title: Diaphragm ultrasound as indicator of respiratory effort in critically ill patients undergoing assisted mechanical ventilation: a pilot clinical study.
abstract: BACKGROUND
  Pressure-support ventilation, is widely used in critically ill patients; however, the relative contribution of patient's effort during assisted breathing is difficult to measure in clinical conditions. Aim of the present study was to evaluate the performance of ultrasonographic indices of diaphragm contractile activity (respiratory excursion and thickening) in comparison to traditional indices of inspiratory muscle effort during assisted mechanical ventilation.
  
  
  METHODS
  Consecutive patients admitted to the ICU after major elective surgery who met criteria for a spontaneous breathing trial with pressure support ventilation were enrolled. Patients with airflow obstruction or after thoracic/gastric/esophageal surgery were excluded. Variable levels of inspiratory muscle effort were achieved by delivery of different levels of ventilatory assistance by random application of pressure support (0, 5 and 15 cmH2O). The right hemidiaphragm was evaluated by B- and M-mode ultrasonography to record respiratory excursion and thickening. Airway, gastric and oesophageal pressures, and airflow were recorded to calculate indices of respiratory effort (diaphragm and esophageal pressure-time product).
  
  
  RESULTS
  25 patients were enrolled. With increasing levels of pressure support, parallel reductions were found between diaphragm thickening and both diaphragm and esophageal pressure-time product (respectively, R = 0.701, p < 0.001 and R = 0.801, p < 0.001) during tidal breathing. No correlation was found between either diaphragm or esophageal pressure-time product and diaphragm excursion (respectively, R = -0.081, p = 0.506 and R = 0.003, p = 0.981), nor was diaphragm excursion correlated to diaphragm thickening (R = 0.093, p = 0.450) during tidal breathing.
  
  
  CONCLUSIONS
  In patients undergoing in assisted mechanical ventilation, diaphragm thickening is a reliable indicator of respiratory effort, whereas diaphragm excursion should not be used to quantitatively assess diaphragm contractile activity.
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Azienda Ospedaliera San Paolo - Polo Universitario, Via A. Di Rudinì, 8-20142, Milano, Italy. michele.umbrello@fastwebnet.it.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. michele.umbrello@fastwebnet.it.
authors.forename: Michele
authors.initials: M
authors.lastname: Umbrello
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Azienda Ospedaliera San Paolo - Polo Universitario, Via A. Di Rudinì, 8-20142, Milano, Italy. formenti.paolo@fastwebnet.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Formenti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. denny89rz@hotmail.com.
authors.forename: Daniela
authors.initials: D
authors.lastname: Longhi
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. andrea.galimberti@ao-sanpaolo.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Galimberti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. ilaria.piva@unimi.it.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Piva
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Azienda Ospedaliera San Paolo - Polo Universitario, Via A. Di Rudinì, 8-20142, Milano, Italy. angelo.pezzi@ao-sanpaolo.it.
authors.forename: Angelo
authors.initials: A
authors.lastname: Pezzi
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Azienda Ospedaliera San Paolo - Polo Universitario, Via A. Di Rudinì, 8-20142, Milano, Italy. giovanni.mistraletti@unimi.it.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. giovanni.mistraletti@unimi.it.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Mistraletti
authors.affiliation: Department of Pulmonary and Critical Care, University of Minnesota, Regions Hospital, St Paul, MN, USA. marini@healthpartners.com.
authors.forename: John J
authors.initials: JJ
authors.lastname: Marini
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Azienda Ospedaliera San Paolo - Polo Universitario, Via A. Di Rudinì, 8-20142, Milano, Italy. g.iapichino@ao-sanpaolo.it.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy. g.iapichino@ao-sanpaolo.it.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Iapichino
mesh_terms: D000368:Aged; D016638:Critical Illness; D003964:Diaphragm / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D010865:Pilot Projects; D011175:Positive-Pressure Respiration; D014463:Ultrasonography; D014939:Work of Breathing