The rising cost of newer inhalational anaesthetic agent like desflurane has influenced increasing number of anaesthesiologist to use minimal flow anaesthesia. We did a randomised prospective study on total of sixty patient, who were divided into two groups of thirty patients each. Two volatile inhalational anaesthetic agents were compared: group I received desflurane (n=30) and group II isoflurane (n=30) in minimal flow anaesthesia. Recovery time was 5.70 ± 2.78 minutes in desflurane group and 8.06 ± 31 minutes in isoflurane group (P value 0.004). Desflurane was found costlier than isoflurane but it has many inherent quality which make it superior to other inhalational agent in use. A further saving by desflurane is due to more rapid recovery and patient remain alert and clear headed permitted more economical use of recovery facilities and discharge of patient.

1. COMPARATIVE EVALUATION OF RECOVERY
CHARACTERISTIC AND CONSUMPTION OF DESFLURANE
VERSUS ISOFLURANE IN MINIMAL FLOW ANESTHESIA

2. Original Article
INTRODUCTION
Minimal flow anaesthesia was defined by Simionescu
as fresh gas flow rate of 250-500mL/min [1]. Its popularity
has varied over the years, with resurgence of interest over
last few years because of economic concern,
environmental factors, advances in monitoring and
introduction of new expensive anaesthetics.
Minimal flow anaesthesia is commonly instituted only
after about 10 to 20 minutes of high fresh gas flow, which
precludes the efficient use of circle system for large
proportion of anaesthetics which are of short duration [2-
4]. There is no general agreement as to what constitutes an
adequate alveolar concentration before flow can be
reduced. However, newer studies have used the
‘equilibration point’ of the inhalational agent as the switch
over point. This means that the physical and chemical
characteristics of individual agents influence the initial
high flow period. There are various techniques of minimal
flow anaesthesia that has been described in the literature.
There are number of reports that desflurane, a newer
anaesthetic agent with less blood gas solubility achieves an
adequate alveolar concentration faster than agents with
comparatively lesser blood gas solubility like isoflurane,
COMPARATIVE EVALUATION OF RECOVERY CHARACTERISTIC AND CONSUMPTION
OF DESFLURANE VERSUS ISOFLURANE IN MINIMAL FLOW ANESTHESIA
Tanuja Mallik*, Sanjeev Aneja**, Rajesh Tope** and V Muralidhar**
*Registrar Anaesthesiology and Intensive Care, **Senior Consultant Anaesthesiologists, Indraprastha Apollo
Hospitals, Sarita Vihar, New Delhi 110 076, India.
Correspondence to: Dr Tanuja Mallik, Registrar Anaesthesia, Indraprastha Apollo Hospitals, Sarita Vihar,
New Delhi 110 076, India.
E-mail: mallik_nmc@yahoo.com
The rising cost of newer inhalational anaesthetic agent like desflurane has influenced increasing number of
anaesthesiologist to use minimal flow anaesthesia. We did a randomised prospective study on total of sixty
patient, who were divided into two groups of thirty patients each. Two volatile inhalational anaesthetic agents
were compared: group I received desflurane (n=30) and group II isoflurane (n=30) in minimal flow
anaesthesia. Recovery time was 5.70 ± 2.78 minutes in desflurane group and 8.06 ± 31 minutes in isoflurane
group (P value 0.004).Desflurane was found costlier than isoflurane but it has many inherent quality which
make it superior to other inhalational agent in use.Afurther saving by desflurane is due to more rapid recovery
and patient remain alert and clear headed permitted more economical use of recovery facilities and discharge
of patient.
Summary: To conclue, we can use desflurane more efficiently with minimal flow anaesthesia with quicker and
clear headed recovery with economical use of recovery staff and facilities.
Key words: Minimal flow, cost, newer volatile anaesthetic agent, desflurane, isoflurane, recovery time,
recovery facilities.
therefore lesser duration of high fresh gas flow is required
and therefore leading to lesser environmental pollution.
METHODS
After obtaining approval from hospital ethics
committee and informed consent from patients, study
carried out, in total of sixty healthy patients. All patient
belonged to American Society of Anaesthesiologists
(ASA) physical status I and II, were between 20 to 60
years of age, of either sex, with haemoglobin of more
than 10gm/dL, undergoing routine surgeries. Patients
with cardiac diseases, with lung disorders, pregnancy
and patient undergoing laparoscopic surgery were
excluded.
A routine pre operative check up of the patients was
conducted one day prior to surgery. No preanaesthetic
medications were administered. Patient were randomly
allocated to two groups depending on the volatile anaes-
thetic agent being used, using concealed envelopes.
Group I received desflurane as the inhalational
anaesthetic agent with minimal flow anaesthesia (n=30).
Group II received isoflurane as anaesthetic agent with
minimal flow anaesthesia.
Apollo Medicine, Vol. 8, No. 2, June 2011 134

3. Original Article
135 Apollo Medicine, Vol. 8, No. 2, June 2011
In our study we used Aestiva (Datex Ohmeda,
Madison, USA) anaesthesia machine. A special connector
for return of sampling gas back to the breathing circuit was
used (one end of this connector was attached to the
exhaust port of respiratory gas monitor and the other end
was attached to the expiratory limb of the breathing
circuit) (Fig 1).
All patients were preoxygenated with 100% oxygen.
Induction of anaesthesia was carried out by administering
intravenous fentanyl 2mcg/kg, propofol 3mg/kg,
atracurium 0.5 mg/kg. Then patient was hand ventilated
with a facemask with fresh gas flow of oxygen 6 ltr/min
for 3min and intermittent boluses of propofol 20mg
intravenously were given. Patient was intubated after 3
min of administration of atracurium. Then the patient was
connected to the anaesthesia machine with a Y-piece
connector of the breathing circuit. Initial high fresh gas
flow mixture of 6 Ltr/min which included oxygen 2ltr/min
and nitrous oxide 4 Ltr/min was used with volatile
inhalational anaesthetic agent. Initial dial setting of
volatile inhalational anaesthetic agent was kept at 1.5%
for isoflurane or 8% for desflurane, i.e., equivalent to 1.3
times of the agent MAC. Once the ratio of expired (Fe) to
inspired (Fi) volatile inhalational agent concentration
(isoflurane/desflurane) become 0.8, high fresh gas flow
reduced to minimal fresh gas flow mixture which included
300 mL/min of oxygen and 200 mL/min of nitrous oxide.
This point when the ratio of expired to inspired
inhalational agent concentration become 0.8 that is uptake
of volatile inhalational anaesthetic agent become 80% (Fe/
Fi = 0.8) was defined as “equilibration point” of the
inhalational anaesthetic agent.
During maintenance phase of anaesthesia inspired
oxygen concentration of minimum of 30% was
maintained throughout with above mentioned fixed
minimal fresh gas flow mixture. Dial setting changed if
needed after flow reduction to maintain MAC of 1 or more
as required depending on the type of surgery, keeping
fresh gas flow constant. Top up doses of nondepolarizing
muscle relaxant and morphine for analgesia was given as
per need. Diclofenac 1 mg/kg in 100 mL normal saline was
given to all patients as a part of multimodal approach to
analgesia.
The vaporiser was switched off with last stitch given
by the surgeon. Depending on the last dose of muscle
relaxant given, patient given reversal agent neostigmine
0.5 mg/kg and glycopyrolate 0.01 mg/kg intravenously
after 20min of last dose of relaxant or if patient started
spontaneously breathing. Thereafter, switched off nitrous
oxide and started oxygen 6 Ltr/min. Once the patient
adequately reversed recovery time and recovery
characteristics was noted and patient extubated. Then
patient transferred to postoperative recovery room and
observed. The patient were examined later on and asked
for any intraoperative awareness.
‘Recovery time’ was defined from the time of
discontinuation of inhalational anaesthetic agent
(vaporiser of desflurane or isoflurane switched off) to the
time patient opened his/her eyes for the first time while
recovering from anaesthesia. And at the time of recovery,
patient recovery characteristic defined by giving score 1 to
3 as mentioned below.
Recovery score
1 No response to painful stimuli
2 Drowsy but arousable by verbal command
3 Awake and responding to command at extubation
Critical event if occurred noted (events which can be
harmful to the patient or lead to abandonment of minimal
flow)
• Hypoxia (oxygen saturation less than 90 %)
• Hypoventilation (end tidal carbon dioxide more than
55mmHg)
• Accidental increase in airway pressure (peak airway
pressure more than 30cm H2O)
• Aborting ventilation (leak in the circuit leading to
abandonment of minimal flow)
• Alteration in hemodynamic (hypotension/
hypertension)
• Others
• All patients were observed for an hour in recovery
room. And before discharge from the recovery room
every patient were asked if he/she had any
intraoperative awareness and made a record of that.
Evaluating parameters
• Recovery time and score
• Consumption and cost of volatile anaesthetic agent
used.
Statistical analysis was done and all separate values
were calculated as mean ± standard deviation (SD).
Independent continuous data was analysed by using an
analysis of variance (ANOVA) or unpaired T-test. P value
of less than 0.05 was considered statistically significant.

4. Original Article
Apollo Medicine, Vol. 8, No. 2, June 2011 136
Mann-Whitney U test used for nonparametric, skewed
(non-normal) distribution for test of significance used.
RESULTS
Total sixty adult patients belonging to ASA physical
status I and II were given general anaesthesia using
minimal flow technique (total fresh gas flow 500 mL/min)
with oxygen, nitrous oxide and a volatile inhalational
agent desflurane or isoflurane. The group were randomly
divided into two groups of thirty patients each (Fig.2).
Group I: Desflurane as inhalational agent in minimal
flow anaesthesia (n=30).
Group II: Isoflurane as inhalational agent in minimal
flow anaesthesia (n=30).
The two groups were comparable with respect to age,
weight, and height and body mass index. There were no
significant clinical and statistical difference in hemo-
dynamic parameters in between the two groups.
Recovery characteristic
Recovery time
Recovery of patients from anaesthesia was quicker in
desflurane group than isoflurane group. Patients recovery
time was 5.70 ± 2.78 minutes in desflurane group while
8.06 ± 31 minutes in isoflurane group (p value 0.004).The
values obtained showed statistically significant difference
(as shown in Table1 )
Recovery score
In the desflurane group twenty eight patients were
awake and alert at the time of recovery showing that
desflurane has an advantage of quicker recovery. Table 2
shows the recovery score in the desflurane group. Twenty
eight patients had a score of 3 and two of them had a score
of 2. On the other hand in the isoflurane group patient only
eighteen patients had a score of 2 versus twelve patients
with a score of 3 showing a delayed recovery. Difference
between the two groups was found statistically significant.
No critical events were recorded in any of the 60
patients.We did not use any depth of anaesthesia
monitoring for our study. But at the end of surgery, before
discharging the patient from recovery room they were
asked for any intraoperative awareness and out of sixty no
patient had awareness.
Consumption and cost of volatile anaesthetic
agent
Consumption of volatile anaesthetic agent used was
calculated by using formula
Consumption = CFTM/d24121, where,
C= agent concentration (%)
F= fresh gas flow (litre/min)
T= time (min)
M= molecular weight
Fig 1. (a) Special connector for return of sampling agas used. Showing one end of the connector attached to the expiratory
limb of breathing circuit. (b) Special connector for return of sampling gas used. Showing second end of connector
attached to the exhaust of Respiratory gas monitors (RGM).
(b)(a)

5. Original Article
137 Apollo Medicine, Vol. 8, No. 2, June 2011
D=density of liquid agent (g/mL)
Inhalational Molecular Density(D)
agent weight(M)
Desflurane 168 1.46
Isoflurane 184.4 1.5
Costs of Inhalational agent calculated by formula:
Cost = consumption × drug acquisition cost per unit of
agent.
Consumption of volatile inhalational anaesthetic
agent
Mean consumption of volatile anaesthetic agent at 5,
10, 15, 30 min and 120 min interval were 0.65 ± 0.53, 0.18
± 0.024, 0.24 ± 0.05, 0.45 ± 0.09 and 0.93 ± 0.70 mL/min
respectively in desflurane/group I. While in isoflurane
group/group II values obtained were 0.22 ± 0.00, 0.38 ±
0.16, 0.45 ± 0.311, and 0.27 ± 0.34 and 0.50 ± 0.30 mL/
min at 5, 10, 15, 30 and 120 min intervals. Statistically
significant difference in consumption was found at 10 min
and 120 min interval. At 10 min desflurane consumption
found to be significantly less than isoflurane and values
obtained were 0.17 ± 0.0 and 0.38 ± 0.16 mL/min
respectively. But at 30 min and 120 min interval
desflurane consumption found to be more than isoflurane.
Values obtained at 30 and 120 min were 0.45 ± 0.09 and
0.93 ± 0.70 mL/min in desflurane group and 0.27 ± 0.34
(b)
(a)
(c)
(d)
Fig 2. (a) Changes in heart rate in paients undergoing surgery
under general anaesthesia using desflurane or
isoflurane; (b) Changes in systolic blood pressure in
patient undergoing surgery under general anaesthesia
using desflurane or isoflurane; (c) Changes in diastolic
blood pressure in patient undergoing surgery under
general anaesthesia using desflurane or isoflurane; (d)
changes in mean blood pressure in patient undergoing
surgery under general anaesthesia using deslurane or
isoflurane.
Table 2. Recovery score
Recovery Group I Group II P value
score Desflurane Isoflurane
(n=30) (n=30)
2 2 18 0.000*
3 28 12
unpaired t-test was used for statistical analysis
P value <0.05(*) statistically significant
Recovery score 2 Drowsy but arousable by verbal command
3Awake and responding to command at extubation
Table1. Recovery time (minute)
Group Mean ± SD of recovery P value
time(min)
I / Desflurane 5.70 ± 2.78 0.004*
II/ Isoflurane 8.06 ± 3.31
Unpaired t-test was used for statistical analysis
P value <0.05(*) statistically significant

6. Original Article
Apollo Medicine, Vol. 8, No. 2, June 2011 138
and 0.50 ± .30 mL/min respectively and the difference was
statistically significant (Table 3 ).
Cost of volatile anaesthetic agent
Average cost (Rs) calculated by formula and values
obtained were Rs 21.83 ± 17.7, 21.83 ± 17.7, 5.96 ± .80,
12.62 ± 2.92 and 39.82 ± 8.12 at 5, 10, 15, 30 and 120 min
interval in desflurane group/ group I, while Rs 4.75 ± 0.00,
8.04 ± 3.34, 9.44 ± 6.45, 5.66 ± 7.05 and 10.57 ± 6.41 at 5,
10, 15, 30 and 120 min interval in isoflurane group/group
II respectively (Table 4). Hence, desflurane was found
more costly than isoflurane.
DISCUSSION
The goals of minimal flow anaesthesia are better
ecology, better economics and superior quality of
anaesthesia. The focus of our study was to achieve the
goals of minimal flow anaesthesia in the most efficient
manner with desflurane and isoflurane. The manipulation
of various factors looked at clear answer to various
questions such as:
What was the basic set up for minimal flow
anaesthesia (monitoring/machine/circuit) administration?
Is it different from that of high flow and low flow
techniques?
• For superior efficacy were there any changes/
modifications required for induction and intubation?
• The minimal flow technique always starts with a high
flow period. Traditionally it used to be administered
for fixed time period as discussed in the review of
literature. But this has changed and therefore what
were the criteria for changeover to minimal flow?
• Did this make a significant impact on the duration of
high flow administration? Did this change with
usage of different inhalational agents?
• Fluctuations in the level of anaesthetic agents may
also affect hemodynamic changes, which may
necessitate the dial setting to be changed or rescue
medications to be used. Were there significant
differences in hemodynamic responses between use
of desflurane and isoflurane? Could they be quickly
overcome by changes in the dial setting?
• What were the other clinical problems encountered
during minimal flow anaesthesia?
• Was there a difference in the recovery?
• How can we influence cost at various stages of
minimal flow anaesthesia?
Administration of minimal flow is clearly different
from usages of high or low flows. A better understanding
of these factors will help in allaying fear of safety and
efficacy. A better understanding would lead to lesser
failure and better control of factors directly under the
anaesthesiologist. The above mentioned questions have
been discussed in the same order.
(i) Machine/Monitoring/ circuit: A leak proof machine,
gas monitoring (O2, N2O agent, end tidal volatile
anaesthetic agent concentration, MAC) and a
capnograph to the breathing circuit are absolutely
essential for conduct of a minimal flow technique
[1- 3]. All machines in our hospital have the
necessary prerequisites for administration of
minimal flow anaesthesia but modification which
was used for the study was the special connector for
the return of sampling gas back to the breathing
Table 4. Cost (mean ± SD) of volatile anaesthetic
agent used during minimal flow anaesthesia
Time Group I/Desflurane Group II/Isoflurane
(min) (Rupees) (Rupees)
(n=30) (n=30)
5 21.83 ±17.74 4.75 ± 0.00
10 21.83 ± 17.74 8.04 ± 3.34
15 5.96 ± 0.80 9.44 ± 6.45
30 12.65 ± 2.92 5.66 ± 7.05
120 39.82 ± 8.12 10.57 ± 6.41
Drug acquisition cost per unit ml of agent in our hospital
Isoflurane is Rs 20.75/mL
Desflurane is Rs 33.33/mL
Table 3.Mean consumption of volatile anaesthetic
agent desflurane or isoflurane during
minimal flow anaesthesia
Time Desflurane Isoflurane P value
(min) consumption consumption
(mL) (mL)
Group I Group II
(n=30) (n=30)
5 0.65 ± 0.53 0.22 ± 0.00 0.62
10 0.17 ± 0.02 0.38 ± 0.16 0.00*
15 0.24 ± 0.05 0.45 ± 0.31 0.06
30 0.45 ± 0.09 0.27 ± 0.34 0.00*
120 0.93 ± 0.70 0.50 ± 0.30 0.01*
Consumption was measured in millilitres (mL)
P value <0.05(*) statistically significant
Since, the distribution is skewed (non normal). Mann Whitney
U test used as test of significance.

7. Original Article
139 Apollo Medicine, Vol. 8, No. 2, June 2011
circuit (one end of this special connector was
attached to the exhaust port of the respiratory gas
monitor and the other end was attached to the
expiratory limb of the breathing circuit)
(ii) Induction and intubation: Mask ventilation with
high flow with an inhalational agent (desflurane or
isoflurane) can lead to an enormous loss of
inhalational agent defeating the purpose of minimal
flow. Also during this period it is difficult to monitor
the level of inhalational agent used. To prevent this
boluses of propofol were used at one minute intervals
(without N2O or inhalational agent) after the initial
induction [4]. This method had been used by Soni, et
al found to be an effective technique and is an
effective alternative to the use of inhalational
agent [4].
(iii) Equilibration time has been found to be an effective
parameter for change over from high flow to minimal
flows. Time intervals to equilibration between
inspired (Fi) and expired (Fe) agent concentrations
were defined as ratio of Fe/Fi of 80% [4]. This ratio is
an effective change over point and helps in effective
denitrogenation and maintenance of constant level of
desflurane and isoflurane after the change over from
high flow to minimal flow anaesthesia. Equilibration
time was also used as change over point by Soni,
et al [4].
(iv) Change over to minimal flows necessitates
adjustment/resetting of flows (O2, N2O) and dial
setting of the vaporiser. A number of studies have
recommended different flows of oxygen/minute and
nitrous oxide/minute (250:250, 300:200 per minute
etc). In our study we used oxygen and nitrous oxide
in the ratio of 300 mL/min and 200 mL/min. Baum
recommends oxygen 250-300 mL/min and nitrous
oxide 200-250 mL/min [5,6]. Coetzee and Stewart,
recommended oxygen 300 mL/min and nitrous oxide
200 mL/min respectively [7]. Higher flow of oxygen
in relation to nitrous oxide is recommended because
in first 30-45 minutes after the start of minimal flow
the nitrous oxide uptake continuously declines and in
longer duration of anaesthesia this gas begins to
accumulate within the breathing system, causing a
slow but continuous decrease of oxygen concen-
tration. Hence, oxygen is set higher to prevent
undesirable fall in inspired oxygen concentration in
long duration surgeries.
(v) In our study initial dial setting of vaporiser were kept
at 1.3 time’s minimum alveolar concentration
(MAC) i.e. desflurane 8% and isoflurane 1.5%. This
method was also used by Soni, et al [4]. Baum
recommends initial vaporiser setting of desflurane 4-
6 % and isoflurane 1-1.5% [6]. Coetzee and Stewart,
et al kept the initial vaporiser setting based on
following calculation:
FEAN= (1.3-FEN2O) × MAC, where FEAN= fractional
expired partial pressure of volatile agent in question,
FEN2O = fractional expired concentration of nitrous oxide.
1.3 times MAC was assumed to be the volatile agent
expired partial pressure sufficient to suppress movement
in 95% of patients [7]. Later on after flow reduction,
vaporiser dial setting was changed to maintain 1MAC
during maintenance of anaesthesia.
In our study the oxygen level varied between a
minimum 34.56 ± 2.89 % and maximum 45.80 ± 4.14%.
At no point of time the concentration fallen below 30%.
There was an initial rise in the oxygen level but drifted
down later. The pattern of oxygen changes have been
similarly noted in other studies as by Togal, et al, they
concluded that there is risk of hypoxia in minimal flow
with 50% N2O and 50% O2 and this can be prevented by
increasing FiO2 ratio [8-10].
Coetzee and Stewart in his multicentre trial concluded
that consumption of soluble agent (like enflurane and
isoflurane) only partially depends on fresh gas flow while
desflurane was the agent where usage was affected by
fresh gas flow setting [7]. These results they said can be
explained by mapelson’s hydraulic analogue model
[7,11].
(vi) Depth of anaesthesia
(a) MAC is useful measure because it mirrors brain
partial pressure, allows comparisons of potency
between agents. MAC values of different
anaesthetics are roughly additive. MAC of nitrous
oxide; isoflurane and desflurane are 105, 1.2 and 6.0
for 30-55 year of age expressed as percentage of 1
atmosphere (i.e. a concentration greater than 100%
means that hyperbaric conditions are required to
achieve 1MAC). Around 1.3 MAC of any of volatile
anaesthetic has been found to prevent movement in
about 95% of patients (an approximation of ED95).
0.3-0.4 MAC is associated with awakening from
anaesthesia (MAC awake). MAC can be altered by
several physiological (age/temperature/pregnancy
etc) and pharmacological (opioid/barbiturate/
ephedrine etc) variables. 0.7-1 MAC likely to be
adequate for preventing awareness as also described
by Miller etal. Use of opioid also decreases the MAC
requirement, which need to be taken in consideration
while calculating MAC.

8. Original Article
Apollo Medicine, Vol. 8, No. 2, June 2011 140
In our study we used 1 MAC or more depending on
type of surgery and asked the patient for any history
of awareness before discharging from recovery room
and we found no patient had any intraoperative
awareness.
(ii) Entropy and BIS and other ways of monitoring depth
of anaesthesia have been described in various
literatures, but we have not included it in our study.
(vii) Minimal flow anaesthesia is very safe if one has
adequate knowledge of how to administer it, the
problem encountered during anaesthesia and how to
tackle it.All this need a good understanding of newer
anaesthesia machine, how to detect any leak in
machine, its safety feature and pharmacokinetics and
dynamics of inhalational agent used and fresh gas
flow used.
(viii)Recovery characteristic: There was more rapid
wake–up with desflurane than isoflurane. Mean
recovery values were 5.70 ± 2.78 and 8.06 ± 31
minutes in desflurane and isoflurane group
respectively and difference was statistically and
clinically significant. Patients had a more clear
headed recovery in the desflurane group: 28 patients
out of 30 were alert and awake and 2 were drowsy
but arousable. Patient in isoflurane group were
mostly drowsy but arousable. 18 patients out of 30
were drowsy but arousable and 12 patients were alert
and awake. And the difference between the two
groups was statistically and clinically significant. No
patient had awareness. Eger El LL, Gong D, Koblin
DD, et al studied the effect of anaesthetic duration on
kinetics and recovery characteristics of desflurane
versus sevoflurane12. And they found that
awakening to response to command or to orientation
is almost twice as rapid after anaesthesia with less
soluble desflurane.
Hence, we can conclude that we can use minimal
flow anaesthesia more efficiently, with availability of
agents like desflurane providing balanced
anaesthesia to patient with stable haemodynamics, a
clear headed recovery, with minimum operating
room pollution.
(ix) Cost: Because of low potency/high MAC
requirement of desflurane is correspondingly large.
The amount of agent has to be supplied into the
breathing system just to replenish the required
alveolar partial pressure, despite the fact that the
individual uptake of this anaesthetic is extremely
low. In our study also, we found total consumption
and cost of desflurane was higher than that of
isoflurane. But while calculating cost we did not
calculated the cost benefit we had, due to use of
desflurane because of its rapid wash in and early flow
reduction to minimal flow that avoided
environmental pollution hazard and also due to
economical use of recovery facilities, as desflurane
has rapid and clear headed recovery.
In an editorial Saidman emphasised the importance of
deciding whether desflurane provides a cost-benefit ratio
that recommends its acceptance over the excellent agent
that preceded it [13-15]. Saidman recognised the potential
benefits of desflurane but argued that these must be
sufficient to meet any increased costs that might be
associated with its adoption in practice. Three factors may
influence the cost of an inhaled anaesthetic:
(a) The price determined by the manufacturer. Because
this is subjected to change, it is not considered here.
(b) Factors inherent to the anaesthetic agent, such as
potency and solubility. Among the factor inherent to
the anaesthetic agent that affects cost is the amount
of vapour produced from 1mL liquid anaesthetic.
The amount of vapour produced as a function of the
specific gravities and molecular weights of
desflurane (1.46 gm/mL and 168 gm respectively)
and isoflurane (1.50 gm/mL and 184 gm). These
values indicate that 1mL liquid desflurane will make
7% more vapour than 1 mL of isoflurane. Consider
now the factors controlled by the anaesthesiologist
that influence cost and how these in turn may be
dictated by the pharmacology of the anaesthetic
agent, namely potency and solubility. Saidman noted
that because desflurane is only one fifth as potent as
isoflurane, a larger liquid volume must be vaporised
to produce an equal level of anaesthesia. This
increased cost of desflurane can be reduced
somewhat by utilizing low flows with closed circuits.
(c) The manner in which the anaesthetic is applied,
particularly flow rate. This is of particular
importance because the decision of the anaesthetist
then is a major determinant of cost. Control and
precision with lower inflow rates can be without loss
of control is possible with desflurane. This is because
of the smaller difference between inspired (Fi) and
end tidal (Fe) concentration. Thus desflurane can be
used at lower flow than isoflurane. The clinician who
chooses to use lower inflow rates with the less
soluble anaesthetic agent will greatly lower cost.
(d) A further saving may be due to the use of desflurane
as it provides a more rapid recovery permitting more

9. Original Article
141 Apollo Medicine, Vol. 8, No. 2, June 2011
economical use of recovery facilities.
(e) Capital costs involved in the adoption of a newer
anaesthetic agent include expense of new vaporised
and cost of converting or purchasing instruments to
analyse the new anaesthetic agents.
Hence, we can conclude that inspite of higher cost of
newer inhalational agent desflurane, with many inherent
quality which make it superior to other agent. Desflurane
can be used more efficiently at minimal flow anaesthesia
with quicker and clear headed recovery, with added
advantage of economical use of recovery staff and
facilities.
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