderness in females
PID and TOA mimic
Ectopic pregnancy mimic
Pitfalls
Misleading findings
Soft abdomen in early perforation
Minimal contamination phase
Retroperitoneal perforation phase
Immunosuppressed blunting
Minimal fever
Minimal leukocytosis
Opioid exposure
Reduced guarding
Persistent peritoneal irritation possible
Differential Diagnosis
Life-threatening mimics
Critical causes
Mesenteric ischemia (ICD-10 K55.9)
Pain out of proportion
Lactate elevation late marker
Ruptured abdominal aortic aneurysm (ICD-10 I71.4)
Hypotension with back pain
Pulsatile mass unreliable
Severe acute pancreatitis with necrosis (ICD-10 K85.9)
Epigastric pain radiating to back
Systemic inflammatory response
Toxic megacolon (ICD-10 K59.31)
Severe colitis with distension
Shock risk
Ectopic pregnancy rupture (ICD-10 O00.9)
Pregnancy possible
Hemoperitoneum risk
Intra-abdominal perforation sources
Upper GI
Perforated peptic ulcer (ICD-10 K27.1, K26.1)
Sudden epigastric pain
NSAID exposure
Perforated gastric malignancy (ICD-10 C16)
Weight loss
Anemia history
Small bowel
Crohn disease perforation (ICD-10 K50)
Chronic diarrhea
Immunosuppression
Typhlitis with perforation (ICD-10 K52.89)
Neutropenia
RLQ pain
Large bowel
Perforated diverticulitis (ICD-10 K57.2)
LLQ pain
Prior episodes
Obstructing colon cancer with perforation (ICD-10 C18)
Obstipation
Weight loss
Stercoral perforation (ICD-10 K63.1)
Severe constipation
Opioid exposure
Biliary
Emphysematous cholecystitis with perforation (ICD-10 K81.0)
Diabetes
RUQ tenderness
Non-perforation causes of peritonitis-like picture
Other causes
Spontaneous bacterial peritonitis (ICD-10 K65.2)
Cirrhosis with ascites
Fever with diffuse pain
PID with tubo-ovarian abscess (ICD-10 N70.93)
Pelvic pain
Vaginal discharge
Laboratory Tests
Initial labs
Core panel
Complete blood count for infection and anemia
Leukocytosis or leukopenia as sepsis marker
Hemoglobin for hemorrhage and baseline
Electrolytes and renal function for resuscitation safety
Creatinine for contrast planning
Potassium for dysrhythmia risk
Liver enzymes and bilirubin for hepatobiliary source
Cholestatic pattern suggests biliary pathology
Transaminitis in shock liver
Glucose for sepsis physiology and management
Hyperglycemia as stress marker
Hypoglycemia as severe sepsis marker
Sepsis and perfusion labs
Perfusion assessment
Lactate in mmol/L
Lactate >= 2 mmol/L suggests hypoperfusion
Lactate >= 4 mmol/L suggests high mortality risk
Venous blood gas
pH trend for shock severity
pCO2 in mmHg for ventilatory status
Arterial blood gas if respiratory failure
PaO2 in mmHg
PaCO2 in mmHg
Microbiology
Blood cultures x 2 before antibiotics if no delay
Useful in shock and immunocompromise
Do not delay antibiotics in shock
Procedural and operative readiness
Perioperative labs
Coagulation studies for operative planning
INR elevation in liver disease
Anticoagulant effect recognition
Type and screen
Transfusion planning
Massive transfusion readiness if hemorrhage concern
Pregnancy test in patients with pregnancy potential
Ectopic rupture exclusion
Imaging and medication planning
Targeted labs by suspected source
Source-specific tests
Lipase for pancreatitis mimic
Mild elevation non-specific
Marked elevation supports pancreatitis
Urinalysis for urinary mimic
Pyuria suggests UTI
Hematuria suggests stone
Serum ketones if ketoacidosis concern
Abdominal pain mimic
Shock mimic
Diagnostic Tests
Scoring Systems
Risk stratification tools
qSOFA
Respiratory rate >= 22 per minute
Altered mentation
Systolic blood pressure <= 100 mmHg
Score >= 2 suggests higher mortality risk
SOFA score framework
Respiratory dysfunction
Coagulation dysfunction
Liver dysfunction
Cardiovascular dysfunction
CNS dysfunction
Renal dysfunction
Mannheim Peritonitis Index
Age > 50 years
Organ failure
Malignancy
Preoperative duration > 24 hours
Origin of sepsis not colonic
Diffuse generalized peritonitis
Exudate type
MRI
Limited role
Indications
CT contraindication and stable patient
Pregnancy with unresolved diagnosis after US
Constraints
Time delay in unstable patient
Limited availability in emergency setting
Findings
Free fluid
Inflammatory changes
Abscess localization
CT
CT abdomen and pelvis
Default imaging in stable suspected perforation
IV contrast preferred for source localization
Oral contrast rarely needed in ED workflow
Key CT findings
Extraluminal free air
Free fluid
Focal bowel wall defect
Localized fat stranding
Abscess
Contrast considerations
Severe allergy history
Alternative regimen selection
Noncontrast CT limitations acknowledgment
Renal dysfunction
Risk-benefit in suspected perforation
Resuscitation and nephroprotection strategy
CT performance notes
High sensitivity for pneumoperitoneum in modern multidetector CT (ACEP Level C, expert consensus)
Retroperitoneal perforation may show subtle air tracking (ACEP Level C, expert consensus)
Ultrasound
Point-of-care ultrasound roles
Shock evaluation
IVC size and collapsibility
Cardiac function estimate
Pericardial effusion exclusion
Abdominal applications
Free intraperitoneal fluid detection
Biliary source assessment
Appendicitis pathway in pediatrics and pregnancy
Limitations
Free air detection unreliable
Operator dependence
Obesity and bowel gas limitations
Plain radiography adjuncts
Upright chest radiograph
Subdiaphragmatic free air detection
Low sensitivity with small perforations
Left lateral decubitus abdomen radiograph
Alternative when unable to stand
Lower yield than CT
Disposition
Level of care and consultation
Mandatory consultation
General surgery consult at suspicion
Peritonitis
Pneumoperitoneum on imaging
ICU consult triggers
Vasopressor requirement
Lactate >= 4 mmol/L
Persistent hypotension after fluids
Transfer triggers
No on-site surgical capability
Immediate transfer initiation after antibiotics
Hemodynamic stabilization before transport
Complex source control need
HPB or colorectal specialty need
ICU bed requirement
Admission criteria
Admit indications
Any suspected perforated viscus
Operative evaluation pathway
Serial exams pathway if contained and stable
Contained perforation with nonoperative plan
IV antibiotics
Serial abdominal exams
Repeat imaging strategy if worsening
Discharge criteria
Rare ED discharge scenarios
No perforation on CT with alternative diagnosis
Reliable follow-up
Pain controlled
Microperforation treated as outpatient per surgery plan
Hemodynamic stability
No peritoneal signs
Tolerating oral intake
Clear return precautions
Treatment
Supportive care bundle
Core measures
NPO status
Aspiration reduction
Operative readiness
IV access
Two large-bore peripheral IV lines
Central venous access if vasopressors needed (Class I, expert consensus)
Gastric decompression
NG tube for persistent vomiting or obstruction concern
Avoid routine NG if no vomiting and no obstruction concern
Analgesia strategy
Opioid titration to comfort
Avoid NSAIDs in suspected ulcer perforation
Antiemetic strategy
Ondansetron or alternative
QT risk awareness
Fluids and vasopressors
Resuscitation hemodynamics
Crystalloid
Balanced crystalloid preferred in sepsis (Class IIa, expert consensus)
Initial bolus 500-1000 mL with reassessment
30 mL/kg reference strategy in shock (Class I, sepsis consensus)
Vasopressor escalation
Norepinephrine infusion as first-line (Class I, sepsis consensus)
Initiate 0.05-0.1 mcg/kg/min
Titrate every 2-5 minutes to MAP >= 65 mmHg
Typical range 0.05-1 mcg/kg/min
Peripheral administration acceptable short term with proximal IV and monitoring (Class IIa, expert consensus)
Frequent site checks for extravasation
Transition to central access when feasible
Vasopressin adjunct
Add if escalating norepinephrine (Class IIa, sepsis consensus)
0.03 units/min fixed dose
Not titrated
Epinephrine adjunct
Add if refractory shock (Class IIb, sepsis consensus)
Initiate 0.02-0.05 mcg/kg/min
Titrate to MAP target
Antibiotics
Empiric intra-abdominal coverage
Timing
Within 1 hour in septic shock (Class I, sepsis consensus)
Within 3 hours in sepsis without shock (Class I, sepsis consensus)
Community-acquired high-risk or severe infection
Piperacillin-tazobactam 4.5 g IV every 6 hours
Renal dose adjustment when eGFR reduced
Extended infusion strategy per local protocol
Cefepime 2 g IV every 8 hours
Add metronidazole 500 mg IV every 8 hours
Neurotoxicity risk in renal dysfunction
Meropenem 1 g IV every 8 hours
Reserve for ESBL risk or severe healthcare exposure
Renal dose adjustment required
Community-acquired lower-risk and stable
Ceftriaxone 2 g IV daily
Add metronidazole 500 mg IV every 8 hours
Suitable for many perforated appendicitis or diverticulitis cases
Ertapenem 1 g IV daily
Option for mixed flora coverage without Pseudomonas coverage
MRSA coverage indications
Prior MRSA colonization or infection
Severe healthcare-associated exposure
Abdominal wall mesh infection concern
Vancomycin IV weight-based dosing per local protocol
Loading 20-25 mg/kg actual body weight in shock
Maintenance guided by levels and renal function
Antifungal coverage indications
Upper GI perforation with severe illness
Recent abdominal surgery or anastomotic leak
Immunocompromised
Fluconazole 800 mg IV load
Then 400 mg IV daily
Avoid if high azole resistance concern
Source control and operative pathway
Surgical management
Early surgery involvement (Class I, expert consensus)
Generalized peritonitis
Free perforation on imaging
Time-to-source-control priority (Class I, sepsis consensus)
As soon as feasible after stabilization
Do not delay for complete normalization of vitals
IR drainage pathway
Abscess without generalized peritonitis
Hemodynamic stability with contained process
Nonoperative pathway selection
Contained perforation on CT
No diffuse peritoneal signs
Close monitoring resources available
Adjunct medications
Stress ulcer and upper GI perforation adjuncts
Pantoprazole 80 mg IV bolus
Then 8 mg/hour infusion for high-risk bleeding concern
Alternative pantoprazole 40 mg IV every 12 hours if no bleed concern
Antiemetics
Ondansetron 4 mg IV
Repeat every 6-8 hours as needed
QT prolongation risk
Metoclopramide 10 mg IV
Avoid in obstruction suspicion
Extrapyramidal symptom risk
Analgesia
Fentanyl 25-50 mcg IV
Repeat every 5-10 minutes to effect
Lower histamine release profile
Hydromorphone 0.2-0.5 mg IV
Repeat every 10-15 minutes to effect
Caution in older adults
Morphine 2-4 mg IV
Repeat every 10-15 minutes to effect
Histamine and hypotension risk
Special Populations
Pregnancy
Physiologic and diagnostic considerations
Pregnancy test early in evaluation
Ectopic rupture mimic
Imaging pathway changes
Imaging selection
Ultrasound first-line for biliary and appendicitis pathways
MRI consideration when US nondiagnostic and stable
CT use when benefits outweigh fetal radiation risk in suspected perforation
Medication considerations
Antibiotic selection
Piperacillin-tazobactam generally acceptable
Avoid tetracyclines
Analgesia
Opioid short-term use acceptable when indicated
Avoid NSAIDs in later pregnancy
Obstetric coordination
OB consult with viable pregnancy and operative planning
Fetal monitoring planning
Delivery planning if near term
Geriatric
Atypical presentations
Minimal fever
Sepsis without hyperthermia
Hypothermia as severe marker
Blunted tenderness
Delayed peritoneal signs
Higher threshold for imaging
Resuscitation nuances
Fluid sensitivity
Smaller boluses with reassessment
Early vasopressor consideration
Medication sensitivity
Lower opioid dosing
Delirium risk reduction strategies
Pediatrics
Presentation considerations
Rapid progression risk
Perforated appendicitis common source
Dehydration and shock earlier onset
Exam limitations
Guarding less reliable
Referred pain patterns common
Imaging pathway
Ultrasound first-line for appendicitis
CT if nondiagnostic and high suspicion
Radiation minimization priority
Weight-based treatment
Antibiotics weight-based dosing per pediatric protocol
Broad gram-negative and anaerobe coverage
Early pharmacy involvement
Background
Epidemiology
Frequency patterns
Common causes in ED
Perforated appendicitis
Perforated diverticulitis
Perforated peptic ulcer
High mortality contexts
Delayed presentation
Diffuse feculent peritonitis
Immunocompromise
Risk distribution
NSAID exposure
Increased peptic ulcer complication risk
Older age amplification
Diverticular disease prevalence
Higher with age
Complicated disease subset at higher risk
Pathophysiology
Contamination biology
Chemical injury phase
Gastric acid and bile irritation
Early severe pain
Bacterial peritonitis phase
Polymicrobial flora with colonic sources
Anaerobe burden increases with distal source
Systemic inflammation phase
Capillary leak and hypovolemia
Vasoplegia in septic shock
Anatomic patterns
Intraperitoneal perforation
Free air under diaphragm
Generalized peritonitis risk
Retroperitoneal perforation
Subtle abdominal signs
Air tracking along psoas or retroperitoneum
Therapeutic Considerations
Core principles
Early antibiotics
Reduce bacteremia risk
Bridge to source control
Early source control (Class I, sepsis consensus)
Surgery or IR drainage
Delay increases organ failure risk
Resuscitation and organ support
Fluids to restore perfusion
Vasopressors for vasoplegia
Coverage rationale
Gram-negative coverage
Enterobacterales common
Pseudomonas risk with healthcare exposure
Anaerobe coverage
Bacteroides fragilis group common in colonic sources
Metronidazole or beta-lactam beta-lactamase inhibitor coverage
Enterococcus considerations
Higher risk in healthcare-associated infection
Broader agents cover when high-risk
Patient Discharge Instructions
Copy discharge instructions
Discharge guidance
Diagnosis explanation
Abdominal pain evaluation without evidence of perforation on current testing
Risk of evolution despite reassuring tests
Return to ED now
Worsening abdominal pain
New rigid abdomen
Persistent vomiting
Fever
Fainting or severe weakness
Confusion
New shortness of breath
Home care
Clear fluids as tolerated if nausea improving
Avoid NSAIDs if ulcer concern
Follow-up
Primary care or surgical clinic within 24-72 hours if symptoms persist
Earlier follow-up if worsening trajectory
Medication safety
Opioid precautions if prescribed
No driving after sedating medications
References
Guidelines and evidence
Professional society and consensus sources
Surviving Sepsis Campaign guidelines for initial resuscitation and vasopressors
MAP target 65 mmHg framework
Early antibiotics and source control emphasis
IDSA and SIS guidance on complicated intra-abdominal infection antibiotics
Empiric gram-negative and anaerobe coverage principles
Risk-stratified broadened therapy principles
Diagnostic imaging references
Radiology practice standards for CT evaluation of pneumoperitoneum
CT superiority over radiography for small free air
Retroperitoneal air recognition patterns
Coding standards
ICD-10 K63.1 perforation of intestine
Mechanical perforation coding context
Source-specific coding often preferred
SNOMED CT perforation of intestine concept
Structured problem list interoperability
Mapping for clinical decision support
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.