Monitoring End-Tidal Carbon Dioxide During Weaning from Cardiopulmonary Bypass in Patients Without Significant Lung Disease

Abstract

End-tidal carbon dioxide tension (PETCO(2)) changes with fluctuations in cardiac output (CO). We compared PETCO(2) to pulmonary artery blood flow (PAQt) during weaning from cardiopulmonary bypass (CPB) in normothermic patients without significant pulmonary disease. Fifteen consecutive adult cardiac surgical patients were prospectively studied during and shortly after weaning from CPB. Before separation from CPB, PETCO(2) and PAQt were measured, the latter by transesophageal Doppler echocardiography. At the time of measurements patients were normothermic, and ventilated at 6 breaths/min with tidal volumes of 10 mL/kg. After separation from CPB, thermodilution cardiac output (TDCO) was measured in addition to PAQt and PETCO(2). Regression and bias analyses were used to compare PETCO(2), PAQt, and TDCO. Seventy measurements were recorded; 31 before separation from CPB and 39 after separation from CPB. A good correlation was seen between PAQt and PETCO(2) (r = 0.88) and between TDCO and PAQt (r = 0.93; mean bias 0.03 L/min; SD 0.52 L/min). The regression analysis of PAQt on PETCO(2) showed greater variability at PETCO(2) levels > 34 mm Hg (n = 22; r = 0.14). Increases in PETCO(2) plateaued at this level, although PAQt continued to increase. When PETCO(2) was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m(2)). When PETCO(2) exceeded 34 mm Hg, all values of PAQt, and 28/29 values of TDCO were more than 5 L/min (>2.5 L/min/m(2)). One patient had TDCO of 4.69 L/min (2.39 L/min/m(2)). In normothermic patients without significant pulmonary disease, PETCO(2) is a useful index of PAQt during separation from CPB. Under the clinical settings in this study, a PETCO(2) greater than 30 mm Hg was invariably associated with a CO more than 4.0 L/min or a cardiac index >2.0 L/min/m(2).

Avaliação da correlação entre o dióxido de carbono expirado e o débito cardíaco em pacientes submetidos à cirurgia cardíaca com circulação extracorpórea

“…Capnography may be a guide to optimize therapy during cardiopulmonary resuscitation 12,13 and to evaluate the quality of cardiac massage 13 or of post-resuscitation prognosis 14,15 . A previous study has shown direct correlation between end tidal CO 2 (P ET CO 2 ) changes and cardiac output measured by thermodilution 16 . This study has observed direct correlation between P ET CO 2 and cardiac output at CPB weaning.…”

“…A capnografia pode ser um guia para otimizar a terapêutica durante a reanimação cardiorrespiratória 12,13 e como um avaliador de qualidade da massagem cardíaca 13 ou do prognóstico pós-reanimação 14,15 . Em estudo anterior foi demonstrada uma correlação direta entre as alterações da fração expirada de dióxido de carbono (P ET CO 2 ) e o débito cardíaco medido por termodiluição 16 . Nesse estudo foi observada uma correlação direta entre a P ET CO 2 e o débito cardíaco no período de saída de circulação extracorpórea.…”

“…Ocorre aumento da água extravascular pulmonar 19 com preenchimento alveolar por células inflamatórias que levam à inativação do surfactante pulmonar e colabamento de algumas áreas, com modificação na relação ventilação/perfusão pulmonar, diminuição da complacência e aumento do trabalho respiratório. A produção de CO 2 depende do metabolismo do organismo que pode ser alterado pela anestesia e pela temperatura corporal, sendo que esta interfere também na solubilidade do gás no sangue 16,20 . Além disso, em pacientes submetidos à cirurgia cardíaca pode ocorrer barocompressão da microvasculatura 18 , além do possível embolismo por micropartículas que aumentam o espaço morto fisiológi-co 8 .…”

“…There is increase in extravascular pulmonary water 19 with alveolar filling by inflammatory cells which leads to pulmonary surfactant inactivation and collapsing of some areas, with changes in pulmonary ventilation/perfusion ratio, decreased patency and increased respiratory work. CO 2 production depends on body metabolism which may be changed by anesthesia and body temperature, this latter also interfering with blood gas solubility 16,20 . In addition, microvasculature barocompression may be observed in patients submitted to cardiac surgery 18 , as well as potential embolism by microparticles which increases physiological dead space 8 .…”

In reply: Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg-raising maneuver: a prospective observational study

“…2,3 Also, in our study, cardiac output and ETCO 2 measurements were performed simultaneously. Fluid responders had a significant change in their cardiac output and ETCO 2 following the PLR maneuver, which is a well-recognized method to assess fluid responsiveness.…”