Med Surg ABGs 🩺✨

pH Review

• Normal pH value: 7.35 - 7.45

• pH indicates if a patient is acidotic, alkalotic, or normal (homeostatic).

CO2 Review

• Controlled by the respiratory system (lungs).

• Normal value: 35 - 45

• Exhaling removes CO_2.

• Holding breath or poor gas exchange leads to CO_2 retention.

• CO_2 is a necessary but potentially harmful gas, especially in excess.

• In respiratory problems, pH and CO_2 move in opposite directions.

Bicarbonate (HCO3) Review

• Controlled by the renal system (kidneys) or metabolic processes.

• Normal value: 22 - 26

• Kidneys control bicarb by either retaining or excreting it.

Acid-Base Imbalances

• Changes in blood hydrogen ion level (H+) or pH indicate an imbalance.

• Acid-base imbalances are symptoms of underlying problems, not diseases themselves.

• If uncorrected, these imbalances can disrupt bodily functions:

  • Changing the shape of hormones and enzymes.

  • Altering electrolyte distribution.

  • Affecting excitable membranes (heart, nerves, skeletal muscles, GI tract).

  • Decreasing the effectiveness of hormones and drugs.

• Promptly determine and correct the underlying cause to prevent systemic changes.

Acidosis Pathophysiology

• pH less than 7.35.

• Results from an actual or relative increase in the amount or strength of acids.

Actual Acid Excess

• Overproduction or under-elimination of hydrogen ions.

  • Examples:

    • Diabetic ketoacidosis (DKA): High glucose levels lead to electrolyte changes and increased hydrogen ions due to glucose breakdown into CO_2.

    • Grand mal seizures: Breathing stops, causing CO_2 and hydrogen ion retention.

  • Under-elimination:

    • Respiratory failure.

    • Renal impairment.

Relative Acidosis

• Not enough base, causing a hydrogen ion build-up.

  • Causes:

    • Underproduction of base (pancreatitis, dehydration).

    • Over-elimination of base (diarrhea).

Metabolic Acidosis

• Overproduction of hydrogen ions.

  • Excessive fat breakdown (e.g., diabetic ketoacidosis).

  • Fad diets (e.g., Atkins, keto):

    • Cutting out carbohydrates forces the body to break down fat for energy, producing fatty acids and ketones, leading to increased hydrogen ion levels.

    • Rapid weight loss can occur, but the body may hoard carbohydrates when reintroduced, leading to weight regain.

  • Anaerobic metabolism:

    • Increased oxygen demand during exercise leads to cellular breakdown, releasing lactate, hydrogen, potassium, and water.

  • Excessive ingestion of acidic substances (e.g., aspirin - acetylsalicylic acid).

• Under-elimination of hydrogen ions:

  • Usually due to renal dysfunction or renal failure.

• Under-production of bicarbonate:

  • Caused by renal issues.

• Over-elimination of bicarbonate:

  • Diarrhea: Stool is normally alkaline therefore excessive diarrhea eliminates too much base.

Respiratory Acidosis

• Due to impairment of respiratory function.

Types of Respiratory Impairment

• Respiratory depression:

  • Chemicals: Opioids, anesthesia, alcohol, electrolyte imbalances.

  • Physical depression: Cerebral edema, stroke, brain tumors.

• Inadequate chest expansion:

  • MSK problems: Fractured ribs cause shallow breathing due to pain.

  • Muscle weakness: Fluid and electrolyte issues.

  • External conditions: Restrictive clothing like bras, obesity.

    • Morbid obesity: Adipose tissue and ascites decrease chest expansion.

• Airway obstruction:

  • Aspiration of food.

  • External constriction (choking).

  • Bronchospasm (asthma).

  • Mucus plugs.

• Decreased alveolar-capillary diffusion:

  • Conditions that decrease gas exchange due to reduced surface area, such as COPD, pulmonary edema, pneumonia, tuberculosis, repeated bronchitis (scar tissue).

Combined Acidosis

• Metabolic and respiratory acidosis together are very dangerous.

• Uncorrected respiratory acidosis can lead to anaerobic metabolism and cellular death, worsening metabolic acidosis.

• Clinical Example: Cardiac or respiratory arrest.

  • Respiratory failure leads to the heart compensating, but the heart also lacks oxygen, causing cardiac cell death.

  • Cardiac arrest means no circulation and no gas exchange.

Acidosis Assessment

• Diet history: Fad diets, low carb diets, starvation.

• Drug history:

  • Over-the-counter medications: Aspirin, anti-inflammatories, antacids.

  • Prescription medications: Diuretics, aspirin.

  • Illegal substances: Cocaine, crack, ice.

• Chronic illnesses: Diabetes, kidney problems, pancreatitis, respiratory issues.

• Acute illnesses: Diarrhea; look for fever (metabolism changes).

Central Nervous System Changes

• Depressed function: Lethargy, confusion, unresponsiveness.

Neuromuscular Changes

• Often correlated with hyperkalemia (due to cell destruction releasing potassium).

• Decreased muscle tone and reflexes.

• Severe cases: Flaccid paralysis, respiratory compromise.

• Assess: Hand grips, foot press, steadiness.

Cardiovascular Signs and Symptoms:

• Early Stages: Tachycardia and increased cardiac output due to low oxygen levels.

• Worsening Acidosis/Hyperkalemia: Dysrhythmias, arrhythmias due to disrupted electrical conduction.

• Decreased peripheral pulses.

• Mass Effect (Severe): Vasodilation, decreased blood pressure and heart rate.

Respiratory Signs and Symptoms:

• Rate and depth of respirations, ease of breathing, use of accessory muscles.

• Pulse oximeter: Measures peripheral tissue oxygenation.

  • Normal value: 95-100%.

• Metabolic Acidosis: Increased rate and depth (Kussmaul respirations) to eliminate CO_2 and hydrogen ions.

• Respiratory Acidosis: Shallow, rapid respirations or decreased respiratory effort leading to CO_2 retention.

Skin Signs and Symptoms:

• Metabolic Acidosis: Warm, dry, pink skin; normal mucous membranes (vasodilation).

• Respiratory Acidosis: Pale, dry or dusky gray, cyanotic (late finding) skin due to ineffective breathing and decreased gas exchange.

Psychosocial Assessment:

• Behavioral changes; confirm with family members.

Electrolyte Monitoring:

• Potassium: Most important electrolyte to monitor; hyperkalemia is common.

Laboratory Assessment

• Arterial Blood Gas (ABG):

  • pH less than 7.35 confirms acidosis but does not identify the cause.

  • Electrolytes may indicate the cause of the imbalance.

Interventions for Metabolic Acidosis:

• Hydration: Dilutes hydrogen ion concentration.

• Drug treatments:

  • Diabetic Ketoacidosis (DKA): Insulin and hydration.

  • Prolonged Diarrhea: Anti-diarrheal medications, hydration.

Interventions for Respiratory Acidosis:

• Maintain airway, enhance gas exchange (Airway, Breathing, Circulation).

• Medications:

  • Bronchodilators: Relax smooth muscle and increase airway diameter.

  • Anti-inflammatories (Steroids): Reduce edema and inflammation.

  • Mucolytics (e.g., Mucomyst): Thin bronchial secretions.

• Oxygen: Little bit has never killed anyone, but not giving any at all has killed a lot.

• Mechanical Ventilation: If oxygen saturation cannot be maintained above 90% or acidosis is uncorrected.

• Pulmonary hygiene:

  • Positioning: Upright, proper body alignment, head of bed elevated.

  • Breathing techniques: pursed lip breathing (hold breath and pucker lips when exhaling).

  • Increased fluid intake: Thins secretions (cautious with cardiac/renal).

Prevention of Complications:

• Assess and reassess frequently.

• Listen to lungs, watch for muscle retractions and accessory muscle use.

• Monitor skin and nail color; be aware that cyanosis is a late finding.

Alkalosis

• Not enough hydrogen ions; pH greater than 7.45.

• Caused by an actual or relative increase in the amount or strength of bases.

  • Take a little time to correct.

Actual Base Excess

• Base (usually bicarbonate) is overproduced or under-eliminated.

  • Causes of excessive bicarbonate intake:

    • Antacids (calcium carbonates).

    • Medical treatments (blood transfusions, hyperalimentation/TPN).

Relative Alkalosis

• Acids have dropped, causing base to rise.

  • Decreased cation levels or acid deficit due to:

    • Imbalances of electrolytes.

    • Prolonged vomiting (loss of hydrochloric acid).

    • Excessive cortisol/aldosterone.

    • Medical treatments (prolonged nasogastric suction).

Respiratory Alkalosis

• Excessive amounts of carbon dioxide blown off through hyperventilation.

  • Causes:

    • Anxiety/Fear.

    • Improper mechanical ventilation.

    • Direct stimulation of the respiratory center (fever, metabolic acidosis, CNS lesions).

Signs and Symptoms of Alkalosis

• Same whether metabolic or respiratory.

• Usually result of hypocalcemia and hypokalemia.

Central Nervous System:

• Overexcitement of central and peripheral nervous systems.

• Dizziness, agitation, confusion, hyperreflexia, seizures.

• Tingling and numbness around the mouth and in the toes (due to hypocalcemia).

Neuromuscular:

• Muscle cramps/twitches (charley horses).

• Problems with reflexes, tetany (hypocalcemia).

• Hypokalemia: Muscle weakness, gait and coordination problems, impaired respirations.

Cardiovascular:

• Increased myocardial irritability and tachycardic.

• Weak peripheral pulses.

• Hypovolemia: Severe hypotension.

• Hypokalemia: Increased sensitivity to digoxin, potential for digoxin toxicity.

Respiratory

• With resiparoty alkalosis; increased rate and depth of respirations.

Treatment

• Treatment focuses on correcting cause, such as breathing in a paper bag to rebreathe CO_2 for anxiety.

Laboratory Assessment:

• pH greater than 7.45 indicates alkalosis but provides no other information.

• Review symptoms, electrolytes, and ABGs.

Interventions:

• Correct the underlying cause to prevent further loss of hydrogen, potassium, and calcium.

• Restore fluid balance.

• Administer medications, fluid and electrolyte replacement, antiemetics for vomiting, antidiarrheals and antibiotics for diarrhea.

• Carefully monitor electrolyte balance, heart rate, rhythm, respiratory status, and oxygen status.

pH Measurement

• Measures hydrogen ion concentration of blood.

Partial Pressure of Carbon Dioxide (PaCO_2)

• Indicates effectiveness of breathing.

• Respiratory problems: pH and CO_2 move in opposite directions.

Bicarbonate (HCO_3)

• Represents the metabolic component of ABGs.

• Metabolic issues: pH and bicarbonate move in the same direction.

Other ABG Components

• Partial Pressure of Oxygen (PaO_2):

  • Partial pressure of oxygen dissolved in the blood. Normal is 80-100; differs from pulse oximeter readings.

• Pulse oximeter: Measures oxygen saturation, indicating gas exchange in peripheral tissues. Normal range is 95-100 %.

ABG Interpretation Steps

• Look at pH: Is it high (alkalosis) or low (acidosis)?

• Determine the cause: Look at CO_2 first to determine a respiratory issue and then also bicarbonate.

Compensation

• The body's attempt to restore normal pH.

• Types of compensation: Uncompensated, partially compensated, fully (completely) compensated.

Term 1: A patient with a history of COPD is admitted with respiratory distress. ABG results show pH 7.30, PaCO2 60 mm Hg, and HCO3- 24 mEq/L. Which acid-base imbalance is the patient experiencing?
Definition 1: Respiratory acidosis

Term 2: A patient is hyperventilating due to anxiety. Which acid-base imbalance is most likely to occur?
Definition 2: Respiratory alkalosis

Term 3: A patient with uncontrolled diabetes mellitus presents with deep, rapid respirations (Kussmaul breathing). Which acid-base imbalance is likely?
Definition 3: Metabolic acidosis

Term 4: A patient has been vomiting excessively for several days. Which acid-base imbalance is the patient at risk for?
Definition 4: Metabolic alkalosis
Term 5: A patient's ABG results show pH 7.50, PaCO2 30 mm Hg, and HCO3- 24 mEq/L. Which condition is the patient experiencing?
Definition 5: Respiratory alkalosis

Term 6: Which electrolyte imbalance is commonly associated with acidosis?
Definition 6: Hyperkalemia

Term 7: A patient with metabolic acidosis is ordered to receive sodium bicarbonate. What nursing intervention is essential when administering this medication?
Definition 7: Monitor the patient for signs of hypernatremia and fluid overload.

Term 8: A patient with respiratory acidosis is receiving mechanical ventilation. Which adjustment on the ventilator would help correct the acid-base imbalance?
Definition 8: Increasing the respiratory rate

Term 9: What is the normal pH range of arterial blood?
Definition 9: 7.35 - 7.45

Term 10: Which organ primarily regulates the bicarbonate (HCO_3) levels in the body?
Definition 10: Kidneys