The effect of high frequency ventilation on precerebral blood flow in a piglet model. † 1512

Infants treated with high frequency ventilation (HFV) may experience inadvertent increases in mean airway pressure (Paw) despite improving compliance. This may lead to increased intrathoracic pressure and reduced cerebral blood flow. We measured precerebral blood flow (PCBF) via an ultrasonic flow probe placed around the common carotid artery. Ten 1-2 week old piglets, without underlying lung disease, were sequentially placed on the following modes of ventilation: conventional (CV), high frequency (HF) (Infant Star Model 950+), high frequency with increased Paw (HFH), high frequency(HF2), high frequency with sigh breaths (HFIMV) and conventional (CV2). Initial CV settings maintained PaO₂ 80-120_mmHg and PaCO₂ 35-45_mmHg. Paw was identical for all modes except HFH, where Paw was increased by 4 cm H₂O. PaO₂and PaCO₂ values were maintained within 5_mmHg. There were no significant differences in mean arterial blood pressure, heart rate or blood gas results. PCBF was unchanged in the CV, HF, HF2, HFIMV and CV2 groups. PCBF fell 27.1% ±1.89 in the HFH group when compared to baseline CV (p<0.0007). In this model of HFV without lung disease, increased Paw led to a significant reduction in PCBF. This implies that infants with normal or improving compliance may experience reduced PCBF if Paw is not judiciously controlled while receiving HFV.Table

Table 1