The pulmonary physician and critical care. 2. The injured lung: conventional and novel respiratory therapy

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.

Early response to inhaled nitric oxide and its relationship to outcome in children with severe hypoxemic respiratory failure

OBJECTIVE

To examine whether the early response to inhaled nitric oxide (iNO) is a measure of reversibility of lung injury and patient outcome in children with acute hypoxemic respiratory failure (AHRF).

DESIGN

Retrospective review study.

SETTING

Pediatric ICUs.

PATIENTS

Thirty infants and children, aged 1 month to 13 years (median, 7 months) with severe AHRF (mean alveolar arterial oxygen gradient of 568+/-9.3 mm Hg, PaO2/fraction of inspired oxygen of 56+/-2.3, oxygenation index [OI] of 41+/-3.8, and acute lung injury score of 2.8+/-0.1). Eighteen patients had ARDS.

INTERVENTIONS

The magnitude of the early response to iNO was quantified as the percentage change in OI occurring within 60 min of initiating 20 ppm iNO therapy. This response was compared to patient outcome data.

MEASUREMENTS AND RESULTS

There was a significant association between early response to iNO and patient outcome (Kendall tau B r=0.43, p < 0.02). All six patients who showed < 15% improvement in OI died; 4 of the 11 patients (36%) who had a 15 to 30% improvement in OI survived, while 8 of 13 (61%) who had a > 30% improvement in OI survived. Overall, 12 patients (40%) survived, 9 with ongoing conventional treatment including iNO, and 3 with extracorporeal support.

CONCLUSIONS

In AHRF in children, greater early response to iNO appears to be associated with improved outcome. This may reflect reversibility of pulmonary pathophysiologic condition and serve as a bedside marker of disease stage.

Permissive hypercapnia with high-frequency oscillatory ventilation and one-lung isolation for intraoperative management of lung resection in a patient with multiple bronchopleural fistulae

We report the use of high-frequency oscillatory ventilation in the operating room during repair of multiple bronchopleural fistulae in a 9-year-old boy. In addition, we used principles of permissive hypercapnia to further minimize barotrauma. There were no cardiovascular consequences due to either the high-frequency ventilation or the permissive hypercapnia. Our goals in employing this strategy were to minimize barotrauma, minimize gas flow through the fistulae, and optimize the surgical results.

Dose-response comparisons of five lung surfactant factor (LSF) preparations in an animal model of adult respiratory distress syndrome (ARDS)

1. We have examined the effects of five different lung surfactant factor (LSF) preparations in the rat lung lavage model. In this model repetitive lung lavage leads to lung injury with some similarities to adult respiratory distress syndrome with poor gas exchange and protein leakage into the alveolar spaces. These pathological sequelae can be reversed by LSF instillation soon after lavage. 2. The tested LSF preparations were: two bovine: Survanta and Alveofact: two synthetic: Exosurf and a protein-free phospholipid based LSF (PL-LSF) and one Recombinant LSF at doses of 25, 50 and 100 mg kg-1 body weight and an untreated control group. 3. Tracheotomized rats (10-12 per dose) were pressure-controlled ventilated (Siemens Servo Ventilator 900C) with 100% oxygen at a respiratory rate of 30 breaths min-1, inspiration expiration ratio of 1:2, peak inspiratory pressure (PIP) of 28 cmH2O at positive end-expiratory pressure (PEEP) of 8 cmH2O. Two hours after LSF administration, PEEP and in parallel PIP was reduced from 8 to 6 (1st reduction), from 6 to 3 (2nd reduction) and from 3 to 0 cmH2O (3rd reduction). 4. Partial arterial oxygen pressure (PaO2, mmHg) at 5 min and 120 min after LSF administration and during the 2nd PEEP reduction (PaO2(PEEP23/3)) were used for statistical comparison. All LSF preparations caused a dose-dependent increase for the PaO2(120'), whereas during the 2nd PEEP reduction only bovine and recombinant LSF exhibited dose-dependency. Exosurf did not increase PaO2 after administration of the highest dose. At the highest dose Exosurf exerted no further improvement but rather a tendency to relapse. The bovine and the Recombinant LSF are superior to both synthetic LSFpreparations.5. In this animal model and under the described specific ventilatory settings, even between bovine LSFpreparations there are detectable differences that are pronounced when compared to synthetic LSFwithout any surfactant proteins. We conclude that the difference between bovine and synthetic LSFpreparations can be overcome by addition of the surfactant protein C.

Prevention and therapy of the adult respiratory distress syndrome

The complex pathophysiology of adult respiratory distress syndrome (ARDS) makes preventive and therapeutic concepts difficult. Ample experimental evidence indicates that ARDS can be prevented by blocking systemic inflammatory agents. Clinically, only heparin, for inhibition of coagulation phenomena, is presently used among this array of approaches. Corticosteroids have not proven to be beneficial in ARDS. Alternative antiinflammatory agents are being proposed and are under current clinical investigation (e.g. indomethacin, acetylcysteine, alpha 1-proteinase inhibitor, antitumor necrosis factor, interleukin 1 receptor antagonist, platelet-activating factor antagonists). Symptomatic therapeutic strategies in early ARDS include selective pulmonary vasodilation (preferably by inhaled vasorelaxant agents) and optimal fluid balance. Transbronchial surfactant application, presently tested in pilot studies, may be available for ARDS patients in the near future and may have acute beneficial effects on gas exchange, pulmonary mechanics, and lung hemodynamics; its impact on survival cannot be predicted at the present time. Strong efforts should be taken to reduce secondary nosocomial pneumonia in ARDS patients and thus avoid the vicious circle of pneumonia, sepsis from lung infection, and perpetuation of multiple organ dysfunction syndrome. Optimal respirator therapy should be directed to ameliorate gas-exchange conditions acutely but at the same time should aim at minimizing potentially aggravating side effects of artificial ventilation (barotrauma, O2 toxicity). Several new techniques of mechanical ventilation and the concept of permissive hypercapnia address these aspects. Approaches with extracorporeal CO2 removal and oxygenation are being used in specialized centers.

Acute effects of inhaled nitric oxide in children with severe hypoxemic respiratory failure

To determine the physiologic effects of inhaled nitric oxide (NO) on oxygenation and hemodynamics in children with severe hypoxemic respiratory failure, we studied the acute response to inhaled NO during mechanical ventilation in 17 pediatric patients. Diagnoses included adult respiratory distress syndrome (ARDS) (10 patients), bronchopulmonary dysplasia with viral pneumonitis (6 patients), and acute pneumonitis, caused by respiratory syncytial virus, without chronic lung disease (1 patient). Gas exchange and hemodynamic measurements were compared before and during exposure to inhaled NO (20 ppm) without changing ventilator settings for 30 minutes. Hemodynamic variables, including pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac index, were measured in 10 patients with ARDS. Inhaled NO acutely improved oxygenation in 15 of 17 patients; mean arterial oxygen tension increased from 58 +/- 13 mm Hg (baseline) to 86 +/- 25 mm Hg after 30 minutes (p < 0.01). Inhaled NO lowered mean pulmonary artery pressure (42 +/- 6 mm Hg at baseline to 31 +/- 6 mm Hg; p < 0.01) and intrapulmonary shunt (39% +/- 7% vs 32% +/- 7%; p < 0.01) without changing systemic arterial pressure or pulmonary capillary wedge pressure. Cardiac index increased by 14% (p < 0.01). Fifteen patients were subsequently treated with low-dose inhaled NO (3 to 10 ppm) for 1 to 24 days; 5 (50%) of 10 patients with ARDS and 7 (100%) of the 7 non-ARDS patients survived. We conclude that inhaled NO acutely improves oxygenation and lowers pulmonary vascular resistance without causing adverse hemodynamic effects in severe hypoxemic respiratory failure in pediatric patients. Inhaled NO may be a useful adjuvant therapy in children with acute hypoxemic respiratory failure, including infants with bronchopulmonary dysplasia, but whether prolonged low-dose inhalational NO therapy can reduce morbidity or improve survival rates remains unknown.