Kaiser Jeffrey R, Gauss C Heath, Williams D Keith
Department of Pediatrics, Division of Neonatology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
Pediatr Res. 2005 Nov;58(5):931-5. doi: 10.1203/01.pdr.0000182180.80645.0c.
Permissive hypercapnia, a strategy allowing high Pa(CO2), is widely used by neonatologists to minimize lung damage in ventilated very low birth weight (VLBW) infants. While hypercapnia increases cerebral blood flow (CBF), its effects on cerebral autoregulation of VLBW infants are unknown. Monitoring of mean CBF velocity (mCBFv), Pa(CO2), and mean arterial blood pressure (MABP) from 43 ventilated VLBW infants during the first week of life was performed during and after 117 tracheal suctioning procedures. Autoregulation status was determined during tracheal suctioning because it perturbs cerebral and systemic hemodynamics. The slope of the relationship between mCBFv and MABP was estimated when Pa(CO2) was fixed at 30, 35, 40, 45, 50, 55, and 60 mm Hg. A slope near or equal to 0 suggests intact autoregulation, i.e. CBF is not influenced by MABP. Increasing values >0 indicate progressively impaired autoregulation. Infants weighed 905 +/- 259 g and were 26.9 +/- 2.3 wk gestation. The autoregulatory slope increased as Pa(CO2)) increased from 30 to 60 mm Hg. While the slopes for Pa(CO2) values of 30 to 40 mm Hg were not statistically different from 0, slopes for Pa(CO2) > or = 45 mm Hg indicated a progressive loss of cerebral autoregulation. The autoregulatory slope increases with increasing Pa(CO2), suggesting the cerebral circulation becomes progressively pressure passive with hypercapnia. These data raise concerns regarding the use of permissive hypercapnia in ventilated VLBW infants during the first week of life, as impaired autoregulation during this period may be associated with increased vulnerability to brain injury.
允许性高碳酸血症是一种允许高动脉血二氧化碳分压（Pa(CO2)）的策略，新生儿科医生广泛应用该策略以使接受机械通气的极低出生体重（VLBW）婴儿的肺损伤最小化。虽然高碳酸血症会增加脑血流量（CBF），但其对VLBW婴儿脑自动调节的影响尚不清楚。在117次气管吸引操作期间及之后，对43例出生后第一周接受机械通气的VLBW婴儿的平均脑血流速度（mCBFv）、Pa(CO2)和平均动脉血压（MABP）进行了监测。由于气管吸引会干扰脑和全身血流动力学，因此在气管吸引期间确定自动调节状态。当Pa(CO2)固定在30、35、40、45、50、55和60 mmHg时，估计mCBFv与MABP之间关系的斜率。接近或等于0的斜率表明自动调节功能完好，即CBF不受MABP影响。大于0的斜率增加表明自动调节功能逐渐受损。婴儿体重为905±259 g，胎龄为26.9±2.3周。随着Pa(CO2)从30 mmHg增加到60 mmHg，自动调节斜率增加。虽然Pa(CO2)值为30至40 mmHg时的斜率与0无统计学差异，但Pa(CO2)≥45 mmHg时的斜率表明脑自动调节功能逐渐丧失。自动调节斜率随Pa(CO2)升高而增加，提示随着高碳酸血症的出现，脑循环逐渐变为压力被动状态。这些数据引发了对出生后第一周接受机械通气的VLBW婴儿使用允许性高碳酸血症的担忧，因为在此期间自动调节功能受损可能与脑损伤易感性增加有关。
