High-frequency jet ventilation versus intermittent positive-pressure ventilation

Airway pressures and cardiorespiratory variables were compared for conventional ventilation (CV) and high-frequency jet ventilation (HFJV), at a similar fraction of inspired O2 (FIO2), positive end-expiratory pressure (PEEP) and PaCO2 in 11 ICU patients. For CV and HFJV, respectively, peak (PAP) and mean airway pressures (Paw) were 15.4 and 9.1 mm Hg and 4.4 and 5 mm Hg. Cardiac index (CI) was 2.54 and 2.60 L/min X m2, total systemic vascular resistance index (SVRI) 2846 and 2923 dyne X sec/cm5 X m2, PaO2 207 and 149 torr, and Qsp/Qt 7% and 11%. HFJV decreased significantly PAP and was less likely to produce pulmonary barotrauma. Cardiac indices were not different, indicating that this variable may be affected by Paw. HFJV neither increased nor decreased CI at similar PEEP and PaCO2 as compared to CV. The decrease in PaO2 and increase in Qsp/Qt may be due to small inspired gas volumes potentiating microatelectasis. On the basis of this study, we recommend initiating HFJV at FIO2 of 0.9 and PEEP of 5 cm H2O, and monitoring both PAP and Paw.     

Experimental studies of continuous positive-pressure ventilation and high-frequency positive-pressure ventilation

The ventilatory pattern of a conventional respirator (SV-900) was compared with that produced by a prototype (system H) of a low-compressive ventilator system for pressure/flow-generated, time-cycled, volume-controlled ventilation. The experimental conditions in this study on 10 dogs were light pentobarbital anaesthesia and normoventilation, using ventilatory frequencies (f) of 20, 40, 50 and 60/min with relative insufflation times (t%) of 25% (SV-900) and 22% (system H). With system H (functionally with a negligible compression volume) the delivered tidal volume of the ventilator (V_{T tot}) was almost equal to the effective tidal volume (V_{T eff}). By increasing f to 60/min, V_{T eff} with system H could be reduced to 65% of that required at a ventilatory frequency of 20/min — in parallel with the reduced tidal volume the peak and mean airway pressures were significantly reduced. With SV-900, V_{T eff} could also be reduced by increasing f to 60/min, but the peak airway pressure was not influenced while the mean airway pressure increased significantly in relation to that at f of 20/min. With an increase in f from 20 to 60/min, the mean airway pressure at normoventilation was significantly higher during ventilation with SV-900 than with system H, and both ventilators gave significant increases in dead space ratio $\text{VD}\text{VT}$ and functional residual capacity (FRC).The pneumotachographic recordings showed two functionally important features of the ventilatory pattern during ventilation with the low-compressive system, namely: (a) that the brief initial accelerating flow rapidly turns into a true decelerating flow during the remaining (i.e., major) part of the inspiratory phase; and (b) that the major fraction of the effective tidal volume is delivered to the lungs during the early phase of inspiration, which gives more time for redistribution of this fraction of inspired gas during the rest of the inspiratory phase.The intrapulmonary gas distribution was studied by analyses of pulmonary nitrogen clearance curves. In terms of nitrogen clearance ratio, measured by nitrogen washout with oxygen, with ventilator system H the intrapulmonary gas distribution was significantly improved in comparison with SV-900 and was independent of ventilatory frequency. It is suggested that a ventilator which has a negligible compression volume and delivers an instantaneous, high initial inspiratory flow may induce more efficient intrapulmonary mixing (convection /distribution) of gas by means of enhanced diffusive mechanisms.     

Effects of intermittent positive-pressure ventilation on cardiac output measurements by thermodilution

Sequential thermodilution measurements of cardiac output in mechanically ventilated patients undergoing cardiac surgery demonstrated a cyclic modulation which correlated with changes in airway pressure, and was not affected by opening the pericardium. There was no satisfactory point for single measurements, which suggests that random thermodilution measurements of cardiac output during intermittent positive-pressure ventilation should be avoided, even when triplicate measurements are performed. To estimate the mean cardiac output, at least two measurements should be made at predetermined points of the ventilatory cycle. We recommend paired measurements at midinspiration and end-expiration.     

压力支持通气与成比例压力支持通气模式对血流动力学状态的影响

目的　探讨压力支持通气 (PSV)与成比例压力支持通气 (PPS)不同通气模式对血流动力学的影响。方法　选择呼吸衰竭行机械通气及脉搏轮廓法持续血流动力学监护患者 2 6例。经治疗进入低辅助通气后比较在PSV、PPS两种通气模式下血流动力学及呼吸力学的差异。结果　PPS模式心输出量 (CO)、心指数 (CI)、每搏量 (SV)较PSV模式明显增加 (P <0 0 5 ) ,外周血管阻力 (SVR)无明显变化 (P >0 .0 5 ) ,气道峰压 (Ppeak)及内源性PEEP(PEEPi)明显下降 (P <0 .0 5 )。结论　PPS模式对机械通气患者的血流动力学状态影响最小 ,较适用于血流动力学不稳定患者。     

Arterial to end-tidal CO2 gradients during spontaneous breathing, intermittent positive-pressure ventilation and jet ventilation

Arterial to end-tidal CO2 tension gradients were measured in 18 dogs during spontaneous breathing (SB), intermittent positive-pressure ventilation (IPPV), and both low-frequency and high-frequency jet ventilation (LFJV and HFJV). The dogs were anesthetized with nembutal and permitted to breathe spontaneously through an 8-mm internal diameter endotracheal tube; blood gas tensions, cardiac output, and end-tidal CO2 partial pressure (PetCO2) were measured. IPPV, LFJV, and HFJV were then instituted in a random sequence and measurements repeated. PaO2, PaCO2 and cardiac output were similar during all four ventilatory modes. The mean PaCO2 differed significantly (p less than .001) from PetCO2 during IPPV, LFJV, and HFJV but not during SB. The mean PaCO2-PetCO2 gradient was 3.7 +/- 1 (SD), 12.6 +/- 5.0, and 24.3 +/- 8 torr during IPPV, LFJV and HFJV, respectively. The large gradients during LFJV and HFJV were not produced by dilution of tracheal CO2 by entrained air or by oxygen delivered by the jet. These results suggest that both LFJV and HFJV may be associated with a large PaCO2-PetCO2 gradient.     

压力支持通气与同步间歇指令通气压力支持水平两种脱机方式的比较

目的：比较压力支持通气（ＰＳＶ）与同步间歇指令通气压力支持水平（ＳＩＭＶＰＳ）两种机械通气方式的脱机效果。方法：对照观察两种通气方式患者在脱机时间、ＰＳ、潮气量（ＶＴ）、呼吸频率（ｆ）、气道闭合压（Ｐ０．１）以及脱机步骤方面的差异。结果：ＰＳＶ脱机成功２５例，ＳＩＭＶＰＳ脱机成功１３例。两种脱机方式的脱机时间、ＰＳ水平、ＶＴ、ｆ和Ｐ０．１比较均无显著性差异（Ｐ均＞０．０５）。ＰＳＶ脱机：短期带机（＜７日）的ＰＳ应≤０．６９ｋＰａ（１ｋＰａ＝１０．２０ｃｍＨ２Ｏ）；长期带机（＞７日）的ＰＳ应达０．４９～０．５９ｋＰａ，并应动态观察Ｐ０．１通气、氧合变化可成功实现脱机。ＳＩＭＶＰＳ脱机：短期带机（＜７日）的ＰＳ应置于０．５９～０．６９ｋＰａ，ＳＩＭＶ的ｆ可逐渐减至６次／ｍｉｎ；长期带机（＞７日）ＳＩＭＶ的ｆ减至４次／ｍｉｎ，并根据患者的耐受情况，同时调整ＰＳ达０．４９ｋＰａ，结合常规参数变化及Ｐ０．１的变化可完成脱机过程。结论：ＳＩＭＶＰＳ脱机优于ＰＳＶ脱机，尤其对不能耐受ＰＳＶ脱机患者采用ＳＩＭＶＰＳ方式可成功实现脱机。ＳＩＭＶＰＳ是一种较佳的脱机方式。     

颈髓损伤后呼吸衰竭机械辅助呼吸模式比较

目的比较颈髓损伤后呼吸衰竭患者使用压力支持通气模式（PSV）与同步间歇指令通气模式（SIMV）的差异。方法观察34例患者在PsV与SIMV时血气分析、呼吸频率、心率、血压、患者主观舒适度的变化。结果在两种通气模式下，患者血压的变化无显著性差异（P〉0．05），血气pH值、PaO2、呼吸频率、心率、主观舒适度有非常显著性差异（P〈0．01），PaCO2有显著性差异（P〈0．05）。PSV模式优于SIMV模式。结论PSV模式较SIMV模式更适合颈髓损伤后呼吸功能不全时的治疗。     

Patient-ventilator interactions during partial ventilatory support: a preliminary study comparing the effects of adaptive support ventilation with synchronized intermittent mandatory ventilation plus inspiratory pressure support

OBJECTIVE: To compare the effects of adaptive support ventilation (ASV) and synchronized intermittent mandatory ventilation plus pressure support (SIMV-PS) on patient-ventilator interactions in patients undergoing partial ventilatory support. DESIGN: Prospective, crossover interventional study. SETTING: Medical intensive care unit, university tertiary care center. PATIENTS: Ten patients, intubated and mechanically ventilated for acute respiratory failure of diverse causes, in the early weaning period, ventilated with SIMV-PS and clinically detectable sternocleidomastoid activity suggesting increased inspiratory load and patient-ventilator dyssynchrony. INTERVENTIONS: Measurement of respiratory mechanics, P0.1, sternocleidomastoid electromyographic activity, arterial blood gases, and systemic hemodynamics in three conditions: 1) after 45 mins with SIMV-PS (SIMV-PS 1); 2) after 45 mins with ASV, set to deliver the same minute-ventilation as during SIMV-PS; 3) 45 mins after return to SIMV-PS (SIMV-PS 2), with settings identical to those of the first SIMV-PS period. MAIN RESULTS: The same minute ventilation was observed during ASV (11.4 +/- 3.1 l/min [mean +/- sd]) as during SIMV-PS 1 (11.6 +/- 3.5 L/min) and SIMV-PS 2 (10.8 +/- 3.4 L/min). No parameter was significantly different between SIMV-PS 1 and 2, hence subsequent results refer to ASV vs. SIMV-PS 1. During ASV, tidal volume increased (538 +/- 91 vs. 671 +/- 100 mL, p <.05) and total respiratory rate decreased (22 +/- 7 vs. 17 +/- 3 breaths/min, p <.05) vs. SIMV-PS. However, spontaneous respiratory rate increased in six patients, decreased in four, and remained unchanged in one. P0.1 decreased during ASV in all patients except three in whom no change was noted (1.8 +/- 0.9 vs. 1.1 +/- 1 cm H2O, p <.05). During ASV, sternocleidomastoid electromyogram activity was markedly reduced (electromyogram index, where SIMV-PS 1 = 100, ASV 34 +/- 41, SIMV-PS 2 89 +/- 36, p <.02) as was palpable muscle activity. No changes were noted in arterial blood gases, pH, or mean systemic pressure during the trial. CONCLUSION: In patients undergoing partial ventilatory support, with clinical and electromyographic signs of increased respiratory muscle loading, ASV provided levels of minute ventilation comparable to those of SIMV-PS. However, with ASV, central respiratory drive and sternocleidomastoid activity were markedly reduced, suggesting decreased inspiratory load and improved patient-ventilator interactions. These preliminary results warrant further testing of ASV for partial ventilatory support.     

Noninvasive positive-pressure ventilation and ventilator-associated pneumonia

There is much interest in the use of noninvasive positive-pressure ventilation (NPPV) to prevent intubation and afford a survival benefit for patients. The risk of pneumonia in patients receiving NPPV has been reported in 12 studies. Compared to patients receiving invasive mechanical ventilation (4 studies), the pneumonia rate is lower with the use of NPPV (relative risk [RR] 0.15, 95% confidence interval [CI] 0.04 to 0.58, p = 0.006). Compared to patients assigned to invasive mechanical ventilation (3 studies), in which some of the patients assigned to NPPV did not respond and were eventually intubated, there was also a benefit for the use of NPPV (RR 0.24, 95% CI 0.08 to 0.73, p = 0.01). In studies in which patients assigned to NPPV were compared to patients assigned to standard therapy (5 studies), in which some of the patients in each group were eventually intubated, there was benefit shown for the use of NPPV (RR 0.56, 95% CI 0.31 to 1.02, p = 0.06). When this meta-analysis is repeated without the results of the negative study for NPPV (extubation failure), there is a stronger benefit in support of NPPV to decrease the risk of pneumonia in the remaining 4 studies (RR 0.38, 95% CI 0.20 to 0.73, p = 0.003). A meta-analysis combining the results from the 12 studies reviewed shows a strong benefit for NPPV (RR 0.31, 95% CI 0.16 to 0.57, p = 0.0002). One randomized controlled trial of continuous positive airway pressure compared with standard treatment in patients who developed acute hypoxemia after elective major abdominal surgery reported a lower rate of pneumonia with continuous positive airway pressure (2% vs 10%, RR 0.19, 95% CI 0.04 to 0.88, p = 0.02). In patients who are appropriate candidates for NPPV or continuous positive airway pressure, the available evidence suggests a benefit in terms of a lower risk of pneumonia. Perhaps "endotracheal-tube-associated pneumonia" is a better term than "ventilator-associated pneumonia."     

Decelerating inspiratory flow waveform improves lung mechanics and gas exchange in patients on intermittent positive-pressure ventilation

The effects of two inspiratory flow waveforms (WFs), decelerating and constant have been studied in 14 patients undergoing intermittent positive-pressure ventilation (IPPV). With tidal volume (VT), inspiratory time, inspiratory-expiratory (I/E) ratio and frequency being kept constant, the decelerating waveform produced statistically significant reduction of peak pressure, total respiratory resistance, work of inspiration, ratio of dead space to tidal volume (VD/VT) and alveolar-arterial gradient for oxygen (A-a)PO2. There was significant increase in total static and kinetic compliances and PaO2, with no significant changes in PaCO2, in cardiac output (CO) and in other haemodynamic measurements.     

无创与有创正压通气对危重肺心病呼吸衰竭患者的疗效评价

目的　评价无创与有创正压通气在危重肺心病呼吸衰竭患者中的治疗效果。方法　 2 0例危重肺心病呼吸衰竭患者随机分为A组和B组 ,每组 10例。A组进行有创通气和常规药物治疗 ,B组进行无创通气和常规药物治疗。结果　A组进行有创通气 2 4h后 ,10例患者均明显好转 ,呼吸频率、心率下降 ,PaO2 上升 ,PaCO2 下降 ,与治疗前比较均有显著差异 (P <0 .0 1)。人工机械通气天数平均为 (9± 4 )d ,住院天数平均为 (15± 5 )d。 10例患者 9例出院 ,1例因呼吸机依赖而死亡。B组无创通气 2 4h后仅 1例治疗有效 ,4例无明显变化 ,5例病情恶化。 9例患者均在 36h之内改为有创通气 ,其中 1例在气管插管时因心跳呼吸骤停死亡 ,2例在有创通气过程中死亡 ,余 6例患者均平稳撤机。人工机械通气天数平均为 (15± 6 )d ,住院天数平均为 (2 1± 6 )d ,与A组比较有显著差异性 (P <0 .0 5 )。结论　危重肺心病呼吸衰竭患者不宜选用无创正压通气 ,应尽早气管插管进行有创通气治疗。     

High-frequency positive-pressure ventilation in neonates

Twenty-five newborn infants with severe respiratory failure responding poorly to conventional mechanical ventilation were switched to high-frequency positive-pressure ventilation (HFPPV) at 90 to 180 cycle/min (mean 158), an estimated tidal volume less than or equal to 3 ml/kg body weight, an inspiratory time of 0.1 sec, and a PEEP of 3 to 17 cm H2O. In all infants, HFPPV increased PaO2 (mean 66 torr) and decreased PaCO2 (mean 14 torr) within 1 h. Fourteen hours after onset of treatment, the FIO2 requirement had decreased from 1.0 to 0.6 in all infants. Mean airway pressure (Paw) with HFPPV was usually less than or equal to Paw during conventional ventilation. In spite of the often high level of PEEP used, pneumothorax occurred in only 2 infants and bronchopulmonary dysplasia in 1. Eighteen (72%) infants survived and none died of respiratory failure. The use of HFPPV might be beneficial in neonates with severe respiratory failure that responds poorly to conventional therapy.     

Hemodynamic effects of continuous positive-pressure ventilation and high-frequency jet ventilation with positive end-expiratory pressure in normal dogs

The hemodynamic effects of high-frequency jet ventilation (HFJV) at 60, 120, 240, and 480 breath/min, and conventional ventilation at 15 breath/min were compared in 6 anesthetized, paralyzed dogs, at 0, 10, and 20 cm H2O of positive end-expiratory pressure (PEEP). On HFJV at the same inspired oxygen, PaCO2, and PEEP levels, hemodynamic function improved significantly. Cardiac output was higher, whereas transmural CVP and pulmonary vascular resistances were lower. The improvement was primarily related to a decrease in mean airway pressure, particularly at higher PEEP levels. When PEEP was applied, hemodynamic function improved even when mean airway pressure was maintained constant. The findings suggest that lung volume was smaller during HFJV, and/or that lung volume changes during each respiratory cycle contributed to differences in venous return and ventricular function.     

同步间歇指令通气辅以压力支持治疗新生儿胎粪吸入综合征的效果与护理

目的探讨同步间歇指令通气（SIMV）联合压力支持（PS）对新生儿胎粪吸入综合征（NMAS）患儿的治疗效果及护理体会。方法将40例NMAS患儿按通气模式不同分为对照组和观察组各加例。对照组患儿接受SIMV,观察组患儿接受SIMV＋PS;观察两组患儿吸氧时间、机械通气时间及住院时间;观察治疗后平均动脉压（MABP）、平均气道压（MAP）及氧合指数（OI）的变化。结果观察组吸氧时间、机械通气时间、住院时间分别为（4．9±1．1）d,（65．7±7．0）h,（7．9±1．4）d,均低于对照组的（5．6±0．7）d,（75．1±9．2）h,（10．1±2．0）d,差异有统计学意义（t值分别为2．401,3．636,4．030;P〈0．05）;两组治疗前后MABP均较平稳;观察组治疗后36hMAP、01分别为（7．4±0．9）cmH2O,（4．7±1．8）,均低于对照组的（8．1±1．1）cmH：0,（10．1±3．4）,差异有统计学意义（t值分别为2．203,6．698;P〈0．05）。结论应用SIMV＋Ps,能改善患儿氧合,降低平均动脉压和气道压,利于早日脱机及减少通气总时间。严密观察患儿病情,做好气道护理可提高治疗效果。     

Strapless oral-nasal interface for positive-pressure ventilation

A custom-fabricated strapless oral-nasal interface (SONI) is described. It was used in the long-term administration of intermittent positive-pressure ventilation (IPPV) by 18 patients with paralytic or restrictive pulmonary insufficiency. This interface is an acrylic shell which is firmly fixed to an orthodontic bite plate; it is designed to form a seal over the nose and mouth for the entry of IPPV. Eight patients were ventilator dependent 24 hours a day. The ten patients who required only nocturnal aid had improvement in daytime arterial blood gases. Although nine of these patients could manage less than 15 minutes of unassisted breathing (free time) supine, all slept supine on SONI IPPV. The 13 patients who underwent sleep monitoring maintained a mean oxygen saturation of 95.3% +/- 1.7% and acceptable end-tidal pCO2 (30 to 45 mmHg). These 13 patients have used SONI IPPV for an average of 22 months (range = 3 to 63 months). Impediments to successful long-term use of a SONI include the presence of a hyperactive gag reflex or stimulation of excessive oral secretions. When combined with mouth IPPV, glossopharyngeal breathing, the intermittent abdominal pressure ventilator, or the cuirass ventilator for daytime use, SONI IPPV is an option for the patient who prefers total ventilatory support by noninvasive means.     

Beat frequencies in high-frequency positive-pressure ventilation

Amplitude modulation of the waveforms of several cardiovascular variables was investigated during high-frequency (1.3 to 3.3 Hz) positive-pressure ventilation (HFPPV). The amplitude modulation of the pulmonary artery pressure wave was most prominent and its beat frequency (BF) was equal to the difference between the heart rate and the ventilation rate. Spectral analysis of the pulmonary artery pressure demonstrated well-defined peaks associated with the BF. No significant physiologic changes in either cardiovascular or pulmonary function were attributable to the presence of the beat phenomenon.