Is body surface area still the best way to determine pump flow rate during cardiopulmonary bypass?

Cerebral Oxygen Saturation Associates with Changes in Oxygen Transport Parameters during Cardiopulmonary Bypass

(1) Background: Adequate organ perfusion during cardiopulmonary bypass (CPB) requires accurate estimation and adjustment of flow rates which conventional methods may not always achieve. Perioperative monitoring of cerebral oxygen saturation (ScO2) may detect changes in oxygen transport. This study aims to compare estimated and measured perfusion flow rates and assess the capacity of ScO2 to detect subtle changes in oxygen transport during CPB. (2) Methods: This observational study included 50 patients scheduled for elective coronary artery bypass grafting (CABG) surgery, all of whom provided written informed consent. Perfusion flow rates were estimated using the DuBois formula and measured using echocardiography and a flow probe in the arterial line of the CPB system. ScO2 was continuously monitored, alongside intermittent measurements of oxygen delivery and extraction ratios. (3) Results: Significant discrepancies were found between estimated flow rates (5.2 [4.8-5.5] L/min) and those measured at the start of the surgery (4.6 [4.0-5.0] L/min). These discrepancies were flow rate-dependent, being more pronounced at lower perfusion rates and diminishing as rates increased. Furthermore, ScO2 showed a consistent correlation with both oxygen delivery (r = 0.48) and oxygen extraction ratio (r = 0.45). (4) Conclusions: This study highlights discrepancies between estimated and actual perfusion flow rates during CPB and underscores the value of ScO2 monitoring as a continuous, noninvasive tool for maintaining adequate organ perfusion, suggesting a need for improved, patient-tailored perfusion strategies.

Our initial experience of monitoring the autoregulation of cerebral blood flow during cardiopulmonary bypass

BACKGROUND

Cerebral blood flow (CBF) is believed to be relatively constant within an upper and lower blood pressure limit. Different methods are available to monitor CBF autoregulation during surgery. This study aims to critically analyze the application of the cerebral oxygenation index (COx), one of the commonly used techniques, using a reference to data from a series of clinical registrations.

METHOD

CBF was monitored using near-infrared spectroscopy, while cerebral blood pressure was estimated by recordings obtained from either the radial or femoral artery in 10 patients undergoing cardiopulmonary bypass. The association between CBF and blood pressure was calculated as a moving continuous correlation coefficient. A COx index > 0.4 was regarded as a sign of abnormal cerebral autoregulation (CA). Recordings were examined to discuss reliability measures and clinical feasibility of the measurements, followed by interpretation of individual results, identification of possible pitfalls, and suggestions of alternative methods.

RESULTS AND CONCLUSION

Monitoring of CA during cardiopulmonary bypass is intriguing and complex. A series of challenges and limitations should be considered before introducing this method into clinical practice.

Compartment syndrome following minimally invasive mitral valve repair: A case report

A 38-year-old Asian male with severe mitral valve regurgitation underwent elective minimally invasive mitral valve repair with artificial chordae and concomitant Cox-Maze procedure. Cardiopulmonary bypass required large peripheral cannulas due to the patient’s increased body surface area with a total bypass time of 216 min. At 10 h, the patient reported progressive right lower extremity pain with evidence of swelling, diffuse paresthesias, and weak peripheral pulses. The patient underwent double-incision lower leg fasciotomies, revealing significant interstitial fluid and bulging muscle chambers. Compartment syndrome demonstrates non-traumatic etiologies. Elevated body mass index, Kawashima Type D femoral artery classification, prolonged bypass times, driven partially due to concomitant Cox-Maze, and larger cannula sizes should increase the index of suspicion.

A retrospective analysis of the mixed venous oxygen saturation as the target for systemic blood flow control during cardiopulmonary bypass

Objectives:

The patient’s body surface area serves as the traditional reference for the determination of systemic blood flow during cardiopulmonary bypass (CPB). New strategies refer to different algorithms of oxygen delivery. This study reports on the mixed venous oxygen saturation (SvO2) as the target for systemic blood flow control. We hypothesise that an SvO2>75% (SvO275) is associated with better preservation of renal function and improved short-term survival.

Methods:

This retrospective, 10-year, observational study analysed 6945 consecutive cardiac surgical cases requiring CPB. Endpoints included rates of acute kidney injury (AKI) and short-term survival, also the estimated glomerular filtration rate (eGFR), lactate levels and blood transfusions.

Results:

Seventy-seven percent of the patients attained the SvO275 target. For this group, the median SvO2 was 78.1 (5.8) %, with a mean oxygen delivery of 331 (78) ml/min per m2 body surface area. Overall incidence of AKI levels (I-III): 7.5% - 2.6% - 0.6%. Incidence of eGFR (<50%): 3.9%, increasing to 6% for haemoglobin levels <80 g/L (p<0.001). Red cell transfusion was more frequent (p<0.001) within this group (30.6%) compared to levels >100 g/L (0.3%). Further, women (52.8%) were transfused more often than men (14.6%). Lactate level at weaning from CPB was 1.3 (0.7) mmol/L. The SvO275 target demonstrated a relative risk reduction of 22.5% (p=0.032) for AKI (I), increasing to 32.3% (p=0.026) for procedures extending >90 minutes. In addition, the risk for death 90-days postop was lower (p=0.039).

Conclusion:

The SvO275 target showed a decreased risk for postoperative AKI and prolonged short-term survival. Good clinical outcomes were also linked to measures of lactate and the eGFR. However, anaemia remains a risk factor for AKI.

Ghrelin Pre-treatment Attenuates Local Oxidative Stress and End Organ Damage During Cardiopulmonary Bypass in Anesthetized Rats

Cardiopulmonary bypass (CPB) induced systemic inflammation significantly contributes to the development of postoperative complications, including respiratory failure, myocardial, renal and neurological dysfunction and ultimately can lead to failure of multiple organs. Ghrelin is a small endogenous peptide with wide ranging physiological effects on metabolism and cardiovascular regulation. Herein, we investigated the protective effects of ghrelin against CPB-induced inflammatory reactions, oxidative stress and acute organ damage. Adult male Sprague Dawley rats randomly received vehicle (n = 5) or a bolus of ghrelin (150 μg/kg, sc, n = 5) and were subjected to CPB for 4 h (protocol 1). In separate rats, ghrelin pre-treatment (protocol 2) was compared to two doses of ghrelin (protocol 3) before and after CPB for 2 h followed by recovery for 2 h. Blood samples were taken prior to CPB, and following CPB at 2 h and 4 h. Organ nitrosative stress (3-nitrotyrosine) was measured by Western blotting. CPB induced leukocytosis with increased plasma levels of tumor necrosis factor-α and interleukin-6 indicating a potent inflammatory response. Ghrelin treatment significantly reduced plasma organ damage markers (lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase) and protein levels of 3-nitrotyrosine, particularly in the brain, lung and liver, but only partly suppressed inflammatory cell invasion and did not reduce proinflammatory cytokine production. Ghrelin partially attenuated the CPB-induced elevation of epinephrine and to a lesser extent norepinephrine when compared to the CPB saline group, while dopamine levels were completely suppressed. Ghrelin treatment sustained plasma levels of reduced glutathione and decreased glutathione disulphide when compared to CPB saline rats. These results suggest that even though ghrelin only partially inhibited the large CPB induced increase in catecholamines and organ macrophage infiltration, it reduced oxidative stress and subsequent cell damage. Pre-treatment with ghrelin might provide an effective adjunct therapy for preventing widespread CPB induced organ injury.

Miniature cardiopulmonary bypass — the Hammersmith experience

The decision to embark on a miniature cardiopulmonary bypass programme requires careful planning. The objective of this paper is to present our experience and initial findings for consideration by our multidisciplinary peers, who may wish to implement this technology at their own hospitals. The paper reviews the evolution of our programme over the first 150 clinical cases and our current position on the advantages and disadvantages of miniature cardiopulmonary bypass. Perfusion (2007) 22, 161—166.

Red blood cell transfusion for infants with single-ventricle physiology

The purpose of this study was to assess how red blood cell (RBC) transfusions impact hemodynamic parameters in infants with single-ventricle lesions. This was a retrospective chart review. The setting was a pediatric cardiac intensive care unit at a tertiary care children's hospital. Fifty-nine patients <1 year of age with single-ventricle physiology who received a blood transfusion between December 2007 and April 2009 were analyzed. They received a total of 183 transfusions. Exclusion criteria included transfusions given within 72 h of cardiac surgery or transfusions given to patients with active bleeding. There were no interventions. The study population was divided into terciles based on pretransfusion hemoglobin (Hgb) concentration. The pretransfusion Hgb concentration in group A was 7.8 to 12.3 gm/dl, in group B was 12.4 to 13.2 gm/dl, and in group C was 13.3 to 15.7 gm/dl. Heart rate, blood pressure, arterial saturation, and cerebral near-infrared spectroscopy (cNIRS) values before transfusion, as well as at 1, 2, 4, 8, and 12 h after transfusion, were collected. There was significant improvement in diastolic blood pressure, arterial saturation, and cNIRS in group A after 12 h. Transfusions given in group B also resulted in improvement in diastolic blood pressure and arterial saturation, with less robust response of cNIRS. In group C, only arterial saturation values increased significantly. RBC transfusions can improve hemodynamics and markers of oxygen delivery in infants with single-ventricle physiology, but further studies are needed to determine an optimal Hgb level in this population. Interventions to increase Hgb above this level may be of limited benefit.

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.