Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation.

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.

The evidence for secretion clearance techniques.

Many acute and chronic respiratory diseases are associated with increased respiratory secretions in the airways. Narrative reviews and a few systematic reviews of secretion clearance techniques have been published. These reviews raise concerns regarding the lack of evidence to support the various secretion clearance techniques. I conducted a comprehensive MEDLINE search of the following subjects: chest physical therapy, chest physiotherapy, postural drainage, forced expiratory technique, autogenic drainage, high-frequency chest wall compression, flutter device and secretions, positive expiratory pressure and secretions, intrapulmonary percussion, mechanical in-exsufflation and secretions. This was followed by a comprehensive search of cross-references to identify additional studies. The results of this review are reported herein. There are a number of methodological limitations of the literature reporting studies of the use of secretion clearance techniques. Most of the studies were small, most used crossover designs, and few used sham therapy. Many studies were limited to short-term outcomes such as sputum clearance with a single treatment session. Despite the clinical observation that retained secretions are detrimental to respiratory function and despite anecdotal associations between secretion clearance and improvements in respiratory function, there is a dearth of high-level evidence to support any secretion clearance technique.

Evaluation of inspiratory rise time and inspiration termination criteria in new-generation mechanical ventilators: a lung model study.

INTRODUCTION: Inspiratory rise time adjustment during pressure ventilation and inspiration termination criteria adjustment during pressure support ventilation are available on some of the newest mechanical ventilators. Both are designed to improve patient-ventilator synchrony. However, the function of these adjuncts during pressure ventilation on these ventilators has not been evaluated. METHODS: Three inspiratory rise times (minimum, medium, and maximum) were evaluated in 5 new-generation mechanical ventilators (Hamilton Galileo, Siemens 300A, Puritan Bennett 840, BEAR 1000, and Dräger Evita 4) during pressure support and pressure assist/control. Three inspiration termination criteria settings (minimum, medium, and maximum) were also evaluated in 2 mechanical ventilators (Hamilton Galileo and Puritan Bennett 840) during pressure support. All evaluations were performed with a spontaneous breathing lung model (compliance 50 mL/cm H2O, resistance 8.2 cm H2O/L/s, respiratory rate 12 breaths/min, inspiratory time 1.0 s, and lung model peak inspiratory flow 60 L/min). Throughout the evaluation, inspiratory pressure was set at 15 cm H2O and positive end-expiratory pressure at 5 cm H2O, resulting in a peak airway pressure of 20 cm H2O. RESULTS: Significant (p < 0.05) and important (> 10%) differences were found among the ventilators at similar rise times (minimum, medium, and maximum) and for each ventilator as rise time was varied. Also, significant (p < 0.05) and important (> 10%) differences were observed between ventilators and within each ventilator when inspiration termination criteria were varied. There were significant (p < 0.05) differences between pressure support and pressure assist/control, but most were < 10%, except those associated with expiration. CONCLUSIONS: Major differences exist for each ventilator as rise time or inspiration termination criteria are varied and among ventilators at similar settings. Inspiration termination criteria adjustment markedly affects transition to exhalation in the Puritan Bennett 840.

Heliox delivery with noninvasive positive pressure ventilation: a laboratory study.

BACKGROUND: There is clinical interest in the use of heliox (helium-oxygen mixture) during noninvasive positive pressure ventilation (NPPV), but delivery of heliox with ventilators designed for NPPV has not been reported. We studied helium concentration ([He]) when an 80%:20% helium:oxygen mixture (heliox) was used with 5 NPPV ventilators (Knightstar, Quantum, BiPAP S/T-D30, Sullivan, and BiPAP Vision). METHODS: A simulated spontaneous breathing lung model was connected to the ventilators with a circuit incorporating a standard leak. Heliox flows of 0, 5, 10, and 18 L/min and oxygen flows of 0 and 10 L/min were titrated into the system at either a proximal position near the lung model or a distal position near the ventilator (titration method). Because the BiPAP Vision has an oxygen delivery module, it was also studied using heliox connected to the air inlet of an oxygen blender, with the blender outlet connected to the oxygen module of the ventilator (blender method). All ventilators were evaluated in spontaneous/timed mode at inspiratory/expiratory pressures of 10/5, 15/5, and 20/5 cm H(2)O. After 5 minutes, [He], oxygen concentration, and pressure in the lung model were recorded. RESULTS: Heliox flow, NPPV settings, site of heliox infusion, and type of ventilator significantly (p < 0.05) affected [He]. [He] was > 60% when heliox flow was 18 L/min in some combinations of settings. The BiPAP S/T-D30 and Quantum occasionally functioned erratically. The BiPAP Vision (blender method) ventilator performed erratically with heliox unless the exhalation port test was bypassed on startup. The addition of heliox flow had no important effect on inspiratory or expiratory positive airway pressure on those breaths during which the ventilators functioned correctly. CONCLUSION: Heliox flow was the most important determinant of [He] when using heliox with NPPV. With heliox there was a potential for ventilator malfunction in some conditions. The clinical implications of these findings remain to be determined.

Tracheal gas insufflation and related techniques to introduce gas flow into the trachea.

Over the past 50 years, a variety of techniques have been developed that have in common the insufflation of gas into the central airway to facilitate carbon dioxide (CO2) clearance. These include continuous insufflation of oxygen, transtracheal jet ventilation, high frequency jet ventilation, transtracheal oxygen administration, intratracheal pulmonary ventilation, and tracheal gas insufflation (TGI). Continuous insufflation of oxygen is a technique used to enhance CO2 removal in the presence of apnea. Transtracheal jet ventilation and high frequency jet ventilation promote bulk gas flow into the lungs. Some techniques, such as transtracheal oxygen administration, provide insufflation of oxygen as an adjunct to spontaneous ventilation. However, other techniques, such as TGI, are used as an adjunct to positive pressure ventilation. Intratracheal pulmonary ventilation provides positive pressure ventilation while bypassing the upper airway. Although some of these techniques are promising adjuncts to mechanical ventilation and may help reduce ventilator-associated lung injury, much remains to be learned about their role in the care of patients with acute lung injury.

Ventilator-induced lung injury and the evolution of lung-protective strategies in acute respiratory distress syndrome.

Traditional ventilator management of acute respiratory distress syndrome (ARDS), emphasizing normalization of blood gases, promoted high rates of conventional barotrauma. Research revealed a broader range of ventilator-induced lung injury, physiologically and histopathologically indistinguishable from ARDS itself. It is now known that overdistention and cyclic inflation of injured lung can exacerbate lung injury and probably promote systemic inflammation, effects minimized by low tidal volumes/plateau pressures and by application of positive end-expiratory pressure. No compelling data suggest a safe interval for nonprotective ventilation in humans; historically defined "low" tidal volumes may remain excessive for certain patients. Protective ventilation, however, entails carbon dioxide accumulation ("permissive hypercapnia"). Despite extensive study, debate remains, even over whether consequent respiratory acidosis is harmful, tolerable with physiologic adaptation, or intrinsically adaptive. Its gross systemic effects seem generally tolerated by critically ill patients; however, subsets, including those with ischemic heart disease, left or right heart failure, pulmonary hypertension, or cranial injury, may be at higher risk. In controlled trials demonstrating mortality benefit from lung-protective ventilation, acidosis was more tightly controlled than in negative studies. Decreased acidosis-associated dyspnea probably explains reduced use of sedatives and paralytics noted in those trials. There may thus be disparate goals in ARDS management: rapid institution of a restrictive ventilatory strategy, and avoidance of significant acidosis. We review data pertaining to ARDS physiology, ventilator-induced lung injury, lung-protective ventilatory strategies, and the physiology of respiratory acidosis. Tracheal gas insufflation is considered as a means to reconcile the clinical goals of ventilatory reduction and control of acidosis.

Pressure support and pressure assist/control: are there differences? An evaluation of the newest intensive care unit ventilators.

BACKGROUND: Pressure support (PS) has been widely studied in both patients and lung models, but there is little data available evaluating pressure assist/control (P A/C, frequently referred to as PCV) and no data comparing the operational capabilities of these two modes on the newest generation of ICU ventilators. We used a spontaneously breathing lung model to evaluate the response of the following new generation ventilators to varying inspiratory demand in both PS and P A/C: Bear 1000, Dräger Evita 4, Hamilton Galileo, Nellcor Puritan-Bennett 840 and 740, Siemens Servo 300A, TBird AVS. METHODS: A bellows-in-a-box lung model was set at a respiratory rate of 12 breaths/min, inspiratory time of 1.0 second, and peak inspiratory flows (modified square wave) of 40, 60, and 80 L/min. Each ventilator was set at three levels of PS and P A/C: 10, 15, and 20 cm H(2)O. On all ventilators, flow-triggering was set as sensitive as possible without causing self-triggering. RESULTS: Trigger pressure, trigger pressure-time product, inspiratory trigger time delay, ventilator-delivered peak flow, inspiratory area as a percent of the ideal inspiratory area, expiratory time delay, supraplateau expiratory pressure change, and expiratory area all varied among ventilators and at different lung model peak flows (p < 0.01 and >/= 10% difference). However, PS and P A/C on a given ventilator only differed with regard to expiratory variables (p < 0. 01 and >/= 10% difference). CONCLUSION: In a given ventilator little difference exists in gas delivery and response variables between PS and P A/C, but performance differences do exist among the ventilators evaluated. Ventilator performance is diminished at high lung model peak flows and low pressure settings. (I)), whereas PS gives control over ending inspiration to the patient. What has not been clearly defined is the gas delivery and ventilator response differences, if any, between these two (PS and P A/C) pressure targeted assist modes. Most new generation intensive care unit (ICU) ventilators provide both pressure support (PS) and pressure assist/control (P A/C) ventilation.19,20 The specific operational difference between these two modes is the mechanism that transitions inspiration to expiration. With pressure support the primary mechanism is a decrease in peak inspiratory flow to a predetermined level, whereas with P A/C mechanical T(I) is preset.19,20 We compared the operation of seven of the newest generation ICU ventilators in a spontaneously breathing lung model in both PS and P A/C. We hypothesized that there would be no difference in variables assessed between PS and P A/C except for the transition to expiration and that there would be no difference in response among ventilators evaluated.

Nitric oxide delivery during high-frequency oscillatory ventilation.

BACKGROUND: Inhaled nitric oxide (NO) is used increasingly in the care of infants with hypoxemic respiratory failure and is frequently combined with high-frequency oscillation (HFO). The aim of this study was to evaluate delivery of NO during HFO using titration into the ventilator circuit or using the INOvent Delivery System. METHODS: NO was delivered into the HFO circuit at three sites (pre-humidifier, post-humidifier, and after the bellows) by continuous titration using a rotameter. The target NO concentration ([NO]) was initially adjusted using a rapid-response chemiluminescence NO analyzer without oscillation at 5, 10, and 20 parts per million (ppm). During the study, gas was sampled 5 cm from the bellows (proximal), 35 cm from the bellows (middle), and at the distal end of the circuit (distal). The ventilator was set at frequencies of 5, 10, and 15 Hz, mean airway pressures of 15, 20, and 25 cm H(2)O, and amplitudes of 20, 30, and 40 cm H(2)O. Soft and hard circuits were evaluated. The fraction of inspired oxygen was 0. 90, the inspiratory time fraction was 33%, and the bias flow was 20 L/min throughout the study. An INOvent Delivery System was also evaluated with the same HFO settings. RESULTS: The fluctuation of [NO] was minimal with continuous titration pre-humidifier at all HFO settings. [NO] fluctuated with titration post-humidifier and after the bellows, especially at the proximal sampling site. At the lung model, however, fluctuation of [NO] was always < 1.5 ppm and usually < 1 ppm. Delivered [NO] was lower than target [NO] with injection after the bellows (> 5%). The soft circuit showed better mixing of NO than the hard circuit. The INOvent Delivery System delivered a stable and accurate [NO] at all settings. [NO(2)] was < 1 ppm at all settings. CONCLUSIONS: Mixing of NO during HFO was acceptable at all the injection sites evaluated, although injection pre-humidifier was preferable because of small fluctuations of [NO]. The INOvent Delivery System was simple to use and delivered an accurate and precise [NO] during HFO.

Nebulizers: principles and performance.

Nebulizers have been used clinically for many years. Despite the increasing use of metered-dose inhalers and dry powder inhalers, it is likely that nebulizers will continue to be used in selected patients. A number of factors affect nebulizer performance, and these should be appreciated by clinicians who use these devices. Several new designs have recently become available that improve the performance of the nebulizer, but their cost-effectiveness remains to be determined.

Pulmonary epitheloid hemangioendothelioma: a peculiar rare tumor of vascular origin.

An extremely rare case of pulmonary epitheloid hemangioendothelioma (PEH), previously known as intravascular bronchoalveolar tumor (IVBAT), in a 38-year-old female is presented. This patient had a history of rheumatoid arthritis and bilateral multiple small pulmonary nodules which progressed over the years. The histopathological diagnosis of PEH was confirmed by immunohistochemical stains. Prognosis of this tumor is very unpredictable. There is no effective treatment for pulmonary epitheloid hemangioendothelioma.

An objective analysis of the pressure-volume curve in the acute respiratory distress syndrome.

To assess the interobserver and intraobserver variability in the clinical evaluation of the quasi-static pressure-volume (P-V) curve, we analyzed 24 sets of inflation and deflation P-V curves obtained from patients with ARDS. We used a recently described sigmoidal equation to curve-fit the P-V data sets and objectively define the point of maximum compliance increase of the inflation limb (P(mci, i)) and the true inflection point of the deflation limb (P(inf,d)). These points were compared with graphic determinations of lower Pflex by seven clinicians. The graphic and curve-fitting methods were also compared for their ability to reproduce the same parameter value in data sets with reduced number of data points. The sigmoidal equation fit the P-V data with great accuracy (R(2) = 0.9992). The average of Pflex determinations was found to be correlated with P(mci,i) (R = 0.89) and P(inf,d) (R = 0.76). Individual determinations of Pflex were less correlated with the corresponding objective parameters (R = 0.67 and 0.62, respectively). Pflex + 2 cm H(2)O was a more accurate estimator of P(inf,d) (2 SD = +/-6.05 cm H(2)O) than Pflex was of P(mci,i) (2 SD = +/-8.02 cm H(2)O). There was significant interobserver variability in Pflex, with a maximum difference of 11 cm H(2)O for the same patient (SD = 1.9 cm H(2)O). Clinicians had difficulty reproducing Pflex in smaller data sets with differences as great as 17 cm H(2)O (SD = 2.8 cm H(2)O). In contrast, the curve-fitting method reproduced P(mci,i) with great accuracy in reduced data sets (maximum difference of 1.5 cm H(2)O and SD = 0.3 cm H(2)O). We conclude that Pflex rarely coincided with the point of maximum compliance increase defined by a sigmoid curve-fit with large differences in Pflex seen both among and within observers. Calculating objective parameters such as P(mci,i) or P(inf,d) from curve-fitted P-V data can minimize this large variability.

Noninvasive positive pressure ventilation for acute respiratory failure.

NPPV is useful in decreasing the intubation rate in carefully selected patients with acute respiratory failure. This is particularly the case for patients with COPD. The results of some studies also suggest a survival benefit for use of NPPV with acute respiratory failure associated with COPD. More severely ill patients and those with excessive secretions, altered neurological status, or hemodynamic compromise may be less likely to successfully respond to NPPV. The initial PaCO2 change and mask tolerance may be predictors of success. It is unknown whether technical issues such as type of ventilator, choice of pressure versus volume ventilation, and nasal versus full facial mask affect outcome for NPPV. Although initiation of mask ventilation may be labor intensive, this effort may add value by avoiding the morbidity and mortality associated with intubation.

The effect of heliox on nebulizer function using a beta-agonist bronchodilator.

OBJECTIVE: To evaluate nebulizer performance when heliox was used to power the nebulizer. METHODS: Conventional and continuous nebulizer designs were evaluated. The conventional nebulizer was used with 5 mg albuterol and flows of 8 L/min air, 8 L/min heliox, and 11 L/min heliox; it was also used with 10 mg albuterol and a heliox flow of 8 L/min. The continuous nebulizer was set to deliver 10 mg of albuterol over 40 min at flows of 2 L/min air, 2 L/min heliox, and 3 L/min heliox; it was also used with 20 mg albuterol and a heliox flow of 2 L/min. A cotton plug at the nebulizer mouthpiece was used to trap aerosol during simulated spontaneous breathing. The amount of albuterol deposited on the cotton plug was determined spectrophotometrically. Particle size was determined using an 11-stage cascade impactor. RESULTS: For both nebulizer designs, particle size and inhaled mass of albuterol decreased significantly (p < 0.001) when the nebulizer was powered with heliox rather than air. When powered with heliox, the reduction in inhaled mass of albuterol was less for the conventional nebulizer (16%) than the continuous nebulizer (67%). The nebulization time, however, was more than twofold greater with heliox (p < 0.001). Increasing the flow of heliox increased the particle size (p < 0.05), inhaled mass of albuterol (p < 0.05), and inhaled mass of particles 1 to 5 microm (p < 0.05) to levels similar to powering the nebulizer with air at the lower flow. Increasing the albuterol concentration in the nebulizer and using the lower heliox flow increased the inhaled mass of albuterol (p < 0.05) while maintaining the smaller particle size produced with that flow. CONCLUSIONS: The use of heliox to power a nebulizer affects both the inhaled mass of medication and the size of the aerosol particles. The flow to power the nebulizer should be increased when heliox is used.

Mechanical ventilation of the patient with chronic obstructive pulmonary disease.

Mechanical ventilation of the patient with COPD is a balance between avoiding overdistension, auto-PEEP, providing adequate gas exchange, and allowing patient-ventilator synchrony. Figure 13 shows an approach that the authors have found helpful to achieve these goals.

Perceptions of control, physical exercise, and psychological adjustment to breast cancer in South African women.

Psychological adjustment and locus of control were measured in 257 South African women both with and without breast cancer. Adjustment was defined as positive affect, negative affect, the balance between the two, satisfaction with various domains of life, and an overall sense of well-being. Health locus of control was measured separately for internal, external, and chance loci. The instrument's reliability was comparable to that reported for U.S. norms. The women with breast cancer reported significantly lower affect and had lower internal and higher external and chance perceptions of control. The more invasive the surgical treatment, the greater the negative impact on adjustment. Data suggested that using written instructions to stress the importance of exercise to rebuild arm strength immediately following the surgery had a long-lasting positive impact on affect. Side of intervention was also related to psychological adjustment. Significant differences across racial groups were found for both adjustment and health locus of control.

Prehospital use of a prototype esophageal detection device: a word of caution!

OBJECTIVE: To determine the effectiveness of a prototype esophageal detection device (EDD) during use in the prehospital setting. DESIGN/SETTING: Prospective convenience sample in a prehospital setting. POPULATION: Intubated adult patients. INTERVENTIONS: The study device was used to determine esophageal or endotracheal placement of endotracheal tubes in intubated patients. Clinical means were used to confirm tube location. A data sheet was completed for each patient. RESULTS: Of 105 uses of the device, 17 of 17 esophageal tubes were identified correctly (100% sensitivity). Sixty-five of 88 tracheal tubes were correctly identified (78% specificity). There was intermediate reinflation of the device on 13 of the 65 tracheal tubes. Five tests were indeterminate. There were no false negatives (negative predictive value 100%), but 18 false positives (positive predictive value 48%). CONCLUSION: This prototype EDD adequately identifies esophageally placed endotracheal tubes. Correct identification of endotracheally placed tubes was less sensitive. Much work needs to be done regarding the use of negative aspiration devices to identify placement of endotracheal tubes.