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Correspondence  |   February 1997
Injection Volume of Saline with Loss of Resistance Method May Affect the Spread of Epidural Anesthesia
Author Notes
  • Director of Anesthesiology and Emergency Medicine, Central Aizu General Hospital, 1–1 Tsuruga-machi, Aizuwakamatsu City, Fukushima Prefecture, 965 Japan.
Article Information
Correspondence
Correspondence   |   February 1997
Injection Volume of Saline with Loss of Resistance Method May Affect the Spread of Epidural Anesthesia
Anesthesiology 2 1997, Vol.86, 507-508. doi:
Anesthesiology 2 1997, Vol.86, 507-508. doi:
To the Editor:-This is a report on the effect of injection volume of saline on the spread of epidural anesthesia. After institutional approval, 30 adult patients (American Society of Anesthesiologists physical status 1–2) who provided informed consent and received elective surgery during epidural anesthesia were assigned randomly into two groups of 15 patients each. There were no statistically significant differences between both groups with regard to age (45 +/- 20 vs. 50 +/- 17 yr), weight (56 +/- 9 vs. 55 +/- 9 kg) and height (156 +/- 10 vs. 157 +/- 9 cm) using the Mann-Whitney U test (values are mean +/- SD).
With patients in the lateral position, an 18-gauge Tuohy needle was inserted via the 4th-5th lumbar interspace and into the epidural space using loss of resistance method and saline. The injection volume of saline into the epidural space was 2 ml in group 1 and 10 ml in group 2. Immediately after the injection, an epidural catheter was directed 5 cm cephalad through the Tuohy needle. The patient was positioned supine. Five minutes after injection of saline, 12 ml of 2% mepivacaine was administered for 1 min through the epidural catheter. Lactated Ringer's solution was administered intravenously at 10 ml/kg/h during and after these procedures. Mean blood pressure, heart rate, and the ranges of hypesthesia and analgesia were measured before anesthesia and 15 min after injection of mepivacaine into the epidural space. The extents of hypesthesia and analgesia were tested by a blinded individual, and assessed with an alcohol swab and a pinprick, respectively. The hemodynamic data are expressed as mean +/- SD and the number of anesthetized spinal segments are expressed as median +/- range.
There were no statistically significant differences between pre-values of both groups in mean blood pressure and heart rate (Mann-Whitney U test). Although mean blood pressure and heart rate did not change significantly 15 min later in group 1, in group 2, mean blood pressure and heart rate significantly decreased (P < 0.05, Wilcoxon signed-rank test). All patients in group 1 obtained hypesthesia and analgesia. In group 2, all patients also obtained hypesthesia, and 13 of 15 patients experienced significant analgesia. Therefore, the statistical analysis of analgesia in group 2 was done with 13 patients. The number of anesthetized spinal segments (above the 2nd sacral dermatome) with regard to hypesthesia were 9 +/- 7 and 14 +/- 11 segments in groups 1 and 2, respectively. The number of anesthetized spinal segments with analgesia in groups 1 and 2 were 5 +/- 11 and 10 +/- 11 (n = 13), respectively. There were significant differences between both groups (P < 0.05, Mann-Whitney U test)(Table 1).
Table 1. Mean Blood Pressure, Heart Rate, and Anesthetized Spinal Segmemts
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Table 1. Mean Blood Pressure, Heart Rate, and Anesthetized Spinal Segmemts
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These data suggest that injection volume of saline before epidural anesthesia with loss of resistance method may affect the extent of anesthesia (i.e., the greater the volume of saline, the greater the extent of anesthesia). Conversely, in two patients in the current study who received 10 ml saline, analgesia was not obtained. Because the two patients did demonstrate satisfactory hypesthesia, the epidural catheter was thought to be in the epidural space. I speculate that the lack of analgesia may be attributed to the dilution of local anesthetic with the prior injected saline. In other words, greater volume of saline may decrease the anesthetic effect in spite of increasing the spread of anesthesia. Further study concerning a relation among injection volume of saline, spread of anesthesia, and anesthetic effect will be needed.
Hiroshi Iwama, M.D., Director of Anesthesiology and Emergency Medicine, Central Aizu General Hospital, 1–1 Tsuruga-machi, Aizuwakamatsu City, Fukushima Prefecture, 965 Japan.
(Accepted for publication November 21, 1996.)
Table 1. Mean Blood Pressure, Heart Rate, and Anesthetized Spinal Segmemts
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Table 1. Mean Blood Pressure, Heart Rate, and Anesthetized Spinal Segmemts
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