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Acid/Base Balances. By: Diana Blum MSN MCC NURS 2140. Acid /Base Balance. Acid base balance is the regulation of free hydrogen ions in extra-cellular fluid. Acids: dissociate in solution to release H+. Bases: combine with free H+ and remove it from solution. Homeostasis.

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Acid base balances


By: Diana Blum MSN


Acid base balance
Acid /Base Balance

Acid base balance is the regulation of free hydrogen ions in extra-cellular fluid.

Acids: dissociate in solution to release H+.

Bases: combine with free H+ and remove it from solution.


  • Hydrogen ion: smallest ionic particle and very reactive

    • Small changes can alter protein and enzyme functioning

      • Affects organ function: heart, kidneys, lungs

      • Affects clotting cascade

      • Affects drug metabolism

  • Plasma PH: indicator of hydrogen ion concentration

    • Ex: pH of 7.50 is equivalent to 50 nmol/L of hydrogen ion

    • As Hydrogen ion increases pH decreases and vice versa

  • Life

    • pH range compatible with life is 6.8-7.8


    • Form hydrogen ions and are proton donors

      • Ex: HCL gives up H+ ion when added to blood

    • Strong acids give up hydrogen easily

      • Lower PH

    • Weak acids keep a grip on their hydrogen ions

      • Higher PH


    • Combine with hydrogen ions

    • Proton acceptors

      • Ex: NaHCO3- (sodium bicarb) removes hydrogen when added to blood

    Carbon dioxide respiratory acid
    Carbon Dioxide/Respiratory Acid

    • Potential acid

      • When dissolved it becomes carbonic acid

    • Body metabolism will constantly produce

      • 288L/day produced and excreted by ventilation

    Metabolic acid
    Metabolic Acid

    • Not many produced on daily basis

    • Main acids are:

      • Lactic

      • Pyruvic

      • Ketoacids

      • Beta hydroxybutyric

    • Eliminated by kidneys or Metabolized by liver

    Defense mechanisms
    Defense Mechanisms

    • First: Buffering

    • 2nd : Changing CO2 level

    • 3rd : changing the level of HCO3 -

    Buffer systems
    Buffer Systems

    • Helps minimize change in pH

    • React quickly to prevent excess changes

    • Primary Buffers: carbonic acid and bicarb

    • Aerobic metabolism:

    • Anaerobic metabolism:

    Buffer continued
    Buffer continued

    • Excess CO2 exhaled

    • Bicarb is retained by glomerular filtration and also excreted by renal tubule

    • So what really happens???

    • Intracellular Buffer is phosphate

    • Protein buffers in blood are plasma protein and hemoglobin

    • Bone is a buffer

    R o m e

    • Respiratory Opposite

      • Example: pH low PCO2 high HCO3 ok= respiratory acidosis

    • Metabolic Equal

      • Example: pH is high HCO3 is high it is metabolic

    Categories of interest
    Categories of Interest

    • Respiratory Acidosis:

    • Respiratory Alkalosis:

    • Metabolic Acidosis:

    • Metabolic Alkalosis:

    The lungs
    The Lungs

    • Regulate plasma pH on minute to minute basis by regulating carbon dioxide.

    • CO2 measured as partial pressure in arterial blood=PaCO2

      • Depth and rate of ventilation will alter

    • Minute Ventilation= how much air moved in 1 minute

      • Increase= blowing off CO2 to compensate

    • Dead Space} wasted ventilation/no part in gas exchange

    Lungs continued
    Lungs continued

    • Respiratory center=

    • Hypercarbic Drive= response to acute respiratory acidosis

      • Determinant of ventilation

    • Hypoxic Drive= Drive to breath…responds to low oxygen levels, high CO2, and acidosis

    • Hyperventilation: low PaCO2/hypocapnia

    • Hypoventilation: high PaCO2/ hypercapnia

    • Kussmals respirations: rapid deep breaths and attempt of lungs to correct pH by decreasing respiratory acid (compensation)


    • Secrete hydrogen ions

    • Reclaim bicarb during the filtering process in the glomerulas.

    • Ammonia


    • pH: 7.35-7.45

    • pCO2: 35-45

    • HCO3: 22-26

    • RR=12-20


    • 1} Assess the pH

    • 2} Is it Respiratory or Metabolic

      • Look at PaCO2

      • Look at Bicarb level

    • 3} Compensation

      • Complete or partial


    • Result from disease, organ dysfunction, pathologic reasons

    • Referred as primary hypercapnia

    • Excess CO2 decreases pH

      • Regulated by RR

    • Management:

      • Treat underlying cause

      • Sodium Bicarb not always given

      • BiPAP

      • CPAP

      • Vent

    • Lower than normal PaCO2

    • Elevated pH

      • Excessive /deep ventilation causes CO2 to be blown off thereby increasing pH

        • Alveolar over ventilation

    • Other Causes: hypoxemia, neuro issues, pregnancy

    • Changes serum electrolytes

    • Management: treat underlying cause

      • Breath into a paper bag

      • Reassure

      • Be calm

      • Explain procedures

    • Increase in total acid level thereby decreasing pH

    • Induced in 2 ways:

      • adding H+ ion or excreting H+ from dietary metabolism

      • Decrease in plasma bicarb to <22

    • Other Causes: ETOH, DM, Aspirin OD, Antifreeze ingestion, GI disturbances

    • Management: assess anion gap, monitor electrolytes and ABGs, treat underlying cause, sodium bicarb admin is controversial

    • Increase Bicarb and pH

    • Other Causes: depletion in K+, Cl-, volume depletion

    • Hypomagnesaemia may also occur

    • Management: correct volume or electrolyte depletion, may get steroids, dialysis,HCL IV in severe cases


    • Body’s normal way to normalize pH by neutralizing the opposite mechanism

    • Important to know cause and effect

      If you only treat compensatory response only pH will become more abnormal

    Compensated uncompensated
    Compensated ? / Uncompensated?

    Uncompensated: Ph and one other value abnormal

    Partially Compensated: ( All values are abnormal)

    Completely Compensated: (pH is the only normal value)

    • When compensation is present, we will see two imbalances. The question then becomes, which is the primary problem, and which imbalance is due to compensation.

    • The clue is the pH.

      • If the pH is leaning toward acidosis or alkalosis, then the parameter with the matching imbalance is the primary problem, and the other is due to compensation.


    • if the pH is normal in the presence of abnormal pO2/pCO2 – compensated

      • (the body has compensatedfor the abnormality and is able to maintain a normal pH)

    • if the pH is abnormal in the presence of abnormal pO2/pCO2 – uncompensated

      • (the body's defense mechanisms are no longer adequate to compensate, allowing the pH to move to an acidotic or an alkalotic state)


    Respiratory acidosis = low ph and high C02 hypoventilation (eg: copd, narcs or sedatives, atelectasis)*Compensated by metabolic alkalosis (increased HC03)examples:ph 7.20 C02 60 HC03 24 (uncompensated respiratory acidosis)ph 7.33 C02 55 HC03 29 (partially compensated respiratory acidosis)ph 7.37 C02 60 HC03 37 (compensated respiratory acidosis)

    Respiratory alkalosis = high ph and low C02 hyperventilation (eg: anxiety, PE, pain, sepsis)*Compensated by metabolic acidosis (decreased HC03)examples:ph 7.51 C02 26 HC03 25 (uncompensated respiratory alkalosis)ph 7.47 C02 32 HC03 20 (partially compensated respiratory alkalosis)ph 7.43 C02 30 HC03 19 (compensated respiratory alkalosis)

    Metabolic acidosis = low ph and low HC03 ex:diabeticketoacidosis, starvation, severe diarrhea*Compensated by respiratory alkalosis (decreased C02)examples:ph 7.23 C02 36 HC03 14 (uncompensated metabolic acidosis)ph 7.31 C02 30 HC03 17 (partially compensated metabolic acidosis)ph 7.38 C02 26 HC03 20 (compensated metabolic acidosis)

    Metabloic alkalosis = high ph and high HC03 ex. severe vomiting, k+ deficit, dieuretics*Compensated by respiratory acidosis (increased C02)example:ph 7.54 C02 44 HC03 29 (uncompensated metabolic alkalosis)ph 7.50 C02 49 HC03 32 (partially compensated metabolic alkalosis)ph 7.44 C02 52 HC02 35 (compensated metabolic alkalosis)

    Nursing management
    Nursing Management

    • Promote healthy behaviors

    • Limit conversations

    • 6 small meals a day

    • Positioning

    • Stress reduction techniques


    • Respiratory Acidosis

    • pH low PCO2 high bicarb ok


    • Metabolic alkalosis

    • pH high Bicarb high

    Acid base problems
    Acid base Problems

    pH 7.5, PaCO2 = 50 mm Hg, HCO3 =30 mEq/L

    Metabolic Alkalosis Partially Compensated.

    pH 7.31, Pa CO2 = 50 mm Hg, HCO3 = 22 mEq/L

    Respiratory Acidosis Uncompensated.

    pH 7.31, PaCO2 = 44 mm Hg , HCO3 = 20 mEq/l

    Metabolic Acidosis Uncompensated.

    More acid base problems
    More, Acid / Base problems.

    pH 7.47, PaCO2 = 48 mm Hg , HCO3 = 30 mEq/L

    Metabolic Alkalosis Partially Compensated.

    pH 7.33, Pa CO2 = 40 mm Hg, HCO3 = 21 mEq/L

    Metabolic Acidosis Uncompensated.

    pH 7.48, Pa CO2 = 44 mm Hg, HCO3 = 30 mEq/L

    Metabolic Alkalosis Uncompensated

    Even more acid base problems
    Even more, Acid /Base Problems

    pH 7.33, PaCO2 = 49 mm Hg, HCO3 = 26 mEq/L

    Respiratory Acidosis Uncompensated.

    pH 7.48, PaCO2 = 33 mm Hg, HCO3 = 24 mEq/L

    Respiratory Alkalosis Uncompensated.

    pH 7.31, PaCO2 = 33 mm Hg, HCO3 = 20 mEq/L

    Metabolic Alkalosis Partially Compensated.

    pH 7.45, Pa CO2 = 34 mm Hg, HCO3 = 20 mEq/L

    Respiratory Alkalosis Compensated.