Novel therapies for acute respiratory failure

Airway pressure release ventilation and pediatrics: theory and practice

Airway pressure release ventilation (APRV) facilitates oxygenation and ventilation by maintaining an elevated baseline airway pressure similar to continuous positive airway pressure (CPAP). APRV differs from CPAP only by the addition of regular, brief release of airway pressure to facilitate carbon dioxide removal. The baseline pressure maintains a near continuous airway pressure to facilitate recruitment, improving ventilation and oxygenation. Pediatric patients who have recruitable lung disease may be well suited to the application of APRV.

High-frequency oscillatory ventilation of the perfluorocarbon-filled lung: Dose-response relationships in an animal model of acute lung injury

OBJECTIVE

To examine dose-response relationships regarding the efficiency of gas exchange and hemodynamic function during high-frequency oscillation and partial liquid ventilation (HFO-PLV) of the perfluorocarbon (PFC)-treated lung in a model of acute lung injury.

SETTING

An animal research laboratory in a university medical center.

DESIGN

A prospective, randomized study comparing animals receiving varying doses (0, 5, 15, and 20 mL/kg) of perflubron during high-frequency oscillatory ventilation (HFOV) with mean airway pressure (Paw) optimized to achieve a minimal percutaneous oxygen saturation (Spo2).

SUBJECTS

Nineteen healthy swine (mean weight 28.9 kg) with saline lavage-induced acute lung injury.

METHODS

Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (Spo2 < or =90% on an Fio2 of 1.0). After lung injury, subjects were converted to HFOV, and lung volume was optimized. HFO-PLV was initiated by instillation of perflubron at a rate of 0.5 mL.kg-1.min-1 to achieve total doses of 5, 15, and 20 mL/kg. After PFC dosing, the only experimental manipulation consisted of adjustment of Paw to achieve an Spo2 of 90% +/- 2% with Fio2 of 0.6. Gas exchange, hemodynamic variables, and pulmonary mechanics data were collected over a 1-hr period. Five control animals were not dosed with perflubron and remained on HFOV for the 1-hr period of data collection.

MEASUREMENTS AND MAIN RESULTS

After lung volume recruitment with HFOV, the initiation of HFO-PLV was best tolerated with the two lower doses in our protocol. There were essentially no changes in Paco2 or pH between groups over the dosing interval. After dosing, analysis of variance demonstrated a PFC dose-dependent effect for oxygenation index (p =.01) only; the lowest oxygenation index was found in the 15 mL/kg group (p =.01). In the 15 mL/kg group, the Paw decreased steadily from 20.6 +/- 3.4 cm H2O at the end of dosing to 18.0 +/- 4.9 cm H2O at 60 mins. The Pao2 increased from 113 +/- 51 torr (15.06 +/- 6.79 kPa) to 134 +/- 49 torr (17.86 +/- 6.53 kPa) during this period and was associated with a decreasing oxygenation index (from 11.4 +/- 2.0 to 9.3 +/- 1.5). The cardiac index and pulmonary vascular resistance did not change significantly during the dosing period and were relatively stable after the completion of dosing.

CONCLUSIONS

The combination of HFOV and perflubron administration was well tolerated hemodynamically and was not associated with deterioration of gas exchange during dosing. Our data suggest that the optimal dose of perflubron to achieve the lowest oxygenation index during HFO-PLV is between 5 and 15 mL/kg. The combination of HFOV and perflubron administration is a novel strategy in the treatment of acute lung injury that shows some promise and merits additional investigation. We hope in future studies to address the histopathologic effects of varying perflubron doses during HFOV in a long-term study of the lung-protective effects of HFO-PLV.

High-frequency oscillatory ventilation of the perfluorocarbon-filled lung: preliminary results in an animal model of acute lung injury

OBJECTIVE

To examine the efficiency of gas exchange, hemodynamic function, and histopathologic evidence of lung protection using high-frequency oscillation of the perfluorocarbon-filled lung in a model of acute lung injury.

SETTING

An animal research laboratory.

DESIGN

A prospective, randomized animal study comparing animals randomized to high-frequency oscillation or high-frequency oscillation and perfluorocarbon administration (perfluoro-octyl bromide, perfubron, or LiquiVent).

SUBJECTS

Ten healthy swine (mean weight, 24.6 kg) with saline lavage-induced acute lung injury.

INTERVENTIONS

Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (Pao2 of <90 torr [11.9 kPa] on a Fio2 of 1.0). After lung injury, subjects were changed to high-frequency oscillatory ventilation and stabilized for 1 hr. High-frequency oscillation of the perfiuorocarbon-filled lung was initiated in five animals with the instillation of 30 mUkg perflubron and five animals continued receiving high-frequency oscillation for a total duration of 2 hrs after the dosing period. Histopathologic evidence of lung injury was quantified by a pathologist using an eight-variable lung injury scoring system to generate a lung injury score.

MEASUREMENTS AND MAIN RESULTS

Administration of perflubron did not produce acute alterations of gas exchange. After the dosing period, there were no differences in gas exchange, hemodynamic function, or pulmonary vascular resistance between the two groups. The perfluorocarbon-treated animals had a significantly lower histopathologic total lung injury score, primarily manifested by significantly less atelectasis.

CONCLUSIONS

The combination of high-frequency oscillatory ventilation and partial liquid ventilation with perfiubron was well tolerated hemodynamically, was not associated with deterioration of gas exchange during dosing, and did not produce significant differences in either gas exchange or hemodynamic variables over a 2-hr period. There was histopathologic evidence that the combination of high-frequency oscillation and perfiubron administration produces improved recruitment in both dependent and nondependent lung regions.

Solubility enhancement of phenol and phenol derivatives in perfluorooctyl bromide

Perfluorinated solvents are gaining popularity as pulmonary ventilation fluids, but they suffer from poor solvent quality in concurrent drug delivery applications. The present study examines the use of a hydrophobic solubilizing agent capable of interacting with model drug solutes by hydrogen bonding with the purpose of enhancing solubility in perfluorooctyl bromide (PFOB). A series of solubilizing agents containing a ketone carbonyl to act as a hydrogen bond acceptor and a perfluoroalkyl chain to maintain the solubility of the putative complex in PFOB are investigated. The solubility of phenol in PFOB is enhanced to the greatest extent by 1-(4-perfluorobutyl phenyl)-1-hexanone (III) where the ketone carbonyl is protected from the electron withdrawing effects of the perfluorobutyl chain by a phenyl ring. Experiments with solubilizers lacking the ketone group suggest that pi-pi bond interactions of III with phenol do not significantly enhance solubility. For a series of phenol derivatives, a rank-order correlation exists between the magnitude of solubility enhancement by III, as reflected by the calculated association constants, and the Hammett sigma parameter of the phenols. Because the O-methyl-substituted phenols do not have the ability to hydrogen bond, their solubility is not enhanced by the presence of III. The results of the present study indicate that solubility of model drug hydrogen bond donating compounds can be enhanced in PFOB by the presence of fluorocarbon-soluble hydrogen bond acceptors.

The current practice patterns of mechanical ventilation for respiratory failure in pediatric patients

OBJECTIVE

To quantify the current practice patterns of mechanical ventilation for respiratory failure in pediatric patients.

DESIGN

Mail survey using 2 hypothetical case studies sent to pediatric critical care physicians.

MEASUREMENTS AND MAIN RESULTS

The required arterial blood gas (ABG) on conventional mechanical ventilation (CMV) is pH = 7.25 to 7.29, PO2 = 50 to 59 torr, O2 saturation = 0.85 to 0.89. Most of our survey participants will treat a patient failing conventional mechanical ventilation in their pediatric intensive care units (PICUs) with inverse ratio ventilation (IRV) (95%) and with high-frequency oscillatory ventilation (HFOV) (92%).

CONCLUSION

Most of the surveyed pediatric critical care physicians practice permissive hypercapnia in the treatment of their patients who receive ventilatory assistance. More than 90% of surveyed pediatric critical care physicians are presently using inverse ratio ventilation and high-frequency oscillatory ventilation. These data suggest that these innovative modes of therapy are already accepted as part of the standard therapeutic spectrum by the surveyed group of physicians.

Inhaled nitric oxide in burn patients with respiratory failure

BACKGROUND

Inhaled nitric oxide (NO) has the potential to improve ventilation/perfusion matching and decrease pulmonary artery pressure in patients with profound respiratory failure.

METHODS

Eight patients, average age of 35 years (range, 2.5-77 years) and burn size 49% (range, 19-80%), with inhalation injury and respiratory failure failing conventional management (average Pao2/FiO2 ratio (PFR) 85) were given inhaled NO at 20 ppm.

RESULTS

An immediate mean increase in PFR of 10% and a decrease in pulmonary artery mean pressure of 7.8% was noted. At 24 hours, the average improvement in PFR was 28% and that in pulmonary artery mean pressure was 7.7%. Although not reaching statistical significance, these changes were more pronounced in those patients who went on to survive. There was no hypotension attributed to NO administration, and maximum methemoglobin levels averaged 0.9%.

CONCLUSIONS

Inhaled NO can be safely administered to selected burn patients with severe respiratory failure who are perceived to be failing conventional support. Although current data are not adequate to support its general use, an immediate and sustained improvement in PFR and pulmonary artery mean pressure may correlate with eventual recovery of pulmonary function. Continued evaluation in controlled settings seems warranted and is in progress.

Advances in conventional and innovative therapies for respiratory distress syndrome in children

Adult respiratory distress syndrome is a phenomenon encountered by many pediatric critical care nurses. Care of these complex patients is multifaceted and requires an in-depth understanding of pathophysiology and therapeutic intervention. Several innovative treatments are now available as biomedical and technical advances have evolved. Outcomes will improve as clinicians improve patient selection, identify therapeutic endpoints, and risk/benefits. This article addresses the current understanding of pathophysiology, innovative treatments, and nursing care issues.

Permissive hypercapnia as a ventilatory strategy in burned children: effect on barotrauma, pneumonia, and mortality

OBJECTIVE

To document the incidence of barotrauma, pneumonia, and respiratory death associated with a mechanical ventilation protocol based on permissive hypercapnia in pediatric burn patients.

DESIGN

Retrospective review.

MATERIALS AND METHODS

Patients were managed using a mechanical ventilation protocol based on permissive hypercapnia, tolerating moderate (pH > 7.20) respiratory acidosis to keep inflating pressures below 40 cm H2O.

MAIN RESULTS

Over a 2.5-year interval, 54 burned children (11% of 495 acute admissions) with an average age of 6.5 years (range 5 weeks to 17 years), average burn size of 44% (range 0 to 98%), and median burn size of 46% required mechanical ventilatory support for an average of 12.5 days (range 1 to 56 days). Inhalation injury was diagnosed in 34 (63%) of the children and 72% percent were admitted within 24 hours of injury. Overt barotrauma occurred in 5.6% of the patients, pneumonia in 32%, and respiratory death in 0%.

CONCLUSIONS

A conventional ventilation protocol based on permissive hypercapnia is associated with acceptable rates of barotrauma and pneumonia. The low incidence of respiratory death associated with this strategy suggests that it also minimizes ventilator-induced lung injury.