The Provo multicenter early high-frequency oscillatory ventilation trial: improved pulmonary and clinical outcome in respiratory distress syndrome

OBJECTIVE

To compare the hospital course and clinical outcome of preterm infants with respiratory distress syndrome treated with surfactant and managed with high-frequency oscillatory ventilation (HFOV) or conventional mechanical ventilation (CV) as their primary mode of ventilator support.

DESIGN

A prospective randomized clinical trial.

SETTING

Three community-based level III neonatal intensive care units.

SUBJECTS

A total of 125 neonates who were 35 weeks or less estimated gestation requiring intubation and assisted ventilation for respiratory distress syndrome with arterial to alveolar oxygen ratio less than .50.

INTERVENTIONS

Patients were randomized to continue CV (61 patients) or be changed to HFOV (64 patients) after exogenous surfactant administration (100 mg/kg). HFOV was used in a strategy to promote lung recruitment and maintain lung volume. Protocol respiratory care guidelines were followed; otherwise routine care was provided by each neonatal intensive care unit.

MEASUREMENTS AND MAIN RESULTS

No differences were noted in demographic features between the two study groups. The study population birth weight was 1.51 +/- .47 kg (mean +/- SD), gestational age was 30.9 +/- 2.5 weeks, and study entry age was 2 to 3 hours. Patients randomized to HFOV demonstrated the following significant findings compared with CV-treated patients: vasopressor support was less intensive; surfactant redosing was not as frequent; oxygenation improved more rapidly and remained higher during the first 7 days; fewer infants required prolonged supplemental oxygen or ventilator support; treatment failure was reduced; more patients survived without chronic lung disease at 30 days; need for continuous supplemental oxygen at discharge was less; frequency of necrotizing enterocolitis illness was lower; there were fewer abnormal hearing tests; and hospital costs were decreased. No differences were seen between the two study groups in the frequency or severity of patent ductus arteriosus, air leak, retinopathy of prematurity, or intraventricular hemorrhage. Length of hospital stay and survival to discharge were similar for HFOV- and CV-treated infants.

CONCLUSIONS

When used early with a lung recruitment strategy, HFOV after surfactant replacement resulted in clinical outcomes consistent with a reduction in both acute and chronic lung injury. Benefit was evident for preterm infants both less than or equal to 1 kg and more than 1 kg. In addition, early HFOV treatment may have had a more global effect on patient health throughout the hospitalization, resulting in reduced morbidity and decreased health care cost.

A bench test evaluation of a neonatal closed tracheal suction system

We tested the hypothesis that a possible mechanism for reduced hypoxia during suctioning with closed tracheal suction systems (CTSS) is the provision of uninterrupted gas delivery and the maintenance of airway pressures. This was accomplished by using a neonatal ventilator and test lung model to permit the insertion of a CTSS (with and without suction applied), measurements of inspiratory and end-expiratory airway pressures proximal and distal to the endotracheal tube (ETT) and measurements of inspired and expired tidal volumes (sampled distal to the ETT). An 8 Fr CTSS was evaluated with 4.5, 4.0, and 3.5 mm ETT, and a 6 Fr CTSS with a 3.5, 3.0, and 2.5 mm ETT. We found that catheter placement without suction caused no changes in proximal airway pressures but distal peak inspiratory pressures decreased as the relationship between suction catheter size and ETT lumen increased, while distal end-expiratory pressures were unchanged. Similarly, distal tidal volumes progressively decreased as the size of the suction catheter occupied more of the ETT lumen. During suctioning with the 6 Fr catheter, proximal airway pressures were virtually unchanged; however, as ETT size decreased, distal airway pressures also decreased. The application of suction only modestly augmented the substantial decrement in measured tidal volumes when compared to catheter insertion alone. For the 8 Fr catheter, suction markedly reduced both proximal and distal airway pressures and tidal volumes. We conclude that the use of the CTSS tested in this neonatal ventilator/test lung model does not preserve continuity of volume or pressure delivery during suction procedures; therefore these cannot be the sole explanation for the reported reduction in suction related hypoxia.

Evaluation of a mainstream capnometer and end-tidal carbon dioxide monitoring in mechanically ventilated infants

We evaluated a new lightweight capnometer with a less than 1 mL deadspace neonatal airway adapter and endotracheal tube connector unit (NAC) for use in mechanically ventilated neonates. The evaluation consisted of: 1) a bench test comparison of air flow resistance between the standard endotracheal tube and connector with the new NAC (flow rates, 1.5 to 12.8 L/min); 2) a determination of the effect of NAC placement on Paco2; 3) pre- and post-NAC pulmonary mechanics; and 4) analysis of paired PetCO2 and PACO2 in 16 infants requiring mechanical ventilation. Paired t test of the slopes of the resistance curves was significant (P = 0.002) while analysis of variance of differential pressures was not (P = 0.29). All post-NAC placement Paco2 were smaller than pre-placement values; there were no differences in pulmonary mechanics, and Petco2 correlated closely with Paco2 (n = 132, r = 0.79) defined as Petco2 = 0.68.Paco2 + 5.52; means +/- 1 SD, Paco2 -Petco2 was 4.7 +/- 4.7 torr and Petco2/Paco2 was 0.86 +/- 0.14.

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.

Role of lung injury in the pathogenesis of hyaline membrane disease in premature baboons

To test the hypothesis that hyaline membrane disease (HMD) has a multifactorial etiology in which barotrauma plays a major role, we compared the immediate institution of high-frequency oscillatory ventilation (HFOV; 15 Hz, n = 5) with positive-pressure ventilation with positive end-expiratory pressure (PPV; n = 7) in premature baboons (140-days gestation) with HMD. Measurements of ventilation settings and physiological parameters were obtained and arterial-to-alveolar O2 (PaO2-to-PAO2) ratio and oxygenation index [(PaO2/PAO2)-to-mean airway pressure ratio (IO2)] were calculated. At death (24 h), static pressure-volume (PV) curves were performed, and phospholipids (PL) and platelet-activating factor (PAF) were measured in lung lavage fluid. Morphological inflation patterns were analyzed using a panel of standards. By design, mean airway pressure was initially higher (19 vs. 13 cmH2O) in the HFOV animals. PaO2-to-PAO2 ratio and IO2 progressively deteriorated in the PPV animals and then stabilized at significantly lower levels than with HFOV. PV curves from HFOV animals had significant increases in lung volume at maximum distending pressure, deflation volume at 10 cmH2O, and hysteresis area compared with PPV, which showed no hysteresis. Seven of seven PPV and only one of five HFOV animals had morphological findings of HMD. PL amount and composition in both groups were consistent with immaturity, even though the quantity was significantly greater in the PPV group. PAF was present (greater than or equal to 0.10 pmol) in six of seven PPV and in the only HFOV animal with HMD. We conclude that HFOV protected PL-deficient premature baboons from changes in gas exchange, lung mechanics, and morphology typical of HMD in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

High-frequency ventilation: its various techniques and clinical applications

High-frequency ventilation can be considered to be ventilation with a tidal volume close to or less than the anatomical dead space. The various techniques of high-frequency ventilation will be discussed including high-frequency positive pressure ventilation, high-frequency jet ventilation or high-frequency flow interruption, and high-frequency oscillatory ventilation. The clinical application of the various types of high-frequency ventilation will be discussed including their use during surgical procedures, their use for various kinds of barotrauma, their usefulness in respiratory failure, their use in newborns with hyaline membrane disease, and their usefulness for respiratory support in emergency situations involving cardiopulmonary resuscitation. The potential use for high-frequency ventilation in the management of battlefield casualties and air evacuation of critically ill patients will also be discussed.

Influence of ventilatory technique on pulmonary baroinjury in baboons with hyaline membrane disease

To assess the influence of ventilatory technique on pulmonary baroinjury in experimental hyaline membrane disease, we randomized 24 premature baboons to six treatment groups according to ventilator (PPV, positive pressure ventilator; HFO, high frequency oscillator; HFI, high frequency flow interrupter) and O2 therapy FIO2 as clinically indicated, or FIO2 1.0). PaCO2 was adjusted by varying pressure amplitude, and for PPV, also by rate (less than 60/min). HFO and HFI were set at a frequency of 10 Hz. Animals were cared for with standard NICU techniques until death or sacrifice at 11 days. One animal died at delivery and was excluded from data analysis. There were no intergroup differences in Paw, Pa/AO2, PaCO2 or oxygenation index (IO2 = [Pa/AO2]/Paw) prior to death of the first study animal at 13 h. Animals who subsequently developed airleak had higher Paw, lower Pa/AO2 and lower IO2 during this period. The degree of airleak was significantly less with HFO compared to PPV or HFI. The effect of O2 exposure did not appear different with respect to the degree of airleak or the frequency of severe tracheal injury, although survival was shortened. Severe tracheal injury was more frequent with HFI compared to PPV or HFO. BPD was found only in 100% O2 exposed animals surviving greater than 1 wk. Management of premature baboons with HFO and appropriate O2 resulted in less severe airleak, 100% survival, and no evidence of severe tracheal injury or BPD. These outcomes were not achieved with clinically similar strategies using PPV or HFI.

Rapid assessment of ventilation by measurement of carbon dioxide elimination during high-frequency ventilation of kittens

Monitoring of the effectiveness of ventilation is a significant problem during high-frequency ventilation (HFV). The time necessary to achieve equilibrium of the arterial tension of carbon dioxide (Paco2) following step changes in ventilation is appreciable, because of large body stores of CO2. Waiting for Paco2 to reach equilibrium is not only time-consuming but a potentially dangerous means of monitoring ventilator adjustments during HFV. Five kittens of mean +/- SD 1,082 +/- 383 gm weight were studied during HFV, both with normal lungs and lungs injured by saline lavage-induced surfactant depletion. The transcutaneous tension of carbon dioxide (Ptcco2) was monitored continuously to determine the time required to achieve equilibrium of Paco2 following a step change in ventilation. The rate of pulmonary CO2 elimination (VECO2) was measured immediately before and immediately after (less than 12 sec) step changes in ventilation and was used to predict the change in Paco2 achieved once equilibrium was reestablished. With normal lungs, equilibration time following step changes in ventilation was found to be approximately 20 minutes. After step decreases in ventilation of the injured lung, achieving equilibrium state took significantly longer, approximately 30 minutes. The Paco2 predicted was significantly related to the change in Paco2 achieved at equilibrium for both normal and injured lung studies. We concluded that direct monitoring of VECO2 during HFV may be a useful clinical monitoring technique, allowing rapid and accurate assessment of the efficiency of ventilation following step changes in ventilation and potentially assisting in optimizing ventilator settings.

Sudden infant death syndrome in infants evaluated by apnea programs in California

Home apnea/bradycardia monitoring is frequently used in the management of infants at increased risk for sudden infant death syndrome (SIDS). However, some infants have died despite evaluation by infant apnea programs, and the benefits of home monitoring remain unproven. To determine the SIDS rate and risk factors of infants evaluated by infant apnea programs, 31 apnea programs and ten home monitor vendors in California were surveyed. Eleven (35%) of the apnea programs and four (40%) of the vendors responded. Information was obtained on 26 infants who died. Thirteen (50%) deaths were due to SIDS. Abnormal sleep studies did not predict death. Fifteen infants died despite a recommendation for home monitoring. Seven deaths occurred in association with technical errors or noncompliance with monitoring. Four deaths were due to nonaccidental trauma. The apnea programs evaluated 3,406 infants during a 5-year period; 1,841 had monitoring recommended. Term infants with apnea, subsequent siblings of SIDS victims, and infants evaluated at referral centers were more likely to have monitoring recommended than premature infants with apnea or infants evaluated at nonreferral centers (P less than .0001). Infants who had monitoring recommended were at equal risk of dying of SIDS as those who did not.