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Size distribution of air bubbles entering the brain during cardiac surgery.

Chung EM, Banahan C, Patel N, Janus J, Marshall D, Horsfield MA, Rousseau C, Keelan J, Evans DH, Hague JP - PLoS ONE (2015)

Bottom Line: Numerous small bubbles detected during cardiopulmonary bypass were estimated by Monte-Carlo simulation to be benign.However, during weaning from bypass, showers containing large macro-bubbles were observed, which were estimated to transiently affect up to 2.2% of arterioles.Although bubbles are alarmingly numerous during surgery, our simulations suggest that the majority of bubbles are too small to be harmful.

View Article: PubMed Central - PubMed

Affiliation: University of Leicester Department of Cardiovascular Sciences, Leicester, United Kingdom; University Hospitals of Leicester NHS Trust, Leicester, United Kingdom; Leicester Cardiovascular Biomedical Research Unit, Leicester, United Kingdom.

ABSTRACT

Background: Thousands of air bubbles enter the cerebral circulation during cardiac surgery, but whether high numbers of bubbles explain post-operative cognitive decline is currently controversial. This study estimates the size distribution of air bubbles and volume of air entering the cerebral arteries intra-operatively based on analysis of transcranial Doppler ultrasound data.

Methods: Transcranial Doppler ultrasound recordings from ten patients undergoing heart surgery were analysed for the presence of embolic signals. The backscattered intensity of each embolic signal was modelled based on ultrasound scattering theory to provide an estimate of bubble diameter. The impact of showers of bubbles on cerebral blood-flow was then investigated using patient-specific Monte-Carlo simulations to model the accumulation and clearance of bubbles within a model vasculature.

Results: Analysis of Doppler ultrasound recordings revealed a minimum of 371 and maximum of 6476 bubbles entering the middle cerebral artery territories during surgery. This was estimated to correspond to a total volume of air ranging between 0.003 and 0.12 mL. Based on analysis of a total of 18667 embolic signals, the median diameter of bubbles entering the cerebral arteries was 33 μm (IQR: 18 to 69 μm). Although bubble diameters ranged from ~5 μm to 3.5 mm, the majority (85%) were less than 100 μm. Numerous small bubbles detected during cardiopulmonary bypass were estimated by Monte-Carlo simulation to be benign. However, during weaning from bypass, showers containing large macro-bubbles were observed, which were estimated to transiently affect up to 2.2% of arterioles.

Conclusions: Detailed analysis of Doppler ultrasound data can be used to provide an estimate of bubble diameter, total volume of air, and the likely impact of embolic showers on cerebral blood flow. Although bubbles are alarmingly numerous during surgery, our simulations suggest that the majority of bubbles are too small to be harmful.

No MeSH data available.


Related in: MedlinePlus

Estimated distribution of bubble sizes detected during cardiac surgery.(a) Distribution of bubble sizes estimated based on analysis of the ultrasound backscatter (MEBR values) from 18667 embolic signals. Overall, the median diameter of bubbles was 33 μm (IQR: 18 to 69 μm). Signals observed following removal of the aortic cross-clamp are shaded. (b) Percentage of emboli, bubble volume, and predicted dissolve times for 18 μm, 38 μm, 100 μm, 500 μm and 1 mm diameter air bubbles.
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pone.0122166.g002: Estimated distribution of bubble sizes detected during cardiac surgery.(a) Distribution of bubble sizes estimated based on analysis of the ultrasound backscatter (MEBR values) from 18667 embolic signals. Overall, the median diameter of bubbles was 33 μm (IQR: 18 to 69 μm). Signals observed following removal of the aortic cross-clamp are shaded. (b) Percentage of emboli, bubble volume, and predicted dissolve times for 18 μm, 38 μm, 100 μm, 500 μm and 1 mm diameter air bubbles.

Mentions: Patient-specific bubble sizing revealed that the majority (85%) of bubbles were less than 100 μm and can be expected to dissolve within minutes, Fig 2. The median bubble diameter from all 18667 signals was 33 μm (IQR: 18 to 71 μm). Conversion of MEBR values to bubble diameters is illustrated in Fig 2(A). Note that the exact form of this curve varies slightly between patients depending on MCA diameter and intra-operative haematocrit levels.[11] A summary of the percentage of bubbles above a particular diameter, and their estimated dissolve times, is provided in Fig 2(B). Only 2.2% of bubbles were larger than 500 μm. Of these, approximately 90 bubbles (0.5%) were estimated to represent clinically significant macrobubbles over 1 mm in diameter.


Size distribution of air bubbles entering the brain during cardiac surgery.

Chung EM, Banahan C, Patel N, Janus J, Marshall D, Horsfield MA, Rousseau C, Keelan J, Evans DH, Hague JP - PLoS ONE (2015)

Estimated distribution of bubble sizes detected during cardiac surgery.(a) Distribution of bubble sizes estimated based on analysis of the ultrasound backscatter (MEBR values) from 18667 embolic signals. Overall, the median diameter of bubbles was 33 μm (IQR: 18 to 69 μm). Signals observed following removal of the aortic cross-clamp are shaded. (b) Percentage of emboli, bubble volume, and predicted dissolve times for 18 μm, 38 μm, 100 μm, 500 μm and 1 mm diameter air bubbles.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383554&req=5

pone.0122166.g002: Estimated distribution of bubble sizes detected during cardiac surgery.(a) Distribution of bubble sizes estimated based on analysis of the ultrasound backscatter (MEBR values) from 18667 embolic signals. Overall, the median diameter of bubbles was 33 μm (IQR: 18 to 69 μm). Signals observed following removal of the aortic cross-clamp are shaded. (b) Percentage of emboli, bubble volume, and predicted dissolve times for 18 μm, 38 μm, 100 μm, 500 μm and 1 mm diameter air bubbles.
Mentions: Patient-specific bubble sizing revealed that the majority (85%) of bubbles were less than 100 μm and can be expected to dissolve within minutes, Fig 2. The median bubble diameter from all 18667 signals was 33 μm (IQR: 18 to 71 μm). Conversion of MEBR values to bubble diameters is illustrated in Fig 2(A). Note that the exact form of this curve varies slightly between patients depending on MCA diameter and intra-operative haematocrit levels.[11] A summary of the percentage of bubbles above a particular diameter, and their estimated dissolve times, is provided in Fig 2(B). Only 2.2% of bubbles were larger than 500 μm. Of these, approximately 90 bubbles (0.5%) were estimated to represent clinically significant macrobubbles over 1 mm in diameter.

Bottom Line: Numerous small bubbles detected during cardiopulmonary bypass were estimated by Monte-Carlo simulation to be benign.However, during weaning from bypass, showers containing large macro-bubbles were observed, which were estimated to transiently affect up to 2.2% of arterioles.Although bubbles are alarmingly numerous during surgery, our simulations suggest that the majority of bubbles are too small to be harmful.

View Article: PubMed Central - PubMed

Affiliation: University of Leicester Department of Cardiovascular Sciences, Leicester, United Kingdom; University Hospitals of Leicester NHS Trust, Leicester, United Kingdom; Leicester Cardiovascular Biomedical Research Unit, Leicester, United Kingdom.

ABSTRACT

Background: Thousands of air bubbles enter the cerebral circulation during cardiac surgery, but whether high numbers of bubbles explain post-operative cognitive decline is currently controversial. This study estimates the size distribution of air bubbles and volume of air entering the cerebral arteries intra-operatively based on analysis of transcranial Doppler ultrasound data.

Methods: Transcranial Doppler ultrasound recordings from ten patients undergoing heart surgery were analysed for the presence of embolic signals. The backscattered intensity of each embolic signal was modelled based on ultrasound scattering theory to provide an estimate of bubble diameter. The impact of showers of bubbles on cerebral blood-flow was then investigated using patient-specific Monte-Carlo simulations to model the accumulation and clearance of bubbles within a model vasculature.

Results: Analysis of Doppler ultrasound recordings revealed a minimum of 371 and maximum of 6476 bubbles entering the middle cerebral artery territories during surgery. This was estimated to correspond to a total volume of air ranging between 0.003 and 0.12 mL. Based on analysis of a total of 18667 embolic signals, the median diameter of bubbles entering the cerebral arteries was 33 μm (IQR: 18 to 69 μm). Although bubble diameters ranged from ~5 μm to 3.5 mm, the majority (85%) were less than 100 μm. Numerous small bubbles detected during cardiopulmonary bypass were estimated by Monte-Carlo simulation to be benign. However, during weaning from bypass, showers containing large macro-bubbles were observed, which were estimated to transiently affect up to 2.2% of arterioles.

Conclusions: Detailed analysis of Doppler ultrasound data can be used to provide an estimate of bubble diameter, total volume of air, and the likely impact of embolic showers on cerebral blood flow. Although bubbles are alarmingly numerous during surgery, our simulations suggest that the majority of bubbles are too small to be harmful.

No MeSH data available.


Related in: MedlinePlus