Partial Scalp Block in Posterior Fossa Surgery

Pain in patients undergoing posterior fossa surgery is regarded as more intense when compared to pain in patients undergoing supratentorial cranial surgeries. The main cause has been attributed to the substantial muscle dissection and trauma in this area.

Opioids remain as the current gold standard drugs for operative pain relief. However, exposure to large doses leads to multiple side effects of varying significance, such as nausea, vomiting, dizziness, constipation, respiratory depression, hypoventilation and disorders of breathing during sleep. Therefore, strategies other than opioids are recommended without sacrificing proper and effective analgesia.

Considering the previously mentioned facts, supplementing general anesthesia with regional anesthesia has been considered and was found to improve intraoperative hemodynamics, surgical field and postoperative analgesia.

In neurosurgery, scalp blocks and local anesthetic infiltration are being used along with general anesthesia either preoperatively to decrease the hemodynamic response to head pinning and surgical incision or postoperatively before emergence from anesthesia to decrease postoperative pain and result in a better outcome.

The current study aims to compare between partial scalp block(greater,lesser and third occipital nerve blocks) on the one hand versus fentanyl infusion on the other hand as pain controlling measures reflected on intraoperative hemodynamics in patients undergoing posterior fossa surgery.

After approval of ethics research committee and obtaining informed written consents from the patient's first degree relatives, 40 patients will be randomly divided by computer designed lists and then concealed in closed serially numbered, opaque envelopes into 2 equal groups to receive either partial scalp block(greater,lesser and third occipital nerve blocks) or fentanyl infusion after induction of general anesthesia by a conventional method and assuming the prone position.

For group N (partial nerve block group): The scalp blocks will be performed bilaterally after assuming the prone position by an anesthesiologist who will not be a part of the study team nor will be involved in the proceeding data analysis or other parts of the study. The Greater occipital will be blocked by injecting 3ml of local anaesthetic at a point half way between the mastoid process the external occipital protuberance along the superior nuchal line, medial to the occipital artery. The Lesser occipital nerve will be blocked by injecting 3ml of local anaesthetic infiltration along the superior nuchal line, 2.5 cm lateral to the greater occipital nerve block. The greater occipital nerve block will also cover the third occipital nerve due to the close location of the two nerves (8).

To anesthetize the dura Lidocaine soaked gauzes will be used and applied for 10 minutes before dural incision.

A placebo infusion (normal saline) was administered at the same rate as fentanyl infusion (1 µg/kg/hr.).

For group F ( Fentanyl group):1µg/kg/hr. of intravenous fentanyl infusion will be administered. A syringe filled with 20 ml of normal saline will be prepared and 3 ml of normal saline will be injected at the same points of the partial scalp block previously mentioned. Both the syringe containing bupivacaine and adrenaline and the placebo syringe will be prepared by a blinded clinical pharmacist, who will not be a part of the study team nor will be involved in the proceeding data analysis or other parts of the study.

The primary outcome will be the systolic blood pressure at time of skin incision. the sample size was calculated using the medcalc software. Based on the study "Bupivacaine scalp nerve block: Hemodynamic response during craniotomy, intraoperative and post-operative analgesia" published in Asian biomedicine (2010).

The total sample size required was 36 participants to be randomly allocated between two groups to achieve a confidence level of 95%, power of study 80% with confidence interval of 1. The sample size was increased to 40 (20 per group) to guard against dropouts.

SPSS software will be used for data analysis. Categorical data will be expressed as frequencies and percentages and will be analyzed using chi-square test. Continuous data will be tested for normality by means of shapiro-wilk test and will be analyzed using unpaired t test, Mann Whitney test, and analysis of variance test (ANOVA) as appropriate. The numerical data will be presented as mean and standard deviation or median and interquartile range as appropriate. A P value less than 0.05 will be considered significant.

Inclusion criteria

• Physical status ASA I and ASA ll.
• Males and females between the ages of 21 and 55.
• Patients undergoing posterior fossa Surgeries.
• Patients with GCS ≥14
• Patients undergoing operation in prone position

Exclusion criteria

• Patient refusal.
• Patients with a history of allergy to opioids or local anesthetics
• GCS (Glasgow coma score) ≤13 upon emergence from anesthesia.
• Patients who will need post-operative ventilation
• Patients who had previous craniotomies
• Patients with contraindication to regional anaesthesia e.g.: local sepsis,
• Patients with pre-existing peripheral neuropathies and coagulopathy.
• Patients who will develop intraoperative surgical complications
• Operations lasting more than 5 hours.