Cava Pressure Research Articles

Venoconstriction of hepatic capacitance vessels during hemorrhage in cats: efferent mechanisms.

Cats anesthetized with pentobarbital sodium were hemorrhaged (1 ml.min-1.kg body wt-1) until arterial pressure declined to 55 mmHg. Hepatic volume was recorded by plethysmography. In controls, 20 +/- 5 (SD) ml/kg was removed and hepatic volume decreased 3.6 +/- 0.8 ml/kg. Splanchnic nerve section or administration of hexamethonium-atropine reduced hemorrhage volumes (to 10.3 +/- 2.3 and 4.8 +/- 1.8 ml/kg, respectively) and liver volume changes (to 1.5 +/- 0.5 and 0.7 +/- 0.3 ml/kg, respectively). Section of only the hepatic nerves had no effect on hemorrhage volume or the decrease in hepatic volume. Section of the hepatic nerves after removal of the adrenals and kidneys also had no significant effect on hemorrhage volume or the decrease in liver volume. We conclude that the hepatic capacitance response to hemorrhage does not require direct sympathetic venoconstriction of the hepatic capacitance vessels. Changes in inferior vena caval pressure play a significant but small role. The splanchnic nerves (excluding hepatic nerves) play a major role, possibly by splanchnic arteriolar constriction. Whereas the liver comprises only 2.5% of the body weight, it contributed 18% of the hemorrhage volume.

Effects of intra-abdominal pressure on renal tissue perfusion during laparoscopy.

An animal model was established to study the effects of elevated intra-abdominal pressure (IAP) on systemic and renal hemodynamics during laparoscopy. In a pilot study in five dogs, we simultaneously recorded carotid artery blood flow (CABF), carotid artery blood pressure (CABP), inferior vena caval pressure (IVCP), renal parenchymal blood flow, and IAP. The renal parenchymal blood flow was measured by a laser Doppler flowmetry (LDF) needle probe and the renal artery blood flow by an ultrasonic Doppler probe, both placed through laparotomy. The reliability and reproducibility of these two measurements at different renal perfusion pressures were documented. The established method was then used to assess the effects of increased IAP on renal hemodynamics during laparoscopy in six pigs. Pneumoperitoneum was achieved by insufflating the abdominal cavity with air. The LDF needle probe was inserted into the renal parenchyma laparoscopically. An increase in IAP from 0 to 40 mm Hg did not influence CABP. However, significant decreases in CABF were seen from 190.8 +/- 59.5 mL/min at 0 mm Hg IAP to 169 +/- 43.6 mL/min at 15 mm Hg. The CABF decreased in a linear fashion as IAP was increasing (correlation coefficient R = 0.976). Renal cortical blood flow (RCBF) decreased from 50.1 +/- 17.7 mL/min per 100 g at 0 mm Hg to IAP to 21.2 +/- 9.6 mL/min per 100 g of tissue at 15 mm Hg. There was an exponential correlation between IAP and RCBF (R = 0.897).(ABSTRACT TRUNCATED AT 250 WORDS)

A new percutaneous technique for establishing venous bypass access in orthotopic liver transplantation

Partial veno-venous bypass (VVB) is commonly used in orthotopic liver transplantation (OLT). Venous access for blood return during VVB classically uses a surgical cutdown on the left axillary vein (LAV), which may prolong operating time and can be associated with significant complications. The authors have developed an alternative means of establishing venous access whereby the anesthesia team places 8.5F venous cannulae preoperatively in one or two vessels (internal jugular, antecubital, or subclavian) percutaneously using the Seldinger technique. These cannulae then serve to accept venous return from below the diaphragm via a centrifugal pump. The aim of the present study was to compare the hemodynamic profiles obtained during the anhepatic phase of OLT in patients in whom either a conventional LAV catheter (group 1) or percutaneous catheters (group 2) were used for return flow from a centrifugal pump. There were no identifiable complications related to venous access in either group of patients. Total operating room time was 800 ± 30 minutes in group 1 and 720 ± 40 minutes in group 2 ( P = 0.17). Hemodynamic parameters were determined from continuous strip chart recordings of arterial, right atrial, and inferior vena caval (IVCP) pressures. Cardiac output (CO) was measured by thermodilution whereas pump flow was determined by an electromagnetic probe. Renal perfusion pressure (RPP) was calculated as the difference between mean arterial pressure (MAP) and IVCP. Bypass pump flow was greater, but not significantly different between group 1 (3.0 ± 0.2 L/min) and group 2 (2.4 ± 0.2 L/min) ( P = 0.09). IVCP was lower in group 1 (19 ± 1) than in group 2 (25 = 2 mmHg) ( P = 0.02). These differences did not prevent the achievement of comparable hemodynamic profiles between groups. Groups 1 and 2, respectively, did not differ with regard to CO 7.1 ± 0.5 versus 6.9 ± 0.6 ( P = 0.81), MAP 79 ± 2 versus 83 ± 3 ( P = 0.30), or RPP 60 ± 3 versus 58 ± 3 ( P = 0.72). Average blood transfused was similar between groups. The authors conclude, based on hemodynamic profiles and the low incidence of complications, that percutaneous placement of 8.5F venous cannulae for VVB return flow is an acceptable alternative to surgical cutdown of the LAV during OLT.

Intra‐Abdominal Venous Pressure During Laparoscopic Cholecystectomy

Superior vena cava (SVC) and inferior vena cava (IVC) pressures were measured serially during laparoscopic cholecystectomy in which the intra-abdominal pressure was maintained at 12mmHg. The influences of alteration of position from 15 degrees head-down to 15 degrees head-up and of the operative procedure of holding the gallbladder up to the right subphrenic space on SVC and IVC pressures were mild. IVC pressure was maintained almost equal to the intra-abdominal pressure during prolonged continuous pneumoperitoneum lasting longer than 60min, while SVC pressure did not change significantly during operation. The discrepancy between SVC and IVC pressures underwent no change during continuous pneumoperitoneum.

Inferior vena caval pressure increase contributes to sodium and water retention during PEEP in awake dogs.

This study compared the hemodynamic, renal, and hormonal effects of an experimentally induced increase in inferior vena caval pressure (IVCP) [to the same extent as during controlled mechanical ventilation (CMV) with positive end-expiratory pressure (PEEP)] with those of CMV with PEEP. Six volume-expanded conscious chronically tracheotomized dogs were studied under three conditions: 4 h of spontaneous breathing at 4 cmH2O continuous positive airway pressure (CPAP); CMV: CPAP for the 1st and 4th h and CMV with PEEP for the 2nd and 3rd h, resulting in a mean airway pressure of 20 cmH2O; and Increased IVCP: 4 h of CPAP, with IVCP increased during the 2nd and 3rd h by inflation of a chronically implanted cuff. Urine volume, sodium excretion, and fractional sodium excretion decreased during the 2nd and 3rd h of CMV and during increased IVCP compared with CONTROL. Glomerular filtration rate, mean arterial pressure, and antidiuretic hormone, atrial natriuretic peptide, and aldosterone plasma concentrations were not affected by CMV or Increased IVCP. Plasma renin activity decreased during CONTROL and Increased IVCP conditions but remained elevated during the 2nd and 3rd h of CMV. We conclude that, in conscious extracellular volume-expanded dogs, IVCP elevation contributes considerably to the water- and sodium-retaining effect of short-term CMV with PEEP.

Self-expandable metallic stent therapy for superior vena cava syndrome: clinical observations.

To study clinical and physiologic aspects of Z-stent therapy for superior vena cava (SVC) syndrome secondary to malignant disease. Signs and symptoms of SVC syndrome were classified, graded, and scored in 11 cases. Six patients with caval pressure higher than 22 mm Hg peripheral to the stenosis underwent stent therapy. Immediately after Z-stent implantation into the stenotic lesion, the diameter of the constriction increased from 3.3 mm +/- 2.0 (mean +/- standard deviation) to 14.0 mm +/- 3.2, the mean caval pressure peripheral to the stenosis decreased from 26.6 mm Hg +/- 2.5 to 8.9 mm Hg +/- 0.7, and the symptom score decreased from 6.7 +/- 1.8 to 1.3 +/- 1.4. The caval pressure, lesion diameter, and symptom score correlated highly with each other. One complication--transient pulmonary edema attributable to volume overload caused by reperfusion--was observed. Mean survival exceeded 7.1 months. Stent placement could be a useful treatment for refractory SVC syndrome.

SHUNT FLOW AND CAVAL PRESSURE GRADIENT DURING VENO-VENOUS BYPASS IN HUMAN ORTHOTOPIC LIVER TRANSPLANTATION

The routine use of veno-venous bypass during the anhepatic phase of orthotopic liver transplantation is controversial. Decreased shunt flows (1.5-3.0 litre min-1), as reported in the literature, may explain the lack of beneficial effects on outcome. We have studied the influence of bypass flows on caval pressure gradient (CPG) and renal perfusion pressure (RPP) in 45 patients undergoing orthotopic liver transplantation using a portofemoro-subclavian veno-venous bypass system. Mean shunt flow was 3.63 litre min-1. Second-order polynomial regressions best described the relationship between shunt flow and CPG (r = 0.674), RPP (r = 0.727), and cardiac output (r = 0.602). Shunt flows less than 3.0 litre min-1 failed to normalize CPG and RPP, whereas flows greater than 5.0 litre min-1 did not substantially improve haemodynamic state.

Nonoperative treatment of membranous obstruction of the inferior vena cava by percutaneous balloon transluminal angioplasty

Percutaneous transluminal angioplasty (PTA) was performed with the inoue balloon catheter in nine patients with membranous obstruction of the inferior vena cava (MOVC) between November 1988 and April 1991. There were five men and four women, aged 30.8 ± 8.5 years. Two patients had had previous surgical treatment. Three patients had complete and six had incomplete MOVC. The caval pressure below the MOVC was 24.0 ± 5.6 and 11.8 ± 5.3 mm Hg ( p < 0.0001) before and after PTA, respectively. The caval diameter at the site of MOVC increased from 1.5 ± 1.7 to 20.3 ± 2.6 mm ( p < 0.0001), and the maximal caval diameter below the MOVC decreased from 28.7 ± 12.9 to 19.8 ± 9.9 mm ( p = 0.006), before and after PTA, respectively. One patient died of massive pulmonary embolism following successful PTA. All the other eight patients remained asymptomatic during an 18.5 ± 11.5 months (range 3.5 to 32) follow-up period. Two-dimensional ultrasonograms showed no recurrence of MOVC. We conclude that PTA with the inoue balloon catheter is an effective and safe alternative to surgical treatment of MOVC.

Hemodynamic Effect of the Prone Position During Anesthesia

We studied 21 patients undergoing lumbar spinal surgery under halothane anesthesia on a convex saddle frame, in order to determine the hemodynamic effect of the prone position. A thermodilution pulmonary arterial catheter was placed in 14 patients (Group PA-1: n = 8; and Group PA-2: n = 6), and an inferior vena caval catheter in the remaining seven patients (Group IVC). Group PA-1 and Group IVC patients were placed in the prone position on a convex saddle frame. In the prone position, the cardiac index (CI) decreased significantly from 3.1 +/- 0.5 to 2.5 +/- 0.3 (l.min-1.m-2, mean +/- s.d., P less than 0.01) without accompanying significant changes in the other hemodynamic variables in Group PA-1. The postural change in Group IVC did not exert a significant effect on the inferior vena caval pressure. Group PA-2 were initially placed in the flat prone position on a flat saddle frame, which produced no significant changes in the hemodynamic variables. Then the convex curvature of the frame was adjusted to the grade appropriate for surgery, which produced a significant reduction in CI (from 2.9 +/- 0.3 to 2.4 +/- 0.4, P less than 0.05). We conclude that the prone position itself may not interfere with the circulatory function. The prone position using a convex saddle frame causes significant reductions in CI, but little change in the other hemodynamic variables.

Problems associated with the measurement of mean circulatory filling pressure by the atrial balloon technique in anaesthetized rats.

To examine the existence of pressure equilibrium between tributary veins and the central vena cava during the mean circulatory filling pressure manoeuvre, pressures in the hepatic portal vein, renal vein, and inferior vena cava were determined at 4-s intervals over a 20-s period of circulatory arrest induced by inflating a right atrial balloon in normal blood volume, 10% volume depletion, and 10% volume expansion states in urethane-anaesthetized rats. Portal vein pressure determined 8 s after arrest during volume depletion and expansion was significantly higher than vena caval pressure (6.2 +/- 0.8 vs. 3.4 +/- 0.2 and 7.7 +/- 0.5 vs. 6.2 +/- 0.4 mmHg (1 mmHg = 133.32 Pa), respectively; p less than 0.01); this pressure disequilibrium continued for 16 s during volume expansion and for the entire 20 s during volume depletion. Renal vein pressure was equal to vena caval pressure during this manoeuvre. Portal vein pressure at normal blood volume was not significantly different from vena caval pressure following circulatory arrest (4.6 +/- 0.3 vs. 3.8 +/- 0.4 mmHg, respectively). Following ganglionic blockade, portal vein pressure was still significantly higher than vena caval pressure for 12 s during volume alterations. At the 8th s of the arrest the portal pressure determined in volume depletion was 3.6 +/- 0.3 mmHg and the inferior vena caval pressure was 2.6 +/- 0.4 mmHg (p less than 0.05). Under the volume expansion condition, the respective values were 6.5 +/- 0.3 and 5.3 +/- 0.4 mmHg (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of central venous pressure monitoring in the intraabdominal inferior vena cava: A canine study

To test the hypotheses that in multiple pathophysiologic settings (1) end-expiratory central venous pressure measurements in the intraabdominal inferior vena cava accurately reflect those in the superior vena cava and (2) mean central venous pressure monitoring is as reliable in the inferior vena cava as it is in the superior vena cava. Simultaneous inferior vena caval and superior vena caval pressures were measured during five ventilatory phases: apnea, end-expiratory mechanical ventilation, maximal inspiratory mechanical ventilation, end-expiratory spontaneous ventilation, and maximal inspiratory spontaneous ventilation. Measurements were repeated after progressive intravascular volume depletion. Eight puppies. Simultaneous inferior vena caval and superior vena caval end-expiratory pressures did not differ significantly (mean differences 0 to 0.1 mm Hg) and the limits of agreement of these measurements were within 2 mm Hg. Differences between mean maximal inspiratory pressures in the inferior vena cava and superior vena cava during mechanical and spontaneous ventilation were -0.7 and 3.6 mm Hg, respectively (p less than 0.01), and the limits of agreement extended beyond 2 mm Hg. Furthermore, mean maximal inspiratory pressures in the superior vena cava differed from end-expiratory pressures in the superior vena cava (1.1 and -3.6 mm Hg, p less than 0.01), whereas those in the inferior vena cava did not differ from end-expiratory superior vena caval pressures. Under the experimental conditions studied (1) end-expiratory intraabdominal inferior vena caval pressures accurately reflected end-expiratory superior vena caval pressures and (2) mean central venous pressure monitoring was as reliable in the inferior vena cava as in the superior vena cava.

Contribution of the large hepatic veins to postsinusoidal vascular resistance

We tested the hypothesis that the larger (greater than 2 mm ID) hepatic veins are the primary site of the portal-to-caval venous pressure gradient in the dog. Double-lumen catheters were inserted through the caval wall into hepatic veins of pentobarbital sodium-anesthetized dogs. One lumen opened at the end, and the other to the side. Each catheter was advanced until stopped and then it was withdrawn. The pressure at either port dropped from 87 +/- 31 to 13 +/- 11% of the portal-to-caval pressure difference as each moved past a transition point (TP). The location of the TP depended on the catheter diameter. Intraportal histamine or norepinephrine, 4 and 2.6 micrograms.min-1.kg body wt-1 respectively, augmented only the pressure measured upstream to the TP. A mathematical model of flow through a vessel with a catheter inside predicted a marked increase in resistance when the ratio of catheter OD to vessel ID exceeded approximately 0.6. Autopsy revealed ratios greater than 0.6 upstream to the TP. A hydraulic model confirmed that this effect caused the appearance of the TP. Given the depth (11.7 cm) at which near caval pressures could be found, even during histamine administration, we conclude that the major pressure gradients in the canine liver must lie upstream to the large hepatic veins.

CONTINUOUS RETROGRADE CEREBRAL PERFUSION DURING PROFOUND HYPOTHERMIC CIRCULATORY ARREST AT OPERATION FOR STANFORD TYPE A DISSECTING ANEURYSM

Three patients with chronic Stanford type A dissecting aneurysm were successfully operated upon using continuous retrograde cerebral perfusion (CRCP) during profound hypothermic circulatory arrest. Following profound hypothermic (14-15°C) circulatory arrest for 30-40 minutes, CRCP was started with a flow rate of 120-550ml/min to maintain a superior vena caval pressure of 15-20 mmHg. The circulatory arrest time was 56-101 minutes. The longer retrograde cerebral perfusion time induced prolonged wakefullness, but no serious neurological complications were encountered. In conclusion, CRCP is useful for cerebral protection during profound hypothermic circulatory arrest.

Hemodynamic effect of the prone position during anesthesia

We studied 21 patients undergoing lumbar spinal surgery under halothane anesthesia on a convex saddle frame, in order to determine the hemodynamic effect of the prone position. A thermodilution pulmonary arterial catheter was placed in 14 patients (Group PA-1: n = 8; and Group PA-2: n = 6), and an inferior vena caval catheter in the remaining seven patients (Group IVC). Group PA-1 and Group IVC patients were placed in the prone position on a convex saddle frame. In the prone position, the cardiac index (CI) decreased significantly from 3.1 +/- 0.5 to 2.5 +/- 0.3 (l.min-1.m-2, mean +/- s.d., P less than 0.01) without accompanying significant changes in the other hemodynamic variables in Group PA-1. The postural change in Group IVC did not exert a significant effect on the inferior vena caval pressure. Group PA-2 were initially placed in the flat prone position on a flat saddle frame, which produced no significant changes in the hemodynamic variables. Then the convex curvature of the frame was adjusted to the grade appropriate for surgery, which produced a significant reduction in CI (from 2.9 +/- 0.3 to 2.4 +/- 0.4, P less than 0.05). We conclude that the prone position itself may not interfere with the circulatory function. The prone position using a convex saddle frame causes significant reductions in CI, but little change in the other hemodynamic variables.

Histomorphometric evaluation of intrahepatic changes following portal overflow in the rat

Intrahepatic changes after an end-to-side renoportal arteriovenous shunt were studied in 60 rats. Portal and vena caval pressures did not increase from 3 weeks to 1 year. The number and diameters of the portal and hepatic vein lumens were determined through morphometric evaluation to calculate the relative areas. The proportion of area composed by the portal veins increased 3 weeks after shunt creation (P less than 0.001), reaching its highest level at 1 year (0.08% in control rats vs. 2.45% +/- 0.1% at 1 year). The proportionate area for hepatic veins also increased after 3 weeks (P less than 0.001), reaching its highest value by 12 weeks (0.49% in controls vs. 1.73% +/- 0.08% at 12 weeks). Our results suggest that there was a dramatic drop in the intrahepatic vascular resistance, especially at the portal bed, which may have compensated for the portal overflow. The theories regarding forward overflow compensatory mechanisms are discussed.

The Inferior Vena Cava Clip

Pulmonary embolism in high-risk patients may be minimized by surgical inferior vena cava (IVC) clipping or by the insertion of caval filters. A percutaneous clipping technique was developed that narrows the cava while allowing caval patency. The caval clip is inserted through a percutaneous translumbar approach under fluoroscopic control. Nine dogs underwent percutaneous translumbar caval clip placement without complications. Three of four dogs, followed-up for 5 to 19 weeks by angiography and caval pressure measurements, showed caval patency. This technique eliminates the risks of surgical IVC clip placement and risks from the insertion of intravascular foreign bodies such as filters.

Effect of superior vena caval hypertension on alloxan-induced lung injury in dogs

To investigate how fast and to what extent superior vena caval hypertension (SVCH) increases lung water in acute increased-permeability state, we studied the time course of lung water accumulation for 3 h in anesthetized dogs under different treatments: 1) controls without intervention (5 dogs), 2) SVCH alone (5 dogs), 3) mild lung microvascular injury induced by low-dose alloxan (75 mg/kg) alone (5 dogs), and 4) SVCH coupled with low-dose alloxan (5 dogs). Neither low-dose alloxan alone nor SVCH alone [superior vena caval pressure (Psvc) = 11.0 +/- 3.1 (SD) mmHg] increased lung water significantly. The SVCH coupled with low-dose alloxan (Psvc = 11.3 +/- 2.7 mmHg) doubled extravascular lung thermal volume measured by the thermal-dye dilution technique within 1 h (5.3 +/- 0.9 ml/kg at base line and 10.9 +/- 4.7 ml/kg at 1 h), then remained unchanged (12.5 +/- 5.7 ml/kg at 3 h). This increase in lung water was confirmed by gravimetric method (5.69 +/- 1.71 g/g blood-free dry wt). We conclude that SVCH is one of the factors that may promote lung water accumulation in increased-permeability state.

Ascites in Cirrhosis: A Medical or Surgical Problem?

Fifty–seven cirrhotic patients with intractable ascites had a portosystemic shunt. In 35 patients, a peritoneovenous shunt had previously failed. Forty–six patients were in Pugh's class B and 11 were in class C. There were three operative deaths (5.3%). Fifty–three (98.2%) of the 54 survivors were cleared of ascites. In one patient, ascites persisted because of postshunt heart failure that resulted in a marked increase of caval pressure. Twenty–seven patients (50%) had late encephalopathy, which was severe and disabling in 12 (22%). One–and three–year survival rates were 72% and 36%, respectively. These results suggest that although portosystemic shunts are remarkably effective in dealing with ascites, the high rate of postoperative encephalopathy is a strong argument against their routine use in the management of intractable ascites in cirrhosis.

Superior vena caval pressure elevation causes pleural effusion formation in sheep

Superior vena caval pressure elevation causes pleural effusion formation in sheep

Transesophageal Doppler echocardiographic demonstration of pulmonary venous flow velocity in restrictive cardiomyopathy and constrictive pericarditis

Restrictive cardiomyopathy and constrictive pericarditis are indolent disabling diseases of diastolic cardiac function. Both are characterized by high vena caval and pulmonary venous pressures and low cardiac output. Because the history and physical examination of these diseases are often similar, separating them on an anatomic basis requires the use of chest x-ray, echocardiography, computerized tomographic scanning or magnetic resonance imaging. On a physiologic basis, intracardiac pressure measurements at cardiac catheterization and digitized analysis of ventricular filling imaged using contrast or radionuclide ventriculography or echocardiography can occasionally differentiate the 2 diseases. Unfortunately, when these tests are equivocal, making the definitive diagnosis requires myocardial biopsy or exploratory thoracotomy. 1 Doppler echocardiography has been used to study vena caval and atrioventricular valvular flow velocities in both constrictive pericarditis and restrictive cardiomyopathy. 2,3 Pulmonary venous flow velocities have been described in patients with constrictive pericarditis before and after pericardiectomy. 4 This report describes the Doppler-derived pulmonary venous flow velocity pattern in patients with restrictive cardiomyopathy, compares this pattern with that of patients with constrictive pericarditis and introduces this technique for the differentiation of restrictive cardiomyopathy from constrictive pericarditis.