Novel 3D ultrasound system for midline single-operator epidurals: a feasibility study on a porcine model.

BACKGROUND: We developed a real-time 3D ultrasound thick slice rendering technique and innovative Epiguide needle-guide as an adjunct to single-operator midline epidural needle insertions. Study goals were to determine feasibility of the technique in a porcine model and compare the visibility of standard and echogenic needles. METHODS: Thirty-four lumbar needle insertions were performed on six intact porcine spines ex vivo. Ultrasound scanning identified the insertion site and, using an Epiguide, the needle was guided into the epidural space through the ligamentum flavum in the midline plane, watched in real-time on the 3D ultrasound. Entry into the epidural space was judged by a loss-of-resistance technique. Needle visibility was rated by the anesthesiologist performing the technique using a 4-point scale; (0=cannot see, 1=poor, 2=satisfactory, 3=excellent), and later by an independent assessor viewing screenshots. The procedure was repeated at all lumbar levels using either the standard or echogenic needle. RESULTS: Successful loss-of-resistance to fluid was achieved in 76% of needle insertions; needle visibility with echogenic needles (94.2% rated satisfactory/excellent) was significantly better than with standard needles (29.4% satisfactory/excellent, P<0.0001). Successful loss-of-resistance was 93% when mean needle visibility was rated as 'excellent'. Inter-observer agreement between assessors was 'near-perfect' (weighted kappa=0.83). CONCLUSION: It is feasible to perform 3D ultrasound-guided real-time single-operator midline epidural insertions, in a porcine model. Echogenic needles were found to consistently improve needle visibility; and improved needle visibility tended to increase successful entry into epidural space.

Diurnal changes in lumbar intervertebral distance, measured using ultrasound.

STUDY DESIGN: This study measured the distances between the tips of the transverse processes of adjacent lumbar vertebrae (L1-L4) in the same subjects after 1 day of normal activities and again the next morning. OBJECTIVES: To determine the feasibility of directly measuring the lumbar intervertebral distance using ultrasound and to determine the magnitude of the diurnal change in the intervertebral distance. SUMMARY OF BACKGROUND DATA: A diurnal variation in height results from, in part, a decrease in height of the intervertebral discs with loading of the spine during the day. Previous estimates of the diurnal changes in disc height have used radiologic, stereophotographic, and magnetic resonance imaging techniques. No previous study has used ultrasound imaging. METHODS: Ultrasound was used to measure the distance between the tips of adjacent lumbar vertebral transverse processes. Measurements were made on six occasions in each of seven subjects after 6:00 PM in the evening and again the following morning before rising. RESULTS: The distance between the tips of adjacent transverse processes could be measured, within an individual, with a reproducibility of better than +/- 7.5% coefficient of variation. Reproducibility of the measurement of the total distance between L1 and L4 was better than +/- 4%. The intervertebral distances between L1 and L4 were significantly greater in the morning than in the evening. The average diurnal change in the total intervertebral distance L1-L4 was 5.3 mm. CONCLUSIONS: The study confirms the feasibility of using ultrasound to directly measure changes in the distances between the lumbar vertebrae.

Sonographic measurement of the fetal femur: factors affecting accuracy.

Variations have been observed in the measurement of fetal femoral diaphysis length by ultrasound. This in vitro study examines the effect of depth, the angle of the bone relative to the axis of the sound beam, the machine, and the observer on the precision of measurement. Using analysis of variance techniques, it demonstrates that three of these factors (depth, angle, and machine) have significant effects. Depth-associated variations were less than one millimeter and are probably not of clinical importance. However, the variations due to changes in angle are highly significant (P = less than 0.001) and may be controlled by obtaining the measurement with the femur perpendicular to the sound beam. Errors due to variation between machines were also highly significant (P = less than 0.001). When determining serial growth patterns, the errors due to variations between machines can be controlled by using the same machine for each examination. The variation between machines is also an important factor to consider when choosing a curve for reference purposes.

Fetal pyelectasis: comparison of postnatal renal pathology with unilateral and bilateral pyelectasis.

The aim of this study was to determine the prenatal fetal pyelectasis which requires postnatal evaluation. This was a retrospective analysis involving 65 infants with complete urological follow-up; 59 had shown prenatal evidence of pyelectasis using previously published standards. Males were more common in both the normal (75 per cent) and the abnormal (77 per cent) postnatal outcome groups. Unilateral prenatal lesions were less common than bilateral, but had significant postnatal pathology in 47 and 26 per cent, respectively (n.s.). Persistent dilatation was likely to be associated with postnatal pathology. A 6 mm threshold of dilatation predicted the 19 infants with significant postnatal pathology. The majority of fetuses with pyelectasis in the study had normal outcomes, with males often showing 'transitory pyelectasis'. A repeat prenatal scan at 30-40 weeks' gestation is recommended for all fetuses where 6 mm or more of renal pelvic dilatation is detected prior to 28 weeks. Postnatal follow-up is required for persistent pyelectasis.

Ultrasound fetal biometry charts for a North American Caucasian population.

PURPOSE: This study was done to produce enhanced fetal biometry charts and graphs presenting percentile values as a function of fetal age. METHODS: The relationships between the ultrasound measurements of 10 fetal parameters and menstrual age were determined by a cross-sectional study. Data were obtained from 508 to 790 fetuses. Anatomic structures were scanned and measured 3 times during 1 routine sonographic examination. The study group consisted of 1,396 Caucasian women who had normal singleton fetuses with confirmation of menstrual dates by sonography before 14 weeks and for whom complete pregnancy outcome information was available. For each of the 10 parameters, percentile curves were derived for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles. RESULTS: Ready-to-use fetal measurement charts and graphs are presented in a format giving the percentile values as a function of fetal age. There were no significant differences between male and female fetuses. CONCLUSIONS: These fetal biometry charts and graphs, obtained from a North American Caucasian population, enhance previously published data.