The location of the PNI
The number of instances of PNI from the records reached n = 783 (studies: 48) while the precise location as to right superior or inferior phrenic nerve was found in n = 627 (studies: 40). It was not surprising that most PNI were most frequently found in RSPV. Five-hundred eighteen PNI (82.6%) occurred in RSPV and 109 (17.4%) in RIPV (p < 0.005). In the CMAP/no-CMAP group, 206 were found in RSPV (77.4%), 60 in RIPV (23.6%), 312 in RSPV (86.4%), and 49 in RIPV (13.6%) based on results from the chi-square test (p = 0.003) as shown in figure 4. It was impossible to collect precise data concerning the transition of transient PNI to persistent PNI combined with vein location in selected studies.