The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

Inhaled Nitric Oxide Improves Oxygenation But Worsens Lung Mechanics In Experimental Respiratory Distress Syndrome

David Garton CRTT,RCP, Randy Scott BS,RRT,RCP, Leo Langga BS,RRT,RCP, Ricardo Peverini MD, Andrew Hopper MD. Loma Linda Children's Hospital, Loma Linda, Ca.

In premature infants, pulmonary hypertension concomitant with severe Respiratory Distress Syndrome (RDS) increases morbidity and mortality, despite exogenous surfactant. Studies have shown that inhaled nitric oxide (INO) improves pulmonary hemodynamics and gas exchange in experimental RDS, yet little is known about the effect of INO on lung mechanics. To study the effects of INO on lung mechanics, we cannulated the trachea, jugular vein and carotid artery of 6 sets of 126-130 day gestational (0.85 term) lamb twins. A modified natural surfactant (beractant) was given prior to delivery and initiation of mechanical ventilation (Sechrist IV 100B). Initial ventilator settings were: rate 40 bpm, PIP set to deliver a tidal volume (V_T) of 8 ml/kg, PEEP 4 cmH_2O, inspiratory time 0.5 seconds, and FIO_2 1.0. FIO_2 and PIP were adjusted to maintain PaO_2 50-80 torr and PaCO_2 35-45 torr. After 2 hours of mechanical ventilation, baseline lung mechanics and arterial blood gases (ABGs) were recorded. Lambs were randomly assigned to receive either 20 ppm INO or no INO (control) for 30 minutes. INO and control assignments were then switched and another 30 minute trial completed. Lung mechanics and ABGs were recorded at the end of each trial. Variables calculated from recorded data were, PaO_2 / FIO_2, V_T, dynamic compliance (C_{DYN}), airway resistance (R_{AW}), and functional residual capacity (FRC). For statistical analysis, normally distributed data were compared by paired t test. Differences were considered statistically significant when p< = 0.05. Data in the table are an increase (+) or decrease (-) mean ± SE of % change from baseline during the study period.

PaO_2/FIO_2 V_T C_{DYN} R_{AW} FRC

INO+45±28% -15±6%-12±6%0.0 -1±9%

CONTROL -15±9%+13±6%+10±6%+6±9%+4±10%

p value =0.070.02 0.06 0.50 0.66

Oxygenation (PaO_2 / FIO_2) improved during INO despite deterioration of V_T and C_{DYN}. The improvement in oxygenation is consistent with previously reported studies. We conclude that while INO may improve oxygenation, it may also worsen lung mechanics. This worsening of lung mechanics could increase the risk of barotrauma and adversely affect long term outcome.

OF-95-142

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