Acid-Base Balance and Electrolytes: Prework Presentation

1. PreWork This powerpoint will only be helpful if you run it as a slide show.

2. PreWork Objectives • Understand the respiratory and metabolic mechanism for eliminating acid • Know the normals for Arterial Blood Gasses and Venous Electrolytes • Explain ADH and Aldosterone effects on sodium and water. • Explain the effects of sodium and free water on volume and serum sodium • Explain hormonal regulation of Ca++ and P04

3. Problem: Metabolism Produces Acid • H2SO4 • H3PO4 • HCl • etc.

4. Getting Rid of Acid Bicarbonate Reabsorption by the Kidneys (Metabolic) HCO3- Blood Carbonic Anhydrase H2CO3 Urine H+

5. Getting Rid of Acid The Lungs Eliminate CO2 (Respiratory) H2CO3 H2O + CO2 HCO3- + H+ Carbonic Acid Acidic

6. Getting Rid of Acid The Lungs Eliminate CO2 (Respiratory) H2CO3 H2O + CO2 HCO3- + H+ Carbonic Acid Acid pH Alveoli

7. Normals • Arterial Blood • pH: 7.35-7.45 • pCO2: 40 • PO2: 100 • HCO3 25

8. Normals • Venous Lytes • Sodium: 140 • Potassium: 4.5 • Chloride 100 • Total CO2 26

9. Total CO2 pCO2 =40mm Hg • 40mm Hg EQUALS • 1.2 mEq / L dissolved CO2 Dissolved in Water….. • + 25 mEq /L of HCO3 • =26 mEq / L = Total CO2 Click Here to Play That Again if you didn’t get it

10. Sodium and Water Prework

11. Volume and Tonicity

12. Salt rules volume Salt Rules Volume This represents normal sodium and volume. Extracellular space is the vascular plus tissue Serum Sodium 140 mEq/L (Unchanged) Serum Sodium 140 mEq/L H20 H20 Note that intracelluar space is 2/3 of total body water Intracellular Intracellular Extracellular

13. Free Water Rules Serum Sodium This represents normal sodium and volume. Extracellular space is the vascular plus tissue No Clinically Significant Volume Change (Water Spreads Out) H20 H20 Serum Sodium 140 mEq/L H20 Serum Sodium 125 mEq/L (hyponatremia) H20 Note that intracelluar space is 2/3 of total body water Intracellular Intracellular Extracellular

14. The Challenge • Figure out how the Renin-Angiotensin-Aldosterone system and how ADH relate to the above examples of sodium and water. What turns them on and what turns them off.

15. Calcium And Phosphate Prework • Prework questions on Calcium and Phosphate will be easy. Exam questions will be slightly less easy.

16. Calcium

17. Calcium • Normal value: • Total: 8.5–10.5 mg/dL (2.1–2.7 mmol/L) • Ionized (free): 4.6–5.2 mg/dL (1.15–1.38 mmol/L) • Function • Bone and teeth • Neuromuscular activity (SA node, AV node) • Endocrine/exocrine function • Platelet function • Muscle cell contraction

18. Calcium Regulation • PTH •  serum calcium • Vitamin D •  serum calcium • Calcitonin •  serum calcium • Calcium homeostasis figure (next slide)

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20. Corrected Calcium • Only ionized (unbound) calcium is active • Calcium must be corrected when there is a low albumin (a larger percent is ionized) • For each 1mg/dl change in albumin from normal, 0.8mg/dl change in Ca2+ • [(4 – alb) x 0.8] + serum Ca2+ • Ex. Alb 2.3 Ca2+ 7.6 • Corrected calcium = • [(4-2.3) x 0.8] + 7.6 = 8.96 mg/dL

21. Hypocalcemia • Serum Ca2+ < 8.5 mg/dL • Pathophysiology • Hypoparathyroidism • Vitamin D deficiency • Hypomagnesemia • Hyperphosphatemia, 2o hypoparathyroidism • Medications/chelating agents • Bisphosphonates, loop diuretics, calcitonin, phenytoin

22. Hypocalcemia • Clinical Presentation • Acute • Fatigue, irritability, confusion, seizures • Muscle cramps, spasms, tetany • Chronic • Prolonged QT interval • Brittle nails, hair loss

23. Hypocalcemia Treatment • Always correct calcium for albumin!! • Depends on acuity and severity • Check a magnesium level (find out why for the exam! ) • Calcium supplementation • IV • PO

24. IV Calcium • Acute symptomatic patients • Calcium chloride • 1 gm IV (27% elemental) • Very irritating to veins • Calcium gluconate • 2-3 gm IV (9% elemental) •  availability in liver disease

25. PO Calcium • Chronic asymptomatic patients • Corrected symptomatic patients • 1-3 g/day of elemental calcium ± vitamin D • Take with meals, in divided doses for best absorption

26. PO Calcium

27. Hypocalcemia Monitoring • Albumin, magnesium levels • Symptomatic patient • Serum and ionized calcium levels every 4-6 hrs after IV calcium • Serum calcium every 24-48 hrs during oral therapy, then 1-2 times weekly

28. Hypercalcemia • Serum Ca2+ > 10.5 mg/dL • Pathophysiology • Primary hyperparathyroidism** • Malignancy** • Other • High bone turnover, sarcoidosis • Medications (thiazides, lithium, vitamin D)

29. Hypercalcemia • Clinical Presentation • Depends on degree and onset • GI – N/V, anorexia, constipation • CV – short QT, prolonged PR & QRS • Neuro – fatigue, weakness, confusion • Renal – polyuria, nocturia, nephrolithiasis

31. Hypercalcemia Treatment

32. Hypercalcemia Treatment • Other treatment options • Gallium nitrate, mithramycin • Monitoring • Albumin • ECG • Serum Ca2+ q 6-12 hrs if symptomatic • Serum Ca2+ daily if mild-moderate

33. Summary of Calcium • Calcium regulation • PTH, Vitamin D, calcitonin • Corrected calcium • Oral calcium products • Treatment of hypercalcemia

34. Phosphorus

35. Phosphorus • Normal value 2.7-4.5 mg/dL • Function • Phospholipid membrane • Supports bone and teeth • Metabolism of nutrients • Source of ATP (energy, kinda critical)

36. Phosphorus • Source • Meats, dairy, eggs • Regulation • Kidney

37. Hypophosphatemia • Mild to Moderate 1-2 mg/dL • Severe < 1 mg/dL • Pathophysiology • Decreased intake/absorption • Vitamin D deficiency, phosphate binders • Increased excretion • Diuretics, hyperparathyroidism • Intracellular shift • Parenteral nutrition, insulin

38. Hypophosphatemia • Clinical Presentation • Neuro – irritability, weakness, seizures • Muscular – myalgia • Hematologic – hemolysis • Pulmonary – respiratory distress • Other – osteomalacia, arrhythmias

39. Hypophosphatemia Tx • Mild – moderate • PO • 50-60 mmol/day divided in 3-4 doses • Neutra-Phos 1-2 packets QID mixed in 2.5 oz water or juice • K-Phos Neutral 1-2 tabs QID with water • NOTE: Dose in mmol NOT mEq

40. Hypophosphatemia Tx • Mild – moderate • IV • 0.08-0.15 mmol/kg IV • Repeat until serum phosphorus > 2 mg/dL

41. Hypophosphatemia Tx • Severe • IV • 0.25-0.5 mmol/kg IV • Repeat until serum phosphorus > 2 mg/dL

42. Phosphorus Replacement *Oral agents

43. Hypophosphatemia • Monitoring • IV therapy • Serum phosphorus every 6 hrs • PO therapy • Serum phosphorus daily • Renal function, BP (IV) • Adverse events – diarrhea (PO), soft tissue calcification, hypocalcemia, hypotension (IV)

44. Hyperphosphatemia • Serum phos > 4.5 mg/dL • Pathophysiology • Decreased urinary excretion • Renal failure, hypoparathyroidism • Increased intake • Parenteral nutrition, phosphate enemas • Extracellular shift • Acidosis

45. Hyperphosphatemia • Clinical Presentation • N/V, muscle pain/weakness, hyperreflexia, tetany • Soft Tissue calcification • Due to calcium-phosphate product • Goal is less than 55.

46. Hyperphosphatemia Tx • Restrict dairy products • Phosphate binders • Aluminum and magnesium-based antacids • No longer first line, avoid in renal failure • Calcium (Drug of first choice unless Calcium is high) • Sevelamer • Binding resin Usually given with meals

47. Hyperphosphatemia • Monitoring • Serum calcium level • Serum phosphorus level daily • Renal function

48. Summary of Phosphorus • IV vs. PO replacement • Give IV phosphorus when severe hypophosphatemia • Medications affecting serum levels • Phosphate-binders, calcium, diuretics, insulin, vitamin D