On two occasions, difficulties positioning the cannula into the IVC were encountered. In both cases, TEE revealed that a long, floppy E valve was the probable cause. One of the cannulae was correctly placed after four attempts, and in the other case, a basket cannula was used in the right atrium.
TEE enabled determination of the cannula position in 148 (98.7%) of 150 cases. In a 49-yr-old male patient (height, 173 cm; weight, 100 kg) with an enlarged heart, neither the IVC/RHV nor the cannula could be visualized. The surgical procedure revealed a rotated heart with a posterior position of the right atrium. Displacement of the mediastinal structures was the probable cause of missed visualization. In the other case in which the position of the cannula could not be determined, visualization of the IVC and RHV was poor before cannulation.
Control of cannula position by TEE demonstrated that 14 cannulae (9.5%) were placed outside the IVC. Twelve had the tip in the RHV, one was placed in a second RHV, and one was coiled in the right atrium.
A significant correlation was found between the E-t distance and cannulation of a hepatic vein (r 2 = 0.103;P = 0.03). A short E-t distance increased the incidence of such cannulation. None of the other measured dimensions of the venous system influenced placement. The apparent sex difference in cannulae placed outside the IVC (women: 6 of 37, 16.2%; men: 8 of 110, 7.3%) did not reach statistical significance (P = 0.11). Neither body length (P = 0.24) nor body mass index (P = 0.99) was associated with the incidence of cannulae positioned outside the IVC.
Placement in the hepatic veins was significantly influenced by cannula type (P < 0.001). The uneven distribution of cannulae prevented further statistical analysis of cannula type. The frequencies of placement outside the IVC for different cannula types are given in Table 3.
All but one cannula placed in the IVC had the tip distal to the inlet of the hepatic vein. The mean distance from the E valve to the tip of the cannula was 8.4 ± 1.9 cm (range, 1.0–12.5 cm) (n = 109).
The CVP was 5.8 ± 3.3 mm Hg before cannulation versus 4.5 ± 3.8 mm Hg after established CPB when the cannula was placed <10 cm into the IVC; it was 5.1 ± 2.2 mm Hg versus 4.6 ± 1.9 mm Hg with the cannula placed >10 cm into the IVC (not significant). When the cannula was located in the RHV, the CVP was 4.6 ± 3.1 mm Hg versus 3.6 ± 2.5 mm Hg, respectively (not significant).
From the start of the study, all venous cannulae that were located outside the IVC were repositioned before CPB was initiated. Eight cannulae placed in the hepatic veins and one placed in the right atrium required an average of 1.5 ± 0.8 (range, 1–3) attempts before they were positioned in the IVC. The five last cannulae observed in the RHV were, however, not repositioned. In each case, the surgeon decided to initiate bypass and observe whether return was sufficient before eventual repositioning of the cannula. Venous return was characterized as “good” in four cases and “acceptable” in one case.
Venous return was registered in 143 patients. It was characterized as “good” in 113 and “acceptable” in 22 patients, giving good or acceptable venous return in 94% of the cases. Poor venous return was observed in eight cases. A closer analysis of these cases revealed that the cannula was placed deep into the IVC in five patients (mean E-tip distance, 10.3 ± 1.3 cm) and in a “normal” position in one patient (E-tip distance, 6.2 cm). In the last two cases, the cannula was repositioned before any measurements could be made. No increase in CVP was observed in any of these patients after CPB was initiated.
This study shows that TEE allows satisfactory determination of the position of the venous cannula in relation to the IVC and RHV in nearly all patients subjected to CPB. The incidence of venous cannulae primarily placed in the RHV was nearly 10% (Fig. 1). The surgeons, being aware of the continuing study, may have reduced the actual numbers of RHV cannulations in the study period. No cannula was positioned in the middle or left hepatic vein. The three main hepatic veins usually enter the IVC at almost the same distance from the right atrium. Consequently, a cannula seen in the IVC distal to the inlet of the RHV is unlikely to be positioned in one of the other main hepatic veins. Monitoring the IVC and RHV will therefore detect whether a hepatic vein is cannulated.
We produced good- or acceptable-quality images of the IVC and the RHV in 95% and 87% of cases, respectively. Meierhenrich et al. (2) studied 34 patients scheduled for abdominal surgery and identified the three main hepatic veins by multiplane TEE in all patients. Pinto et al. (3), Nomura et al. (4), and Gårdebäck et al. (5), studying 29, 45, and 8 cardiac surgical patients, respectively, obtained hepatic vein flow patterns by TEE in all cases before cannulation. These studies all support the position that the IVC and RHV are well visualized by TEE.
The cannulae used in this study contain a metal coil that may induce acoustic shadowing and obscure the image of the RHV and the IVC. Furthermore, the hepatic veins collapse to some degree during CPB circulation. Imaging of the IVC and hepatic veins is therefore easier before cannulation and initiation of CPB. Identification of the central veins before and close monitoring of them during cannulation makes it easier to decide whether the cannula is correctly positioned.
A short distance between the E valve and the upper margin of the inlet of the RHV (E-t) was associated with a significantly increased incidence in cannulation of the hepatic veins. The distance between the E valve and the lower margin of the same inlet (E-s) had no influence on cannulation of the hepatic veins. These measurements are not truly independent, and hence this result should be interpreted with caution.
Statistically, we cannot identify which cannula type is more likely to enter the hepatic vein, despite the uneven frequency displayed in Table 3. The small-diameter cannula (29/29F) was not more frequently placed in hepatic veins. This indicates that the cannula diameter is not decisive for positioning in a hepatic vein. The uneven tendency to enter the hepatic veins may depend on the difference in the site of insertion or the difference in the frequency of use.
The physiological consequences of cannulae placed in the hepatic veins were not the primary focus of our study. The surgeons were therefore informed of the finding, and most cannulae in the hepatic veins were immediately repositioned. Acceptable flow from five cannulae in the hepatic vein showed that venous return was not necessarily impeded by hepatic vein placement. This corresponds well with the fact that the observed frequency of cannulae placed in hepatic veins exceeds the generally observed frequency of problems with venous return. The perfusionists evaluated venous return after being informed of the position of the cannula. This may have influenced their evaluation of venous return to some degree. Their estimation of poor venous return was, however, based on the specific criteria of having sufficient venous return to meet a preoperative set pump flow.
The TEE mapping of the venous system should not be considered as anatomically exact measurements. The IVC and RHV diameters were taken from a longitudinal view and may consequently underestimate the true values. The imaging plane may have been oblique, and E-t and E-s do not necessarily represent the shortest distance between the E valve and the RHV. These factors may have contributed to the considerable individual variation found for all these variables. The significantly larger E-s distance in men than in women probably reflects the larger height in men.
The E-tip distance is less accurate than the above-mentioned measurements because it was calculated from two measurements: E-s and s-tip. However, it still gives a good picture of cannula position in the venous system. Our results indicate that placement of the cannula deep in the IVC is associated with reduced venous return.
A casuistic report has recently been published proposing TEE as a potential method to determine the position of venous cannulae in cardiac surgery (6). However, no systematic TEE study of surgical cannulation of the IVC has previously been published.
As TEE has become an integrated part of cardiac anesthesia and surgery, the extra effort of examining cannula placement is negligible. Placement of the cannula in a hepatic vein is frequent and easily detected, especially if the IVC/RHV is monitored during cannulation. A position of the cannula deep in the IVC is also easily visualized. Further studies are needed before the full clinical usefulness of this method can be determined. We strongly recommend that the position of the venous cannula be determined in all cases of poor venous return during CPB.
1. Bennett EV Jr, Fewel JG, Ybarra J, et al. Comparison of flow differences among venous cannulas. Ann Thorac Surg 1983; 36: 59–65.
2. Meierhenrich R, Gauss A, Georgieff M, Schütz W. Use of multi-plane transoesophageal echocardiography in visualization of the main hepatic veins and acquisition of Doppler sonography curves: comparison with the transabdominal approach. Br J Anaesth 2001; 87: 711–7.
3. Pinto FJ, Wranne B, St. Goar FG, et al. Hepatic venous flow assessed by transesophageal echocardiography. J Am Coll Cardiol 1991; 17: 1493–8.
4. Nomura T, Lebowitz L, Koide Y, et al. Evaluation of hepatic venous flow using transesophageal echocardiography in coronary artery bypass surgery: an index of right ventricular function. J Cardiothorac Vasc Anesth 1995; 9: 9–17.
5. Gårdebäck M, Settergren G, Brodin L-Å. Hepatic blood flow and right ventricular function during cardiac surgery assessed by transesophageal echocardiography. J Cardiothorac Vasc Anesth 1996; 10: 318–22.
© 2003 International Anesthesia Research Society
6. Sastre Rincón JA, Hernández Valero A, Fernández Pérez A, Muriel Villoria C. A simple method to control a malposition of inferior venous cannula in cardiac surgery using transesophageal echocardiography. Eur J Cardiothorac Surg 2002; 22: 146.