Physical properties and Pharmacology of Desflurane

Desflurane is the most recent volatile agent to enter mainstream anaesthetic practice. It has been welcomed for surgical techniques where a fast onset and rapid recovery from anaesthesia are particularly desirable, such as major head and neck surgery. 

Maintenance of general anaesthesia. 

In addition, its low solubility (blood/gas coefficient) and subsequent smaller volume of distribution are benefificial to patients undergoing lengthy surgery or bariatric patients, in whom the volume of distribution of lipid-soluble drugs is greater.

Physical properties 

Desflurane is a colourless agent which is stored in amber-coloured bottles without preservative. It is non-flammable at commercial concentrations. Desflurane is stable in the presence of soda lime but should be protected from light. Desflurane has an ethereal and pungent odour. 

Desflurane has a boiling point close to room temperature (23.5°C) and a vapour pressure of 88.5kPa at 20°C. A standard vaporiser cannot be used to deliver desflurane as small temperature and/or pressure fluctuations would result in a variable output. A special vaporiser (TEC 6) has been developed which heats the desflurane to 39°C and pressurises it to 2 atmospheres. The TEC 6 vaporiser therefore requires a source of electricity.

Systemic effects

RS: 

• Dose-dependent respiratory depression, with depression of the ventilatory response to PaCO2. This exceeds the effect of other volatile agents at concentrations >1 MAC. 

• Irritant to the upper respiratory tract, particularly at concentrations > 6%. 

• Stimulation of coughing, breath holding and laryngospasm precludes its use as an induction agent. 

CVS: 

• Dose-related reduction in SVR, myocardial contractility and MAP. 

• Heart rate unchanged at lower steady-state concentrations but increases with higher concentrations. 

• Cardiac output tends to be maintained as per isoflurane. 

• In concentrations >1 MAC, an increase in sympathetic activity, leading to increased HR and MAP. 

• No detectable coronary steal. 

• Does not sensitise the myocardium to catecholamines.

CNS:

• Causes general anaesthesia and reduction in cerebral metabolic rate. 

• Dose-dependent EEG depression. 

• Does not induce seizure activity at any depth of anaesthesia. 

• Dose-dependent alteration in cerebral autoregulation (vasodilatation) at concentrations > 1 MAC, which can result in an increase in ICP.

• Dose-dependent muscle relaxation. 

• Potentiation of effects of NMBAs.

GI/GU:

• Uterine relaxation.

• Increased risk of PONV.

Other: 

• Malignant hyperthermia trigger

Pharmacology 

Uptake: 

• With a blood/gas partition coefficient of 0.42, equilibration of alveolar with inspired concentrations of desflurane is rapid compared with other available volatile agents. This leads to a rapid onset and recovery from anaesthesia. 

Metabolism: 

• Approximately 0.02% of inhaled desflurane is metabolised in the body. 

Excretion: 

• Approximately 99.98% is excreted unchanged from the lungs.