The American review of respiratory disease
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Am. Rev. Respir. Dis. · May 1990
Hyperdynamic sepsis modifies a PEEP-mediated redistribution in organ blood flows.
Changes in organ blood flow (Q) produced by 20 cm H2O positive end-expiratory pressure (PEEP) were measured before and after the induction of hyperdynamic sepsis in nine unanesthetized sheep. During the baseline nonseptic study, PEEP was associated with a 9% fall in thermodilution-measured systemic Q, although arterial perfusing pressures were unaffected. Concurrently, microsphere-derived Q was maintained to the brain and heart, but fell to liver, spleen, pancreas, kidney, large intestine, and gastrocnemius. ⋯ We postulate that differences noted in the distribution of organ Q between the nonseptic and hyperdynamic septic studies after the application of PEEP were secondary to the vasculopathy of sepsis and/or an alteration in the function of specific organ microcirculations. However, these data do not address whether the changes in organ Q distribution after a PEEP-mediated depression in systemic Q during sepsis significantly restricted tissue DO2. The inability to acutely reverse the PEEP-mediated changes in organ Q after restoring systemic Q by a fluid infusion also suggests the need to evaluate alternative methods of support to organ Q in acute respiratory failure secondary to sepsis when the addition of PEEP acutely depresses systemic DO2.
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In order to investigate whether the changes in PaO2 reported during acid-base disturbances are due to modifications of ventilation/perfusion relationships or only to extrapulmonary factors, we studied the hemodynamics and blood gases of eight critically ill patients maintained in constant mechanical ventilation, before and after selective correction of metabolic alkalosis by infusion of 1 N hydrochloric acid (HCl). HCl infusion decreased arterial pH from 7.55 to 7.40 (p less than 0.001) and increased PaO2 from 76 to 98 mm Hg (p less than 0.05) at the end of the study. ⋯ In patients with QS/QT greater than 20% (n = 4), QS/QT decreased from 27 to 22% (p less than 0.05), hemoglobin saturation increased from 93 to 96% (p less than 0.05), and PaO2 increased from 65 to 100 mm Hg (p less than 0.05), which reflects an improvement in ventilation/perfusion relationships, probably because of enhanced hypoxic pulmonary vasoconstriction. These data indicate that metabolic alkalosis deteriorates pulmonary ventilation/perfusion relationships in patients with marked respiratory failure (QS/QT greater than 20%), and that reversing this effect with HCl infusion can improve PaO2 significantly.