Acute effects of ventilator settings on respiratory motor output in patients with acute lung injury

OBJECTIVE: During assisted mechanical ventilation, changes in ventilator settings may acutely affect the respiratory motor output via the mechanoreceptor reflex feedback system, thus interfering with patient management. This feedback system in mechanically ventilated patients with parenchymal lung injury remains largely unexplored. To investigate this, the early response of respiratory motor output to varying ventilator settings was determined in 13 sedated patients with acute lung injury. DESIGN: During assist/control and pressure support (PS) ventilation changes in (1) tidal volume (V(T)) at fixed inspiratory flow (V'(I)), (2) V'(I) at fixed V(T) and (3) PS level were employed and the response of respiratory motor output was followed for two breaths after the change. Respiratory motor output was assessed by total pressure generated by the respiratory muscles (Pmus), computed from esophageal pressure (Pes). RESULTS: Neural expiratory time increased with increasing V(T) and PS, while it remained constant with V'I changes. Neural inspiratory time (T(I)n) increased with decreasing V'(I) and PS, but was not affected by V(T) changes. None of the changes in ventilator settings influenced significantly the rate of rise of Pmus, used as an index of respiratory drive. The changes in respiratory timing resulted in significant changes in breathing frequency, which increased with decreasing V(T) and PS and increasing V'(I). The time integral of Pmus, an index of respiratory effort, increased with increasing T(I)n. These acute responses were not related to the severity of deterioration of respiratory system mechanics. CONCLUSIONS: We conclude that alterations in commonly used ventilator settings induce acute changes in respiratory timing, without affecting the respiratory drive. These changes, probably mediated via mechanoreceptor reflex feedback, are dependent on the type of the alteration in the ventilator settings.     

Effect of helium-oxygen (heliox) gas mixtures on the function of four pediatric ventilators

OBJECTIVE: To evaluate the effects of helium on the function of four ventilators commonly used in pediatrics: the Bird VIP, Bird VIP Gold, Servo 300, and Servo 900C. DESIGN: Prospective setting. SETTING: Research laboratory at a university hospital. SUBJECTS: Helium was administered as an 80:20 mixture of helium-oxygen through the air inlet of the ventilator. Delivered fraction of inspired oxygen (Fio(2)) was compared with the Fio(2) set on the blender dial. Inspiratory displayed tidal volume was recorded as an indicator of what the ventilator "believed" it had delivered and was compared with the V(T) displayed during ventilation with 100% oxygen (control). Actual delivered V(T) was measured by a Neonatal Bicore connected to the side port of a "bag-in-box" spirometer, making measurements independent of inspired gas properties, and was compared with V(T) delivered during ventilation with 100% oxygen. INTERVENTIONS: Five gas mixtures were evaluated: Fio(2) = 0.2, 0.4, 0.6, 0.8, and 1.0 (balance helium). MEASUREMENTS AND MAIN RESULTS: Delivered Fio(2) was less than set Fio(2) on the Servo 900C and VIP ventilators. V(T) displayed was minimally altered by helium during volume-controlled ventilation but substantially decreased during pressure-controlled ventilation, particularly with the Bird ventilators. During volume-controlled ventilation, V(T) delivered was substantially increased by helium with the Bird and, to a lesser degree, the Servo 900C ventilators. In contrast, V(T) delivered decreased slightly in helium with the Servo 300. The same pattern, but with a decreased magnitude, was observed for V(T) delivered during pressure-controlled ventilation. CONCLUSIONS: The addition of helium has a significant effect on Fio(2) delivery, displayed inspiratory V(T), and actual delivered V(T) during both volume- and pressure-controlled ventilation in four ventilators commonly used in pediatric critical care. These effects are both ventilator specific and ventilation mode specific, mandating vigilance during helium ventilation in clinical practice.     

A laboratory evaluation of 2 mechanical ventilators in the presence of helium-oxygen mixtures

BACKGROUND: Helium-oxygen (heliox) mixtures are being used more frequently with mechanical ventilators. Newer ventilators continue to be developed that have not yet been evaluated for safety and efficacy of heliox delivery. We studied the performance of 2 previously untested ventilators (Servo-i and Inspiration) during heliox administration. METHODS: We measured tidal volume (V(T)) delivery, gas blending, gas analyzing, and pressure stability in the presence of heliox. A heliox (80% helium/20% oxygen) tank was attached to the 50-psi air inlet. We compared the set V(T) (ie, set on the ventilator) and the exhaled V(T) (measured by the ventilator) to the delivered V(T) (measured with a lung model). Pressure measurements were also evaluated. We also compared the ventilator-setting fraction of inspired oxygen (F(IO(2))) to the F(IO(2)) measured by the ventilator and the F(IO(2)) measured with a supplemental oxygen analyzer. RESULTS: Heliox significantly affected both the exhaled V(T) measurement and the actual delivered V(T) (p < 0.001) with both the Servo-i and the Inspiration. Neither peak inspiratory pressure (in the pressure-controlled ventilation mode) nor positive end-expiratory pressure were adversely affected by heliox with either ventilator. Introducing heliox into the gas-blending systems caused only a small error in F(IO2) delivery and monitoring. CONCLUSIONS: Both Ventilators cycled consistently with heliox mixtures. In most cases, actual delivered V(T) can be reliably calculated if the F(IO2) and the set V(T) or the measured exhaled V(T) is known. With the Servo-i, at high helium concentrations the exhaled V(T) measurement was unreliable and caused a high-priority alarm condition that couldn't be disabled. A supplemental oxygen analyzer is not necessary with either device for heliox applications.     

Patient-ventilator interactions during volume-support ventilation: asynchrony and tidal volume instability--a report of three cases

During pressure-support ventilation, tidal volume (V(T)) can vary according to the level of the patient's respiratory effort and modifications of the thoraco-pulmonary mechanics. To keep V(T) as constant as possible, the Siemens Servo 300 ventilator proposes an original modification of pressure-support ventilation, called volume-support ventilation (VSV). VSV is a pressure-limited mode of ventilation that uses V(T) as a feedback control: the pressure support level is continuously adjusted to deliver a preset V(T). Thus, the ventilator adapts the inspiratory pressure level, breath by breath, to changes in the patient's inspiratory effort and the mechanical thoraco-pulmonary properties. The clinician sets V(T) and respiratory frequency, and the ventilator calculates a preset minute volume. It has been shown that ineffective respiratory efforts can occur during pressure-support ventilation.     

不同频率辅助通气对机械通气患者血流动力学的影响

目的探讨不同频率辅助通气对机械通气患者血流动力学的影响。方法选择重症加强治疗病房(ICU)尝试撤机阶段的12例危重病患者,机械通气模式均为双水平气道正压(BiPAP)通气,仅调整通气频率,保持吸气压力及呼气末正压(PEEP)不变,按随机原则将呼吸频率先后设置为5、10、15和20次/min,记录各设置调整20min后的呼吸力学、氧合及血流动力学指标变化。结果1随着设定呼吸频率的增加,平均气道压(Pmean)、控制通气分钟通气量(VEcontrol)逐渐增加,而自主呼吸分钟通气量(VEspont)则逐渐减少(P均<0.01),患者各呼吸频率间总的呼吸频率、分钟通气量(VE)均无明显变化,动脉血二氧化碳分压(PaCO2)、氧合指数(PaO2/FiO2)差异也无显著性(P均>0.05);2随着设定呼吸频率的降低,每搏量指数(SI)、心排血指数(CI)、全心舒张末期容积指数(GEDVI)、胸腔内血容积指数(ITBVI)显著增加(P均<0.01),但患者各呼吸频率间心率(HR)、中心静脉压(CVP)、平均动脉压(MAP)、体循环阻力指数(SVRI)及血管外肺水指数(EVLWI)相对恒定(P均>0.05);3CI与GEDVI呈显著正相关(r=0.569,P<0.01)。结论对于机械通气的患者,随着自主呼吸与控制通气比例的增加,心脏前负荷增加,心排血量增加。     

Adoption of lower tidal volume ventilation improves with feedback and education

OBJECTIVE: To determine whether feedback and education improve adoption of lung-protective mechanical ventilation (ie, with lower tidal volume [V(T)]). METHODS: We conducted a retrospective study of ventilator settings; we used data from 3 consecutive studies of patients with acute lung injury and/or acute respiratory distress syndrome, in the intensive care units of 2 university hospitals in the Netherlands. At site 1 we conducted a time series study of before and after education and feedback about lung-protective mechanical ventilation, and we compared the results from site 1 to the ventilation strategies used at site 2, which did not undergo the education and feedback intervention. Feedback and education consisted of presentations of actual ventilator settings, advised ventilator settings, and discussions on potential reasons for not using lower V(T). RESULTS: Two studies were performed at site 1, in 1999-2000 (Study 1, n = 22) and in 2002 (Study 2, n = 12). In 2003-2004, Study 3 was performed simultaneously at site 1 (n = 8) and site 2 (n = 17). At site 1, the mean +/- SD V(T) was 10.9 mL/kg predicted body weight (PBW) (95% CI 10.3-11.6) in Study 1 and 9.9 mL/kg PBW (95% CI 9.0-10.8) in Study 2 (difference not significant). After the feedback and education intervention at site 1, V(T) declined to 7.6 mL/kg PBW (95% CI 6.5-8.7) in Study 3 (p = 0.003). At site 2, where no feedback or education were given, V(T) was 10.3 mL/kg PBW (95% CI 9.5-11.0) in Study 3 (p < 0.001 vs Site 1). CONCLUSIONS: Adoption of a lower-V(T) ventilation strategy in patients with acute lung injury or acute respiratory distress syndrome is far from complete in the Netherlands. Adoption of a lower-V(T) strategy improves after feedback and education.     

Measurement of pulsatile tidal volume, pressure amplitude, and gas flow during high-frequency percussive ventilation, with and without partial cuff deflation

OBJECTIVE: With a high-frequency percussive ventilator and a mechanical lung model, to measure tidal volume (V(T)), pulsatile pressure amplitude (difference between peak and nadir pulsatile pressure [DeltaP];), and mean airway pressure (P (aw)) at various pulsatile frequencies, pulsatile inspiratory-expiratory ratios (I:E(p)), and pressures (measured at the interface between the pulse-generator and the endotracheal tube [P(vent)]). METHODS: With the endotracheal tube inside an artificial trachea, we manipulated the high-frequency percussive ventilation settings and adjuncts, including pulsatile frequency, I:E(p), and P(vent) by manipulating pulsatile flow. We also studied the effects of partially deflating the endotracheal tube cuff. We measured P (aw), pulsatile pressure amplitude at the carina (DeltaP(c)), and pulsatile V(T) at the carina. With the cuff partly deflated, we measured the fraction of inspired oxygen (F(IO(2))) in the gas efflux above and below the cuff. RESULTS: Increasing the pulsatile frequency from 300 cycles/min to 600 cycles/min and changing the I:E(p) from 1:3 to 1:1 significantly reduced V(T) (p < 0.001). P (aw) and DeltaP(c) were unaffected by the change in pulsatile frequency or I:E(p), except when we did not preserve the pulsatile flow. The measured V(T) range was from 19.1 mL (at 600 cycles/min) to 47.3 mL (at 300 cycles/min). Partial cuff deflation did not significantly reduce P (aw) or DeltaP(c), but it did significantly reduce V(T) and F(IO(2)). CONCLUSION: During high-frequency percussive ventilation, the pulsatile frequency is inversely related to V(T). Partial cuff deflation reduces the delivered F(IO(2)).     

Patient-ventilator synchrony during pressure-targeted versus flow-targeted small tidal volume assisted ventilation

PURPOSE: Low tidal volume (V(T)) delivered by flow-targeted breaths reduces ventilator-induced lung injury but may increase patient breathing effort because of limited flow. We hypothesized that a variable-flow, pressure-targeted breath would improve breathing effort versus a fixed flow-targeted breath. MATERIALS AND METHODS: We compared pressure assist-control ventilation and volume assist-control ventilation (VACV) in 12 patients with acute respiratory failure receiving 6 to 8 mL/kg V(T). Backup frequency, V(T), inspiratory time, applied positive end-expiratory pressure and fraction of inspired oxygen were held constant. Patient breathing effort was assessed by airway pressure (Paw) drop below baseline 0.1 second after the breath initiation (P(0.1)), the maximal Paw drop during the triggering phase (Ptr), the magnitude of ventilator work during flow delivery, and the presence of an active expiratory effort during cycling and air trapping judged by the magnitude of residual flow at end-expiration. RESULTS: Compared with VACV, pressure assist-control ventilation decreased P(0.1), Ptr (by 25% and 16%, respectively), and evidence for trapped gas but not ventilator work during flow delivery or cycle dys-synchrony. Peak inspiratory flow was comparable between the 2 modes. CONCLUSIONS: In patients receiving small V(T) VACV with increased breathing effort, variable-flow, pressure-targeted ventilation may provide more comfort by decreasing respiratory drive during the triggering phase.     

Work of breathing during lung-protective ventilation in patients with acute lung injury and acute respiratory distress syndrome: a comparison between volume and pressure-regulated breathing modes

BACKGROUND: Pressure-control ventilation (PCV) and pressure-regulated volume-control (PRVC) ventilation are used during lung-protective ventilation because the high, variable, peak inspiratory flow rate (V (I)) may reduce patient work of breathing (WOB) more than the fixed V (I) of volume-control ventilation (VCV). Patient-triggered breaths during PCV and PRVC may result in excessive tidal volume (V(T)) delivery unless the inspiratory pressure is reduced, which in turn may decrease the peak V (I). We tested whether PCV and PRVC reduce WOB better than VCV with a high, fixed peak V (I) (75 L/min) while also maintaining a low V(T) target. METHODS: Fourteen nonconsecutive patients with acute lung injury or acute respiratory distress syndrome were studied prospectively, using a random presentation of ventilator modes in a crossover, repeated-measures design. A target V(T) of 6.4 + 0.5 mL/kg was set during VCV and PRVC. During PCV the inspiratory pressure was set to achieve the same V(T). WOB and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100). RESULTS: There was a nonsignificant trend toward higher WOB (in J/L) during PCV (1.27 + 0.58 J/L) and PRVC (1.35 + 0.60 J/L), compared to VCV (1.09 + 0.59 J/L). While mean V(T) was not statistically different between modes, in 40% of patients, V(T) markedly exceeded the lung-protective ventilation target during PRVC and PCV. CONCLUSIONS: During lung-protective ventilation, PCV and PRVC offer no advantage in reducing WOB, compared to VCV with a high flow rate, and in some patients did not allow control of V(T) to be as precise.     

急性肺损伤患者血清肺表面活性物质蛋白A的变化及其意义

目的；动态观测急性肺损伤虱血清肺表面活性物质蛋白Ａ（ＳＰ－Ａ）的变化，并探讨其临床意义。方法：选择符合ＡＬＩ诊断标准并已给予机械通气治疗的患者２０例，于入组时和出组时抽取静脉血，多数患者在观察期间病情有明显变化时重复抽血，共收集静脉血标本７１例次；并同时记录动脉血气测值和呼吸机参数，计算动脉血氧分压与吸入气氧浓度比值和静态总呼吸顺应性。     

The effects of tidal volume demand on work of breathing during simulated lung-protective ventilation

BACKGROUND: Lung-protective ventilation (LPV) can result in a ventilator tidal volume (V(T)) below patient V(T) demand, which may elevate work of breathing (WOB). Increasing the ventilator inspiratory flow may not sufficiently reduce WOB, because the patient's flow-time requirements may exceed the ventilator's flow-time delivery pattern. We investigated (1) the effects of V(T) demand on WOB during LPV and (2) which ventilator pattern best reduced WOB while achieving LPV goals. METHODS: A standard WOB lung model simulated assisted breathing. Using 3 ventilators (Hamilton Veolar, Hamilton Galileo, and Dr?ger Evita 2 dura), we tested volume-control ventilation with a constant flow pattern (VCV-CF), volume-control ventilation with a decelerating flow (VCV-DF), and pressure-control ventilation (PCV). Simulated V(T) demand was increased from 50-125% of the ventilator-delivered V(T) (400 mL) as ventilator inspiratory time (T(I)) was decreased (0.95, 0.80, 0.65, and 0.45 s) relative to simulated T(I) (0.8 s). WOB was measured with a pulmonary mechanics monitor. RESULTS: During VCV-CF and VCV-DF, a V(T) demand of > or = 100% drastically increased WOB, attributable to imposed WOB from the inspiratory valve. Increasing inspiratory flow by using the decelerating flow pattern and/or decreasing T(I) reduced WOB, but generally not to normal levels. "Double-triggered" breaths, with excessive V(T) delivery, often occurred when ventilator T(I) was well below simulated T(I). PCV was most effective in reducing WOB, but V(T) delivery exceeded the LPV target unless T(I) was reduced. CONCLUSIONS: Given our dual goals of reducing both WOB and V(T) during LPV, VCV-DF with relatively brief T(I) appeared to be the best option, followed by PCV with a relatively brief T(I).     

Outcomes of patients admitted to a chronic ventilator-dependent unit in an acute-care hospital.

The outcomes in 61 patients admitted to a chronic ventilator-dependent unit (CVDU) at Saint Marys Hospital in Rochester, Minnesota, during an 18-month period are summarized. This unit was designed for patients who could not be weaned from mechanical ventilators after repeated attempts. Most patients had been ventilator dependent for more than 21 days, but some patients were admitted to the CVDU after briefer periods if special circumstances suggested that weaning from mechanical ventilation would be difficult. The unit was organized to provide a multidisciplinary approach to the general medical and respiratory management of these patients, including a physiologic evaluation of the respiratory system to determine the actual cause of ventilator dependence and complete medical, nursing, and psychosocial assessments to help adopt a plan of care and weaning from the ventilator. Of the numerous causes for ventilator dependence in this study group, chronic obstructive pulmonary disease was the most frequent underlying diagnosis. Of the 61 patients admitted to the CVDU, 58 survived, and 53 were liberated from the mechanical ventilator. Ultimately, 35 patients were dismissed directly home from the CVDU. Five of these patients required nocturnal mechanical ventilation. An additional eight patients were dismissed home after rehabilitation. After being weaned from mechanical ventilation, 11 patients were eventually transferred to nursing homes, and 3 additional patients were transferred to a local hospital or physical medicine unit. One patient remains in the CVDU. Thus, the CVDU has successfully liberated patients from ventilator dependence. In addition, because of a decreased need for nursing care, the unit has been cost-effective.     

Triggering of the ventilator in patient-ventilator interactions

With current ventilator triggering design, in initiating ventilator breaths patient effort is only a small fraction of the total effort expended to overcome the inspiratory load. Similarly, advances in ventilator pressure or flow delivery and inspiratory flow termination improve patient effort or inspiratory muscle work during mechanical ventilation. Yet refinements in ventilator design do not necessarily allow optimal patient-ventilator interactions, as the clinician is key in managing patient factors and selecting appropriate ventilator factors to maintain patient-ventilator synchrony. In patient-ventilator interactions, unmatched patient flow demand by ventilator flow delivery results in flow asynchrony, whereas mismatches between mechanical inspiratory time (mechanical T(I)) and neural T(I) produce timing asynchrony. Wasted efforts are an example of timing asynchrony. In the triggering phase, trigger thresholds that are set too high or the type of triggering methods induces wasted efforts. Wasted efforts can be aggravated by respiratory muscle weakness or other conditions that reduce respiratory drive. In the post-triggering phase, ventilator factors play an important role in patient-ventilator interaction; this role includes the assistance level, set inspiratory flow rate, T(I), pressurization rate, and cycling-off threshold, and to some extent, applied PEEP. This paper proposes an algorithm that clinicians can use to adjust ventilator settings with the goal to eliminate or reduce patients' wasted efforts.     

COPD机械通气患者运用NAVA技术的研究进展

慢性阻塞性肺疾病(COPD)患者由于存在呼吸受限、呼吸困难、气短等现象,常需进行机械通气治疗,但长期进行机械通气治疗会导致患者对呼吸机产生依赖,造成脱机困难,并造成肺损伤等系列并发症,对治疗产生不良影响。因此,需要优化通气模式,减少因通气过度或不足造成的不良影响。NAVA作为一种新型机械通气模式,可以通过收集监测到的膈肌电信号(Edi)触发呼吸机功能,根据患者实际需求调整通气量,更好实现人机同步。本文通过对COPD机械通气患者运用NAVA技术的最新进展进行研究、总结,以期为后续提高临床机械通气治疗效果提供参考依据。     

Peak pressures during manual ventilation

INTRODUCTION: Manual (bag) ventilation sometimes achieves better oxygenation than does a mechanical ventilator. We speculated that clinicians might generate very high airway pressure during manual ventilation (much higher than the pressure delivered by a mechanical ventilator), and that the high airway pressure causes alveolar recruitment and thus improves oxygenation. Such high pressure might injure alveoli in some patients. METHODS: We tested the hypothesis that manual ventilation may involve substantially higher pressure than is delivered by a mechanical ventilator. We asked experienced respiratory therapists to manually ventilate a lung model that was set to represent several typical clinical scenarios. RESULTS: We found that the peak airway pressure generated by the therapists was sometimes in excess of 100 cm H(2)O. CONCLUSIONS: The high airway pressure during manual ventilation would be considered extreme in the context of conventional mechanical ventilation, which raises questions about whether manual ventilation causes barotrauma.     

Evaluation of ventilators used during transport of ICU patients – a bench study

OBJECTIVES: To evaluate portable ventilators. DESIGN AND SETTINGS: Bench study. MATERIALS AND METHODS: Five portable ventilators used for transporting ICU patients [Osiris 1, (ventilator a), Osiris 2, (ventilator b), Oxylog 1000, (ventilator c), Oxylog 2000, (ventilator d), AXR1a, (ventilator e)] and three ICU ventilators which can be used for this purpose [Horus, (ventilator f), T-Bird, (ventilator g), and SV 300, (ventilator h)] were compared using a test lung regarding: 1) their capability to maintain set tidal volumes (V(T)) of 300 ml, 500 ml, and 800 ml under a normal condition A [resistance (R) 5 cmH(2)O/l/s and compliance (C) 100 ml/cmH(2)0] and two abnormal conditions B (R 20-C 30) and C (R 50-C 100); 2) trapped volume (expired V(T)relative to inspired V(T)at 0.7 s, 1 s, and 1.4 s), an estimate of the expiratory resistance of both circuit and valve; and 3) the triggering system assessed from the measurements of Delta t, Delta P for two inspiratory efforts at a PEEP of 0 cmH(2)0 and 5 cmH(2)0 in ventilators b, d, f, g, and h. Flow and airway pressure were measured with an independent physiologic recording system. RESULTS: 1) V(T). For ventilators a-h, the mean+/-SD changes of a set V(T)of 300 ml were -2.6+/-0.2%, -9.7+/-0.2%, 0+/-0%, -6.1+/-0.2%, 1.0+/-0.3%, -2.1+/-1.7%, 0.3+/-0%, and -1.3+/-0.1% ( P<0.001), respectively, during condition B relative to A. Similar results were obtained for a V(T)of 500 ml and 800 ml and during condition C relative to A; 2) Trapped volume. For ventilators a-h, trapped volume averaged 1+/-1%, 20+/-0%, 30+/-0.4%, 20+/-1%, 1+/-0%, 19+/-0%, 15+/-0%, and 14+/-0% at 0.7 s ( P <0.001) and 0.6+/-0%, 5+/-0%, 0.5+/-0%, 0+/-0%%, 0+/-0%, 0.6+/-0%, 0+/-0%, and 0+/-0% at 1.4 s ( P=NS); and 3) the triggering system of Oxylog 2000 was poor whereas it was of good quality for Horus, T-Bird, SV 300, and Osiris 2. CONCLUSIONS: The small portable ventilators presently investigated varied between each other and were less accurate than ICU ventilators.     

Clients' experiences of living at home with a mechanical ventilator

Title.  Clients' experiences of living at home with a mechanical ventilator.
Aim.  This paper reports on a study of how clients experience living with home mechanical ventilation and how they experience care and supervision of healthcare personnel.
Background.  The number of people living at home with mechanical ventilators is increasing, and this is considered a successful approach to reducing incapacity and mortality.
Method.  Qualitative interviews were conducted with 10 service users in 2006. The informants were 18–75 years old and had varying diagnoses and levels of functioning. The interviews were tape recorded, transcribed and analysed by qualitative content analysis.
Findings.  Two main themes emerged: Theme 1. Having a home ventilator enhances quality of life – a life worth living. The ventilator treatment builds up strength and improves well-being. Participants emphasized that it was important to feel in control of their own situation and had an overriding wish to live a normal and active life; Theme 2. Competence and continuity of healthcare personnel are factors for success. The experience was that competence and follow-up by healthcare personnel varied, and that good quality teaching and information were important.
Conclusion.  Users of home mechanical ventilators should be active partners in their own care so that their experience is taken into account. It is important for clients having home mechanical ventilation to be empowered and have control in their daily lives, as well as having competent caregivers and continuity of care.     

Effects of continuous, expiratory, reverse, and bi-directional tracheal gas insufflation in conjunction with a flow relief valve on delivered tidal volume, total positive end-expiratory pressure, and carbon dioxide elimination: a bench study

INTRODUCTION: Tracheal gas insufflation (TGI) can increase total positive end-expiratory pressure (total-PEEP) when flow is delivered in a forward direction, necessitating adjustments to maintain total-PEEP constant. When TGI is delivered throughout the respiratory cycle, additional adjustments are needed to maintain tidal volume (V(T)) constant. OBJECTIVE: Determine if bi-directional TGI (bi-TGI) (simultaneous flows toward the lungs and upper airway) in combination with a flow relief valve eliminates the increase in total-PEEP and maintains a constant V(T), thus simplifying TGI administration. METHODS: Using an artificial lung model and pressure control ventilation, we studied the effect of TGI at 10 L/min on inspired V(T), total-PEEP, and CO(2) elimination during 6 conditions: (1) control (no TGI, no catheter in the airway), (2) baseline (catheter in the airway but no TGI), (3) continuous TGI, (4) expiratory TGI, (5) reverse TGI, and (6) bi-TGI. Each condition was studied under 3 inspiration-expiration ratios (1:1, 1:2, and 2:1). A preset flow relief valve was inserted into the ventilator circuit during all TGI conditions with continuous flow. SETTING: University research laboratory. RESULTS: CO(2) elimination efficiency was similar under all conditions. Total-PEEP increased with continuous TGI and expiratory TGI, decreased during reverse TGI, and was unchanged during bi-TGI. With the flow relief valve in place, and no adjustment in mechanical ventilation, the change in minute ventilation ranged from 0% to 10%, with the least change during bi-TGI (0-5%). During bi-TGI, gas flow was equivalent in both directions during dynamic conditions and the flow relief valve consistently removed gas at 10 L/min under various pressures. CONCLUSIONS: Our data from an artificial lung model support that continuous bi-TGI minimizes the change in total-PEEP seen during other TGI modalities. The flow relief valve compensated for the extra gas volume delivered by the TGI catheter, thereby eliminating the need to make ventilator adjustments. Used in combination with a flow relief valve, bi-TGI appears to offer unique advantages by providing a simpler method to deliver TGI. Further testing is indicated to determine if similar benefits occur in the clinical setting.     

Long-term home mechanical ventilation in the United States

Patients requiring prolonged mechanical ventilation are rapidly increasing in number. Improved ICU care has resulted in many patients surviving acute respiratory failure to require prolonged mechanical ventilation during convalescence. Also, mechanical ventilation is increasingly used as a therapeutic option for patients with symptomatic chronic hypoventilation, with an increased effort to predict nocturnal hypoventilation to initiate ventilation earlier. There are continued efforts by ventilator manufacturers to improve home ventilators. These factors point to a likely increase in the number of patients receiving home mechanical ventilation in the United States. Unfortunately, there are no comprehensive databases or national registry of home ventilator patients-therefore the number of home ventilator patients is unknown. There are real challenges to providing mechanical ventilation in the home, which include caregiver training, adequacy of respiratory care, and reimbursement.