Sisse Anette Thomassen

Should blood flow during cardiopulmonary bypass be individualized more than to body surface area

Blood flow during cardiopulmonary bypass (CPB) is calculated on body surface area (BSA). Increasing comorbidity, age and weight of today’s cardiac patients question this calculation as it may not reflect individual metabolic requirement. The hypothesis was that a measured cardiac index (CI) prior to normothermic CPB is a better estimate. A cross-over study, with random allocation to CPB blood flow for 20 minutes based on either a calculation (2.4 L/min/m2) or on CI, with a switch to the opposite flow for another 20 minutes, was performed. Twenty-two elective cardiac surgery patients with normal ventricular function were included. Effect parameters were cerebral oxygenation, mixed venous saturation and arterial lactate. CI varied from 1.9 to 3.1 L/min/m2 (median 2.4 L/min/m2). No differences in effect parameters were seen. In conclusion, a CPB blood flow based on an individual estimate did not improve cerebral and systemic oxygenation compared to a blood flow based on BSA.

Regional muscle tissue saturation is an indicator of global inadequate circulation during cardiopulmonary bypass : a randomized porcine study using muscle, intestinal and brain tissue metabolomics

Background: Muscle tissue saturation (StO2) measured with near-infrared spectroscopy has generally been considered a measurement of the tissue microcirculatory condition. However, we hypothesized that StO2 could be more regarded as a fast and reliable measure of global than of regional circulatory adequacy and tested this with muscle, intestinal and brain metabolomics at normal and two levels of low cardiopulmonary bypass blood flow rates in a porcine model. Methods: Twelve 80 kg pigs were connected to normothermic cardiopulmonary bypass with a blood flow of 60 mL/kg/min for one hour, reduced randomly to 47.5 mL/kg/min (Group I) or 35 mL/kg/min (Group II) for one hour followed by one hour of 60 mL/kg/min in both groups. Regional StO2 was measured continuously above the musculus gracilis (non-cannulated leg). Metabolomics were obtained by brain tissue oxygen monitoring system (Licox) measurements of the brain and microdialysis perfusate from the muscle, intestinal mucosa and brain. A non-parametric statistical method was used. Results: The systemic parameters showed profound systemic ischaemia during low CPB blood flow. StO2 did not change markedly in Group I, but in Group II, StO2 decreased immediately when blood flow was reduced and, furthermore, was not restored despite blood flow being normalized. Changes in the metabolomics from the muscle, colon and brain followed the changes in StO2. Conclusion: We found, in this experimental cardiopulmonary bypass model, that StO2 reacted rapidly when the systemic circulation became inadequate and, furthermore, reliably indicate insufficient global tissue perfusion even when the systemic circulation was restored after a period of systemic hypoperfusion.

Cerebral blood flow measured by positron emission tomography during normothermic cardiopulmonary bypass: an experimental porcine study:

Background: Mean arterial blood pressure (MAP) and/or pump flow during normothermic cardiopulmonary bypass (CPB) are the most important factors of cerebral perfusion. The aim of this study was to explore the influence of CPB blood flow on cerebral blood flow (CBF) measured by dynamic positron emission tomography (PET) using 15O-labelled water with no pharmacological interventions to maintain the MAP. Methods: Eight pigs (69-71 kg) were connected to normothermic CPB. After 60 minutes (min) with a CPB pump flow of 60 mL/kg/min, the pigs were changed to either 35 mL/kg/min or 47.5 mL/kg/min for 60 min and, thereafter, all the pigs returned to 60 mL/kg/min for another 60 min. The MAP was measured continuously and the CBF was measured by positron emission tomography (PET) during spontaneous circulation and at each CPB pump flow after 30 min of steady state. Results: Two pigs were excluded due to complications. CBF increased from spontaneous circulation to a CPB pump flow of 60 mL/kg/min. A reduction in CPB pump flow to 47.5 mL/kg/min (n=3) resulted in only minor changes in CBF while a reduction to 35 mL/kg/min (n=3) caused a pronounced change (correlation coefficient (R2) 0.56). A return of CPB pump flow to 60 mL/kg/min was followed by an increase in CBF, except in the one pig with the lowest CBF during low flow (R2=0.44). CBF and MAP were not correlated (R2=0.20). Conclusion: In this experimental porcine study, a relationship was observed between pump flow and CBF under normothermic low-flow CPB. The effect of low pump flow on MAP showed substantial variations, with no correlation between CBF and MAP.

The association between a three-day ticagrelor discontinuation and perioperative bleeding complications

OBJECTIVES Dual antiplatelet therapy at the time of cardiac surgery is associated with excessive perioperative bleeding. International guidelines, therefore, recommended discontinuing oral adenosine diphosphate receptor antagonists prior to non-emergency surgery. In this study, we analysed whether a 3-day ticagrelor discontinuation was sufficient to avoid major bleeding complications. METHODS This study is a retrospective cohort analysis of 3377 patients undergoing coronary artery bypass or single-valve surgery from January 2013 to September 2017. Patients exposed to ticagrelor prior to surgery were compared with control patients exposed to aspirin only. Outcome measures included transfusion requirements, bleeding volumes, the need for re-exploration and the composite outcome major bleeding complication. Data were retrieved from the the Western Denmark Heart Registry. RESULTS During the study period, 101 patients were preoperatively exposed to ticagrelor, whereas 3276 patients were exposed to aspirin only. Propensity-score matching resulted in 90 pairs of patients. Overall, ticagrelor exposure was associated with a greater risk of major bleeding complications compared with control patients [31 vs 12%, relative risk 2.6, 95% confidence interval (CI) 1.4-4.8]. While ticagrelor exposure within 0-72 h before surgery (n = 42) was associated with a substantially increased risk of major bleeding complications (48 vs 10%, relative risk 5.0, 95% CI 1.9-13.4), ticagrelor exposure 72-120 h before surgery (n = 48) showed no statistically significant association (17 vs 15%, relative risk 1.1, 95% CI 0.4-2.9). CONCLUSIONS In our historical cohort, ticagrelor exposure 0-72 h prior to cardiac surgery was associated with an increased risk of major bleeding complications. On the other hand, ticagrelor exposure 72-120 h prior to surgery was not associated with a clinically relevant increase in major bleeding complications.

Keep Ventilating the Lungs While the Heart is Still Ejecting on Femoro-femoral Cardiopulmonary Bypass

Femoro-femoral cardiopulmonary bypass (CPB) followed by deep hypothermic circulatory arrest is one of the modalities used for ascending aortic pseudoaneurysm repair to achieve cardiac unloading and to avoid severe hemorrhage due to the risk of rupture during the sternal entry. However, due to the limited size of the cannulas, it can be challenging to achieve total cardiopulmonary support. Therefore, despite the achievement of total cardiopulmonary support, the heart may still be able to eject antegrade blood flow that meets the retrograde blood flow from the arterial side of the CPB. The point where the blood flow meets in the aorta is called the watershed area. If the antegrade blood flow is large due to a left ventricular ejection, the watershed area will be located in the descending aorta. Therefore, if ventilation is stopped, deoxygenated blood will be ejected to the cerebral circulation. Cerebral near-infrared spectroscopy (NIRS) may be used as a noninvasive and continuous measurement of regional brain oxygen saturation (rSO2). This case demonstrates that cerebral desaturation due to discontinued mechanical ventilation, when the heart was still ejecting during the initial phase of femoro-femoral CPB, immediately was detected by a pronounced drop bilaterally: In the left frontal lobe, rSO2 fell from 56% to 21%, and in the right frontal lobe it fell from 47% to 25%. The authors recommend monitoring cerebral saturation using NIRS in the case of femoro-femoral CPB.