Pulmonary mechanics generated by positive end-expiratory and continuous negative pressure.

Pulmonary function measurements were studied on equivalent levels of positive end-expiratory pressure (PEEP) and continuous negative pressure (CNP) while controlling for transpulmonary pressure (TPP). Four adult rabbits were anesthetized, instrumented, and ventilated with intermittent mandatory ventilation by using peak inspiratory pressure (PIP) of 16 cm H2O, PEEP 0 cm H2O, CNP 0 cm H2O, inspiratory time 0.3 seconds, rate 20/min, and fraction of inspired oxygen of 0.3. Subsequently, equal amounts of PEEP and CNP were alternated for 15-minute ventilation periods. PIP was changed to approximate the TPP in each PEEP/CNP pair. There was a significant decrease in PCO2 and increase in pH, mechanical tidal volume, minute ventilation, functional residual capacity, and total dynamic compliance on CNP. These differences could not be explained by changes in TPP.

Intermittent mandatory ventilation with continuous negative pressure compared with positive end-expiratory pressure for neonatal hypoxemia.

The use of continuous negative pressure was prospectively studied in 30 preterm and term hypoxemic (PaO2 < 45 mm Hg) neonates. Infants were randomly assigned to either positive end-expiratory pressure or continuous negative pressure if conventional positive pressure ventilation failed to improve oxygenation. Crossover to the alternative therapy occurred if infants remained hypoxemic after 2 hours. In the continuous negative pressure group, 2 (13%) crossed over to positive end-expiratory pressure, whereas 11 (73%) in the positive end-expiratory pressure group crossed over to continuous negative pressure (p = 0.003). Only five patients remained in the positive end-expiratory pressure group 36 hours after randomization. Compared with positive end-expiratory pressure, continuous negative pressure significantly increased PaO2 (69 +/- 17 mm Hg vs 36 +/- 8 mm Hg) and arterial-alveolar ratio (0.098 +/- 0.070 vs 0.057 +/- 0.014) 30 minutes after randomization and after crossover to continuous negative pressure (60 +/- 12 mm Hg vs 37 +/- 5 mm Hg, and 0.154 +/- 0.096 vs 0.058 +/- 0.009). The use of continuous negative pressure did not increase morbidity. Overall survival was 83.3%. Only three infants were referred to extracorporeal membrane oxygenation. Rescue therapy with continuous negative pressure is effective in infants with refractory hypoxemia and may be considered before referral for extracorporeal membrane oxygenation.

Reintroduction of continuous negative pressure ventilation in neonates: two-year experience.

Continuous negative pressure ventilation utilizes subatmospheric pressure around the thorax to improve oxygenation. It has not been routinely used since the mid-1970s. We treated 37 infants with the combination of continuous negative pressure (CNP) and intermittent mandatory ventilation (IMV), after failing to attain a PaO2 of greater than or equal to 50 torr on IMV alone. Lung diseases included pulmonary interstitial emphysema (PIE), respiratory distress syndrome (RDS), and pulmonary artery hypertension (PAH) due either to meconium aspiration syndrome (MAS) or other causes (non-MAS). All infants had evidence of severe parenchymal pulmonary disease, or pulmonary artery hypertension resulting in persistent hypoxemia and hypotension. In the PIE group, CNP was started later in the course of the disease, and both positive pressure and oxygen were maintained for a longer period. The group of infants with non-MAS PAH required CNP and positive pressure ventilation for the shortest period of time. The infants with PIE also had a greater incidence of bronchopulmonary dysplasia (BPD) and intraventricular hemorrhage (IVH). In addition, three patients with PIE died. In the non-MAS patients with PAH, no complications and no deaths occurred. The response to CNP was a rapid improvement in oxygenation in all groups with the greatest increase of PaO2 in the non-MAS PAH infants: from 30 torr prior to the initiation of CNP to 140 torr within 30 minutes. No significant changes in pH or PaCO2 occurred in any group. Significant decreases in ventilator rate, mean airway pressure (Paw) and FIO2 in peak inspiratory pressure were possible by 12 hours of CNP.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous negative pressure and intermittent mandatory ventilation in the management of pulmonary interstitial emphysema: a preliminary study.

We reviewed the clinical courses of 12 prematurely born newborns who were placed in continuous negative pressure (CNP) in an Isolette negative pressure ventilator for refractory hypoxemia while receiving intermittent positive pressure mandatory ventilation. All patients had severe lung disease as documented by an increased oxygenation index and bilateral pulmonary interstitial emphysema on x-ray examination. Patients were separated into two groups--survivors and nonsurvivors, with six patients in each group. Initiation of CNP resulted in a significant initial improvement in oxygenation in both groups seen as a 52% decrease in the oxygenation index in survivors and a 57% decrease in the oxygenation index in nonsurvivors (P less than .05). The survivors characterized themselves by showing a further sustained improvement in the oxygenation index--31.4 +/- 9.1 to 6.9 +/- 5.0 (P less than .01)--and a significant decrease in the mean airway pressure--11.6 +/- 4.6 cm H2O to 5.0 +/- 1.9 cm H2O (P less than .05). Four of the six survivors showed radiographic resolution of pulmonary interstitial emphysema. CNP was initiated at a mean age of 68.3 hours in the survivors. Nonsurvivors were initiated in CNP at a mean age of 134.3 hours, but went on to clinically deteriorate owing to irreversible hypoxemia and acidosis. Both oxygenation index and mean airway pressures were virtually unchanged compared with their initial values. The exact mechanisms by which CNP improves pulmonary function in this group of infants is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous negative pressure in the treatment of infants with pulmonary hypertension and respiratory failure.

We report the successful use of continuous negative pressure (CNP) with standard intermittent mandatory ventilation (IMV) in five patients suffering from respiratory failure and persistent pulmonary hypertension of the newborn (PPHN). These infants all fulfilled criteria for use of extracorporeal membrane oxygenation (ECMO) with PaO2 less than 40 torr, alveolar-arterial oxygen difference (AaDO2) greater than 620 mm Hg, and oxygenation index (OI) greater than 50. Despite a considerable amount of conventional ventilation with mean airway pressures (PAW) between 14 and 26 cm water, none of these patients were able to improve oxygenation. All infants demonstrated significant improvement in ventilation requirements after initiation of CNP as reflected by a decrease in PAW, proximal inspiratory pressure (PIP), and IMV. Oxygenation dramatically improved in all infants. All five patients survived without any pulmonary or neurological complications at discharge. Availability of CNP may circumvent the need for ECMO in infants with severe lung disease and PPHN.