BACKGROUND AND OBJECTIVE: To investigate the clinical application of a mathematical model of pulmonary gas exchange, which ascribes hypoxaemia to shunt and ventilation/perfusion mismatch. Ventilation/perfusion mismatch is quantified by deltaPO2, which is the drop in oxygen pressure from alveoli to lung capillaries. Shunt and deltaPO2 were used to describe changes in oxygenation after coronary artery bypass grafting. METHODS: Fourteen patients were studied 2-4 h after surgery and on postoperative days 2, 3 and 7. On each occasion inspired oxygen fraction was changed in four to six steps to obtain arterial oxygen saturation (SaO2) in the range of 90-100%, enabling construction of FEO2/SaO2 curves. Measurements of ventilation, circulation and oxygenation were entered in a previously described mathematical model of pulmonary gas exchange. RESULTS: We found that oxygenation was most impaired 3 days after surgery. By fitting the mathematical model to the FEO2/SaO2 curve, we found that shunt remained constant throughout the study period. However, deltaPO2 increased from 0.5 kPa (median, range 0-3.8) 2-4 h after surgery, to 3.2 kPa (range 1.2-6.4, P < 0.05) on day 2, and to 4.0 kPa (range 1.2-8.3) on day 3. On day 7, deltaPO2 decreased to 2.2 kPa (range 0-3.5, P < 0.05). CONCLUSIONS: Ventilation/perfusion mismatch (deltaPO2), rather than shunt, explains the changes in postoperative oxygenation. The model of pulmonary gas exchange may serve as a useful and potentially non-invasive clinical tool for monitoring patients at risk of postoperative hypoxaemia.
BACKGROUND AND OBJECTIVE: To investigate the clinical application of a mathematical model of pulmonary gas exchange, which ascribes hypoxaemia to shunt and ventilation/perfusion mismatch. Ventilation/perfusion mismatch is quantified by deltaPO2, which is the drop in oxygen pressure from alveoli to lung capillaries. Shunt and deltaPO2 were used to describe changes in oxygenation after coronary artery bypass grafting. METHODS: Fourteen patients were studied 2-4 h after surgery and on postoperative days 2, 3 and 7. On each occasion inspired oxygen fraction was changed in four to six steps to obtain arterial oxygen saturation (SaO2) in the range of 90-100%, enabling construction of FEO2/SaO2 curves. Measurements of ventilation, circulation and oxygenation were entered in a previously described mathematical model of pulmonary gas exchange. RESULTS: We found that oxygenation was most impaired 3 days after surgery. By fitting the mathematical model to the FEO2/SaO2 curve, we found that shunt remained constant throughout the study period. However, deltaPO2 increased from 0.5 kPa (median, range 0-3.8) 2-4 h after surgery, to 3.2 kPa (range 1.2-6.4, P < 0.05) on day 2, and to 4.0 kPa (range 1.2-8.3) on day 3. On day 7, deltaPO2 decreased to 2.2 kPa (range 0-3.5, P < 0.05). CONCLUSIONS: Ventilation/perfusion mismatch (deltaPO2), rather than shunt, explains the changes in postoperative oxygenation. The model of pulmonary gas exchange may serve as a useful and potentially non-invasive clinical tool for monitoring patients at risk of postoperative hypoxaemia.
Authors: S E Rees; C Allerød; D Murley; Y Zhao; B W Smith; S Kjaergaard; P Thorgaard; S Andreassen Journal: J Clin Monit Comput Date: 2006-09-15 Impact factor: 2.502
Authors: Lars P Thomsen; Dan S Karbing; Bram W Smith; David Murley; Ulla M Weinreich; Søren Kjærgaard; Egon Toft; Per Thorgaard; Steen Andreassen; Stephen E Rees Journal: J Clin Monit Comput Date: 2013-02-21 Impact factor: 2.502
Authors: Savino Spadaro; Salvatore Grasso; Dan Stieper Karbing; Giuseppe Santoro; Giorgio Cavallesco; Pio Maniscalco; Francesca Murgolo; Rosa Di Mussi; Riccardo Ragazzi; Stephen Edward Rees; Carlo Alberto Volta; Alberto Fogagnolo Journal: J Clin Monit Comput Date: 2020-08-20 Impact factor: 2.502
Authors: Zsuzsanna Cserép; Eszter Losoncz; Roland Tóth; Attila Tóth; Boglárka Juhász; Piroska Balog; Péter Vargha; János Gál; Richard J Contrada; Paul R J Falger; Andrea Székely Journal: BMC Cardiovasc Disord Date: 2014-11-29 Impact factor: 2.298
Authors: Dan S Karbing; Søren Kjaergaard; Bram W Smith; Kurt Espersen; Charlotte Allerød; Steen Andreassen; Stephen E Rees Journal: Crit Care Date: 2007 Impact factor: 9.097