Acid-base Balance:- Part 3 – Respiratory Acidosis and Alkalosis

May 28, 2022Chemical pathologyLab Tests

Respiratory Acidosis and Alkalosis

Sample for Respiratory Acidosis and Alkalosis

1. The better choice is the Radial artery.
   1. The sample may be taken from the femoral artery or brachial.
   2. It can be drawn from the indwelling arterial line.
2. The tests are done immediately because oxygen and carbon dioxide are unstable.
   1. Place the sample on ice and immediately transfer it to the lab.
3. Arterial blood is better than venous blood.
4. For venous blood syringe or tube be filled, and apply a tourniquet for a few seconds.
5. Arterial blood is risky, and a trained person should do it.
   1. Never apply a tourniquet.
   2. Don’t apply the pull to the plunger of the syringe.

Arterial VS Venous blood

Arterial blood (ABG):

1. Arterial blood (ABG)  gives a good mixture of blood from various areas of the body.
2. Arterial blood color is bright red.
3. Arterial blood measurement gives a better status of lung oxygenation.
   1. If arterial O2 concentration is normal, indicate lung function is normal.
   2. If mixed venous O2 concentration is low, indicating the heart and circulation are failing.
4. Arterial blood gives information about the lung’s ability to regulate the acid-base balance through the retention or release of CO2.
   1. Can check the effectiveness of the kidneys in maintaining the appropriate bicarbonate level.

Venous blood (VBG)

1. It gives information about the local area from where the blood sample is taken.
   1. Venous blood color is dark red.
   2. Metabolism of the extremity varies from area to area.
   3. In shock,  the extremities are cold, and less blood perfusion.
   4. During the local exercise of the extremities, such as opening and closing the fist with power.
   5. In case there is an infection of the sample area.
2. A blood sample from the central venous catheter is not a good mix of blood from various parts of the body.  For well-mixed blood sample should be taken from the right ventricle or the pulmonary artery, which is not an easy procedure.
3. A blood sample from the central venous catheter:
   1. Shows low O2 concentration, which means that:
      1. Either the lungs have not oxygenated the arterial blood well.
      2. Or the Heart is not circulating the blood effectively.

Difference between arterial and venous blood:

Precautions for the collection of blood

1. Avoid pain and anxiety in the patient, which will lead to hyperventilation.
   1. Hyperventilation due to any cause leads to decreased CO2 and increased pH.
2. Keep blood cool during transit.
3. Don’t clench your finger or fist. This will leads to lower CO₂ and increased acid metabolites.
4. pCO₂ values are lower in the sitting or standing position in comparison with the supine position.
5. Don’t delay the performance of the test.
6. Avoid air bubbles in the syringe.
7. Excess of heparin decreases the pCO₂,  maybe 40% less.
8. Not proper mixing of the blood before running the test may give a false result.
9. A prolonged tourniquet or muscular activity decreases venous pO₂ and pH.
10. The best way to collect arterial or venous blood is anaerobic.
11. Arterial blood precautions:
    1. Only syringe and needle, no tourniquet, no pull on the plunger.
12. Venous blood precautions:
    1. The heparinized evacuated tube’s needle and a syringe filled, drawn a few seconds after the tourniquet.
    2. Liquid heparin is the only suitable anticoagulant with the proper amount.
       1. Less amount will lead to clot formation.
       2. The increased amount will lead to an increase in CO2 and a decrease in pH.
       3. This will leads to a dilutional error.
13. Glass collection devices are better than plastic.

Definition of acid-base disturbance and control:

1. H⁺ ions and electrolytes disturbances may be:
   1. Acute.
   2. Chronic.
   3. Modest or severe.
   4. Simple or mixed.
2. When there is an accumulation of H⁺ ions is called acidosis.
   1. When blood pH is declining below 7.3, this process is called acidemia.
3. When there is a deficiency of H⁺ ions is called alkalosis.
   1. Blood pH rises above 7.45 is called alkalemia.
4. There are conditions related to the respiratory system that leads to respiratory acidosis or alkalosis.
5. There are metabolic conditions related to kidneys, and abnormality of intake/output leads to metabolic acidosis/alkalosis.
6. The blood pH is normally maintained at 7.38 to 7.42. Any deviation from this range indicates a change in the H⁺ ions concentration.
   1. Blood pH is a negative logarithm of [H⁺] as shown in the following equation:
      1. 1. pH = log₁₀ [H⁺]
      2. This equation shows that an increase in the H⁺ ions will lead to a fall in the blood pH is called acidemia.
      3. So a decrease in the H⁺ ions will lead to an increase in the pH of the blood called alkalemia.
      4. The conditions which cause the change in the pH are called acidosis and alkalosis.
7. The following diagram can explain how pH is maintained by the arterial carbon dioxide tension  (pCO2)  and plasma bicarbonate (HCO3^–).
   

   The acid-base mechanism, the role of lungs and kidneys

8. Plasma HCO3^– decrease in the plasma caused by gastrointestinal or renal losses will increase H⁺ ions and lowers the pH.
   

   Acid-base buffer system

Indications for the diagnosis of respiratory Alkalosis/acidosis:

1. In the case of chronic lung disease.
2. Cardiopulmonary arrest.
3. Sleep apnea.
4. Myasthenia gravis.
5. Laryngospasm.
6. Chronic obstructive pulmonary disease.

Respiratory acidosis

Definition:

With respiratory failure, CO2 accumulates (hypercapnia). This state will raise the pCO2 and causes the pH to drop, and lead to acidosis.

This is a decrease in alveolar ventilation in relation to the metabolic production of the CO2 that produces respiratory acidosis by the increase in carbonic acid.

Respiratory Acidosis and Alkalosis: Respiratory acidosis

Pathophysiology of respiratory acidosis:

1. Alveolar ventilation provides the necessary oxygen for oxidative metabolism and eliminates the CO2 produced by these metabolic processes.
2. There is a depression in the ventilation, resulting in excess CO2 (hypercapnia) in the blood circulation.
3. A decrease in alveolar ventilation in relation to the metabolic production of CO2 produces respiratory acidosis by an increase in H2CO3 acid.
4. The arterial CO2 tension (or pressure) PaCO2 is >45 mm Hg.

Respiratory acidosis and the role of the lungs

5. This is seen in respiratory failure, where CO2 accumulates, called hypercapnia.
6. This condition will raise the pCO2 and causes the pH to drop.
7. To compensate, the HCO3^– will increase, but this is not sufficient to restore the pH to a normal level.
   1. CO2  level rises, and this retained CO2 combines with water and forms H2CO3.
   2. H2CO3 dissociates to release H⁺ and HCO3^–  ions.
   3. Increased paCO2  and free H⁺ ions stimulate the medulla to increase the respiratory rate and expel the CO2.
   4. As the pH falls, to 2.3, diphosphoglycerate accumulates in the RBCs, which will alter the Hb (hemoglobin) to release the O2 (oxygen).
      1. Hb picks up H⁺ ions and CO2 and removes both from the blood circulation.
   5. If the respiratory mechanism fails, rising paCO2 stimulates the kidneys, retains HCO3^– and Na⁺ (sodium) ions, and starts excreting H⁺ ions.
8. Total CO2 may rise to a very high level of chronic respiratory acidosis.

Respiratory acidosis

Signs and symptoms of respiratory acidosis:

1. There is often breathlessness.
2. The patient is restless.
3. There is a headache, dyspnoea, and tachypnea.
4. There is apprehension followed by lethargy.
5. The patient will have disorientation.
6. There are muscle twitching and tremors.
7. Skin will be warm and flushed due to raised CO2 causing vasodilatation.
8. There may be hypertension or hypotension.
9. There are atrial and ventricular arrhythmias.
10. The patient will have convulsions and ultimately goes into a coma.

Causes of respiratory acidosis:

1. Acute respiratory acidosis:
   1. This occurs with sudden obstruction to:
      1. The airway.
      2. Chest trauma damages the respiratory muscles.
      3. Acute paralysis or depression of the CNS respiratory center.
   2. HCO3^– rises 1 meq/L for each 10 mmHg rise in pCO₂.
2. Chronic respiratory acidosis:
   1. This chronic respiratory acidosis is difficult to treat as compared to acute respiratory acidosis.
   2. This will take place by:
      1. Chronic obstructive pulmonary diseases like bronchitis, emphysema, pulmonary fibrosis, or scarring.
      2. Accumulation of the CO2 lasting days, weeks, or months will provoke a sustained increase in HCO3^– generation and leads to enhanced renal excretion of the H+ ions with chronic CO 2 retention.
      3. HCO3^– rises 3.5 meq/L for each 10 mm Hg rise in pCO 2.
      4. The serum level of Na⁺ and K⁺ may be normal or mildly raised.
3. Suppression of the medullary respiratory center:
   1. Sleep apnea.
   2. Sedation medicines.
   3. Cardiopulmonary arrest.
4. Upper respiratory obstruction:
   1. Laryngospasm.
   2. Aspiration of the foreign body or vomitus.
   3. Obstruction in sleep apnea.
5. Defective respiratory muscle function:
   1. Myasthenia gravis.
   2. Guillain-barre syndrome.
   3. Botulism.
   4. Hypokalemia (severe).
   5. Poliomyelitis.
   6. Myxedema.
   7. Amyotrophic lateral sclerosis.
6. Defect in the pulmonary gas exchange:
   1. Acute respiratory distress syndrome.
   2. Pneumothorax.
   3. Hemothorax.
   4. Severe asthma.
   5. Severe pneumonia.
   6. Chronic obstructive pulmonary disease.

Lab diagnosis of respiratory acidosis:

1. pH = <7.35 to 7.45.
2. paCO2 = >45 mm Hg.
3. HCO3^– = Normal (in the acute stage).
4. HCO3^– = Increased (in the chronic stage).
   

   Acid-base balance: Respiratory acidosis and compensatory mechanism

Treatment of respiratory acidosis

1. Treatment of the pulmonary causes:
   1. If there is obstruction by the foreign body, remove that immediately.
   2. There may be a need for mechanical ventilators.
   3. Give bronchodilators.
   4. If there is pneumonia, then start antibiotics.
   5. If there is pneumothorax, then put chest tube.
   6. In the case of pulmonary embolism, start thrombolytic and anticoagulants.
   7. Remove the secretions by bronchoscopy.
2. Treatment of chronic obstructive pulmonary disease (COPD):
   1. Give O2 at a slow rate.
   2. Start bronchodilators.
   3. Start corticosteroids.
3. You can also give I/V sodium bicarbonate.
4. Other drugs are needed for the treatment of the cause.

Respiratory Alkalosis

Definition:

1. This is due to over-breathing, causing excessive CO2 excretion, leading to a rise in blood pH.

Pathophysiology of respiratory alkalosis:

1. Overbreathing causes excessive CO2 exhaled out and causes the blood pH to rise.

Respiratory alkalosis

2. Acute respiratory alkalosis interacts with intracellular and protein buffers before affecting the HCO3^– system.
3. After the adjustment, blood HCO3^– drops 5 meq/L for every 10 mmHg decline in pCO2.
4. Alkalosis causes plasma proteins to have a more negative charge that in turn binds more ionized Ca^++.
5. This hypocalcemia increases neuromuscular excitability and leads to tetany.
6. Respiratory alkalosis occurs when there are alveolar hyperventilation and excessive reduction in plasma CO2 levels. This is called hypocapnia.
7. In the case of initial hypoxemia, there is increased ventilation mostly mediated by the chemoreceptors in the carotid body; these are located near the carotid artery’s bifurcation.
8. Kidneys compensate by decreasing H+ excretion and HCO3¯ reabsorption.
9. The PaCO2 is <35 mm Hg.
   

   Respiratory alkalosis changes

Causes of respiratory alkalosis:

1. Pulmonary diseases due to hypoxemia:
   1. Pneumonia.
   2. Pulmonary embolism.
   3. Pulmonary edema.
   4. High-altitude syndrome.
   5. Severe anemia.
   6. Congestive heart failure.
2. Stimulation of the medullary (respiratory) center:
   1. Hepatic encephalopathy.
   2. Sepsis with fever.
   3. Salicylates toxication.
   4. Hyperventilation syndrome.
   5. Pregnancy when there is increased progesterone.
   6. Cerebrovascular accidents.
   7. Pontine tumors.
3. Hypermetabolic conditions:
   1. Fever.
   2. Anemia.
   3. Thyrotoxicosis.
   4. Hysteria.
   5. Cirrhosis.
   6. Gram-negative sepsis.
   7. Pregnancy.

Signs and symptoms of respiratory alkalosis:

1. The central and peripheral nervous system is stimulated, leading to:
   1. There is light-headedness or Dizziness.
   2. The patient may be agitated.
   3. Confusion.
   4. Tingling of the extremities appears first around the mouth and in the fingers and toes, called circumoral and peripheral paresthesia.
   5. There is a carpopedal spasm, twitching, and muscle weakness.
   6. Light-headedness and weakness may occur and progress to unconsciousness.
   7. Convulsions.
2. Ultimately the patient goes into a coma.
3. Deep and rapid respirations are the primary symptoms that cause respiratory alkalosis.

Diagnosis of respiratory alkalosis:

1. The blood pH is >7.42.
2. Decreased pCO2.
3. HCO3: H2CO3  = 20:0.5
4. Decreased H2CO3 level.
5. HCO3^– = Normal in acute stage
6. HCO3^– = Less than normal in the chronic stage.
   

   Acid-base base: Respiratory alkalosis and compensatory mechanism

Treatment of respiratory alkalosis:

1. If there is intoxication like salicylates, then induce emesis or use gastric lavage.
2. May need treatment for fever or sepsis.
3. O2-therapy for acute hypoxemia.
4. In the case of CNs disease, treat those diseases.
5. Ask the patient to breathe in the paper bags.
6. Ventilators are needed.
7. Treatment is mostly not needed.
8. It is important to diagnose the cause and treat the underlying disease.

Table showing characteristic features of respiratory acidosis and alkalosis:

Panic values:

Summary of the parameters needed for the acid-base balance: