Hypoventilation - Wikipedia
Hypoventilation and oxygen desaturation deteriorate during sleep secondary to a Metabolic production of carbon dioxide occurs rapidly. Thus The relationship between ventilation and PaCO2 can be expressed as PaCO2. Hyperventilation; Anxiety, pain; Anemia; Shock; Some degrees of pulmonary pCO2 (partial pressure of carbon dioxide) reflects the the amount of carbon PO2 (partial pressure of oxygen) reflects the amount of oxygen gas dissolved in the. Hypoventilation occurs when ventilation is inadequate (hypo meaning "below") to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide.
After encountering two such cases, including one with a fatal coma, the authors set up a study to examine the effect of oxygen on intracranial pressure that is, cerebrospinal fluid pressures measured through a lumbar puncture in similar patients. The authors found that, in all four studied subjects with emphysema and cyanosis, oxygen therapy led to increased cerebrospinal fluid pressures, which returned to baseline when oxygen was stopped.
Davies and Mackinnon hypothesized that oxygen intoxication could have led to accumulation of carbon dioxide CO2 in the body and cautioned against the use of oxygen in these patients. In response to this article, Donald [ 2 ] described an emphysema patient who developed a hypercapnic 16 kPa coma during oxygen therapy and who had rapid clinical improvement after oxygen therapy was discontinued. The author, referring to such patients, stated the following theory: The removal of the anoxic stimulus causes them to hypoventilate with further retention of carbon dioxide'.
Oxygen-induced hypercapnia in COPD: myths and facts
Reading these early reports about oxygen-induced hypercapnia in patients with chronic obstructive pulmonary disease COPDone might think that not much has changed over the years. Despite subsequent studies and reviews [ 3 ] describing the effect of oxygen on the ventilator drive in patients with COPD, disproving the 'hypoxic drive' theorem, many clinicians are still being taught during their medical training that administration of oxygen in patients with COPD can be dangerous given that it induces hypercapnia through the 'hypoxic drive' mechanism; that is, increasing arterial O2 tension will reduce the respiratory drive, leading to a dangerous hypercapnia.
This misconception has resulted in the reluctance of clinicians and nurses to administer oxygen to hypoxemic patients with COPD. In most cases, this is an unwise decision, putting at risk the safety of patients with acute exacerbation of COPD.
In this concise paper, we will discuss the impact and pathophysiology of oxygen-induced hypercapnia in patients with acute exacerbation of COPD.
The authors found that PaCO2 increased from 8.
More than two decades later, this study was repeated [ 5 ]. Effects on Alveolar Carbon Dioxide As discussed in alveolar carbon dioxidethe partial pressure of CO2 in the alveolus is inversely proportional to the rate of alveolar ventilation. When alveolar ventilatory rates decline, the rate at which CO2 is eliminated by the lungs correspondingly decreases, thus yielding increased partial pressures of alveolar CO2 PACO2.
Consequently, hypoventilation is always accompanied by increased alveolar carbon dioxide values and in turn increased arterial carbon dioxide values, yielding hypercapnia and potentially respiratory acidosis.
Effects on Alveolar Oxygen Declining alveolar ventilation rates also reduce the rate at which alveolar air is refreshed with oxygen-rich external air. As discussed in alveolar oxygenthis yields a decrease in the partial pressure of oxygen in the alveolar space PAO2.
This can be quantitatively appreciated from the "Alveolar Gas Equation" described in the alveolar oxygen page which demonstrates how increased values for alveolar carbon dioxide PACO2 will result in reduced values for alveolar oxygen PAO2.
Because the alveolar oxygen tension determines the arterial partial pressure of oxygen, a hypoventilating individual can display sufficient decreases in their arterial oxygen tension to be considered hypoxemic. Diagnosis A-a Gradient As described in oxygen pulmonary gas exchangelower alveolar partial pressures of oxygen will reduce the oxygen diffusion gradient between the alveolar space and the blood in the pulmonary capillaries.
This will result in a slowing in the rate of oxygen diffusion from the alveolar space to the pulmonary capillaries; however, in the absence of other overt pathology, the partial pressures of oxygen in these two compartments should equalize by the end of the pulmonary capillaries. Consequently, in a healthy individual at high elevations, the A-a Gradient will be normal.