How does procedure failure rate affect power analysis?

I am currently conducting medical research. It is a randomized blinded clinical trial to compare patient indicators of rehabilitation after a surgical procedure . One group of patients receives an injection of local anesthetic near a sensory nerve; the second group of patients receives the same injection of local anesthetic near the same nerve but also receives a catheter near the nerve to provide a continuous infusion of local anesthetic. The two groups are measured on certain parameters of rehabilitation over a 24-hour period and data from both groups will be compared. The injections and catheter placement are done using ultrasound and there is a failure rate--either because the medication was not placed in the right place (primary failure) or the catheter becomes dislodged (under the skin) at some point during the study period(secondary failure) We will not know if the injection was improperly placed or if the catheter became dislodged during the 24 hour period.(The catheter could also work initially and become dislodged at some unknown point during the study) If the study is randomized is it necessary to know (or have an estimate of ) the failure rate of injections of local anesthetic. and catheter placements in order to determine the appropriate number of study patients to ensure that the results will be sufficiently powered?