We experienced a case of cardiovascular surgery with CVP ≥ 50 mmHg for 48 min, with a maximum of 78 mmHg. CVP is often elevated during CPB. This is frequently not recognized as a serious problem because it is often caused by impingement of the tip of the CVP measurement catheter in the vessel wall. In our patient, we could not recognize that the cause of the high CVP was obstruction of the venous cannula because the flow rate of the CPB did not decrease when the CVP increased; however, we were able to confirm this using ultrasonography.
Ultrasonography is now a very familiar diagnostic tool and is commonly used to guide nerve blocks, place catheters, and diagnose all types of lesions. An attempt has been made to estimate the CVP from the end-expiratory diameter of the IJV and the proportion of the cross-surface areas of the IJV and common carotid artery measured using ultrasonography [2, 3]. Even during CPB, it is possible to infer CVP from the properties of the IJV. In our patient, ultrasonography showed that the IJV was tense and did not collapse even when compressed with the probe, confirming that the CVP was elevated. Ultrasonography was useful in objectively determining that the CVP was actually high when a high CVP was measured using a pressure transducer.
TEE is commonly used as one of the tools to monitor intraoperative hemodynamics for both cardiac and noncardiac surgery [4, 5]. Though the azygos veins usually cannot be identified by transthoracic echocardiography, they can be identified by TEE [6]. However, the confluence between the azygos veins and the SCV can be included in the blind zone of TEE, preventing observation of the confluence with TEE. That is, an unexpected inflow conduit into an azygos vein, as in our case, could not be observed by TEE; therefore, alternative methods are warranted. While the observation of the IJV by cervical echocardiography cannot directly diagnose the misinsertion of inflow conduits into the azygos vein, it is possible to indirectly detect abnormal blood removal states by evaluating the tension of the IJV. Observation of IJV by cervical echocardiography can be useful in differentiating false high CVP due to obstruction of the central venous catheter from actual high CVP due to poor blood removal if CVP elevates during cardiopulmonary bypass.
Our patient had no neurological sequelae despite prolonged exposure to a very high CVP. CPP is determined by the mean arterial pressure minus the ICP. When the SVC cannula is occluded, as in this case, the ICP may increase and the CPP may decrease. In an experiment in pigs, Tovedal et al. reduced the flow rate of the SVC cannula by 75% during CPB and then performed pressor treatment or release of obstruction. CPP decreased after SVC cannula occlusion and recovered after both treatments [1]. In our patient, the regional cerebral oxygen saturation (rSO2) did not decrease during SVC cannula occlusion. Additionally, no neurological sequelae remained, although the ICP may have been elevated, as inferred from signs of congestion, such as nasal bleeding. This may be due to the fact that reflux by the roller pump increased the arterial pressure as the CVP increased and CPP was maintained. In other words, CVP elevation with a rise in blood pressure during CPB may indicate that the CVP is actually rising due to central venous congestion.
In conclusion, we encountered a case in which obstruction of the venous cannula was recognized by IJV ultrasonography. Ultrasonography can be useful as a tool to determine the cause of elevated CVP.