van Heerde Marc, van Genderingen Huib R, Leenhoven Tom, Roubik Karel, Plötz Frans B, Markhorst Dick G
Department of Pediatric Intensive Care, VU University Medical Center, Amsterdam, The Netherlands.
Crit Care. 2006 Feb;10(1):R23. doi: 10.1186/cc3988.
The ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators.
A computer-controlled piston-driven test lung was used to simulate a spontaneously breathing patient. The test lung was connected to a high-frequency oscillatory ventilation (HFOV) ventilator by an endotracheal tube. The inspiratory and expiratory airway flows and pressures at various places were sampled. The spontaneous breath rate and volume, tube size and ventilator settings were simulated as representative of the newborn to adult range. The fresh gas flow rate was set at a low and a high level. The imposed WOB was calculated using the Campbell diagram.
In the simulations for newborns (assumed body weight 3.5 kg) and infants (assumed body weight 10 kg) the imposed WOB (mean +/- standard deviation) was 0.22 +/- 0.07 and 0.87 +/- 0.25 J/l, respectively. Comparison of the imposed WOB in low and high fresh gas flow rate measurements yielded values of 1.63 +/- 0.32 and 0.96 +/- 0.24 J/l (P = 0.01) in small children (assumed body weight 25 kg), of 1.81 +/- 0.30 and 1.10 +/- 0.27 J/l (P < 0.001) in large children (assumed body weight 40 kg), and of 1.95 +/- 0.31 and 1.12 +/- 0.34 J/l (P < 0.01) in adults (assumed body weight 70 kg). High peak inspiratory flow and low fresh gas flow rate significantly increased the imposed WOB. Mean airway pressure in the breathing circuit decreased dramatically during spontaneous breathing, most markedly at the low fresh gas flow rate. This led to ventilator shut-off when the inspiratory flow exceeded the fresh gas flow.
Spontaneous breathing during HFOV resulted in considerable imposed WOB in pediatric and adult simulations, explaining the discomfort seen in those patients breathing spontaneously during HFOV. The level of imposed WOB was lower in the newborn and infant simulations, explaining why these patients tolerate spontaneous breathing during HFOV well. A high fresh gas flow rate reduced the imposed WOB. These findings suggest the need for a demand flow system based on patient need allowing spontaneous breathing during HFOV.
对于自主呼吸的机械通气患者，呼吸机和气管内导管会增加额外的工作量。呼吸总功（WOB）包括弹性功和阻力功。在一项实验台测试中，我们使用3100 A/3100 B SensorMedics高频振荡呼吸机评估了所施加的WOB。
使用计算机控制的活塞驱动测试肺来模拟自主呼吸的患者。测试肺通过气管内导管连接到高频振荡通气（HFOV）呼吸机。对不同部位的吸气和呼气气道流量及压力进行采样。模拟了代表新生儿至成人范围的自主呼吸频率和潮气量、导管尺寸及呼吸机设置。将新鲜气体流速设置为低水平和高水平。使用坎贝尔图计算所施加的WOB。
在新生儿（假设体重3.5 kg）和婴儿（假设体重10 kg）的模拟中，所施加的WOB（均值±标准差）分别为0.22±0.07和0.87±0.25 J/l。在低新鲜气体流速和高新鲜气体流速测量中所施加的WOB比较结果显示，小儿（假设体重25 kg）分别为1.63±0.32和0.96±0.24 J/l（P = 0.01），大龄儿童（假设体重40 kg）分别为1.81±0.30和1.10±0.27 J/l（P < 0.001），成人（假设体重70 kg）分别为1.95±0.31和1.12±0.34 J/l（P < 0.01）。高吸气峰流速和低新鲜气体流速显著增加了所施加的WOB。自主呼吸期间呼吸回路中的平均气道压力显著下降，在低新鲜气体流速时最为明显。这导致当吸气流量超过新鲜气体流速时呼吸机停止工作。
在儿科和成人模拟中，HFOV期间的自主呼吸导致了相当大的额外WOB，这解释了HFOV期间自主呼吸患者出现不适的原因。在新生儿和婴儿模拟中额外WOB水平较低，这解释了为什么这些患者能很好地耐受HFOV期间的自主呼吸。高新鲜气体流速降低了额外WOB。这些发现表明需要一种基于患者需求的按需流量系统，以允许在HFOV期间自主呼吸。
