Alteration of Pulmonary Oxygenation by Pulmonary Artery Occluded Pressure Measurements in Mechanically Ventilated Patients

Alteration of Pulmonary Oxygenation by Pulmonary Artery Occluded Pressure Measurements in Mechanically Ventilated PatientsThe measurements of PAOP using a flow-directed, balloon-tipped PAC may produce rapid onset of significant hypoxemia either by temporary cessation of mechanical ventilation or by occlusion of a major pulmonary arterial vasculature. The former has been well recognized and thus a simple electronic circuit was constructed for the measurements without separation of the patient from the ventilator. The latter decrease in Pa02 due to inflating the balloon of the PAC per se has recently been reported by us and others. Although the information obtained with inflating the PAC balloon is invaluable and contributes greatly to the management of both critically ill and anesthetized patients, the decrease in Pa02 could cause deterioration of the patients condition in some situations. Therefore, we expanded our study to know its incidence and to examine the types of patients who tend to develop a remarkable decrease in Pa02 during PAOP measurements and whether the changes in Pa02 are related to the existing level of pulmonary vascular tone.

Methods
Studies were performed on 101 anesthetized adult patients (27 to 82 years of age) who were in the supine position and who required a Swan-Ganz triple-lumen PAC and general anesthesia for surgery. This study was approved by our local review committee. Primary disorders in these patients included pulmonary carcinoma (n = 21), mitral or aortic valve disease (n = 18), coronary artery disease (n = 12), other cardiac disease (n = 7), hepatic carcinoma (n = 10), abdominal aortic aneurysm (n = 7) and other disorders (n = 26). Anesthesia technique maintained was selected from the following: enflurane, 1.5 to 2.0 percent, inspired, NgO, 02; moderate-dose Fentanyl, 2 to 10 jig/kg, NaO, Oa; cervical epidural anesthesia plus NaO, Oz; lumbar epidural anesthesia plus N20, 02; high-dose Fentanyl, 70 to 100 M-g/kg, NaO, Oa. After induction of anesthesia, a catheter was inserted into the left radial artery and a flow-directed, balloon-tipped catheter (PAC, 7.5 Fr, American Edwards Laboratories) was directed into the pulmonary artery through the right internal jugular vein. The PAC was placed in the most proximal position of the pulmonary artery, which gave a satisfactory PAOP by inflating the balloon with 1.5 ml of air. The location of the tip of the PAC was documented from a chest radiograph taken before surgery. All patients were mechanically ventilated with a FIo2 of 0.33 or 0.5, tidal volume of 10 to 12 ml/kg and respiratory rate of 10 to 12 breaths per minute, without PEEP. read more

After steady-state condition was established, hemodynamic values of each patient such as SAP, HR, PAP, RAP, and PetC02 (Normocap Datex) were measured and recorded continuously. An arterial blood sample also was taken for arterial blood gas analysis (PaOa, PaC02, pHa, base excess; Corning, model 175) while the PAC balloon was still deflated in each patient. Then the PAC balloon was inflated for 2 min with 1.5-ml of air and the previously noted measurements were repeated. Cardiac output was measured by the thermodilution method in triplicate with 10 ml of iced 5 percent dextrose solution with a CO computer (COM-1 TM, American Edwards Laboratories) before inflation of the balloon. All measurements were performed before surgery. Accuracy of the PAOP reading was assured by demonstrating a and v atrial waveforms in its tracing and when the mean PAOP was lower or equal to the DPAP. Data for paired samples were analyzed using Students t test. Chi-square analysis with Yates correction and linear regression analysis with least squares method were utilized to provide type of patients and a relationship between changes in Pa02 and the other variables as appropriate. Statistical significance was accepted when p values were less than 0.05.

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