Acid-Base Balance and Blood Gases

Acid-Base Balance and Arterial Blood Gases

• Acid-base balance is crucial for homeostasis, maintaining a stable environment in the body.
• Imbalances can arise from various health conditions, including diabetes mellitus, vomiting, diarrhea, and respiratory illnesses (e.g., COPD, asthma, bronchitis, flu, COVID-19).

Purpose

• The purpose of maintaining a steady balance of acids and bases.
• This balance is essential for the body to function correctly.
• Health problems can disrupt this carefully maintained balance.

How and Why...

• Arterial Blood Gases (ABGs) are essential for evaluating acid-base status.
• pH measures the concentration of hydrogen ions (H+).
• PaCO2 reflects the lungs' ability to eliminate carbon dioxide (CO2).
• HCO3- reflects the kidney's ability to regulate bicarbonate (HCO3-) levels.

pH

• pH is a measure of hydrogen ion concentration.
• High H+ concentration indicates acidity, low H+ indicates alkalinity.
• Normal blood pH ranges from 7.35 to 7.45.
• Acidosis occurs when pH falls below 7.40; alkalosis occurs when pH exceeds 7.40.

Compensation

• The body employs various mechanisms to correct pH imbalances.
• Compensatory mechanisms typically involve the lungs (acting quickly) and the kidneys (acting more slowly).
• Respiratory compensatory mechanisms happen within minutes/hours.
• Renal compensatory mechanisms happen over hours to days.

Compensation Mechanisms

• Chemical buffers (present in the tissue) quickly address minor changes in acid-base balance.
• Respiratory systems regulate CO2 to correct mild to moderate shifts.
• Renal systems regulate bicarbonate (HCO3-) to address more permanent issues.
• Renal compensation requires up to five days to complete.

Acid-Base Control Actions & Mechanisms: Respiratory

• The respiratory system is crucial for maintaining proper pH balance.
• Hyperventilation is a rapid response; to lower CO2.
• Hypoventilation is a slower response; to increase CO2.

Regulators of Acid/Base: Respiratory System

• The respiratory system eliminates CO2 from the body.
• The respiratory center (located in the medulla) regulates breathing.
• Changes in breathing rate and depth affect the level of CO2, influencing acid-base balance.
• Altered respiratory rate directly corresponds to CO2 levels and H+ ions (acid).

Regulators of Acid/Base: Renal System

• The renal system removes or retains hydrogen and bicarbonate ions.
• This helps control the levels of electrolytes in blood.
• Reabsorption/secretion of electrolytes help maintain balance.
• Older adults' renal compensation may be less effective in dealing with acidic loads.

Alterations in Acid-Base Balance

• Imbalances arise when compensatory mechanisms fail.
• Respiratory imbalances involve either excess or insufficient CO2 levels.
• Metabolic imbalances involve issues with bicarbonate levels.

Respiratory Acidosis

• Excess carbonic acid triggers respiratory acidosis, often due to hypoventilation.
• Hallmark of respiratory acidosis: increased PaCO2 with decreased PaO2.
• Acute causes: rapid build-up of CO2 as seen in hypoventilation, often leading to pH below 7.35.
• Chronic causes: long-term CO2 build-up (e.g., in COPD) where the body gets time to compensate with pH in the normal range.
• Symptoms: include confusion, nausea, vomiting, and tachycardia.

Common Causes: Respiratory acidosis

• Conditions like COPD, barbiturate or sedative overdose, chest wall abnormalities, pneumonia, respiratory muscle weakness, or mechanical hypoventilation can cause respiratory acidosis.

Respiratory Alkalosis

• Loss of carbonic acid, typically due to hyperventilation.
• Triggers include anxiety, pain, acute hypoxia, and other stimuli.
• Symptoms include anxiety, dizziness, tingling, and confusion.

Common Causes: Respiratory Alkalosis

• Conditions like hyperventilation, hypoxia, pulmonary emboli, anxiety, fear, musculoskeletal issues, and mechanical hyperventilation can trigger respiratory alkalosis.

Metabolic Acidosis

• Reduced bicarbonate or excessive acid.
• Common causes include diabetic ketoacidosis, lactic acidosis, starvation, severe diarrhea, renal issues, and kidney failure.
• Symptoms include hyperventilation (Kussmaul respirations), coolness of the skin, confusion, and decreased blood pressure.

Common Causes: Metabolic Acidosis

• Conditions like diabetic ketoacidosis, lactic acidosis, starvation, severe diarrhea, renal tubular acidosis, and renal failure are common causes.

Metabolic Alkalosis

• Excess bicarbonate or acid loss.
• Triggers include prolonged vomiting, excessive gastric suctioning, excessive use of antacids, diuretic therapy, and potassium deficiency.
• Symptoms include slow shallow respiration, confusion, anorexia, and muscle cramps.

Common Causes: Metabolic Alkalosis

• Conditions like prolonged vomiting, excessive gastric suctioning, diuretic use, and potassium deficiency can trigger metabolic alkalosis.

Interpretation of ABGs

• Analyzing ABGs involves examining pH, PaCO2, and HCO3- levels.
• The ROME method can help determine whether acidosis or alkalosis is present and the compensation status.
• The interpretation involves identifying which components of the ABGs are abnormal, and whether the remaining components are compensating or not.
• Full Compensation: All components normalize; Partial compensation: pH is still abnormal.

Explore the vital concepts of acid-base balance and the role of arterial blood gases in maintaining homeostasis in the human body. This quiz will assess your understanding of how pH, PaCO2, and HCO3- impact health and the consequences of imbalances caused by various conditions. Test your knowledge on this essential aspect of physiology.