Olfactory Stimulation for Very Low Birth Weight Infants

1\) For the premature infants who use non-invasive ventilation, place a single layer of gauze soaked in breast milk on the air outlet of the non-invasive ventilator. When inhaling oxygen with a high-flow nasal cannula, the same measure is performed, and the breast milk and sterile gauze soaked in breast milk are replaced every 4 hours. 2) For the premature infants who withdrawn from assisted ventilation, place the breast pad near the infants' nose, and replace the breast milk pad every 4 hours. Acquisition of breast milk pads: use the same brand of breast milk pads; put the breast milk pads used between 00:00 and 07:00 every day (use time \> 2 hours) into the same brand of milk storage bags, and use two left and right at the same time. 3) If the premature infants don't have any ventilation support, the breast milk stimulation method is the same as 2). This intervention will continue until premature infants discharge from hospital.

Nursing is performed according to existing nursing practices. Nasal feeding is generally used.