Comment on: Comparison of Intraabdominal and Trocar Site Local Anaesthetic Infiltration Efficacy on Postoperative Analgesia After Laparoscopic Cholecystectomy

Dear Editor,

I read a very informative and interesting article that was published in TJAR in the December 2016 issue, in which the effects of the trocar site vs. the intraperitoneal local infiltration were compared with a control group, in patients who underwent laparoscopic cholecystectomy (1).

I have some queries/comments regarding the above-mentioned article (1).

In the results section, the p values are mentioned as ‘>‘ or ‘<‘ in some places instead of ‘=‘. For example, the p value of EtCO₂ between the two groups is mentioned as p>0.0125; however, I believe that it should be p=0.125 (insignificant), which is also applicable to the p values of visual analogue score (VAS) and total morphine consumption. The p value mentioned in the first sentence of the results section of the abstract, i.e. ‘There were no statistical significant differences between the clinical and demographic properties among the three groups (p≥0.005)’, is also incorrect; it should have been as p>0.05. It is a normal practice to mention the p-values as such (p=xxxx), from which, it can be interpreted as significant, if the value is <0.05, and insignificant, if the value is >0.05, provided 0.05 is considered as the cutoff value, based on the level of significance. I believe it is more precise to use the term ‘comparable’ if the p value is >0.05 for demographic and baseline parameters, although the term ‘insignificant’ is also commonly used. These are only typographical errors, which can occur with anybody and can be considered “insignificant”.

However, the main point of contention in the abovementioned article is the interpretation of the results of one parameter, i.e. ‘shoulder pain’.

Shoulder pain was least in the intra-peritoneal group (six), followed by the trocar infiltration group (eight) and then the control group (seventeen); please refer to Table 1 of the article. However, the authors have incorrectly interpreted these results in the fourth paragraph of the discussion section, although the other two parameters, namely VAS scores and morphine consumption, were correctly interpreted.

Because of this misinterpretation, the subsequent sentence, i.e. “The higher incidence of shoulder pain in the group in which we intraperitoneally administered a local anaesthesia can be explained by the fact that the local anaesthesia was diluted and that a drain was used to observe potential bile leakages” is factually and logically incorrect. The incidence of shoulder pain was lowest in the “intra-peritoneal” group, among all the three groups. In addition, although there is an effect of dilution in the intra-peritoneal group, the amount of local anaesthetic in the subdiaphragmatic region would be still higher than that in the trocar infiltration group. Initially, I thought that there would not be the possibility of any amount of local anaesthetic in the subdiaphragmatic region in the trocar infiltration group. This line of thinking helped me to unearth the fact that the incidence of shoulder pain was “lowest” in the “intra-peritoneal” group. However, I realised later that there would be possibility of some amount of local anaesthetic in the subdiaphragmatic region in trocar infiltration group, [albeit, lesser than intra-peritoneal group] which could explain the fact that the incidence of shoulder pain was significantly lesser in the trocar group also when compared to the control group. There could be some spillage of local anaesthetic in the trocar group, which can explain this fact.

In the results section of the article (1), the sentence ‘group III [control] had more frequent shoulder pain than groups I and II (p<0.05)’ is correct (17 vs. 8 and 6, respectively). Nevertheless, if we compare groups I and II, shoulder pain is slightly lower in the group II (intra-peritoneal) than in the group I (trocar infiltration), i.e. (6 vs. 8). Although this may not be statistically significant, it explains my assessment.

I hope that the authors, reviewers, and editor will agree with my line of thinking.

Kandil et al. (2) observed that the referred pain was significant if the duration of surgery was >45 min. Here, the duration of surgeries among all three groups was ‘comparable’, with p=0.557 and the same average of 45 min in all three groups (1). Hence, duration of the surgery cannot be considered as a contributing factor in this study.