Presented at the Neonatal Society 2008 Autumn Meeting.
Merchant N1,2, Edwards AD1,2, Groves A1,2, Counsell S1, Hajnal J1, Srinivasan L1,2, Thomson MA2, Allsop J1, Rutherford M1, Boardman JP1,2
1 Division of Clinical Sciences, Imperial College London and MRC Clinical Sciences Centre Hammersmith
2 Division of Neonatology, Imperial College Comprehensive Biomedical Research Centre, Du Cane Road, London, W12 0HS
Background: Preterm infants can safely undergo magnetic resonance (MR) imaging while receiving mechanical ventilation (1,2). However this population is increasingly cared for using nasal continuous positive airway pressure (nCPAP) and it is not known if this can be successfully used during MR imaging at 3.0 Tesla.
Aims: 1) To describe a customized system for MR image acquisition from preterm infants requiting nCPAP; and 2) to test the clinical stability of a consecutive cohort of preterm infants undergoing MR imaging.
Patients & Methods: 53 preterm infants weighing less than 1500g were imaged for research between 01/05/2007 and 31/5/2008 in the 3T MR imaging suite situated within the Neonatal Intensive Care Unit. Ethical approval was granted by Hammersmith and Queen Charlotte’s and Chelsea Research Ethics Committee. At the time of the scan, median post menstrual age was 30 weeks (range 26.7-37.1) and weight 930g (660-1480g).
Preparation for imaging: Infants were dressed in two layers of metal-free clothing, plastic wrap and a hat prior to transport to the MR suite where the ambient temperature is 28°C. MR compatible ECG leads, skin temperature and pulse oximetry probes were sited and the infant swaddled in pre-warmed sheets but not sedated. Acoustic noise is minimised by applying moldable dental putty to the ears, covering them with neonatal ear muffs (Natus) and surrounding the head with a vacuum-evacuated bag filled with polystyrene balls that also aids immobilization. Infusions are run from remote drivers and all care supervised by a neonatologist.
Ventilatory support: Piped gases and an air / oxygen blender are fitted to the wall of the MR suite. nCPAP is delivered using the Bubble nCPAP Infant Delivery System BC161 (Fisher and Paykel). Gas flow (6-8L/min) is warmed and humidified in a radiofrequency shielded unit situated beyond the 5 Gauss line and lengthened delivery tubing insulated to minimize heat loss. nCPAP pressure was 5-8cmH20.
Results: Images were successfully acquired in 51/53 cases. The median scan time was 55 minutes (range 30-85). Images were not acquired from two infants because skin temperature was <36°C before beginning scanning. 15 infants received nCPAP, 19 received supplemental oxygen by nasal cannulae, and 17 breathed spontaneously in air. There were no significant adverse events. 41 infants (80%) had transient self-correcting desaturations that did not require intervention (duration <30s and none SaO2<80%). In 10 infants, a desaturation occurred that required interruption of the scan for assessment, with or without adjustment of airway position or an increase in FiO2. This was less common among infants receiving nCPAP (1/15) or breathing spontaneously in air (2/17), and more frequent among infants receiving oxygen by nasal cannulae (7/19). 46 (90%) infants had a skin temperature >36°C at completion of the scan. The lowest recorded skin temperature at the end of the scan was 35.7°C. There was no relationship between weight and skin temperature at end of scan; or use of nCPAP and skin temperature <36°C at end of scan (p=0.14 Fisher’s exact).
Conclusion: Preterm infants can be imaged successfully at 3.0T while undergoing nCPAP.
References
1.Battin M, Maalouf EF, Counsell SJ et al. Early Human Development 1998; 52:101-110.
2. Maalouf EF and Counsell SJ. In Rutherford M, ed 1. MRI of the neonatal brain. Edinburgh: Saunders, 2002: 17-21.