acid base balance

ACID BASE BALANCE

General Information

  • Presented by: Maegen MacKenzie, MSN, RN, CNE at Austin Community College.

STUDY RECOMMENDATIONS

  • Study Lewis et al. (12th ed.) for "Acid-Base Imbalances". Check Blackboard for specific pages covered.

  • Know normal lab values for Arterial Blood Gas (ABG) results. Understand how abnormal lab results indicate acidosis, alkalosis, and compensation.

  • Use the Learning Guide on Acid-Base Balance to guide your studies.

  • Attend the scheduled ABG Workshop hosted by Professor MacKenzie.

  • Study case studies for each acid-base balance disorder.

  • Review the Learning Guide thoroughly.

ALTERATIONS IN ACID-BASE BALANCE

  • Definition: An acid-base imbalance happens when there is an alteration in the ratio of 20:1 between base and acid content.

  • Maintaining a steady balance between acids and bases is vital for homeostasis.

  • Acid-base imbalances occur when compensatory mechanisms fail.

  • Common diagnoses leading to acid-base imbalances:

    • Diabetes mellitus

    • Chronic obstructive pulmonary disease (COPD)

    • Kidney disease

HOW DO WE MEASURE ACID-BASE BALANCE?

  • The measurement of hydrogen ions (H+) concentration is termed pH.

  • The acidity or alkalinity of a solution depends on its hydrogen ion concentration:

    • Increase in H+ concentration: Leads to acidity.

    • Decrease in H+ concentration: Leads to alkalinity.

  • Blood pH is slightly alkaline, with a normal range of 7.35 to 7.45:

    • Acidosis: pH < 7.35

    • Alkalosis: pH > 7.45

NORMAL pH VALUES

  • Normal blood pH = 7.4.

    • 7.35 (normal) < 7.4 < 7.45 (normal)

  • Potential outcomes based on pH:

    • 6.80 - Death (Acidosis)

    • 7.45 - Normal

    • 7.80 - Death (Alkalosis)

  • Ratio of bicarbonate to carbonic acid in normal state:

    • Bicarbonate: 20 parts

    • Carbonic Acid: 1 part

CLASSIFICATION OF ACID-BASE IMBALANCES

  • Acid-base imbalances can be classified as:

    • Respiratory:

    • Result from retention or excess of CO2.

    • Can also occur due to an abnormal excretion or “blow off” of CO2.

    • Metabolic:

    • Involves alteration of bicarbonate (HCO3-) either alone or in combination with change in carbonic acid.

ACID-BASE REGULATION

  • Various metabolic processes produce acids that must be neutralized and excreted to maintain acid-base balance.

  • There are three main compensatory mechanisms for neutralizing acids:

    1. Buffer System: Immediate response.

    2. Respiratory System: Intermediate response within minutes to hours, but temporary.

    3. Renal System: Long response of 2-3 days to respond maximally; can maintain balance indefinitely in chronic imbalances.

BUFFER SYSTEM

  • The buffer system is the primary regulator of acid-base balance and the fastest acting.

  • Buffers cannot maintain pH without the proper functioning of the respiratory and renal systems.

  • Buffers in extracellular fluid (ECF) change strong acids to weak acids or bind acids through:

    • Carbonic acid-bicarbonate

    • Phosphate

    • Protein

    • Hemoglobin

  • Cells can act as a buffer by shifting H+ ions in and out in exchange for potassium (K+).

  • Alkalosis can induce hypokalemia; hence, K+ levels should be monitored.

ACIDOSIS AND ALKALOSIS

ACIDOSIS:

  • In acidosis, hydrogen ions move into the cells and potassium moves out to maintain balance, which may cause increased potassium levels.

ALKALOSIS:

  • In alkalosis, hydrogen ions are released from the cells, driving potassium into the cells, which decreases potassium levels.

RESPIRATORY SYSTEM

  • Chemical reaction:
    extCO<em>2+extH</em>2extO<br>ightleftharpoonsextH<em>2extCO</em>3ext(carbonicacid)<br>ightleftharpoonsextH++extHCO3−ext{CO}<em>2 + ext{H}</em>2 ext{O} <br>ightleftharpoons ext{H}<em>2 ext{CO}</em>3 ext{ (carbonic acid)} <br>ightleftharpoons ext{H}^+ + ext{HCO}_3^-

  • Respiratory compensation is fast-acting, but temporary.

  • In this mechanism, the respiratory system alters the rate and depth of breathing to blow off CO2 through hyperventilation or retain CO2 through hypoventilation.

  • Increased respirations: Increased CO2 elimination and decreased CO2 in blood.

  • Decreased respirations: CO2 retention, exacerbating acidosis.

RENAL SYSTEM

  • Slowest acting compensatory system but most efficient and long-lasting.

  • Normal renal function can maintain acid-base balance against chronic conditions. In cases of renal failure, the renal system loses the ability to correct pH.

  • The renal system primarily conserves bicarbonate and excretes acid using three mechanisms:

    1. Secretion of free hydrogen (H+) ions.

    2. Combining H+ with ammonia (NH3) to form ammonium.

    3. Excretion of weak acids.

ARTERIAL BLOOD GAS (ABG)

INTRODUCTION

  • Definition: An ABG is a blood test that measures the acidity (pH), and levels of oxygen (O2), carbon dioxide (CO2), and bicarbonate (HCO3) from an artery.

  • Purpose: To check the patient's lung function related to oxygen transfer and carbon dioxide removal, as well as to detect possible acid-base imbalances indicating respiratory, metabolic, or renal disorders.

FIVE KEY COMPONENTS OF ABG

  1. pH

  2. Partial pressure of carbon dioxide (PaCO2)

  3. Bicarbonate (HCO3)

  4. Partial pressure of oxygen (PaO2)

  5. Oxygen saturation (spO2)

NORMAL VALUES IN ABG

  • pH: 7.35 - 7.45

  • PaCO2: 35 - 45 mmHg

  • HCO3 (bicarbonate): 22 - 26 mEq/L

  • PaO2: 80 - 100 mmHg

  • SpO2: 95 - 100%

ACID-BASE IMBALANCES

  • Compensation is the body’s way of attempting to self-correct an acid-base imbalance:

    • Uncompensated: The pH is out of the normal range with no compensatory measures. Usually represents an acute change.

    • Partially Compensated: The pH is out of the normal range, but evidence of compensatory measures is present.

    • Compensated: pH returns to the normal range, indicating successful correction of the imbalance.

RESPIRATORY ACIDOSIS

  • Occurs due to inadequate breathing, leading to the buildup of PaCO2 or respiratory acid.

  • The excess CO2 combines with water to form carbonic acid, resulting in acidosis, common in obstructive pulmonary disorders.

  • Symptoms:

    • Decreased blood pressure

    • Drowsiness, confusion, and headache

    • Dysrhythmias

  • Kidney Compensation: The kidneys respond by conserving HCO3 and excreting increased H+.

CAUSES OF RESPIRATORY ACIDOSIS

  • **Conditions: **

    • Obstructive lung disease

    • Sedative overuse

    • Atelectasis

    • Severe pneumonia

    • Weak chest wall muscles

    • Brain trauma

    • Pulmonary edema or embolism

    • Mechanical hypoventilation

  • All these conditions share a mechanism of hypoventilation and CO2 retention.

NURSING CARE AND TREATMENT FOR RESPIRATORY ACIDOSIS

  • Monitor for signs of respiratory distress.

  • Administer oxygen as prescribed.

  • Assess central nervous system symptoms (CNS); be vigilant for somnolence.

  • Encourage patients to turn, cough, and breathe deeply every hour to facilitate CO2 blow off.

  • Provide appropriate respiratory treatments and hydration.

  • Perform suctioning as necessary.

  • Monitor electrolytes closely.

  • Administer antibiotics if indicated (e.g., pneumonia).

  • Employ telemetry and oxygen monitoring as needed.

METABOLIC ACIDOSIS

  • This condition manifests as a decrease in bicarbonate and accumulation of lactic acid; common in diarrhea, ketosis, and kidney disorders.

  • Symptoms:

    • Similar to respiratory acidosis, with possible gastrointestinal symptoms (N/V/D).

  • Compensation: Lungs increase CO2 excretion, leading to Kussmaul respirations (deep, rapid breathing).

  • Kidneys excrete acids and retain bicarbonate as compensatory measures.

CAUSES OF METABOLIC ACIDOSIS

  • Common Causes:

    • Diabetic ketoacidosis

    • Shock-induced lactic acidosis

    • Malnutrition

    • Renal insufficiency (acute or chronic)

    • Severe diarrhea (GI losses)

NURSING CARE AND TREATMENT FOR METABOLIC ACIDOSIS

  • Monitor for signs of respiratory distress.

  • Assess the level of consciousness (CNS).

  • Administer IV fluids (insulin for DKA if indicated).

  • Monitor electrolyte levels, and consider dialysis for renal failure patients.

RESPIRATORY ALKALOSIS

  • Characterized by elevated pH and decreased PaCO2; it occurs with hyperventilation.

  • Symptoms:

    • Lightheadedness

    • Confusion

    • Tachycardia

    • Nausea/vomiting

    • Neuromuscular symptoms

CAUSES OF RESPIRATORY ALKALOSIS

  • Conditions leading to hypoxemia from acute pulmonary disorders, hyperventilation, fever, pain, and mechanical ventilation, which often necessitates serial ABG labs.

NURSING CARE AND TREATMENT FOR RESPIRATORY ALKALOSIS

  • Monitor respiratory status diligently.

  • Provide a calm environment to mitigate anxiety that may exacerbate hyperventilation.

  • Encourage slow, deep breaths to reduce CO2 loss.

  • Breathing into a paper bag may help reset CO2 levels.

  • Keep an eye on electrolyte levels.

  • Monitor ventilated patients carefully.

METABOLIC ALKALOSIS

  • Occurs when bicarbonate concentration increases, raising blood pH.

  • Situations such as excessive vomiting, dehydration, or endocrine disorders can lead to this condition.

SYMPTOMS OF METABOLIC ALKALOSIS

  • Symptoms are similar to those of respiratory alkalosis but with hypoventilation as a compensatory mechanism.

CAUSES OF METABOLIC ALKALOSIS

  • Key Causes:

    • Overuse of diuretics (leads to loss of H+ and K+)

    • Excessive vomiting (loss of hydrochloric acid and potassium)

    • Ingestion of baking soda

    • Long-term GI suctioning

    • Hyperaldosteronism (kidney retains sodium, leading to H+ loss)

NURSING CARE AND TREATMENT FOR METABOLIC ALKALOSIS

  • Monitor respiratory status closely; slow respiratory rates may lead to hypoxemia.

  • Carefully observe patients undergoing nasogastric suctioning.

  • Monitor electrolyte levels diligently.

  • Administer antiemetic medications as needed for excessive vomiting.

  • Address underlying causes of alkalosis.

ABG INTERPRETATION

  • Normal Values:

    • pH: 7.35 - 7.45

    • PaCO2: 35 – 45 mmHg

    • HCO3: 22 – 26 mEq/L

    • PaO2: 80 - 100 mmHg

    • SpO2: 95 - 100%

  • Acid-Base Mnemonic—ROME:

    • Respiratory Opposite:

    • Alkalosis: ↑ pH, ↓ PaCO2

    • Acidosis: ↓ pH, ↑ PaCO2

    • Metabolic Equal:

    • Acidosis: ↓ pH, ↓ HCO3−

    • Alkalosis: ↑ pH, ↑ HCO3−

ABG INTERPRETATION METHOD

  1. Where is the party?

  2. Who is the party pooper?

  3. Is the “Life of the Party” helping to make the party better?

CASE STUDY EXERCISES

  • Example clinical interpretation:

    • Consideration of a 64-year-old female with pneumonia requiring prolonged mechanical ventilation showing ABG results of:
      extpH=7.48,extPaO<em>2=85extmmHg,extPaCO</em>2=30extmmHg,extHCO3=25extmEq/Lext{pH} = 7.48, ext{PaO}<em>2 = 85 ext{ mmHg}, ext{PaCO}</em>2 = 30 ext{ mmHg}, ext{HCO}_3 = 25 ext{ mEq/L}

    • Detailed analysis steps:

    1. Check pH to determine normality:

    2. Analyze PaCO2 and HCO3 against normal ranges.

  • Final evaluation leads to the determination of Respiratory Alkalosis.

  • Additional clinical scenario examples may be presented for further practice.