EXHALED NITRIC OXIDE IN RABBITS WITH RESPIRATORY
FAILURE INDUCED BY MECONIUM ASPIRATION AND TREATED WITH SURFACTANT AND
MECHANICAL VENTILATION
Xiao-Wei
Hu, You-Rong Zhu, Bo Sun
Laboratory of Pediatric Respiratory and Critical Care
Medicine, Children's Hospital, Fudan University, Shanghai, China
Objective:
To evaluate endogenous nitric oxide concentration
(eNO) from low airways of rabbits with meconium aspiration treated with
surfactant and mechanical ventilation.
Methods:
Anesthetized and mechanically ventilated adult
rabbits (n=19, 2.0-3.5 kg) were allocated to three groups: (1) normal (N,
n=5), (2) control (C, n=8), (3) pulmonary surfactant (S, n=6). Meconium
suspension (25 mg/ml) was instilled at 3 ml/kg into the lungs of both C and
S groups through an endotracheal tube, and the N group was given 3 ml/kg of
saline intratracheally. All the animals were ventilated with pressure
support mode (PSV, 5-15 cmH2O) and continuous positive airway pressure at
2-3 cmH2O, to provide a tidal volume of 6-8 ml/kg for 6 hours of treatment.
The triggered PSV frequency and FiO2 were adjusted to maintain PaCO2
between 35-45 mmHg and PaO2 above 60 mmHg, respectively. The S group was
given a bolus of porcine lung derived surfactant phospholipids at 150 mg/kg
when acute lung injury developed. By a chemiluminescence NO analyzer, the
peak level of eNO was detected and averaged from 15 consecutive breaths
using an online method while the ventilator was on pr!
essure
control mode with a frequency (F) and I:E set at 30/min and 1:2 for 1
minute, respectively.
Results:
Meconium instillation induced in both the C and S groups lung injury in 45
min as reflected by reduction of mean values of PaO2/FiO2 from 381 to 189
mmHg (p <0.01). The instillation of bolus surfactant slowed the deterioration
of the PaO2/FiO2 during the treatment ( p<0.05 vs. C). The eNO of the C
group decreased from 40.2?.7 ppb at baseline to 21.9?.4 ppb after 30
minutes of meconium instillation and further decreased to 5.0?.5 ppb at 6
h, whereas eNO of the N group was 37.0?.1 ppb at baseline to 36.3?.4 ppb at
30 minutes after the saline instillation, and maintained at 25.3?.3 ppb at
6 h ( p<0.01 vs. C group; p<0.01 vs. N at baseline). The eNO of the S
group was decreased from 24.1?.0 ppb at 30 minute after meconium instillation
to 7.5?.9 ppb at 6 h. There was no difference of eNO at baseline for FiO2
at 0.5 and 1.0 (28.5?.5 vs 28.1?.4 ppb, n=11), and for F at 20/min and
40/min ( 28.8?.6 vs 28.2?.1 ppb, n=10), respectively. The S group had lower
wet/dry !
lung
weight ratio than the C group (4.9?.8 vs 6.1?.9, p<0.01).
Conclusions:
Meconium aspiration in rabbits decreased eNO.
Surfactant treatment did not alter the endogenous NO production but
alleviated the deterioration of oxygenation and facilitated lung fluid
absorption. Intratracheal intubation and mechanical ventilation did not
cause substancial reduction of eNO.