Fluid Overload

Fluid overload is an excess of total body water and sodium, expressed as expanded extracellular fluid volume, producing oedema, effusions and, when severe, pulmonary oedema. It is usually due to a failure of sodium and water excretion (heart failure, kidney failure, nephrotic syndrome, cirrhosis) or to excessive intravenous administration.

The pathophysiology is renal sodium retention: in heart failure and cirrhosis, a fall in effective arterial volume activates the sympathetic nervous system, renin-angiotensin-aldosterone axis and vasopressin; in kidney disease, there is a reduced filtered sodium load or intrinsic tubular sodium avidity; in nephrotic syndrome, primary tubular sodium retention contributes.

Fluid overload of 10% or more of body weight in critically ill patients is associated with higher mortality, prolonged ventilation and impaired kidney recovery. Percentage overload is calculated as (current weight minus admission weight) divided by admission weight, multiplied by 100.

• Weight gain of 2 kg or more in 3 days, pitting oedema, ascites, pleural effusions
• Elevated JVP, hepatojugular reflux, third heart sound
• Bibasal crackles, orthopnoea, paroxysmal nocturnal dyspnoea, hypoxia
• Hypertension; hyponatraemia (dilutional)
• Weight and chest radiograph changes: Kerley B lines, bat wing pattern, cardiomegaly
• Bowel wall oedema, hepatic congestion, intra-abdominal hypertension

Red flags: respiratory rate above 30 breaths/min, oxygen saturation below 90%, frothy sputum, systolic blood pressure below 90 mmHg with congestion (cardiogenic shock), intra-abdominal pressure above 12 mmHg, oliguria, potassium above 6.0 mmol/L in anuric patients.

• Bedside: daily weights, fluid balance chart, JVP, lung ultrasound (B-lines, 3 or more B-lines in each of 2 or more zones on each side), inferior vena cava ultrasound (diameter above 2.1 cm with less than 50% collapse)
• Natriuretic peptides: BNP above 100 pg/mL or NT-proBNP above 300 pg/mL suggests heart failure (higher thresholds in kidney disease and older adults: NT-proBNP above 1000 pg/mL)
• Creatinine, urea, electrolytes, albumin, urinary protein:creatinine ratio, liver tests
• Echocardiography for ventricular function and valves
• Chest radiograph
• Differentiate cause: low albumin and heavy proteinuria (nephrotic), portal hypertension and ascites (cirrhosis), cardiac dysfunction, kidney failure, iatrogenic (positive balance in intravenous charts)

Differentials: pneumonia, pulmonary embolism, chronic venous insufficiency, lymphoedema, drug induced oedema (amlodipine, pioglitazone, NSAIDs, minoxidil) and capillary leak.

Emergency: acute pulmonary oedema

• Sit upright, high flow oxygen to keep saturations 94% to 98%; continuous positive airway pressure 5 to 10 cmH2O for respiratory distress.
• Furosemide 40 to 80 mg intravenously (80 to 200 mg if eGFR is below 30 mL/min/1.73 m2 or previously on diuretics); repeat or double after 2 hours if output is below 100 mL/h. Infuse at no more than 4 mg/min to avoid ototoxicity at high doses.
• Glyceryl trinitrate infusion 10 to 200 microg/min titrated to keep systolic pressure above 100 mmHg, or sublingual 400 to 800 microg.
• Avoid routine opioids.
• Cardiogenic shock: dobutamine 2.5 to 10 microg/kg/min and urgent senior assessment.

Chronic management

• Sodium restriction below 2 g daily; fluid restriction of 1 to 1.5 L daily when hyponatraemic (sodium below 125 mmol/L).
• Loop diuretic oral furosemide 40 to 120 mg daily (bumetanide 1 to 4 mg; torasemide 20 to 100 mg), divided twice daily with intravenous use when gut oedema limits absorption.
• Add sequential nephron blockade for resistance: metolazone 2.5 to 10 mg daily, hydrochlorothiazide 25 to 50 mg, or acetazolamide 250 to 500 mg intravenously; monitor sodium and potassium daily.
• Target weight loss 0.5 to 1 kg daily (do not exceed 1 kg daily).
• Add spironolactone 25 to 100 mg daily (up to 400 mg daily in cirrhosis) and consider SGLT2 inhibitor in heart failure and chronic kidney disease.
• Stop contributing drugs and review intravenous fluid prescription.

Specialist: renal replacement therapy

• Ultrafiltration or haemodialysis for fluid overload unresponsive to maximal diuretics (furosemide 200 mg intravenous bolus or infusion 20 to 40 mg/h), anuria, severe hyperkalaemia or pulmonary oedema with kidney failure. Net ultrafiltration rate no more than 10 to 13 mL/kg/h.

Monitoring. Hourly urine output, daily weight, electrolytes and creatinine every 12 hours during diuresis; stop or reduce when creatinine rises more than 30% above baseline with signs of hypovolaemia.

Special groups. In the critically ill, aim for a negative balance only after shock resolves. Children: furosemide 1 mg/kg intravenously, maximum 40 mg in a single dose.