Arterial Blood Gas

ABG and ABB

Metabolic Acidosis

 Risk factors: more ingestion of acids or less production of HCO3

 Etiology: lactic acidosis, ketoacidosis, uremic acidosis; diarrhea (more bicarbonate losses)

 Patho: compensatory hyperventilation

 Hyperkalemia: shift of acid from plasma to ICF

 Low pH, less HCO3, PaCo2 normal or low if compensation is occurring

 cardiac dysrhythmias & CNS dysfunction

 headache, diarrhea, tremors

 Sodium bicarbonate may be given when a patient is experiencing lactic acidosis secondary to shock. It is administered cautiously because the carbon dioxide produced crosses rapidly into the cells and may cause paradoxical worsening of intracellular hypercarbia and acidosis.

Metabolic Acidosis

Nursing Responsibilities

 Monitor cardiovascular status closely, noting: BP, PR and rhythm, capillary refill, warmth and color of extremities

 Institute safety precautions, such as: keeping bed side rails up, keeping bed brakes locked, securing all invasive lines properly

Metabolic Alkalosis

 Risk factors:

 Hypovolemia (prolonged vomiting or gastric suctioning)

 Excess aldosterone

 Etiology:

 Acid loss or base gain

 Iatrogenic base administration

 Prolonged vomiting (loss of HCL)

 Renal excretion of HCO3 will fix the problem

Metabolic Alkalosis

 Patho: respiratory compensation is limited/slow respirations

 Hypokalemia: K+ moves from ECF to ICF due to hydrogen ions moving out of the cell to ECF

 Depleted body stores (K+):

 Loop diuretics? NGT?

 Signs and Symptoms:

 cardiac dysrhythmias; tetany/seizures; confusion; muscle twitching, agitation

 high pH; more HCO3; normal PaCo2 or elevated if compensation occurs

Metabolic Alkalosis

Nursing Responsibilities

 Institute safety precautions, such as: keeping bed side rails up, keeping bed brakes locked, securing all invasive lines properly

 Monitor respiratory rate and pattern, lung sounds, skin color, and mental status

 Provide tx to correct the underlying cause as ordered

 Promote adequate hydration

 Correct electrolyte deficits, particularly of K and Na as ordered

Respiratory Acidosis

 Risk factors:

 Excess acid in body fluids

 Etiology:

 Hypoventilation

 COPD; Cystic Fibrosis; airway obstruction; spinal cord injury; CVA; respiratory depressant drugs; inadequate mechanical ventilation

Respiratory Acidosis

 Patho:

 Hypercapnia; CO2 diffuses easily across biological membranes

 Clinical:

 Decreased pH

 High PaCo2

 HCO3 is normal or increased in renal compensation

 Signs and Symptoms

 Dyspnea, wheezing, tachypnea

 Vasodilatation

 Cardiac arrhythmias; tachycardia

 Somnolence & decreased ventilation

Respiratory Acidosis

Nursing Responsibilities

 Monitor ABG values

 Administer low flow O2 therapy to a pt with chronic PCO2 above 50 mmHg

 Position the patient in semi-Fowler’s or another comfortable position to ease the work of breathing

 Improve ventilation with bronchodilators; postural drainage; antibiotic thx; regular coughing, turning, and deep breathing & mechanical ventilation as appropriate

Respiratory Acidosis

Nursing Responsibilities

 Maintain a quiet, relaxing environment

 Keep needed items within the patient’s reach

 Monitor cardiovascular status, noting: BP, PR and rhythm, capillary refill, warmth and color of extremities

 Maintain fluid and electrolyte balance

 Intervene to correct the underlying cause

Respiratory Alkalosis

 Risk factors:

 Relative excess of base in body fluids secondary to > ventilatory elimination of CO2; pneumonia; shock; severe anemia

 Etiology:

 hypoxemia (<PaO2) causing rate & depth of ventilation to increase (hyperventilation)

Respiratory Alkalosis

 Patho: Buffer response is to shift acid from ICF to the blood by moving HCO3 into the cells in exchange of chloride

 High pH; less PaC02; HCO3 normal or low due to compensation

 nausea, vomiting, tingling of fingers, lightheadedness, inability to concentrate

Respiratory Alkalosis

Nursing Responsibilities

 Monitor ABG values and respiratory rate and pattern

 Institute and maintain seizure precautions as necessary

 Assess sources of anxiety and intervene to help reduce anxiety

 Encourage slow, deep breathing; instruct the patient to breathe into and out of a paper bag, if necessary, to reverse hyperventilation

 Assist the patient with activities as necessary

Arterial Blood Gases

 Reflect oxygenation, gas exchange, and acid-base balance

 PaO2 is the partial pressure of oxygen dissolved in arterial blood

 SaO2 is the amount of oxygen bound to hemoglobin

 Oxygen is transported from the alveoli into the plasma

Arterial Blood Gases

 Ranges

 PaO2 80 - 100 mm Hg at sea level

 < 80 mm Hg = hypoxemia

 < 60 mm Hg may be seen in COPD patients

 < 40 mm Hg is life threatening

 SaO2 93 - 100 % is a normal saturation

 Hypoxia is decreased oxygen at the tissue level

Arterial Blood Gas Interpretation

 pH: negative log of H+ concentration

 In blood:

 Normal range: 7.35 - 7.45

 Acidosis = pH less than 7.35

 Alkalosis = pH greater than 7.45

 A pH < 7.0 or > 7.8 can cause death

Arterial Blood Gas Interpretation

 PaCO2: partial pressure of carbon dioxide dissolved in the arterial plasma

 Normal: 35 - 45 mm Hg

 Is regulated in the lungs

 A primary respiratory problem is when PaCO2 is:

 > 45 mm Hg = respiratory acidosis

 < 35 mm Hg = respiratory alkalosis

 HCO3 will be normal (22 - 26 mEq/L)

Arterial Blood Gas Interpretation

 HCO3 (bicarbonate)

 Normal: 22 -26 mEq/L

 Is regulated by the kidneys

 A primary metabolic or renal disorder is when the HCO3

 is < 22 = metabolic acidosis or

 > 26 = metabolic alkalosis

 PaCo2 is normal

Arterial Blood Gas Interpretation

 Compensation:

 body attempts to recover from primary problem and return to homeostasis

 Primary metabolic acidosis can cause the patient to breathe faster to compensate (blow off CO2) by creating a respiratory alkalosis state

 This would be labeled as: Metabolic acidosis with a compensatory respiratory alkalosis

 pH 7.30, PaCO2 = 28 & HCO3 = 15

 Are PaCo2 & HCO3 below normal? Yes! Compensation!

Interpreting ABGs:

(A Systematic Approach)

step 1 Evaluate the pH

acidosis = < 7.35 --------------- 7.35-7.45 = normal --------------- > 7.45 = alkalosis or compensated state

step 2 Evaluate the pCO2

resp. acidosis =if>45 ------------35-45=normal;-------------if<35= resp. alkalosis

go to HCO3

step 3 Evaluate HCO3

metab. acidosis =if<22-----------22-26=normal-----------if>26= metab. alkalosis





Note: If CO2 and HCO3 are both abnormal, look to see which one has a change that matches the change in the pH (i.e., CO2 acts as an acid; HCO3 acts as a base). This match will be the primary imbalance, while the other system is compensating.