ANESTHESIA AND ANALGESIA . . . Current Researches VOL.54, NO.1, JAN.-FEB.,1975
133
An Evaluation of Manually Operated Self-Inflating Resuscitation Bags EDWARD CARDEN, M.A., M.B., B.Chir., F.R.C.P.(C)* TREVOR HUGHES, M.B., Ch.B., F.F.A.R.C.S.?
Eight resuscitators were tested, of which five have recently been improved by t h e manufacturers (Air Shields Ambu, Danish-made Ambu, Pulmonator, Laerdal Resusci 11, and Air Viva). One had a n addition made t o improve its oxygen (On)-delivering capacity ( H o p e bag fitted with Blount collar) and two were new, t h e Air Bird, with and without high Oz-concentration delivering system. The first five
resuscitators were all in some way a n improvement over their earlier counterparts. However, some still malfunction, some d o not deliver adequate O2 concentrations f o r hospital use, and there is still a great variability i n their performance. I n some, freezing a t low temperatures or clogging of valves with mucus a r e special hazards.
P
brated, the pressure reading on the screen was equivalent to volume in the test lung. This reading was used by the bag squeezers to indicate volume.
REXIOUS tests carried out on self-inflating manually operated resuscitatorsl-4 have shown great variations in all aspects of function. This paper reports tests carried out on eight self-inflating manually operated resuscitation bags (fig. 1).Five have recently been improved by their manufacturers (Pulmonator, Laerdal Resusci 11, Air Viva, Danish-made Ambu, and Air Shields Ambu), another has a modification fitted to improve 0, delivery (Hope, with Blount adapter); the two remaining are new (two versions of the Air Bird resuscitator).
EXPERIMENTAL METHODS Oxygen concentrations delivered were measured with various ventilatory patterns and 0, flows, the bags being connected, in turn, to a calibrated test lung adjusted to a compliance of 0.05 L./cm. of water and a resistance of 5 cm./L./sec. water. The Calibrated test lung was connected to a HewlettPackard recorder via a Statham P23B transducer. The pressure developed was read on a screen. With the system correctly cali-
The 0, concentration was measured by a polarographic 0, electrode on a small bypass limb between the bag and the test lung and displayed on an IBC 0,analyzer, model 145MPA. The electrode was connected to the bypass limb via 20-gauge tubing, so that gas leakage from the system was minimal. The test lung was ventilated with volumes of 600 and 900 ml. at 10 and 20 times/min. by rapidly squeezing the bag with one hand and then releasing it, to allow it to refill as quickly as possible. These four patterns of ventilation were performed with an 0, flow to the bag under test of 5,10, and 15 L./min. from a Calibrated backpressure-compensated 0, flowmeter. The bags were ventilated until the 0, concentrations delivered and recorded on the IBC recorder were constant. (This usually took between 60 and 180 seconds. )
*Chief, Anesthesiology Section VA Wadsworth Hospital Center and Associate Professor, Department of Anesthesiology, UCLA School of Medicine, Los Angeles, California 90024. ?Department of Anesthesiology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27514. Paper received: 2/15/74 Accepted for publication: 5/17/74
A N E S T H E SAND ~ ANALGESIA . . . Current Researches VOL.54, No. 1, JAN.-FEB.,1975
134
FIG. 1. The resuscitator bags. From left to right: Top row, Air Viva, Danish Ambu. Middle row, Laerdal Resusci 11, Air Shields Ambu, Bird (high 0, concentration version). Bottom row, Pulmonator, Hope with Blount adapter, Bird.
FWLMONATOR
AIR BIRD
LAERDAL
AIR VIVA
I5
10
5
.-
--+ 100
-
._
i
300
400
500
600
700
800
Tidal
Rate
?
200
/mm Volume
0
-I 15-
lL
AIR SHIELDS
_.._
- 20
600 900
_ _ _ 20
N
0 10 -
5-
I
100m300400500600700800
FIG.2. Graphs showing oxygen concentrations delivered experimentally with varying amounts of 0, flow and varying ventilation patterns.
Resuscitation Bags . . . Carden and Hughes
Measurements were repeated by three observers with two bags of identical design in all instances except the Pulmonator, when only one bag was used. The results, none of which varied more than 7 percent, were averaged (fig. 2 ) . It was found that when ventilation of the lung at 20 times 900 ml. was attempted, the lung would not empty fully after each inflation; in fact, only 750 to 850 ml. tidal volume was obtained. The results of further tests to determine other characteristics are shown in the table. The volumes of the bags were measured by filling them with water from graduated cylinders, and the maximum tidal volumes delivered by the bags was measured by ventilating the test lung, using one and two hands without O2 flow. (In bags in which the 0, is fed directly into the bag, higher readings were obtained with 0, flowing.) Effect of Temperature on Bags.-Bags were tested at temperatures to which they would be subjected if left in the physician's car in summer or winter. After equilibration with hot air at 150" F. in a hot-air oven, the maximum rate of ventilation was measured to see if the heat would slow the expansion of the bag to a degree which could be dangerous. A volunteer was ventiIated with the heated bag, and any malfunctioning of the valve was noted. The effect of cold was determined after the bags had equilibrated at 0" F. in a deep freeze. The maximum rate of ventilation that could be developed by squeezing with one hand was noted (many were frozen solid). A volunteer was then ventilated with those bags which were compressible, and the air-intake and inflating valves were checked for function. Influence of Mucus on Inflating Valve.Mucus was obtained by collecting the contents of anesthesia suction bottles. With the bag connected to the test lung and ventilation at 900 ml. 10 times/min., 5 ml. of mucus was introduced into the inflation valve. The functioning of the valve was then checked for sticking or leakage. Other Tests.-To determine the maximum pressure generated, each bag was connected directly to a Statham P23B transducer and Hewlett-Packard Multi-channel recorder and was squeezed as hard as possible with one hand. This was done by three investigators and the results (none of which differed by more than 10 percent) were averaged to the nearest whole number. The presence or absence of a safety valve, its construction and blow-off pressure, were
135 also noted, and whether this could be bypassed by an occluding finger if higher pressures were needed. The type of inflating valve and the method of 0, entrainment were also noted. The volume of the reservoir tube (if one was incorporated) was then measured, using water, and the ease of servicing, which includes dismantling, cleaning, and sterilizing, was graded by the Department of Respiratory Therapy on a scale of from 1 to 4,4 being the most easily serviced.
RESULTS AND DISCUSSION Three different methods of O2 enrichment were incorporated in the bags tested. These determine to a large extent the amount of 0.)to be delivered to the patient. In bags where the 0, is delivered around the air-intake valve, the resulting 0, concentrations are low (Pulmonator, Air Shields, and Bird) ; but they are unlikely to develop excessive interior pressures, nor are they particularly cumbersome to use. In bags where the O2 is delivered into a reservoir tube, the 0, concentration delivered to the patient is high (Laerdal Resusci 11, Hope with Blount collar, and Air Bird with special attachment) ; but because of the added dimensions of the reservoir, the bags become more cumbersome. They are unlikely to develop excessive pressure in the patient's airway even if the inflating valve jams in the inflating position. The longer the reservoir tube, the higher the 0., concentration and, provided there is no way for room air to leak into the reservoir tube system close to the resuscitator itself (for example, Hope bag), there is no reason why the bag should not be capable of delivering 100 percent 0, to the patient. The third method entails O2 being fed directly into the bag (Air Viva and Ambu) . The advantage of this is that the bag is not cumbersome and is capable of delivering high 0, concentrations, but there is an increased likelihood that the inflating valve will jam in the inspiratory position, and excessive pressures would then be applied to the patient's lungs, possibly causing a pneumothorax if the bag is not rapidly disconnected from the patient. This is therefore not a good method for 0, enrichment unless the resuscitator is being used by technically competent personnel who understand its dangers. It was noted that all inflating valves of the sliding-disc variety had a tendency to
Maximum rate/min. Valve function
0
0
0
+
PVC
PVC
+
Conductive rubber Natural rubber lining neoprene PVC
Latex foam rubber neoprene cover
Bag material
Sliding disc
Silicone shutter Silicone shutter
Sliding disc
Hinged silicone flap valve
Silicone shutter
Type of inflating valve
Fed into reservoir
Variable
1960
4
Stuck in inflating position
Optional
87
40
48 OK 40 Jammed
Fed into reservoir
880
reservoir
A i r Bird with
PVC or RTV silicone
Silicone shutter
2045
2
OK
Leak
80
0
OK
820 1200
Blows around intake valve
Air Bird
1130 1410
Hope with Blount collar
Fed into the bag
500 Fed into reservoir
Fed into the bag
Blows around intake valve
Blows around intake valve
Type of Ozentrainment
Size of reservoir, ml.
1760
1800
2060
1500
1840
Volume, ml.
3
3
2
1
4
OK
OK
Stuck in inflating position
OK
OK
Effect of mucus on valve
Ease of cleaning
Bag. stretches
No
Yes
70
No
65
80
52
OK
20
OK 104
OK
60
790 1210
56 OK
1040 1200
Ambu
No
78/40
64 OK
52 OK
48
OK
700 1060
830 1270
720 1240
Laerdal Rerurci II
Air Viva
Ambu Pulmonotor
Air Shields
Safety valve
Pressure, em. water Infinite resistance
0" F
150" F Maximum rate/min. Valve function
Maximum tidal volume 1 hand 2 hands
TABLE
Construction and Performance Data on Resuscitation Bags Tested
Resuscitation Bags . . . Carden and Hughes
malfunction, while those made of silicone, whether a hinged flap or a silicone disc, functioned perfectly in the presence of moisture, mucus, and extremes of temperature. Bags frozen solid at 0" F. are probably unsuitable outdoors where temperatures of this order are likely to occur. The Laerdal Resusci I1 and the Danish-made Ambu did function quite effectively at this temperature, but the American-made Ambu, which has a different type of air-intake valve, malfunctioned because this valve froze shut; otherwise, the bag and inflating valve behaved adequately. Further Details.-The new Pulmonator is a modification of the earlier model; the bag is larger and has the same inflating valve (a modification of the Leigh valve), and a similar method of 0, entrainment; it is now made of pink polyvinyl chloride. The Pulmonator delivered adequate tidal volumes and the valves functioned well; however, it did not deliver high 0, concentrations even when connected to an 0 , flow of 15 L./min. It would be of limited value when placed in hospitals or other situations where 0, is available or when increased inspired O2 concentrations are desired. The Air Viva is manufactured in Australia. The latest model has a safety valve which, as before, consists of a small plastic ball held in place by a spring designed to blow off at 40 cm. of water pressure. Pressures above this can be exerted in this model, if needed, by occluding the valve escape port with the finger tip (the earlier model had three exit holes, so this could not be done). It delivered high 0, concentrations even with relatively low 0, flows, and functioned well under dry conditions; however, moisture or mucus on the valve tended to make it stick in the inflation position, and with the 0, flow going directly into the bag, this could constitute a dangerous situation if the bag were not immediately disconnected from the patient. It should not cause a pneumothorax, however, unless the safety valve jams shut. It is the only bag in which some rebreathing occurs. The latest model of the Laerdal Resusci I1 is similar to earlier models testeda-5 but has a simpler 0, entrainment valve, consisting of three pieces rather than five. As before, it delivered high 0, concentrations and also functioned well at low temperatures. Its reservoir attachment makes it somewhat cumbersome and its modular construction
137 makes it more likely to fall apart during resuscitation, or for pieces to he lost. The new Air Bird resuscitator looks somewhat like the Air Viva but has a different inflating valve, with silicone shutters. It was easily cleaned, and functioned well even in the presence of mucus. In common with some pediatric resuscitators, it has a built-in leak to prevent excessive pressures being delivered, but this did not function well (80 cm. of water pressure against an infinite resistance). The 0, flow is into a circular reservoir around the air intake valve; consequently only low 0, concentrations were achieved (around 250 torr* at 15 L. 0, flow). Although it did not work at all at 0"F., a special version of this bag is available for low temperature use, made from room temperature vulcanized silicone (this was not tested here). The second version of the Air Bird had a 3-foot-long 0, reservoir tube (with an airintake valve and a small plastic bag on the far end) attached to the circular 0, reservoir. This greatly increased the O2 concentration delivered, allowing up to 100 percent to be delivered to the patient. However, this made it the most cumbersome of all to use. The Hope bag was tested with a Blount collar6 fitted around the air intake ports to increase the 0, concentration delivered. The reservoir used when testing this bag with the Blount collar was the same as with the Luerdal Resusci I Z (500 ml.), but the 0, concentrations obtained were not as high (500 torr maximum). The reason for this is that the Blount collar did not fit snugly onto the resuscitator and allowed a fair amount of air to leak around the adapter, thereby lowering the O2 concentration delivered.' The adapter and reservoir tube make the bag more cumbersome, and if a safety valve (available as an optional extra) had been fitted, the adapter would make it impossible to block the valve's exhaust port to increase the delivered pressure when needed. Under cold conditions, the inflating valve was frozen by the water vapor in the volunteer's exhaled gas, and at normal temperatures it tended to stick when mucus was present. The Air Shields Ambu incorporates the Ambu E II inflating valve; this has silastic shutters which are not affected by m u m or changes in temperature. As expected, the 0, *Torr: 1 mm. Hg at 0"C. and standard gravity.
138
.
ANESTHESIA AND ANALGESIA . . Current Researches VOL. 54, N O . 1, JAN.-FEB.,1975
concentrations delivered were quite low because of the type of O2entrainment system. It is probable that this bag will soon be taken out of production and the Air Shields Company will market the Danish made Ambu Bag.
and the Ohio Chemical Company for their assistance in supplying bags for testing, and Constantine Kargas for his invaluable technical assistance.
REFERENCES
The Danish made Ambu is similar to the Ambu bags tested previously1 but the expansile skeleton, instead of being foam rubber, is now a hollow ball of natural rubber. This will correct the tendency in the older bag for the foam rubber to fragment and block the patient’s airway.8 This model delivered high O2 concentrations, but the inflation valve tended to jam with fresh gas flows of 15 L./min. and it, therefore, should be limited to a 10 L. 0.’ flow. The design of this bag is such that, if jamming does occur, the neoprene cover stretches and the maximum pressure developed is limited to 70 cm. of water. This would be dangerous if the bag were not disconnected from the patient or if the patient had emphysematous bullae, etc., which might rupture under such pressure. ACKNOWLEDGMENT The authors thank the Bird Corporation, Laerdal Incorporated, Narco Incorporated,
1. Carden E, Bemstein M: Investigation of the
nine most commonly used resuscitator bags. JAMA 212:589-592. 1970
2. Franke W, Emmrich P, Ahnefeld FW: Charakteristik verschiedener Beatmungsbeutel und Balle. Anaesthesist 17:191-196, 1968
3. Manually operated emergency ventilation devices. Med Lett Drugs Ther 2:54-56, 1969 4. The manually operated resuscitators. Health Devices 1:13-17, 1971 5. Fkdick LF: Hand-operated self-inflating resuscitation equipment-a re-evaluation.Anesth & Analg 50: 554-556, 1971 6. Ziecheck Hn: A method for increased inspired O9 concentration with the Hope resuscitator. Resp Care 18:409-411, 1973
7. Blount percent adaptor. Health Devices 2: 294, 1973 8. Loveday R, Hurter DG: Hazard of selfinflating resuscitation bags. Brit Med J 4:111, 1969
Riches, though they may reward virtue, cannot cause it.
-Owen Feltham
*
*
*
I haven’t any time to make money, and I don’t want any anyhow. Money is more trouble than it’s worth. --Horace Greeley
133
An Evaluation of Manually Operated Self-Inflating Resuscitation Bags EDWARD CARDEN, M.A., M.B., B.Chir., F.R.C.P.(C)* TREVOR HUGHES, M.B., Ch.B., F.F.A.R.C.S.?
Eight resuscitators were tested, of which five have recently been improved by t h e manufacturers (Air Shields Ambu, Danish-made Ambu, Pulmonator, Laerdal Resusci 11, and Air Viva). One had a n addition made t o improve its oxygen (On)-delivering capacity ( H o p e bag fitted with Blount collar) and two were new, t h e Air Bird, with and without high Oz-concentration delivering system. The first five
resuscitators were all in some way a n improvement over their earlier counterparts. However, some still malfunction, some d o not deliver adequate O2 concentrations f o r hospital use, and there is still a great variability i n their performance. I n some, freezing a t low temperatures or clogging of valves with mucus a r e special hazards.
P
brated, the pressure reading on the screen was equivalent to volume in the test lung. This reading was used by the bag squeezers to indicate volume.
REXIOUS tests carried out on self-inflating manually operated resuscitatorsl-4 have shown great variations in all aspects of function. This paper reports tests carried out on eight self-inflating manually operated resuscitation bags (fig. 1).Five have recently been improved by their manufacturers (Pulmonator, Laerdal Resusci 11, Air Viva, Danish-made Ambu, and Air Shields Ambu), another has a modification fitted to improve 0, delivery (Hope, with Blount adapter); the two remaining are new (two versions of the Air Bird resuscitator).
EXPERIMENTAL METHODS Oxygen concentrations delivered were measured with various ventilatory patterns and 0, flows, the bags being connected, in turn, to a calibrated test lung adjusted to a compliance of 0.05 L./cm. of water and a resistance of 5 cm./L./sec. water. The Calibrated test lung was connected to a HewlettPackard recorder via a Statham P23B transducer. The pressure developed was read on a screen. With the system correctly cali-
The 0, concentration was measured by a polarographic 0, electrode on a small bypass limb between the bag and the test lung and displayed on an IBC 0,analyzer, model 145MPA. The electrode was connected to the bypass limb via 20-gauge tubing, so that gas leakage from the system was minimal. The test lung was ventilated with volumes of 600 and 900 ml. at 10 and 20 times/min. by rapidly squeezing the bag with one hand and then releasing it, to allow it to refill as quickly as possible. These four patterns of ventilation were performed with an 0, flow to the bag under test of 5,10, and 15 L./min. from a Calibrated backpressure-compensated 0, flowmeter. The bags were ventilated until the 0, concentrations delivered and recorded on the IBC recorder were constant. (This usually took between 60 and 180 seconds. )
*Chief, Anesthesiology Section VA Wadsworth Hospital Center and Associate Professor, Department of Anesthesiology, UCLA School of Medicine, Los Angeles, California 90024. ?Department of Anesthesiology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27514. Paper received: 2/15/74 Accepted for publication: 5/17/74
A N E S T H E SAND ~ ANALGESIA . . . Current Researches VOL.54, No. 1, JAN.-FEB.,1975
134
FIG. 1. The resuscitator bags. From left to right: Top row, Air Viva, Danish Ambu. Middle row, Laerdal Resusci 11, Air Shields Ambu, Bird (high 0, concentration version). Bottom row, Pulmonator, Hope with Blount adapter, Bird.
FWLMONATOR
AIR BIRD
LAERDAL
AIR VIVA
I5
10
5
.-
--+ 100
-
._
i
300
400
500
600
700
800
Tidal
Rate
?
200
/mm Volume
0
-I 15-
lL
AIR SHIELDS
_.._
- 20
600 900
_ _ _ 20
N
0 10 -
5-
I
100m300400500600700800
FIG.2. Graphs showing oxygen concentrations delivered experimentally with varying amounts of 0, flow and varying ventilation patterns.
Resuscitation Bags . . . Carden and Hughes
Measurements were repeated by three observers with two bags of identical design in all instances except the Pulmonator, when only one bag was used. The results, none of which varied more than 7 percent, were averaged (fig. 2 ) . It was found that when ventilation of the lung at 20 times 900 ml. was attempted, the lung would not empty fully after each inflation; in fact, only 750 to 850 ml. tidal volume was obtained. The results of further tests to determine other characteristics are shown in the table. The volumes of the bags were measured by filling them with water from graduated cylinders, and the maximum tidal volumes delivered by the bags was measured by ventilating the test lung, using one and two hands without O2 flow. (In bags in which the 0, is fed directly into the bag, higher readings were obtained with 0, flowing.) Effect of Temperature on Bags.-Bags were tested at temperatures to which they would be subjected if left in the physician's car in summer or winter. After equilibration with hot air at 150" F. in a hot-air oven, the maximum rate of ventilation was measured to see if the heat would slow the expansion of the bag to a degree which could be dangerous. A volunteer was ventiIated with the heated bag, and any malfunctioning of the valve was noted. The effect of cold was determined after the bags had equilibrated at 0" F. in a deep freeze. The maximum rate of ventilation that could be developed by squeezing with one hand was noted (many were frozen solid). A volunteer was then ventilated with those bags which were compressible, and the air-intake and inflating valves were checked for function. Influence of Mucus on Inflating Valve.Mucus was obtained by collecting the contents of anesthesia suction bottles. With the bag connected to the test lung and ventilation at 900 ml. 10 times/min., 5 ml. of mucus was introduced into the inflation valve. The functioning of the valve was then checked for sticking or leakage. Other Tests.-To determine the maximum pressure generated, each bag was connected directly to a Statham P23B transducer and Hewlett-Packard Multi-channel recorder and was squeezed as hard as possible with one hand. This was done by three investigators and the results (none of which differed by more than 10 percent) were averaged to the nearest whole number. The presence or absence of a safety valve, its construction and blow-off pressure, were
135 also noted, and whether this could be bypassed by an occluding finger if higher pressures were needed. The type of inflating valve and the method of 0, entrainment were also noted. The volume of the reservoir tube (if one was incorporated) was then measured, using water, and the ease of servicing, which includes dismantling, cleaning, and sterilizing, was graded by the Department of Respiratory Therapy on a scale of from 1 to 4,4 being the most easily serviced.
RESULTS AND DISCUSSION Three different methods of O2 enrichment were incorporated in the bags tested. These determine to a large extent the amount of 0.)to be delivered to the patient. In bags where the 0, is delivered around the air-intake valve, the resulting 0, concentrations are low (Pulmonator, Air Shields, and Bird) ; but they are unlikely to develop excessive interior pressures, nor are they particularly cumbersome to use. In bags where the O2 is delivered into a reservoir tube, the 0, concentration delivered to the patient is high (Laerdal Resusci 11, Hope with Blount collar, and Air Bird with special attachment) ; but because of the added dimensions of the reservoir, the bags become more cumbersome. They are unlikely to develop excessive pressure in the patient's airway even if the inflating valve jams in the inflating position. The longer the reservoir tube, the higher the 0., concentration and, provided there is no way for room air to leak into the reservoir tube system close to the resuscitator itself (for example, Hope bag), there is no reason why the bag should not be capable of delivering 100 percent 0, to the patient. The third method entails O2 being fed directly into the bag (Air Viva and Ambu) . The advantage of this is that the bag is not cumbersome and is capable of delivering high 0, concentrations, but there is an increased likelihood that the inflating valve will jam in the inspiratory position, and excessive pressures would then be applied to the patient's lungs, possibly causing a pneumothorax if the bag is not rapidly disconnected from the patient. This is therefore not a good method for 0, enrichment unless the resuscitator is being used by technically competent personnel who understand its dangers. It was noted that all inflating valves of the sliding-disc variety had a tendency to
Maximum rate/min. Valve function
0
0
0
+
PVC
PVC
+
Conductive rubber Natural rubber lining neoprene PVC
Latex foam rubber neoprene cover
Bag material
Sliding disc
Silicone shutter Silicone shutter
Sliding disc
Hinged silicone flap valve
Silicone shutter
Type of inflating valve
Fed into reservoir
Variable
1960
4
Stuck in inflating position
Optional
87
40
48 OK 40 Jammed
Fed into reservoir
880
reservoir
A i r Bird with
PVC or RTV silicone
Silicone shutter
2045
2
OK
Leak
80
0
OK
820 1200
Blows around intake valve
Air Bird
1130 1410
Hope with Blount collar
Fed into the bag
500 Fed into reservoir
Fed into the bag
Blows around intake valve
Blows around intake valve
Type of Ozentrainment
Size of reservoir, ml.
1760
1800
2060
1500
1840
Volume, ml.
3
3
2
1
4
OK
OK
Stuck in inflating position
OK
OK
Effect of mucus on valve
Ease of cleaning
Bag. stretches
No
Yes
70
No
65
80
52
OK
20
OK 104
OK
60
790 1210
56 OK
1040 1200
Ambu
No
78/40
64 OK
52 OK
48
OK
700 1060
830 1270
720 1240
Laerdal Rerurci II
Air Viva
Ambu Pulmonotor
Air Shields
Safety valve
Pressure, em. water Infinite resistance
0" F
150" F Maximum rate/min. Valve function
Maximum tidal volume 1 hand 2 hands
TABLE
Construction and Performance Data on Resuscitation Bags Tested
Resuscitation Bags . . . Carden and Hughes
malfunction, while those made of silicone, whether a hinged flap or a silicone disc, functioned perfectly in the presence of moisture, mucus, and extremes of temperature. Bags frozen solid at 0" F. are probably unsuitable outdoors where temperatures of this order are likely to occur. The Laerdal Resusci I1 and the Danish-made Ambu did function quite effectively at this temperature, but the American-made Ambu, which has a different type of air-intake valve, malfunctioned because this valve froze shut; otherwise, the bag and inflating valve behaved adequately. Further Details.-The new Pulmonator is a modification of the earlier model; the bag is larger and has the same inflating valve (a modification of the Leigh valve), and a similar method of 0, entrainment; it is now made of pink polyvinyl chloride. The Pulmonator delivered adequate tidal volumes and the valves functioned well; however, it did not deliver high 0, concentrations even when connected to an 0 , flow of 15 L./min. It would be of limited value when placed in hospitals or other situations where 0, is available or when increased inspired O2 concentrations are desired. The Air Viva is manufactured in Australia. The latest model has a safety valve which, as before, consists of a small plastic ball held in place by a spring designed to blow off at 40 cm. of water pressure. Pressures above this can be exerted in this model, if needed, by occluding the valve escape port with the finger tip (the earlier model had three exit holes, so this could not be done). It delivered high 0, concentrations even with relatively low 0, flows, and functioned well under dry conditions; however, moisture or mucus on the valve tended to make it stick in the inflation position, and with the 0, flow going directly into the bag, this could constitute a dangerous situation if the bag were not immediately disconnected from the patient. It should not cause a pneumothorax, however, unless the safety valve jams shut. It is the only bag in which some rebreathing occurs. The latest model of the Laerdal Resusci I1 is similar to earlier models testeda-5 but has a simpler 0, entrainment valve, consisting of three pieces rather than five. As before, it delivered high 0, concentrations and also functioned well at low temperatures. Its reservoir attachment makes it somewhat cumbersome and its modular construction
137 makes it more likely to fall apart during resuscitation, or for pieces to he lost. The new Air Bird resuscitator looks somewhat like the Air Viva but has a different inflating valve, with silicone shutters. It was easily cleaned, and functioned well even in the presence of mucus. In common with some pediatric resuscitators, it has a built-in leak to prevent excessive pressures being delivered, but this did not function well (80 cm. of water pressure against an infinite resistance). The 0, flow is into a circular reservoir around the air intake valve; consequently only low 0, concentrations were achieved (around 250 torr* at 15 L. 0, flow). Although it did not work at all at 0"F., a special version of this bag is available for low temperature use, made from room temperature vulcanized silicone (this was not tested here). The second version of the Air Bird had a 3-foot-long 0, reservoir tube (with an airintake valve and a small plastic bag on the far end) attached to the circular 0, reservoir. This greatly increased the O2 concentration delivered, allowing up to 100 percent to be delivered to the patient. However, this made it the most cumbersome of all to use. The Hope bag was tested with a Blount collar6 fitted around the air intake ports to increase the 0, concentration delivered. The reservoir used when testing this bag with the Blount collar was the same as with the Luerdal Resusci I Z (500 ml.), but the 0, concentrations obtained were not as high (500 torr maximum). The reason for this is that the Blount collar did not fit snugly onto the resuscitator and allowed a fair amount of air to leak around the adapter, thereby lowering the O2 concentration delivered.' The adapter and reservoir tube make the bag more cumbersome, and if a safety valve (available as an optional extra) had been fitted, the adapter would make it impossible to block the valve's exhaust port to increase the delivered pressure when needed. Under cold conditions, the inflating valve was frozen by the water vapor in the volunteer's exhaled gas, and at normal temperatures it tended to stick when mucus was present. The Air Shields Ambu incorporates the Ambu E II inflating valve; this has silastic shutters which are not affected by m u m or changes in temperature. As expected, the 0, *Torr: 1 mm. Hg at 0"C. and standard gravity.
138
.
ANESTHESIA AND ANALGESIA . . Current Researches VOL. 54, N O . 1, JAN.-FEB.,1975
concentrations delivered were quite low because of the type of O2entrainment system. It is probable that this bag will soon be taken out of production and the Air Shields Company will market the Danish made Ambu Bag.
and the Ohio Chemical Company for their assistance in supplying bags for testing, and Constantine Kargas for his invaluable technical assistance.
REFERENCES
The Danish made Ambu is similar to the Ambu bags tested previously1 but the expansile skeleton, instead of being foam rubber, is now a hollow ball of natural rubber. This will correct the tendency in the older bag for the foam rubber to fragment and block the patient’s airway.8 This model delivered high O2 concentrations, but the inflation valve tended to jam with fresh gas flows of 15 L./min. and it, therefore, should be limited to a 10 L. 0.’ flow. The design of this bag is such that, if jamming does occur, the neoprene cover stretches and the maximum pressure developed is limited to 70 cm. of water. This would be dangerous if the bag were not disconnected from the patient or if the patient had emphysematous bullae, etc., which might rupture under such pressure. ACKNOWLEDGMENT The authors thank the Bird Corporation, Laerdal Incorporated, Narco Incorporated,
1. Carden E, Bemstein M: Investigation of the
nine most commonly used resuscitator bags. JAMA 212:589-592. 1970
2. Franke W, Emmrich P, Ahnefeld FW: Charakteristik verschiedener Beatmungsbeutel und Balle. Anaesthesist 17:191-196, 1968
3. Manually operated emergency ventilation devices. Med Lett Drugs Ther 2:54-56, 1969 4. The manually operated resuscitators. Health Devices 1:13-17, 1971 5. Fkdick LF: Hand-operated self-inflating resuscitation equipment-a re-evaluation.Anesth & Analg 50: 554-556, 1971 6. Ziecheck Hn: A method for increased inspired O9 concentration with the Hope resuscitator. Resp Care 18:409-411, 1973
7. Blount percent adaptor. Health Devices 2: 294, 1973 8. Loveday R, Hurter DG: Hazard of selfinflating resuscitation bags. Brit Med J 4:111, 1969
Riches, though they may reward virtue, cannot cause it.
-Owen Feltham
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I haven’t any time to make money, and I don’t want any anyhow. Money is more trouble than it’s worth. --Horace Greeley
