Acid Base Balance

1. Acid Base Balance NURS 108 ECC Majuvy L. Sulse MSN, RN, CCRN

2. TERMS • Acid • Substance that dissociates or lose ions • Acidosis • Process that adds acids or eliminates base from body fluids • Hydrogen ions increased • pH is decreased<7.35 • Base • Substance that accepts ions • Alkalosis • Process that adds base or eliminates acid from body fluids

3. TERMS • pH • Negative logarithm of hydrogen ion concentration in the blood • Normal range-7.35-7.45 (N=7.40) • Inversely proportional to hydrogen concentration • Increase in H ions=low pH (acidosis) • Decrease in H ions=high pH (alkalosis) • Anion gap • Normal=5-15 • Helpful in differential diagnosis of acidosis • Calculated by subtracting anions from cations (Anion gap=Na+K –Cl+HCO3)

4. TERMS • PaO2 • Partial pressure of O2 dissolved in arterial blood • Normal value= 80-100mmHg • SaO2 • Amount of O2 bound to hemoglobin • 3% of O2 dissolved in plasma • 97% bound to hemoglobin • Normal range-93-100%

5. TERMS • PaCO2 • Partial pressure of carbon dioxide dissolved in arterial blood • Normal range =35-45mmHg • Regulated in the lungs • Hypoventilation- respiratory acidosis-CO2 retention • Hyperventilation- respiratory alkalosis- CO2 excretion • HCO3 • Concentration of sodium bicarbonate in the blood • Normal range= 22-26mEq • Regulated in the kidneys • Metabolic alkalosis >26mEq • Metabolic acidosis < 22mEq

6. Oxyhemoglobin Dissociation Curve

7. Oxyhemoglobin Dissociation Curve • Low paO2 at tissue level (hypoxia)=Shift to right-O2 readily released from the hemoglobin • Acidemia, Hyperthermia, hypercarbia • High PaCO2 at pulmonary capillary level=Shift to left-O2 more bound to hemoglobin • Alkalosis, hypothermia, hypocarbia, high altitude, carcon monoxide poisoining

8. Acid-Base Regulation • Buffer system • Substance that reacts with an acid or base to prevent a large change in pH • Fast acting and a primary regulator of acid base balance • Can react in two ways • As an acid-releasing H ions • As a base-binding a H ion • Carbonic acid/bicarbonate system H+HCO3=H2CO3=H20+ CO2

9. Respiratory Mechanism • 2nd line of defense against changes in fluid pH • Under control of the nervous system • Regulates the excretion and retention of carbonic acid • If pH is down-rate & depth of ventilation increased • If pH is up- rate and depth of ventilation is decreased • Rapid action following alteration in acid base balance

10. Neural regulation of respiration and Hydrogen Ion concentration IncreasedPaCO2 Increased H+ Decreased rate and depth of respiration Inhibition of central chemoreceptors Stimulation of Chemoreceptors Decreased PaCO2 Decreased H+ Increased rate and depth of respiration

11. Renal Mechanism • 3rd line of defense • Strongest of all mechanisms but takes long to completely respond (24-48 hrs) • Operates on 3 mechanisms • Movement of bicarbonate • Formation of acids • Formation of ammonium

12. Renal Mechanism • Movement of bicarbonate • When H ions are high-bicarbonates are reabsorbed from the kidneys and back to circulation • When H ions are low-bicarbonates remain in the kidneys and excreted in the urine • Formation of acids • Phosphate (HPO4) draws and combines with H ions into the urine forming an acid (H2PO4) and excreted in the urine • Formation of ammonium • Ammonia (NH3) is secreted in the urine-combines with H ions to form Ammonium (NH4)-excreted in urine

13. Compensation • Body attempts to correct for the changes in body/blood pH • Respiratory system- more sensitive to aci-base changes thus can begin compensation within seconds to minutes • Renal compensation-more powerful but does not get stimulated until imbalance is sustained for several hours to days

14. Compensation • Respiratory- Rapid • Metabolic acidosis- increase in depth and rate of respiration to blow off CO2-pH returns to normal • Metabolic alkalosis-lungs decrease the rate & depth of respiration-paCO2 returns to normal • Renal • Respiratory acidosis-kidneys increase excretion of H ions or increase reabsorption of bicarbonates-pH returns to normal • Respiratory alkalosis-kidneys reabsorb more H ions or excrete more bicarbonates

15. Compensation • pH –within normal 7.35-7.45 • HCO3-must be abnormal • pCO2- & HCO3 going in the same direction • Example • pH -7.37 pCO2-60 HCO3- 38

16. Acid Base Imbalances • Metabolic Acidosis-low pH, low HCO3,K elevated, • Overproduction of H ions • Excessive breakdown of fatty acids-ketoacidosis (DKA & Starvation) releases H ions • Hypermetabolism-lactic acidosis- excessive exercise, seizure, fever, hypoxia • Excessive intake of acid substances-ASA, alcoholic beverages • Under elimination of H ions –kidney failure • Underproduction of bicarbonates-renal/liver failure, dehydration • Overproduction of bicarbonates-but presence of diarrhea

17. Metabolic Acidosis-Clinical Manifestations • Neurologic- • Headache, drowsiness, confusion, coma • Neuromascular • Decrease in muscle tone and deep tendon reflexes • Respiratory • Deep rapid respirations-Kaussmaul breathing • Cardiovascular • Low BP arrhythmias • Warm flushed skin due to vasodilation • GI • Nausea, vomiting, diarrhea, abdominal pain

18. Metabolic Acidosis-Interventions • Hydration • Treat or control the causative cause • DKA- hydration & insulin • Diarrhea-rehydration & antidiarrheals • Bicarbonate is administered only if serum bicarbonate levels are low

19. Acid Base Imbalances • Respiratory Acidosis-low pH, high pCO2, K • Retention of CO2 • Respiratory depression • Anesthesia, drugs, trauma, neurologic disease, • Inadequate chest expansion • Skeletal deformities, muscle weakness, obesity, tumor • Airway obstruction • asthma, COPD, bronchiolitis • Reduced alveolar-capillary diffusion • Thrombus, pneumonia, TB, Cystic fibrosis, atelectasis, ARDS,

20. Respiratory Acidosis- Manifestations • Neurologic • Disorientation, drowsiness, dizziness, headache, coma • Respiratory • hypoventilation • Cardiovascular • Low BP, arrhythmias • Neuromascular • seizures

21. Respiratory Acidosis-Interventions • Maintain patent airway, enhance gas exchange, adequate oxygenation • Pulmonary hygiene-positioning breathing techniques • Ventilatory support • Prevention of complications • Drug therapy aimed at • Increasing diameter of airways • Induce relaxation • Increase bronchodilation • Thin secretions

22. Combined Respiratory & Metabolic Acidosis • Can occur simultaneously • Leads to anaerobic metabolism and lactic acidosis • Acidosis more profound than that caused by respiratory or metabolic acidosis • May lead to cardiac arrest

23. Acid Base Imbalances • Metabolic Alkalosis-high pH hallmarked by an increased in bicarbonate and rising paCO2, low K & Ca • Base excess • Ingestion of bicarbonates, acetates, citrates, and lactates • Acid deficit • Prolonged vomiting, Cushing’s syndrome, Thiazide diuretics, prolonged NGT suctioning

24. Metabolic Alkalosis-Manifestations • Neurologic • Dizziness, irritability, nervousness, confusion • Respiratory • Hypoventilation-a compensatory action • Cardiovascular • Tachycardia, arrhythmia related to low K • Neuromascular • Tetany, tremors, tingling of fingers & toes, hypertonic muscles, cramps & seizures • GI • Anorexia, nausea & vomiting

25. Metabolic Alkalosis-Interventions • Restore normal fluid & electrolyte balance • Drug therapy to restore electrolyte balance • K sparing diuretics • Antiemetics • Avoid administration of alkaline substances-Na Bicarbonate or antacids

26. Acid Base Imbalances • Respiratory Alkalosis-high pH, low bicarbonate, low PaCo2,low K & Ca • Co2 level is so low because of hyperventilation • Direct stimulation of respiratory center due to fever, compensation for metabolic acidosis, CNS lesions, drugs, pain • ventilation settings too high or fast • Anxiety, fear

27. Respiratory alkalosis-Manifestations • Neurologic • Light headedness, lethargy, confusion • Respiratory • Hyperventilation- lungs cannot compensate for the respiratory problem • Cardiovascular • Tachycardia, arrhythmias • Neuromascular • Numbness, tetany, tingling of extremity, • Hyperflexia, seizures • GI • Nausea, vomiting, epigastric pain

28. Respiratory alkalosis-Interventions • Monitor for indications of respiratory failure • Use rebreather mask • Provide mechanical ventilatory support • Reduce O2 consumption to minimize hyperventilation-reduce fever, pain, anxiety and promote comfort • Monitor labs-ABGs, lytes

29. Arterial Blood Gases • Provides acid-base status • Provides information on the origin of the imbalance • Provides an idea of body’s ability to regulate pH • Provides reflection of overall oxygenation status • Finding interpreted in conjunction with patient clinical history, physical assessment, and previous ABG

30. Steps in determining ABGs • 1)Determine if pH is acidotic or alkalotic • 2)Analyze the pCO2 to determine respiratory acidosis or metabolic. CO2 is controlled by the lungs, • high CO2=acidosis, low CO2 =alkalosis • 3)Analyze HCO3 to determine metabolic acidosis or alkalosis. HCO3 is the metabolic component controlled by the kidney • high HCO3=alkalosis, low HCO3=acidosis • 4)Determine if CO2 or HCO3 matches the acid or base alteration of pH. • If pH is acidotic and CO2 is high=respiratory acidosis • .If pH and HCO3 high= metabolic acidosis • 5)Decide if the body is attempting to compensate for the pH change

31. Normal Blood Gas Values

32. What acid-base disorders are represented by the following arterial blood tests • pH pCo2 HCO3 • 7.18 68 28 • 7.56 50 32 • 7.21 51 19 • 7.32 49 22 • 7.50 22 29 • 7.49 32 31 • 7. 37 57 17