Evaluation of bronchodilator responsiveness in mechanically ventilated patients

Influence of Mechanical Ventilation Modes on the Efficacy of Nebulized Bronchodilators in the Treatment of Intubated Adult Patients with Obstructive Pulmonary Disease

BACKGROUND

Little has been reported in terms of clinical outcomes to confirm the benefits of nebulized bronchodilators during mechanical ventilation (MV). Electrical Impedance Tomography (EIT) could be a valuable method to elucidate this gap.

OBJECTIVE

The purpose of this study is to evaluate the impact of nebulized bronchodilators during invasive MV with EIT by comparing three ventilation modes on the overall and regional lung ventilation and aeration in critically ill patients with obstructive pulmonary disease.

METHOD

A blind clinical trial in which eligible patients underwent nebulization with salbutamol sulfate (5 mg/1 mL) and ipratropium bromide (0.5 mg/2 mL) in the ventilation mode they were receiving. EIT evaluation was performed before and after the intervention. A joint and stratified analysis into ventilation mode groups was performed, with p < 0.05.

RESULTS

Five of nineteen procedures occurred in controlled MV mode, seven in assisted mode and seven in spontaneous mode. In the intra-group analysis, the nebulization increased total ventilation in controlled (p = 0.04 and ⅆ = 2) and spontaneous (p = 0.01 and ⅆ = 1.5) MV modes. There was an increase in the dependent pulmonary region in assisted mode (p = 0.01 and ⅆ = 0.3) and in spontaneous mode (p = 0.02 and ⅆ = 1.6). There was no difference in the intergroup analysis.

CONCLUSIONS

Nebulized bronchodilators reduce the aeration of non-dependent pulmonary regions and increase overall lung ventilation but there was no difference between the ventilation modes. As a limitation, it is important to note that the muscular effort in PSV and A/C PCV modes influences the impedance variation, and consequently the aeration and ventilation values. Thus, future studies are needed to evaluate this effort as well as the time on ventilator, time in UCI and other variables.

Inhalation therapy in patients receiving mechanical ventilation: an update

Incremental gains in understanding the influence of various factors on aerosol delivery in concert with technological advancements over the past 2 decades have fueled an ever burgeoning literature on aerosol therapy during mechanical ventilation. In-line use of pressurized metered-dose inhalers (pMDIs) and nebulizers is influenced by a host of factors, some of which are unique to ventilator-supported patients. This article reviews the impact of various factors on aerosol delivery with pMDIs and nebulizers, and elucidates the correlation between in-vitro estimates and in-vivo measurement of aerosol deposition in the lung. Aerosolized bronchodilator therapy with pMDIs and nebulizers is commonly employed in intensive care units (ICUs), and bronchodilators are among the most frequently used therapies in mechanically ventilated patients. The use of inhaled bronchodilators is not restricted to mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) and asthma, as they are routinely employed in other ventilator-dependent patients without confirmed airflow obstruction. The efficacy and safety of bronchodilator therapy has generated a great deal of interest in employing other inhaled therapies, such as surfactant, antibiotics, prostacyclins, diuretics, anticoagulants and mucoactive agents, among others, in attempts to improve outcomes in critically ill ICU patients receiving mechanical ventilation.

Placement of the nebulizer before the humidifier during mechanical ventilation: Effect on aerosol delivery

BACKGROUND

Therapeutic aerosols are commonly used in mechanically ventilated patients. The position of the nebulizer in the ventilator circuit and the humidification of inhaled gases can influence the efficiency of aerosol delivery. We evaluated the effect of nebulizer position on the pulmonary bioavailability of nebulized ipratropium in ventilated patients without known preexisting respiratory disease.

METHODS

The study included 38 mechanically ventilated and sedated patients after open heart surgery. Ipratropium (500 microg) was delivered by an ultrasonic nebulizer. Patients were randomized into 2 groups: the nebulizer positioned before the heat humidification system (group 1, n = 19) or at the end of the inspiratory limb before the Y-piece (group 2, n = 19). The amount of ipratropium in the urine collected during the 4 hours after drug administration was measured by mass spectrometry.

RESULTS

There were no statistically significant differences in tidal volume or respiratory rate between groups. There were no significant differences between the 2 groups in the amount of drug excreted (group 1 vs 2: 13,237 +/- 2313 pg/mL vs 15,529 +/- 3204 pg/mL) or in pulmonary bioavailability (.9% +/- .1% vs 1.1% +/- .2%).

CONCLUSION

The position of the nebulizer in the ventilatory circuit had no effect on the pulmonary bioavailability of ipratropium.

A prospective randomized controlled blinded study of three bronchodilators in infants with respiratory syncytial virus bronchiolitis on mechanical ventilation

OBJECTIVE

To study patients with respiratory syncytial virus bronchiolitis in respiratory failure to make specific measurements reflecting airway resistance before and after treatment with commonly used agents. We hypothesized that racemic epinephrine would decrease airways resistance more effectively than levalbuterol, and levalbuterol would decrease airways resistance more effectively than racemic albuterol. Normal saline was used as a control.

DESIGN

Prospective, randomized, controlled, blinded study.

SETTING

Tertiary Pediatric Intensive Care Unit in a University affiliated hospital in the northeastern United States.

PATIENTS

Twenty-two patients with respiratory syncytial virus bronchiolitis and in respiratory failure were enrolled. All were intubated and ventilated in a volume control mode and sedated.

INTERVENTIONS

In a randomized, blinded fashion patients were given four agents: norepinephrine, levalbuterol, racemic albuterol, and normal saline at 6 hr intervals.

MEASUREMENTS

As indicators of bronchodilation, peak inspiratory pressure and inspiratory respiratory system resistance were measured before and 20 mins after each agent was given. Thus, each patient acted as his/her own control.

MAIN RESULTS

There were small but statistically significant decreases in peak inspiratory pressure after racemic epinephrine treatment, levalbuterol, and racemic albuterol. There was no change in peak inspiratory pressure after inhaled normal saline. Inspiratory respiratory system resistance fell significantly after all treatments, including saline. Heart rate rose significantly after inhaled bronchodilator treatments (p < 0.05 for all treatments).

CONCLUSIONS

Similar statistically significant bronchodilation occurred after all three bronchodilators as indicated by a decrease in peak inspiratory pressure and respiratory system resistance, but these changes were small and probably clinically insignificant. However, side effects of bronchodilators, such as tachycardia, also occurred, and these may be clinically significant. Thus the benefit of bronchodilator treatment in these patients is small, does not differ among the drugs we studied and of questionable value.

How best to deliver aerosol medications to mechanically ventilated patients

Pressurized metered-dose inhalers (pMDIs) and nebulizers are employed routinely for aerosol delivery to ventilator-supported patients, but the ventilator circuit and artificial airway previously were thought to be major barriers to effective delivery of aerosols to patients receiving mechanical ventilation. In the past two decades, several investigators have shown that careful attention to many factors, such as the position of the patient, the type of aerosol generator and its configuration in the ventilator circuit, aerosol particle size, artificial airway, conditions in the ventilator circuit, and ventilatory parameters, is necessary to optimize aerosol delivery during mechanical ventilation. The best techniques for aerosol delivery during noninvasive positive-pressure ventilation are not well established as yet, and the efficiency of aerosol delivery in this setting is lower than that during invasive mechanical ventilation. The most efficient methods of using the newer hydrofluoroalkane-pMDIs and vibrating mesh nebulizers in ventilator-supported patients also require further evaluation. When optimal techniques of administration are employed, the efficiency of aerosolized drug delivery in mechanically ventilated patients is comparable to that achieved in ambulatory patients.

Termination of inspiration by phase-dependent respiratory vagal feedback in awake normal humans

Imperceptible levels of proportional assist ventilation applied throughout inspiration reduced inspiratory time (TI) in awake humans. More recently, the reduction in TI was associated with flow assist, but flow assist also reaches a maximum value early during inspiration. To test the separate effects of flow assist and timing of assist, we applied a pseudorandom binary sequence of flow-assisted breaths during early, late, or throughout inspiration in eight normal subjects. We hypothesized that imperceptible flow assist would shorten TI most effectively when applied during early inspiration. Tidal volume, integrated respiratory muscle pressure per breath, TI, and TE were recorded. All stimuli (early, late, or flow assist applied throughout inspiration) resulted in a significant increase in inspiratory flow; however, only when the flow assist was applied during early inspiration was there a significant reduction in TI and the integrated respiratory muscle pressure per breath. These results provide further evidence that vagal feedback modulates breathing on a breath-by-breath basis in conscious humans within a physiological range of breath sizes.

Modulation of breathing using imperceptible unloading

We investigated the role of V(T) and V(T)/T(I) modulation of breathing in awake human subjects. We applied a PRBS of volume (incrementing ramp) or flow (decrementing wave) assist at levels below the perceptual threshold in order to stimulate respiratory feedback. We modeled the PRBS data with linear difference equations to obtain impulse-response profiles of V(T), V(T)/T(I), T(I) and factorial(P(MUS)). We limited cortical responses to our stimuli by applying sub-threshold levels of assist, and we limited humoral effects (O2 and CO2) by augmenting mechanical respiratory output intermittently and by small amounts. We found that flow or volume assist elicited similar significant increases in V(T) and V(T)/T(I). During flow assist there was a significant decrease in factorial(P(MUS)) and T(I) was reduced, albeit not significantly; however, volume assist did not modify T(I) or factorial(P(MUS)). The earlier onset of flow assist, relative to volume assist, may explain the difference between the responses. We conclude that vagally mediated inspiratory flow receptors in the chest wall or lungs may modulate breathing on a breath by breath basis when small, imperceptible increases in airflow occur early during inspiration. Furthermore, lung volume feedback during imperceptible unloading (occurring at the end of inspiration) was less effective. Finally, pseudorandom unloading with imperceptible stimuli provides a useful tool to study reflex regulation of ventilation in awake subjects without confounding cortical influences.

Identification of respiratory vagal feedback in awake normal subjects using pseudorandom unloading

Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus.

A comparison of bronchodilator therapy delivered by nebulization and metered-dose inhaler in mechanically ventilated patients

BACKGROUND

The optimal method of delivering bronchodilators in mechanically ventilated patients is unclear. The purpose of this study was to compare the pulmonary bioavailability of albuterol delivered by the nebulizer, the metered-dose inhaler (MDI) and spacer, and the right-angle MDI adaptor in ventilated patients using urinary analysis of drug levels.

METHODS

Mechanically ventilated patients who had not received a bronchodilator in the previous 48 h and who had normal renal function were randomized to receive the following: (1) five puffs (450 microg) of albuterol delivered by the MDI with a small volume spacer; (2) five puffs of albuterol delivered by the MDI port on a right-angle adaptor; or (3) 2.5 mg albuterol delivered by a nebulizer. Urine was collected 6 h after the administration of the drug, and the amounts of albuterol and its sulfate conjugate were determined in the urine by a chromatographic assay.

RESULTS

Thirty patients were studied, 10 in each group: their mean age and serum creatinine level were 62 years and 1.3 mg/dL, respectively. With the MDI and spacer, (mean +/- SD) 169+/-129 microg albuterol (38%) was recovered in the urine; with the nebulizer, 409+/-515 microg albuterol (16%) was recovered in the urine; and with the MDI port on the right-angle adaptor, 41+/-61 microg albuterol (9%) was recovered in the urine (p = 0.02 between groups). The level of albuterol in the urine was below the level of detection in four patients in whom the drug was delivered using the right-angle MDI adaptor.

CONCLUSION

The three delivery systems varied markedly in their efficiency of drug delivery to the lung. As previous studies have confirmed, this study has demonstrated that using an MDI and spacer is an efficient method for delivering inhaled bronchodilators to the lung. The pulmonary bioavailability was poor with the right-angle MDI port. This port should not be used to deliver bronchodilators in mechanically ventilated patients.

Mechanical ventilation in obstructive lung disease

This article reviews selected topics relevant to the use of mechanical ventilation in patients with severe airflow obstruction. Areas discussed include the bedside assessment of respiratory system mechanics, the ventilatory determinants of dynamic pulmonary hyperinflation, the role of controlled hypoventilation with permissive hypercapnia, and the delivery of bronchodilators during mechanical ventilation.

Predictors of extubation success and failure in mechanically ventilated infants and children

OBJECTIVE

To predict extubation success and failure in mechanically ventilated infants and children using bedside measures of respiratory function.

DESIGN

Prospective collection of data.

SETTING

A university-affiliated children's hospital with a 51-bed critical care unit.

PATIENTS

All infants and children who were mechanically ventilated for at least 24 hrs, except neonates < or = 37 wks gestation and patients with neuromuscular disease.

INTERVENTIONS

Bedside measurements of cardiorespiratory function were obtained immediately before extubation.

MEASUREMENTS AND MAIN RESULTS

Extubation failure was defined as reintubation within 48 hrs of extubation in the absence of upper airway obstruction. Failure rates were calculated for different ranges (selected a priori) of preextubation measures of breathing effort, ventilatory support, respiratory mechanics, central inspiratory drive, and integrated indices useful in adults. Effort of spontaneous breathing was assessed by the respiratory rate standardized to age, the presence of retractions and paradoxical breathing, inspiratory pressure, maximal negative inspiratory pressure (maximal negative inspiratory pressure), inspiratory pressure/maximal negative inspiratory pressure ratio, and tidal volume indexed to body weight of a spontaneous breath. Ventilatory support was measured by the fraction of inspired oxygen (F10(2)), mean airway pressure, oxygenation index, and the fraction of total minute ventilation provided by the ventilator. Respiratory mechanics were assessed by determination of peak ventilatory inspiratory pressure and dynamic compliance. Central inspiratory drive was assessed by mean inspiratory flow. Frequency to tidal volume ratio and the compliance, rate, oxygenation, and pressure indexed to body weight, the integrated indices useful in predicting extubation failure in adults, were also calculated. Thirty-four of the 208 patients who were studied were reintubated for an overall failure rate of 16.3% (95% confidence interval 11.3% to 21.4%). The reasons for reintubation were poor effort (n = 8), excessive effort (n = 14), altered mental status or absent airway reflexes (n = 2), cardiovascular instability (n = 3), inadequate oxygenation (n = 3), respiratory acidosis (n = 3), and undocumented (n = 1). Extubation failure increased significantly with decreasing tidal volume indexed to body weight of a spontaneous breath, increasing F10(2), increasing mean airway pressure, increasing oxygenation index, increasing fraction of total minute ventilation provided by the ventilator, increasing peak ventilatory inspiratory pressure, or decreasing mean inspiratory flow (p < .05). Dynamic compliance showed a trend of increasing failure rate with decreasing dynamic compliance but did not reach statistical significance (p = .116). Respiratory rate standardized to age, inspiratory pressure, maximal negative inspiratory pressure, inspiratory pressure/maximal negative inspiratory pressure ratio, frequency to tidal volume ratio, and compliance, rate, oxygenation, and pressure did not show any trend in failure rate with increasing or decreasing values. Threshold values that defined a low risk (< or = 10%) and a high risk (> or = 25%) of extubation failure could be determined for tidal volume indexed to body weight of a spontaneous breath, F10(2), mean airway pressure, oxygenation index, fraction of total minute ventilation provided by the ventilator, peak ventilatory inspiratory pressure, dynamic compliance, and mean inspiratory flow. Neither a low nor a high risk of failure could be defined for frequency to tidal volume ratio or the compliance, rate, oxygenation, and pressure (CROP) index.

CONCLUSIONS

Bedside measurements of respiratory function can predict extubation success and failure in infants and children. Both a low risk and a high risk of failure can be determined using these measures. Integrated indices useful in adults do not reliably predict extubation success or failure in

Initiation of mechanical ventilation in the emergency department

Mechanical ventilation is frequently initiated by emergency physicians. Further, the physician on duty in the emergency department is frequently responsible for evaluating ventilated patients who decompensate in the intensive care unit when other physicians are not present in the hospital. A bewildering array of features on new mechanical ventilators has made their appropriate and effective use increasingly complex. Knowledge of the pathophysiology of acute respiratory failure and changes in lung physiology during positive pressure ventilation will aid the emergency physician in choosing an appropriate ventilator modality and initial settings to maximally benefit patients with respiratory insufficiency due to various causes. An appreciation of the adverse effects of mechanical ventilation and problems commonly encountered in patients on ventilators will prepare the emergency physician to rapidly assess and effectively manage the patient who deteriorates in this setting.

Elevated static compliance of the total respiratory system: early predictor of weaning unsuccess in severed COPD patients mechanically ventilated

OBJECTIVE

To assess in a group of COPD patients mechanically ventilated for an episode of acute respiratory failure the respiratory mechanics with a simple and non invasive method at the bedside in order to evaluate if these parameters may be predictive of weaning failure or success.

DESIGN

A prospective study.

SETTING

Intensive care and intermediate intensive care units.

PATIENTS

23 COPD patients ventilated for acute respiratory failure and studied within 24 hours from intubation.

METHODS

Using end-expiratory and end-inspiratory airway occlusion technique, we measured PEEPi, static compliance of the respiratory system (Crs, st) maximum respiratory resistance (Rrsmax) and minimum respiratory resistance (Rrsmin).

MEASUREMENTS AND RESULTS

The weaned group (A) and the not weaned group (B) were not different regarding to static PEEPi (group A 8.5 +/- 4.0 vs group B 8.9 +/- 2.6 cmH2O), TO Rrsmax (22.4 +/- 5.3 versus 22.2 +/- 9.0 cmH2O/1/s) and to Rrsmin (17.6 +/- 5.5 versus 17.9 +/- 8.0 cmH2O/1/s), while a significant difference (p < 0.001) has been found in Cst, rs (62.7 +/- 17.% versus 111.6 +/- 18.0 ml/cm H2O). The threshold value of 88.5 ml/cmH2O was identified by discriminant analysis and provided the best separation between the two groups, with a sensitivity of 0.85 and a specificity of 0.87.

CONCLUSION

Cst, rs measured non invasively in the first 24 h from intubation, provided a good separation between the patients who were successfully weaned and those who failed.

Comparison of one versus two bronchodilators in ventilated COPD patients

OBJECTIVE

To compare the bronchodilating effect of a single drug, ipratropium bromide (IBr), with that of its combination with fenoterol (IBr+F).

DESIGN

The study was triple blind and randomized.

SETTING

Medical-surgical intensive care unit.

PATIENTS

12 patients with acute exacerbation of chronic obstructive pulmonary disease (COPD) requiring mechanical ventilation for severe respiratory failure.

INTERVENTIONS

Before administering each drug, peak airway pressure (Ppeak), end inspiratory pressure (Pei), resistive pressure (Pres), and auto positive--end expiratory pressure (auto-PEEP) were measured. Inspiratory system resistance (Rins) and dynamic respiratory system compliance (C) were calculated. Arterial pH and blood gas determinations were made. These measurements were repeated 60 min after administration of each therapeutic regimen. For ipratropium bromide alone the dose was 0.04 mg. When the combination of drugs was used, the doses were 0.04 mg for ipratropium bromide and 0.1 mg for fenoterol.

MEASUREMENTS AND RESULTS

With the combination of both drugs, all the pressures in the airway, as well as the auto-PEEP and the Rins were significantly reduced (p < 0.05) with respect to baseline values. With ipratropium bromide alone, no significant changes were observed either in the pressures or in the inspiratory resistance. No significant changes were observed either in the pH or blood gases with any of the treatments. The combination of both drugs produced significantly reduction in Pei and auto-PEEP when compared with ipratropium bromide alone.

CONCLUSIONS

The combination of both drugs is more effective than ipratropium bromide alone at the doses used in this study.

Delivery of ultrasonic nebulized aerosols to a lung model during mechanical ventilation

Ultrasonic nebulizers may be particularly suitable for the administration of therapeutic aerosols to patients undergoing mechanical ventilation, but the amount of aerosol that reaches the patients' respiratory tract during ultrasonic nebulization has not been adequately studied. The delivery through an endotracheal tube of nebulized aerosols labeled with 99mTechnetium human serum albumin was therefore measured for five commercially available ultrasonic nebulizers using an in vitro model representing mechanical ventilation of an adult patient. Delivery of aerosol through the endotracheal tube ranged from 3.1 +/- 0.3% for Samsonic to 10.1 +/- 2.0% for Portasonic using 3 ml nebulizer solution. Increasing the volume of nebulizer solution to 18 ml (not possible for the Portasonic) increased delivery to 11.5 +/- 2.0 for the DP 100, 8.7 +/- 3.1 for Ultraneb, and 15.9 +/- 1.8% for Samsonic. Addition of a 600 ml aerosol storage chamber to the ventilator circuit increased delivery for the Samsonic (18 ml solution) to 22.3 +/- 5.0%. Aerosol delivery was also increased by reducing the respiratory rate and minute volume and by increasing the inspiratory time settings on the ventilator. These results confirm the potential value of ultrasonic nebulizers during mechanical ventilation and indicate that clinical trials in ventilated patients are warranted.

Interrupter mechanics of patients admitted to a chronic ventilator dependency unit

We analyzed the results of interrupter mechanics tests of 73 consecutive patients who were admitted to a chronic ventilator dependency unit. The purposes of this study were (1) to establish guidelines for grading the severity of airway obstruction based on interrupter mechanics measurements; (2) to estimate the prevalence of airway obstruction in this population; (3) to compare interrupter test results with the clinical assessment of airway function; and (4) to characterize the distribution of bronchodilator-induced changes in isorecoil flow. Measurements from 65 of 73 patients (89%) were considered technically adequate. Of 65 patients, 29 (45%) showed signs of flow limitation during passive expiration. All patients with severe obstruction documented with spirometry during clinical stability were flow-limited and achieved maximal flows < or = 0.45 L/s at recoil pressures of 10 cm H2O. In contrast to measures of expiratory dynamics, the inspiratory resistance of the respiratory system was a poor index of severity of obstruction. In seven of 12 patients, interrupter testing failed to substantiate a clinical diagnosis of severe obstruction while revealing unsuspected obstruction in six of 25 (24%) patients. The administration of 270 micrograms of albuterol increased flows at comparable recoil pressures by > or = 0.1 L/s in 29% of 41 patients. Changes in flow were unimodally distributed and were not correlated with severity of obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of extrinsic positive end-expiratory pressure on mechanically ventilated patients with chronic obstructive pulmonary disease and dynamic hyperinflation

OBJECTIVE

To examine the circulatory and respiratory effects of extrinsic positive end-expiratory pressure (PEEPe) in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation during controlled mechanical ventilation.

DESIGN

Different levels of PEEPe were applied randomly in mechanically ventilated patients with COPD and dynamic hyperinflation.

SETTING

Respiratory Intensive Care Unit of a University Hospital.

PATIENTS

9 patients with acute respiratory failure and dynamic hyperinflation due to acute exacerbation of COPD.

INTERVENTIONS

PEEPe 35%, 58% and 86% of intrinsic PEEP (PEEPi) were applied.

MEASUREMENTS AND RESULTS

Using flow-directed pulmonary artery catheters hemodynamic measurements were obtained, while simultaneously lung volumes, airflows and airway pressures were recorded. In order to estimate alveolar pressures (Palv), rapid airway occlusions during passive expiration were also performed. At no level of PEEPe were significant changes in cardiac output, gas exchange variables, dead space, airways inflation resistances and respiratory system static end-inspiratory compliance observed. At high level of PEEPe central venous, mean pulmonary arterial and pulmonary capillary wedge pressures were increased significantly. All but one patient were flow-limited during passive expiration. PEEPe 86% of PEEPi caused a significant increase in end-expiratory lung volume and total PEEP. Iso-volume pressure-flow curves showed volume-dependence expiratory flow limitation in 2 patients, while in 8 patients volume-dependence of critical driving pressure (Palv-mouth pressure) that decreased flows was also observed.

CONCLUSIONS

The effects of PEEPe on iso-volume flow and hence on lung mechanics and hemodynamics, depend on many factors, such as airways resistances, lung volumes and airway characteristics, making the patient response to PEEPe unpredictable.

Pulmonary deposition of a nebulised aerosol during mechanical ventilation

BACKGROUND

There is increasing use of therapeutic aerosols in patients undergoing mechanical ventilation. Few studies have measured aerosol delivery to the lungs under these conditions with adequate experimental methods. Hence this study was performed to measure pulmonary aerosol deposition and to determine the reproducibility of the method of measurement during mechanical ventilation.

METHODS

Nine male patients were studied during mechanical ventilation after open heart surgery and two experiments were performed in each to determine the reproducibility of the method. A solution of technetium-99m labelled human serum albumin (99mTc HSA (50 micrograms); activity in experiment 1, 74 MBq; in experiment 2, 185 MBq) in 3 ml saline was administered with a Siemens Servo 945 nebuliser system (high setting) and a System 22 Acorn nebuliser unit. Pulmonary deposition was quantified by means of a gamma camera and corrections derived from lung phantom studies.

RESULTS

Pulmonary aerosol deposition was completed in 22 (SD 4) minutes. Total pulmonary deposition (% nebuliser dose (SD)) was 2.2 (0.8)% with 1.5% and 0.7% depositing in the right and left lungs respectively; 0.9% of the nebuliser activity was detected in the endotracheal tube or trachea and 51% was retained within the nebuliser unit. Considerable variability between subjects was found for total deposition (coefficient of variation (CV) 46%), but within subject reproducibility was good (CV 15%).

CONCLUSIONS

Administration of aerosol in this way is inefficient and further research is needed to find more effective alternatives in patients who require mechanical respiratory support. This method of measurement seems suitable for the assessment of new methods of aerosol delivery in these patients.

Respiratory compliance in infants--a preliminary evaluation of the multiple interrupter technique

Measurements of total respiratory system compliance (Crs) using the multiple occlusion technique (MOT) in spontaneously breathing infants can be difficult to interpret in the presence of an unstable end-expiratory level. Similarly, measurements using the passive flow volume technique (PFV) are invalidated if there is alinearity of the expiratory time constant (Trs), irrespective of respiratory effort. For possibly overcoming these problems, we assessed the feasibility of a technique using multiple interruptions of of a single expiration (MIT), obtaining several pairs of volume-pressure data, from one expiration, which relate to a single end-expiratory level. Crs was measured in 16 infants aged 0.5 to 20 months using the MOT, MIT, and PFV technique. The MOT and the MIT each failed in one (different) infant, both succeeding where the other failed. The PFV technique failed in five infants in whom no acceptable plateau of airway pressure during occlusion and no Trs could be obtained from a single breath. Failure to obtain a linear Trs was accompanied by failure of the MIT in only one infant. Individual differences between the MIT and the MOT were less than 9%. However, the PFV measurements varied from -16.3% and +25.7% of the values from MIT or MOT. The greatest differences between Crs values coincided with the greatest differences between volume intercepts of the extrapolated volume-pressure (MOT, MIT) and flow-volume (PFV) data. From this preliminary study, the MIT proved as successful as the MOT, requiring fewer occluded breaths to measure Crs. In infants with a rapid respiratory rate, the data from several expirations can be merged and analyzed as for the MOT.

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.

Metered dose inhalers for bronchodilator delivery in intubated, mechanically ventilated patients

We determined the relative efficacy of two bronchodilator aerosol delivery methods in 18 intubated mechanically ventilated patients with airways obstruction. Two treatment arms, consisting of albuterol 270 micrograms (three puffs) from a metered dose inhaler and albuterol 2.5 mg from a saline solution nebulized with an updraft inhaler, were compared in a single blind, randomized crossover design. Pulmonary function was evaluated using an interrupter technique. Changes in passive expiratory flow at respiratory system recoil pressures between 6 and 10 cm H2O provided the therapeutic endpoints. Paired measurements were made before and 30 minutes after drug delivery. The MDI and NEB resulted in similar improvements in iso-recoil flow (mean increase for both groups = 0.1 L/s). Treatment sequence, severity of obstruction, and bronchodilator responsiveness had no effect on relative efficacy. Albuterol caused a small but significant increase in heart rate that was similar following both delivery methods. We conclude that bronchodilator aerosol delivery with metered dose inhalers provides a viable alternative to nebulizer therapy in intubated mechanically ventilated patients and may result in a cost savings to hospitals and patients.

Dose-response effects and time course of effects of inhaled fenoterol on respiratory mechanics and arterial oxygen tension in mechanically ventilated patients with chronic airflow obstruction

To investigate the dose-response relationship and the time course of the effects of fenoterol (a selective beta 2-adrenergic agonist) on respiratory function in mechanically ventilated patients with acute respiratory failure due to exacerbation of chronic airflow obstruction (CAO), seven consecutive acutely ill patients were studied within 3 days of the onset of mechanical ventilation. Airflow, airway pressure, and changes in lung volume were measured with the transducers of the 900 C Servo Ventilator, the last by electronic integration. The end-expiratory lung volume (EELV), the intrinsic positive end-expiratory pressure (PEEPi), the static respiratory compliance (Cstrs), maximum and minimum respiratory resistance (Rrsmax and Rrsmin), and arterial oxygen tension (PaO2), were measured under control conditions (all patients were receiving aminophylline infused at a constant rate) 5, 15, and 30 min after administration of 4 ml aerosolized saline solution and 5, 15, and 30 min after inhalation of 0.4, 0.8, and 1.2 mg fenoterol. After the last dose, measurements were repeated at 60, 120, and 180 min. We found that, on average, while saline did not cause any significant change in respiratory mechanics, a low dose (0.4 mg) of inhaled fenoterol was followed by a rapid (5 min) and significant decrease in Rrsmax (-33%), Rrsmin (-28%), EELV (-34%), and PEEPi (-44%), with a slight but not significant further fall with higher doses. However, changes were short-lasting, and by 2 h after the end of administration were no longer significant. PaO2 dropped significantly on average, with a maximum mean fall of 15 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchodilators in patients with chronic obstructive pulmonary disease on mechanical ventilation. Utilization of metered-dose inhalers

Bronchodilators are used widely in the acute exacerbations of chronic obstructive pulmonary disease (COPD), although their effectiveness is not clearly established. We used three bronchodilators in 20 patients with COPD who were being mechanically ventilated. Two of the bronchodilators, ipratropium bromide and salbutamol, were administered from metered-dose inhalers (MDI) through an adapter to the endotracheal tube, and the third, aminophylline, was administered in the form of intravenous infusion. Before administering each drug, peak airway pressure, end-inspiratory pressure, resistive pressure, and auto positive end-expiratory pressure (auto-PEEP) were measured, and inspiratory resistance (Rins) and compliance were calculated. Heart rate (HR) and blood pressure were also recorded, and arterial pH and blood gas determinations were made. These measurements were repeated 60 min after the administration of aminophylline, 15 and 60 min after administering salbutamol, and 30 and 60 min after administering ipratropium bromide. With these three drugs, airway pressures were reduced, as well as auto-PEEP and Rins, with respect to basal values (p less than 0.05). The changes in compliance were only significant with salbutamol (p less than 0.05). HR was only significantly modified with aminophylline (p less than 0.05). No blood gas change was observed with any of the three drugs. It can be concluded that: (1) the three drugs used in this study were equally effective in producing significant bronchodilation in patients on mechanical ventilation for severe acute exacerbation of COPD; (2) the administration of bronchodilators by MDI in intubated patients through a special adapter was as effective as the intravenous administration of aminophylline.

Doxofylline and respiratory mechanics. Short-term effects in mechanically ventilated patients with airflow obstruction and respiratory failure

To assess the short-term effects of a methylxanthine (doxofylline) on respiratory mechanics in mechanically ventilated patients with airway obstruction and respiratory failure, nine consecutive patients were examined within three days from the onset of mechanical ventilation. Flow, changes in pulmonary volume, and Paw were measured using a ventilator (Servo 900C). End-expiratory and end-inspiratory airway occlusion was performed to measure PEEPi, Cstrs, Rrsmax, and Rrsmin. Measurements were performed before and at 5, 15, and 30 minutes after an intravenous loading dose of doxofylline (5 to 6 mg/kg). We found that doxofylline determined, on the average, a marked decrease in respiratory resistance (Rrsmax and Rrsmin, -27.2 percent and -36.5 percent, respectively) without significant changes in Cstrs and Pmax. The PEEPi, reflecting pulmonary dynamic hyperinflation, was also significantly decreased by doxofylline (-41 percent, on the average). The Pmax was not reliable for evaluation of a single patient, since changes in the elastic pressure can offset changes in the resistive one. No patient experienced significant side effects due to doxofylline. We conclude that (1) the effects of therapy can be assessed noninvasively at bedside in critically ill patients; (2) doxofylline is a rapid and efficient bronchodilator in mechanically ventilated patients with ARF and airflow obstruction; and (3) the decrease in the respiratory resistance and PEEPi, associated with an improved mechanical efficiency of the respiratory muscles at a lower pulmonary volume, can provide better conditions for the patient-ventilator interaction and for weaning.