Furosemide is the most commonly used diuretic in critical care and is frequently used in the management of acute kidney injury (AKI). However, the benefits of furosemide administration in AKI has long been questioned and there are concerns over the possible harmful effects of furosemide including diuretic-induced AKI. To further evaluate the role of furosemide in management of AKI, let us consider a case.
A 3 year male neutered 15 kg Springer Spaniel presents to your hospital having been diagnosed with AKI. Initial blood work revealed severe azotemia (creatinine 7.92mg/dL [700 μmol/L], BUN 98 mg/dL [35 mmol/L]) and borderline hyperkalaemia (4.2 mmol/L). After 12 hours of fluid therapy at 4 ml/kg/hr repeat blood work reveals a worsening azotemia (creatinine 9.05mg/dL [800μmol/L]) and hyperkalemia 6 mmol/L. Urine output is 0.1 ml/kg/hr. The dog now weighs 17.25 kg, has chemosis, pleural and peritoneal fluid. Do you give furosemide, or do you recommend immediate hemodialysis?
You decide to give a single dose of 0.25 mg/kg furosemide and there was no further urine production over the next 2 hours. You then give a 1 mg/kg bolus and the dog produces 6 ml/kg/hr of urine. Over the next 12 hours the UOP increases to 10 ml/kg/hr and the creatinine has increased to 9.61mg/dL [850μmol/L]. What does this mean?
To answer these questions, we need to understand the pharmacology of furosemide.
Furosemide exerts its action by exclusively inhibiting the Na/K/2Cl (NKCC2) co-transporter on the luminal membrane of the thick ascending loop of Henle. In plasma, 98% of furosemide is protein bound. To reach the site of action protein bound furosemide is secreted from the plasma in to the lumen of the proximal tubules via an organic anion transporter (OAT1), where it is then delivered to its site of action in the thick ascending limb. The inhibition of this transporter and subsequent decrease in sodium and chloride resorption results in natriuresis and diuresis, dissipating the medullary osmotic gradient and concurrently causing a reduction in calcium and magnesium reabsorption (Figure 2). Increased distal delivery of sodium leads to sodium potassium exchange promoting kaliuresis. Na/K/CL transporters are not confined to the kidney, NKCC1 transporters are present in organs including the vasculature, respiratory tract and ear.
Back to the case
Despite fluid therapy the dog has a worsening azotemia, hyperkalemia and is oliguric. It also has signs of fluid overload demonstrated by a 15% weight gain, chemosis, pleural and peritoneal fluid (Claure-Del Granado & Mehta 2016). Fluid overload, oligo/anuria and hyperkalemia are all indicators for CRRT (Bellomo et al, 2009).
The question is should furosemide be administered initially, in place of hemodialysis?
The benefit of furosemide in management of AKI has long been questioned. Diuretics have been found to be a risk factor for AKI (Levi et al, 2012) and various studies have shown furosemide to either exhibit neutral or deleterious effects in AKI treatment (Gram et al 2011, Mehta et al 2002, Krzych et 2019). One such observational study looking at diuretic use in AKI (diagnosed by elevated serum creatinine only) found diuretic use to be associated with an increased risk of death and non-recovery of renal function (Mehta et al 2002). A more recent study using the Kidney Disease: Improving Global Outcomes (KDIGO) criteria for diagnosis of AKI (figure 3) showed furosemide administration to be associated with improved short-term survival and recovery of renal function in critically ill patients with AKI, particularly those with AKI UO stage 2-3 (Zhao et al 2020). Some studies suggest the use of furosemide in AKI can lead to a delay in the initiation of renal replacement therapy (RRT) and early RRT itself has been associated with improved recovery of renal function but also with increased risk of adverse events (Fayd et al 2018, Zarbock et al 2016). However, a more recent publication showed furosemide not to have a significant effect on the requirement for RRT or outcome (Krzych et al 2019).
AKI is commonly reported as an adverse effect of diuretic use and a worsening azotemia is not uncommonly seen post diuretic administration. However, this azotemia should not be automatically interpreted as true worsening of renal function. Whilst most creatinine undergoes glomerular filtration, some is actively secreted in to the proximal convoluted tubules via the same organic acid transporter as furosemide (OAT1). In patients with renal disease this secretion increases relative to glomerular filtration. Furosemide may compete with creatinine for this transporter and this can lead to a relative inconsequential increase in creatinine (Andreev et al 1999). Furthermore, creatinine is measured as a concentration in serum; an increase in serum creatinine concentration in combination with increase in hematocrit may purely indicate a reduction intravascular volume and effective decongestion; termed “pseudo-worsening renal function” rather than actual worsening of renal function (Bagshaw et al 2007).
Furosemide may compete with creatinine for the transporter (OAT1) and this can lead to a relative inconsequential increase in creatinine.(Andreev et al, 1999)
Furosemide also has proposed beneficial effects in the management of AKI including resolution of intra-renal congestion via renal vascular dilation and decrease in energy expenditure and oxygen consumption of tubular cells via inactivation of metabolically active NKCC2 transporters (Ho et al 2010). Furosemide has a particularly important role in the management of fluid overload associated with AKI as promotion of diuresis can result in a reduction in renal venous congestion (Joannidis et al 2017).
Furosemide has the potential to lead to significant diuresis in patients with AKI but high doses of frusemide (1-2 mg/kg) may be required to ensure furosemide reaches its site of action in the presence of significant tubular dysfunction. However, repeated doses may lead to significant increases in side effects, particularly ototoxicity. Therefore, repeated furosemide administration in patients with fluid overload who are not diuretic-responsive is not recommended. Hemodialysis is usually recommended in these cases (Joannidis et al 2017).
The diuresis associated with furosemide treatment in AKI is not a direct indication of beneficial effect of furosemide on renal function, instead it is an indicator of functional tubular cells (Ho et al 2010). Furosemide administration may therefore be a useful tool to predict the severity of AKI, commonly termed a furosemide stress test. One human study has shown that UOP < 200mls at 2 hours post administration of 1-1.5 mg/kg furosemide intravenously was associated with an increased risk of renal associated death (Chawla et al 2013).
Again..Back to the case
Furosemide administration was chosen in this case over immediate hemodialysis.
The dog produced a large volume of urine post furosemide administration and, thus, may be considered “furosemide responsive.” This response to furosemide may indicate less severe tubular dysfunction but this is not synonymous with full renal recovery. This dog still remains at increased risk of longstanding renal injury and death. Post furosemide administration the dog became markedly polyuric and the azotemia worsened. This worsening azotemia secondary to successful diuresis, is not unexpected. However, careful monitoring of blood pressure, hydration status, including body weight is important alongside monitoring and matching urinary output in all AKI patients and one should be extra vigilant when diuretics have been used as part of the case management.
The Bottom Line
Furosemide use has a role in management of oligo/anuric AKI and associated fluid overload and may be a useful tool to determine disease severity. However, inappropriate use of furosemide in a hypovolemic and dehydrated patient could contribute to worsening of the AKI.
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