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Eur Respir J 2007; 30:185-187
Copyright ©ERS Journals Ltd 2007

The effect of gas standardisation on exhaled breath condensate pH and PCO2

S. Dodig1, I. Cepelak2, D. Plavec1, Z. Vlasic1, B. Nogalo1 and M. Turkalj1

1 Srebrnjak Children's Hospital, Reference Center for Clinical Paediatric Allergology of the Ministry of Health and Social Welfare, and 2 Dept of Medical Biochemistry and Hematology, Faculty of Pharmacy and Biochemistry, University of Zagreb, Zagreb, Croatia.

To the Editors:

We read with interest the recent article by Kullmann et al. 1 reporting the effect of gas standardisation on exhaled breath condensate (EBC) pH. pH can be determined immediately upon sampling, without gas standardisation 2, or following EBC gas standardisation in case of delayed analysis 3–5. The influence of ambient air and analytical sample preparation pose a major problem for pH and carbon dioxide tension (PCO2) determination in EBC. In gas standardisation (argon bubbling or CO2-free gas), CO2 is removed from the sample, thus reducing the effect of CO2 on pH determination. Kullmann et al. 1 even proposed CO2 standardisation at a PCO2 of 5.33 kPa, physiological alveolar PCO2. Based on the experience with gas determination in blood, which should not be exposed to ambient air, the aim of our study was to determine PCO2 and pH in argon-overlined EBC immediately upon sampling. To our knowledge, it was the first analysis of argon-overlined EBC.

EBC was collected from a total of 53 children (18 children with gastro-oesophageal reflux (GER), 22 asthmatics and 13 healthy controls), aged 5–16 yrs. All asthmatics received their regular anti-asthmatic treatment with inhaled corticosteroids (ICS) or ICS plus long-acting ß2-agonists for 4 weeks. Chronic cough due to GER was diagnosed by 24-h oesophageal pH monitoring. The study protocol was approved by the hospital ethics committee (Srebrnjak Children's Hospital, Zagreb, Croatia) and written informed consent was obtained from the parents. Daily between 10:00–12:00 h, two EBC samples were obtained from each subject. EBC was collected using an EcoScreen condenser (Erich Jaeger GmbH, Hoechberg, Germany). The subjects were instructed to breathe tidally for 15 min, wearing a nose clip. The obtained condensate (1.5–2.2 mL) was then deaerated with argon in two ways: 1) sample A obtained on day 1 was argon overlined (6 L·min–1 for 2 min); and 2) sample B obtained on day 2 was submitted to argon bubbling (350 mL·min–1 for 10 min). pH and PCO2 were determined using an Ecosys II analyzer (Eschweiler GmbH & Co. KG, Kiel, Germany) with 3–5 min of EBC A and B sample collection.

The values of pH and PCO2 showed statistically significant differences according to the method of sample argonisation (fig. 1Go). The pH values were significantly lower, and the PCO2 values were significantly higher in samples A than in samples B. The mean increase in pH of sample B was 0.509 (7.485±0.429 to 7.994±0.264), 0.642 (6.873±0.312 to 7.515±0.222) and 0.630 (6.788±0.397 to 7.418±0.253) in controls, asthmatics and GER patients, respectively (p = 0.0000). The mean decrease in PCO2 in sample B was significant in controls, asthmatics and GER patients (2.22±0.97 to 0.52±0.12, 2.08±1.13 to 0.53±0.11, and 2.25±1.17 to 0.53±0.12, respectively; p = 0.0000). Comparison of pH and PCO2 measured in children with asthma and GER (in both samples A and B) with those in controls showed no significant difference (considered to be p>0.05).


Figure 1
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  		Fig. 1— Mean a) pH and b) carbon dioxide tension (PCO2) values in controls, asthmatics and patients with gastro-oespophageal reflux (GER). {square}: sample A, argon overlining; blk14: sample B, argon bubbling. #: p = 0.0000.

 
The stability of the analytes influenced by the atmosphere is ensured by the procedure of argon over-lining 2. Using gas standardisation, CO2 was removed from the sample. These results suggest the PCO2 values in gas-standardised EBC to be clinically useless; therefore, EBC samples should be submitted to argon overlining for PCO2 determination. PCO2 should be determined as soon as possible (i.e. within 5 min of condensate preparation). During that period, argon overlining delays CO2 release and pH increase. In our study, the mean pH of sample A was in the neutral range in healthy children and in the acid range in children with asthma and GER, which is consistent with current literature 6–8, while the pH of the gas-standardised sample was within the alkaline range, again in agreement with other literature 3–5.

Despite some limitations of the study, such as the lack of EBC sampling on two consecutive days instead of sample analysis before and after gas standardisation, the results obtained could serve as a basis with which to solve some pre-analytical issues.

In conclusion, when pH and carbon dioxide tension can be determined immediately upon sampling, we consider that exhaled breath condensate sample argon over-lining should be performed.

REFERENCES

  1. Kullmann T, Barta I, Lazar Z, et al. Exhaled breath condensate pH standardised for CO2 partial pressure. Eur Respir J 2007;29:496–501.[Abstract/Free Full Text]
  2. Ojoo JC, Mulernnan SA, Kastelik JA, Morice AH, Redington AE. Exhaled breath condensate pH and exhaled nitric oxide in allergic asthma and cystic fibrosis. Thorax 2005;60:22–26.[Abstract/Free Full Text]
  3. Vaughan J, Ngamtrakulpanit L, Pajewski TN, et al. Exhaled breath condensate pH is a robust and reproducible assay of airway acidity. Eur Respir J 2003;22:889–894.[Abstract/Free Full Text]
  4. Nicolaou N, Lowe LA, Murray CS, Woodcock A, Simpson A, Custovic A. Exhaled breath condensate pH and childhood asthma: unselected birth cohort study. Am J Respir Crit Care Med 2006;174:254–259.[Abstract/Free Full Text]
  5. Niimi A, Nguyen LT, Usmani O, Mann B, Chung KF. Reduced pH and chloride levels in exhaled breath condensate of patients with chronic cough. Thorax 2004;59:608–612.[Abstract/Free Full Text]
  6. Borrill ZL, Smith JA, Naylor J, Woodcock AA, Singh D. The effect of gas standardisation on exhaled breath condensate pH. Eur Respir J 2006;28:251–252.[Free Full Text]
  7. Hunt JF, Fang K, Malik R, et al. Endogenous airway acidification: implications for asthma pathophysiology. Am J Respir Crit Care Med 2000;16:694–699.
  8. Carraro S, Folesani G, Corradi M, Zanconato S, Gaston B, Baraldi E. Acid-base equilibrium in exhaled breath condensate of allergic asthmatic children. Allergy 2005;60:476–481.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]




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