title: Measurement of twitch transdiaphragmatic, esophageal, and endotracheal tube pressure with bilateral anterolateral magnetic phrenic nerve stimulation in patients in the intensive care unit.
abstract: OBJECTIVE
  In the critically ill, respiratory muscle strength usually has been assessed by measuring maximum inspiratory pressure. The maneuver is volitional, and results can be unreliable. The nonvolitional technique of bilateral anterolateral magnetic stimulation of the phrenic nerves, producing twitch transdiaphragmatic pressure, has been successful in normal subjects and ambulatory patients. In this study we used the technique in the intensive care unit and explored the measurement of twitch endotracheal tube pressure as a less invasive technique to assess diaphragmatic contractility.
  
  
  METHODS
  Clinical study to quantify diaphragm strength in the intensive care unit.
  
  
  METHODS
  Patients from three London teaching hospital intensive care units and high-dependency units.
  
  
  METHODS
  Forty-one intensive care patients were recruited. Of these, 33 (20 men, 13 women) were studied.
  
  
  METHODS
  Esophageal and gastric balloon catheters were passed through the anaesthetized nose, and an endotracheal tube occlusion device was placed in the ventilation circuit, next to the endotracheal tube. Two 43-mm magnetic coils were placed anteriorly on the patient's neck, and the phrenic nerves were stimulated magnetically.
  
  
  RESULTS
  On phrenic nerve stimulation, twitch gastric pressure, twitch esophageal pressure, twitch transdiaphragmatic pressure, and twitch endotracheal tube pressure were measured. Forty-one consecutive patients consented to take part in the study, and twitch pressure data were obtained in 33 of these. Mean transdiaphragmatic pressure was 10.7 cm H2O, mean twitch esophageal pressure was 6.7 cm H2O, and mean twitch endotracheal tube pressure was 6.7 cm H2O. The mean difference between twitch esophageal pressure and twitch endotracheal tube pressure was 0.02 cm H2O. Correlation of the means of twitch endotracheal tube pressure to twitch esophageal pressure was 0.93, and that for twitch endotracheal tube pressure to transdiaphragmatic pressure was 0.78.
  
  
  CONCLUSIONS
  Transdiaphragmatic pressure can be measured in the critically ill to give a nonvolitional assessment of diaphragm contractility, but not all patients can be studied. At present, the relationship of twitch endotracheal tube pressure to transdiaphragmatic pressure is too variable to reliably represent a less invasive measure of diaphragm strength.
authors.affiliation: Kings College Hospital, London, UK.
authors.forename: A C
authors.initials: AC
authors.lastname: Watson
authors.forename: P D
authors.initials: PD
authors.lastname: Hughes
authors.forename: M
authors.initials: M
authors.lastname: Louise Harris
authors.forename: N
authors.initials: N
authors.lastname: Hart
authors.forename: R J
authors.initials: RJ
authors.lastname: Ware
authors.forename: J
authors.initials: J
authors.lastname: Wendon
authors.forename: M
authors.initials: M
authors.lastname: Green
authors.forename: J
authors.initials: J
authors.lastname: Moxham
mesh_terms: D000328:Adult; D000368:Aged; D003964:Diaphragm / Q000294:innervation / Q000503:physiopathology*; D004947:Esophagus / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D007385:Intermittent Positive-Pressure Ventilation; D007442:Intubation, Intratracheal; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D010791:Phrenic Nerve; D011312:Pressure; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000294:innervation / Q000503:physiopathology; D012133:Respiratory Paralysis / Q000175:diagnosis*; D015300:Ventilator Weaning