RESPIRATORY ACID-BASE IMBALANCES
I. Pathophysiology—the body has the remarkable ability to
maintain plasma pH within a narrow range of 7.35 to 7.45.
a. Accomplished by chemical buffering mechanisms involving
the lungs and kidneys
i. Lungs compensate for acid-base imbalances resulting from
altered levels of metabolic acids.
ii. Kidneys compensate for acid-base imbalances resulting
from altered levels of carbonic acid.
b. Although simple acid-base imbalances (e.g., respiratory
acidosis) do occur, mixed acid-base imbalances are more
common (e.g., the respiratory acidosis and metabolic
acidosis that occur with cardiac arrest).
(PRIMARY CARBONIC ACID EXCESS)
a. Acute respiratory acidosis: develops when an abrupt failure
of ventilation occurs
i. Due to rapid development of problem, metabolic compensation
ii. PaCO2 greater than 47 mm Hg with accompanying
acidemia (pH 7.25)
b. Chronic respiratory acidosis: progressive failure of ventilation
i. Allows for some degree of compensation through
increased renal reabsorption of HCO3
ii. PaCO2 greater than 47 mm Hg, normal or near normal
pH, and elevated serum bicarbonate (HCO3 greater than
30 mm Hg)
II. Compensatory Mechanisms—occurs over 3 to 5 days
a. Increased respiratory rate
b. Hemoglobin (Hgb) buffering
c. Forming bicarbonate ions and deoxygenated Hgb
d. Increased renal ammonia acid excretions with reabsorption
a. Alveolar hypoventilation, reduced CO2 elimination, excess
of carbonic acid (H2CO3)
b. Conditions causing a decrease in respiratory rate and volume:
i. Central nervous system (CNS) disorders, such as with
depression of the central respiratory center; for example,
brainstem disease or trauma, tumors, encephalitis, stroke,
or drugs such as use of “downers” or overdose of
sedatives or barbiturate poisoning
ii. Pulmonary disorders of the airways or those causing airway
obstruction, such as asthma or chronic obstructive
pulmonary disease (COPD) exacerbation, bronchiectasis,
aspiration of foreign body, acute pulmonary edema,
acute laryngospasm, smoke inhalation, excessive CO2
intake (for example, use of rebreathing mask, CO2
iii. Neuromuscular disorders restricting chest movement and
inability to ventilate adequately, such as myasthenia
gravis, amyotrophic lateral sclerosis (ALS), Guillain-
Barré syndrome, muscular dystrophy, botulism
iv. Severe restrictive ventilatory defects, such as interstitial
fibrosis, thoracic deformities, hemothorax and pneumothorax,
atelectasis, acute respiratory distress syndrome
(ARDS), spinal cord injuries, anesthesia and surgery,
severe obesity (Pickwickian syndrome)
This condition does not occur in isolation; rather, it is a complication
of a broader health problem, disease, or condition
for which the severely compromised client requires admission
to a medical-surgical or subacute unit.
Plans of care specific to predisposing factors and disease or
medical condition, such as the following:
Cerebrovascular accident (CVA)/stroke
Chronic obstructive pulmonary disease (COPD) and
Craniocerebral trauma (acute rehabilitative phase)
Eating disorders: obesity
Alcohol: acute withdrawal
Spinal cord injury (acute rehabilitative phase)
Ventilatory assistance (mechanical)
Fluid and electrolyte imbalances
Metabolic acidosis—primary base bicarborate deficiency
Metabolic alkalosis—primary base bicarborate excess
1. Achieve homeostasis.
2. Prevent or minimize complications.
3. Provide information about condition, prognosis, and
treatment needs as appropriate.
1. Physiological balance restored.
2. Free of complications.
3. Condition, prognosis, and treatment needs understood.
4. Plan in place to meet needs after discharge.