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In pneumopericardium, a rare but potentially life threatening differential diagnosis of chest pain with a broad variety of causes, rapid diagnosis and adequate treatment are crucial. In upright posteroanterior chest radiography, the apical limit of a radiolucent rim, outlining both the left ventricle and the right atrium, lies at the level of the pulmonary artery and ascending aorta, reflecting the anatomical limits of the pericardium. The band of gas surrounding the heart may outline the normally invisible parts of the diaphragm, producing the continuous left hemidiaphragm sign in an upright lateral chest radiograph. If haemodynamic conditions are stable, the underlying condition should be treated and the patient should be monitored closely. Acute haemodynamic deterioration should prompt rapid further investigation and cardiac tamponade must be actively ruled out. Spontaneous pneumopericardium in a 20 year old man is presented, and its pathophysiology described.

Acute lung injury can cause a vagally mediated atypical diaphragm activation pattern in spontaneously breathing rabbits. Modulation of PEEP facilitates development of phasic diaphragm electrical activity, whereupon implementation of NAVA can efficiently maintain unloading of the respiratory muscles without delivering excessive tidal volume in rabbits with intact vagal function.

With increasing pressure support ventilation (PSV), a form of pneumatically triggered ventilation, there can be an increase in wasted inspiratory efforts (neural inspiratory efforts that fail to trigger the ventilator). With neurally adjusted ventilatory assist (NAVA), a mode of ventilation controlled by the electrical activity of the diaphragm (EAdi), synchrony should be maintained at high levels of assist. The aim of this study was to evaluate the response to increasing levels of PSV and NAVA on synchrony and diaphragm unloading in lung-injured rabbits. Animals were ventilated on PSV or NAVA in random order, each at three levels. We measured neural and ventilator respiratory rates, EAdi, transdiaphragmatic pressure (Pdi), and tidal volume (VT). At low PSV, 95% of neural efforts were triggered, compared with high PSV, where only 66% of the neural efforts were triggered. During NAVA, all neural efforts were triggered, regardless of level. Increasing NAVA levels reduced EAdi and Pdi-time products by 48% (p Ͻ 0.05) and 66% (p Ͻ 0.05). In contrast, increasing PSV did not reduce the diaphragm electrical activity-time product and increased the transdiaphragmatic pressuretime product (p Ͻ 0.05) due to the increased wasted efforts. We conclude that synchrony with the ventilator is an important determinant for diaphragm unloading. (Pediatr Res 61: 289-294, 2007) P atient-triggered ventilation in the pediatric intensive care unit setting is common (1) and compared with conventional mechanical ventilation has been shown to improve VT (2), work of breathing (2), and oxygenation (3) and to reduce blood pressure fluctuations (4) and transpulmonary pressure (5) in newborns. Despite these findings, a recent meta-analysis indicates that patient-triggered ventilation has no impact on mortality (6). One possible explanation for this may be that even though patient-triggered ventilation was used, synchronous ventilation may not have actually been achieved, an observation not reported in many trials.A common form of patient-triggered ventilation is PSV, a mode of partial ventilatory assist that is triggered by pressure or flow, is pressure targeted, and flow cycled. It is generally believed that increasing the level of assist with PSV unloads the respiratory muscles (7,8). However, investigators have demonstrated there may be a significant amount of respiratory work to trigger the ventilator (9), and there may be wasted inspiratory efforts, where the patient makes an inspiratory effort, but the ventilator fails to trigger. These asynchronies are aggravated at higher levels of assist (9,10) and possibly at higher respiratory rates because expiratory time is too short to allow complete exhalation. Dynamic hyperinflation puts the diaphragm at a mechanical disadvantage, thereby affecting the ability to trigger the ventilator.NAVA is a mode of partial ventilatory assist in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi) (11). The EAdi represents the final neural output of the respiratory c...

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NAVA can be effective in delivering non-invasive ventilation even when the interface with the patient is excessively leaky, and can unload the respiratory muscles while maintaining synchrony with the subject's demand.