Acid-Base Balance

Acid-Base Balance

Bicarb - Carbonic Acid Ratio

ABG Values KNOW THIS FOR THE EXAM 

• Normal pH: 7.35-7.45

• Acidosis: pH of less than 7.35.

• Alkalosis: pH of greater than 7.45

• HCO3 (bicarb): Norm 22-26 mEq/L 

  • Memory aide: 2+2+2=6

• PaCO2: Norm 35-45 mmHG

• PaO2: Norm 80 to 100

• SaO2: Norm 95% to 99%

• BE (base excess): Norm -2 to +2 mEq/L (< -2 base deficit, > 2 base excess)

Base (bicarb) Excess/Deficit

• BE/BD:  a calculated value. Reflects an excess or deficit in the total amount of base present to buffer body acids.

• Reflects metabolic disturbances only

• Always “-” in metab acidosis.  Always “+” in metab alkalosis.  Normal = “-2 to +2”

Compensation vs Correction

• In Both: abnormal, pH is returned toward normal.

Compensation

• abnormal pH is returned toward normal by the body's natural physiological response to an acid-base imbalance - if PaCO2 is high, HCO3 is retained to compensate. 

• Example:  In Resp acidosis, kidneys compensate by retaining HCO3

Correction

• abnormal pH is returned toward normal by the medical interventions and treatment provided to resolve the underlying cause of the imbalance. 

• Example:  

  • In Resp. Acidosis, perform CPT, suctioning, administer bronchodilators to correct imbalance

Interpreting ABGs

ABG Interpretation

• What is the pH?

  • Acidosis < 7.35 - 7.45 > Alkalosis

• Is it compensated or uncompensated?

  • Normal = compensated  

  • Not normal = uncompensated

ABG Interpretation

• What is the PaCO2?

  • Normal

  • Alkalosis < 35 - 45 >Acidosis

• What is the HCO3?

  • Normal

  •  Acidosis < 22 - 26 > Alkalosis

• Is the pH a result of respiratory or metabolic factors?

ABG Baby

• pH          7.48 Alkalosis

• PaCO2    30 Alkalotic

• HCO3     23 Normal

• What is the baby’s last name? What is the pH? 

  • Alkalosis

• What is the baby’s first name?  Compensated vs Uncompensated? Is the pH within normal range?

  • pH not within range, uncompensated

• What is the baby’s middle name?  Who is the baby daddy?

  • The father (the cause) is the one with the same last name. Mr. Respiratory bec he is alkalot

The Baby Daddy

• Mr. Respiratory (fast acting)

  • Fixed by suctioning and giving O2

• Mr. Metabolic (not so fast)

  • IV, electrode infusion

Try this

• pH          7.12 (pH and PaCO2 is both going lower= metabolic) 

• PaCO2  20  

• HCO3     7

• What is the baby’s last name? What is the pH? 

  • Acidosis

• What is the baby’s first name?  Compensated vs Uncompensated? Is the pH within normal range?

  • Uncompensated

• What is the baby’s middle name?  Who is the baby daddy?

  • PaCO2 (respiratory) - alkalotic

  • HCO3 (metabolic) - acidotic

  • Which one matches the pH?

  • Uncompensated Metabolic Acidosis

• What is the baby’s last name - the pH?

  • Alkalosis

• What is the first name - the pH?

  • Compensated

• What is the middle name?

  • PaCO2 (respiratory) - alkalotic

  • HCO3 (metabolic) - acidotic

  • Which one matches the pH?

  • Compensated Respiratory Alkalosis

Respiratory Acidosis - Causes (­High PaCO2, Low pH)

• Acid Excess, Build up of CO2

  • Hypoventilation

  • Respiratory failure

  • COPD

  • Narc or sedative OD

  • Airway obstruction

  • Pain, post-op (shallow breaths)

Respiratory Acidosis symptoms

• Headache, Seizures

• Hypoventilation with hypoxia

• Confusion, Lethargy, Dizziness

• Low BP

• Warm, flushed skin

Respiratory Acidosis collaborative care

• Bed in High Fowlers

• Bronchodilators: ipratropium, albuterol

• Narc antagonists: naloxone

• Hydration

• Encourage cough and deep breathing

Respiratory Alkalosis - Causes (Low PaCO2, High pH)

• Acid Deficit

  • Hyperventilation

  • Salicylate OD

  • Fever

  • Anxiety, CNS disorders

  • Mechanical over-ventilation 

Respiratory Alkalosis - Symptoms

• Think vasoconstriction

  • Lightheadedness, dizziness

  • Confusion, Headache

  • Numbness, tingling in extremities

  • Tetany

  • Muscle cramps

  • Hyperactive reflexes, Seizures

  • Hyperventilation

  • Arrhythmias, Tachycardia 

Respiratory Alkalosis - Interventions

• Assist pt to breathe more slowly (paper bag, nonrebreather mask)

• Salicylate: Activated charcoal or Alkaline diuresis with extra KCl

Metabolic Acidosis - Causes (Low HCO3, Low pH)

• Bicarbonate Deficit

  • Diabetic Ketoacidosis

  • Lactic acid accumulation (shock)

  • Severe diarrhea (intestines get rid of base)

  • Kidney disease (hold in urine which is acidic)

  • Starvation 

  • Cardiac Arrest

Metabolic Acidosis - Symptoms

• Confusion, Lethargy, Seizures

• Increased resp. rate & depth (Kussmaul resp.). Blowing off excess CO2 and acid

• Nausea, Vomiting, Diarrhea

• Arrhythmias, low BP, bradycardia (acidosis changes NA and K and decreases cardiac output)

• Muscle weakness

Metabolic Acidosis - Interventions

• Monitor I/O

• Monitor LOC

• IV Sodium Bicarb

• Tx underlying problem

Metabolic Alkalosis - Causes (High HCO3, High pH)

• Bicarbonate Excess

  • Prolonged vomiting or gastric suction (removing stomach acid)

  • Corticosteroid therapy

  • Severe potassium depletion

  • Excessive Alkali administration: Antacids

  • Excessive Diuretic therapy (K+ losing diur)

Metabolic Alkalosis - Symptoms

• Symptoms related to  decreased calcium - dizziness, tingling of fingers/toes, muscle hypertonicity (tetany)

• Tremors 

• Decreased resp. rate & depth

• Arrhythmias, Tachycardia

• Lethargy, Irritability

• Muscle cramps

Metabolic Alkalosis - Interventions

• Monitor I/O

• Monitor LOC, VS esp resp

• Check electrolytes, especially calcium

• IV fluid

• Tx underlying problem

Elderly Concerns

• Changes in pH are less well tolerated

• For every year above age 60, “normal” PaO2 decreases by 1 mmHg

• Decreased respiratory function

• Renal response not as efficient

A patient has the following arterial blood gas (ABG) results: pH 7.48, PaO2 86 mm Hg, PaCO2 44 mm Hg, HCO3 29 mEq/L. When assessing the patient, the nurse would expect the patient to experience which of the following?

1. Warm, flushed skin. 

2. Respiratory rate of 36.

3. Blood pressure of 94/52.

4. Hypertonic muscles with cramping.

A patient has the following arterial blood gas (ABG) results: pH 7.31, PaO2 86 mm Hg, PaCO2 55 mm Hg, HCO3 26 mEq/L. The nurse would anticipate which intervention for this the patient?

1. Breathing in a paper bag. 

2. Administer a bronchoconstriction medication.

3. Bed in high fowlers.

4. Restrict fluids.