During the intervention, when refilling the desflurane vaporizer, we observed that the product was no longer clear (Fig. 1A). The vaporizer was removed from the anaesthesia circuit and after 1hour of observation, a supernatant was found to cover the wall of the level monitor (Fig. 1B). This discolaration, reported in the literature,^1-3 is due to the accumulation of oxidized by-products of butylate hydroxytoluene (BHT) (E-321) (2,6-bis(1,1-dimethylethyl)-4-methylphenol, C₁₅H₂₄O, P. M.: 220.35) (Fig. 2) an antioxidant present in the elastomer used to seal desflurane bottles,^1,3 authorized for use in the food industry.

Source: Authors.

Figure 1 Desflurane yellowed. Initial appearance and appearance after one hour at rest. 

Source: Authors.

Figure 2 BHT oxidado en radicales resonantes-quinonas (coloreados). BHT=butylate hydroxytoluene. 

Desflurane must be stored at a temperature of 15 to 30 °C. The probability of yellowing is higher when this temperature is exceeded. BHT and its by-products have higher boiling points than desflurane and remain trapped in the vaporizer sink and do not flow into the gas circuit. They are not associated with deleterious effects for the patients, although the contamination made evident by BHT oxidation creates interactions of unpredictable consequences. We believe it is important to be aware of this discoloration phenomenon and prevent its occurrence.