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March
1998
In rats breathing
from a nonrebreathing system, substitution of desflurane for isoflurane
toward the end of anesthesia incompletely restores the time of recovery
toward that of desflurane.
Gong DH, Weiskopf
RB, Neumann MA, Laster MJ, Eger EI. Anesth Analg 1998;86:198-210.
[see
abstract below ]
Less soluble inhaled
agents such as desflurane leave the body more rapidly and allow a more
rapid emergence than more soluble anesthetics such as isoflurane. However,
desflurane is more expensive to administer than isoflurane. Therefore,
in an effort to limit costs and retain rapid emergence, some practitioners
use isoflurane to maintain anesthesia, and switch to desflurane or sevoflurane
for the last 15 to 30 minutes. These authors sought to answer the question
whether the goals of economy and rapid emergence could both be maintained
by switching anesthetic agents.
In this study, rats received 1.2 MAC of desflurane for the final 15, 30
or 60 minutes of a 2 hour, 1.2 MAC isoflurane anesthetic, using a nonrebreathing
system. Specifically, the testing regimens were either 120 min of 1.2
MAC desflurane; 120 min of 1.2 MAC isoflurane; then, 90 min of 1.2 MAC
isoflurane followed by 30 min 1.2 MAC desflurane; 1.2 MAC isoflurane for
60 or 105 min; and 1.2 MAC desflurane for 60 or 15 minutes. Early recovery
was measured as the time required for the rat to right itself twice. Late
recovery was tested by the ability to remain atop a rod rotating at 8
rpm for 60 seconds.
The results of the single-agent portion of the experiment showed that
both early (righting reflex) and late (rota-rod performance) recovery
occurred significantly sooner after 120 minutes of anesthesia with desflurane
alone than after 120 minutes of anesthesia with isoflurane alone. In the
cross-over anesthetics, a final period of desflurane for 30 minutes or
longer produced a righting reflex time that was not different from desflurane,
but a final 15 minutes of desflurane did not improve the righting time
. For later rota-rod recovery, progressively longer cross-over periods
with desflurane produced progressively shorter recovery intervals. However,
no crossover duration to desflurane produced the rapidity to late recovery
seen with desflurane alone.
These authors found that substituting a less soluble anesthetic, desflurane
for isoflurane for the last 30-60 minutes of a 120 min anesthetic produced
a substantial improvement in early recovery but a smaller and incomplete
improvement in late recovery in rats. There are however, several caveats.
The authors used a nonrebreathing system, which produces maximal isoflurane
washout. However, a partial rebreathing system is used clinically, and
this would prolong the elimination of isoflurane and lengthen the recovery
time; this would result in diminishing the beneficial effects of crossing
over to desflurane for the end of anesthetic. This scenario represents
current typical practice. Instead, a clinician could use higher fresh
gas flows to produce nonrebreathing, which would improve emergence benefits.
However, a crossover technique using high fresh gas flows to eliminate
the isoflurane would also introduce desflurane at these high fresh gas
flows, and the total anesthetic would be more expensive than if desflurane
alone were used at low fresh gas flow rates.
In conclusion, substitution of desflurane for isoflurane in the latter
part of an anesthetic improved early recovery but had a lesser effect
on later recovery, in rats. In order to obtain the maximal improvement
in recovery high fresh gas flow rates would be needed during the crossover
period, and this would result in an increased total anesthetic cost.
Return to the Current
Literature Review Front Page , or read the abstract:
ABSTRACT
The lower
solubility of desflurane allows a more rapid emergence from anesthesia than
after anesthesia with the more soluble but less expensive anesthetic, isoflurane.
Some practitioners use isoflurane for maintenance of anesthesia, crossing
over to desflurane later in maintenance in an attempt to combine the cost-effectiveness
of isoflurane with rapid emergence from desflurane.
We hypothesized that this maneuver would not accomplish its goals. Twenty-four
male Sprague-Dawley rats received 1.2 minimum alveolar anesthetic concentration
(MAC) of desflurane for the final 15, 30, or 60 min of a 2-h, 1.2-MAC isoflurane
anesthetic in a nonrebreathing anesthesia system. We measured the time from
cessation of anesthetic administration to the time each rat righted himself
twice. Immediately after righting for the second time, we tested each rat�s
ability to remain atop a rotating rod (Rota-Rod) for 60 s continuously.
Early (righting reflex) and late (Rota-Rod) recovery occurred more rapidly
(P < 0.001) after 120 min of anesthesia with desflurane alone than after
120 min of anesthesia with isoflurane alone. A cross-over period of 30 min
or longer produced a righting reflex time that did not differ from that
round with desflurane alone, but a 15-min cross-over did not. Progressively
longer cross-over periods led to proportionally better Rota-Rod performance,
but no cross-over duration produced the rapidity of recovery seen with desflurane
alone.
We concluded that in a nonrebreathing system, switching to desflurane during
the last 30 min of anesthesia substantially improved early recovery but
produced a much smaller improvement in later recovery.
Implications: The newer inhaled anesthetics offer the advantage of
lower solubility, and thus more rapid emergence from anesthesia, than do
the older inhaled anesthetics. However, they can be more expensive to use.
This study demonstrates that substituting the newer anesthetic, desflurane,
toward the end of anesthesia for an older anesthetic of greater solubility,
isoflurane, does not produce recovery comparable to that of desflurane alone.
Furthermore, this technique can be more costly than using desflurane throughout
anesthesia.
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