Smith Brendan, Vu Eric, Kibler Kathleen, Rusin Craig, Easley Ronald B, Andropoulos Dean, Heinle Jeffrey, Czosnyka Marek, Licht Daniel, Lynch Jennifer, Brady Ken
Pediatric Cardiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
Anesthesiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX, USA.
Paediatr Anaesth. 2017 Sep;27(9):905-910. doi: 10.1111/pan.13194. Epub 2017 Jun 27.
Autoregulation monitoring has been proposed as a means to identify optimal arterial blood pressure goals during cardiopulmonary bypass, but it has been observed that cerebral blood flow is pressure passive during hypothermic bypass. When neonates cooled during cardiopulmonary bypass are managed with vasodilators and controlled hypotension, it is not clear whether hypothermia or hypotension were the cause of impaired autoregulation.
We sought to measure the effect of both arterial blood pressure and hypothermia on autoregulation in a cohort of infants cooled for bypass, hypothesizing a collinear relationship between hypothermia, hypotension, and dysautoregulation.
Cardiopulmonary bypass was performed on 72 infants at Texas Children's Hospital during 2015 and 2016 with automated physiologic data capture, including arterial blood pressure, nasopharyngeal temperature, cerebral oximetry, and a cerebral blood volume index derived from near infrared spectroscopy. Cooling to 18°C, 24°C, and 30°C was performed on 33, 12, and 22 subjects, respectively. The hemoglobin volume index was calculated as a moving correlation coefficient between mean arterial blood pressure and the cerebral blood volume index. Positive values of the hemoglobin volume index indicate impaired autoregulation. Relationships between variables were assessed utilizing a generalized estimating equation approach.
Hypothermia was associated with hypotension, dysautoregulation, and increased cerebral oximetry. Comparing the baseline temperature of 36°C with 18°C, arterial blood pressure was 44 mm Hg (39-52) vs 25 mm Hg (21-31); the hemoglobin volume index was 0.0 (-0.02 to 0.004) vs 0.5 (0.4-0.7) and cerebral oximetry was 59% (57-61) vs 88% (80-92) (Median, 95% CI of median; P<.0001 for all three associations by linear regression with generalized estimation of equations with data from all temperatures measured).
Arterial blood pressure, temperature, and cerebral autoregulation were collinear in this cohort. The conclusion that hypothermia causes impaired autoregulation is thus confounded. The effect of temperature on autoregulation should be delineated before clinical deployment of autoregulation monitors to prevent erroneous determination of optimal arterial blood pressure. Showing the effect of temperature on autoregulation will require a normotensive hypothermic model.
自动调节监测已被提议作为一种在体外循环期间确定最佳动脉血压目标的方法，但据观察，在低温体外循环期间脑血流量是压力被动的。当在体外循环期间冷却的新生儿使用血管扩张剂和控制性低血压进行管理时，尚不清楚低温或低血压是否是自动调节受损的原因。
我们试图测量动脉血压和低温对一组因体外循环而冷却的婴儿自动调节的影响，假设低温、低血压和自动调节障碍之间存在共线关系。
2015年至2016年期间，德克萨斯儿童医院对72例婴儿进行了体外循环，并自动采集生理数据，包括动脉血压、鼻咽温度、脑血氧饱和度以及通过近红外光谱得出的脑血容量指数。分别对33例、12例和22例受试者进行了冷却至18°C、24°C和30°C的操作。血红蛋白容量指数计算为平均动脉血压与脑血容量指数之间的移动相关系数。血红蛋白容量指数的正值表明自动调节受损。使用广义估计方程方法评估变量之间的关系。
低温与低血压、自动调节障碍和脑血氧饱和度增加有关。将36°C的基线温度与18°C进行比较，动脉血压分别为44 mmHg（39 - 52）和25 mmHg（21 - 31）；血红蛋白容量指数分别为0.0（-0.02至0.004）和0.5（0.4 - 0.7），脑血氧饱和度分别为59%（57 - 61）和88%（80 - 92）（中位数，中位数的95%置信区间；通过对所有测量温度的数据进行带有广义估计方程的线性回归分析，所有三个关联的P <.0001）。
在该队列中，动脉血压、温度和脑自动调节是共线的。因此，低温导致自动调节受损的结论存在混淆。在临床应用自动调节监测仪之前，应明确温度对自动调节的影响，以防止错误地确定最佳动脉血压。要展示温度对自动调节的影响，将需要一个正常血压的低温模型。
