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Hypercapnic acidosis and compensated hypercapnia in control and pulmonary hypertensive piglets
K Jane Lee1, Guillermo Hernandez, John B Gordon
1Critical Care Division, Department of Pediatrics, Medical College of Wisconsin, Milwaukee, USA.
Insights
Hypercapnic acidosis increases pulmonary vascular resistance in piglets. This effect is not reversed by normalizing pH and occurs similarly in piglets with and without pulmonary hypertension.
Area of Science:
- Physiology
- Pediatric Critical Care
- Respiratory Medicine
Background:
- Low tidal volume ventilation strategies can lead to hypercapnia (elevated carbon dioxide levels).
- Hypercapnia increases pulmonary vasomotor tone, potentially worsening pulmonary hypertension in children.
- Preexistent pulmonary hypertension may exacerbate the effects of hypercapnic acidosis.
Purpose of the Study:
- To investigate if hypercapnic acidosis effects are exaggerated in piglets with preexistent pulmonary hypertension.
- To determine if normalizing pH attenuates the pulmonary hemodynamic effects of hypercapnic acidosis.
- To assess the impact of hypercapnic acidosis on pulmonary vascular resistance index (PVRI) in a piglet model.
Main Methods:
- A piglet model was used to induce chronic pulmonary hypertension via two weeks of hypoxia.
- Hemodynamic responses were measured in control and pulmonary hypertensive piglets.
- Measurements were taken under normocapnic, hypercapnic acidotic, and compensated hypercapnic conditions during normoxia and hypoxia.
Main Results:
- Hypercapnic acidosis increased both normoxic and hypoxic PVRI in control piglets.
- Buffering the pH with bicarbonate did not attenuate the pressor effects of hypercapnia.
- Piglets with chronic pulmonary hypertension showed elevated baseline PVRI but responded similarly to hypercapnic acidosis as control piglets.
Conclusions:
- Acute hypercapnic acidosis increases pulmonary vascular resistance in both normal and pulmonary hypertensive subjects.
- Buffering pH does not acutely reverse the detrimental pulmonary hemodynamic effects of hypercapnia.
- These findings suggest potential risks of hypercapnic acidosis in pediatric patients, regardless of preexistent pulmonary hypertension.
Abstract:
Low tidal volume/inspiratory pressure ventilator strategies result in hypercapnia, which has been shown to increase pulmonary vasomotor tone. This may be particularly detrimental in infants and children with preexistent pulmonary hypertension. In this study, a piglet model of chronic hypoxia-induced pulmonary hypertension was used to test the hypotheses that: 1) the effects of hypercapnic acidosis are exaggerated by preexistent pulmonary hypertension; and 2) the pulmonary hemodynamic effects of hypercapnic acidosis are attenuated by normalizing pH. Pulmonary hypertension was induced by 2 weeks of hypoxia. Hemodynamic responses were measured in control and pulmonary hypertensive piglets during both normoxia and hypoxia under normocapnic, hypercapnic acidotic, and compensated hypercapnic conditions. We found that: 1) hypercapnic acidosis increased both normoxic and hypoxic pulmonary vascular resistance index (PVRI) in control piglets; 2) the pressor effects of hypercapnia were not attenuated by infusing bicarbonate to normalize the pH; and 3) piglets with chronic hypoxia-induced pulmonary hypertension had elevated baseline normoxic and hypoxic PVRI, but responded to hypercapnic acidosis and compensated hypercapnia in a similar way to control piglets. These data suggest that acute hypercapnic acidosis may have deleterious effects on the pulmonary hemodynamics of normal and pulmonary hypertensive subjects which may not be acutely reversed by buffering the pH.