Single lever Humphrey A.D.E.lowflow universal anaesthetic breathing system

David Humphrey MBBS(Lond.) DA (S.A.) 0 John G. Brock-Utne MA MB BCH (TCD) FFA (S.A.) (Bergen) 0 John W. Downing MB BCH FFA ( S . A . ) FFARCS (Eng.) 0 0 From the Faculty of Medicine, Departments of Anaes- thetics and Physiology, University of Natal , PO Box 17039, 4013 Congella, Durban , South Africa , where Preliminary reports were presented at the 1985 South African Society of Anaesthetists Congress, Durban and at the 1985 18th Scandinavian Society of Anaesthesiol- ogists Congress , Iceland A clinical trial involving ten anaesthetized adultpatients was conducted during controlled ventilation using the Humphrey A.D.E. system in the Mapleson "E" mode (lever down). With each patient acting as his or her own control, the parallel (non-coaxial) and coaxial versions of the single lever Humphrey A.D.E. system were compared, using capnography, to the Bain system (Mapleson D/E). All three systems behaved similarly with predicta. ble patient normocarbia when a fresh gas flow of 70 ml.kg- t.min-t was used. The A.D.E. system has the added advantage that the switch from controlled to spontaneous ventilation (or vice versa) is achieved quickly and simply. Spontaneous, assisted or automatic controlled ventilation could be instituted at any time merely by the appropriate lever position. - ABBREVIATIONS A.D.E. = Humphrey A.D.E. anaesthetic breath ing system _A.D.E. = A.D.E. set in A mode A._D.E. = A.D.E. set in D mode A.D._E. = A.D.E. set in E mode FGF = Fresh gas flow PICO2 = Minimum inspired carbon dioxide tension PI~CO2 = End-expired (or end-tidal) carbon dioxide tension PaCOz = Arterial carbon dioxide tension Humphrey etal.: CONTROLLED VENTILATION WITH THE A.D.E. BREATHING SYSTEM FIGURE I Photograph of the single lever parallel (noncoaxial) version of the Humphrey A.D._E.system set in the "E" mode (lever down). Both the reservoir bag and expiratory valve are automatically excluded, thus making simple tubes of the inspiratory and expiratory limbs (see Figures 2-4), While the ventilator remains attached to the expiratory ventilator port on the underside at all times, it is included in circuit only with the lever down, Coaxial tubing can replace the parallel tubes if desired (Figure 3). only 51 m l . k g - t . m i n - t to p r e v e n t rebreathing o f alveolar g a s e s , a n d to be m o r e efficient t h a n the Magill s y s t e m w h i c h required a m e a n flow o f 71 m l . k g - t . m i n - I . T h e Bain s y s t e m w a s m a r k e d l y less efficient than b o t h A . D , E . or Magill s y s t e m s , and required a m e a n F G F o f 150 m l - k g - l . m i n - I . However, d u r i n g controlled ventilation, similar function o f the A . D . E, a n d t h e B a i n s y s t e m s c a n be predicted, since both a r e c o n v e r t e d into M a p l e s o n E s y s t e m s * that are functionally two s i m p l e t u b e s (Figure 4). T h e B a i n s y s t e m h a s b e e n u s e d extensively in this m o d e b e c a u s e PaCO2 can b e predictably determined by the fresh g a s flow set b y the anaesthetist. Identical p e r f o r m a n c e o f the original dual lever A . D . E , s y s t e m a n d the B a i n s y s t e m h a s been confirmed d u r i n g controlled ventilation. 6 W e now present the results o f c a p n o g r a p h s t u d i e s o n anaesthetised adult patients d u r i n g controlled ventilation with both v e r s i o n s o f the n e w single lever *See appendix. FIGURE 2 Diagram of the parallel(non-coaxial) single lever Humphrey A.D.E. system with an exploded view of the eytinder mechanism. (a) When the lever is upright (A mode, spontaneous and manual respiration) and inspiratcyryreservoir bag and expiratoryvalve are in circuit, while the ventilator is excluded. (b) When the lever is down (E mode), the ventilator is now included with the exclusion of the reservoir bag and exhaus! valve. The system is simply two tubes, as is the Bain circuit during controlled ventilation (see Figure 4). Note that the pressure-limiting device stays in circuit in either mode. FGF = fresh gas flow. (Reproduced from Humphrey,4 with permission. FIGURE 3 Diagram of the single lever coaxial Humphrey A_.D.E. system. The same main body as in Figure 2 is used but the parallel tubing is replaced by a coaxial set. The position of the lever and function of the system remain identical. FIGURE 4 Diagrams of the (a) Bain, (b) coaxial A.D.E_. and (c) non-coaxial parallel A.D._E. systems showing the func!ional parts when used for controlled ventilation. All are simply two tubes (Mapleson E systems), since the valve on each system has been closed (Bain) or excluded (A.D._E.) and the reservoir bag removed (Bain) or excluded (A.D._E.). Methods A similar protocol and anaesthetic induction technique as has been previously presenteds was employed. Ten patients scheduled for elective peripheral surgery and of ASA physical status I were selected. Each patient gave informed consent. Anaesthesia was induced with thiopentone, the trachea was intubated and anaesthesia was maintained with halothane and nitrous oxide with oxygen. However, in this study, the use of narcotic analgesics during anaesthesia was permitted as required. Muscle relaxation was achieved with alcuronium 0.15 to 0.25 mg'kg - t IV as an initial dose, with smaller increments being given as necessary. Ventilation was controlled using a fluid logic, time cycled, flow generator Nuffield 200 ventilator (Penlon Ltd., Abingdon, Oxon, England) attached to the expiratory valve-bypass outlet of the A.D._E. system via two standard 22 mm corrugated tubes with a total volume of about one litre. This ventilator is of the "bag squeezer" variety and is suitable Humphreyetal.: C O N T R O L L E D V E N T I L A T I O N W I T H T H E A , D . E . B R E A T H I N G SYSTEM for Bain type and circle systems. Tidal volumes were calculated as normally recommended for the Bain system at approximately 10ml.kg-l-min -~ with the respiratory rate set between 12 and 15 breaths.min - l , and fresh gas flows adjusted to 70ml.kg-J'min - j . Both A.D._E. systems and the Bain circuit were compared twice in each patient, the initial order of testing being randomized, six patients being connected to an A.D._E. system first. Clinical trials Investigations were conducted with both parallel and coaxial versions of the single lever A.D.E_. systems set in their Mapleson E mode with the lever in the down position (Figures 1-3). With the ventilator connected to the expiratory valve-bypass outlet, tidal volumes, ventilation frequency and fresh gas flows were set, as above. The Bain system was used in the conventional way with the ventilator attached to the expiratory Iimb with the reservoir bag removed and the exhaust valve fully closed. Within patient comparisons in ten subjects were made between both A.D.E_. systems and the Bain, without alteration of any of the ventilation or fresh gas parameters. Both versions of the single lever A.D.E. systems were also examined towards t (...truncated)