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Introduction
Spinal anesthesia is the anesthetic technique of choice in a range of surgical procedures: general surgery, ObGy, orthope dics and urology. It is based on the injection of one dose of local anesthetic into the subarachnoid space at the level of the lumbar spine. The spinal needles used vary in their design and gauge.
Following the administration of spinal anesthesia, a residual volume may be observed in the needle. This vol ume may vary depending on the needle manufacturer. There are no publications researching how significant this volume is.
An inadequate dose selection is a cause for failed spinal anesthesia and according to the literature ranges between 1 and 17% of the spinal anesthesia.
The purpose of this post-interventional trial was to mea sure the residual volume contained inside the chamber of three 27 gauge spinal needles from three different manu facturers and to assess whether there are any statistically significant differences.
Methods
An observational, analytical, cross-section, non-randomized trial was designed, in which spinal needles used for the administration of spinal anesthesia were successively recruited.
Three brands of 27 gauge needles available in the Colom bian market were collected:
BD Whitacre pencil point spinal needle (BD Medical Franklin Lakes, NJ. USA), 27 GA 0.40 x 90 mm.
Spinocan Quinke sharp tip (Braun Medical Inc., Bethlehem,
PA, USA) 27 GA 0. 42x 88mm.
Disposable spinal needle (Dr.J Tianjin Hanaco Medical Co. Tianjin, China). 27 GA 0.38x 90mm.
To measure the residual volume, an Automatic Micropipette of 100 to 1000 lU was used, (volume mea surement capacity 0.1μl up to 10 ml) EASY40+ LABBOX.
A convenience sample of 13 measurements per manu facturer of spinal needles was selected, for a total of 39 samples. For the administration of spinal anesthesia, hypoder mic disposable 3 ml/cc needles were used, connected through a thread to the spinal needles.
The specimens that during their use showed evidence of failure for the administration of the drug, any defective speci mens or with defects or deformities after threading the syringe to the spinal needle, were all excluded.
The involvement of anesthesiologists was required. The anesthesiologist who administered the spinal anesthesia was informed about the intention to measure the residual volume so that after preparing the dose, without disconnecting the syringe from the spinal needle, the residual volume inside the needle shall be placed in a plastic measuring tube.
The volume of the dose administered in the anesthesia, and the number of barbotages was not taken into account.
The second independent and trained anesthesiologist measured the residual volume in each needle with the micropipette (precision volumes from 0.1μl to 10 ml).
The process was repeated with the 39 samples collected. In order to take the measurements and analyze them, the spinal needles were classified in accordance with the manufacturer and the residual volumes identified inside (Fig.1).
Results
This observational trial did not require patient intervention. Thirteen non-randomized samples were taken per each type of 27G spinal needle (BD Whitacre, Spinocan Quinke and Dis posable spinal needle) for a total of thirty-nine (39) samples (Table 1).
Table 1 Measurement of residual volume in the spinal needles chamber #27.
| SpinocanQuinke | Disposable spinal needle | Whitacre Needle |
| 0.12 | 0.11 | 0.015 |
| 0.14 | 0.13 | 0.02 |
| 0.11 | 0.08 | 0.01 |
| 0.12 | 0.09 | 0.15 |
| 0.11 | 0.1 | 0.05 |
| 0.14 | 0.12 | 0.015 |
| 0.1 | 0.11 | 0.02 |
| 0.08 | 0.09 | 0.05 |
| 0.1 | 0.18 | 0.015 |
| 0.14 | 0.16 | 0.01 |
| 0.12 | 0.18 | 0.015 |
| 0.14 | 0.21 | 0.05 |
| 0.12 | 0.14 | 0.05 |
Source: Authors.
A statistical analysis was completed using the t-test func tion, Microsoft Excel data analysis tool (Table 2).
Table 2 Statistical analysis of the samples.
| Type of needle | Needle number | Number of samples | Sum Residual Vol. (ml) | Average Residual Vol. (ml) | Variance | Standard deviation |
| Spinocan Quincke Braun | 27 | 13 | 1.54 | 0.12 | 0.00035 | 0.019 |
| Disposable spinal needle | 27 | 13 | 1.7 | 0.13 | 0.00166 | 0.041 |
| Whitacre Needle | 27 | 13 | 0.47 | 0.04 | 0.00145 | 0.038 |
Source: Authors.
The residual volume obtained from the Whitacre 27 G pencil tip needles (average residual volume of 0.04ml), manufactured in the United States, showed a statistically significant difference as compared against the residual vol ume in the Disposable spinal needle (average residual volume 0.13 ml) manufactured in China and Spinocan Quinke man ufactured by Braun in the United States (average residual volume 0.12 ml), with a P value of less than α = 0.01.
Although the length of the Whitacre needle is 90 mm, 2 mm longer than the Quinke 88 mm needle, there was not a favorable difference for Quinke. The Whitacre needle has an inner diameter of 0.40mm, 0.02mm larger than the Dispos able spinal needle 0.38 mm needle, but showed no advantage either.
Discussion
Spinal anesthesia is used to perform different surgical proce dures in general surgery, ObGy, orthopedics, and urology.1-3) In Colombia we have different brands of 27 G spinal needles. This is the most common smaller gauge found. This paper results from the observation of a residual volume found after spinal anesthesia in those spinal needles after use. The pur pose of the trial was to determine whether there are any volume differences, regardless of the technical data sheet of each needle.
The dose of local anesthetic, the use of opioids, and bar-botage were not considered in each sample. Therefore, he constitution of the volume collected may not be implied. To do so, high-efficient liquid chromatography techniques are required, but these are beyond the scope of this study.4 The collection and measurement techniques in each sample taken were standardized. A significant difference in favor of the BD Whitacre pencil tip needle was shown. These are the needles with the smallest residual volume at the end of the adminis tration of anesthesia.
There is a trend to use low volumes in short procedures or in some patients in whom peripheral vasodilatation could compromise the cardiac output, with negative effects on vital organs.5-8 One of the causes of failed spinal anesthesia is a mistake in selectingthe anestheticdose.9,10Theuse ofsmaller residual volume needles could be a determining factor when selecting a low dose technique.
This trial has some weaknesses worth mentioning: the number of cases recruited per each group, the lack of previ ous studies to determine the sample size, the percentage of residual volume versus the general volume administered, and the measured composition of the residual volume measured.
Conclusions
The study showed that the BD Whitacre pencil point needles retain less residual volume following spinal anesthesia. No clinical implications may be derived from this finding. New studies are needed to ratify these results.
Ethical disclosures
Protection of human and animal subjects. The authors declare that no experiments were performed on humans or animals for this study.
Confidentiality of data. The authors declare that they have fol lowed the protocols of their work center on the publication of patient data.
Right to privacy and informed consent. The authors declare that no patient data appear in this article.
