Transient versus persistent phrenic nerve injury (primary outcome).
From 10,341 records, information about 783 PNI (7.7%) was found; 589 (5.7%) were transient, while 194 (1.9%) were persistent. In the CB-1 generation (n = 4164 records with 4492 CB-1 balloons), PNI was found in 302 cases (7.2%), in the CB-2 generation (n = 5957) was found in 466 cases (7.8%), and in the CB-ST (n =102), 15 (1.96%) were found. After obtaining the results from studies reporting relevant detailed data, we observed that the number of PNI in the CMAP and non-CMAP groups was similar and did show statistical difference (p = 0.56, odds ratio [OR]: 0.96; 95% CI [0.82–1.11]). The transient subgroup was seen significantly more often in the CMAP group, while the PPNI was present more often without CMAP use (Table 3).
Dividing PNI into transient and persistent PNI in CMAP and non-CMAP group showed statistical significance for all variants except transient PNI in the CB-2 group. A statistical difference was found in almost all CBA generations with the highest incidence in persistent PNI in CB-1 (OR 3.4) and CB-2 (OR: 3.4 and 1.99, respectively). The inverse situation was found in transient PNI in the CB-1 group (OR: 0.47). Combined data from different CBA generations with and without CMAP use are presented in the Forrest plot in figure 2A. The funnel plot of the selected studies for the analysis shows the risk of bias in figure 2B. The only insignificance was noticed between TPNI in the CB-2 generation (CMAP/nonCMAP) (p = 0.75; OR: 1.03). For this record, a Kaplan Meier’s log- rank test was preformed and yielded a value of p = 0.77.
By obtaining the results from studies reporting relevant, detailed, intra-operative data regarding PNI, including time to PNI (n = 243) and temperature to PNI (n = 150), a significant difference between CMAP and non-CMAP groups was noticed. The mean difference for time to PNI was significant for CMAP and non-CMAP groups. The shortest time to PNI was found in the CMAP CB-1 and CB-2 groups (both 137 s). The longest time to PNI was observed in non-CMAP groups reaching 153 and 141 s for CB-1 and CB-2, respectively. The mean difference nadir temperature to PNI was lowest for CB1 (–59 ºC at which the CMAP value could not be dispersed), for CB-2 non-CMAP and CMAP (–53 and –50 ºC), which achieved statistical significance. The summarized graphs with heterogeneity values are shown in figure 3.