The effects of intrapleural pressure on respiratory insufficiency

Vitamin A deficiency (VAD), teratogenic, and surgical models of congenital diaphragmatic hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a congenital malformation that occurs with a frequency of 0.08 to 0.45 per 1,000 births. Children with CDH are born with the abdominal contents herniated through the diaphragm and exhibit an associated pulmonary hypoplasia which is frequently accompanied by severe morbidity and mortality. Although the etiology of CDH is largely unknown, considerable progress has been made in understanding its molecular mechanisms through the usage of genetic, teratogenic, and surgical models. The following review focuses on the teratogenic and surgical models of CDH and the possible molecular mechanisms of nitrofen (a diphenyl ether, formerly used as an herbicide) in both induction of CDH and pulmonary hypoplasia. In addition, the mechanisms of other compounds including several anti-inflammatory agents that have been linked to CDH will be discussed. Furthermore, this review will also explore the importance of vitamin A in lung and diaphragm development and the possible mechanisms of teratogen interference in vitamin A homeostasis. Continued exploration of these models will bring forth a clearer understanding of CDH and its molecular underpinnings, which will ultimately facilitate development of therapeutic strategies.

Extravascular lung water after pneumonectomy and one-lung ventilation in sheep

OBJECTIVE

To compare the single thermodilution and the thermal-dye dilution techniques with postmortem gravimetry for assessment of changes in extravascular lung water after pneumonectomy and to explore the evolution of edema after injurious ventilation of the left lung.

DESIGN

Experimental study.

SETTING

University laboratory.

SUBJECTS

A total of 30 sheep weighing 35.6 +/- 4.6 kg. The study included two parts: a pneumonectomy study (n = 18) and an injurious ventilation study (n = 12).

METHODS

Sheep were anesthetized and mechanically ventilated with an FiO2 of 0.5, tidal volume of 6 mL/kg, and positive end-expiratory pressure of 2 cm H2O. In the pneumonectomy study, sheep were assigned to right-sided pneumonectomy (n = 7), left-sided pneumonectomy (n = 7), or lateral thoracotomy only (sham operation, n = 4). In the injurious ventilation study, right-sided pneumonectomy was followed by ventilation with a tidal volume of 12 mL/kg and positive end-expiratory pressure of 0 cm H2O (n = 6) or by ventilation with a tidal volume of 6 mL/kg and positive end-expiratory pressure of 2 cm H2O for 4 hrs (n = 6). Volumetric variables, including extravascular lung water index (EVLWI), were measured with single thermodilution (STD; EVLWI(STD)) and thermal-dye dilution (TDD; EVLWI(TDD)) techniques. We monitored pulmonary hemodynamics and respiratory variables. After the sheep were killed, EVLWI was determined for each lung by gravimetry (EVLWI(G)).

RESULTS

In total, the study yielded strong correlations of EVLWI(STD) and EVLWI(TDD) with EVLWI(G) (n = 30; r = .83 and .94, respectively; p < .0001). After pneumonectomy, both the left- and the right-sided pneumonectomy groups displayed significant decreases in EVLWI(STD) and EVLWI(TDD). The injuriously ventilated sheep demonstrated significant increases in EVLWI that were detected by both techniques. The mean biases (+/-2 SD) compared with EVLWI(G) were 3.0 +/- 2.6 mL/kg for EVLWI(STD) and 0.4 +/- 1.6 mL/kg for EVLWI(TDD).

CONCLUSIONS

After pneumonectomy and injurious ventilation of the left lung, TDD and STD displayed changes in extravascular lung water with acceptable accuracy when compared with postmortem gravimetry. Ventilator-induced lung injury seems to be a crucial mechanism of pulmonary edema after pneumonectomy.

Idiopathic postpneumonectomy pulmonary edema: Hyperinflation of the remaining lung is a potential etiologic factor, but the condition can be averted by balanced pleural drainage

OBJECTIVES

Idiopathic postpneumonectomy pulmonary edema is a leading cause of mortality after pneumonectomy. Postoperative hyperinflation of the remaining lung is an etiologic factor. We have demonstrated avoidance of postpneumonectomy pulmonary edema solely by changing management of the pneumonectomy space to a balanced drainage system. In sheep, we tested the following hypothesis: (1) Postoperative induced hyperinflation of the remaining lung can cause postpneumonectomy pulmonary edema. (2) A balanced drainage system can prevent its development.

METHODS

We performed 37 right-sided pneumonectomies in adult sheep. In experiment 1, after surgery, 10 sheep had continuous suction (5 kPa) applied through an intercostal catheter placed in the empty hemithorax to induce mediastinal shift and hyperinflation of the left lung without adverse hemodynamic sequelae. In experiment 2, 27 sheep were randomly allocated into 3 equal groups regarding management of the residual empty right hemithorax: balanced drainage, no intercostal drainage, and clamp-release intercostal underwater drainage. A fourth group of 9 sheep served as a sham controls placebo with the same anesthetic and a right thoracotomy.

RESULTS

All sheep tolerated surgery without adverse event. In experiment 1, there was significant mediastinal shift at necropsy in all sheep and 60% (n = 6) had postpneumonectomy pulmonary edema develop in the left lung (P = .023 vs sham). In experiment 2, incidences of postpneumonectomy pulmonary edema were as follows: 0 in balanced group (P = .057 vs other groups), 3 (30%) in no-drainage group, and 3 (30%) in clamp-release group. Only the 12 sheep with postpneumonectomy pulmonary edema had respiratory distress; the rest had uneventful recoveries.

CONCLUSION

In a sheep model of postpneumonectomy pulmonary edema, hyperinflation from mediastinal shift is an etiologic factor. A balanced drainage system averts postpneumonectomy pulmonary edema. This is the first time such a causal relationship has been demonstrated, supporting our continued use of balanced drainage after pneumonectomy.

Acute lung injury and acute respiratory distress syndrome after pulmonary resection

The occurrence of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) after thoracic surgery are perplexing and persistent problems. Variously described as postpneumonectomy pulmonary edema, noncardiogenic pulmonary edema, and postlung resection pulmonary edema, ALI and ARDS may be considered a single entity, with ALI being the less severe form of ARDS. It is characterized by the acute onset of hypoxemia with radiographic infiltrates consistent with pulmonary edema, without elevations in the pulmonary capillary wedge pressure. Although this syndrome does not occur frequently and is usually without identifiable cause, the mortality is high. However, the phenomenon has not been rigorously studied owing to the low incidence, with primarily retrospective case series reported. Thus, the nomenclature, risks, and pathogenesis are not well defined. Interest in this syndrome has recently been renewed as the rate of other perioperative complications has declined. ALI/ARDS is reviewed with a focus on potential etiologies and the spectrum of available interventions.

Intraoperative solumedrol helps prevent postpneumonectomy pulmonary edema

BACKGROUND

Postpneumonectomy pulmonary edema and pneumonia are life threatening and seemingly unavoidable complications after pneumonectomy. We theorized that an intraoperative dose of intravenous steroids (as a prophylactic measure to reduce pulmonary injury to the remaining lung) just before pulmonary artery ligation might decrease this problem.

METHODS

Seventy-two patients (52 men) who had pneumonectomy during two time periods were studied prospectively. Thirty-five patients received 250 mg of methylprednisolone sodium succinate (Solumedrol; Upjohn, Kalamazoo, MI) just before pulmonary artery ligation (S group) and 37 did not (non-S group). Groups were matched for known or suspected preoperative, intraoperative, and postoperative risk factors for postpneumonectomy pulmonary edema.

RESULTS

The incidence of postpneumonectomy pulmonary edema or adult respiratory distress syndrome was less in the S group (0 of 35, 0% versus 5 of 37, 13.5%, p = 0.049), the overall major complication rate was less in the S group (7 of 35, 20% versus 16 of 37, 43%, p = 0.04), and the length of hospital stay was shorter in the S group (6.1 days versus 11.9 days, p = 0.02). In addition, there were no bronchopleural fistulas in the S group compared with two (both right-sided) in the non-S group.

CONCLUSIONS

The intraoperative intravenous administration of 250 mg of methylprednisolone sodium succinate just before pulmonary artery ligation during pneumonectomy may reduce the incidence of postpneumonectomy pulmonary edema and adult respiratory distress syndrome as well as decrease other major complications and shorten the hospital stay. It does not seem to increase the incidence of bronchopleural fistula. Further randomized trials are needed.

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

BACKGROUND/PURPOSE

Congenital diaphragmatic hernia (CDH) is associated with pulmonary hypoplasia that limits survival. The authors' knowledge on lung mechanics and lung volumes in these patients with hypoplastic lungs is still limited. Therefore, the authors performed measurements of functional residual capacity (FRC), compliance of the respiratory system (CRS), and tidal volume in 5 full-term infants (gestational age, 38 to 40 weeks; birth weight, 2,800 to 3,530 g) before and after surgical repair of neonatal CDH.

METHODS

The authors studied the influence of different levels of positive end-expiratory pressure (PEEP) and suction via inserted ipsilateral chest tube connected to a water seal on lung volume and lung mechanics. A computerized tracer gas (SF6) washout method was used for serial measurements of FRC. Compliance of the respiratory system was determined according to insufflatory method.

RESULTS

The authors found a preoperative compliance between 1.5 and 3.9 mL/kPa/kg and a preoperative FRC between 9.1 and 12.9 mL/kg indicating severe hypoplasia of the lungs in all patients. Immediately after surgical repair of CDH, compliance decreased to 85% (78% to 91%) of preoperative value, and FRC increased to 132% (110% to 150%) of preoperative value under mechanical ventilation while at 4 cm of water of PEEP and at -10 cm of water of suction via chest drain with the need of high fraction of inspired oxygen. After reduction of PEEP from 4 to 2 or 1 cm of water and lowering suction from -10 cm of water to -2 or 0 cm of water FRC decreased to 103% (80% to 122%) of preoperative value and compliance, and tidal volume improved to 135% (110% to 147%) of preoperative value resulting in increased alveolar ventilation, correction of acidosis and improvement in oxygenation. During the first days after surgery inadequate high PEEP or strong suction via chest tube drainage resulted in increase in FRC paralleled by decrease in compliance indicating overdistension of these hypoplastic lungs.

CONCLUSIONS

The data show that overdistension of hypoplastic lungs in infants with CDH can be detected and excluded by repeated measurements of FRC and compliance in these critical ill infants. These data might help setting appropriate ventilator parameters, adequate suction via chest drain, and thereby improve gas exchange and outcome.

Pathophysiology of Postpneumonectomy Pulmonary Edema

Pulmonary edema is a rare, potentially fatal complica tion associated with major resection of the lung, usually pneumonectomy. Although pulmonary edema in this setting can often be attributed to a variety of causes such as cardiac failure, bacterial pneumonia, and fluid overload, the specific syndrome of postpneumonec tomy pulmonary edema (PPE) occurs in the absence of these factors. PPE remains a diagnosis of exclusion, and its pathophysiology is poorly understood. Overzealous perioperative fluid administration has traditionally been implicated in clinical cases of postpneumonectomy pulmonary edema, but there is a body of evidence suggesting several other potential mechanisms. These include increases in cardiac output secondary to cat echolamine release, interruption of mediastinal lym phatic drainage, endothelial injury secondary to release of humoral factors or stretching of intercellular junc tions, hyperinflation, and other unknown factors.

Congenital diaphragmatic hernia: determination of the optimal time for operation by echocardiographic monitoring of the pulmonary arterial pressure

Preoperative stabilization and delayed operation rather than emergency repair of congenital diaphragmatic hernia (CDH) may improve survival, but there are no clear criteria for how long operation should be delayed. Because increased pulmonary vascular resistance (PVR) may be an important risk factor, we used Doppler echocardiography to study patients with CDH presenting with respiratory distress immediately after birth. During the study period 10 patients were admitted, but 2 were moribund on admission and died shortly thereafter. In the remaining patients the pulmonary arterial pressure (PAP) and direction of ductal shunt were estimated by Doppler echocardiography. Initial PAPs were in the range of 45 to 90 mm Hg, with bidirectional or right-to-left shunt through the ductus arteriosus. Reduction of pressure to 25 to 55 mm Hg, or reversal of shunt to left-to-right, reflecting decreased PVR, occurred after ventilation for 3 to 20 days (mean, 8 days). Patients underwent operation after there was evidence of reduced PVR. None developed persistent fetal circulation, and all 8 patients survived. We conclude that postponing operation until PVR has decreased seems to improve survival in patients with CDH presenting within hours of birth.

Indication and results of thoracic surgical procedures in premature infants

This analysis concerns three groups of malformations: Congenital diaphragmatic hernia, patent ductus arteriosus, and oesophageal atresia. We registered a total mortality rate for all congenital diaphragmatic hernias and defects of 28.5%; the rate in full-term neonates was 27.6% and in premature infants 33.6%. Of 65 infants with a patent ductus arteriosus and a birth weight less than 1500 g, 14 died (21.5%). In most cases death was caused by sepsis. Among the 159 patients with oesophageal atresia who were treated in our hospital, 58 were premature infants. During the last 20 years, the total mortality rate among our patients was 28.9%. We had a mortality rate of 44.8% in premature infants and of 19.8% in full-term neonates. An analysis of the last 10 years showed a survival rate of 97% in healthy infants (group A in Waterston's classification). In group C, the most disadvantageous group (premature infants, severe anomalies), the rate was 61%.

Chest size and symmetry in congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia have significantly increased chest circumferences. This implies that intrathoracic volumes are increased as well. Forces produced by the herniated abdominal viscera seem to provide the chief impetus for this change. Other factors may also contribute, for thoracic enlargement is asymmetric and not always ipsilateral to the hernia. The contribution of an enlarged chest to respiratory insufficiency, persistence of the fetal circulation, and hyperinflation is not fully understood, but may have relevance in evaluating new approaches to therapy.

Pulmonary barotrauma in congenital diaphragmatic hernia: experimental study in lambs

A left diaphragmatic hernia was created surgically in 20 fetal lambs between 93 and 110 days of gestation. Ten animals were alive with defects at cesarean section near term (135 to 140 days). These animals and two controls were submitted to various transpulmonary pressure gradients (inspiratory pressure minus pleural pressure). Hemodynamic and ventilatory studies were performed after the correction of the hernia. Morphometric analysis of the lung was carried out in all cases. The results showed a highly significant linear correlation between the transpulmonary pressure gradient employed and the pulmonary interstitial emphysema found at morphometry. Our data suggest that using low ventilatory pressures and not draining the pleural cavity results in less trauma to both lungs and may prevent one of the components of the pulmonary hypertension so often seen in newborns with congenital diaphragmatic hernia.

"Balanced" thoracic drainage is the method of choice to control intrathoracic pressure following repair of diaphragmatic hernia

Respiratory failure from pulmonary hypoplasia continues to be the major cause of death in newborn infants with diaphragmatic hernia. Recent investigations have suggested that postnatally induced pulmonary injury can result from excessive positive or negative intrathoracic pressure and contribute to the respiratory deterioration. Therefore, the method of thoracic drainage on the side of the diaphragmatic hernia is critical in controlling and maintaining normal intrathoracic pressure in both intrathoracic spaces. No chest tube or an ipsilateral chest tube connected to water seal, can result in either excessive negative or positive intrathoracic pressure and, therefore, both methods should be avoided. Recently, we employed a "balanced" intrathoracic drainage system which maintains the ipsilateral intrathoracic pressure within the normal physiologic range of +2 to -8 cm H2O regardless of the degree of pulmonary hypoplasia, presence of an ipsilateral pulmonary air leak, straining by the infant, or mechanical ventilation. This system is simple, requires no suction apparatus, and is easily assembled with equipment readily available within the hospital. This technique has been utilized in 18 newborn infants with diaphragmatic hernia and pulmonary hypoplasia. There have been no complications which specifically could be related to the balanced drainage system.

Reversion to fetal circulation in congenital diaphragmatic hernia: a preventable postoperative complication

A review of 26 patients with congenital diaphragmatic hernia, diagnosed in the first 24 hours of life, supports the hypothesis that the postoperative fetal circulation syndrome is an iatrogenic complication, due to the rapid expansion of both lungs, when they are severely hypoplastic. This complication is preventable, when no aspiration of air from the chest cavity is done, and when no tube attached to an underwater seal is inserted. When assisted ventilation is necessary, small volumes at a rapid rate allows satisfactory gaseous exchanges, without pulmonary overinflation.