Maintaining an accurate fluid and electrolyte balance
VOL: 97, ISSUE: 23, PAGE NO: 40
Mandy Sheppard, RGN, is an independent training and development consultantArthur Foyle, 62, has had an elective repair of an abdominal aortic aneurysm. He spent one night in the postoperative recovery unit and has now transferred back to the surgical ward.
There are a number of reasons why Mr Foyle's fluid and electrolyte balance needs to be closely monitored at this stage in his postoperative recovery. Reduced intake Mr Foyle was nil by mouth preoperatively and remains so on his first postoperative day. He is therefore dependent on intravenous therapy to maintain his hydration. An accurate fluid balance chart is essential to keep a record of intake. The use of a volumetric pump may help to administer constant volumes of fluid each hour. The patient, who is nil by mouth, is completely reliant on the intravenous fluid therapy to maintain hydration. Any interruptions in that therapy should be addressed as quickly as possible. Fluid loss - Mr Foyle would have lost some fluid during the operation. This may have been the result of bleeding or evaporation from his peritoneum. The fluid balance records for the perioperative period, showing any recordable loss and fluid replacement, are an essential part of Mr Foyle's fluid balance history, particularly if it should become necessary to undertake a full assessment of fluid status. - Mr Foyle's nasogastric tube is on free drainage, which is a source of both fluid and electrolyte loss. The fluid balance chart should record this loss and the intravenous fluids infused. Daily blood tests for electrolyte levels will monitor his electrolyte balance. In this case intravenous therapy will provide a volume of fluid to maintain Mr Foyle's hydration and electrolyte balance while he remains nil by mouth and to replace the electrolytes currently being lost via the nasogastric drainage. - Mr Foyle has two wound drains that drain minimal amounts but should be accounted for on the fluid balance chart. Specific fluid balance considerations
The type of surgery Mr Foyle had has influenced his immediate postoperative management. To apply a graft to the aneurysm site, the aorta had to be clamped for a period of time above the renal arteries. In addition, there was a period of about five minutes during the operation when Mr Foyle was hypotensive (his blood pressure fell to 70/40mmHg but responded to fluid replacement). In combination, these factors may have resulted in a severe decrease in renal perfusion which can, in some cases, progress to acute renal failure. Many aspects of Mr Foyle 's postoperative management aim to prevent the development of acute renal failure or enable the early detection of any renal dysfunction. - An adequate intravenous fluid intake is essential. This is monitored by fluid balance chart records and any clinical measurements that may suggest dehydration, such as hypotension, cool peripheries, oliguria and tachycardia. Additional clinical assessment tools can be used to detect dehydration and may include loss of skin turgor, dry mucous membranes or delayed capillary refill time. In addition, Mr Foyle has a triple lumen central line, one lumen of which has been dedicated to CVP measurement. In combination with other clinical measurements, trends in CVP readings can provide a useful fluid balance indicator. - Another reason for the central line is the safe and effective administration of dopamine. At low doses, such as 3µg/kg/min, dopamine can be used to improve renal perfusion, particularly in situations where kidney function may be at risk. At higher doses, dopamine can exert effects on both heart rate and blood pressure, both of which are not required for Mr Foyle. For these reasons the dose has to be accurately administered, and in this case this is achieved using a syringe pump. In addition, dopamine has a short half-life, so to maintain its clinical effect it has to be given as a continuous intravenous infusion and not as bolus doses. - An important indicator of renal function is urine output. Hourly measurements and recording of urine volumes are essential at this stage. A normal urine output for an adult is 0.5ml/kg/hr. So for an adult weighing 70kg, a urine output of 35ml/hr would be considered normal. Mr Foyle is passing in excess of this amount (50-100ml/hr). This may be caused by the dopamine infusion. The electrolyte potassium can be lost via urine and a sustained urine output of this nature may cause hypokalaemia (a low plasma potassium level). To guard against this, potassium is added to his intravenous fluid regime and his plasma potassium levels are checked on a daily basis. - The plasma levels of urea and creatinine are two other important indicators of renal function. Both substances will rise above their normal plasma values (2.5-6.6mmol/L and 55-120µmol/L respectively) in acute renal failure so both will be monitored daily. Conclusion
Any postoperative patient can be at risk of fluid and electrolyte imbalance. This risk can be heightened if the patient is nil by mouth postoperatively with additional sources of fluid and electrolyte loss. In addition, certain types of surgery or complications during surgery may increase any risk of fluid or electrolyte imbalance. - The patient's name has been changed