Intra-abdominal abscess

Updated May 21, 2025

Background

Overview

Definition

Intra-abdominal abscesses are localized collections of pus within the abdominal cavity, often resulting from an intra-abdominal infection or a perforation of the gastrointestinal tract.

Pathophysiology

Intra-abdominal abscesses commonly occur as complications of intra-abdominal infections, such as diverticulitis (diverticular abscess), appendicitis (periappendiceal abscess), IBD, pelvic inflammatory disease (tubo-ovarian abscess), or following abdominal surgery, gastrointestinal tract perforation, or penetrating abdominal trauma. Abscesses confined to single organs or structures can also occur, such as in the liver (pyogenic or amebic), spleen, subphrenic area, or psoas muscle.

Disease course

Intra-abdominal abscesses often present with abdominal pain, fever, tachycardia, tachypnea, and leukocytosis. A palpable abdominal mass, peritoneal findings, ileus, and anorexia may also be present.

Guidelines

Key sources

The following summarized guidelines for the evaluation and management of intra-abdominal abscess are prepared by our editorial team based on guidelines from the American Gastroenterological Association (AGA 2024), the European Crohn's and Colitis Organisation (ECCO 2024), the Infectious Diseases Society of America (IDSA 2024), the Academy of Emergency Medicine and Care (AcEMC/SIFIPAC/SICUT/WSES/ACOI/SICG 2022), the Center for Disease Control (CDC 2021), ...

Classification and risk stratification

Risk assessment: as per IDSA 2024 guidelines, assess disease severity for risk stratification in patients with complicated intra-abdominal infections. Consider using the APACHE II as the preferred severity of illness score for risk stratification within 24 hours of hospital or ICU admission in adult patients with complicated intra-abdominal infection, if a severity of illness score is used.

APACHE II

Calculator

When to use

Age (years)

< 45

45-54

55-64

65-74

≥ 75

Rectal temperature (°C [°F])

< 30 [< 86]

30-31.9 [86-89.5]

32-33.9 [89.6-93.1]

34-35.9 [93.2-96.7]

36-38.4 [96.8-101.2]

38.5-38.9 [101.3-102.1]

39-40.9 [102.2-105.7]

≥ 41 [≥ 105.8]

Mean arterial pressure (mmHg)

≥ 160

130-159

110-129

70-109

50-69

< 50

Arterial pH

≥ 7.7

7.6-7.69

7.5-7.59

7.33-7.49

7.25-7.32

7.15-7.24

< 7.15

Heart rate (bpm)

≥ 180

140-179

110-139

70-109

55-69

40-54

< 40

Respiratory rate (rpm)

≥ 50

35-49

25-34

12-24

10-11

6-9

< 6

Serum sodium (mEq/L)

≥ 180

160-179

155-159

150-154

130-149

120-129

111-119

< 111

Serum potassium (mEq/L)

≥ 7.0

6.0-6.9

5.5-5.9

3.5-5.4

3.0-3.4

2.5-2.9

< 2.5

Serum creatinine (mg/dL)

≥ 3.5

2.0-3.4

1.5-1.9

0.6-1.4

< 0.6

Acute renal failure

Yes

Hematocrit (%)

≥ 60

50-59.9

46-49.9

30-45.9

20-29.9

< 20

White blood cell count (×10**3/mcL)

≥ 40

20-39.9

15-19.9

3-14.9

1-2.9

< 1

Glasgow Coma Scale (GCS)

Oxygenation (use PaO₂ if FiO₂ < 50% or non-intubated, otherwise use A-a gradient; mmHg)

PaO₂ > 70

PaO₂ 61-70

PaO₂ 55-60

PaO₂ < 55

A-a < 200

A-a 200-349

A-a 350-499

A-a ≥ 500

Setting

Nonoperative

Emergency surgery

Elective surgery

Severe organ failure (liver cirrhosis, congestive heart failure, chronic lung disease, chronic kidney disease on dialysis) or immunocompromise

Yes

Calculation

Please enter all the required inputs.

The Acute Physiology and Chronic Health Evaluation II (APACHE II) is a severity-of-disease classification system, specifically designed for critically ill patients admitted to the intensive care unit (ICU). It is a composite score that incorporates 12 physiological variables (including vital signs, arterial blood gas measurements, and serum biochemical parameters), age, and chronic health status. The score ranges from 0 to 71, with higher scores indicating a higher severity of illness and a higher risk of mortality. The APACHE II score is primarily used to predict ICU mortality, and it can also provide an estimate of ICU length of stay. It is a valuable tool for risk stratification, enabling clinicians to identify patients who may require more intensive monitoring and intervention, and facilitating communication about patient prognosis. However, the APACHE II score should not be used in isolation to guide clinical decision-making, as it does not account for all individual patient factors. It is also not applicable to pediatric patients or to patients admitted to the ICU after cardiac surgery, as it was not validated in these populations.

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Diagnostic investigations

Diagnostic imaging: as per IDSA 2024 guidelines, consider obtaining abdominal CT as the initial diagnostic imaging in non-pregnant adult and adolescent patients with suspected acute intra-abdominal abscess.

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Diagnostic procedures

Intra-abdominal culture: as per IDSA 2024 guidelines, consider obtaining intra-abdominal cultures to guide antimicrobial therapy in adult and pediatric patients with complicated intra-abdominal infections undergoing a procedure for source control.

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Specific circumstances

Pregnant patients: as per IDSA 2024 guidelines, consider obtaining ultrasound or MRI as the initial diagnostic imaging in pregnant patients with suspected acute intra-abdominal abscess.

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