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Canadian Journal of Anesthesia 54:141-145 (2007)
© Canadian Anesthesiologists' Society, 2007
Reports of Original Investigations

Preoxygenation with the Mapleson D system requires higher oxygen flows than Mapleson A or circle systems

[La préoxygénation avec le système Mapleson D requiert un débit d’oxygène plus élevé que les systèmes Mapleson A ou en cercle]

Samar Taha, MD, Mohamad El-Khatib, PhD FAARC, Sahar Siddik-Sayyid, MD FRCA, Carla Dagher, MD, Jules-Marie Chehade, MD and Anis Baraka, MD FRCA

From the Department of Anesthesiology, American University of Beirut Medical Center, Beirut, Lebanon.

Address correspondence to: Dr. Anis Baraka, Professor and Chairman, Department of Anesthesiology, American University of Beirut Medical Center, P.O. Box 11 0236 Beirut, Beirut, Lebanon. Phone: 961 1 350000, ext. 6380; E-mail: abaraka{at}aub.edu.lb


   Abstract
TOP
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Purpose: This study investigates the efficacy of preoxygenation with Mapleson A and Mapleson D breathing systems vs the circle system with CO2 absorber.

Methods: Thirteen healthy volunteers underwent tidal volume breathing for three minutes via facemask using Mapleson A, Mapleson D breathing systems or the circle system with CO2 absorber while breathing 100% O2 at flow rates of 5 L·min–1 and 10 L·min–1. Each volunteer acted as his/her own control by going through each of six preoxygenation protocols in random order. Fractional end-tidal O2 concentration (FETO2) was measured at 30-sec intervals. The results were compared among the three anesthesia systems at the two fresh gas flow rates.

Results: At a fresh gas flow rate of 5 L·min–1, the Mapleson A and circle systems achieved FETO2 values of 90.8 ± 1.4% and 90.0 ± 1.1%, respectively, compared with the lower FETO2 (81.5 ± 6.3%, P < 0.05), achieved with the Mapleson D system. When breathing O2 at 10 L·min–1, the FETO2 values after three minutes were similar with the Mapleson A, circle, and Mapleson D breathing systems (91.8 ± 2.3%, 91.2 ± 1.7%, 90.6 ± 2.7%, respectively).

Conclusion: When using the Mapleson A and the circle systems for preoxygenation, an oxygen flow rate of 5 L·min–1 can adequately preoxygenate the patient within three minutes, while an oxygen flow of 10 L·min–1 is required to achieve a similar fractional end-tidal O2 concentration with the Mapleson D system.


   Introduction
TOP
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
PREOXYGENATION essentially depends on denitrogenation of the functional residual capacity (FRC) of the patient’s lungs and replacing the nitrogen with oxygen. Hamilton and Eastwood have shown that denitrogenation is 95% complete within two to three minutes when breathing 100% oxygen using the circle CO2 absorber system at a fresh gas flow (FGF) rate of 5 L·min–1 and tidal volume breathing.1 Monitoring preoxygenation by measuring fractional end-tidal oxygen concentration (FETO2) is probably the best surrogate marker of lung denitrogenation.2–4

Mapleson suggested that the degree of rebreathing during spontaneous breathing is less with Mapleson A system than with Mapleson D system.5 Such differences in the degree of rebreathing may affect the efficacy of preoxygenation. This study was designed to investigate the hypothesis that oxygen flow and anesthetic system type may influence the efficacy of preoxygenation.


   Methods
TOP
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
The study was approved by the institutional Research Ethics Board and informed consent was obtained from all volunteers prior to their participation in the study. Thirteen non-smoking healthy subjects (five females and eight males) with no history of heart or lung disease were enrolled. Subjects were not recruited if they were edentulous or if they had a beard. Also excluded were individuals < 20 or > 40 yr of age, and those who weighed < 55 kg or > 90 kg.

The subjects were asked to lie supine, and were familiarized with the procedures by breathing normally while maintaining a tight-fitting facemask. A pulse oximeter (Novametrix, Wallingford, CT, USA) was applied to a finger tip for continuous monitoring of oxygen saturation.

A standard anesthesia machine (Datex ADU AS/3 Anesthesia Monitor, Helsinki, Finland) was used throughout the study. Three anesthetic systems were investigated: the circle system, an adult Mapleson A system (Magill system) and an adult Mapleson D system. The Mapleson A and Mapleson D systems consisted of 107 cm corrugated tubes and a 2-L capacity breathing bag. The circle system consisted of an absorber (Datex-Ohmeda Compact Absorber containing 550 g of soda lime), two 150-cm corrugated breathing tubes, and a 2-L capacity breathing bag. Prior to each preoxygenation trial, the anesthesia systems were flushed for five minutes with 100% O2 at a flow rate of 10 L·min–1 to eliminate any residual air or nitrous oxide.

The reservoir bag was fully inflated using the oxygen flush, and the mask was partially occluded with the palm of the hand. Preoxygenation was performed with 100% O2 and a tight fitting facemask. Tidal volume breathing for three minutes was performed using the three anesthetic systems, while subjects breathed 100% O2 at FGF rates of 5 L·min–1 and 10 L·min–1 in random order. Each volunteer acted as his/her own control by going through each of six protocols of preoxygenation in a random order, separated by rest periods of five minutes breathing room air. The randomization sequence was computer-generated.

Side stream respiratory gases were sampled from a sampling port placed next to the mask and filter. Measurements of inspired fraction of oxygen (FIO2) and FETO2 were recorded using a calibrated gas monitor (Datex ADU AS/3 Anesthesia Monitor, Helsinki, Finland). Calibration with known gas mixtures was carried out according to the manufacturer’s specifications.

Sample size calculation was based upon an expected clinically significant change in FETO2 of 10%. Assuming a type I error of 5% and a type II error of 10%, with a standard deviation estimate of 10% derived from a pilot study, at least ten subjects were needed for the study. For all subjects, the FIO2 and the FETO2 values were collected during tidal volume breathing at 30-sec intervals during preoxygenation for a period of three minutes. The means and standard deviations of the FIO2 and the FETO2 values obtained with the Mapleson A, the Mapleson D, and the circle systems at each 30-sec interval (i.e., at 30 sec, 60 sec, 90 sec, 120 sec, 150 sec, and 180 sec) were compared at O2 flow rates of 5 L·min–1 and 10 L·min–1 using a paired Student’s t test and repeated measures ANOVA with the Dunnett’s correction for post hoc analysis. Also, non-linear regression analysis was used for assessing the changes in FETO2 over time and the respective correlation coefficients were determined. Statistical significance was assumed when P < 0.05.


   Results
TOP
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
All subjects completed all six phases of the study protocol. Using an O2 flow of 5 L·min–1, the FIO2 increased to maximal levels of 96.0 ± 2.7% and 94.8 ± 3.7% within 30 sec of preoxygenation with the Mapleson A system and the circle system, respectively. However, with the Mapleson D system, the FIO2 at 30 sec was significantly lower (86.7 ± 8.3%) as compared to the Mapleson A and the circle systems. At an O2 flow of 10 L·min–1, the FIO2 increased in the Mapleson A, the circle, and the Mapleson D systems within 30 sec of preoxygenation, up to 98.3 ± 1.2%, 98.1 ± 0.8%, and 97.6 ± 1.9% respectively, with no significant differences among the three systems.

Using an O2 flow of 5 L·min–1, the FETO2 values increased significantly from a baseline value of 17.2 ± 1.2% to 90.8 ± 1.4% after three minutes of preoxygenation with the Mapleson A system, and from a baseline of 17.1 ± 1.3% to 90.0 ± 1.1% with the circle CO2 absorber system. Also, after three minutes of preoxygenation, the FETO2 value with the Mapleson D system was 81.5 ± 6.3%, which was lower (P = 0.001) than that achieved with the Mapleson A system (90.8 ± 1.4%) and the circle absorber system (90.0 ± 1.1% ) (Figure 1Go). The FETO2 values at each time interval and after three minutes of preoxygenation were not different between the Mapleson A and the circle system. In contrast, when the Mapleson D system was used, the FETO2 at each time interval throughout the preoxygenation period was significantly lower than that achieved with both the Mapleson A and the circle absorber systems.


Figure 1
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  		FIGURE 1 The fractional end-tidal oxygen concentrations (FETO2) for the Mapleson A, the circle, and the Mapleson D anesthesia systems during preoxygenation with 100% O2 for three minutes at a fresh gas flow rate of 5 L·min–1. *P < 0.05 vs Mapleson A system; {dagger}P < 0.05 vs circle system.

 
Using an O2 flow of 10 L·min–1 for preoxygenation, the FETO2 values increased at all time intervals throughout the preoxygenation period with the three systems. After three minutes, the FETO2 values were not significantly different when comparing the Mapleson A, the circle system, and the Mapleson D systems (91.8 ± 2.3%, 91.2 ± 1.7%, 90.6 ± 2.7% respectively) (Figure 2Go). At an O2 flow of 10 L·min–1, the FETO2 with the Mapleson D system at 180 sec (90.6 ± 2.7%) was not significantly different from the FETO2 values of the Mapleson A and the circle absorber systems at 180 sec when using an O2 flow of 5 L·min–1 (90.8 ± 1.42% and 90.0 ± 1.1% respectively).


Figure 2
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  		FIGURE 2 The fractional end-tidal oxygen concentrations (FETO2) for the Mapleson A, the circle, and the Mapleson D anesthesia systems during preoxygenation with 100% O2 for three minutes at a fresh gas flow rate of 10 L·min–1.

 
Comparing the rate of preoxygenation for each system at 5 L·min–1 vs 10 L·min–1 showed that when using the Mapleson D system increasing the O2 flow from 5 L·min–1 to 10 L·min–1 resulted in significant increases in FETO2 values at 30, 60, 90, 120, 150, and 180 sec throughout the preoxygenation period (Figure 3Go). However, with the Mapleson A system, increasing the O2 flow from 5 L·min–1 to 10 L·min–1 increased the FETO2 values at 30, 60, 90, 120, and 150 sec during the preoxygenation period, resulting in similar FETO2 values at 180 sec (Figure 4Go). Also, with the circle absorber system, increasing the O2 flow from 5 L·min–1 to 10 L·min–1 increased the FETO2 values at 30, 60, 90, 120, and 150 sec during the preoxygenation period, resulting in similar FETO2 values at 180 sec (Figure 5Go).


Figure 3
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  		FIGURE 3 The fractional end-tidal oxygen concentration (FETO2) with the Mapleson D system during preoxygenation with 100% O2 for three minutes at fresh gas flow rates of 5 L·min–1 vs 10 L·min–1. *P < 0.05 vs 10 L·min–1.

 

Figure 4
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  		FIGURE 4 The fractional end-tidal oxygen concentration (FETO2) with the Mapleson A anesthesia system during preoxygenation with 100% O2 for three minutes at fresh gas flow rates of 5 L·min–1 vs 10 L·min–1. *P < 0.05 vs 10 L·min–1.

 

Figure 5
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  		FIGURE 5 The fractional end-tidal oxygen concentration (FETO2) with the circle system during preoxygenation with 100% O2 for three minutes at fresh gas flow rates of 5 L·min–1 vs 10 L·min–1. *P < 0.05 vs 10 L·min–1.

 
The FETO2 increased exponentially over time with the Mapleson D (r2 = 0.998) (Figure 3Go), the Mapleson A (r2 = 0.999) (Figure 4Go), and the circle (r2 = 0.998) (Figure 5Go) systems. The most significant increases in FETO2 with all three systems occurred during the first 60 to 90 sec of preoxygenation (Figure 2Go).


   Discussion
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
The present report shows that with an O2 flow of 5 L·min–1, the FETO2 achieved with the Mapleson D system after three minutes of preoxygenation is significantly lower than that achieved by the Mapleson A and the circle CO2 absorber systems. Increasing the O2 flow to 10 L·min–1 improved both the FIO2 and the FETO2 values obtained with the Mapleson D system to the same levels achieved by using an O2 flow of 5 L·min–1 with the Mapleson A and the circle CO2 absorber systems. The decreased FETO2 with the Mapleson D anesthesia system at 5 L·min–1 can be attributed to a higher degree of rebreathing, as reflected by the lower FIO2 levels throughout the preoxygenation period.

Preoxygenation depends on spontaneous breathing of 100% O2 in order to denitrogenate the FRC of the lungs and to increase the O2 stores in the FRC. Hamilton and Eastwood have shown that denitrogenation is 95% complete in two to three minutes at an O2 flow of 5 L·min–1 and tidal volume breathing using the circle CO2 absorber system.1 Other anesthesia systems such as the Mapleson A (Magill system), and Mapleson D system including the Bain modification,6 may also be used for preoxygenation.

On a theoretical basis, Mapleson suggested that rebreathing during spontaneous ventilation may be less with the Mapleson A system compared to Mapleson D system.5 With the Mapleson A system, the FGF is delivered distally near the reservoir bag, while the overflow valve is located proximally near the patient end of the system, which decreases the degree of rebreathing. In contrast, with the Mapleson D system, the FGF is delivered proximal to the patient, while the outlet valve is distally located near the reservoir bag, which increases the possibility of rebreathing. Baraka et al. have shown in spontaneously breathing children that a FGF equal to one-minute volume can adequately prevent CO2 rebreathing when using the Mapleson A system.7 In contrast, a FGF equivalent to two-minute volumes is required to eliminate rebreathing when the Mapleson D system is used.7 In adult patients using the Magill system, Kain et al. have even shown that a FGF equivalent to alveolar ventilation volume can adequately prevent rebreathing.8 The circle system includes unidirectional inspiratory and expiratory valves that can minimize rebreathing of exhaled gases and subsequently improve the rate of preoxygenation.

The degree of rebreathing as monitored by the FIO2 using the different anesthesia systems can affect the washout of exhaled nitrogen from the FRC and hence may explain our results concerning preoxygenation by the different anesthesia systems as evidenced by the FETO2. Thus, using an O2 flow equivalent to one alveolar minute ventilation volume in adults (i.e., 5 L·min–1) provides adequate preoxygenation within three minutes when the Mapleson A and the circle absorber systems are used. In contrast, when the Mapleson D system is used, an O2 flow equivalent to two alveolar minute ventilation volumes (i.e., 10 L·min–1) is required to achieve the same degree of preoxygenation.

The FETO2 increased exponentially over time during preoxygenation with the three anesthesia systems. This exponential increase in FETO2 is equivalent to, and mirrors the exponential wash-out of nitrogen during the preoxygenation period.9 In the present report using tidal volume breathing and an O2 flow of 10 L·min–1 with all three systems, the most significant rate of increase in FETO2 up to and greater than 70%, occurred within the first 60 to 90 sec of the preoxygenation period.

In conclusion, the present report shows that when using the Mapleson A and the circle CO2 absorber systems for preoxygenation, an O2 flow of 5 L·min–1 can adequately preoxygenate the patient by tidal volume breathing within three minutes, while an O2 flow of 10 L·min–1 is required to achieve a similar fractional end-tidal O2 concentration with the Mapleson D system.


   Footnotes
 
Accepted for publication November 8, 2006. Revision accepted November 16,2006.

Competing interest: None declared.


   References
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
1 Hamilton WK, Eastwood DW. A study of denitrogenation with some inhalation anesthetic systems. Anesthesiology 1955; 16: 861–7.[Medline]

2 Myles PS, Heap M, Langley M. Agreement between end-tidal oxygen concentration and the alveolar gas equation: pre and post cardiopulmonary bypass. Anaesth Intensive Care 1993; 21: 240–1.

3 Gagnon C, Fortier LP, Donati F. When a leak is unavoidable, preoxygenation is equally ineffective with vital capacity or tidal volume breathing. Can J Anesth 2006; 53: 86–91.[Abstract/Free Full Text]

4 Baraka AS, Taha SK, El-Khatib MF, Massouh FM, Jabbour DG, Alameddine MM. Oxygenation using tidal volume breathing following maximal exhalation. Anesth Analg 2003; 97: 1533–5.[Abstract/Free Full Text]

5 Mapleson WW. The elimination of rebreathing in various semi-closed anaesthetic systems. Br J Anaesth 1954; 26: 323–32.

6 Rooney MJ. Pre-oxygenation: a comparison of two techniques using a Bain system. Anaesthesia 1994; 49: 629–32.[Medline]

7 Baraka A, Brandstater B, Muallem M, Seraphim C. Rebreathing in a double T-piece system. Br J Anaesth 1969; 41: 47–53.[Abstract/Free Full Text]

8 Kain ML, Nunn JF. Fresh gas economics of the Magill circuit. Anesthesiology 1968; 29: 964–74.[Medline]

9 Olegard C, Sondergaad S, Houltz E, Lundin S, Stenqvist O. Estimation of functional residual capacity at the bedside using standard monitoring equipment: a modified nitrogen washout/washin technique requiring a small change of the inspired oxygen fraction. Anesth Analg 2005; 101: 206–12.[Abstract/Free Full Text]





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