Life-threatening increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO), although the mechanisms remain unknown. In vitro data suggest that exogenous NO exposure inhibits endothelial NO synthase (NOS) activity. Thus the objectives of this study were to determine the effects of inhaled NO therapy and its acute withdrawal on endogenous NOS activity and gene expression in vivo in the intact lamb. Six 1-mo-old lambs were mechanically ventilated and instrumented to measure vascular pressures and left pulmonary blood flow. Inhaled NO (40 ppm) acutely decreased left pulmonary vascular resistance by 27. 5 +/- 4.7% (P < 0.05). This was associated with a 207% increase in plasma cGMP concentrations (P < 0.05). After 6 h of inhaled NO, NOS activity was reduced to 44.3 +/- 5.9% of pre-NO values (P < 0.05). After acute withdrawal of NO, pulmonary vascular resistance increased by 52.1 +/- 11.6% (P < 0.05) and cGMP concentrations decreased. Both returned to pre-NO values within 60 min. One hour after NO withdrawal, NOS activity increased by 48.4 +/- 19.1% to 70% of pre-NO values (P < 0.05). Western blot analysis revealed that endothelial NOS protein levels remained unchanged throughout the study period. These data suggest a role for decreased endogenous NOS activity in the rebound pulmonary hypertension noted after acute withdrawal of inhaled NO.

Objective The aim of the study was to assess the association of initial lactate (L0) with mortality in children with severe sepsis. Methods This prospective cohort study included 74 patients younger than 18 years with severe sepsis admitted to the pediatric intensive care unit (PICU) of a tertiary, academic children's hospital with lactate measured within 3 hours of meeting severe sepsis or septic shock. The primary outcome was in-hospital mortality. The secondary outcomes included PICU and hospital length of stay. Results Although overall mortality was 10.5% (n = 18), patients with L0 measured (n = 72) had a higher mortality (16% vs 6%, P = 0.03) and higher median PRISM-III risk of mortality scores (P = 0.02) than those who did not. Median L0 was no different between nonsurvivors and survivors (3.6 mmol/L [interquartile range, 2.0–9.0] in nonsurvivors vs 2.3 mmol/L [interquartile range, 1.4–3.5] in survivors, P = 0.11). However, L0 was independently associated with PRISM-III score (coefficient, 1.12; 95% confidence interval, 0.4–1.8; P = 0.003) with an increase in mean PRISM-III score of 1.12 U for every 1 mmol/L increase in L0, with L0 accounting for 12% of the variability in PRISM-III scores between patients. There was no association between L0 and PICU or hospital length of stay. Conclusions Although our single center study did not demonstrate that an elevated early lactate is associated with mortality in pediatric severe sepsis, L0 did correlate strongly with PRISM-III, the most robust measure of mortality risk in pediatrics. Therefore, early lactate measurement may be important as an early biomarker of disease severity. These data should be validated in a larger, multicenter, prospective study.

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Inhaled nitric oxide (NO) is currently used as an adjuvant therapy for a variety of pulmonary hypertensive disorders. In both animal and human studies, inhaled NO induces selective, dose‐dependent pulmonary vasodilation. However, its potential interactions with other simultaneously used pulmonary vasodilator therapies have not been studied. Therefore, the objective of this study was to determine the potential dose‐response interactions of inhaled NO, oxygen, and alkalosis therapies. Fourteen newborn lambs (age 1–6 days) were instrumented to measure vascular pressures and left pulmonary artery blood flow. After recovery, the lambs were sedated and mechanically ventilated. During steady‐state pulmonary hypertension induced by U46619 (a thromboxane A2 mimic), the lambs were exposed to the following conditions: Protocol A, inhaled NO (0, 5, 40, and 80 ppm) and inspired oxygen concentrations (FiO2) of 0.21, 0.50, and 1.00; and Protocol B, inhaled NO (0, 5, 40, and 80 ppm) and arterial pH levels of 7.30, 7.40, 7.50, and 7.60. Each condition (in randomly chosen order) was maintained for 10 min, and all variables were allowed to return to baseline between conditions. Inhaled NO, oxygen, and alkalosis produced dose‐dependent decreases in mean pulmonary arterial pressures (P < 0.05). Systemic arterial pressure remained unchanged. At 5 ppm of inhaled NO, alkalosis and oxygen induced further dose‐dependent decreases in mean pulmonary arterial pressures (P<0.05). At inhaled NO doses >5 ppm, alkalosis induced further dose‐independent decreases in mean pulmonary arterial pressure, while oxygen did not. We conclude that in this animal model, oxygen, alkalosis, and inhaled NO induced selective, dose‐dependent pulmonary vasodilation. However, when combined, a systemic arterial pH >7.40 augmented inhaled NO‐induced pulmonary vasodilation, while an FiO2 >0.5 did not. Therefore, weaning high FiO2 during inhaled NO therapy should be considered, since it may not diminish the pulmonary vasodilating effects. Further studies are warranted to guide the clinical weaning strategies of these pulmonary vasodilator therapies. Pediatr Pulmonol. 1999; 28:3–11. © 1999 Wiley‐Liss, Inc.

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