Dear Editor

We thank Dr Chan for his comments relating to the recently published guidelines for the diagnosis and management of spontaneous pneumothorces.[1] Dr Chan raises the contentious issue of estimation of the size of a pneumothorax from a plain chest radiograph. We have attempted to use a variation of the method of Axel based on the largest distance from the chest wall to the pleural line and using the assumption that because volume of the lung and the hemi-thorax are roughly proportional to the cube of their diameters, the volume of pneumothorax can be estimated by measuring an average diameter of the lung and the hemithorax, cubing these diameters and finding the ratios.[2]

As Dr Chan rightly points out this is not an exact science as the lungs have a propensity not to maintain a constant shape when they collapse. CT of thorax, when compared with plain radiograph, gives a more accurate estimate of the volume of the pneumothorax. However, while CT may be the only way to give an exact estimate of pneumothorax volume and pattern of lung collapse, it is not often feasible in the emergency room. The correlation co-efficient between CT and plain radiograph is 0.71, p<_0.01.3 thus="thus" while="while" cxr="cxr" is="is" not="not" as="as" effective="effective" ct="ct" it="it" does="does" still="still" provide="provide" a="a" useful="useful" and="and" reasonably="reasonably" accurate="accurate" estimate="estimate" of="of" pneumothorax="pneumothorax" size="size" in="in" most="most" cases="cases" using="using" the="the" method="method" outlined="outlined" current="current" guidelines.="guidelines." we="we" suggest="suggest" that="that" guideline="guideline" an="an" improvement="improvement" on="on" _1993="_1993" guidelines="guidelines" which="which" tended="tended" to="to" underestimate="underestimate" potentially="potentially" importance="importance" pneumothorax.="pneumothorax." choosing="choosing" distance="distance" _2="_2" cms="cms" above="above" volume="volume" usually="usually" _50="_50" gives="gives" emergency="emergency" room="room" physician="physician" easy="easy" use="use" fairly="fairly" reliable="reliable" adhere="adhere" to.="to." has="has" been="been" shown="shown" secondary="secondary" pneumothoraces="pneumothoraces" this="this" are="are" unlikely="unlikely" respond="respond" simple="simple" aspiration="aspiration" will="will" hopefully="hopefully" guidance="guidance" patients="patients" treat="treat" with="with" intercostals="intercostals" tube="tube" drainage.4="drainage.4" supported="supported" by="by" evidence="evidence" now="now" clear="clear" unambiguous="unambiguous" guideline.="guideline." also="also" hope="hope" suggesting="suggesting" _="_" _2cms="_2cms" depth="depth" should="should" be="be" aspirated="aspirated" may="may" reduce="reduce" number="number" needle="needle" injuries="injuries" lung="lung" parenchyma="parenchyma" would="would" have="have" much="much" greater="greater" approximation="approximation" chest="chest" wall="wall" primary="primary" spontaneous="spontaneous" cm="cm" depth.="depth." p="p"/> As Dr Chan points out the American College of Chest Physicians have suggested a different arbitrary system for estimating pneumothorax size suggesting that ‘small’ pneumothoraces were defined by distances <3 cms from apex to cupula of lung and ‘large’ pneumothoraces had distances > 3cms.[5] This seems to have been arbitrarily defined and we are not provided with evidence to support these measurements. Several authors have suggested different distances ranging from 1-4 cms on plain radiograph or more complex equations depending on distances from the pleural line to chest wall at three separate distances or even routine use of CT incorporating even more complex mathematics.[6,7] Dr Chan comments on the lack of evidence regarding CXR classification – we have completed an analysis of the CXR appearances in spontaneous pneumothorax, relating them to the various guidelines, and submitted it as an abstract for the winter meeting of the British Thoracic Society. Bearing in mind that the guidelines are primarily prepared for use by relatively inexperienced and non-specialist junior medical staff, who often have to make management decisions in the middle of the night, we would suggest that the BTS guidelines have combined a fairly robust and accurate scientific approach with an easy to interpret and implement guideline to estimate and treat spontaneous pneumothoraces. Finally, we would again take the opportunity to stress that no matter what the size of a pneumothorax, the decision as to what constitutes appropriate treatment depends not just on the size of a pneumothorax on a chest radiograph, but more importantly, on the clinical status of the patient.

References

(1) Henry M, Arnold T, Harvey J. BTS guidelines for the management of spontaneous pneumothorax. Thorax 2003; 58(Suppl 11):ii39-52.

(2) Axel L. A simple way to estimate the size of pneumothoraces. Invest Radiol 1981;105:1147-1150.

(3) Engdahl O, Toft T, Boe J. Chest radiograph - a poor method for determining the size of a pneumothorax. Chest 1993;103:26-29.

(4) Baumann MH, Strange C, Heffner JE, et al. Management of spontaneous pneumothorax. An American College of Chest Physicians Delphi Consensus Statement. Chest 2001; 119: 590-602.

(5) Archer GJ, Hamilton AAD, Upadhyag R, et al. Results of simple aspiration of pneumothoraces. Br J Dis Chest 1985; 79:177-182.

(6) Collins CD, Lopez A, Mathie A, Wood V, Jackson JE, Roddie ME. Quantification of Pneumothorax size on chest radiographs using intrapleural distances: Regression analysis based on volume measurements from helical CT. Am J Radiol 1995;165:1127-1130.

Dear Editor,

It is generally appreciated that the practice of stepping-down inhaled corticosteroid (ICS) therapy in patients with stable asthma is poorly implemented, albeit in the background of limited evidence.¹ Indeed, the appreciation for stepping-down ICS therapy once asthma control is attained is well established within the Global Initiative for Asthma (GINA) guidelines² and has recently been adopted by the British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network (SIGN) consortium.¹

In the latter guidelines, it is recommended that a 25 – 50% of reduction in ICS dose be implemented at 3-monthly intervals.¹ A large study in primary care has shown that patients with stable asthma on moderately high doses of ICS can be safely stepped-down without compromising asthma control.³ However, there are currently no data evaluating the practice of stepping-down ICS therapy in patients with stable asthma in secondary care. Despite transforming the management of asthma, ICS therapy exposes an individual to both local and systemic adverse effects.⁴ Indeed, when taken at high doses, the ICS dose-response curve for systemic adverse effects becomes steep, with little further therapeutic gain.^5,6 Furthermore, the addition of second-line controller therapy may be more advantageous than merely increasing the ICS dose alone.⁷

We carried out a retrospective study to establish whether asthmatic patients attending a respiratory clinic in secondary care were being advised to reduce their ICS dose following a period of stability.

Methods

We assessed patients with asthma being followed-up in the respiratory clinic and retrospectively analysed data for the preceding 12-month period. Strict exclusion criteria were applied. Patients who were actively receiving or had received either oral or parenteral corticosteroids, or immunosuppressive therapy during the 12-month period were not considered eligible for inclusion. Patients also had to be exacerbation-free during this period. Classification of asthma severity was based on GINA guidelines.²

Results

Sixty consecutive patients with asthma were assessed in clinic. 2 patients were receiving parenteral corticosteroids, 4 patients were receiving immunosuppressant therapy, 14 patients were receiving oral corticosteroids, and 28 patients had an asthma exacerbation during the preceding 12 months. Therefore, using strict exclusion criteria, 12 patients were included in the data analysis.

Patient demographic data are shown in Table 1. 3 men and 9 women with mean ± standard error of mean age of 56 ± 6 years and forced expiratory volume in 1 second (FEV₁) of 1.97 ± 0.26 l (73 ± 6 % predicted) completed the study. The mean BDP equivalent ICS daily dose was 1267 ± 140 µg and patients had either moderate (n = 6) or severe (n = 6) asthma. 2 out of 12 patients had step-down in ICS therapy where one patient (number 10) had a 33% reduction in ICS dose from an initial daily dose of BDP 1500µg, having had stable asthma for 11 months, while the other patient (number 11) had a 50% reduction in ICS dose from an initial daily dose of fluticasone propionate (FP) 1000µg, having had stable asthma for 8 months. The remaining 10 out of 12 patients continued on the same dose of ICS despite having had stable asthma during the preceding 12 months. There were no significant differences in any outcomes comparing patients with and without step-down in ICS therapy.

Table 1 Patient demographic details

Discussion

This is the first study to demonstrate that stepping-down ICS therapy in patients with stable asthma is not being routinely adopted in secondary care. Most of the patients were maintained on their usual dose of ICS irrespective of the fact that their asthma had been clinically stable during the preceding 12 months. It is noteworthy that no deterioration in asthma control occurred in the two patients who had step-down in ICS therapy.

We appreciate that our cohort of patients were small in numbers. This was simply a reflection of the difficulty in recruiting patients for such a study in secondary care. Asthma is a chronic condition that is mainly managed in primary care. Indeed, patients who are referred for specialist input, consist primarily of difficult-to-control asthmatics or those who pose diagnostic uncertainties. Therefore, patients with asthma are seldom followed-up in secondary care, especially when diagnosis has been established and treatment commenced. Furthermore, many patients being actively followed-up in secondary care consist of severe asthmatics requiring oral or parenteral corticosteroids, with some requiring immunosuppressant therapy. Such patients were excluded from our study due to the strict criteria that was employed. The requirement for patients not to have an exacerbation or a course of corticosteroids during the preceding 12 months further reduced our number of suitable patients. Therefore, we acknowledge that the population of asthmatics in secondary care may not reflect the true asthmatic population as a whole when compared to those seen in primary care. Nevertheless, these asthmatics do fulfill the criteria for step-down in ICS therapy and there was indeed no reason to treat them any differently in keeping with current guidelines.

A possible reason for the lack of the adoption of stepping-down ICS therapy in secondary care could be attributable to the relatively selective asthmatic population served by secondary care physicians, where most patients have severe, brittle or difficult-to-control asthma. When such patients are using appropriate pharmacotherapy and clinically stable, there is understandably a disinclination to titrate therapy downwards, in case one offsets the control of asthma, which has been difficult to attain in the first instance. Another reason for the less-than-ideal implementation of stepping-down ICS therapy may be attributable to the fairly recent adoption and recommendation of such an approach in asthma management by the BTS and SIGN consortium, owing in part to the substantial lack of available data on this issue.

The rationale behind recommending stepping-down ICS therapy once asthma control is achieved is indisputable. ICS has the propensity to be absorbed from the lungs and gastrointestinal tract into the systemic circulation, leading to adverse effects in a variety of body systems.⁴ Additionally, studies have shown that most of the therapeutic benefit of ICS can be achieved at fairly low doses; 100 – 250µg daily for FP⁵ and 400µg daily for budesonide.⁶ Moreover, the validity of high dose ICS therapy has been put into question in light of recent data showing that stepping-up therapy by doubling the dose of ICS may be ineffective in influencing asthma exacerbations.^8,9 With the increasing popularity of combination ICS and long-acting ß₂-agonist inhalers (67% of our patient cohort), stepping-down is more complicated as it is more difficult to reduce the ICS dose without first splitting the combination inhaler into its separate moieties.

In conclusion, secondary care physicians need to have a heightened awareness in terms of stepping-down ICS therapy in patients with stable asthma. Failing to do so may expose patients to unnecessary and prolonged treatment with high doses of ICS with potentially serious long-term adverse sequelae. Stepping-down ICS therapy not only reflects good practice but is also in accordance with current asthma guidelines.

References

1. BTS/SIGN. The British Thoracic Society and Scottish Intercollegiate Guidelines Network 2004 update to the British guideline on the management of asthma. Available at: http://www.brit-thoracic.org.uk/docs/asthmafull.pdf.
2. GINA. The National Heart, Lung, and Blood Institute and World Health Organisation 2004 update to the Global Initiative for Asthma guideline on the global strategy for asthma management and prevention. Available at: http://www.brit-thoracic.org.uk/docs/asthmafull.pdf.
3. Hawkins G, McMahon AD, Twaddle S, et al. Stepping down inhaled corticosteroids in asthma: randomised controlled trial. BMJ 2003;326:1115-20.
4. Lipworth BJ, Jackson CM. Safety of inhaled and intranasal corticosteroids: lessons for the new millennium. Drug Saf 2000;23:11-33.
5. Holt S, Suder A, Weatherall M, et al. Dose-response relation of inhaled fluticasone propionate in adolescents and adults with asthma: meta-analysis. BMJ 2001;323:253-6.
6. Masoli M, Holt S, Weatherall M, et al. Dose-response relationship of inhaled budesonide in adult asthma: a meta-analysis. Eur Respir J 2004;23:552-8.
7. Shrewsbury S, Pyke S, Britton M. Meta-analysis of increased dose of inhaled steroid or addition of salmeterol in symptomatic asthma (MIASMA). BMJ 2000;320:1368-73.
8. Harrison TW, Oborne J, Newton S, et al. Doubling the dose of inhaled corticosteroid to prevent asthma exacerbations: randomised controlled trial. Lancet 2004;363:271-5.
9. FitzGerald JM, Becker A, Sears MR, et al. Doubling the dose of budesonide versus maintenance treatment in asthma exacerbations. Thorax 2004;59:550-6.

Dear Editor,

I would like to share my views again after hearing from you that what clinical criteria and biochemical parameters for the remission in asthma have been used in your study. What partameters were compared for the asthma remission in spirometery values pre and post remission phases.

In the complete clinical remission what predictors have been taken into consideration for the remission. No doubt remissions do occur but what should be the definitive clinical, biochemical and spirometric parameters that can be considered in future if an asthmatic is to remit.

I would be obliged to get educated on this interesting subject from a learned and experienced researcher S Guerra.

Thankin you

Dr.Anil Bhatia
Senior consultant physician.(visiting)
apollo hospital.
delhi
rangappu@hotmail.com

Dear Editor,

I have been working on the twitch pressure of mouth, diaphragmatic and tracheal (airway) for several years and had done the work about the relationship between the twitch pressure of mouth or the twitch pressure of tracheal and twitch pressure of diaphragmatic in ventilated patients because of respiratory failure or during general anaesthesia because of abdomen operation. Recently, when I read of the article 'Can diaphragmatic contractility be assessed by airway twitch pressure in mechanically ventilated patients?' (Thorax 2003;58;58-62), I found that I had some different ideals from the writers.

First, of the 133 twitches recorded in our patients, 37 were discarded for the following reasons: cardiogenic changes in oesophageal pressure (n=4); my ideal is that cardiogenic changes in oesophageal pressure is always present and the twitch pressure was different when the stimulation was given during different cardiac cycle. The measurement of oesophageal pressure was effected by cardiac cycle and the effect was larger in lying position than in sitting position. The negative pressure of thoracic cavity did not affected the effect of cardiac cycle on the oesophageal pressure. The function of diaphragm was overestimated by the twitch oesophageal pressure measured during systole phrase, but underestimated by that during diostolic phrase and the effect of cardiac cycle on the oesophageal pressure could be eliminated by mathematical filter.

In one of my studies, 25 patients were involved. The dynamical oesophageal pressure were measured in the sitting position, the supine positions before and during general anaesthesia and twitch oesophageal pressure were measured in the supine positions before general anaesthesia. The changing value of dynamical oesophageal pressure in the sitting position, the supine positions before and during general anaesthesia was respectively (1.6±1.1）cmH2O(2.7±1.2)cmH2O and (2.3±1.2)cmH2O and there was a significant difference between sitting position and the supine position before general anaesthesia (P<_0.01 or="or" during="during" general="general" anaesthesia="anaesthesia" p0.05="p0.05" while="while" there="there" was="was" not="not" different="different" between="between" the="the" supine="supine" positions="positions" before="before" and="and" p="p"/>0.05).

The twitch oesophageal pressure during systole and diostolic phrase were respectively (16.3±6.6) cmH2O and (14.1±6.1) cmH2O and there was a significant differentiation (P=0.000) and a relationship (r=0.920, P=0.000) between them, but after eliminated by mathematical filter, they were respectively (15.2±6.2）cmH2O and （15.0±6.0）cmH2O (P>0.05) and had not a differentiation each other (P>0.05).

The mathematical filter method was shown below:

Second, the reason that Paw tw was more negative than Poes tw in 10 of 13 patients was that the compression of the oesophagus and balloon by the heart could, from a functional stand point, increase the elastance of the anatomical structures surrounding the balloon, and the increased elastance of these structures would dampen the transmission of intrathoracic pressure to the lumen of the oesophagus. However, my opinion was that the basic pressure before twitch was the key point. Before twitch the tracheal pressure was 0, and the oesophageal pressure was negative. However, after twitch stimulation, the end point of pressure was almost the same, As a result, the Paw tw was more negative than Poes tw.

Third, patient 6 had the total PEEP, airway pressure and oesophageal pressure was respectively 6.1, ¨C2.8 and ¨C3.6 cmH2O. The PEEP was higher, before twitch stimulation, the abdominal muscle may contracted and reduced the oesophageal and tracheal pressure, especially the later. In my opinion, in these respiratory patients, the twitch pressure should be measured under sedation to make exact the result. I hope future discussion.

Best regards!

ZG Zheng MD and professor

Guangzhou Institute of Respiratory Disease