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Is cerebral blood flow/metabolic mismatch during rewarming a risk factor after profound hypothermic procedures in
J van der Linden1, R Ekroth, C Lincoln
1Brompton Hospital, London, UK.
Insights
During deep hypothermia in children undergoing cardiac surgery, cerebral blood flow and oxygen consumption significantly decrease. Rewarming speed correlated with lower venous oxygen saturation, suggesting potential causes for postoperative cerebral dysfunction.
Area of Science:
- Cardiovascular Surgery
- Pediatric Anesthesiology
- Cerebral Physiology
Background:
- Profound hypothermia is used in pediatric cardiac surgery to reduce metabolic demand.
- Understanding the relationship between cerebral blood flow (CBF) and cerebral oxygen consumption (CMRO2) is crucial during hypothermic procedures.
- The alpha-stat method is commonly employed for pH management during hypothermia.
Purpose of the Study:
- To investigate the relationship between cerebral blood flow and oxygen consumption in children during cardiac operations with profound hypothermia.
- To assess the impact of deep hypothermia and rewarming on cerebral oxygenation.
- To identify potential causes of postoperative cerebral dysfunction.
Main Methods:
- Six children undergoing cardiac operations with profound hypothermia (nasopharyngeal temperature reduced to 15°C) were studied.
- A combination of topical and core cooling techniques was utilized.
- Cerebral blood flow, oxygen consumption, and jugular bulb venous saturation were monitored.
Main Results:
- Cerebral blood flow and oxygen consumption decreased significantly with decreasing temperature.
- At 15°C, CBF was reduced to 25% of awake levels, and CMRO2 to 25% of asleep levels.
- Jugular bulb venous saturation decreased significantly during topical cooling and rewarming, indicating a mismatch between CBF and CMRO2, with rewarming speed correlating with decreased saturation.
Conclusions:
- Periods of cerebral blood flow and metabolic mismatch during cooling and rewarming may contribute to postoperative cerebral dysfunction.
- A moderate rewarming speed is recommended to mitigate risks associated with cerebral oxygenation imbalances.
- Further research into optimizing rewarming strategies is warranted.
Abstract:
The relation between cerebral blood flow and oxygen consumption was studied in six children during cardiac operations with profound hypothermia. A combination of topical cooling and core cooling was used to reduce the nasopharyngeal temperature to 15 degrees C. The alpha-stat principle for pH management was used. Blood flow and oxygen consumption decreased significantly with temperature. At a nasopharyngeal temperature of 15 degrees C, blood flow was reduced to 25% of the awake level, corresponding to 34% of the asleep value obtained 15-30 min after intubation. Oxygen consumption decreased to 25% of the asleep value. During stable profound hypothermia, venous saturation in the jugular bulb was at the same level as 15 min after intubation (70%). Markedly lower values were observed during topical cooling, and particularly during rewarming (down to 21%), indicating a mismatch between cerebral blood flow and oxygen consumption. The speed of rewarming correlated with the fall in venous oxygen saturation (rs = 0.82, P less than 0.05). It is suggested that periods of cerebral blood flow/metabolic mismatch during topical cooling and rewarming may explain postoperative cerebral dysfunction after deep hypothermic procedures. A moderate speed of rewarming is advocated.