Oxford Handbook of Critical Care (3 edn)
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Diuretics
Types
Loop diuretics, e.g. furosemide, bumetanide.
Osmotic diuretics, e.g. mannitol.
Thiazides, e.g. metolazone.
Potassium‐sparing diuretics, e.g. amiloride, spironolactone, potassium canrenoate.
Uses
To increase urine volume.
Control of chronic oedema (thiazides, loop diuretics).
Control of hypertension (thiazides).
To promote renal excretion (e.g. forced diuresis, hypercalcaemia).
Routes
IV (mannitol, furosemide, bumetanide, potassium canrenoate).
PO (metolazone, furosemide, bumetanide, amiloride, spironolactone).
Modes of action
Osmotic diuretics—reduce distal tubular water reabsorption.
Thiazides—inhibit distal tubular Na+ loss and carbonic anhydrase, and increase Na+ and K+ exchange. This reduces the supply of H+ ions for exchange with Na+ ions, producing an alkaline natriuresis with potassium loss.
Loop diuretics—inhibit Na+ and Cl− reabsorption in the ascending loop of Henlé.
Potassium‐sparing diuretics—inhibit distal tubular Na+ and K+ exchange.
Side effects
Hypovolaemia.
Hyponatraemia or hypernatraemia.
Hypokalaemia.
Hyperkalaemia with potassium‐sparing diuretics.
Oedema formation (mannitol).
Reduced catecholamine effect (thiazides).
Hyperglycaemia (thiazides).
Metabolic alkalosis (loop diuretics).
Hypomagnesaemia (loop diuretics).
Pancreatitis (furosemide).
Notes
It is important to correct pre‐renal causes of oliguria before resorting to diuretic use.
Diuretics do not prevent renal failure, but may convert oliguric to polyuric renal failure.
If there is inadequate glomerular filtration, mannitol is retained and passes to the extracellular fluid to promote oedema formation.
Potassium‐sparing diuretics should be avoided with ACE inhibitors as there is an increased risk of hyperkalaemia.
Drug dosages
| Oral | IV | Infusion | |
|---|---|---|---|
Mannitol | 100g over 20min 6‐hourly | ||
Metolazone | 5–10mg od | ||
Furosemide | 20–40mg 6–24 hourly | 5–80mg 6–24 hourly | 1–10mg/h |
Bumetanide | 0.5–1mg 6‐24 hourly | 0.5–2mg 6–24 hourly | 1–5mg/h |
Amiloride | 5–10mg 12–24 hourly | ||
Spironolactone | 100–400mg od | ||
K+ canrenoate | 200–400mg od |
| Oral | IV | Infusion | |
|---|---|---|---|
Mannitol | 100g over 20min 6‐hourly | ||
Metolazone | 5–10mg od | ||
Furosemide | 20–40mg 6–24 hourly | 5–80mg 6–24 hourly | 1–10mg/h |
Bumetanide | 0.5–1mg 6‐24 hourly | 0.5–2mg 6–24 hourly | 1–5mg/h |
Amiloride | 5–10mg 12–24 hourly | ||
Spironolactone | 100–400mg od | ||
K+ canrenoate | 200–400mg od |
See also:
Dopamine
The effects of dopamine are dependent on the dose infused. Dopamine was used widely at low doses in an attempt to secure preferential DA1 stimulation and increase renal perfusion. However, a large, multicentre, randomised, controlled study comparing ‘renal dose’ dopamine and diuretics showed no difference in the incidence of renal failure. The previous widespread use of low dose dopamine (<3mcg/kg/min) has thus diminished considerably. Higher doses increase cardiac contractility via B1 stimulation and produce vasoconstriction via α stimulation. Where vasoconstriction is inappropriate, this will reduce renal perfusion. However, there is evidence of natriuresis and diuresis by enhanced Na+ transport in the ascending loop of Henlé. This effect is similar to that of a loop diuretic. In addition to the renal effects of DA1 stimulation, there may be preferential perfusion of the splanchnic bed though any benefits to patients have yet to be shown.
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