Peripheral Perfusion Index as an Early Predictor of Successful Caudal Block in Pediatric Patients Undergoing Lower Abdominopelvic Surgeries Under General Anesthesia

The aim of this study is to assess early predictability of peripheral perfusion index to success of caudal block in pediatric patients undergoing lower abdominopelvic surgeries. Preoperative assessment will be done which includes full history taking, clinical examination, standard laboratory investigations. Demographic data (age, weight, and sex) will be recorded.

All patients will be instructed to fast for 6 hours preoperatively while allowing clear fluids up to 2 hours prior to anesthesia as per the standard nil per oral (NPO) guidelines.

In the operating room, all patients will be monitored during the operation using: electrocardiography (ECG), pulse oximeter (SpO2), automated non-invasive arterial pressure (NIAP) measurement cuff, end tidal carbon dioxide (capnogram), volatile anesthetic monitoring, core temperature monitoring using a nasopharyngeal probe, and Masimo pulse oximeter probe for measuring PPI which will be applied to the big toe of the patient's foot and wrapped with gauze to reduce heat loss and to avoid the interference of ambient light.

Normothermia will be maintained using warm intravenous fluids and a forced air warm blanket.

Induction of general anesthesia will be done using inhalational sevoflurane at 8%, and after loss of consciousness, a peripheral intravenous access will be placed under complete aseptic condition. Fentanyl citrate at 1 µg/kg will be slowly injected intravenously then laryngeal mask with appropriate size will be inserted.

Maintenance of anesthesia will be with 50% oxygen-air mixture, and sevoflurane titrated to a minimum alveolar concentration MAC of 2%. Ringer acetate will be administered as the intraoperative maintenance fluid at the rate of 6 mL/kg/h.

The baseline value of PPI, heart rate (HR), and mean arterial pressure (MAP) will be recorded, corresponding to the value at 0 minute (T0) measured after induction of general anesthesia and before caudal block in supine position. The caudal block will be performed under complete aseptic conditions with the patient in the left lateral decubitus position with the hips and knees flexed using the landmark technique. Sterilization by Povidone Iodine will take place and insertion of the cannula will begin till appreciating the loss of resistance at which the needle is will be held and the cannula is advanced. After negative aspiration for blood and cerebrospinal fluid, 1mL/kg of 0.25% of bupivacaine hydrochloride will be injected at the rate of 1mL/3s and the patient will be turned supine immediately and surgical skin incision will be allowed to start 10 minutes after.

Following the caudal block, PPI, HR, and MAP will be recorded at 2, 5, 7, 10 (at skin incision), 15, and 20 minutes. Successful caudal block will be predicted as any or both of the following criteria achieved, whichever occurred earlier:

* ≥100% increase of PPI value from baseline. * No tachycardia or hypertension on surgical stimulation (HR or MAP increase \> 20% of baseline).

Percentage of successful blocks predicted with these criteria will be plotted against postoperative pain score as a main determinant of caudal block success with successful block defined as the following:

• Postoperative pain score as assessed by Children and Infants' Postoperative Pain Scale (CHIPPS) at 0 h and 30 min postoperatively is \<4 out of 10.

A failed caudal block is defined based on failure to achieve the aforementioned criteria. And in case of block failure, an intravenous bolus of 1-2 ug/kg fentanyl will be administered intraoperatively, and a rescue post-operative analgesia in the form of bolus intravenous nalbuphine at a dose of 0.2 mg/kg will be provided to patients accordingly.

Patients will be divided into two groups based on success of the block: group (S) caudal success group, and group (F) caudal failure group. Both groups will receive the standard management (caudal block under general anesthesia) for the required procedure. There will not be a control group for this study.