Venous Return Resistance Research Articles

Effects of Retroperitoneal or Transperitoneal Pneumoperitoneum on Inferior Vena Cava Hemodynamics and Cardiopulmonary Function: A Prospective Real-Time Comparison.

Objective: To evaluate the effects of CO2 pneumoperitoneum on venous hemodynamics and cardiopulmonary function during transperitoneal or retroperitoneal laparoscopic surgery. Materials and Methods: A single-institution prospective study. Forty-three patients with renal-cell carcinoma undergoing retroperitoneal (22) or transperitoneal (21) laparoscopic partial nephrectomy were enrolled. Hemodynamic functions were monitored by minimally invasive FloTrac/Vigileo system. Transesophageal echocardiography was used to measure the diameter and blood flow of the inferior vena cava (IVC). Measured parameters were recorded at baseline, 10, 30, 60 minutes following insufflation to 14 mm Hg and 10 minutes following desufflation. Results: For hemodynamic changes in the transperitoneal laparoscopic surgery (TPL) and retroperitoneal laparoscopic surgery (RPL), transperitoneal CO2 insufflation resulted in a rapid parallel increase in central intravenous pressure (CVP), peak airway pressure (AWP), and IVC blood flow velocity after the first 30 minutes of pneumoperitoneum (p < 0.05). In contrast, CVP, AWP, and IVC blood flow velocity increased progressively in RPL. The variation of those parameters was significantly lower than that of TRL (p < 0.001; p = 0.002; p = 0.004). The mean maximum CVP in the two groups was 20 and 16 mm Hg, respectively. The IVC diameter at the cavoatrial junction was significantly reduced in TPL after 10 minutes of insufflation, but it remained unchanged in RPL throughout the surgery. For cardiopulmonary function changes, heart output decreased after a short period of pneumoperitoneum, but no statistical differences were observed between the two groups. The increments of partial pressure of arterial carbon dioxide and end-tidal carbon dioxide tension were significantly higher in RPL than TPL (p < 0.001; p < 0.001). Conclusions: Compared with retroperitoneal pneumoperitoneum, transperitoneal pneumoperitoneum has significant effects on IVC hemodynamics. Elevated intra-abdominal pressure (IAP) causes higher AWP and venous return resistance, which lead to the significant increase of CVP during transperitoneal approach. Adjusting the balance between IAP and CVP might be an effective way to control intravenous bleeding. Clinical Trial Registry: Registration number: ChiCTR2000038291.

Comparison of mean systemic pressure in patients with acute circulatory failure receiving passive leg raising vs. pneumatic leg compression

Background: Driving pressure of venous return (VR) is determined by a pressure gradient between mean systemic pressure (Pms) and central venous pressure (CVP). While passive leg raising (PLR) and pneumatic leg compression PC (PC) can increase VR, no study has explored the effects of these two procedures on Pms and VR-related hemodynamic variables. Methods: Forty patients with acute circulatory failure were enrolled in this analysis. All patients obtained both PLR and PC, and were measured for Pms, CVP, mean arterial pressure (MAP), cardiac output (CO), VR resistance (RVR), and systemic vascular resistance (SVR) at baseline and immediately after procedures. To minimize carry over effect, the patients were divided in 2 groups based on procedure sequence which were 1) patients receiving PLR first then PC (PLR-first), and 2) patients receiving PC first then PLR (PC-first). Both groups waited for a washout period before performing the 2 second procedure. Primary outcome was difference in Pms between PLR and PC procedures. Secondary outcome were differences in CVP, MAP, CO, RVR, and SVR between PLR and PC procedures. Results: No difference was found in baseline characteristics and no carry over effect was observed between the 2 groups of patients. Compared with baseline, both PLR and PC significantly increased Pms, CVP, MAP, and CO. PLR increased Pms (9.0±2.3 vs 4.8±1.7 mmHg, p&lt;0.001), CVP (4.5±1.2 vs. 1.6±0.7 mmHg, p&lt;0.001), MAP (22.5±5.6 vs. 14.4±5.0 mmHg, p&lt;0.001), and CO (1.5±0.5 vs. 0.5±0.2 L/min, p&lt;0.001) more than PC. However, PC, also significantly increased RVR (16 ± 27.2 dyn.s/cm5, p=0.001) and SVR (78.4 ± 7.2 dyn.s/cm5, p&lt;0.001) but no difference in PLR group. Conclusion: Among patients with acute circulatory failure, PLR increased Pms, CVP, MAP, and CO more than PC.

Comparison of mean systemic pressure in patients with acute circulatory failure receiving passive leg raising vs. pneumatic leg compression

Background: Driving pressure of venous return (VR) is determined by a pressure gradient between mean systemic pressure (Pms) and central venous pressure (CVP). While passive leg raising (PLR) and pneumatic leg compression PC (PC) can increase VR, no study has explored the effects of these two procedures on Pms and VR-related hemodynamic variables. Methods: Forty patients with acute circulatory failure were enrolled in this analysis. All patients obtained both PLR and PC, and were measured for Pms, CVP, mean arterial pressure (MAP), cardiac output (CO), VR resistance (RVR), and systemic vascular resistance (SVR) at baseline and immediately after procedures. To minimize carry over effect, the patients were divided in 2 groups based on procedure sequence which were 1) patients receiving PLR first then PC (PLR-first), and 2) patients receiving PC first then PLR (PC-first). Both groups waited for a washout period before performing the 2 second procedure. Primary outcome was difference in Pms between PLR and PC procedures. Secondary outcome were differences in CVP, MAP, CO, RVR, and SVR between PLR and PC procedures. Results: No difference was found in baseline characteristics and no carry over effect was observed between the 2 groups of patients. Compared with baseline, both PLR and PC significantly increased Pms, CVP, MAP, and CO. PLR increased Pms (9.0±2.3 vs 4.8±1.7 mmHg, p&lt;0.001), CVP (4.5±1.2 vs. 1.6±0.7 mmHg, p&lt;0.001), MAP (22.5±5.6 vs. 14.4±5.0 mmHg, p&lt;0.001), and CO (1.5±0.5 vs. 0.5±0.2 L/min, p&lt;0.001) more than PC. However, PC, also significantly increased RVR (16 ± 27.2 dyn.s/cm5, p=0.001) and SVR (78.4 ± 7.2 dyn.s/cm5, p&lt;0.001) but no difference in PLR group. Conclusion: Among patients with acute circulatory failure, PLR increased Pms, CVP, MAP, and CO more than PC.

Effects of Prone Positioning on Venous Return in Patients With Acute Respiratory Distress Syndrome.

To examine the effects of prone positioning on venous return and its determinants such as mean systemic pressure and venous return resistance in patients with acute respiratory distress syndrome. Prospective monocentric study. A 25-bed medical ICU. About 22 patients with mild-to-severe acute respiratory distress syndrome in whom prone positioning was decided. We obtained cardiac index, mean systemic pressure, and venous return resistance (the latter two estimated through the heart-lung interactions method) before and during prone positioning. Preload responsiveness was assessed at baseline using an end-expiratory occlusion test. Prone positioning significantly increased mean systemic pressure (from 24 mm Hg [19-34 mm Hg] to 35 mm Hg [32-46 mm Hg]). This was partly due to the trunk lowering performed before prone positioning. In seven patients, prone positioning increased cardiac index greater than or equal to 15%. All were preload responsive. In these patients, prone positioning increased mean systemic pressure by 82% (76-95%), central venous pressure by 33% (21-59%), (mean systemic pressure - central venous pressure) gradient by 144% (83-215)%, while it increased venous return resistance by 71% (60-154%). In 15 patients, prone positioning did not increase cardiac index greater than or equal to 15%. In these patients, prone positioning increased mean systemic pressure by 28% (18-56%) (p < 0.05 vs. patients with significant increase in cardiac index), central venous pressure by 21% (7-54%), (mean systemic pressure - central venous pressure) gradient by 28% (23-86%), and venous return resistance by 37% (17-77%). Eleven of these 15 patients were preload unresponsive. Prone positioning increased mean systemic pressure in all patients. The resulting change in cardiac index depended on the extent of increase in (mean systemic pressure - central venous pressure) gradient, of preload responsiveness, and of the increase in venous return resistance. Cardiac index increased only in preload-responsive patients if the increase in venous return resistance was lower than the increase in the (mean systemic pressure -central venous pressure) gradient.

Experts consensus on the management of the right heart function in critically ill patients

Experts consensus on the management of the right heart function in critically ill patients

Bedside assessment of passive leg raising effects on venous return

Passive leg raising (PLR) provides a reversible fluid-loading challenge and can be used to predict fluid responsiveness. The amount of blood volume recruited by this maneuver called stressed volume (Vs) is unknown. The present study aims to assess the quantitative effects of passive leg raising on venous return at bedside. We conducted a prospective interventional study. Nine mechanically ventilated postoperative cardiac surgery patients with preserved left ventricular function were enrolled. Cardiac output (CO) was continuously monitored by PiCCO™ via the pulse contour method. Ten second intervals of inspiratory breath holding at four plateau pressures (5, 15, 25 and 35cm H(2)O) were performed to measure the relationship between blood flow (CO) and central venous pressure (CVP). These were used to determine mean systemic filling pressure (Pmsf) and Vs. Patients were studied at three successive steps: semirecumbent position, after PLR and back in the semirecumbent position after volume expansion (VE). Similar to VE, PLR significantly increased Pmsf from 19.7 (17.0-22.6) mmHg at baseline to 22.0 (18.5-27.8) mmHg (p <0.05). CO increased 11.1% (9.5-20) with PLR and 14.8% (4.2-19.9) with VE. Venous return resistance was unchanged throughout the three conditions, whereas the the pressure gradient for venous return (Pmsf-CVP) increased during PLR (p=0.058) and during VE (p < 0.05). Baseline circulatory compliance was 1.14 (0.52-2.65)mlmmHg(-1)kg(-1). Vs increased to 3.5 (1.1-3.9) mlkg(-1) with PLR. The effect of transient hemodynamic changes on venous return induced by passive leg raising can be directly measured in intensive care patients using inspiratory-hold procedures. This technique makes quantification of PLR feasible and could be used clinically to assess fluid responsiveness.

Importance of atrial compliance in cardiac performance.

Effects of changes in atrial compliance on cardiac performance were analyzed using a circulatory analog model. The atrium was assumed to be a noncontracting chamber with a constant compliance. It connected the venous return system, which was represented by mean circulatory filling pressure and a venous return resistance in accordance with Guyton's concept, with the ventricle, which was characterized by a time-varying elasticity. Atrial compliance was increased from near zero to a value at which atrial volume was twice ventricular stroke volume, while the parameters of ventricular contractility were kept unchanged. Cardiac output increased from 2,400 to 3,240 ml/min with increases in atrial compliance from 0.1 to 20 ml/mm Hg (venous return resistance 0.1 mm Hg sec/ml), whereas mean atrial pressure simultaneously decreased from 3.0 to 2.2 mm Hg. This result indicates that cardiac performance in terms of the cardiac output-mean atrial pressure relationship was markedly improved by increases in atrial compliance in spite of constant ventricular contractility. The analysis of the model strongly suggests that natural atrial compliance in situ, by pooling venous return flow during systole and supplying it to the ventricle during diastole, facilitates the transformation of the continuous venous return flow into the intermittent ventricular filling flow.