Respiratory information from flow-volume curves confirmed to be useful
Respiratory parameters during mechanical ventilation may be obtained using flow-volume curves, a new study suggests. While there may be a significant difference, pre-anaesthetic airway resistance appears to estimate the intra-anaesthetic airway resistance in the absence of obstructions.
The prospective, observational study included 526 patients above the age of 15 years. Patients were scheduled for surgery to be performed under general anaesthesia and would undergo orotracheal intubation with a normal or spiral endotracheal tube for airway management.
Airway resistance was calculated for each patient using the flow-volume curves before (pre-anaesthetic) and during general anaesthesia (intra-anaesthetic). Endotracheal tube resistance was also calculated to correct airway resistance values.
Of the patients included, 98 were found to have a forced expiratory volume in the first second/forced vital capacity (FEV1/FVC) ratio <70 percent. Those who have airflow obstructions presented with significantly higher airway resistance prior to anaesthesia (p<0.001). On the other hand, no difference in intra-anaesthetic airway resistance was found regardless of airflow obstructions (p=0.48).
In patients without airflow obstructions, the pre- and intra-anaesthetic airway resistances were much closer to each other in value, having a mean difference of <1.0 cmH2O L-1s-1. Regardless, the parameters remained significantly different (p<0.001).
Finally, the FEV1/FVC ratio was not related to the intra-anaesthetic airway resistance in any way, even if the ratio reflected the pre-anaesthetic airway resistance values.
The findings thus show that, in patients without airflow obstructions, there is minimal but significant difference between pre- and intra-anaesthetic airway resistance values. This implies that information from flow-volume curves may be used for mechanical ventilation.