We retrospectively reviewed 60 normal magnetic resonance imaging scans to assess the anatomical shape of the thecal sac at the L3 ⁄ 4 and L4 ⁄ 5 vertebral interspaces. In all cases the thecal sac was oval at L3 ⁄ 4 but in 26 (43%; 95% CI 31-55%) the thecal sac changed from oval at the L3 ⁄ 4 interspace to triangular at L4 ⁄ 5 (with the apex of the triangle presenting to the posterior epidural space). We propose that this anatomical variant would make it more difficult to obtain cerebrospinal fluid at the lower level, as a slightly lateral approach could lead to identification of the epidural space but failure to puncture the thecal sac. This may offer an explanation for a 'dry tap' when a lower interspace is chosen. Damage to the conus is a potentially serious complication of inserting a needle into the thecal sac. This can occur during spinal or combined spinalepidural (CSE) anaesthesia or lumbar puncture. Following a number of case reports [1,2] it was recommended by Reynolds that these procedures should be performed at the lowest possible palpable interspace, which could be between the spinous processes of L4 and L5 or occasionally lower. It has been found that, especially during the needle-throughneedle CSE technique, the epidural space can sometimes be located but cerebrospinal fluid (CSF) not obtained because of failure to puncture the dura as the spinal needle protrudes from the Tuohy needle. The incidence of this is reported to be between 5% and 16% [3][4][5]. We have observed that this problem may occur more frequently when the lowest palpable interspace is used, with easier thecal puncture when the procedure is performed one interspace higher. We therefore undertook a retrospective review of normal lumbar magnetic resonance imaging (MRI) scans to determine if there was an anatomical reason underlying these observations.
MethodsApproval was obtained from the Trust's Audit Department and the Local Research Ethics Committee considered formal review unnecessary. Magnetic resonance imaging scans of the lumbar spine with T1 and T2 weighted sagittal and axial images were retrospectively reviewed. All patients had been referred for MRI scan for the investigation of lower back pain and the scans had been reported as anatomically normal. An initial number of 100 patients was proposed but as our search criteria were very strict, looking only for normal MRI studies performed for non-neurological conditions, a total of 60 scans was found after hand searching several years of reports. A hypothetical calculation, based on our findings after 60, showed that doubling our sample size further would reduce our 95% CI by only ± 3%.On an initial review of a small number of scans it was noted that in some cases there was a change in shape of the spinal canal and thecal sac within it, on the axial images, from oval at the mid space of L3 ⁄ 4 to triangular at the mid space of L4 ⁄ 5. The review of subsequent scans was then based on this initial observation and a series of
BackgroundPreterm delivery interrupts the acquisition of nutrient stores that normally occurs during the later period of gestation. Energy and nutrient needs of preterm infants can be 20 to 300% greater than those of term infants. Little is known about the nutritional status or requirements of preterm lambs that are chronically ventilated. Therefore, we compared the nutritional status of chronically ventilated preterm lambs to term lambs.HypothesisWe hypothesized that serum glucose and fructose concentrations differ between ventilated preterm lambs and normal term lambs.MethodsPlasma samples, obtained at 0, 24, 48, 72h of life from preterm lambs (n=21; delivered at ˜130d gestation) and term lambs (n=7; term gestation ˜147d), were analyzed by enzymatic assays to determine glucose and fructose concentrations. Preterm lambs were managed by conventional mechanical ventilation (CV) or nasal continuous positive airway pressure (nCPAP) for 24 or 72h. Orogastric feeding of ewe's colostrum was begun within 6h of life and advanced as tolerated. Dextrose infusion (D10-12.5%) was also provided to maintain serum glucose concentration. Dextrose load (g/kg/d) was calculated from 24h intakes. Term lambs nursed ad libitum.ResultsNo significant differences for glucose or fructose concentrations were found between preterm and term lambs (e.g., glucose at 24h: 172±87 mg/dL (preterm; X±SD) vs 138± 56 (term) at 24h of life). No significant differences for dextrose load were found between the two preterm lamb groups (e.g., at 72h: 41±23 g/kg/d for CV vs 41± 15 for nCPAP).ConclusionGlucose and fructose nutritional status in preterm lambs was matched to that of term lambs. Whether protein and mineral status were maintained remains to be determined.
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