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Fluid and Electrolyte Management. Old-School Routine Maintenance Fluid in a Perioperative Patient. Recall the 4:2:1 rule: the volume per hour (and kCal /hr) is 4x10kg+2x10kg+the balance of the patient’s weight in kg
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Old-School Routine Maintenance Fluid in a Perioperative Patient • Recall the 4:2:1 rule: the volume per hour (and kCal/hr) is 4x10kg+2x10kg+the balance of the patient’s weight in kg • Consider “Party Hard” Andy who weighs, say, 80kg, then his maintenance fluid intake would be 4x10+2x10+60=120mL/hr or 2880 mL/day and 2880kCal/day
Routine Maintenance Fluid in a Perioperative Patient • Remember from my burns blurb the 4:2:1 rule. It’s still widely used. • The long-standing concept first presented in 1957 by Holliday and Seger of the 4-2-1 rule for crystalloid delivery has been challenged more recently. • The focus of this challenge is on reduction of free water administration because of increased postoperative hyponatremia related to increased secretion of ADH • Up To Date goes as low as 2L per day
From 1st principles then, Andy needs 2400mLs of fluid and 80 to 160mmol sodium • There are 154mmol sodium in a litre of 0.9% so we only need say, 800mL of that, the other 1600mL can be made up of 5% glucose. • So what we have is 0.9% diluted down to 0.3% and glucose diluted down to 3.3% • Conveniently, Baxter makes 0.3% NaCl and 3.3% premix so we just need 2400mL daily • We also need to add the other ions. Baxter potassium comes in premix bags (hospitals won’t let you play with vials any more) +/-sodium and glucose and this needs to be taken into account. But how much potassium do we give?
What about his NG tube • What does the stomach secrete? • What about the duodenum, jejunum, pancreas and biliary secretions? Do we need to consider all of them?
The Answer is • Basically we don’t care, at this stage, about anything beyond the pyloric sphincter because that will all be reabsorbed (hopefully – we monitor the NG aspirate for volume, changes in colour or presence of faecal matter. We also measure the patient’s weight daily for determining fluid overload or underload) • So we replace the volume and electrolyte losses secreted by salivary glands and the stomach • The theoretical 1.5-3.5L per day is for a healthy individual eating food. Postoperative Andy nil by mouth will be secreting far less and replacement • HOWEVER • The stomach secretes lots of H+ and causes alkalosis • How does alkalosis change plasma K+ concentration?
Andy’s NG Tube • Alkalosis generally causes hypokalaemia as H+ is released from the intracellular compartment into the interstitial compartment along its concentration gradient • Potassium does the opposite and will move into the intracellular compartment to make up the ion balance • The result is hypokalaemia caused by NG aspiration (and prolonged emesis) • Intravenous glucose should be given with caution to a hypokalaemic patient because it will exacerbate the hypokalaemia when the insulin kicks in (rapid effect within 15 min) • A safe bet in this case is to use straight saline but if you want to be precise, Baxter make K+/Na+/glucose combinations premixed