To our knowledge, this is the first study to evaluate the effect of patient position on cerebrospinal fluid opening pressure in a pediatric population. Despite finding a statistical difference in opening pressure between the flexed and extended position, this difference is relatively small and of doubtful clinical significance. Measurement of opening pressure in a single position can be of benefit to both the operator and patient, as patient movement during performance of lumbar puncture introduces the potential for lumbar puncture complications such as needle displacement, which can lead to increased time of the procedure, and even failure of the lumbar puncture. Additionally, since procedural sedation is often used, dual position opening pressure measurement increases time of the lumbar puncture, may arouse the calm patient, and therefore may increase the sedation time or even administration of additional sedative medications. However, in the current study, we were unaware of complications that occurred as a result of moving the patient from the flexed to extended position.
Our results are similar to previous reports that found, on average, small differences (i.e., < 2 cm H2
O) in opening pressure between positions in adults.4,5
Both studies also found that some patients surprisingly had an increase in cerebrospinal fluid opening pressure when moving from the flexed to the extended position, but neither offered an explanation or hypothesis regarding this finding.4,5
A wide range of opening pressure values were observed in our study, although a majority of patients in our study had an opening pressure greater than 20 cm H2
O. Three of 4 patients with a greater than 5 cm H2
O change in opening pressure when moved from the flexed to the extended position, had an opening pressure greater than 20 cm H2
O, although some suggest that a normal opening pressure in children can be as high as 28 cm H2
We found a significant negative correlation between mean opening pressure and change in opening pressure, suggesting that a larger decrease in opening pressure occurs at a higher opening pressure; however, the decreases were relatively small in magnitude. In adults, most changes in opening pressure greater than 5 cm H2
O when moving from flexed or extended position also occurred in subjects with an opening pressure greater than 20 cm H2
Degree of sedation has anecdotally been reported to affect the opening pressure in children.9
The results from our study found that the difference in opening pressure between positions was not influenced by depth of sedation. Whether depth of sedation independently influences opening pressure (e.g., deeper sedation results in a lower opening pressure), has not been studied and could not be addressed in our small sample size.
Our study had some degree of selection bias since not all patients enrolled in our study had their opening pressure measured in both the flexed and extended lateral recumbent positions. It is unclear what factors influenced some physicians to measure opening pressure in both positions while others measured opening pressure in just one position. Either most physicians are unaware of the need to move the patient from the flexed to the extended position, or they are fearful that moving the patient may cause them to displace the spinal needle and lose cerebrospinal fluid flow. The percentage of patients being diagnosed with headache or idiopathic intracranial hypertension was higher in our study group as compared to those subjects who were excluded from the analysis. This bias may reflect added attention in obtaining an accurate opening pressure in those subjects with a suspicion of high intracranial pressure. Another limitation of our study is that a majority of patients were sedated for their lumbar puncture. Our findings may not be applicable to other centers that do not sedate patients for lumbar puncture.
Lumbar puncture performed in the extended, rather than the flexed lateral recumbent position results in a statistically significant decrease in cerebrospinal fluid opening pressure, although the magnitude of the difference is small and of doubtful clinical significance. Therefore, sedated children undergoing lumbar puncture in the flexed lateral recumbent position do not need to have their legs extended to obtain another opening pressure measurement.