Prisman Eitan, Slessarev Marat, Azami Takafumi, Nayot Dan, Milosevic Michael, Fisher Joseph
Department of Anesthesiology, University Health Network and the University of Toronto, Canada.
Int J Radiat Biol. 2007 Jul;83(7):457-62. doi: 10.1080/09553000701370894.
Carbogen has long been under investigation as an adjuvant to radiotherapy of tumors. A major factor confounding its evaluation is its inconsistency in raising blood partial pressure of CO(2) (pCO(2)). We investigated whether a new partial rebreathing method would provide better control of pCO(2) than carbogen.
We compared the efficacy of each method in 10 healthy volunteers. Volunteers breathed 1.5, 3 and 5% carbogen in 5-min stages via the usual non-rebreathing circuit. All the volunteers then breathed 100% O(2) through a commercial sequential gas delivery (SGD) circuit modified by attaching a reservoir to its exhalation port. Hypercarbia was induced by step reductions in oxygen flow to the SGD circuit. We monitored minute ventilation and end-tidal pCO(2) (ETpCO(2)) as a surrogate for its arterial value.
Inhalation of 1.5 and 3% carbogen did not increase ETpCO(2) from baseline (40 +/- 1.5 mmHg); 5% carbogen increased ETpCO(2) to 45 +/- 1.6 mmHg (p < 0.001). With the SGD circuit, reducing O(2) flow to 4.3 +/- 0.7 l/min increased ETpCO(2) in all subjects from 41 +/- 2.0 mmHg (baseline) to 46 +/- 2.1 mmHg (p < 0.001). Voluntary hyperventilation reduced ETpCO(2) with 5% carbogen but not with SGD (p = 0.379).
We confirm previous observations that carbogen inhalation does not result in a predictable rise in ETpCO(2) and suggest that a precise and stable target ETpCO(2) can instead be induced by simply controlling O(2) flow into a modified SGD circuit. We hoped that the reliable control of pCO(2) will enable studies that address first, the efficacy of raising ETpCO(2) on specific tumor blood flow, and eventually, its benefit as an adjuvant to radiotherapy.
长期以来，二氧化碳混合气一直作为肿瘤放射治疗的辅助剂进行研究。影响其评估的一个主要因素是其在提高血液二氧化碳分压（pCO₂）方面的不一致性。我们研究了一种新的部分重复呼吸方法是否比二氧化碳混合气能更好地控制pCO₂。
我们比较了这两种方法在10名健康志愿者中的效果。志愿者通过常规的无重复呼吸回路，分5分钟阶段吸入1.5%、3%和5%的二氧化碳混合气。然后，所有志愿者通过在呼气端口连接一个储气袋进行改装的商用顺序气体输送（SGD）回路呼吸100%氧气。通过逐步减少向SGD回路输送的氧气流量来诱发高碳酸血症。我们监测分钟通气量和呼气末pCO₂（ETpCO₂）作为动脉值的替代指标。
吸入1.5%和3%的二氧化碳混合气未使ETpCO₂ 高于基线水平（40±1.5 mmHg）；5%的二氧化碳混合气使ETpCO₂ 升高至45±1.6 mmHg（p<0.001）。使用SGD回路时，将氧气流量减少至4.3±0.7 l/min，所有受试者的ETpCO₂ 从41±2.0 mmHg（基线）升高至46±2.1 mmHg（p<0.001）。自主过度通气可降低5%二氧化碳混合气组的ETpCO₂，但对SGD组无此作用（p = 0.379）。
我们证实了之前的观察结果，即吸入二氧化碳混合气不会导致ETpCO₂ 出现可预测的升高，并表明通过简单地控制进入改装后的SGD回路的氧气流量，可以诱导出精确且稳定的目标ETpCO₂。我们希望对pCO₂ 的可靠控制将有助于开展相关研究，首先是提高ETpCO₂ 对特定肿瘤血流的疗效，最终是其作为放射治疗辅助剂的益处。
