London 2003
Page 5 of 7

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New anaesthesia administration systems

Dr G Lockwood

 

In this talk I will describe the development of a machine to facilitate xenon anaesthesia. It is an attempt to make a system acceptable to the anaesthetist who wishes to use the gas but wants to minimise the change to his practice.

Our solution has been to create an automatic gas mixing system with a low-pressure outlet. The gas mixture can be delivered at more than 5 l min-1 so that a high-flow breathing system can be employed. However, the reserve volume of the mixing system is very small and the mixture can only be produced de novo at about 2 l min-1. In order to maintain high flows, waste gases from the scavenging port of the patient breathing system must be returned to the gas mixer for recycling, and the complete system of gas generator and patient breathing system is then completely closed. This is not the first time that a closed system has been formed from two physically distinct components so that it appears that the patient is breathing from a high-flow system1.

In its present form the system uses a cylinder of oxygen and a cylinder of balance gas, which may be air or xenon. The addition of these gases to the gas mixture is controlled by mass flow controllers, and the composition of the gas mixture within the machine is measured by a fuel cell and a paramagnetic analyser for oxygen, an ultrasonic xenon analyser and an infra-red analyser for carbon dioxide. The automatic control algorithms are very simple: if the system gas has less than the amount of oxygen set by the operator then oxygen is added; if the reservoir volume reduces then balance gas is added. This control system has been used successfully before2. Operation is simple if it is used as an oxygen-air mixer but, for use with xenon, the machine – as well as the patient – must be denitrogenated.

Initial use as an oxygen-air mixer showed it to be an interesting monitor of oxygen consumption. When used as a continuous-flow source for an oxygenator during cardiopulmonary bypass, the effect of temperature changes on oxygen consumption and respiratory quotient were apparent. At the time of writing it has not yet been used as a xenon-oxygen gas source for patients.

 

 

1.     Jackson DE. A new method for the production of general analgesia and anaesthesia with a description of the apparatus used. J Lab Clin Med 1915; 1: 1-12

2.     Humphrey SJE, White DC. A servo-controlled anaesthetic machine. Br J Anaesth 1990; 66: 400P

 

 

 

 

Professor M Maze

 

Anesthesiology 2003; 98(3):690-698

 

   Xenon Attenuates Cardiopulmonary Bypass-induced Neurologic and

   Neurocognitive Dysfunction in the Rat

 

   Daqing Ma, M.D., Ph.D. *; Hong Yang, M.D. †; John Lynch, M.D. ‡; Nicholas P. Franks, Ph.D. §; Mervyn Maze, M.B., Ch.B., F.R.C.P., F.R.C.A.

   Hilary P. Grocott, M.D., F.R.C.P.C. #

 

   Background:

 

   With clinical data suggesting a role for excitatory amino acid neurotransmission in the pathogenesis of cardiopulmonary bypass (CPB)-associated brain injury,

   the current study was designed to determine whether xenon, an N-methyl-D-aspartate receptor antagonist, would attenuate CPB-induced neurologic and

   neurocognitive dysfunction in the rat.

 

   Methods:

 

   Following surgical preparation, rats were randomly divided into four groups: (1) sham rats were cannulated but did not undergo CPB; (2) CPB rats were

   subjected to 60 min of CPB using a membrane oxygenator receiving a gas mixture of 30% O2, 65% N2, and 5% CO2; (3) CPB + MK801 rats received

   MK801 (0.15 mg/kg intravenous) 15 min prior to 60 min of CPB with the same gas mixture; and (4) CPB + xenon rats underwent 60 min of CPB using an

   oxygenator receiving 30% O2, 60% xenon, 5% N2, and 5% CO2. Following CPB, the rats recovered for 12 days, during which they underwent standardized

   neurologic and neurocognitive testing (Morris water maze).

 

   Results:

 

   The sham and CPB + xenon groups had significantly better neurologic outcome compared to both the CPB and CPB + MK801 groups on postoperative days

   1 and 3 (P < 0.05). Compared to the CPB group, the sham, CPB + MK801, and CPB + xenon groups had better neurocognitive outcome on postoperative

   days 3 and 4 (P < 0.001). By the 12th day, the neurocognitive outcome remained significantly better in the CPB + xenon group compared to the CPB group

   (P < 0.01).

 

   Conclusion:

 

   These data indicate that CPB-induced neurologic and neurocognitive dysfunction can be attenuated by the administration of xenon, potentially related to its

   neuroprotective effect via N-methyl-D-aspartate receptor antagonism.