Success rates in infant lumbar punctures may be declining as we do fewer and fewer (doing fewer is a good thing, except that we get less experience). One thing that can improve success is early stylet removal. The stylet is kept in when entering the skin in order to avoid the very rare complication of intraspinal epidermoid tumors. However, once the needle is past the epidermis and dermis, such that a plug of skin tissue cannot be cored out by the hollow needle and deposited into the spinal canal, the stylet can be removed. Here are two excellent FOAMed discussions of this practice and the advantages: http://pemcincinnati.com/blog/wwdwwd-early-stylet-removal-lp/ and https://pedemmorsels.com/spinal-needle-stylet/