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Fluids and Electrolytes

Fluids and Electrolytes . Bruce R. Wall, MD, FACP Texas Health Dallas Presbyterian October 14 th , 2010. RBF=1000ml/min; RPF=600ml/min GFR=120ml/min or 172.8L/day. Key Concepts. Volume status (EABV) “think” saline in ECF Cannot be measured in the lab…

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Fluids and Electrolytes

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  1. Fluids and Electrolytes Bruce R. Wall, MD, FACP Texas Health Dallas Presbyterian October 14th, 2010

  2. RBF=1000ml/min; RPF=600ml/minGFR=120ml/min or 172.8L/day

  3. Key Concepts • Volume status (EABV) “think” saline in ECF • Cannot be measured in the lab… • TBW (Total Body Water) “think” [Na+ mEq/L] Laboratory result… must examine the patient • IV FLUID orders: Volume - Water - K+ - Acid/base

  4. 3 Key Concepts in Fluid and Electrolyte Physiology • Cell membrane permeability • Osmolality • Electroneutrality

  5. Cell Membrane Permeability

  6. Osmolarity vs Osmolality • Osmolarity is defined as the concentration of the solute per liter of solution • Osmolality is concentration of the solute/kg solvent (usually plasma or urine) • Sodium accounts for 97-98% of plasma osmolality (range 287  7 mOsm/Kg) • mOsm/kg = 2X[Na+ mEq/L] + (glucose mg/dL)/18 + (BUN mg/dL)/2.8

  7. Electroneutrality • Primary extracellular cation is SODIUM • Primary intracellular cation is POTASSIUM • Plasma (ECF) is the only compartment readily accessible

  8. Body Fluid Compartments • Adult humans are 50% - 70% water • Women and the elderly have higher % of body fat than young men, and thus less water. • For all practical purposes, assume that TBW = 0.60 X WT (kg)

  9. Body Fluid Compartments • 70 kg male (TBW=0.6 X wt) • IntraCellFluid 28L (70 kg X 40% = 28) • ECF 14L (70 kg X 20% = 14) • Extravascular 10.5L (70 kg X 15% = 10.5) • Intravascular 6.3L (70 kg X 9% = 6.3)

  10. Distribution of Sodium Extracellular Na+ 16% 81% 3% Intracellular *Plasma EABV

  11. Body Fluid Compartments • The composition of the ECF is roughly the same as the interstitial space with the exception of proteins which are trapped within the vascular lumens. • The distribution of fluid between these two spaces is determined by Starling Forces.

  12. Volume Homeostasis • ECF Volume is linked to total body sodium • Important: Total body sodium is not concentration • Concentration depends not only on amount of sodium but also the amount of water • Total body sodium is regulated by the kidneys • Input minus output equals accumulation…

  13. Volume Depletion (a.k.a Hypovolemia) • Decreased ECF volume is always sensed as a decrease in the “Effective Arterial Blood Volume (EABV)” • The EABV signals the kidney whether to reabsorb or excrete sodium. • No direct measure of the EABV, it is determined by blood volume, cardiac output, and systemic vascular resistance • Decreased “EABV” results in Na+ retention and expansion of ECF volume

  14. Clinical Signs of Hypovolemia • Orthostatic hypotension • Tachycardia • Flat neck veins • Dry mucous membranes • Absent axilliary sweat • Decreased skin turgor • Decreased CVP

  15. Common IV Fluids

  16. Management of Hypovolemia • The primary fluid prescribed for hypovolemia is Normal Saline • In the management of hypovolemia, there is no place for ½NS or D5W…. • Transfusion • Albumin • Hetastarch (Hespan ®) or Plasmanate ®

  17. IV fluids: continued • Addition of an isotonic fluid (0.9% NaCl) expands the ECF but doesn’t change the IntraCellularFluid • Addition of a hypotonic fluid (D5W) will cause movement of water into the cells. • Addition of a hypertonic fluid (3% saline) will cause movement of water out of the cells.

  18. Why is Normal Saline the “drug of choice”? • If you give 1 Liter of Normal Saline (0.9% NaCl), the NaCl is restricted to the ECF, therefore the entire liter stays in this space. 75% (750 ml) in the interstitial fluid and 25% (250 ml) in the intravascular space.

  19. Body Fluid Compartments • 70 kg male (TBW=0.6 X wt) • IntraCellFluid 28L (70 kg X 40% = 28) • ECF 14L (70 kg X 20% = 14) • Extravascular 10.5L (70 kg X 15% = 10.5) • Intravascular 6.3L (70 kg X 9% = 6.3)

  20. IV Fluids: what about 0.45% saline? • Think of 0.45% NaCl as 500ml of saline and 500 ml of water. • The saline distributes to the ECF compartment alone. 75% (375 ml) in the interstitial space and 25% (125 ml) in the intravascular space. • The water distributes 66% (330 ml) to the intracellular space & 33% (170 ml) to the ECF. Of the 170 ml to ECF, only 25% or 42.5 ml stays in the intravascular space.

  21. Fluid Prescriptions Thus of our 1L 0.45NaCl, only 125 + 42.5 = 167.5 ml stays in the intravascular space

  22. When should you use hypotonic solutions? • If there is a need to administer water to the patient (because of a water deficit state) • Maintenance fluids (not volume replacement) • D5W, D5¼NS or D5½NS may be used in combination with bicarbonate if there is a need to administer base.

  23. Clinical Signs & Symptoms of Volume Expansion • Jugular venous distension +/- S3 gallop • Dyspnea • Ascites – this could be debated • Pulmonary edema • Pleural effusions • Peripheral edema (remember hypoalbuminemia)

  24. Management of Hypervolemia • Goal of treatment • Removal of extracellular fluid • Loop Diuretics • Salt restriction (PO and IV) • Dialysis/CVVHD • Phlebotomy • Rotating tourniquets

  25. Pathways of Water Balance

  26. Calculate the Water Deficit… • [0.6] x (wt in Kg) X [{Na/140} – 1] The water deficit should be fixed in the form of water (D5W or tap water). Water repletion is over and above the maintenance fluids which may be either isotonic or hypotonic.

  27. How do you write IV Fluid orders?Input – output = accumulation • Volume balance • Water balance • Potassium (deficit, CKD, Mg++, presence of acidosis or alkalosis) • Acid base (administration of bicarbonate or HCl)

  28. Case I: Mild Hyponatremia • 65 yo WF smoker @ small cell carcinoma • No evidence of CHF on physical exam • Na+ 122 mEq/l K+6.1 • Mild respiratory acidosis GFR normal • No dyrenium, amiloride, or aldactone • Positive history for Lovenox (DVT) for 2 weeks

  29. Case I: hyponatremia - continued • PE: normal vitals (no tilt) comfortable at rest extremities - no edema no confusion • Random U Na+ elevated at 40 mEq/L • Uosm 600 TSH is WNL • 1) Differential Diagnosis • 2) IV fluid orders (NPO for cardiac evaluation)

  30. Patient receives saline • Diagnosis = SIADH • IV saline administered: 1 liter = 300mosm • Urine 600 mosm, provides for excretion of 300 mosm of sodium chloride in 500ml of urine • Allows patient to “keep” 500 ml of water • Sodium falls to 119 mEq/L

  31. Case II: HIV possible sepsis • 25 yo male with HIV • Admitted with streptococcal sepsis with meningitis • History of IVDA with baseline CKD • ARF = BUN 80mg% creatinine 2.5mg% • Volume depletion on exam • NPO (unresponsive) Mild metabolic acidosis • Sodium 133 mEq/L • IV fluids?

  32. Case III: history of CHF • 70 yo diabetic, known CHF, mild CKD • Admitted with acute coronary syndrome • NPO for cardiac cath • Recent increase in diuretics caused acute deterioration in GFR: BUN > 110 creat 2.2mg% • Euvolemic on exam (maybe a little dry?) • Na+ 125mmole/L • IV Fluids?

  33. Case IV: DKA • 45 yo WF IDDM X 20 yrs • Non-functional glucometer… • N&V for 18 hrs… indigestion/pain for 2 hrs • No dyspnea No blood in emesis or stool • ‘too sick’ to administer insulin • PMH - DM HBP Lipids CKD

  34. DKA: continued • 130/60 tilting to 95/50 P110 R24 Afebrile Neck: veins impossible to assess Lungs: few rales, WOB increased Cor: I/VI m, soft S3, increased HR Abd:benign, non-distended Ext: 1+edema • WBC 12K Hct 35% 2+proteinuria 5-10 WBC/HPF • EKG: 2mm ST elevation III and AVF

  35. DKA: continued • Na+ 131 K+ 3.2 Cl- 104 • HCO3 5mEq/l BUN 70 Creat 2.0 • anion gap 22 mEq • pH 7.18 pCO2 18 pO2 80 • (1.5)(HCO3) + 8 [+/- 2mEq] = pCO2 • Dx? Volume status? Na+? K+? • acid/base issues? IV fluids?

  36. Case V: Rhabdomyolysis • 24 yo SWAT team member of GPD • August 1998 “106 degrees in the shade” • full gear running drill - collapse in field • BP 100/60 P 130 T 102.8 rectal • Skin warm Neck veins: nl Lungs: clear • Cor: increased HR MS: tender back/gluteal region, no edema

  37. Rhabdo: continued • Urine looks red… scant volume… heme + • U Na+ <10 FeNa+ low Na+ 149 • K+ 5.9 Anion gap 22 Bun 15 Creat 2.4 • Ca++ 6.5 Phos 8.5 CPK 50,000 • “As you rapidly cool down the patient:” • Diagnosis? Volume status? • Cause of Hyperkalemia? • IVF orders?

  38. Case VI: Ascites • 65 yo retired engineer with known cirrhosis • ETOH exposure Hx GIB/varices • Meds: Beta blocker Aldactone Furosemide (no NSAID’s) • Decreased intake for several days; increasing abd pain - severe, diffuse, no radiation; minimal emesis no gross hemorrhage in stool

  39. Ascites: continued • PE: barely awake confabulates barely follows • tremulous T 101.8 BP 90/60 red palms spider angiomata muscle wasting massive ascites very tender abdomen guaiac positive stool 1+ edema 2+ ankles • Lab: WBC 20K Hct 34% Bili 4 albumin 2.4 INR 2.5 AG 12 Na+128 K+ 5.0 FeNa<1; ascites with 3000 WBC and positive gram stain • BUN 80 Creat 3mg% Decreased U Na+ < 15

  40. Ascites: continued • Differential diagnosis? • Volume status? • Acid base status? • IV fluids? (TPN?)

  41. Case VII – Metabolic acidosis • Patient with recurrent diarrhea complains of muscle weakness • No carpopedal spam, Trousseau’s of Chvostek’s • EKG reveals ST-segment and T-wave changes and PVC’s compatible with hypokalemia

  42. Case VII: continued • Plasma [Na+] = 140 meq/L • [K+] = 1.3 meq/L • [CL-] = 117 meq/L • [HCO3] = 10 meq/L • [albumin] = 4.1 g/dL (3.5 – 5 g/dL) • [Ca++] = 6.3 mg/dL (8.8 – 10.5 mg/dL) • arterial pH = 7.26 • pCO2 = 23 mm Hg • Correction MA effect K+? Correct hypo Ca++?

  43. Case VIII: Chronic Li+ • 40 yo female NPO X 48 hours post complicated cholecystectomy • Admission [Na+] = 146 mmoles • Developes profound hypotension requiring transfer to ICU (without myocardial infarction) • Current [Na+] = 175 mmoles • IV fluid orders?

  44. Case IX: AKI • 60 yo attorney ANURIC AKI SEPSIS • MSOF: lungs, cardiac, liver, renal, bone marrow, nutrition, skin, CNS • Intermittent HD • [Na+] 130 [K+] 3.3 BUN 40 mg% Creat 5mg% • IVF orders? TPN? Tube feeds?

  45. Case X: acute water intoxication • 20 yo SMU student brought to ER by fraternity • Unresponsive hypothermic hypotensive • Sodium 106 mEq/L Mild azotemia • Calculated water load > 8 liters… • IVF?

  46. Summary Most common error in writing IV Fluid orders: 1) administration of NS in pts with SIADH 2) inadequate volume replacement in sepsis or pre-renal azotemia

  47. Questions? Next month: hemodialysis therapy…

  48. Hyponatremic Patient Symptomatic Asymptomatic Acute (<48 hrs) Chronic (>48 hrs) Risk Factors for Neurologic Complications? Treatment of Hyponatremia

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