Determinants of Aortic Pressure Variation During Positive-Pressure Ventilation in Man: Materials and Methods

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Determinants of Aortic Pressure Variation During Positive-Pressure Ventilation in Man: Materials and MethodsPatients
After approval of our protocol by the Institutional Review Board committee of the University of Pittsburgh, we studied 17 sequential patients undergoing elective coronary artery bypass surgery at the University of Pittsburgh Medical Center. The first 15 patients studied on the protocol are described below, whereas the last 2 patients were used to validate the accuracy of the LV area measurements. Informed consent was obtained. Profiles of the 15 initial patients are summarized in Table 1. General anesthesia was induced by using high-dose narcotics and oxygen with no inhalation anesthetics. All patients were instrumented and monitored with a flow-directed balloon-tipped pulmonary artery catheter, central aortic catheter (femoral arterial line), endotracheal tube, and ECG. Airway pressure at the proximal end of the endotracheal tube was also monitored, and ventilation was provided with a volume-cycled ventilator (Servo Ventilator 900; Siemens-Elena; Solna, Sweden). All pressures were calibrated at zero at the midaxillary level, and they were transduced by using high-displacement transducers (TXX-R; Viggo-Spec-tramed; Oxnard, CA). order antibiotics online

We excluded patients with a contraindication to the use of transesophageal echocardiography (TEE), simultaneous use of an intra-aortic balloon pump (IABP), lack of sinus rhythm, numerous premature ventricular complexes during the data acquisition periods, and the inability to obtain an adequate transgastric view from the midpapillary level. In the criteria put forward by Schnittger et al, an inadequate echocardiographic view was defined as < 75% of the perimeter of the ventricular image being defined by contiguous endocardial echoes. In practice, no patients were excluded because of a contraindication to the use of the TEE, and only 2 patients out of 17 were excluded because of the inability to obtain an appropriate echocardiographic image. The TEE probe was positioned at the beginning of the experiment and not moved until the data acquisition was completed. As a further form of quality control, the quality of the TEE images was analyzed on-line by a cardiac anesthesiologist. The images were recorded on videotape and reviewed by a cardiologist who specialized in echocardiography, using the same criteria. Because the purpose of our study was to examine the effect of positive-pressure on LV volume and SAP, subsequent analysis was performed using only the TEE images that both observers, who were blinded to the other’s opinions, agreed were acceptable in quality.
Table 1—Steady-State Apneic Hemodynamic Data

SubjectSystolic Pa, mm HgDiastolic Pa, mm Hg HR,min CO,L/min FAC,%Ppao, mm HgPra, mm HgSystolic Ppa, mm HgDiastolic Ppa, mm Hg