Recently, Kang et al1 published an article in the Journal of Pain Research titled “Advantages of Combining Epidural Anesthesia with Conscious Sedation Under Fluoroscopy Guided in Lumbar Spine Surgery.” The results mentioned in the original article1 are inaccurate because the authors did not take into account the physicochemical factors of local interaction of drug solutions which affect their local pharmacokinetics at the injection sites. Essentially an article by Kahn et al1 is devoted to the study of the peculiarities of the local action of drug solutions when injected into the soft tissues of the spine. The data search strategy included the relationship between local anesthesia retention time and patient age. Local action factors such as the concentration, volume, pH of drug solutions have not been taken into account. It is not possible to repeat the results in the original article1 using the same methods. In the section “Technique of anesthesia and postoperative progress”, it is indicated that “… a single injection of the mixture was administered 5 to 10 ml of half of 0.325% of ropivacaine with epinephrine 1: 200,000, diluted in 5 to 10 ml of radioactive contrast medium (BONOREX®) (Figure 1).”
First, it is impossible to accurately assess the reason for the duration of the pharmacological effect in the original article,1 without taking into account at least the exact value of the concentration of ropivacaine in the mixture and the exact value of its volume when injected after diluting 5-10 mL of local anesthetic solution in 5-10 mL of solution of radiocontrast. They needed a different study design. It was necessary to evaluate the effectiveness of two doses of a local anesthetic, namely, in the first group only 5 ml, and in the second group only 10 ml of a half solution of ropivacaine 0.325% with epinephrine 1: 200,000. In addition, they had to divide each group into 2 more subgroups: in the first and second subgroups, dilute a solution of the specified local anesthetic in 5 ml and 10 ml of radiocontrast dye. (BONOREX®), respectively. By the way, the above proposal is not new and unknown to anesthesiologists, because in previous similar articles other authors took into account the exact volume and concentration of the local anesthetic solution.2 In addition, it was necessary to specify a specific radioactive contrast medium, its formulation, the concentration of its ingredients and its acid (alkaline) activity.
Second, for their study, the authors had to take into account the acid activity of the diluted solution in each of the 4 subgroups, since the acid activity of a 0.325% solution of ropivacaine in solution with 1: 200 epinephrine 000 differs from the acid activity of a radiocontrast dye solution (BONOREX®). Therefore, the mixture of these drugs in each of the 4 subgroups has a different acidity. In addition, the acid activity of drug solutions may be different for drugs produced by different pharmaceutical companies and under different serial numbers for the same pharmaceutical company.3 By the way, the value of acidic activity of drug solutions is included in the standard list of controlled indicators of the quality of drugs.4 In addition, the pH indicator can be determined using a pH meter in a biochemical laboratory.
In our opinion, Kang et al could provide more precise and valuable information if they took into account that the mechanism of action of local anesthetics depends on their dose, concentration, volume and acidity of the mixture injected into the soft tissues.
Additionally, Kang et al the study did not consider the pharmaceutical companies that produced a 0.325% solution of ropivacaine solution with 1: 200,000 epinephrine, as well as the year of manufacture and the lot number of the drug used. It should be added that the authors did not take into account the radioactive contrast product used. The fact is that radioactive contrast agents used in X-ray examinations can be grouped into positive (iodine agents, barium sulfate) and negative (air, carbon dioxide, methylcellulose) agents. From the point of view of clinical pharmacology, it is inappropriate to assess the pharmacological effect of a mixture prepared by diluting a solution of a certain drug with a solution of an unspecified drug with unknown physicochemical properties. Determining the actual values of physical and chemical indicators of the quality of injectable solutions may improve the accuracy of research results in the future.
The authors do not point out any conflicts of interest in this communication.
1. Kang SY, Kashlan ON, Singh R, et al. Interests of the combination of epidural anesthesia by conscious sedation under fluoroscopic guidance in lumbar spine surgery. J Pain Res. 2020; 13: 211-219. doi: 10.2147 / JPR.S227212
2. Ristev G, Sipes AC, Mahoney B, Lipps J, Chan G, Coffman JC. Beginning of labor analgesia with injection of local anesthetic through the epidural needle in relation to the catheter. J Pain Res. 2017; 10: 2789-2796. doi: 10.2147 / JPR.S145138
3. Kasatkin A, Urakov A, Nigmatullina A, Kopytov M. Balanced crystalloid versus 0.9% sodium chloride: what we forget in our research. Anesthesiology. 2021; 134: 353-354. doi: 10.1097 / ALN.0000000000003614
4. United States Pharmacopoeia Convention. United States Pharmacopeia 36 and National Formulary 31. Rockville, MD: United States Pharmacopeial Convention; 2013.