Cardiopulmonary bypass and the central nervous system: potential for cerebral protection

Measurement of gaseous microemboli in the prime before the initiation of cardiopulmonary bypass

Introduction:

The use of cardiopulmonary bypass is associated with a risk of neurocognitive deficit caused by gaseous microemboli. Flushing the empty bypass circuit with carbon dioxide, which is more soluble than air, may reduce the amount of gaseous microemboli in the priming solution before the initiating of cardiopulmonary bypass.

Method:

We measured the amount of gaseous microemboli in twenty primed bypass circuits. Ten circuits were flushed with carbon dioxide before being primed and ten circuits were non-flushed. All circuits in both groups were primed with crystalloid priming. An ultrasonic clinical bubble counter was used to count gaseous microemboli in the prime for 20 minutes.

Results:

The median numbers of gaseous microemboli counts were highest during the first minute in both groups, with a significantly lower median value in the group flushed with carbon dioxide (397.5) versus the non-flushed group (1900). In the 20th minute, the median values of gaseous microemboli were significantly lower (p<0.023) in the flushed (0.5) versus non-flushed (10.75) groups. The gaseous microembolic count in the flushed group remained lower than in the non-flushed group when tested minute by minute throughout the whole 20-minute period.

Conclusion:

Flushing the bypass circuits with carbon dioxide before priming significantly decreased the number of gaseous microemboli in the priming solution.

The Effects of Isoflurane-Induced Electroencephalographic Burst Suppression on Cerebral Blood Flow Velocity and Cerebral Oxygen Extraction During Cardiopulmonary Bypass

We investigated the effects of isoflurane-induced burst suppression, monitored with electroencephalography (EEG), on cerebral blood flow velocity (CBFV), cerebral oxygen extraction (COE), and autoregulation in 16 patients undergoing cardiac surgery. The experimental procedure was performed during nonpulsatile cardiopulmonary bypass (CPB) with mild hypothermia (32 degrees C) in fentanyl-anesthestized patients. Middle cerebral artery transcranial Doppler flow velocity, right jugular vein bulb oxygen saturation, and jugular venous pressure (JVP) were continuously measured. Autoregulation was tested during changes in mean arterial blood pressure (MAP) within a range of 40-80 mm Hg, induced by sodium nitroprusside and phenylephrine before (control) and during additional isoflurane administration to an EEG burst-suppression level of 6-9/min. Isoflurane induced a 27% decrease in CBFV (P < 0.05) and a 13% decrease in COE (P < 0.05) compared with control. The slope of the positive relationship between CBFV and cerebral perfusion pressure (CPP = MAP - JVP) was steeper with isoflurane (P < 0.05) compared with control, as was the slope of the negative relationship between CPP and COE (P < 0.05). We conclude that burst-suppression doses of isoflurane decrease CBFV and impair autoregulation of cerebral blood flow during mildly hypothermic CPB. Furthermore, during isoflurane administration, blood flow was in excess relative to oxygen demand, indicating a loss of metabolic autoregulation of flow.

IMPLICATIONS

The effects of isoflurane on cerebral blood flow velocity (CBFV) and oxygen extraction (COE) as a function of perfusion pressure were studied. When added to fentanyl anesthesia, isoflurane induced a 27% and 13% decrease in CBFV and COE, respectively. CBFV became more pressure-dependent with isoflurane indicating an impaired autoregulation.

Anaesthetic considerations for patients undergoing hypothermic cardiopulmonary bypass for complex neurovascular lesions: case presentation and review

The anaesthetic management of a 38-year-old woman having excision of a meningioma involving the superior sagittal sinus is described. The procedure was performed using low flow moderate hypothermic cardiopulmonary bypass with central cannulation. Relevant literature is reviewed.

Post-ischemic RSR13 amplifies the effect of dizocilpine on outcome from transient focal cerebral ischemia in the rat

In a recent study of focal cerebral ischemia in rats, pre-ischemic administration of the synthetic allosteric hemoglobin modifier RSR13 (2-[4-[[3,5-dimethylanilino) carbonyl] methyl] phenoxy]-2-methylproprionic acid) reduced cerebral infarct size when combined with the NMDA receptor antagonist dizocilpine (MK-801) but not when given alone. We hypothesized that post-ischemic RSR13 administration would enhance neuroprotection afforded by NMDA receptor antagonism in a rat model of transient middle cerebral artery occlusion (MCAO). Fasted normothermic Wistar rats underwent 75 min of temporary MCAO. At onset of reperfusion, rats randomly received: (1) 0.9% NaCl (vehicle) i.v. alone (n=16); (2) 0.9% NaCl+dizocilpine (0.25 mg/kg) i.v. (n=16); or (3) RSR13 (150 mg/kg)+dizocilpine (0.25 mg/kg) i.v. (n=17). Seven days later, neurologic deficit and cerebral infarct size were determined. Dizocilpine alone compared to vehicle reduced mean+/-S.D. subcortical (52+/-24 mm(3) vs. 122+/-64 mm(3), P=0.003) and cortical (35+/-35 mm(3) vs. 125+/-72 mm(3), P=0.00074) infarct volumes. When compared to dizocilpine alone, the combination of RSR13+dizocilpine further reduced subcortical (37+/-14 mm(3) vs. 52+/-24 mm(3), P=0. 034) and cortical (8+/-19 mm(3) vs. 35+/-35 mm(3), P=0.018) infarct size. RSR13+dizocilpine improved neurologic scores vs. either dizocilpine alone (P=0.0014) or vehicle (P=10(-7)). The combination of NMDA receptor antagonism and a RSR13 mediated rightward shift of the oxy-hemoglobin dissociation curve improved outcome from MCAO. Because this occurred after reperfusion, our results suggest that the post-ischemic brain continues to suffer from hypoperfusion defects, which are amenable to therapy by enhanced O(2) delivery. The results also support the concept that neuroprotective strategies, which combine drugs with different mechanisms of action, may yield cumulative benefits.

The effects of propofol on cerebral blood flow velocity and cerebral oxygen extraction during cardiopulmonary bypass

We investigated the effects of burst-suppression doses of propofol on cerebral blood flow velocity (CBFV), cerebral oxygen extraction (COE), and dynamic autoregulation in 20 patients undergoing cardiac surgery. The experimental procedure was performed during nonpulsatile cardiopulmonary bypass (CPB) with stable hypothermia (32 degrees C) in fentanyl-anesthetized patients. Middle cerebral artery transcranial Doppler flow velocity, right jugular bulb oxygen saturation, and jugular venous pressure (JVP) were continuously measured. Dynamic autoregulation was tested by stepwise changes in mean arterial pressure (MAP) within a range of 40-80 mm Hg by sodium nitroprusside and phenylephrine before (control) and during propofol infusion, with a stable plasma concentration (approximately 9 microg/mL). Propofol induced a 35% decrease in CBFV (P < 0.0001) and a 10% decrease in COE (P < 0.05) compared with control. The slopes of the curves relating CBFV and COE to cerebral perfusion pressure (CPP = MAP - JVP) were less pronounced with propofol (P < 0.01 and P < 0.05, respectively). We conclude that propofol decreases CBFV and improves dynamic autoregulation during moderate hypothermic CPB. Furthermore, during propofol infusion, cerebral blood flow was in excess relative to oxygen demand, as indicated by the decrease in COE.

IMPLICATIONS

In this study, we evaluated the effects of propofol on continuously measured cerebral blood flow velocity (CBFV) and cerebral oxygen extraction as a function of perfusion pressure. Propofol induced 35% and 10% decreases in CBFV and cerebral oxygen extraction, respectively. The slope of the curve relating cerebral perfusion pressure to CBFV decreased with propofol.

Early extubation and neurologic examination following combined carotid endarterectomy and coronary artery bypass grafting using remifentanil

Carotid endarterectomy (CEA) and coronary artery bypass grafting (CABG) as a combined procedure is occurring with increasing frequency. CEA-CABG incurs the morbidity of both procedures, and considerations for this procedure include anesthetic techniques that provide hemodynamic stability and prompt emergence from anesthesia. We present, to our knowledge, the first reported use in a combined CEA-CABG of the novel opioid remifentanil as a component of the anesthetic technique to achieve these goals. Remifentanil allows for early neurologic evaluation without sacrificing the hemodynamic stability of traditional, high-dose opioid techniques.