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 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 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.

Some Baxter IV Fluids

From 1 st 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 of that 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) So we replace the volume and electrolyte losses secreted by salivary glands and the stomach The theoretical L 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 often causes hypokalaemia as H+ is released from the intracellular compartment into the interstitial compartment along its concentration gradient Potassium generally 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