Hypercapnia - ANSWER A condition marked by a PaCO2 level above 45
mmHg. Also known as hypercarbia.
Hypoxemia - ANSWER Decreased oxygen levels in the blood that
results when PaO2 falls below 80 mmHg.
Respiratory acidosis - ANSWER A condition that is caused by an excess
of dissolved carbon dioxide, or carbonic acid. It is characterized by a pH
of less than 7.35 and a PaCO2 greater than 45 mmHg. It may be caused
by hypoventilation.
Ventilation - ANSWER The exchange of oxygen and carbon dioxide.
Pathophysiology and Etiology - ANSWER Both acute and chronic
respiratory acidosis result from carbon dioxide retention caused by
alveolar hypoventilation.
Hypoxemia (decreased oxygen) frequently accompanies respiratory
acidosis.
Acute Respiratory Acidosis - ANSWER Results from a sudden failure of
ventilation (the exchange of oxygen and carbon dioxide).
Chest trauma, aspiration of a foreign body, acute pneumonia, and
overdoses of narcotic or sedative medications can lead to this condition.
PaCO2 rises rapidly and the pH falls markedly. A pH of 7 or lower can
occur within minutes, resulting in death if not corrected
The serum bicarbonate level is unchanged initially because the
compensatory response of the kidneys continues over hours to days.
Hypercapnia & Acute Respiratory Acidosis - ANSWER (increased
carbon dioxide levels) affects neurologic function and the cardiovascular
system. Carbon dioxide rapidly crosses the blood-brain barrier. Cerebral
, blood vessels dilate, and if the condition continues, intracranial pressure
increases and papilledema (swelling and inflammation of the optic nerve
where it enters the retina) develops. Peripheral vasodilation also occurs,
and the pulse rate increases to maintain cardiac output.
The primary problem is alveolar hypoventilation with increased PaCO2.
Respiratory acidosis can be caused by - ANSWER Acute pulmonary
edema, central nervous system depression, chest wall disorders,
trauma, oversedation, asthma, obstructive sleep apnea, obesity, and
pulmonary infections.
Chronic respiratory acidosis is associated with - ANSWER chronic
respiratory or neuromuscular conditions such as COPD, asthma, cystic
fibrosis, and multiple sclerosis.
These conditions affect alveolar ventilation because of airway
obstruction, structural changes in the lung, and limited chest wall
expansion.
Patients with chronic respiratory acidosis have - ANSWER COPD with
chronic bronchitis and emphysema.
Chronic Respiratory Acidosis - ANSWER The PaCO2 increases over
time and remains elevated. The kidneys retain bicarbonate, increasing
bicarbonate levels, and the pH often remains close to the normal range
because of adequate metabolic compensation.
Carbon Dioxide and Chronic Respiratory Acidosis - ANSWER The acute
effects of hypercapnia may not develop when carbon dioxide levels rise
gradually, allowing compensatory changes to occur.
When carbon dioxide levels are chronically elevated, the respiratory
center becomes less sensitive to the gas as a stimulant of the
respiratory drive. The PaO2 provides the primary stimulus for
respirations.
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