To the Editor:- The loss-of-resistance technique in the most common method of locating a needle in the epidural space. [1]However, the use of air in children may result in patchy analgesia. [1]There is also a small risk of air embolism. [2]We use a pressure-guided method for identification of the epidural space in children. After the trachea is intubated, epidural puncture is performed with a 19-gauge, 5 cm Tuohy needle at the lumbar intervertebral space using a median approach in the lateral flexed position. Before starting the puncture, the pressure transducer with saline-filled sterile tubing is connected to the Tuohy needle. The zero level was set at the midline of the back before measurement. As the needle advances through tissue, the recorded pressure rises, eventually to the pressure applied, to transducer flush the reservoir bag. As soon as the tip of the needle enters the epidural space, the pressure suddenly decreases, and the pressure tracing is synchronized with the heart beats (Figure 1).

To evaluate this technique, we performed a prospective trial. The study protocol was approved by our Institutional Research Committee, and informed consent was obtained from the parent of each patient. Fifty patients (American Society of Anesthesiologists physical status I) aged 1 - 8 yr, scheduled for elective inguinal hernia repair were studied. Each consecutive patient was randomly assigned to one of the two groups (n = 25 each) according to the techniques for identification of the epidural space as follows: pressure-guide group and standard group (using loss of resistance to saline injection). Routine monitoring (blood pressure [BP], electrocardiography, heart rate [HR], precordial stethoscope, and pulse oximetry) was established, and general anesthesia was performed with sevoflurane and nitric oxide in oxygen. After tracheal intubation, the patient was placed in the lateral decubitus position, and epidural puncture was carefully performed with a 19-gauge Tuohy needle at L2 - 3 intervertebral space with each method. A catheter was inserted and advanced approximately 3 cm into the epidural space. The patient was then placed supine, 0.5 ml/kg bupivacaine, 0.25%, was injected through a catheter into the epidural space. Fifteen minutes after bupivacaine injection, surgical procedures were started. A successful block was defined as one in which there was no hemodynamic response to surgical stimuli during a 10-min period after incision. A positive response was defined as a 15-mmHg increase in systolic blood pressure or a 20-beats/min increase in heart rate. The patients who showed positive responses were regarded as not having successful epidural anesthesia, they were immediately administered sevoflurane, 3 - 4%

Patient demographic data (age, body weight) were compared between groups using the unpaired Student's t test. Success rates and incidence of complications were compared between groups using the Fisher's exact probability test. A probability value < 0.05 was considered the minimum level of statistical significance.

Demographic data, success rates, and complications were shown in Table 1. No significant differences between groups were observed.

When a stylet is used at skin puncture in the patient with a shorter distance than expected between skin and epidural space, an unexpected dural puncture cannot be avoided. We recommend that a Tuohy needle without a stylet should be connected to the pressure line in shallow subcutaneous tissue just after starting procedure to avoid an unexpected dural puncture in patients with a shorter distance than expected. The power of the study in relation to the sample size may limit the interpretation of the current results. At least 150 patients would need to be studied to exclude a type II error in success rate and at least 637 patients would need to be studied to exclude dural puncture rate. [3] 

There are several airless techniques to identify the epidural space during intervertebral epidural anesthesia in children. [1,4]In addition to these techniques, we will recommend our visible and reliable pressure-guided method of airless identification of the epidural space in children.

Tomohide Suwa, M.D.

Resident in Anesthesia; Tsukuba University Hospital; Tsukuba City, Japan

Shinichi Inomata, M.D.

Shigeyuki Saito, M.D.

Assistant Professor

Hidenori Toyooka, M.D.

Professor and Chairman; Department of Anesthesiology; Institute of Clinical Medicine; University of Tsukuba; Tsukuba City, Japan

(Accepted for publication April 24, 1998.)

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Fisher LD, van Belle G: Sample sizes for observational studies, Biostatistics. Edited by Fisher LD, van Belle G. New York, Wiley-Interscience, 1993, pp 844-6
Yamashita M, Tsuji M: Identification of the epidural space in children. The application of a micro-drip infusion set. Anaesthesia 1991; 46:872-4.