The blood–gas partition coefficient

A partition coefficient (λ) describes the relative affinity of a volatile anaesthetic for two phases and how that anaesthetic distributes itself between the two phases when equilibrium has been achieved. The blood–gas partition coefficient (λb/g), or Ostwald coefficient for blood–gas, is a pharmacological term used to describe the solubility of a volatile anaesthetic agent. Volatile agents with a low blood–gas partition coefficient (less soluble) will exert a high partial pressure and produce a more rapid onset and offset of anaesthetic action.

Efficacy of inhaled methoxyflurane for procedural analgesia in paediatric burns: a pilot study

Background: Methoxyflurane (MF), a volatile anaesthetic agent is known for its analgesic properties in sub anaesthetic concentrations. It has been used as an analgesic agent for short procedures in both adults and children in the prehospital setting and in the emergency department. We conducted a pilot study to investigate the use of MF for burn dressing changes in children. Methods: A prospective case series was conducted in the paediatric burns ward amongst children aged 4–9 years. During burns dressing changes MF was administered using a hand-held patient-controlled device. An investigator monitored vital signs together with pain scores, sedation levels and levels of satisfaction of staff. Results: Twelve patients were enrolled for the study. The majority of the burn wounds were classified as partial-thickness wounds. Methoxyflurane was used as the sole agent for analgesia and sedation for the procedure. No major adverse events were noted. Analgesia and sedation levels were sufficient and appropriate respectively for the majority of the patients during the initial exposure of the wound and the application of the new dressing. However, during the scrubbing of the burn wound analgesia and sedation proved insufficient in four and seven of the patients respectively. Conclusion: In our setting the use of MF for inpatient burn wound dressing changes may be insufficient as a sole agent in the paediatric patient. We suggest it may be used as an adjunct to current practice. Further, larger studies are required to delineate the appropriate role MF can play in the paediatric burns setting.

Closed Circuit Anaesthesia in Ventilated Patients using the Komesaroff Vaporizer within the Circle

A study was undertaken to assess the performance of the Komesaroff vaporizer, placed within the circuit, in ventilated patients during maintenance of closed circuit anaesthesia with halothane or isoflurane. Following intravenous induction, anaesthesia was maintained by inhalation. This was achieved using a conventional vaporizer outside the circle for the first 10 minutes to manage the fast uptake phase. The fresh gas flow was then reduced to the basal oxygen requirement with the Komesaroff vaporizer within the circle maintaining inhalational anaesthesia. Complete isolation of the circuit was achieved by returning all anaesthetic gases to the circuit following analysis and using a bag-in-bottle ventilator. The Komesaroff vaporizer dial was positioned at between the first and second division and end-tidal volatile anaesthetic agent levels were measured. This study demonstrated that at dial positions I or 1.5 with either agent, the end-tidal volatile concentration plateaued at clinically acceptable levels. The Komesaroff vaporizer can therefore be used safely in ventilated patients to maintain closed circuit anaesthesia provided clinical observation and monitoring are meticulous.

Inhalational Induction with Sevoflurane in an Adult with Severe Complex Central Airways Obstruction

Sevoflurane is a newly available volatile anaesthetic agent which is suitable for inhalational induction of anaesthesia. Due to concerns about obstructing the upper airway as anaesthesia deepens, its use has until now been avoided in patients with upper airway obstruction. We used its smooth induction and recovery properties however to anaesthetize a patient with central airway obstruction and coexistent ischaemic heart disease. Sevoflurane proved to be a very satisfactory agent in this situation.

Patient Awareness during Anaesthesia: An Analysis of 2000 Incident Reports

Amongst the first 2000 incidents reported to the Australian Incident Monitoring Study there were 16 cases in which patient recall of perioperative events was consistent with awareness. Awareness that occurred in 3 of 10 cases during anaesthesia was attributed to low concentrations of volatile anaesthetic agent; the conduct of anaesthesia appeared to be unremarkable in the other 7. The remaining 6 cases involved the inadvertent paralysis of patients prior to induction of anaesthesia, most commonly by “syringe swap” when suxamethonium was given instead of fentanyl. Some of these patients were significantly distressed. These preliminary findings suggest that incident monitoring should be useful in the study of awareness associated with anaesthesia and the development of strategies to prevent it.

An Evaluation of Three Volatile Anaesthetic Agent Monitors

Three volatile anaesthetic agent monitors (Datex Normac Anesthetic Agent Monitor, Engstrom Emma Multigas Monitor and Penlon Halothane Meter) were evaluated for the effects of nitrous oxide or water vapour, and for their linearity, stability, and rate of response to a change in concentration of various anaesthetic agents under simulated working conditions. None was affected by nitrous oxide, and only the Engstrom Emma was affected by water vapour. Linearity was satisfactory for all three devices but stability, with respect to zero and gain drift, was satisfactory only for the Datex Normac and Penlon Meter. Rates of response for 10% to 90% of source signal ranged from 0.8 seconds for the Datex Normac to about three seconds for the Penlon Meter.

Hazards of Anaesthetic Scavenging: Case Reports and Brief Review

Two cases are presented of misadventure occurring in association with the use of anaesthetic scavenging equipment. The first case demonstrates how easily the scavenging line linking the venting port of a mechanical ventilator to the scavenging interface can become accidentally obstructed. The second case suggests that the proper use of scavenging equipment will effectively eliminate any possibility of recognising by smell an accidental overdose of volatile anaesthetic agent. Previous reports of scavenging hazards are briefly reviewed. It is concluded from this review that scavenging suction should be‘low-vacuum’, that a relief valve must be included in the scavenging pathway proximal to any site of potential obstruction, and that the appearance and function of a scavenging interface must be simple and immediately obvious.