DeHaven C B, Kirton O C, Morgan J P, Hart A M, Shatz D V, Civetta J M
Division of Surgical Critical Care, Department of Surgery, University of Miami School of Medicine, Ryder Trauma Center, FL, USA.
Crit Care Med. 1996 Jun;24(6):976-80. doi: 10.1097/00003246-199606000-00017.
There is increased awareness of imposed work of breathing contributing to apparent ventilatory dependency. This study evaluates the impact of tachypnea as an indicator of ventilatory failure during a room air-5 cm H2O continuous positive airway pressure, spontaneous breathing, preextubation trial when associated with increased imposed work of breathing.
Prospective, descriptive, 1-yr data collection.
University hospital trauma intensive care unit (ICU).
Mechanically ventilated trauma ICU patients surviving to discharge.
Patients were weaned to minimal mechanical ventilator support and underwent a 20-min room air-continuous positive airway pressure preextubation trial (FIO2 = 0.21, continuous positive airway pressure = 5 cm H2O [0.5 kPa]). When passed (PaO2 >/= 55 torr [>/= 7.3 kPa], PaCO2 </= 45 torr [</= 6.0 kPa] with prior eucapnea, arterial pH >/= 7.35, respiratory rate </= 30 breaths/min), extubation followed. If patients failed due to hypoxia, ventilatory support resumed. If tachypnea was the reason for failure, work of breathing was measured. If patient work of breathing was </= 1.1 joule/L, extubation proceeded despite tachypnea. If patient work of breathing was > 1.1 joule/L, imposed work of breathing was measured, and if residual "physiologic" work of breathing (patient work of breathing minus imposed work of breathing) was </= 0.8 joule/L, patients were extubated.
Of 589 extubations, 105 (18%) were classified as false negatives based on a preextubation rate of > 30 breaths/min. Of these, 97 were successfully extubated despite tachypnea ranging from 32 to 56 breaths/min, when combined with either a patient work of breathing </= 1.1 joule/L or physiologic work of breathing </= 0.8 joule/L. The rate of extubation failure within 72 hours was 7.8% (8/105) in the tachypneaic group, compared with 7.9% (38/484) for those patients with a respiratory rate of </= 30 breaths/min. Some of the stimulus for the tachypnea was possibly due to increased imposed work of breathing, as the increased respiratory rate usually abated within 18 hrs after extubation. The reliance on a respiratory rate of </= 30 breaths/min as an absolute preextubation criterion would have resulted in a sensitivity of 82%, a specificity of 17%, a positive predictive value of 92%, a negative predictive value of 8%, and an overall accuracy of 77%. The average duration of mechanical ventilation during the study period decreased by 2 days, from 8.6 to 6.3 days (p=.03).
Tachypnea as a marker of respiratory distress is sensitive, but is not sufficiently specific to be used as a criterion in preextubation trials. Reliance on tachypnea as a preextubation trial failure criterion is likely to prolong intubation and ventilatory support for a large number of patients. Patient risks, determined by the extubation failures and reintubation rate, are the same.
人们越来越意识到呼吸做功增加会导致明显的通气依赖。本研究评估了在室内空气 - 5 cm H₂O 持续气道正压、自主呼吸、拔管前试验期间，呼吸急促作为通气衰竭指标与呼吸做功增加相关时的影响。
前瞻性、描述性、为期1年的数据收集。
大学医院创伤重症监护病房（ICU）。
存活至出院的机械通气创伤ICU患者。
患者撤机至最低机械通气支持水平，并进行20分钟的室内空气 - 持续气道正压拔管前试验（吸入氧分数 = 0.21，持续气道正压 = 5 cm H₂O [0.5 kPa]）。试验通过（动脉血氧分压≥55 托 [≥7.3 kPa]，动脉血二氧化碳分压≤45 托 [≤6.0 kPa] 且之前呼吸正常，动脉血pH值≥7.35，呼吸频率≤30次/分钟）后进行拔管。如果患者因缺氧失败，则恢复通气支持。如果呼吸急促是失败原因，则测量呼吸做功。如果患者呼吸做功≤1.1焦耳/升，尽管呼吸急促仍进行拔管。如果患者呼吸做功>1.1焦耳/升，则测量呼吸附加功，如果残余“生理”呼吸功（患者呼吸功减去呼吸附加功）≤0.8焦耳/升，则对患者进行拔管。
在589次拔管中，105次（18%）因拔管前呼吸频率>30次/分钟被归类为假阴性。其中，97例尽管呼吸急促（呼吸频率为32至56次/分钟），但结合患者呼吸功≤1.1焦耳/升或生理呼吸功≤0.8焦耳/升，成功进行了拔管。呼吸急促组72小时内的拔管失败率为7.8%（8/105），而呼吸频率≤30次/分钟的患者为7.9%（38/484）。呼吸急促的部分原因可能是呼吸附加功增加，因为呼吸频率增加通常在拔管后18小时内缓解。将呼吸频率≤30次/分钟作为绝对的拔管前标准，其敏感性为82%，特异性为17%，阳性预测值为92%，阴性预测值为8%，总体准确率为77%。研究期间机械通气的平均持续时间从8.6天减少到6.3天，减少了2天（p = 0.03）。
呼吸急促作为呼吸窘迫的标志物是敏感的，但特异性不足以作为拔管前试验的标准。将呼吸急促作为拔管前试验失败标准可能会延长大量患者的插管和通气支持时间。由拔管失败和再插管率决定的患者风险是相同的。
