Fluids and Electrolytes Lori F Gentile UF Surgery

Fluid Compartments Total body water(TBW)= ICF + ECF = 50-60% weight ICF = 2/3 TBW ECF = 1/3 TBW Interstitial fluid = 2/3 ECF Intravascular fluid(blood volume) = 1/3 ECF Estimates of TBW should be adjusted down approximately 10 to 20% in obese individuals and up by 10% in malnourished individuals. The highest percentage of TBW is found in newborns, with approximately 80% of their total body weight comprised of water. This decreases to about 65% by 1 year of age and thereafter remains fairly constant.

Composition of Fluid Compartments ICF = K, Mg, Phos, proteins Na determines intracellular/extracellular osmotic pressure ECF = plasma & interstitial fluid very similar. Plasma has a higher protein concentration. Na is confined to the ECF(1/3 plasma, 2/3 interstitial space) - IVF w/Na expands the interstitial space more than it does the intravascular space.

Maintenance Fluid: Composition What is D5 NS + 20KCl? D5 = 5% glucose = 5g dextrose/100mL of solution or 50g/L (prevents mobilization of protein as fuel source) 1L NS = 154mEq Na, 154mEq Cl 20KCl = 20mEq KCl per L What is LR? 1L LR = Na 130 mEq, K 4 mEq, Ca 3 mEq, Cl 109 mEq and lactate 28 mEq. The electrolyte content is isotonic (273 mOsmol/L) in relation to the ECF (approx. 280 mOsmol/L). The pH of the solution is 6.6.

Maintenance IVF: Adults MIVF rate calculation: 4 / 2 / 1 rule (per hour) For the first 10kg → 4mL/kg/hr For the next 10-20kg → 2mL/kg/hr For each kg after 20kg → 1mL/kg/hr Typical MIVF: D5 1/2NS +20KCl Electrolyte requirements: Sodium = 2-3 mEq/kg/day Potassium = 0.5-1 mEq/kg/day

IVFs After Surgery Fluid Loss during surgery- 0.5-1L/hour, + blood loss Calculate initial MIVF rate with 4-2-1 rule, then adjust for blood loss Use LR/NS for first 24 hours, then switch to D5 2 NS +20KCl Daily BMPs while NPO to manage electrolytes

Resuscitation Remember your ABC’s C = includes IV access Important: what is adequate IV access? Evaluate hemodynamic status: look at BP, HR, skin perfusion, temperature, mental status Start with isotonic crystalloid fluids Initial bolus: 20mL/kg in children, 2L in adults Assess response to bolus: If responsive, continue evaluation If unresponsive, THERE IS A PROBLEM THAT YOU NEED TO IDENTIFY NOW: bleeding, cardiac tamponade, spinal cord injury, tension PTX, MI, myocardial contusion, air embolism

Assessment of Volume Status Daily weights Swelling/edema Edema pattern on CXR UOP UOP > 0.5mL/kg/h adults UOP for children > 1mL/kg/h

Case #1: Presentation H&P: 6wk-old, first-born M p/w 5d h/o projectile nonbilious, postprandial emesis - otherwise, pt w/good appetite PE: firm, mobile “olive” in epigastrum, and visible gastric peristaltic waves U/S: pyloric muscle elongated & thickened (4mm thick) Questions: What is the diagnosis? What is the associated metabolic/electrolyte abnormality? What is the management? Olive most easily palpated after vomiting - often felt in the RUQ

Electrolyte Abnormalities GI (vomiting/diarrhea) – K and Cl Stomach – H and Cl Bile/Pancreas – bicarb Hypochloremic, hypokalemic metabolic alkalosis

Hyperkalemia Renal failure (missed dialysis), hemolysis Peaked T waves on EKG Management – confirm lab value (r/o lab hemolysis) Calcium gluconate for heart (stabilizes membranes) NaBicarb, 10U insulin, 1 amp dextrose Kayexalate / Dialysis Hyokalemia can cause an ileus

Hyponatremia Hypernatremia – tx with free water SIADH, Rule out hyperglycemia (pseudohyponatremia) Water restriction, diuresis, replacment Slow Na correction (1mEq/hr) Avoid central pontine myelinosis Hypernatremia – tx with free water

Hypercalcemia Seen in hyperthyroidism, parathyroid tumors, bone metastates, renal failure Bones, stones, moans, psychiatric overtones Tx: NS + lasix Avoid LR (has Ca) Avoid thiazide diuretics (retains Ca) Calcitonin, dialysis

Case #1: Resolution Dx: Hypertrophic pyloric stenosis (HPS) Metabolic abnormality: hypochloremic, hypokalemic metabolic alkalosis with paradoxical aciduria Loss of H+ and Cl- with vomiting Initial excretion of Na-bicarbonate in response to Cl loss Aldosterone acts to promote K excretion for Na retention Finally, H exchanged for Na, resulting in paradoxic aciduria Treatment: +/- NS bolus, when UOP is demonstrated, K is added to IVF D5 ½ NS + 20K @ 1.5-2x maintenance Must resolve electrolyte abnormalities prior to surgery Pyloromyotomy: laparoscopic vs. open Advance PO intake as tolerated

Take Home Points 4-2-1 rule for calculation of MIVF rate ABC(DE) is important in many situations Bolus IVF are not the same as MIVF Action is required if a patient is unresponsive to initial resuscitation