A 57 yr old male with Type 2 Diabetes Mellitus presents to Emergency with an acute abdomen and signs of shock. CT scan reveals intra-abdominal fluid. At operation, faecal peritonitis is found. Following definitive surgery, the patient  is admitted  to the ICU. He is oliguric. Initial investigations reveal a blood urea of 24.2 mmol/L and a creatinine of 385 micromol/L. The rest of the plasma biochemistry was unremarkable.


a) List the possible causes of renal impairment in this patient?

b) What initial interventions, monitoring and investigations would you perform on admission of the patient to ICU

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College Answer


a) List the possible causes of renal impairment in this patient?

Pre-renal
Hypoperfusion due to hypovolemia, sepsis/vasodilation/Ileus 
Myocardial dysfunction/silent infarct in Diabetic

Renal

Pre-existing diabetic renal dysfunction
Possible drug toxicity eg metformin or contrast load

Post Renal
Obstruction
Surgical mal-adventure
Abdominal compartment syndrome

B) What initial interventions, monitoring and investigations would you perform on admission of the patient to ICU

Interventions 
Assess airway, breathing, circulation while receiving handover
Flush catheter
Assess for signs of hypovolaemia and fluid challenge prn
Stop all nephrotoxins
Check intra-abdominal pressure

Monitoring 
invasive blood pressure monitoring
Measure preload -CVP
Consider cardiac output monitoring/echocardiogram

Investigations 
CXR, ECG
Check gentamicin level if this has been administered ? CBC, coags and troponin, ELFT
Ultrasound kidneys (probably not if CT was done and no evidence obstruction)

Discussion

The first part of this question is a straightforward exercise in generating differentials.

Using a familiar framework, this list might resemble the following:

Vascular causes:

  • Renal artery/vein damage intraoperatively
  • Abdominal compartment syndrome causing decreased renal perfusion

Infectious causes:

  • Sepsis-associated kidney injury
  • Hypotension due to septic shock resulting in ATN

Drug-related causes:

  • Nephrotoxins, such as antibiotics or CT contrast

Traumatic causes:

  • Damage to the ureters or bladder perforation

If one wishes to increase the breath of one's differentials, one may peruse the tabulated causes of acute renal failure in the Required Reading section.

b) is a "discuss your investigations and management" question. Though it may not seem so from the model answer, I expect the college were looking for a structured response. Thus:

A) - secure airway and confrim ETT position

B) - ensure ventilation supports adequate respiratory compensation for the metabolic acidosis, and adequate oxygenation to support normal organ function

- Ensure PEEP is adequate to sustain oxygenation in the face of increased intra-abdominal pressure, but not so high as to impair the venous return from the abdominal organs.

C) - Ensure adequate organ perfusion by the careful use of vasopressors and inotropes

D) - Protect the patient from hyperglycaemia with monitoring and the use of insulin;

- strongly consider using sedating agents which do not rely on renal clearance

E) - Correct electrolyte abnormalities and investigate for toxic drug levels eg. gentamicin

F) - Ensure optimal hydration and consider renal replacement therapy to clear toxic drugs and to correct uremia and acid-base status

- Investigate the integrity of the renal tract and renal vessel patency by ultrasound

G) - Consider the relevance of nutrition in this patient, and commence TPN if a prolonged ileus is anticipated

H) - Ensure a normal haemoglobin (70-90g/L)

I) - Tailor antibiotic dosing to decreased glomerular filtration, and avoid nephrotoxic agents.

A more generic approach to the oligoanuric patient is presented in the Required Reading section.

References

Mindell, Joseph A., and Glenn M. Chertow. "A practical approach to acute renal failure." Medical Clinics of North America 81.3 (1997): 731-748.

Sladen, Robert N. "Oliguria in the ICU: systematic approach to diagnosis and treatment." Anesthesiology Clinics of North America 18.4 (2000): 739-752.

Sanjay Subramanian, John A. Kellum, and Claudio Ronco "Oliguria" in: Critical Care Nephrology by Ronco, Bellomo and Kellum (2009) pp. 341