Document Detail

Detection of endotracheal tube obstruction by analysis of the expiratory flow signal.
MedLine Citation:
PMID:  9876979     Owner:  NLM     Status:  MEDLINE    
OBJECTIVE: Acute obstruction of endotracheal tubes (ETT) increases airway pressure, decreases tidal volume, increases the risk of dynamic hyperinflation by prolonging the duration of passive expiration, and prevents reliable calculation of tracheal pressure. We propose a computer-assisted method for detecting ETT obstruction during controlled mechanical ventilation. The method only requires measurement of the expiratory flow. DESIGN: Computer simulation; prospective study in two cases; retrospective study in one case and in seven patients with the adult respiratory distress syndrome (ARDS). SETTING: Laboratory of the Section of Experimental Anaesthesiology (University of Freiburg); surgical adult intensive care units in a university hospital (University of Basel) and in a university affiliated hospital (Zentralklinikum Augsburg). PATIENTS: 3 patients with partial ETT or bronchial obstructions and 7 ARDS patients. MEASUREMENTS AND RESULTS: Expiratory flow was measured using a pneumotachograph and integrated to obtain expiratory volume. The time-constant of passive expiration (tauE) as a function of expired volume [tauE(V(E)) function] was calculated from the expiratory volume/flow curve. We investigated the tauE(V(E)) function of data obtained from: (1) computer simulation of mechanically ventilated homogeneous and inhomogeneous lungs intubated with ETTs of different sizes; (2) one patient with an artificial ETT obstruction of 7.5 and 25% of the cross-sectional area of the ETT (case 1); (3) one patient with ETT obstruction due to secretions (case 2); (4) one patient with acute bronchial constriction (case 3); (5) seven ARDS patients who showed an increase in airway resistance of more than 2 cm H2O x s/l. It was found that an ETT obstruction caused an increase in tauE in early expiration (at high flow), whereas tauE in late expiration was virtually unchanged. The reason for this is the flow dependency of the increase in ETT resistance produced by ETT obstruction. Unlike ETT obstruction, an increase in pure airway resistance produced an increase in tauE throughout expiration. CONCLUSIONS: An ETT obstruction can be reliably distinguished from an increase in pure airway resistance by a characteristic pattern change in the tauE(V(E)) function, which can be detected easily even by an automated pattern recognition system.
J Guttmann; L Eberhard; C Haberthür; G Mols; V Kessler; M Lichtwarck-Aschoff; K Geiger
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Intensive care medicine     Volume:  24     ISSN:  0342-4642     ISO Abbreviation:  Intensive Care Med     Publication Date:  1998 Nov 
Date Detail:
Created Date:  1999-03-05     Completed Date:  1999-03-05     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7704851     Medline TA:  Intensive Care Med     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1163-72     Citation Subset:  IM    
Section of Experimental Anaesthesiology, Clinic of Anaesthesiology, Germany.
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MeSH Terms
Airway Obstruction / diagnosis*,  etiology*
Airway Resistance*
Diagnosis, Differential
Equipment Failure
Intubation, Intratracheal / adverse effects*,  instrumentation
Middle Aged
Prospective Studies
Respiration, Artificial / adverse effects*
Respiratory Distress Syndrome, Adult / therapy*
Retrospective Studies
Signal Processing, Computer-Assisted*
Spirometry / methods*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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