Surfactant therapy in infants and children: three years experience in a pediatric intensive care unit

Despite the established success of surfactant application in neonates, the use of surfactant in older children is still a matter of discussion. We hypothesized that surfactant application in children with acute respiratory distress syndrome (ARDS) secondary to a pulmonary or systemic disease or after cardiac surgery improves pulmonary function. We also asked whether repeated treatment could further improve pulmonary function. To answer these questions, we measured oxygenation index (OI) and hypoxemia score after the first and after a second application of surfactant (50-100 mg/kg body wt) at least 24 h later. We enrolled 19 children (older than 4 weeks) for a retrospective chart review study, and six of them underwent cardiac surgery. Demographic data were extracted. OI and hypoxemia score were estimated before and 2 and 24 h after surfactant application. Lung injury score was calculated before and 24 h after surfactant application. Outcome measures included survival, duration of mechanical ventilation, and pediatric ICU and hospital stay. The median patient age was 9.0 (quarter percentile 3.7/25) months. The median weight was 8.4 (4.1/11.5) kg. The median lung injury score before the first surfactant application was 2.3 (2.3/2.6). Hospital duration and pediatric ICU stay for all patients was 31.0 (20.0/49.5) days and 27.0 (15.5/32.5) days, respectively. The duration of mechanical ventilation was 24.0 (18.5/31.0) days. The overall mortality was 53%. Twenty-four hours after the first surfactant application, pulmonary function significantly improved. The median OI was 14 (5.5/26) before and 7 (4.5/14.5) 24 h after surfactant application (P= 0.027). The hypoxemia score was 91.7 (69.9/154.2) before and 148.4 (99.2/167.6) 24 h after surfactant application (P = 0.0026). Seven children received a second application, which did not further improve pulmonary function. The lung injury score was not influenced by either surfactant application. We conclude that a single surfactant application improves pulmonary function in children with ARDS. A second application of surfactant showed no further benefit. Outcome was not affected in our study population.

Cold water submersion and cardiac arrest in treatment of severe hypothermia with cardiopulmonary bypass

In the paediatric population, submersion injury with drowning or near-drowning represents a significant cause of morbidity and mortality. This study reviews retrospectively our own experiences and the literature on the use of cardiopulmonary bypass (CPB) to rewarm paediatric victims of cold water submersion who suffer severe hypothermia (<28 degrees C) and cardiac arrest (asystole or ventricular fibrillation). In addition to three children treated at our institution, nine other victims were found in the literature. In this cohort of 12 children aged between 2 and 12 years, there was a tendency to better outcome with lower core temperature at the beginning of extracorporeal circulation (mean temperature in nine survivors, 20 degrees C; in three non-survivors, 25.5 degrees C). The lowest temperature survived was 16 degrees C. Neither base excess, pH nor serum potassium levels were reliable prognostic factors. The lowest base excess in a survivor was -36.5 mmol/l, the lowest pH 6.29. We consider CPB as the method of choice for resuscitation and rewarming of children with severe accidental hypothermia and cardiac arrest (asystole or ventricular fibrillation). Compared with adults, children, especially smaller ones, require special consideration with regard to intravenous cannulation as drainage can be inadequate using femoral-femoral cannulation. In hypothermic children we advocate, therefore, emergency median sternotomy. Until more information regarding prognostic factors are available, children who are severely hypothermic and clinically dead after submersion in cold water--even if for an unknown length of time--should receive cardiopulmonary resuscitation (CPR) and be transported without delay to a facility with capabilities for CPB instituted via a median sternotomy.

Neonatal and pediatric extracorporeal membrane oxygenation using nonocclusive blood pumps: the Vienna experience

Neonatal and pediatric extracorporeal membrane oxygenation (ECMO) is carried out commonly using occlusive blood pumps. Centrifugal pumps provide simple and safe technology for transportation on ECMO. The assistence respiratoire extra corporelle (AREC) system enables single needle venovenous ECMO for infants. We report on our experience with neonatal and pediatric ECMO treatments using nonocclusive blood pumps. One-hundred forty-six ECMO treatments were performed for cardiac, neonatal, and pediatric indications in 54, 19, and 27% of cases. Centrifugal pumps were used in 99, and the AREC system in 42 cases. Hospital mortality was estimated retrospectively and influence of type of pump, type of ECMO belonging to indication group, and lactate at ECMO installation were estimated. Irreversible organ failure leading to ECMO termination was investigated within groups of indications. Survival (recent 50 ECMO treatments) was 80, 70, 43, and 30% after meconium aspiration syndrome, acute respiratory distress syndrome, cardiac surgery, and prolonged resuscitation. Lactate exceeding 100 mg/dl at ECMO installation predicted significantly worse outcome. Cerebral damage was the main reason for ECMO termination in all but persistent circulatory failure in the cardiac group. Myocardial recovery resulted in all except 2 cardiac cases. Nonocclusive blood pumps can be used safely in neonatal and pediatric ECMO. Early installation may improve outcome markedly. In cardiac cases results of surgery should be thoroughly investigated on the table before ECMO installation to prevent hopeless ECMO treatments.

Life threatening cardiopulmonary failure in an infant following protamine reversal of heparin after cardiopulmonary bypass

Life threatening cardiopulmonary failure following protamine reversal of heparin after cardiopulmonary bypass (CPB) was reported to occur in adults but rarely in children. Atrial septal defect closure was performed in a 6-week-old infant erroneously suspected to suffer from right atrial thrombosis in addition. Protamine administration after CPB led to critical pulmonary hypertension and severe haemorrhagic pulmonary oedema resulting in severe hypoxia. Inhaled nitric oxide, together with high frequency oscillation ventilation supplemented by intravenous prostacycline, enabled complete recovery of cardiopulmonary and neurological function. Life threatening cardiovascular compromise after intravenous protamine can occur even in young infants which then require challenging paediatric critical care.

Severe respiratory failure following charcoal application in a toddler

Charcoal has been commonly used for enteral detoxication with few adverse effects. In toddlers charcoal can often be simply applied via a gastric tube. Regurgitation and aspiration is considered a rare event. We report the case of a 19-month-old boy who suffered endobronchial charcoal contamination followed by acute airway obstruction and severe respiratory failure despite a commonly used tube placement verification technique. Immediate intubation, tracheal suctioning, intravenous bronchodilators, and high frequency oscillatory ventilation (HFOV) were used to control hypercarbia and hypoxia. Eventually charcoal removal by bronchoscopy was successful. Chest X-ray investigation did not reflect the true amount of charcoal deposited endobronchially at any time. We conclude that gastric tube application of charcoal in children carries a risk of aspiration. This may lead to life-threatening respiratory failure with the need to provide artificial ventilation and bronchial lavage.

A pulsatile pneumatically driven neonatal extracorporeal membrane oxygenation system using neck vessel cannulas tested with neonatal mock circulation

In posthypoxic circulatory failure, pulsatility of flow generated by mechanical support devices significantly influences outcome. Pneumatically driven assist devices can create highly pulsatile flow, but need large graft cannulas implanted by thoracotomy in children and neonates. Emergency application is therefore hindered. We conducted an in vitro study using neonatal mock circulation (NMC) to test whether an extracorporeal membrane oxygenation (ECMO) system driven by a commercially available pneumatic assist device also can be operated through commonly used neonatal neck vessel cannulas. Using the pneumatically operated Medos ventricular assist device (VAD) 10 ml ventricle along with the Jostra M8/HEC40 oxygenator/heat exchanger, a neonatal ECMO system was assembled and connected to the NMC by means of commercially available neonatal neck vessel cannulas. Effective ECMO flow, combined circulation flow, and circulation pressures were measured during various working settings (ventricle driving pressures [systolic/diastolic (mbar)]: low: +100/-25, moderate: +200/-50, high: +300/-99) and loading conditions (device working against 0, 50, and 100% native circulation flow). Additionally, maximum possible ECMO flow through various sizes of neonatal ECMO cannulas and resulting pressure gradients were assessed. High pressure settings were necessary to achieve 100 ml/kg/min pulsatile circulation flow in case of zero native circulation. With residual 30% native circulation flow, 100 ml/kg/min pulsatile circulation flow could be established by moderate pressure settings. Low preload or high systemic vascular resistance reduced ECMO flow markedly. We concluded that in the described setting a pneumatically driven neonatal ECMO system could be operated even through commonly used neonatal neck vessel cannulas. It was necessary to accept partial emptying of the artificial ventricle and tapering of driving pressures with increasing native circulation.

Traumatic pharyngo-oesophageal perforation in the newborn: a condition mimicking oesophageal atresia

Two newborn infants with traumatic perforation of the pharyngo-oesophageal region are presented. This injury was induced by pharyngeal suction catheters and/or vigorous attempts at nasogastric or tracheal intubation during resuscitation of the newborn. The true nature of this condition remained unrecognized and the babies were thus referred with a tentative diagnosis of oesophageal atresia. The perforation itself could be treated successfully without surgery, despite a severe complication in one infant resulting from inadvertent use of barium sulphate contrast medium. Raising awareness of the possibility of this injury should help in avoiding this complication by gentle and skilful action during newborn resuscitation, particularly in the premature infant.

Permissive hypoxemia permitted postoperative weaning from artificial ventilation after repair of pulmonary atresia

Survival after corrective surgery of pulmonary atresia was associated with low right ventricular pressure, indicating normal pulmonary vascular resistance. Therefore increased fractional inspiratory oxygen concentration, inhaled nitric oxide and intravenous prostacyclin were considered to be effective measures during postoperative intensive care. In a 20-year-old female, conduit repair and unifocalisation of pulmonary atresia with ventricular septal defect and systemic to pulmonary arterial collaterals were performed despite preexisting one-sided pulmonary hypertension. During the following postoperative period, normal arterial oxygen saturation aimed at by means of a high fractional inspiratory oxygen concentration, resulted in persistent pulmonary oedema despite fluid restriction. After several trials of weaning from artificial ventilation, permissive hypoxemia was eventually successful.

[Partial left ventriculectomy (Batista-procedure) as an alternative to transplantation and as a rescue procedure]

Partial left ventriculectomy (Batista operation) is one of several surgical options for the treatment of end-stage heart disease. In a 17-year-old patient who could not be accepted as a candidate for heart transplantation, this procedure was performed as an acute rescue procedure in conjunction with reduction of the left ventricle, single-stitch reconstruction of the mitral valve and removal of a ventricular thrombus. Following temporary dependence on mechanical circulatory support the patient was transferred to his own country. The clinical experience is discussed, including aspects of the surgical technique, postoperative complications, indication, relevance of mitral reconstruction and rhythm problems. It is concluded that partial left ventriculectomy can be used to treat end-stage dilated cardiomyopathy, even as an emergency operation. Further studies and experience are needed to clarify the long-term effects and clinical limitations of the procedure.

Intravenous prostacyclin mitigates inhaled nitric oxide rebound effect: A case control study

Although extracorporeal membrane oxygenation (ECMO) improves oxygenation, pulmonary vascular resistance may be increased due to endothelial function impairment. Inhaled nitric oxide (iNO) is increasingly used for treatment of pulmonary hypertension after surgical repair of congenital heart defects, with or without ECMO. One of the main complications of its application is deterioration of oxygenation following withdrawal of iNO. To test whether intravenous prostacyclin applied prior to and during iNO withdrawal can mitigate this rebound effect, we conducted a retrospective case control study. The rebound effect was defined as a 5% decrease of oxygenation saturation within 4 h after iNO withdrawal. Twelve children suffering from pulmonary hypertension (2 after ECMO) and treated with iNO received 10 ng/kg/min prostacyclin intravenously 24 h prior to iNO withdrawal (Group 1). Twelve children treated with iNO (3 after ECMO) who received no prostacyclin prior to iNO withdrawal were matched as controls. The rebound effect occurred in 1 out of 12 children in Group 1 and in 8 out of 12 children in Group 2 (p = 0. 0039). We conclude that application of intravenous prostacyclin prior to and during iNO withdrawal may be able to mitigate the rebound effect.

Proposed entry criteria for postoperative cardiac extracorporeal membrane oxygenation after pediatric open heart surgery

While extracorporeal membrane oxygenation (ECMO) is being used increasingly after pediatric cardiac surgery, criteria are lacking for initiating ECMO after bypass weaning. To develop clinically useful ECMO entry criteria based on parameters readily available, children were examined at postoperative pediatric intensive care unit (PICU) admission. Using hospital mortality as the primary outcome, univariate and multiple logistic regressions were performed to estimate the predictive value of clinical (age, weight, and diagnosis) and laboratory (arterial blood pressure, pH, lactate, creatine kinase, and arterial and central venous oxygen saturation [ScvO2]) variables. Data from 218 children over a 2 year period were analyzed retrospectively. Univariate regression demonstrated that age, weight, diagnosis, blood pressure, venous and arterial saturation, and lactate were significantly associated with postoperative mortality (p < 0.05). In multiple regression, ScvO2 and lactate level were found to be independent predictors and were used in a predictive model (ScvO2 odds ratio: 2.03-828.6, p = 0.016) (lactate odds ratio: 1.58 -4.20, p = 0.0002) (R2 = 0.70). Applying an 80% risk of mortality to establish entry criteria as in neonatal ECMO, PICU admission values of lactate > 70 mg/dl if ScvO2 < 60% or lactate >163 mg/dl if ScvO2 > 60% are proposed to serve as postoperative ECMO entry criteria if bypass weaning has been possible but is followed by low cardiac output.

Early detection of neurologic injury and issues of rehabilitation after pediatric cardiac extracorporeal membrane oxygenation

Neurological impairment results in a significant population of children after extracorporeal membrane oxygenation (ECMO) for treatment of otherwise intractable circulatory failure. Pre-ECMO hypoxia/ischemia, reperfusion injury, and impaired cerebral perfusion during low output situations possibly aggravated by harmful effects of a pulsatile perfusion are discussed in terms of possible etiological reasons. To develop preventive strategies or to enable curative measure, early detection of neuronal injury seems mandatory. Electroencephalographic surveillance and/or monitoring of evoked potentials and monitoring of cerebral oxygenation by means of near infrared spectroscopy or jugular venous bulb oxygen saturation, as well as measurements of serum neuron specific enolase, S-100 protein, and brain type creatine kinase can be employed clinically. To improve functional outcome following neuronal injury, early rehabilitation seems essential to minimize the resulting effects on physical, cognitive, and emotional development.

Aortopulmonary collateral artery embolization during postoperative extracorporeal membrane oxygenation after arterial switch procedure

Aortopulmonary collateral arteries sometimes complicate cyanotic congenital heart defects. Combined with a relevant left-right shunt, this could result in massive airway bleeding during and after corrective surgery. A preoperatively diagnosed 1.2 mm small aortopulmonary collateral artery in a newborn suffering from transposition of the great arteries caused life-threatening airway bleeding during surgery. Postoperative extracorporeal membrane oxygenation (ECMO) was necessary, and coil embolization was performed on ECMO to terminate pulmonary bleeding.

Surgical aspects of pediatric cardiac extracorporeal membrane oxygenation

Because children with severe myocardial dysfunction have limited therapeutic options, mechanical support of a failing heart is a matter of great interest. In the setting of cardiogenic shock or severe low cardiac output and hypoperfusion, extracorporeal membrane oxygenation (ECMO) can produce decisive improvements. The criteria for successful treatment include appropriate patient selection, improved surgical techniques and experience, higher recognition and anticipation of complications, and minimized delay in initiation of ECMO. Because the need for mechanical circulatory support may arise pre-, intra-, and postoperatively, every pediatric cardiac surgeon must be familiar with the principles and the surgical aspects of ECMO.

Pulmonary failure after Norwood procedure: indication for extracorporeal membrane oxygenation? A case report

Today some authors consider univentricular repair a contraindication for postoperative cardiac extracorporeal membrane oxygenation (ECMO). The question is whether or not ECMO is indicated as pulmonary support in case of an overwhelming pulmonary infection during the postoperative course after a Norwood procedure. During the prolonged weaning period after a Norwood procedure using a 4 mm aortopulmonary shunt, proven respiratory syncytial virus (RSV) bronchiolitis occurred at the time of expected weaning from artificial ventilation. Venovenous ECMO was able to improve oxygenation, but when pulmonary opacification failed to resolve, ECMO was terminated after 12 days.

Acute clinical deterioration in a patient with end-stage dilated cardiomyopathy and left ventricular thrombus formation

The case of a 17-year-old male patient with severe end-stage dilated cardiomyopathy and a large thrombus formation within the cavum of the left ventricle is reported. After an acute thrombectomia combined with a partial left ventriculectomy (Batista procedure), the patient was successfully treated with an appropriate left ventricular assist device (LVAD) system using a centrifugal nonocclusive pump (Biomedicus, Medtronic, Anaheim, CA, U.S.A.). Mechanical support was removed on Day 9, and the patient was discharged from the hospital on Day 19. The effectiveness of emergency mechanical support in patients with very unfavorable prognoses is discussed.

Extracorporeal membrane oxygenation discontinuation despite technically successful reoperation: A case report

Death remains a probable outcome of pediatric cardiac extracorporeal membrane oxygenation (ECMO) despite increasing efforts to improve the results. On venoarterial ECMO, in an obviously hopeless situation, the decision to withdraw a life supporting measure resulting in the sudden death of a child places a heavy burden on the team. After valvulotomy of critical aortic stenosis in a prenatally diagnosed term neonate, ECMO had to be installed during postoperative resuscitation. Despite technically successful homograft implantation while on ECMO complicated by postoperative bleeding, advancing multiorgan failure resulted in ECMO withdrawal. As shown in this case report, exact termination criteria are lacking but are necessary to prevent increasing team and resource related conflicts in pediatric cardiac ECMO.

A centrifugal pump driven tidal flow extracorporeal membrane oxygenation system tested with neonatal mock circulation

In 1993, Chevalier published his experiences with tidal flow venovenous extracorporeal membrane oxygenation (ECMO) featuring a single lumen cannula, non-occlusive roller pump, and alternating clamps. Using a neonatal mock circulation (NMC), which enables different hemodynamic states for neonatal ECMO research, the tested hypothesis was that it is possible to create a centrifugal pump driven tidal flow neonatal venovenous ECMO system. Additionally, the resulting hemodynamic effects in a condition of circulatory impairment were investigated. The ECMO circuit tested was assembled using a pediatric centrifugal pump head, a distensible reservoir, and a rotary clamp separating drainage from the injection phase. Using the NMC, end tidal volumes, mock circulation flow, and arterial and venous pressures were measured at different pump speeds after the drainage and injection phases. Effective venovenous ECMO flow (evvEF) was calculated. Mock circulation baseline values (ECMO clamped) were compared to values during tidal flow ECMO. At 3,000 rpm, a centrifugal pump speed of 75 ml/kg/min evvEF was reached, and it increased with higher pump speeds. At this point, the end tidal mock circulation flow (representing cardiac output) after drainage differed significantly from that during the injection phase (p < 0.01) but not from the baseline value. The end tidal arterial and venous pressures after the drainage phase were found to be significantly decreased compared to the baselines (p < 0.01). In conclusion, a centrifugal pump driven tidal flow venovenous ECMO system can be created enabling sufficient tidal volumes. Tested in the described NMC simulating posthypoxic circulatory impairment, significant hemodynamic effects could be demonstrated. Animal experiments for confirmation are necessary.

[Hypoplastic left-heart syndrome. Initial intensive care experiences with the Norwood operation in Vienna]

Palliative surgery of the hypoplastic left heart syndrome (HLHS), whereby both pulmonary and systemic circulation are restored, was first described by Norwood in 1983. Careful ventilatory and pharmacologic modulation of the ratio of pulmonary to systemic vascular resistance are a crucial part of pre-, peri- and postoperative management. We report our experience in 3 of 7 newborns with HLHS who underwent the Norwood operation. Hemodynamic and respiratory parameters were evaluated retrospectively in these patients and we analysed the influence of diagnostic and therapeutic interventions on the course of disease before and after operation. During prostaglandin therapy two of three patients required mechanical ventilation preoperatively because of pulmonary hyperperfusion. Decreased myocardial contractility, oliguria and increased pulmonary vascular resistance characterized the postoperative course. The management included a careful application of inotropic support when necessary, adaptation of the ventilatory setting in order to modulate pulmonary perfusion and, in addition, institution of peritoneal dialysis. One patient died from staphylococcus aureus and superinfection with respiratory syncytial virus on day 41 after the operation. Maintaining an optimal balance between pulmonary and systemic blood flow is an essential aspect of postoperative management. Serum lactate and central venous oxygen saturation are helpful parameters in monitoring therapeutic measures in these patients. We conclude from our preliminary experience, that the Norwood operation might be an alternative therapeutic approach for newborns with HLHS in whom heart transplantation is not possible.

Oral administration of methylglyoxal leads to kidney collagen accumulation in the mouse

Methylglyoxal (MG) is a physiological substrate of the glyoxalase system which is impaired in the diabetic state and implicated in the development of diabetic complications. Like other reactive aldehydes in diabetes mellitus (DM) this carbonyl can bind to and modify proteins which may lead to changes of biochemical and biophysical properties of connective tissue proteins, a hallmark of diabetes mellitus. As previous studies on MG effects were confounded by other aldehydes found in DM, we decided to administer MG to 10 healthy, female OF-1 mice for a period of five months, at a level of 50 mg/kg body weight per day using 10 healthy untreated litter mates as controls. The left kidneys were taken for the determination of total kidney collagen, fluorescence, acid solubility of collagen and the right kidneys were used for the determination of glomerular basement membrane thickness. Total kidney collagen was significantly higher in the MG treated mice compared to control mice. Only about half the amount of collagen could be extracted from kidneys of MG treated animals indicating reduced solubility. Fluorescence in proteins from extracted kidneys of MG treated animals was about twice that of untreated animals. Glomerular basement membrane thickness was significantly higher in MG treated animals. Our findings indicate that MG can increase glomerular basement membrane thickness and the suggested underlying mechanism may be decreased solubility by increased cross linking as reflected by elevated protein fluorescence and decreased acid salt extraction. The involvement of MG in the development of diabetic complications postulated by others is herewith clearly supported by our findings.

A simple neonatal mock circulation enabling pulsatility and different hemodynamical states for neonatal ECMO research: application to assess the effect of a centrifugal pump operated neonatal ECMO system on the circulation

In neonates, extracorporeal membrane oxygenation (ECMO) is increasingly used for circulatory support, e.g., after cardiac surgery. For training purposes and for research, animal experiments are usually required, complicated by increasing social issues, high costs, and limited reproducibility. Therefore, we designed a mechanical neonatal mock circulation (NMC) model enabling pulsatility and various hemodynamic conditions commonly occurring in neonates. Connected to a flow and pressure reading interface, a computer assisted data management system was installed. A nonocclusive roller pump combined with stiff and elastic tubing segments (for aortic pressure regulation and venous capacity) as well as constant and variable resistance (and optionally a patent duct) are essential features of the NMC system. To show the investigational potential, we studied the influence of venoarterial and venovenous ECMO on the NMC performance during normal circulation, hypovolemia, high arterial resistance, the combination of both, and in low cardiac output. By assessing the significant effects of ECMO on the circulatory function of the NMC, its feasibility and investigational properties could be demonstrated.

Extracorporeal membrane oxygenation in neonates

BACKGROUND

Extracorporeal membrane oxygenation (ECMO), originally developed as an artificial replacement for respiratory assistance, is decreasingly used in neonates with respiratory failure. Nevertheless, there is a constant need for this invasive and expensive neonatal treatment modality.

INTERVENTION

Review of our experience (80 recent ECMO performances because of circulatory failure) and the literature.

RESULTS

In contrary to reduced ECMO performances out of respiratory insufficiency in neonates, ECMO as circulatory support is increasingly used. Neonatal sepsis, pre- and postoperative cardiac failure, combined circulatory and respiratory failure after resuscitation and with congenital diaphragmatic hernia result in a permanent need for ECMO, whenever there are fewer ECMO treatments per year. Nonocclusive pumps, portable devices, small priming volumes and tapered anticoagulation protocols enable survival through ECMO even in virtually hopeless hemodynamic conditions. Special efforts in investigation and prevention of permanent neurological impairment, especially after severe pre-ECMO hypoxia seem to be mandatory.

CONCLUSION

ECMO remains an important tool in neonatal and pediatric intensive care. However, the number of ECMO therapies was reduced due to respiratory therapeutic progress, but indications and ECMO technology have changed.

The transcription of the XRCC1 gene in spleen following ionizing irradiation in radiosensitive and radioresistant mice

The XRCC1 gene was described to play a role for the sensitivity of mammalian cell lines towards ionizing irradiation. Cells with a mutation of this gene present with decreased single strand break repair, reduced recombination repair, show increased double strand breaks and sister chromatid exchange is increased up to tenfold. The goal of our study was to investigate the transcription of this gene in the spleen following ionizing irradiation in the mouse. Furthermore, we intended to examine whether radiation sensitive (RS) mice would show a transcriptional pattern different from radiation resistant (RR) mice. Radiation sensitive BALB/c/J Him mice and radiation resistant C3H He/Him mice were untreated or whole body irradiated with X-ray at 4 and 6 Gy and sacrificed 5, 15 and 30 min after irradiation. mRNA was isolated from the spleen and hybridized with probes for XRCC1 and beta-actin as a house keeping gene control. Transcription of XRCC1 was not different in unirradiated or 4 Gy-irradiated mouse RR or RS mouse strains. When irradiated at 6 Gy, RR mice showed an approximately threefold increase of mRNA XRCC1/mRNA beta actin as early as 15 min after irradiation. We conclude that radiation resistant mice show a higher transcription level for the XRCC1 gene in the spleen early after high dose X-ray whole body irradiation. This finding is the first in vivo study on XRCC1 of this kind and may in part explain the differences in the radiation sensitivity between the two strains studied.