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

Polito A, Ricci Z, Di Chiara L, Giorni C, Iacoella C, Sanders SP, Picardo S - Cardiovasc Ultrasound (2006)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Hospital, Rome, Italy. angpolito@hotmail.com <angpolito@hotmail.com>

ABSTRACT

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.

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Related in: MedlinePlus

Mean cerebral blood flow velocities (CBFV) expressed in percentages of baseline for patients with immediate and delayed rewarming. Flow velocities remained below the baseline in immediate rewarming group, but for group of delayed rewarming mean flow velocity was comparable with baseline at all postbypass measurement (From 17).
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Figure 6: Mean cerebral blood flow velocities (CBFV) expressed in percentages of baseline for patients with immediate and delayed rewarming. Flow velocities remained below the baseline in immediate rewarming group, but for group of delayed rewarming mean flow velocity was comparable with baseline at all postbypass measurement (From 17).

Mentions: The introduction of deep hypotermic cardiopulmonary bypass (DHCPB) with or without deep hypothermic circulatory arrest (DHCA) in children who need complex aortic arch reconstruction has substantially improved operating conditions and therefore reduced cardiac morbidity. The aim of hypothermia during CPB is to reduce metabolic activity, CBF and cerebral metabolic rate of oxygen (CMRO2), so that it is possible to maintain energy stores and provide organ protection during low flow state [9,10]. Profound hypothermia with continuous low-flow cardiopulmonary bypass (low-flow CPB) has been suggested as being superior to DHCA in preventing neurological damage [11,12], hypothetically providing an indefinite period of cerebral perfusion. The most important factor ruling cerebral hemodynamics is cerebral autoregulation, in order to maintain CBF constant throughout a wide range of arterial pressure. This autoregolatory mechanism is deeply affected by temperature. Taylor and coworkers [13] found that autoregulation is preserved during normothermic CPB, it begins to be altered at temperature less than 25°C, and it is lost at temperature less than 20°C, while previous studies had shown that autoregulation is intact during moderately hypothermic CPB (25° to 32°C) [10], and it is lost during deep hypothermic CPB (18° to 22°C) (Figure 3). However, this loss of autoregulation is most likely caused by a state of "cold-induced vasoparesis", in which cerebral vascular resistance increases with temperature reduction. Jonassen and coworkers [14] showed that a significant proportion of patients treated with profound hypothermia and either low-flow CPB or circulatory arrest exhibited a TCD pattern consistent with increased cerebral vascular resistance in the early postoperative period, whereas this pattern was not present in patients treated with moderately hypothermic CPB. There was a tendency for this pattern to occur with greater frequency in patients who had a period of circulatory arrest (Figure 4). While CBF decreases in a linear manner, CMRO2 decreases exponentially with temperature reduction. Therefore, CBF/CMRO2 during DHCPB increases favouring luxury perfusion of the brain. Normal coupling of CBF/CMRO2 is present before and after CPB, as well as during normothermic CPB and α-stat management [10]. During CPB rewarming, CBF returns to baseline values, except in patients exposed to periods of DHCA where CBF remains decreased (Figure 5) [15]. Astudillo et al. [16] demonstrated that low cerebral perfusion immediately following DHCA is characterized by a prolonged period of absent diastolic CBFV in MCA: this finding was explained by an increased intracranial pressure after total circulatory arrest procedure, while patients subjected to continuous low-flow perfusion technique showed a CBFV close to baseline values at skin closure. It must be remarked however, that a significant age difference between the two groups was present, being the patients subjected to circulatory arrest younger than the patients in the non arrest group. An interesting finding from the group of Rodriguez [17] is that a delay in rewarming on reperfusion after DHCA improved recovery of a diastolic doppler signal compared with patients who underwent immediate rewarming. In the group undergoing cold reperfusion, postbypass CBF velocity was not different from baseline (Figure 6). Taylor and coworkers [13] used the TCD as an indicator of perfusion during repair of congenital heart defects requiring moderate or profound hypothermia and low-flow CPB. The principal finding of this study was the immediate loss of detectable CBFV in the middle cerebral artery when cerebral perfusion pressure (CPP) decreased below 9 mmHg: they clearly conclude that CPP is a crucial parameter, rather then pump flow rate, in impacting brain perfusion. They also confirmed the loss of cerebral autoregulation between 23° and 25°. However, Jonassen et al [14], in agreement with data from van der Linden [2], showed detectable cerebral blood flow at pump flow rate and mean arterial pressure (MAP) values lower than those reported by Taylor. Possible explanations may include the use of vasodilators, the increased sensitivity of the TCD apparatus by removal of the low-pass filter and the avoidance of jugular central venous lines that can theoretically impede regional cerebral venous drainage in small infants and thus decreasing CPP. A more recent study from Zimmermann et al. [18] performed in 28 neonates undergoing the arterial switch operation with α-stat acid-base management, showed that cerebral perfusion can be detected by TCD in the MCA in some neonates at bypass flow as low as 10 ml/kg per minute. However a minimum bypass flow rate of 30 ml/kg per minute was needed to detect cerebral perfusion in all neonates. All patients with a MAP of 19 mmHg or greater, regardless of pump flow rate, had detectable cerebral perfusion by TCD but correlation between MAP and CPB pump flow rates was minimal, confirming the conclusions of Taylor that mean arterial blood pressure alone is a poor indicator of CPP.


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

Polito A, Ricci Z, Di Chiara L, Giorni C, Iacoella C, Sanders SP, Picardo S - Cardiovasc Ultrasound (2006)

Mean cerebral blood flow velocities (CBFV) expressed in percentages of baseline for patients with immediate and delayed rewarming. Flow velocities remained below the baseline in immediate rewarming group, but for group of delayed rewarming mean flow velocity was comparable with baseline at all postbypass measurement (From 17).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1764902&req=5

Figure 6: Mean cerebral blood flow velocities (CBFV) expressed in percentages of baseline for patients with immediate and delayed rewarming. Flow velocities remained below the baseline in immediate rewarming group, but for group of delayed rewarming mean flow velocity was comparable with baseline at all postbypass measurement (From 17).
Mentions: The introduction of deep hypotermic cardiopulmonary bypass (DHCPB) with or without deep hypothermic circulatory arrest (DHCA) in children who need complex aortic arch reconstruction has substantially improved operating conditions and therefore reduced cardiac morbidity. The aim of hypothermia during CPB is to reduce metabolic activity, CBF and cerebral metabolic rate of oxygen (CMRO2), so that it is possible to maintain energy stores and provide organ protection during low flow state [9,10]. Profound hypothermia with continuous low-flow cardiopulmonary bypass (low-flow CPB) has been suggested as being superior to DHCA in preventing neurological damage [11,12], hypothetically providing an indefinite period of cerebral perfusion. The most important factor ruling cerebral hemodynamics is cerebral autoregulation, in order to maintain CBF constant throughout a wide range of arterial pressure. This autoregolatory mechanism is deeply affected by temperature. Taylor and coworkers [13] found that autoregulation is preserved during normothermic CPB, it begins to be altered at temperature less than 25°C, and it is lost at temperature less than 20°C, while previous studies had shown that autoregulation is intact during moderately hypothermic CPB (25° to 32°C) [10], and it is lost during deep hypothermic CPB (18° to 22°C) (Figure 3). However, this loss of autoregulation is most likely caused by a state of "cold-induced vasoparesis", in which cerebral vascular resistance increases with temperature reduction. Jonassen and coworkers [14] showed that a significant proportion of patients treated with profound hypothermia and either low-flow CPB or circulatory arrest exhibited a TCD pattern consistent with increased cerebral vascular resistance in the early postoperative period, whereas this pattern was not present in patients treated with moderately hypothermic CPB. There was a tendency for this pattern to occur with greater frequency in patients who had a period of circulatory arrest (Figure 4). While CBF decreases in a linear manner, CMRO2 decreases exponentially with temperature reduction. Therefore, CBF/CMRO2 during DHCPB increases favouring luxury perfusion of the brain. Normal coupling of CBF/CMRO2 is present before and after CPB, as well as during normothermic CPB and α-stat management [10]. During CPB rewarming, CBF returns to baseline values, except in patients exposed to periods of DHCA where CBF remains decreased (Figure 5) [15]. Astudillo et al. [16] demonstrated that low cerebral perfusion immediately following DHCA is characterized by a prolonged period of absent diastolic CBFV in MCA: this finding was explained by an increased intracranial pressure after total circulatory arrest procedure, while patients subjected to continuous low-flow perfusion technique showed a CBFV close to baseline values at skin closure. It must be remarked however, that a significant age difference between the two groups was present, being the patients subjected to circulatory arrest younger than the patients in the non arrest group. An interesting finding from the group of Rodriguez [17] is that a delay in rewarming on reperfusion after DHCA improved recovery of a diastolic doppler signal compared with patients who underwent immediate rewarming. In the group undergoing cold reperfusion, postbypass CBF velocity was not different from baseline (Figure 6). Taylor and coworkers [13] used the TCD as an indicator of perfusion during repair of congenital heart defects requiring moderate or profound hypothermia and low-flow CPB. The principal finding of this study was the immediate loss of detectable CBFV in the middle cerebral artery when cerebral perfusion pressure (CPP) decreased below 9 mmHg: they clearly conclude that CPP is a crucial parameter, rather then pump flow rate, in impacting brain perfusion. They also confirmed the loss of cerebral autoregulation between 23° and 25°. However, Jonassen et al [14], in agreement with data from van der Linden [2], showed detectable cerebral blood flow at pump flow rate and mean arterial pressure (MAP) values lower than those reported by Taylor. Possible explanations may include the use of vasodilators, the increased sensitivity of the TCD apparatus by removal of the low-pass filter and the avoidance of jugular central venous lines that can theoretically impede regional cerebral venous drainage in small infants and thus decreasing CPP. A more recent study from Zimmermann et al. [18] performed in 28 neonates undergoing the arterial switch operation with α-stat acid-base management, showed that cerebral perfusion can be detected by TCD in the MCA in some neonates at bypass flow as low as 10 ml/kg per minute. However a minimum bypass flow rate of 30 ml/kg per minute was needed to detect cerebral perfusion in all neonates. All patients with a MAP of 19 mmHg or greater, regardless of pump flow rate, had detectable cerebral perfusion by TCD but correlation between MAP and CPB pump flow rates was minimal, confirming the conclusions of Taylor that mean arterial blood pressure alone is a poor indicator of CPP.

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatric Cardiology and Cardiac Surgery, Bambino Gesù Hospital, Rome, Italy. angpolito@hotmail.com <angpolito@hotmail.com>

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus