Control of tracheal cuff pressure: a pilot study using a pneumatic device

OBJECTIVE: To evaluate the efficacy of a simple mechanical device to maintain constant endotracheal cuff pressure (Pcuff) during mechanical ventilation (large encased inflatable cuff connected to the endotracheal cuff and receiving constant pressure from a heavy mass attached to an articulated arm). DESIGN AND SETTING: Single-center, prospective, randomized, crossover, pilot study in a medical intensive care unit. PATIENTS AND PARTICIPANTS: Nine consecutive mechanically ventilated patients (age 62+/-20 years, SAPS II score 39+/-15). INTERVENTIONS: Control day: Pcuff monitored and adjusted with a manometer (Hi-Lo, Tyco Healthcare) according to current recommendations (twice a day and after each intervention on the tracheal tube); initial target Pcuff 22-28 cmH20. Prototype day: test device connected to the endotracheal cuff; same initial target. Continuous Pcuff recording during both days. Control and prototype days in random order. RESULTS: Pcuff values over 50 cmH20 were recorded in six patients during the control day (178+/-159min), never during the prototype day. During the control day, Pcuff was between 30 and 50 cmH20 for 29+/-25% of the time, vs 0.3+/-0.3% during the prototype day (p<0.01). Pcuff was between 15 and 30 cmH20 for 56+/-36% of the time during the control day, vs 95+/-14% during the prototype day p<0.01). During the control day, Pcuff was below 15 cmH20 for 15+/-17% of the time, vs 4.7+/-15% during the prototype day (p<0.05). CONCLUSIONS: The tested device successfully controlled Pcuff with minimal human resource consumption. Prospective studies are required to assess its clinical impact.     

对机械通气患者气管套管气囊压力的临床观察

目的判断机械通气患者气管套管气囊压力和注气量是否合适。方法对30例机械通气老年患者的气管套管气囊压力和注气量的实际值和理想值进行精确测量。结果53.3％的患者气囊实际压力和注气量过高，大于理想值。其中气囊实际注气量大于理想注气量3～5ml，气囊压力超过理想压力2～26cmH2O(0．2～2．6kPa)。结论临床大部分气管套管气囊压力和注气量偏高，应对机械通气患者的气管套管压力和注气量定期进行精确测量和调整，以减少气管套管对气管粘膜的损伤。     

机械通气气管套囊控制指标对家兔气管黏膜的影响

目的探讨机械通气气管套囊指标对急性肺损伤兔气管黏膜组织超微结构的影响。方法健康兔90只,按气囊压力不同分为A（气囊压力30cmH2O,气囊充气时间1h、2h、4h、8h）、B（气囊压力20cmH2O,气囊充气时间1h、2h、4h、8h）、C（气囊压力20cmH2O,每隔2h、4h、8h气囊放气10、20、30min）、D（对照组）4组,分别对气管黏膜进行电镜超微结构观察。结果气囊压力20cmH2O维持〈8h,上皮少量纤毛缺失,柱状上皮细胞轻度肿胀,每隔4h放气20min,上皮细胞层次较清晰,细胞形态基本正常。结论气囊压力在20cmH2O对气管黏膜的损伤最轻;气囊充气4h后放气时间≥20min再充气,可减轻气管黏膜损伤。     

Effects of body temperature on ventilator-induced lung injury

PURPOSE: To evaluate the effects of body temperature on ventilator-induced lung injury. MATERIAL AND METHODS: Thirty-four male Sprague-Dawley rats were randomized into 6 groups based on their body temperature (normothermia, 37 +/- 1 degrees C; hypothermia, 31 +/- 1 degrees C; hyperthermia, 41 +/- 1 degrees C). Ventilator-induced lung injury was achieved by ventilating for 1 hour with pressure-controlled ventilation mode set at peak inspiratory pressure (PIP) of 30 cmH2O (high pressure, or HP) and positive end-expiratory pressure (PEEP) of 0 cmH2O. In control subjects, PIP was set at 14 cmH2O (low pressure, or LP) and PEEP set at 0 cmH2O. Systemic chemokine and cytokine (tumor necrosis factor alpha , interleukin 1 beta , interleukin 6, and monocyte chemoattractant protein 1) levels were measured. The lungs were assessed for histological changes. RESULTS: Serum chemokines and cytokines were significantly elevated in the hyperthermia HP group compared with all 3 groups, LP (control), normothermia HP, and hypothermia HP. Oxygenation was better but not statistically significant in hypothermia HP compared with other HP groups. Cumulative mean histology scores were higher in hyperthermia HP and normothermia HP groups compared with control and normothermia HP groups. CONCLUSIONS: Concomitant hyperthermia increased systemic inflammatory response during HP ventilation. Although hypothermia decreased local inflammation in the lung, it did not completely attenuate systemic inflammatory response associated with HP ventilation.     

Assessment of airway closure from deflation lung volume–pressure curve: sigmoidal equation revisited

OBJECTIVE: To assess a sigmoidal equation for describing airway closure. DESIGN: Experimental study. SETTING: University laboratory. PARTICIPANTS: Eight piglets mechanically ventilated on zero end-expiratory pressure (ZEEP). INTERVENTIONS: Control and lung saline lavage. MEASUREMENTS AND RESULTS: Lungs were inflated up to transpulmonary pressure of 30 cmH(2)O at constant flow (0.12l s(-1)) then deflated at the same flow rate up to the point at which oesophageal pressure was constant, which was assumed to represent complete airway closure. The deflation volume-transpulmonary pressure curve was fitted to: (1) a sigmoidal equation focusing on inflexion point and pressure at maximal compliance increase and (2) an exponential equation above an inflexion point determined by eyeballing. Data deviate from the exponential equation at the point of airway closure onset. The zero-volume intercept was determined. Complete airway closure was reached at -8.3+/-3.5cmH(2)O in control conditions and at -1.3+/-3.7 cmH(2)O after lavage (p < 0.05). Between control and lavage, onset of airway closure was 3.0+/-1.9 vs. 6.0+/-2.8 cmH(2)O (p <0.05), inflexion point 3.2+/-1.8 vs. 7.7+/-2.6 cmH(2)O (p <0.001), pressure at maximal compliance increase -1.9+/-0.7 vs. -0.03+/-2.1cmH(2)O (p <0.05) and zero-volume intercept -1.5+/-1.4 vs. 0.3+/-2.3cmH(2)O (p <0.05). CONCLUSIONS: During mechanical ventilation airways stay open and close around ZEEP in control but are closed above ZEEP after lavage. Inflexion point might reflect onset of airways closure in control. Pressure at maximal compliance increase was not a marker of complete airways closure. In control and lavage, pressure at maximal compliance increase and zero-volume intercept were reasonably equivalent.     

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.     

Effect of end-inspiratory pause duration on plateau pressure in mechanically ventilated patients

OBJECTIVE: To compare the values of plateau pressure (Pplat) recorded at different times after end-inspiratory occlusion and those of static elastance (Est,rs) and total resistance (Rrs) of the respiratory system. DESIGN: Physiological study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: Eleven patients with ARDS and ten patients with COPD requiring tracheal intubation and mechanical ventilation were investigated. COPD patients were investigated on zero end-expiratory pressure (ZEEP) and ARDS patients on both ZEEP and positive end-expiratory pressure (PEEP). MEASUREMENTS AND RESULTS: Respiratory mechanics were assessed using the rapid airway occlusion technique. Tracheal pressure (Ptr) was measured downstream the endotracheal tube. Ptr was recorded 0.5 s, 1 s, 2 s, 3 s, and 5 s after a 5-s end-inspiratory occlusion. Est,rs and Rrs were computed at the same times using standard formula. In ARDS patients on ZEEP, Pplat amounted to 20+/-5, 20+/-5, 19+/-5, 19+/-5, and 18+/-5 cmH(2)O at 0.5, 1, 2, 3 and 5 s, respectively (P <0.001). In COPD patients, these values were 18+/-4 cmH(2)O, 17+/-4 cmH(2)O, 17+/-4 cmH(2)O, 16+/-4 cmH(2)O, and 16+/-4 cmH(2)O (P <0.001). Except for one ARDS patient on PEEP, Pplat was always less than 35 cmH(2)O, regardless of the time of measurement. As compared to 5 s, measurements at 0.5 s resulted in overestimation of Est,rs by 14% and 29% and in underestimation of Rrs by 34% and 24%, in ARDS and COPD patients, respectively. CONCLUSIONS: Very early post-occlusion values of Pplat were statistically greater than at 3 s or 5 s. This probably has no major impact on the occurrence of volutrauma. Clinicians must be aware, however, that Est,rs and Rrs are greatly modified by the time of recording of Pplat.     

Physiologic comparison between conventional mechanical ventilation and transtracheal open ventilation in acute traumatic quadriplegic patients

OBJECTIVE: To evaluate the efficacy of mechanical ventilation administered through a small-bore, uncuffed tracheotomy tube, so-called transtracheal open ventilation (TOV), in comparison with conventional mechanical ventilation via a cuffed tracheal tube (endotracheal invasive ventilation, EIV). DESIGN: Physiologic study. SETTING: Intensive care unit of a referral trauma center. PATIENTS: Ten acute quadriplegic patients. INTERVENTIONS: In acute quadriplegic patients receiving EIV, TOV was subsequently applied via an uncuffed, small-bore tube (internal diameter of 4 or 5 mm). MEASUREMENTS AND MAIN RESULTS: Compared with EIV, arterial blood gases were not significantly different after 1 hr of TOV (Pao2/Fio2, 222.8 +/- 60.9 vs. 218.5 +/- 60.3; Paco2, 37.8 +/- 7.1 torr [5.04 +/- 0.95 kPa] vs. 35.5 +/- 6.8 torr [4.73 +/- 0.91 kPa], for EIV and TOV, respectively). Respiratory rate (19.5 +/- 4.7 vs. 19.6 +/- 5 breaths/min) and inspiratory effort (pressure-time product of esophageal pressure during a 1-min period, 125.9 +/- 48.4 vs. 112.8 +/- 36.4 cm H2O.sec.min) were also no different between the two modes. After 24 hrs of TOV, compared with EIV and TOV after 1 hr, respiratory rate and arterial blood gases remained stable, and the pressure-time product of esophageal pressure during a 1-min period was slightly, but significantly, reduced (83.5 +/- 16.6 cm H2O.sec.min, p < .05). CONCLUSIONS: In acute quadriplegic patients receiving mechanical ventilation, TOV was as effective as EIV in providing ventilatory support.     

Fluid leakage past tracheal tube cuffs: evaluation of the new Microcuff endotracheal tube

Objective This study compared the recently introduced Microcuff endotracheal tube HVLP ICU featuring an ultrathin (7-µm) polyurethane cuff membrane with endotracheal tubes from different manufacturers regarding fluid leakage past the tube cuff.Design In vitro setup.Measurements and results The following endotracheal tubes (ID 7.5 mm) were compared: Mallinckrodt HiLo, Microcuff HVLP ICU, Portex Profile Soft Seal, Rüsch Super Safety Clear, and Sheridan CF. A vertical PVC trachea model (ID 20 mm) was intubated, and cuffs were inflated to 10, 15, 20, 25, 30, and 60 cmH₂O. Colored water (5 ml) was added to the top of the cuff. The amount of leaked fluid past the tube cuff within 5, 10, and 60 min was recorded. Experiments were performed four times using two examples of each tube brand. Fluid leakage past tube cuffs occurred in all conventional endotracheal tubes at cuff pressures from 10 to 60 cmH₂O. In the Microcuff tube cuff pressure fluid leakage was observed within 10 min only at 10 cmH₂O. Results with the Microcuff tube were significantly better than all other tube brands at cuff pressures of 10–30 cmH₂O.Conclusions Within the acceptable upper limit for tracheal cuff pressure (25–30 cmH₂O) the Microcuff endotracheal tube was the only one of the tested tubes to prevent fluid leakage in our in vitro setup. In vivo studies are required to confirm these findings.This study was supported by Microcuff GmbH, Weinheim, Germany, by providing the Microcuff tubes without charge. No financial support was obtained from the manufacturer for the study. Dr. Weiss and Dr. Gerber serve on the Medical Board of Microcuff GmbH for the development of a newly designed pediatric cuffed tracheal tube.     

Tidal volume delivery during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

OBJECTIVE: a) Characterize how ventilator and patient variables affect tidal volume during high-frequency oscillatory ventilation; and b) measure tidal volumes in adults with acute respiratory distress syndrome during high-frequency oscillatory ventilation. DESIGN: Observational study. SETTING: Research laboratory and medical intensive care unit. PATIENTS: Test lung and patients with acute respiratory distress syndrome. INTERVENTIONS: Using a previously validated hot wire anemometer placed in series with a Sensormedics 3100B high-frequency ventilator, an endotracheal tube, and a test lung, tidal volume was measured at different combinations of frequency (4, 6, 8, 10, and 12 Hz), pressure amplitude (50, 60, 70, 80, and 90 cm H2O), mean airway pressure (20, 30, and 40 cm H2O), test lung compliance (10, 30, and 50 mL/cm H2O), endotracheal tube internal diameter (6, 7, and 8 mm), bias flow (20, 30, and 40 L/min), and inspiratory/expiratory ratio (1:2 and 1:1). In patients, tidal volume was measured at baseline ventilator settings and at baseline frequency +/-2 Hz and baseline pressure amplitude +/-10 cm H2O. MEASUREMENTS AND MAIN RESULTS: Measured tidal volumes were 23-225 mL during high-frequency oscillatory ventilation of the test lung. A 2-Hz increase in frequency and a 10-cm H2O increase in pressure amplitude caused a 21.3% +/- 4.1% decrease and 21.4% +/- 3.4% increase in tidal volume, respectively. Decreasing endotracheal tube internal diameter from 8 mm to 7 mm and from 7 mm to 6 mm caused a 15.3% +/- 1.7% and 18.9% +/- 2.1% reduction in tidal volume, respectively. Increasing bias flow from 20 L/min to 30 L/min increased tidal volume by 11.2% +/- 3.9%. Further increases in bias flow, changes in compliance, and changes in mean airway pressure had little effect. Tidal volumes measured in acute respiratory distress syndrome patients were 44-210 mL. A 2-Hz increase in frequency was associated with a 23.1% +/- 6.3% decrease in tidal volume. In contrast to the test lung data, a 10-cm H2O increase in pressure amplitude resulted in only a 5.6% +/- 4.5% increase in tidal volume. CONCLUSIONS: Tidal volumes are not uniformly small during high-frequency oscillatory ventilation. The primary determinant of tidal volume in adults with acute respiratory distress syndrome during high-frequency oscillatory ventilation with the Sensormedics 3100B is frequency. Test lung findings suggest that endotracheal tube internal diameter is also an important determinant of tidal volume.     

Continuous breathing circuit flow and tracheal tube cuff leak: sources of error during pediatric indirect calorimetry.

OBJECTIVE: To determine whether continuous gas flow in the breathing circuit or an airleak around the tracheal tube cuff will introduce errors into the measurement of oxygen consumption (VO2) with indirect calorimetry. DESIGN: Nonrandomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: Ten healthy, anesthetized mongrel dogs, weighing 8 to 12 kg. INTERVENTIONS: Data were recorded at seven levels of flow, from 0 to 12 L/min in excess of minute ventilation, through a continuous breathing circuit. Data were recorded at five levels of tracheal tube cuff leak from 0% to 40% of inspiratory minute volume. MEASUREMENTS AND MAIN RESULTS: VO2 was measured using an indirect calorimeter with constant internal gas flow and calculated from results of blood gas analysis, cooximetry, and thermodilution cardiac output determinations at all levels of continuous breathing circuit flow and cuff leak. BP, heart rate, respiratory rate, arterial and mixed venous blood gases, and body temperature were measured to assess stability of cardiopulmonary function. Continuous breathing circuit flow did not affect the accuracy of indirect calorimetry until the total flow reached a critical value (11.5 L/min) that was slightly below the internal flow constant of the metabolic monitor (12.4 L/min). At higher circuit flows, measured VO2 decreased in a linear fashion, while calculated VO2 remained unchanged. Above the critical flow, the error of indirect calorimetry correlated significantly only with the total circuit flow (r2 = .64), not with the exhaled concentration of CO2 (r2 = .005) or the inspiratory-expiratory oxygen difference (r2 = .004). The continuous flow rate at the critical circuit flow was 66 +/- 15% of the subjects' peak inspiratory flow. Increasing tracheal tube cuff leak produced a progressive decrease in measured VO2 but not in calculated VO2. The difference between measured and calculated VO2 was linearly related to the magnitude of the leak (r2 = .56), and was statistically significantly larger at all levels of cuff leak, when compared with measurements during complete cuff seal. CONCLUSIONS: An indirect calorimeter in which measurement of VO2 is based on internal constant flow rather than spirometry can be used to accurately measure VO2 from a continuous-flow breathing circuit, if the total circuit flow is less than the internal flow. This limitation may restrict the use of continuous flow to a level below the subject's peak inspiratory flow. The accuracy of indirect calorimetry cannot be guaranteed for any amount of tracheal tube cuff leak.     

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.     

探讨不同体位喉罩充气容积与气囊内压的变化

目的探讨仰卧位与俯卧位喉罩套囊不同充气容积时气囊内压的变化。方法择期行腰椎手术的患者40例(男24例,女16例),年龄22⁶7岁,体重5067岁,体重50⁷0 kg,BMI<30 kg/m2,ASA分级Ⅰ70 kg,BMI<30 kg/m2,ASA分级Ⅰ^Ⅱ级。麻醉诱导后置入4号Supreme喉罩,分别测量仰卧位(A组)与俯卧位(B组)套囊充气容量范围为5Ⅱ级。麻醉诱导后置入4号Supreme喉罩,分别测量仰卧位(A组)与俯卧位(B组)套囊充气容量范围为5³0 ml(每5 ml递增)时套囊内压及气道峰压并记录相对应的实际潮气量。记录喉罩拔出过程中恶心呕吐、呛咳、误吸、低氧血症和喉罩四周血迹程度的情况;术后24 h内患者咽喉疼痛、声音嘶哑、吞咽困难等发生情况。结果充入相同容量的气体时,A组的气道峰压和气囊内压要明显低于B组(P<0.05)。仰卧位套囊充气容量为1530 ml(每5 ml递增)时套囊内压及气道峰压并记录相对应的实际潮气量。记录喉罩拔出过程中恶心呕吐、呛咳、误吸、低氧血症和喉罩四周血迹程度的情况;术后24 h内患者咽喉疼痛、声音嘶哑、吞咽困难等发生情况。结果充入相同容量的气体时,A组的气道峰压和气囊内压要明显低于B组(P<0.05)。仰卧位套囊充气容量为15²5 ml时,气囊内压为(23.5±3.1)25 ml时,气囊内压为(23.5±3.1)^(46.3±4.5)cmH2O,有92.5%(46.3±4.5)cmH2O,有92.5%¹00%的患者实际潮气量达到90%设定潮气量;充气容量为30 ml时,气囊内压为(64.5±5.5)cmH2O,大于推荐的60 cmH2O气囊内压。俯卧位套囊充气容量为15100%的患者实际潮气量达到90%设定潮气量;充气容量为30 ml时,气囊内压为(64.5±5.5)cmH2O,大于推荐的60 cmH2O气囊内压。俯卧位套囊充气容量为15²0 ml时,气囊内压为(31.8±3.7)20 ml时,气囊内压为(31.8±3.7)^(50.2±3.0)cmH2O,有95%(50.2±3.0)cmH2O,有95%¹00%的患者实际潮气量达到90%设定潮气量;充气容量为25 ml时,气囊内压为(67.0±6.6)cmH2O,大于推荐的60 cmH2O。喉罩拔出过程中所有患者均未发生恶心呕吐、呛咳、误吸,有1例拔出喉罩后有低氧血症,有2例拔出喉罩后,喉罩带血;术后24 h所有患者均未有声音嘶哑及吞咽困难,有1例术后有咽喉疼痛。结论俯卧位喉罩所需的充气容量明显减少,且在相同充气容积时俯卧位的囊内压明显高于仰卧位,在临床工作中需根据实际体位选择最合适的充气容量。     

环状软骨压迫对食管引流型喉罩通气道插入操作和通气功能的影响

目的 评价环状软骨压迫(CP)对食管引流型喉罩通气道(PLMA)插入操作和正压通气功能的影响.方法 50例按美国麻醉医师协会(ASA)标准身体状态分级为Ⅰ级的择期整形外科手术患者被纳入研究.静脉麻醉诱导后,于CP下插入PLMA,保留专用引导器并将通气罩内压充气至60 cm H2O(1 cm H2O=0.098 kPa).观察肺通气满意度,测定气道密封压,并采用光导纤维支气管镜(FOB)评价通气罩的解剖位置.暂时终止CP,采用专用引导器进一步推送PLMA到达理想位置,并重新调整通气罩内压至60 cm H2O.再次评价上述指标,并记录CP下和非CP下正压通气时的呼潮气量和吸气峰压,观察经PLMA插入胃管的情况并评价引流管解剖位置的FOB评分.结果 与在CP下插入PLMA比较,在临时解除CP并进一步推送PLMA后,肺通气满意度(良好和尚可为50例比14例)、气道密封压[(27±7)cm H2O比(21±7)cm H2O]和通气罩解剖位置的FOB评分均显著改善(P均＜0.05).在将PLMA推送至理想位置后,虽然在CP和非CP时的正压通气呼潮气量差异无显著性,但CP时的吸气峰压[(28±5)cm H2O]却显著高于非CP时[(14±2)cm H2O,P＜0.05].结论 CP可阻碍将PLMA插入到理想位置,在暂时终止CP的情况下,采用专用引导器可将PLMA插入到理想位置,而且CP可显著增加正压通气的吸气峰压.     

吸痰对人工气道套囊内压力的影响

目的 通过观察吸痰时及吸疾后30min人工气道套囊压力的变化,探讨吸痰对人工气道套囊压力的影响.方法 吸痰前用测压表调整人工气道套囊压力为30CMH2O,持续监测吸痰时的套囊最高压力、患者有无咳嗽,以及吸痰后5min、10min、15min、30min的压力,并记录吸痰后套囊压力降至25cmH2O时所需时间.结果 在吸痰过程中81.25%(78/96)患者发生咳嗽.本组套囊内压力平均明显升高至(89.42±31.37)cmH20,咳嗽者套囊内平均压力为(96.00±25.99)cmH2O,高于无咳嗽者套囊内平均压力(60.89±37.14)cmH2O,差异有统计学意义(P<0.01).吸痰时套囊内压力升高者较保持者更易下降至正常低限(25cmH2O),差异有统计学意义(P<0.01).结论 患者吸痰过程中容易发生咳嗽,人工气道套囊内压力波动明显,建议临床上在吸痰后30min内调整套囊内压力,必要时应立即调整,避免囊内压力过低或过高对患者的伤害.     

Indirect calorimetry in mechanically ventilated infants and children: measurement accuracy with absence of audible airleak.

OBJECTIVE: To establish the effect of an audible airleak (around an endotracheal tube) on oxygen consumption (VO2) measurements in pediatric ICU patients. DESIGN: Prospective trial comparing VO2 measurements before and after deflation of the endotracheal tube cuff. SETTING: Pediatric ICU in a large pediatric tertiary care center. PATIENTS: Twenty critically ill infants and children receiving mechanical ventilatory support via cuffed endotracheal tube. INTERVENTIONS: Deflation of endotracheal tube cuff. MEASUREMENTS AND MAIN RESULTS: The presence (group 1, n = 9) or absence (group 2, n = 11) of an audible airleak with the cuff deflated was confirmed by two independent observers. The percent difference in VO2 was calculated for both groups using the following formula: ([VO2 cuff up - VO2 cuff down]/VO2 cuff up) x 100. An audible airleak associated with cuff deflation (group 1) caused a significant (p = .0012) reduction of VO2 by 45.6% (mean difference in VO2 = 45.6%). In contrast, with no audible airleak after cuff deflation (group 2), only minimal changes in VO2 (mean difference in VO2 = -0.4%) were observed. CONCLUSIONS: These data suggest that if no audible airleak is detected, VO2 determined by indirect calorimetry may be reliably measured in infants and children with a noncuffed endotracheal tube.     

A comparison of intratracheal pulmonary ventilation to conventional ventilation in a surfactant deficient animal model

OBJECTIVE: To compare intratracheal pulmonary ventilation (ITPV) with conventional ventilation in a rabbit model of surfactant deficiency. DESIGN: A prospective randomized animal study. SETTING: The Children's National Medical Center Research Animal Facility in Washington, DC. SUBJECTS: Adult male New Zealand white rabbits (n = 20), weighing 1.4-4.2 kg. INTERVENTIONS: After anesthesia and catheter placement, rabbits were tracheotomized, paralyzed, and placed on the conventional ventilator. We determined pulmonary functions at baseline. We washed surfactant out of the lungs by using serial bronchoalveolar lavages. Pulmonary function studies were determined after completion of the bronchoalveolar lavages and were used as an indication of severity of lung injury. Animals were randomized into two groups: We placed ten animals on ITPV, using the ITPV reverse thruster catheter designed by Kolobow and a prototype ITPV ventilator designed at Children's National Medical Center; we placed ten animals on conventional ventilation using the Sechrist iv-100 ventilator. Arterial blood gases were drawn every 15 mins, and the ventilator settings were adjusted to the minimal level that would maintain arterial blood gases in the following ranges: pH 7.35-7.45, PaCO2 30-40 torr (3.995.33 kPa), PaO2 50-70 torr (6.66-9.33 kPa). Animals were ventilated with the randomized ventilation techniques for 4 hrs. MEASUREMENTS AND MAIN RESULTS: Peak inspiratory pressure, mean airway pressure, and positive end-expiratory pressure were measured at the distal end of the endotracheal tube. We recorded these variables plus respiratory rate at baseline and every 30 mins for a total of 4 hrs of ventilation. Lung compliance did not differ between groups at the postlavage study period (ITPV, 0.56+/-0.13 mL/cm H2O/kg; conventional 0.49+/-0.15 mL/cm H2O/kg). At the end of the 4 hr study period, peak inspiratory pressure (ITPV, 26.2+/-4.6 cm H2O; conventional, 32.4+/-5.04 cm H2O, p = .007) and positive end-expiratory pressure (ITPV, 3.9+/-1.96 cm H2O; conventional, 6.3+/-1.42 cm H2O, p = .005) were lower in the ITPV ventilation group. Peak inspiratory pressure was significantly lower in the ITPV group by 2 hrs into the study. CONCLUSION: In this model of surfactant deficiency lung injury, ventilation and oxygenation were achieved at significantly lower ventilator settings using ITPV compared with conventional ventilation. Long-term studies are needed to determine whether this reduction in ventilation is maintained, and if so, if lung injury is reduced.     

Repeated derecruitments accentuate lung injury during mechanical ventilation

OBJECTIVE: This study was performed to test the hypothesis that derecruitment itself might accentuate lung injury during mechanical ventilation. SETTING: Randomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: New Zealand White rabbits (2.8-3.5 kg). INTERVENTION: Twenty-four rabbits were ventilated in pressure-controlled mode with constant tidal volume (10 mL/kg). After lung injury was induced by repeated saline lavage (PaO2 <100 torr, 13.3 kPa), a pressure-volume curve was drawn to calculate the lower inflection point (Pflex), and randomization was done. The control group (n = 8) received ventilation with positive end-expiratory pressure (PEEP) fixed at Pflex for 3 hrs. The nonderecruitment group (n = 8) was ventilated at PEEP of 2 mm Hg (2.7 cm H2O) for the initial hour and then PEEP of Pflex for the remaining 2 hrs. The derecruitment group (n = 8) was ventilated for 3 hrs with six 30-min cycles consisting of 10 mins at PEEP of 2 mm Hg (2.7 cm H2O) and 20 mins at PEEP of Pflex to induce repeated derecruitments. MEASUREMENTS AND MAIN RESULTS: Variables of gas exchange, mechanics, and hemodynamics were measured, and histologic evaluation was done. In the control group, Pao2 remained >500 torr (66.7 kPa) for 3 hrs. In the nonderecruitment group, PaO2 was 40 +/- 16 (mean +/- SD) torr (5.3 +/- 2.1 kPa) at 1 hr but increased to >500 torr (66.7 kPa) for the remaining 2 hrs after increase in PEEP to Pflex. In the derecruitment group, there was progressive decline in Pao2 with each derecruitment to 220 +/- 130 torr (29.3 +/- 17.3 kPa) at 3 hrs (p <.05 compared with other groups). Histologically there was more hyaline membrane formation in the derecruitment group compared with control (p <.05) and significantly higher mean bronchiolar injury score in the derecruitment group (1.92 +/- 0.78) than both control (0.50 +/- 0.50) and nonderecruitment (0.78 +/- 0.42) groups (p <.05). CONCLUSION: Repeated derecruitments can accentuate lung injury during mechanical ventilation.     

Non-invasive pressure support ventilation in patients with acute respiratory failure after bilateral lung transplantation

OBJECTIVE: To evaluate non-invasive ventilation (NIV) prospectively in a group of patients developing acute respiratory failure (ARF) after bilateral lung transplantation (BLT). SETTING: General intensive care unit (ICU) of Rome "La Sapienza" University. PATIENTS: Twenty-one patients (18 with cystic fibrosis) undergoing BLT. RESULTS: All consecutive patients developing ARF (according to predefined criteria) and requiring ventilatory support, received non-invasive pressure support ventilation through a face-mask (PEEP 5 cmH2O, PSV 14+/-2 cmH2O) for a mean period of 5+/-4 days. Eighteen out of 21 patients avoided intubation and were discharged from the ICU; 3 patients required intubation: 1 of them survived while 2 developed septic shock and died. CONCLUSIONS: NIV administration was well tolerated and avoided intubation in the large majority of patients (86%); in NIV responders the rate of complications was low and ICU mortality nil. NIV should be considered as an interesting alternative to conventional ventilation in patients who require ventilatory support after BLT.     

Automatic control of tracheal tube cuff pressure in ventilated patients in semirecumbent position: a randomized trial

OBJECTIVE: The aspiration of subglottic secretions colonized by bacteria pooled around the tracheal tube cuff due to inadvertent deflation (<20 cm H2O) of the cuff plays a relevant role in the pathogenesis of ventilator-associated pneumonia. We assessed the efficacy of an automatic, validated device for the continuous regulation of tracheal tube cuff pressure in preventing ventilator-associated pneumonia. DESIGN: Prospective randomized controlled trial. SETTING: Respiratory intensive care unit and general medical intensive care unit. PATIENTS: One hundred and forty-two mechanically ventilated patients (age, 64 +/- 17 yrs; Acute Physiology and Chronic Health Evaluation II score, 18 +/- 6) without pneumonia or aspiration at admission. INTERVENTIONS: Within 24 hrs of intubation, patients were randomly allocated to undergo continuous regulation of the cuff pressure with the automatic device (n = 73) or routine care of the cuff pressure (control group, n = 69). Patients remained in a semirecumbent position in bed. MEASUREMENTS AND MAIN RESULTS: The primary end point variable was the incidence of ventilator-associated pneumonia. Main causes for intubation were decreased consciousness (43, 30%) and exacerbation of chronic respiratory diseases (38, 27%). Cuff pressure <20 cm H2O was more frequently observed in the control than the automatic group (45.3 vs. 0.7% determinations, p < .001). However, the rate of ventilator-associated pneumonia with clinical criteria (16, 22% vs. 20, 29%) and microbiological confirmation (11, 15% vs. 10, 15%), the distribution of early and late onset, the causative microorganisms, and intensive care unit (20, 27% vs. 16, 23%) and hospital mortality (30, 41% vs. 23, 33%) were similar for the automatic and control groups, respectively. CONCLUSIONS: Cuff pressure is better controlled with the automatic device. However, it did not result in additional benefits to the semirecumbent position in preventing ventilator-associated pneumonia.