肥胖产妇腰椎横切面超声：硬膜外腔深度的超声测定值和实际值的关系

背景非肥胖产妇在腰椎穿刺术前，行超声扫描可有效辅助硬膜外穿刺针的放置。在本研究中，我们通过超声技术估计皮肤至硬膜外腔的深度并且确定最适腰椎穿刺点，对超声影像学辅助肥胖产妇行腰椎穿刺术进行评价。方法本研究选择46例要求硬膜外分娩镇痛的肥胖产妇，孕前体重指数（prepregnancybodymasSindex，BMI）〉30kg／m2。由一位研究者确定背中线、椎间隙，并在L3-4水平超声扫描并测定皮肤至硬膜外腔的距离，即超声深度（ultrasounddepth，UD）。然后，由麻醉科医师在未知UD的前提下，在预定穿刺点进行硬膜外穿刺术，并根据无菌穿刺针的刻度，记录皮肤至硬膜外腔的实际深度（needledepth，ND）。采用Pearson相关系数和配对t检验对UD和ND的一致性进行分析。采用Bland．Allman分析确定95％置信区间。结果孕前BMI为30—79kg／m。的患者，分娩时BMI为33—86kg时。UD和ND的Pearson相关系数为0．85（95％置信区间：0．75—0．91），一致性相关系数为0．79（95％置信区间：0．71—0．88）。UD平均值（±标准差）为6．6±1．0cm，ND平均值（±标准差）为6．3±0．8cm（差异为0．3cm，P=0．002）。95％置信区间为1．3±0．7cm。在预定穿刺点成功穿刺的产妇占76．1％，其中67．4％的产妇一次试穿成功。结论肥胖产妇应用超声技术测定的硬膜外腔深度和实际值存在良好的一致性。因此，肥胖产妇腰椎穿刺术前行超声检查，可能是引导硬膜外穿刺针成功放置的有效手段。

BACKGROUND： Prepuncture lumbar ultrasound scanning is a reliable tool to facilitate labor epidural needle placement in nonobese parturients. In this study, we assessed prepuncture lumbar ultrasound scanning as a tool for estimating the depth to the epidural space and determining the optimal insertion point in obese parturients. METHODS： We studied 46 obese parturients, with prepregnancy body mass index （BMI） 〉30 kg/m2, requesting labor epidural analgesia. Ultrasound imaging was done by one of the investigators to identify the midline, the intervertebral space, and the distance from the skin to the epidural space （ultrasound depth, UD） at the level of L3 -4. Subsequently, an anesthesiologist blinded to the UD located the epidural space through the predetermined insertion point and marked the actual distance from the skin to the epidural space （needle depth, ND） on the needle with a sterile marker. The agreement between the UD and the ND was calculated using the Pearson correlation coefficient and a paired t-test. Bland-Altman analysis was used to determine the 95% limits of agreement between the UD and the ND. RESULTS： The prepregnancy BMI ranged from 30 to 79 kg/m2, and the BMI at delivery was 33 - 86 kg/m2. The Pearson correlation coefficient between the UD and the ND was 0. 85 （95% confidence interval： 0.75 -0. 91 ）, and the concordance correlation coefficient was 0. 79 （95% confidence interval： 0. 71 -0. 88）. The mean （ ＋ SD） ND and UD were 6. 6 ± 1.0 cm and 6. 3± 0. 8 cm, respectively （difference = 0. 3 cm, P = 0. 002）. The 95% limits of agreement were 1.3 cm to -0.7 cm. Epidural needle placement using the predetermined insertion point was done without reinsertion at a different puncture site in 76. 1% of parturients and without redirection in 67.4%. CONCLUSIONS： We found a strong correlation between the ultrasound-estimated distance to the epidural space and the actual measured needle distance in obese parturients. We suggest that prepuncture lumbar ultrasound may be a useful guide to facilitate the placement of epidural needles in obese parturients.