Cerebral vascular effects of aortovenous cannulations for pediatric cardiopulmonary bypass

Clinical relevance of transcranial Doppler in a cardiac surgery setting: embolic load predicts difficult separation from cardiopulmonary bypass

BACKGROUND

During cardiac surgery, transcranial Doppler (TCD) represents a non-invasive modality that allows measurement of red blood cell flow velocities in the cerebral arteries. TCD can also be used to detect and monitor embolic material in the cerebral circulation. Detection of microemboli is reported as a high intensity transient signal (HITS). The importance of cerebral microemboli during cardiac surgery has been linked to the increased incidence of postoperative renal failure, right ventricular dysfunction, and hemodynamic instability. The objective of this study is to determine whether the embolic load is associated with hemodynamic instability during cardiopulmonary bypass (CPB) separation and postoperative complications.

METHODS

A retrospective single-centre cohort study of 354 patients undergoing cardiac surgery between December 2015 and March 2020 was conducted. Patients were divided in tertiles, where 117 patients had a low quantity of embolic material (LEM), 119 patients have a medium quantity of microemboli (MEM) and 118 patients who have a high quantity of embolic material (HEM). The primary endpoint was a difficult CPB separation. Multivariate logistic regression was used to determine the potential association between a difficult CPB separation and the number of embolic materials.

RESULTS

Patients who had a difficult CPB separation had more HITS compared to patients who had a successful CPB separation (p < 0.001). In the multivariate analysis, patients with MEM decreased their odds of having a difficult CPB weaning compared to patients in the HEM group (OR = 0.253, CI 0.111-0.593; p = 0.001). In the postoperative period patients in the HEM group have a higher Time of Persistent Organ Dysfunction (TPOD), a longer stay in the ICU, a longer duration under vasopressor drugs and a higher mortality rate compared to those in the MEM and LEM groups.

CONCLUSION

The result of this study suggests that a high quantity of cerebral embolic material increases the odds of having a difficult CPB separation. Also, it seems to be associated to more complex surgery, a longer CPB time, a higher TPOD and a longer stay in the ICU. Six out of eight patients who died in this cohort were in the HEM group.

The Correlation of Two Cerebral Saturation Monitors With Jugular Bulb Oxygen Saturation in Children Undergoing Cardiopulmonary Bypass for Congenital Heart Surgery

Background:

Near-infrared spectroscopy (NIRS) is a noninvasive monitoring technique that measures regional cerebral oxygen saturation (rSO2).

Objectives:

The primary aim was to compare the output of 2 NIRS-based cerebral oximetry devices, FORESIGHT (CAS Medical Systems Inc, Branford, Connecticut) and INVOS (Covidien, Boulder, Colorado), to venous oxygen saturations from the jugular venous bulb at cannulation and decannulation of the superior vena cava (SVC). Secondary objectives included evaluating correlations of cerebral saturation, as measured by the NIRS devices, with mean arterial blood pressure (MAP), measured by an invasive arterial line, and end-tidal CO2 (ETCO2).

Methods:

Near-infrared spectroscopy, MAP, and ETCO2 data were collected at 13 defined events during each case when hemodynamic instability was expected. At SVC cannulation and decannulation, a 0.1 mL sample of blood was collected from the jugular bulb by the surgeon using a long angiocatheter. The oxygen saturation of these blood samples was measured using an AVOX device and compared with contemporaneous readings from the NIRS probes. Mixed-effects linear regression was used to correlate MAP or ETCO2 with cerebral oxygen saturation (by NIRS) at each time point.

Results:

Children undergoing cardiopulmonary bypass for congenital heart surgery (n = 34) were enrolled in the study. At SVC cannulation, both INVOS ( r = .78) and FORESIGHT ( r = .59) were correlated with AVOX data at P < .001, although the correlation with INVOS was significantly stronger ( P = .003). At SVC decannulation, INVOS ( r = .68; P < .001) and FORESIGHT ( r = .60; P < .001) were similarly correlated with jugular venous rSO2. Correlations of rSO2 (by NIRS) with MAP and ETCO2 levels were stronger than correlations between rSO2 change and change in MAP or ETCO2.

Conclusion:

INVOS correlated more strongly than FORESIGHT with the jugular bulb rSO2 at SVC cannulation but may have underestimated oxygen saturation at low rSO2 values. Data from both NIRS devices were correlated with MAP and ETCO2 over the case duration.

Cerebral blood flow during cardiopulmonary bypass in pediatric cardiac surgery: the role of transcranial Doppler--a systematic review of the literature

Background

Transcranial Doppler Ultrasound (TCD) is a sensitive, real time tool for monitoring cerebral blood flow velocity (CBFV). This technique is fast, accurate, reproducible and noninvasive. In the setting of congenital heart surgery, TCD finds application in the evaluation of cerebral blood flow variations during cardiopulmonary bypass (CPB).

Methodology

We performed a search on human studies published on the MEDLINE using the keyword "trans cranial Doppler" crossed with "pediatric cardiac surgery" AND "cardio pulmonary by pass", OR deep hypothermic cardiac arrest", OR "neurological monitoring".

Discussion

Current scientific evidence suggests a good correlation between changes in cbral blood flow and mean cerebral artery (MCA) blood flow velocity. The introduction of Doppler technology has allowed an accurate monitorization of cerebral blood flow (CBF) during circulatory arrest and low-flow CPB. TCD has also been utilized in detecting cerebral emboli, improper cannulation or cross clamping of aortic arch vessels. Limitations of TCD routine utilization are represented by the need of a learning curve and some experience by the operators, as well as the need of implementing CBF informations with, for example, data on brain tissue oxygen delivery and consumption.

Conclusion

In this light, TCD plays an essential role in multimodal neurological monitorization during CPB (Near Infrared Spectroscopy, TCD, processed electro encephalography) that, according to recent studies, can help to significantly improve neurological outcome after cardiac surgery in neonates and pediatric patients.

New developments in pediatric cardiac anesthesia

As the practice of pediatric cardiac anesthesia continues to grow, anesthesiologists now routinely care for patients ranging in size from less than 2 kg to more than 100 kg. New clinical and laboratory research has enhanced our understanding of the effects of anesthetic drugs on the pediatric myocardium, and improvements in survival statistics for even the smallest and sickest infants have shifted the emphasis to evaluation of quality of life and neurological outcome in pediatric cardiac patients. The use of circulatory support in infants and children, both for rapid resuscitation and for more chronic indications such as bridge to transplantation, also continues to evolve, with the recent introduction of pulsatile and axial pumps for pediatric use. This article reviews anesthetic agents, bleeding and coagulation, neurological monitoring, and mechanical circulatory support in the treatment of infants and children.

Neurological Monitoring for Congenital Heart Surgery

The incidence of neurological complications after pediatric cardiac surgery ranges from 2% to 25%. The causes are multifactorial and include preoperative brain malformations, perioperative hypoxemia and low cardiac output states, sequelae of cardiopulmonary bypass, and deep hypothermic circulatory arrest. Neurological monitoring devices are readily available and the anesthesiologist can now monitor the brain during pediatric cardiac surgery. In this review we discuss near-infrared cerebral oximetry, transcranial Doppler ultrasound, and electroencephalographic monitors for use during congenital heart surgery. After review of the basic principles of each monitoring modality, we discuss their uses during pediatric heart surgery. We present evidence that multimodal neurological monitoring in conjunction with a treatment algorithm may improve neurological outcome for patients undergoing congenital heart surgery and present one such algorithm.

Transcranial Doppler during suspected brain death in children: Potential limitation in patients with cardiac "shunt"

OBJECTIVES: We report a potential limitation of transcranial Doppler for assessing cerebral circulation during suspected brain death in children. DESIGN: Review of two case series identified during our clinical practice. PATIENTS: Eight children with suspected brain death and seven with intact-brain and cardiovascular anomalies. MEASUREMENTS AND MAIN RESULTS: Brain-death criteria included lack of cerebral-brainstem reactivity, electrocortical silence and absent blood flow by brain scintigraphy ((99m)Tc-hexamethylpropylenamine oxime). Five intracranial Doppler patterns were found in eight cases of suspected brain death: A) orthograde continuous flow; B) reduced systolic flow velocity with absence of diastolic flow; C) reduced systolic flow velocity with retrograde diastolic flow, sometimes with antegrade late diastolic flow; D) systolic spikes of very low flow velocity; and E) absence of Doppler signals. Only patterns "C," "D," and "E" were associated with the absence of supra- and infratentorial brain perfusion. The most common Doppler alterations in patients with intact-brain and cardiovascular anomalies were the absence of diastolic flow (pattern "B") or the presence of retrograde flow during diastole (pattern "C"). CONCLUSION: Transcranial Doppler monitoring of pediatric patients may have value in identifying patients who have severe cerebral compromise, who may progress to brain death. However, key Doppler alterations, such as absent or retrograde flow during diastole, are not uniquely associated with the diagnosis of brain death, particularly in the setting of congential heart disease. The use of conventional methodology for the diagnosis of brain death in infants and children remains the "gold standard."

Effect of Trendelenburg head position during cardiac deairing on cerebral microemboli in children: a randomized controlled trial

OBJECTIVES

We prospectively evaluated the effects of head position during cardiac deairing on the Doppler ultrasonography-detected cerebral microemboli in children and the association between the embolic counts and the clinical assessment of deairing.

METHODS

Children requiring exposure of the systemic ventricle under cardiopulmonary bypass were randomized to Trendelenburg (-15 degrees ) and horizontal (0 degrees ) head positions during and after standard surgical deairing. Complexity of repair was categorized as follows: group I consisted of single simple lesions, and group II consisted of multiple complex lesions. Transcranial Doppler ultrasonography identified high-intensity transient signals in the right middle cerebral artery within the first 5 minutes after aortic declamping (release) and from this ending period until cardiopulmonary bypass termination (residual). Electrocardiographic alterations after deairing were documented. A predefined 5-point scale was used by the surgeon for blinded assessment of deairing.

RESULTS

High-intensity transient signals were identified in 97% of 128 patients (aged 5 days to 17 years). The median total high-intensity transient signal count was 60 (25th-75th quartiles, 14-189). Head position or surgeon did not affect the rate of high-intensity transient signals (P >.20). During the residual interval, occurrence of HITS in group I was less than that in group II (P <.05), but there was no difference at release. The incidence of high-intensity transient signals and electrocardiographic alterations correlated with the clinical assessment of deairing (P <.01).

CONCLUSIONS

Trendelenburg head position as a complement of cardiac deairing in children does not decrease the cerebral microembolic load compared with the horizontal head position. The cerebral microembolic count and the occurrence of electrocardiographic alterations usually increases when the surgeon is less confident in the efficacy of deairing.