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

Instrumental dead space: A glass ceiling for extremely low birth weight preterm infants? A dead space washout bench study

BACKGROUND

When ventilating extremely low birth weight infants, clinicians face the problem of instrumental dead space, which is often larger than tidal volume. Hence, aggressive ventilation is necessary to achieve CO₂ removal. Continuous tracheal gas insufflation can wash out CO₂ from dead space and might also have an impact on O₂ and water vapor transport. The objective of this bench study is to test the impact of instrumental dead space on the transport of CO₂ , O₂ , and water vapor and the ability of continuous tracheal gas insufflation to remedy this problem during small tidal volume ventilation.

METHODS

A test-lung located in an incubator at 37°C was ventilated with pressure levels needed to reach different tidal volumes from 1.5 to 5 mL. End-tidal CO₂ at the test-lung exit, O₂ concentration, and relative humidity in the test-lung were measured for each tidal volume with and without a 0.2 L/min continuous tracheal gas insufflation flow.

RESULTS

CO₂ clearance was improved by continuous tracheal gas insufflation allowing a 28%-44% of tidal volume reduction. With continuous tracheal gas insufflation, time to reach desired O₂ concentration was reduced from 20% to 80% and relative humidity was restored. These results are inversely related to tidal volume and are particularly critical below 3 mL.

CONCLUSION

For the smallest tidal volumes, reduction of instrumental dead space seems mandatory for CO₂ , O₂ , and water vapor transfer. Continuous tracheal gas insufflation improved CO₂ clearance, time to reach desired O₂ concentration and humidification of airways and, thus, may be an option to protect lung development.

Asymmetrical Lung Injury: Management and Outcome

Among mechanically ventilated patients, asymmetrical lung injury is probably extremely frequent in the intensive care unit but the lack of standardized measurements does not allow to describe any prevalence among mechanically ventilated patients. Many past studies have focused only on unilateral injury and have mostly described the effect of lateral positioning. The good lung put downward might receive more perfusion while the sick lung placed upward receive more ventilation than supine. This usually results in better oxygenation but can also promote atelectasis in the healthy lung and no consensus has emerged on the clinical indication of this posture. Recently, electrical impedance tomography (EIT) has allowed for the first time to precisely describe the distribution of ventilation in each lung and to better study asymmetrical lung injury. At low positive-end-expiratory pressure (PEEP), a very heterogeneous ventilation exists between the two lungs and the initial increase in PEEP first helps to recruit the sick lung and protect the healthier lung. However, further increasing PEEP distends the less injured lung and must be avoided. The right level can be found using EIT and transpulmonary pressure. In addition, EIT can show that in the two lungs, airway closure is present but with very different airway opening pressures (AOPs) which cannot be identified on a global assessment. This may suggest a very different PEEP level than on a global assessment. Lastly, epidemiological studies suggest that in hypoxemic patients, the number of quadrants involved has a strong prognostic value. The number of quadrants is more important than the location of the unilateral or bilateral nature of the involvement for the prognosis, and hypoxemic patients with unilateral lung injury should probably be considered as requiring lung protective ventilation as classical acute respiratory distress syndrome.

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.

Research in high flow therapy: mechanisms of action

Recently, heater/humidifier devices that use novel methods to condition breathing gases from an external source have been introduced. The addition of sufficient warmth and high levels of humidification to breathing gas has allowed for higher flow rates from nasal cannula devices to be applied to patients (i.e., high flow therapy). This article provides a review of the proposed mechanisms behind the efficacy of high flow therapy via nasal cannula, which include washout of nasopharyngeal dead space, attenuation of the inspiratory resistance associated with the nasopharynx, improvement in conductance and pulmonary compliance, mild distending pressure and reduction in energy expenditure for gas conditioning.

Permissive hypercapnia: role in protective lung ventilatory strategies

PURPOSE OF REVIEW

Hypercapnia is a central component of current protective ventilatory strategies. This review aims to present and interpret data from recent clinical and experimental studies relating to hypercapnia and its role in protective ventilatory strategies.

RECENT FINDINGS

Increasing clinical evidence supports the use of permissive hypercapnia, particularly in acute lung injury/acute respiratory distress syndrome, status asthmaticus, and neonatal respiratory failure. However, there are no clinical data examining the contribution of hypercapnia per se to protective ventilatory strategies. Recent experimental studies provide further support for the concept of therapeutic hypercapnia, whereby deliberately elevated PaCO2 may attenuate lung and systemic organ injury. CO2 administration attenuates experimental acute lung injury because of adverse ventilatory strategies, mesenteric ischemia reperfusion, and pulmonary endotoxin instillation. Hypercapnic acidosis attenuates key effectors of the inflammatory response and reduces lung neutrophil infiltration. At the genomic level, hypercapnic acidosis attenuates the activation of nuclear factor-kappaB, a key regulator of the expression of multiple genes involved in the inflammatory response. The physiologic effects of hypercapnia, both beneficial and potentially deleterious, are increasingly well understood. In addition, reports suggest that humans can tolerate extreme levels of hypercapnia for relatively prolonged periods without adverse effects.

SUMMARY

The potential for hypercapnia to contribute to the beneficial effects of protective lung ventilatory strategies is clear from experimental studies. However, the optimal ventilatory strategy and the precise contribution of hypercapnia to this strategy remain unclear. A clearer understanding of its effects and mechanisms of action is central to determining the safety and therapeutic utility of hypercapnia in protective lung ventilatory strategies.

Pulmonary applications of perfluorochemical liquids: ventilation and beyond

In this review of liquid ventilation, concepts and applications are presented that summarise the pulmonary applications of perfluorochemical liquids. Beginning with the question of whether this alternative form of respiratory support is needed and ending with lessons learned from clinical trials, the various methods of liquid assisted ventilation are compared and contrasted, evidence for mechanoprotective and cytoprotective attributes of intrapulmonary perfluorochemical liquid are presented and alternative intrapulmonary applications, including their use as vehicles for drugs, for thermal control and as imaging agents are presented.