Intra-Abdominal Infection & Peritonitis — SAQ

Stem

A 56-year-old man with known alcohol-related cirrhosis (Child-Pugh B) and ascites is brought to the emergency department by his family with 24 hours of increasing drowsiness and a single rigour. On examination he is jaundiced, has palmar erythema and spider naevi, temperature 38.6 degrees C, pulse 102, BP 100/60, GCS 14 (E4V4M6). Abdomen is soft with a fluid thrill and mild diffuse tenderness; bowel sounds are normal. He has no rebound or guarding. Bloods: WBC 14.8 (neutrophilia), bilirubin 96 micromol per L, INR 1.7, creatinine 110 micromol per L, sodium 128 mmol per L, ascitic total protein 0.9 g per dL. ^[2]

Questions

a) State the single most important bedside investigation, the diagnostic threshold, and the diagnosis. (3 marks)

The key investigation is a diagnostic ascitic tap (paracentesis) in the left iliac fossa, sending fluid for cell count and differential, Gram stain, culture (inoculated into blood-culture bottles at the bedside — positivity rises from 42 to 91 percent with this technique), protein, albumin, glucose, LDH.^[4]

The diagnostic threshold for spontaneous bacterial peritonitis (SBP) is an ascitic neutrophil (PMN) count of over 250 cells per mm cubed (0.25 x 10 to the 9 per L) — regardless of culture result. Treatment must be started empirically before culture returns. ^[2]

In this clinical context (cirrhotic with ascites, fever, hepatic encephalopathy, low ascitic protein), the diagnosis is spontaneous bacterial peritonitis (SBP) — primary peritonitis. ^[2]

b) Give the definitive antibiotic and adjunctive therapy, with doses and rationale. (4 marks)

• IV cefotaxime 2 g every 6 hours (the dose tested in the prospective randomised multicentre trial, in which resolution was 77 to 79 percent and hospital survival 69 to 79 percent on about 9 days of therapy; modern practice shortens the course with ascitic monitoring) or ceftriaxone 2 g IV daily.^[2] This covers the typical SBP organisms (E. coli, Klebsiella, Streptococcus pneumoniae) which are monomicrobial Gram-negative aerobes or pneumococci. Anaerobic cover is not required for primary SBP. Adjust to culture sensitivities.
• IV albumin 1.5 g per kg at diagnosis and 1 g per kg on day 3 (the Sort 1999 NEJM regimen). Albumin expands the effective arterial volume, counteracts the splanchnic vasodilation that drives hepatorenal syndrome, and is proven to reduce renal impairment (33 to 10 percent), in-hospital mortality (29 to 10 percent) and 3-month mortality (41 to 22 percent).^[1]
• A repeat tap at 48 hours: if the ascitic PMN has not fallen substantially (to under half its baseline value), suspect secondary peritonitis (search for a perforation with CT) or a resistant organism (broaden antibiotics).
• He should be started on secondary SBP prophylaxis (norfloxacin 400 mg daily — one-year recurrence 68 percent without it versus 20 percent with it — or ciprofloxacin 500 mg daily) once the acute episode has been treated,^[3] and referred for liver transplantation evaluation (an episode of SBP is an indication for transplant assessment in a suitable candidate).

c) Two days into treatment his creatinine rises to 230 micromol per L despite antibiotic response and a fluid challenge with albumin. Name the complication and outline its management. (3 marks)

The complication is hepatorenal syndrome - AKI (HRS-AKI) precipitated by SBP. Diagnostic criteria (International Club of Ascites): a rise in serum creatinine by over 0.3 mg per dL within 48 hours or by 50% from baseline in cirrhosis with ascites, AFTER excluding other causes and after a trial of albumin 1 g per kg per day (max 100 g) for 2 days. ^[2]

Management: ^[2]

• Continue albumin (it is part of both diagnosis and treatment).
• Add a vasoconstrictor: IV terlipressin (with glypressin) plus albumin, or noradrenaline infusion in ICU, to reverse splanchnic vasodilation.
• Avoid nephrotoxins (NSAIDs, aminoglycosides, contrast).
• Urgent liver transplant evaluation — definitive therapy for HRS-AKI in cirrhosis.

Model answer

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Diagnosis: Spontaneous bacterial peritonitis (SBP), the commonest life-threatening infection in cirrhosis, complicating roughly 10-30% of cirrhotics with ascites. ^[1]

Bedside test: Diagnostic ascitic tap — ascitic PMN over 250 cells per mm cubed. ^[1]

Antibiotic: IV cefotaxime 2 g every 6 hours (trial dose) or ceftriaxone 2 g daily, shortened with clinical and ascitic monitoring. ^[1]

Albumin: 1.5 g per kg at diagnosis, 1 g per kg day 3 (Sort 1999 NEJM) — reduces renal impairment 33 to 10 percent, in-hospital mortality 29 to 10 percent, 3-month mortality 41 to 22 percent. ^[1]

Prophylaxis: Norfloxacin 400 mg daily indefinitely; liver transplant referral. ^[1]

Complication: HRS-AKI — treat with albumin plus terlipressin (or noradrenaline), avoid nephrotoxins, transplant evaluation. ^[1]

Common errors

• Not doing a diagnostic tap in every cirrhotic with ascites who is admitted or decompensates. ^[1]
• Waiting for ascitic culture to start treatment (must treat on PMN count alone).
• Forgetting albumin (the single most common error — and the one that costs lives via HRS).
• Using oral quinolones alone to treat established SBP (inadequate ascitic levels; they are for prophylaxis).
• Adding anaerobic cover to SBP treatment (anaerobes suggest secondary peritonitis — search for a perforation).
• Treating a cirrhotic with ascites and a polymicrobial culture as SBP (it is secondary peritonitis and needs source control).

Examiner notes

A core SAQ that rewards three things: (1) recognising SBP as a MEDICAL peritonitis in a cirrhotic (not surgical); (2) reproducing the cefotaxime + albumin regimen precisely with doses; and (3) naming HRS-AKI as the feared complication and its mechanism (splanchnic vasodilation -> effective arterial underfilling -> renal vasoconstriction). The discriminating details are the albumin doses (1.5 g per kg day 1, 1 g per kg day 3), the criteria for HRS-AKI diagnosis, and the recognition that an SBP episode mandates liver transplant referral. ^[1]

References4ShowHide

1. [1]Sort P, Navasa M, Arroyo V, et al. Effect of intravenous albumin on renal impairment and mortality in patients with cirrhosis and spontaneous bacterial peritonitis N Engl J Med, 1999.PMID 10432325
2. [2]Rimola A, Salmerón JM, Clemente G, et al. Two different dosages of cefotaxime in the treatment of spontaneous bacterial peritonitis in cirrhosis: results of a prospective, randomized, multicenter study Hepatology, 1995.PMID 7875666
3. [3]Ginés P, Rimola A, Planas R, et al. Norfloxacin prevents spontaneous bacterial peritonitis recurrence in cirrhosis Hepatology, 1990.PMID 2210673
4. [4]Runyon BA, Umland ET, Merlin T Inoculation of blood culture bottles with ascitic fluid J Clin Microbiol, 1987.PMID 3541825