COMPARATIVE EVALUATION OF RECOVERY

CHARACTERISTIC AND CONSUMPTION OF DESFLURANE

VERSUS ISOFLURANE IN MINIMAL FLOW ANESTHESIA

Original Article

INTRODUCTION

Minimal flow anaesthesia was defined by Simionescuas fresh gas flow rate of 250-500mL/min [1]. Its popularityhas varied over the years, with resurgence of interest overlast few years because of economic concern,environmental factors, advances in monitoring andintroduction of new expensive anaesthetics.

Minimal flow anaesthesia is commonly instituted onlyafter about 10 to 20 minutes of high fresh gas flow, whichprecludes the efficient use of circle system for largeproportion of anaesthetics which are of short duration [2-4]. There is no general agreement as to what constitutes anadequate alveolar concentration before flow can bereduced. However, newer studies have used the‘equilibration point’ of the inhalational agent as the switchover point. This means that the physical and chemicalcharacteristics of individual agents influence the initialhigh flow period. There are various techniques of minimalflow anaesthesia that has been described in the literature.There are number of reports that desflurane, a neweranaesthetic agent with less blood gas solubility achieves anadequate alveolar concentration faster than agents withcomparatively lesser blood gas solubility like isoflurane,

COMPARATIVE EVALUATION OF RECOVERY CHARACTERISTIC AND CONSUMPTIONOF 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 ofanaesthesiologist to use minimal flow anaesthesia. We did a randomised prospective study on total of sixtypatient, who were divided into two groups of thirty patients each. Two volatile inhalational anaesthetic agentswere compared: group I received desflurane (n=30) and group II isoflurane (n=30) in minimal flowanaesthesia. Recovery time was 5.70 ± 2.78 minutes in desflurane group and 8.06 ± 31 minutes in isofluranegroup (P value 0.004).Desflurane was found costlier than isoflurane but it has many inherent quality whichmake it superior to other inhalational agent in use. A further saving by desflurane is due to more rapid recoveryand patient remain alert and clear headed permitted more economical use of recovery facilities and dischargeof patient.

Summary: To conclue, we can use desflurane more efficiently with minimal flow anaesthesia with quicker andclear 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 requiredand therefore leading to lesser environmental pollution.

METHODS

After obtaining approval from hospital ethicscommittee and informed consent from patients, studycarried out, in total of sixty healthy patients. All patientbelonged to American Society of Anaesthesiologists(ASA) physical status I and II, were between 20 to 60years of age, of either sex, with haemoglobin of morethan 10gm/dL, undergoing routine surgeries. Patientswith cardiac diseases, with lung disorders, pregnancyand patient undergoing laparoscopic surgery wereexcluded.

A routine pre operative check up of the patients wasconducted one day prior to surgery. No preanaestheticmedications were administered. Patient were randomlyallocated to two groups depending on the volatile anaes-thetic agent being used, using concealed envelopes.Group I received desflurane as the inhalationalanaesthetic agent with minimal flow anaesthesia (n=30).Group II received isoflurane as anaesthetic agent withminimal flow anaesthesia.

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135 Apollo Medicine, Vol. 8, No. 2, June 2011

In our study we used Aestiva (Datex Ohmeda,Madison, USA) anaesthesia machine. A special connectorfor return of sampling gas back to the breathing circuit wasused (one end of this connector was attached to theexhaust port of respiratory gas monitor and the other endwas attached to the expiratory limb of the breathingcircuit) (Fig 1).

All patients were preoxygenated with 100% oxygen.Induction of anaesthesia was carried out by administeringintravenous fentanyl 2mcg/kg, propofol 3mg/kg,atracurium 0.5 mg/kg. Then patient was hand ventilatedwith a facemask with fresh gas flow of oxygen 6 ltr/minfor 3min and intermittent boluses of propofol 20mgintravenously were given. Patient was intubated after 3min of administration of atracurium. Then the patient wasconnected to the anaesthesia machine with a Y-piececonnector of the breathing circuit. Initial high fresh gasflow mixture of 6 Ltr/min which included oxygen 2ltr/minand nitrous oxide 4 Ltr/min was used with volatileinhalational anaesthetic agent. Initial dial setting ofvolatile inhalational anaesthetic agent was kept at 1.5%for isoflurane or 8% for desflurane, i.e., equivalent to 1.3times of the agent MAC. Once the ratio of expired (Fe) toinspired (Fi) volatile inhalational agent concentration(isoflurane/desflurane) become 0.8, high fresh gas flowreduced to minimal fresh gas flow mixture which included300 mL/min of oxygen and 200 mL/min of nitrous oxide.This point when the ratio of expired to inspiredinhalational agent concentration become 0.8 that is uptakeof volatile inhalational anaesthetic agent become 80% (Fe/Fi = 0.8) was defined as “equilibration point” of theinhalational anaesthetic agent.

During maintenance phase of anaesthesia inspiredoxygen concentration of minimum of 30% wasmaintained throughout with above mentioned fixedminimal fresh gas flow mixture. Dial setting changed ifneeded after flow reduction to maintain MAC of 1 or moreas required depending on the type of surgery, keepingfresh gas flow constant. Top up doses of nondepolarizingmuscle relaxant and morphine for analgesia was given asper need. Diclofenac 1 mg/kg in 100 mL normal saline wasgiven to all patients as a part of multimodal approach toanalgesia.

The vaporiser was switched off with last stitch givenby the surgeon. Depending on the last dose of musclerelaxant given, patient given reversal agent neostigmine0.5 mg/kg and glycopyrolate 0.01 mg/kg intravenouslyafter 20min of last dose of relaxant or if patient startedspontaneously breathing. Thereafter, switched off nitrousoxide and started oxygen 6 Ltr/min. Once the patientadequately reversed recovery time and recovery

characteristics was noted and patient extubated. Thenpatient transferred to postoperative recovery room andobserved. The patient were examined later on and askedfor any intraoperative awareness.

‘Recovery time’ was defined from the time ofdiscontinuation of inhalational anaesthetic agent(vaporiser of desflurane or isoflurane switched off) to thetime patient opened his/her eyes for the first time whilerecovering from anaesthesia. And at the time of recovery,patient recovery characteristic defined by giving score 1 to3 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 beharmful to the patient or lead to abandonment of minimalflow)

• Hypoxia (oxygen saturation less than 90 %)

• Hypoventilation (end tidal carbon dioxide more than55mmHg)

• Accidental increase in airway pressure (peak airwaypressure more than 30cm H2O)

• Aborting ventilation (leak in the circuit leading toabandonment of minimal flow)

• Alteration in hemodynamic (hypotension/hypertension)

• Others

• All patients were observed for an hour in recoveryroom. And before discharge from the recovery roomevery patient were asked if he/she had anyintraoperative awareness and made a record of that.

Evaluating parameters

• Recovery time and score

• Consumption and cost of volatile anaesthetic agentused.

Statistical analysis was done and all separate valueswere calculated as mean ± standard deviation (SD).Independent continuous data was analysed by using ananalysis of variance (ANOVA) or unpaired T-test. P valueof less than 0.05 was considered statistically significant.

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Mann-Whitney U test used for nonparametric, skewed(non-normal) distribution for test of significance used.

RESULTS

Total sixty adult patients belonging to ASA physicalstatus I and II were given general anaesthesia usingminimal flow technique (total fresh gas flow 500 mL/min)with oxygen, nitrous oxide and a volatile inhalationalagent desflurane or isoflurane. The group were randomlydivided into two groups of thirty patients each (Fig.2).

Group I: Desflurane as inhalational agent in minimalflow anaesthesia (n=30).

Group II: Isoflurane as inhalational agent in minimalflow anaesthesia (n=30).

The two groups were comparable with respect to age,weight, and height and body mass index. There were nosignificant clinical and statistical difference in hemo-dynamic parameters in between the two groups.

Recovery characteristic

Recovery time

Recovery of patients from anaesthesia was quicker indesflurane group than isoflurane group. Patients recoverytime was 5.70 ± 2.78 minutes in desflurane group while8.06 ± 31 minutes in isoflurane group (p value 0.004).Thevalues obtained showed statistically significant difference(as shown in Table1 )

Recovery score

In the desflurane group twenty eight patients wereawake and alert at the time of recovery showing thatdesflurane has an advantage of quicker recovery. Table 2shows the recovery score in the desflurane group. Twentyeight patients had a score of 3 and two of them had a scoreof 2. On the other hand in the isoflurane group patient onlyeighteen patients had a score of 2 versus twelve patientswith a score of 3 showing a delayed recovery. Differencebetween the two groups was found statistically significant.

No critical events were recorded in any of the 60patients.We did not use any depth of anaesthesiamonitoring for our study. But at the end of surgery, beforedischarging the patient from recovery room they wereasked for any intraoperative awareness and out of sixty nopatient had awareness.

Consumption and cost of volatile anaestheticagent

Consumption of volatile anaesthetic agent used wascalculated 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 expiratorylimb of breathing circuit. (b) Special connector for return of sampling gas used. Showing second end of connectorattached to the exhaust of Respiratory gas monitors (RGM).

(b)(a)

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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 ofagent.

Consumption of volatile inhalational anaestheticagent

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/minrespectively in desflurane/group I. While in isofluranegroup/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. Statisticallysignificant difference in consumption was found at 10 minand 120 min interval. At 10 min desflurane consumptionfound to be significantly less than isoflurane and valuesobtained were 0.17 ± 0.0 and 0.38 ± 0.16 mL/minrespectively. But at 30 min and 120 min intervaldesflurane consumption found to be more than isoflurane.Values obtained at 30 and 120 min were 0.45 ± 0.09 and0.93 ± 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 surgeryunder general anaesthesia using desflurane orisoflurane; (b) Changes in systolic blood pressure inpatient undergoing surgery under general anaesthesiausing desflurane or isoflurane; (c) Changes in diastolicblood pressure in patient undergoing surgery undergeneral anaesthesia using desflurane or isoflurane; (d)changes in mean blood pressure in patient undergoingsurgery under general anaesthesia using deslurane orisoflurane.

Table 2. Recovery score

Recovery Group I Group II P valuescore Desflurane Isoflurane

(n=30) (n=30)

2 2 18 0.000*3 28 12

unpaired t-test was used for statistical analysisP value <0.05(*) statistically significantRecovery score 2 Drowsy but arousable by verbal command3 Awake and responding to command at extubation

Table1. Recovery time (minute)

Group Mean ± SD of recovery P valuetime(min)

I / Desflurane 5.70 ± 2.78 0.004*II/ Isoflurane 8.06 ± 3.31Unpaired t-test was used for statistical analysisP value <0.05(*) statistically significant

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and 0.50 ± .30 mL/min respectively and the difference wasstatistically significant (Table 3 ).

Cost of volatile anaesthetic agent

Average cost (Rs) calculated by formula and valuesobtained 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 mininterval 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/groupII respectively (Table 4). Hence, desflurane was foundmore costly than isoflurane.

DISCUSSION

The goals of minimal flow anaesthesia are betterecology, better economics and superior quality ofanaesthesia. The focus of our study was to achieve the

goals of minimal flow anaesthesia in the most efficientmanner with desflurane and isoflurane. The manipulationof various factors looked at clear answer to variousquestions such as:

What was the basic set up for minimal flowanaesthesia (monitoring/machine/circuit) administration?Is it different from that of high flow and low flowtechniques?

• For superior efficacy were there any changes/modifications required for induction and intubation?

• The minimal flow technique always starts with a highflow period. Traditionally it used to be administeredfor fixed time period as discussed in the review ofliterature. But this has changed and therefore whatwere the criteria for changeover to minimal flow?

• Did this make a significant impact on the duration ofhigh flow administration? Did this change withusage of different inhalational agents?

• Fluctuations in the level of anaesthetic agents mayalso affect hemodynamic changes, which maynecessitate the dial setting to be changed or rescuemedications to be used. Were there significantdifferences in hemodynamic responses between useof desflurane and isoflurane? Could they be quicklyovercome by changes in the dial setting?

• What were the other clinical problems encounteredduring minimal flow anaesthesia?

• Was there a difference in the recovery?

• How can we influence cost at various stages ofminimal flow anaesthesia?

Administration of minimal flow is clearly differentfrom usages of high or low flows. A better understandingof these factors will help in allaying fear of safety andefficacy. A better understanding would lead to lesserfailure and better control of factors directly under theanaesthesiologist. The above mentioned questions havebeen discussed in the same order.

(i) Machine/Monitoring/ circuit: A leak proof machine,gas monitoring (O2, N2O agent, end tidal volatileanaesthetic agent concentration, MAC) and acapnograph to the breathing circuit are absolutelyessential for conduct of a minimal flow technique[1- 3]. All machines in our hospital have thenecessary prerequisites for administration ofminimal flow anaesthesia but modification whichwas used for the study was the special connector forthe return of sampling gas back to the breathing

Table 4. Cost (mean ± SD) of volatile anaestheticagent 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 ± 0.0010 21.83 ± 17.74 8.04 ± 3.3415 5.96 ± 0.80 9.44 ± 6.4530 12.65 ± 2.92 5.66 ± 7.05120 39.82 ± 8.12 10.57 ± 6.41

Drug acquisition cost per unit ml of agent in our hospitalIsoflurane is Rs 20.75/mLDesflurane is Rs 33.33/mL

Table 3.Mean consumption of volatile anaestheticagent desflurane or isoflurane duringminimal 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 0.6210 0.17 ± 0.02 0.38 ± 0.16 0.00*15 0.24 ± 0.05 0.45 ± 0.31 0.0630 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 significantSince, the distribution is skewed (non normal). Mann WhitneyU test used as test of significance.

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circuit (one end of this special connector wasattached to the exhaust port of the respiratory gasmonitor and the other end was attached to theexpiratory limb of the breathing circuit)

(ii) Induction and intubation: Mask ventilation withhigh flow with an inhalational agent (desflurane orisoflurane) can lead to an enormous loss ofinhalational agent defeating the purpose of minimalflow. Also during this period it is difficult to monitorthe level of inhalational agent used. To prevent thisboluses of propofol were used at one minute intervals(without N2O or inhalational agent) after the initialinduction [4]. This method had been used by Soni, etal found to be an effective technique and is aneffective alternative to the use of inhalationalagent [4].

(iii) Equilibration time has been found to be an effectiveparameter for change over from high flow to minimalflows. Time intervals to equilibration betweeninspired (Fi) and expired (Fe) agent concentrationswere defined as ratio of Fe/Fi of 80% [4]. This ratio isan effective change over point and helps in effectivedenitrogenation and maintenance of constant level ofdesflurane and isoflurane after the change over fromhigh flow to minimal flow anaesthesia. Equilibrationtime was also used as change over point by Soni,et al [4].

(iv) Change over to minimal flows necessitatesadjustment/resetting of flows (O2, N2O) and dialsetting of the vaporiser. A number of studies haverecommended different flows of oxygen/minute andnitrous oxide/minute (250:250, 300:200 per minuteetc). In our study we used oxygen and nitrous oxidein the ratio of 300 mL/min and 200 mL/min. Baumrecommends oxygen 250-300 mL/min and nitrousoxide 200-250 mL/min [5,6]. Coetzee and Stewart,recommended oxygen 300 mL/min and nitrous oxide200 mL/min respectively [7]. Higher flow of oxygenin relation to nitrous oxide is recommended becausein first 30-45 minutes after the start of minimal flowthe nitrous oxide uptake continuously declines and inlonger duration of anaesthesia this gas begins toaccumulate within the breathing system, causing aslow but continuous decrease of oxygen concen-tration. Hence, oxygen is set higher to preventundesirable fall in inspired oxygen concentration inlong duration surgeries.

(v) In our study initial dial setting of vaporiser were keptat 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]. Baumrecommends initial vaporiser setting of desflurane 4-6 % and isoflurane 1-1.5% [6]. Coetzee and Stewart,et al kept the initial vaporiser setting based onfollowing calculation:

FEAN= (1.3-FEN2O) × MAC, where FEAN= fractionalexpired partial pressure of volatile agent in question,FEN2O = fractional expired concentration of nitrous oxide.1.3 times MAC was assumed to be the volatile agentexpired partial pressure sufficient to suppress movementin 95% of patients [7]. Later on after flow reduction,vaporiser dial setting was changed to maintain 1MACduring maintenance of anaesthesia.

In our study the oxygen level varied between aminimum 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 drifteddown later. The pattern of oxygen changes have beensimilarly noted in other studies as by Togal, et al, theyconcluded that there is risk of hypoxia in minimal flowwith 50% N2O and 50% O2 and this can be prevented byincreasing FiO2 ratio [8-10].

Coetzee and Stewart in his multicentre trial concludedthat consumption of soluble agent (like enflurane andisoflurane) only partially depends on fresh gas flow whiledesflurane was the agent where usage was affected byfresh gas flow setting [7]. These results they said can beexplained by mapelson’s hydraulic analogue model[7,11].

(vi) Depth of anaesthesia

(a) MAC is useful measure because it mirrors brainpartial pressure, allows comparisons of potencybetween agents. MAC values of differentanaesthetics are roughly additive. MAC of nitrousoxide; isoflurane and desflurane are 105, 1.2 and 6.0for 30-55 year of age expressed as percentage of 1atmosphere (i.e. a concentration greater than 100%means that hyperbaric conditions are required toachieve 1MAC). Around 1.3 MAC of any of volatileanaesthetic has been found to prevent movement inabout 95% of patients (an approximation of ED95).0.3-0.4 MAC is associated with awakening fromanaesthesia (MAC awake). MAC can be altered byseveral physiological (age/temperature/pregnancyetc) and pharmacological (opioid/barbiturate/ephedrine etc) variables. 0.7-1 MAC likely to beadequate for preventing awareness as also describedby Miller etal. Use of opioid also decreases the MACrequirement, which need to be taken in considerationwhile calculating MAC.

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In our study we used 1 MAC or more depending ontype of surgery and asked the patient for any historyof awareness before discharging from recovery roomand we found no patient had any intraoperativeawareness.

(ii) Entropy and BIS and other ways of monitoring depthof anaesthesia have been described in variousliteratures, but we have not included it in our study.

(vii) Minimal flow anaesthesia is very safe if one hasadequate knowledge of how to administer it, theproblem encountered during anaesthesia and how totackle it. All this need a good understanding of neweranaesthesia machine, how to detect any leak inmachine, its safety feature and pharmacokinetics anddynamics of inhalational agent used and fresh gasflow used.

(viii) Recovery characteristic: There was more rapidwake–up with desflurane than isoflurane. Meanrecovery values were 5.70 ± 2.78 and 8.06 ± 31minutes in desflurane and isoflurane grouprespectively and difference was statistically andclinically significant. Patients had a more clearheaded recovery in the desflurane group: 28 patientsout of 30 were alert and awake and 2 were drowsybut arousable. Patient in isoflurane group weremostly drowsy but arousable. 18 patients out of 30were drowsy but arousable and 12 patients were alertand awake. And the difference between the twogroups was statistically and clinically significant. Nopatient had awareness. Eger El LL, Gong D, KoblinDD, et al studied the effect of anaesthetic duration onkinetics and recovery characteristics of desfluraneversus sevoflurane12. And they found thatawakening to response to command or to orientationis almost twice as rapid after anaesthesia with lesssoluble desflurane.

Hence, we can conclude that we can use minimalflow anaesthesia more efficiently, with availability ofagents like desflurane providing balancedanaesthesia to patient with stable haemodynamics, aclear headed recovery, with minimum operatingroom pollution.

(ix) Cost: Because of low potency/high MACrequirement of desflurane is correspondingly large.The amount of agent has to be supplied into thebreathing system just to replenish the requiredalveolar partial pressure, despite the fact that theindividual uptake of this anaesthetic is extremelylow. In our study also, we found total consumptionand cost of desflurane was higher than that of

isoflurane. But while calculating cost we did notcalculated the cost benefit we had, due to use ofdesflurane because of its rapid wash in and early flowreduction to minimal flow that avoidedenvironmental pollution hazard and also due toeconomical use of recovery facilities, as desfluranehas rapid and clear headed recovery.

In an editorial Saidman emphasised the importance ofdeciding whether desflurane provides a cost-benefit ratiothat recommends its acceptance over the excellent agentthat preceded it [13-15]. Saidman recognised the potentialbenefits of desflurane but argued that these must besufficient to meet any increased costs that might beassociated with its adoption in practice. Three factors mayinfluence the cost of an inhaled anaesthetic:

(a) The price determined by the manufacturer. Becausethis is subjected to change, it is not considered here.

(b) Factors inherent to the anaesthetic agent, such aspotency and solubility. Among the factor inherent tothe anaesthetic agent that affects cost is the amountof vapour produced from 1mL liquid anaesthetic.The amount of vapour produced as a function of thespecific gravities and molecular weights ofdesflurane (1.46 gm/mL and 168 gm respectively)and isoflurane (1.50 gm/mL and 184 gm). Thesevalues indicate that 1mL liquid desflurane will make7% more vapour than 1 mL of isoflurane. Considernow the factors controlled by the anaesthesiologistthat influence cost and how these in turn may bedictated by the pharmacology of the anaestheticagent, namely potency and solubility. Saidman notedthat because desflurane is only one fifth as potent asisoflurane, a larger liquid volume must be vaporisedto produce an equal level of anaesthesia. Thisincreased cost of desflurane can be reducedsomewhat by utilizing low flows with closed circuits.

(c) The manner in which the anaesthetic is applied,particularly flow rate. This is of particularimportance because the decision of the anaesthetistthen is a major determinant of cost. Control andprecision with lower inflow rates can be without lossof control is possible with desflurane. This is becauseof the smaller difference between inspired (Fi) andend tidal (Fe) concentration. Thus desflurane can beused at lower flow than isoflurane. The clinician whochooses to use lower inflow rates with the lesssoluble anaesthetic agent will greatly lower cost.

(d) A further saving may be due to the use of desfluraneas it provides a more rapid recovery permitting more

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economical use of recovery facilities.

(e) Capital costs involved in the adoption of a neweranaesthetic agent include expense of new vaporisedand cost of converting or purchasing instruments toanalyse the new anaesthetic agents.

Hence, we can conclude that inspite of higher cost ofnewer inhalational agent desflurane, with many inherentquality which make it superior to other agent. Desfluranecan be used more efficiently at minimal flow anaesthesiawith quicker and clear headed recovery, with addedadvantage of economical use of recovery staff andfacilities.

REFERENCES

1. Bengtson JP. Reservation of humidity and heat ofrespiratory gases during anesthesia – a labaroratoryinvestigation. Acta Anaesth Scand 1987; 31:127-131.

2. American Society of Anesthesiology (ASA) Standards forbasic anesthetic monitoring. In Miller RD, ed, Anesthesia,5th ed. Churchill Livingstone, Philadelphia, 1999; 1468-1469.

3. American Society for testing and materials, ed, ASTMdesignation: F1161-88; Standard specification forminimum performance and Safety requirement forcomponents and system of anesthesia gas machine.ASTM Standards, 1988; 509-532.

4. Nel R Ooi, Lee DJH, Soni N. New agent , the circlesystem and short procedure: Anaesthesia, 1997; 52:364-381.

5. Virtue RW. Minimal flow nitrous oxide anaesthesia.Anesthesiology 1974; 40: 196-198.

6. Baum Jan A. Lowflow anesthesia; the theory and practiceof low flow minimal flow and closed system anaesthesia.2nd ed, Butterwoth-Heinemann, Melbourn; 2001; 176:254.

7. Coetzee JF, Stewart LJ . Fresh gas flow is not the onlydeterminant of volatile agent consumption, a multicentricstudy of low flow anaesthesia: Br J Anaesth, 2002; 88:46-55.

8. Togal T, Demirbilck S, Koroglu A, Ersoy O. Minimal andmedium flow anaesthesia with isoflurane and desflurane:Effect on inspired and expired oxygen and anaesthesiagas concentrations . The Internet J Anesth, 2008; 18: 2.

9. Straub JM, Hausdorfer. Accumulation of acetone in bloodduring long term anesthesia with closed system. Br JAnesth 1993; 70:363-4.

10. Versichelen L, Rolly G, Vermulen H. Accumulation offoreign gases during closed circuit anaesthesia. Britishjournal of Anaesthesia. 1996; 76: 668-672.

11. Mapelson WW. Pharmacokinetics of inhaledanesthetics. In Prys-Roberts, Hug, CC jr., eds.Pharmacokinetics of Anesthesia. Oxford; BlackwellScientific Publishers, 1984; 89-111.

12. Eger El LL, Gong D, Koblin DD, et al, Anesth Analg 1998;86: 414-421.

13. Bailey CR, Rieggier R Cashman J N. Anesthesia: Costcomparison and recommendation for economic saving.Anesthesia 1993; 48: 906-909.

14. Saidman L. The role of desflurane in the practise ofanaesthesia (editorial) Anaesthesiology, 1991; 74: 399-401.

15. Weiskopf RB, Eger El LL. Comparing the cost of inhaledanaesthetics Anaesthesiology, 1993; 79: 1413-1418.

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