Breathing gas perfluorocarbon measurements using an absorber filled with zeolites

H. Proquitté*, M. Rüdiger, R. R. Wauer and G. Schmalisch

Clinic of Neonatology, CCM, Charité Childrens University Hospital, Schumannstr. 20/21, D-10098 Berlin, Germany

Corresponding author. E-mail: hans.proquitte@charite.de

Accepted for publication: June 30, 2003


    Abstract
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Background. Perfluorocarbon (PFC) has been widely used in the treatment of respiratory diseases; however, PFC content of the breathing gases remains unknown. Therefore, we developed an absorber using PFC selective zeolites for PFC measurement in gases and investigated its accuracy.

Methods. To generate a breathing gas with different PFC contents a heated flask was rinsed with a constant air flow of 4 litre·min–1 and 1, 5, 10, and 20 ml of PFC were infused over 20 min using an infusor. The absorber was placed on an electronic scale and the total PFC volume was calculated from the weight gain.

Results. Steady-state increase in weight was achieved 3.5 min after stopping the infusion. The calculated PFC volume was slightly underestimated but the measuring error did not exceed –1% for PFC less than 1 ml. The measurement error decreased with increasing PFC volume.

Conclusions. This zeolite absorber is an accurate method to quantitatively determine PFC in breathing gases and can be used as a reference method to validate other PFC sensors.

Br J Anaesth 2003; 91: 736–8

Keywords: pharmacology, liquid ventilation, fluorocarbons


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Perfluorocarbon (PFC) is used experimentally in combination with conventional mechanical ventilation to treat respiratory diseases. Depending on PFC use in partial liquid ventilation (PLV),1 or as both an aerosol2 and vapor3 there are a number of reasons to measure the PFC content of the breathing gases. Knowledge of the quantity of evaporated PFC during exhalation4 under PLV allows continuous substitution of PFC loss. In aerosol therapy, PFC content of the inspiratory breathing gas is difficult to adjust5 and PFC measurements could provide optimal adjustments.

Measurements of the PFC concentration in breathing gas are rarely performed4 6 because of technical problems. Measuring PFC requires both a specific PFC analyser and a flow-measuring device. Commercial mass spectrometers for PFC measurements are too expensive and cumbersome for clinical use and other commercial PFC sensors are currently not available.

The aim of our in vitro study was to develop a simple technique for PFC measurements in breathing gases using an absorber containing specific PFC adsorbing zeolites.


    Methods and results
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Equipment
The perfluorooctane (C8F18) (PF5080; 3M Neuss, Germany) used has a molecular mass of 438 g mol–1 and a boiling point of 101°C. At 25°C PF5080 has a density of 1.77g cm–3, a dynamic viscosity of 1.4 mPa s–1, a surface tension of 15 mN m–1, and a vapor pressure of 5.9 kPa. The absorber developed consists of a glass tube (length 33 cm; inner diameter 6.5 cm), which was filled with 265 g of zeolite DAY-F63 (De-Aluminated Zeolite; Degussa AG, Frankfurt/Main, Germany) and is closed by rubbers and connecting ports on both sides. The airflow resistance is 1.2 cm H2O litre s–1 determined by the backpressure at 5 litre min–1.

The zeolites7 are small hollow cylinders with a mean length of 7 mm and an inner and outer diameter of 2 and 5 mm, respectively. In a pilot study the absorption of gas moles adsorbed to DAY-F63 was measured as a function of partial pressure (McBain Langmuir isotherme). A high specificity of DAY-F63 to PF 5080 could be shown. Providing that the temperature of the absorber was higher than the temperature of the breathing gas no adsorption of water vapor was measured. PFC can be removed from the zeolites by heating (>300°C). Therefore, the zeolites were heated before each measurement in order to utilize the full capacity of the absorber. All measured PFC volumes were below the total capacity of the absorber, which is 48 ml PFC resulting from 0.181 ml PFC/gzeolite.

Air from a central gas supply was adjusted (4 litre min–1) by a laboratory rotameter (Aalborg Instruments and Controls Inc., Orangeburg, NY, USA) and delivered into a sealed flask (50 cm inner diameter, height of 82 cm) in which PFC volumes of 1, 5, 10, or 20 ml were infused over 20 min using a perfusor with a 20 ml syringe (both Braun Melsungen AG, Melsungen, Germany). The set-up was placed within an incubator to maintain a constant temperature of 37°C and achieve complete evaporation of the infused PFC. PFC enriched gas was passed through the absorber, which was placed on an electronic scale with a resolution of 0.01 g (LC 2200 P; Sartorius, Göttingen, Germany) to determine the PFC adsorption by weight gain over time. The scale was connected to a computer using Winwedge software (V1.1b, T.A.L. Enterprises, Philadelphia, USA). The sampling time of the software was set to 5 s and the weight of the absorber was measured over 30 min.

The adsorbed PFC volume was calculated from the weight gain of the absorber divided by the density of PF 5080. Each measurement was repeated five times. The adsorbed PFC volumes are represented as median and range to illustrate the low scattering of the absolute values using STATGRAPHICS Plus (Version 5, Manugistics Inc., Rockville, MD, USA).

Absorber function and measurement accuracy
After the start of the infusion, the weight of the absorber rises linearly with a delay time of 3.5 min caused by the transport of the gas through the tubes. After stopping of PFC infusion, with the same delay time, a plateau in the weight curve is reached and the weight gain of the absorber was calculated. Table 1 shows that in all measurements the total PFC volume was slightly underestimated. However, deviations did not exceed –1% and the extent of the measuring error decreased with increasing PFC volume.


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Table 1 Accuracy of gas PFC measurements using the zeolite absorber. The adsorbed PFC volume was calculated from the weight gain of the absorber corrected for the density of the PFC
 

    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Zeolites, crystalline microporous aluminosilicates of differing chemical compositions, polarities and pore sizes,8 known for recovering anesthetics7 allow adsorption of fluorocarbons because of interactions in the zeolite pores.9 By preventing both water condensation in the absorber and PFC condensation in the connecting tubes, the weight gain of the zeolite absorber over time allows precise measurements with volume errors less than 1% for PFC volumes greater than 1 ml.

Possible alternatives for measuring PFC concentrations in breathing gases are the use of thermal conduction and mass transfer of gases4 and an infrared adsorption technique,6 requiring both a PFC and an air-flow sensor. Sited between the tracheal tube and the Y-piece of the ventilator, the PFC sensor increases the apparative dead-space considerably. This hampers mechanical ventilation of small individuals with stiff lungs, a target group for PFC application. The zeolite absorber can be attached to the end of the ventilatory circuit without increasing apparative dead-space and the increase in the expiratory resistance is negligible. However, such an absorber is subject to methodological limitations. The drawback that condensed water and other volatile substances, for example anaesthetics, can be adsorbed to zeolites and thus impair PFC measurements must be eliminated. The method is slow and does not allow breath-to-breath analysis. Furthermore, the duration of measurement is limited by the adsorption capacity of the zeolites and PFC flow measurements are only possible under steady-state conditions. Nevertheless, this is a suitable method with which to measure evaporated PFC accurately and it can be used to calibrate other PFC sensors because of its precision. Moreover, this apparatus is readily available and can be simply adapted to commonly used ventilators.


    Acknowledgements
 
The authors would like to thank Betram Foitzik and Ludwik Kurzidim for their assistance. The work was supported by the Grant 01ZZ9511 from the German Ministry of Education and Research.


    References
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 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Fuhrman BP, Paczan PR, DeFrancisis M. Perfluorocarbon-associated gas exchange Crit Care Med 1991; 19: 712–22[ISI][Medline]

2 Kandler MA, von der Hardt, Schoof E, Dotsch J, Rascher W. Persistent improvement of gas exchange and lung mechanics by aerosolized perfluorocarbon. Am J Respir Crit Care Med 2001; 164: 31–5[Abstract/Free Full Text]

3 Bleyl JU, Ragaller M, Tscho U, et al. Vaporized perfluorocarbon improves oxygenation and pulmonary function in an ovine model of acute respiratory distress syndrome. Anesthesiology 1999; 91: 461–9[ISI][Medline]

4 Shaffer TH, Foust R, Wolfson MR, Miller TF jr. Analysis of perfluorochemical elimination from the respiratory system. J Appl Physiol 1997; 83: 1033–40[Abstract/Free Full Text]

5 Gregor T, Schmalisch G, Burkhardt W, Proquitte H, Wauer R, Rüdiger M. Aerosolization of perfluorocarbons during mechanical ventilation: an in vitro study. Intensive Care Med 2003; 29: 720–6[ISI][Medline]

6 Mazzoni M, Nugent L, Klein D, Hoffman J, Sekins KM, Flaim SF. Dose monitoring in partial liquid ventilation by infrared measurement of expired perfluorochemicals. Biomed Instrum Technol 1999; 33: 356–64[Medline]

7 Janchen J, Bruckner JB, Stach H. Adsorption of desflurane from the scavenging system during high-flow and minimal-flow anaesthesia by zeolites. Eur J Anaesthesiol 1998; 15: 324–9[CrossRef][ISI][Medline]

8 Jansen JC, Stoecker M, Karge HG, Weitkamp J. Advanced zeolite science and applications. Stud Surface Sci Catal 1994; 85: 73–7

9 Stach H, Sigrist K, Radeke KH, Riedel V. Investigations of the adsorption of halogenated hydrocarbons on microporous adsorbents. Part 3. Gaschromatographic measurement of the initial heat of adsorption Q0 on charcol. Chem Tech 1995; 47: 55–61[ISI]





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