Intratracheal pulmonary ventilation versus conventional mechanical ventilation in a rabbit model of surfactant deficiency

Influence of Alveolar Fluid on Aquaporins and Na+/K+-ATPase and Its Possible Theoretical or Clinical Significance

OBJECTIVE

Pulmonary edema is the most common pathophysiological change in pulmonary disease. Aquaporins (AQPs) and Na⁺/K⁺-ATPase play pivotal roles in alveolar fluid clearance. This study aimed to explore the influence of increased alveolar fluid on the absorption of lung fluid.

STUDY DESIGN

Eighty New Zealand rabbits were randomly divided into eight groups (n = 10 in each group), and models of different alveolar fluid contents were established by the infusion of different volumes of normal saline (NS) via the endotracheal tube. Five animals in each group were sacrificed immediately after infusion to determine the wet/dry ratio, while the remaining animals in each group were killed 4 hours later to determine the wet/dry ratio at 4 hours. Additionally, lung specimens were collected from each group, and quantitative real-time PCR (qRT-PCR), western blot, and immunohistochemical (IHC) analyses of AQPs and Na⁺/K⁺-ATPase were performed.

RESULTS

The qRT-PCR analysis and western blot studies showed markedly decreased mRNA and protein levels of AQP1 and Na⁺/K⁺-ATPase when the alveolar fluid volume was ≥6 mL/kg, and the mRNA level of AQP5 was significantly reduced when the alveolar fluid volume was ≥4 mL/kg. In addition, IHC analysis showed the same results. At 4 hours, the lung wet/dry ratio was significantly increased when the alveolar fluid volume was ≥6 mL/kg; however, compared with 0 hours after NS infusion, there was still a significant absorption of alveolar fluid for a period of 4 hours.

CONCLUSION

The results of this study suggest that increased alveolar fluid may induce the downregulation of the mRNA and protein expression of AQPs and Na⁺/K⁺-ATPase, which appear to affect alveolar fluid clearance in rabbit lungs. Early intervention is required to avoid excessive alveolar fluid accumulation.

KEY POINTS

· The expression levels of AQPs and Na+/K+--ATPase were significantly decreased as alveolar fluid increased.. · At 4 hours, wet/dry ratio was significantly increased when infusion volume was ≥ 6 mL/kg.. · Early intervention is required to avoid excessive alveolar fluid accumulation..

Established severe BPD: is there a way out? Change of ventilatory paradigms

Improved survival of extremely preterm newborn infants has increased the number of infants at risk for developing bronchopulmonary dysplasia (BPD). Despite efforts to prevent BPD, many of these infants still develop severe BPD (sBPD) and require long-term invasive mechanical ventilation. The focus of research and clinical management has been on the prevention of BPD, which has had only modest success. On the other hand, research on the management of the established sBPD patient has received minimal attention even though this condition poses large economic and health problems with extensive morbidities and late mortality. Patients with sBPD, however, have been shown to respond to treatments focused not only on ventilatory strategies but also on multidisciplinary approaches where neurodevelopmental support, growth promoting strategies, and aggressive treatment of pulmonary hypertension improve their long-term outcomes. In this review we will try to present a physiology-based ventilatory strategy for established sBPD, emphasizing a possible paradigm shift from acute efforts to wean infants at all costs to a more chronic approach of stabilizing the infant. This chronic approach, herein referred to as chronic phase ventilation, aims at allowing active patient engagement, reducing air trapping, and improving ventilation-perfusion matching, while providing sufficient support to optimize late outcomes. IMPACT: Based on pathophysiological aspects of evolving and established severe BPD in premature infants, this review presents some lung mechanical properties of the most severe phenotype and proposes a chronic phase ventilatory strategy that aims at reducing air trapping, improving ventilation-perfusion matching and optimizing late outcomes.

Wet lung leading to RDS: the lung ultrasound findings and possible mechanisms - a pilot study from an animal mode

BACKGROUND

Clinically, the lung ultrasound (LUS) showed wet lung could cause respiratory distress syndrome (RDS) in newborns. This work aimed to investigate LUS changes over time and its potential mechanism as alveolar fluid increase in a rabbit model.

METHODS

A total of 35 New Zealand Rabbits were randomly assigned to seven groups. Models of various alveolar fluid levels were induced by infusion of different volumes of normal saline (NS) via the endotracheal tube. LUS was performed before NS infusion, immediately after NS infusion and 4 h after NS infusion. To appraise LUS changes and its potential mechanism as alveolar fluid increase, histopathological examination, the mRNA and protein expression of surfactant protein (SP), and immunohistochemistry (IHC) were performed. The expression levels of SP-B and SP-C proteins were detected using western blotting, and the relative expression levels of SP-B and SP-C mRNA were detected using qRT-PCR.

RESULTS

The results showed that LUS changed from B-line to lung consolidations accompanied by air-bronchograms in some locations of lungs at 4 h when the injection volume ≥ 6 ml/kg. Histopathological examination showed alveoli collapse, inflammatory cell infiltration and alveolar wall thickened. SP-B and SP-C mRNA and protein expression were statistically significantly reduced when the injection volume ≥6 ml/kg (p < .05). IHC staining displayed the same findings.

CONCLUSIONS

As alveolar fluid increase, LUS changed from wet lung to RDS after 4 h. The possible mechanism was that the SP protein expression was significantly reduced. LUS can be used to guide the administration of exogenous surfactant in this situation.

Using lung ultrasound to quantitatively evaluate pulmonary water content

BACKGROUND

Increases in extravascular lung water (EVLW) can lead to respiratory failure. This study aimed to investigate whether the B-line score (BLS) was correlated with the EVLW content determined by the lung wet/dry ratio in a rabbit model.

METHODS

A total of 45 New Zealand rabbits were randomly assigned to nine groups. Among the animals, models of various lung water content levels were induced by the infusion of different volumes of warm sterile normal saline (NS) via the endotracheal tube. The arterial blood gas, spontaneous respiratory rate, and PaO₂ /FiO₂ ratio were detected before and after infusion. In addition, the B-lines were determined before and immediately after infusion in each group. Finally, both lungs were resected to determine the wet/dry ratio. In addition, all lung specimens were analyzed histologically, and EVLW was quantified using the BLS based on the number and confluence of B-lines in the intercostal space.

RESULTS

The BLS increased with increasing infusion volume. The BLS was statistically correlated with the wet/dry ratio (r² = .946) and with the PaO₂ /FiO₂ ratio (r² = .916). Furthermore, a repeatability study was performed for the lung ultrasound (LUS) technology (Bland-Altman plots), and the results suggest that LUS had favorable intraobserver and interobserver reproducibility.

CONCLUSIONS

This study is the first to suggest that the BLS can serve as a sensitive, quantitative, noninvasive, and real-time indicator of EVLW in a rabbit model of lung water accumulation. Notably, the BLS displayed an obvious correlation with the experimental gravimetry results and could also be used to predict the pulmonary oxygenation status.

The effect of a peptide-containing synthetic lung surfactant on gas exchange and lung mechanics in a rabbit model of surfactant depletion

Background

Currently, a new generation of synthetic pulmonary surfactants is being developed that may eventually replace animal-derived surfactants used in the treatment of respiratory distress syndrome. Enlightened by this, we prepared a synthetic peptide-containing surfactant (Synsurf) consisting of phospholipids and poly-l-lysine electrostatically bonded to poly-l-glutamic acid. Our objective in this study was to investigate if bronchoalveolar lavage (BAL)-induced acute lung injury and surfactant deficiency with accompanying hypoxemia and increased alveolar and physiological dead space is restored to its prelavage condition by surfactant replacement with Synsurf, a generic prepared Exosurf, and a generic Exosurf containing Ca²⁺.

Methods

Twelve adult New Zealand white rabbits receiving conventional mechanical ventilation underwent repeated BAL to create acute lung injury and surfactant-deficient lung disease. Synthetic surfactants were then administered and their effects assessed at specified time points over 5 hours. The variables assessed before and after lavage and surfactant treatment included alveolar and physiological dead space, dead space/tidal volume ratio, arterial end-tidal carbon dioxide tension (PCO₂) difference (mainstream capnography), arterial blood gas analysis, calculated shunt, and oxygen ratios.

Results

BAL led to acute lung injury characterized by an increasing arterial PCO₂ and a simultaneous increase of alveolar and physiological dead space/tidal volume ratio with no intergroup differences. Arterial end-tidal PCO₂ and dead space/tidal volume ratio correlated in the Synsurf, generic Exosurf and generic Exosurf containing Ca²⁺ groups. A significant and sustained improvement in systemic oxygenation occurred from time point 180 minutes onward in animals treated with Synsurf compared to the other two groups (P < 0.001). A statistically significant decrease in pulmonary shunt (P < 0.001) was found for the Synsurf-treated group of animals, as well as radiographic improvement in three out of four animals in that group.

Conclusion

In general, surfactant-replacement therapy in the animals did not fully restore the lung to its prelavage condition. However, our data show that the formulated surfactant Synsurf improves oxygenation by lowering pulmonary shunt.

Epithelial restitution and wound healing in inflammatory bowel disease

Inflammatory bowel disease is characterized by a chronic inflammation of the intestinal mucosa. The mucosal epithelium of the alimentary tract constitutes a key element of the mucosal barrier to a broad spectrum of deleterious substances present within the intestinal lumen including bacterial microorganisms, various dietary factors, gastrointestinal secretory products and drugs. In addition, this mucosal barrier can be disturbed in the course of various intestinal disorders including inflammatory bowel diseases. Fortunately, the integrity of the gastrointestinal surface epithelium is rapidly reestablished even after extensive destruction. Rapid resealing of the epithelial barrier following injuries is accomplished by a process termed epithelial restitution, followed by more delayed mechanisms of epithelial wound healing including increased epithelial cell proliferation and epithelial cell differentiation. Restitution of the intestinal surface epithelium is modulated by a range of highly divergent factors among them a broad spectrum of structurally distinct regulatory peptides, variously described as growth factors or cytokines. Several regulatory peptide factors act from the basolateral site of the epithelial surface and enhance epithelial cell restitution through TGF-β-dependent pathways. In contrast, members of the trefoil factor family (TFF peptides) appear to stimulate epithelial restitution in conjunction with mucin glycoproteins through a TGF-β-independent mechanism from the apical site of the intestinal epithelium. In addition, a number of other peptide molecules like extracellular matrix factors and blood clotting factors and also non-peptide molecules including phospholipids, short-chain fatty acids (SCFA), adenine nucleotides, trace elements and pharmacological agents modulate intestinal epithelial repair mechanisms. Repeated damage and injury of the intestinal surface are key features of various intestinal disorders including inflammatory bowel diseases and require constant repair of the epithelium. Enhancement of intestinal repair mechanisms by regulatory peptides or other modulatory factors may provide future approaches for the treatment of diseases that are characterized by injuries of the epithelial surface.

Carbon dioxide clearance in rabbits during expiratory phase intratracheal pulmonary ventilation

The purpose of this study was to compare the efficacy of CO2 removal during conventional mechanical ventilation (CMV) with and without expiratory phase intratracheal pulmonary ventilation (expiratory ITPV or Exp-ITPV); and to compare CO2 clearance during Exp-ITPV, in pressure-controlled ventilation (PCV) and in volume-controlled ventilation (VCV) modes. Seven anesthetized rabbits were tracheotomized and intubated using a 4 mm endotracheal tube. Venous and arterial lines were established. The rabbits were paralyzed, mechanically ventilated, and ventilation parameters were adjusted to achieve baseline arterial hypercapnia. Animals were then ventilated during 30-minute trials of CMV and Exp-ITPV, in both PCV and VCV modes. A custom-built, microprocessor-controlled solenoid valve was used to limit ITPV gas flow to the expiratory phase. Proximal and carinal airway pressures and hemodynamic variables were continuously recorded, and arterial blood gases were analyzed at the end of each trial. Exp-ITPV, as compared with CMV, reduced arterial PCO2 by 12% and 21% in PCV and VCV modes, respectively (p < 0.02 and p < 0.001; one-sided paired t test), without significant changes in other cardiorespiratory variables. In conclusion, Exp-ITPV is more effective than CMV in clearing CO2 through a small endotracheal tube. Exp-ITPV is also more effective in VCV mode than PCV mode.

Intratracheal pulmonary ventilation improves gas exchange during laparoscopy in a pediatric lung injury model

BACKGROUND/PURPOSE

This study was aimed at determining whether intraoperative intratracheal pulmonary ventilation (ITPV) could prevent/treat respiratory complications of laparoscopy in a model of pediatric pulmonary insufficiency.

METHODS

Severe lung injury was induced in 0- to 2-month-old lambs (n = 5) by endotracheal saline lavage. Animals then underwent establishment of CO2 pneumoperitoneum. Intraperitoneal pressures were progressively raised from 0 to 15 mm Hg, at intervals of 5 mm Hg. At each interval, blood gas and hemodynamic data were recorded, 20 minutes after initiation of both conventional ventilation and pure ITPV. All ventilatory parameters were constant and identical on both modes of ventilation.

RESULTS

On conventional ventilation, severe respiratory acidosis and hypoxemia ensued at intraperitoneal pressures of 5 mm Hg and 10 mm Hg or more, respectively. Compared with conventional ventilation, ITPV led to statistically significant decreases in PCO2 at intraperitoneal pressures of 5 mm Hg (43.2 +/- 5.2 vs 56.1 +/- 6.6 mm Hg) and 10 mm Hg (45.1 +/- 3.2 vs 61 +/- 6.3 mm Hg) and to significant increases in PO2 at 10 mm Hg (92 +/- 10.2 vs 61 +/- 8.1 mm Hg), resolving the acidosis and hypoxemia at those pressure levels.

CONCLUSIONS

Compared with conventional ventilation, ITPV improves both CO2 removal and oxygenation during CO2 pneumoperitoneum in a pediatric lung injury model. Intratracheal pulmonary ventilation may be a safer intraoperative mode of ventilation for neonates and children with respiratory failure who require laparoscopy.

Tracheal gas isufflation-aided mechanical ventilation during carbon dioxide-induced pneumoperitoneum in rabbits

Despite numerous benefits of laparoscopic procedures, the serious hypercapnia and respiratory acidosis in hypercapnic patients with decreased pulmonary compliance during carbon dioxide-induced pneumoperitoneum (CDP) may be developed. Tracheal gas insufflation (TGI) has been shown to be a useful adjunct to controlled mechanical hypoventilation. This study was undertaken to identify whether TGI superimposed on controlled mechanical ventilation (CMV) improve ventilatory efficiency during CDP in rabbits. Sixteen paralyzed and anesthetized rabbits were used. The animals were assigned to two groups-CMV group: CMV alone; TGI group: CMV superimposed by TGI with flow rate of 2L/min. The animals were insufflated to intra-abdominal pressure of 8 mmHg with CO2 gas. Then, tidal volume (V(T)) was changed to maintain the set peak inspiratory pressure (PIP) value, while other ventilatory settings were kept constant. The set PIP value corresponding to 30, 60, and 90 min after the start of peritoneal insufflation of CO2 were 15, 22, and 25 cm H2O, respectively. During CDP with TGI, PaCO2 decreased significantly (p<0.01) from CMV without TGI of 82.1 +/- 14.1 to 47.5 +/- 5.5, 58.1 +/- 9.9 to 40.0 +/- 4.6, 47.1 +/- 9.4 to 32.7 +/- 5.1 mmHg at PIP of 15, 22, and 25 cm H2O, respectively. The inspired V(T) decreased significantly (p<0.05) from CMV without TGI of 18.4 +/- 3.9 to 12.8 +/- 2.8 ml at PIP of 15 cm H2O. TGI superimposed on CMV is more effective than CMV alone in enhancing ventilatory efficiency during CDP in rabbits.

Tracheobronchial injury during intratracheal pulmonary ventilation in rabbits

OBJECTIVE

We compared tracheobronchial injury following short-term intratracheal pulmonary ventilation (ITPV) and conventional mechanical ventilation (CMV) in a healthy rabbit model. ITPV, a form of tracheal gas insufflation, has been shown to decrease deadspace ventilation and increase CO2 removal and therefore may reduce ventilator-induced lung injury.

SETTING

Medical center laboratory.

SUBJECTS

Twenty-five rabbits.

INTERVENTIONS

Rabbits were randomly assigned to either ITPV or CMV (n = 15 and 10, respectively). Both groups were mechanically ventilated for 8 hrs at the same ventilator settings (FIO2, 0.4; rate, 30 breaths/min; flow, 4 L x min(-1); positive end-expiratory pressure, 4 cm H2O; tidal volume, 40 mL). Peak, mean, and end-expiratory carinal pressures, ITPV flow rate, and hemodynamic variables were continuously monitored. Tissue samples for histologic analysis were obtained postmortem from the trachea contiguous to the tip of the endotracheal tube, the distal trachea, the carina, and the main bronchus. The histologic sections were scored, in a single-blind fashion, for ciliary damage, ulceration, hemorrhage, overall inflammation, intraepithelial inflammatory infiltrate, and edema.

MEASUREMENTS AND MAIN RESULTS

ITPV was associated with significantly lower Paco and deadspace ventilation ratio than CMV. The combined tracheobronchial injury scores for all samples were significantly higher in the ITPV group compared with the CMV group (p <.005; Mann-Whitney U test). The ITPV injury scores, compared with CMV injury scores, were significantly higher at the carina and main bronchus (p <.01; Kruskal-Wallis test followed by Dunn's multiple comparison test). The area adjacent to the endotracheal tube showed the same degree of damage in both groups. Analysis of the injury scores in individual damage categories demonstrated the greatest difference in the ulceration category (p <.001).

CONCLUSIONS

In our study, ITPV, compared with CMV at the same minute ventilation, was associated with a significantly greater difference in tracheobronchial damage at the carina and main bronchus. We postulate that this difference may have been caused by the turbulence of the gas flow generated by the small-caliber ITPV catheter used in our neonatal-size animal model.

Intratracheal pulmonary ventilation versus conventional mechanical ventilation: continuous carinal pressure monitoring at low and high flows and frequencies

We continuously measured proximal and carinal pressures at low and high flow rates and frequencies during conventional mechanical ventilation (CMV) and intratracheal pulmonary ventilation (ITPV), using an artificial lung. The proximal peak inspiratory pressure (PIP), carinal PIP, proximal positive end expiratory pressure (PEEP), and carinal PEEP, or negative end expiratory pressure (NEEP), were measured during simulated CMV and ITPV. Two levels of frequency (30 and 90 per min) and two gas flow rates (3 and 6 L/min) were examined, in both dry and humid states (four combinations of gas flow and frequency at each state). The gas flow and inspiratory time were held constant throughout the CMV and ITPV trials. Humidification of the ventilatory circuit during ITPV prevented the accurate measurement of carinal pressures. This problem was solved by introducing a continuous "bias flow" of 11 ml/min into the pressure monitoring line. A combination of low gas flow and low frequency with CMV showed no significant differences between the proximal and carinal PIP, as well as the proximal and carinal PEEP. The same combination with ITPV, however, resulted in a significantly lower carinal PIP and PEEP, compared to proximal PIP and PEEP. Carinal PIP and PEEP during ITPV were also significantly lower than those observed during CMV with a low flow and low frequency rates. During both CMV and ITPV, using a combination of a high flow rate with a high breathing frequency, carinal PIPs were significantly lower than proximal PIPs. ITPV, however, generated much larger differences between proximal and carinal PIPs than the CMV. A significant NEEP was generated at the carinal level during ITPV with high flow rates, both with high and low frequencies. The NEEP did not occur with a low gas flow, in combination with either a low frequency or a high frequency. The "bias flow" had no significant effect on carinal pressures. In conclusion, ITPV, compared with CMV, generates a significantly lower carinal PIP, but it may also generate carinal NEEP. For safety reasons, therefore, it is essential to monitor carinal pressures continuously in patients treated with ITPV.

Intratracheal pulmonary ventilation in a rabbit lung injury model: continuous airway pressure monitoring and gas exchange efficacy

OBJECTIVES

To compare carinal pressures vs. proximal airway pressures, and gas exchange efficacy with a constant minute volume, in lung-injured rabbits during conventional mechanical ventilation (CMV) and intratracheal pulmonary ventilation (ITPV); and to evaluate performance of a prototype ITPV gas delivery and continuous airway pressure monitoring system.

DESIGN

Prospective controlled study.

SETTING

Animal research laboratory at a teaching hospital.

SUBJECTS

Sixteen adult female rabbits.

INTERVENTIONS

Anesthetized rabbits were tracheostomized with a multilumen endotracheal tube. Anesthesia and muscle relaxation were maintained continuously throughout the study. Proximal airway pressures and carinal pressures were recorded continuously. The injection port of the multilumen endotracheal tube was used for the carinal pressure monitoring. To prevent obstruction of the port, it was flushed with oxygen at a rate of 11 mL/min. CMV was initiated with a pressure-limited, time-cycled ventilator set at an FiO2 of 1.0 and at a flow of 1.0 L/kg/min. The pressure limit of the ventilator was effectively disabled. A normal baseline for arterial blood gases was achieved by adjusting the inspiratory/expiratory time ratios. ITPV was established using a flow of 1.0 L/kg/min through a reverse thrust catheter, at the same baseline and inspiratory/expiratory ratio. Carinal positive end-expiratory pressure was maintained at a constant value of 2 cm H2O by adjusting the expiratory resistance of the ventilator circuit Lung injury was achieved over a 30-min period by three normal saline lavages of 5 mL/kg each. After lung injury, all animals were consecutively ventilated for 1 hr with CMV, for 1 hr with ITPV, and again for 1 hr with CMV. Six rabbits were ventilated at 30 breaths/min (group 1), and ten rabbits were ventilated at 80 breaths/min (group 2). Four rabbits in group 2 were subjected, 1 hr after return to CMV from ITPV, to another session of ITPV, with positive end-expiratory pressure gradually being increased to 4, 6, and 8 cm H2O for 15 mins each.

RESULTS

No significant differences were observed in carinal peak inspiratory pressure between CMV and ITPV modes, at both low and high frequencies of breathing, indicating that the inspired tidal volume remained constant during both modes of ventilation. Significant gradients were noted between proximal airway and carinal peak inspiratory pressure during ITPV but not during CMV. Initiation of ITPV, at a flow of 1.0 L/kg/min, required an increase in the ventilator expiratory resistance to maintain a constant level of positive end-expiratory pressure (2 cm H2O) as measured at the carina. During ITPV, the PaCO2 was significantly reduced by 20% at 30 breaths/min (p < .05) and by 22% at 90 breaths/min (p < .01), compared with CMV. Arterial oxygenation was significantly enhanced with a positive end-expiratory pressure of 6 and 8 cm H2O (p < .05 and .001, respectively), compared with a positive end-expiratory pressure of 2 cm H2O during ITPV. All components of the new prototype gas delivery and airway pressure monitoring system functioned without failure, at least for 3 hrs of the CMV, ITPV, and CMV trials.

CONCLUSIONS

ITPV in saline-lavaged, lung-injured rabbits at breathing frequencies of 30 and 80 breaths/min, compared with CMV at the same minute ventilation, can improve CO2 exchange. During ITPV, significant pressure gradients can develop between carinal and proximal airway pressures. Continuous carinal pressure monitoring is therefore necessary for the safe clinical application of ITPV. Reliable carinal pressure monitoring can be achieved by adding a small bias flow through the carinal pressure monitoring port. Although ITPV can remove CO2 from injured lungs efficiently, simultaneous addition of positive end-expiratory pressure can further improve arterial oxygenation.

A comparison of intratracheal pulmonary ventilation to conventional ventilation in a surfactant deficient animal model

OBJECTIVE

To compare intratracheal pulmonary ventilation (ITPV) with conventional ventilation in a rabbit model of surfactant deficiency.

DESIGN

A prospective randomized animal study.

SETTING

The Children's National Medical Center Research Animal Facility in Washington, DC.

SUBJECTS

Adult male New Zealand white rabbits (n = 20), weighing 1.4-4.2 kg.

INTERVENTIONS

After anesthesia and catheter placement, rabbits were tracheotomized, paralyzed, and placed on the conventional ventilator. We determined pulmonary functions at baseline. We washed surfactant out of the lungs by using serial bronchoalveolar lavages. Pulmonary function studies were determined after completion of the bronchoalveolar lavages and were used as an indication of severity of lung injury. Animals were randomized into two groups: We placed ten animals on ITPV, using the ITPV reverse thruster catheter designed by Kolobow and a prototype ITPV ventilator designed at Children's National Medical Center; we placed ten animals on conventional ventilation using the Sechrist iv-100 ventilator. Arterial blood gases were drawn every 15 mins, and the ventilator settings were adjusted to the minimal level that would maintain arterial blood gases in the following ranges: pH 7.35-7.45, PaCO2 30-40 torr (3.995.33 kPa), PaO2 50-70 torr (6.66-9.33 kPa). Animals were ventilated with the randomized ventilation techniques for 4 hrs.

MEASUREMENTS AND MAIN RESULTS

Peak inspiratory pressure, mean airway pressure, and positive end-expiratory pressure were measured at the distal end of the endotracheal tube. We recorded these variables plus respiratory rate at baseline and every 30 mins for a total of 4 hrs of ventilation. Lung compliance did not differ between groups at the postlavage study period (ITPV, 0.56+/-0.13 mL/cm H2O/kg; conventional 0.49+/-0.15 mL/cm H2O/kg). At the end of the 4 hr study period, peak inspiratory pressure (ITPV, 26.2+/-4.6 cm H2O; conventional, 32.4+/-5.04 cm H2O, p = .007) and positive end-expiratory pressure (ITPV, 3.9+/-1.96 cm H2O; conventional, 6.3+/-1.42 cm H2O, p = .005) were lower in the ITPV ventilation group. Peak inspiratory pressure was significantly lower in the ITPV group by 2 hrs into the study.

CONCLUSION

In this model of surfactant deficiency lung injury, ventilation and oxygenation were achieved at significantly lower ventilator settings using ITPV compared with conventional ventilation. Long-term studies are needed to determine whether this reduction in ventilation is maintained, and if so, if lung injury is reduced.

Comparison of intratracheal pulmonary ventilation and hybrid intratracheal pulmonary ventilation with conventional mechanical ventilation in a rabbit model of acute respiratory distress syndrome by saline lavage

OBJECTIVES

To study changes in PaCO2 and PaO2 during intratracheal pulmonary ventilation (ITPV) and hybrid intratracheal pulmonary ventilation (h-ITPV) compared with conventional mechanical ventilation (CMV) in a rabbit model of respiratory failure, and to define the technique of h-ITPV that combines conventional mechanical ventilation and ITPV.

DESIGN

Prospective, interventional study.

SUBJECTS

Twelve adult New Zealand White rabbits.

INTERVENTIONS

Surfactant deficiency was induced by saline lavage, and rabbits were randomized to either ITPV or h-ITPV. The study consisted of four phases: phase 0, CMV after saline lavage, ventilator rate 30 breaths/min; phase I, ITPV or h-ITPV initiated at the same pressure and rate as in phase 0; phase II, ITPV or 1.0 L/min h-ITPV bias flow, with peak inspiratory pressure (PIP) decreased and ventilator rate increased to achieve the lowest tidal volume while maintaining adequate gas exchange; and phase III, animals returned to CMV.

MEASUREMENTS AND MAIN RESULTS

In phase I, no difference in PaCO2 was observed between ITPV, h-ITPV, or CMV. There was a decrease in PaO2 when switching from CMV to ITPV but not to h-ITPV. In phase II, it was possible to decrease PIP (average of 37% for ITPV and 36% for h-ITPV) and tidal volume (average of 64% for ITPV and 53% for h-ITPV) without compromising gas exchange (p < .05). Oxygenation tended to improve from phase 0 to the end of phase II. In phase III, PaCO2 increased (average of 71% for ITPV and 79% for h-ITPV) and pH decreased (p < .05). Normocapnia was achieved using significantly higher PIP and tidal volume, compared with phase 0 (p < .05).

CONCLUSIONS

ITPV and h-ITPV can effectively ventilate and oxygenate rabbits with surfactant-deficient lungs at tidal volumes and therefore pressures lower than required with CMV. Maximum benefit appears to occur at high ventilator rates. These findings suggest that both modes of ventilation may represent powerful new tools in the management of patients with acute respiratory failure. (Crit Care Med 2000; 28:774-781)

A new ventilator improves CO2 removal in newborn lambs with congenital diaphragmatic hernia

OBJECTIVES

To demonstrate improved ventilation with intratracheal pulmonary ventilation (ITPV) in new-born lambs with congenital diaphragmatic hernia, using a new microprocessor controlled ITPV-specific ventilator.

DESIGN

Prospective study, with each animal serving as its own control (paired data).

SETTING

Large animal research laboratory.

SUBJECTS

Diaphragmatic hernias were created surgically in seven fetal sheep on gestational day 100 (term = 145 days).

INTERVENTIONS

Lambs (2.7 to 5.0 kg) were delivered by cesarean section anywhere between gestational days 136 and 140. Arterial and venous catheterizations, bilateral chest tube thoracostomies, and tracheostomies were performed while the lambs received placental bypass. Initially, congenital diaphragmatic hernia lambs were supported on conventional pressure control mechanical ventilation to achieve steady state with measurements of baseline vital signs, arterial blood gases, and ventilatory settings. ITPV was instituted while maintaining constant peak carinal pressures and oxygen saturations. Statistical comparisons were made using the paired t-test.

MEASUREMENTS AND MAIN RESULTS

Postductal Paco2 decreased from 110+/-21 (SD) torr (14.7+/-2.8 kPa) to 52+/-24 torr (6.93+/-3.2 kPa; p= .0014) on ITPV. Simultaneously, pH improved from 7.04+/-0.07 to 7.31+/-0.15 (p = .0012) and minute ventilation increased from 0.66+/-0.40 to 4.00+/-1.35 L/min (p = .0016). Peak carinal pressures and postductal Pao2 were unchanged.

CONCLUSIONS

ITPV significantly improved CO2 removal in newborn lambs with diaphragmatic hernias without increasing airway pressures or changing oxygenation. Based on these results, we are conducting human clinical trials.

Use of intratracheal pulmonary ventilation versus conventional ventilation in meconium aspiration syndrome in a newborn pig model

OBJECTIVE

To determine whether intratracheal pulmonary ventilation (ITPV) allows for effective oxygenation and ventilation at lower mean airway pressures and peak inspiratory pressures than conventional ventilation in a piglet model of meconium aspiration syndrome.

DESIGN

Prospective, interventional study.

SETTING

The animal research laboratory at Children's National Medical Center, Washington, DC.

SUBJECTS

Twenty newborn piglets, 2 to 7 days of age, weighing 1.8 to 2.8 kg.

INTERVENTION

Animals were anesthetized, paralyzed, intubated, and ventilated. Femoral arterial and venous catheters were inserted; 5 mL/kg of 20% meconium in normal saline was instilled into the endotracheal tube. Animals were randomized to either ITPV or conventional ventilation, and settings were adjusted to maintain ideal blood gases, i.e., pH 7.35 to 7.45, PCO2 40 to 45 torr (5.3 to 6 kPa), PO2 80 to 100 torr (10.7 to 13.3 kPa), and SaO2 > or = 90%. Ventilatory settings were adjusted as needed to a maximum of: FIO2 1.0, peak inspiratory pressure 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and respiratory rate 80 breaths/min.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases were taken every 30 mins for 4 hrs and ventilatory settings were adjusted to maintain optimal blood gases. Heart rate, mean arterial blood pressure, and arterial saturation were monitored continuously. The animals in the ITPV group had significantly lower peak inspiratory pressure at 1, 2, 3, and 4 hrs after meconium instillation (p < .018) and significantly lower mean airway pressure at 2, 3, and 4 hrs after meconium instillation (p < .03). The mean peak inspiratory pressure in the ITPV animals ranged from 17 +/- 2.7 cm H2O at baseline to 16.6 +/- 5.7 cm H2O at 4 hrs compared with 16.5 +/- 2.7 cm H2O at baseline to 31.8 +/- 9.1 cm H2O at 4 hrs in the conventionally ventilated animals (p < .04). The mean airway pressure ranged from 6.3 +/- 1.1 mm Hg at baseline to 6.8 +/- 2.5 mm Hg at 4 hrs in the ITPV group compared with 5.5 +/- 1.2 mm Hg at baseline to 10.7 +/- 3.4 mm Hg at 4 hrs in the conventional ventilation group (p < .03). The lungs of the ITPV animals were less hemorrhagic and had less pathologic evidence of injury than the lungs of the conventionally ventilated animals.

CONCLUSIONS

These results indicate that ITPV can be used to effectively ventilate and oxygenate piglets with meconium aspiration syndrome at lower mean airway pressures and peak inspiratory pressures than conventional ventilation. This lower pressure causes less injury to the lungs of the animals.