Monitoring and optimization of the microcirculation during CPB

Microcirculatory Alterations in Cardiac Surgery: A Comprehensive Guide

Microcirculation is essential for cellular life and its functions. It comprises a complex network of capillaries, arterioles, and venules, which distributes oxygenated blood across and within organs based on regional metabolic demands. Because previous research indicated that organ function is linked to microcirculatory function, it is crucial to maintain sufficient and effective microcirculatory function during major surgery. Impaired microcirculation can lead to inadequate tissue perfusion, potentially resulting in perioperative complications and an unfavorable outcome. Indeed, changes in microcirculation in cardiovascular disease and cardiac surgery have a direct correlation with prolonged stays in the postoperative intensive care unit and high mortality rates within 30 days. Additionally, cardiopulmonary bypass, a regularly employed method in cardiac surgery, has been proven to induce microcirculatory malfunction and, thus, lead to postoperative multiple organ dysfunction. As global hemodynamic parameters can remain stable or improve, whereas microcirculation is still compromised, tracking microcirculatory variables could lead to the development of targeted microcirculatory treatment within hemodynamic management. Therefore, it is necessary to enhance the use of microcirculatory monitoring in the medical domain to assist physicians in the therapeutic management of patients undergoing cardiac surgery. This potentially can lead to better hemodynamic management and outcomes. This review article concentrates on the use of handheld video microscopes for real-time microcirculatory assessment of cardiac surgery patients in the immediate and early postoperative period. Emphasis is placed on integrating microcirculatory monitoring with conventional hemodynamic monitoring in the therapeutic management of patients undergoing cardiac surgery.

Postoperative thrombocytopenia and subsequent consequences in acute type A aortic dissection

OBJECTIVES

To ascertain if postoperative thrombocytopenia following open aortic surgery with a median sternotomy can predict early- and intermediate-term morbidity and mortality.

METHODS

From January 2018 to December 2022, a comparison was made between patients who had and didn't have postoperative thrombocytopenia (defined as a nadir < 75 × 103/μL after 72 h of open aortic surgery with median sternotomy). Intermediate-term mortality during follow-up was the main result, with cerebrovascular accident and acute renal injury requiring dialysis as secondary events. Inverse probability treatment weighting (IPTW) was used to account for selection bias between groups. The Kaplan-Meier method with the log-rank test was used to assess intermediate-term survivals following IPTW modification. To identify the nonlinear link between platelet nadir and mortality probability, a generalized additive mix model was applied. To help increase power in testing for the overall effect of platelet nadir on outcomes in the generalized additive mix model, the hazard ratios and 95% CIs for each subgroup and their interactions were examined.

RESULTS

The study included 457 patients, 347 male (75.9%), with mean age of 54 ± 12 years. The last follow-up was done on April 14th, 2023 and the median follow-up time was 16 (6-31) months. Following IPTW, patient characteristics were balanced among cohorts. Platelet nadir was found to be significantly inversely related to early-term mortality (IPTW-adjusted hazard ratio = 0.968 (0.960, 0.977), p < 0.001), and AKI requiring dialysis (IPTW-adjusted hazard ratio = 0.979 (0.971, 0.986), p < 0.001). A nonlinear relationship between platelet nadir and mortality risk probability during follow-up visually showed that the likelihood of mortality decreased with platelet nadir increased. In confounder-adjusted survival ('postoperative thrombocytopenia not acquired' vs 'postoperative thrombocytopenia'; HR: 0.086 [95% CI: 0.045-0.163]; p < 0.01) analysis, non-acquired postoperative thrombocytopenia was associated with a lower risk of mortality, and the treatment benefit was validated in IPTW-adjusted analysis, which showed an HR of 0.067.

CONCLUSIONS

Early postoperative thrombocytopenia following type A aortic dissection surgery is a risk factor for morbidity and mortality. Because postoperative thrombocytopenia can indicate a poor prognosis, monitoring early postoperative platelets helps identify individuals who may develop late postoperative problems, which is performed by this affordable biomarker.

Characteristics of sublingual microcirculatory changes during the early postoperative period following cardiopulmonary bypass-assisted cardiac surgery-a prospective cohort study

BACKGROUND

Persistent microcirculatory dysfunction associated with increased morbidity and mortality. Interventions in the early resuscitation can be tailored to the changes of microcirculation and patient's need. However, there is usually an uncoupling of macrocirculatory and microcirculatory hemodynamics during resuscitation. Current research on the patterns of microcirculatory changes and recovery after cardiopulmonary bypass (CPB)-assisted cardiac surgery is limited. This study aimed to analyze changes in the microcirculatory parameters after CPB and their correlation with macrocirculation and to explore the characteristics of microcirculatory changes following CPB-assisted cardiac surgery.

METHODS

Between December 2018 and January 2019, 24 adult patients with indwelling pulmonary artery catheters after elective cardiac surgery using CPB were enrolled in this study. Both microcirculatory and macrocirculatory parameters were collected at 0, 6, 16, and 24 hours after admission to the intensive care unit (ICU). Video images of sublingual microcirculation were analyzed to obtain the microcirculatory parameters, including total vascular density (TVD), perfused small vessel density (PSVD), the proportion of perfused small vessels (PPV), microvascular flow index (MFI), and flow heterogeneity index (HI). The characteristics of microcirculatory parameter change following cardiac surgery and the correlation between microcirculatory parameters and macroscopic hemodynamic indicators, oxygen metabolic indicators, and carbon dioxide partial pressure difference (PCO2gap) were analyzed.

RESULTS

There were significant differences in the changes of TVD (P=0.012) and PSVD (P=0.005) during the first 24 hours postoperatively in patients who underwent CPB-assisted cardiac surgery. The microcirculatory density parameters (TVD: r=-0.5059, P=0.0456; PVD: r=-0.5499, P=0.0273) were correlated with oxygen delivery index (DO2I) at 24 hours after surgery. The microcirculatory flow parameters (PPV: r=0.4370, P=0.0327; MFI: r=0.6496, P=0.0006; and HI: r=-0.5350, P=0.0071) had a strong correlation with PCO2gap at 0 hour after surgery.

CONCLUSIONS

TVD and PSVD might be two most sensitive indicators affected by CPB-assisted cardiac surgery. There was no consistency between microcirculation and macrocirculation until 24 hours following cardiac surgery, meaning the improvement of systemic hemodynamic indicators does not guarantee correspondently improvement in microcirculation. Early controlled oxygen supply after CPB-assisted cardiac surgery may be conducive to the resuscitation of patients to a certain extent.

A nomogram for reduced cardiac function in postoperative acute type A aortic dissection patients with acute kidney injury undergoing continuous renal replacement therapy

Background

This study aimed to develop a nomogram to predict reduced cardiac function for acute kidney injury (AKI) patients who received continuous renal replacement therapy (CRRT) after acute type A aortic dissection (ATAAD) surgery.

Methods

This study was a retrospective analysis. ATAAD patients with preoperative normal ejection fraction (EF) and postoperative AKI with CRRT admitted between January 2014 and November 2021 were included. The reduced cardiac function was defined as EF <50%. The data were analyzed by the univariate and multivariate logistic regression analyses. A diagnostic model was established by a nomogram, and its discriminative performance was validated by the received operating characteristic (ROC) curve and concordance (C) statistic. The calibration of the diagnostic model was tested by calibration curves and the HosmerLemeshow test. The clinical utility was evaluated by the decision curve analysis (DCA).

Result

In total, 208 patients were eligible for analysis, of which 98 patients with reduced cardiac function. The logistic regression analyses showed age ≥60 years old, history of coronary atherosclerotic disease, preoperative pericardial tamponade, and cardiopulmonary bypass time were risk factors for reduced cardiac function, which were further employed in the nomogram. As results, nomogram revealed a high predictive power (C statistic = 0.723, 0.654–0.792; the bootstrap-corrected concordance C statistic = 0.711, the area under the ROC curve = 0.723). The calibration curves showed good consistency between the predicted and the actual probabilities (calibration curve: Brier points = 0.208, Emax = 0.103, Eavg = 0.021; Hosmer-Lemeshow test, P = 0.476). DCA showed that the nomogram could augment net benefits and exhibited a wide range of threshold probabilities in the prediction of EF reduction.

Conclusion

This nomogram is an effective diagnostic model for predicting the reduced cardiac function in postoperative ATAAD patients with AKI undergoing CRRT and can be used to protect postoperative renal functions and facilitate patient-specific care after ATAAD surgery.

Efficacy of Pulsatile Flow Perfusion in Adult Cardiac Surgery: Hemodynamic Energy and Vascular Reactivity

Background: The role of pulsatile (PP) versus non-pulsatile (NP) flow during a cardiopulmonary bypass (CPB) is still debated. This study’s aim was to analyze hemodynamic effects, endothelial reactivity and erythrocytes response during a CPB with PP or NP. Methods: Fifty-two patients undergoing an aortic valve replacement were prospectively randomized for surgery with either PP or NP flow. Pulsatility was evaluated in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE). Systemic (SVRi) and pulmonary (PVRi) vascular resistances, endothelial markers levels and erythrocyte nitric-oxide synthase (eNOS) activity were collected at different perioperative time-points. Results: In the PP group, the resultant EEP was 7.3% higher than the mean arterial pressure (MAP), which corresponded to 5150 ± 2291 ergs/cm³ of SHE. In the NP group, the EEP and MAP were equal; no SHE was produced. The PP group showed lower SVRi during clamp-time (p = 0.06) and lower PVRi after protamine administration and during first postoperative hours (p = 0.02). Lower SVRi required a higher dosage of norepinephrine in the PP group (p = 0.02). Erythrocyte eNOS activity results were higher in the PP patients (p = 0.04). Renal function was better preserved in the PP group (p = 0.001), whereas other perioperative variables were comparable between the groups. Conclusions: A PP flow during a CPB results in significantly lower SVRi, PVRi and increased eNOS production. The clinical impact of increased perioperative vasopressor requirements in the PP group deserves further evaluation.

Clinical risk score for postoperative pneumonia following heart valve surgery

Background:

Postoperative pneumonia (POP) is one of the most common infections following heart valve surgery (HVS) and is associated with a significant increase in morbidity, mortality, and health care costs. This study aimed to identify the major risk factors associated with the occurrence of POP following HVS and to derive and validate a clinical risk score.

Methods:

Adults undergoing open HVS between January 2016 and December 2019 at a single institution were enrolled in this study. Patients were randomly assigned to the derivation and validation sets at 1:1 ratio. A prediction model was developed with multivariable logistic regression analysis in the derivation set. Points were assigned to independent risk factors based on their regression coefficients.

Results:

POP occurred in 316 of the 3853 patients (8.2%). Multivariable analysis identified ten significant predictors for POP in the derivation set, including older age, smoking history, chronic obstructive pulmonary disease, diabetes mellitus, renal insufficiency, poor cardiac function, heart surgery history, longer cardiopulmonary bypass, blood transfusion, and concomitant coronary and/or aortic surgery. A 22-point risk score based on the multivariable model was then generated, demonstrating good discrimination (C-statistic: 0.81), and calibration (Hosmer-Lemeshow χ² = 8.234, P = 0.312). The prediction rule also showed adequate discriminative power (C-statistic: 0.83) and calibration (Hosmer-Lemeshow χ² = 5.606, P = 0.691) in the validation set. Three risk intervals were defined as low-, medium-, and high-risk groups.

Conclusion:

We derived and validated a 22-point risk score for POP following HVS, which may be useful in preventive interventions and risk management.

Trial Registration:

Chictr.org, ChiCTR1900028127; http://www.chictr.org.cn/showproj.aspx?proj=46932

Risk factors for postoperative pneumonia after cardiac surgery: a prediction model

Background

Postoperative pneumonia is the main infectious complication following cardiac surgery and is associated with significant increases in morbidity, mortality and health care costs. The aim of this study was to identify potential risk factors related to the occurrence of postoperative pneumonia in adult patients undergoing cardiac surgery and to develop a predictive system.

Methods

Adult patients who underwent open heart surgery in our institution between 2016 and 2019 were enrolled in this study. Preoperative and intraoperative variables were collected and analyzed. A multivariate prediction model for evaluating the risk of postoperative pneumonia was established using logistic regression analysis via forward stepwise selection, and points were assigned to significant risk factors based on their regression coefficient values.

Results

Postoperative pneumonia occurred in 530 of the 5,323 patients (9.96%). Prolonged stays in the postoperative intensive care unit (ICU) and hospital, as well as higher mortality (25.66% versus 0.65%), were observed in patients with postoperative pneumonia. Multivariate analysis identified 13 independent risk factors including patient demographics, comorbidities, cardiac function, cardiopulmonary bypass (CPB) duration, and blood transfusion. The prediction model showed good discrimination (C-statistic: 0.80) and was well calibrated (Hosmer-Lemeshow χ²=7.907, P value =0.443). A 32-point risk score was generated, and then three risk intervals were defined.

Conclusions

We derived and validated a prediction model for postoperative pneumonia after cardiac surgery incorporating 13 easily discernible risk factors. The scoring system may be helpful for individualized risk estimations and clinical decision-making.

Pulsatile Versus Nonpulsatile Flow During Cardiopulmonary Bypass: Extent of Hemolysis and Clinical Significance

Pulsatile flow has been used during cardiopulmonary bypass (CPB) for decades and its use is increasing with advancing extracorporeal technology. Pulsatile flow generates higher circuit pressures and shear forces than nonpulsatile flow at comparable pump flow and patient mean arterial pressure. Very little is known about the effect this has on erythrocytes. We included 62 adult patients (32 in the pulsatile group and 30 in the nonpulsatile group) undergoing elective coronary artery bypass grafting in this prospective observational study. Blood samples were collected at routine sampling times throughout surgery and were analyzed for the presence of free heme and globin using mass spectroscopy. Patient characteristics, CPB, and aortic cross-clamp times, pump flow as well as patient mean arterial pressure were similar in both groups. Maximum circuit pressure in the pulsatile flow group was statistically significantly higher than that in the nonpulsatile flow group (257.12 vs. 190.64 mmHg, p < 0.0001). Both heme and globin levels were higher in the pulsatile flow group. This reached statistical significance with globin at 30 minutes of CPB and with heme after aortic unclamping. We conclude that pulsatile CPB using roller pumps results in a greater extent of hemolysis. The clinical significance, however, is not yet known.