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Magnetic phrenic nerve stimulation to assess diaphragm function in children following liver transplantation
Gerrard F. Rafferty1, Anne Greenough, Terezia Manczur
1Department of Child Health (Drs. Rafferty, Greenough, and Manczur), the Department of Respiratory Medicine and Allergy (Dr. Polkey, Ms. Harris, and Dr. Moxham), and the Department of Surgery (Mr. Heaton and Mr. Rela), Guy's, King's and St Thomas' School of Medicine, King's College Hospital, Bessemer Rd, London SE5 9PJ.
Abstract:
BACKGROUND: An accurate and practical test of diaphragm function in children in the intensive care unit is desirable. Diaphragm dysfunction can occur after liver transplantation and may be a contributory factor in the respiratory complications after the procedure. OBJECTIVE: Our aim was to assess if magnetic stimulation (MS) of the phrenic nerves could be used to assess diaphragm strength in children receiving intensive care. SETTING: Pediatric intensive care unit. PATIENTS: Eight supine, ventilated, sedated children (mean age, 7.3; range, 0.6-15 yrs) were studied within 12 hrs of liver transplantation. INTERVENTIONS: MS was performed using either 90-mm double circular coils or 43-mm figure of eight coils placed over the phrenic nerves on the anterior aspect of the neck. Measurements: The produced diaphragm force was assessed by measuring the transdiaphragmatic pressure (Pdi) with balloons in the mid-esophagus and stomach. During MS, the endotracheal tube was briefly occluded by using a pneumatic valve. MAIN RESULTS: Supramaximal diaphragm force responses were obtained in all subjects; mean Pdi, 7.8 (sd, 3.1) cmH(2)O for left, 5.2 (sd, 3.4) cmH(2)O for right, and 14.8 (sd, 9.2) cmH(2)O for bilateral stimulation. Bland and Altman analysis indicated close agreement between esophageal and airway pressure during MS (mean difference, -0.76 [sd, 0.99] cmH(2)O for left stimulation, 0.81 [sd, 1.25] cmH(2)O for right stimulation, and -0.63 [sd, 1.55] cmH(2)O for bilateral stimulation). In three children, there was a >50% difference between the Pdi generated after left and right unilateral MS and the results of MS indicated complete right hemidiaphragm paralysis in one child. CONCLUSION: MS of the phrenic nerves provides a practical technique for assessing diaphragm function in children receiving intensive care. Measurement of airway pressure during MS may provide a noninvasive technique for assessing diaphragm strength when the use of balloon catheters is contraindicated.