SCALP Block Model in Sprague-Dawley Rats; In Vivo Experimental Study and Model Identification

Introduction: The SCALP block is an important regional anesthesia method. In this study, we analyzed the SCALP block model for the first time in a rat model. Materials and Methods: In this study, 16 rats were divided into four different groups. Six nerve blocks were planned in both halves of the skull for the SCALP block, and three entry points were determined for each. Bupivacaine (Marcaine, AstraZeneca) 0.5 mg/kg was injected in the "low-dose" group, 1 mg/kg in the "medium-dose" group, 2 mg/kg in the "high-dose" group, and 4 mg/kg in the "very high-dose" group. A midline fronto-occipital incision was made, and a craniectomy was performed. At 0, 30, 60, 90, and 120 minutes after the surgical procedure, the rats were evaluated using the Rat Grimace Scale, and their pain scores were evaluated. At the end of 2 hours, the rats were sacrificed, blood samples were taken, and methemoglobin levels were studied. Finally, a comparative analysis was performed between the four groups. Results: In 30, 60, 90, and 120 minutes after surgery, the differences between the grimace scores between low-dose and medium-dose and high-dose and low-dose groups were statistically significant (p<0.001). There was no significant difference between the high-dose and very high-dose groups regarding the grimace scale (p>0.05). Methemoglobin levels were statistically significantly higher after SCALP block with a very high dose of bupivacaine than blockade with a high dose of bupivacaine (p<0.001). Therefore, very high-dose bupivacaine injection was not superior to high-dose bupivacaine injection in pain control. In addition, very high doses of bupivacaine injection can be associated with increased morbidity and mortality due to increased methemoglobin levels. Conclusion: In this SCALP block technique described in rats, a 2 mg/kg bupivacaine injection can be considered an appropriate dosage for both safety and efficacy.