Zhongtao Du

Superior vena cava drainage improves upper body oxygenation during veno-arterial extracorporeal membrane oxygenation in sheep

IntroductionDifferential hypoxia is a pivotal problem in patients with femoral veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) support. Despite recognition of differential hypoxia and attempts to deliver more oxygenated blood to the upper body, the mechanism of differential hypoxia as well as prevention strategies have not been well investigated.MethodsWe used a sheep model of acute respiratory failure that was supported with femoral VA ECMO from the inferior vena cava to the femoral artery (IVC-FA), ECMO from the superior vena cava to the FA (SVC-FA), ECMO from the IVC to the carotid artery (IVC-CA) and ECMO with an additional return cannula to the internal jugular vein based on the femoral VA ECMO (FA-IJV). Angiography and blood gas analyses were performed.ResultsWith IVC-FA, blood oxygen saturation (SO2) of the IVC (83.6 ± 0.8%) was higher than that of the SVC (40.3 ± 1.0%). Oxygen-rich blood was drained back to the ECMO circuit and poorly oxygenated blood in the SVC entered the right atrium (RA). SVC-FA achieved oxygen-rich blood return from the IVC to the RA without shifting the arterial cannulation. Subsequently, SO2 of the SVC and the pulmonary artery increased (70.4 ± 1.0% and 73.4 ± 1.1%, respectively). Compared with IVC-FA, a lesser difference in venous oxygen return and attenuated differential hypoxia were observed with IVC-CA and FA-IJV.ConclusionsDifferential venous oxygen return is a key factor in the etiology of differential hypoxia in VA ECMO. With knowledge of this mechanism, we can apply better cannula configurations in clinical practice.

Comparison of low molecular weight hydroxyethyl starch and human albumin as priming solutions in children undergoing cardiac surgery

Human albumin is the conventional cardiopulmonary bypass circuit primer. However, it has high manufacturing costs. Crystalloid and colloid solutions have been developed as alternatives, including a new generation of non-ionic hydroxyethyl starch (HES). The efficacy of hydroxyethyl starch with a 130 molecular weight and substitution degree of 0.4 (hydroxyethyl starch 130/0.4) was compared with human albumin for use in cardiopulmonary bypass surgery in American Society of Anesthesiologists’ grade I-II pediatric congenital heart disease patients. Efficacy was evaluated by comparing perioperative hemodynamic parameters, including plasma colloid osmotic pressure, renal function, blood loss, allogeneic blood volumes and plasma volume substitution. The hydroxyethyl starch group exhibited significantly higher preoperative colloid osmotic pressure (p<0.01) and significantly lower operative renal function and postoperative allogeneic blood volumes than the human albumin group. No significant differences were observed in serum creatinine, glucose, hematocrit or lactic acid levels (p>0.05). Our results indicate that hydroxyethyl starch may be a viable alternative to human albumin in pediatric patients undergoing relatively simple cardiopulmonary bypass surgeries.

Preoperative intra-aortic balloon pump improves the clinical outcomes of off-pump coronary artery bypass grafting in left ventricular dysfunction patients.

Severe left ventricular (LV) dysfunction patients undergoing off-pump coronary artery bypass grafting (OPCAB) are often associated with a higher mortality. The efficacy and safety of the preoperative prophylactic intra-aortic balloon pump (IABP) insertion is not well established. 416 consecutive patients with severe LV dysfunction (ejection fraction ≤35%) undergoing isolated OPCAB were enrolled in a retrospective observational study. 191 patients was enrolled in the IABP group; the remaining 225 patients was in control group. A total of 129 pairs of patients were propensity-score matched. No significant differences in demographic and preoperative risk factors were found between the two groups. The postoperative 30-day mortality occurred more frequently in the control group compared with the IABP group (8.5% vs. 1.6%, p = 0.02). There was a significant reduction of low cardiac output syndrome in the IABP group compared with the control group (14% vs. 6.2%, p = 0.04). Prolonged mechanical ventilation (≥48 h) occurred more frequently in the control group (34.9% vs. 20.9%, p = 0.02). IABP also decreased the postoperative length of stay. Preoperative IABP was associated with a lower 30-day mortality, suggesting that it is effective in patients with severe LV dysfunction undergoing OPCAB.

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.

Discrepancy between blood gas concentration measurements and carbon dioxide removal rate

Dear Editor, We read with great interest the article by Hermann and colleagues entitled “A novel pump-driven veno-venous gas exchange system during extracorporeal CO2 removal” [1]. We agree that in patients with extracorporeal membrane oxygenation (ECMO), increasing sweep gas flow results in effective CO2 removal, which can be further reinforced by increasing blood flow. The CO2 transfer rate was calculated according to the equations shown in the Appendix of their paper. We have several questions about the equations. First, we noted that the CO2 content equation does not have the same units on both sides of the equation: the units on the left side are mL/dL, whereas those on the right are mL/ dL + mMol/L. We suggest that the equation should be revised according to the units. Second, the CO2 content calculated from blood gas may not reflect the real CO2 content because the blood gas bicarbonate (HCO3) was calculated using the Henderson–Hasselbalch equation, and some factors may cause an erroneous calculation of the HCO3 value [2]. The CO2 removal rate in our center was calculated using the following formula [3]:

Timing of Intra-Aortic Balloon Pump Placement Before Off-Pump Coronary Artery Bypass Grafting and Clinical Outcomes: IABP PLACEMENT BEFORE OPCAB AND OUTCOMES

We aimed to evaluate the timing of preoperative intra-aortic balloon pump (IABP) placement and outcomes in patients undergoing off-pump coronary artery bypass grafting (OPCAB). Patients with prophylactic IABP placement before OPCAB presenting between January 1, 2010 and December 31, 2013 were included. Patients were categorized into two groups based on the timing of preoperative IABP placement: less than 2 h (Group A, n = 223) and more than 2 h (Group B, n = 94). According to the European System for Cardiac Operative Risk Evaluation (EuroSCORE), patients were divided into two subgroups: middle-low EuroSCORE (<6, Groups A1 and B1) and high EuroSCORE (≥6, Groups A2 and B2). Clinical data were compared between groups. Groups contained the following numbers of patients: Group A1, 163; Group A2, 60; Group B1, 60; and Group B2, 34. There was a significant difference in length of ICU and hospital stay between Group A and Group B, respectively (40.5 [22, 64] vs. 26.25 [18, 46.5] hours, P = 0.006; 16 [11, 22] vs. 11 [8, 14] days, P = 0.000). Duration of IABP support, ICU length of stay, hospital length of stay, and cost of hospitalization were significantly higher in Group A1 than in Group B1, respectively (73.69 ± 44.12 vs. 64.03 ± 40.93 h, P = 0.013; 36 [20, 56.5] vs. 25.5 [17, 43.75] hours, P = 0.035; 15(11,21) vs. 9(7.25, 12) days, P = 0.000; 109.53(101.20, 131.1) vs. 102.7(95.94, 115.32) thousands CNY, P = 0.009). The length of hospital stay was also significantly higher in Group A2 than in Group B2 (18(13, 26) vs. 13(11, 15) hours, P = 0.000). Preoperative placement of IABP greater than 2 h prior to OPCAB is of benefit, especially in those with high EuroSCORE. The optimal time for prophylactic IABP placement requires further study.

Mortality risk factors from converting off-pump coronary artery bypass to on-pump coronary artery bypass

Introduction: A number of large-scale retrospective studies revealed that off-pump coronary artery bypass (OPCAB) was superior to on-pump coronary artery bypass (ONCAB). The aim of the study was to investigate risk factors for mortality when OPCAB is converted to ONCAB. Methods: Patients who underwent OPCAB conversion to ONCAB at the Beijing Anzhen Hospital between January 2003 and January 2013 were assigned to the non-survivor and survivor groups. Background demographics, illness history and preoperative, intraoperative and postoperative variables were compared. Results: Of the 247 cases, 15.4% of the patients died. Patients in the non-survivor group were older and more frequently had diabetes mellitus (DM), arrhythmia, myocardial infarction (MI) in the past 30 days (all p<0.05) and MI combined with mitral regurgitation (p<0.0001); they more frequently had bigger left ventricular end-diastolic dimension (p=0.0019), greater fall in blood pressure, ventricular fibrillation for longer periods, longer conversion time and bypass graft occlusion. All patients in the non-survivor group received intra-aortic balloon pump compared to 89.5% in the survivor group and extracorporeal membrane oxygenation was more common. Left main coronary artery disease (OR=4.431, 95%CI: 2.440-8.048, p<0.0001), blood pressure decline ⩽40 mmHg (OR=0.509, 95%CI: 0.447-0.580, p<0.0001) and time for conversion to ONCAB ⩾20 min were independently associated with mortality. Rates of postoperative complications, such as renal failure, cerebral infarction or hemorrhage, MI and redo sternotomy, were higher in the non-survivor group. Conclusions: Conversion from OPCAB to ONCAB is associated with high mortality. Risk factors include left main artery disease and duration of blood pressure decline >40 min.

Shall we consider more of the intra-aortic balloon pump effects on microcirculation in cardiogenic shock patients supported by venoarterial extracorporeal membrane oxygenation?

e800 www.ccmjournal.org December 2014 • Volume 42 • Number 12 The authors reply: We read with great interest the comment by Hastings and Wagner (1) on our recent publication (2). They correctly point out that prognostic models for comatose patients after cardiac arrest (CA) are not uniform and describe the potential role of electroencephalographic bispectral index (BIS) and transesophageal echocardiography (TEE) in this setting. Our proposed prognostication approach encompasses a multimodal assessment including clinical, neurophysiological, and laboratory tools that are widely available nowadays in many ICUs. Furthermore, our model includes tools recently discussed and proposed by several independent groups, which seems to reinforce its potential generalizability in this specific clinical situation (3, 4). In particular, based on the data from those studies (5, 6), we strongly believe that clinical neurological assessment at repeated time points following CA represents a key factor. Hastings and Wagner (1) propose the integration of BIS and TEE for early prognostic assessment. We indeed agree with them that these tools are promising. There are, however, some limitations that might preclude their widespread utilization for post-CA coma prognostication, at least currently. First, it is well recognized that electroencephalography (EEG) performed with a standard 10–20 montage and including background reactivity testing is far more informative than BIS. Although the latter represents a considerable reduction and compression of data and BIS evolution over time has been demonstrated to help in prognostication (7), the relationship between a detailed EEG assessment and neuronal death inferred by blood neuronspecific enolase (NSE) levels has been recently outlined (8). In addition, the prognostic robustness of early EEG background reactivity assessment has been repeatedly established (2, 5) and shows reasonable interrater agreement (9). Second, standard EEG allows detection and management of seizures, which may be missed using the BIS alone. Therefore, based on what precedes, we believe that BIS monitoring cannot be considered as a full substitute of standard EEG. Regarding TEE, prognostic information in post-CA patients is still relatively limited and was not considered in recent guidelines and expert recommendations (4, 6, 10); therefore, at present time, this investigation should not be considered as a routine assessment. In summary, we agree with Hastings and Wagner (1) that outcome prognostication after CA should be performed taking into account as much information coming from as many tools as possible; it would be in fact very interesting to integrate cardiac and simplified EEG-derived variables to current standard clinical examination and electrophysiological and laboratory tests. Indeed, this approach illustrates the multimodality as described in our recent study (2), which we and others believe is paramount to minimize false predictions and reduce the uncertainty on coma prognostication. Adding novel tools, such as BIS and/or TEE, or more sophisticated analysis of cognitive evoked potentials (e.g., mismatch negativity paradigms) (11), holds great promise. Further studies are needed before these novel tools can be incorporated in current ICU practice. Until then, repeated clinical examination combined with electrophysiological assessment (including standard EEG and somatosensory evoked potentials) and serum NSE sampling should be recommended. Dr. Rossetti’s institution received grant support from the Swiss National Science Foundation (CR32I3_143780) and received unrestricted research grants from Eisai, Sage Pharmaceuticals, and UCB. Dr. Oddo received grant support from the Swiss National Science Foundation (320030_138191).