Independent and combined effects of inhaled nitric oxide, liquid perfluorochemical, and high-frequency oscillatory ventilation in premature lambs with respiratory distress syndrome

Conventional Gas Ventilation, Liquid-Assisted High-Frequency Oscillatory Ventilation, and Tidal Liquid Ventilation in Surfactant-Treated Preterm Lambs

This study was designed to compare the efficacy and potential protective or injurious effects of tidal liquid ventilation (TLV), liquid-assisted high-frequency oscillatory ventilation (LA-HFOV), and high PEEP conventional mechanical ventilation (CMV) in neonatal respiratory distress syndrome. Preterm lambs (124–126 days gestation), prophylactically treated with natural surfactant, were allocated to one of the treatment modalities or to an untreated fetal control group (F), euthanised after tracheal ligation. LA-HFOV animals received an intratracheal loading dose of 5 mL.kg-1 followed by a continuous intrapulmonary instillation of 12 mL.kg-1;h-1 FC-75 perfluorocarbon liquid. The ventilation strategies aimed at keeping clinically appropriate arterial blood gases for a study period of 5 hours. A histological lung injury score was calculated and semiquantitative morphometry was performed on lung tissue fixed by vascular perfusion.

The alveolar-arterial pressure difference for O2 was significantly lower throughout the study in TLV compared to CMV lambs; at 1, 2, and 5 hours, oxygenation was better in TLV when compared to LA-HFOV. Total lung injury scores in TLV lambs were significantly lower than in either CMV or LA-HFOV animals, but higher when compared to F. CMV and LA-HFOV induced an excess of collapsed and overdistended alveoli, whereas in TLV alveolar expansion was normally distributed around predominantly normal alveoli. CMV and LA-HFOV, but not TLV, were associated with an excess of dilated airways.

Thus, in the ovine neonatal RDS model, TLV compared favourably to either gas ventilation strategy by its more uniform ventilation, reduced lung injury, and improved gas exchange.

An extracorporeal artificial placenta supports extremely premature lambs for 1 week

PURPOSE

The treatment of extreme prematurity remains an unsolved problem. We developed an artificial placenta (AP) based on extracorporeal life support (ECLS) that simulates the intrauterine environment and provides gas exchange without mechanical ventilation (MV) and compared it to the current standard of neonatal care.

METHODS

Extremely premature lambs (110-120 days; term=145d) were used. AP lambs (n=9) were cannulated (jugular drainage, umbilical vein reinfusion) for ECLS. Control lambs (n=7) were intubated, ventilated, given surfactant, and transitioned to high-frequency oscillatory ventilation. All lambs received parenteral nutrition, antibiotics, and steroids. Hemodynamics, blood gases, hemoglobin, and circuit flows were measured.

RESULTS

Four premature lambs survived for 1 week on the AP, with one surviving 6 days. Adequate oxygenation and ventilation were provided by the AP. The MV lambs survived 2-8 hours. Each of these lambs experienced a transient improvement with surfactant, but developed progressive hypercapnea and hypoxia despite high airway pressures and HFOV.

CONCLUSIONS

Extremely premature lambs were supported for 1 week with the AP with hemodynamic stability and adequate gas exchange. Mechanically ventilated lambs succumbed within 8 hours. Further studies will assess control of fetal circulation and organ maturation on the AP.

Inhaled nitric oxide and inhaled prostacyclin in acute respiratory distress syndrome: what is the evidence?

The mortality for acute respiratory distress syndrome remains unacceptably high. Two vasodilators, inhaled prostacyclin and inhaled nitric oxide, are reviewed in this article. Knowledge of inhaled prostacyclin has grown substantially in the past 30 years, but less research exists about its utility in acute respiratory distress syndrome. Inhaled prostacyclin and other prostaglandin derivatives are used in acute respiratory distress syndrome with increasing frequency. Currently, only randomized controlled trials exist for inhaled nitric oxide in acute respiratory distress syndrome patients. Randomized controlled trials with consistent dosing methods are needed for both vasodilators to better define their role in the treatment of acute respiratory distress syndrome.

High-frequency oscillatory ventilation associated with inhaled nitric oxide compared to pressure-controlled assist/control ventilation and inhaled nitric oxide in children: Randomized, non-blinded, crossover study

PURPOSE

To compare the acute oxygenation effects of high-frequency oscillatory ventilation (HFOV) plus inhaled nitric oxide (iNO) with pressure-controlled assist/control ventilation (PCACV) plus iNO in acute hypoxemic respiratory failure (AHRF) children.

METHODS

Children with AHRF, aged between 1 month and 14 years under PCACV with PEEP ≥ 10 cmH(2) O were randomly assigned to PCACV (PCVG, n = 14) or HFOV (HFVG, n = 14) in a crossover design. Oxygenation indexes and hemodynamic variables were recorded at enrollment (Tind), 1 hr after PCACV start (T0) and then every 4 hr (T4h, etc.).

RESULTS

PO(2)/FiO(2) significantly increased after 4 hr compared to enrollment in both groups [(PCVG-Tind: 111.95 ± 37 < T4h: 143.88 ± 47.5 mmHg, P < 0.05; HFVG-Tind: 123.76 ± 33 < T4h: 194.61 ± 62.42 mmHg, P < 0.05)] without any statistical differences between groups. At T8h, PO(2)/FiO(2) was greater for HFVG compared with PCVG (HFVG: 227.9 ± 80.7 > PCVG: 171.21 ± 52.9 mmHg, P < 0.05). FiO(2) could be significantly reduced after 4 hr for HFVG (HFVG-T4h: 0.53 ± 0.09 < Tind: 0.64 ± 0.2; P < 0.05) but only after 8 hr for PCVG. Comparing groups at T8h, it was observed that FiO(2) decrease was greater for HFVG (HFVG: 0.47 ± 0.06 < PCVG: 0.58 ± 0.1; P < 0.05).

CONCLUSION

Both ventilatory techniques with iNO improve oxygenation. HFOV causes earlier FiO(2) reduction and increased PO(2)/FiO(2) ratio compared to PCACV at 8 hr. However, at the end of the protocol, there was no significant difference and no clinical improvement derived from the application of both ventilatory strategies with iNO. It is not possible to say what would have happened if a different conventional ventilatory mode and a fully protective ventilatory strategy had been used, given the fact that our study is non-blind, and that a limited number of patients were included in each group.

Inhaled nitric oxide improves lung structure and pulmonary hypertension in a model of bleomycin-induced bronchopulmonary dysplasia in neonatal rats

Whether inhaled nitric oxide (iNO) prevents the development of bronchopulmonary dysplasia (BPD) in premature infants is controversial. In adult rats, bleomycin (Bleo) induces lung fibrosis and pulmonary hypertension, but the effects of Bleo on the developing lung and iNO treatment on Bleo-induced neonatal lung injury are uncertain. Therefore, we sought to determine whether early and prolonged iNO therapy attenuates changes of pulmonary vascular and alveolar structure in a model of BPD induced by Bleo treatment of neonatal rats. Sprague-Dawley rat pups were treated with Bleo (1 mg/kg ip daily) or vehicle (controls) from day 2 to 10, followed by recovery from day 11 to 19. Treatment groups received early ( days 2–10), late ( days 11–19), or prolonged iNO therapy (10 ppm; days 2–19). We found that compared with controls, Bleo increased right ventricular hypertrophy (RVH), and pulmonary arterial wall thickness, and reduced vessel density alveolarization. In each iNO treatment group, iNO decreased RVH ( P < 0.01) and wall thickness ( P < 0.01) and restored vessel density after Bleo ( P < 0.05). iNO therapy improved alveolarization for each treatment group after Bleo; however, the values remained abnormal compared with controls. Prolonged iNO treatment had greater effects on lung structure after bleomycin than late treatment alone. We conclude that Bleo induces lung structural changes that mimic BPD in neonatal rats, and that early and prolonged iNO therapy prevents right ventricle hypertrophy and pulmonary vascular remodeling and partially improves lung structure.

Inhaled nitric oxide in the management of preterm infants with severe respiratory failure

OBJECTIVE

Elevated pulmonary vascular resistance and poor ventilation-perfusion matching are commonly found in preterm infants with severe respiratory distress syndrome (RDS) and respiratory failure. Inhaled nitric oxide (iNO) can improve gas exchange and decrease pulmonary vascular resistance. This study was conducted to determine whether iNO therapy improves oxygenation in such infants.

STUDY DESIGN

Between July 2000 and 2006, 65 preterm infants (birth weight, <1500 g; gestational age, <31 weeks) with severe RDS and respiratory failure requiring mechanical ventilation and an oxygenation index (OI)>or=25 were randomly divided into two groups. Group A infants (n=32) received iNO therapy. iNO was started at a dose of five parts per million (p.p.m.). The maximal dose of NO was 20 p.p.m. Group B infants (n=33) did not receive iNO therapy, receive inhaled oxygen placebo only, was served as control group. Mechanical ventilation and iNO therapy were managed by neonatologists who were not involved in safety monitoring, data analysis and interpretation, or manuscript preparation. This study was randomized but not blinded.

RESULT

The OI was significantly lower (P<0.01) in the iNO therapy group than in the control group at 30 min, 3, 12 and 24 h after initiating iNO therapy. Six infants in the iNO-treated group and 10 infants in the control group died. Post hoc analyses did not reveal any significant differences in the incidences of chronic lung disease (CLD), intracranial hemorrhage (ICH), patent ductus arteriosus (PDA), retinopathy of prematurity (ROP) or duration of intubation between the iNO-treated and the control groups.

CONCLUSION

We conclude that iNO therapy leads to an improvement in oxygenation without short-term side effects (such as pulmonary hemorrhage, intracranial hemorrhage, pneumothorax or acute deterioration) in premature infants with severe RDS and respiratory failure. However, iNO therapy does not significantly reduce mortality rate or the incidences of CLD, ICH, PDA or ROP.

Hypoxia-inducible factors HIF-1alpha and HIF-2alpha are decreased in an experimental model of severe respiratory distress syndrome in preterm lambs

Respiratory distress syndrome (RDS) secondary to preterm birth and surfactant deficiency is characterized by severe hypoxemia, lung injury, and impaired production of nitric oxide (NO) and vascular endothelial growth factor (VEGF). Since hypoxia-inducible factors (HIFs) mediate the effects of both NO and VEGF in part through regulation by prolyl-hydroxylase-containing domains (PHDs) in the presence of oxygen, we hypothesized that HIF-1alpha and -2alpha in the lung are decreased following severe RDS in preterm neonatal lambs. To test this hypothesis, fetal lambs were delivered at preterm gestation (115-day gestation, term = 145 days; n = 4) and mechanically ventilated for 4 h. Lambs developed respiratory failure characterized by severe hypoxemia despite treatment with mechanical ventilation with high inspired oxygen concentrations. Lung samples were compared with nonventilated control animals at preterm (115-day gestation; n = 3) and term gestation (142-day gestation; n = 3). We found that HIF-1alpha protein expression decreased (P < 0.05) and PHD-2 expression increased (P < 0.005) at birth in normal term animals before air breathing. Compared with age-matched controls, HIF-1alpha protein and HIF-2alpha protein expression decreased by 80% and 55%, respectively (P < 0.005 for each) in preterm lambs with RDS. Furthermore, VEGF mRNA was decreased by 40%, and PHD-2 protein expression doubled in RDS lambs. We conclude that pulmonary expression of HIF-1alpha, HIF-2alpha, and the downstream target of their regulation, VEGF mRNA, is impaired following RDS in neonatal lambs. We speculate that early disruption of HIF and VEGF expression after preterm birth and RDS may contribute to long-term abnormalities in lung growth, leading to bronchopulmonary dysplasia.

Combining lung-protective strategies in experimental acute lung injury: The impact of high-frequency partial liquid ventilation

OBJECTIVE

To evaluate the independent and combined effects of high-frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV) on gas exchange, pulmonary histopathology, inflammation, and oxidative tissue damage in an animal model of acute lung injury.

DESIGN

Prospective, randomized animal study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

Fifty New Zealand White rabbits.

INTERVENTIONS

Juvenile rabbits injured by lipopolysaccharide infusion and saline lung lavage were assigned to conventional ventilation (CMV), PLV, HFOV, or high-frequency partial liquid ventilation (HF-PLV) with a full or half dose (HF-PLV1/2) of perfluorochemical (PFC). Uninjured ventilated animals served as controls. Arterial blood gases were obtained every 30 mins during the 4-hr study. Histopathologic evaluation was performed using a lung injury scoring system. Oxidative lung injury was assessed by measuring malondialdehyde and 4-hydroxynonenal in lung homogenates.

MEASUREMENTS AND MAIN RESULTS

HFOV, PLV, or a combination of both methods (HF-PLV) resulted in significantly improved oxygenation, more favorable lung histopathology, reduced neutrophil infiltration, and attenuated oxidative damage compared with CMV. HF-PLV with a full PFC dose did not provide any additional benefit compared with HFOV alone. HF-PLV1/2 was associated with decreased pulmonary leukostasis compared with HF-PLV.

CONCLUSIONS

The combination of HFOV and PLV (HF-PLV) does not provide any additional benefit compared with HFOV or PLV alone in a combined model of lung injury when lung recruitment and volume optimization can be achieved. The use of a lower PFC dose (HF-PLV1/2) is associated with decreased pulmonary leukostasis compared with HF-PLV and deserves further study.

Hypoleptinemia in gastric cancer patients: relation to body fat mass, insulin, and growth hormone

BACKGROUND

It remains elusive whether there are other causes besides body fat mass wasting contributing to decreased leptin level in cancer cachexia patients. This study attempts to explore possible factors influencing leptin levels in patients with gastric cancer.

METHODS

Hormones levels (including leptin, insulin, growth hormone (GH), insulin-like growth factor I, glucagons, and cortisol), acute phase reactant, and body composition were measured in 88 gastric cancer patients and 24 healthy controls. All patients were divided into weight-loss (48 patients) or nonweight-loss (40 patients) groups and cachexia (body mass index <18; 13 patients) or noncachexia (75 patients) groups. The detection was repeated 3 months after radical surgery in 16 patients.

RESULTS

Compared with the controls, leptin levels decreased in gastric cancer patients with and without weight loss (p < .001 and p = .003, respectively), even when the percentage of fat mass was adjusted (p = .004 and 0.018, respectively). GH and insulin levels also changed significantly. Similar results were also found in patients with and without cachexia. Multivariate regression analysis showed that the percentages of fat mass (standardized coefficient [SC] = 0.631, p < .001), GH (SC = -0.244, p = .005) and insulin (SC = 0.201, p = .020) were significantly correlated with leptin. In the 16 patients who underwent radical surgery, leptin levels remained low and no significant changes in the other hormones were detected.

CONCLUSIONS

Our results showed that low leptin levels in gastric cancer patients depended not only on the percentage of fat mass, but also on GH and insulin levels. Chronic high GH and low insulin levels may inhibit the leptin secretion.

High-frequency oscillatory ventilation: what large-animal studies have taught us!

BACKGROUND

Much of the information on the physiologic effects, mechanisms of gas exchange, and potential utility of high-frequency oscillation (HFO) has been acquired in animal studies. Specifically, large animal data have been useful in assessing adult application because large animals present many of the same concerns and challenges as adults.

OBJECTIVE

To review the literature on HFO testing in large animal models, identifying contributions to the understanding of mechanisms of action and the physiology of HFO.

RESULTS

Large animal studies have clarified the mechanisms of gas exchange during HFO, identified approaches to setting mean airway pressure based on lung mechanics, and identified a potentially better approach to applying partial liquid ventilation.

CONCLUSION

The study of HFO in large animal models has been essential to our understanding of the optimal approach to applying HFO in human studies.

High-frequency oscillatory ventilation and adjunctive therapies: Inhaled nitric oxide and prone positioning

OBJECTIVE

To review the use of high-frequency oscillatory ventilation (HFOV) with adjunctive therapies (inhaled nitric oxide [iNO] and prone positioning [PP]) in adult patients with acute respiratory distress syndrome (ARDS).

DATA SOURCES

Published studies evaluating the use of iNO, PP, and HFOV in adult patients with ARDS.

DATA SUMMARY

Despite ongoing preclinical and clinical research, the therapeutic armamentarium for ARDS remains limited. Although a pressure- and volume-limited strategy aimed at mitigating ventilator-associated lung injury has demonstrated mortality benefit, patients with severe ARDS may still develop life-threatening hypoxemia. As a result, various salvage therapies aimed at improving oxygenation, including HFOV, iNO, and PP alone or in combination, have been evaluated in patients with refractory ARDS. Although the few preclinical and clinical trials of combination therapy to date have shown promising improvements in oxygenation and other physiological variables, with few adverse clinical events, the impact on survival awaits the performance of large randomized trials.

CONCLUSIONS

There is limited clinical data to recommend the widespread use of combination therapy in patients with ARDS. In the subset of patients with life-threatening hypoxemia from refractory ARDS, combination therapy is safe and may be considered for salvage therapy. More rigorous randomized, controlled trials are needed to help delineate the therapeutic role of combination therapy in adults with ARDS.

Liquid ventilation: an adjunct for respiratory management

Although significant advances in respiratory care have reduced mortality of patients with respiratory failure, morbidity persists, often resulting from iatrogenic mechanisms. Mechanical ventilation with gas has been shown to initiate as well as exacerbate underlying lung injury, resulting in progressive structural damage and release of inflammatory mediators within the lung. Alternative means to support pulmonary gas exchange while preserving lung structure and function are therefore required. Perfluorochemical (PFC) liquids are currently used clinically in a number of ways, such as intravascular PFC emulsions for volume expansion/oxygen carrying/angiography and intracavitary neat PFC liquid for image contrast enhancement or vitreous fluid replacement. As a novel approach to replace gas as the respiratory medium, liquid assisted ventilation (LAV) with PFC liquids has been investigated as an alternative respiratory modality for over 30 years. Currently, there are several theoretical and practical applications of LAV in the immature or mature lung at risk for acute respiratory distress and injury associated with mechanical ventilation.

Meconium is a source of pro-inflammatory substances and can induce cytokine production in cultured A549 epithelial cells

Inflammation plays an important role in the pathogenesis of meconium aspiration syndrome, and pneumonitis is one of the major characteristics. We have previously shown that meconium has chemotactic properties because of the presence of IL-8. We hypothesize that IL-8 and other proinflammatory substances in meconium may amplify inflammation in meconium aspiration syndrome, inducing endogenous cytokine production by lung epithelial cells. We measured proinflammatory substances in first-pass meconium from healthy newborns and evaluated the effect of sterile meconium on cytokine production in cultured A549 alveolar epithelial cells in vitro. IL-1beta, IL-6, IL-8, and tumor necrosis factor-alpha were measured by ELISA, and heme was measured spectrophotometrically. After incubation of meconium samples with A549 cells, cytokine concentrations in the supernatant were measured. Meconium samples contained variable amounts of IL-1beta, IL-6, IL-8, tumor necrosis factor-alpha, and heme. On stimulation of A549 cells with meconium, the IL-8 concentration in the culture supernatant significantly increased above baseline measurements, whereas tumor necrosis factor-alpha showed a variable pattern and IL-1beta or IL-6 remained unchanged. There was no quantitative relationship between the concentration of the measured cytokines and heme in meconium and cytokine release by the A549 cells after meconium exposure. Meconium contains proinflammatory substances. All samples induced IL-8 release and some induced tumor necrosis factor-alpha release in cultured A549 epithelial cells. We speculate that proinflammatory substances in meconium can induce lung inflammation in meconium aspiration syndrome in two ways: directly via cytokines and heme present in meconium and indirectly by inducing cytokine release by the epithelial lung cells.

Bronchopulmonary dysplasia-oxidative stress and antioxidants

There is increasing evidence that oxidative stress is implicated in the development of bronchopulmonary dysplasia. Several important factors contribute to augmented oxidative stress in the newborn and especially the preterm infant: first, because of its immaturity, the lung of preterm infants is frequently exposed to oxygen therapy and hyperoxia. Second, the antioxidant defense and its ability to be induced during an hyperoxic challenge are impaired. Third, the preterm infant has an increased susceptibility to infection and inflammation, which increases oxidative stress. Fourth, free iron, which catalyzes the production of toxic reactive oxygen species, can be detected in preterm infants. The molecular and cellular mechanisms for free radical-induced injury are now understood in more detail, and it is clear that oxidative stress plays an important role in triggering apoptosis, in serving as second messenger and in signal transduction. This new insight might lead to novel and efficient therapies. So far, there has been no significant breakthrough regarding antioxidant therapies. Care should, however, be exercised in supplementing the preterm infant with antioxidants since this may affect growth and development.

Acute oxygenation response to inhaled nitric oxide when combined with high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

OBJECTIVE

To prospectively evaluate the oxygenation effect of inhaled nitric oxide (INO) delivered during high-frequency oscillatory ventilation in adult patients with the acute respiratory distress syndrome and oxygenation failure. DESIGN Prospective, clinical study.

SETTING

Intensive care unit of a university teaching hospital.

PATIENTS

A total of 23 adults (14 women, 9 men, 44.9 +/- 17.5 yrs, Acute Physiology and Chronic Health Evaluation II score of 28.6 +/- 7.1) with acute respiratory distress syndrome (lung injury score, 3.5 +/- 0.4) with Fio2 of > or = 0.6 and mean airway pressure of >or=28 cm H2O.

INTERVENTIONS

INO was initiated at a dose of 5 ppm, and subsequently titrated according to a protocol, to determine the dose (5, 10, or 20 ppm) resulting in the greatest increase in Pao2/Fio2. Blood gas measurements were obtained 10-15 mins after initiation or any increase in INO dosage to assess the effect on Pao2/Fio2.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases and ventilator settings were recorded at four time points: during conventional ventilation just before initiating high-frequency oscillatory ventilation, during high-frequency oscillatory ventilation just before initiating INO, after 30 mins on the optimal dose of INO, and 8-12 hrs after starting INO. Oxygenation index ([Fio2 x mean airway pressure x 100]/Pao2) and Pao2/Fio2 ratios were calculated at the same time intervals. At 30 mins after INO initiation, 83% of patients had a significant increase in blood oxygen tension, defined as > or = 20% increase in Pao2/Fio2. The mean change in Pao2/Fio2 at 30 mins was 38%. In these 19 patients, Pao2/Fio2 was highest at 20 ppm in four patients, at 10 ppm in eight patients, and at 5 ppm in seven patients. Compared with baseline measurements, Pao2/Fio2 improved significantly at both 30 mins (112 +/- 59 vs. 75 +/- 32, p=.01) and 8-12 hrs after INO initiation (146 +/- 52 vs. 75 +/- 32, p<.0001). In addition, oxygenation index was reduced at 8-12 hrs compared with baseline measurements (26 +/- 13 vs. 40 +/- 17, p=.08).

CONCLUSIONS

INO delivered at doses of 5 to 20 ppm during high-frequency oscillatory ventilation increases Pao2/Fio2 and may be a safe and effective rescue therapy for patients with severe oxygenation failure.

Interactive effects of high-frequency oscillatory ventilation and inhaled nitric oxide in acute hypoxemic respiratory failure in pediatrics

OBJECTIVE

High-frequency oscillatory ventilation (HFOV) and inhaled nitric oxide (iNO) have been reported to improve oxygenation in children with acute hypoxemic respiratory failure (AHRF), but their roles in the treatment of AHRF remains unknown. The use of HFOV improves oxygenation by increasing lung recruitment. iNO can improve oxygenation in AHRF, but it may have limited efficacy in patients with poor lung inflation. Based on these findings, we hypothesized that the combined treatment of HFOV and inhalation of low-dose NO would improve oxygenation and survival in children with severe AHRF compared with children treated with conventional mechanical ventilation (CMV) or either treatment alone.

SETTING

Tertiary pediatric intensive care units at seven academic centers.

DESIGN

Post hoc analysis of data from children enrolled in a multicenter, randomized, masked study of the use of iNO in the treatment of AHRF.

PATIENTS

A total of 108 pediatric patients with AHRF defined as an oxygenation index of >15 twice within 6 hrs. Mode of ventilation (HFOV or CMV) was determined by the patient's physician based on guidelines to maximize oxygenation. The patient was then randomized to treatment with or without iNO. Comparisons were made between patients who were treated with HFOV plus iNO (n = 14), HFOV alone (n = 12), CMV plus iNO (n = 35), and CMV alone (n = 38).

INTERVENTIONS

Ventilation with CMV or HFOV with or without iNO.

MEASUREMENTS AND MAIN RESULTS

We found that the change in Pao /Fio ratio was greatest in the HFOV plus iNO group compared with the other treatment groups at 4 hrs (p =.02) and 12 hrs (p =.01). After 24 hrs of treatment, both HFOV plus iNO and HFOV alone resulted in greater improvement in Pao2/Fio2 ratio than either CMV alone or CMV plus iNO (p =.005). After 72 hrs, treatment with HFOV alone resulted in a greater improvement in Pao2/Fio2 ratio than either CMV alone or CMV plus iNO (p =.03). There was no difference in predefined treatment failures between treatment groups.

CONCLUSIONS

We conclude that the combination of HFOV with iNO causes a greater improvement in oxygenation than either treatment strategy alone in children with severe AHRF. We speculate that the enhanced lung recruitment by HFOV enhances the effects of low dose iNO on gas exchange.

Neonatal respiratory failure

The classic entity of neonatal distress syndrome, as a lung disease expressing predominant surfactant deficiency, is currently changing to a more complex disease of the developing lung as a result of the number of extremely immature preterm infants. Prenatal factors, such as the fetal inflammatory response syndrome influence short- and long-term outcome in these premature infants presenting with respiratory distress syndrome at birth. Therefore, various previously dismissed treatment strategies, such as surfactant prophylaxis or newer anti-inflammatory approaches have to be reinvestigated in this emerging population. Despite the resurrection of a new picture of bronchopulmonary dysplasia, lung injury induced by mechanical ventilation remains a major issue in neonatal intensive care. With the advance in understanding of mechanical ventilation, it is becoming evident, that improvement in outcome can not be achieved by restoring normal lung physiology in the diseased lung using sophisticated ventilators and ventilation modes. A more disease specific ventilator strategy that will target as early as possible homogenous lung opening while at the same time avoiding overdistention of the lung, has the potential to affect outcome. The possible antiinflammatory properties of surfactant-proteins, nitric oxide and corticosteroids, despite some drawbacks, may show to have a synergistic effect. However, this needs further exploration.

Lung injury in acute pancreatitis: mechanisms, prevention, and therapy

Lung injury is the most pertinent manifestation of extra-abdominal organ dysfunction in pancreatitis. The propensity of this retroperitoneal inflammatory condition to engender a diffuse and life-threatening lung injury is significant. Approximately one third of patients will develop acute lung injury and acute respiratory distress syndrome, which account for 60% of all deaths within the first week. The variability in the clinical course of pancreatitis renders it a vexing entity and makes demonstration of the efficacy of any specific intervention difficult. The distinct pathologic entity of pancreatitis-associated lung injury is reviewed with a focus on etiology and potential therapeutic maneuvers.

Liquid ventilation

Partial liquid ventilation (PLV) developed considerably in the clinical and experimental fields during the past few years. In addition to improved oxygenation and lung mechanics by perfluorocarbon (PFC) administration, recent animal studies have tried to optimize PLV by evaluating the most appropriate ventilatory mode to use during PLV and by adjusting the best level of positive end-expiratory pressure (PEEP). Other pathophysiological aspects of acute lung injury that may be positively affected by liquid ventilation have been studied, including regional blood flow redistribution, reduction in ventilator-induced lung injury, and antiinflammatory properties of PFC. Although the precise dosing of PFC is debated, evidence from several experimental studies supports the use of smaller doses of PFC because larger doses increase the occurrence of baro- and volutrauma. In the clinical field, after promising data from preliminary studies, an international randomized controlled trial is on the verge of completion.

Lung volume recruitment in lambs during high-frequency oscillatory ventilation using respiratory inductive plethysmography

Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. We measured Delta changes in lung volume above end-expiratory volume (V(RIP)) during HFOV and studied whether changes in V(RIP) parallel changes in mean airway pressure. Calibration of the plethysmograph was made by serial injections of a known gas volume in six term (140 d gestation) and eight preterm (125 d gestation) lambs. Linear regression analysis of the relationship between injected gas volume and V(RIP) showed strong correlation (r(2) = 0.93-1.00 term animals, r(2) = 0.86-1.00 preterm animals). The pressure volume curves from the calibration with the injected gas volumes also correlated well with the pressure volume curves extrapolated from changes in V(RIP). Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.

Decreased use of neonatal extracorporeal membrane oxygenation (ECMO): how new treatment modalities have affected ECMO utilization

OBJECTIVE

Over the last decade, several new therapies, including high-frequency oscillatory ventilation (HFOV), exogenous surfactant therapy, and inhaled nitric oxide (iNO), have become available for the treatment of neonatal hypoxemic respiratory failure. The purpose of this retrospective study was to ascertain to what extent these modalities have impacted the use of neonatal extracorporeal membrane oxygenation (ECMO) at our institution.

METHODS

Patients from 2 time periods were evaluated: May 1, 1993 to November 1, 1994 (group 1) and May 1, 1996 to November 1, 1997 (group 2). During the first time period (group 1), HFOV was not consistently used; beractant (Survanta) use for meconium aspiration syndrome (MAS), persistent pulmonary hypertension of the newborn (PPHN), and pneumonia was under investigation; and iNO was not yet available. During the second time period (group 2), HFOV and beractant treatment were considered to be standard therapies, and iNO was available to patients with oxygenation index (OI) >/=25 x 2 at least 30 minutes apart, or on compassionate use basis. Patients were included in the data collection if they met the following entry criteria: 1) OI >15 x 1 within the first 72 hours of admission; 2) EGA >/=35 weeks; 3) diagnosis of MAS, PPHN or sepsis/pneumonia; 4) <5 days of age on admission; and 5) no congenital heart disease, diaphragmatic hernia, or lethal congenital anomaly.

RESULTS

Of the 49 patient in group 1, 21 (42.8%) required ECMO therapy. Of these ECMO patients, 14 (66.6%) had received diagnoses of MAS or PPHN. Only 3 of the patients that went on to ECMO received beractant before the initiation of bypass (14.3%). All ECMO patients in group 1 would have met criteria for iNO had it been available. Of all patients in group 1, 18 (36.7%) were treated with HFOV, and 13 (26.5%) received beractant. Of the 47 patients in group 2, only 13 (27.7%) required ECMO therapy (compared with group 1). Of these ECMO patients, only 5 (38.5%) had diagnoses of MAS or PPHN, with the majority of patients (61.5%) requiring ECMO for sepsis/pneumonia, with significant cardiovascular compromise. Only 5 of these ECMO patients, all outborn, did not receive iNO before cannulation because of the severity of their clinical status on admission. Of all patients in group 2, 41 (87.2%) were treated with HFOV (compared with group 1), 42 (89.3%) received beractant (compared with group 1), and 18 (44.7%) received iNO.

CONCLUSIONS

The results indicate that ECMO was used less frequently when HFOV, beractant and iNO was more commonly used. The differences in treatment modalities used and subsequent use of ECMO were statistically significant. We speculate that, in this patient population, the diagnostic composition of neonatal ECMO patients has changed over time.

Partial liquid ventilation for acute respiratory distress syndrome

PLV represents an intriguing alternative paradigm in the approach to the patient with ALI. Within the past decade, substantial information has become available regarding this technique. Clearly, PLV is feasible in patients with ALI and ARDS, and it appears to be safe with respect to short-term effects on hemodynamics and lung physiology, as well as long-term toxicity (although further research in this area is warranted). Although PLV has not yet been proven to be superior to traditional mechanical ventilation for patients with ALI or ARDS, PLV possesses an intriguing combination of physical, physiologic, and biologic effects: "Liquid PEEP" effect--e.g., more effective recruitment of dependent lung zones than achieved by gas ventilation Anti-inflammatory effects Lavage of alveolar debris Mitigation of ventilator-induced lung injury Direct anti-inflammatory effects--e.g., decreased macrophage release of proinflammatory cytokines, etc. Prevention of nosocomial pneumonia Combination with other modalities--e.g., exogenous surfactant replacement, inhaled NO, prone position Enhanced delivery of drugs or gene vectors into the lung. The results of ongoing and future clinical trials will be necessary to establish whether PLV improves clinical outcomes in patients with ALI or ARDS, or specific subgroups of such patients. Significant work also remains to be done to define the optimum dose level of PLV and the most appropriate ventilatory strategies.

High-frequency oscillatory ventilation and partial liquid ventilation after acute lung injury in premature lambs with respiratory distress syndrome

OBJECTIVE

Conventional mechanical ventilatory support (CV) contributes to lung injury in premature lambs with respiratory distress syndrome, a disease that is characterized by progressive deterioration of gas exchange and increased lung inflammation. Lung recruitment strategies, such as high-frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV), improve gas exchange and attenuate lung inflammation when instituted immediately after birth. However, whether these recruitment strategies are effective as rescue treatment after established lung injury is unknown. To determine the separate and combined effects of HFOV and PLV when initiated after the establishment of acute lung injury in severe respiratory distress syndrome, we studied the effects of these strategies on gas exchange and histologic signs of acute lung injury in premature lambs.

DESIGN

Animals were intubated, treated with surfactant and ventilated with 1.00 FIO2 for 4 hrs. After 2 hrs, animals were either continued on CV (controls) or treated with one of three strategies: HFOV; CV + PLV; or HFOV + PLV. The response to low-dose inhaled nitric oxide (5 ppm) was measured in each group at the end of the study.

SETTING

An animal laboratory affiliated with University of Colorado School of Medicine.

SUBJECTS

A total of 20 premature lambs at 115-118 days of gestation (term = 147 days).

MEASUREMENTS AND MAIN RESULTS

In comparison with control animals, each of the rescue therapies improved PaO2 after 1 hr of treatment. The HFOV and HFOV + PLV groups had higher PaO2 than CV + PLV or CV alone (p < .05). Mean airway pressure (Paw) was lower in the PLV groups during CV or HFOV compared with their controls (p < .05). Inhaled NO improved PaO2 in all groups; however, the increase in PaO2 was greatest in the HFOV + PLV group (p < .05). Histologic examination and myeloperoxidase assay were not different between groups.

CONCLUSION

We conclude that each lung recruitment strategy improved oxygenation in premature lambs with established lung injury.

First intention high-frequency oscillation with early lung volume optimization improves pulmonary outcome in very low birth weight infants with respiratory distress syndrome

OBJECTIVES

The lack of decline in chronic lung disease of prematurity despite the generalized use of surfactant and alternative modes of ventilation such as high-frequency oscillation (HFO) has been attributed to some misunderstanding of how HFO has to be used. We used a new ventilatory strategy in very low birth weight (VLBW) infants, by initiating HFO immediately after intubation and attempting early lung volume optimization before surfactant was administered.

STUDY DESIGN

The outcome of 32 VLBW infants, managed with first intention HFO over a period of 24 months (September 1, 1996 and August 31, 1998) was compared by chart review with 39 historical controls, consecutively managed with conventional mechanical ventilation (CMV) over a period of 24 months (January 1, 1994 and December 31, 1995).

SETTING

An 11-bed tertiary care pediatric and neonatal intensive care unit of a university teaching hospital.

RESULTS

The 2 groups of patients were similar in demographic distribution of birth weight, gestational age, race, and gender. Patients on first intention HFO were ventilator-dependent (median [95% confidence interval]: 5 [3-6] vs 14 [6-23] days) and oxygen-dependent (12 [4-17] vs 51 [20-60] days) for a shorter time than patients on CMV. The incidence of chronic lung disease at 36 weeks of gestational age was significantly lower in the HFO group compared with the CMV group (0% vs 34%).

CONCLUSIONS

First intention HFO with early lung volume optimization shortened the need for respiratory support and improved pulmonary outcome of VLBW infants with respiratory distress syndrome significantly.