Positioning of infants in the neonatal intensive care unit for lumbar puncture as determined by bedside ultrasonography
Selim ÖNCEL1, Ayla GÜNLEMEZ2, Yonca ANIK3, Müge ALVUR4
1Division of Pediatric Infectious Diseases, 2Division of Neonatology, 3Department of Radiology, 4Department of Family MedicineKocaeli University Faculty of Medicine - TURKEY
Performing a lumbar puncture (LP) for diagnosing or ruling out meningitis in neonates is a standard of care despite the ongoing debate on whether LP is required in every workup for suspected sepsis.[1–3] The clinician seeks ways to avoid a traumatic tap and to get a sufficient amount of cerebrospinal fluid, which should be feasible in a still infant with the widest interspinous space (the space between the spinous processes of two adjacent vertebrae) possible.The positioning of the infant undergoing LP, which includes lateral recumbent or sitting positions with the neck or hip flexed or neutral, has not been standardized and is at the physician's disposal. In adults, studies have been conducted and uniformly showed that the maximal interspinal distance can be obtained with maximal hip flexion.[4,5] Most neonatologists prefer placing the infant in lateral recumbent position with the knees drawn up to the chest.Although there are studies looking at either positioning of hospitalized neonates without ultrasound or positioning and ultrasound in the emergency department, to our knowledge and as evidenced by a Pubmed search with keywords “lumbar puncture” and “ultrasound”, there are no studies assessing the optimum LP position for hospitalized neonates.[7–9] Safety, as well as the ease of the LP is a very important issue in this age group, especially considering the vulnerability of infants hospitalized in neonatal intensive care units.Realizing the paucity of data in this common field of pediatric infectious diseases and neonatology, we have designed a study to measure the interspinous distance in infants in various positions with concomitant heart rate (HR) and transcutaneous oxygen saturation (OS) measurements.
PATIENTS AND METHODS
This prospective and observational study of convenience sample of sick neonates was carried out in the Neonatal Intensive Care Unit of the Kocaeli University Research and Practice Hospital from November 2010 to February 2011. A patient in the neonatal intensive care unit was enrolled if her/his clinical condition does not pose a risk for the positioning maneuvers described below and if she/he did not undergo any spinal taps previously. After obtainment of parental consent, transcutaneous baseline OS and HR were measured. The infants were enrolled and held in two lateral recumbent and two upright positions by a neonatologist (A. G.). The lateral recumbent positions were 1) lateral recumbent without flexing the hips, in which the infant lies on her left side with hips and knees in neutral position and 2) lateral recumbent with maximal hip flexion, in which the infant lies on her left side with hips and knees flexed till the point of resistance. The upright positions were 1) sitting without flexing the hips, in which the infant sits with knees in neutral position and 2) sitting with maximal hip flexion, in which the infant sits with hips and knees flexed till the point of resistance. Measurements of OS, HR, and interspinous distances were made at these four positions. Care was taken to avoid neck flexion as this maneuver is known to be associated with a significant decrease in OS and a higher risk for potential morbidity.Measurements were made digitally in the four positions by a pediatric radiologist (Y. A.) on the digital still images on-screen obtained via a Toshiba Diagnostic Ultrasound System Model SSA-660A ultrasound device with a high-frequency (10 MHz) linear transducer, that was placed on the spine in the sagittal plane at the level of an imaginary line between right and left posterior superior iliac crests, which corresponds to L3-L4 and L4-L5 interspaces and has been reported as the appropriate sites for LP in all ages. The interspinous space was ensured to be the same place in all four positions by putting a mark with a pen on that imaginary line and not lifting the probe between the positions. The distance between the points of maximal curvature of the two adjacent spinous processes were measured as the interspinous (interspace) distance, since these points are the landmarks palpated by the physician performing the LP. Simultaneous HR and OS readings were recorded with each of the four positions.Statistical analysis: Data were analyzed with PSPP software (licensed under GPLv3). Descriptive figures were given as median/mean [standard deviation (SD) or (minimum-maximum)]. The differences between positions were examined using a paired t-test. P-values less than 0.05 was considered statistically significant.The study was approved by the Research Evaluation Committee of the Kocaeli University Faculty of Medicine (approval no.: 2010/24).
Fifty one infants (22 girls and 29 boys) with postnatal ages 1-83 days were enrolled in the study. The median/mean (minimum-maximum) postnatal and corrected ages of the patients were 10/17.82 (1-83) and 35.70/36.47 (31.43-45.90), respectively. Eleven (21.6%) patients' postnatal ages were beyond the neonatal period (>28 days). The birth weights of 4 (7.8%), 11 (21.6%) and 21 (41.2%) infants were in the extremely low (<1,000 g), very low (1,000-1,500 g) and low (1,500-2,500 g) ranges, respectively. The actual weights of 1 (2.0%), 8 (15.7%), 28 (54.9%), and 14 (27.5%) neonates were <1,000 g, 1,000-1,500 g, 1,501-2,500 g, and >2,500 g, respectively.Having the patient sit with maximal hip flexion provided the largest interspinous space for the grand majority of the infants (P = 0.001). The lateral recumbent position without flexing the hips has resulted in the narrowest interspinous space for a LP (P=0.001, for all positions).Although providing significantly larger interspinous spaces, sitting positions with/without flexion have resulted in significant increases in HR with respect to lateral recumbent position without flexion (P=0.01 and P=0.002, respectively). Similarly, statistically significant drops in OSs have been observed between lateral recumbent and sittting with flexion (P=0.007), lateral recumbent with flexion and sitting without flexion (P=0.015), and lateral recumbent with flexion and sitting with flexion positions (P=0.002). No adverse hypoxic events occurred during the procedure.
In adults, the position providing the significantly greatest interspinous space was obtained with the so-called “sitting, feet supported position” in which the patient touches her/his ankles while sitting. This position resembles our sitting with maximal hip flexion position in newborns. In a survey assessing the infant LP practices of pediatric emergency attending physicians, the lateral decubitus position was preferred by 82%. In a study carried on healthy preterm infants without measuring interspinous distances, Gleason et al. found that although PO2 decreased and the HR increased with each position for LP, the decrease was significantly greater in the recumbent position with maximal hip flexion. Cadigan and al., in their study assessing the recumbent without flexing the hips and recumbent with maximal hip flexion positions in healthy newborns in their well-child visits, also found that the latter position provided wider interspinous spaces.HR and OS differed significantly with positioning of the infants in our study; however this did not result in any apparent changes in clinical status.Although there are few infants weighing less than 1,500 g in our study population, our results show that sitting flexed position is a safe alternative to traditional flexed recumbent position.The limitations of our study may include small sample size, convenience sample, patients' exclusion if they had spinal taps or were too ill for positioning, absence of performed LPs, paucity of low (1,000 – 1,500 g) and very-low-weight (<1,000 g) infants in the study population, which prevented us from making satisfactory statistical comparisons, observers' unblindness to patient position during the procedure, and measurement of spinous processes from the point of maximal curvature although the interspinous space is truly the space between adjacent vertebrae.
Sitting flexed position, which seems to be sufficiently safe and serve to enhance the success rate of an LP should be favored for sick neonates whenever the infant's condition permit a spinal tap. Studies enrolling infants necessitating an LP in real-life conditions, especially those with low and very low weights will further enlighten the field and confirm our conclusions.
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