Acidbase Disorders

1. Acid-Base Disorders Base Acid • Dr.C.S.N.Vittal

2. ACIDS, BASES AND SALTS • CHEMICAL COMPOUNDS CAN BE PROTON DONORS OR ACCEPTORS • PROTON DONORS ARE ACIDS • PROTON ACCEPTORS ARE BASES • ACIDS AND BASES REACT TO NEUTRALIZE EACH OTHER FORMING SALTS

3. H+ ion & pH SCALE • H+ ion conc. of plasma: 0.000 000 04 mol/L or 40 nmol/L • pH is the negative logarithm of hydrogen ion conc. Normal : 7.35 – 7.45

4. ACID/BASE BALANCE AND THE BLOOD [OH -] [H+] Acidic Alkaline (Basic) Neutral pH 7 0 14 Arterial Blood Venous Blood Acidosis Alkalosis 7.4 DEATH DEATH 8.0 Normal 7.35-7.45 6.8

5. Types of acids in the body • Most acid comes from carbohydrate and fat metabolism (15,000 to 20,000 mmol of CO2 daily) • CO2 combines with water (H2O) in the blood to create carbonic acid (H2CO3), which in the presence of the enzyme carbonic anhydrase dissociates into H+ and HCO3−. • The H+ binds with Hb in the blood and is released with oxygenation in the alveoli, the above reaction is reversed, creating H2O and CO2, which is exhaled • Very little metabolic acid is produced (1mEq/kg/d) which is eliminated by kidney and liver.

6. Bases in the body • Most base comes from metabolism of anionic amino acids (glutamate and aspartate) and from oxidation and consumption of organic anions such as lactate and citrate, which produce HCO3−

7. Acid Base Balance Buffer Base Acid Base Respiratory Kidney

8. Acid Base Balance Buffer Base Base Acid Kidney Respiratory

9. Lungs Metabolism Input Output Kidneys Maintenance of Normal [H+] Buffers Acid-Base Homeostasis

11. Acid Base Disorder Acid Base

13. Abnormal acid-base balances • Increased renal net acid excretionwith resulting increase in serum bicarbonate Low Increased pCO2 • Decreased renal net acid excretionwith resulting decrease in serum bicarbonate High Decreased pCO2 • Hyperventilation with decreased pCO2 Low • Decreased HCO3- • Hypoventilation with increased pCO2 • Increased HCO3- High

14. Acid-Base Disorders Dr. CSN Vittal

15. Acid Base Terminology – Abnormal process or disease which reduces pH and increase in acid OR decrease in alkali Acidemia – Abnormal process or disease which reduces pH and increase in acid OR decrease in alkali Acidosis

16. Acid Base Terminology Alkalemia – alkaline blood: pH > 7.35 ( iin H+conc) – Abnormal process or disease which increases pH or decrease in acid OR increase in alkali Alkarlosis

17. --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID xxxx 2570/00 Measured 37.00 C pH 7.463 pCO2 44.4 mm Hg pO2 113.2 mm Hg Corrected 38.60 C pH 7.439 pCO2 47.6 mm Hg pO2 123.5 mm Hg Calculated Data HCO3 act 31.1 mmol / L HCO3std 30.5 mmol / L BE 6.6 mmol / L O2 CT 14.7 mL / dl O2 Sat 98.3% Ct CO2 32.4 mmol / L pO2 (A-a) 32.2 mm Hg pO2 (a/A) 0.79 Entered Data Temp 38.6 0 C Ct Hb 10.5 g/dl FiO2 30.0 % The Anatomyof a Blood Gas Report Measured Values Temp Correction ? Any Value Calculated Data Which are the useful ones? Entered Data Derived from other sources

18. Steps in Acid-Base Analysis Step 1. Consider the clinical settings! Anticipate the disorder ! Step 2. Look at the pH? Step 3. Who is the culprit for changing pH?...Metabolic / Respiratory process Step 4. If respiratory…… acute and /or chronic? Step 5. If compensations appropriate? Step 6. If metabolic, Anion gap increased and/or normal or both?et Step 7. Is more than one disorder present? Mixed one?

21. Mnemonics

22. Respiratory Acidosis

23. Respiratory Acidosis • Respiratory acidosis is the most common cause of acid-base imbalance • Occurs when a person breathes shallowly, or gas exchange is hampered by diseases such as pneumonia, cystic fibrosis, or emphysema

24. Chronic • The PaCO2 is elevated above the upper limit of the reference range, with a normal or near-normal pH secondary to renal compensation and an elevated serum bicarbonate • (i.e., HCO3- > 30 mm Hg). • Acute • The PaCO2 is elevated above the upper limit of the reference range (i.e. > 45 mm Hg) with an accompanying acidemia (i.e., pH < 7.34)< 7.35). Respiratory Acidosis

25. Respiratory Acidosis - Acute Abrupt failure of ventilation, h PaCO2 • Neuromuscular disorders • CNS Depression • Brain stem Injury • Musculoskeletal Disorders • GBS • Myasthenia • Airway Obstructive Disease • Asthma • Foreign Body • Laryngeal Edema • Pulmonary Embolism • Drugs • Sedatives • Barbiturates

26. Respiratory Acidosis - Chronic • COPD • Obesity hypoventilation syndrome (i.e. Pickwickian syndrome) • Neuromuscular disorders • Amyotrophic lateral sclerosis • Severe restrictive ventilatory defects • Interstitial fibrosis • Thoracic deformities

27. Respiratory Acidosis Acute respiratory acidosis: Change in pH = 0.8 x (40 - PaCO2) Chronic respiratory acidosis: Change in pH = 0.3 x (40 - PaCO2)

28. Respiratory Acidosis Symptoms: • Symptoms of the disease that causes respiratory acidosis are usually noticeable • Shortness of breath • Easy fatigue • Chronic cough or Wheezing. • When respiratory acidosis becomes severe, • Confusion • Irritability • Lethargy may be apparent.

29. Respiratory Acidosis Treatment: Supportive • Treat the underlying cause • Improve alveolar gas exchange • Assisted ventilation • Bicarbonate must not be infused to treat the acidosis because it generates more CO2

30. Respiratory Alkalosis

31. Respiratory Alkalosis • Rapid breathing due to high fever • Hysterical condition • Assisted ventilation • Drugs - Salicylates (early stages) • Interstitial Lung Disease • Cirrhosis, Liver Failure • Anxiety • Gram negative Septicemia • Hypoxia and severe anemia or high altitude

32. Respiratory Alkalosis Symptoms • Tingling and numbness • Parasthesias • Lethargy • Tetany • Unconsciousness • Vasospasm of cerebral vassals - Hypercapnia

33. Respiratory Alkalosis Treatment • Treat underlying cause

34. Metabolic Acidosis

35. Metabolic Acidosis • Increased H+ Load • Increased HCO3- Loss

36. Alb- Alb- Alb- HCO3- HCO3- HCO3- A- Na+ Na+ Na+ Cl- Cl- Cl- Metabolic AcidosisTypes : 1) “Normal Anion Gap”, 2) “ h Anion Gap”  [Na+] - ([Cl-] + [HCO3-]) No Anion gap M acidosis High Anion gap M acidosis

37. Anion Gap • The difference between major plasma cations and major plasma anions. Anion gap = ([Na+] +[K+]) - ([Cl--] +[HCO3-]) Gap = [ Na+ + K+ ] - [ Cl- - HCO3-] 15 = [140 + 5 ] - [ 105 - 25 ] mMol/L] Normal Anion Gap Children 9 mo. 19 yrs = 8 + 2 mMol /L Adults = 12 + 2 mMol /L

38. Anion Gap Metabolic Acidosis Accumulation of unmeasured anions | Low HCO3andhAG • ethanol • remia • iabetic • etoacidosis • araldehyde • nfection • actic acid • thylene glycol • alicylates • M • U • D • K • P • I • L • E • S

39. Non Anion Gap Metabolic Acidosis Loss of HCO3 or External acid infusion | Low HCO3 AG < 12 • GI Losses of Bicarbonate (Diarrhoea) • Renal Losses • Renal Tubular Acidosis • Renal Toxins • Carbonic Anhydrase Inhibitors • Ureteral Diversion • Compensation for Resp. Acidosis • HCl or NH4Cl Infusion, • TPN

40. Decrease in Anion Gap Metabolic Acidosis • Hypoalbuminemia • Increased K+, Ca++ and Mg++ • Due to Lithium in blood

41. Metabolic Acidosis Clinical Features • Increased work of breathing : • Deep rapid breathing (Kussmaul’s) • Peripheral Vasodilatation, • collapse, shock, impaired cardiac function • Lethargy, drowsiness, confusion, stupor • Hyperkalemia • Nonspecific: Nausea, Vomiting • Chronic Acidosis: • Osteopenia – CaCo3 loss • Muscle weakness – Glutamine loss

42. Metabolic Acidosis Management Principles: • Identify cause • Initial goal : Bring the pH ~ 7.25 (For cardiac contractility & responsiveness to catecholamines) Sodabicarb : Dose: 1-2 mEq/Kg [1 ml of 7.5% NaHCO3 = 0.9 mEq] [Bicarb deficit (mEq/L) = Body wt.(Kg) x 0.3 x Base excess] • Half as bolus • Half as infusion over 12 – 24 hrs.

43. Metabolic Acidosis Management – Contd. • Volume depletion: - Fluid replacement • DKA: Volume replacement + Insulin therapy • Poisoning: Dialysis • CHF: - Slow replacement of fluid - THAM (tromethamine; tris-hydroxymethylaminomethane) as infusion over 3 - 6 hours Dose (in ml) is: weight (kg) x standard base excess

44. Metabolic Acidosis Management – Contd. • Acetazolamide poisoning, DKA: • Potassium replacement : Serum K+ should be > 3.5 mEq/L before administering HCO3 – • Hypoadrenal states: • Steroid replacement.

45. H+ H+ H+ H+ K+ H+ K+ K+ K+ H+ H+ K+ H+ K+ K+ K+ HYPERKALEMIA • Hyperkalemia causes acidosis • Acidosis causes hyperkalemia HYPERKALEMIA ACIDOSIS

46. H+ H+ H+ H+ K+ K+ H+ K+ K+ H+ H+ K+ H+ K+ K+ K+ HYPERKALEMIA • Hyperkalemia causes acidosis • Acidosis causes hyperkalemia HYPERKALEMIA ACIDOSIS

47. Metabolic Alkalosis

48. Metabolic Alkalosis Increase in extra-cellular pH (above 7.45) due to primary increase in plasma bicarbonate Very Dangerous: • Shifts O2 dissociation curve to Lt. • Causes vasoconstriction of all vessels except pulmonary circulation • Suppresses ventilation • Decreases ionized Ca++ and shifts K+ into cells – hypocalcemia and hypokalemia Types: 1) Chloride responsive 2) Chloride resistant

49. Metabolic Alkalosis Issues to ponder • What generated the alkalosis? • What is maintaining the alkalosis – what is preventing kidney from excreting the alkali ?

50. Metabolic Alkalosis Causes Chloride-Responsive (Urinary Chloride <15 mEq/L) • Gastric losses (Cong hypertrophic pyloric stenosis) • Emesis • Nasogastric suction • Diuretics (loop or thiazide) • Chloride-losing diarrhea • Low chloride formula • Cystic fibrosis