Chapter 8 Mapleson Breathing Systems The Mapleson systems are characterized by the absence of unidi rectional valves to

di rect gases to or from the patient. Because there is no device fo r absorb ing CO2 ,

the fresh gas f low must wash CO2 out of the c ircui t . For this reason, these sys tems

are sometimes cal led carbon dioxide washout c ircui ts or flow-control led breathing

systems .

These sys tems were f irs t classif ied into f ive basic types: A through E (1). A s ix th,

the Mapleson F system, was added la ter (2). The c lassification is shown in Figure

8.1. There are many variat ions of these systems, but only the ones in common use

wi l l be discussed.

Because there is no c lear separa tion of insp ired and expired gases , rebreathing wi l l

occur when the insp iratory f low exceeds the f resh gas f low. The composi tion of the

inspired mix ture wil l depend on how much rebreath ing takes p lace. A number of

s tudies designed to determine the fresh gas f low needed to prevent rebreath ing

wi th these systems have been performed, wi th of ten wide ly dif fering results . This is

part ly because dif ferent criteria have been used to def ine the onset of rebreathing

and because variables such as minute venti lation , respiratory waveform, CO2

production, patient responsiveness, and stimulation and physiological dead space

may be unpredictable in anesthetized pat ien ts (3,4 ,5). Monitoring end-t idal CO2 is

the best method to de termine the optimal f resh gas f low. It should be noted that

wi th rebreathing, the arterial CO2 to end-tidal CO2 gradient decreases (6).

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View Figure

Figure 8.1 The Mapleson systems. Components include a reservoir bag, corrugated tubing, APL valve, fresh gas inlet, and patient connection. They lack CO2 absorbers, unidirectional valves, and separate inspiratory and expiratory limbs. (Redrawn from Mapleson WW. The elimination of rebreathing in various semiclosed anesthetic systems. Br J Anaesth 1954;26:323–332

[CrossRef] [Medline Link]

.)

Mapleson A System Configurations Classic Form The Mapleson A sys tem (Magil l at tachment or system) is shown in Figure 8 .1A. It

differs from the other Mapleson systems in that f resh gas does not enter the system

near the pat ien t connect ion but enters at the other end of the sys tem near the

reservoir bag. A corrugated tubing connects the bag to the adjustable pressure

l imi ting (APL) valve a t the pat ien t end of the system.

View Figure

Figure 8.2 Lack modification of the Mapleson A system. The coaxial version is shown. APL, adjustable pressure limiting.

A sensor for a nondiverting respiratory gas moni tor or the sampling s i te for a

diverting monitor (Chapter 22) may be placed between the APL valve and the

corrugated tubing. In adul ts , i t may be placed between the APL valve and the

patient. In small pat ients , th is loca tion could resul t in excessive dead space. I t

could also be placed between the neck of the bag and i ts mount, between the bag

and the corrugated tubing, or in the fresh gas supply tube. However, in these

locat ions, the concentrat ion shown on the moni to r may differ substant ially from the

inspired concentra tion, especially during contro lled venti lation .

Lack Modification The Lack modif ication of the Mapleson A system (Fig. 8 .2) has an added

“expira tory” l imb, which runs from the patien t connect ion to the APL valve at the

machine end of the sys tem (7,8). This makes it easier to adjust the valve and

fac i li tates scavenging excess gases, but it inc reases the work of breathing s ligh tly

(3).

The Lack system is available in bo th a dual (para llel ) tube arrangement and a tube-

wi th in-a-tube (coaxial ) configuration in which the expira tory l imb runs concentrica lly

inside the outer inspiratory l imb (9).

Techniques of Use For spontaneous vent i lat ion, the APL valve is kept in the ful ly open posit ion.

Excess gas exi ts through i t during the lat ter part of exhalation .

For contro lled or assisted venti la tion, intermit tent posit ive pressure is appl ied to

the bag. The APL valve is partial ly c losed so that when the bag is squeezed,

suff ic ient pressure to inf late the lungs is achieved. The APL valve opens during

inspiration .

Functional Analysis Spontaneous Respiration The sequence of events during the respiratory cycle using the Magil l system with

spontaneous venti la tion is shown in Figure 8.3 (10,11). As the patient exha les (Fig.

8.3C), f i rs t dead space and then alveolar gases f low into the corrugated tubing

toward the bag. At the same t ime,

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f resh gas flows into the bag. When the bag is full , the pressure in the sys tem rises

unti l the APL valve opens. The f i rs t gas vented wil l be alveolar gas . The remainder

of exhalat ion, which contains only alveolar gas, exhausts through the open APL

valve. The cont inu ing inf low o f fresh gas reverses the f low o f exhaled gases in the

corrugated tubing. Some a lveolar gas that bypassed the APL valve now returns and

ex its through it . If the f resh gas f low is high (Fig. 8.3A), i t wi l l a lso force the dead

space gas out. If the fresh f low gas is intermediate (Fig . 8.3D), some dead space

gas wi l l be re ta ined in the system. If the fresh gas f low is low (Fig. 8 .3E), more

alveolar gas wi l l be retained.

View Figure

Figure 8.3 Magill system with spontaneous ventilation. (See text for details.) (Redrawn from Kain ML, Nunn JF. Fresh gas economies of the Magill circuit. Anesthesiology 1968;29:964–974

[Fulltext Link] [CrossRef]

[Medline Link] .)

At the start of inspiration , the f i rs t gas inhaled wi l l be from dead space between the

patient and the APL valve. The next gas wil l be e ither a lveolar gas (if the f resh gas

f low is low), dead space gas (if the f resh gas f low is intermediate), o r fresh gas (if

the fresh gas f low is high) (Fig. 8.3B). Changes in respiratory pattern have l i tt le

ef fect on rebreathing (11 ,12,13).

With the c lassic Magi ll sys tem, invest igators have found that rebreathing begins

when the f resh gas f low is reduced to 56 to 82 mL/kg/minute (3,14,15,16,17), or

58% to 83% of minute volume (3,10,18,19,20,21). Fresh gas f lows of 51 to 85

mL/kg/minute (3,14,22,23,24) and 42% to 88% of minute volume (3 ,19 ,23) have

been recommended to avoid rebreathing.

Controlled or Assisted Ventilation During contro lled or assisted venti la tion (F ig. 8.4), the pattern of gas f low changes.

During exha lat ion (Fig. 8 .4A), the pressure in the system wi l l remain low and no

gas wi l l escape through the APL valve, unless the bag becomes distended. Al l

exhaled gases, both dead space and alveo lar, remain in the corrugated tub ing , wi th

alveolar gas nearest the patient. If the tidal volume is large, some alveolar gas may

enter the bag (25).

View Figure

Figure 8.4 Magill system with controlled ventilation. (See text for details.)

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At the start of inspiration (Fig . 8.4B), gases in the tubing f low to the patient.

Because a lveolar gas occup ies the space nearest the pat ient, i t wi l l be inhaled f irs t .

As the pressure in the system rises, the APL valve opens so that gas both exi ts

through the APL valve and f lows to the pat ient. When all the exhaled gas has been

driven from the tube, fresh gas f i lls the tubing (Fig. 8.4C). Some fresh gas enters

the pat ient, and some is vented through the valve. Thus, during control led

venti lation , there is cons iderable rebreathing of alveolar gases and venting of fresh

gas. The composi tion of the inspired gas mixture depends on the respiratory

pattern (25,26). The system becomes more ef fic ient as the expira tory phase is

prolonged. Mos t invest igators believe tha t it is i l logica l to use the Mapleson A

system for control led vent i lat ion. However, i f the APL valve in the Mapleson A

system does not vent gas during inspirat ion, the Mapleson A system can be as

ef fic ient as the Mapleson D during control led venti la tion (27).

During assisted venti lation , the Mapleson A sys tem is somewhat less eff ic ient than

wi th spontaneous venti la tion but is more eff icient than wi th controlled venti la tion

(28).

Hazards A mechanical venti lator that vents excess gases should not be used with this

system, because the ent i re system then becomes dead space. The venti lators found

on mos t anes thesia machines in the Un ited States are unsui table for use with the

Mapleson A system.

Cases have been reported where a Lack c i rcu it was incorrec tly manufac tured or

assembled so that the f resh gas inle t was mounted ad jacent to the APL valve ra ther

than the reservoir bag (29,30,31). This would resul t in a substantial increase in

dead space.

Preuse Checks The Mapleson A sys tem is tested for leaks by occluding the pat ient end of the

system, c los ing the APL valve, and pressurizing the system. Opening the APL valve

wi l l conf i rm proper funct ioning of that component. In addi tion, the user or a pa tient

should breathe through the system.

The coaxial Lack system requ ires addit ional tes ting to conf irm the in tegri ty o f the

inner tube. One method is to attach a tracheal tube to the inner tubing at the

patient end of the sys tem (32). Blowing down the tube wi th the APL valve c losed

wi l l produce movement of the bag if there is a leak between the two limbs . Another

method is to occlude both l imbs at the pat ient connect ion wi th the APL valve open

and then squeeze the bag (33). I f there is a leak in the inner l imb, gas wi l l escape

through the APL valve, and the bag wil l collapse.

Mapleson B System The Mapleson B sys tem is shown in F igure 8.1B. The fresh gas inlet and APL valve

are both located near the pat ient port . The reservo ir bag is at the patient end of the

system, separa ted f rom the fresh gas inlet by corrugated tubing .

Techniques of Use To use the Mapleson B system with spontaneous respirat ion, the APL valve is

opened comple tely. Excess gas is vented through the valve during exhala tion.

Assis ted or controlled venti lation is accompl ished by c los ing the APL valve

suff ic iently to allow the lungs to be inf lated. Excess gases are vented during

inspiration .

Functional Analysis Spontaneous Respiration As the pat ient exhales, dead space gas wi l l pass down the corrugated tubing , along

wi th f resh gas. A t the end of exhalat ion , the tubing near the pat ient wi l l be f i l led

wi th f resh gas and some alveolar gas. When the bag reaches fu ll capacity, the APL

valve opens , and both f resh gas and alveolar gas wi l l ex i t f rom the system. When

the pat ient begins to inspire , the APL valve c loses, and the pat ient inha les f resh

gas and gas f rom the tub ing . No gas wi l l be inhaled from the bag if the volume of

the tub ing exceeds the tidal volume.

To avoid rebreathing, the f resh gas f low must be equa l to peak inspira tory f low ra te

(normally 20 to 25 L /minute) (34). A f resh gas f low more than double minute volume

has been recommended (34,35), but f lows as low as 0 .8 to 1 .2 t imes minute volume

may be su ff ic ient (25).

Controlled or Assisted Ventilation The behav ior of the Mapleson B system during controlled or assisted venti lation is

s imilar to that of the Mapleson A, but it is sl ight ly more eff icient because fresh gas

accumulates at the pat ient end of the tubing during the expiratory pause (25,34).

Because the composi tion of inspired gas is great ly inf luenced by the venti latory

pattern , this system has variable performance during controlled venti lat ion (25). A

f resh gas flow of 2 to 2 .5 t imes minute volume has been recommended (25,34,36).

Mapleson C System The Mapleson C system is identical to the Mapleson B system except that the

corrugated tubing is omitted (Fig. 8.1C).

Techniques of Use Use of this system is s imilar to tha t described for the Mapleson B system.

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Functional Analysis

The Mapleson C system behaves s imila rly to the Mapleson B system. With

spontaneous venti la tion, the Mapleson C system is almos t as effic ient as the

Mapleson A when the expira tory pause is minimal, but i t becomes less eff ic ien t as

the expiratory pause increases (11 ,13,37). A f resh gas f low of 2 t imes minute

volume has been recommended for spontaneous breathing. During contro lled

venti lation , a fresh gas f low o f 2 to 2.5 times minute volume is recommended

(25,38).

Mapleson D System The Mapleson D, E, and F systems al l have a T-piece near the pat ient and function

s imilarly. The T-piece is a three-way tubular connector with a pat ient connec tion

port, a fresh gas port, and a port for connection to a corrugated tubing. The

Mapleson D system is popular because excess gas scavenging is relatively easy,

and i t is the mos t ef fic ient of the Mapleson systems during contro lled venti lation.

Configuration Classic Form The Mapleson D system is shown in Figures 8 .1D and 8 .5. A length of tubing

connec ts the T-p iece at the pat ient end to the APL valve and the reservoir bag

adjacent to it . The length of the tubing determines the distance the user can be

f rom the pat ien t but has min imal effec ts on venti lat ion (39).

The sensor or sampling s i te for a respiratory gas monitor may be placed between

the bag and i ts mount, between the corrugated tubing and the T-piece, or be tween

the corrugated tub ing and the APL valve. In adul ts , i t may be placed between the T-

piece and the patient.

View Figure

Figure 8.5 Mapleson D system. A tube leading to the scavenging system is attached to the APL valve.

A bidirec tional posi t ive end-exp iratory pressure (PEEP) valve may be placed

between the corrugated tubing and the APL valve of the Mapleson D system (40).

This permits PEEP to be adminis te red during manua l or mechanical venti la tion.

However, some PEEP valves wil l c lose when a negative pressure is app lied, so

spontaneous breathing is impossib le wi th that type of PEEP valve in the system.

The PEEP valve may be placed in the hose leading to the anesthesia venti lato r. In

this location, it wi l l be effective only during mechanical vent i lat ion. A unidi rect ional

PEEP valve can be used a t the bag attachment s ite by using special connectors

and unid irect ional valves (41). Such an arrangement al lows PEEP to be applied

during spontaneous or mechanical but not manual venti la tion (40).

Bain Modification In the Bain modi fica tion (F ig. 8.6), the fresh gas supply tube runs coaxial ly ins ide

the corrugated tub ing and ends at the poin t where the f resh gas wou ld en ter if the

c lassic Mapleson D form were used (42). The outer tube is c lear so that the inner

tube can be inspected (43). The outer tubing of most commercially available

versions of the Bain system is narrower than conventiona l corrugated tub ing (25).

The Bain system is available wi th a meta l head with channels dri l led into it . This

provides a f ixed pos it ion for the reservoir bag and APL valve and a ttachment of

corrugated tubing. Some heads also have a pressure manometer.

A long version of the Bain system may be used for remote anes thesia in locat ions

such as the magnetic resonance imag ing (MRI) uni t (44). Compared with the usual

Bain sys tem, static compliance is increased with a

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reduc tion in peak inspira tory pressure and tidal volume with the same vent ilator

se tt ings. Also , PEEP is increased. A longer Bain sys tem also presents increased

resistance to spontaneous breathing (45).

View Figure

Figure 8.6 Bain modification of the Mapleson D system. The fresh gas supply tube is inside the corrugated tubing. APL, adjustable pressure limiting; Pt, patient.

Techniques of Use For spontaneous respirat ion , the APL valve is lef t open, and excess gases are

vented during expiration. Manual ly control led or assisted vent i lation is performed

by part ia lly clos ing the APL valve and squeezing the bag. Excess gases are vented

during inspira tion. Mechan ically control led venti lat ion is achieved by connecting the

hose from a vent ilator in p lace of the reservoir bag and c los ing the APL valve.

Excess gases are vented through the vent i la tor spi ll valve.

Functional Analysis Spontaneous Breathing During exha lat ion (Fig. 8 .7), exhaled gases mix wi th f resh gases and move through

the corrugated tube toward the bag. After the bag has f i l led, gas exi ts v ia the APL

valve. During the expiratory pause, fresh gas pushes exhaled gases down the

corrugated tubing.

During inspirat ion, the pat ient wi l l inhale gas from the f resh gas inlet and the

corrugated tubing. If the fresh gas f low is high, all the gas drawn from the

corrugated tube wi l l be f resh gas . If the f resh gas f low is low, some exhaled gas

containing CO2 wi l l be inhaled. The venti la tory pattern wi l l help to determine the

amount of rebreathing. Factors tha t tend to dec rease rebreath ing inc lude a high

inspiratory:expiratory (I :E) t ime rat io, a s low rise in inspira tory f low rate , a low f low

rate during the last part of exhalat ion, and a long expiratory pause, wi th the long

expiratory pause having the greates t effect (11,12,13,37,46,47,48).

As gas containing CO2 is inhaled , the end-tidal CO2 wil l r ise. I f the patien t's

spontaneous respiration then inc reases , the end-tidal CO2 wil l fal l whi le inspired

CO2 wi l l increase (49). Prov ided rebreath ing is not extreme, a normal end-t ida l CO2

can be achieved but on ly at the cost of inc reased work on the part of the pat ient.

The end-tidal CO2 tends to reach a plateau. At that point, no matte r how hard the

patient works , the end-tidal CO2 cannot be lowered further. I f the patien t's

respira tion is depressed, end-t idal CO2 wil l rise further (49).

End-t idal CO2 depends on both the ratio of minute volume and f resh gas f low and

their absolu te values (49). I f expired volume is greater than fresh gas f low, end-

t ida l CO2 wi l l be determined mainly by f resh gas flow. I f f resh gas f low is greater

than minute volume, end-t idal CO2 wi l l be determined main ly by minute volume.

Recommendations for f resh gas f lows based on body weight vary f rom 100 to 300

mL/kg/minute (14,17,23,24,29,50,51). Mos t studies have recommended tha t the

f resh gas flow be 1.5 to 3.0 times the minute volume (20,23,50,52,53,54,55,56)

whi le o thers have held tha t a fresh gas f low approximately equal to tota l venti lation

is adequate (57). In terms of body surface area, f resh gas

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f lows of 4000 to 4700 mL/m2/minute have been recom-mended (58).

View Figure

Figure 8.7 Functioning of the Mapleson D system. (See text for details.) Pt, patient; F.G.F., fresh gas flow.

Controlled Ventilation During exha lat ion (Fig. 8 .7), gases f low f rom the pat ient down the corrugated

tubing. At the same time, f resh gas enters the tubing. During the expiratory pause,

the fresh gas f low continues and pushes exhaled gases down the tubing .

During inspirat ion, f resh gas and gas from the corrugated tubing enter the pat ient.

I f the f resh gas f low is low, some exhaled gases may be inhaled. Prolonging the

inspiratory t ime, inc reasing the resp iratory rate, or adding an inspira tory plateau

wi l l inc rease rebreath ing (47,59). Rebreathing can be decreased by al lowing a long

expiratory pause so that fresh gas can f lush exhaled gases f rom the tubing .

When the fresh gas flow is high , there is li tt le rebreathing, and the end-tidal CO2 is

determined mainly by minute venti la tion. Tidal volume, the volume of the expiratory

l imb, and expiratory resistance also affect it (60). When minute volume

substant ia lly exceeds the fresh gas flow, the f resh gas f low is the main factor

control ling CO2 elimination. The higher the fresh gas f low, the lower the end-t idal

CO2 .

Combining f resh gas flow, minute volume, and arte rial CO2 levels , a series of

curves can be construc ted (Fig. 8.8). An inf ini te number of combinat ions of f resh

gas f low and minute volume can be used to produce a given PaCO2. High f resh gas

f lows and low minute volumes or h igh minute volumes and low f resh gas f lows or

combinations in between can be used. In F igure 8.8, at the lef t, wi th a high f resh

gas f low, the c i rcu it is a nonrebreathing one and end-tidal CO2 depends only on

venti lation . Such high f lows are uneconomical and are associated wi th lost heat and

humidi ty . End-t idal CO2 depends on minute volume, which is dif ficul t to adjust

accurate ly, especial ly in smal l patients. On the right is the reg ion of

hyperventi lat ion and part ial rebreathing . End-tida l CO2 is regulated by adjusting the

f resh gas flow. Lower f resh gas f lows (and inc reased rebreathing) are associated

wi th higher humidi ty , less heat loss, and greater fresh gas economy.

Hypervent ilation can be used without inducing hypocarbia. Ind iv idual dif ferences in

dead space:t idal volume are minimized at high levels of minute volume. For these

reasons, in most cases , i t is advantageous to aim fo r the right s ide of the graph. In

patients with stif f lungs , poor cardiac performance, or hypovolemia , using the lef t

s ide of the graph and a relatively small total venti lat ion with a h igh f resh gas f low

may be better (61).

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View Figure

Figure 8.8 Mapleson D system used with controlled ventilation. Each isopleth represents a constant level of PaCO2. Note that essentially the same PaCO2 can be achieved for fresh gas flows from 100 to 240 mL/kg/minute. (Redrawn from Froese AB. Anesthesia circuits for children [ASA Refresher Course]. Park Ridge, IL: ASA, 1978 .)

Formulas to predict fresh gas f low requirements have been based on body weight

(62,63,64), minute volume (65), and body surface area (66). I f the system is used

for patients undergo ing laparoscopy, the fresh gas f low needs to be increased to

overcome the CO2 that is absorbed f rom the abdomen (67).

With assis ted vent i lat ion, the eff ic iency o f the Mapleson D sys tem is intermediate

between that for spontaneous and controlled venti lation (28). Sligh tly higher f resh

gas f lows should be used.

Bain System Hazards

I f the inner tube of the Bain system becomes detached from its connections at

ei ther end or develops a leak at the machine end, if the f resh gas supply tube

becomes k inked or twis ted , if the system is incorrect ly assembled (such as using

standard corrugated tubing), or if there is a defect in the meta l head so tha t fresh

gas and exhaled gas mix , the entire l imb becomes dead space

(43,68,69,70,71,72,73). In one case, i t was reported that a manufacturing defec t

caused the inner tube to be blocked (74).

Preuse Checks The Mapleson D System is tested fo r leaks by occluding the pat ien t end, closing

the APL valve, and pressurizing the system. The APL valve is then opened. The

bag should def late easi ly if the valve and scavenging sys tem are work ing properly.

Ei ther the user o r a pat ient should breathe through the system to detect

obstruct ions.

The Bain modi f ication of the Mapleson D requires special test ing to confi rm the

integri ty of the inner tubing. This can be perfo rmed by se tt ing a low f low on the

oxygen f lowmeter and occluding the inner tube (wi th a f inger or the barrel of a

smal l syringe) at the pat ient end while observ ing the f lowmeter indicator. If the

inner tube is in tact and correctly connected, the indicator wi l l fa ll (70,75). The

integri ty of the inner tube can a lso be conf irmed by activat ing the oxygen f lush and

observ ing the bag (76). A Venturi effect caused by the high f low at the patient end

wi l l create a negative pressure in the outer exhalation tubing, and this wi l l cause

the bag to def late. I f the inner tube is not intact, th is maneuver wil l cause the bag

to inf la te s light ly . However, this test wi l l not detect a system in which the inner tube

is omitted or does not ex tend to the pat ient port or one tha t has ho les at the pat ien t

end of the inner tube (77 ,78).

Continuous Positive Airway Pressure During one-lung venti la tion using a double-lumen tube (Chapter 20), a mod if ied

Mapleson D system attached to the lumen leading to the nondependent lung is

of ten used to apply continuous posi t ive airway pressure (CPAP) to tha t lung.

A number of conf igurat ions have been described

(79,80,81,82,83,84,85,86,87,88,89,90,91,92,93). One is shown in Figure 8.9. A

source o f oxygen is connected to the sys tem. The APL valve is set to mainta in the

desired pressure . A PEEP valve may be added to funct ion as a high-pressure re lief

device (94).

Mapleson E System The Mapleson E (T-piece) sys tem is shown in Figure 8.1E. A length of tubing may

be attached to the T-piece to form a reservo ir. I t does not have a bag. The

expiratory port may be enclosed in a chamber f rom which excess gases are

evacuated.

The sensor or sampling s i te for the respira tory gas monitor may be placed between

the expiratory port and the expiratory tub ing . In larger pa tients, i t may be p laced

between the T-piece and the pat ient, but this locat ion

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should be avoided in small pa tients because i t increases dead space.

View Figure

Figure 8.9 System for continuous positive airway pressure. (See text for details.) PEEP, positive end-expiratory pressure; APL, adjustable pressure limiting.

Numerous modif icat ions of the original T-p iece have been made. Many have the

f resh gas inle t extend ing ins ide the body of the T-piece toward the pat ien t

connec tion to minimize dead space. A pressure-l imi t ing device may be added to the

system.

Use of the Mapleson E system for anes thesia has dec reased because of the

diff icul ty in scavenging excess gases. I t is commonly used to administer oxygen or

humidif ied gas to patients breath ing spontaneous ly.

Techniques of Use For spontaneous vent i lat ion, the expiratory l imb is open to a tmosphere. Control led

venti lation can be performed by inte rmittently occluding the exp iratory l imb and

al lowing the f resh gas f low to inf late the lungs. Assisted respira tion is d if f icu lt to

perform.

Functional Analysis The sequence of events during the respiratory cycle is similar to that of the

Mapleson D system shown in Figure 8 .7. The presence or absence and the amount

of rebreathing or ai r di lut ion wi l l depend on the f resh gas f low, the patient's minute

volume, the volume of the exhalation limb, the type of vent i lat ion (spontaneous or

control led), and the respiratory pattern.

Rebreathing With spontaneous vent i lat ion, no rebreathing can occur i f there is no exhalat ion

l imb. If there is an expiratory l imb, the fresh gas flow needed to prevent rebreathing

wi l l be the same as for the Mapleson D system. During controlled vent i lat ion, there

can be no rebreathing, because only f resh gas wi l l inf la te the lungs.

Air Dilution No air dilu tion can occur during controlled venti lat ion. During spontaneous

venti lation , ai r di lut ion cannot occur i f the volume of the tubing is greater than the

patient 's t idal volume. I f there is no expiratory l imb or i f the volume of the l imb is

less than the pat ient's tida l volume, air dilution can be prevented by provid ing a

f resh gas flow that exceeds the peak inspira tory f low rate , normally three to five

t imes the minute volume. A fresh gas f low of two times minute volume and a

reservoir vo lume one thi rd of the t idal volume wil l prevent ai r dilu tion (95).

Hazards Controll ing venti la tion by intermitten tly occluding the exp iratory l imb may lead to

overinf la tion and

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barotrauma. Th is is a danger with th is system in particular because the anes thesia

provider does not have the “fee l” of the bag during inf la tion that she or he has wi th

other systems. The pressure-buffering effect of the bag is absent, and there is no

APL valve to moderate the pressure in the lungs. To overcome th is potential

hazard, i t has been recommended tha t a pressure-limi ting dev ice be placed in the

system (96).

Mapleson F System

The Mapleson F (Jackson-Rees, Rees, Jackson-Rees modification of the T-piece)

system has a bag with a mechanism for vent ing excess gases (97) (Fig. 8 .1F). The

mechanism can be a hole in the tail or s ide of the bag that is occluded by us ing a

f inger to p rov ide pressure. I t may be f it ted with a device to prevent the bag f rom

co llaps ing wh ile at the same t ime allowing excess gases to escape. An anesthesia

venti lato r may be used in place of the bag (98). An APL valve may be placed near

the pat ient connec tion to prov ide protect ion from high pressure (99).

Scaveng ing can be perfo rmed by enclosing the bag in a chamber from which waste

gases are suct ioned (100) o r by attaching various dev ices to the re lief mechanism

in the bag (101).

Techniques of Use For spontaneous respirat ion , the rel ief mechanism is lef t ful ly open. For assisted or

control led respirat ion, the relief mechanism is occluded suff iciently to dis tend the

bag. Respiration can then be controlled or assisted by squeezing the bag.

Al te rnately, the hole in the bag can be occ luded by the user's finger during

inspiration . For mechanica l venti la tion, the bag is replaced by the hose from a

venti lato r.

A heat and moisture exchanger (HME) can be used wi th a Mapleson F system either

by insert ing i t be tween the patient and the T-piece or by using the gas sampling

port on the HME as the f resh gas inlet (102). However, this wi l l result in mos t of the

f resh gas being vented f rom the distal end of the expira tory limb during

spontaneous respiration (103,104,105). To overcome th is problem, the expiratory

l imb can be part ial ly or total ly occluded, the f resh gas f low inc reased, o r the HME

not used wi th spontaneous respiration.

Functional Analysis The Mapleson F sys tem functions much l ike the Mapleson D system. The f lows

required to prevent rebreath ing during spontaneous and control led respirat ion are

the same as those required with the Mapleson D sys tem. This system offers less

work of breathing than a pediatric c i rc le system (106). Whi le one study did f ind that

there was less work of breathing with the Jackson-Rees system, i t was considered

by other invest igators to be a negl ig ib le dif ference and of importance in only the

s ickest patients breathing spontaneously (107).

PEEP does not affect end-tidal CO2 during control led venti la tion but causes an

increase during spontaneous breathing when fresh gas f lows are less than three

t imes minute volume (108). PEEP should not be applied by us ing an underwater

seal (109).

I f a heat and moisture exchanger (Chapter 11) is added to the Mapleson F system

during an inhalation induction , the inc reased resistance wi l l resul t in more of the

f resh gas flow entering the expiratory l imb, delaying induct ion (104).

Hazards The hazards of the Mapleson F system are the same as those desc ribed for the

Mapleson E system. Excess ive pressure is less l ikely to develop, because there is

a bag in the system.

I f a vent i lator that uses a ram of oxygen to produce inspira tion is used wi th a T-

piece system, a disconnec tion at the common gas out let may not be detected by an

ai rway pressure moni to r due to the high resistance of the f resh gas tubing (110).

Respiratory Gas Monitoring with the Mapleson Systems All of the Mapleson sys tems except the A system have the fresh gas inlet near the

patient connect ion port. This may make i t diff icul t to get a re liable sample of

exhaled gases. One s tudy examined four sampl ing s ites (Fig . 8.10): at the junct ion

of the breathing sys tem and e lbow connector, a t the corner of the elbow connec tor,

2 cm dista l in the elbow connec tor, and in the tracheal tube connector (111). I t was

found that if sampling were carried out at the two s i tes c losest to the patient,

values were accurate. Signif icant errors were noted when samples were taken f rom

the corner of the e lbow connector but only if a high f resh gas f low was used.

Signif icant errors were noted when sampling was performed at the junction o f the

breathing sys tem and elbow connector even i f low fresh gas f lows were used. A

cannula that projects into the airway can be used to improve sampl ing (112).

In another s tudy involv ing infan ts and children, sampl ing at the junct ion of the

tracheal tube and breathing system resul ted in falsely low end-t idal CO2 values in

patients weighing less than 8 kg (59). The accuracy of measurements can be

improved by insert ing a small heat and mois ture exchanger between the breathing

system and the tracheal tube connector (113). However, using a dev ice a t this s ite

wi l l inc rease dead space and may resul t

P.219

in excessive resistance so that spontaneous resp iration cannot be used (103,114).

View Figure

Figure 8.10 Respiratory gas sampling with a Mapleson system. Accurate values for expiratory concentrations can be obtained by sampling at sites 3 and 4. Sampling at site 2 will yield accurate values only if the fresh gas flow is not high. Sampling at site 1 will yield inaccurate values even at low fresh gas flows. (Redrawn from Gravenstein N, Lampotang S, Beneken JEW. Factors influencing capnography in the Bain circuit. J Clin Monit 1985; 1:6–10

[Medline Link] .)

Advantages of the Mapleson Systems

• The equipment is simple, inexpens ive, and rugged. With the exception of the

APL valve, there are no moving parts. The components are easy to

disassemble and can be disinfected or steri l ized in a variety of ways . For

these reasons, they cont inue to be a popular cho ice to provide pos it ive

pressure vent i lat ion in emergencies (115).

• Variations in minute volume affect end-tidal CO2 less than in a c i rc le system.

• In coaxial sys tems (Lack , Bain), the inspiratory l imb is heated by the warm

exhaled gas in the coaxial expira tory tubing.

• Resis tance is usual ly low at f lows likely to be experienced in pract ice

(116,117,118,119). A commonly held v iew is that the work of breathing

during spontaneous vent ilat ion is sign if icantly less wi th these sys tems than

wi th the c i rc le system. However, s tudies indicate that this is not always the

case (120,121,122). The work of breath ing may be inc reased if the APL valve

is not oriented properly .

• These sys tems are l igh twe ight and not bulky. They are not l ikely to cause

drag on the mask or trachea l tube or accidental ex tubation.

• They are easy to posi tion conveniently. A long Mapleson D system with an

aluminum APL valve may be used to vent i late a patient in the MRI uni t (123).

• Compression and compliance volume losses are less wi th the Mapleson

systems than with the ci rcle system.

• Changes in fresh gas concentrat ions resul t in rapid changes in inspira tory

gas composit ion.

• Since there is no CO2 absorbent, there wil l be no product ion of poss ib ly tox ic

products such as carbon monoxide and compound A (Chapter 9).

Disadvantages of the Mapleson Systems

• These sys tems requ ire high gas f lows . This resul ts in higher costs, increased

atmospheric po llut ion, and dif f icul ty assessing spontaneous vent i la tion.

P.220

• Because of the high f resh gas f low, inspired heat and humidity tend to be

low, un less a humidif icat ion device is used (124).

• The optimum fresh gas f low may be diff icult to determine. I t is necessary to

change the f low when changing f rom spontaneous to controlled vent i lat ion or

v ice versa . Anything that causes the f resh gas f low to be lowered presents a

hazard, because rebreathing may occur.

• In the Mapleson A, B, and C systems the APL valve is loca ted c lose to the

patient, where it may be inaccessible to the user. In addi tion , scavenging is

awkward . This disadvantage can be overcome by using the Lack modif ica tion

of the Mapleson A.

• The Mapleson E and F sys tems are diff icul t to scavenge, and ai r di lut ion can

occur wi th the Mapleson E system.

• Mapleson sys tems are not sui tab le for pa tients with mal ignant hyperthermia,

because i t may not be possible to increase the fresh gas flow enough to

remove the increased CO2 load (125).

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Questions For the fol lowing quest ions, select the correct answer.

1. In which of the following is the fresh gas inlet most distant from the patient connection port? A. Mapleson A

B. Map leson B

C. Mapleson C

D. Mapleson D

E. Map leson E

View Answer2. Which of the following is most efficient during spontaneous ventila tion?

A. Mapleson A

B. Map leson B

C. Mapleson C

D. Mapleson D

E. Map leson E

View Answer3. Which of the following systems lacks a reservoir bag? A. Mapleson A

B. Map leson B

C. Mapleson C

D. Mapleson D

E. Map leson E

View Answer4. Which of the following is the most effic ient during controlled ventilation?

A. Mapleson A

B. Map leson B

C. Mapleson C

D. Mapleson D

E. Map leson E

View Answer5. Advantages of the Mapleson systems include a ll of the following except

A. Buffering effect on end-tidal CO2

B. Simple, inexpensive equipment

C. Usefu l in treating malignant hyperthermia

D. Ligh tweight

E. Ease of disassembly

View Answer