Response of blood gas tensions to aminophylline and isoprenaline in patients with asthma

A new bronchodilator, rimiterol hydrobromide (R 798): An open study of the bronchodilator, cardiovascular and arterial oxygen changes in asthmatic patients

IN this study, rimiterol has been shown to have a rapid, potent and fairly well maintained bronchodilator effect when given as an aerosol.When given in doses of three (1.5 mg.) and nine (4.5 mg.) times a previously reported 'reference' dose (0.5 mg.), there were no statistically significant increases in heart rate and no untoward changes in the electrocardiogram.The small reductions in arterial oxygen saturation recorded were appreciably less than those reported for the same patients after exercise.The circadian variation in P.E.F.R. was measured in four asthmatic patients and the increase occurring in the afternoon may mask the waning effect of a bronchodilator drug. This would appear to increase the difficulty of interpreting the results of bronchodilator trials extending over several hours.

Blood gas tensions in adult asthma: a systematic review and meta-regression analysis

OBJECTIVE

The last half-century has seen substantial changes in asthma treatment and care. We investigated whether arterial blood gas parameters in acute and non-acute asthma have changed historically.

METHODS

We performed a systematic search of the literature for studies reporting P(aO2) , P(aCO2) and forced expiratory volume in 1 s, percentage of predicted (FEV1%). For each of the blood gas parameters, meta-regression analyses examined its association with four background variables: the publication year, mean FEV1%, mean age and female fraction in the respective studies.

RESULTS

After screening, we included 43 articles comprising 61 datasets published between 1967 and 2013. In studies of habitual-state asthma, mean P(aO2) was positively associated with the publication year (p = 0.001) and negatively with mean age (p < 0.01). Mean P(aCO2) showed a positive association with publication year (p = 0.001) and a negative association with female fraction (p < 0.05). In acute asthma studies, blood gas levels were unassociated with publication year and mean age, mean P(aO2) was positively associated with FEV1% (p < 0.05) whereas mean P(aCO2) showed a negative association with FEV1% (p < 0.05) for studies with mean FEV1% <40. In neither acute nor habitual-state studies was mean arterial pH associated with any of the predictor variables.

CONCLUSIONS

In studies of habitual-state asthma, mean reported P(aO2) and P(aCO2) levels were found to have increased since 1967. In acute asthma studies, mean P(aO2) and P(aCO2) were associated with mean FEV1% but not with either publication year or patient age.

Gas exchange in disease: asthma, chronic obstructive pulmonary disease, cystic fibrosis, and interstitial lung disease

Ventilation-perfusion (VA/Q) inequality is the underlying abnormality determining hypoxemia and hypercapnia in lung diseases. Hypoxemia in asthma is characterized by the presence of low VA/Q units, which persist despite improvement in airway function after an attack. This hypoxemia is generally attenuated by compensatory redistribution of blood flow mediated by hypoxic vasoconstriction and changes in cardiac output, however, mediator release and bronchodilator therapy may cause deterioration. Patients with chronic obstructive pulmonary disease have more complex patterns of VA/Q inequality, which appear more fixed, and changes in blood flow and ventilation have less benefit in improving gas exchange efficiency. The inability of ventilation to match increasing cardiac output limits exercise capacity as the disease progresses. Deteriorating hypoxemia during exacerbations reflects the falling mixed venous oxygen tension from increased respiratory muscle activity, which is not compensated by any redistribution of VA/Q ratios. Shunt is not a feature of any of these diseases. Patients with cystic fibrosis (CF) have no substantial shunt when managed according to modern treatment regimens. Interstitial lung diseases demonstrate impaired oxygen diffusion across the alveolar-capillary barrier, particularly during exercise, although VA/Q inequality still accounts for most of the gas exchange abnormality. Hypoxemia may limit exercise capacity in these diseases and in CF. Persistent hypercapnic respiratory failure is a feature of advancing chronic obstructive pulmonary disease and CF, closely associated with sleep disordered breathing, which is not a prominent feature of the other diseases. Better understanding of the mechanisms of hypercapnic respiratory failure, and of the detailed mechanisms controlling the distribution of ventilation and blood flow in the lung, are high priorities for future research.

Effects of salmeterol on arterial blood gases in patients with stable chronic obstructive pulmonary disease. Comparison with albuterol and ipratropium

Administration of beta-adrenergic agonist bronchodilators to patients with airways obstruction commonly results in transient decreases in Pa(O(2)) levels despite bronchodilation, an effect that has been attributed to these drugs' pulmonary vasodilator action. We compared the acute effects on gas exchange of salmeterol with those of albuterol and the anticholinergic agent ipratropium in 20 patients with stable chronic obstructive pulmonary disease (COPD). Each agent was given in recommended dosage on separate days in a double-blind, crossover format, and the patients' arterial blood gases (ABGs) were measured at baseline and at intervals to 120 min. Small but statistically significant declines in Pa(O(2)), the primary outcome variable, were found after administration of both salmeterol and albuterol. The decline in PaO2 after salmeterol was of lesser magnitude but was more prolonged than that after albuterol, the greatest mean change being -2.74 +/- 0.89 mm Hg (mean +/- SEM) at 30 min after salmeterol, and -3.45 +/- 0.92 mm Hg at 20 min after albuterol. Following ipratropium, the corresponding change was -1.32 +/- 0.85 mm Hg at 20 min. These declines, which were almost entirely attributable to increases in the alveolar-arterial difference in oxygen tension Delta(A-a)DO2 tended to be more marked in subjects with higher baseline PaO2 values. No subject experienced a decline in PaO2 to levels below 59 mm Hg. There were no significant differences among the three drugs studied. We conclude that despite small decreases in PaO2 after each of the three drugs, the declines were small transient, and of doubtful clinical significance.

Effects of inhaled bronchodilators on pulmonary hemodynamics at rest and during exercise in patients with COPD

INTRODUCTION

Inhaled anticholinergic drugs are often recommended for use as a first-line therapy for patients with COPD because they provide similar or more effective bronchodilating actions, as well as fewer side effects. It is not known, however, which class of bronchodilators is more advantageous for pulmonary hemodynamics, particularly during exercise.

OBJECTIVES

To compare the effects of oxitropium and fenoterol on pulmonary hemodynamics in patients with COPD at rest and during exercise.

PATIENTS

The study participants consisted of 20 consecutive male patients with stable COPD, a mean (+/- SD) age of 68+/-8 years old, and an FEV1/FVC ratio of 47.5+/-10.0%.

METHODS

Eleven patients inhaled two puffs of oxitropium, and nine patients inhaled two puffs of fenoterol. Seven members of each group performed incremental exercise using a cycle ergometer. The hemodynamic measurements with right heart catheterization were performed by taking the average of three consecutive respiratory cycles before and after the administration of inhaled bronchodilators at rest and during exercise.

RESULTS

At rest, despite a similar improvement of spirometric data with the two drugs, fenoterol, not oxitropium, caused significant increases in heart rate and cardiac output, a decrease in pulmonary vascular resistance, and a deteriorated Pao2. During exercise, however, both drugs similarly attenuated elevations in the mean pulmonary arterial pressure (40+/-12 to 38+/-10 mm Hg by oxitropium, and 41+/-9 to 36+/-9 mm Hg by fenoterol), the mean pulmonary capillary wedge pressure, and the mean right atrial pressure.

CONCLUSION

Our findings indicate that both classes of bronchodilators are equally beneficial in the attenuation of right heart afterload during exercise in patients with COPD.

Determining the optimum dose for the intravenous administration of nicardipine in the treatment of acute heart failure--a multicenter study. The Nicardipine Heart Failure Study Group

Nicardipine is a potent arteriolar vasodilator with a negligible negative inotropic effect. Although intravenous administration of this drug has been reported to be effective in the treatment of heart failure, the optimal dose by this route is not clear. This study was designed to determine the optimum dose for the intravenous infusion of nicardipine in the treatment of heart failure. In Trial 1, nicardipine was administered intravenously at a dose of 0.5 microgram/kg per min to 14 patients with acute heart failure. The dose was increased to 1.0 microgram/kg per min in 13 cases with marked improvement at 2 h. In Trial 2, nicardipine was administered in a double-blind manner to 53 patients at 3 different rates of infusion for 2 h: 1.0 (Group 1, n = 19), 2.0 (Group 2, n = 15), and 3.0 (Group 3, n = 19) micrograms/kg per min. Neither heart rate nor mean right atrial pressure changed in any of the 3 groups. Favorable hemodynamic effects were evident in all groups beginning 30 min after the start of infusion, with an increase in cardiac index (control vs 2 h after infusion, L/min per m2) (Group 1: 2.2 +/- 0.4 vs 3.1 +/- 0.8, Group 2: 2.2 +/- 0.4 vs 2.9 +/- 0.5, Group 3: 2.3 +/- 0.3 vs 3.1 +/- 0.7, all p < 0.01 compared to the control) and a decrease in diastolic pulmonary artery pressure (Group 1: 26 +/- 10 vs 19 +/- 7, Group 2: 27 +/- 10 vs 20 +/- 8, Group 3: 26 +/- 7 vs 18 +/- 5 mmHg, all p < 0.01). The decrease in systolic pressure was greatest in Group 3 (Group 1: 141 +/- 31 vs 119 +/- 18, Group 2: 149 +/- 25 vs 118 +/- 17, Group 3; 147 +/- 27 vs 107 +/- 14 mmHg, all p < 0.01 compared to control, and p < 0.05 between Groups 1 and 3). The intravenous drip infusion of nicardipine is effective in the treatment of heart failure by inducing an increase in cardiac output and a decrease in pulmonary artery wedge pressure. The optimal dose in this study was 1.0 microgram/kg per min.

Effects of inhaled anticholinergic drug on dyspnea and gas exchange during exercise in patients with chronic obstructive pulmonary disease

To elucidate the effect of oxitropium bromide (OTB), an anticholinergic drug, on dyspnea and gas exchange during exercise in patients with chronic obstructive pulmonary disease (COPD), we performed the cycle exercise test on 19 patients with COPD (mean age, 72.0 +/- 1.9 years; mean FEV1, 1.28 +/- 0.07 L) before and after inhalation of OTB, 300 micrograms, or placebo, 300 micrograms, in randomized fashion. Spirometry was performed immediately before and 30 min after inhalation of either OTB or placebo. Dyspnea during exercise was evaluated using the Borg scale (BS) and the slope of the regression between BS and oxygen uptake (VO2) during exercise (Borg scale slope: BSS). Arterial oxygen saturation (SaO2) was continuously monitored by pulse oximeter during and after exercise. We also measured the recovery time, which was defined as the time to recover decreases in SaO2 after exercise. After OTB, spirometric indices were improved (delta FEV1 16.8 +/- 0.9 percent) and maximal VO2 during exercise increased significantly (from 986 +/- 46 ml/min to 1,156 +/- 55 ml/min, p < 0.01), but not after placebo. The maximal scores of BS and the BSS were significantly decreased after OTB, but not after placebo. Although the SaO2 at rest and during exercise did not differ with or without either OTB or placebo, the recovery time after OTB (77.3 +/- 6.8 s) was significantly shorter than that before administration (98.4 +/- 14.6 s) (p < 0.01). We conclude that the inhaled OTB produces small but significant improvement both in dyspnea during exercise and in exercise performance in stable COPD and may contribute to improve the quality of life in some patients with COPD. However, gas exchange during exercise of COPD patients is little affected by OTB.

A comparison of the effects of ipratropium bromide and metaproterenol sulfate in acute exacerbations of COPD

Thirty-two patients presenting with acute exacerbations of chronic obstructive pulmonary disease were entered into the following double-blind, crossover study. First (time 0), patients inhaled either ipratropium bromide (54 micrograms) or metaproterenol sulfate (1.95 mg) via a metered dose inhaler (MDI) attached to a device (Inspirease) (phase 1). After 90 minutes, they inhaled whichever of the two medications they had not received in phase 1. This is referred to as phase 2. Pulmonary function (FEV1 and FVC) was measured at time 0, and at 30, 60, and 90 minutes following phase 1 treatment, and at 30, 60, and 90 minutes following phase 2 treatment (120, 150, and 180 minutes from the start of the study). Arterial blood gas samples (n = 20) were obtained at entry into the study and 30 and 90 minutes after phase 1 medication. The groups did not differ in age, degree of airway obstruction, hypoxemia, or theophylline usage at the start of the study. In phase 1, at 90 minutes, pulmonary function in both groups significantly and similarly improved. For ipratropium, FEV1 improved from 0.62 +/- 0.08 L to 0.88 +/- 0.11 L (p less than 0.01) and for metaproterenol FEV1 improved from 0.69 +/- 0.06 to 0.92 +/- 0.09 L (p less than 0.01). There was no further improvement with phase 2 treatment for either group. Thirty minutes after inhaling ipratropium, there was a small but significant rise in PO2 (5.8 +/- 3.0 mm Hg; p less than 0.05) while metaproterenol inhalation resulted in a 6.2 +/- 1.2 mm Hg decline in PO2 (p less than 0.05). These changes were not sustained at 90 minutes. We concluded that for acute exacerbations of COPD, both ipratropium and metaproterenol are effective medications when administered via an MDI attached to a device (Inspirease). However, ipratropium may be a safer choice as it initially did not cause a decline in blood oxygenation.

Changes in airflow obstruction and oxygen saturation in response to exercise and bronchodilators in cystic fibrosis

The airway response to exercise and inhaled terbutaline was assessed in 25 patients with cystic fibrosis (CF), seeking evidence for the possible deleterious effects of bronchial muscle relaxation. We postulated that "early" and "late" flows, taken from the full maximum expiratory flow volume curve, might move paradoxically in patients with unstable airways. Oxygen saturation was measured continuously; desaturation occurred early in exercise with partial recovery thereafter. This was unrelated to changes in expiratory airflow measurements. Both during and after exercise, and after inhaled bronchodilator, changes in expiratory airflow measurements were strikingly variable. Changes in individual measurements should be interpreted in relationship to the within-subject variability of the test in patients with CF. During exercise, there was a significant increase in mean FEV1; this was most marked in patients with worst lung function. Two patients (both with severe lung disease) showed paradoxical changes in early and late flows. After exercise, only two patients showed the asthmatic pattern of postexercise bronchoconstriction. After inhaled bronchodilator, the group as a whole showed small but statistically significant increases in expiratory airflow measurements. Those with highest baseline FEV1 had the greatest bronchodilator response; this is the opposite of the pattern observed in asthma. Paradox did not occur after bronchodilators and only one patient showed a significant fall in late expiratory airflow. This pattern of expiratory airflow changes is compatible with the concept of airway instability in which any beneficial effects of bronchial tone reduction are canceled out by the effects of compression of damaged airways rendered more compliant by loss of bronchial wall tone. We did not observe any clinically important deleterious effects from this mechanism.

Review of acute severe asthma

Status asthmaticus in the 1980s is still occasionally a fatal disorder. Preventable causes appear to be common: failing to appreciate the severity of the illness and undertreatment, particularly with steroids. Thus, an objective data base, early treatment, and frequent reassessment are of paramount importance. Despite intensive therapeutic intervention, mechanical ventilation may be required. In managing the ventilator in these patients, efforts should be directed at minimizing peak airway pressures while vigorous conventional modalities are continued. The need to use mechanical ventilation does not imply that the course of the disease will worsen, and the long-term outlook generally is good. Thus, even a low mortality rate is troubling. Once the acute process has resolved, educating the patient and close follow-up are essential.

High-dose inhaled albuterol in severe chronic airflow limitation

Higher doses of inhaled albuterol have been shown to cause slightly more bronchodilatation than standard doses from a metered-dose inhaler in patients with severe chronic airflow limitation. Higher doses, however, carry an increased risk of side effects, and the optimum dose balancing benefit and adverse effects have yet to be established. We have therefore looked at objective and subjective evidence of beneficial and adverse effects after 4 doses of albuterol in 30 patients with chronic bronchitis, severe airflow limitation, and less than 200 ml increase in FEV1 after 200 micrograms inhaled albuterol. Subjects were given placebo, 400 micrograms, 1 mg, 2 mg, and 4 mg albuterol by dry powder inhaler in random order on separate days in a double-blind study, and FEV1, relaxed VC, PEFR, 12-min walk distance, finger tremor, oxygen saturation, heart rate, and arrhythmias were measured at intervals over 6 h. With increasing doses of albuterol, there was a significant dose-related increase in FEV1, VC, and PEFR, the maximal mean changes being 196 ml, 480 ml, and 50 L/min, respectively. The duration of effect was longer with the higher doses. There was a dose-related increase in heart rate, tremor amplitude, and supraventricular ectopic beats and a dose-related fall in oxygen saturation. There was no drug-related effect on the frequency of ventricular ectopic beats either at rest or during the walk tests. The largest increases in walk distance occurred after the 1 and 2 mg doses and the least after the 4 mg dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Worsening oxygenation in the mechanically ventilated patient. Causes, mechanisms, and early detection

Hypoxemia or worsening oxygenation is a common problem in the ICU. Ventilator-related problems, patient-related problems, including progression of the underlying disease process or superimposed disorders, and interventions, procedures, and medications can all adversely affect the patient's oxygenation status. Each of these causes should be sought for in a rapid and expeditious manner and appropriate corrective actions taken.

Effects of fenoterol on oxygen transport in patients with chronic airflow obstruction

A rise in cardiac output and a fall in arterial oxygen tension are well known side effects of bronchodilator drugs, particularly beta-adrenergic agonists. In recent years, fenoterol (Berotec), an effective beta-adrenergic agonist, has been used at increasing rates in asthmatic subjects, as well as in patients with chronic obstructive pulmonary disease (COPD). The effects of fenoterol on systemic hemodynamics or arterial oxygenation (or both) in patients with COPD have not been investigated; in these individuals, who often have increased sympathetic tone and hypoxemia even at rest, cardiovascular stimulation and a fall in arterial oxygen tension would be particularly undesirable side effects. In 14 patients with COPD (seven without a reversible component of airflow obstruction [group 1]; and seven with a reversible component of airflow obstruction [group 2]), we studied all of the important parameters of oxygen transport before and 60 minutes after administration of fenoterol. Studies were performed at rest and after exercise. At baseline, group 1 showed a faster heart rate, a lower cardiac output, a lower arterial oxygen flow, a wider arteriovenous oxygen content difference (C[a-v]O2), and a higher fraction of oxygen extracted by the tissues from a given arterial oxygen flow. In both groups, all measured parameters, including cardiac output and arterial oxygen pressure (PaO2) remained statistically unchanged one hour after administration of fenoterol; with exercise, the heart rate, blood pressure, minute ventilation, oxygen consumption, C(a-v)O2, and the percentage of oxygen extracted from arterial oxygen flow, as well as cardiac output and PaO2, increased in all instances; the exercise responses were not affected by the drug. These results suggest that at the time of its maximal effect on the airways (60 minutes), fenoterol has no untoward effect on the oxygen transport system, at rest or during exercise, in patients with COPD with or without a reversible component.

Effects of an anticholinergic bronchodilator on arterial blood gases of hypoxemic patients with chronic obstructive pulmonary disease. Comparison with a beta-adrenergic agent

Adrenergic bronchodilators have the potential drawback that they may increase hypoxemia in spite of relieving air-flow obstruction in patients with asthma. Anticholinergic bronchodilators are of interest as alternatives to beta-adrenergic agents, particularly in patients with chronic bronchitis and emphysema, yet little is known of the effects of either class of agent on gas exchange in patients with this diagnosis. We compared their effects on gas exchange in 12 patients with chronic bronchitis and emphysema who also had arterial hypoxemia in a double-blind crossover study. We found that nebulized atropine methonitrate, a quaternary ammonium anticholinergic bronchodilator, resulted in only minor and statistically insignificant effects on gas exchange at all times for as long as 60 min after its inhalation. In contrast, the beta-adrenergic bronchodilator metaproterenol hydrochloride resulted in a statistically significant decrease in the PaO2, the greatest mean decrease being 5.0 +/- 2.5 mm Hg (mean +/- 1 SD). The effects of metaproterenol on arterial blood gases in this population of patients were more prolonged than those previously reported in asthmatic subjects with lesser degrees of hypoxemia. An anticholinergic bronchodilator might be preferable in patients with hypoxemia caused by chronic bronchitis and emphysema in that it does not carry the risk of worsening systemic hypoxemia.

Ventilation-perfusion inequality in chronic asthma

The prevalence and variability of ventilation-perfusion (VA/Q) inequality was examined in 26 stable, symptomatic, asthmatic subjects (mean FEV1/FVC, 79% predicted; mean FEF75, 43% predicted) studied once a week for 9 consecutive weeks. We used a recent modification of the multiple inert gas elimination technique allowing frequent serial studies without the need for sampling arterial blood. The VA/Q inequality was expressed as log SD (the second moment) of the distributions of blood flow (Q) and ventilation (V) on a log scale. Log SDQ averaged 0.74, and in every patient log SDQ exceeded the 95% upper limit of normal (0.60) in 2 wk or more. In only 5 patients was mean log SDQ less than 0.6. The ventilation distribution was less abnormal, with mean log SDV exceeding the 95% normal upper limit in only 4 patients. Bimodal blood-flow distributions containing low VA/Q units were observed at some point in 24 of 26 subjects, but occurrence was variable, and in only one third of all measurements was bimodality found. Analysis of variance showed that 70 to 75% of the total variance of log SD was due to intersubject differences, about 20% was due to random changes over time, and the remaining 7 to 9% was not explained by either and was due mostly to experimental error. Arterial PO2 measured 3 times in each subject was inversely related to log SDQ (r = 0.76), but only 60% of the variance in PaO2 was explained by VA/Q mismatch, the rest being due presumably to variation in mixed venous PO2 and similar extrapulmonary factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Tomography of regional ventilation and perfusion using krypton 81m in normal subjects and asthmatic patients

Single photon emission computed tomography, a rotating gamma camera, and continuous inhalation or infusion of krypton 81m (half life 13 seconds) were used to measure regional ventilation (V), perfusion (Q), and ventilation-perfusion (V/Q) ratios in five normal subjects in supine, prone, and lateral decubitus postures and in three asthmatic patients (supine posture only) before and after inhalation of 2.5 mg nebulised salbutamol. Vertical and horizontal gradients of V, Q, and V/Q were examined at three levels in each lung in regions of 1.9 cm3 size. In normal subjects V and Q increased along the axis of gravity in all postures and at all levels in the lung except for V in the prone position. Smaller horizontal gradients were found with an increase in V and Q from caudal to cranial--again except in the prone posture, where the gradient was slightly reversed. Constraint to outward motion of the ventral chest and abdominal wall is the most likely explanation for the different behaviour in the prone posture. In chronic asthma the vertical gradients of V and V/Q were the reverse of normal, but the Q gradient was normal. Bronchodilator treatment did not affect the vertical or horizontal gradients significantly, but analysis of individual regions showed that, relatively, V/Q worsened in 42% of them; this was associated in two thirds with an increase in fractional Q. After inhalation of beta agonist local vasodilatation may influence V/Q ratios in some units more than bronchodilatation.

Adverse reactions to beta 2-agonist bronchodilators

Beta 2-Agonists are safe and effective bronchodilator drugs. Their major adverse effects of skeletal muscle tremor, tachycardia and various metabolic effects are mediated by beta-adrenoceptor stimulation and are reversible. Skeletal muscle tremor is the most frequent dose-limiting side effect. It may be reduced by commencing treatment with a low dose and if it persists another beta 2-agonist may be tried. Other side effects such as cardiac arrhythmias and reduction in PaO2 are a serious potential problem in some susceptible asthmatics. However, they are infrequent or of a mild degree and are generally outweighed by the good control of asthma produced by beta 2-agonists. Side effects from beta 2-agonist therapy can be minimised by use of the inhaled route which selectively delivers the drug to the airways. Furthermore, selective tolerance develops to their side effects. The dose of a beta 2-agonist should be assessed on the basis of therapeutic effect and the level of tolerance to its side effects. Recommended doses of beta 2-agonists used for long term therapy do not cause clinically significant desensitisation of airway beta-adrenoceptors, although this may become a relevant problem in patients who are regularly receiving very high doses. Intravenous beta 2-agonists have a place in the treatment of severe asthma not responding to nebuliser therapy. In this life-threatening situation with severe airflow obstruction, monitoring of heart rate, PaO2, plasma potassium and the electrocardiogram should be mandatory and supplemental oxygen given so that serious adverse effects are presented.

Ventilation-perfusion relationships in symptomatic asthma. Response to oxygen and clemastine

Continuous distributions of ventilation-perfusion (VA/Q) ratios were measured in ten subjects with moderately severe symptomatic asthma. Six of the subjects had only minimal VA/Q inequality (mean log SD of bloodflow 0.5) despite having airways obstruction similar to that in the four subjects with marked VA/Q inequality (mean log SD of bloodflow 1.0). The six patients with minimal VA/Q inequality developed marked widening of their VA/Q distributions while breathing 100 percent oxygen (mean log SD bloodflow 1.1), and four of these patients maintained more modest widening after receiving an intravenous antihistamine, clemastine (mean log SD bloodflow 0.75). The four subjects with a wide control VA/Q distribution showed smaller changes while breathing pure oxygen and no change after receiving clemastine. FEV1 improved with clemastine treatment in the first four patients only. The results suggest that the majority of patients with moderately severe asthma have compensatory pulmonary vasoconstriction, causing better VA/Q matching which is responsive to hypoxia and, possibly, histamine. The data demonstrate a relationship between active compensatory vasoconstriction and airway sensitivity to antihistamine.

Oxygen as a driving gas for nebulisers: safe or dangerous?

Changes in blood gas tensions occurring when 100% oxygen or air was used as the driving gas for nebulised salbutamol were studied in 23 patients with severe airways obstruction. The patients fell into three groups: nine had chronic bronchitis and emphysema with carbon dioxide retention, seven had emphysema and chronic bronchitis without carbon dioxide retention, and seven had severe asthma (no carbon dioxide retention). When oxygen was used as the driving gas patients who retained carbon dioxide showed a mean rise of 1.03 kPa (7.7 mm Hg) in their pressure of carbon dioxide (Pco2) after 15 minutes (p less than 0.001) but the Pco2 returned to baseline values within 20 minutes of stopping the nebuliser. The other two groups showed no rise in Pco2 with oxygen. When air was used as the driving gas none of the groups became significantly more hypoxic. Although it is safe to use oxygen as the driving gas for nebulisers in patients with obstructive airways disease with normal Pco2, caution should be exercised in those who already have carbon dioxide retention.

Control of asthma

Developments of the past decade have greatly improved the likelihood that patients can control their asthma. Inhaled medications are basic to a regimen that may include bronchodilators only, or bronchodilators along with cromoglycate and steroid to the extent required to achieve and maintain control. The regimen is modified for the individual and designed to control symptoms while avoiding an overdose of any one agent and overuse of inhaled bronchodilators (a sign of their lessening effectiveness). The regimen outlined emphasizes controlling asthma day to day and providing effective intervention early to prevent attacks from becoming severe.

Use of peak expiratory flow rates to eliminate unnecessary arterial blood gases in acute asthma

Arterial blood gas (ABG) measurements are used frequently in acute asthma. Because ABGs are expensive and may have significant side effects, a method is needed to identify those patients at risk for a significantly abnormal ABG. We studied the use of peak expiratory flow rates (PEFR) to identify those patients at such risk. Data from 89 emergency visits by 51 asthmatic patients were analyzed. A small but significant correlation between ABG parameters and PEFR was observed (P less than 0.05). No patient with a PEFR greater than or equal to 25% predicted has a PaCO2 greater than 45 mm Hg or pH less than 7.35. This suggests that only those patients with a PEFR less than 25% predicted are at risk for significant hypercarbia or acidosis. We concluded that PEFR may be used as a simple screening tool to safely eliminate ABGs in at least 40% of acute asthmatic patients.

The effect of oral prednisolone on gas exchange in chronic bronchial asthma

Patients with bronchial asthma frequently have a fall in arterial oxygen tension following bronchodilator treatment in spite of a reduction in airway resistance. Administration of 0.11 mM (40 mg) prednisolone in a single dose resulted in an improvement of both airway obstruction and hypoxaemia in chronic asthmatic patients. The arterial oxygen tension, alveolar-arterial oxygen tension difference and venous admixture effect all showed a statistically significant improvement as did the dynamic lung volumes and specific airway conductance.

Terbutaline in the treatment of status asthmaticus

The effect of administration of terbutaline on the pulmonary and cardiovascular systems was studied in ten children with status asthmaticus. Terbutaline (0.01 to 0.04 mg/kg of body weight) was given subcutaneously in multiple doses. A significant decrease in respiratory rate and in arterial blood pressure, with no significant change in cardiac rate, was seen only after the first dose of terbutaline. There was a decrease in mean arterial carbon dioxide tension and an increase in mean arterial oxygen pressure. There was gross clinical improvement following administration of terbutaline in nine of the ten patients. One patient who failed to respond to administration of terbutaline also failed to respond to intravenously administered isoproterenol. We conclude that terbutaline is effective in the treatment of status asthmaticus, with only modest effects on the cardiovascular system.

Response of patients with chronic obstructive lung disease to the regular administration of nebulized isoproterenol. A double-blind crossover study

The effect of the regular use of neublized isoproterenol in 14 patients with symptomatic chronic obstructive lung disease (COLD) was evaluated in a double-blind crossover 16-week study. FEV1, FVC and SGaw were measured before and 45 minutes after bronchodilator therapy every two weeks, while arterial blood gases were measured every eight weeks, before and 45 minutes after bronchodilator therapy. When the patients were considered as a group, there was no significant difference in mean symptom scores or objective pulmonary functions during the drug and placebo periods. Four patients had significantly higher (p less than .05) and two patients significantly lower mean values for at least one of the pulmonary function tests during the isoproterenol period. The patient who is most likely to benefit from isoproterenol on a regular basis appears to have the following characteristics; (1) consistent improvement in pulmonary function tests 45 minutes after use of nebulized bronchodilator; (2) moderate rather than severe COLD; and (3) a relatively normal DLCO.

Comparison of the cardiopulmonary effects of subcutaneously administered epinephrine and terbutaline in patients with reversible airway obstruction

The cardiopulmonary effects of epinephrine and terbutaline were compared in a doubleblind crossover study in 23 subjects with chronic obstructive airway disease. On each of three days each subject received a single subcutaneous dose of saline, 0.25 mg of epinephrine or 0.5 mg of terbutaline. Treatment with epinephrine produced significant increases in forced vital capacity (FVC), forced expiratory volume in one second (FEV-1), maximal expiratory flow rate (MEFR) and maximal mid-expiratory flow (MMEF). Terbutaline caused even more pronounced increases in all four parameters and exhibited a longer duration of action. Neither drug altered arterial pH, arterial oxygen pressure (PaO-2), or arterial carbon dioxide pressure (PaCO-2). With regard to cardiovascular effects, no alterations in either systolic or diastolic pressure were observed. Administration of epinephrine and terbutaline caused statistically significant increases in heart rate. The effect of terbutaline was more pronounced that that of epinephrine. In addition, terbutaline caused a heart rate-related depression of the T-wave of the lead 2 ECG. Neither drug altered any of the hematologic, hemochemical or urinary parameters monitored before and after treatment. Side effects were seen in eight subjects after administration of saline solution, in 13 subjects after epinephrine and in 19 subjects after terbutaline. None of these side effects was considered clinically serious and none required treatment. It is concluded from this study that subcutaneously administered terbutaline is a more effective bronchodilator than epinephrine.