Elevated preoperative von Willebrand factor is associated with perioperative thrombosis in infants and neonates with congenital heart disease.

Essentials Perioperative thrombosis is a major cause of morbidity and mortality in congenital heart disease. Neonates and infants undergoing repair of congenital heart lesions were prospectively followed. Elevated von Willebrand factor (VWF) to ADAMTS-13 activity ratios typified the postoperative period. Thrombosis was associated with preoperative VWF activity and cryoprecipitate transfusion SUMMARY: Background The surgical repair of congenital heart malformations is frequently complicated by perioperative thrombosis of unclear etiology. An imbalance between von Willebrand factor (VWF) and ADAMTS-13 is an emerging variable in thrombosis. Objectives To describe perioperative changes to VWF, ADAMTS-13 and NETosis, and evaluate clinical and biochemical associations with postoperative thrombosis. Methods Neonates and infants undergoing palliation or definitive surgical repair of congenital heart malformations were recruited (n = 133). Preoperative and postoperative plasma levels of VWF, ADAMTS-13 and markers of NETosis were determined. Patients were followed for up to 30 days for the occurrence of thrombosis. Univariate and multivariate logistic regression analyses were conducted to identify variables associated with thrombosis. Results We identified significant postoperative increases in VWF activity, VWF level, DNA-histone complexes and cell-free DNA with an overall decrease in ADAMTS-13 activity. Patients experiencing postoperative thrombotic events (9%) were characterized by surgery performed at a lower intraoperative temperature, higher preoperative lactic acid levels, and higher preoperative VWF activity and level. A multivariate logistic regression model identified preoperative VWF activity (odds ratio (OR) 8.39 per IU mL-1 , 95% confidence interval [CI] 1.73-40.55) and transfusion of cryoprecipitate (OR 1.10 per mL kg-1 , 95% CI 1.03-1.17) as being associated with thrombosis. Conclusions Pediatric patients undergoing surgical repair of congenital heart malformations are exposed to high levels of VWF with diminished or minimal change to ADAMTS-13 in the immediate postoperative period. Elevated preoperative VWF activity is associated with postoperative thrombosis in pediatric congenital heart disease.

Implications of hypoxia on mucosal barrier function.

Epithelial cells which line mucosal surfaces (e.g. lung, intestine) critically function as a semi-permeable barrier to the outside world. Mucosal organs are highly vascular with extensive metabolic demands, and for this reason, are particularly susceptible to diminished blood flow and resultant tissue hypoxia. Recent work from a number of groups have defined the critical molecular and cellular determinants of barrier function in hypoxic/ischemic tissues. Here, we will briefly highlight some of these studies from both a basic and clinical viewpoint and provide a perspective on future work related to tigh tjunction function in mucosal hypoxia.

Lung growth after reduced size transplantation in a sheep model.

BACKGROUND: The growth of mature allografts is a critical issue in pediatric lung transplantation. This study explores the architectural changes of mature sheep lung when submitted to two different compensatory growth forces: either transplantation into a neonatal host or expansion in an otherwise empty adult hemithorax. METHODS: Right upper lobes (RUL) (mean+/-SEM, 66.7+/-1.9 kg) from 4- to 5-year old (adult sheep) were transplanted into newborn (n=6) lambs (5.4+/-0.3 kg, 5+/-2 days old) that were then allowed to survive for 45 days. Changes in pulmonary volume and architecture were measured before and after transplantation. Allografts were compared with both normal adult RUL (n=10) and adult (65.8+/-2.2 kg and 4 to 5 year old) RUL that remained in situ for 45 days after resection of the corresponding middle and lower lobes (n=6). Statistical differences were analyzed using two-sample and paired t tests. RESULTS: In adult animals, RUL remaining in the otherwise empty hemithorax compensated by an 85% increase in volume (251.5+/-18.7 ml vs. 466+/-32.8 ml) (P<0.0001). Concomitant increases in total internal alveolar surface area (48%) and alveolar size were prominent. The number of alveoli per volume decreased proportionately to the increases in volume (P<0.0001). There was no significant change in the calculated number of alveoli (345.6+/-40.5 x 10(6)) compared with the normal adult RUL (402.4+/-40.7x10(6)) (P=0.37). Transplant recipients received a reduced-size normal adult RUL (49%) in volume (125.3+/-21.5 ml). Allografts 45 days after transplantation showed a 73% increase in volume (216.4+/-21.3 ml) (P<0.0001) with a parallel (83%) increase in total internal alveolar surface area (P=0.008). The number of alveoli per volume remained constant (P=0.21) despite the increase in volume. There was therefore a significant increase in the calculated number of alveoli from before transplantation (172.5+/-35.9x 106) compared with that observed 45 days after transplantation (389.7+/-77.7x10(6)) (P=0.012). CONCLUSIONS: We conclude that mature sheep RUL parenchyma compensates with dilation of the respiratory structures in the adult animal, whereas there is alveolar multiplication when transplanted into newborn recipients.

The use of expandable metallic stents for acute tracheal stenosis in the growing lamb.

PURPOSE: Expandable metallic stents (Palmaz stents) have been used in the treatment of tracheobronchial obstruction in children and adults. The authors investigated their utility in the management of acute airway stenosis in a growing animal model. METHODS: A model for tracheal stenosis was developed in young lambs (mean age, 4 weeks; mean weight, 8.6 kg). Via an anterior tracheotomy, a circumferential mucosal injury to the trachea was produced with electrocautery in 31 lambs. In the control group (n = 10) no further intervention was used. In the treatment groups, either serial balloon dilatation of the stricture was performed (n = 6), or expandable metallic stents were inserted across the stricture (n = 15). All animals were monitored daily for signs of respiratory distress. Body weights, fluoroscopic airway measurements and rigid bronchoscopy were performed at least weekly. RESULTS: The average weekly rate of airway growth was 8.2% +/- 5.5% of the tracheal cross-sectional area (CSA). All animals displayed severe stenosis (mean, 90.2% +/- 7.5% of CSA) within 13.1 +/- 4 days after the injury. All animals in the control group had severe respiratory distress, weight loss and died within 14.6 +/- 2.8 days after injury. Serial balloon dilatation of the stricture alone failed to relieve symptoms in all six animals in this group, who died within 20 +/- 1 days after the injury, despite two to three dilatations each. With placement of expandable metallic stents, only 3 of 15 lambs died (two of pneumonia, one of iatrogenic perforation). The remaining 12 remained symptom-free and gained weight during a 2-month follow-up period. However, fluoroscopic examination showed partial collapse of the stents in all of these animals (mean, 44.7% +/- 21.6% of CSA) requiring an average of 2 +/- 0.7 bronchoscopic dilatations. Pathological evaluation showed more pronounced granulation tissue in the stented animals. CONCLUSIONS: The authors conclude that expandable metallic stents provide an effective tool in the management of acute tracheal stenosis. However, airway growth, tissue reaction, and the mechanical properties of the stent require close monitoring and stent adjustment.

Insulin-like growth factor-I gene expression in three models of accelerated lung growth.

BACKGROUND/PURPOSE: We have learned previously that in utero tracheal ligation reverses the structural and physiological effects of surgically created congenital diaphragmatic hernia. In addition, we have discovered that postnatal lung growth similarly can be accelerated using liquid-based airway distension with perfluorocarbon. Another model of accelerated lung growth is that of compensatory growth seen after neonatal pneumonectomy. In all of these models, growth has occurred because of an increase in alveolar number rather than enlargement of preexisting alveoli. However, the molecular mechanisms underlying these processes remain unknown. The purpose of this study was to determine if gene expression could be altered by changes in physical forces in the prenatal and postnatal lung. METHODS: The three models of accelerated lung growth studied were the following: (1) The prenatal group, consisted of fetal lambs (n = 12) that underwent the surgical creation of a left diaphragmatic hernia at 90 days' gestation. Six of these animals also underwent simultaneous tracheal ligation. (2) The PFC group consisted of five neonatal animals that underwent isolation of the superior segment of the right upper lobe, with intrabronchial distension with perfluorocarbon to 7 to 10 mm Hg pressure for a 3-week period. (3) The postpneumonectomy group consisted of four neonatal animals that underwent left pneumonectomy. In the fetal study, lungs were retrieved at term (130 days), and in the postnatal study, lungs were retrieved 3 weeks after initial intervention. In all cases, RNA was extracted from snap-frozen lung samples and Northern blot analysis performed. RESULTS: Insulinlike growth factor-I, insulinlike growth factor-II, and vascular endothelial growth factor gene expression were analyzed by densitometry. Insulinlike growth factor-I gene expression was found to be decreased in association with experimental diaphragmatic hernia (P = .005), but restored to normal with tracheal ligation. Insulinlike growth factor-I gene expression was significantly increased in both postnatal models of accelerated lung growth (P = .022, P = .016). No significant differences were found in insulinlike growth factor-II or vascular endothelial growth factor gene expression. CONCLUSIONS: The authors conclude from these preliminary data that (1) insulin like growth factor-I gene expression is reduced in experimental fetal diaphragmatic hernia and restored to normal by tracheal ligation, and (2) insulinlike growth factor-I gene expression is increased in both the liquid-based airway distension and postpneumonectomy models of accelerated postnatal lung growth. The authors speculate that all of these manipulations exploit a natural pathway essential for normal lung growth.

Pulmonary blood flow distribution during partial liquid ventilation.

Regional pulmonary blood flow was investigated with radiolabeled microspheres in four supine lambs during the transition from conventional mechanical ventilation (CMV) to partial liquid ventilation (PLV) and with incremental dosing of perfluorocarbon liquid to a cumulative dose of 30 ml/kg. Four lambs supported with CMV served as controls. Formalin-fixed, air-dried lungs were sectioned according to a grid; activity was quantitated with a multichannel scintillation counter, corrected for weight, and normalized to mean flow. During CMV, flow in apical and hilar regions favored dependent lung (P < 0.001), with no gradient across transverse planes from apex to diaphragm. During PLV the gradient within transverse planes found during CMV reversed, most notably in the hilar region, favoring nondependent lung (P = 0.03). Also during PLV, flow was profoundly reduced near the diaphragm (P < 0.001), and across transverse planes from apex to diaphragm a dose-augmented flow gradient developed favoring apical lung (P < 0.01). We conclude that regional flow patterns during PLV partially reverse those noted during CMV and vary dramatically within the lung from apex to diaphragm.

Effects of nitric oxide on hyperinflation-induced pulmonary hypertension in the isolated-perfused lung.

OBJECTIVE: To determine if nitric oxide decreases pulmonary vascular resistance in hyperinflation-induced pulmonary hypertension. DESIGN: Isolated-perfused lamb lung model. SETTING: Experimental animal laboratory in a university setting. SUBJECTS: Ten isolated-perfused lamb lungs harvested from subjects with a mean age of 29 days. INTERVENTIONS: After induction of anesthesia, endotracheal intubation, and mechanical ventilation, lungs were perfused via an extracorporeal circuit. Ventilatory pressures were set to provide tidal volumes of 10 mL/kg and ventilatory rates were adjusted to maintain a Paco2 of 40 +/- 5 torr (3.5 +/- 0.7 kPa). The perfusion system consisted of a blood reservoir, a membrane oxygenator, and a nonocclusive roller pump. Blood flow was increased progressively to 50 mL/kg/min, maintaining a pulmonary arterial pressure of < 25 mm Hg and a left atrial pressure between 2 and 5 mm Hg. End-expiratory lung volume was measured using a nitrogen washout method. Baseline data were collected after a 1-hr stabilization period. Lung volume was increased to achieve 25% (moderate hyperinflation) and 50% (severe hyperinflation) increments in pulmonary vascular resistance. Nitric oxide (80 parts per million) was administered to the preparation after each increment in lung volume. MEASUREMENTS AND MAIN RESULTS: Mean pulmonary arterial pressure, mean left atrial pressure, pulmonary vascular resistance, and static lung compliance were measured at baseline and after moderate and severe hyperinflation, both before and after nitric oxide administration. Significant decreases in pulmonary vascular resistance were found when the preparation was ventilated with nitric oxide at baseline (43% decrease) and during hyperinflation induced pulmonary hypertension at both moderate (31% decrease) and severe (23% decrease) levels of hyperinflation. CONCLUSIONS: Inhaled nitric oxide significantly reduces pulmonary vascular resistance, even when pulmonary hypertension is induced by airway hyperinflation and supraphysiologic lung volumes. These data suggest that the use of nitric oxide following lung transplantation may allow for effective management of pulmonary hypertension in patients who receive allografts from undersized donors. Further clinical experience will be crucial in precisely defining the range of donor-recipient size mismatch that can be adequately managed and the time course over which nitric oxide can be administered safely and effectively to these patients.

University of Wisconsin cerebroplegia in a piglet survival model of circulatory arrest.

BACKGROUND: Previous acute studies in immature piglets at our institution have demonstrated improved recovery of cerebral blood flow, intracellular pH, and high-energy phosphates with the administration of multidose University of Wisconsin solution as cerebroplegia during a period of deep hypothermic circulatory arrest (HCA). In an effort to define further the clinical applicability of this technique, we have developed a survival model of swine cardiopulmonary bypass (CPB) and HCA. METHODS: 12 Yorkshire pigs (age 4 to 5 weeks) were placed on CPB via the right femoral artery and right atrium. Animals were cooled to a rectal temperature of 15 degrees C and submitted to 90 minutes of HCA. Group UW (n = 6) received a single infusion of 50 mL/kg of 4 degrees C University of Wisconsin solution delivered antegrade to the cerebral circulation. The control group (n = 6) received no intervention. Animals were reperfused, rewarmed to 35 degrees C, and weaned from CPB. Neurologic assessments using neurologic deficit scoring (0 = normal, 500 = brain death) and overall performance categories (1 = normal, 5 = brain death) were performed at 24-hour intervals for 5 days. On the 5th postoperative day all brains were perfusion-fixed and examined for histologic evidence of neuronal injury (0 = normal, 5 = severe injury). RESULTS: All animals were extubated 18 to 20 hours postoperatively. There was no significant difference between the mean neurologic score of the two groups. The mean day 5 neurologic deficit score was 108 for the UW group and 68 for the control group (p > 0.05). The day 5 overall performance category was 2.8 for the UW group and 2.0 for the control group (p > 0.05). Three of the UW animals but none of the control animals experienced generalized seizures. Histologic examination revealed more severe damage in UW animals, primarily in the cerebral cortex. Injury was more widespread in UW animals, involving cerebellum and hippocampus. The mean histologic injury score was 3.8 for UW animals and 2.4 for the control group (p = 0.06). CONCLUSIONS: A clinically relevant survival model of CPB with HCA in immature swine is feasible. Cold UW solution as single-dose cerebroplegia is not beneficial, and may be injurious to the immature swine brain subjected to CPB and HCA. Further studies are indicated to determine optimal composition and administration of cerebroplegic solutions.