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Desflurane

Created: 20/4/2004

 

 Desflurane

Uses: Induction and maintenance of general anaesthesia.

Chemical: Halogenated ether.


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.

Effects

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

References

[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


[ii] The effect of auricular acupuncture on anaesthesia with desflurane.
Taguchi A et al.
Anaesthesia 2002; 57(12): 1159-63

[iii] Renal responses to desflurane and isoflurane in patients with renal insufficiency.
Litz RJ et al.
Anesthesiology 2002; 97(5): 1133-6


Related examination questions

1. Desflurane:

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

FTFTT

2. Final Viva: Compare the cardiovascular effects of desflurane, sevoflurane and isoflurane.

 


ArticleDate:20040420
SiteSection: Article
 
   
    
                                            
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