Wrong Answer: a. Fluid overload can be addressed with diuretics or RRT. Diuretics, especially loop diuretics are considered first line therapy for this patient, considering that the patient has still has some preserved urine output of 15-30 millilitres per hour. RRT can be commenced later if fluid balance is refractory to medical therapy (diuretics).

Wrong Answer: b. The optimal timing of RRT for AKI has yet to be discovered and clinical practice is very variable. There has been considerable debate on early versus late RRT in AKI. Several trials such as the ELAIN (2016), AKIKI (2016), IDEAL-ICU (2018), and STAART_AKI (2021) have compared early versus late RRT in AKI. The definitions of early versus late RRT used in these trials are enumerated below:

Right Answer: The renal prognosis can be determined by assessing the response to the furosemide stress test. The 'furosemide stress test' can improve the detection of worsening acute kidney injury (AKI).

Mechanism of action of furosemide and rationale for the furosemide stress test (FST):
Furosemide, a loop diuretic, is not efficiently removed by the glomerulus during filtration. Therefore, the concentration of furosemide in the tubules is not influenced by the rate at which the glomerulus filters substances. Furosemide is carried from the peritubular capillaries to the proximal tubule.
It subsequently enters the tubular lumen through active secretion via the proximal convoluted tubule's human organic anionic transporter system. Furosemide enters the thick ascending loop of Henle and blocks the luminal chloride transport, which reduces the reabsorption of sodium. This causes a rise in the excretion of sodium in the urine (natriuresis) and leads to an increase in urine flow.

Therefore, the fact that furosemide elicits a rapid increase in urine production suggests that the kidneys have a healthy blood flow, the ability to secrete substances in the proximal tubules, and the proper functioning of the thick ascending loop of Henle. This also implies that the kidneys have a good reserve of functional capacity in patients with acute kidney injury (AKI). Therefore, the rise in urine production following the injection of furosemide can be utilized to evaluate the effectiveness of tubular function in individuals experiencing early acute kidney injury (AKI).

Performing the FST:
Those who have not previously taken furosemide (furosemide-naïve) are administered a single dose of 1 mg/kg. In comparison, those who have previously taken furosemide (furosemide-exposed) are given a single dose of 1.5 mg/kg. If the urine output response in patients with stage 1 and 2 acute kidney injury (AKI) is less than 200 mL over the next 2 hours, there is a high risk of progressing to stage 3 AKI and a high likelihood of requiring renal replacement therapy (RRT).

Wrong Answer: d. Antibiotic dosing is not dependent on vasopressor requirement.

Wrong Answer: Tigecycline is mainly eliminated through bile (about 69%) and gut. Renal elimination is only 13%.[1]

Wrong Answer: Only about 20% of a moxifloxacin dose is excreted via the kidneys as unmetabolised moxifloxacin, major part is eliminated via biliary/faecal routes.[2]

Wrong Answer:Ceftriaxone is eliminated by both renal (33-67%) and hepatobiliary excretion. Generally, dose adjustment is not required for patients with renal dysfunction, unless they also have liver dysfunction or take doses exceeding 2 g/day.[3]

Right Answer:Pharmacokinetic data from twelve subjects with creatinine clearances ranging from 0 to 144 ml per min per 1.73 m2 suggest that cefazolin is cleared primarily by the glomerulus, with tubular and biliary secretion playing a secondary role.[4]

Wrong Answer: There is no correlation between doxycycline elimination and renal function, therefore extra-renal mechanisms of elimination become predominant in patients with renal dysfunction.[5]

Nephro-critical care pearls:

Antibiotics such as azithromycin, ceftriaxone, clindamycin, doxycycline, linezolid, metronidazole, moxifloxacin, nafcillin, oxacillin, rifampin, and tigecycline do not require dose adjustment in patients with severe renal disease.