Influence of end expiratory pressure on cerebral blood flow in preterm infants

Clinical factors associated with abnormal general movements of preterm newborns during hospitalization in a neonatal intensive care unit

INTRODUCTION

There is no clarity about which clinical variables during hospitalization in the Neonatal Intensive Care Unit (NICU) are associated with abnormal General Movements (GMs).

OBJECTIVE

To describe the trajectory of GMs of preterm newborns and explore the association between clinical variables and the presence of abnormal GMs during the NICU stay.

METHODS

Fifty-eight preterm newborns (33 males), with a mean gestational age at birth of 31,93 week's postmenstrual age, were evaluated using the GMs assessment by Hadders-Algra method. Clinical variables recorded weekly throughout the hospitalization period. The weekly association between clinical variables and the presence of abnormal GMs was tested using the Generalized Estimating Equations (GEE) model.

RESULTS

Preterm infants were recorded for up to sixteen weeks and more than half of the infants (56.9 %) had abnormal movements in at least one week during hospitalization. The absence of peri-intraventricular hemorrhage (PIVH) grades I-II and non-invasive ventilatory support and/or oxygen therapy on the day of the evaluation reduced, respectively, by 77.3 % (OR = 0.23; p > 0.0001) and 64.3 % (OR = 0.36; p > 0.0001) the chance of having an abnormal classification. In addition, each day of increased invasive mechanical ventilation increased the chance of having an abnormal classification by 1.11 times (OR = 0.025; p > 0.0001).

CONCLUSION

PIVH grades I-II, longer durations of mechanical ventilation and the presence of non-invasive ventilatory support and/or oxygen therapy are associated with abnormal movements during stay in the neonatal period. The data suggest that development outcome of infants having these conditions should be closely monitored.

Increased peak end-expiratory pressure in ventilated preterm lambs changes cerebral microvascular perfusion: direct synchrotron microangiography assessment

Positive end-expiratory pressure (PEEP) improves oxygenation in mechanically ventilated preterm neonates by preventing lung collapse. However, high PEEP may alter cerebral blood flow secondarily to the increased intrathoracic pressure, predisposing to brain injury. The precise effects of high PEEP on cerebral hemodynamics in the preterm brain are unknown. We aimed to assess the effect of PEEP on microvessels in the preterm brain by using synchrotron radiation (SR) microangiography, which enables in vivo real-time high-resolution imaging of the cerebral vasculature. Preterm lambs (0.8 gestation, n = 4) were delivered via caesarean section, anesthetized, and ventilated. SR microangiography of the right cerebral hemisphere was performed with iodine contrast administered into the right carotid artery during PEEP ventilation of 5 and 10 cmH₂O. Carotid blood flow was measured using an ultrasonic flow probe placed around the left carotid artery. An increase of PEEP from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm) in all four lambs. Additionally, the higher PEEP increased the cerebral contrast transit time in three of the four lambs. Carotid blood flow increased in two lambs, which also had increased carbon dioxide levels during PEEP 10. Our results suggest that PEEP of 10 cmH₂O alters the preterm cerebral hemodynamics, with prolonged cerebral blood flow transit and engorgement of small cerebral microvessels likely due to the increased intrathoracic pressure. These microvascular changes are generally not reflected in global assessment of cerebral blood flow or oxygenation.NEW & NOTEWORTHY An increase of positive end-expiratory pressure (PEEP) from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm). This suggests increased intrathoracic pressure due to high PEEP can drive microvessel engorgement in the preterm brain, which may play a role in cerebrovascular injury.

Respiratory support for premature neonates in the delivery room: effects on cardiovascular function and the development of brain injury

The transition to newborn life in preterm infants is complicated by immature cardiovascular and respiratory systems. Consequently, preterm infants often require respiratory support immediately after birth. Although aeration of the lung underpins the circulatory transition at birth, positive pressure ventilation can adversely affect cardiorespiratory function during this vulnerable period, reducing pulmonary blood flow and left ventricular output. Furthermore, pulmonary volutrauma is known to initiate pulmonary inflammatory responses, resulting in remote systemic involvement. This review focuses on the downstream consequences of positive pressure ventilation, in particular, interactions between cardiovascular output and the initiation of a systemic inflammatory cascade, on the immature brain. Recent studies have highlighted that positive pressure ventilation strategies are precursors of cerebral injury, probably mediated through cerebral blood flow instability. The presence of, or initiation of, an inflammatory cascade accentuates adverse cerebral blood flow, in addition to being a direct source of brain injury. Importantly, the degree of brain injury is dependent on the nature of the initial ventilation strategy used.

Cardiorespiratory effects of changes in end expiratory pressure in ventilated newborns

BACKGROUND

Positive pressure ventilation in premature infants can improve oxygenation but may diminish cerebral blood flow and cardiac output. Low superior vena cava (SVC) flow increases risk of intraventricular haemorrhage, and higher mean airway pressure is associated with low SVC flow. Whether this is a direct effect of positive pressure ventilation or a reflection of severity of lung disease is not known. This study aimed to determine if positive end expiratory pressure (PEEP) in ventilated newborns could be increased without clinically relevant cardiorespiratory changes.

METHOD

Ventilated newborns were studied before and 10 min after increasing PEEP (5 cm H(2)O to 8 cmH(2)O) and again when PEEP returned to baseline. Echocardiographic and respiratory function measurements were collected during the intervention.

RESULTS

In 50 infants, increased PEEP was associated with a non-significant difference in mean SVC flow of -5 ml/kg/min (95% CI -12 to 3 ml/kg/min) but a significant reduction in right ventricular output of 17 ml/kg/min (95% CI 5 to 28 ml/kg/min). The increase in lung compliance was non-significant (median difference 0.02 ml/cmH(2)O/kg) and the decrease in lung resistance (18 cmH(2)O/l/s; 95% CI 10 to 26 cm H(2)O/l/s) was significant. Changes (%) in lung compliance and SVC flow, when corrected for Paco(2), were positively associated (regression coefficient 0.4%; 95% CI 0.2% to 0.6%).

CONCLUSION

A short-term increase in PEEP does not lead to significant changes in systemic blood flow, although 36% of infants in the present study had clinically important changes in flow (+/-25%). The intervention can improve dynamic lung function, especially airway resistance. Improvements in compliance tend to be associated with improvements in blood flow.

Neonatal venous cerebral hemorrhage

Intracranial pathological changes can occur as a result of impaired craniocervical venous return. Thrombosis of central venous access catheters was demonstrated in two neonates born at 38 and 27 weeks' gestation. Neither infant developed hemorrhage of prematurity as confirmed on cranial ultrasonography. Clinical evidence of vena cava thrombosis and associated spontaneous intraventricular hemorrhage developed on Day 24 and 36, respectively, and these findings were confirmed on imaging studies. In one infant the hemorrhage was accompanied by communicating hydrocephalus.

The cause of the intracranial disease was attributable to the retrograde cerebral venous congestion. This, together with the primitive venous bed developing in the periventricular region, was associated with the spontaneous hemorrhage in the region of the foramen of Monro.

To the authors' knowledge, this is the first report in the English-language literature of spontaneous neonatal intra-cerebral hemorrhage, due to thrombosis of the superior or inferior vena cava.

The natural history of this condition is resolution without sequelae after appropriate therapeutic intervention for the vena cava thrombosis.