From the Department of Cardiothoracic Anesthesiology, Heart Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
Section of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
Anesth Analg. 2019 Jun;128(6):1081-1088. doi: 10.1213/ANE.0000000000003418.
Near-infrared spectroscopy (NIRS) is used worldwide to monitor regional cerebral oxygenation (rScO2) during cardiopulmonary bypass (CPB). Intervention protocols meant to mitigate cerebral desaturation advocate to increase mean arterial pressure (MAP) when cerebral desaturation occurs. However, the isolated effect of MAP on rScO2 is uncertain. The aim of the present study was in a randomized, blinded design to elucidate the effect of 2 distinct levels of MAP on rScO2 values during CPB.We hypothesized that a higher MAP would be reflected in higher rScO2 values, lower frequency of patients with desaturation, and a less pronounced cerebral desaturation load.
This is a substudy of the Perfusion Pressure Cerebral Infarct trial, in which we investigated the impact of MAP levels during CPB on ischemic brain injury after cardiac surgery. Deviation in rScO2 was a predefined outcome in the Perfusion Pressure Cerebral Infarct trial. Patients were randomized to low MAP (LMAP; 40-50 mm Hg) or high MAP (HMAP; 70-80 mm Hg) during CPB. CPB pump flow was fixed at 2.4 L/min/m, and MAP levels were targeted using norepinephrine. Intraoperatively, NIRS monitoring was performed in a blinded fashion, with sensors placed on the left and right side of the patient's forehead. NIRS recordings were extracted for offline analysis as the mean value of left and right signal during prespecified periods. Mean rScO2 during CPB was defined as the primary outcome in the present study.
The average MAP level during CPB was 67 mm Hg ± SD 5.0 in the HMAP group (n = 88) and 45 mm Hg ± SD 4.4 in the LMAP group (n = 88). Mean rScO2 was significantly lower in the HMAP group during CPB (mean difference, 3.5; 95% confidence interval, 0.9-6.1; P = .010). There was no difference in rScO2 values at specified time points during the intraoperative period between the 2 groups. Significantly more patients experienced desaturation below 10% and 20% relative to rScO2 baseline in the HMAP group (P = .013 and P = .009, respectively), and the cerebral desaturation load below 10% relative to rScO2 baseline was more pronounced in the HMAP group (P = .042).
In a randomized blinded study, we observed that a higher MAP induced by vasopressors, with a fixed CPB pump flow, leads to lower mean rScO2 and more frequent and pronounced cerebral desaturation during CPB. The mechanism behind these observations is not clear. We cannot exclude extracranial contamination of the NIRS signal as a possible explanation. However, we cannot recommend increasing MAP by vasoconstrictors during cerebral desaturation because this is not supported by the findings of the present study.
近红外光谱（NIRS）被广泛用于监测体外循环（CPB）期间的局部脑氧合（rScO2）。旨在减轻脑缺氧的干预方案主张在发生脑缺氧时增加平均动脉压（MAP）。然而，MAP 对 rScO2 的单独影响尚不确定。本研究的目的是在一项随机、盲法设计中阐明 CPB 期间 2 种不同水平的 MAP 对 rScO2 值的影响。我们假设较高的 MAP 将反映在较高的 rScO2 值、较低的缺氧患者频率和较低的脑缺氧负荷上。
这是 Perfusion Pressure Cerebral Infarct 试验的一项子研究，我们在该试验中研究了 CPB 期间 MAP 水平对心脏手术后缺血性脑损伤的影响。rScO2 偏差是 Perfusion Pressure Cerebral Infarct 试验中的一个预先确定的结果。患者在 CPB 期间被随机分配到低 MAP（LMAP；40-50mmHg）或高 MAP（HMAP；70-80mmHg）。CPB 泵流量固定在 2.4L/min/m，使用去甲肾上腺素靶向 MAP 水平。术中以盲法进行 NIRS 监测，传感器放置在患者额头的左侧和右侧。NIRS 记录在离线分析中作为预设时间段内左侧和右侧信号的平均值提取。CPB 期间的平均 rScO2 定义为本研究的主要结局。
CPB 期间 HMAP 组的平均 MAP 水平为 67mmHg±SD5.0（n=88），LMAP 组为 45mmHg±SD4.4（n=88）。CPB 期间 HMAP 组的平均 rScO2 明显较低（平均差异，3.5；95%置信区间，0.9-6.1；P=0.010）。在两组之间的手术期间的特定时间点，rScO2 值没有差异。HMAP 组中更多的患者经历了 rScO2 基线以下 10%和 20%的缺氧（P=0.013 和 P=0.009，分别），HMAP 组中 rScO2 基线以下 10%的脑缺氧负荷更明显（P=0.042）。
在一项随机、盲法研究中，我们观察到，使用血管加压药诱导的较高 MAP（CPB 泵流量固定）会导致 CPB 期间 rScO2 平均值降低，并且更频繁和更明显的脑缺氧。这些观察结果的背后机制尚不清楚。我们不能排除 NIRS 信号的颅外污染作为一种可能的解释。然而，我们不能建议在发生脑缺氧时使用血管收缩剂来增加 MAP，因为这与本研究的结果不符。
