title: Alveolar pressure monitoring: an evaluation in a lung model and in patients with acute lung injury.
abstract: OBJECTIVE
  We evaluated an algorithm for continuous on-line monitoring of alveolar pressure over time in a lung model with lower and upper inflection points and variable resistance ratios and in patients with acute lung injury. The algorithm is based on "static" pressure/volume curves obtained from tracheal pressure measurements under dynamic conditions.
  
  
  METHODS
  Experimental and clinical evaluation of algorithm in a university hospital laboratory and intensive care unit.
  
  
  METHODS
  Ten patients undergoing postoperative respiratory therapy (feasibility of tracheal measurement) and ten patients with acute lung injury undergoing ventilator treatment (evaluation of algorithm).
  
  
  RESULTS
  Direct tracheal pressure measurements with a catheter inserted through the endotracheal tube. Comparison of measured alveolar and the dynostatic alveolar pressure vs. time in a lung model with changes in five ventilatory parameters. Examples of clinical monitoring are reported. In the model there was excellent agreement between alveolar pressures obtained by the algorithm, the dynostatic alveolar pressure, and measured alveolar pressure at all ventilator settings. For inspiratory/expiratory resistance ratios between 1:2.1-2.1:1, the dynostatic alveolar pressure was within +/-1.5 cm H(2)O of measured alveolar pressure. In patients the technique for direct tracheal pressure measurement using a catheter inserted through the endotracheal tube functioned satisfactorily with intermittent air flushes for cleansing.
  
  
  CONCLUSIONS
  Using a thin tracheal pressure catheter inserted through the endotracheal tube alveolar pressure allows continuous bedside monitoring with ease and precision using the dynostatic algorithm. The method is unaffected by tube and connector geometry or by secretions.
authors.affiliation: Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, Gothenburg, Sweden. soren.sondergaard@swipnet.se.
authors.forename: S
authors.initials: S
authors.lastname: Sondergaard
authors.affiliation: Department of Anaesthesia and Intensive Care, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: S
authors.initials: S
authors.lastname: Kárason
authors.affiliation: Department of Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Wiklund
authors.affiliation: Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Lundin
authors.affiliation: Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: O
authors.initials: O
authors.lastname: Stenqvist
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000403:Airway Resistance; D000465:Algorithms; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D008170:Lung Compliance; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D008991:Monitoring, Physiologic / Q000379:methods* / Q000592:standards; D011175:Positive-Pressure Respiration; D011312:Pressure; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D011669:Pulmonary Wedge Pressure; D012128:Respiratory Distress Syndrome / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy; D015656:Respiratory Mechanics; D013990:Tidal Volume; D014132:Trachea / Q000503:physiopathology*