Effect of increasing mean arterial blood pressure on microcirculation in patients with cardiogenic shock supported by extracorporeal membrane oxygenation.

BACKGROUND: Little is known about the effect of mean arterial blood pressure (MAP) augmentation on the microcirculation in cardiogenic-shock patients with peripheral veno-arterial extracorporeal membrane oxygenation (ECMO) support. We investigated the effect of increasing MAP on the microcirculation in cardiogenic-shock patients with ECMO support. METHODS: A single-center prospective observational study under taken in ICU patients undergoing ECMO support for post-cardiotomy cardiogenic shock was carried out. Patients with MAP <60 mmHg treated with ECMO support were the study cohort. Inotropic and vasopressor agents (dopamine, dobutamine, norepinephrine or epinephrine) were administered to maintain the MAP at 60-90 mmHg. Hemodynamic and microcirculatory data were obtained at a baseline MAP of <60 mmHg and 1 h after target MAP was reached. As parameters of microcirculation, we measured thenar eminence tissue oxygenation (StO2) and its change during the vessel obstruction test and cerebral tissue oxygenation (rSO2) with near-infrared spectroscopy. RESULTS: Seventeen patients were enrolled in the study. MAP of all patients increased and reached predefined therapeutic targets (52 [50-54.5] vs.74 [70-78.5] mmHg; p < 0.001). To obtain these targets, doses of inotropic agents were increased (inotrope score increased from 14 [15.5-28] µg/kg/min; p < 0.001). No obvious changes were observed in thenarmuscleStO2 and cerebral rSO2. Thenar muscle StO2 desaturation slope and resaturation slopes during the vessel obstruction test were also unchanged. CONCLUSIONS: Increasing MAP from <60 mmHg to 60-90 mmHg did not affect microcirculation variables in cardiogenic-shock patients with ECMO support.

Influence of high-flow modified ultrafiltration on brain oxygenation and perfusion during surgery for children with ventricular septal defects: a pilot study.

BACKGROUND: Modified ultrafiltration (MUF) can be performed in infants with ventricular septal defects (VSDs) after cardiopulmonary bypass (CPB) to reduce haemodilution and its potential adverse effects. High-flow MUF might reduce ultrafiltration duration and hasten the necessary correction of haemodilution during CPB. However, its influence on brain oxygenation remains controversial. OBJECTIVE: This non-randomized, prospective, pilot study aimed to investigate the influence of high-flow MUF on brain oxygenation in infants with VSDs. METHODS: High-flow MUF (≥20 mL/kg/min) was performed in twenty infants. Brain oxygen saturation (rSO2) and tissue haemoglobin index (tHI) were non-invasively and continuously measured intraoperatively using near-infrared spectroscopy (NIRS). Transcranial Doppler non-invasively detected the mean flow velocity of the middle cerebral artery (Vmean). RESULTS: rSO2 increased significantly during MUF, as did tHI, Vmean, mean arterial pressure and haematocrit (all p<0.05). No correlation was found between changes in rSO2 and changes in other parameters (all p≥0.05). CONCLUSION: In infants with ventricular septal defects managed with CPB during VSDs repair, high-flow MUF did not reduce brain oxygenation.

Pharmacokinetic model of unfractionated heparin during and after cardiopulmonary bypass in cardiac surgery.

BACKGROUND: Unfractionated heparin (UFH) is widely used as a reversible anti-coagulant in cardiopulmonary bypass (CPB). However, the pharmacokinetic characteristics of UFH in CPB surgeries remain unknown because of the lack of means to directly determine plasma UFH concentrations. The aim of this study was to establish a pharmacokinetic model to predict plasma UFH concentrations at the end of CPB for optimal neutralization with protamine sulfate. METHODS: Forty-one patients undergoing CPB during cardiac surgery were enrolled in this observational clinical study of UFH pharmacokinetics. Patients received intravenous injections of UFH, and plasma anti-FIIa activity was measured with commercial anti-FIIa assay kits. A population pharmacokinetic model was established by using nonlinear mixed-effects modeling (NONMEM) software and validated by visual predictive check and Bootstrap analyses. Estimated parameters in the final model were used to simulate additional protamine administration after cardiac surgery in order to eliminate heparin rebound. Plans for postoperative protamine intravenous injections and infusions were quantitatively compared and evaluated during the simulation. RESULTS: A two-compartment pharmacokinetic model with first-order elimination provided the best fit. Subsequent simulation of postoperative protamine administration suggested that a lower-dose protamine infusion over 24 h may provide better elimination and prevent heparin rebound than bolus injection and other infusion regimens that have higher infusion rates and shorter duration. CONCLUSION: A two-compartment model accurately reflects the pharmacokinetics of UFH in Chinese patients during CPB and can be used to explain postoperative heparin rebound after protamine neutralization. Simulations suggest a 24-h protamine infusion is more effective for heparin rebound prevention than a 6-h protamine infusion.

Effects of intra-aortic balloon pump on cerebral blood flow during peripheral venoarterial extracorporeal membrane oxygenation support.

BACKGROUND: The addition of an intra-aortic balloon pump (IABP) during peripheral venoarterial extracorporeal membrane oxygenation (VA ECMO) support has been shown to improve coronary bypass graft flows and cardiac function in refractory cardiogenic shock after cardiac surgery. The purpose of this study was to evaluate the impact of additional IABP support on the cerebral blood flow (CBF) in patients with peripheral VA ECMO following cardiac procedures. METHODS: Twelve patients (mean age 60.40±9.80 years) received VA ECMO combined with IABP support for postcardiotomy cardiogenic shock after coronary artery bypass grafting. The mean CBF in the bilateral middle cerebral arteries was measured with and without IABP counterpulsation by transcranial Doppler. The patients provided their control values. The mean CBF data were divided into two groups (pulsatile pressure greater than 10 mmHg, P group; pulsatile pressure less than 10 mmHg, N group) based on whether the patients experienced cardiac stun. The mean cerebral blood flow in VA ECMO (IABP turned off) alone and VA ECMO with IABP support were compared using the paired t test. RESULTS: All of the patients were successfully weaned from VA ECMO, and eight patients survived to discharge. The addition of IABP to VA ECMO did not change the mean CBF (251.47±79.28 ml/min vs. 251.30±79.47 ml/min, P=0.96). The mean CBF was higher in VA ECMO alone than in VA ECMO combined with IABP support in the N group (257.68±97.21 ml/min vs. 239.47±95.60, P=0.00). The addition of IABP to VA ECMO support increased the mean CBF values significantly compared with VA ECMO alone (261.68±82.45 ml/min vs. 244.43±45.85 ml/min, P=0.00) in the P group. CONCLUSION: These results demonstrate that an IABP significantly changes the CBF during peripheral VA ECMO, depending on the antegrade blood flow by spontaneous cardiac function. The addition of an IABP to VA ECMO support decreased the CBF during cardiac stun, and it increased CBF without cardiac stun.

Beneficial effect of preventative intra-aortic balloon pumping in high-risk patients undergoing first-time coronary artery bypass grafting-a single center experience.

Although intra-aortic balloon pumping (IABP) has been used widely as a routine cardiac assist device for perioperative support in coronary artery bypass grafting (CABG), the optimal timing for high-risk patients undergoing first-time CABG using IABP is unknown. The purpose of this investigation is to compare preoperative and preventative IABP insertion with intraoperative or postoperative obligatory IABP insertion in high-risk patients undergoing first-time CABG. We reviewed our IABP patients' database from 2002 to 2007; there were 311 CABG patients who received IABP treatment perioperatively. Of 311 cases, 41 high-risk patients who had first-time on-pump or off-pump CABG (presenting with three or more of the following criteria: left ventricular ejection fraction less than 0.45, unstable angina, CABG combined with aneurysmectomy, or left main stenosis greater than 70%) entered the study. We compared perioperatively the clinical results of 20 patients who underwent preoperative IABP placement (Group 1) with 21 patients who had obligatory IABP placement intraoperatively or postoperatively during CABG (Group 2). There were no differences in preoperative risk factors, except left ventricular aneurysm resection, between the two groups. There were no differences in indications for high-risk patients between the two groups. The mean number of grafts was similar. There were no significant differences in the need for inotropes, or in cerebrovascular, gastrointestinal, renal, and infective complications postoperatively. There were no IABP-related complications in either group. Major adverse cardiac event (severe hypotension and/or shock, myocardial infarction, and severe hemodynamic instability) was higher in Group 2 (14 [66.4%] vs. 1 [5%], P < 0.0001) during surgery. The time of IABP pumping in Group 1 was shorter than in Group 2 (72.5 +/- 28.9 h vs. 97.5 +/- 47.7 h, P < 0.05). The duration of ventilation and intensive care unit stay in Group 1 was significantly shorter than in Group 2, respectively (22.0 +/- 1.6 h vs. 39.6 +/- 2.1 h, P < 0.01 and 58.0 +/- 1.5 h vs. 98.5 +/- 1.9 h, P < 0.005). There were no differences in mortality between the two groups (n = 1 in Group 1 and n = 3 in Group 2). Preoperative and preventative insertion of IABP can be performed safely in selected high-risk patients undergoing CABG, with results comparable to those in patients who received obligatory IABP intraoperatively and postoperatively. Therefore, earlier IABP support as part of surgical strategy may help to improve the outcome in high-risk first-time CABG patients.

[Monitoring cerebral oxygenation using near infrared spectroscopy during cardiopulmonary bypass surgery].

To avoid cerebral hypoxia caused by the imbalance between cerebral oxygen supply and consumption, regional cerebral oxygenation of patients need to be monitored at real time during cardiopulmonary bypass (CPB) surgery, and the physiological parameters can be regulated and emergent treatment can be used according to it. Using the near infrared (NIR) instrument developed by our group, cerebral oxygenation of the patients under cardiac surgery was monitored. The instrument consists of a two-wavelength near infrared light source and two near infrared detectors. Hemoglobin concentration changes of regional cerebral tissue were calculated, and by steady-state spatially resolved spectroscopy (SRS) algorithm, regional cerebral oxygen saturation (rSO2) was also calculated. Physiological parameters of patients, such as mixed venous oxygen saturation (SvO2), were measured by another monitor during CPB. Hemoglobin concentration changes were easily disturbed, but the anti-disturbance ability of rSO2 was good. The value of rSO2 could be detected all over the surgeries, but SvO2 could be detected only during CPB. There were positive correlations between rSO2 and SvO2 in most of the patients, but the correlation coefficients were not very high. This was because SvO2 reflects the saturation of the main venous, but rSO2 reflects regional cerebral oxygenation. So the physiological meaning of rSO2 and SvO2 is different. The results indicate that cerebral oxygenation of patients can be reflected by rSO2 during CPB, while only monitoring SvO2 is not enough.

Monitoring cerebral oxygen saturation during cardiopulmonary bypass using near-infrared spectroscopy: the relationships with body temperature and perfusion rate.

During cardiopulmonary bypass (CPB) because of weak arterial pulsation, near-IR spectroscopy (NIRS) is almost the only available method to monitor cerebral oxygenation noninvasively. Our group develops a NIRS oximeter to monitor regional cerebral oxygenation especially its oxygen saturation (rScO2). To achieve optimal coupling between the sensor and human brain, the distances between the light source and the detectors on it are properly chosen. The oximeter is calibrated by blood gas analysis, and the results indicate that its algorithm is little influenced by either background absorption or overlying tissue. We used it to measure the rScO2 of 15 patients during CPB. It is shown that rScO2 is negatively correlated with body temperature and positively with perfusion rate. There are two critical stages during CPB when rScO2 might be relatively low: one is the low-perfusion-rate stage, the other is the early rewarming stage. During cooling, the changes of total hemoglobin concentration (C(tHb)) compared with its original value is also monitored. It is shown that C(tHb) decreases to a small extent, which may mainly reflect cerebral vasoconstriction induced by cooling. All these results indicate that NIRS can be used to monitor cerebral oxygenation to protect cerebral tissue during CPB.