The parallel Lack anaesthetic breathing system

Mapleson's Breathing Systems

Mapleson breathing systems are used for delivering oxygen and anaesthetic agents and to eliminate carbon dioxide during anaesthesia. They consist of different components: Fresh gas flow, reservoir bag, breathing tubes, expiratory valve, and patient connection. There are five basic types of Mapleson system: A, B, C, D and E depending upon the different arrangements of these components. Mapleson F was added later. For adults, Mapleson A is the circuit of choice for spontaneous respiration where as Mapleson D and its Bains modifications are best available circuits for controlled ventilation. For neonates and paediatric patients Mapleson E and F (Jackson Rees modification) are the best circuits. In this review article, we will discuss the structure of the circuits and functional analysis of various types of Mapleson systems and their advantages and disadvantages.

An interchangeable Mapleson A-E breathing system is practical and cost effective

BACKGROUND

In locations where oxygen and anesthesia gas supplies are limited, and where circle systems are not practical, means to reduce fresh gas flow during maintenance of inhalational anesthesia are of potential value. We investigated whether a common transport breathing apparatus could be modified to allow interchange between Mapleson D (Map-D) and Mapleson A (Map A) configurations.

METHODS

A common Map-D transport system was converted to a Map-A system by switching positions of the exhaust valve and the elbow connector where fresh gas is delivered; these two breathing systems were compared in this study. The key question was whether rebreathing of CO2 could be eliminated at a lower fresh gas flow rate (FGF) with the Map-A design. A structured protocol was followed.

RESULTS

A mean decrease in FGF of 2.8 l/min was seen with the Map-A apparatus when compared with the Map-D (P=0.003). With no significant differences in physiologic or anesthetic variables, FGF/V(E) was significantly lower with the Mapleson A configuration than with the Mapleson D system design (1.1 vs. 1.8; P=0.007). The extent to which FGF could be lowered when switching between Mapleson D and A systems correlated strongly with the patients' respiratory rate while under anesthesia (r=0.45, P<0.01).

CONCLUSIONS

Cost and resource savings can be realized through the use of a breathing system modification that achieves appropriate ventilation at lower fresh gas flows.

A clinical evaluation of the ‘mini parallel Lack’ breathing system in cats and comparison with a modified Ayre's T‐piece

OBJECTIVE

To evaluate the suitability of a 'mini parallel Lack' (MPL) breathing system for use in spontaneously breathing cats and to compare the fresh gas flow requirement with that of a modified Ayre's T-piece (MATP).

ANIMALS

Twenty client-owned cats, ASA I and II, presented for elective procedures requiring anaesthesia.

MATERIALS AND METHODS

Pre-anaesthetic medication and induction of anaesthesia were carried out using several techniques commonly used in our teaching hospital. Anaesthesia was maintained with halothane or isoflurane vaporized in either oxygen or with a mixture of oxygen and nitrous oxide. Both breathing systems were evaluated in each cat, with the order of use randomized. Initial fresh gas flows were 300 mL kg(-1) minute(-1) for the MPL and 500 mL kg(- 1) minute(-1) for the MATP. After a 20-minute stabilization period, fresh gas flow was reduced by 200 mL minute(-1) every 5 minutes until re-breathing--defined as an increase in the inspired partial pressure of carbon dioxide to 0.3 kPa (2 mm Hg)--was detected. The fresh gas flow was then increased in 100 mL minute(-1) increments until re-breathing was no longer detectable, and this value was recorded as the minimum fresh gas flow requirement for the breathing system in use. The procedure was then repeated for the second breathing system. Minimum fresh gas flow requirements were compared using a paired Students t-test. Cardiopulmonary variables were compared using anova. Valve opening pressure was measured in the MPL using a manometer.

RESULTS

The mean (+/-SD) fresh gas flow that prevented re-breathing with the MPL (510 +/- 170 mL minute(-1); equivalent to 142 +/- 47 mL kg(-1) minute(-1)) was significantly lower than that required for the MATP (1430 +/- 560 mL minute(-1); equivalent to 397 +/-155 mL kg(-1) minute(-1)). There were no significant differences in cardiopulmonary variables attributable to the use of the two breathing systems. The MPL valve opening pressure was 1.1 cm H2O.

CONCLUSIONS

The MPL breathing system used lower gas flows than the MATP without affecting cardiovascular or respiratory function. Clinical relevance In spontaneously breathing cats, the MPL offers the advantages of a reduction in cost and atmospheric pollution because less volatile agent is vaporized.

[Pros or cons of accessory anesthetic circuits. I. Arguments for their use]

In addition to the circle breathing system, which represents the main circuit of the anaesthetic machine, the use of an accessory breathing system (ABS), either a partial rebreathing system according to Mapleson's classification, or a system including a non-rebreathing valve, is appropriate for the anaesthetic management of many patients, depending on their physical status, age, indication and duration of surgery. The same safety rules, namely full checking procedure before use of the system and monitoring of inhaled gases and end-tidal CO2 must be applied as for the main circle system. Potential complications resulting from non compliance with these rules cannot be considered valuable reasons for denying the use of breathing systems that have safely been used for decades in millions of patients.