Presentation: Clear colourless liquid that should be protected from light.
Mode of action: mechanism of general anaesthesia remains unclear.
Routes: Administered by inhalation. Because of the high saturated vapour pressure, Desflurane is administered by a specific pressurised and heated vaporiser. Induction dose, 4-11%; maintenance, 2-6%.
Tec 6 Desflurane vaporiser:
Because of the volatility of this agent, it requires a different vaporiser to contain, transfer and vaporise it. The saturated vapour pressure at room temperature (20 degrees C) is 88.5 kPa -87% of one atmosphere. This means that desflurane is nearly boiling at room temperature. The vaporiser is a gas/vapour blender, not a variable bypass type.
Classification of vaporiser (Anesth Analg 1993; 76: 1338-41)
Electrically heated, dual circuit gas/vapour blender, constant- temperature, agent specific and out-of-circuit.
Function: Heats the agent to 39 degrees C, which produces a vapour pressure of around 1550 mmHg. Electronic controls inject pure vapour into the fresh gas flow stream from the flowmeters, controlled by the concentration control dial, and a transducer (which senses the fresh gas flow rate and adjusts the vapour output accordingly). Requires electrical power and has alarms. In use, it is similar to variable bypass vaporisers: it fits in the interlocks, and is mounted on the back bar in a similar way. It is accurate at low flows (i.e. considerably less than 1 L/min total fresh gas flow). It may be filled during use. A mark on a liquid crystal display indicates when the liquid level is one bottle low (250 ml). There is an alarm for low liquid level. The unit requires a warm-up period. Internal switches cut out the system if temperature increases above 57 degrees C or if the vaporiser is tilted or becomes empty.
Cardiovascular system: Causes a decrease in myocardial contractility, but sympathetic tone is well preserved. Does not sensitise the myocardium to circulating catecholamines. Causes a dose-dependent decrease in systemic vascular resistance, thus leading to a decrease in mean arterial pressure. Heart rate may increase via an indirect autonomic effect. Does not cause ‘coronary steal’.
Respiratory system: Respiratory depressant. Decreases tidal volume, although may increase respiratory rate. Decreases response to hypoxia and hypercapnia. Irritant to the respiratory tract at concentrations greater than 6%.
Cental nervous system: Principal effect is general anaesthesia; little analgesic effect. Causes cerebral vasodilatation, leading to increased cerebral blood flow. Decreases cerebral oxygen consumption and is not associated with epileptiform activity. Causes a centrally mediated decrease in skeletal muscle tone.
Abdominal system: Does not decrease hepatic blood flow.
Genitourinary system: Decreases renal cortical blood flow.
Toxicity: Trigger agent for malignant hyperthermia. Unsuitable for use during gaseous induction.
Absorption: Coefficients: blood/gas:0.42, oil/gas: 19; minimum alveolar concentration: 5-10
Desflurane is exceptionally insoluble in blood; the alveolar concentration therefore reaches the inspired concentration very rapidly, resulting in a rapid induction of anaesthesia.
Distribution: Initially to areas of high blood flow (brain, heart, liver and kidney). Later to less well-perfused organs.
Metabolism: 0.02% is metabolised, predominantly to trifluoroacetic acid.
Excretion: Via the lungs, predominantly unchanged. Elimination is rapid due to its low solubility.
Special points: Potentiates action of depolarising and non-depolarising muscle relaxants
[i] Desflurane compared with propofol for postoperative sedation in the intensive care unit.
Meiser A et al.
Br J Anaesth 2003; 90(3): 273-80
[iii] Renal responses to desflurane and isoflurane in patients with renal insufficiency.
[ii] The effect of auricular acupuncture on anaesthesia with desflurane.
Taguchi A et al.
Anaesthesia 2002; 57(12): 1159-63
Litz RJ et al.
Anesthesiology 2002; 97(5): 1133-6
Related examination questions
a) is a fluorinated methylisopropyl ether
b) boils at 23 degrees C
c) is safe to use in patients with malignant hyperpyrexia
d) stimulates the sympathetic system when the inspired concentration is suddenly increased
e) prolongs the duration of muscle relaxants
2. Final Viva: Compare the cardiovascular effects of desflurane, sevoflurane and isoflurane.