 Just recently our ICU team was called to the wards to look at a 74-year-old gentleman with sudden shortness of breath and low peripheral saturation. He was known to suffer from hypertensive heart disease and now presented with acute pulmonary oedema. After giving oxygen over a non-rebreathing mask, he was administered furosemide (Lasix) intravenously and brought to the unit for non-invasive ventilation. Interestingly a discussion started on whether giving Lasix as a first line agent in the acute setting of pulmonary oedema is beneficial or not. A quick look into to current literature gave no clear answer and reading further into the topic revealed unusual properties of Lasix we hadn't been really aware of so far. We all use and love Lasix, but do we really know the drug? The Beginning of Lasix Furosemide (sometimes also called frusemide) was first developed by 'Farbwerke Hoechst AG' in Frankfurt am Main, Germany, a company that was founded back in the year 1863. Karl Stürm, Walter Siedel and Rüdi Weyer set the basis with the invention of N-substituted-3-Carboxy-6-Halo-Sulfanilamide, and it's derivates, one of them being furosemide. The researchers soon noticed its saluretic (sodium Na, potassium K and chloride Cl) and diuretic effect in almost equivalent proportions. As these substances did not cause any acidosis nor alkalosis, they suggested their future use for the treatment of oedema and hypertension.   The Naming of Furosemide Researchers soon noticed that the diuretic effect of furosemide lasted for about 6 hours... 'LAsts for SIX hours'... and therefore gave it the name: LASIX! What is Furosemide Furosemide is an organic anion from the group of loop diuretics (as are bumetanide and torasemide) and is sold under the brand name of Lasix©. Its indications are for the treatment of oedema due to heart or liver disease as well as kidney disease. It is also used for the treatment of mild or moderate hypertension. Furosemide has become one of the cornerstones in the treatment of heart failure.  How does it work? Furosemide can be applied by oral intake as a tablet or as an intravenous injection. Once in the bloodstream, it is predominantly bound to proteins (>90%). Loop diuretics do not undergo glomerular filtration. In fact, they pass the glomerulus and are actively secreted across proximal tubular cells by organic anion transporters and the multidrug resistance-associated protein 4 (area A). It is important to know that non-steroidal anti-inflammatory drugs (NSAID) and endogenous uremic anions compete with this loop diuretic secretion and can cause 'diuretic resistance'. Once loop diuretics have reached the tubular system, they bind to sodium-potassium-chloride co-transporters (NKCC2) in the ascending limb of the loop of Henle and block the reabsorption of these ions directly (area B). Further down at the macula densa they inhibit the same co-transporter (area B) thereby stimulating renin secretion and inhibiting tubuloglomerular feedback. This results in preserved glomerular filtration despite increased salt delivery to the macula densa. All this finally results in the loss of sodium, chloride and potassium and therefore loss of water.  Other Effects Furosemide also interacts with other sodium-potassium-chloride co-transporters (NKCC1) elsewhere in the body: - Blocking NKCC1 in the ear probably explains the ototoxicity of loop diuretics - Blocking NKCC1 in smooth muscle cells causes vasodilation - Blocking NKCC1 in the afferent arteriole and near the macula densa elevates renin secretion and the generation of angiotensin II These complex interactions on haemodynamics explain that the net response in each patient might be different. On the one hand, loop diuretics dilate blood vessels directly and increase the level of vasodilatory prostaglandins. On the other hand, some of these effects counteract each other making it difficult to predict which effect will finally predominate. Many studies have looked closer into the vasoactive properties of furosemide. Current evidence indicates that it has a systemic venodilator effect which actually reduced preload acutely. The same investigators found a reduction in the right atrial pressure and the pulmonary capillary wedge pressure, presumably reflecting the systemic venodilator effect of furosemide. While the acute venodilator effect may be beneficial to the failing heart, its action on arteries might be detrimental. Several studies have shown that in patients with chronic heart failure furosemide causes arterial vasoconstriction. Also, there is one study showing that pulmonary vascular resistance in healthy volunteers rose significantly. Francis GS et al. described how the administration of furosemide actually led to decreased LV function, increased LV filling pressures, increases in MAP, SVR, plasma renin activity, and plasma noradrenaline levels. Beneficial venodilator response predominates over arterial vasoconstriction in patients with (1) myocardial infarction and (2) salt depleted volunteers. Venous relaxant effect has not been demonstrated in patients with chronic heart failure. In this setting detrimental arterial vasoconstriction seems to predominate. Pardeep S et al. Br J Clin Pharmacol. 2000 Jul; 50(1): 9–13. Francis GS et al. Ann Int Med 1985; 103(1): 1-6. Pharmacological Properties Administered furosemide orally has a limited and highly variable bioavailability. The diuretic effect starts within the first hour, and the duration of action is around 6 hours (4-8 hours). Injected furosemide intravenously is approximately twice as potent on a per-milligramme basis as oral doses. In acute decompensated heart failure sodium retention becomes more avid and higher peak levels might be required to become more effective. This can be achieved by giving furosemide intravenously. Once a loop diuretic is administered, the excretion of sodium chloride is increased for several hours. This is then followed by a period of very low sodium excretion resulting in a so-called 'post-diuretic retention'. How to use Furosemide for Acute Decompensated Heart Failure (ADHF) So far for the basics of furosemide, but what about its usage for acutely decompensated heart failure? Should furosemide be given as soon as possible or not? The 2013 ACCF/AHA guidelines for the management of patients with heart failure give diuretics a class I recommendation. The evidence behind these recommendations though is level B or level C only! So these recommendations are not really helpful to answer this question. The authors in UpToDate® mention diuretics directly after the use of oxygen. For patients with evidence of volume overload their recommendation is to give loop diuretics immediately (Grade 1B) as there is evidence that in this setting this may improve outcomes. They also suggest that patients with ADHF usually are volume overloaded, therefore indicating that most patients should receive diuretics ASAP. The only exception they mention where some delay in inducing diuresis might be required is in patients with severe hypotension or cardiogenic shock. There is reasonable doubt that patients with ADHF are usually volume overloaded, as suggested by UpToDate®. Zile MR et al. demonstrated that while most patients with acute pulmonary oedema have increased filling pressures, most did not have significant increases from their dry weight on presentation! Fallick et al. actually argue that it isn't fluid gain but rather shift in fluids from other compartments, mainly shift from the splanchnic circulation, which usually is very compliant. And as mentioned above, there is evidence that giving a straight shot of furosemide might actually influence haemodynamics negatively in different ways (decreased LV function, increased LV filling pressures, increases in MAP, SVR, plasma renin activity and plasma noradrenaline levels). In conclusion there is no straight forward answer to this question, but I would put it down as follows:  - Furosemide should not be routinely used for the immediate treatment of acute decompensated heart failure (ADHF)/ acute pulmonary oedema - However, in patients with evidence of volume overload the administration of early furosemide (preferentially given as an intravenous bolus) seems beneficial and improves outcome. But beware, most patients are not volume overloaded! - In urgent situations the focus should be on early non-invasive ventilation and the administration of nitroglycerin! David H et al. N Engl J Med 2017;377:1964-75. Wilson S et al., UpToDate.com 2018 WRITING COMMITTEE MEMBERS, Yancy CW, Jessup M, et al. 2013 ACCF/AHA guideline for the management of heart failure: a report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines. Circulation 2013; 128:e240. Zile MR, Bennett TD, St John Sutton M, et al. Circulation 2008 Sep 30;118(14):1433-41 Fallick C et al. Circ Heart Fail 2011; 4: 669-75.
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