Cardiopulmonary Effects of an Anterior Mediastinal Mass in Dogs Anesthetized with Halothane

The authors evaluated the cardiac effects of an anterior mediastinal mass to better understand the acute cardiovascular collapse that has been associated with anesthesia and positive-pressure ventilation. An 800-ml-capacity intravenous bag was placed within the anterior mediastinum of 12 dogs to simulate a mediastinal mass. After mediastinal mass inflation, the authors measured cardiac index (CI) during periods of spontaneous ventilation (SV), SV with added continuous positive airway pressure (CPAP), intermittent positive-pressure ventilation (IPPV), and continuous positive-pressure ventilation (CPPV). Similar mediastinal mass volumes resulted in similar decreases in CI during SV (169 ± 51 to 105 ± 10 ml · kg−1 · min−1); CPAP (175 ± 48 to 122 ± 34 ml · kg−1 · min−1); IPPV (151 ± 15 to 93 ± 24 ml · kg−1 · min−1); and CPPV (183 ± 56 to 117 ± 46 ml · kg−1 · min−1). The authors also found, by linear regression, that the relationship between CI and mass volume was similar during both SV and IPPV. In six dogs, transesophageal echocardiography (TEE) was used to measure ventricular short axis dimensions. The authors found that mass inflation caused left ventricular end-diastolic dimension to decrease significantly by 6 ± 2 mm and 4 ± 1 mm during SV or IPPV, respectively, and right ventricle dimensions to increase by 2 ± 1 mm and 3 ± 1 mm during SV or IPPV, respectively. The changes in chamber dimensions were similar with either SV or IPPV. These results suggest that the decrease in CI associated with a mediastinal mass results from an increase in right ventricular afterload, causing right ventricular enlargement. Subsequently, there is impingement on the left ventricle volume because of interventricular interdependence.