Joyce C J, Hickling K G
Department of Intensive Care, Christchurch Public Hospital, New Zealand.
Br J Anaesth. 1996 Nov;77(5):678-83. doi: 10.1093/bja/77.5.678.
Low volume ventilation with permissive hypercapnia is becoming widely used in the treatment of acute respiratory distress syndrome. A mathematical model was developed to examine the effects of hypoventilation on pulmonary gas exchange in lungs with a range of shunt fractions. Hypoventilation did not worsen gas exchange, provided the inspired oxygen concentration was high enough to maintain PAO2 at an adequate level. In lungs with a high shunt fraction, some improvement in gas exchange may result, but these effects are small. A rightwards shift of the oxygen-haemoglobin dissociation curve induced by hypercapnia, is likely to be beneficial rather than detrimental in patients with acute respiratory distress syndrome. This analysis was limited to the direct effects of hypoventilation in lungs with constant shunt fractions, and did not encompass a number of possible secondary effects such as changes in cardiac output with PaCO2, changes in shunt fraction associated with a reduction in mean airway pressure and possible direct effects of hypercapnia on the pulmonary vasculature or airways.
小潮气量通气联合允许性高碳酸血症在急性呼吸窘迫综合征的治疗中应用日益广泛。我们建立了一个数学模型，以研究不同分流分数的肺脏中通气不足对肺气体交换的影响。只要吸入氧浓度足够高，能将动脉血氧分压维持在适当水平，通气不足就不会使气体交换恶化。在分流分数较高的肺脏中，气体交换可能会有一些改善，但这些影响很小。高碳酸血症引起的氧合血红蛋白解离曲线右移，对急性呼吸窘迫综合征患者可能有益而非有害。该分析仅限于具有恒定分流分数的肺脏中通气不足的直接影响，并未涵盖一些可能的继发效应，如心输出量随二氧化碳分压的变化、与平均气道压降低相关的分流分数变化，以及高碳酸血症对肺血管或气道的可能直接影响。
