Before Src Bosutinib US visualization, palpation of bony landmarks was the only available technique for identifying the lumbar interspinous spaces. Stiffler et al. [11] reported difficulty in palpating landmarks in 5% of patients with normal BMI, 33% in those who were overweight, and in 68% of obese patients. The spinous processes of some obese patients can be located more than 5cm from the skin, with the ligamentum flavum as deep as 8cm, and at extremes of 11-12cm deep [12]. Grau et al. [13] determined that at term, the optimum puncture area on the skin for epidural cannulation is smaller, the soft tissue channel between the spinal processes is narrower, and the epidural space is also narrower. Each of these changes would most likely be exaggerated in those patients who are morbidly obese.

Other reasons include difficulty in patient positioning and an increased likelihood for false positivity to the loss of resistance technique when locating the epidural space [13, 14]. The use of ultrasonography (US) for placing epidural catheters has become increasingly popular and has been shown to reduce epidural catheter failure rates and placement attempts [15, 16]. US can be used to identify the epidural space, localize midline, provide an estimation of depth from skin to the epidural space, and estimate the point of insertion and the angle of needle insertion [16�C19]. Prepuncture visualization of the epidural space has been shown to decrease the number of attempts for epidural placement and decrease the incidence of accidental dural puncture, especially among new resident trainees [12, 15, 16].

The presence of increased adipose tissue makes GSK-3 US visualization of the epidural space more challenging, and a significant problem when using US in obese parturients is that decreased visualization of the epidural space makes estimation of the distance from the skin to the epidural space less predictable [12].In a previous study, we investigated the use of US for epidural catheter placement in laboring parturients, found high correlation between estimated US depth and actual needle depth (ND); (Pearson’s correlation coefficient ��0.91) [16], and derived an epidural depth equation (EDE) using stepwise multivariate linear regression for predicting the distance from the skin to the epidural space in the lower lumbar intervertebral area.In a study by Balki et al. [20] on morbidly obese parturients using US, they found a Pearson’s correlation coefficient of 0.85 between the US estimated distance to the epidural space and the actual needle depth (ND).