ACID-BASE BALANCE

Definition and Measurement
  - Acidity or alkalinity is measured using a pH scale that runs from 0 to 14.
  - The pH scale reflects the change in hydrogen ions in a solution.
  - Neutral: pH of 7
  - Acidic: pH less than 7
  - Basic/Alkaline: pH greater than 7
  - The physiological processes in the body require a delicate acid-base balance.
  - Blood pH is measured in samples from arteries or veins, with normal serum pH ranging from 7.35 to 7.45, averaging at 7.40.
Importance of Acid-Base Balance
- The body maintains acid-base balance primarily using buffer systems.

Regulation of Acid-Base Status
  - Multiple systems regulate acid-base status:
    1. Bicarbonate-Carbonic Acid Buffer System
    2. Respiratory System
    3. Kidneys

Primary Buffer in extracellular fluid and blood plasma.
Components:
- Carbonic acid (H₂CO₃) - a weak acid.
- Bicarbonate ion (HCO₃⁻) - a weak base.
Mechanism:
  - Neutralizes strong acids/bases by converting them into weak ones, preventing significant pH changes.
  - Equilibrium Reaction:
    CO_{2} + H_{2}O
ightleftharpoons H_{2}CO_{3}
ightleftharpoons H^{+} + HCO_{3}^{-}
Significance:
- Lungs control CO₂ levels (acid part).
- Kidneys control HCO₃⁻ levels (base part) for acid-base homeostasis.

Most Plentiful Buffer in the body, accounting for about two-thirds of the buffering power in blood and in cells.
Components:
- Plasma proteins (e.g., albumin) and hemoglobin in red blood cells.
Mechanism:
- Composed of amino acids with positively charged (amino) and negatively charged (carboxyl) regions.
- These charged sites can bind/release H+ or OH− ions to counter a pH change.
Significance:
- Hemoglobin buffers H+ ions produced during the conversion of CO₂ into bicarbonate.

Important for intracellular fluid and urine buffering.
Components:
- Dihydrogen phosphate ion (H₂PO₄⁻) - a weak acid.
- Hydrogen phosphate ion (HPO₄²⁻) - a weak base.
Mechanism:
  - Similar to bicarbonate system:
    - Addition of strong acid:
      HPO_{4}^{2-} + H^{+}
ightleftharpoons H_{2}PO_{4}^{-}
    - Addition of strong base:
      H_{2}PO_{4}^{-} + OH^{-}
ightleftharpoons HPO_{4}^{2-} + H_{2}O
Significance:
- Plays a critical role in the kidneys by excreting excess H+ into urine.

Definition: Acidosis occurs when blood pH is below 7.35, resulting from an excess of acid or loss of bicarbonate.

Cardiovascular:
  - Decreased cardiac contractility.
  - Arrhythmias (abnormal heart rhythms).
  - Low blood pressure (hypotension).
  - Heart is less responsive to medications (e.g., epinephrine).
Respiratory:
- Rapid, deep breathing (Kussmaul respirations) to expel CO₂ and raise pH.
- In respiratory acidosis, shallow/slowed breathing leads to hypoxemia and shortness of breath.
Neurological:
- Symptoms include headache, confusion, lethargy, drowsiness, stupor, and coma.
- High CO₂ levels can cause blurred vision and anxiety.
Musculoskeletal:
- Chronic metabolic acidosis may lead to bone density loss (osteoporosis) and muscle wasting due to buffering of acid using bone/muscle stores.
Electrolytes:
- Hyperkalemia (high potassium levels) occurs as H+ ions shift into cells and K+ ions shift out to maintain ion balance.

Definition: Alkalosis occurs when blood pH is above 7.45, typically leading to neuromuscular excitability and electrolyte imbalances.

Neuromuscular:
- Increased excitability leading to symptoms such as numbness, tingling (paresthesia), muscle twitching, cramps, and muscle spasms (tetany).
- Severe cases may result in seizures.
Cardiovascular:
- Arrhythmias and decreased myocardial contractility.
- Decreased cerebral blood flow leading to lightheadedness and confusion.
Respiratory:
- Compensatory hypoventilation (slowed breathing) to retain CO₂ and lower pH.
- This can result in hypoxia for patients with pre-existing respiratory issues.
Electrolytes:
- Hypokalemia (low potassium levels) and decreased levels of ionized calcium, causing muscle and nerve symptoms.

Imbalance Type	Primary pH Status	Primary Component Directional Trend	Compensation Component (Expected)
Respiratory Acidosis	↓ Acidosis (<7.35)	↑ PaCO₂ Increased (>45 mmHg)	↑ HCO₃⁻ (Metabolic Base)
Respiratory Alkalosis	↑ Alkalosis (>7.45)	↓ PaCO₂ Decreased (<35 mmHg)	↓ HCO₃⁻ (Metabolic Base)
Metabolic Acidosis	↓ Acidosis (<7.35)	↓ HCO₃⁻ Decreased (<22 mEq/L)	↓ PaCO₂ (Respiratory Acid)
Metabolic Alkalosis	↑ Alkalosis (>7.45)	↑ HCO₃⁻ Increased (>26 mEq/L)	↑ PaCO₂ (Respiratory Acid)

Imbalance Type	pH Status	Primary Causes	Treatment and Management
Respiratory Alkalosis	Increased (pH>7.45)	Hyperventilation (rapid, deep breathing), hypoxia, pulmonary disease, anxiety, pain, fever, drugs (salicylates)	Cease the cause (e.g., oxygen therapy, controlled breathing)
Respiratory Acidosis	Decreased (pH<7.35)	CO₂ retention from hypoventilation (e.g., COPD, brain injury, obesity)	Correct respiratory impairment and oxygen; consider sodium bicarbonate if severe
Metabolic Alkalosis	Increased (pH>7.45)	Loss of gastric acid (vomiting), hypovolemia, diuretics	Correct cause (e.g., antiemetics for vomiting); consider sodium bicarbonate
Metabolic Acidosis	Decreased (pH<7.35)	Loss of bicarbonate (diarrhea), overproduction of acid (e.g., DKA), chronic renal failure	Address underlying causes; hydration, insulin for DKA, bicarbonate for severe acidosis

Patient: 35-year-old with severe panic attack.
Symptoms: Rapid, deep breathing, numbness, tingling around mouth and hands.
Cause: Hyperventilation leading to CO₂ loss.
ABG Analysis:
  - pH: 7.53 (Increased Alkalosis)
  - PaCO₂: 28 (Decreased)
  - HCO₃⁻: 24 (Normal)
Summary: Elevated pH indicates respiratory alkalosis; symptoms stem from increased neuromuscular excitability.

Patient: 70-year-old with chronic renal failure.
Symptoms: Confusion, rapid, deep respirations (Kussmaul breathing).
ABG Analysis (Compensated):
  - pH: 7.30 (Decreased Acidosis)
  - PaCO₂: 30 (Decreased)
  - HCO₃⁻: 18 (Decreased)
Summary: Low pH and decreased HCO₃⁻ confirm metabolic acidosis; respiratory compensation is evident with decreased PaCO₂. Risks include decreased cardiac contractility and hyperkalemia.