Biometry of the infrarenal inferior vena cava measured by computed tomography. Clinical applications

Influence of breathing movements and Valsalva maneuver on vena caval dynamics

AIM: To study changes produced within the inferior vena cava (IVC) during respiratory movements and identify their possible clinical implications.

METHODS: This study included 100 patients (46 women; 54 men) over 18 years of age who required an abdominal computed tomography (CT) and central venous access. IVC cross-sectional areas were measured on CT scans at three levels, suprarenal (SR), juxtarenal (JR) and infrarenal (IR), during neutral breathing and again during the Valsalva maneuver. All patients were instructed on how to perform a correct Valsalva maneuver. In order to reduce the total radiation dose in our patients, low-dose CT protocols were used in all patients. The venous blood pressure (systolic, diastolic and mean) was invasively measured at the same three levels with neutral breathing and the Valsalva maneuver during venous port implantation. From CT scans, three-dimensional models of the IVC were constructed and a collapsibility index was calculated for each patient. These data were then correlated with venous pressures and cross-sectional areas.

RESULTS: The mean patient age was 51.64 ± 12.01 years. The areas of the ellipse in neutral breathing were 394.49 ± 85.83 (SR), 380.10 ± 74.55 (JR), and 342.72 ± 49.77 mm² (IR), and 87.46 ± 18.35 (SR), 92.64 ± 15.36 (JR) and 70.05 ± 9.64 mm² (IR) during the Valsalva (Ps < 0.001). There was a correlation between areas in neutral breathing and in the Valsalva maneuver (P < 0.05 in all areas). Large areas decreased more than smaller areas. The collapsibility indices were 0.49 ± 0.06 (SR), 0.50 ± 0.04 (JR) and 0.50 ± 0.04 (IR), with no significant differences in any region. Reconstructed three-dimensional models showed a flattening of the IVC during Valsalva, adopting an ellipsoid cross-sectional shape. The mean pressures with neutral breathing were 9.44 ± 1.78 (SR), 9.40 ± 1.44 (JR) and 8.84 ± 1.03 mmHg (IR), and 81.08 ± 21.82 (SR), 79.88 ± 19.01 (JR) and 74.04 ± 16.56 mmHg (IR) during Valsalva (Ps < 0.001). There was a negative correlation between cross-sectional caval area and venous blood pressure, but this was not statistically significant in any of the cases. There was a significant correlation between diastolic and mean pressures measured during neutral breathing and in Valsalva.

CONCLUSION: Respiratory movements have a major influence on IVC dynamics. The increase in intracaval pressure during Valsalva results in a significant decrease in the IVC cross-sectional area.

Abdominal Computed Tomography and the Placement of Inferior Vena Caval Filters

BACKGROUND

Standard cavography is performed with iodinated contrast material with plain film or digital subtraction technique. However, preplacement imaging may change final inferior vena cava filter (IVC) placement in 11 to 26% of patients. This study will examine the use and reliability of incidental spiral computed abdominal tomography (CAT) scans for the placement of IVC filters.

METHODS

Over a 25-month period, CAT scan data were prospectively collected on patients at high risk for pulmonary embolism (PE) or with PE that required an IVC filter. CAT scans were then evaluated specifically for vena cava anatomy and relationship to renal veins and lumbar spine. IVC filters were then placed before cavography under fluoroscopy (performed only to confirm accurate placement) based on the static relationship of the renal veins/IVC and spine.

RESULTS

One hundred twenty-two patients had IVC filters placed. In the last 78 eligible patients, CAT scan placement was verified with post deployment cavography. IVC filters were deployed an average of 3.25 mm below the lowest renal vein with no veins misidentified. No strut malposition was noted on post deployment cavography. 12.1% had findings by CAT scan that altered some aspect of IVC filter placement.

CONCLUSIONS

Admission or same hospital stay spiral CAT scan can provide enough anatomic detail to safely guide placement of an IVC filter. IVC filters can be deployed at bedside without contrast cavography if the preplacement CAT scan is adequate.

Optimal conduit size for extracardiac Fontan operation

BACKGROUND

Lack of conduit growth potential and thrombogenicity are the main drawbacks of the extracardiac Fontan operation (ECFO). Optimal size of the conduit according to the patients age and inferior vena cava diameter has not been established.

OBJECTIVES

We set out to ascertain whether the optimal dimensions of the conduit could be determined before an ECFO.

METHODS

Actual and expected age-related inferior vena cava diameters were compared with the extracardiac conduit diameter in 20 patients after ECFO. In 50 other pediatric and adult patients, the distance between intrapericardial part of the inferior vena cava and the undersurface of the right pulmonary artery (IVC-RPA) was measured. Cases of conduit thrombosis were analyzed.

RESULTS

The actual diameter of the inferior vena cava was variable and has a weak correlation with anthropometric data and expected diameter (R=0.07-0.23, P=0.32-0.76). The IVC-RPA distance correlated with height (R=0.87, P=0.0001), but was also variable. At the age of 2-4 years and body weight 12-15 kg IVC diameter and IVC-RPA distance are equal to 60-80% of adult values. Conduit thrombosis developed in two patients with unfavorable Fontan hemodynamics and oversized conduits.

CONCLUSIONS

Considering the inferior vena cava size, ECFO may be performed at the age of 2-3 years and at a body weight 12-15 kg, when a hemodynamically optimal almost adult sized conduit can be implanted. Optimization of the conduit is necessary on the basis of the actual inferior vena cava diameter and IVC-RPA distance. Anticoagulation postoperatively should be considered to prevent conduit thrombosis in patients with suboptimal Fontan circulation

The inferior vena cava diameter as a marker of dry weight in chronic hemodialyzed patients

We have previously reported that the diameter of the inferior vena cava (IVC) reflects the amount of body fluid in hemodialyzed (HD) patients. The present study was undertaken to depict the criteria of IVC diameters for determining dry weight (DW) in anuric HD patients. In healthy subjects, the maximal diameters during quiet expiration (IVCe) and the minimal diameters during quiet inspiration (IVCi) were 16.7 +/- 3.2 and 5.7 +/- 5.4 mm, respectively (mean +/- SD). The collapsibility index (CI, 1 - IVCi/IVCe), which inversely correlates with the central venous pressure, was 0.68 +/- 0.29. In anuric HD patients, the IVCe/CI values before and after HD were 14.9 +/- 3.2/0.68 +/- 0.24 and 8.2 +/- 2.3/0.94 +/- 0.09, respectively. IVCe decreased proportionally to the amount of ultrafiltration. In HD patients with hypervolemic pulmonary edema, the IVCe and CI values were 22.4 +/- 2.9 and 0.22 +/- 0.11, respectively. We proposed that IVCe/CI after HD is 8 +/- 3 mm/0.9 +/- 0.1 as the markers of DW in anuric HD patients and that an IVCe value > or = 22 mm together with a CI < or = 0.22 implies the warning level of body fluid retention.