ABG

Disrupted Homeostasis: Acidosis & Alkalosis

  • Overview of conditions that can disrupt the body's homeostasis, focusing on acidosis and alkalosis.

Arterial Blood Gasses (ABGs)

  • Arterial blood gases are critical indicators of oxygenation and acid-base balance in the body.

  • Acceptable ABG Values:

    • pH: 7.35 to 7.45

    • PaO2: 80 to 100 mm Hg

    • PaCO2: 35 to 45 mm Hg

    • HCO3 (Bicarbonate): 21 to 28 mEq/L

    • Base excess/deficit: 0 ± 2 mEq/L

    • SaO2 (O2 saturation): 95% to 100%

ABG Analysis: Respiratory

  • Acidosis:

    • pH is Low.

    • PaCO2 is High.

  • Alkalosis:

    • pH is High.

    • PaCO2 is Low.

ABG Analysis: Metabolic Acidosis

  • Metabolic Acidosis:

    • pH is Low.

    • HCO3 is Low.

  • Alkalosis:

    • pH is High.

    • HCO3 is High.

  • Kidneys involved in metabolic processes influencing acid-base balance.

Arterial Blood Gas Values Summary

Condition

pH

PaCO2

HCO3

Respiratory Acidosis

↑

Normal


Respiratory Alkalosis

↑

↓

Normal

Metabolic Acidosis

Normal

↓


Metabolic Alkalosis

PH ↑

Normal

↑

ABG Analysis Steps

  • Step 1: Look at pH value.

  • Step 2: Determine which values are within the normal range:

    • Normal pH: 7.35 to 7.45

    • Normal PaCO2: 35 to 45 mm Hg

    • Normal HCO3: 22 to 26 mEq/L

  • Step 3: Combine findings to establish a diagnosis related to homeostasis:

    • Respiratory Acidosis: Low pH, High PaCO2.

    • Metabolic Acidosis: Low pH, Low HCO3.

    • Respiratory Alkalosis: High pH, Low PaCO2.

    • Metabolic Alkalosis: High pH, High HCO3.

Respiratory Acidosis: Hypoventilation

  • Causes:

    • Respiratory depression from opioids, poisons, and anesthetics.

    • Neurological conditions such as brain tumors, cerebral aneurysms, strokes or overhydration, trauma (e.g., Guillain-Barré syndrome) affecting respiratory effort.

    • Inadequate expansion due to muscle weakness, pneumothorax, hemothorax, flail chest, obesity, sleep apnea, tumors, or deformities.

    • Airway obstruction resulting from neck edema, lymph node enlargement, foreign bodies, or excessive mucus.

    • Alveolar-capillary blockages such as pulmonary embolus, acute respiratory distress syndrome, chest trauma, drowning, or pulmonary edema.

    • Inadequate mechanical ventilation related to spinal problems or rib injuries.

  • Results of Respiratory Acidosis:

    • Elevated CO2 levels.

    • Increased or normal H+ concentration.

  • Manifestations:

    • Vital signs may show initial tachycardia and hypertension; these can degrade to bradycardia and hypotension as acidosis progresses.

    • Dysrhythmias may be seen, such as ventricular fibrillation in patients undergoing anesthesia.

    • Neurologically: Initially, clients may experience anxiety, irritability, and confusion, progressing to lethargy and possibly coma.

    • Respiratory symptoms include ineffective and shallow breathing.

    • Skin may present as pale or cyanotic.

  • Chronic Respiratory Acidosis:

    • Common in clients with chronic pulmonary diseases, obesity, and sleep apnea.

  • Nursing Care:

    • Oxygen therapy to improve oxygenation.

    • Maintaining a patent airway and enhancing gas exchange through positioning, breathing techniques, ventilatory support, bronchodilators, and mucolytics.

Respiratory Alkalosis: Hyperventilation

  • Causes:

    • Hyperventilation often due to fear, anxiety, intracerebral trauma, salicylate toxicity, or excessive mechanical ventilation.

    • Hypoxemia stemming from asphyxiation, high altitudes, shock, or early-stage asthma or pneumonia.

  • Results of Respiratory Alkalosis:

    • Decreased CO2 levels.

    • Normal or decreased H+ concentration.

  • Manifestations:

    • Vital signs typically show tachypnea (rapid breathing).

    • Neurologically: Patients may present with an inability to concentrate, numbness, tingling, tinnitus, and potential loss of consciousness.

    • Cardiovascular symptoms may include tachycardia and dysrhythmias.

    • Respiratory patterns are characterized by rapid, deep breaths.

  • Nursing Care:

    • Oxygen therapy to correct hypoxemia.

    • Anxiety reduction strategies for the patient.

    • Rebreathing techniques to restore CO2 levels to normal (e.g., paper bag breathing).

Metabolic Acidosis

  • Causes:

    • Excess production of hydrogen ions due to conditions like diabetic ketoacidosis (DKA), starvation, and lactic acidosis from heavy exercise, seizure activity, or hypoxia.

    • Excessive intake of acids from substances such as ethyl alcohol, methyl alcohol, and acetylsalicylic acid (aspirin).

    • Inadequate elimination of hydrogen ions may occur in kidney failure or severe lung problems.

    • Inadequate bicarbonate production due to conditions such as kidney failure, pancreatitis, or impaired liver function.

    • Excessive bicarbonate elimination through diarrhea.

  • Results of Metabolic Acidosis:

    • Decreased HCO3

    • Increased H+ concentration.

  • Manifestations:

    • Dysrhythmias may occur due to electrolyte imbalances.

    • Vital signs may indicate bradycardia, weak peripheral pulses, hypotension, and tachypnea.

    • Neurologically: Patients may present with headache, drowsiness, and confusion.

    • Respiratory signs often show rapid, deep respirations (Kussmaul respirations).

    • Skin appears warm, dry, and pink in color.

  • Nursing Care:

    • Care routines will vary with the underlying causes:

    • For DKA, insulin administration is crucial.

    • For GI losses, administer antidiarrheal medications and rehydrate.

    • If blood bicarbonate is low, administer sodium bicarbonate at a rate of 1 mEq/kg.

Metabolic Alkalosis

  • Causes:

    • Base Excess:

    • Oral ingestion of excess bases (e.g., antacids).

    • Parenteral administration of bases through blood transfusions or sodium bicarbonate.

    • Acid Deficit:

    • Loss of gastric secretions through prolonged vomiting or nasogastric suction.

    • Potassium depletion due to thiazide diuretics, laxative overuse, Cushing’s syndrome, or hyperaldosteronism.

  • Results of Metabolic Alkalosis:

    • Increased HCO3

    • Decreased H+ concentration.

  • Manifestations:

    • Vital signs may indicate tachycardia and normotensive or hypotensive states.

    • Dysrhythmias such as atrial tachycardia or other ventricular issues may arise when the pH exceeds normal limits.

    • Neurologically: Patients may exhibit numbness, tingling, muscle weakness, tetany, hyperreflexia, confusion, or convulsions.

    • Respiratory: Skeletal muscle depression can result in ineffective breathing patterns.

  • Nursing Care:

    • Treatment will vary:

    • For GI losses: Administer antiemetics, fluids, and electrolyte replacements.

    • For potassium depletion, it is essential to discontinue the causative agent.