MA

Acid Base- Balance

Blood pH and why it matters

  • For body to function correctly, blood pH must stay in a narrow range.

  • Lower pH more hydrogen inons

  • Higher pH less hydrogen

  • Body works constantly to keep pH steady by controlling how much H+ are presnt

    • Buffers in blood

      • HCO3

        • Quickly soak up or release H+

    • The lungs

      • Control how much CO2 you have breath out

    • The kidneys

      • Controls how much acid or base is removed from the body.

  • Acidic: low pH ( a measurable property) a solution

  • Acidotic: moving towards acidity; hypoventilation patient

  • Acidosis: conditions where blood pH < 7.35

Where Acids come from

  • Your body makes acids every day

    • Volatile acid

      • Can turn into a gas and leave the body through the lungs

      • Carbonic acid, which comes form CO2 combining with water in the red blood cell

      • When you breathe out, your lungs get rid of the CO2,

        • Respiratory acidosis CO2 build up.

    • Respiratory alkalosis. breath to much CO2 out.

    • Fixed Acids:

      • These acids are produced by normal metabolism and cannot be removed by the lungs

      • They are handled by the kidneys

      • Common examples

        • Lactic Acid

        • Ketone Acid

      • Metabolic acidosis: kidneys cannot get rid of the acids fast enough.

How the body keeps balance;

  • To keep the pH between 7.35 and 7.45

  • The lungs act quickly, within minutes to adjust breathing and remove or retain CO2

  • The kidneys act more slowly over hours or days by excreting hydrogen ions or conserving bicarbonate to neutralize acid

  • Buffers in the blood act instantly to stabilize pH by pairing acids and bases together.

Buffer system

  • What a buffer does:

    • A buffer acts like a pH shock absorber.

    • Whenever acid H+ builds up the buffer soaks it up.

    • When the blood becomes too basic the buffer can release H+ to bring the pH back down

    • Without buffers every breath or meal would cause dangerous swing in blood pH.

  • Isohydric (Hemoglobin) buffer system

    • Found mainly inside red blood cells

    • Hemoglobin the same molecules that carries oxygen can also pick up hydrogen ions when the blood becomes acidic

    • When CO2 enters a red blood cell it forms carbonic acid. The acid splits releaseing H+ which hemoglobin grabs and holds

    • This keeps blood pH stable while also allowing CO2 to be carried back to the lungs for exhalation.

  • Bicarbonate buffer system (open system)

    • Most important

    • Uses bicarbonate and CO2 to maintain pH

    • When blood becomes too acidic bicarbonate binds with H+ to form carbonic acid which breaks down into the water and CO2 and the lungs exhale the Co2

    • When blood becomes too basic the system reverses CO2 combines with water to make more acid.

    • While in teh blood, bicarbonate ion serves to neutralize acid introduced to the blood thorugh other metabolic processes (lactic acid), any bases are neutralized by carbonic acid.

  • NOn-Bicarbonate closed

    • Include phosphates and proteins inside cells and body fluids

    • They can’t get rid fo CO2 through breating, so theyre called closed

    • Instead thy bind or release H+ direclty

    • Phosphates work well in teh kidneys and inside cells where pH can change quickly

    • Protiens trhoguht the body also have side groups that can grab or let go of H+.

How all buffers work togther:

  • All buffer systems act simultaneously to keep pH steady. If one system starts to get overwhelemed like CO2 is rising the others jump in to help until the lungs or kidneys can correct the imbalance

  • Clinical Relevance for Respiratory Therapists

    •ABG interpretation is built around this chemistry:

    •PaCO₂ represents the acid side (controlled by breathing).

    •HCO₃⁻ represents the base side (controlled by kidneys).

    •When you see an ABG with low pH and high CO₂, you know the bicarbonate system is trying to buffer but can’t keep up — the patient is in respiratory acidosis.

Henderson-Hasselbalch Equation

  • The Henderson–Hasselbalch equation is a formula that shows how the pH of blood depends on the balance between acids and bases — specifically the relationship between bicarbonate (HCO₃⁻) and carbon dioxide (CO₂).

  • •6.1 is a constant that reflects the natural properties of carbonic acid in the body.

    •[HCO₃⁻] = the amount of base (bicarbonate) in the blood, controlled mainly by the kidneys.

    •PaCO₂ = the amount of acid (carbon dioxide) in the blood, controlled mainly by the lungs.

    •0.03 = a constant used to convert the pressure of CO₂ into the same units as bicarbonate.

  • The pH depends on the ration between bicarbonate and carbon dioxide.

    • When bicarbonate increases (base ) pH rises, blood becomes more alkaline

    • When CO2 increases (more acid) pH falls, blood acidic.

  • Its not about the absolute amounts its about the balance.

  • A normal ratio of HCO3: CO2 is about 20:1, which gives a normal blood pH of 7.4

    • Co2 normal is 35-45 (35 alka, 45 acid) if its off its a respiratory problem.

    • HCo2 normal is 22-26 (22 acid)(26 alka)

Respiratory vs. metabolic control:

  • Respiratory , controlled by lungs changes Co2 (acid). Hypoventilation increases CO2, and lowers pH.

  • Metabolic, crontrolled by the kidneys, HCO3 (base) renal failure decrease and lowers pH ( metabolic acidosis.)