Brochard L, Harf A, Lorino H, Lemaire F
Département de Physiologie, Hôpital Henri Mondor, Créteil, France.
Am Rev Respir Dis. 1989 Feb;139(2):513-21. doi: 10.1164/ajrccm/139.2.513.
Persistent inability to tolerate discontinuation from mechanical ventilation is frequently encountered in patients recovering from acute respiratory failure. We studied the ability of inspiratory pressure support, a new mode of ventilatory assistance, to promote a nonfatiguing respiratory muscle activity in eight patients unsuccessful at weaning from mechanical ventilation. During spontaneous breathing, seven of the eight patients demonstrated electromyographic signs of incipient diaphragmatic fatigue. During ventilation with pressure support at increasing levels, the work of breathing gradually decreased (p less than 0.02) as well as the oxygen consumption of the respiratory muscles (p less than 0.01), and electrical signs suggestive of diaphragmatic fatigue were no longer present. In addition, intrinsic positive end-expiratory pressure was progressively reduced. For each patient an optimal level of pressure support was found (as much as 20 cm H2O), identified as the lowest level maintaining diaphragmatic activity without fatigue. Above this level, diaphragmatic activity was further reduced and untoward effects such as hyperinflation and apnea occurred. When electrical diaphragmatic fatigue occurred, the activity of the sternocleidomastoid muscle was markedly increased, whereas it was minimal when the optimal level was reached. We conclude that in patients demonstrating difficulties in weaning from the ventilator: (1) pressure support ventilation can assist spontaneous breathing and avoid diaphragmatic fatigue (pressure support allows adjustment of the work of each breath to provide an optimal muscle load); (2) clinical monitoring of sternocleidomastoid muscle activity allows the required level of pressure support to be determined to prevent fatigue.
急性呼吸衰竭康复期患者常常出现持续无法耐受机械通气撤离的情况。我们研究了一种新的通气辅助模式——吸气压力支持，对8例机械通气撤机失败患者促进呼吸肌非疲劳性活动的能力。在自主呼吸期间，8例患者中有7例表现出膈肌早期疲劳的肌电图征象。在逐渐增加水平的压力支持通气期间，呼吸功逐渐降低（p<0.02），呼吸肌耗氧量也逐渐降低（p<0.01），提示膈肌疲劳的电征象不再出现。此外，内源性呼气末正压逐渐降低。对于每例患者，都找到了一个最佳压力支持水平（高达20cmH₂O），该水平被确定为维持膈肌活动且无疲劳的最低水平。高于此水平，膈肌活动进一步降低，并出现诸如过度充气和呼吸暂停等不良影响。当出现膈肌电疲劳时，胸锁乳突肌的活动明显增加，而达到最佳水平时其活动最小。我们得出结论，对于撤机困难的患者：（1）压力支持通气可辅助自主呼吸并避免膈肌疲劳（压力支持可调整每次呼吸的功以提供最佳肌肉负荷）；（2）对胸锁乳突肌活动进行临床监测可确定所需的压力支持水平以预防疲劳。
