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  FLUIDS & ELECTROLYTES

  Normal values (mEq/L) {memorize these}
  Mg    Phos    K    Ca    HCO3    Cl    Na
  1.5-2.5    2.5-4.5    3.5-5    8-10.5    24-30    95-105    135-145
 
  Normal Physiology
  Percent of body weight: 60-40-20-15-5 -> Total body water-intracl-extracl-interstit-intravasc
  7% of body weight = intravascular (approx 5L in 70kg pt)
  Obese, elderly=less muscle, thus TBW<60% of weight
  Osmolarity = 2[Na] + [Gluc]/18 + BUN/2.8
  [H+] = 24 PaCO2/[HCO3]
  0.1 change in pH = 0.4mEq/L change in K
  ADH secreted when: osm increases (intracranial recep), volume decreases (RA, LA)

  Fluids
  Calculation of maintenance rate
    4-2-1 rule: ml IVF/kg/hour [or for pt's >20kg use Tej's rule: weight + 40ml] {use ideal body weight}    
  Remember 42ml/hr = 1 L/day (for quick conversion between fluid rate per hour and daily fluid)
  POD 2 or 3: 3rd space fluid mobilizes; decrease IVFs to prevent overload (esp in CHF, renal failure pts)
  Stress response to surgery/trauma = increased ADH/Aldo
  Dehydration: hypernatremia draws fluid from cells=blunts picture of volume depletion
  Prerenal: BUN:Cr >20, FeNa (=UNaPCr/UCrPNa) <1%, UNa<20
  Maintenance fluids: D5 ½ NS + 20mEq KCl (D5 ¼ NS for kids); No LR (causes alkalosis)
  Urine output should be =0.5ml/kg/hr (1.0 in kids)
  Bolus: LR or NS only; No D5 (causes hyperglycemia); No hypotonic solutions (extravasates)

  IVF composition (mEq/L)
    NS: (0.9%): Na 154, Cl 154
    LR: Na 130, Cl 109, lactate 28, K 4, Ca 3 (lactate becomes HCO3); {more “physiologic” than NS}
    D5: 5 grams glucose/100ml (added into other IVF solutions, such as D5 1/2NS)

  Electrolyte abnormalities (hyper usually causes decreased DTRs {deep tendon reflexes}, decreased respirations)
  ---Na
  HypoNa: Seizures, coma, increased DTRs
          Causes: usually hypotonic IVF
      PseudohypoNa: hyperglycemia, hyperlipidemia
      Hypovolemia: dehydration, diuretics
      Euvolemia: SIADH
      Hypervolomeia: CHF, RF, cirrhosis
  HyperNa: Symptoms: seizures, resp depression
          Causes: GI loss, perspiration, burn, DI, hyperAldosteronism
  Correct Na slowly (0.5mEq/hr) to prevent central pontine myelinolisis

  ---K
  HypoK:  Ileus, tetany; EKG - flat T wave, U wave, Afib
     Causes: intracellular shift, vomit/NGT, diarrhea, renal loss (also check Mg, Phos)
     Paradoxical aciduria (due to decreased K and decreased vol)
     Rx: PO K replace <40mEq/hr, IV replace <10mEq/hr 
  HyperK: EKG - peaked T, VFib
      Causes: intracellular shift, renal disease, hemolysis, crush injury, meds – NSAIDS, ACEI, low Aldo, Digoxin
      Rx: Check digoxin and CK levels ("C BIG K Drop")
        <6.5: diuretics (furosemide)
        6.5-7.5: 10 units insulin IV & 25gr glucose IV over 5mins (w/ EKG)
        >7.5: 10-30ml 10% Ca gluconate IV over 5mins

  ---Cl
  HypoCl: No specific symptoms
      Causes: vomiting, acidosis, CRF, diuretics
  HyperCl: rare in surgery pts

  ---Ca
  HypoCa: Perioral/hand parasthesias, Chvostek sign, Trousseau, seizure, increased DTRs
      EKG: long PR, long QT
      Causes: parathyroid surgery, renal failure (low vit D), short bowel syndrome (fat binds Ca), pancreatitis, blood transfusions
      Rx: Ca gluconate, vit D, thiazides
  HyperCa: Stones, bones, moans, groans, psychic overtones (depression)
      EKG: long PR, short QT
      Causes: CHIMPANZEES – Ca supplements, HyperPTH, Iatrogenic (thiazides),Mets, Paget’s, Addison’s, Neoplasm, ZE synd,                                                         Excess vitamin A/D, Sarcoidosis
      Rx: NS or ½ NS – large volumes, bisphosphonates, steroids

  ---Mg
  HypoMg: HypoCa symptoms (low Mg causes low PTH = low Ca)
      Causes: starvation (EtOH), malabsorption (Crohn’s)
      Rx: 50-100mEq/day IV Mg
  HyperMg: decreased DTRs (pregnant pts), decreased respirations
      Causes: iatrogenic, rarely-renal failure
      Rx: hyperK Rx (IV Ca)

  ---Phos
  HypoPhos: Dizziness, anorexia, weakness, respiratory failure (diaphragm)
      Causes: malabsorption, EtOH, hyperPTH, shifts, diuretics, refeeding syndrome
      Rx: replete Phos
  HyperPhos: No symtpoms
      Causes: renal failure, hypoPTH, cellular shifts, sarcoidosis
      Rx: aluminum antacids, diuretics

  Acid Base
  Change in PaCO2 of 10mmHg = reciprocal change in pH of 0.08
  Change in HCO3 of 10mEq = direct change in pH of 0.15

  --Respiratory acidosis
  Do not correct hypercapnia too quickly - this may cause arrhythmias or decrease cerebral perfusion

  --Metabolic acidosis
  1. Loss of HCO3: diarrhea, renal tubule disorders
  2. Excess acid: hypoxic vs. non-hypoxic
  If pH remains <7.25, may give HCO3 1mg/kg bolus + 0.5mg/kg Q10min (controversial)

  --Respiratory alkalosis
  Due to hyperventilation, often in intubated patients
  Acute hypocapnia can cause cerebral vasoconstriction (up to 50%)

  --Metabolic alkalosis
  Often due to contraction alkalosis (hypovolemia, hypoK, hypoCl)
  Contraction alkalosis: low vol= hi aldo= increased H+ secretion

  Miscellaneous
      Vomiting results in hypovolemia, metabolic alkalosis, hypoCl, hypoK (increased Aldo)
      Isotonic volume contraction: diarrhea
      Hypertonic volume contraction: perspiration, fever, DI
      Hypernatremia: every 3 mEq rise in Na = 1 L of water deficit
      SIADH Rx: H2O restriction, demeclocyline/lithium, lasix / K (dilutes urine)    


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