65034942

7/30/2019 65034942

1/8

Increased lung clearance of isoflurane shortens emergence

in obesity: a prospective randomized-controlled trial

R. KATZNELSON, F. NAUGHTON, Z. FRIEDMAN, D. LEI, J. DUFFIN, L. FEDORKO, M. WASOWICZ, A. VAN RENSBURG, J. MURPHYand J. A. FISHERDepartment of Anesthesia and Pain Management, University Health Network, Toronto General Hospital, Toronto, ON, Canada

Background: There is a concern that obesity may play arole in prolonging emergence from fat-soluble inhalationalanaesthetics. We hypothesized that increased pulmonaryclearance of isoflurane will shorten immediate recoveryfrom anaesthesia and post-anaesthesia care unit (PACU)stay in obese patients.Methods: After Ethics Review Board approval, 44 ASA IIII patients with BMI430kg/m2 undergoing elective gy-naecological or urological surgery were randomized aftercompletion of surgery to either an isocapnic hyperpnoea(IH) or a conventional recovery (C) group. The anaesthesiaprotocol included propofol, fentanyl, morphine, rocuro-nium and isoflurane in air/O2. Groups were comparedusing unpaired t-test and ANOVA.Results: Minute ventilation in the IH group before extubationwas 22.6 2.7 vs. 6.3 1.8l/min in the C group. Compared

with C, the IH group had a shorter time to extubation (5.4 2.7vs. 15.8 2.7 min, Po0.01), initiation of spontaneous ventilation(2.7 2.3 vs. 6.5 4.5 min, Po0.01), BIS recovery 475 (3.2 2.3vs. 8.9 5.8min, Po0.01), eye opening (4.6 2.9 vs. 13.6 7.1min, Po0.01) and eligibility for leaving the operating room(7.1 2.9 vs. 19.9 11.9 min, Po0.01). There was no differencein time for eligibility for PACU discharge.Conclusion: Increasing alveolar ventilation enhancesanaesthetic elimination and accelerates short-term recov-ery in obese patients.

Accepted for publication 31 May 2011

r 2011 The AuthorsActa Anaesthesiologica Scandinavicar 2011 The Acta Anaesthesiologica Scandinavica Foundation

OBESITY (BMI 3035 kg/m

2

) presents specificrelated challenges in providing secure airway

access1 and adequate ventilation during surgeryand weaning. The patients ventilatory vulnera-bility is also increased during emergence. Thesafest approach is to promote a rapid restorationof consciousness and ventilatory self-sufficiency.2

Traditionally, anaesthetics with low blood/gassolubility35 have been preferred for their greaterpulmonary clearance for a given minute ventila-tion. Alveolar ventilation, has also been shownto be an independent determinant of anaesthetic

clearance68 but its efficacy in obesity is unknown.We hypothesized that in obese patients, increases

in pulmonary clearance of isoflurane would accel-erate the short-term recovery from anaesthesiasuch as time to extubation. As the initial phaseof gas elimination accounts for the greater part ofthe reduction in body content of the anaesthetic,9

we also hypothesized that the early greater anaes-thetic clearance would reduce the time from theend of anaesthesia (turning isoflurane vaporizer

off) to the readiness for post-anaesthesia care unit(PACU) discharge.

Methods

This is a prospective randomized-controlled trialthat was registered at Clinical.Trials.gov on 22July 2008 (the clinical Trials.gov Identifier isNCT00752492). After Institutional Ethics ReviewBoard approval, recruitment was started in August2008 and finished in May 2010. Figure 1 depictsthe study flow diagram. Signed informed con-

sent was obtained from 44 ASA IIII patientswith BMI430 kg/m2 undergoing elective gynaeco-logical or urological surgery. Exclusion criteriawere contra-indications to any part of the studyanaesthetic protocol, a history of coronary arterydisease, pulmonary hypertension, chronic obstruc-tive lung disease, New York Heart Associationclass 43, alcohol consumption of more than twostandard drinks a day, a history of psychiatricillness such as dementia, schizophrenia and bipolar

995

Acta Anaesthesiol Scand 2011; 55: 9951001Printed in Singapore. All rights reserved

r 2011 The Authors

Acta Anaesthesiologica Scandinavica

r 2011 The Acta Anaesthesiologica Scandinavica Foundation

ACTA ANAESTHESIOLOGICA SCANDINAVICA

doi: 10.1111/j.1399-6576.2011.02486.x
http://localhost/var/www/apps/conversion/tmp/scratch_8/Clinical.Trials.govhttp://localhost/var/www/apps/conversion/tmp/scratch_8/Trials.govhttp://localhost/var/www/apps/conversion/tmp/scratch_8/Trials.govhttp://localhost/var/www/apps/conversion/tmp/scratch_8/Clinical.Trials.gov

7/30/2019 65034942

2/8

disorder, and daily consumption of benzodiaze-pines, opiate narcotics or other psychoactive drugs.

Patients arrived in the operating room withoutpremedication with sedatives. Standard operatingroom monitors consisting of 5-lead ECG, a bloodpressure cuff and a pulse oximeter were applied, aswell as BIS (Aspect Medical Systems, Newton,MA). Additional monitors during maintenanceincluded spirometry, oesophageal temperature,end-tidal and inspired gas and anaesthetic vapourconcentrations, tidal volume, airway pressures

(Datex A/S 3, GE Healthcare, Madison, Wisconsin,USA) and a peripheral nerve stimulator. Data fromthe Datex AS/3 were digitalized at 60 Hz using aDI-720 analog-to-digital converter (Dataq, Akron,OH) and recorded continuously.

After pre-oxygenation, anaesthesia was inducedwith propofol 23 mg/kg, fentanyl 12mg/kgand rocuronium 0.60.8 mg/kg. All drug dosesand ventilation regimens were calculated basedon the estimation of the ideal body weight.10 After

endotracheal intubation, patients lungs wereventilated via a circle anaesthetic circuit with aCO2 absorber at initial settings of tidal volume7 ml/kg ideal weight, respiratory rate 10 andPEEP 5 cmH2O. Ventilator settings (AS-3 Datex,GE Healthcare) and fresh gas flows were adjustedto maintain end-tidal PCO2 (PEtCO2) values at40 3 mmHg and SaO2 497%. Fresh gas flowconsisted of a mixture of air and O2 at o2l/minduring maintenance. The end-tidal isofluraneconcentration was maintained above 0.7 MAC

and titrated according to clinical signs of depthof anaesthesia and to maintain BIS values in therange of 4050. Supplemental doses of fentanyl(50100mg) and morphine ((24 mg) were adminis-tered as clinically indicated. Supplemental doses ofrocuronium (2030 mg) were added if the train-of-four stimulation demonstrated two or morevisible twitches or as required to provide foradequate surgical relaxation. Fifteen minutesbefore the anticipated end of surgery, the isoflurane

Assessed for eligibility (n= 536)

Excluded (n= 492)Not meeting inclusion criteria (n=432)Declined to participate (n= 27)Other reasons (missed in clinic,

cancelled surgery, premedication with

lorazepam) (n= 33)

Analysed (n= 20)

Lost to follow (n= 0)

Discontinued intervention (n= 0)

Allocated to IH group (n= 22)

Received allocated intervention (n= 20)

Did not receive allocated intervention (n= 2)

( 1-protocol violation, 1- postoperative

mechanical ventilation)

Lost to follow-up (n= 0)

Discontinued intervention (n= 0)

Allocated to C group (n= 22)

Received allocated intervention (n=20)

Did not receive allocated intervention (n=2)

( 1-protocol violation, 1- postoperativemechanical ventilation)

Analysed (n= 20)

Allocation

Analysis

Follow-Up

Randomized (n= 44)

Enrollment

Fig. 1. Protocol flow diagram.

R. Katznelson et al.

996

7/30/2019 65034942

3/8

concentration was adjusted to maintain BIS valuesin the range 5560. Patients were randomlyallocated to either an isocapnic hyperpnoea (IH)or a Control (C) group according to a computer-generated randomization code in predeterminedsize blocks of four. The randomization sequencewas prepared and kept by a research coordinator.

A sealed envelope containing the designation ofthe cohort was released to the anaesthesiologist inthe OR during the skin closure. After the last stitch,train-of-four stimulation was performed and in thepresence of at least one visible twitch the residualneuro-muscular block was reversed by administer-ing neostigmine in doses up to 0.05mg/kgand glycopyrrolate 0.01 mg/kg lean body weight.Then, the isoflurane vaporizer was turned off.

In the C group, air flow was turned off andthe O2 flow was set at 15l/min to prevent anyrebreathing of anaesthetic vapour. Ventilatory as-

sistance was provided intermittently to maintainSaO2 497% and PEtCO2 at 4050 mmHg to hastenthe return of spontaneous ventilation. Patientsrandomized to the IH group were disconnectedfrom the circle circuit and connected to the self-inflating bag attached to the IH system7,11 (Clear-Matet, Thornhill Research Inc., Toronto, ON,Canada). Ventilation was assisted to maintain atidal volume of 810 ml/kg and a respiratory rateof 2025 breaths/min, with minute ventilation of1520 l/min. PEtCO2 was maintained in the rangeof 4050 mmHg by adjusting the O2 flow to the self-

inflating bag. The minimum criteria for extubationfor both groups was spontaneous ventilation withtidal volumes of 67 ml/kg of lean body weight,following commands and ability to lift the head offthe pillow. The following OR events were recorded:duration of anaesthesia (beginning of induction toturning off the vaporizer), duration of surgery(skin incision to skin closure), time of resumptionof spontaneous ventilation, arousal (opening eyesin response to verbal command), BIS value exceed-ing 75, extubation, time to fulfilment of criteria forleaving the OR (stable vital signs, adequate ventila-

tion and following simple commands) and time toeligibility for PACU discharge.

On arrival in the PACU, the patients were placedin a semi-recumbent position with the back ofthe stretcher tilted at 301. O2 was administeredvia a face mask at 6 l/min. Post-operative analgesiawas provided in the same manner in both groupsof patients, according to standard practice: ketor-olac 1530 mg i.v., morphine 2 mg i.v. or fentanyl50100mcg i.v. q 5 min prn for breakthrough

pain. Patient-controlled analgesia was used if clini-cally indicated. Patients were assessed at 10-minintervals during the first hour after PACU admis-sion by the PACU nurse who was blinded tothe patients group allocation. This assessmentincluded a Richmond Agitation Sedation Score,12

a pain score from a standardized 10 cm visual

analogue score (0 no pain, 10 worst, unbearablepain) and Aldrete score13 (assessing activity, con-sciousness and vital signs). Patients were consid-ered ready for discharge when the Aldrete scorewas 10 and the pain score was o5.

Any occurrences of nausea and vomiting, shiver-ing or respiratory complications, and unexpectedprolonged PACU stay were documented. All timeintervals were measured from the end of anaethe-sia defined as a turning isoflurane vaporizer off tillthe event.

Data analysis

Continuous measures were compared through aseries of independent-samples t-test. Categoricalmeasures were tested through chi-square tests. Anytests resulting in a P-value ofo0.05 were consideredstatistically significant at an a-level of 0.05. Catego-rical values are presented as N(%), while continuousmeasures are summarized as the mean SD unlessotherwise specified. A series of non-parametricMannWhitney U-test was performed to determinewhether pain/sedation/Aldrete scores differed sig-

nificantly between the groups.

Power analysisIn a previous study,7 IH reduced the time from theend of anaesthesia until readiness for discharge fromPACU by 20 19 min. With b set at 0.2 (power50.8)and a50.05, 20 patients in each group were suffi-cient to test this hypothesis. Therefore, consideringan attrition rate of 10%, we proposed to test a total of44 patients.

Results

Comparison of the primary endpointThe patients in the IH group had significantlyshorter times to initiation of spontaneous breath-ing, eye opening, extubation and readiness to leaveOR (Table 1). Five patients (two in IH group andthree in the C group) demonstrated a decrease inthe level of consciousness after extubation. Three ofthese patients (one in the IH group and two in the

Isoflurane clearance and anaesthesia recovery in obesity

997

7/30/2019 65034942

4/8

C group) required the insertion of an oral airway tomaintain upper airway patency. One patient (in theC group) had to be re-intubated in the OR.

On arrival in the PACU, patients in the IH grouphad higher Aldrete scores than the patients in the Cgroup (Fig. 2). Otherwise, there were no clinicallysignificant differences between the groups in readi-ness to discharge to the floor and incidences of

nausea, vomiting and shivering (Table 1). The totalpost-operative administered dose of analgesic andantiemetic medications in the PACU and the aver-age RASS and pain scores were similar.

Comparison of experimental conditions betweengroupsTwenty-two patients were randomized to eachgroup. Four patients (two in each group) were

excluded from the analysis: one patient in eacharm of the study underwent elective post-operativemechanical ventilation because of the extent ofthe surgical procedure. Two other patients were

excluded due to protocol violation: one patient inthe C group received midazolam intraoperativelyand one patient in the IH group received propofolin the last 10 min before the skin closure. Data fromthe remaining 40 patients (20 in each group) wereanalysed. The demographic and surgical character-istics are presented in Table 2. Anaesthetic manage-ment was comparable in the two groups (Table 3).Minute ventilation in the IH group before extubationwas 22.6 2.7 vs. 6.3 1.8l/min in the C groupbut there were no differences in exhaled isofluraneconcentration [0.08 0.08% (IH) vs. 0.13 0.1% (C),

P50.17] or PEtCO2s [43 4.2 mmHg (IH) vs. 40.44.5 mmHg (C), P50.07] immediately before extuba-tion. All patients in the IH group tolerated IH with-out haemodynamic or respiratory instability.

Discussion

Traditionally, the differences in pulmonary clear-ance of anaesthetics are attributed to the effect of

Table 1

Immediate and intermediate outcome parameters of obese patients undergoing gynaecological and urological surgery.

Outcome in minutes from turning off vaporizer to IH (N520) Control (N520) P-value

Initiation of spontaneous ventilation 2.7 2.3 6.5 4.5 0.002BIS475 3.2 2.3 8.9 5.8 o0.01Eyes opening 4.6 2.9 13.6 7.1 o0.01Extubation 5.4 2.7 15.8 8.7 o0.01Eligibility to leave OR 7.1 2.9 19.9 11.9 o0.01

First pain medication in the PACU 38.5 14.2 48.9 24.5 0.15Eligibility for discharge from PACU 91.9 16.5 107.8. 40.9 0.15Re-hypnotization after extubation, n (%) 2 (10%) 3 (15%) 1.0Incidence of nausea or vomiting, n (%) 3 (15%) 1 (5%) 0.34Incidence of shivering, n (%) 1 (5%) 1 (5%) 1Incidence of postoperative hypoxaemia, n (%) 0 1 (5%) 1.0

IH, isocapnic hyperpnoea; PACU, post-anaesthesia care unit.

6.5

7

7.5

8

8.5

9

9.5

0 10 20 30 40 50 60 70 80

Time (minutes)

Aldretescores

IH

Control

P=0.02

Fig. 2. Aldrete Scores in post-anaesthesia care unit (PACU).

Table 2

Demographic and surgical characteristics of obese patientsundergoing gynaecological and urological surgery.

Characteristic IH (n520) Control (n520)

Age (years) 55.6 7.7 58.5 9.8Males/female 7/13 10/10BMI (kg/m2) 35.1 3.3 36.7 8.9Laparotomy/laparoscopy 6/14 5/17Length of surgery (min) 182.5 52.4 162.1 65.4Duration of anaesthesia (min) 210.7 52.8 192.9 64.0

IH, isocapnic hyperpnoea.


998

7/30/2019 65034942

5/8

blood-gas solubility (l).14 However, review of thedeterminants of fractional clearance of anaesthesia(F) [Equation (1)] indicates that in addition tocardiac output ( _Q), alveolar ventilation ( _VA) alsoaffects anaesthetic clearance:

F 100% 1

1 l _Q _VA1

In this study, we found that for isoflurane,increasing F alone via IH markedly shortened thetime to extubation (as a milestone recovery) inobese patients by two-thirds (5.4 vs. 15.8 min).Whereas the time to extubation in the controlcohort was similar to those previously reported inobese subjects anaesthetized with isoflurane (14,5

273 and 12.2min2), IH shortened the time to ex-tubation to that in obese patients anaesthetized

with desflurane (6.715

and 5.6min2

), as predictedpreviously.7 The time to extubation with IH in thisstudy was also similar to that in our previous studywhere IH was applied after isoflurane anaesthesiain non-obese patients (6.6 min8).

On arrival to the PACU, patients who had re-ceived IH had more stable airway control and weremore responsive as measured by the Aldrete scores,compared with patients in the control group. How-ever, contrary to our hypothesis, there was nodifference between the groups in any of the outcomemeasures. The anaesthesia duration in our study

was 23 h. Although after 2 h the obese group hadnot been saturated to any significant degree, we hadexpected that greater body clearance from VRG andMG as well as the FG acting as a depot for anaes-thetic would provide better intermediate recoverymeasures. That IH does not affect intermediaterecovery is consistent with the lack of clinicallyimportant differences in intermediate recoverymetrics when anaesthetics of different blood/gaspartition coefficients are studied. In morbidly obese

patients anaesthetized with sevoflurane and isoflur-ane, Sollazzi et al.5 found faster time to extubation,but no significant difference in recovery parametersafter the first 10 min. In morbidly obese patients,comparisons of recovery profiles from anaesthesia

sevoflurane vs. isoflurane,3

desflurane vs. isoflur-ane2 or sevoflurane vs. desflurane16 showed littledifference in intermediate recovery. In a previousstudy in our institution where IH was applied toenhance recovery in non-obese patients anaesthe-tized with isoflurane, we noted only small differ-ences between IH and control patients in theintermediate recovery period.8

Effect of obesity on the rate of recoveryMACawake is not affected by obesity.

17 Obesity may

prolong emergence from anaesthesia because of agreater volume of distribution of anaesthetic. Leanbody mass makes up 2040% of excess weight inobesity10 and would contribute to the musclegroup content of the anaesthetic. Similarly, thehighly perfused organs such as the heart, kidneys,intestines and liver are surrounded by increasedamount of pericardial, perinephric, mesentericand omental fat that exchange the anaestheticwith these organs by intertissue diffusion,10,14

increasing the anaesthetic content of the VRG.All three of the currently available inhalational

agents are highly fat soluble, isoflurane the mostso. The greater the fat solubility of the anaesthetic,the lower its partial pressure for a given massdissolved in the fat. During anaesthetics of 24 h,the partial pressure of anaesthetic in the bulk fatremains below MACawake, continuing the diffusionof anaesthetic from the blood to the fat, evenafter the patient wakes up.15,18 In obesity, the fatcompartment receives a lower percentage of thecardiac output (2% vs. 5% in lean),10 resulting in

Table 3

Intra-operative medications administered to obese patients undergoing gynaecological and urological surgery.

Medication IH (N520) Control (N520) P-value*

Propofol (mg) (median, min, max) 200.0 (150.0, 400.0) 250.0 (140.0, 400.0) 0.67Fentanyl (mg) (median, min, max) 250.0 (150.0, 500.0) 250.0 (125.0, 550.0) 0.89Rocuronium (mg) (median, min, max) 110.0 (50.0, 250.0) 95.0 (60.0, 280.0) 0.09Ketorolac (mg) (median, min, max) 0.0 (0.0, 30.0) 0.0 (0.0, 30.0) 0.94Morphine (mg) (median, min, max) 5.5 (2.0, 7.0) 4.5 (2.0, 6.0) 0.34

Granisetron (mg) (median, min, max) 1.0 (0, 1.0) 1.0 (0, 1.0) 0.97Isoflurane (MAC-h)w 3.2 0.9 2.9 1.1 0.09

*Because of the distributional properties of the data, MannWhitney U-test were used instead of t-test for these group comparisons.wMAC-h (MAC-hour) was calculated as average MAC length of exposure.IH, isocapnic hyperpnoea.


999

7/30/2019 65034942

6/8

a prolongation of the time constant of exchangeof the fat compartment with the blood. As a result,the functional fat mass10,19 is only a small proportionof the increased fat mass in obesity. Measuredwashout4,20 and recovery times for anaesthetics last-ing 24 h are about the same for obese and non obesepatients.19,21 The small effect of the total fat mass on

blood concentrations of anaesthetic leaves the maindeterminants for times for emergence such as thebody stores of anaesthetic in VRG and MG and thelung clearance, which is related to l and _VA.

Five patients in our study demonstrated signs ofre-hypnotization after extubation (two in the IHgroup and three in the C group). It is unlikely thatthe decrease in the level of consciousness was aresult of the redistribution of anaesthetic from thefat. First, as discussed above, during emergence,the fat partial pressure is well below MACawake.Second, the time constants for the equilibration of

inhalational agents with fat are very long (2110minwith isoflurane) compared with those in the lungand vessel-rich group (0.4 and 5.8 min, respec-tively),22 which reflect the times to extubation.Indeed, no differences have been found in thetime of emergence between obese and non-obesepatients with desflurane,19 sevoflurane,20 isoflur-ane,4 enflurane and halothane.23 When either sevo-flurane or desflurane is used, the wake-up timedoes not show any correlation when regressedagainst BMI for BMI between 35 and 47 kg/m2. Apossible contributing effect to the rebound ob-

served in both groups could be the cumulativeeffect of fentanyl and morphine, which can berelatively long acting in obese patients.24 At theend of the anaesthetic, the presence of a trachealtube often simulates coughing and respiration andmaintains arousal. However, after extubation, thewithdrawal of stimulation could lead to hypoven-tilation and a reduced lung clearance of residualanaesthetic from the blood and tissues, resulting inre-hypnotization.

IH

Hyperventilation is not commonly used to increaseF as it also results in hypocapnia and has anundesirable effect on cerebral blood flow anddelayed re-establishment of spontaneous ventila-tion. IH11,25 is a method developed to increase Fby increasing VA without affecting PaCO2. Themethod maintains PaCO2 constant by providing afixed gas flow while passively increasing the inspiredconcentration of CO2 proportionally to increases inminute ventilation.26,27

Study limitationsIn previous studies of the effect of IH on anaes-thetic recovery,7,8,11 the anaesthesia context wasstandardized by avoiding the variable effects ofdrug distribution caused by pre-recovery taperingof anaesthetic levels.28 In the current study, anaes-thetic depth was reduced 15 min before the end of

surgery to allow BIS values to increase from 4550to 5560 ranges, more in keeping with the commonpractice when using anaesthetics with a greaterblood/gas partition coefficient.

ConclusionThis study demonstrates that increased pulmonaryclearance of isoflurane at the termination of anaes-thesia shortens short-term recovery even in thepresence of obesity. It has no effect on readinessfor PACU discharge.

Acknowledgements

Funding: This study was funded by the Physicians ServicesIncorporated Foundation.Conflict of interest: R. Katznelson, J. Duffin, L. Fedorko and J.Fisher are in the team that developed ClearMateTM and areshareholders in Thornhill Research Inc. (TRI), a for-profitcompany incorporated according to the guidelines of theUniversity Health Networks (UHN) Technology Developmentand Commercialization Office.

References

1. Lee JJ, Larson RH, Buckley JJ, Roberts RB. Airway main-tenance in the morbidly obese. Anesth Rev 1980; 7: 336.

2. Juvin P, Vadam C, Malek L, Dupont H, Marmuse JP,Desmonts JM. Postoperative recovery after desflurane,propofol, or isoflurane anesthesia among morbidly obesepatients: a prospective, randomized study. Anesth Analg2000; 91: 7149.

3. Torri G, Casati A, Albertin A, Comotti L, Bignami E,Scarioni M, Paganelli M. Randomized comparison of iso-flurane and sevoflurane for laparoscopic gastric banding inmorbidly obese patients. J Clin Anesth 2001; 13: 56570.

4. Torri G, Casati A, Comotti L, Bignami E, Santorsola R,Scarioni M. Wash-in and wash-out curves of sevofluraneand isoflurane in morbidly obese patients. Minerva Anes-tesiol 2002; 68: 5237.

5. Sollazzi L, Perilli V, Modesti C, Annetta MG, Ranieri R,Tacchino RM, Proietti R. Volatile anesthesia in bariatricsurgery. Obes Surg 2001; 11: 6236.

6. Stoelting RK, Eger EI. II The effects of ventilation andanesthetic solubility on recovery from anesthesia. Anesthe-siology 1969; 30: 2906.

7. Katznelson R, Minkovich L, Friedman Z, Fedorko L, BeattieWS, Fisher JA. Accelerated recovery from sevofluraneanesthesia with isocapnic hyperpnoea. Anesth Analg2008; 106: 48691.

8. Van Katznelson R, Rensburg A, Friedman Z, Wasowicz M,Djaiani GN, Fedorko L, Minkovich L, Fisher JA. Isocapnic


1000

7/30/2019 65034942

7/8

hyperpnoea shortens postanesthetic care unit stay afterisoflurane anesthesia. Anesth Analg 2010; 111: 4038.

9. Bailey JM. Context-sensitive half-times and other decre-ment times of inhaled anesthetics. Anesth Analg 1997;85: 6816.

10. Lemmens HJ. Perioperative pharmacology in morbid obe-sity. Curr Opin Anaesthesiol 2010; 23: 48591.

11. Vesely A, Fisher JA, Sasano N, Preiss D, Somogyi R, ElBeheiry H, Prabhu A, Sasano H. Isocapnic hyperpnoea

accelerates recovery from isoflurane anaesthesia. Br JAnaesth 2003; 91: 78792.12. Sessler CN, Gosnell MS, Grap MJ, Brophy GM, ONeal PV,

Keane KA, Tesoro EP, Elswick RK. The Richmond Agita-tion-Sedation Scale: validity and reliability in adult inten-sive care unit patients. Am J Respir Crit Care Med 2002;166: 133844.

13. Aldrete JA, Kroulik D. A postanesthetic recovery score.Anesth Analg 1970; 49: 92434.

14. Eger EI, Shafer SL. Tutorial: context-sensitive decrement timesfor inhaled anesthetics. Anesth Analg 2005; 101: 68896.

15. Arain SR, Barth CD, Shankar H, Ebert TJ. Choice of volatileanesthetic for the morbidly obese patient: sevoflurane ordesflurane. J Clin Anesth 2005; 17: 4139.

16. De Baerdemaeker LE, Struys MM, Jacobs S, Den Blauwen

NM, Bossuyt GR, Pattyn P, Mortier EP. Optimization ofdesflurane administration in morbidly obese patients: acomparison with sevoflurane using an inhalation bolustechnique. Br J Anaesth 2003; 91: 63850.

17. Tabo E, Ohkuma Y, Sakuragi Y, Arai T. MAC-awake andwake-up time of isoflurane and sevoflurane with referenceto the concentration of gas, duration of inhalation andpatients age and obesity. Masui 1995; 44: 18892.

18. Eger EI, Shafer SL. The complexity of recovery fromanesthesia. J Clin Anesth 2005; 17: 41112.

19. Lemmens HJ, Saidman LJ, Eger EI, Laster MJ. Obesitymodestly affects inhaled anesthetic kinetics in humans.Anesth Analg 2008; 107: 186470.

20. Casati A, Bignami E, Spreafico E, Mamo D. Effects ofobesity on wash-in and wash-out kinetics of sevoflurane.

Eur J Anaesthesiol 2004; 21: 2435.

21. La Colla G, La Colla L, Turi S, Poli D, Albertin A, PasculliN, Bergonzi PC, Gonfalini M, Ruggieri F. Effect of morbidobesity on kinetic of desflurane: wash-in wash-out curvesand recovery times. Minerva Anestesiol 2007; 73: 2759.

22. Yasuda N, Targ AG, Eger EI. Solubility of I-653, sevoflur-ane, isoflurane, and halothane in human tissues. AnesthAnalg 1989; 69: 3703.

23. Cork RC, Vaughan RW, Bentley JB. General anesthesia formorbidly obese patients an examination of postoperative

outcomes. Anesthesiology 1981; 54: 3103.24. Cheymol G. Effects of obesity on pharmacokinetics implica-tions for drug therapy. Clin Pharmacokinet 2000; 39: 21531.

25. Sasano H, Vesely AE, Iscoe S, Tesler JC, Fisher JA. A simpleapparatus for accelerating recovery from inhaled volatileanesthetics. Anesth Analg 2001; 93: 118891.

26. Takeuchi A, Vesely A, Rucker J, Sommer LZ, Tesler J,Lavine E, Slutsky AS, Maleck WH, Volgyesi G, Fedorko L,Iscoe S, Fisher JA. A simple new method to accelerateclearance of carbon monoxide. Am J Respir Crit Care Med2000; 161: 18169.

27. Sommer LZ, Iscoe S, Robicsek A, Kruger J, Silverman J,Rucker J, Dickstein J, Volgyesi GA, Fisher JA. A simplebreathing circuit minimizing changes in alveolar ventila-tion during hyperpnoea. Eur Respir J 1998; 12: 698701.

28. Strum EM, Szenohradszki J, Kaufman WA, Anthone GJ,Manz IL, Lumb PD. Emergence and recovery characteris-tics of desflurane versus sevoflurane in morbidly obeseadult surgical patients: a prospective, randomized study.Anesth Analg 2004; 99: 184853.

Address:Rita KatznelsonDepartment of Anesthesia and Pain ManagementUniversity Health NetworkToronto General Hospital200 Elizabeth Street, EN3-453TorontoON, Canada M5G 2C4

e-mail: [email protected]


1001
mailto:[email protected]:[email protected]

7/30/2019 65034942

8/8

Copyright of Acta Anaesthesiologica Scandinavica is the property of Wiley-Blackwell and its content may not

be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written

permission. However, users may print, download, or email articles for individual use.

Documents

65034942