The effect of hypo-, normo-, and hypercapnia induced by mechanical ventilation on intrapulmonary shunt.

Abstract

The effects of hypo-, normo- and hypercapnia on the variations in arterial oxygenation and their indices in critical patients with acute respiratory failure (ARF) receiving mechanical ventilation are studied. It is a prospective and randomized study carried out in multidisciplinary ICU. Fifteen ARF patients, intubated and mechanically ventilated, were studied within the first 48 h of evolution. Three stages were delimited: I) 30 min after the beginning of anaesthesia; II) 30 min after adding 30 cm of dead space (VD); III) 30 min after replacing the previous VD with VD of 60 cm. Ventilation parameters and FiO2 were kept stable. Stage I was characterized by respiratory alkalosis and stage II by normal acid-base balance with an increase in PaO2 (p < 0.01) and a decrease in intrapulmonary shunt (Qsp/Qt) (p < 0.001); the indices alveolar to arterial oxygen tension gradient [P(A-a)O2], respiratory index (R.I.) and estimated shunt (Est Shunt) also decreased significantly, whereas arterial to alveolar oxygen tension ratio (PaO2/PAO2) and arterial oxygen tension to inspired oxygen fraction ration (PaO2/FiO2) increased significantly. In stage III there was pure hypercapnic acidosis, with decreases in PAO2 (p < 0.001), P(A-a)O2 (p < 0.01) and R.I. (p < 0.05), while PaO2, Qsp/Qt, Est Shunt, PaO2/PAO2 and PaO2/FiO2 remained stable with respect to the previous situation. The observed PaO2 differs (p < 0.05) from the expected PaO2 in stage III. It is suggested that local or regional modifications of pulmonary perfusion are responsible for the observed variations. The P(A-a)O2 and R.I. indices do not make it possible to differentiate the causes of arterial hypoxemia in the presence of hypercapnia.

• Authors: J H Boix, F Alvarez, M Tejeda, E Peydro, D Olivares, A Arnau
• Journal: Revista espanola de fisiologia (Rev Esp Fisiol) Vol. 50 Issue 2 Pg. 89-95 (Jun 1994) ISSN: 0034-9402 [Print] Spain
• PMID: 7800919 (Publication Type: Clinical Trial, Journal Article, Randomized Controlled Trial)

Chemical References

• Carbon Dioxide
• Oxygen

Topics

• Acute Disease
• Adult
• Aged
• Alkalosis (blood, etiology, physiopathology)
• Carbon Dioxide (blood)
• Female
• Humans
• Hypercapnia (etiology, physiopathology)
• Hypocapnia (etiology, physiopathology)
• Male
• Middle Aged
• Oxygen (blood)
• Partial Pressure
• Prospective Studies
• Respiration, Artificial (adverse effects)
• Respiratory Dead Space
• Respiratory Function Tests
• Respiratory Insufficiency (blood, physiopathology)