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Biomedical subjects

R M Kacmarek

Publications and source records attributed to R M Kacmarek.

At least 19 recordsLinked to original sources
PubMed1997

Evaluation of electrochemical nitric oxide and nitrogen dioxide analyzers suitable for use during mechanical ventilation.

OBJECTIVE: Inhaled nitric oxide (NO) is increasingly being used in the treatment of diseases characterized by hypoxemia and pulmonary hypertension. To avoid complications, accurate quantitative analysis of NO and NO2 is necessary during this therapy. We evaluated the accuracy of electrochemical NO and nitrogen dioxide (NO2) analyzers suitable for use during mechanical ventilation. METHODS: We evaluated six electrochemical NO analyzer brands (Bedfont, B & W, Dräger, EIT, Pulmonox, Saan). All were calibrated and used per manufacturer's specifications. An adult mechanical ventilator was used to produce serial dilutions of NO with O2 for [NO] of 0-80 ppm. F1O2 settings of 0.90, 0.70, 0.50, 0.30, and 0.21 were used. Settings of low, moderate, and high ventilation pressures were evaluated. Gas was sampled from the inspiratory limb of the ventilator circuit using either a sidestream or mainstream technique. [NO] was also measured using a calibrated chemiluminescence analyzer. For the analyzers that measured NO2, serial dilutions of 8.5 ppm NO2 with O2 were analyzed using chemiluminescence and the electrochemical analyzers. RESULTS: Bias +/- precision for [NO] by individual devices ranged from 1.8 +/- 1.9 ppm to -1.0 +/- 0.7 ppm. There were significant differences in the bias between analyzers (P < 0.001), pressure settings (P < 0.001), and NO level (P < 0.017). The difference in bias between levels of F1O2 was not significant (P = 0.062). Bias +/- precision for NO2 ranged from 0.18 +/- 0.12 ppm to -0.14 +/- 0.13 ppm, with a significant difference between analyzers (P < 0.001). CONCLUSIONS: The bias and precision of these analyzers was acceptable for clinical use. The devices tended to be most accurate at [NO] < or = 20 ppm-the clinical conditions at which NO is most commonly used.

Administration, Inhalation↗
PubMed1997

Inaccuracies of nitric oxide delivery systems during adult mechanical ventilation.

BACKGROUND: Various systems to administer inhaled nitric oxide (NO) have been used in patients and experimental animals. We used a lung model to evaluate five NO delivery systems during mechanical ventilation with various ventilatory patterns. METHODS: An adult mechanical ventilator was attached to a test lung configured to separate inspired and expired gases. Four injection systems were evaluated with NO injected either into the inspiratory circuit 90 cm proximal to the Y piece or directly at the Y piece and delivered either continuously or only during the inspiratory phase. Alternatively, NO was mixed with air using a blender and delivered to the high-pressure air inlet of the ventilator. Nitric oxide concentration was measured from the inspiratory limb of the ventilator circuit and the tracheal level using rapid- and slow-response chemiluminescence analyzers. The ventilator was set for constant-flow volume control ventilation, pressure control ventilation, pressure support ventilation, or synchronized intermittent mandatory ventilation. Tidal volumes of 0.5 l and 1 l were evaluated with inspiratory times of 1 s and 2 s. RESULTS: The system that premixed NO proximal to the ventilator was the only one that maintained constant NO delivery regardless of ventilatory pattern. The other systems delivered variable NO concentration during pressure control ventilation and spontaneous breathing modes. Systems that injected a continuous flow of NO delivered peak NO concentrations greater than the calculated dose. These variations were not apparent when a slow-response chemiluminescence analyzer was used. CONCLUSIONS: NO delivery systems that inject NO at a constant rate, either continuously or during inspiration only, into the inspiratory limb of the ventilator circuit produce highly variable and unpredictable NO delivery when inspiratory flow is not constant. Such systems may deliver a very high NO concentration to the lungs, which is not accurately reflected by measurements performed with slow-response analyzers.

Adult↗
PubMed1997

Unloadiing of the work of breathing by proportional assist ventilation in a lung model.

OBJECTIVES: Proportional assist ventilation is devised to increase airway pressure in proportion to inspiratory effort. A systematic study of the performance of this new mode of ventilation has not been presented. We tested in the laboratory the capability of proportional assist ventilation to unload the work of breathing in proportion to ventilatory drive, under a variety of mechanical loads. DESIGN: During variations of "ventilatory drive" (i.e., tidal volume), unloading of the work of breathing by proportional assist ventilation was contrasted with unloading by pressure-support ventilation. SETTING: The respiratory laboratory of a university-affiliated teaching hospital. SUBJECT: A bellows-in-a-box lung model, powered by a sine wave air flow generator. INTERVENTIONS: Proportional assist and pressure-support ventilation were preset to provide comparable support at a baseline "ventilatory drive" of 0.7-L tidal volume. The set levels of proportional assist and pressure-support ventilation were subsequently applied to five tidal volumes, from 0.2 to 1.2 L. Three levels of inspiratory support and three settings of mechanical load were evaluated. MEASUREMENTS AND MAIN RESULTS: Proportional assist ventilation significantly (p < .05) reduced the work of breathing of the lung model at all but the lowest tidal volume (0.2 L). The preset proportion of ventilatory support (30%, 50%, and 70%) unloaded the work of breathing uniformly as ventilatory drive was varied at tidal volumes of > or = 0.5 L, but not always at tidal volumes of < or = 0.4 L. In contrast, pressure-support ventilation overassisted low tidal volumes and underassisted high tidal volumes (p < .05). CONCLUSIONS: In a lung model, a prototype system delivering proportional assist ventilation provided uniform unloading of the work of breathing as the ventilatory drive was varied within a tidal volume range of 0.5 to 1.2 L. These findings confirm the theoretical modeling of proportional assist ventilation. This system, however, failed to properly unload low tidal volumes of 0.2 to 0.4 L.

Humans↗
PubMed1996

Inhaled nitric oxide. A bronchodilator in mild asthmatics with methacholine-induced bronchospasm.

Nitric oxide (NO) reduces airway tone in the methacholine-treated guinea pig. We examined whether low levels of inhaled NO gas would relax airway smooth muscle tone in patients with mild asthma subjected to methacholine-induced bronchospasm. Thirteen adult volunteers with mild asthma inspired increasing concentrations of methacholine until their baseline forced expiratory volume in one second (FEV1, 3.29 +/- 0.17 L, mean +/- SEM) decreased by > or = 20% (2.33 +/- 0.18 L, p < 0.01). Thereafter, they sequentially inhaled 100 parts per million (ppm) NO, 40% O2; 40% O2; and 100 ppm NO, 40% O2 while spirometry was performed. Subsequent inhalation of isoproterenol returned the FEV1 levels to baseline. Inhaling 100 ppm NO increased FEV1 to 2.66 +/- 0.18 L (p < 0.01), and this increase was maintained after NO was discontinued. FEV1 did not change during the second period of NO inhalation. Similar results were observed for vital capacity, but no significant effect was noted on forced expiratory flow at 25% of vital capacity or peak expiratory flow. Subjects were then divided into a responder subgroup, which showed a mean increase in FEV1 after initial NO inhalation of 560 +/- 150 ml, and a nonresponder subgroup, which showed a mean increase in FEV1 of 129 +/- 29 ml. Our data suggest that inhalation of nitric oxide by patients with mild asthma with methacholine-induced bronchospasm results in a minor but significant relaxation of airway tone.

Administration, Inhalation↗
PubMed1996

Tracheal gas insufflation-pressure control versus volume control ventilation. A lung model study.

Tracheal gas insufflation (TGI) has been recommended as an adjunct to mechanical ventilation in the presence of elevated Pa CO2. Based on our initial clinical experience with continuous flow TGI and pressure control ventilation (PCV), we were concerned about elevation in peak airway pressure as TGI was applied. In a lung model, we evaluated the effects of continuous flow TGI during both PCV and volume control ventilation (VCV). A single compartment lung model was configured with an artificial trachea into which an 8-mm endotracheal tube was positioned. TGI was established with a 16-G catheter positioned 2 cm beyond the tip of the endotracheal tube. Ventilation was provided by a Puritan-Bennett 7200ae ventilator with PCV 20 cm H2O or VCV with a tidal volume (VTt) similar to that with PCV. A rate of 15 breaths/min and PEEP of 10 cm H2O were used throughout. Inspiratory times (TI) of 1.0, 1.5, 2.0, and 2.5 s were used with TGI of 0, 4, 8, and 12 L/min. Lung model compliance (ml/cm H2O) and resistance (cm H2O/L/s) combinations of 20/20, 20/5, and 50/20 were used. Auto-PEEP, VT, and peak alveolar and airway opening pressures increased as TGI and Ti increased, regardless of lung mechanics settings (p<0.01). All increases were greater with VCV than PCV (p<0.05). Continuous flow TGI with both PCV and VT-uncorrected VCV may result in marked increases in Vt and system pressures, especially at long TI.

Airway Resistance↗
PubMed1996

Medication nebulizer performance. Effects of diluent volume, nebulizer flow, and nebulizer brand.

BACKGROUND: Medication nebulizers are commonly used to delivery aerosolized medications to patients with respiratory disease. We evaluated output and respirable aerosol available to the patient (inhaled mass) for 17 medication nebulizers using a spontaneous breathing lung model. METHODS: Three nebulizer fill volumes (3, 4, and 5 mL containing 2.5 mg of albuterol) and 3 oxygen flows (6, 8, and 10 L/min) were evaluated using the 17 nebulizers. A cotton plug at the nebulizer mouthpiece was used to trap aerosol during simulated spontaneous breathing. Following each trial, the amount of albuterol remaining in the nebulizer and the amount deposited in the cotton plug were determined spectrophotometrically. Aerosol particle size was determined using an 11-stage cascade impactor. RESULTS: Increasing fill volume decreased the amount of albuterol trapped in the dead volume (p < 0.001) and increased the amount delivered to the patient (p < 0.001). Increasing flow increased the mass output of particles in the respirable range of 1 to 5 microns (p = 0.004), but the respirable mass delivered to the patient was affected to a greater extent by nebulizer brand (p < 0.001) than flow. Although 2.5 mg of albuterol was placed into the nebulizers, less than 0.5 mg in the respirable range of 1 to 5 microns was delivered to the mouthpiece. CONCLUSIONS: The performance of medication nebulizers is affected by fill volume, flow, and nebulizer brand. When they are used for research applications, the nebulizer characteristics must be evaluated and reported for the conditions used in the investigation.

Administration, Inhalation↗
PubMed1995

The delivery of aerosolized steroids from MDIs with nozzle extensions: quantitative laboratory evaluation of a method to improve aerosol delivery to intubated patients.

OBJECTIVE: Pulmonary deposition of aerosolized drug from a metered dose inhaler (MDI) is low with intubated patients. In the laboratory, extension of the MDI nozzle to the endotracheal tube tip has been shown to increase the delivered dose of albuterol. The objectives of this study were to determine the dose of aerosolized steroid (beclomethasone and triamcinolone) delivered through a MDI nozzle extension, the effect of nozzle extension length and number of actuations on the delivered dose, and particle size delivered through the nozzle extension. DESIGN: A 19-G catheter was used as the MDI nozzle extension. The nozzle extension was attached to a 60-ml syringe via the Luer-Lok connection, and the distal end was directed through a hole drilled into a 15-ml capped tube. The MDI was placed into the syringe and actuated by pressing the syringe plunger. Drug delivered through the nozzle extension into the tube was dissolved in methanol (beclomethasone) or ethanol (triamcinolone). Nozzle extension lengths of 10 cm, 20 cm and 30 cm were studied. For each nozzle extension length, delivery was assessed using one, two, three and five actuations of each drug. Drug remaining in the nozzle extension was recovered by rinsing with the appropriate solvent. Aerosol particle size leaving the nozzle extension was determined using a seven-stage cascade impactor. Beclomethasone and triamcinolone concentrations were determined by spectrophotometry at 239 nm. SETTING: Respiratory care laboratory of a university teaching hospital. RESULTS: For the pooled results, 70.2 +/- 14.1% of the dose was delivered through the nozzle extension, with no difference between beclomethasone and triamcinolone (p = 0.838). The proportion of drug delivered through the 10-cm extension (76.7 +/- 8.4%) was greater than that from the 20-cm (66.1 +/- 16.5%) and 30-cm (67.7 +/- 13.9%) extensions (p = 0.001). Less drug was delivered through the extension with one actuation (54.1 +/- 17.7%) than with two (71.2 +/- 7.7%), three (77.2 +/- 5.5%), or five actuations (78.2 +/- 4.3%) (p < 0.001). There was a decrease in MMAD with increasing nozzle extension length (3.14 +/- 0.61 microns for 10 cm, 2.97 +/- 0.28 microns for 20 cm, 2.37 +/- 0.27 microns for 30 cm; p = 0.005). CONCLUSIONS: A high proportion of aerosolized steroid was delivered with a MDI actuated through a nozzle extension. The proportion delivered through the nozzle extension was significantly less with longer nozzle extensions and with fewer actuations, but this may not be clinically important. Although particle sizes were smaller from longer nozzle extensions, all were within the respirable range. These results suggest that steroids can be delivered efficiently using a MDI nozzle extension.

Aerosols↗
PubMed1995

Weekly ventilator circuit changes. A strategy to reduce costs without affecting pneumonia rates.

BACKGROUND: Mechanical ventilator circuits are commonly changed at 48-h intervals. This frequency may be unnecessary because ventilator-associated pneumonia often results from aspiration of pharyngeal secretions and not from the ventilator circuit. We compared the ventilator-associated pneumonia rates and costs associated with 48-h and 7-day circuit changes. METHODS: Ventilator circuits were changed at 48-h intervals during the control period (November 1992 to April 1993) and at 7-day intervals during the study period (June 1993 to November 1993). Nosocomial pneumonias were prospectively identified using the criteria of the Centers for Disease Control and Prevention. The annual cost difference of changing circuits at 48-h and 7-day intervals was calculated using the distribution of ventilator days for the control and study periods. RESULTS: There were 1,708 patients, 9,858 ventilator days, and a pneumonia rate of 9.64 per 1,000 ventilator days in the control group (48-h circuit changes). There were 1,715 patients, 9,160 ventilator days, and 8.62 pneumonias per 1,000 ventilator days when circuits were changed at 1-week intervals (study group). Using a logistic regression model, there were significantly greater odds of developing a ventilator-associated pneumonia in surgical patients (odds ratio 1.77, P = 0.02) and patients in critical care units (odds ratio 1.54, P = 0.05), but no significant risk of ventilator-associated pneumonia in patients in whom circuits were changed at 1-week intervals (odds ratio 0.82, P = 0.22). Changing circuits at 7-day intervals resulted in a 76.6% ($111,530) reduction in the annual cost for materials and salaries. CONCLUSIONS: We found no difference in pneumonia rates with ventilator circuit changes at 48-h and 7-day intervals. Ventilator circuits can be safely changed at weekly intervals, resulting in large cost savings.

Adult↗
PubMed1995

Nitrogen dioxide production during mechanical ventilation with nitric oxide in adults. Effects of ventilator internal volume, air versus nitrogen dilution, minute ventilation, and inspired oxygen fraction.

BACKGROUND: Inhaled nitric oxide (NO) may be useful in the treatment of adult respiratory distress syndrome and other diseases characterized by pulmonary hypertension and hypoxemia. NO is rapidly converted to nitrogen dioxide (NO2) in oxygen (O2) environments. We hypothesized that in patients whose lungs are mechanically ventilated and in those with a long residence time for NO in the lungs, a clinically important [NO2] may be present. We therefore determined the rate constants for NO conversion in adult mechanical ventilators and in a test lung simulating prolonged intrapulmonary residence of NO. METHODS: NO (800 ppm) was blended with nitrogen (N2), delivered to the high-pressure air inlet of a Puritan-Bennett 7200ae or Siemens Servo 900C ventilator, and used to ventilate a test lung. The ventilator settings were varied: minute ventilation (VE) from 5 to 25 l/min, inspired O2 fraction (FIO2) from 0.24 to 0.87, and [NO] from 10 to 80 ppm. The experiment was then repeated with air instead of N2 as the dilution gas. The effect of pulmonary residence time on NO2 production was examined at test lung volumes of 0.5-4.0 l, VE of 5-25 l/min, FIO2 of 0.24-0.87, and [NO] of 10-80 ppm. The inspiratory gas mixture was sampled 20 cm from the Y-piece and from within the test lung. NO and NO2 were measured by chemiluminescence. The rate constant (k) for the conversion of NO to NO2 was determined from the relation 1/[NO]t-1/[NO]o = k x [O2] x t, where t = residence time. RESULTS: No NO2 was detected during any trial with VE 20 or 25 l/min. With N2 dilution and the Puritan-Bennett 7200ae, NO2 (< or = 1 ppm) was detected only at a VE of 5 l/min with an FIO2 of 0.87 and [NO] > or = 70 ppm. In contrast, [NO2] values were greater with the Servo 900C ventilator than with the Puritan-Bennett 7200ae at similar settings. When NO was diluted with air, clinically important [NO2] values were measured with both ventilators at high [NO] and FIO2. Rate constants were 1.46 x 10(-9) ppm-2.min-1 when NO was mixed with N2, 1.17 x 10(-8) ppm-2.min-1 when NO was blended with air, and 1.44 x 10(-9) ppm-2.min-1 in the test lung. CONCLUSIONS: [NO2] increased with increased FIO2 and [NO], decreased VE, blending with air, and increased lung volumes. Higher [NO2] was produced with the Servo 900C ventilator than the Puritan-Bennett 7200ae because of the greater residence time. With long intrapulmonary residence times for NO, there is a potential for NO2 production within the lungs. The rate constants determined can be used to estimate [NO2] in adult mechanical ventilation systems.

Adult↗
PubMed1995

Permissive hypercapnia as a ventilatory strategy in burned children: effect on barotrauma, pneumonia, and mortality.

OBJECTIVE: To document the incidence of barotrauma, pneumonia, and respiratory death associated with a mechanical ventilation protocol based on permissive hypercapnia in pediatric burn patients. DESIGN: Retrospective review. MATERIALS AND METHODS: Patients were managed using a mechanical ventilation protocol based on permissive hypercapnia, tolerating moderate (pH > 7.20) respiratory acidosis to keep inflating pressures below 40 cm H2O. MAIN RESULTS: Over a 2.5-year interval, 54 burned children (11% of 495 acute admissions) with an average age of 6.5 years (range 5 weeks to 17 years), average burn size of 44% (range 0 to 98%), and median burn size of 46% required mechanical ventilatory support for an average of 12.5 days (range 1 to 56 days). Inhalation injury was diagnosed in 34 (63%) of the children and 72% percent were admitted within 24 hours of injury. Overt barotrauma occurred in 5.6% of the patients, pneumonia in 32%, and respiratory death in 0%. CONCLUSIONS: A conventional ventilation protocol based on permissive hypercapnia is associated with acceptable rates of barotrauma and pneumonia. The low incidence of respiratory death associated with this strategy suggests that it also minimizes ventilator-induced lung injury.

Acidosis, Respiratory↗
PubMed1995

Cardiorespiratory effects of volume- and pressure-controlled ventilation at various I/E ratios in an acute lung injury model.

Numerous approaches to the provision of mechanical ventilation during acute lung injury are currently available. Of these, pressure control inverse ratio ventilation has been considered superior to volume control ventilation with PEEP with respect to improving gas exchange and minimizing cardiovascular compromise. However, no study systematically compares volume-controlled (VC) and pressure-controlled (PC) ventilation while maintaining mean airway pressure (MAP) constant at varying I/E ratios. We studied the effect of VC and PC with PEEP at normal (1:2) and inverse I/E ratios (2:1 and 4:1) on gas exchange, lung mechanics, and hemodynamics in a sheep lung injury model. Severe lung injury was induced in 12 sheep with bilateral lung lavages using normal saline; prelavage PO2 230 +/- 50 mm Hg, PEEP 5 cm H2O and postlavage, pretreatment PO2 70 +/- 20 mm Hg, PEEP 10 cm H2O, both at FIO2 0.50. MAP was kept constant throughout the study at 25 +/- 2 cm H2O while ventilating all animals with a VT of 10 ml/kg and a rate of 20/min by randomized application of VC and PC with I/E ratios of 1:2, 2:1, and 4:1. Despite liberal fluid administration, all ventilatory modes depressed cardiac output compared with preinjury values. However, gas exchange and hemodynamics did not differ among ventilation modes or I/E ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The response of flow-triggered infant ventilators.

Patient-triggered ventilation (PTV) has not been feasible for infants because of large trigger pressures and long delay times with pressure-triggered systems. Recently, four infant ventilators with flow triggering have become available. We questioned if delay times, trigger pressures, and trigger work with these ventilators would be acceptable for PTV in infants. All ventilators were attached via 3-, 4-, and 5-mm endotracheal tubes to a spontaneously breathing infant lung model. The lung simulator was set at an inspiratory time of 0.65 s, tidal volume of 15, 30, and 45 ml, and 0 and 5 cm H2O positive end-expiratory pressure (PEEP). Delay time, trigger pressure, and trigger work were determined from pressure measured at the proximal airway, trachea, and alveolus. There were significant differences between the endotracheal tube sizes, sites of measurement, ventilatory demand and ventilator brand at each PEEP level for delay time, trigger pressure, and trigger work (p < 0.001). Delay time was greatest with the 3-mm endotracheal tube at high ventilatory drive (maximum 138.2 +/- 2.1 ms). Both trigger pressure (minimum 0.23 +/- 0.02 cm H2O) and trigger work (minimum 0.05 +/- 0.01 g.ml) increased with decreasing endotracheal tube size, increasing ventilatory demand, use of PEEP, and site of measurement: alveolus > trachea > airway (maximum: trigger pressure 5.04 +/- 0.02 cm H2O; trigger work 114.48 +/- 0.88 g.ml). PTV may not be appropriate under conditions of increased ventilatory drive and small endotracheal tube size in infants.

Age Factors↗
PubMed1995

The effects of applied vs auto-PEEP on local lung unit pressure and volume in a four-unit lung model.

BACKGROUND: The application of positive end-expiratory pressure (PEEP) and maintenance of increased mean airway pressure (MAP) has been associated with improved oxygenation in adult respiratory distress syndrome. Recently, attention has been directed toward elevating MAP by establishing auto-PEEP when ventilating with an inverse inspiratory to expiratory ratio in opposition to applied PEEP. We theorized that FRC distribution and local lung unit end-expiratory pressure (EEP) would be different when equal levels of PEEP were established by applying PEEP or by producing auto-PEEP. METHODS: Using a four-chamber lung model with each chamber having a different time constant (TC), we applied equal levels of applied PEEP (I:E ratio 1:3) and auto-PEEP (I:E ratio 3:1) and evaluated local lung unit EEP and end expiratory lung volume (EELV). RESULTS: During all trials with applied PEEP, local lung unit EEP was equal to applied PEEP, whereas during auto-PEEP local EEP differed (p < 0.01). At a tracheal auto-PEEP level of 12.7 cm H2O, the lung unit with the longest TC (slow lung unit) had an EEP of 15.8 cm H2O, while the shortest TC unit (fast lung unit) had an EEP of 10.1 cm H2O (p < 0.01). Similarly, local EELVs were more maldistributed with auto-PEEP than with applied PEEP. At a tracheal PEEP level of 12.7 cm H2O, the EELV increase in the slow lung unit with auto-PEEP was 1,054 mL vs 918 with applied PEEP (p < 0.01), whereas the fast lung unit's EELV increase with auto-PEEP was 142 mL compared with 212 mL with applied PEEP (p < 0.01). CONCLUSION: Comparing equal levels of the auto-PEEP with applied PEEP, a greater maldistribution of local lung unit EEP and EELV was established with the auto-PEEP. During auto-PEEP, the greatest EEP and EELV occurred in the slow lung unit, and the lowest EEP and EELV developed in the fast lung unit.

Adult↗
PubMed1994

Prolonged inhalation of low concentrations of nitric oxide in patients with severe adult respiratory distress syndrome. Effects on pulmonary hemodynamics and oxygenation.

BACKGROUND: Nitric oxide (NO) inhalation selectively decreases pulmonary artery hypertension and improves arterial oxygenation in patients with the adult respiratory distress syndrome (ARDS). In this study of patients with severe ARDS, we sought to determine the effect of inhaled NO dose and time on pulmonary artery pressure and oxygen exchange and to determine which patients with ARDS are most likely to show this response. METHODS: Thirteen patients with severe ARDS (hospital mortality 67%) inhaled 0-40 parts per million (ppm) NO. Seven of these patients continued to breathe 2-20 ppm NO for 2-27 days. RESULTS: Inhaling 5-40 ppm NO decreased mean pulmonary artery pressure in a dose-related fashion (from 34 +/- 7 to 30 +/- 7 mmHg at 20 ppm NO). Systemic arterial pressure did not change. The ratio of arterial oxygen tension to inspired oxygen fraction increased (from 126 +/- 36 to 149 +/- 38 mmHg) and the venous admixture decreased (from 31.2 +/- 5.5 to 28.2 +/- 5.2%) without a clear dose-response effect. During prolonged NO inhalation, 2-20 ppm NO effectively reduced mean pulmonary artery pressure (38 +/- 7 vs. 31 +/- 6 mmHg) and increased arterial oxygen tension (79 +/- 10 vs. 114 +/- 27 mmHg) without evidence of tachyphylaxis. The decrease of pulmonary vascular resistance during NO inhalation correlated with the level of pulmonary vascular resistance without NO (r = -0.72). The reduction of venous admixture correlated with the level of venous admixture without NO (r = -0.78). CONCLUSIONS: Long-term NO inhalation at low concentrations selectively decreases mean pulmonary artery pressure and improves arterial oxygen tension in patients with ARDS. The selective pulmonary vasodilation effect is most pronounced in ARDS patients with the greatest degree of pulmonary vasoconstriction.

Administration, Inhalation↗
PubMed1994

Imposed work and oxygen delivery during spontaneous breathing with adult disposable manual ventilators.

BACKGROUND: Manual ventilators (resuscitators) are used primarily to ventilate the lungs of patients lacking spontaneous ventilatory effort. However, in many settings patients are allowed to breathe through the manual ventilator. Although many aspects of manual ventilator function have been studied, very little has been reported on the use of manual ventilators during spontaneous breathing. The purpose of this study was to evaluate inspiratory and expiratory imposed work of breathing and oxygen delivery during spontaneous breathing through disposable manual ventilators. METHODS: Simulated spontaneous breathing was established with a two-chambered test lung, with one chamber serving as the test chamber and the other as the driving chamber. Imposed work of breathing was evaluated with decelerating inspiratory flow at a rate of 20 breaths/min at tidal volume (VT) 0.25 1 and peak flow 40 l/min, at VT 0.5 l and peak flow 80 l/min, and VT 0.81 and peak flow 120 l/min. Flow (integrated to volume) and pressure were measured between the manual ventilator and test lung, and inspiratory and expiratory imposed work of breathing were calculated by integration of the volume-pressure curve. Oxygen concentration was measured with an oxygen analyzer placed between the manual ventilator and the test lung at 20 breaths/min, VT 0.5 l, and flow 45 l/min. An oxygen flow of 15 l/min was added to the device for all evaluations. Two of the manual ventilators had built-in positive end-expiratory pressure valves, and imposed work was evaluated at 10 cmH2O with these. RESULTS: There were significant differences in imposed work between inspiration and expiration (P < 0.001) and among the three levels of ventilatory demand (P < 0.001). For each ventilatory demand, there was a significant difference in work between manual ventilator brands for inspiratory work and expiratory work (P < 0.001). At a VT of 0.5 l and peak flow of 80 l/min, the pooled inspiratory imposed work for all manual ventilators was 0.44 +/- 0.12 J/l, and the pooled expiratory imposed work was 0.29 +/- 0.05 J/l. With 10 cmH2O positive end-expiratory pressure, the inspiratory imposed work was very high (> 1 J/l). Four of the devices were unable to deliver more than 0.85 oxygen concentration at the spontaneous ventilatory pattern evaluated. CONCLUSIONS: Adult disposable manual ventilators produce a substantial imposed work of spontaneous breathing, which is increased with the addition of positive end-expiratory pressure. With some manual ventilators, a high oxygen concentration may not be delivered during spontaneous breathing. We recommend that patients not be allowed to spontaneously breathe through disposable manual ventilators.

Adult↗
PubMed1994

Comparison of inspiratory work of breathing between flow-triggered and pressure-triggered demand flow systems in rabbits.

OBJECTIVES: Flow-triggered continuous positive airway pressure decreases the inspiratory work of breathing in adults when compared with pressure-triggered continuous positive airway pressure. However, the effect of flow-triggered continuous positive airway pressure on work of breathing in neonates is not known. Our objective was to determine if flow-triggering was superior to pressure triggering in the presence of narrow endotracheal tubes, such as those tubes used in neonates. DESIGN: Prospective evaluation using within-animal comparison of flow-triggering and pressure-triggering demand flow systems. SETTING: The animal laboratory in a university hospital. SUBJECTS: Six spontaneously breathing white rabbits, tracheostomized and intubated with 3- and 4-mm inner diameter endotracheal tubes. INTERVENTIONS: The animals were connected to a ventilator through a standard respiratory circuit. The ventilator was randomly operated in the following modes: flow-triggered continuous positive airway pressure, pressure-triggered continuous positive airway pressure, flow-triggered with 5 cm H2O pressure support ventilation, and pressure-triggered with 5 cm H2O pressure support ventilation. MEASUREMENTS AND MAIN RESULTS: Esophageal pressure, airway pressure, and flow signals were monitored. Control data were obtained while the rabbits were breathing room air through the endotracheal tube. With 3-mm inner diameter endotracheal tubes, the negative deflection of esophageal pressure during flow-triggered continuous positive airway pressure was significantly less than control; however, negative deflection of esophageal pressure during pressure-triggered continuous positive airway pressure did not significantly differ from control. The application of 5 cm H2O pressure support ventilation with flow-triggering decreased negative deflection of esophageal pressure significantly compared with flow-triggered continuous positive airway pressure, pressure-triggered continuous positive airway pressure, and control. With endotracheal tube inner diameter of 4 mm, flow-triggered continuous positive airway pressure and pressure-triggered continuous positive airway pressure did not show any differences compared to control. Negative deflection of esophageal pressure differed under all conditions except control when results with the 3-mm inner diameter endotracheal tube were compared with the 4-mm inner diameter endotracheal tube. CONCLUSIONS: Flow-triggering is superior to pressure-triggering in the presence of a 3-mm inner diameter endotracheal tube. This difference was not clear with a 4-mm inner diameter endotracheal tube. The size of the endotracheal tube may be the most important variable in evaluating the approach used to ventilate small neonates.

Air Pressure↗
PubMed1994

Effects of disposable or interchangeable positive end-expiratory pressure valves on work of breathing during the application of continuous positive airway pressure.

OBJECTIVE: To determine which of a series of disposable or interchangeable positive end-expiratory pressure (PEEP) devices functions with the least imposition of inspiratory and expiratory work during continuous positive airway pressure. DESIGN: Prospective laboratory evaluation performed on a lung model. SETTING: Research laboratory at a university medical center. INTERVENTIONS: A spontaneously breathing lung model, created from a training test lung and a volume ventilator, were used to simulate a patient spontaneously breathing at a tidal volume of 0.4 L, peak inspiratory flow of 40 L/min, an inspiration/expiration ratio of 1:2, and a respiratory rate of 20 breaths/min. Ten PEEP valves attached to a continuous high-flow system were evaluated. MEASUREMENTS AND MAIN RESULTS: All of the PEEP valves studied imposed high levels of both inspiratory and expiratory work of breathing. The BE-171 and BE-142 valves (Instrumentation Industries) imposed the least amount of inspiratory work. In general, imposed inspiratory work accounted for approximately 70% to 80% of total imposed work of breathing. CONCLUSIONS: All of the disposable/interchangeable PEEP valves that were studied imposed a considerable amount of both inspiratory and expiratory work, even when the continuous flow provided exceeded the peak inspiratory flow demands of the lung model. The primary reason for the high imposed work levels is the high gas-flow resistance of all of the valves studied.

Airway Resistance↗