Factors determining the doses of local anesthetic agents in unilateral inguinal hernia repair

Background Today, local anesthesia is used in specialized hernia clinics in most cases. The technique for establishing local anesthesia for inguinal surgery may differ among surgeons. Few articles to date have mentioned the exact doses of local agents. This prospective study aimed to research the doses of local anesthetic agents needed in practice and determine the patient-related and other factors which affected those doses. Methods Three hundred consecutive patients who underwent an elective unilateral inguinal hernia repair were planned to be included in the study. Lidocaine as a short-acting, medium-lasting agent and bupivacaine 0.5% as a long-acting agent were chosen. Gender, age, body mass index (BMI), side of hernia (right/left), concomitant disease, history of hernia (primary/recurrent), type of hernia (indirect/direct), Gilbert class of hernia (1-6), size of hernia (small or medium/large or massive), hernia sac content (omentum/intestine), time shift (8 am to 4 pm/later than 4 pm), duration of operation, and institutional experience (first 150 cases vs. latter 150 cases) were recorded. Results There were 277 male and 23 female patients. The mean age was 49.73 years (range 16-83; median 50.00). The mean volume of total anesthetic agents (lidocaine + bupivacaine) was 19.79 ml (range 5.5-40; median 19.5). The mean volumes separately were 101.79 mg for lidocaine (range 30-200; median 100) and 48.12 mg for bupivacaine (range 12.5-110; median 50). The patients were discharged after a median time of 2 h postoperatively. Univariate analysis for the total dose of the two agents showed that younger age (<= 60 vs. >= 61 years), larger size of hernia, longer duration of operation (>= 61 vs. <= 60 min), recurrent hernia, hernia sac content (omentum > intestine), and higher BMI (>= 25.1 vs. <= 25.0) were significant parameters. On the other hand, BMI, recurrent hernia, size of hernia, and omentum in the hernia sac were factors that significantly affected the mean lidocaine dose. Higher BMI and recurrent hernia also caused a higher need for bupivacaine. In addition, significantly lower doses of bupivacaine was used in older patients. The significant independent parameters in the multivariate analysis were duration of operation, sac content, and BMI for lidocaine dose, whereas the duration of operation and sac content were determinative for the sum volume of the two agents. None of the recorded parameters were found to be significant for bupivacaine dose in the logistic regression. Conclusions This prospective study showed, again, the feasibility of local anesthesia in elective inguinal hernia repair in all patient groups with different characteristics. The mean and maximum doses of local anesthetic agents were well within safety limits, even in recurrent and large hernias. Younger age, large hernias, recurrent hernias, omental mass in the hernia sac, high BMI, and duration of operation might be the factors affecting local anesthetic doses. The significant independent parameters in the multivariate analysis were duration of operation, sac content, and BMI for lidocaine dose, whereas the duration of operation and sac content were determinative for the sum volume of lidocaine and bupivacaine.