G. Polese P.Lubli A. Mazzucco A. Luzzani A. Rossi Effects of open heart surgery on respiratory mechanics Received: 14 January 1999 Accepted: 1 July 1999 Supported by Grant 407, from Telethon, Rome, Italy G. Polese ( ) ) Centro Regionale Fibrosi Cistica, Azienda Ospedaliera di Verona, P.le Stefani 1, I-37126 Verona, Italy Tel.: + 39 (45) 8 07 22 93 Fax: + 39 (45) 8 07 20 42 email: gpolese@qubisoft.it P.Lubli × A. Luzzani 2 Servizio di Anestesia e Rianimazione, Università di Verona, Verona, Italy A. Mazzucco Istituto di Cardiochirurgia, Università di Verona, Verona, Italy A. Rossi Divisione di Pneumologia, Azienda Ospedaliera di Verona, Verona, Italy Abstract Objective: To investigate the changes in respiratory mechan- ics in patients undergoing cardiac surgery before and after the opera- tion. Design: Prospective physiological study. Setting: Operating theatre of the In- stitute of Cardiac Surgery, Verona, Italy. Patients: 8 patients needing heart surgery because of a coronary by- pass or mitral valve replacement. Measurements and results: We mea- sured respiratory mechanics before and immediately after the surgical procedure with two techniques: (1) the rapid airway occlusion tech- nique during constant flow inflation at different lung volumes, and (2) the negative expiratory pressure (NEP) technique. We found that static and dynamic elastance (15.3 ± 3.3 and 19.0 ± 5.5 cmH 2 O/l, respectively) and respiratory resis- tance, both airway and total flow re- sistance (5.8 ± 2.5 and 10.3 ± 4 cmH 2 O´l 1 ´ s, respectively) be- fore surgery were slightly higher than in normal anaesthetised sub- jects. In all patients, the static infla- tion V-P curves fitted the power function and exhibited a slight up- ward concavity towards the volume axis (a = 16.9 ± 3.5, b = 0.74 ± 0.07), indicating that elastance decreased with inflating volume. Whereas ela- stance increased by 30 %, neither intrinsic positive end-expiratory pressure, which was small, averaging 1.5 ± 1.2 cmH 2 O, nor flow resistance changed after surgery. With the NEP technique, four patients exhib- ited expiratory flow limitation dur- ing the tidal expiration, for about 67 % of the exhaled volume, without changes after surgery. Arterial car- bon dioxide tension (32 ± 4 mm Hg) and pH (7.46 ± 0.07) did not change, whereas arterial oxygen tension (PaO 2 ) (242 ± 34 mm Hg) decreased significantly by about 70 mm Hg, on average, with a constant fractional inspired oxygen (0.50). Conclusions: This study shows that (1) respiratory mechanics can be abnormal in patients undergoing cardiac surgery, including expiratory flow limitation; (2) elastance increa- ses and PaO 2 decreases after sur- gery; (3) simple, noninvasive techni- ques are available to measure re- spiratory mechanics in the operating theatre. Key words Cardiac surgery × Respiratory mechanics × Flow limitation × Interrupter Intensive Care Med (1999) 25: 1092±1099 Ó Springer-Verlag 1999 ORIGINAL