外源性呼气末正压对气道压力的影响

目的探讨外源性呼气末正压（PEEP）对气过压力影响的规律。方法通过模拟肺（静态顺应性为28ml／cmH2O,气道阻力为0．8cmH2O·L－1·S-1）试验,设置不同的PEEP,观察气道压力（修压、平均压、平台压）的变化。结果外源性PEEP从0增加至3cmH2O时,气过压力增幅最大,平均每增加1cmH2OPEEP,气道峰压、平台压增加3．5～4．1cmH2O,当PEEP增加至12cmH2O时,气道峰压和平台压增加了20cmH2O以上。结论外源性PEEP对气造压力的影响,可产生一种“扩大”效应,这种“扩大”效应在低水平的PEEP时尤为显著。在使用人工机械通气时,如需设置外源性PEEP时,必须严密监测气道压力的变化,以防止肺损伤。     

肺保护性机械通气和传统机械通气治疗新生儿急性呼吸衰竭临床观察

目的观察传统机械通气和肺保护性机械通气治疗新生儿急性呼吸衰竭的临床情况。方法选择40例急性呼吸衰竭新生儿患儿，随机分为两组，A组用传统机械通气，B组用肺保护性机械通气。A组潮气量（VT）10～12ml／kg，气道峰压（PIP）〈25cmH2O，呼气末正气（PEEP）（5．0±1．5）cmH2O，呼吸频率（RR）60次／min；B组VT为5～8ml／kg，PEEP为（7．6±1．5）cmH2O，RR为40～60次／分。结果转归比较：两组所有病人均治愈。呼吸机参数比较：两组在维持SaO2在90％以上且PaCO2〈8．0kPa的呼吸机各项参数，A组的VT（10．11±1．20）ml／kg、PIP（24．01±2．10）cmH2O、PEEP（7．50±1．50）cmH2O，两组VT、PIP差异有非常显著性（P〈0．01），两组PEEP的差异无显著性（P〉0．05）。血气比较：pH值A组7．35±0．10，B组7．25±0．15；PaCO2为A组（6．90±0．72）kPa，B组（93．0±2.8）kPa；两组pH、PaCO2、SaCO2（％）值比较差异均无显著性（P均〉0．05）。两组并发症比较：A组肺损伤4例，循环系统并发症3例，B组无。结论传统策略和肺保护性策略通气均能治愈新生儿急性呼吸衰竭，但后者并发症较少。在维持PH、PaCO2、PaO2、SaO2基本相同的情况下，肺保护性通气的呼吸机参数VT和PIP较传统通气明显降低。     

Comparison of methods of bag and mask ventilation for neonatal resuscitation.

BACKGROUND: There are a variety of manual bagging devices used for neonatal resuscitation. To our knowledge, there has been no comparison of the ability of different operators to utilize such devices for the delivery of predetermined inspiratory and end-expiratory pressures. In addition, the use of prolonged inflation may be of benefit for infants who require bag and mask ventilation, and there has been no evaluation of the ability of a variety of operators to reliably deliver such breaths using currently available equipment. METHODS: We utilized a neonatal manikin (Laerdal Armonk, NY) with a functional larynx and lungs, and a clear cushioned mask (Owens-BriGam, Morganton, NC). We studied a latex-free disposable anesthesia type bag (Model 5126 Vital Signs, Totawa, NJ), a Jackson-Rees (JR) type anesthesia bag (Model E191 Anesthesia Associates, San Marcos, CA) fitted with a Norman elbow and a flow-control tail-piece (Dupaco, Oceanside, CA), and the Neopuff (Fisher and Paykel, Auckland, New Zealand), an FDA approved mechanical device that is flow-controlled and pressure-limited, specifically designed to facilitate neonatal resuscitation. The ventilating pressures were continuously recorded throughout the process. We evaluated neonatal nurses, neonatal nurse practitioners, neonatal staff and fellows, pediatric residents and neonatal respiratory therapists. RESULTS: The peak inspiratory pressure (PIP) was significantly different between operators using either anesthesia bag, P<0.001. Similar results were found for positive end-expiratory pressure (PEEP) with a significant difference among the operator groups, P<0.001. All the differences in post hoc analysis were between the therapists and the other groups, P<0.05. Therapists produced significantly higher pressures than the other groups for both PIP and PEEP (P<0.001). The PIP was similar for all groups using the Neopuff device. The PIP and PEEP delivered by the Neopuff differed from the other two devices independent of the operators (P<0.05). On post hoc analysis, there was a significant difference between the disposable anesthesia bag and Neopuff for both PIP and PEEP for the therapists, whereas among the non-therapists, there was a difference in PIP with the JR device producing a greater PIP (26.6+/-3.8 cmH(2)O) compared with the Neopuff and disposable anesthesia bag (24.8+/-1.1 cmH(2)O, 24.8+/-4.3 cmH(2)O). The level of PEEP was significantly different among all three devices for the non-therapists (1.3+/-1.6 cmH(2)O, Disposable; 2.9+/-1.2 cmH(2)O, JR; 4.7+/-0.5 cmH(2)O, Neopuff; P<0.05). Only the therapists were able to consistently deliver PEEP with the anesthesia bags, whereas all operators could generate the target PEEP with the Neopuff (P<0.05). We compared the pressure delivered during the first second to the pressure delivered during the fifth second during prolonged 5-s inflations. The absolute differences between the first and fifth second for the Neopuff versus the anesthesia bags were significantly different with a median of 7.1 cmH(2)O for the anesthesia bags compared with 0.2 cmH(2)O for the Neopuff, P<0.001, reflecting the difficulty in obtaining and maintaining the target inflation pressures. CONCLUSIONS: Our experience suggests that the Neopuff, a purpose-built neonatal resuscitator ventilator, facilitates the delivery of the desired airway pressures while maximizing the operators ability to obtain and maintain a patent airway, and facilitates the delivery of prolonged inflations. Further research is required to determine the clinical benefit of end-expiratory pressure and prolonged inflations in neonatal resuscitation.     

Translaryngeal tracheostomy in acute respiratory distress syndrome patients

OBJECTIVE: To prevent gas exchange deterioration during translaryngeal tracheostomy (TLT) in patients with acute respiratory distress syndrome (ARDS) ventilation is maintained through a small diameter endotracheal tube (ETT; 4.0 mm i.d.) advanced beyond the tracheostoma. We report on the feasibility of uninterrupted ventilation delivered through a high-resistance ETT in ARDS patients, and relevant ventilatory adjustments and monitoring. DESIGN AND SETTING: Prospective, observational clinical study in an eight-bed intensive care unit of a university hospital. Patients: Eight consecutive ARDS patients scheduled for tracheostomy. INTERVENTIONS: During TLT volume control ventilation was maintained through the 4.0-mm i.d. ETT. Tidal volume, respiratory rate, and inspiratory to expiratory ratio were kept constant. Fractional inspiratory oxygen was 1. Positive end expiratory pressure (PEEP) set on the ventilator (PEEP(vent)) was reduced to maintain total PEEP (PEEP(tot)) at baseline level according to the measured intrinsic PEEP (auto-PEEP). MEASUREMENTS AND MAIN RESULTS: Data were collected before tracheostomy and while on mechanical ventilation with the 4.0-mm i.d. ETT. Neither PaCO(2) nor PaO(2) changed significantly (54.5+/-10.0 vs. 56.4+/-7.0 and 137+/-69 vs. 140+/-59 mmHg, respectively). Auto-PEEP increased from 0.6+/-1.1 to 9.8+/-6.5 cmH(2)O during ventilation with the 4.0-mm i.d. ETT. By decreasing PEEP(vent) we obtained a stable PEEP(tot) (11.4+/-4.3 vs. 11.8+/-4.3 cmH(2)O), and end-inspiratory occlusion pressure (26.7+/-7.4 vs. 28.0+/-6.6 cmH(2)O). Peak inspiratory pressure rose from 33.8+/-8.1 to 77.8+/-12.7 cmH(2)O. CONCLUSIONS: The high-resistance ETT allows ventilatory assistance during the whole TLT procedure. Assessment of stability in plateau pressure and PEEP(tot) by end-inspiratory and end-expiratory occlusions prevent hyperinflation and possibly barotrauma.     

Post-cardiac arrest temperature manipulation alters early EEG bursting in rats

OBJECTIVES: Hypothermia improves outcomes after cardiac arrest (CA), while hyperthermia worsens injury. EEG recovers through periodic bursting from isoelectricity after CA, the duration of which is associated with outcome in normothermia. We quantified burst frequency to study the effect of temperature on early EEG recovery after CA. METHODS: Twenty-four rats were divided into three groups, based on 6h of hypothermia (T=33 degrees C), normothermia (T=37 degrees C), or hyperthermia (T=39 degrees C) immediately post-resuscitation from 7-min asphyxial CA. Temperature was maintained using surface cooling and re-warming. Neurological recovery was defined by 72-h neurological deficit score (NDS). RESULTS: Burst frequency was higher during the first 90min in rats treated with hypothermia (25.6+/-12.2min(-1)) and hyperthermia (22.6+/-8.3min(-1)) compared to normothermia (16.9+/-8.5min(-1)) (p<0.001). Burst frequency correlated strongly with 72-h NDS in normothermic rats (p<0.05) but not in hypothermic or hyperthermic rats. The 72-h NDS of the hypothermia group (74, 61-74; median, 25-75th percentile) was significantly higher than the normothermia (49, 47-61) and hyperthermia (43, 0-50) groups (p<0.001). CONCLUSIONS: In normothermic rats resuscitated from CA, early EEG burst frequency is strongly associated with neurological recovery. Increased bursting followed by earlier restitution of continuous EEG activity with hypothermia may represent enhanced recovery, while heightened metabolic rate and worsening secondary injury is likely in the hyperthermia group. These factors may confound use of early burst frequency for outcome prediction.     

A comparison of three neonatal resuscitation devices

BACKGROUND: Ventilation during neonatal resuscitation involves the use of self-inflating bags, flow-inflating bags, and T-piece resuscitators. The ability of operators to deliver desired peak inspiratory pressures (PIP), positive end expiratory pressures (PEEP), prolonged inflations and the length of time to transition between different pressures has not been compared for all three of these devices. OBJECTIVE: To compare the ability of neonatal resuscitation personnel to deliver predetermined ventilation interventions using these devices in advance of a clinical trial of neonatal resuscitation. DESIGN/METHODS: We studied 31 operators (neomatologists, neonatal respiratory therapists, neonatal fellows, a pediatrician, pediatric residents, neonatal nurse practitioners, and neonatal nurses) using a T-piece resuscitator (Neopuff), Fisher and Paykel Healthcare, Auckland, New Zealand), a self-inflating bag (Baby Blue II, Vital Signs, Totowa, NJ), and a flow-inflating bag (Model E191 Anesthesia Associates, San Marcos, CA). The self-inflating bag was tested with and without the manufacturer's PEEP valve. Using a continuous pressure recording system and a neonatal manikin, we evaluated the ability to deliver a consistent PIP of 20 or 40 cmH2O and a PEEP of 5 cmH2O during 30 s of ventilation, the ability to maintain a 5 s inflation at a PIP of 20 cmH2O and the time to transition from a PIP of 20 to 40 cmH2O. Each device was evaluated with and without a qualitative CO2 detector (Pedicap) Nellcor Pleasanton, CA). RESULTS: The T-piece resuscitator delivered the desired PIP more precisely and consistently compared with the self-inflating bag at a target of 20 cmH2O (maximum PIP 20.7 cmH2O, S.D.=0.8 versus 24.7 cmH2O, S.D.=2.8; p<0.001). At a target of 40 cmH2O, the maximum pressure delivered with the T-piece resuscitator was significantly less than both the flow-inflating bag and the self-inflating bag (39.7 cmH2O, S.D.=2.1 versus 44 cmH2O, S.D.=3.3 versus 45.3 cmH2O, S.D.=4.7; p<0.001). It took significantly longer to increase the PIP from 20 to 40 cmH2O using the T-piece resuscitator compared to the self-inflating bag or the flow-inflating bag (5.7 s versus 2.2 s versus 1.8 s; p<0.001), and three operators could not make the transition in the allotted 15 s time limit. During the 5 s prolonged inflation, the T-piece resuscitator and the flow-inflating bag maintained a pressure greater than 18 cmH2O for a longer time than the self-inflating bag (4 s versus 3.7 s versus 2.2 s; p<0.001). The self-inflating bag with the PEEP valve in place provided significantly less PEEP than both the T-piece resuscitator and the flow-inflating bag (3.6 cmH2O versus 4.4 cmH2O versus 4.4 cmH2O; p<0.005). The Pedicap did not significantly affect any of the observed results, and there were no consistent operator differences between different disciplines or years of experience. CONCLUSIONS: The T-piece resuscitator delivered the desired pressures more accurately, but required greater time to increase the PIP from 20 to 40 cmH2O. It was difficult to maintain a prolonged inflation and deliver the desired PEEP with the self-inflating bag even with the PEEP valve in place. There is a need for improvement in the design and function of current manual resuscitation devices and for prospective trials to evaluate the optimal method of bag and mask ventilation during resuscitation of the newborn infant.     

"Ideal PEEP" is superior to high dose partial liquid ventilation with low PEEP in experimental acute lung injury

OBJECTIVE: To determine the effects of a high dose partial liquid ventilation (PLV) approximating the amount of the functional residual capacity (FRC) with low levels of positive end-expiratory pressure (PEEP) compared to a lung-protective strategy with volume-controlled mechanical ventilation (vcMV) with a PEEP level above the lower inflection point (LIP) on pulmonary gas exchange, haemodynamics, respiratory mechanics and lung injury in an experimental model of acute lung injury (ALI). DESIGN: Prospective, randomised, controlled study. METHODS: Twenty-four anaesthetised, tracheotomised and mechanically ventilated (FIO(2) 1.0) pigs underwent induction of ALI by repeated saline wash-out of surfactant. Animals were randomly assigned to receive either PLV ( PLV, n=8) with 30 ml/kg of perfluorocarbons (PF 5080, 3 M, Germany) and a PEEP level of 5 cmH(2)O, to receive vcMV with a PEEP level of 1 cmH(2)O above the LIP ( (ideal) PEEP, n=8), or to receive vcMV with a PEEP level of 5 cmH(2)O ( Controls, n=8). MEASUREMENTS AND RESULTS: Measurements of pulmonary gas exchange, respiratory mechanics and haemodynamics were performed hourly for a 6 h period. In the (ideal) PEEP group, intra-pulmonary shunt (Qs/Qt) decreased from 55+/-5% after induction of ALI to 10+/-3% ( p<0.05 versus Controls and versus PLV) and PaO(2) increased from 52+/-4 to 566+/-19 mmHg after 6 h of treatment ( p<0.05 versus Controls and versus PLV). In the PLV group, Qs/Qt decreased from 50+/-5% after induction of ALI to 24+/-3% ( p<0.05 versus Controls) and PaO(2) increased from 59+/-5 to 306+/-35 mmHg after 6 h of treatment ( p<0.05 versus Controls). In the PLV group and in Controls, mean pulmonary artery pressure (MPAP) was significantly increased from 27+/-2 to 38+/-2 mmHg and from 29+/-1 to 40+/-1 mmHg, respectively, 6 h after induction of ALI ( p<0.05 versus (ideal) PEEP), while in the (ideal) PEEP group, MPAP was maintained between 26+/-1 and 31+/-2 mmHg for 6 h after ALI. Cardiac output (CO) decreased significantly in the (ideal) PEEP group compared to Controls ( p<0.05), while CO did not change in the PLV group and in Controls. The compliance of the respiratory system (C(RS)) increased in the (ideal) PEEP group after induction of ALI from 11+/-2 to 22+/-5 ml/mbar ( p<0.05 versus Controls and versus PLV) and in the PLV group from 10+/-2 to 13+/-3 ml/mbar after 6 h of treatment ( p<0.05 versus Controls). On histological examination, the highest total injury scores were found in animals of the PLV group ( p<0.05 versus Controls and versus (ideal) PEEP), while the lowest total lung injury score was found in the dependent lung regions of the (ideal) PEEP group ( p<0.05 versus Controls). CONCLUSION: In this porcine model of ALI, vcMV with a PEEP level of 1 cmH(2)O above the LIP was superior to high dose PLV with a PEEP of 5 cmH(2)O in improving gas exchange and lung mechanics. In terms of lung damage, the treatment in the (ideal) PEEP group resulted in the lowest total lung injury scores.     

Effects of positive end-expiratory pressure in an experimental model of acute myocardial infarct in wistar rats

ABSTRACT: Our purpose in this study was to access the pulmonary effects of mechanical ventilation with positive end-expiratory pressure (PEEP; 10 cmH2O) or without PEEP (zero PEEP-ZEEP) in a rat model of acute myocardial infarction that resulted in hypotension but not in pulmonary congestion. METHODS: Wistar rats were anesthetized (1.5% isoflurane) and myocardial infarct was induced by ligature of the anterior interventricular coronary artery. Rats with myocardial infarct were compared with sham-operated (Sham) and closed thorax groups. RESULTS AND CONCLUSION: There was a significant decrease in MAP in the acute myocardial infarct group (92.5 +/- 4.2 mmHg) when compared with closed chest group (113.0 +/- 4.4 mmHg). There was no significant difference between acute myocardial infarct and Sham groups in PEEP or ZEEP. Mechanical ventilation for 120 min resulted in a significant increase in respiratory system elastance in the groups ventilated with ZEEP (2.59 +/- 0.17 and 2.32 +/- 0.17 cmH2O.mL, Sham and acute myocardial infarct groups, respectively). This effect of mechanical ventilation was not observed in the presence of PEEP in both groups. There was no significant increase in the amount of perivascular pulmonary edema measured in all groups studied. Mean airspace linear intercept and lung tissue distortion index also did not show statistically significant difference between Sham and acute myocardial infarct groups. We conclude that in this experimental model of acute myocardial infarct (12.4 +/- 4.1% area of necrotic tissue and 26.4 +/- 4.0% area of ischemic tissue), there was a protective pulmonary effect of PEEP.     

呼气末正压对急性呼吸窘迫综合征绵羊内脏器官灌注的影响

目的　观察呼气末正压 (PEEP)对急性呼吸窘迫综合征 (ARDS)绵羊内脏器官灌注的影响。方法　内毒素 (LPS)静脉注射复制绵羊ARDS模型 ,维持心脏最佳前负荷 ,依次调整PEEP为 5、 10、15cmH2 O ,观察不同PEEP对血流动力学、呼吸力学、氧代谢及内脏器官灌注的影响。结果　与基础值(PEEP =0cmH2 O)比较 ,PEEP 5、 10、 15cmH2 O组心率、平均动脉压、肺动脉压、中心静脉压、肺动脉嵌顿压及心输出量差异无显著性意义 ,但PEEP 10、 15cmH2 0组动脉氧分压和动脉氧饱和度均同步明显增加 ,氧合指数也从 ( 10 4 6 4± 2 5 2 1)mmHg提高到 ( 136 2 5± 38 5 4 )和 ( 135 37± 37 5 6 )mmHg (P <0 0 5 ) ,PEEP 5、 10、 15cmH2 O组肠黏膜pH值 (pHi)与基础比较 ,差异无显著性意义 (P >0 0 5 )。各组肠黏膜与动脉二氧化碳分压差 (Pg aCO2 )也无明显差异。全身氧输送、血乳酸无明显改变 (P >0 0 5 )。与基础值比较 ,PEEP各组平均气道压、气道平台压及肺动态顺应性显著增加 ,PEEP 15cmH2 O组气道峰压也明显增高(P <0 0 5 )。结论　维持心脏最佳前负荷状态下 ,血流动力学和氧输送可保持稳定 ,PEEP在 15cmH2 O以下对ARDS绵羊内脏灌注无明显影响     

评分法选择PEEP对ARDS病人的临床价值

目的：研究评分法选择PEEP对ARDS病人的临床价值。方法：对1999年～2004年88例ARDS病人随机使用两种方法选择PEEP进行机械通气。其中评分组（实验组）51例，根据评分法四项指标得分数总和，如评分大于等于6分则PEEP用20-25cmHO；3～5分则PEEP用12～20cmH2O；评分小于等于2分则PEEP用5～12cmH2O；传统方法组（对照组）37例，PEEP均使用5～12cmH2O。分别检测两组病例通气开始时、通气后24h时的血气分析，计算两组病例入ICU30d时病死率，观察其并发症发生情况。结果：实验组较对照组痛死率明显下降，具有极显著差异，P〈0．01；且实验组中采用低PEEP小组的病死率亦较对照组低，具有显著差异，P〈0．05。实验组与对照组在通气24h时都能较通气开始时改善病人的血气情况，且实验组较对照组PaO2升高更明显，具有极显著差异，P〈0．001，而pH、PaCO2在两组无显著差异，P〉0．05。两组均未发生气压伤，实验组较对照组并发MOF的发生率低，具有显著差异，P〈0．05；血压明显下降的发生率高，具有显著差异，P〈0．05，但能纠正。结论：采用评分法选择PEEP较传统方法有更高的临床价值，可明显降低削RDS病人痛死率，改善病人的氧合情况，并且并发症较少或可控制。     

Setting positive end-expiratory pressure during jet ventilation to replicate the mean airway pressure of oscillatory ventilation

BACKGROUND: High-frequency ventilation can be delivered with either oscillatory ventilation (HFOV) or jet ventilation (HFJV). Traditional clinician biases may limit the range of function of these important ventilation modes. We hypothesized that (1) the jet ventilator can be an accurate monitor of mean airway pressure (P (aw)) during HFOV, and (2) a mathematical relationship can be used to determine the positive end-expiratory pressure (PEEP) setting required for HFJV to reproduce the P (aw) of HFOV. METHODS: In phase 1 of our experiment, we used a differential pressure pneumotachometer and a jet adapter in-line between an oscillator circuit and a pediatric lung model to measure P (aw), PEEP, and peak inspiratory pressure (PIP). Thirty-six HFOV setting combinations were studied, in random order. We analyzed the correlation between the pneumotachometer and HFJV measurements. In phase 2 we used the jet as the monitoring device during each of the same 36 combinations of HFOV settings, and recorded P (aw), PIP, and DeltaP. Then, for each combination of settings, the jet ventilator was placed in-line with a conventional ventilator and was set at the same rate and PIP as was monitored during HFOV. To determine the appropriate PEEP setting, we calculated the P (aw) contributed by the PIP, respiratory rate, and inspiratory time set for HFJV, and subtracted this from the goal P (aw). This value was the PEEP predicted for HFJV to match the HFOV P (aw). RESULTS: The correlation coefficient between the pneumotachometer and HFJV measurements was r = 0.99 (mean difference 0.62 +/- 0.30 cm H(2)O, p < 0.001). The predicted and actual PEEP required were highly correlated (r = 0.99, p < 0.001). The mean difference in these values is not statistically significantly different from zero (mean difference 0.25 +/- 1.02 cm H(2)O, p > 0.15). CONCLUSIONS: HFJV is an accurate monitor during HFOV. These measurements can be used to calculate the predicted PEEP necessary to match P (aw) on the 2 ventilators. Replicating the P (aw) with adequate PEEP on HFJV may help simplify transitioning between ventilators when clinically indicated.     

Induced hypothermia as a new approach to lung rest for the acutely injured lung

OBJECTIVE: To investigate whether low-frequency ventilation during hypothermia could attenuate lung injury associated with endotoxin and mechanical ventilation. DESIGN:: Experimental animal study. SETTING: University-affiliated animal laboratory. SUBJECTS: Forty-eight Sprague-Dawley rats. INTERVENTIONS:: Lipopolysaccharide was administered to rats intratracheally to induce acute lung injury. After 1 hr of this treatment, animals were assigned to normothermia-only (NO, rectal temperature 37 degrees C, ventilatory frequency 90/min), normothermia-lung rest (NR, 37 degrees C, 45/min), hypothermia-only (HO, 27 degrees C, 90/min), or hypothermia-lung rest (HR, 27 degrees C, 45/min). After 1 hr of injurious ventilation, the lungs of the rats were removed for bronchoalveolar lavage and histologic examination. MEASUREMENTS AND MAIN RESULTS: Compared with the normothermia groups (NO, NR), the neutrophil counts (per milliliter) (NO, 7708 +/- 5704; NR, 10,479 +/- 11,152; HO, 1638 +/- 955; HR, 805 +/- 591) and interleukin-1beta levels (pg/mL) (1180 +/- 439, 1081 +/- 652, 620 +/- 426, 420 +/- 182, respectively) in the bronchoalveolar lavage fluid, the wet-to-dry lung weight ratios (6.0 +/- 0.4, 5.7 +/- 0.4, 5.6 +/- 0.2, 5.2 +/- 0.2, respectively), and histologic acute lung injury scores (8.3 +/- 2.7, 10.4 +/- 3.1, 3.5 +/- 2.1, 3.1 +/- 2.2, respectively) of the hypothermia groups (HO, HR) were lower (all p < .001). Compared with the HO group, the neutrophil counts and protein content (HO, 1367 +/- 490 mug/mL vs. HR, 831 +/- 369 mug/mL) in the bronchoalveolar lavage fluid, the serum lactate dehydrogenase levels (units/mL) (9.1 +/- 3.6 vs. 5.3 +/- 1.5), and the wet-to-dry lung weight ratios of the HR group were lower (all p < .05). CONCLUSIONS: Reduction of ventilatory frequency in conjunction with hypothermia attenuated many variables of acute lung injury in rats. Use of hypothermia could be exploited as a new approach to lung rest for the ventilatory management of the acutely injured lung.     

机械通气对急性肺损伤大鼠细胞凋亡的影响

目的 研究不同潮气量及不同呼气末正压(PEEP)水平对急性肺损伤(AU)大鼠支气管和肺组织细胞凋亡的影响,并初步探讨细胞凋亡在呼吸机相关性肺损伤(VILI)中的作用机制.方法 选用40只SD大鼠,制作ALI模型,随机(随机数字法)分为:(1)小潮气量组(LV组),潮气量8 mL/kg,不加PEEP;(2)大潮气量组,潮气量30 mL./kg,不加PEEP;(3)小潮气量+ 2PEEP组(LV2P组),潮气量8 mL/kg,同时给PEEP 2 cmH2O(1 crnH2O =0.098 kPa);(4)小潮气量+5PEEP组(LV5P组),潮气量8 mL/kg,同时给PEEP 5 cmH2O;(5)小潮气量+8PEEP组(LV8P组),潮气量8 mL/kg,同时给PEEP 8 cmH2O.通气2h后处死动物,留取肺标本.用脱氧核糖核苷酸末端转移酶介导的末端标记法(TUNEL)分析肺组织中的细胞凋亡情况,用免疫组化法检测肺组织中caspase-3蛋白的表达及分布.结果 大潮气量组支气管和肺组织细胞凋亡的明显增加(P＜0.01),caspase-3蛋白酶表达最强.采用PEEP后,支气管和肺组织细胞凋亡减少,capase-3蛋白酶表达弱阳性,以LV5P组最为显著(P＜0.01).结论 小潮气量对肺组织有保护作用,采用PEEP后保护作用更加明显,细胞凋亡在VILI的发生中有重要作用.     

Treatment of ventilation-induced lung injury with exogenous surfactant

OBJECTIVE: It has been demonstrated that pulmonary surfactant plays a role in the pathophysiology of ventilation-induced lung injury (VILI). Therefore, we investigated whether exogenous surfactant might restore lung function and lung mechanics in an established model of VILI. DESIGN: Prospective, randomized, animal study. SETTING: Experimental laboratory of a university. SUBJECTS: Twenty-four adult male Sprague-Dawley rats. INTERVENTIONS: First, a group of six animals were killed immediately after induction of anesthesia and used as healthy controls. Then, in 18 rats, VILI was induced by increasing peak inspiratory pressure (PIP) to 45 cmH2O without positive end-expiratory pressure (PEEP) for 20 min. Thereafter, animals were randomly divided into three groups of six animals each: one group was killed immediately after VILI and served as VILI-control. In the other two groups, ventilator settings were changed to a PIP of 30 cmH2O and a PEEP of 10 cmH2O, and a respiratory rate of 40 bpm. One group received a bolus of surfactant and the other group received no treatment. MEASUREMENTS AND RESULTS: Blood gas tension and arterial blood pressures were recorded every 30 min for 2 h. After the study period, a pressure-volume curve was recorded. Then, a broncho-alveolar lavage (BAL) was performed to determine protein content, minimal surface tension, and surfactant composition in the BAL fluid. Oxygenation, lung mechanics, surfactant function and composition were significantly improved in the surfactant-treated group compared to the ventilated and non-ventilated control groups. CONCLUSION: We conclude that exogenous surfactant can be used to treat VILI.     

不同肺保护性通气策略对肺切除术术中通气和术后肺部并发症的影响

目的:评估小潮气量联合不同水平呼气末正压(positive end-expiratory pressure,PEEP)对胸腔镜下肺切除术患者通气氧合和术后肺部并发症(postoperative pulmonary complications,PPCs)的影响。方法:选取空军军医大学唐都医院2019年12月至2020年12月择期行胸腔镜下肺切除患者100例,采用随机数字表法分为两组:低水平PEEP组(LP组)和高水平PEEP组(HP组);LP组于单肺通气(one lung ventilation,OLV)时设置潮气量(tidal volume,V_T)6 mL/kg,PEEP≤5 cmH₂O,HP组于相同时间点设置V_T 6 mL/kg,PEEP 6~10 cmH₂O。分别于OLV前(T1)、OLV 60 min(T2)、手术结束(T3)采取桡动脉血液行血气分析;记录T1、T2、T3的心率(heart rate,HR)、脉搏血氧饱和度(pulse oxygen saturation,SpO₂)、收缩压/舒张压(systolic blood pressure/diastolic blood pressure,SBP/DBP)、呼气末二氧化碳分压(partial pressure of end-expiratory carbon dioxide,P_ETCO₂)、V_T、吸气峰压(peak pressure,Ppeak)、平台压(plateau pressure,Pplat);记录术后7 d内PPCs、胸腔引流管拔除时间、术后3 d内胸腔引流管引流量及术后住院时间。结果:与T1时比较,T2、T3时两组患者HR无明显变化;T2时平均动脉压(mean arterial pressure,MAP)明显降低(P<0.05);两组Ppeak、Pplat明显升高,动态肺顺应性(dynamic compliance,Cdyn)明显降低(P<0.05);两组患者氧合指数(oxygenation index,OI)明显降低,肺泡气-动脉血氧分压差(alveolar gas-arterial oxygen partial pressure difference,A-aDO₂)明显升高;T2时两组呼吸指数(respiratory index,RI)明显升高,T3时LP组RI明显升高(P<0.05)。与LP组比较,T2时HP组Ppeak明显升高;T2、T3时,HP组Pplat明显升高,驱动压(driving pressure,DP)明显降低,Cdyn明显增高(P<0.05);T2、T3时HP组OI明显升高,A-aDO₂、RI明显降低(P<0.05)。两组术后7 d PPCs及住院时间差异无统计学意义。结论:小潮气量6 mL/kg联合较高水平PEEP 6~10cmH₂O可改善胸腔镜下肺切除术患者OLV时通气氧合情况,利于术中麻醉管理。     

Influence of respiratory rate on gas trapping during low volume ventilation of patients with acute lung injury

OBJECTIVE: Reduction in tidal volume (Vt) associated with increase in respiratory rate to limit hypercapnia is now proposed in patients with acute lung injury (ALI). The aim of this study was to test whether a high respiratory rate induces significant intrinsic positive end-expiratory pressure (PEEPi) in these patients. DESIGN: Prospective crossover study. SETTING: A medical intensive care unit. INTERVENTIONS AND MEASUREMENTS: Ten consecutive patients fulfilling criteria for severe ALI were ventilated with a 6 ml/kg Vt, a total PEEP level at 13+/-3 cmH(2)O and a plateau pressure kept at 23+/-4 cmH(2)O. The respiratory rate was randomly set below 20 breaths/min (17+/-3 breaths/min) and increased to 30 breaths/min (30+/-3 breaths/min) to compensate for hypercapnia. External PEEP was adjusted to keep the total PEEP and the plateau pressure constant. PEEPi was computed as the difference between total PEEP and external PEEP. The lung volume retained by PEEPi was then measured. RESULTS: Increase in respiratory rate resulted in significantly higher PEEPi (1.3+/-0.4 versus 3.9+/-1.1 cmH(2)O, p<0.01) and trapped volume (70+/-43 versus 244+/-127 ml, p<0.01). External PEEP needed to be reduced from 11.9+/-3.4 to 9.7+/-2.9 cmH(2)O ( p<0.01). PaO(2) was not affected but the alveolar-arterial oxygen tension difference slightly worsened with the high respiratory rate (p<0.05). CONCLUSIONS: An increase in respiratory rate used to avoid Vt reduction-induced hypercapnia may induce substantial gas trapping and PEEPi in patients with ALI.     

Ability of dynamic airway pressure curve profile and elastance for positive end-expiratory pressure titration

OBJECTIVE: To evaluate the ability of three indices derived from the airway pressure curve for titrating positive end-expiratory pressure (PEEP) to minimize mechanical stress while improving lung aeration assessed by computed tomography (CT). DESIGN: Prospective, experimental study. SETTING: University research facilities. SUBJECTS: Twelve pigs. INTERVENTIONS: Animals were anesthetized and mechanically ventilated with tidal volume of 7 ml kg(-1). In non-injured lungs (n = 6), PEEP was set at 16 cmH(2)O and stepwise decreased until zero. Acute lung injury was then induced either with oleic acid (n = 6) or surfactant depletion (n = 6). A recruitment maneuver was performed, the PEEP set at 26 cmH(2)O and decreased stepwise until zero. CT scans were obtained at end-expiratory and end-inspiratory pauses. The elastance of the respiratory system (Ers), the stress index and the percentage of volume-dependent elastance (%E (2)) were estimated. MEASUREMENTS AND MAIN RESULTS: In non-injured and injured lungs, the PEEP at which Ers was lowest (8-4 and 16-12 cmH(2)O, respectively) corresponded to the best compromise between recruitment/hyperinflation. In non-injured lungs, stress index and %E (2) correlated with tidal recruitment and hyperinflation. In injured lungs, stress index and %E (2) suggested overdistension at all PEEP levels, whereas the CT scans evidenced tidal recruitment and hyperinflation simultaneously. CONCLUSION: During ventilation with low tidal volumes, Ers seems to be useful for guiding PEEP titration in non-injured and injured lungs, while stress index and %E (2) are useful in non-injured lungs only. Our results suggest that Ers can be superior to the stress index and %E (2) to guide PEEP titration in focal loss of lung aeration.     

Partial liquid ventilation and positive end-expiratory pressure reduce ventilator-induced lung injury in an ovine model of acute respiratory failure

OBJECTIVE: To examine the isolated and combined effects of positive end-expiratory pressure (PEEP) and partial liquid ventilation (PLV) on the development of ventilator-induced lung injury in an ovine model. DESIGN: Prospective controlled animal study. SETTING: University-based cardiovascular animal physiology laboratory. SUBJECTS: Thirty-eight anesthetized supine sheep weighing 22.3 +/- 2.2 kg. INTERVENTIONS: Animals were ventilated for 6 hrs (respiratory rate, 15; FIO2, 1.0, inspiratory/expiratory ratio, 1:1) with one of five pressure-controlled strategies, expressed as peak inspiratory pressure (PIP)/PEEP: low-PIP, 25/5 cm H2O (n = 8); high-PIP, 50/5 cm H2O (n = 8); high-PIP-PLV, 50/5 cm H2O-PLV (n = 8); high-PEEP, 50/20 cm H2O (n = 7); and high-PEEP-PLV, 50/20 cm H2O-PLV (n = 7). MEASUREMENTS AND MAIN RESULTS: Compared with the low-PIP control, high-PIP ventilation increased airleak, shunt, histologic evidence of lung injury, neutrophil infiltrates, and wet lung weight. Maintaining PEEP at 20 cm H2O or adding PLV reduced the development of physiologic shunt and dependent histologic injury indexes. Neither higher PEEP nor PLV reduced the high incidence of barotrauma observed in high-PIP animals. CONCLUSIONS: We conclude that application of PLV or PEEP at 20 cm H2O may improve gas exchange and afford lung protection from ventilator-induced lung injury during high-pressure mechanical ventilation in this model.     

盐酸戊乙奎醚对长时间全麻手术肺内分流的影响

目的：观察术前应用阿托品、盐酸戊乙奎醚或术中应用呼气末正压（PEEP）机械通气对长时间全麻手术患者肺内分流的影响。方法：45例美国麻醉医师协会（ASA）Ⅰ~Ⅱ级行择期广泛全子宫切除＋盆腔淋巴结清扫术的宫颈癌患者随机分为3组,每组15例。阿托品组术前静脉注射阿托品0.25mg,术中行间歇正压通气（IPPV）,PEEP值设为0cmH2O;盐酸戊乙奎醚组术前静脉注射盐酸戊乙奎醚1mg,术中行IPPV,PEEP值设为0cmH2O;PEEP组术前静脉注射阿托品0.25mg,术中行IPPV,PEEP值设为6cmH2O。各组患者吸空气状态下,于全麻前5min及苏醒拔管后1h行血气分析,计算术前和术后肺泡-动脉氧分压差[P（A-a）O2],比较各组P（A-a）O2以及术后不良反应和并发症的发生情况。结果：阿托品组、盐酸戊乙奎醚组和PEEP组分别有14例、15例和14例患者完成研究。阿托品组术后P（A-a）O2显著大于术前P（A-a）O2（P〈0.05）;盐酸戊乙奎醚组和PEEP组术后P（A-a）O2与术前P（A-a）O2差异无统计学意义（P〉0.05）;3组间术后P（A-a）O2与术前P（A-a）O2的差值存在显著差异（PEEP组〈盐酸戊乙奎醚组〈阿托品组,P〈0.05）。盐酸戊乙奎醚组术后口干时间显著长于其他两组（P〈0.05）;阿托品组有1例发生术后低氧血症;3组术后均未发生认知功能障碍。结论：长时间手术全麻机械通气患者,术前仅应用阿托品术后肺内分流显著增加;术前应用盐酸戊乙奎醚或术中联合PEEP通气可预防肺内分流的增加。     

Clinical results with the "open lung concept"

Elements of the "open lung concept" are being increasingly included in clinical ventilatory strategies. Despite encouraging experimental investigations to date, relatively few studies exist that examine the clinical application of the complete concept. The aim of this study was to prove that with effective recruitment maneuvers and titrated PEEP levels this concept is applicable in clinical settings. We sought to determine if it was possible to achieve a significant improvement in oxygenation and also to examine what side-effects resulted. Twenty consecutive patients who had had an acute lung injury (ALI) for less than 72 hours, with an oxygenation index (P/F-Ratio = quotient from arterial partial pressure of oxygen [PaO2] and the inspiratory fraction of oxygen [FiO2]) of less than 200 torr, and with a PEEP > or = 10 cmH2O were treated using a recruitment manoeuvre (RM). A PEEP was titrated to keep the lung open, and the patients were kept under pressure-controlled ventilation. The P/F-Ratio increased while using a recruitment pressure of 66 +/- 13 cmH2O from 137 +/- 41 to 381 +/- 150 torr (p < 0.001). The titrated PEEP which kept the lung open after recruitment was 17 +/- 3 cmH2O. One patient developed a pneumothorax. The dose of norepinephrine was increased in ten patients from 0.24 +/- 0.12 to 0.31 +/- 0.1 microgram/kg/min. Due to elevated liver enzymes within the first 48 hours, titrated PEEP had to be decreased in three patients. The clinical application of the "open lung concept" demonstrated a quick and effective improvement in oxygenation in many patients. Side-effects in some patients limited the use of high PEEP levels.