Cerebral oxygen metabolism during total body flow and antegrade cerebral perfusion at deep and moderate hypothermia.

The aim of this study is to evaluate the effect of temperature on cerebral oxygen metabolism at total body flow bypass and antegrade cerebral perfusion (ACP). Neonatal piglets were put on cardiopulmonary bypass (CPB) with the initial flow rate of 200mL/kg/min. After cooling to 18°C (n=6) or 25°C (n=7), flow was reduced to 100mL/kg/min (half-flow, HF) for 15min and ACP was initiated at 40mL/kg/min for 45min. Following rewarming, animals were weaned from bypass and survived for 4h. At baseline, HF, ACP, and 4 h post-CPB, cerebral blood flow (CBF) was measured using fluorescent microspheres. Cerebral oxygen extraction (CEO(2) ) and cerebral metabolic rate of oxygen (CMRO(2) ) were monitored. Regional cranial oxygen saturation (rSO(2) ) was continuously recorded throughout the procedure using near-infrared spectroscopy. At 18°C, CBF trended lower at HF and ACP and matched baseline after CPB. CEO(2) trended lower at HF and ACP, and trended higher after CPB compared with baseline. CMRO(2) at ACP matched that at HF. Cranial rSO(2) was significantly greater at HF and ACP (P<0.001, P<0.001) and matched baseline after CPB. At 25°C, CBF trended lower at HF, rebounded and trended higher at ACP, and matched baseline after CPB. CEO(2) was equal at HF and ACP and trended higher after CPB compared with baseline. CMRO(2) at ACP was greater than that at HF (P=0.001). Cranial rSO(2) was significantly greater at HF (P=0.01), equal at ACP, and lower after CPB (P=0.03). Lactate was significantly higher at all time points (P=0.036, P<0.001, and P<0.001). ACP provided sufficient oxygen to the brain at a total body flow rate of 100mL/kg/min at deep hypothermia. Although ACP provided minimum oxygenation to the brain which met the oxygen requirement, oxygen metabolism was altered during ACP at moderate hypothermia. ACP strategy at moderate hypothermia needs further investigation.

An in vitro study of the effectiveness of carbon dioxide flushing of arterial line filters.

Gaseous microemboli (GMEs) have been connected to neurologic impairment and other ischemic complications after surgery. The components of the extracorporeal circuit (ECC) have a large influence on GME production. This in vitro study investigates the use of carbon dioxide flushing of the 38-microm Medtronic Affinity CB351 and 38-microm Medtronic Affinity 351 arterial line filters (ALFs) to decrease GMEs and time for air to clear the ALE An adult circuit was implemented with a silicone oxygenator for vacuum-assisted gas removal and to reduce air before ALE The 48 filters were separated into four equal groups: flushed coated and non-coated and non-flushed coated and non-coated. Carbon dioxide flushing was performed at 6 L/min for 3 minutes. ALFs were retrograde primed at 200 mL/min. An Emboli Detection and Classification Quantifier (EDAC) was used to gather data. The average total emboli and time to clear (seconds) for flush coated were 20.25 +/- 16.78 and 142.17 +/- 174.80 seconds, respectively, flushed non-coated were 30.5 +/- 34.65 and 124.17 +/- 131.40 seconds, non-flushed coated were 162.08 +/- 79.90 and 390.42 +/- 84.36 seconds, and non-flushed non-coated were 163.67 +/- 212.67 and 305.92 +/- 179.36 seconds. Flushed filters had an average total emboli count of 25.375 +/- 27.14 and an average time to clear of 13.167 +/- 151.51 seconds. Non-flushed filters had an average total emboli count of 162.875 +/- 157.11 and an average time to clear of 348.167 +/- 143.70 seconds. Coated and non-coated filters for total emboli and time to clear had p values of .86 and .24, respectively. Flushed and non-flushed filters had total emboli and time to clear p values of < .001 and < .001, respectively. No significant difference was found between coated and non-coated filters involving total embolic count and time to clear. A significant difference was found in total embolic count and time to clear between flushed and non-flushed filters. This study shows that fewer emboli and faster embolic clearance time correlate with carbon dioxide flushing of the ALE.