Objective: Changes in renal hemodynamics occur in
patients with severe COPD, especially during an acute exacerbation.
Renal hemodynamics are affected by changes in oxygen and carbon dioxide
levels, but these changes have not been well defined, particularly in
the acute clinical situation. We wished to determine whether oxygen or
carbon dioxide levels have the predominant effect on renal hemodynamics
in patients with an acute exacerbation of COPD.
Design: Fourteen patients with an acute exacerbation of
COPD and a Pao2 < 64 mm Hg were studied.
Initially, the patients breathed room air (hypoxemia). Then their
arterial oxygen saturation was raised to approximately 95%
(normoxemia) and then to 98 to 99% (hyperoxemia). Finally, 1 L/min of
carbon dioxide was added to the circuit (hyperoxemic hypercapnia).
Using duplex ultrasonography, the pulsatility index (PI) of an
intrarenal artery was measured after 10 min at each level of
oxygenation. The PI is an index of distal renovascular resistance.
Results: The PI fell significantly from room-air values on
inducing hyperoxemia (p < 0.05). This suggests decreased
renovascular resistance and increased renal blood flow. When
hyperoxemic hypercapnia was induced, the PI rose significantly from the
hyperoxemia level (p < 0.001).
hypoxemic patients, renovascular resistance decreased when hyperoxemia
was induced. This fall in renovascular resistance was reversed with the
addition of carbon dioxide. This suggests that acute changes in carbon
dioxide levels might have a more dominant role than oxygen levels in
determining renovascular resistance.