Acid-Base Balance

1. Acid-Base Balance Janis Rusin APN, MSN, CPNP-AC Pediatric Nurse Practitioner Lurie Children’s Transport Team

2. Objectives • Discuss the mechanisms for maintaining normal acid-base balance • Define respiratory and metabolic acidosis and alkalosis • Identify the common causes of acid base imbalance • Define and differentiate between respiratory distress and failure • Discuss interventions on transport for a patient with acid-base imbalance

3. Acid-Base Balance • The human body must be maintained in a very narrow range of acid-base balance • We use pH as our measure of acidity or alkalinity • pH stands for “power” of hydrogen • Normal pH is 7.35-7.45-Not a whole lot of wiggle room! • Normal cellular metabolism occurs within this range • The 2 major organs responsible for maintaining acid base balance are: • The lungs-Respiratory balance • The kidneys-Metabolic balance

4. Chemistry Flashback! • An acid is a substance that releases hydrogen ions (when it dissociates) • A base is a substance that accepts the hydrogen ions • A buffer is a substance that protects the pH from derangements by binding with hydrogen ions HA  H+ + A-

5. The Bicarbonate Buffer System • The bicarbonate buffer system is what we monitor clinically to assess acid base balance • This system works in the plasma • Relationship of carbon dioxide (CO2) to bicarbonate (HCO3-) • CO2 is the acid and HCO3- is the base

6. Balancing Act • Lungs • CO2 is an end product of normal cellular metabolism • The lungs regulate the CO2 level through respiration • Rapid response-quick fix! • The lungs cannot regulate bicarbonate levels • Kidneys • The renal tubules reabsorb bicarbonate • Excess hydrogen ions are excreted in the urine • Slower process • The kidneys cannot regulate CO2 levels

7. Clinical Applications • Acidosis (blood pH < 7.35) • A pathologic condition that causes an increase in the hydrogen ion concentration • Alkalosis (blood pH > 7.45) • A pathologic condition that causes a decrease in the hydrogen ion concentration • A simple acid base disorder has just one disturbance • The respiratory and metabolic systems compensate for each others deficiencies • If there is more than one disturbance, the patient is said to have a mixed acid base disorder

8. Types of Acid Base Disorders • Metabolic Alkalosis • Metabolic Acidosis • Respiratory Alkalosis • Respiratory Acidosis

9. Metabolic Alkalosis • An elevation in the serum pH associated with a decrease in hydrogen ion concentration and increase in bicarbonate ion concentration • Chloride plays a big role • 2 main categories • Chloride Responsive • Chloride levels are < 10 mEq/L • Chloride Resistant • Chloride levels are > 20 mEq/L

10. Metabolic Alkalosis • Chloride Responsive • Hydrogen ions are lost • Vomiting • Loss of HCL from stomach contents, as well as Na and K • Excessive NG suctioning • Loss of both Hydrogen and Chloride ions • The kidneys retain Na and K instead of H in order to maintain the Na-K pump function • Diuretics • Pull H2O from the extracellular space which is low in bicarb • Results in an increased concentration of bicarb • More bicarb available to bind with Hydrogen • Post hypercapnia • Compensation by kidneys to retain bicarb in presence of hypercapnia • Metabolic alkalosis occurs transiently once PaCO2 levels corrected

11. Metabolic Alkalosis • Chloride Resistant • Bicarbonate is retained • Hypokalemia • Low serum K causes K to shift out of the cells and H to shift into the cells • Excessive base intake • Antacids • Hypertension • Aldosterone levels are elevated • Results in Na and H2O retention • Hydrogen and excess K are dumped by kidney • K shifts into cells

12. Metabolic Acidosis • A decrease in pH associated with a low serum bicarbonate concentration • Three primary mechanisms: • Bicarbonate is lost form the body • Kidney function is impaired and acid cannot be excreted properly • Endogenous or exogenous addition of acid to the body • Common Diagnoses leading to MA • Diarrhea • Insulin Dependent Diabetes Mellitus (IDDM) • Lactic Acidosis • Poor perfusion and shock • Renal Failure

13. Metabolic Acidosis • Diarrhea • Most common cause of MA • Bicarbonate is lost in excessive stool • The kidneys are unable to keep up with the losses • Potassium is also lost in the stool • Volume depletion results in aldosterone release • Sodium is retained leading to further loss of K • Hypokalemia results

14. Metabolic Acidosis • Diabetic Ketoacidosis • Insulin deficiency occurs stimulating the release of excess glucagon • Glucagon stimulates the release of fatty acids from triglycerides • Fatty acids are oxidized in the liver to ketone bodies, beta-hydroxybutrate and aceto-acetic acid • These acids result in MA • In addition, the DKA patient become volume depleted due to excessive urination • Shock develops and further exacerbates the acidosis

15. Metabolic Acidosis • Lactic acidosis • Hypoxia or poor tissue perfusion • Cells are forced into anaerobic metabolism producing lactic acid • Shock • Excessive exercise • Ethanol toxicity • Ethanol interferes with gluconeogenesis • Anaerobic metabolism • Renal Failure • Distal RTA • Failure of the distal tubule to properly excrete hydrogen ions • Fanconi syndrome • Failure of the proximal renal tubule to reabsorb bicarbonate, phosphate and glucose • Causes include: • Genetics • Medications such as tetracycline and antiretrovirals • Lead poisoning

16. Anion Gap • Calculation that determines the gap between concentrations of positive (cations) and negative (anions) ions • Useful in determining the cause of metabolic acidosis • Calculated by: • (Na+ + K+) – (HCO3- + Cl-) = 10-12mEq/L

17. Anion Gap • Normal Anion Gap • The loss of bicarbonate is compensated for by the retention of chloride • Also known as Hyperchloremic Metabolic Acidosis • Diarrhea • Renal Failure, Proximal RTA • Elevated Anion Gap • MA due to increased H+ load • MUDPILES • Methanol • Uremia • DKA • Propylene Glycol • Isoniazid • Lactic Acid • Ethylene Glycol (antifreeze) • Salicylates

18. Respiratory Alkalosis • A condition in which the carbon dioxide content is significantly reduced (hypocapnia) • Caused by: • Hyperventilation • Occurs within minutes of onset of hyperventilation • Pulmonary disease • CHF • Hypermetabolic states • Fever • Anema • Hyperthyroid

19. Respiratory Acidosis • Occurs when ventilation of CO2 is inadequate and CO2 is retained (hypercapnia) • Causes include airway obstruction, respiratory depression, pneumonia, asthma, pulmonary edema, chest trauma • The renal buffer system is not effective for acute RA • Chronic respiratory acidosis can be well compensated for by the kidneys

20. So, how do we make the diagnosis? • Arterial Blood Gas-Normal Values • pH (7.35-7.45) • PCO2 (35-45) • PO2 (80-100) • HCO3 (22-26) • Base Excess/Deficit (-2 to +2) • Venous Blood Gas-Normal Values • pH (7.31-7.41) • PCO2 (40-50) • PO2 (35-40) • HCO3 (22-26) • Base Excess/Deficit (-2 to +2)

21. Blood Gas Analysis • Step 1: Look at the pH • < 7.35 is acidic • > 7.45 is alkalotic • Step 2: Look at the PCO2 • <35 is alkalotic • > 45 is acidic • Step 3: Look at the HCO3 • < 22 is acidic • > 26 is alkalotic • Step 4:Match the pH to either the PCO2 or HCO3 • Whichever one goes in the same direction as pH determines the primary disorder • Respiratory = CO2 • Metabolic = HCO3 • Step 5:Which one goes in the opposite direction of the pH? • This is the compensatory system • Step 6: Look at the PO2 • Determines presence of hypoxia

22. Blood Gas Analysis 26 HCO3 22 Blood Gas Interpretation 45 PaCO2 35 Normal Values Respiratory Acidosis Metabolic Alkalosis Metabolic Acidosis Respiratory Alkalosis pH 7.35-7.45 AcidemiaAlkalemia

23. Mixed Acid Base Disorders • When to suspect a mixed acid base disorder: • The expected compensatory response does not occur • Compensatory response occurs, but level of compensation is inadequate or too extreme • Whenever the PCO2 and HCO3 become abnormal in the opposite direction. • In simple acid base disorders, the direction of the compensatory response will always be in the same as the direction of the initial abnormal change. • pH is normal but PCO2 or HCO3- is abnormal • General rule: • If the pCO2 is elevated and HCO3 is reduced, then both respiratory and metabolic acidosis are present • If the pCO2 is reduced and the HCO3 is elevated, then both respiratory and metabolic alkalosis are present

24. Respiratory Distress • A compensated state in which oxygenation and ventilation are maintained • Define oxygenation and ventilation • How will the blood gas look? • Characterized by any increased work of breathing • Flaring, retractions, grunting • What is grunting?

25. Respiratory Failure • Compensatory mechanisms are no longer effective • Inadequate oxygenation and/or ventilation resulting in acidosis • Abnormal blood gas with hypercapnia and/or hypoxia • Will begin to see decreasing LOC due to hypercapnia • Medical emergency! Must protect airway! • Strongly consider intubation

26. Respiratory Failure-Causes • Pulmonary Causes • Diffusion impairment • Atelectasis • Pneumonia • Bronchiolitis • Acute lung injury • Pulmonary edema • Shunting and V/Q mismatch • Non-Pulmonary Causes • Respiratory muscle compromise or fatigue • Impairment of the nervous systems control of breathing • Guillain-Barre • Muscular Dystrophy • Central hypoventilation syndrome • Sedatives • Head injury • Upper airway obstructions

27. Indications for intubation • Inability to protect airway • No cough or gag • Decreasing LOC • GCS < 8 • Cardiac or respiratory arrest • Acute respiratory acidosis • Refractory hypoxemia despite 100% FiO2

28. Goals of ventilation • Correct acidosis • Rest the respiratory muscles • Correct hypoxemia • Allows for delivery of high FiO2 • PEEP • Improves cardiac function • Decreases preload • Decreases metabolic demand

29. Initial Ventilator settings

30. Correction of hypoxia and hypercarbia

31. Match the Gas • Which patient does this gas belong to? • pH 7.09 PCO2 98 PO2 218 HCO3 30 • A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness • B) 9 y/o with new onset Diabetic Ketoacidosis • C) A 30 y/o patient presenting with a panic attack • D) A 25y/o in a skiing accident presenting in respiratory distress

32. Match the Gas • pH 7.09 PCO2 98 Po2 218 HCO3 30 • A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness • Chronic Respiratory Failure • Uncompensated Respiratory Acidosis

33. Match the Gas • Which patient does this gas belong to? • pH 7.55 PCO2 28PO2 63 HCO3- 23 • A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness • B) 9 y/o with new onset Diabetic Ketoacidosis • C) A 30 y/o patient presenting with a panic attack • D) A 25y/o in a skiing accident presenting in respiratory distress

34. Match the Gas • Which patient does this gas belong to? • pH 7.55 PCO2 28 PO2 63 HCO3- 23 • C) A 30 y/o patient presenting with a panic attack • Hyperventilation • Uncompensated Respiratory alkalosis

35. Match the Gas • Which patient does this gas belong to? • pH 6.94 PCO2 26.6 PO2 55.7 HCO3 5.7 BD -27 • A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness • B) 9 y/o with new onset Diabetic Ketoacidosis • C) A 30 y/o patient presenting with a panic attack • D) A 25y/o in a skiing accident presenting in respiratory distress

36. Match the Gas • pH 6.94 PCO2 26.6 PO2 55.7 HCO3 5.7 BD -27 • B) 9 y/o with new onset Diabetic Ketoacidosis • DKA • Uncompensated Metabolic Acidosis

37. Match the Gas • Which patient does this gas belong to? • pH 7.27 PCO2 54.8 PO2 70 HCO3 26BD -1 • A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness • B) 9 y/o with new onset Diabetic Ketoacidosis • C) A 30 y/o patient presenting with a panic attack • D) A 25y/o in a skiing accident presenting in respiratory distress

38. Match the Gas • pH 7.27 PCO2 54.8 PO2 70 HCO3 26BD -1 • D) A 25y/o in a skiing accident presenting in respiratory distress • Acute Respiratory Distress • Uncompensated Respiratory Acidosis

39. Questions?