Good short-term agreement between measured and calculated tracheal pressure  M. Lichtwarck-Aschoff, A. Helmer, R. Kawati, M. Lattuada, U.H. Sjöstrand, N. Zügel, J. Guttmann, G. Hedenstierna  British Journal of Anaesthesia  Volume 91, Issue 2, Pages 239-248 (August 2003) DOI: 10.1093/bja/aeg169 Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 1 Tracings of calculated and measured tracheal and proximal airway pressure in a representative animal during VC without PEEP. Pprox (dotted line): Airway pressure measured at the proximal outlet of the tracheal tube; measured Ptr (heavy line): tracheal pressure measured directly at the carina; calculated Ptr (1) (thin line): PRohrer calculated according to 4; calculated Ptr (2) (thin line): PBlasius–Ito calculated according to 2. British Journal of Anaesthesia 2003 91, 239-248DOI: (10.1093/bja/aeg169) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 2 Tracings of calculated and measured tracheal and proximal airway pressure in a representative animal during PS. Pprox (dotted line): Airway pressure measured at the proximal outlet of the tracheal tube; measured Ptr (heavy line): tracheal pressure measured directly at the carinal level; calculated Ptr (1) (thin line): PRohrer calculated according to 4; calculated Ptr (2) (thin line): PBlasius–Ito calculated according to 2. British Journal of Anaesthesia 2003 91, 239-248DOI: (10.1093/bja/aeg169) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 3 Tracings of calculated and measured tracheal and proximal airway pressure in a representative animal during bi-level positive airway pressure (BiPAP) ventilation. Pprox (dotted line): Airway pressure measured at the proximal outlet of the tracheal tube; measured Ptr (heavy line): tracheal pressure measured directly at the carinal level; calculated Ptr (1) (thin line): PRohrer calculated according to 4; calculated Ptr (2) (thin line): PBlasius–Ito calculated according to 2. British Journal of Anaesthesia 2003 91, 239-248DOI: (10.1093/bja/aeg169) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 4 Agreement between calculated and measured tracheal pressure (PRohrer calculated according to 4) during VC with a PEEP of 12 cm H2O in surfactant-deficient animals. Bias and limits of agreement are indicated for distinct pressure points: 0.1 s after start of inspiration; peak airway pressure; 0.25 s past peak; 0.5 s past peak; 1 s past peak; last end-expiratory point. British Journal of Anaesthesia 2003 91, 239-248DOI: (10.1093/bja/aeg169) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 5 Flow-dependent resistive pressure decrease over the tracheal tube when ID is 7.5 mm (top) and when ID is 8.0 mm (middle). Assuming a constant inspiratory flow pattern and a narrowing of the native ID 8 tracheal tube to a 7.5 ID tracheal tube, the flow-dependent error in calculated tracheal pressure PRohrer is depicted at the bottom (deviation from true Ptr). When narrowing is from 8 to 7.5 mm ID and flow is 18 litre min−1, the calculated PRohrer overestimates the true Ptr by 0.11 cm H2O; with 48 litre min−1 overestimation is 1.06 cm H2O, and with 90 litre min−1 overestimation is 3.98 cm H2O, respectively. British Journal of Anaesthesia 2003 91, 239-248DOI: (10.1093/bja/aeg169) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions