Adjunct pharmacotherapy in acute lung disease in children

Mechanical ventilation, while accepted as standard therapy for critically ill infants and children with respiratory failure, has significant morbidity and mortality. While recent emphasis on low tidal volume ventilation and low airway pressures may result in decreased lung stretch and limit lung disease, adjunctive therapies have been tried to reduce the stressors of mechanical ventilation. Therapies included inhaled nitric oxide, heliox and surfactant. There are compelling physiological reasons why these drugs may be of benefit in these patients. However, our understanding of their role is hindered by studies with small numbers of patients and its use in diseases with varied pulmonary pathology. Studies have shown potential for benefit of inhaled nitric oxide in newborns with hypoxemic respiratory failure and pulmonary hypertension, surfactant in respiratory distress syndrome in preterm neonates and heliox in severe upper airway obstruction. However, the use in other respiratory conditions has led to mixed results and hence paucity of firm recommendations.

Hypothermia pediatric head injury trial: the value of a pretrial clinical evaluation phase

BACKGROUND

The utility of a pretrial clinical evaluation or run-in phase prior to conducting trials of complex interventions such as hypothermia therapy following severe traumatic brain injury in children and adolescents has not been established.

METHODS

The primary objective of this study was to prospectively evaluate the ability of investigators to adhere to the clinical protocols of care including the cooling and rewarming procedures as well as management guidelines in patients with severe traumatic brain injury (Glasgow Coma Scale<or=8) treated with 24 h of hypothermia therapy. A secondary objective was to evaluate the ability of study research assistants to complete the study case report form using a procedures manual. The study was conducted at 18 sites in Canada, the United Kingdom and France prior to proceeding to a randomized controlled trial (RCT). After 2 patients were enrolled at each center, an independent clinical evaluation committee examined the process of care and the completeness of data collection. Centers were permitted to enroll patients in the RCT once they met pre-established adherence criteria.

RESULTS

Seventeen of the 18 centers completed the pretrial clinical evaluation phase demonstrating compliance with study procedures and proceeded to an RCT of hypothermia therapy. One center enrolled only 1 patient in the pretrial clinical evaluation phase due to small numbers of patients with traumatic brain injury, and therefore, did not proceed to the RCT. Three centers were required to enroll more than 2 patients in the pretrial clinical evaluation phase prior to proceeding to the RCT because of problems with adherence to the clinical protocols at two centers and the training of new study personnel at another center. Of the 39 patients enrolled during the pretrial clinical evaluation phase, 8 (20.5%) died and 22 (62.9%) had a good outcome defined as normal, mild or moderate disability assessed using the Pediatric Cerebral Performance Category score at 6 months following injury.

DISCUSSION

The pretrial clinical evaluation phase was useful to ensure compliance with complex hypothermia therapy and consensus-based clinical management guidelines of care successfully implemented across 17 of 18 centers. This study maneuver allowed us to complete a subsequent RCT in 225 children following severe traumatic brain injury.

Hyperbaric oxygen therapy for cerebral palsy: two complications of treatment

There is growing interest in the use of hyperbaric oxygen therapy (HBO(2)) for children with cerebral palsy. Although there is no rigorous evidence to support this management, private hyperbaric centers have been established throughout the United States and Canada. There is likely to be increasing pressure on pediatricians and other health professionals to prescribe HBO(2). We describe 2 children with cerebral palsy who suffered significant morbidity immediately after treatment with hyperbaric oxygen. Both the temporal association and pathologic findings suggest that the hyperbaric treatment is likely to have been responsible for the resulting complications. As with any new therapy, we suggest waiting for the results of a randomized, controlled trial before recommending this treatment.

Partial liquid ventilation with perfluorocarbon in acute lung injury: light and transmission electron microscopy studies

Liquid ventilation using perfluorocarbon has been shown to improve gas exchange in animal models of acute lung injury as well as in children with acute respiratory distress syndrome. This study was designed to define structural features of lung injury following partial liquid ventilation (PLV) using light and transmission electron microscopy in a rabbit model of acute respiratory distress. Animals were treated with either conventional mechanical ventilation (CMV-gas) (n = 6) or PLV (n = 5) for 4 h after the induction of acute lung injury with saline lavage. Control animals were killed after the lung injury. PLV significantly improved alveolar-arterial oxygen tension and the oxygen index compared with CMV (P < 0.05). Morphometric studies using light microscopy show less alveolar hemorrhage, less edema, and fewer hyaline membranes in the PLV group (P < 0.05). Polymorphonuclear leukocyte sequestration in lung capillaries (11.4 +/- 1.5 versus 19.2 +/- 3 x 10(8)/ml, P < 0.05, PLV versus CMV) and migration into airspaces (3.1 +/- 1.2 versus 4.5 +/- 1.1 x 10(8)/ml, P < 0.05, PLV versus CMV) were lower in the gravity-dependent lung regions. There were fewer alveolar macrophages in the PLV group compared with other groups (P < 0.05). Fluorescence microscopy analysis shows fewer type II alveolar epithelial cells in the CMV group and brighter type II cells in the PLV group. Transmission electron microscopy studies show more alveolar wall damage in the CMV group, with type II cells detached from their basement membrane with fewer surfactant-containing lamellar bodies. We conclude that quantitative histologic analysis shows less lung damage and inflammation when perfluorocarbon is combined with CMV in the management of acute respiratory distress syndrome.

Evaluation of a mathematical model to predict intrapulmonary shunt non-invasively

PURPOSE

We have previously published a mathematical model of oxygen transport. Using several physiological assumptions, the model provides a non-invasive estimate of intrapulmonary shunt. During a larger study of lung injury in a pig model, we had the opportunity to check the validity of our assumptions and the accuracy of the model's predictions.

METHODS

We used six female pigs, average weight 12.8 kg. Following general anesthesia, tracheostomy and insertion of pulmonary venous and arterial lines, lung injury was induced by repeated saline lung lavage. Using hemodynamic measurements made at different levels of inspired oxygen, intrapulmonary shunt was calculated both by the traditional shunt equation and also by our mathematical model based on non-invasive measurements of FIO2 and SaO2.

RESULTS

There was good agreement between the two methods of shunt calculation. Using linear regression the correlation coefficient was 0.95. Bland and Altman analysis showed a bias of -0.8 and precision of 12%.

CONCLUSION

In a controlled setting, intrapulmonary shunt can be estimated from non-invasive measurements to a reasonable degree of accuracy. However, the calculation requires too many assumptions to be of general clinical value. The equations used provide a validated physiological model that acts as a useful tool for teaching cardiorespiratory physiology.

Effect of hyperventilation on regional cerebral blood flow in head-injured children

OBJECTIVES

To study cerebral blood flow and cerebral oxygen consumption in severe head-injured children and also to assess the effect of hyperventilation on regional cerebral blood flow.

DESIGN

Prospective cohort study.

SETTING

Pediatric intensive care unit at a tertiary-level university children's hospital.

PATIENTS

Twenty-three children with isolated severe brain injury, whose admission Glasgow Coma Scores were <8.

INTERVENTIONS

PaCO2 was adjusted by altering minute ventilation. Cerebral metabolic measurements were made at three levels of PaCO2 (>35, 25 to 35, and <25 torr [>4.7, 3.3 to 4.7, and <3.3 kPa]) after allowing 15 mins for equilibrium.

MEASUREMENTS AND MAIN RESULTS

Thirty-eight studies (each study consisting of three sets of measurements at different levels of PaCO2) were performed on 23 patients. At each level of PaCO2, the following measurements were made: xenon-enhanced computed tomography scans; cerebral blood flow; intracranial pressure; jugular venous bulb oxygen saturation; mean arterial pressure; and arterial oxygen saturation. Derived variables included: cerebral oxygen consumption; cerebral perfusion pressure; and oxygen extraction ratio. Cerebral blood flow decreased below normal after head injury (mean 49.6 +/- 14.6 mL/min/100 g). Cerebral oxygen consumption decreased out of proportion to the decrease in cerebral blood flow; cerebral oxygen consumption was only a third of the normal range (mean 1.02 +/- 0.59 mL/min/100 g). Neither cerebral blood flow nor cerebral oxygen consumption showed any relationship to time after injury, Glasgow Coma Score at the time of presentation, or intracranial pressure. The frequency of one or more regions of ischemia (defined as cerebral blood flow of <18 mL/min/100 g) was 28.9% during normocapnia. This value increased to 73.1% for PaCO2 at <25 torr.

CONCLUSIONS

Severe head injury in children produced a modest decrease in cerebral blood flow but a much larger decrease in cerebral oxygen consumption. Absolute hyperemia was uncommon at any time, but measured cerebral blood flow rates were still above the metabolic requirements of most children. The clear relationship between the frequency of cerebral ischemia and hypocarbia, combined with the rarity of hyperemia, suggests that hyperventilation should be used with caution and monitored carefully in children with severe head injuries.

Post-traumatic fat embolism in the inferior vena cava

Histologically, pulmonary fat embolism is seen in up to 97% of traumatized patients, yet almost all of them are asymptomatic. Although clinically significant, fat embolism syndrome is not common; it is a frequent cause of death when it does occur. The authors report the computed tomographic demonstration of fat embolism in the inferior vena cava of a patient who sustained multiple fractures. To their knowledge, no similar case has ever been described.