Mechanical Vibration in Neonatal Transport: A Randomized Study of Different Mattresses

Abstract

OBJECTIVE:To test the hypothesis that a gel mattress is most effective in attenuating mechanical vibration in neonatal transport, we performed a randomized block study of four mattress combinations (none, foam, gel, gel on foam) using mannequins and an ambulance traveling on fixed routes (city, highway). STUDY DESIGN:Mechanical vibration was assessed by measuring vertical accelerations at two locations: the forehead of a 2000-gm mannequin and the transport incubator base. From time histories of these accelerations, root mean square (RMS) values and power spectral density functions were calculated. The effect of the mattress on the transmission of vibration was determined from ratios of the RMS values at the two locations. An RMS ratio of Ͻ1.0 indicates attenuation, whereas a ratio of Ͼ1.0 indicates accentuation of vibration. From the power spectral density functions, the natural frequency of the system was determined for each mattress combination in relation to the natural frequencies of the ambulance. To determine the effect of the weight of the mannequin on vibration, additional measurements were performed using a 300-gm mannequin. RESULTS:All the observed RMS ratios were Ͼ1. The highest ratios were observed on the city route in the absence of the gel mattress. The gel mattress, used alone or with the foam mattress, in contrast to foam or no mattress, shifted the natural frequency of the system away from the natural frequencies of the ambulance, avoiding a large amplification of vibration. A decrease in the weight of the mannequin caused the gel mattress to be less effective in attenuating vibration. CONCLUSION:A gel mattress, used alone or with a foam mattress, results in the least accentuation of vibration, but vibration in ambulance transport is not attenuated by any of the mattress combinations. The hazard of vibration may be particularly relevant when transporting extremely low birth weight neonates. These findings indicate a need for study and design of more effective devices that can reduce the vibratory stress. Journal of Perinatology 2000; 5:307-310.In the perinatal health care system, sick newborn infants often are transported from community hospitals to specialized care facilities. It is also common to transport convalescing newborn infants back to community hospitals before home discharge. During these transports, infants are exposed to prolonged, low-frequency, high-amplitude mechanical vibration. [1][2][3] In adult humans and experimental animals, this vibration has adverse effects on cardiorespiratory function, 4 -8 the peripheral and central nervous system, 8 -10 electroencephalographic activity, 11 body temperature, 12 metabolic and endocrinologic function, 8 and the gastrointestinal system. 8 In addition, vibration may contribute to general discomfort, motion sickness, vomiting, and increased intracranial pressure 8,13 and may also compromise clinical observation. 14 Vibration has deleterious effects on pregnant women and fetuses. Vibration is associated with the risk of premature delivery in...

Neonatal head and torso vibration exposure during inter-hospital transfer

“…Compared to the incubator chassis, spectral density in the 3–20 Hz range is up to four times higher at the torso and forehead sensor sites, indicating that vibration is amplified over this spectral range. This finding is in agreement with a previous study by Gajendragadkar et al, 13 in which the mattress system amplified vibration magnitude by factors of between 2.2 to 3.4 (sponge) and 1.1 to 2.1 (gel type). However, this previous study is not directly comparable, as it compared RMS values computed from 50 Hz low-pass-filtered acceleration data.…”

“…This frequency lies close to the 14 Hz chassis vibration peak, believed to originate from the engine and transmission, and so is easily excited. Mattress-induced resonance was highlighted in a previous study by Gajendragadkar et al, 13 who found vibration gain factors which are comparable to those measured in this study. However, this is the first study to demonstrate, in real patients, that the neonatal head is exposed to mechanical vibration hazard in excess of that simply observed at the incubator chassis.…”

“…Root-mean-square (RMS) vibration power spectral density was computed, concluding that vibration exposure reaches high levels compared to adult workplace limits. Campbell et al 12 measured similar vibration magnitudes, their analysis method differing from Shenai by use of a multi-axis accelerometer, while Gajendragadkar et al 13 used manikins together with three-axis accelerometers (on the manikin’s head and transport incubator chassis) to measure both vibration exposure during different transport routes and the isolation properties of mattress configurations. However, these studies did not use standardised methodologies to quantify the hazards associated with whole-body vibration (WBV): Shenai was limited by single-axis measurements, Gajendragadkar failed to validate manikin models against patients, and all three failed to use standardised axis-dependent frequency weightings.…”

Sound and vibration: effects on infants’ heart rate and heart rate variability during neonatal transport

“…The accelerometer was fastened in the incubator directly under the mattress, and in theory, a vibration-dampening effect of the foam mattress on which the infant was lying cannot be excluded. However, this appears unlikely, as it has been shown that foam mattresses, like the one we used, do not attenuate vibration (14). In contrast, in adults an experimental model with constant acceleration amplitude and variable vibration frequencies showed an influence in HRV (15) and another showed that hand-transmitted vibrations lead to decreased HRV (16).…”

Finding Comfortable Routes for Ambulance Transfers of Newborn Infants

“…Data collection was embraced by the neonatal transport group with almost 1,700 journeys in 12 months recorded. Attaching to the neonatal trolley, along with more than 50 times the amount of data in any previous study [6], [7], [11], [12], allows a better understanding of what the baby is experiencing.…”