Acid-Base Balance and Blood Gases

Acid-Base Balance and Blood Gases

• Learning objectives include reviewing pH balance, classifying acid-base disorders, describing pH imbalances in acid-base disorders, and describing the role of blood gases in acid-base balance.

pH Review

• Acids are ionic compounds that dissociate in water to form hydrogen ions (H+). The strength of an acid is determined by the concentration of H+ ions in solution. A higher H+ concentration indicates a stronger acid.
• Bases are ionic compounds that dissociate to form negatively charged hydroxide ions (OH-). The strength of a base is determined by the concentration of OH- in solution. A higher OH- concentration indicates a stronger base.

Neutralisation Reaction

• When acids and bases are mixed, they react to neutralize each other if equal numbers of hydrogen and hydroxide ions are present. This results in the formation of salt and water.

pH Scale

• The pH scale measures the acidity or basicity of a substance. A pH of 7.0 is neutral. Values below 7.0 are acidic, and values above 7.0 are basic (alkaline).
• The normal pH range for arterial blood is 7.35-7.45. A pH outside this range may be indicative of acidosis (lower pH) or alkalosis (higher pH). Survival range is from 6.8–8.0.

The Body and pH

• A table describing variables, primary disorders, and normal arterial gas ranges related to acid-base balance.

Diagnosis using ABGs

• Acidemia is a decrease in blood pH due to acidosis.
• Alkalemia is a increase in blood pH due to alkalosis.
• Normal pH range is 7.35 - 7.45.

Diagnosis using ABGs (cont.)

• Analyze pCO2 to determine respiratory disorders. For example, acidemia with elevated pCO2 indicates respiratory acidosis, while alkalemia with lowered pCO2 indicates respiratory alkalosis.

Diagnosis using ABGs (cont.)

• Analyze HCO3- to diagnose metabolic disorders. For example, alkalemia with elevated HCO3- indicates metabolic alkalosis, while acidemia with lowered HCO3- indicates metabolic acidosis.

Buffer Systems

• Chemical buffers (e.g., bicarbonate, phosphate, protein, and hemoglobin) provide the first line of defense against pH shifts.

• Physiological buffers (e.g., respiratory and renal mechanisms) offer a second line of defense, with differing timescales.

H+ Gain and Loss

• Factors contributing to H+ gain include CO2 in blood combining with water via carbonic anhydrase, non-volatile acids from metabolism (e.g., lactic acid), loss of bicarbonate in diarrhea/non-GI fluids, and loss of bicarbonate in urine.

• Factors contributing to H+ loss include the use of H+ in metabolism of organic anions, loss in vomit, loss in urine, and hyperventilation.

Acid-Base Imbalances

• Compensation is the body's response to acid-base imbalances, which may be complete or partial.
• Respiratory compensation occurs through hyper/hypoventilation when metabolic issues arise. Renal compensation works through metabolic alterations when respiratory issues are present.

Compensation (CO2 retention causing acidemia)

• The body compensates for CO2 retention (causing acidemia) by secreting H+ ions and retaining HCO3-.

Acid-Base Imbalances (Types of Symptoms)

• Different symptoms arise in both acidosis and alkalosis, affecting systems like the central nervous system, respiratory, heart, muscular, and digestive.

Respiratory Acidosis

• Caused by excessive CO2 in blood (hypercapnia), often due to conditions like respiratory depression, drug overdose, paralysis of respiratory muscles, or conditions like emphysema.
• Compensation includes kidneys eliminating hydrogen ions and retaining bicarbonate ions.
• Symptoms include breathlessness, restlessness, lethargy, disorientation, tremors, convulsions, coma, rapid breathing initially then becoming depressed, and skin warm/flushed.
• Treatment involves restoring ventilation, IV lactate solution, and treating the underlying dysfunction or disease.

Respiratory Alkalosis

• Caused by excessive loss of CO2 (hypocapnia) often due to hyperventilation.

• Conditions that stimulate the respiratory centre include oxygen deficiency, pulmonary disease, congestive heart failure (due to hypoxia), acute anxiety, salicylate intoxication, fever, anemia, cirrhosis and Gram-negative sepsis.

• Compensation involves kidneys conserving hydrogen ions and excreting bicarbonate ions.

• Treatment includes treating the underlying cause, breathing into a paper bag, and IV chloride-containing solution.

Metabolic Acidosis

• Occurs when there is bicarbonate deficit (blood bicarbonate levels below 22mEq/L), caused by loss of bicarbonate through diarrhea, accumulation of acids, failure of the kidneys to excrete H+.
• Compensation mechanisms include increased ventilation, renal excretion of H+ ions, and K+ exchange with H+ in extracellular fluid.
• Symptoms include headache, lethargy, nausea, vomiting, diarrhea, and coma, potentially culminating in death.
• Treatment involves IV lactate solutions.

Metabolic Alkalosis

• Occurs when there is an excess of bicarbonate (blood bicarbonate levels above 26mEq/L), caused by excess vomiting, excessive alkaline drug use, certain diuretics, endocrine disorders, or heavy antacid ingestion.
• Symptoms include slow and shallow respiration, hyperactive reflexes (tetany), electrolyte depletion, atrial tachycardia, and dysrhythmias.
• Compensation involves renal dysfunction.
• Treatment includes restoring electrolytes, IV chloride-containing solutions, and treating the underlying disorder.

This quiz focuses on the essential concepts of acid-base balance and the role of blood gases. You'll explore the fundamentals of pH, acid-base disorders, and the effects of hydrogen and hydroxide ions in neutralization reactions. Perfect for students looking to solidify their understanding of these critical topics.