1. Fluids and Electrolytes
Lori F Gentile
UF Surgery

2. 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.

3. 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.

4. 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.

5. 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 = mEq/kg/day

6. IVFs After Surgery
Fluid Loss during surgery L/hour, + blood loss
Calculate initial MIVF rate with 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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 x maintenance
Must resolve electrolyte abnormalities prior to surgery
Pyloromyotomy: laparoscopic vs. open
Advance PO intake as tolerated

15. 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