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Clinical update no. 424 15 October 2015 From N Engl J Med: A 72-year-old man with long-standing heart failure and ischaemic heart disease is admitted to the hospital. Management has been a low-sodium diet, enalapril 2.5 mg bd, carvedilol 6.25 mg bd, hydrochlorothiazide 25 mg bd. He is 70kg, with a 2kg weight gain from a clinic visit the previous week. He has been more short of breath with a cough. Temp 38.3 C, BP 122/78, HR 78, RR 32. Examination findings are posterior rhales IV fluids are isotonic or hypotonic based on the Na and K concentration. Dextrose is metabolised and does not affect tonicity. on the right, with no wheeze or rhonchi. There Giving hypotonic maintenance IV fluids is is no peripheral oedema or visceromegally. associated with hyponatraemia. There are Na 133, K 3.3, Cl 94, pCO2 30, creatinine 145 (eGFR 42). CXR shows right lower lobe pneumonia and IV antibiotics are given. over 100 reports of iatrogenic deaths or permanent neurologic impairment from hyponatraemic encephalopathy. Acutely ill patients may have excess antidiuretic What is the best strategy for maintenance hormone (ADH; or AVP) which impairs intravenous fluids to support this patient? excretion of free water. Rapid volume expansion with 0.9% saline as compared with balanced electrolyte solutions Options given included: oral fluids, IV saline at may result in complications. 60 or 80 ml/hr, 0.45% saline, K replacement and changing the diuretic to spirinolactone. See the full text for details and other useful clinical scenarios on fluid replacement. The safest maintenance fluid is 5% dextrose in 0.9% saline at 100 - 120 ml/hr in adults. In children the calculation is 100 ml/kg/24 hours for the first 10 kg of body weight, plus The risk is for more severe hyponatraemia and fluid overload, with CCF and renal 50 ml/kg between 10-20kg, plus 20 ml/kg above 20 kg. impairment. Dosing adjustments for Hypotonic fluids should be administered only if antibiotics and other medications is required. there is a specific indication (such as renal Tachypnoea at rest with a risk of tiring makes H2O loss in diabetes insipidus), and they giving oral fluids unwise. IV fluid with 5% should be avoided if hyponatraemia is dextrose in a solution of 0.9% saline plus 20 present. In patients at risk for cerebral mmol KCL/litre at 60 ml/hr (75% oedema, Na should be kept at >140 mmol/kg. maintenance) would be appropriate. Avoid hypotonic fluids. Adjust for the volume given with IV medications. Risk of further renal Virtually all studies evaluating hospital- impairment and hyperkalaemia with the ACE acquired hyponatraemia have shown that it is inhibitor is a concern which could be related to giving hypotonic fluids. Hypotonic exacerbated by changing to a potassium fluids should not be given to children. sparing diuretic. Available at http://www.heti.nsw.gov.au/programs/emergency-medicine-training/emergencymedicine-training-test/educational-resources/em-clinical-updates/ Early symptoms of hyponatraemic rise in serum Na if given for hyponatraemia encephalopathy are headache, nausea, from SIADH, where the correct approach is vomiting, and generalized weakness, fluid restriction. progressing to seizures and pulmonary oedema which can be of abrupt onset. Chronic hyponatraemia can give subtle neurologic impairment with gait disturbances and falls. It can be difficult to correct with fluid restriction and isotonic fluids are relatively ineffective. Balanced Salt Solutions as Compared with 0.9% Saline 0.9% saline has a nonphysiological chloride concentration, and a low pH when packed in plastic bags but not glass. Large volumes may lead to hyperchloraemic metabolic acidosis and acute kidney injury. Alternatives such as Hartmann’s solution contain calcium and may be incompatible with blood products and some medications. There Hypotonic fluids (5% dextrose in 0.18 or is no ideal balanced solution. Hartmann’s and 0.45% saline) should be avoided. Plasmalyte may reduce complications from Water and electrolyte replacement in children advocating hypotonic fluids is based on calculations made in the 1950s based on calorie and energy requirements, are opinion based, and have no evidence to support them. The routine practice of giving hypotonic fluids (Na <130 mmo/L) should be abandoned for both adults and children. Nevertheless practice guidelines continue to recommend hypotonic fluids. large volumes of 0.9% saline, though the evidence for that is limted. There are insufficient data to suggest that 0.9% saline is unsafe as a maintenance fluid. Dextrose is provided in maintenance fluids to limit tissue catabolism, but it does not provide complete nutritional support. These solutions can be hyperosmolar nut not hypertonic, since the dextrose is rapidly metabolized The default maintenance solution for adults is 5% dextrose in a solution of 0.9% saline administered at 100-120 ml/hr. A hypotonic fluid may be required if there is a Concerns over giving isotonic fluids and the risk of sodium and fluid overload are not supported by a large body of evidence. clinically significant renal concentrating defect with ongoing free-water losses or to aid in the correction of established hypernatraemia. Isotonic fluids were superior for the Studies evaluating maintenance fluid for prevention of hyponatraemia. Fluid restriction oedematous states are lacking. with hypotonic fluids was not effective in preventing hyponatraemia. Isotonic fluids are most appropriate for the vast majority of hospitalised patients. This includes children in a range of medical and A common practice is to add 20 mmol/L of KCl, but evidence for this is lacking unless treating hypokalaemia. Enlarge Table for composition of fluids postoperative settings. There needs to be caution with renal disease, heart failure, and cirrhosis, and studies had notable exclusions. Isotonic fluids should not lead to hypernatraemia or fluid overload in most patients, though volume requirements should not be exceeded. Giving 0.9% saline can induce a diuresis and lead to an excessive Available at http://www.heti.nsw.gov.au/programs/emergency-medicine-training/emergencymedicine-training-test/educational-resources/em-clinical-updates/