Identification of cervicothoracic intervertebral spaces by surface landmarks and ultrasound.

PURPOSE: Precise localization of the cervicothoracic vertebral levels is essential for accurate placement of epidural catheters. Previous studies have demonstrated that anesthesiologists are inaccurate when using surface anatomy to locate lumbar vertebral levels. Our study was designed to determine the agreement between anatomical landmarks and the ultrasound technique in identifying the T7-8 and C7-T1 intervertebral spaces. METHODS: Adult healthy volunteers were assessed for the identification of cervicothoracic intervertebral spaces, initially in the anatomic position (AP)-upright, back straight, arms at the sides, and palms forward and then in the epidural position (EP) routinely used for epidural placement-seated, back arched, neck flexed, and arms across the chest. The T7 and C7 spinous processes were identified by one investigator using the inferior tip of the scapula and the vertebra prominens, respectively, as landmarks. Ultrasound was then used by a second investigator to identify the intervertebral spaces corresponding to the previously marked levels. RESULTS: Fifty-five volunteers (23 males, 32 females) were recruited. The T7-8 intervertebral space determined by ultrasound coincided with the landmark findings in the AP and in the EP in 18% and 36% of the cases, respectively. The C7-T1 interspace identified by ultrasound corresponded with the surface landmarks in the AP and in the EP in 53% and 58% of the cases, respectively. In most cases, when the surface landmark and ultrasound findings of T7-8 did not agree, the surface landmark identified a lower interspace than ultrasound. CONCLUSION: Identification of cervicothoracic intervertebral spaces by surface landmarks corresponded poorly with their identification using ultrasound. However, compared with the upright position, agreement in identifying the T7-8 interspace improved in the epidural position.

Sonoanatomy of the thoracic spine in adult volunteers.

BACKGROUND AND OBJECTIVES: Ultrasonography of the lumbar spine provides information to facilitate the placement of neuraxial anesthesia. Likewise, thoracic spine ultrasound (US) might conceivably improve the quality and safety of thoracic epidural anesthesia. The objective of this study was to advance our understanding in this area by providing a detailed description of the sonoanatomy of the thoracic spine. METHODS: This was a prospective, observational, cohort study in 61 adult volunteers. We performed US scanning of all thoracic interspaces in the right paramedian sagittal oblique (PSO) and transverse median (TM) planes. The images were classified as conclusive and inconclusive, depending on the visibility of ligamentum flavum-dura mater complex (Lf-Dm). The primary outcome was the presence of conclusive images. The secondary outcomes were measurements of various distances between sonoanatomic elements. Data are presented as mean (SD), unless otherwise specified. RESULTS: Overall, the incidence of conclusive images was higher in the PSO than in the TM plane (74.5% [15.4%] versus 37.5% [39.7%], P < 0.001). In the lower thoracic levels, 98% of images were conclusive in both planes, but the number of conclusive images decreased progressively in the upper thoracic levels, more so in the TM than in the PSO plane. The mean depth to Lf-Dm was similar when measured in both PSO (4.0 [0.7] cm) and TM planes (4.1 [0.7] cm). CONCLUSIONS: Ultrasound imaging of the thoracic spine in the PSO plane provides better views of the Lf-Dm compared with the TM plane. A upper incidence of inconclusive sonograms should be expected in the upper thoracic segments, which can be attributed to the narrower acoustic windows at these levels.

Ultrasound imaging of the thoracic spine in paramedian sagittal oblique plane: the correlation between estimated and actual depth to the epidural space.

BACKGROUND: Ultrasound (US) imaging of the spine has been shown to be a reliable tool to facilitate lumbar epidural needle placement; however, its feasibility in thoracic epidural placement is still unknown. The objective of this study was to assess the accuracy and reliability of prepuncture US imaging in the paramedian sagittal oblique plane to estimate the depth to the epidural space and optimum insertion point for guiding epidural needle placement at the mid-low thoracic level. METHODS: This prospective study included 35 healthy adult patients who requested thoracic epidural analgesia before their upper abdominal surgeries. Ultrasound imaging was done in the paramedian sagittal oblique plane at the desired thoracic level to identify the intervertebral space, the distance from the skin to the epidural space (US depth [UD]) and the needle insertion point. Subsequently, a staff anesthesiologist 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 and concordance correlation coefficients and Bland-Altman analysis with 95% limits of agreement. RESULTS: The average patient age was 56 (SD, 14) years, and body mass index was 28 (SD, 6) kg/m2. The precision of the agreement between UD and ND estimated by Pearson correlation coefficient was 0.75, and the accuracy was 0.80, whereas the concordance correlation coefficient was 0.60 (confidence interval, 0.43-0.78). The mean UD and ND were 4.3 (SD, 0.96) and 5.0 (SD, 1.2) cm, respectively. The Bland-Altman analysis showed a mean difference of -0.71 cm (95% limits of agreement, 0.8 to -2.2 cm). There was a significant direct correlation of the ND with the body mass index (r2 = 0.27, P = 0.008). The mean number of attempts was 1 (p25-p75 = 1-2), and the epidural space was identified with 2 or less redirections in 88% of the cases. CONCLUSIONS: We found a good correlation between the US-estimated distance to the epidural space and the actual measured needle distance in our patients. We suggest that our proposed prepuncture US method, using the paramedian sagittal oblique approach, can be a useful guide to facilitate the placement of epidural needles at mid-low thoracic levels. A randomized controlled trial is necessary to confirm the utility of prepuncture US in thoracic epidural placement.