Nitrogen dioxide production in a nitric oxide inhalation system using the Servo Ventilator 900C

Nitrogen dioxide reducing ascorbic acid technologies in the ventilator circuit leads to uniform NO concentration during inspiration

Conventional inhaled NO systems deliver NO by synchronized injection or continuous NO flow in the ventilator circuitry. Such methods can lead to variable concentrations during inspiration that may differ from desired dosing. NO concentrations in these systems are generally monitored through electrochemical methods that are too slow to capture this nuance and potential dosing error. A novel technology that reduces NO2 into NO via low-resistance ascorbic-acid cartridges just prior to inhalation has recently been described. The gas volume of these cartridges may enhance gas mixing and reduce dosing inconsistency throughout inhalation. The impact of the ascorbic-acid cartridge technology on NO concentration during inspiration was characterized through rapid chemiluminescence detection during volume control ventilation, pressure control ventilation, synchronized intermittent mandatory ventilation and continuous positive airway pressure using an in vitro lung model configured to simulate the complete uptake of NO. Two ascorbic acid cartridges in series provided uniform and consistent dosing during inspiration during all modes of ventilation. The use of one cartridge showed variable inspiratory concentration of NO at the largest tidal volumes, whereas the use of no ascorbic acid cartridge led to highly inconsistent NO inspiratory waveforms. The use of ascorbic acid cartridges also decreased breath-to-breath variation in SIMV and CPAP ventilation. The ascorbic-acid cartridges, which are designed to convert NO2 (either as substrate or resulting from NO oxidation during injection) into NO, also provide the benefit of minimizing the variation of inhaled NO concentration during inspiration. It is expected that the implementation of this method will lead to more consistent and predictable dosing.

Combined effects of inhaled nitric oxide and positive end-expiratory pressure during mechanical ventilation in acute respiratory distress syndrome

We studied the combined effects of inhaled nitric oxide (INO) and positive end expiratory pressure (PEEP) during mechanical ventilation in patients with acute respiratory distress syndrome (ARDS). Eleven patients received 0 and 4 parts per million of INO in random order for 30 min at PEEP levels of 0, 5, and 10 cm H2O. Respiratory and cardiovascular parameters were measured. The addition of INO and PEEP significantly improved arterial oxygenation (p < 0.005 and p < 0.0001, respectively). The combined effect of INO and PEEP on arterial oxygenation was remarkable during 10 cm H2O PEEP. There was synergistic effect on arterial oxygenation by combining INO and 10 cm H2O PEEP. The present study showed that the combination of INO and 10 cm H2O PEEP enhanced arterial oxygenation in patients with ARDS.

Nitric oxide inhalation for paraquat-induced lung injury

BACKGROUND

When ingested, concentrated paraquat can cause either rapid death from multisystem failure and cardiovascular shock or delayed death from progressive pulmonary fibrosis. Diquat ingestion does not usually cause pulmonary fibrosis, but produces early onset acute renal failure.

CASE REPORT

A 52-year-old male ingested approximately 50 mL of a solution containing 13% paraquat and 7% diquat (about 6650 mg of paraquat and 3500 mg of diquat), and subsequently developed adult respiratory distress syndrome and pulmonary fibrosis. Survival prediction employing the criteria of Hart et al. for paraquat plasma levels was 30%. From the probable amount of paraquat ingested, severe toxicity was expected. The clinical course was not consistent with significant diquat toxicity. Treatment included oral Fuller's earth, forced diuresis, hemofiltration, N-acetylcysteine, methylprednisolone, cyclophosphamide, vitamin E, colchicine, and delayed continuous nitric oxide inhalation. The patient recovered and pulmonary function was subsequently normal.

CONCLUSION

It is unclear which, if any, of the above treatments contributed to recovery, but the encouraging outcome suggests a possible benefit of nitric oxide inhalation in paraquat poisoning which deserves further study.

Efficacy of inhaled nitric oxide in children with ARDS

STUDY OBJECTIVE

Data concerning inhaled nitric oxide (iNO) on pediatric ARDS is rare. We investigated the effects of iNO on pediatric ARDS in order to examine the ability to predict a response to iNO, the optimal concentration of iNO, the effects of < or = 1 ppm nitric oxide (NO), and the effect of iNO on PaCO2.

SETTING

ICU at Kumamoto (Japan) University Hospital.

PATIENTS AND INTERVENTIONS

Seven children with ARDS. The initial responses to 16 ppm NO and the dose-response effects of 0.13 to 16 ppm NO were assessed.

MEASUREMENTS AND RESULTS

Sixteen ppm of iNO improved oxygenation in all seven children. The use of iNO significantly increased the ratio of arterial oxygen tension to the fraction of inspired oxygen (PaO2/FIO2). A correlation between the NO-induced increase in PaO2/FIO2 and the baseline PaO2/FIO2 was observed (r=0.93, p<0.01). Dose-response tests showed that the optimal concentration of iNO was < or = 4 ppm, improvements in PaO2/FIO2 could be observed with concentrations of < or = 1 ppm NO, and iNO induced a slight decrease in PaCO2.

CONCLUSIONS

In children with ARDS, iNO frequently improves oxygenation and induces a slight decrease in PaCO2, with the baseline PaO2/FIO2 functioning as a predictor of all NO response. Improvements of PaO2 and PaCO2 were observed with concentrations of iNO of < or = 1 ppm, a level in which the risk of a toxic reaction in children is minimal. Effects on outcome need verification in larger controlled trials.