PERITONITIS

✓ Medically ReviewedDISEASEID: MDBT0120🚨 TRIAGE: EMERGENCYICD-10: K65.9

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Definition

CLINICAL DEFINITION

Peritonitis is acute inflammation of the peritoneum (membrane lining the belly cavity). It most often results from bacterial contamination (germ entry) or translocation (movement across gut wall). It causes diffuse belly pain with guarding (tensing when touched). It often progresses to rigidity (board-like stiffness) with fever and sepsis (life-threatening response to infection).

IN PLAIN ENGLISH

Belly lining gets infected or irritated. It causes severe belly pain and tenderness. The belly often feels hard and hurts to touch. It needs emergency hospital care.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Peritonitis is not simple gastroenteritis (stomach bug) or mild indigestion alone. It is not isolated ascites (fluid in belly) without inflammation (redness and swelling). It is not chronic peritoneal thickening (scarring) without acute infection.

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Word Breakdown

peri-

=around

tone-

=stretch, referring to peritoneum (membrane lining the belly cavity)

-itis

=inflammation

Literal Meaning: inflammation of the stretched membrane around organs

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Abbreviations

SBP=Spontaneous bacterial peritonitis - infection of belly fluid without gut hole

PD=Peritoneal dialysis - dialysis through the belly lining

MPI=Mannheim Peritonitis Index - risk score for leak-related infection

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Synonyms & Variants

Acute peritonitis›Generalised peritonitis›Peritoneal inflammation›

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Category-Specific Context

Peritonitis is a Disease because it is a clinical syndrome (group of linked signs) with many causes. It ranges from spontaneous infection (without hole) to secondary infection (from gut leak). It often leads to sepsis (severe infection response) with organ failure (organs stop working). Care targets the cause with vital function support.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentIntensive Care UnitGeneral Surgery WardGastroenterology and Hepatology ServicePeritoneal Dialysis Unit

USAGE & DOCUMENTATION NOTES

Use peritonitis for diffuse lining irritation with peritonism (signs of irritation). Specify type when known, such as spontaneous or secondary or dialysis-related. Do not use for localised tenderness (sore spot) without systemic features (fever or fast heart rate). Document guarding (tensing) with rigidity (stiffness) and rebound (pain on release).

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Perforation (hole) or translocation (germ movement) seeds the sterile cavity (clean space). Bacteria trigger alarm proteins and immune cascade. Vessel widening with fluid escape causes third-spacing (fluid trapped outside vessels). Low blood volume with sepsis (severe infection response) follows. Without source control (stopping the leak), multiorgan failure (many organs failing) develops.

PRIMARY CAUSES

Perforated peptic ulcer (stomach hole)

Stomach hole spills acid and bacteria causing chemical injury then bacterial lining inflammation

Perforated appendicitis (burst appendix)

Dead appendix wall ruptures and releases bowel germs triggering diffuse infection

Diverticular perforation (colon pouch burst)

Colon pouch ruptures and spills faecal bacteria producing severe inflammation

Anastomotic leak after bowel surgery (failed join)

Failed surgical join leaks bowel contents seeding the cavity with mixed germs

Spontaneous bacterial peritonitis in cirrhosis (liver scarring)

Gut germs cross swollen wall into belly fluid without visible hole due to weak defence

Peritoneal dialysis-related infection (belly dialysis)

Touch contamination or catheter film introduces skin germs into fluid infecting the lining

Gallbladder perforation or ischaemic bowel with necrosis (dead wall)

Dead wall loses barrier function and lets bile with bowel germs invade the cavity

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Epidemiology

Prevalence:Peritonitis is common in emergency care worldwide. Spontaneous infection (without hole) is common in cirrhosis (liver scarring) with ascites (belly fluid). Secondary infection (leak-related) follows perforation (hole) and surgery. Dialysis-related cases occur in belly dialysis programs.

Age Group:Peritonitis occurs at any age from childhood to old age. Appendiceal burst peaks in children and young adults. Diverticular burst with cancer hole rises with age. Spontaneous belly fluid infection affects adults with cirrhosis (liver scarring).

Geographic Distribution:Peritonitis occurs worldwide without strict borders. Outcomes vary with access to surgery (operation) and intensive care (close support unit). Spontaneous belly fluid infection follows cirrhosis (liver scarring) prevalence. Dialysis-related infection follows home belly treatment use.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Perforated peptic ulcer (stomach hole)
Perforated appendicitis (burst appendix)
Diverticular perforation with faecal contamination (stool in cavity)
Mesenteric ischaemia with bowel necrosis (dead gut)
Ruptured ectopic pregnancy (pregnancy outside womb)
Anastomotic leak after bowel surgery (failed join)

URGENT EVALUATION TRIGGERS

Rigid abdomen with guarding and rebound tenderness
Hypotension with tachycardia or altered mental status
Fever with worsening abdominal pain
Absent bowel sounds with vomiting and swelling
Cloudy dialysis fluid or worsening belly fluid pain with fever

Contraindications & Precautions

SPECIAL PRECAUTIONS

Do not mask pain with painkillers without full assessment (exam)
Avoid delay for scans when belly irritation signs are clear
Use sterile method for needle drainage and filter treatment
Counsel home treatment patients on clean hands with prompt reporting

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Sepsis (life-threatening response to infection) with shock (persistent low pressure)
Low blood volume from fluid shift out of vessels
Intra-abdominal abscess (pocket of pus) with fistula (abnormal channel)
Adhesions (scar bands) with later bowel blockage
Multiorgan failure involving lungs, kidneys and circulation
Death

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Peritonism

Sounds similar and describes signs of lining irritation, but it is the clinical finding rather than the disease itself

Periostitis

Sounds similar due to peri prefix, but it is inflammation of bone covering, not belly lining

Parametritis

Confused with pelvic pain and fever, but it is infection around the womb, not diffuse belly lining infection

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Acute pancreatitis

Key Distinguishing Feature: Upper belly pain radiating to back with raised lipase and less diffuse stiffness, scan shows pancreas inflammation without free air

Acute cholecystitis

Key Distinguishing Feature: Right upper pain with pressed-breath tenderness and gallbladder wall changes, usually without diffuse rebound

Small bowel obstruction

Key Distinguishing Feature: Wave-like pain with swelling and high-pitched sounds early, scan shows transition point without diffuse contamination

Ruptured ectopic pregnancy

Key Distinguishing Feature: Lower belly pain with vaginal bleeding and positive pregnancy test, with blood rather than pus

Mesenteric ischaemia

Key Distinguishing Feature: Pain out of proportion to exam early, with acid build-up and vessel block on dye scan

Inflammatory bowel disease flare

Key Distinguishing Feature: Chronic diarrhoea and bleeding history with mucosal ulcers, without frank hole or free air in most cases

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Clinical Pearls

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Examine for persistent tensing with board-like hardness to flag surgical abdomen (needs operation). Do not wait for fever to act.

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Keep low threshold for needle sampling in cirrhosis (liver scarring) with belly fluid. Spontaneous infection (without hole) may show only fever or confusion.

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Treat cloudy belly dialysis fluid as peritonitis until proven otherwise. Send cell number with germ test promptly per local plan.

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Re-image early when infection persists after treatment as resistant germs or hidden pus may remain. Involve surgery with critical care and review antibiotics.

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Example Usage & SOAP

CLINICAL SENTENCE

""A 64-year-old man with sudden diffuse abdominal pain shows guarding and rigidity concerning for secondary peritonitis from perforation.""

IN A SOAP NOTE

S: Severe diffuse belly pain worse on movement with fever and vomiting, no prior episode. O: Temp 38.6C, BP 92/58, HR 118, RR 24, SpO2 94 percent on air, diffuse tenderness with guarding (tensing) and rigidity (board-like stiffness) plus rebound (pain on release) with absent bowel sounds (silent gut). A: Secondary peritonitis with sepsis (severe infection response) likely from perforated viscus (hole in gut). P: Resuscitate with fluids and oxygen, send blood cultures (germ tests) with lactate (shock marker), give broad-spectrum antibiotics (germ killers), urgent CT with surgical review for source control (stop the leak).

DIFFERENTIAL DIAGNOSIS CONTEXT

Diffuse pain with guarding (tensing) favours peritonitis with hole over pancreas or gallbladder disease. Diffuse hardness with rebound (pain on release) and free air (escaped gas) favours perforation (hole). Localised upper pain with raised lipase (pancreas enzyme) favours pancreatitis instead. Check rigidity (hardness) with scan and pregnancy test.

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Classifications & Scoring

GRADING SYSTEM

Mannheim Peritonitis Index

Operative risk score for secondary peritonitis that stratifies severity using clinical and operative factors to guide prognosis.

SCORING TOOL

SOFA score

Organ failure score tracking breathing, clotting, liver, circulation, brain and kidney function in sepsis with peritonitis.

SCORING TOOL

qSOFA

Bedside prompt for sepsis risk using mentation, breathing rate and blood pressure in suspected peritonitis with infection.

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Prognosis

SHORT-TERM OUTCOME

Short term risk is high without rapid treatment. Early antibiotics (germ killers) with source control (stopping the leak) improve survival. Delay increases severe infection with shock (very low blood pressure) and organ failure (organs stop working). Abnormal vitals and labs predict worse course.

LONG-TERM PROGNOSIS

Long term outcome follows cause and underlying health. Many recover fully after treated hole or appendix infection. Cirrhosis (liver scarring) with repeat episodes has poorer outlook. Scar bands may cause later blockage with chronic pain.

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References & Coding

ICD-10 DIAGNOSTIC CODE

K65.9

LITERATURE CITATIONS & GUIDELINES

[1]WHO ICD-10 K65 Peritonitis

[2]WSES Consensus on intra-abdominal infection

[3]EASL Guidance on cirrhosis with spontaneous bacterial peritonitis

[4]Harrison's Principles of Internal Medicine abdominal disorders

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.