Discussion
Pain, HD, pain, ’ pain, NRS
The present study was conducted to compare the effects of cooling and lidocaine sprays on needle insertion pain in HD patients using a crossover design. Because pain is subjective and pain is what the patient tells us according to the literature, it is difficult to compare patients’ pain scores to each other. On the other hand, patients undergoing HD frequently experience needle pain, which also affects their perception of pain; as a result, comparing the pain score of patients after receiving various interventions to themselves creates a more accurate picture of the effect of the intervention on pain control. Therefore, a crossover design was used in this study in a way that the participants can be compared to themselves, controlling for any possible confounding variables.Moreover, this crossover design allows the comparison of various interventions. Although it was impossible to compare the pain scores at different times and after different interventions due to a carry-over effect, the present study results can help supplement the existing knowledge regarding cooling and lidocaine sprays. On the other hand, despite a two-week wash-out time, a carry-over effect in the crossover design was a significant issue that requires further investigation and more evidence on time needed to wash out the effects of similar interventions on pain in future studies.The interventions’ effects were compared for the first time, controlling for baseline scores. Although the results showed no significant difference between cooling spray and lidocaine spray interventions, the difference in the scores of the two interventions was significant. More reliable results can be obtained by conducting further studies with a more extended wash-out period and a larger sample size.The effects of cooling spray and lidocaine in various forms have been investigated in different studies, and different results have been reported. For example, Page and Taylor’s study on venous cannulation-induced pain showed that the pain reduction of cooling spray was less than topical lidocaine [Moreover, Dalvandi et al.’s study revealed that the pain after receiving a cooling spray was significantly less than the control group (in the case of cannulation without any intervention) and more than the EMLA cream [The results of Moon et al.’s study investigating the effectiveness of cooling spray and lidocaine injection in propofol injection pain showed that both groups receiving cooling and lidocaine sprays experienced less pain than the control group; however, there was no significant difference between the two groups of lidocaine and cooling sprays in terms of pain score [Limited studies have shown that cooling spray is ineffective in reducing pain [The NRS has inherent time and shortcomings. Furthermore, additional contributors to patients’ pain, such as catastrophizing tendencies, might be evident if additional or different rating scales were used to better clarify the patients’ phenotype.Because HD patients need to be connected to the dialysis machine after needle insertion, it was difficult to evaluate the pain score immediately after the needle insertion; therefore, this evaluation was carried out in all patients within one minute after the needle insertion into the skin. The issue of whether the pain scores one minute after the needle insertion can be different from the score reported by the patient immediately after the needle insertion needs further investigation.To the best of our knowledge, a limited number of studies compared the effect of cooling and lidocaine sprays in a crossover design. Therefore, compared to other studies, one of the advantages of this study is that it exposed a group of patients to three forms of intervention. On the other hand, the investigation of the sequence, period, and carry-over effects is one of the advantages of this study. The presence of a carry-over effect despite the 2-week wash-out period can raise one of the most important issues for further investigation in the field of pain studies.This study has some limitations. Pain is subjective, and its evaluation can be associated with problems. On the other hand, patients undergoing HD treatment frequently experience needle pain that affects their perception of pain. Repeating a painful procedure (e.g., venous cannulation) might also shape patient expectations and preferences, and any intervention insulted by these issues might produce nocebo or placebo effects. The characteristics of vascular access can also be effective in pain perception. An attempt was made to cover this limitation using a crossover design. However, due to the significant carry-over effect, it was not possible to compare the scores after different interventions at different times in one group, which is another limitation of this study. Moreover, blinding was not possible in this study due to the cooling nature of the cooling spray and the apparent difference between lidocaine and placebo sprays. However, an attempt was made to ensure that covering lidocaine and placebo sprays was the same. Another limitation of this study was the small sample size.