Ultrasound Guided Spinal Anesthesia in Non Obese Obstetric Patients

Overview

The classical method for spinal anesthesia relies on the use of bony landmarks to identify the level and point of entry of the spinal needle. Over the years, in experienced hands, this method consistently proved to be successful and safe. The introduction of ultrasound to guide neuraxial anaesthesia into clinical practice was relatively slow compared to peripheral nerve blocks or central venous catheterization. This could be due to the technical difficulties posed by the bony structures surrounding the spinal cord and its dura that blocks the path of the ultrasound beam. Many anesthetists are reluctant to change their conventional landmark technique, particularly with most studies showing no change in the success rate between ultrasound guided and the landmark techniques. Several studies however showed that the ultrasound guided approach reduces the number of attempts to achieve a successful block and reduces the procedure time particularly in obese patients and those with technical difficulties. In this study the investigators are trying to answer the following question : Is there any advantage in using ultrasound to guide spinal anaesthesia in non obese obstetric patients with easily palpable bony landmarks?

Patients will be randomized using a web based randomization program into two groups: Ultrasound guided spinal anesthesia (US) \& conventional spinal anesthesia (C). In both groups, the level of the third or fourth lumbar inter-space (L3/4 or L4/5) will be identified using either ultrasound (transverse and longitudinal approach) or palpation method using anatomical landmarks. All ultrasound examinations and spinal anesthesia will be performed by 3 anesthetists with experience in ultrasound guided neuraxial block (between 100 and 200 cases). The ultrasound examination will be done using Logiq e TM ultrasound machine (GE Solingen Germany) with 4C RS 2 - 5.5MHz Broadband multi-frequency probe. The predetermined point of entry for the introducer needle will be marked on the patient's back. The spinal anaesthesia will be administered with the patient in the sitting position, using a 26 gauge pencil point needle (PortexTM) with 15 mg of heavy Bupivacaine and 20 micrograms of Fentanyl. An independent observer, who is blinded to the method used to identify the point of entry of the introducer needle, will be collecting the data.The spinal anesthesia will be labeled as successful if a bilateral block to the sixth thoracic dermatome (T6) , judged by loss of cold and touch discrimination, is established 5 minutes after the spinal injection.