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We describe a new technique specially designed for weaning from mechanical ventilation: carbon dioxide mandatory ventilation (CO2MV). CO2MV is based on feedback between end tidal expired partial pressure of carbon dioxide and ventilatory mode, contro
A SIMPLE VAPORIZER IMPROVISED FROM A CARBON DIOXIDE ABSORBER CANISTER
J.W.R. MCINTYREAND J.G. PURDELL-LEwIS
An empty British Oxygen Company (B.O.C.) Mk. 4 carbon dioxide absorption cannister was modified for use as a vaporizer by placing a layer of flannelette bandage over the horizontal perforated septu m and adding a base plate with an exit port for anaesthetic vapour. Aliquots of liquid anaesthetic were injected from a syringe through the top of the cannister and vaporised by air drawn through the cannister. Laboratory testing showed that this could be a useful way of administering inhalational anaesthesia in the absence of compressed gas supply. KEY WORDS: EQUIPMENT, vaporizer.
MANY EXAMPLES of apparatus employing air as the carrier gas for the vapour of a volatile anaesthetic agent have been manufactured. Probably the most extensively stockpiled in various countries is the E.M.O. apparatus. ~'z However, such systems may not be readily available when they are required and when it is necessary to improvise an inhalational anaesthesia delivery system. Our purpose is to describe the adaptation of a readily available piece of equipment as a vaporizer and to remind anaesthetists of important differences in the situation when the cylinders of oxygen are not available. The item of equipment used as a vaporizer was an empty canister from a British Oxygen Company (B.O.C.) Mk. 4 carbon dioxide absorber. This is cylindrical and placed vertically is 18 cm high, 13cm in diameter and has a multiperforated septum located horizontally half-way down. Its volume is approximately 1700 ml. For use as a vaporizer the additions made were a layer or more of cotton bandage (Flannelette, McLean Converting Hospital Division, Toronto) resting on the septum, and a base plate 0.5 cm thick with an exit port 15 mm in diameter. Liquid anaesthetic was introduced by rapidly injecting aliquots from a syringe via a 22 gauge needle through the top of the cannister toward the centre of the flannelette. The vaporizer was to be used as a "draw over" model in conjunction with a self inflating resuscitation bag and a non-rebreathing valve (Figure 1). The performance of the vaporizer was tested in the laboratory using a Harvard animal respirator
FIGURE 1 Vapour delivery system assembled for
pump to draw air through it and a halothane meter (Cavitron Model 73) to measure the concentration of halothane delivered. Variables of particular interest while using the vaporizer were the volume of air employed for ventilation, the quantity of liquid halothane injected, the number of layers of flannelette used as a vaporizing surface, and resistance to flow through the vaporizer. All experiments were done at approximately 21~ room temperature, barometric pressure 93.1 kPa (700 mm Hg), a relative humidity of 30 per cent, and employing a respiratory rate of 12/minute. The resistance to air flow for the duration of the experiments was found not to be clinically significant (Figure 2). The delivery of halothane vapour was influenced by the number of layers of flannelette (Figure 3) and by the volume of halothane injected (Figure 4). The volume of ventilation (air drawn throughthe vaporizer) has J.W.R. Mclntyre, F.R.C.P.(C); J.G. PurdelI-Lewis, a marked effect on halothane delivery (Figure 5), F.R.C.P.(C): Department of Anaesthesia, University but the concentration was well maintained for the of Alberta, Edmonton, Alberta. duration of the experiment (Figure 6). 174 Canad. Anaesth. Soc. J., vol. 28, no. 2, March 1981
HALOTHANE CONCENTRATK3fl WITH DFFERENT VOLUMES I~JECTED AT TI~E 0
/'"'%% f jl
4 La y~'$ Flant~el~tte Mh~e Volurle G0 urn~
",, \ '\
FIGURE 2 izer.
Resistance to airflow through the vapor-
T~ME n~m ~ I o s
FIGUaE 4 Influence of volume of liquid halothane introduced and the thickness of the vaporizing surface
H~.OmANECO~CeN'r~Ar~N more than t rayer
on the halothane delivery from the vaporizer.
2.0 rrd H~iottlar~ iljectod at Irne 0
F~GURE 3 Halothane delivery from the vaporizer when 2.0ml was introduced while air was drawn through it at 5 l/rain. In discussing this drug delivery system it should be stated that the vaporizer design is similar in appearance to the Denis Browne " T o p H a t " , 3 though in use it is more akin to an item familiar to World War II anaesthetists - the Flagg can. 4 In a review of equipment employed in the early days of anaesthesia Thomas s has described many related devices. As far as the vaporizing surface is concerned its character is of considerable importance. The classic experiments were performed by Hewitt & Symes 6 in 1912. They found a double layer of flannelette offered an advantage over a single layer. Most contemporary anaesthetists are unfamiliar with the " o p e n d r o p " or " r a g and bottle" technique of liquid anaesthetic delivery in which the drug is dropped on to gauze or flannelette stretched o v e r a metal frame held over the patient's face, perhaps incurring a degree of rebreathing. The frames are unlikely to be available. The technique proposed here utilizes readily available equipment and abolishes the problem of rebreathing expired gases. Though air unsupplemented by oxygen has been successfully used as a vehicle for anaesthetic vapours for more than a century, it is a novelty for many anaesthetists and justifies comment.
~ t. 0s mtHalolha•e in~ctr~lpet"rain
tO e a c h Halothane injection
TIME ~ minutes
FIGURE 5 The effect of variations in volume of air drawn through the vaporizer on delivery of halothane vapour from it. EFFECT OF REPEAT INJECTIONS OF HALOTHANE - - - in~OlO~ 0,5 ~ HalOlr,,.lr~ at ~ne 0 I~tlCm 0.5 rlw Halolha~ r,er rain Readl~$ takoll Irnm~tMy ~ to each Jmect~=l 4 layml ~mnelQt~e P.(mnv ~ 7 v ~
Cuta~on ol H~k~tha~ ~jae,on
TI,E ~ m~
FIGURE 6 Hflothane vapour delivery from the vaporizer following serial injections of liquid halothane.
During induction o f anaesthesia arterial oxygen saturation diminishes rapidly if apnoea occurs (Figure 7), so tracheal intubation must be achieved rapidly. Similarly restoration o f spon-
CANADIAN ANAESTHETISTS' SOCIETY JOURNAL
ARTERIAL OXYGEN SATURATION & TENSION DURING APNEA
Following Oxygen Ventilation
Following Air Ventilation tO0,
APNEA, hrne in rain Atle~ WEIT~M[J~I s dl Ane~t~e~,olo0y 20 624Ilg$9'
FIGURE 7 Comparison o f the effects o f apnoea on arterial oxygen saturation following ventilation with air or oxygen. EFFECT OF ADDING O 2
tion is desirable if95 per cent oxygen saturation is to be achieved consistently; but Mushin has stated that an inspired oxygen of 30-50 per cent is necessary during controlled respiration, it Nunn has clearly indicated the need during general anaesthesia for increasing the inspired oxygen concentration above that of atmospheric air. Is It appears that it is better for patients if air is supplemented with oxygen, should this be possible. In our experiments supplementing air with oxygen at a flow of 1.5 l/min provided an Flo2 of not less than 0.3 over a wide range of minute volumes (Figure 7), In conclusion, an empty B.O.C. Mk. 4 carbon dioxide absorber cannister removed from the mounting and with the addition of some flannelette and a base plate with exit port can fun(:tion satisfactorily as a vaporizer. However, creation of a similar vaporizer out of such other materials as may be available should be done with caution, if halogenated anaesthetic agents are to be used, as interaction between the drug and the plastic or the metal 13 may occur.
.s E 6o
.~_ 40.5 1.0 1.5 2.0
3.0 4.0 I Oz/min
I. BOULTON, T.B. Anaesthesia in difficult situation:L Anaesthesia 21 : 513 (1966). 2. EPSTEIN, H.G. & MACn~TOSH, SIR ROBERT. An anaesthetic inhaler with automatic thermocompensation. Anaesthesia II: 83 (1956). 3. BROWNE, DENIS. Anaesthesia for tonsillectomy. Br. Med. J. I1: 632(1928). 4. FLAGG, P.J. The Art of Anaesthesia. Philadelphia J.P. Lippincott Co. 1939. 5. THOMAS K. BRYN. The development of anaesthesia apparatus. Blackwell Oxford, Ist Edition, 1975. 6. HEWlTT, SIR FREDERICK & SYMES, W. LEGGE. On
the percentages of ether vapour administered in
FiO2 FIGURE 8 Effect on the delivered Floz of adding oxygen to air drawn through the vaporizer.
taneous respiration at the termination of artificial ventilation cannot be easily achieved without causing hypoxia. Cole and Parkhouse 7 have reviewed blood oxygen saturation during anaesthesia with volatile agents including ether, t r i c h l o r e t h y l e n e , halothane, and the azeotropic h a l o t h a n e - e t h e r mixture vaporized in room air. They state t h a t air is a satisfactory vehicle for most patients but e m p h a s i z e that respiration m u s t n e v e r be o b s t r u c t e d , depressed, or inadequate. Such a view has received qualified s u p p o r t from o t h e r sources. 4"9'1~l k e z o n o , et al. s state that w h e n air is the diluent artificial ventila-
10. I I. 12. 13.
so-called "open ether" methods. Lancet I: 215, 1912. COLE, P.V. & PARKHOUSE, JAMES. Clinical experience with the E.M.O. inhaler. Post Grd. Med. J;. 39:476 (1963). IKEZONO, E., HARMEL, M.H. & KING, B.D. Pulmonary ventilation and arterial oxygen saturation during ether-air anesthesia. Anesthesiology 20:597 (1959). PAPANTONY, M. & LANDMESSER, C.M. Portable unit for Fluothane in Air Anesthesia ("PUFFA"). Anesthesiology 21 : 768 (1960). POPPELBAUM, H.F. Rediscovery of air for anaesthesia in thoracic surgery. Proc. Roy. Soc. Med. 53:289 (1960). MusHIN, W.W. Discussion. Proc. Roy. Soc. Med. 53:294 0900). NUNN, J.F. Applied Respiratory Physiology. London, Butterworths (1969), pg. 294. EPSTEIn, H.G. Inhalers used in trials for administering mixture of fluothane vapour with air or medical gases. Br. Med. J. 2:489 (1957).
McINTYRE & PURDELL-LEWIS: A SIMPLE VAPORIZER R~SUM~ Un canister d'absorption de gaz carbonique fabriqu~ par la British Oxygen Company a 6t6 modifi6 de fa~on h le transformer en vaporisateur en plaqant une couche de flanelle de coton sur la s6paration perfor6e et en y ajoutant une plaque de fond avec une ouverture pour la sortie de la vapeur anesth6sique. De petites quantites d'anesth6sique liquide ont 6t6 inject6s ~ l'aide d'une seringue par la pattie sup6rieure et vaporis6es dans l'air aspir6 dans le canister. Des 6preuves de laboratoire ont montr6 que ce dispositif pourrait 6tre une m6thode utile pour administrer les agents d'inhalation en I'absence de gaz comprim~.