Robert A. deLemos

Undetectable interleukin (IL)-10 and persistent IL-8 expression early in hyaline membrane disease: a possible developmental basis for the predisposition to chronic lung inflammation in preterm newborns.

We are interested in determining whether premature birth alters expression of counterregulatory cytokines which modulate lung inflammation. Production of proinflammatory cytokines tumor necrosis factor α, IL-1β, and IL-8 is regulated in part by the antiinflammatory cytokine IL-10. For preterm newborns with hyaline membrane disease, deficiencies in the ability of lung macrophages to express antiinflammatory cytokines may predispose to chronic lung inflammation. We compared the expression of pro- and antiinflammatory cytokines at the mRNA and protein level in the lungs of preterm and term newborns with acute respiratory failure from hyaline membrane disease or meconium aspiration syndrome. Four sequential bronchoalveolar lavage (BAL) samples were obtained during the first 96 h of life from all patients. All patients rapidly developed an influx of neutrophils and macrophages. Over time, cell populations in both groups became relatively enriched with macrophages. The expression of proinflammatory cytokine mRNA and/or protein was present in all samples from both patient groups. In contrast, IL-10 mRNA was undetectable in most of the cell samples from preterm infants and present in the majority of cell samples from term infants. IL-10 concentrations were undetectable in lavage fluid from preterm infants with higher levels in a few of the BAL samples from term infants. These studies demonstrate that1) IL-10 mRNA and protein expression by lung inflammatory cells is related to gestational age and 2) during the first 96 h of life neutrophil cell counts and IL-8 expression decrease in BAL from term infants, but remain unchanged in BAL samples from preterm infants.

Ventilatory management of infant baboons with hyaline membrane disease: The use of high frequency ventilation

Abstract: We tested the hypothesis that high frequency oscillatory ventilation (HFOV) would result in decreased pulmonary barotrauma in infants with hyaline membrane disease by comparing HFOV at 10 Hz to conventional positive pressure ventilation with continual distending airway pressure (PPV/PEEP) in premature baboons with hyaline membrane disease. Nineteen baboon fetuses were randomized to one of two treatment groups, delivered at 140 ± 2 days, and, after stabilization and instrumentation of PPV/PEEP, placed in their respective ventilator group. Animals on conventional ventilation were managed by adjustment of tidal volume and frequency (to 1 Hz) to keep PaCO2 below 55 and by adjustment of the mean airway pressure. One of the “HFOV” group died of cardiovascular complications before going on HFOV and was eliminated from data analysis. The remaining HFOV baboons survived the 11-day experimental period without evidence of airleak. Six of the 11 prematures treated with PPV/PEEP developed pulmonary interstitial emphysema and/or pneumothorax and five of the animals died within 48 h. The intergroup differences in airleak were significant (p < 0.05). Mean airway pressure (measured at the proximal airway) was higher initially with HFOV but then was lowered more rapidly than in the PPV/PEEP animals. The arterial to alveolar oxygen ratio rose and the FIO2 could be lowered more rapidly with HFOV than with conventional ventilation. These differences reached significance by 20 h. After 60 h there were no significant differences between HFOV and the PPV/PEEP survivors. HFOV resulted in more uniform saccular expansion, higher arterial to alveolar oxygen ratio, less oxygen exposure, and decreased acute barotrauma when compared to PPV/PEEP. Although initially mean airway pressure was in the HFOV animals this was not associated with measurable baroinjury. These data support the efficacy of HFOV in the treatment of prematures with hyaline membrane disease.

Proximal, Tracheal, and Alveolar Pressures during High-Frequency Oscillatory Ventilation in a Normal Rabbit Model

ABSTRACT: To study the effect of different high-frequency oscillatory ventilation parameters on airway pressure we measured oscillatory pressure amplitude (| Paw |) and mean airway pressure (Paw)at three sites in open-chested normal rabbits: proximal, trachea, and alveolus. Five animals were studied to test a new pleural capsule design, which was then used in two groups of animals to measure right upper (n = 4)or middle (n = 5) lobe alveolar pressures. Animals were randomly sequenced through combinations of frequency (10, 15, and 20 Hz) and fractional inspiratory time (T) (0.3 and 0.5) while normoxic and encapnic. During capsule testing, we noted that alveolar pressures increased (p < 0.05) with increasing capsule mass. suggesting that compressive forces from the capsule may alter the capsule measurement. We thus used a lowmass (430 mg) transducer system in the rabbit high-frequency oscillatory ventilation experiments. Using multifactorial analysis of variance, we found significant main effects of Ti on Paw, and of measurement site on both |Paw| and Paw (p < 0.009). Frequency did not influence variations in either |Paw| Paw. For both Ti settings, alveolar upper lobe Paw was lower compared with that of the middle lobe (p < 0.0005). Lengthening Ti (03 to 0.5) increased tracheal Paw in each capsule group (p < 0.0005). At Ti = 0.5, tracheal Paw exceeded Paw measured proximally (p < 0.05). Our data support in vivo alveolar Paw inhomogeneity and demonstrate significant changes in pressures within the lung related to Ti during high-frequency oscillatory ventilation.

High-frequency oscillatory ventilation Versus intermittent mandatory ventilation : early hemodynamic effects in the premature baboon with hyaline membrane disease

ABSTRACT: We studied the hemodynamic consequences during the first 24 h of life in premature baboons (140 d) with hyaline membrane disease that were treated with high-frequency oscillatory ventilation (HFOV) or conventional intermittent mandatory ventilation (IMV). Cardiac output and organ blood flow were measured at three time-points using the radiolabeled microsphere technique. Seven of seven HFOV and six of eight IMV animals survived the 24-h period. By design, initial mean airway pressure (Paw) was higher in the HFOV group (p < 0.01). HFOV Paw was progressively reduced during the study period because of improving oxygenation as measured by the arterial to alveolar oxygen ratio. In contrast, it was necessary to increase Paw in the IMV animals to maintain the arterial to alveolar oxygen ratio. By 23 h, the IMV group required higher Paw than the HFOV group (p < 0.05) and had a lower arterial to alveolar oxygen ratio (p < 0.05). We found no significant differences in left ventricular output, effective systemic flow, organ blood flow, or central venous pressure between the two groups at 3, 8, or 23 h. The HFOV strategy used in our study resulted in significant improvement in oxygenation during the initial 24 h of treatment without adverse effect on left ventricular output, cerebral blood flow, or central venous pressure. We conclude that when appropriate changes in Paw are made during HFOV in response to improvement in arterial oxgenation and changes in lung inflation as assessed by chest radiographs HFOV can be achieved without depressing cardiovascular dynamics more than during conventional therapy with IMV.

Diffuse Alveolar Damage in the Evolution of Bronchopulmonary Dysplasia in the Baboon

ABSTRACT: Pulmonary immaturity, oxygen exposure that elicits cellular damage by free radicals, and barotrauma induced by mechanical ventilation are implicated in the pathogenesis of bronchopulmonary dysplasia. In the adult counterpart of adult respiratory distress syndrome, diffuse alveolar damage characterizes a histopathological sequence of lung findings that can occur during the disease course. Although adult respiratory distress syndrome has many etiologies, elevated oxygen exposure is known to be a contributor to the ensuing lung injury. In bronchopulmonary dysplasia, oxygen exposure is thought to be a primary agent of injury. The evolution of the histopothological findings in the premature baboon model of hyaline membrane disease/bronchopulmonary dysplasia was investigated in this study and compared to that in oxygen-treated adult baboons with adult respiratory distress syndrome. Findings from lung specimens of 121 prematurely delivered baboons at 0, 0.5, 1, 2, 3–6, 7–11+ days after delivery document that the premature lung has a delayed and more blunted exudative response when compared to that of human and baboon adults. Saccular edema, not hyaline membranes, is the dominant histopathological finding in the exudative phase of diffuse alveolar damage and occurs later (7–11 days) in infant lungs when compared to comparably treated adult lungs in which maximal exudative changes are seen at 3–6 days. The reparative response in the premature baboon is characterized by saccular wall thickening and fibrosis, with less intramural organization of exudate in saccular/alveolar spaces when compared to adults. The airway changes in the premature are more severe than those seen in adult disease. These findings indicate that diffuse alveolar damage does occur in the immature lung albeit with differing characteristics when contrasted to comparably injured adults.

Pulmonary interstitial emphysema treated by high-frequency oscillatory ventilation

Twenty-seven low birth weight infants who developed pulmonary interstitial emphysema (PIE) and respiratory failure while on conventional ventilation were treated with high-frequency oscillatory ventilation (HFOV). The mean birth weight was 1.2 kg (range 0.55 to 2) with gestational age of 28 wk (range 25 to 34). Ten patients died, six of whom had documented sepsis with shock and were therefore excluded from analysis. All patients showed initial improvement on HFOV. Surviving patients showed continued improvement in oxygenation and ventilation at increasingly lower fraction of inspired oxygen and proximal airway pressure with resolution of PIE, while nonsurvivors progressively developed chronic respiratory insufficiency with continued PIE from which recovery was not possible. Overall survival in nonseptic patients was 80% (16 of 20). We found HFOV to be effective in the treatment of PIE and hypothesieze that interstitial airleak is decreased during HFOV because adequate ventilation is provided at lower peak distal airway pressures.

Continuous-flow ventilation as an alternative to assisted or controlled ventilation in infants.

ECENT reports confirm that assisted R mechanical ventilation increases the incidence of intact survival in infants with respiratory failure from respiratory distress syndrome (RDS) Design of a ventilator for use with small children presents specific and unique problems. Initiation of the ventilatory cycle on patient demand has proven unreliable, particularly in small premature infants with low tidal volumes and rapid respiratory rates.7 The design of most available infant ventilators allows gas flow to the patient only during the inspiratory phase of the respirator cycle. Thus, failure of the infant to breathe synchronously with the machine results in ineffective gas exchange. To overcome this handicap, controlled respiration using hyperventilation or paralysis is commonly employed.

Extracorporeal membrane oxygenation and high-frequency oscillatory ventilation: potential therapeutic relationships

Eighteen neonates 33 to 42 wk gestational age with severe respiratory failure were referred for extracorporeal membrane oxygenation (ECMO). Sixteen ultimately met the ECMO criteria, of whom 15 were first offered high-frequency oscillatory ventilation (HFOV). Seven responded to HFOV alone and did not require ECMO treatment. Eight of the nine remaining patients were placed on ECMO support with HOFV. Infants who responded to HFOV alone tended to have pneumonia more than meconium aspiration, to be smaller and more immature, to have higher Apgar scores, and to have suffered severe hypoxia (alveolar-arterial oxygen pressure difference over 600 torr) for less time than the ECMO group. Although patient numbers are small, a trend is noted which favors HFOV treatment alone in terms of the duration of HFOV, the total duration of assisted ventilation, the rapidity with which extubation was accomplished, and the length of hospital stay.

Pulmonary interstitial emphysema in the premature baboon with hyaline membrane disease.

During experiments designed to develop an appropriate ventilatory strategy for high-frequency ventilation (HFV) in the premature baboon with hyaline membrane disease (HMD), we observed the development of pulmonary interstitial emphysema (PIE). Four study groups of 5 animals each received positive-pressure ventilation and positive end-expiratory pressure (PPV/PEEP) or HFV and 1 of 3 sighing techniques. Pathologically, all animals ventilated with PPV/PEEP or HFV with a carefully controlled intermittent sigh developed dilatation of the distal conducting airway and alveolar duct, with poorly expanded pulmonary saccules. The imposition of a sigh with inappropriate timing or excessive volume ruptured the dilated airway walls and caused interstitial air to accumulate. This was evident from the location of striking dilation of the distal airways and pseudocysts in areas of atelectasis. Thus, early in the course of HMD when saccular aeration is minimal, the pathogenesis of PIE is related to airway rather than alveolar rupture.

A comparison of ventilation strategies for the use of high-frequency oscillatory ventilation in the treatment of hyaline membrane disease

To assess the efficacy of high frequency oscillatory ventilation (HFOV) in the management of infants with hyaline membrane disease (HMD), we compared two HFOV strategies with conventional positive pressure ventilation with positive end expiratory pressure (PPV) for 24 h in premature baboons (140 d gestation). Three out of 14 PPV, five out of five HFOV‐E (begun at birth; 15 Hz; I:E 1:2), and none of 10 HFOV‐L (begun after 3 h PPV; 10 Hz; I:E 1:2) were killed at 24 h for morphologic examination. Physiologic (Paw, Pa/AO2, IO2, B. P., pulse, blood gases) data on all animals in each group were assessed at each 3 h interval and over time. Intergroup differences in radiographs at 0 and 24 h and in morphology were quantitatively assessed by comparison with a panel of standards. All animals had radiographic HMD. Initial Paw was set higher with HFOV‐E (16.8) than PPV or HFOV‐L (14.1, 14.1). PPV baboons required increasing Paw to maintain constant Pa/AO2. Six out of 14 PPV animals developed airleak and three out of three had morphologic HMD. In contrast Pa/AO2 was higher in both HFOV groups at lower Paw by 24 h. None of 15 HFOV animals developed airleak. HFOV‐E lungs had dramatic differences in morphology with uniform saccular opening and decreased edema and hyaline membranes compared to PPV. HFOV‐L had less dramatic effects because of lower Paw and delayed application. Early use of HFOV at a high Paw favorably alters the course of HMD. Unless closely monitored, this strategy results in lung overinflation which may adversely affect venous return and cardiac output.