靜脈空氣栓塞對狗血流動力學之影響：空氣、二氧化碳及氧氣的比較

Hemodynamic Changes Caused by Venous Gas Embolism in Dogs: Comparisons among Air, Carbon Dioxide and Oxygen

背景：由先前實驗得知，經狗中央靜脈注射微量空氣所導出的校正曲線可用來估算大量空氣栓塞的體積。因此我們推測若在人體經靜脈注射微量二氧化碳亦可導出校正曲線。但進入人體試驗前，需於動物中測試經靜脈注射大量二氧化碳對狗血流動力學之影響，並比較空氣與氧氣栓塞的影響。方法：選21隻狗，分三組（即空氣、二氧化碳及氧氣組），每組各7隻。麻醉插管後，經中央靜脈累績給予氣體（即空氣、二氧化碳及氧氣），每劑量的注射相隔10分鐘。然後測量平均動脈壓、肺動脈壓、中央靜脈壓、潮氣末二氧化碳濃度、心跳及混合靜脈氧飽合度。結果：與二氧化碳相比，中央靜脈注射與等體積氧氣或空氣，在體積超過2.5 mL/kg時，產生明顯平均動脈壓及潮氣二氧化碳濃度減少(P<0.05)。注射氧氣或空氣所引起的肺動脈壓及中央靜脈壓的增加與所注射之氣體量成正比。與基礎值相比，注射二氧化碳不會引起明顯的肺動脈壓及中央靜脈壓的增加(P<0.05)，至於心跳及混合靜脈氧飽和度，注射前後三組均無顯著差異。結論：與空氣及氧氣相比，經狗中央靜脈注射累積體積的二氧化碳所引起的血流動力學變化，影響較少。

Background: The volume of a bulky venous air emboli (VAE) can be estimated based on the calibration curve generated by injections of minute amount of air into the right atrium (RA) of dogs. We speculated that in patients similar VAE calibration curves could be generated using CO2 injections. As part of pre-clinical evaluation of the usefulness of CO2 injection, the present study was designed to determine whether injection of CO2 into the RA would cause less hemodynamic changes in dogs as compared with that of air or O2. Methods: Twenty-one anesthetized mongrel dogs were divided into 3 groups, i.e., groups air, CO2 and O2 (n = 7 each). Animals were injected a bolus of gas (air, CO2 or O2) in increasing volumes (from 0.25 to 4.0 mL/kg) into the RA via a central venous catheter at 10-min intervals. We measured the maximal changes in mean arterial pressure (MAP), pulmonary arterial pressure (PAP), central venous pressure (CVP), end-tidal CO2 (ETCO2), heart rate (HR), and mixed venous O2 saturation (SvO2). Results : After venous injections, dogs receiving O2 or air showed greater decreases in MAP and ETCO2 as compared with those receiving CO2 (volume > 2.5 mL/kg; P < 0.05). The increases in PAP and CVP bore direct relation to O2 and air volume. In the CO2 group, the maximal changes in PAP and CVP were subtle as compared with the baseline (P < 0.05). There were no significant differences in HR and SvO2 among three groups. Conclusions: Injections of CO2 in increasing volumes into the RA of dogs caused less hemodynamic changes in comparison with that of air and O2.