Interventions for escalation of therapy for acute exacerbations of asthma in children: an overview of Cochrane Reviews

BACKGROUND

Asthma is an illness that commonly affects adults and children, and it serves as a common reason for children to attend emergency departments. An asthma exacerbation is characterised by acute or subacute worsening of shortness of breath, cough, wheezing, and chest tightness and may be triggered by viral respiratory infection, poor compliance with usual medication, a change in the weather, or exposure to allergens or irritants. Most children with asthma have mild or moderate exacerbations and respond well to first-line therapy (inhaled short-acting beta-agonists and systemic corticosteroids). However, the best treatment for the small proportion of seriously ill children who do not respond to first-line therapy is not well understood. Currently, a large number of treatment options are available and there is wide variation in management.

OBJECTIVES

Main objective - To summarise Cochrane Reviews with or without meta-analyses of randomised controlled trials on the efficacy and safety of second-line treatment for children with acute exacerbations of asthma (i.e. after first-line treatments, titrated oxygen delivery, and administration of intermittent inhaled short-acting beta₂-agonists and oral corticosteroids have been tried and have failed) Secondary objectives - To identify gaps in the current evidence base that will inform recommendations for future research and subsequent Cochrane Reviews - To categorise information on reported outcome measures used in trials of escalation of treatment for acute exacerbations of asthma in children, and to make recommendations for development and reporting of standard outcomes in future trials and reviews - To identify relevant randomised controlled trials that have been published since the date of publication of each included review METHODS: We included Cochrane Reviews assessing interventions for children with acute exacerbations of asthma. We searched the Cochrane Database of Systematic Reviews. The search is current to 28 December 2019. We also identified trials that were potentially eligible for, but were not currently included in, published reviews. We assessed the quality of included reviews using the ROBIS criteria (tool used to assess risk of bias in systematic reviews). We presented an evidence synthesis of data from reviews alongside an evidence map of clinical trials. Primary outcomes were length of stay, hospital admission, intensive care unit admission, and adverse effects. We summarised all findings in the text and reported data for each outcome in 'Additional tables'.

MAIN RESULTS

We identified 17 potentially eligible Cochrane Reviews but extracted data from, and rated the quality of, 13 reviews that reported results for children alone. We excluded four reviews as one did not include any randomised controlled trials (RCTs), one did not provide subgroup data for children, and the last two had been updated and replaced by subsequent reviews. The 13 reviews included 67 trials; the number of trials in each review ranged from a single trial up to 27 trials. The vast majority of comparisons included between one and three trials, involving fewer than 100 participants. The total number of participants included in reviews ranged from 40 to 2630. All studies included children; 16 (24%) included children younger than two years of age. Most of the reviews reported search dates older than four years. We have summarised the published evidence as outlined in Cochrane Reviews. Key findings, in terms of our primary outcomes, are that (1) intravenous magnesium sulfate was the only intervention shown to reduce hospital length of stay (high-certainty evidence); (2) no evidence suggested that any intervention reduced the risk of intensive care admission (low- to very low-certainty evidence); (3) the risk of hospital admission was reduced by the addition of inhaled anticholinergic agents to inhaled beta₂-agonists (moderate-certainty evidence), the use of intravenous magnesium sulfate (high-certainty evidence), and the use of inhaled heliox (low-certainty evidence); (4) the addition of inhaled magnesium sulfate to usual bronchodilator therapy appears to reduce serious adverse events during hospital admission (moderate-certainty evidence); (5) aminophylline increased vomiting compared to placebo (moderate-certainty evidence) and increased nausea and nausea/vomiting compared to intravenous beta₂-agonists (low-certainty evidence); and (6) the addition of anticholinergic therapy to short-acting beta₂-agonists appeared to reduce the risk of nausea (high-certainty evidence) and tremor (moderate-certainty evidence) but not vomiting (low-certainty evidence). We considered 4 of the 13 reviews to be at high risk of bias based on the ROBIS framework. In all cases, this was due to concerns regarding identification and selection of studies. The certainty of evidence varied widely (by review and also by outcome) and ranged from very low to high.

AUTHORS' CONCLUSIONS

This overview provides the most up-to-date evidence on interventions for escalation of therapy for acute exacerbations of asthma in children from Cochrane Reviews of randomised controlled trials. A vast majority of comparisons involved between one and three trials and fewer than 100 participants, making it difficult to assess the balance between benefits and potential harms. Due to the lack of comparative studies between various treatment options, we are unable to make firm practice recommendations. Intravenous magnesium sulfate appears to reduce both hospital length of stay and the risk of hospital admission. Hospital admission is also reduced with the addition of inhaled anticholinergic agents to inhaled beta₂-agonists. However, further research is required to determine which patients are most likely to benefit from these therapies. Due to the relatively rare incidence of acute severe paediatric asthma, multi-centre research will be required to generate high-quality evidence. A number of existing Cochrane Reviews should be updated, and we recommend that a new review be conducted on the use of high-flow nasal oxygen therapy. Important priorities include development of an internationally agreed core outcome set for future trials in acute severe asthma exacerbations and determination of clinically important differences in these outcomes, which can then inform adequately powered future trials.

Breathing Hydrogen-Oxygen Mixture Decreases Inspiratory Effort in Patients with Tracheal Stenosis

BACKGROUND

Hydrogen-oxygen mixture (H2-O2) may reduce airway resistance in patients with acute severe tracheal stenosis, yet data supporting the clinical use of H2-O2 are insufficient.

OBJECTIVES

To evaluate the efficacy and safety of breathing H2-O2 in acute severe tracheal stenosis.

METHODS

Thirty-five consecutive patients with severe acute tracheal stenosis were recruited in this prospective self-control study. Air, H2-O2 and O2 inhalation was given in 4 consecutive breathing steps: air for 15 min, H2-O2 (6 L per min, H2:O2 = 2: 1) for 15 min, oxygen (3 L per min) for 15 min, and H2-O2 for 120 min. The primary endpoint was inspiratory effort as assessed by diaphragm electromyography (EMGdi); the secondary endpoints were transdiaphragmatic pressure (Pdi), Borg score, vital signs, and impulse oscillometry (IOS). The concentration of H2 in the ambient environment was obtained with 12 monitors. Adverse reactions during the inhalation were recorded.

RESULTS

The mean reduction in the EMGdi under H2-O2 was 10.53 ± 6.83%. The EMGdi significantly decreased during 2 H2-O2 inhalation steps (Steps 2 and 4) compared with air (Step 1) and O2 (Step 3) (52.95 ± 15.00 vs. 42.46 ± 13.90 vs. 53.20 ± 14.74 vs. 42.50 ± 14.12% for Steps 1 through 4, p < 0.05). The mean reduction in the Pdi under H2-O2 was 4.77 ± 3.51 cmH2O. Breathing H2-O2 significantly improved the Borg score and resistance parameters of IOS but not vital signs. No adverse reactions occurred. H2 was undetectable in the environment throughout the procedure.

CONCLUSIONS

Breathing H2-O2 may reduce the inspiratory effort in patients with acute severe tracheal stenosis and can be used for this purpose safely.

High flow nasal heliox improves work of breathing and attenuates lung injury in a newborn porcine lung injury model

BACKGROUND

High flow nasal cannula (HFNC) has been shown to improve ventilation and oxygenation and reduce work of breathing in newborns with respiratory distress. Heliox, decreases resistance to airflow, reduces the work of breathing, facilitates the distribution of inspired gas, and has been shown to attenuate lung inflammation during the treatment of acute lung injury.

HYPOTHESIS

Heliox delivered by HFNC will decrease resistive load, decrease work of breathing, improve ventilation and attenuate lung inflammation during spontaneous breathing following acute lung injury in the newborn pig.

METHODS

Spontaneously breathing neonatal pigs received Nitrox or Heliox by HFNC and studied over 4 hrs following oleic acid injury. Gas exchange, pulmonary mechanics and systemic inflammation were measured serially. Lung inflammation biomarkers were assessed at termination.

RESULTS

Heliox breathing animals demonstrated lower work of breathing reflected by lower tracheal pressure, phase angle and phase relationship. Ventilation efficiency index was greater compared to Nitrox. Heliox group showed less lung inflammation reflected by lower tissue interleukin-6 and 8.

CONCLUSION

High flow nasal Heliox decreased respiratory load, reduced resistive work of breathing indices and attenuated lung inflammatory profile while ventilation was supported at less pressure effort in the presence of acute lung injury.

[Utility of heliox during treatment of upper airway obstruction secondary to bilateral vocal cord paralysis after thyroidectomy]

Helium is a noble gas whose low density decreases airway resistance. This property is utilized when a mixture of helium and oxygen (heliox) is employed in certain clinical situations, particularly in the context of airway obstruction. We report the case of a woman with severe upper airway obstruction due to bilateral vocal cord paralysis after thyroidectomy. Heliox was used temporarily to reduce respiratory effort and avoid the need for tracheal intubation while the obstruction was being treated with antiinflammatory drugs.

Helium-Hyperoxia, Exercise, and Respiratory Mechanics in Chronic Obstructive Pulmonary Disease

RATIONALE

Hyperoxia and normoxic helium independently reduce dynamic hyperinflation and improve the exercise tolerance of patients with chronic obstructive pulmonary disease (COPD). Combining these gases could have an additive effect on dynamic hyperinflation and a greater impact on respiratory mechanics and exercise tolerance.

OBJECTIVE

To investigate whether helium-hyperoxia improves the exercise tolerance and respiratory mechanics of patients with COPD.

METHODS

Ten males with COPD (FEV(1) = 47 +/- 17%pred [mean +/- SD]) performed randomized constant-load cycling at 60% of maximal work rate breathing air, hyperoxia (40% O(2), 60% N(2)), normoxic helium (21% O(2), 79% He), or helium-hyperoxia (40% O(2), 60% He).

MEASUREMENTS

Exercise time, inspiratory capacity (IC), work of breathing, and exertional symptoms were measured with each gas.

RESULTS

Compared with air (9.4 +/- 5.2 min), exercise time was increased with hyperoxia (17.8 +/- 5.8 min) and normoxic helium (16.7 +/- 9.1 min) but the improvement with helium-hyperoxia (26.3 +/- 10.6 min) was greater than both these gases (p = 0.019 and p = 0.007, respectively). At an isotime during exercise, all three gases reduced dyspnea and both helium mixtures increased IC and tidal volume. Only helium-hyperoxia significantly reduced the resistive work of breathing (15.8 +/- 4.2 vs. 10.1 +/- 4.1 L . cm H(2)O(-1)) and the work to overcome intrinsic positive end-expiratory pressure (7.7 +/- 1.9 vs. 3.6 +/- 2.1 L . cm H(2)O(-1)). At symptom limitation, tidal volume remained augmented with both helium mixtures, but IC and the work of breathing were unchanged compared with air.

CONCLUSION

Combining helium and hyperoxia delays dynamic hyperinflation and improves respiratory mechanics, which translates into added improvements in exercise tolerance for patients with COPD.

Effect of inhaled furosemide on air hunger induced in healthy humans

Recent evidence suggests that inhaled furosemide relieves dyspnoea in patients and in normal subjects made dyspnoeic by external resistive loads combined with added dead-space. Furosemide sensitizes lung inflation receptors in rats, and lung inflation reduces air hunger in humans. We therefore hypothesised that inhaled furosemide acts on the air hunger component of dyspnoea. Ten subjects inhaled aerosolized furosemide (40 mg) or placebo in randomised, double blind, crossover experiments. Air hunger was induced by hypercapnia (50+/-2 mmHg) during constrained ventilation (8+/-0.9 L/min) before and after treatment, and rated by subjects using a 100 mm visual analogue scale. Subjects described a sensation of air hunger with little or no work/effort of breathing. Hypercapnia generated less air hunger in the first trial at 23+/-3 min after start of furosemide treatment (58+/-11% to 39+/-14% full scale); the effect varied substantially among subjects. The mean treatment effect, accounting for placebo, was 13% of full scale (P=0.052). We conclude that 40 mg of inhaled furosemide partially relieves air hunger within 1h and is accompanied by substantial diuresis.

Use of heliox in children

For over 70 years, helium-oxygen mixture (heliox) has been promoted as adjunctive therapy to overcome airflow-obstructive disorders and lesions. In the past 2 decades heliox has gained widespread support in many pediatric emergency departments and intensive care units, in treatment of infants and children with both upper and lower airway obstruction. Because heliox is less dense than air or oxygen, it provides more laminar flow in obstructed airways, and it is purported to reduce work of breathing, respiratory distress, and postextubation stridor. Clinical evidence of the effectiveness of heliox in pediatric patients with airflow obstruction is relatively sparse and appears in the literature primarily as case presentations, case series, and small, uncontrolled studies. This article reviews the rationale and methods for heliox treatment of children with asthma, airway obstruction, bronchiolitis, and croup.

Heliox and noninvasive positive-pressure ventilation: a role for heliox in exacerbations of chronic obstructive pulmonary disease?

Evidence-based respiratory therapy for exacerbations of chronic obstructive pulmonary disease (COPD) includes oxygen, inhaled bronchodilators, and noninvasive positive-pressure ventilation. Examining the physics of gas flow, a case can be made either for or against the use of helium-oxygen mixture (heliox) in the care of patients with COPD. The evidence for the use of heliox in patients with COPD exacerbation is not strong at present. Most of the peer-reviewed literature consists of case reports, case series, and physiologic studies in small samples of carefully selected patients. Some patients with COPD exacerbation have a favorable physiologic response to heliox therapy, but predicting who will be a responder is difficult. Moreover, the use of heliox is hampered by the lack of widespread availability of an approved heliox delivery system. Appropriately designed randomized controlled trials with patient-important outcomes, such as avoidance of intubation, decreased intensive-care-unit and hospital days, and decreased cost of therapy, are sorely needed to establish the role of heliox in patients with COPD exacerbation, including those receiving noninvasive positive-pressure ventilation. Lacking such evidence, the use of heliox in patients with COPD exacerbation cannot be considered standard therapy.

Opportunities and risks of using heliox in your clinical practice

Helium-oxygen mixture (heliox) has been advocated for clinical use since 1934, and there has been a growing array of clinical applications. Until recently, administering heliox has required jury-rigging by modifications and/or extension of available devices not designed for use with heliox. This paper reviews devices required to administer heliox and considers how devices designed to deliver air and/or oxygen have been adapted for use with heliox. Use of devices outside of their design limits adds risk and liability, whereas using Food-and-Drug-Administration cleared devices for heliox administration reduces the risk and liability.

Helium-oxygen decreases inspiratory effort and work of breathing during pressure support in intubated patients with chronic obstructive pulmonary disease

OBJECTIVE

To evaluate the impact of helium-oxygen (He/O2) on inspiratory effort and work of breathing (WOB) in intubated COPD patients ventilated with pressure support.

DESIGN AND SETTING

Prospective crossover interventional study in the medical ICU of a university hospital.

PATIENTS AND PARTICIPANTS

Ten patients.

INTERVENTIONS

Sequential inhalation (30 min each) of three gas mixtures: (a) air/O2, (b) He/O2 (c) air/O2, at constant FIO2 and level of pressure support.

MEASUREMENTS AND RESULTS

Inspiratory effort and WOB were determined by esophageal and gastric pressure. Throughout the study pressure support and FIO2 were 14+/-3 cmH2O and 0.33+/-0.07 respectively. Compared to Air/O2, He/O2 reduced the number of ineffective breaths (4+/-5 vs. 9+/-5 breaths/min), intrinsic PEEP (3.1+/-2 vs. 4.8+/-2 cmH2O), the magnitude of negative esophageal pressure swings (6.7+/-2 vs. 9.1+/-4.9 cmH2O), pressure-time product (42+/-37 vs. 67+/-65 cmH2O s(-1) min(-1)), and total WOB (11+/-3 vs. 18+/-10 J/min). Elastic (6+/-1 vs. 10+/-6 J/min) and resistive (5+/-1 vs. 9+/-4 J/min) components of the WOB were decreased by He/O2.

CONCLUSIONS

In intubated COPD patients ventilated with pressure support He/O2 reduces intrinsic PEEP, the number of ineffective breaths, and the magnitude of inspiratory effort and WOB. He/O2 could prove useful in patients with high levels of PEEPi and WOB ventilated in pressure support, for example, during weaning.

Language of dyspnea in panic disorder

Dyspnea is a key symptom in panic attacks. This study investigated different types of dyspnea induced by the 35% CO2 challenge test given to patients with panic disorder (PD). The types of dyspnea provide room for possible conjectures on neurophysiological pathways involved in the experience of breathing discomfort in PD and in the panic-respiration connection. Factor analysis applied to the Dyspnea Questionnaire identified three main factors: breathing effort, sense of suffocation, and rapid breath. Factor scores for breathing effort and sense of suffocation significantly discriminated between patients who did and those who did not report CO2-induced panic attacks. Factor scores for breathing effort significantly discriminated between patients whose reaction resembled their unexpected panic attacks and those whose reaction did not. A dissociation between an increased central respiratory command and a decreased mechanical efficiency of the respiratory response in patients with PD may underlie the breathing effort factor during the CO2 challenge. The sense of suffocation factor was found to be linked to chemosensitivity. Although involved in CO2 reactivity, it may not be a central factor in unexpected panic attacks.

Helium-oxygen reduces work of breathing in mechanically ventilated patients with chronic obstructive pulmonary disease

OBJECTIVE

To evaluate whether helium-oxygen mixture reduces inspiratory work of breathing (WOB) in sedated, paralyzed, and mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (COPD).

DESIGN AND SETTING

Open, prospective, randomized, crossover study in the medical intensive care unit in a university hospital.

PATIENTS AND PARTICIPANTS

23 patients admitted for acute exacerbation of COPD and mechanically ventilated.

MEASUREMENTS

Total WOB (WOBt), elastic WOB (WOBel), resistive WOB (WOBres), and WOB due to PEEPi (WOBPeepi) were measured. Static intrinsic positive end expiratory pressure (PEEPi), static compliance (Crs), inspiratory resistance (Rins), inspiratory (tinsp) and expiratory time constant (texp) were also measured. These variables were compared between air-oxygen and helium-oxygen mixtures.

RESULTS

WOBt significantly decreased with helium-oxygen (2.34+/-1.04 to 1.85+/-1.01 J/l, p<0.001). This reduction was significant for WOBel (1.02+/-0.61 J/l to 0.87+/-0.47, p<0.01), WOBPeepi (0.77+/-0.38 J/l to 0.54+/-0.38, p<0.001), and WOBres (0.55+/-0.19 J/l to 0.44+/-0.24, p<0.05). PEEPi, Rins, tinsp and texp significantly decreased. Crs was unchanged.

CONCLUSIONS

Helium-oxygen mixture decreases WOB in mechanically ventilated COPD patients. Helium-oxygen mixture could be useful to reduce the burden of ventilation.

Apneusis follows disruption of NMDA-type glutamate receptors in vagotomized ground squirrels

The influences of N-methyl-D-aspartate (NMDA) type glutamate receptor antagonism, by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine maleate (MK-801), on breathing pattern and ventilatory chemoresponses, were assessed in anaesthetized vagotomized spontaneously breathing golden-mantled ground squirrels, Spermophilus lateralis. MK-801 was administered by either bilateral pressure micro-injection into a region of the rostral dorsolateral pons, containing the medial and lateral Parabrachial and Kölliker-Fuse nuclei (the Parabrachial complex, PbC), or by systemic injection. Both treatments induced apneusis. These data indicate that functional NMDA receptor-mediated processes located within the PbC terminate inspiration and actively prevent apneusis in vagotomized ground squirrels. Although both hypercapnia and hypoxia stimulated breathing during the apneusis, the responses were generally slight. The breathing frequency component of the hypercapnic ventilatory response was completely eliminated supporting the hypothesis that the PbC is an integral component of the control network for CO(2) chemoreflex responses. Differences in the results of systemic versus PbC MK-801 illustrate that NMDA receptor-mediated processes outside the PbC do influence ventilation. Our data also show that such processes outside the PbC lengthen both inspiration and expiration in this species, slowing ventilation, and are necessary for the expression of the hypoxic ventilatory response.

[Heliox in pediatrics]

Heliox is composed of oxygen and helium and its low specific gravity allows a modification of the gas flow within the airway. Breathing heliox favors a laminar flow and therefore decreases the work of breathing. Its usefulness in the child is established in croup or in post-extubation stridor. It can be considered if conventional treatment fails to improve the child's breathing pattern. Its major goal is to avoid invasive manoeuvers as much as possible.

Mechanism of respiratory insufficiency in pure or mixed drug-induced coma involving benzodiazepines

OBJECTIVE

We tested the hypothesis that the mechanism of respiratory insufficiency in drug-induced coma involving benzodiazepines is an increase in upper airway resistance.

METHODS

Eighteen nonintubated and seven intubated (control) patients were poisoned with hypnotic sedatives involving benzodiazepines. Neurological and respiratory parameters were measured by polysomnography before and after flumazenil. Flumazenil was administered as escalating bolus doses followed by a continuous infusion.

RESULTS

Upon entry, Glasgow Coma Score was 7 +/- 1 in nonintubated and 5 +/- 1 in intubated patients. Snoring with flow limitation and obstructive apnea were recorded in 16 and 5 among the 18 nonintubated patients, respectively. Central apnea was not observed. Total pulmonary resistance was 2.5-fold higher in nonintubated patients than in intubated patients. Total and resistive work of breathing (WOB) was significantly greater in the nonintubated group. Flumazenil bolus administration was associated with an improvement in Glasgow Coma Score from 7 +/- 1 to 13 +/- 1 in the nonintubatedpatients, and from 5 +/- 1 to 11 +/- in the intubated patients. Mean effective bolus doses were 0.3 +/- 0.1 mg in nonintubated patients and 0.6 +/- 0.1 mg in intubated patients. Tidal and minute volumes increased significantly, and WOB decreased significantly in nonintubated patients. In nonintubated patients, the decrease in total WOB resulted from a significant decrease in resistive WOB.

CONCLUSION

Drug-induced coma involving benzodiazepines is characterized by snoring with flow limitation and obstructive apnea. The mechanism of respiratory insufficiency in nonintubated patients with drug-induced coma involving benzodiazepines is an increase in upper airway resistance and WOB.

Breathing He-O2 increases ventilation but does not decrease the work of breathing during exercise

We previously observed an increase in minute ventilation (V E) with resistive unloading (He-O2 breathing) in healthy elderly subjects with normal pulmonary function. To investigate the effects of resistive unloading in elderly subjects with mild chronic airflow limitation (FEV(1)/FVC: 61 +/- 4%), we studied 10 elderly men and women 70 +/- 3 yr of age. These subjects performed graded cycle ergometry to exhaustion, once breathing room air and once breathing a He-O2 gas mixture (79% He, 21% O2). V E, pulmonary mechanics, and PET(CO2) were measured during each 1-min increment in work rate. Data were analyzed by paired t test at rest, at ventilatory threshold (VTh), and during maximal exercise. V E was significantly (p < 0.05) increased at VTh (3.4 +/- 4.0 L/min or 12 +/- 15% increase) and maximal exercise (15.2 +/- 9.7 L/min or 22 +/- 13% increase) while breathing He-O2. Concomitant to the increase in V E, PET(CO2) was decreased at all levels (p < 0.01), whereas total work of breathing against the lung was not different. We concluded that V E is increased during He-O2 breathing because of resistive unloading of the airways and the maintenance of the relationship between the work of breathing and exercise work rate.

Helium oxygen mixtures in the intensive care unit

Heliox, a mixture of helium and oxygen, has a density that is less than that of air. Breathing heliox leads to a reduction in resistance to flow within the airways, and consequently to a decrease in the work of breathing (WOB), particularly in disorders that are characterized by increased airways resistance. Beneficial effects have been observed in patients with asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis, bronchopulmonary dysplasia and upper airways obstruction. Until we have conclusive data that attest to the efficacy of heliox in such conditions, its use will remain controversial. Meanwhile, it appears wise not to incorporate heliox therapy into routine practice because of technical complications and high costs.

Flumazenil abolishes midazolam-induced increase in the work of nasal breathing

PURPOSE

To evaluate the effects of midazolam sedation followed by flumazenil antagonism on the work of nasal breathing in normal humans.

METHODS

We measured minute ventilation through the nasal route, respiratory frequency, nasal resistance (Rn) and the work of nasal breathing under three conditions: awake, during midazolam sedation, and after flumazenil antagonism in eight healthy human subjects. A custom-made, partitioned face mask enabled nasal and oral airflow to be measured separately. To calculate Rn and the work of nasal breathing, nasal mask and oropharyngeal pressure was also measured.

RESULTS

Total resistive work spent on the upstream segment of the nasal route per minute (Wn) (J x min(-1)) was greater during midazolam sedation (3.6 +/- 2.9) than while awake (1.6 +/- 0.9) and after flumazenil antagonism (1.7 +/- 0.6), respectively (mean +/- SD) (P < 0.05). Total resistive work spent on the upstream segment of nasal breathing (WnNnE) (JxL(-1)) increased from 0.31 +/- 0.14 to 0.75 +/- 0.61 after midazolam administration (P < 0.05) and decreased to 0.31 +/- 0.10 after flumazenil. Following midazolam administration, a strong correlation was observed between changes in WnNnE and changes in Rn r = 0.852, P < 0.0001), whereas there was no correlation between changes in Wn and changes in Rn r = 0.159, P = 0.279).

CONCLUSION

The work of breathing spent on the upstream segment of the nasal route increases during midazolam sedation and returns to baseline after flumazenil antagonism.

Helium-oxygen mixture does not improve gas exchange in mechanically ventilated children with bronchiolitis

STATEMENT OF FINDINGS: Varying concentrations of helium-oxygen (heliox) mixtures were evaluated in mechanically ventilated children with bronchiolitis. We hypothesized that, with an increase in the helium:oxygen ratio, and therefore a decrease in gas density, ventilation and oxygenation would improve in children with bronchiolitis. Ten patients, aged 1-9 months, were mechanically ventilated in synchronized intermittent mandatory ventilation (SIMV) mode with the following gas mixtures delivered at 15-min intervals: 50%/50% nitrogen/oxygen, 50%/50% heliox, 60%/40% heliox, 70%/30% heliox, and return to 50%/50% nitrogen/oxygen. The use of different heliox mixtures compared with 50%/50% nitrogen/oxygen in mechanically ventilated children with bronchiolitis did not result in a significant or noticeable decrease in ventilation or oxygenation.

Effect of salbutamol on dynamic hyperinflation in chronic obstructive pulmonary disease patients

Expiratory flow limitation (EFL), which promotes dynamic hyperinflation and increased work of breathing, often occurs in chronic obstructive pulmonary disease (COPD). The purpose of this study was to assess the effect of bronchodilators on EFL and end-expiratory lung volume in patients with moderate-to-severe COPD. EFL was assessed by applying negative expiratory pressure (NEP) at the mouth during tidal expiration. EFL was present when expiratory flow did not increase or increased only in the early phase of expiration with NEP. In 18 patients (age 65+/-2 yrs; forced expiratory volume in one second (FEV1)=45+/-4% predicted) pulmonary function tests and a series of NEP (-3.5 cmH2O) test breaths were performed at rest in a sitting position before and 20 min after inhalation of 400 microg of salbutamol. EFL was detected in 11 patients and persisted after salbutamol in all of these flow-limited (FL) patients. After bronchodilator administration FL patients exhibited a significant decrease in functional residual capacity (FRC) associated with an increase in inspiratory capacity (IC). In contrast, no changes in FRC and IC were observed in the seven non flow-limited (NFL) patients after administration of salbutamol. Except for one NFL patient, the other 17 patients (six NFL and 11 FL) had no reversibility of their bronchial obstruction (delta FEV1 <10% pred). In conclusion, patients with chronic obstructive pulmonary disease and expiratory flow limitation, even if nonresponders in terms of forced expiratory volume in one second, may benefit from bronchodilators because they can breathe, still in a flow-limited manner, at a lower lung volume.

Language of dyspnea in assessment of patients with acute asthma treated with nebulized albuterol

To investigate whether the language of dyspnea provides relevant clinical information in addition to that provided by ratings of overall dyspnea intensity when assessing subjective response to therapy, we conducted a prospective study in a cohort of 25 patients with acute asthma presenting to the emergency department of a tertiary care hospital. Patients received nebulized albuterol treatments every 20 min with a maximum of three doses. At presentation and after each treatment, patients completed spirometry, rated overall dyspnea intensity on a modified Borg scale, and selected phrases that described qualities of breathlessness from a 15-item questionnaire. Paired Student's t tests revealed significant improvements in FEV1 (from 1.39 +/- 0.66 L to 1.80 +/- 0.76 L, p < 0. 001) and reductions in dyspnea intensity (from 5.12 +/- 2.08 to 2.82 +/- 1.59, p < 0.001) after the first albuterol treatment. Dyspnea intensity continued to decrease significantly in response to the second treatment, modified Borg rating 2.26 +/- 1.52, although there was no positive bronchodilator response. The results from Cochran Q tests revealed that the frequency of the experience of "chest tightness" decreased significantly across the phases of treatment. However, the sensations of "work" or "breathing effort" persisted at the same time that the FEV1 revealed ongoing airways obstruction. We conclude that attention to the language of dyspnea would alert health care providers to residual air flow obstruction despite decreases in overall dyspnea intensity.

Work of breathing in anesthetized patients: laryngeal mask airway versus tracheal tube

STUDY OBJECTIVE

To compare the work of breathing associated with the laryngeal mask airway (LMA) and tracheal tube (TT) in spontaneously breathing anesthetized patients.

DESIGN

Randomized, prospective, controlled trial.

SETTING

University teaching hospital.

SUBJECTS

20 ASA physical status I and II patients scheduled for elective peripheral surgery with general anesthesia.

INTERVENTIONS AND MEASUREMENTS

A standardized anesthetic protocol was utilized, and patients were allowed to breathe spontaneously through a circle absorption system. Patients were randomly assigned to receive either LMA (n = 10) or TT (n = 10) for airway management. Work of breathing was determined after the patients' ventilatory status had been allowed to stabilize for 15 minutes and before the onset of the surgical stimulus. Airflow and esophageal pressures were measured using a pneumotachograph and an esophageal balloon, respectively, and the values were subsequently integrated to determine work of breathing.

MAIN RESULTS

The two groups were similar with respect to demographic characteristics and the end-tidal concentrations of carbon dioxide and isoflurane. Work of breathing per minute through the LMA (1.4+/-0.3 J/min) was significantly lower than that through the TT (1.9+/-0.4 J/min).

CONCLUSION

In healthy, anesthetized, spontaneously breathing patients, work of breathing is significantly lower through the LMA than the TT.

Susceptibility to upper airway obstruction during partial neuromuscular block

BACKGROUND

Airway obstruction after anesthesia may be caused or exaggerated by residual neuromuscular block, with loss of muscle support for collapsible upper airway structures.

METHODS

Six male volunteers were studied before treatment, during stable partial neuromuscular block with vecuronium at a mean train-of-four (TOF) ratio of 50% (95% CI, 36-61%), and after reversal by neostigmine. Catheter-mounted transducers were placed in the pharynx and esophagus to estimate, respectively, the upper airway resistance, and the work of breathing (calculated as the time integral of the inspiratory pressure developed by the respiratory muscles, esophageal pressure time product) during quiet breathing, during breathing 5% carbon dioxide, and while breathing with an inspiratory resistor. Breathing with pressure at the airway opening held at pressures from -5 to 40 cm H2O were also tested to assess airway collapsibility.

RESULTS

Although breathing through a resistor increased upper airway resistance from 1.2 (0.67, 1.72) cm H2O x l(-1) x s to 2.5 (1.32, 3.38) cm H2O x l(-1) x s, and carbon dioxide stimulation reduced resistance to 0.8 (0.46, 1.33) cm H2O x l(-1) x s, no effect of partial neuromuscular block (mean TOF ratio, 52%) on upper airway properties could be shown.

CONCLUSIONS

Neuromuscular block with a TOF ratio of 50% can be present yet clinically difficult to detect in patients recovering from anesthesia. This degree of block has no effect on airway patency in volunteers, even during challenge. Airway obstruction during recovery from anesthesia thus is more likely to be caused by residual effects of general anesthetic agents or centrally acting analgesics, either alone or perhaps in concert with residual neuromuscular block.

Effect of bedtime alcohol on inspiratory resistance and respiratory drive in snoring and nonsnoring men

We measured inspiratory resistance (R1), inspiratory occlusion pressure (P0.1), and the ventilatory responses to hypercapnia and isocapnic hypoxia during waking and during stage 2 non-rapid eye movement sleep in nine young men who were habitual snorers. They were studied on 2 nights during the 3 hours after receiving a bedtime drink containing either a placebo or 100-proof vodka (1.5 ml/kg) in orange juice. We compared the results with those we reported previously in 10 nonsnoring but otherwise similar men. Waking R1 was the same in nonsnorers and snorers, and it was not affected by ethanol. During sleep on the control night, R1 increased by 70% in nonsnorers and by 280% in snorers. On the ethanol night, the increase from waking to sleeping was more than doubled in both nonsnorers and snorers. P0.1 and the responses to hypercapnia and hypoxia showed no differences between nonsnorers and snorers, therefore the results from the two groups were pooled. Minute ventilation and the hypercapnic response decreased from waking to sleeping and P0.1 was more negative during sleep, but there was no significant effect of ethanol. There was a significant correlation between the changes from waking to sleeping in R1 and P0.1 on the ethanol night suggesting that inspiratory effort increased in response to the increased resistance. The response to isocapnic hypoxia showed no effect of either sleep state or drink. Inspiratory time did not change but mean inspiratory flow (VT/T1) was significantly reduced during sleep on both control and ethanol nights. The duty cycle ratio (T1/Ttot) was significantly increased during sleep on the ethanol night. Despite its great effect on inspiratory resistance, especially in snorers, ethanol, in the dose used in our study, does not augment the depression of minute ventilation or of the hypercapnic response that occur normally in stage 2 non-rapid eye movement sleep. After ethanol, our subjects showed the decreased VT/T1 and the increased T1/Ttot that occur normally during sleep in response to an inspiratory resistive load. However, they also showed increased inspiratory effort. The combination of increased inspiratory resistance and greater inspiratory effort would increase the tendency of an unstable upper airway to collapse and could account for the aggravation of obstructive sleep apnea by ethanol.

Inhaled helium-oxygen revisited: effect of inhaled helium-oxygen during the treatment of status asthmaticus in children

OBJECTIVES

To assess the effects of breathing a low-density gas mixture on dyspnea and the pulsus paradoxus in children with status asthmaticus.

DESIGN

In an urban academic tertiary referral center, 18 patients, aged 16 months to 16 years, who were being treated for status asthmaticus with continuously inhaled beta-agonist and intravenously administered methylprednisolone and had a pulsus paradoxus of greater than 15 mm Hg received either an 80%:20% helium-oxygen gas mixture (HELIOX patients) or room air (control patients) at 10 L/min by nonrebreathing face mask in a double-blind, randomized, controlled trial. In all patients, baseline data, including pulsus paradoxus (determined by sphygmomanometer or arterial catheter blood pressure readings), respiratory rate, heart rate, investigator-scored dyspnea index, and oxygen saturation, were compared with values obtained 15 minutes during and after intervention. In a subset of patients, peak flows before and after breathing HELIOX or room air were measured. When clinically indicated, arterial blood gases were obtained.

RESULTS

The pulsus paradoxus (in millimeters of mercury) fell significantly from an initial mean value of 23.3 +/- 6.8 to 10.6 +/- 2.8 with HELIOX breathing (p < 0.001) and increased again to 18.5 +/- 7.3 after cessation of HELIOX. Peak flow increased 69.4% +/- 12.8% during HELIOX breathing (p < 0.05). The dyspnea index decreased from an initial mean value of 5.7 +/- 1.3 to 1.9 +/- 1.7 with HELIOX breathing (p < 0.0002) and increased again to 4.0 +/- 0.5 after cessation of HELIOX breathing. In control patients, there was no significant difference in pulsus paradoxus or dyspnea index at any time during the study period. Mechanical ventilation was averted in three patients in whom dyspnea lessened dramatically during breathing of HELIOX.

CONCLUSION

During acute status asthmaticus, inhaled HELIOX significantly lowered the pulsus paradoxus, increased peak flow, and lessened the dyspnea index. Moreover, HELIOX spared three patients a planned intubation and caused no apparent side effects. Thus HELIOX reduces the work of breathing and may forestall respiratory failure in children with status asthmaticus, thus preventing the need for mechanical ventilation.

Treatment of acute bronchospasm with beta-adrenergic agonist aerosols delivered by a nasal bilevel positive airway pressure circuit

STUDY OBJECTIVE

To determine whether beta-adrenergic agonist aerosols are more effective in treating acute bronchospasm if delivered by nasal bilevel positive airway pressure (BiPAP) than by a small-volume nebulizer (SVN). We hypothesized that BiPAP would reduce the work of breathing in asthmatic patients and thereby hasten improvement of bronchospasm from beta-agonist therapy. Previous trials with aerosols given by intermittent positive-pressure breathing were unrewarding, but BiPAP is unique in that inspiratory (IPAP) and expiratory (EPAP) support pressures may be set separately.

DESIGN

Convenience-randomized prospective clinical study.

SETTING

Emergency department of an urban tertiary care teaching hospital.

PARTICIPANTS

Afebrile, wheezing patients between 18 and 40 years of age.

INTERVENTIONS

Patients were randomly assigned to receive two doses of aerosolized albuterol (2.5 mg in 3 mL normal saline solution), 20 minutes apart, delivered by either SVN (n = 40) or BiPAP (n = 60) by nosemask or facemask (IPAP, 10 cm H2O; EPAP, 5 cm H2O).

RESULTS

Peak expiratory flow rate (PEFR), arterial blood oxygen saturation (by pulse oximetry), and pulse and respiratory rates were measured at baseline and after each treatment. The two treatment groups had similar values for pulse oximetry, pulse rate, respiratory rate, and percent of predicted peak expiratory flow rate (%PPEFR) at entry, and all patients experienced similar changes in the first three of these variables through the course of treatment. BiPAP patients had a significantly greater increase in %PPEFR after each treatment (P = .0011) and from baseline to completion (P = .0013). Increase in absolute PEFR was greater in the BiPAP group (from 211 +/- 89 [mean +/- SD] to 357 +/- 108 L/minute for BiPAP, from 183 +/- 60 to 280 +/- 87 L/minute for SVN; P = .0001).

CONCLUSION

In this population, response to initial ED management of bronchospasm, as measured by PEFR, was better with aerosols delivered by BiPAP than with those delivered by SVN.

Acetazolamide-induced inhibition of carbonic anhydrase influences energy metabolism and respiratory work in healthy subjects

To assess the usefulness of acetazolamide in weaning a patient from a respirator, we monitored the changes in the respiratory quotient ratio (RQ ratio), the ventilation volume (VE; l/min.), carbon dioxide elimination (VCO2; ml/min.), the oxygen consumption (VO2; ml/min.) and the metabolic energy expenditure (EE; Cal/day) for 6 hours before (baseline) and after the intravenous administration of acetazolamide, 6 mg/kg, in 12 healthy adult volunteers. The RQ ratio decreased significantly from 0.88 to 0.82 after the injection of acetazolamide, 6 mg/kg, and remained below baseline throughout the 6 hours of observation. VCO2 decreased significantly and VE increased significantly after acetazolamide administration. There were no significant changes in VO2 or EE. The RQ ratio increased only slightly, from 0.85 to 0.87, in the control group (no acetazolamide). No significant changes in VCO2 or VE were observed in the control group. Findings suggest that acetazolamide may alter the main pathway of energy metabolism from being carbohydrate-dominant to being fat-dominant, with a resulting fall in CO2 production to maintain the adequate work of ventilation. The inhibition of carbonic anhydrase by acetazolamide may be useful in reducing respiratory work in a patient who is weaned from a respirator.

Heliox improves pulsus paradoxus and peak expiratory flow in nonintubated patients with severe asthma

Heliox is a blend of helium and oxygen with a gas density less than that of air that decreases airway resistance (Raw) in patients ventilated for status asthmaticus. We tested whether breathing an 80:20 mixture of helium:oxygen would reduce pulsus paradoxus (PP) and increase peak expiratory flow (PEF) in patients presenting to the emergency room with an exacerbation of asthma. After receiving 30 min of beta-agonist aerosols and intravenously administered methylprednisolone, 27 patients whose PP remained greater than 15 mm Hg and whose PEF remained less than 250 L/min consented to breathe heliox or room air for 15 min. PP decreased and PEF increased with time in control patients, indicating a time-related effect of routine bronchodilator therapy (p < 0.05). PP decreased in 15 of 16 patients during heliox, and the change with heliox was significantly greater than that during air breathing (p < 0.01). PEF measured with a Wright's peak flow meter calibrated for heliox increased in all patients breathing heliox. Again, the increase in PEF during heliox breathing was significantly greater than the corresponding change in control patients breathing air (p < 0.001). To the extent that PP reflects the inspiratory fall in pleural pressure, this reduction in PP indicates a substantial reduction in inspiratory Raw when the less dense gas is inspired through narrowed bronchi having turbulent flow regimes. The 35% increase in PEF while breathing heliox signals a similar reduction in expiratory Raw, which might diminish the hyperinflation often observed during an exacerbation of asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of opioids on inspiratory muscle fatigue during inspiratory resistive loading

The effect of opioids on inspiratory muscle function under high mechanical load is still unknown. Even less clear is the extent to which opioids influence the shift of the electromyographic power spectrum of the inspiratory muscles to lower frequencies during ventilatory stress. We studied seven healthy subjects breathing against high inspiratory threshold loads until exhaustion while keeping the minute ventilation constantly high. We compared runs with and without administration of 0.2 mg kg-1 of morphine sulphate intramuscularly; two subjects were given 30 mg morphine sulphate so that we could study the effect of higher opioid concentration. The endurance time (Tlim), the diaphragmatic electromyogram (EMG), the transdiaphragmatic pressures (Pdi) and the ventilatory effort sensation were analysed. Morphine did not have any effect on Tlim or on the effort sensation elicited by the inspiratory resistance in both concentrations. Analysing the spectral shifts of the diaphragmatic EMG, we did not find any significant difference in the decrease of the centroid frequency between drug and control runs. Furthermore, the activation pattern of the diaphragm and the intercostal muscles, evaluated from the percentage contribution of oesophageal and gastric pressures on the transdiaphragmatic pressure swings, did not change following the administration of morphine. Our study shows that morphine does not change the function of the inspiratory muscles during high-resistive breathing. Morphine does not affect the electromyographic power spectrum of the diaphragm during those resistive breathing runs, either. This points out that during stressful ventilatory situations, the shift of the electromyographic power spectrum is attributed to a peripheral (muscular) event consequent to muscle fatigue and not to the elaboration of endogenous opioids.

Effects of albuterol inhalation on the work of breathing during weaning from mechanical ventilation

The work of breathing is a major determinant of the success of weaning from mechanical ventilation. The aim of this study was to assess whether an inhaled bronchodilator could reduce the mechanical load on the respiratory muscles and diminish the work. For this purpose, 15 intubated patients in the process of weaning from mechanical ventilation inhaled the beta 2-agonist bronchodilator albuterol via a spacer device filled with 1 mg of the drug and connected to the endotracheal tube. During spontaneous breathing, the mean work of breathing diminished significantly after albuterol, from 9.35 +/- 1.05 to 8.33 +/- 1.13 J/min (p less than 0.01), and seven patients exhibited a decrease superior or equal to 15%. This decrease resulted from a marked reduction in lung and airway resistance, from 12.0 +/- 1.7 to 9.8 +/- 1.4 cm H2O.L-1.s (p less than 0.05). No significant changes were observed in the breathing pattern, intrinsic PEEP or arterial blood gas measurements after albuterol, and peripheral cardiovascular effects were not significant. In seven patients, we were able to compare the changes that occurred after albuterol in the work of breathing during weaning from mechanical ventilation with the changes in pulmonary function induced by albuterol after extubation, as assessed by the forced oscillation method. A close correlation was found between the two types of change, further indicating that the reduction in the work of breathing was more likely to occur in patients with the largest bronchodilating effect of albuterol at baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of codeine on the sensations elicited by loaded breathing

The present study examined the effect of codeine, a centrally acting opiate, on the respiratory sensations elicited in normal subjects by breathing to exhaustion against externally applied inspiratory threshold loads. Subjects were tested on two separate days following the double-blind, randomized administration of either placebo or codeine (90 mg). The intensity of the sensations of effort and discomfort experienced during two loaded breathing trials (a "high" load that was 73% of the maximum inspiratory pressure (MIP) and a "low" load that was 63% of the MIP) was evaluated using category (Borg) scores on each day of study. To verify that the dosage of codeine administered was sufficient to produce analgesia, we also determined the effect of this dosage on the time that subjects could tolerate immersion of one hand in ice water. Codeine altered neither the perceived effort nor the sense of discomfort associated with breathing against external loads and had no appreciable effect on the time to exhaustion during loaded breathing trials. This dose of codeine did, however, increase the time that ice water immersion could be tolerated and reduced the rate at which the sense of discomfort increased over time during ice water trials. These results indicate that, provided the pressure-time index of respiratory muscle contraction remains constant, analgesic doses of codeine alter neither the sensations elicited by loaded breathing nor the total time that breathing against a fatiguing inspiratory load can be tolerated.

Meclofenamate increases ventilation in lambs

To investigate the effects of the prostaglandin synthetase inhibitor, meclofenamate, on postnatal ventilation, we studied 11 unanaesthetised, spontaneously-breathing lambs at an average age of 7.9 +/- 1.1 days (SEM; range 5-14 days) and an average weight of 4.9 +/- 0.5 kg (range 3.0-7.0 kg). After a 30-min control period we infused 4.23 mg/kg meclofenamate over 10 min and then gave 0.23 mg/h per kg for the remainder of the 4 h. Ventilation increased progressively from a control value of 515 +/- 72 ml/min per kg to a maximum of 753 +/- 100 ml/min per kg after 3h of infusion (P less than 0.05) due to an increased breathing rate; the effects were similar during both high- and low-voltage electrocortical activity. There were no significant changes in tidal volume, heart rate, blood pressure, arterial pH or PaCO2, the increased ventilation resulted from either an increase in dead space ventilation or an increase in CO2 production. This study indicates that meclofenamate causes an increase in ventilation in lambs but no changes in pH of PaCO2. The mechanism and site of action remain to be defined.

Indoor and outdoor pollutants and the upper respiratory tract

The health effects of both indoor and outdoor air pollutants are of increasing concern. The health effects of outdoor air pollutants traditionally have been assessed through measurements of lower respiratory tract changes. However, it has been shown that one outdoor air pollutant, sulfur dioxide, decreases nasal mucus flow and increases nasal airway resistance. Along with cigarette smoke, indoor air pollutants such as formaldehyde, cadmium, and ammonium or sulfate ions have been shown to alter upper airway mucociliary function. Emissions from wood stoves are known to irritate the upper airways. Measurement of nasal airway resistance using posterior rhinomanometry allows quantification of nasal function. This technique recently has been used to demonstrate that adolescents with allergic asthma have increased work of breathing after inhalation of 0.5 ppm sulfur dioxide. Another study using posterior rhinomanometry showed that clerical workers had increased work of breathing after exposure to carbonless copy paper as compared with bond paper. This brief review of upper respiratory tract changes after pollutant exposure should serve as a reminder that a complete clinical history must include questions designed to ascertain the patient's exposure history to both outdoor and indoor air pollutants. These exposures can have a major impact on the health of the upper respiratory system.

Theophylline as a bronchodilator in COPD and its combination with inhaled beta-adrenergic drugs

The bronchodilating action of theophylline in COPD has been examined, with emphasis on its combined use with inhaled beta 2 agonists. The suggestion is made that failure to recognize the nonlinearity of the dose-response curves for bronchodilators has resulted in underestimating their combined action. Recent studies suggest that systemic theophylline has somewhat different actions on the airways in COPD than inhaled beta agonists, and that more bronchodilation may be possible when the two are used together than large doses of either one. By analogy, with asthma the suggestion is also made that the addition of theophylline is also likely to provide a more constant bronchodilation, reducing peak-trough variations in flow. The most complete clinical comparison to date suggests that, in currently sanctioned doses, a regimen containing both theophylline and an inhaled beta 2 agonist provides significantly greater bronchodilation than either drug alone, with fewer patient withdrawals. Further carefully designed studies are needed to resolve this issue, and particularly, to identify those patients who will derive the greatest benefit from a combined regimen.

Effects of barbiturate anesthesia on functional residual capacity and ribcage/diaphragm contributions to ventilation

The effect of iv methohexital infusion anesthesia on functional residual capacity (FRC) (helium dilution) in 14 surgical patients (age 23 to 59 years) was determined. Eight subjects were studied wearing an inflatable mask, sealed with surgical lubricant. They showed a mean +/- SD 3.5 +/- 6.4% FRC decrease (no significance). Six subjects studied via mouthpiece awake and via endotracheal tube during anesthesia showed a mean 22 +/- 19% reduction in FRC, significantly greater than face mask studies (P less than 0.05). The greatest FRC decrease occurred in subjects with repetitive or protracted coughing after intubation. The serum methohexital level was 6.6 +/- 3.6 micrograms/ml for intubated patients, and 6.0 +/- 1.1 micrograms/ml in those with face mask (no significance). The depth of anesthesia was sufficient to produce a 50% reduction in ventilatory response to CO2 rebreathing, from 15.8 to 8.7 l/min/% CO2. Respitrace plethysmography indicated a 38 +/- 12% ribcage contribution to tidal volume during quiet breathing, which increased to 47 +/- 14% with CO2 breathing (end-tidal FCO2 9-10%). There was no dimunition of ribcage contribution during anesthesia in either group, irrespective of CO2 concentration. The authors interpret their findings to indicate that iv methohexital anesthesia does not produce FRC reduction, in contrast to an inhaled anesthetic such as halothane. It is proposed that this difference may be related to maintenance of coordinated ribcage/diaphragm muscle activity, because ribcage activity is markedly suppressed by halothane. In addition, it is proposed that FRC reduction in intubated subjects was the result of a confounding variable, namely coughing in response to the endotracheal tube.

Physiologic effects of terbutaline on pulmonary function of infants with bronchopulmonary dysplasia

This study defines the physiologic changes in pulmonary mechanics induced by subcutaneous terbutaline administration in ventilator-dependent infants with severe bronchopulmonary dysplasia (BPD). Eight such infants (mean +/- SEM weight = 2.56 +/- 0.32 kg, postnatal age = 13.0 +/- 3.2 weeks) were chosen for the study. Pulmonary mechanics and arterial blood gases were measured in the control state and at 30 and 60 minutes following the subcutaneous injection of 5 micrograms/kg terbutaline. There was a significant (p less than 0.001) improvement in lung compliance from baseline values at 30 minutes and at 60 minutes (38%). A significant (p less than 0.05) decrease of 23% in the average pulmonary resistance at 30 minutes and a 26% decrease at 60 minutes from control values were observed. An increase in the I/E ratio occurred in all patients at 60 minutes (p less than 0.01). In addition, clinical improvement was noted in six of eight infants. Administration of terbutaline demonstrated a significant improvement in the pulmonary mechanics of infants with severe BPD.

Control of larynx during loaded breathing in normal subjects

We examined laryngeal resistance (Rla) in six normal subjects in control and four kinds of loaded breathing: hypercapnia, chest strapping, added external resistance, and inhaled methacholine. Rla was measured with a low-frequency sound methed (Sekizawa et al., J. Appl. Physiol. 55: 591-597, 1983). In control and the four kinds of loaded breathing, changes in Rla were tightly coupled with ventilation and Rla decreased during inspiration and increased during expiration. Hypercapnia and chest strapping significantly decreased Rla in both inspiration and expiration in all subjects. Added external resistance decreased inspiratory Rla in all subjects, but decreased expiratory Rla in three subjects, did not change it in two subjects, and increased it in one subject. Inhaled methacholine increased Rla in both inspiration and expiration in all subjects. The present study suggests that although laryngeal movement is tightly coupled with ventilation, laryngeal aperture may be determined by the complex competition of dilating and constricting mechanisms associated with the activity of the respiratory center and neural reflexes from the airway.

Halothane anesthesia reduces pulmonary function in the newborn lamb

To study the effects of anesthesia on respiratory function of the neonate, the authors investigated the effect of breathing 100% oxygen and of breathing oxygen plus 0.75 MAC halothane on functional residual capacity, lung and airway resistance, expired minute volume, work of breathing, lung compliance, and blood gases and pH in nine 5-8-day-old, 4.6-7.7-kg lambs. Breathing 100% oxygen increased PaO2 but had no effect on PaCO2, minute ventilation, or lung mechanics. Three-fourths MAC halothane depressed minute ventilation 34% +/- 13% (P less than 0.05) and increased PaCO2 50% +/- 5% (P less than 0.05). Lung and airway resistance increased 59% +/- 26% (P less than 0.05); work of breathing decreased (P less than 0.05); and lung compliance was unchanged. Functional residual capacity was reduced 32% +/- 6% (P less than 0.05), which may be due to loss of diaphragm and intercostal muscle function and to an inability to take deep breaths. The authors conclude that 0.75 MAC halothane significantly impairs the pulmonary function of lambs who breathe spontaneously. Similar changes in human infants could account for the hypoxemia and hypercarbia that often are seen during anesthesia.

Influence of brotizolam on the ventilatory and mouth-occlusion pressure response to hypercapnia in patients with chronic obstructive pulmonary disease

Effect of 0.25 mg brotizolam on patients with chronic obstructive lung disease of moderate to severe degree was studied. There was no difference between the slopes of ventilation vs alveolar CO2 for brotizolam and placebo as compared with base line values. Mouth-occlusion pressures did not change under the influence of drug or placebo. Brotizolam (0.25 mg) is without adverse side-effects on respiratory centre output or on mechanics of ventilation.

The effect of pulmonary stretch receptor activity on the respiratory response to ammonia-inhalation

The contribution of pulmonary stretch receptor (SR) activity to the changes in breathing pattern (f, VT, tI, tE, tI: tE) following inhalation of ammonia vapour has been studied in rabbits at three levels of lung distension, i.e., three levels of SR activity, and during reversible SO2-blockade of SR. The result show that the increase in breathing frequency (f) and the decrease in tidal volume (VT) due to ammonia inhalation are almost identical for animals with and without blockade of SR, whereas the duration of inspiration and expiration (tI, tE) as well as their relationship (tI:tE) vary considerably, the variations depending on the level of SR activity. For a given tI the expiration was longer in animals with SR intact than in animals with SR blocked. It is concluded that in rabbits the increased activity of SR after inhalation of ammonia counteracts significantly the predominant effects of irritant (deflation) receptor stimulation, thus rendering possible a longer expiration.