Pressure-release tracheal gas insufflation reduces airway pressures in lung-injured sheep maintaining eucapnia

Tracheal gas insufflation with partial liquid ventilation to treat LPS-induced acute lung injury in juvenile piglets

OBJECTIVES

Partial liquid ventilation (PLV) with perfluorocarbons (PFC) seems not superior to conventional ventilation clinically. We hypothesized that a combination of continuous tracheal gas insufflation (TGI) with protective strategy of PLV (low dose of PFC, low inflation pressure, moderate inhalation of oxygen and moderate anesthesia) would improve cardiopulmonary function in acute lung injury.

METHODS

Twenty-four healthy juvenile piglets were anesthetized and mechanically ventilated at PEEP of 2 cmH(2)O with a peak inspiratory pressure of 10 cmH(2)O and FIO(2) of 0.4. The piglets were challenged with lipopolysaccharide and randomly assigned to four groups (n = 6 each): (1) mechanical ventilation alone (MV); (2) PLV with perfluorodecalin (10 ml/kg); (3) TGI with continuous airway flow 2 L/min; and (4) combination of PLV and TGI. The outcome was assessed functionally and histologically.

RESULTS

All treatments except MV improved pH, PaO(2)/FIO(2), PaCO(2), ventilation efficacy index (VEI) and tidal volume. Both PLV-associated treatments also improved heart rate, respiratory rate, pulse contour cardiac output, systemic vascular resistance, dynamic lung compliance, mean airway resistance and mean airway pressure. The combination group resulted in higher PaO(2)/FIO(2), VEI and a better lung histology score than any other treatments.

CONCLUSIONS

The new protective strategy may provide a better treatment for sepsis-induced acute lung injury.

Helmet ventilation and carbon dioxide rebreathing: effects of adding a leak at the helmet ports

OBJECTIVE

We examined whether additional helmet flow obtained by a single-circuit and a modified plateau valve applied at the helmet expiratory port (open-circuit ventilators) improves CO(2) wash-out by increasing helmet airflow.

DESIGN AND SETTING

Randomized physiological study in a university research laboratory.

PARTICIPANTS

Ten healthy volunteers.

INTERVENTIONS

Helmet continuous positive airway pressure and pressure support ventilation delivered by an ICU ventilator (closed-circuit ventilator) and two open-circuit ventilators equipped with a plateau valve placed either at the inspiratory or at the helmet expiratory port.

MEASUREMENTS AND RESULTS

We measured helmet air leaks, breathing pattern, helmet minute ventilation (Eh)), minute ventilation washing the helmet (Ewh)), CO(2) wash-out, and ventilator inspiratory assistance. Air leaks were small and similar in all conditions. Breathing pattern was similar among the different ventilators. Inspiratory and end-tidal CO(2) were lower, while (Eh) and (Ewh) were higher only using open-circuit ventilators with the plateau valve placed at the helmet expiratory port. This occurred notwithstanding these ventilators delivered a lower inspiratory assistance.

CONCLUSIONS

Additional helmet flow provided by open-circuit ventilators can lower helmet CO(2) rebreathing. However, inspiratory pressure assistance significantly decreases using open-circuit ventilators, still casting doubts on the choice of the optimal helmet ventilation setup.

Continuous tracheal gas insufflation during partial liquid ventilation in juvenile rabbits with acute lung injury

To examine the hypothesis that combined treatment with tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) may improve pulmonary outcome relative to either treatment alone in acute lung injury (ALI), saline lavage lung injury was induced in 24 anesthetized, ventilated juvenile rabbits that were then randomly assigned to receive ( n = 6/group) 1) conventional mechanical ventilation (CMV) alone, 2) continuous TGI at 0.5 l/min, 3) PLV with perfluorochemical liquid, and 4) combined TGI and PLV (TGI + PLV), and subsequently ventilated with minimized pressures and tidal volume (Vt) to keep arterial Po2 (PaO2) >100 Torr and arterial Pco2 (PaCO2) at 45-60 Torr for 4 h. Gas exchange, lung mechanics, myeloperoxidase, IL-8, and histomorphometry [including expansion index (EI)] were assessed. The CMV group showed no improvement in lung mechanics and gas exchange; all treated groups had significant increases in compliance, PaO2, ventilation efficacy index (VEI), and EI, and decreases in PaCO2, oxygenation index, physiological dead space-to-Vt ratio (Vd/Vt), myeloperoxidase, and IL-8, relative to the CMV group. TGI resulted in lower peak inspiratory pressure, Vt, Vd/Vt, and greater VEI vs. PLV group; PLV resulted in greater compliance, PaO2, and EI vs. TGI. TGI + PLV resulted in decreased peak inspiratory pressure, Vt, Vd/Vt, and increased VEI compared with TGI, improved compliance and EI compared with PLV, and a further increase in PaO2 and oxygenation index and a decrease in PaCO2 vs. either treatment alone. These results indicate that combined treatment of TGI and PLV results in improved pulmonary outcome than either treatment alone in this animal model of ALI.

Application of tracheal gas insufflation to acute unilateral lung injury in an experimental model

In unilateral lung injury, application of global positive end-expiratory pressure (PEEP) may cause overdistension of normal alveoli and redistribution of blood flow to diseased lung areas, thereby worsening oxygenation. We hypothesized that selective application of tracheal gas insufflation (TGI) will recruit the injured lung without causing overdistension of the normal lung. In eight anesthetized dogs, left lung saline lavage was performed until Pa(O(2))/FI(O(2)) fell below 100 mm Hg. Then, the dogs were reintubated with a Univent single lumen endotracheal tube that incorporates an internal catheter to provide TGI. After injury, increasing PEEP from 3 to 10 cm H(2)O did not change gas exchange, hemodynamics, or lung compliance. Selective TGI, while keeping end-expiratory lung volume (EELV) constant, improved Pa(O(2))/FI(O(2)) from 212 +/- 43 to 301 +/- 38 mm Hg (p < 0.01) while Pa(CO(2)) and airway pressures decreased (p < 0.01). During selective TGI, reducing tidal volume to 5.2 ml/kg while keeping EELV constant, normalized Pa(CO(2)), did not affect Pa(O(2))/FI(O(2)), and decreased end-inspiratory plateau pressure from 16.6 +/- 1.0 to 11.9 +/- 0.5 cm H(2)O (p < 0.01). In unilateral lung injury, we conclude that selective TGI (1) improves oxygenation at a lower pressure cost as compared with conventional mechanical ventilation, (2) allows reduction in tidal volume without a change in alveolar ventilation, and (3) may be a useful adjunct to limit ventilator-associated lung injury.

Mechanical ventilation in acute lung injury and acute respiratory distress syndrome

Mechanical ventilation provides life-sustaining support for most patients with acute lung injury and acute respiratory distress syndrome; however, traditional approaches to mechanical ventilation may cause ventilator-associated lung injury, which could exacerbate or perpetuate respiratory failure caused initially by conditions such as pneumonia, sepsis, and trauma. This article reviews the theory, laboratory data, and results of recent clinical trials that suggest that modified ventilator strategies can reduce ventilator-associated lung injury and improve clinical outcomes.