Changes of cerebral blood flow and carbon dioxide reactivity of cerebral vessels in children after cardiopulmonary resuscitation / 中华急诊医学杂志

Objective To observe the changes of cerebral blood flow velocities and carbon dioxide (CO_2) reactivity of cerebral vessels in children after cardiopulmonary resuscitation,and the relationship between the changes of cerebral blood flow and outcome.Methods The waveforms,cerebral blood flow velocities of left middle cerebral artery and extracranial internal carotid artery were monitored by Transcranial Doppler (TCD) in 35 post-resuscitation children. Glasgow coma score (GCS) was estimated at the same time.They were divided into three groups according to the diastolic blood flow velocities:low perfusion group,high perfusion group and near-normal perfusion group.CO_2 reactivity of cerebral vessels was induced by hyperventilation in 26 children under ventilation.Results In both low and high perfusion groups,GCS and CO_2 reactivity of cerebral vessels were significantly lower than that of near-normal perfusion group (P＜0.05);the numbers of died and withdrawing treatment patients were significantly higher than that of near-normal perfusion group (P＜0.01).Conclusion TCD monitoring is a useful technique for estimating cerebral perfusion,outcome and CO_2 reactivity of cerebral vessels of children after cardiopulmonary resuscitation.A secondary ischemic event may be caused by a forced hyperventilation therapy in the condition without TCD monitoring in post-resuscitation patients.

Clival Window Videomicroscopy of Basilar Artery Reactivity in Newborn Piglet

This report is the author's in vivo study of basilar artery reactivity to physiologic and pharmacologic stimuli in a newborn animal model. Isoflurane-anesthetized and ventilated piglets(less than 3 days of age) were placed supinely, the pharyngeal muscles retracted, and a 9 mm diameter hole was drilled in the clivus. The dura was incised in a circular fashion and coagulated, and a stainless steel and glass window with inflow and outflow ports was affixed to the clivus with dental cement. Using a color camera mounted on a triocular stereomicroscope, images of the basilar artery were recorded to Super-VHS tape, and stimulus-induced changes in vessel diameter were determined off-line from the videotape record using an image analysis system. Induction of moderate hypercapnia(PaCO2=69+/-3 mmHg) dilated the basilar artery 21+/-4%(p=0.002;n=5);hypocapnia(PaCO2=21+/-0.5 mgHg) constricted the artery 10+/-3%(p=0.05;n=5). A reduction in cerebral perfusion pressure induced by hemorrhagic hypotension to a mean arterial pressure(M ABP) of 34+/-0.5 mmHg was associated with a 9+/-1.6% reduction(p=0.0005;n=11) in basilar artery diameter. Superfusion of the clival window with the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine(L-NMMA)(100 microM) decreased artery diameter 20+/-5.6%(p=0.01;n=6). Superfusion of 10 microM and 100 microM adenosine caused dose-dependent increases in artery diameter of 9.3+/-4%(p=0.02;n=4) and 13+/-5%(p=0.03;n=5), respectively. These results indicate that, while reactivity to CO2 is intact in the newborn basilar artery, autoregulatory adjustment in brainstem blood flow in newborns may be limited due to basilar artery constriction in response to systemic hypotension. Nitric oxide provides a tonic vasodilative influence on basilar artery tone in the neonate.

Transcranial Doppler CO2 Test as an Indicator of Cerebral Vasoreactivity and Prognosis in Patients with Regional CBF Alteration

The assessment of cerebral vasoreactivity provides information on the reserve capacity of cerebral circulation in patients with cerevrovascular disease. It also allows for the diagnosis of impending ischemia and control of the effect of initiated corrective measures. The authors had performed transcranial doppler(TCD) studies to measure the CO2 reactivity of the entire basal cerebral arteries in 30 cases of age-adjusted control group and 42cases of disease group and 42 cases of disease group between the 3rd and 7th day after insult. The disease group involved 14 cases of head injury, 10 cases of intraventricular hemorrhage, 10 cases of subarachnoid hemorrhage and 8 cases of hydrocephalus. All patients were examined by single photon emission computed tomography(SPECT) and results of the 2 groups were compared with respect to their CO2 reactivities. In the patient group, the mean blood flow velocity(MBFV), pusatility index(PI) and MI index(middle cerebral artery MBFV/internal cerebral artery MBFV) had not changed but the CO2 index was significantly lower than that in the same age group of normal control. The regions showing abnormal ROI(region of interest) on SPECT well corresponded with the regions showing decreased CO2 reactivity on TCD. Both the increase of MBFV and the decrease of Pl were noted in the cerebral arteries with decreased CO2 reactivity. This indicates that the very arterial walls were dilated. As for the relationships between the investigated variables, ROI increased as the clinical status worsen(r=-0.05, p=0.0008). The acute prognosis(prognosis after 3month of insult) had positive correlation with CO2 index(r=0.32, p=0.04) of clinical status, while on the other hand, its correlation with ROI index was negative(r=0.40, p=0.0094). Transcranial doppler CO2 test provides useful information for the understanding of hemodynamic status, prognosis and beneficial effects of specific therapy. It is concluded that CO2 index measured during the subacute stage of insult correlates well with the acute prognosis.

Brain Stem Blood Flow During Hypercapnia, Hypocapnia, Hypoxia, and Hemorrhagic Hypotension in Newborn Piglet

Changes of brain stem blood flow(BBF) during physiologic stimulation, such as hypoxia, hypo-and hypercapnia, and hemorrhagic hypotension, were studied by hydrogen clearance technique through closed clival window in the brain stem of nerborn piglet. Induction of moderate hypercapnia(PaCO2=65.4+/-2.11mmHg) caused prominent increases in BBF(354+/-39%;p<0.0001). Conversely, in response to moderate hypocapnia(PaCO2=23.9+/-0.64mmHg), a significant decreases in BBF(-30.38+/-3.22%;p<0.0001) was observed. During severe hypoxia(PaO2=3.7+/-1.4mmHg)moderate increases in BBF(161+/-51.4%;p=0.005) occurred. Interestingly, in response to systemic hypotension(Mean Arterial Blood Pressure=34+/-0.7mmHg), a nonsignificant reduction of BBF was recorded(-14+/-10%;p=0.240). These findings suggest that CO2 reactivity of newborn piglet posterior circulation is high;however, hypoxic reactivity is relatively moderate, and BBF is autoregulated during systemic hypotension.