The effect of rapid thoracoabdominal compressions on intracranial pressure in newborn lambs

The influence of intra-abdominal hypertension on the central nervous system: current insights and clinical recommendations, is it all in the head?

INTRODUCTION

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome are a common occurrence in ICU patients. The deleterious effects of IAH on organ function are well known and increasingly appreciated in recent years, especially where renal and respiratory function are concerned.

METHODS

This review will focus on the available literature from the last years. A Medline and PubMed search was performed in order to find an answer to the question "What is the impact of increased IAP on neurologic function in the critically ill?"

RESULTS

The amount of data on the influence of IAH on the central nervous system is more scarce, but several animal and human studies have demonstrated a clear correlation between intra-abdominal pressure (IAP) and intracranial pressure (ICP). This correlation is probably due to transmission of the increased IAP to the thorax leading to increased intrathoracic, pleural pressure and central venous pressure, decreased venous return from the brain and increased ICP. This hypothesis is supported by the observation that the increase in ICP is abolished when a sternotomy and pleuropericardotomy are performed, and by the fact that abdominal decompression has produced good results in treating refractory intracranial hypertension (ICH) in patients with both IAH and ICH.

CONCLUSIONS

A close relationship between IAP and ICP has been observed in several animal and human studies. The clinical impact of this association is dependent on the baseline ICP and the compensatory reserve of the patient. Some studies have reported good results in treating refractory ICH by abdominal decompression in patients with concomitant IAH. Monitoring of IAP and ICP in risk patients is essential.

Head circumference and chronic positive pressure ventilation in children: a pilot study

METHODS

We reviewed the cases of 11 children <12 years of age with complex medical conditions and respiratory failure requiring chronic positive pressure ventilation (CPPV). We conducted a within-group comparison of average head circumference (HC) percentiles with each child's age-expected 50th percentile value and a between-groups comparison with children with no history of ventilation. We examined the relationship between HC, peak levels of positive inspiratory pressure (PIP), and length of time on CPPV.

RESULTS

We found that children on CPPV had an average HC value at the 71st percentile, significantly greater (p=0.009) than the age-expected 50th percentile; that children on CPPV had a greater (p=0.003) average HC percentile compared with children with complex medical conditions not on CPPV; and that peak levels of PIP had a moderately strong correlation to HC (r=0.689, p=0.019).

CONCLUSION

We conclude that children on CPPV have larger than expected HC and HC appears related to the peak level of PIP. Research to further investigate the relationship between HC and CPPV in children appears to be warranted.

Isovolume pressure/flow curves of rapid thoracoabdominal compressions in infants without respiratory disease

To assess whether flow limitation can be achieved during rapid thoracoabdominal compressions (RTC), we performed esophageal pressure measurements in 11 healthy infants less than 3 months of age. Recordings of esophageal pressure were obtained with an esophageal balloon placed in the lower esophagus. RTCs were started at 20 cm H2O and increased to 140 cm H2O or until the infant responded with glottic closure to the compression. Flow limitation was assessed from isovolume pressure flow curves at peak flow and flow at FRC (V'max, FRC). The transmission of jacket pressure was higher at peak flow than at FRC for pressures below 60 cm H2O, due to active inspiration during the compression. Active inspiration was not observed at compression pressures above 80 cm H2O, as reflected by a plateau in the esophageal pressure tracing. Esophageal pressure increased parallel to the compression pressure at jacket pressures below 60 cm H2O. The relationship between jacket pressure and esophageal pressure became curvilinear at high compression pressures and plateaued at compressions above 100 cm H2O, so that further increases in jacket pressure did not increase esophageal pressure. Flow limitation was seen in all infants studied, as indicated by a lack of increase in flow with increasing esophageal pressures for V'max, FRC. Jacket compression pressures of 60 cm H2O and esophageal pressures of 20 cm H2O were sufficient to reach maximal expiratory flow. These data indicate that jacket pressure is a poor indicator of pleural pressure at high compression pressures in young healthy infants, and high pressures are not needed, as flow limitation is seen during RTCs at moderate compression pressures.