Cerebral and Limb Tissue Oxygenation During Peripheral Venoarterial Extracorporeal Life Support.

Femoral access in extracorporeal life support (ECLS) has been associated with regional variations in arterial oxygen saturation, potentially predisposing the patient to ischemic tissue damage. Current monitoring techniques, however, are limited to intermittent bedside evaluation of capillary refill among other factors. The aim of this study was to assess whether cerebral and limb regional tissue oxygen saturation (rSO2) values reflect changes in various patient-related parameters during venoarterial ECLS (VA-ECLS). This retrospective observational study included adults assisted by femorofemoral VA-ECLS. Bifrontal cerebral and bilateral limb tissue oximetry was performed for the entire duration of support. Hemodynamic data were analyzed parallel to cerebral and limb rSO2. A total of 23 patients were included with a median ECLS duration of 5 [1-20] days. Cardiac arrhythmias were observed in 12 patients, which was associated with a decreased mean rSO2 from 61%±11% to 51%±10% during atrial fibrillation and 67%±9% to 58%±10% during ventricular fibrillation (P<0.001 for both). A presumably sudden increase in cardiac output due to myocardial recovery (n=8) resulted in a significant decrease in mean cerebral rSO2 from 73%±7% to 54%±6% and from 69%±9% to 53%±8% for the left and right cerebral hemisphere, respectively (P=0.012 for both hemispheres). Also, right radial artery partial gas pressure for oxygen decreased from 15.6±2.8 to 8.3±1.9 kPa (P=0.028). No differences were found in cerebral desaturation episodes between patients with and without neurologic complications. In six patients, limb rSO2 increased from on average 29.3±2.7 to 64.0±5.1 following insertion of a distal cannula in the femoral artery (P=0.027). Likewise, restoration of flow in a clotted distal cannula inserted in the femoral artery was necessary in four cases and resulted in increased limb rSO2 from 31.3±0.8 to 79.5±9.0; P=0.068. Non-invasive tissue oximetry adequately reflects events influencing cerebral and limb perfusion and can aid in monitoring tissue perfusion in patients assisted by ECLS.

Impact of Distinct Oxygenators on Pulsatile Energy Indicators in an Adult Cardiopulmonary Bypass Model.

The quantification of pulse energy during cardiopulmonary bypass (CPB) post-oxygenator is required prior to the evaluation of the possible beneficial effects of pulsatile flow on patient outcome. We therefore, evaluated the impact of three distinctive oxygenators on the energy indicators energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) in an adult CPB model under both pulsatile and laminar flow conditions. The pre- and post-oxygenator pressure and flow were measured at room temperature using a 40% glycerin-water mixture at flow rates of 1, 2, 3, 4, 5, and 6 L/min. The pulse settings at frequencies of 40, 50, 60, 70, and 80 beats per minute were according to the internal algorithm of the Sorin CP5 centrifugal pump. The EEP is equal to the mean pressure, hence no SHE is present under laminar flow conditions. The Quadrox-i Adult oxygenator was associated with the highest preservation of pulsatile energy irrespective of flow rates. The low pressure drop-high compliant Quadrox-i Adult oxygenator shows the best SHE performance at flow rates of 5 and 6 L/min, while the intermediate pressure drop-low compliant Fusion oxygenator and the high pressure drop-low compliant Inspire 8F oxygenator behave optimally at flow rates of 5 L/min and up to 4 L/min, respectively. In conclusion, our findings contributed to studies focusing on SHE values post-oxygenator as well as post-cannula in clinical practice. In addition, our findings may give guidance to the clinical perfusionist for oxygenator selection prior to pulsatile CPB based on the calculated flow rate for the individual patient.

Hemodilution Combined With Hypercapnia Impairs Cerebral Autoregulation During Normothermic Cardiopulmonary Bypass.

OBJECTIVE: To investigate the influence of hemodilution and arterial pCO2 on cerebral autoregulation and cerebral vascular CO2 reactivity. DESIGN: Prospective interventional study. SETTING: University hospital-based single-center study. PARTICIPANTS: Forty adult patients undergoing elective cardiac surgery using normothermic cardiopulmonary bypass. INTERVENTIONS: Blood pressure variations induced by 6/minute metronome-triggered breathing (baseline) and cyclic 6/min changes of indexed pump flow at 3 levels of arterial pCO2. MEASUREMENTS AND MAIN RESULTS: Based on median hematocrit on bypass, patients were assigned to either a group of a hematocrit ≥28% or<28%. The autoregulation index was calculated from cerebral blood flow velocity and mean arterial blood pressure using transfer function analysis. Cerebral vascular CO2 reactivity was calculated using cerebral tissue oximetry data. Cerebral autoregulation as reflected by autoregulation index (baseline 7.5) was significantly affected by arterial pCO2 (median autoregulation index amounted to 5.7, 4.8, and 2.8 for arterial pCO2 of 4.0, 5.3, and 6.6 kPa, p≤0.002) respectively. Hemodilution resulted in a decreased autoregulation index; however, during hypocapnia and normocapnia, there were no significant differences between the two hematocrit groups. Moreover, the autoregulation index was lowest during hypercapnia when hematocrit was<28% (autoregulation index 3.3 versus 2.6 for hematocrit ≥28% and<28%, respectively, p = 0.014). Cerebral vascular CO2 reactivity during hypocapnia was significantly lower when perioperative hematocrit was<28% (p = 0.018). CONCLUSIONS: Hemodilution down to a hematocrit of<28% combined with hypercapnia negatively affects dynamic cerebral autoregulation, which underlines the importance of tight control of both hematocrit and paCO2 during CPB.

Contemporary Oxygenator Design Relative to Hemolysis.

Hemolysis is a well-known phenomenon during cardiovascular surgery and generally attributed to cardiopulmonary bypass, particularly when using high-resistant oxygenators. This study aimed at investigating whether transoxygenator pressure drop can be considered an independent factor of hemolysis. Additionally, intraoxygenator blood distribution and shear stress were assessed. A low-resistant (LR, n = 3), a moderate-resistant (MR, n = 3), and a high-resistant (HR, n = 3) clinically used membrane oxygenator were tested in vitro using a roller pump and freshly drawn heparinized porcine blood. Flow rates were set to 2 and 4 L/min and maximum flow compliant to the oxygenator type for 1 hour each. As a control, the oxygenator was excluded from the system. Blood samples were taken every 30 minutes for plasma-free hemoglobin assay and transoxygenator pressure was measured inline. Intraoxygenator blood distribution was assessed using an ultrasound dilution technique. Despite the relatively broad spectrum of pressure drop and resultant transoxygenator pressure drops (LR: 14-41 mmHg, MR: 29-115 mmHg, HR: 77-284 mmHg, respectively), no significant association (R2 = .074, p = .22) was found with the normalized index of hemolysis. The shear stress of each oxygenator at maximum flow rate amounted to 3.0 N/m2 (LR), 5.7 N/m2 (MR), and 8.4 N/m2 (HR), respectively. Analysis of blood flow distribution curves (kurtosis and skewness) revealed intraoxygenator blood flow distribution to become more homogeneous when blood flow rates increased. Contemporary oxygenators were shown not to be a predominant factor for red blood cell damage.

Hypovolemia in extracorporeal life support can lead to arterial gaseous microemboli.

Next to severely decreased pump flow, hypovolemia in extracorporeal life support (ELS) can result in subatmospheric venous line pressure. Such pressure may lead to degassing and resultant gaseous microemboli (GME), with potential changes in neurological clinical outcome. CME activity resulting from degassing was investigated in relation to subatmospheric venous line pressure, partial oxygen pressure (pO2 ), and hematocrit in a model of a centrifugal pump-based circuit for long-term ELS. Additionally, a device that provides instantaneous volume buffer capacity during hypovolemia was evaluated in relation to GME appearance. An exponential relationship was found between decreasing venous line pressure and GME downstream of the centrifugal pump (P = 0.001). Arterial bubble activity appeared at subatmospheric venous line pressures of -200 mm Hg and less. A rising (pO2 ) increased formation of GME (P = 0.05). A rise in hematocrit, in contrast, did not affect embolic activity (P = 0.22). With simulated hypovolemia, volume buffer capacity added to the venous line dampened fluctuations of venous line pressure by approximately 40%, but a significant reduction in GME formation could not be found (P = 0.22). Moreover, the device enabled a 14% higher support flow. With ELS flow being related to patient volume status, hypovolemia can diminish support. A coherent decrease of venous line pressure triggers degassing of blood-dissolved gases and causes arterial GME, which can become massive during persistent conditions of limited venous return. Incorporation of a volume buffer capacity device into the extracorporeal support circuit enables a higher and more stable support flow in critically low patient filling.

Pulse conductance and flow-induced hemolysis during pulsatile cardiopulmonary bypass.

In this study, the hypothesis was tested that a low-resistant, high-compliant oxygenator provides better pulse conductance and less hemolysis than a high-resistant, low-compliant oxygenator during pulsatile cardiopulmonary bypass. Forty adults undergoing coronary artery bypass surgery were randomly divided into two groups using either an oxygenator with a relatively low hydraulic resistance (Quadrox BE-HMO 2000, Maquet Cardiopulmonary AG, Hirrlingen, Germany) or with a relatively high hydraulic resistance (Capiox SX18, Terumo Cardiovascular Systems, Tokyo, Japan). The phase shift between the flow signals measured at the inlet and outlet of the oxygenator was used to assess compliance. Pulse conductance in terms of pressure attenuation was calculated by dividing the outlet pulse pressure of the oxygenator by the inlet pulse pressure. A normalized index was used to assess hemolysis. The phase shifts in time of the flow pulses were 36 +/- 6 ms in the low-resistant (high-compliant) oxygenator, and 14 +/- 2 ms in the high-resistant (low-compliant) oxygenator group (P < 0.001). The low-resistant, high-compliant oxygenator provided 27% better pulse conductance compared with the high-resistant, low-compliant oxygenator (0.84 +/- 0.02 and 0.66 +/- 0.01, respectively, P < 0.001). Inlet pulse pressures were significantly higher (29%) in the high-resistant, low-compliant (Capiox) group than in the low-resistant, high-compliant (Quadrox) group (838 +/- 38 mm Hg and 648 +/- 25 mm Hg respectively, P < 0.001), but no significant difference in hemolysis was found. A low-resistant, high-compliant oxygenator provides better pulse conduction than a high-resistant, low-compliant oxygenator. However, the study data could not confirm the association of high pressures with increased hemolysis.

Laboratory performance testing of venous cannulae during inlet obstruction.

Venous cannulae undergo continuous improvements to achieve better and safer venous drainage. Several cannula tests have been reported, though cannula performance during inlet obstruction has never been a test criterion. In this study, five different cannulae for proximal venous drainage were tested in a mock circulation that enabled measurement of hydraulic conductance after inlet obstruction by vessel collapse. Values for hydraulic conductance ranged from 1.11 x 10(-2) L/min/mm Hg for a Thin-Flex Single Stage Venous Cannula with an open-end lighthouse tip to 1.55 x 10(-2) L/min/mm Hg for a DLP VAD Venous Cannula featuring a swirled tip profile, showing a difference that amounts to nearly 40% of the lowest conductance value. Excessive venous drainage results in potentially dangerous high-negative venous line pressures independent of cannula design. Cannulatip design featuring swirled and grooved tip structures increases drainage capacity and enhances cannula performance during inlet obstruction.

Quantification of recirculation as an adjuvant to transthoracic echocardiography for optimization of dual-lumen extracorporeal life support.

PURPOSE: Proper cannula positioning in single site veno-venous extracorporeal life support (vv-ELS) is cumbersome and necessitates image guidance to obtain a safe and stable position within the heart and the caval veins. Importantly, image-guided cannula positioning alone is not sufficient, as possible recirculation cannot be quantified. METHODS AND RESULTS: We present an ultrasound dilution technique allowing quantification of recirculation for optimizing vv-ELS. CONCLUSION: We suggest quantification of recirculation in addition to image guidance to provide optimal vv-ELS.

Quantitative assessment of cardiac load-responsiveness during extracorporeal life support: case and rationale.

We describe a case of a patient assisted by extracorporeal life support, in which we obtained the dynamic filling index, a measure for venous volume during extracorporeal life support, and used this index to assess cardiac load-responsiveness during acute reloading. While reloading, the obtained findings on cardiac pump function by the dynamic filling index were supported by trans-esophageal echocardiography and standard pressure measurement. This suggests that the dynamic filling index can be used to assess cardiac load-responsiveness during extracorporeal life support.

Dynamic filling index: a novel parameter to monitor circulatory filling during minimized extracorporeal bypass.

OBJECTIVE: To evaluate the dynamic filling index, a novel parameter to monitor changes in venous return and drainable volume, in circulatory assisted patients. Minimized extracorporeal bypass systems lack volume buffering capacity, demanding tight control of drainable volume to maintain bypass flow. Therefore, with patients on minimized bypass quantitative assessment of venous drainable volume is crucial. METHODS: In seven patients undergoing coronary artery bypass grafting using minimized extracorporeal bypass we utilized luxation of the heart to induce a reduction in venous return. The speed of the centrifugal pump was transiently and periodically reduced to monitor resultant changes in bypass flow. The dynamic filling index, a measure of drainable volume, was calculated as Deltaflow/Deltaspeed. RESULTS: With luxation, the dynamic filling index was significantly reduced (from 2.4 +/- 0.2 to 2.0 +/- 0.2 ml/rotation, p = 0.001; 95% confidence interval of mean difference: 0.23-0.46 ml/rotation), whereas routinely recorded parameters, like bypass flow, pump inlet and arterial line pressure, did not change significantly. The intra-measurement reproducibility for the dynamic filling index was 0.5 ml/rotation (20% of the mean), suggesting good potential for this parameter to monitor on-pump venous return in patients. CONCLUSION: The dynamic filling index can detect small changes in venous return and drainable volume which remain unrevealed by routinely recorded parameters. This index could be a valuable tool to monitor and control circulatory filling in individual patients supported by minimized extracorporeal bypass.

An in vitro and in vivo study of the detection and reversal of venous collapse during extracorporeal life support.

The objective of this study was to investigate venous collapse (VC) related to venous drainage during the use of an extracorporeal life support circuit. A mock circulation was built containing a centrifugal pump and a collapsible vena cava model to simulate VC under controlled conditions. Animal experiments were performed for in vivo verification. Changing pump speed had a different impact on flow during a collapsed and a distended caval vein in both models. Flow measurement in combination with pump speed interventions allows for the detection and quantitative assessment of the degree of VC. Additionally, it was verified that a quick reversal of a VC situation could be achieved by a two-step pump speed intervention, which also proved to be more effective than a straightforward decrease in pump speed.