5.2 Acute Abdomen, Septic Peritonitis & Canine Parvoviral Enteritis

Acute Abdomen, Septic Peritonitis & Canine Parvoviral Enteritis

The term acute abdomen describes sudden, severe abdominal pain or distension resulting from intra-abdominal pathology that frequently requires emergency medical or surgical intervention. Rapid triage, point-of-care abdominal ultrasonography (AFAST), and definitive peritoneal fluid analysis are essential to differentiate medical conditions (e.g., uncomplicated pancreatitis) from surgical catastrophes (e.g., gastrointestinal rupture with septic peritonitis).

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1. Triage & Diagnostic Approach to the Acute Abdomen

Clinical Manifestations of Abdominal Sepsis & Pain

• Physical Posturing: The classic "prayer position" (downward-dog / play-bow posture: thoracic limbs flat on the ground with hindquarters elevated) is adopted to shift visceral weight off the painful cranial abdomen and diaphragm.
• Abdominal Guarding: Rigid, board-like abdominal wall contraction upon palpation, vocalization, or reluctance to assume lateral recumbency.
• Perfusion Indicators of Sepsis: Early distributive/hyperdynamic septic shock manifests with hyperemic ("brick-red") mucous membranes, rapid CRT (<1.0 second), bounding pulses, and pyrexia; decompensated sepsis leads to pale/muddy mucous membranes, hypothermia, prolonged CRT, and profound hypotension.

Point-of-Care Ultrasonography: Abdominal FAST (AFAST)

AFAST rapidly screens for free peritoneal effusion across four standardized acoustic windows:

1. Diaphragmatico-Hepatic (DH) Window: Cranial midline, beneath xiphoid; evaluates gallbladder, liver lobes, and pericardium/pleural space.
2. Spleno-Renal (SR) Window: Left caudolateral flank; evaluates left kidney, spleen, and left gutter.
3. Cysto-Colic (CC) Window: Caudal ventral midline; evaluates urinary bladder, descending colon, and uterine/prostatic structures.
4. Hepato-Renal (HR) Window: Right caudolateral flank; evaluates right kidney, liver lobes, and right gutter.

Abdominal Fluid Score (AFS 0–4): Scores range from 0 (no fluid detected) to 4 (fluid present in all 4 quadrants), tracking the volume of effusion and response to therapy.

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2. Abdominocentesis & Fluid Analysis: Diagnostic Criteria for Septic Peritonitis

When free abdominal fluid is identified, abdominocentesis must be performed immediately using a 20G–22G needle, over-the-needle catheter, or ultrasound-guided aspiration. If effusion volume is minimal, Diagnostic Peritoneal Lavage (DPL) using 20 mL/kg of warm isotonic saline can be utilized.

[Abdominal Fluid Analysis Protocol]
                 │
      Fluid Collected via Abdominocentesis
                 │
    ┌────────────┴────────────┐
Cytology (Diff-Quik)       POC Biochemical Testing
    │                         │
Look for Intracellular     Compare Fluid vs. Peripheral Blood:
Bacteria in Neutrophils    • Glucose Gradient (Fluid < Blood by >20 mg/dL)
                           • Lactate Gradient (Fluid > Blood by >2.0 mmol/L)

The 3 Core Diagnostic Criteria for Septic Peritonitis

Common Etiologies of Septic Peritonitis

• Gastrointestinal Perforation: Linear or discrete foreign bodies, perforating gastroduodenal ulcers (associated with NSAIDs or corticosteroid administration), and GI neoplasia.
• Surgical Wound Dehiscence: Classically occurs 3 to 5 days post-operatively (during the lag phase of wound healing before significant fibroplasia and collagen synthesis occur).
• Ruptured Viscus: Ruptured pyometra, ruptured prostatic abscess, necrotizing cholecystitis, or penetrating bite wounds.

3. Pre-Operative Stabilization Prior to Emergent Laparotomy

While septic peritonitis is an absolute surgical emergency, a patient should never be taken directly to the operating theater in unresuscitated septic shock. Mortality is dramatically minimized by a rapid 1-to-2-hour stabilization period:

1. Hemodynamic Resuscitation: Administer balanced isotonic crystalloids (titrated boluses of 15–20 mL/kg) to restore intravascular volume, targeting a Mean Arterial Pressure (MAP) >65 mmHg, normalization of heart rate, and reduction in blood lactate. If hypotension refractory to volume occurs, initiate a vasopressor infusion (Norepinephrine 0.1–1.0 mcg/kg/min).
2. Broad-Spectrum 4-Quadrant Antimicrobial Therapy: Administer parenteral bactericidal antimicrobials immediately after fluid samples are collected for culture:
   • Option 1 (Gold Standard): Ampicillin-sulbactam (Unasyn) (30–50 mg/kg IV q8h) + Enrofloxacin (5–10 mg/kg IV q24h) or Marbofloxacin.
   • Option 2: Cefazolin (22–30 mg/kg IV q8h) + Enrofloxacin + Metronidazole (10 mg/kg IV q12h).
3. Multimodal Analgesia: Utilize pure $\mu$-opioid agonists (e.g., Methadone 0.2–0.4 mg/kg IV or Fentanyl CRI 2–5 mcg/kg/hr). NSAIDs are strictly contraindicated due to acute kidney injury risk, impaired mucosal perfusion, and gastrointestinal ulceration.

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4. Canine Parvoviral Enteritis: Pathophysiology & Barrier Collapse

Canine Parvovirus Type 2 (CPV-2) is a non-enveloped, extremely hardy single-stranded DNA virus with a strict predilection for rapidly dividing host tissues:

Primary Pathological Targets

1. Intestinal Crypt Epithelium: CPV-2 infects and lyses the germinal crypt cells of the small intestinal mucosa (jejunum and ileum). Because crypt cells are required to renew the villi, destruction of the crypts leads to massive villous blunting, atrophy, and collapse. This produces catastrophic malabsorption, protein loss, and severe hemorrhagic diarrhea.
2. Bone Marrow & Lymphoid Tissue: The virus invades hematopoietic progenitor cells in the bone marrow and lymphoid organs (thymus, spleen, lymph nodes), resulting in profound panleukopenia (characterized by severe neutropenia and lymphopenia).
3. Mucosal Barrier Breakdown & Sepsis: Denudation of the intestinal epithelial lining allows commensal enteric bacteria (e.g., Escherichia coli, Clostridium spp., Klebsiella) and endotoxins (LPS) to breach the lamina propria, translocating directly into the portal vein and bloodstream. This triggers systemic endotoxemia, bacteremia, septic shock, and Disseminated Intravascular Coagulation (DIC).

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5. Biosecurity, Isolation Protocols & Disinfection

Because CPV-2 is non-enveloped, it exhibits exceptional environmental stability and resistance to standard quaternary ammonium disinfectants and alcohols, persisting on surfaces for months to years.

• Isolation Protocols: Patients must be housed in a dedicated, negative-pressure isolation ward. Strict barrier nursing is mandatory: disposable gowns, nitrile gloves, dedicated shoe covers/booties, and separate medical equipment (thermometers, stethoscopes, Doppler).
• Effective Disinfectants:
  • Accelerated Hydrogen Peroxide (AHP) (e.g., Rescue/Prevail at 1:16 to 1:64 dilution, 5–10 minute contact time).
  • Potassium Peroxymonosulfate (e.g., Virkon-S 1% solution).
  • Sodium Hypochlorite (Household Bleach): 1:30 dilution with water, requiring a minimum of 10 minutes of active wet contact time on pre-cleaned surfaces.

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6. Inpatient Intensive Care & Early Enteral Nutrition (EEN)

Successful management of severe parvoviral enteritis requires comprehensive critical nursing interventions:

1. Fluid & Electrolyte Resuscitation

• Administer balanced crystalloids (Plasmalyte-A or Normosol-R) to match maintenance needs plus aggressive replacement of ongoing fluid losses from profuse vomiting and diarrhea.
• Potassium Supplementation: Supplement fluids with Potassium Chloride (KCl) (20–40 mEq/L) to prevent severe hypokalemic weakness and gastrointestinal ileus.
• Dextrose Supplementation: Add 2.5% to 5.0% Dextrose to IV fluids to counteract severe hypoglycemia caused by sepsis, depletion of glycogen stores, and high metabolic demand.

2. Antiemetic & Prokinetic Pharmacotherapy

• Maropitant (Cerenia): Neurokinin-1 ($NK_1$) receptor antagonist (1.0 mg/kg IV or SC q24h); provides visceral analgesia in addition to potent antiemetic control.
• Ondansetron: Serotonin $5\text{-HT}_3$ receptor antagonist (0.5 mg/kg IV q8h).
• Metoclopramide: $5\text{-HT}_4$ agonist and dopaminergic antagonist administered as a CRI at 1.0–2.0 mg/kg/24 hours to stimulate gastric emptying and upper intestinal motility once mechanical obstruction/intussusception is definitively ruled out.

3. Early Enteral Nutrition (EEN) via Nasogastric (NG) Tube

• Evidence-Based Paradigm Shift: Historical protocols mandating prolonged "NPO" (nothing by mouth) until vomiting ceases are obsolete and deleterious. Luminal nutrition is the sole energy source for enterocytes.
• Clinical Benefits of EEN: Placing an NG tube within 12 to 24 hours of admission for continuous trickle microenteral feeding (using liquid veterinary recovery diets) maintains mucosal tight junctions, stimulates mucosal blood flow, prevents villous atrophy, accelerates clinical recovery, and significantly reduces duration of hospitalization.

4. Antimicrobial Coverage

• Parenteral broad-spectrum bactericidal antibiotics (e.g., Ampicillin 22 mg/kg IV q8h combined with Enrofloxacin 5–10 mg/kg IV q24h [or Cefazolin + Aminoglycoside once rehydrated]) are administered to prevent systemic bacterial sepsis resulting from enteric translocation.