Effect of PEEP and suction via chest drain on functional residual capacity and lung compliance after surgical repair of congenital diaphragmatic hernia: preliminary observations in 5 patients

Positive End-expiratory Pressure Ventilation Increases Extravascular Lung Water Due to a Decrease in Lung Lymph Flow

Positive end-expiratory pressure (PEEP) is used to improve gas exchange, increase functional residual capacity, recruit air spaces, and decrease pulmonary shunt in patients suffering from respiratory failure. The effect of PEEP on extravascular lung water (EVLW), however, is still not fully understood. This study was designed as a prospective laboratory experiment to evaluate the effects of PEEP on EVLW and pulmonary lymph flow (QL) under physiologic conditions.

Twelve adult sheep were operatively prepared to measure haemodynamics of the systemic and pulmonary circulation, and to assess EVLW. In addition, the lung lymphatic duct was cannulated and a tracheostomy performed. The animals were then mechanically ventilated in the awake-state without end-expiratory pressure (PEEP 0). After a two-hour baseline period, PEEP was increased to 10 cmH2O for the duration of two hours, and then reduced back to 0 cmH2O. Cardiopulmonary variables, QL, and arterial blood gases were recorded intermittently; EVLW was determined two hours after each change in PEEP.

The increase in PEEP resulted in a decrease in QL (7±1 vs 5±1 ml/h) and an increase in EVLW (498±40 vs 630±58 ml; P<0.05 each) without affecting cardiac output. As PEEP was decreased back to baseline, QL increased significantly (5±1 vs 10±2 ml/h), whereas EVLW returned back to baseline.

This study suggests that institution of PEEP produces a reversible increase in EVLW that is linked to a decrease in QL.

Lower Distending Pressure Improves Respiratory Mechanics in Congenital Diaphragmatic Hernia Complicated by Persistent Pulmonary Hypertension

OBJECTIVE

To investigate the effects of distending pressures on respiratory mechanics and pulmonary circulation in newborn infants with congenital diaphragmatic hernia (CDH) and persistent pulmonary hypertension (PPHN).

STUDY DESIGN

In total, 17 consecutive infants of ≥37 weeks of gestational age with CDH and PPHN were included in this prospective, randomized, crossover pilot study. Infants were assigned randomly to receive 2 or 5 cmH₂O of positive end-expiratory pressure (PEEP) for 1 hour in a crossover design. The difference between peak inspiratory pressure and PEEP was kept constant. Respiratory mechanics, lung function, and hemodynamic variables assessed by Doppler echocardiography were measured after each study period.

RESULTS

At 2 cmH₂O of PEEP, tidal volume and minute ventilation were greater (P < .05), and respiratory system compliance was 30% greater (P < .05) than at 5 cmH₂O. PaCO₂ and ventilation index were lower at 2 cmH₂O than at 5 cmH₂O (P < .05). Although preductal peripheral oxygen saturation was similar at both PEEP levels, postductal peripheral oxygen saturation was lower (median [range]: 81% [65-95] vs 91% [71-100]) and fraction of inspired oxygen was greater (35% [21-70] vs 25% [21-60]) at 5 cmH₂O. End-diastolic left ventricle diameter, left atrium/aortic root ratio, and pulmonary blood flow velocities in the left pulmonary artery were lower at 5 cmH₂O.

CONCLUSIONS

After surgical repair, lower distending pressures result in better respiratory mechanics in infants with mild-to-moderate CDH. We speculate that hypoplastic lungs in CDH are prone to overdistension, with poor tolerance to elevation of distending pressure.

Ventilation modalities in infants with congenital diaphragmatic hernia

Neonates with congenital diaphragmatic hernia are among the more complex patients to support with mechanical ventilation. They have particular features that add to the difficulties already present in the neonatal patient. A ventilation strategy tailored to the patient's underlying physiology rather than mode of ventilation is a crucial issue for clinicians treating these delicate patients.

Antenatal and postnatal lung and vascular anatomic and functional studies in congenital diaphragmatic hernia: implications for clinical management

Congenital diaphragmatic hernia is characterized by fetal and neonatal lung hypoplasia as well as vascular hypoplasia. Antenatal imaging studies have been performed that attempt to quantify the degree of hypoplasia and its impact on infant prognosis. Prenatal and perinatal growth of the lung and vasculature are interdependent and their continued coordinated growth is critical for survival after birth in this patient population. Lung protection strategies appear to improve survival in newborns with diaphragmatic hernia, but a subset of infants remain who demonstrate sufficiently severe lung hypoplasia that we are unable to provide support long-term after birth. Fetal intervention is a strategy designed to enhance fetal lung growth towards improving survival in this most severely affected group, though other therapies to enhance postnatal lung and vascular growth should be concurrently investigated. However, any of these interventions will require careful selection of those infants at risk for poor outcome and thorough follow up, since long-term morbidity is significant in children with diaphragmatic hernia.

Functional residual capacity measurement by heptafluoropropane in ventilated newborn lungs: in vitro and in vivo validation

OBJECTIVE

Heptafluoropropane is an inert gas commercially used as propellant for inhalers. Since heptafluoropropane can be detected in low concentrations, it could also be used as a tracer gas to measure functional residual capacity and ventilation homogeneity. The aim of the present study was to validate functional residual capacity measurements by heptafluoropropane wash-in/wash-out (0.8%) during mechanical ventilation in small, surfactant-depleted lungs using a newborn piglet model.

DESIGN

Prospective laboratory and animal trial.

SETTING

Animal laboratory in a university setting.

SUBJECTS

Sixteen newborn piglets (age<12 hrs, median weight 1390 g [705-4200 g]) before and after surfactant depletion (Pao2<100 torr in Fio2=1.0) by lung lavage.

INTERVENTIONS

Heptafluoropropane was measured with a new infrared mainstream sensor connected with the flow sensor of the Dräger Babylog 8000. Accuracy and precision of the measurement technique were tested in a mechanical lung model with a volume range from 11 to 35 mL. Reproducibility of the method and its sensitivity to detect changes of functional residual capacity were assessed in vivo by variation of ventilatory variables.

MEASUREMENTS AND MAIN RESULTS

In vitro the absolute error of functional residual capacity was <1 mL (relative errors<3%) with a coefficient of variation<4%. The coefficient of variation of consecutive in vivo measurements was only slightly higher (<5.1%). Measurement of heptafluoropropane concentrations in blood showed no significant accumulation for repeated functional residual capacity measurements within short time periods. After lung lavage, the functional residual capacity decreased from 20.9 mL/kg to 14.5 mL/kg (p<.05) despite increased ventilatory pressures, and lung clearance index (p<.001) and moment ratios (p<.01) increased significantly due to uneven alveolar ventilation. In healthy lungs, the increase in peak inflation pressure and positive end-expiratory pressure by 3-4 cm H2O had only a moderate effect on functional residual capacity (20.9+/-8.6 vs. 26.0+/-11.9 mL/kg, p=.17) and no effect on ventilatory homogeneity, whereas in surfactant-depleted lungs the functional residual capacity increased from 14.5+/-6.7 mL/kg to 29.9+/-12.6 mL/kg (p<.001) and lung clearance index and moment ratios decreased significantly (p < .01).

CONCLUSIONS

Heptafluoropropane is a suitable tracer gas for precise functional residual capacity measurements tested in vitro and allows for reproducible measurements in ventilated small lungs without any adverse effects on mechanical ventilation. The sensitivity of the method is sufficiently high to demonstrate the effect of changes in ventilatory settings on the functional residual capacity and ventilation homogeneity.

Lung function tests in neonates and infants with chronic lung disease of infancy: functional residual capacity

This is the second paper in a review series that will summarize available data and discuss the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses the expansive subject of measurements of lung volume using plethysmography and gas dilution/washout techniques. Following orientation of the reader to the subject area, we focus our comments on areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. Measurements of lung volume are important both for assessing growth and development of lungs in health and disease, and for interpreting volume-dependent lung function parameters such as respiratory compliance, resistance, forced expiratory flows, and indices of gas-mixing efficiency. Acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC), with treatments aimed at securing optimal lung recruitment. While FRC may remain reduced in established chronic lung disease of infancy, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas-trapping, secondary to airway obstruction. Ideally, accurate and reliable bedside measurements of FRC would be feasible from birth, throughout all phases of postnatal care (including assisted ventilation), and during subsequent long-term follow-up. Although lung volume measurements in extremely preterm infants were described in a research environment, resolution of several issues is required before such investigations can be translated into routine clinical monitoring.

Evidence-based management of infants with congenital diaphragmatic hernia

The mortality rate associated with congenital diaphragmatic hernia (CDH) varies widely between centers and remains relatively high despite widespread use of new therapeutic modalities. Many of these have been implemented without properly controlled studies. Over the past 10 to 15 years, only 9 randomized trials enrolling a total of approximately 250 infants with CDH have been published. The limited evidence available suggests that better outcomes are observed by delivering infants with CDH at experienced centers, by delaying surgical repair until hemodynamic and respiratory stability is achieved, and by the judicious utilization of nonaggressive mechanical ventilation and permissive hypercapnea. Other therapeutic modalities, such as high frequency oscillatory ventilation, inhaled nitric oxide, and ECMO, may provide additional advantages for selected infants. There is a dire need to establish networks of centers that manage enough infants with CDH, to conduct appropriately sized randomized trials that can answer some of the critical questions about the management and long-term outcome of these infants.

Is surfactant therapy beneficial in the treatment of the term newborn infant with congenital diaphragmatic hernia?

OBJECTIVES

To determine the impact of surfactant replacement on survival, need for extracorporeal membrane oxygenation (ECMO), and chronic lung disease in term infants with prenatally diagnosed congenital diaphragmatic hernia (CDH).

STUDY DESIGN

Prenatally diagnosed infants born at > or =37 weeks' gestation with immediate distress at delivery and no other major congenital anomalies, who were enrolled in the CDH Registry, were analyzed. For univariate analysis, chi 2 tests were used for categoric variables and unpaired t tests for nominal variables. Multiple logistic regression was used to calculate adjusted odds ratios.

RESULTS

Eligible infants (n = 522) were identified. Demographic variables were similar between the surfactant-treated (n = 192) and nonsurfactant-treated (n = 330) groups, with the exception of race (white, 88.0% vs 71.2%; P =.0007). The use of ECMO and incidence of chronic lung disease were higher (59.8 vs 50.6, P =.04; 59.9 vs 47.6, P =.0066) and survival lower in the surfactant-treated cohort (57.3 vs 70.0, P =.0033). Adjusted logistic regression for use of ECMO, survival, and chronic lung disease resulted in odds ratios inconsistent with an improved outcome associated with surfactant use.

CONCLUSIONS

This analysis shows no benefit associated with surfactant therapy for term infants with a prenatal diagnosis of isolated CDH.

Impact of a current treatment protocol on outcome of high-risk congenital diaphragmatic hernia

BACKGROUND

There is considerable debate regarding the optimal management of congenital diaphragmatic hernia (CDH) in high-risk infants (those cases presenting with respiratory distress within 2 hours of birth or those diagnosed prenatally). The aim of this study was to analyze patient outcomes using a new treatment protocol for CDH in a tertiary care non-extracorporeal membrane oxygenation (ECMO) neonatal unit.

METHODS

The records of 78 consecutive neonates with CDH presenting to Bambino Gesù Children's Hospital from 1996 to 2001 were analyzed retrospectively. Of these infants, 70 high-risk patients were identified (prenatal diagnosis or respiratory distress requiring intubation and assisted ventilation within 2 hours after birth), regardless of associated anomalies, medical condition on presentation, or degree of pulmonary hypoplasia. A prenatal diagnosis was made in 46 of 70 (66%) patients. Associated lethal malformations were present in 6 of the children (8.5%). The patients were placed in 3 historical groups: group 1, 19 patients from 1996 to 1997, group 2, 22 patients from 1998 to 1999, and group 3, 29 patients from 2000 to 2001. In the first 2 groups, a new protocol was introduced using inhaled nitric oxide (iNO) and high-frequency oxygen ventilation (HFOV). In the third group, gentle ventilation and permissive hypercarbia were also used routinely. Mortality and severe morbidity--defined as O2 requirement at discharge, need for a tracheostomy, neurologic impairment, or bilateral hearing loss-were evaluated when the patients were at 6 months old. Univariate analysis was performed.

RESULTS

The 3 groups were comparable with respect to predictive risk factors such as side of hernia, prenatal diagnosis, polyhydramnios, stomach and liver in the thorax, associated lethal malformations, and patch. Overall survival rate significantly increased from 47% (9 of 19) in group 1 and 50% (11 of 22) in group 2 to 90% (26 of 29) in group 3 (P =.02). None of the 19 patients in group 1 had severe morbidity compared with 2 of 22 (9%) patients in group 2 and 2 of 29 (7%) patients in group 3. Hearing loss was observed in 4 patients. Mortality rate and preoperative pneumothorax significantly decreased in group 3 compared with groups 1 and 2 (P =.03 and P =.00, respectively).

CONCLUSIONS

(1) The application of new treatment protocol for CDH, using gentle ventilation and permissive hypercarbia, produced a significant increase in survival with concomitant decrease in morbidity. (2) The rate of pneumothorax was significantly decreased by the introduction of permissive hypercarbia and gentle ventilation. (3) As more infants survive CDH without the use of ECMO, severe long-term sequelae of CDH can be recognized in these children.