Bispectral index monitoring of propofol sedation during ultrasound guided nerve block for inguinal herniorraphy: A randomized prospective study.

BACKGROUND: Patient's awareness can be reduced during ultrasound guided nerve block for inguinal herniorraphy with propofol sedation. The study was aimed to evaluate the clinical efficacy of direct visualization of anatomy of inguinal region by ultrasound and benefits of bispectral index (BIS) monitoring.
MATERIALS AND METHODS: After approval, 40 adult male consented patients of ASA grade I-III of 18-58 years with body mass index <25 were randomized into two groups of 20 patients each. A high frequency (8-13 MHz) linear transducer was used to perform the ilioinguinal and iliohypogastric nerves (ILHN and ILIN) block between the internal oblique and transversus abdominis muscles with 20 mL of 0.75% ropivacaine. The propofol infusion rate for sedation in patients of group I (non-BIS) was managed clinically and in patients of group II (BIS) was managed with BIS index of 65-75. Any surgical or anesthetic complications were recorded. The two groups were compared by evaluating the propofol consumption during surgery.
RESULTS: Ultrasonographic visualization of the ILHN and ILIN was possible in all patients and inguinal herniorraphy was performed uneventfully. The mean dose of propofol required for sedation was 5.45 mg/kg/h in patients of group I (non-BIS) while 4.92 mg/kg/h in patients of group II (BIS). The mean propofol consumption was not statistically significant (P = 0.12). All patients were hemodynamically stable and there was no respiratory depression during propofol sedation.
CONCLUSION: Ultrasonography has facilitated the clinically effective nerve block for inguinal herniorraphy and BIS monitoring has ensured amnesia and faster emergence.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Ilioinguinal and iliohypogastric nerves (ILHN and ILIN) block is an efficient technique for inguinal herniorraphy with advantage of minimal hemodynamic changes, early ambulation, and ability to place the nerve block in the supine position.[1] Ultrasound guidance allows direct visualization of the nerves, detection of anatomical variations, use of less volume of local anesthetic drug[2] and no injury of adjacent structures.[34]

There may be a risk of airway obstruction and hypoxia when intravenous sedation technique combines with nerve blocks. It can be minimized with bispectral index (BIS) monitoring during sedation. The BIS values of 65-75 have been advocated to ensure amnesia and faster emergence.[56]

The study was aimed to evaluate the clinical efficacy of direct visualization of anatomy of ILHN and ILIN by ultrasound and clinical benefits of BIS monitoring.

MATERIALS AND METHODS

After approval from Institutional Ethical Committee and written informed consent, 40 adult male patients of ASA grade I-III of 18-58 years old with body mass index <25, scheduled for elective unilateral inguinal surgery were enrolled for this prospective randomized controlled study. Patients suffering from severe cardiac or respiratory disease, liver or renal disease, any allergy or contraindication to any study drug, previous surgery of inguinal region, deranged coagulation profile or refusal to technique, were excluded from the study.

All patients were randomized by computer generated number into two equal groups of 20 patients each, based on intraoperative sedation monitoring technique. The rate of propofol infusion for sedation in patients of group I (non-BIS) was managed clinically while sedation in patients of group II (BIS) was managed with BIS values of 65-75.

After arrival to operation theatre, the routine monitoring for pulse oximetry, non-invasive blood pressure and electrocardiography was carried out and intravenous infusion of lactated ringer was started.

Ultrasound guided block technique

A SonoSite MicroMaxx portable ultrasound unit with high frequency (8-13 MHz) 38 mm linear transducer probe was used to identify the ILHN and ILIN, which supply the inguinal region. The ILHN and ILIN nerves run between internal oblique and transversus abdominis muscles, medial to the anterior superior iliac spine, and pierce the internal oblique muscle to lie deep to aponeurosis.[7]

Patient was laid supine and the linear probe was placed in the axial plane, cephalad of the anterior superior iliac spine oriented in a slightly caudal direction, at the level of a triangle of petit or where the three muscle layers are most distinct on ultrasound. These nerves were identified as hypo echoic structures between the internal oblique and transversus abdominis muscles.[89] Using an in-plane approach, the needle was advanced from anterior to posterior obliquely to transversus abdominis plane and after a negative aspiration test 20 mL of 0.75% ropivacaine was injected. The appropriate spread of local anesthetic was monitored by ultrasound between the internal oblique and transversus abdominis muscles space. The total time taken for the procedure was 10-15 min.

Skin incision was performed after infiltration of the incision site with 10 mL of lidocaine 1% in all patients, because the cutaneous innervation of the ILIN is variable, and there are no accurate clinical tests of its assessment.

Sedation was induced with midazolam 0.04 mg/kg as bolus, followed by propofol infusion. The propofol infusion rate was adjusted according to randomization schedule. The level of sedation was monitored in patients of group I (non-BIS) clinically with a 4-point rating scale (0: Fully alert, 1: Sleepy, but easily arousable with the verbal command, 2: Sleepy but hardly arousable, and 3: Unconscious patient) and was maintained at scale 2. In patients of group II (BIS), the sedation was monitored with BIS and was maintained between BIS values of 65 to 75. During sedation, spontaneous breathing was maintained and patients were given oxygen at a rate of 3 L/min via Hudson facemask.

They were monitored for hemodynamic stability, respiratory depression or any other surgical and anesthetic complication.

The need for additional intraoperative local anesthesia or deepening of sedation level with large doses of propofol was defined as a failed block. After completion of surgery, the total consumption of propofol was noted.

Statistical analysis

Study population size was based to ensure power 0.80 for clinically significance. Assuming a 5% drop out rate, the final sample size was set at 40 patients. The Chi-square test and Students’ unpaired test were used for statistical analysis. P < 0.05 was considered statistically significant.

RESULTS

We studied 40 adult consented male patients who met the inclusion criterion for ultrasound guided nerve block for open inguinal herniorraphy under propofol sedation. Both groups were comparable with respect to the demographic profile and operational factors [Table 1].

Table 1

Demographic profile and intra-operative data

The ILHN and ILIN were visualized by ultrasound in all patients and successful block was achieved. The surgical anesthesia was clinically effective and inguinal herniorraphy could be performed uneventfully in all patients. There were no surgical or anesthetic complications. None of the patient needed supplemental analgesia.

All patients remain hemodynamically stable. None of the patient has shown respiratory depression during propofol sedation. The mean dose of propofol required for sedation was 5.45 mg/kg/h in patients of group I (non-BIS) while 4.92 mg/kg/h in patients of group II (BIS). The mean propofol consumption was not statistically significant (P = 0.12).

Post-operatively, there was no recall of intraoperative events in any patient. All were completely awake and were able to walk without any difficulty. All patients were discharged from the hospital next day.

DISCUSSION

The ultrasound guidance for ILHN and ILIN blocks for inguinal herniorraphy has gave us an opportunity to readily identify the anatomical variation in the inguinal region for effective surgical anesthesia. Although, there was no significant difference between the two groups in the mean dose of propofol consumption, BIS monitoring has ensured amnesia and faster emergence from propofol sedation. All patients remained hemodynamically stable and were able to breath spontaneously without any respiratory depression of propofol sedation technique. No addition analgesia or deep sedation of propofol was needed to complete the inguinal herniorraphy.

The use of ultrasonography in regional anesthesia has caused more success, shorter onset time as compared to conventional “fascial click” technique. It allows direct visualization of the nerves, detection of anatomical variations, and prevents damage to the structures adjacent to nerves. The selective ILHN and ILIN block provided good quality surgical anesthesia and early discharge of the patient.[101112]

The large volume of local anesthetic could be injected in a fan shape manner to encounter the technical difficulties of conventional fascial click technique for inguinal nerves block. The use of ultrasound as an aid to regional anesthesia promotes higher precision of local anesthetic deposition and has increased the safety of patients from drug toxicity as reduced volume of local anesthetic drug is required for successful block.[1314] Studies using ultrasound guidance have suggested that more accurate placement of smaller amount of local anesthetic does not reduce the efficacy, but potentially reduces the unwanted side-effects of femoral nerve palsy. The femoral nerve palsy is thought to be volume related and occurs as a result of an unnecessary spread of local anesthetic between the muscle layers.[1516] Ala-Kokko et al. have demonstrated large plasma concentrations of bupivacaine after ILHN and ILIN block that were performed with the fascial click method using 0.39 mL/kg of 0.5% bupivacaine.[17]

In the present study, successful block was achieved using 0.3 mL/kg of 0.75% ropivacaine without affecting the quality of surgical analgesia for inguinal herniorraphy with early ambulation and hospital discharge.

Bispectral analysis may reduce patient awareness during anesthesia, facilitated a faster wake-up time and perhaps a shorter stay in the recovery room. Bispectral values of 65-75 have been advocated as a measure of sedation. In order to achieve the desired level of propofol sedation, a target concentration of the propofol in the blood must be delivered. Significant correlations between plasma propofol concentration and BIS values have been reported by many investigators. BIS monitoring may be used to monitor sedation levels to reflect the propofol concentration. Gan et al. also observed the faster emergence when BIS monitoring was used during general anesthesia.[18]

CONCLUSION

Ultrasonography has enabled the accurate placement of the needle for clinically effective ILHN and ILIN block for inguinal herniorraphy. BIS monitoring has ensured amnesia and faster emergence after surgery. The technique proved to be effectual for day care surgery.