Make a note of this topic for 5 marks in dnb final Anesthesia exam
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Abdominal Compartment Syndrome (ACS) - DNB Final Anesthesia (5 Marks)
Definition & Key Thresholds
| Term | Definition |
|---|---|
| IAP (normal) | 0-5 mmHg in healthy adults; 5-7 mmHg in critically ill |
| IAH | IAP ≥ 12 mmHg (sustained/repeated) |
| ACS | IAP > 20 mmHg + new organ dysfunction/failure |
| APP | Abdominal Perfusion Pressure = MAP - IAP (target > 60 mmHg) |
WSACS (World Society of Abdominal Compartment Syndrome) Grading of IAH:
- Grade I: 12-15 mmHg
- Grade II: 16-20 mmHg
- Grade III: 21-25 mmHg
- Grade IV: > 25 mmHg
Classification
Primary ACS - direct abdominal/pelvic injury or disease:
- Blunt/penetrating trauma, intra-abdominal hemorrhage, ruptured AAA, bowel obstruction, severe pancreatitis
Secondary ACS - no abdominal injury:
- Massive fluid resuscitation, sepsis, burns, capillary leak, ascites
Recurrent ACS - re-develops after surgical decompression
Etiology (4 Mechanisms)
- Diminished abdominal wall compliance - major trauma, burns, obesity, tight closures
- Increased intraluminal volume - ileus, gastroparesis, toxic megacolon, constipation
- Increased extraluminal volume - hemoperitoneum, ascites, severe pancreatitis, retroperitoneal hematoma
- Capillary leak / fluid resuscitation - massive transfusion, sepsis, damage control surgery
Pathophysiology - Organ System Effects
Cardiovascular: IAP compresses IVC -> reduced venous return -> decreased CO -> diaphragm displacement increases intrathoracic pressure -> reduced ventricular compliance
Pulmonary: Reduced tidal volume and FRC -> atelectasis, raised airway pressures -> hypoxemia + hypercarbia
Renal: Reduced renal arterial and venous flow -> reduced GFR; oliguria at IAP ~15 mmHg; anuria at IAP > 30 mmHg; RAAS activation worsens fluid retention
GI: Splanchnic hypoperfusion -> mucosal ischemia -> bacterial translocation -> hepatic hypoperfusion -> metabolic acidosis
Neurological: Reduced cerebral venous drainage -> raised ICP -> hypercapnia worsens cerebral blood flow
Diagnosis
Clinical: Tense, distended abdomen + hemodynamic/respiratory instability. Physical exam alone is unreliable - objective measurement is mandatory.
Gold standard - Bladder (intravesical) pressure measurement:
- Clamp Foley catheter aseptically
- Connect via 3-way stopcock, zero transducer at mid-axillary line at iliac crest
- Instill 25 mL sterile saline
- Measure at end-expiration, patient supine
- Trend every 6 hours in at-risk patients
Interpretation:
- < 5 mmHg: normal
- 10-15 mmHg: common post-abdominal surgery/obesity
-
25 mmHg: highly suggestive of ACS
Contraindications to bladder measurement: Bladder trauma, neurogenic bladder, BPH, pelvic hematoma, pelvic fractures
Imaging signs of IAH (not diagnostic, suggestive):
- Peritoneal-to-abdominal height ratio > 0.52
- Max AP:transverse abdominal diameter ratio > 0.8
- Bowel wall thickening, diaphragmatic elevation, IVC < 3 mm
Management
Non-surgical (Medical) - First line
| Category | Intervention |
|---|---|
| Intraluminal decompression | NGT decompression, rectal tube, endoscopy |
| Extraluminal decompression | Percutaneous drainage (ascites, hematoma) |
| Abdominal wall compliance | Adequate sedation + neuromuscular blockade, remove constrictive dressings, eschar release |
| Fluid optimization | Hypertonic saline/colloids, goal-directed fluid resuscitation, consider hemodialysis/ultrafiltration |
| Ventilation | Low tidal volume strategy |
| GI motility | Prokinetics, minimize enteral feeds |
Surgical - Emergent Laparotomy (decompressive)
Indication: Failure of multiple conservative measures, progressive organ dysfunction
Procedure:
- Emergent laparotomy with full-length midline fasciotomy
- Fascia left open ("open abdomen") - covered with negative pressure wound therapy (NPWT)
- Reassess in few days for fascial closure (mesh or primary)
Complications of open abdomen:
- Fistula formation
- Protein loss from peritoneal fluid
- Abdominal wall retraction + ventral hernia
- Wound infections
- Recurrent ACS in up to 20%
Prognosis & Prevention
- IAH is an independent predictor of mortality - higher grade = worse outcome
- Prolonged recovery: weeks-months of multi-organ failure, extended ventilation, dialysis
- Mortality is high if untreated or delayed
Prevention in ICU:
- Judicious fluid use; avoid significantly positive fluid balance
- Low tidal volume ventilation
- Intestinal prokinetics
- Regular IAP monitoring in all at-risk patients
High-Yield Exam Points (Quick Recall)
- ACS = IAP > 20 mmHg + organ dysfunction
- IAH = IAP ≥ 12 mmHg
- Normal IAP = 0-5 mmHg; critically ill = 5-7 mmHg
- Oliguria at 15 mmHg, anuria at > 30 mmHg
- Bladder pressure: 25 mL saline, end-expiration, supine, zeroed at iliac crest mid-axillary line
- WSACS established standardized guidelines in 2004
- Surgery: emergent laparotomy + open abdomen + NPWT
- Recurrent ACS occurs in up to 20% post-decompression
- Non-surgical specialists are less familiar with ACS than surgical specialists - high clinical suspicion is key
This note covers the full scope expected for a 5-mark answer in the DNB Final Anesthesia exam: definition, classification, pathophysiology with organ systems, diagnosis (bladder pressure technique), management algorithm (non-surgical to surgical), and complications. Reproduce it in a structured format in your exam for maximum marks.
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