Comparison of two administration techniques of inhaled nitric oxide on nitrogen dioxide production

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.

Increased Alveolar and Plasma Gelatinases Activity during Postpump Syndrome: Inhibition by Inhaled Nitric Oxide

Postpump syndrome is associated with systemic inflammation. Matrix metalloproteinases (MMP)-2 and -9 contribute to proinflammatory and platelet-activator reactions. Nitric oxide (NO) is involved in the regulation of MMPs. The objectives of our study were to investigate the intensity of inflammation induced by 3 different surgical procedures, the effects of inflammation on the activity of MMPs, and the regulation of inflammation by inhaled NO (20 ppm). Inhaled NO was initiated immediately after tracheal intubation and maintained for the total duration of the experiments. Thirty pigs were equally randomized into 6 groups [sham; sham + NO; cardiopulmonary bypass; bypass + NO; bypass + lipopolysaccharide (1 microg/kg for 50 min); bypass + lipopolysaccharide + NO] and animals were subjected to anesthesia and mechanical ventilation up to 24 h. The levels of MMP-2 and MMP-9 in plasma and bronchoalveolar lavage were measured using zymography. Bypass resulted in a time-dependent rise in MMP activity, an effect potentiated by lipopolysaccharide. Inhaled NO attenuated the effects of bypass + lipopolysaccharide. These results confirm that MMP-2 and MMP-9 are associated with the inflammatory process causing the postpump syndrome. Preemptive and continuous administration of inhaled NO helps to prevent increased MMP-2 and MMP-9 activity.

Pre-emptive and continuous inhaled NO counteracts the cardiopulmonary consequences of extracorporeal circulation in a pig model

Cardiopulmonary bypass (CPB) activates a systemic inflammatory response characterized clinically by alterations in cardiovascular and pulmonary function. The aim of this study was to measure the cardiopulmonary consequences in sham-operated pigs, and in animals subjected to CPB in the presence or absence of lipopolysaccharide (LPS). We also investigated, if the perioperative administration of inhaled NO exerts significant cardiopulmonary effects in an anaesthetized and mechanically ventilated pig model of extracorporeal circulation. Thirty pigs were randomized into six equal groups (sham; sham+INO; CPB; CPB+INO; CPB+LPS; CPB+LPS+INO) and subjected to anaesthesia with mechanical ventilation for up to 24h. We found that CPB+LPS group has the highest degree of lung injury. We also demonstrated that there was a significant difference on the cardiovascular parameters (heart rate, central venous pressure, stroke volume index, and mean systemic arterial blood pressure) between the CPB groups and the sham groups. The deteriorated lung mechanics was associated with a decrease in active subfraction of surfactant (LA) with time during the procedure (P=0.0003), on which inhaled NO had only an initial beneficial effect. In our model, inhaled NO had no long-term beneficial effect on lung mechanics and surfactant homeostasis despite improving lung haemodynamics, inflammation, and oxygenation. We conclude from this study that the use of pre-emptive and continuous inhaled NO therapy has protective and safe effects against lung ischemia/reperfusion associated with CPB.

The anti-inflammatory effect of inhaled nitric oxide on pulmonary inflammation in a swine model

Cardiopulmonary bypass (CPB) is associated with an inflammatory process that leads to lung injury. In this study, we hypothesized that inhaled nitric oxide (INO) possesses the ability to modulate CPB-induced inflammation. Fifteen male pigs were randomly divided into 3 groups: Sham, CPB+LPS (CPB and lipopolysaccharide), and CPB+LPS+INO. INO (20 parts per million) was administered for 24 h after anesthesia. CPB was performed for 90 min, and LPS was infused (1 µg/kg) after CPB. Bronchoalveolar lavage (BAL) fluid and blood were collected at T0(before CPB), at 4 h, and at 24 h. At 24 h, BAL interleukin-8 (IL-8) levels were not increased as expected in the CPB+LPS group compared with the Sham group, but they were reduced significantly in the CPB+LPS+INO group. Cell hypo reactivity observed in the groups receiving LPS also seemed to downregulate endothelial nitric oxide synthase NOS protein expression relative to the Sham group. Nitrite and nitrate (NOx) concentrations were decreased significantly in the groups without INO. Moreover, animals treated with INO showed higher rates of pulmonary apoptosis compared with their respective controls. These results demonstrate that NOx production is reduced after CPB and that INO acts on the inflammatory process by diminishing neutrophils and their major chemoattractant, IL-8. INO also increases cell apoptosis in the lungs under inflammatory conditions, which may explain, in part, how it resolves pulmonary inflammation.Key words: CPB, nitric oxide, apoptosis, LPS, IL-8.

During neonatal mechanical ventilatory support, the delivered nitric oxide concentration is affected by the ventilatory setting

OBJECTIVE

To assess whether the delivered nitric oxide (NO) concentration is affected by a change in the ventilatory setting during neonatal mechanical ventilatory support.

DESIGN

Prospective, experimental study.

SETTING

Laboratory at Nagoya City University Medical School.

INTERVENTIONS

This study was performed by using a pressure-limited, time-cycled, ventilatory support with a neonatal circuit and a 50-mL silicone test lung. NO in N2 gas was administrated into the inspiratory limb at a distance of 4 cm, 80 cm, or 160 cm from the Y piece connected to the adapter of an endotracheal tube. The NO concentration was measured every 0.5 sec by a chemiluminescence analyzer at the Y piece.

MEASUREMENT AND MAIN RESULTS

NO concentrations were compared with each of the ventilatory settings of peak inspiratory pressure (PIP) (10-30 cm H2O), positive end-expiratory pressure (0-10 cm H2O), ventilatory flow (10, 20, 30 L/min), and ventilatory rate (30, 40, 50, 60, 70 breaths/min), respectively. The NO concentration was significantly lower when NO was added at 4 cm than at 80 cm or 160 cm from Y piece at the same ventilatory setting of PIP, positive end-expiratory pressure and ventilatory flow, respectively, (p < .01). Although the NO concentration was increased as the settled PIP level was increased (p < .01 or p < .05), it was not changed when the settled positive end-expiratory pressure level was increased. A decrease was seen in the NO concentration as the settled ventilatory flow was increased (p < .01). Lastly, the NO concentration fluctuated greatly in association with the settled ventilatory rate.

CONCLUSION

The NO concentration delivered to patients is influenced by the ventilatory setting during neonatal mechanical ventilatory support.

Effect of nitric oxide predilution on inhaled nitrogen dioxide concentrations

We examined the possibility that predilution of a concentrated nitric oxide (NO) source with nitrogen, before contact with oxygen, can reduce the inspired nitrogen dioxide (NO2) concentration during administration of nitric oxide. A Manley Blease and a Siemens Servo 900 C ventilator delivered 10, 20, 40, 60 and 80 parts per million (ppm) NO using an NO source of 1000, 400 and 200 ppm. With the Manley Blease system, predilution from 1000 to 200 ppm NO reduced the inhaled NO2 concentration from 0.14 to 0.05 ppm (p < 0.01) at 10 ppm inhaled NO, and from 1.20 to 1.00 ppm (p < 0.01) at 40 ppm inhaled NO. With the Siemens Servo 900 C ventilator, inspiratory NO2 concentrations decreased from 0.21 to 0.11 ppm (p < 0.01) at 10 ppm inhaled NO, and from 1.49 to 1.16 ppm (p < 0.01) at 40 ppm NO. Predilution from 1000 to 400 ppm NO reduced the inspired NO2 concentrations by < 3% using either ventilator when the inspirated NO concentration was 80 ppm. Predilution of NO with nitrogen significantly reduced the inspired NO2 concentrations for nitric oxide concentrations between 10 and 40 ppm, but offered no clinically relevant advantage at higher NO concentrations.

Delivery of inhaled nitric oxide using the Ohmeda INOvent Delivery System

OBJECTIVES

We evaluated the Ohmeda INOvent Nitric Oxide Delivery System, which uses an inspiratory flow sensor to inject a synchronized and proportional nitric oxide (NO) flow into the mechanical ventilator circuit. This system should deliver a constant NO concentration independent of ventilator mode, minute ventilation, fraction of inspired oxygen, or ventilator brand. It should also minimize nitrogen dioxide (NO2) formation.

METHODS

NO delivery by the INOvent and a premixing NO delivery system were compared using two ventilators (Puritan-Bennett 7200 and Servo 900C). NO concentration was measured within the trachea of an attached lung model using a fast-response chemiluminescence NO analyzer. NO concentration was also measured in the inspiratory limb using the electrochemical analyzer of the INOvent. For three NO concentrations (2, 5, and 20 ppm), the ventilators were set for constant flow volume control ventilation, pressure control ventilation, and spontaneous breathing with pressure support ventilation or synchronized intermittent mandatory ventilation. Different tidal volumes (300, 500, 750, and 1,000 mL) and inspiratory times (1 and 2 s) were evaluated. NO2 formation for both ventilators and delivery systems were evaluated at 20 ppm and 95% O2-.

RESULTS

Regardless of ventilatory pattern, both systems delivered a constant NO concentration. The error between the target and the delivered NO dose for the INOvent was -1.3+/-3.6% with the Puritan-Bennett 7200 and -3.9+/-4.3% with the Servo 900C. For the premixing system, the error was -5.5+/-4.8% with the Puritan-Bennett 7200 and -6.7+/-6.2% with the Servo 900C. NO2 concentrations were 0.5+/-0.1 ppm during NO delivery by the INOvent, 5.8+/-1.6 ppm when NO was premixed with air, 0.3+/-0.1 ppm when NO was premixed with N2.

CONCLUSION

The INOvent provides a constant NO concentration independent of the ventilatory pattern, and NO2 formation is minimal.

The use of inhaled nitric oxide in a wide variety of clinical problems

Inhaled nitric oxide (NO) clearly decreased pulmonary vascular resistance in pediatric patients with pulmonary hypertension, regardless of the underlying origin of the pulmonary hypertension. In persistent pulmonary hypertension of the neonate (PPHN) and CHD, the use of inhaled NO appears to improve the outcome of these patients. In acute respiratory distress syndrome (ARDS) and surfactant deficiency the role of inhaled NO therapy remains unclear. The use of inhaled NO is safe in a carefully monitored setting with a delivery system designed to minimize the generation of NO2.

Inhaled nitric oxide in acute respiratory distress syndrome: a pilot randomized controlled study

This pilot randomized controlled clinical trial of patients with ARDS was implemented to study the impact of inhaled nitric oxide (inhNO) on lung function, morbidity, and mortality. Thirty patients with ARDS were randomly allocated to usual care or usual care plus inhNO. The optimal dose of inhNO was determined to be between 0.5 and 40 parts-per-million daily. All therapeutic interventions were standardized. ARDS resulted mainly from sepsis (25 of the 30). During the first 24 h, the hypoxia score increased greatly in patients treated with inhNO +70.4 mm Hg (+59%) versus +14.2 mm Hg (+9.3%) for the control group (p = 0.02), venous admixture decreased from 25.7 to 15.2% in the inhNO group, and from only 19.4 to 14.9% in the control group (p = 0.05). After the first day of therapy no further beneficial effect of inhNO was detected. Forty percent of the patients treated with inhNO were alive and weaned from mechanical ventilation within 30 d after randomization compared with 33.3% in the control group (p = 0.83). The 30-d mortality rate was similar in the two groups; most deaths (11 of 17) were due to multiple organ dysfunction syndrome. This study shows that inhNO, in this population, may improve gas exchange but does not affect mortality.