Haemodynamic and Bispectral index response to insertion of the Streamlined Liner of the Pharynx Airway (SLIPA[TM]): comparison with the laryngeal mask airway.
The newly developed supralaryngeal airway Streamlined Liner of the Pharynx Airway (SLIPA[TM]) has been compared successfully to the LMA[TM] but the haemodynamic response to its insertion has not been evaluated in a randomised study. We compared haemodynamic and Bispectral index (BIS) responses to insertion of the SLIPA[TM] with classic LMA[TM] after standardising the anaesthetic technique using BIS to monitor and control the anaesthetic depth. One hundred patients were randomised to receive either a classic LMA[TM] or SLIPA[TM] following induction with fentanyl and propofol titrated to a target BIS of 40 and compared heart rate, mean arterial pressure and BIS responses to insertion. There was a significant rise in mean arterial pressure from the pre-stimulus value (73.8 (10.6] mmHg, mean [+ or -] SD) at two and three minutes (P < 0.05) following insertion of the LMA[TM] with maximum rise (80.8 (11.5] mmHg) seen at two minutes There was a significant rise in mean arterial pressure from the pre-stimulus value (73.2 (12.6] mmHg) at one, two, three, four and five minutes (P < 0.05) following insertion of the SLIPA[TM] with maximum rise (86.9 (15.1] mmHg) observed at three minutes Mean arterial pressure was significantly higher (P < 0.05) with SLIPA[TM] at two, three, four and five minutes BIS increased significantly (P < 0.05) at one, two, three, four and five minutes following insertion of both the devices, but there was no significant difference between the groups There was a significantly higher (P= 0.001) incidence of blood on the device with the SLIPA[TM] (20/50 vs 6/50 with LMA[TM]). Thus, insertion of SLIPA[TM] causes significantly higher blood-pressure response but similar BIS response compared to the LMA[TM].
Key Words: SLIPA, LMA, haemodynamic responses
The Laryngeal Mask Airway-Classic[TM] (LMA-C[TM]) has been considered the 'gold standard' among the supralaryngeal airway devices. It is relatively expensive and requires maintenance procedures such as cleaning and autoclaving. Even then, there remains the risk of cross-infection and possible transmission of prion diseases (1,2). The Streamlined Liner of the Pharynx Airway (SLIPA[TM]) is a new, simple, inexpensive, single-use device made from soft blow-moulded plastic (ethylenevinyl-acetate copolymer) (3). It is a hollow, preformed, boot-shaped airway with "toe, bridge and heel" (Figure 1) and conforms to the hypopharynx without a cuff mechanism (Figure 2). It has been designed to decrease the risk of aspiration should limited volume regurgitation occur. The hollow chamber of SLIPA[TM] has been shown to hold up to 50 ml of regurgitated fluid, thus offering some protection against aspiration (4). Because of the preformed shape it has been found to be more stimulating, requiring greater depth of anaesthesia for insertion (4).
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Propofol has been shown to provide optimal conditions for insertion of the LMA[TM] (5-7) and adding fentanyl further improves the conditions (8). Absence of motor response to jaw thrust has been shown to indicate adequate depth of anaesthesia for insertion of LMA[TM] (9). Previous studies have shown that LMA[TM] can be successfully inserted when the Bispectral index (BIS) is between 40 and 60 (10, 11). Our own experience earlier in a sample study revealed that a target BIS of 50 led to unacceptably high incidence of patient movement in response to LMA[TM] insertion.
We planned to compare heart rate (HR), mean arterial pressure (MAP) and BIS responses following insertion of SLIPA[TM] and classic LMA[TM] with the BIS at value around 40. We also evaluated the success rate, ease of insertion, oropharyngeal leak pressure and incidence of complications with either airway.
After obtaining approval from the Institutional Ethics Committee and written informed consent, we studied 100 patients of either gender (aged 25 to 60 years, ASA I or II) undergoing elective minor radiotherapy, gynaecological and general surgical procedures of short to moderate duration in supine or lithotomy position. Patients were excluded if they suffered from diabetes mellitus, gastro-oesophageal reflux disease, severe systemic disease, morbid obesity or if they were pregnant or allergic to anaesthetic medications used. Age, gender, weight, height, Mallampati grade and thyroid cartilage width (measured using a scale) were recorded at the time of pre-anaesthetic evaluation. Following premedication with oral diazepam 0.15 mg/kg and ranitidine 150 mg the night before and on the morning of surgery, patients were randomised by tossing a coin (just before the patient was brought to the operating theatre) to receive either classic LMA[TM] or SLIPA[TM] as the airway device. LMA[TM] was sized according to standard practice. Sizing (4) of SLIPA[TM] was performed by matching the width of thyroid cartilage with that of bridge of the SLIPA[TM], by a single investigator in all the patients.
In the anaesthetic room, pulse oximeter (SP[O.sub.2]), electrocardiogram, noninvasive arterial pressure cuff (Datex Ohmeda monitor) and BIS monitor (BIS Xp, Aspect Medical Systems, Newton, MA, U.S.A.) were attached and an intravenous cannula was inserted. Data from the monitors were logged directly on to a computer and events were marked by a person not aware of the device being used. Following intravenous fentanyl 1.5 [micro]g/kg and preoxygenation for three minutes using a Bain circuit, anaesthesia was induced with propofol infusion titrated to achieve target BIS of 40. After the loss of eyelash reflex, nitrous oxide ([N.sub.2]O) was started ([N.sub.2]O:[O.sub.2]=70:30) and ventilation was assisted. Once the BIS [less than or equal to] 45 was achieved, the study device (lubricated with KY jelly) of predetermined size was inserted according to the manufacturer's instructions. After confirming absence of motor response to jaw thrust, an LMA[TM] was inserted using the standard technique (12) and jaw thrust by an assistant was used to facilitate insertion of the SLIPA[TM] in all patients. All device insertions were performed by a single investigator who is experienced in LMA[TM] use, but had not performed any insertion of the SLIPA[TM] prior to this study. The following events were marked: loss of consciousness, insertion of the device and recovery (obeying command). The following parameters were noted: ease of insertion (easy, moderate or difficult), time taken for insertion (from picking up the device to completed insertion), time taken for ventilation (from picking up the device to obtaining first successful breath), number of attempts (maximum of three), airway reaction to insertion (coughing, gagging, laryngospasm, bronchospasm), oropharyngeal leak pressure (measured by audible/palpable leak in the neck with peak inspiratory pressure using positive pressure), airway reaction on removing the device (coughing, gagging, laryngospasm, bronchospasm) and duration of anaesthesia (from beginning of propofol infusion to obeying commands).
If the first attempt was unsuccessful, mask ventilation was resumed before any subsequent attempt. After insertion of the device, patients were allowed to breathe spontaneously and propofol infusion was continued to maintain BIS [approximately equal to] 40. Intraoperatively, HR, MAP, BIS, Sp[O.sub.2] and end-tidal carbon dioxide (ETC[O.sub.2]) were monitored and recorded online. Heart rate, MAP and BIS just before insertion of the device were taken as prestimulus values and were compared with values at one, two, three, four and five minutes after the insertion.
At the end of the procedure, propofol infusion was stopped, [N.sub.2]O was discontinued and the airway device was removed when BIS reached 60 to avoid adverse airway response to removal as SLIP[TM] is known to be more stimulating (4) and BIS 60 is still considered as deep plane of anaesthesia. The airway was subsequently managed with a facemask until the patient regained consciousness. Airway injury, if any, was noted and the device was examined for visible blood, regurgitated material and any damage. After the patients started obeying commands, they were shifted to recovery area and queried for sore throat (quantified on a 101 point Numerical Rating Score [NRS]), dysphagia and hoarseness by indirect questioning, and again after two hours.
Parametric data were analysed using the independent t-test and count data were compared using the Chi-square test. Heart rate, MAP and BIS response to insertion of the device were analysed using analysis of variance (ANOVA) and group comparison was done using the independent t-test. A P value <0.05 was considered significant. Results are expressed as mean [+ or -] SD or percentage (%). Haemodynamic and BIS data from the 'failed case' were excluded from the analysis. Sample size was chosen on the basis of similar studies done earlier (4,11), using [alpha]=0.05 and [beta]=0.2.
The two groups were comparable with respect to age, gender, weight, height, body surface area, body mass index, Mallampati score or duration of anaesthesia (Table 1). The large number of female patients in the study represents patients undergoing radiological procedures for carcinoma of the cervix. The overall success rate of insertion, time taken for insertion and the number of attempts were comparable between the two devices (Table 2). Though the time taken for ventilation was higher in the LMA[TM] group (23.9  seconds, mean [SD]) than the SLIP[TM] group (20.3 [10.3] seconds), the difference was statistically not significant (P=0.059). Though there was a higher success rate in the first attempt with SLIP[TM] (91.8%) than LMA[TM] (81.6%), the difference was statistically not significant. The ease of insertion was rated as easy in 42%, moderate in 56% and difficult in 2% of the patients in the SLIP[TM] group as compared to 76%, 22% and 2% respectively in the LMA[TM] group and the difference between the two groups was significant (P=0.002). There was one "failed case" in each group. "Failed LMA" was due to inadequate seal (leak occurred at 5 cm[H.sub.2]O) and "Failed SLIPA" due to airway obstruction; both cases were managed subsequently with a facemask. None of the patients had Sp[O.sub.2] <92% or ETC[O.sub.2] >50 mmHg. There was no clinically significant hypotension or hypertension in either group. One patient coughed and one had gag response to insertion of SLIP[TM]. One patient in each group coughed on removal of the respective airway. On removal of the device, blood was noticed in significantly higher (P=0.001) number of cases in the SLIP[TM] group (20/50) as compared to the LMA[TM] group (6/50). The incidence of "blood on device" in the SLIP[TM] group decreased with the number of insertions performed (48% in the initial 25 insertions as compared to 32% in the subsequent insertions). Only one patient in the SLIP[TM] group complained of sore throat (NRS 30) postoperatively. One patient in the LMA[TM] group complained of dysphagia and hoarseness of voice which subsided on the following day without any treatment. There was neither any case of clinically detectable regurgitation or aspiration nor any trauma to the airway. LMA[TM] size 3 and 4 and SLIPA[TM] sizes 47 to 53 were used. Most common sizes of SLIPA[TM] used were size 47 and 49 as the majority of patients were females of small to moderate build. Selection of SLIPA[TM] was felt to be appropriate in all the cases. Bite-block was not used in any patient in the SLIPA[TM] group (bite-block used with LMA[TM]). Performances of the devices are shown in Table 2.
Time taken for insertion of SLIPA[TM] showed a short learning curve of about 13 cases (Figure 3), with longer duration of insertion attempts in the initial cases. There was increased resistance felt during insertion when the bridge of the SLIPA[TM] was crossing the base of the tongue in majority of cases. In two edentulous patients, insertion of the SLIPA[TM] was very "smooth".
Baseline values of HR, MAP and BIS were comparable between the two groups (Table 3). Following insertion of LMA[TM], there was a significant rise in MAP from the pre-stimulus value (73.8 [10.6] mmHg) at two and three minutes (P <0.05) and the maximum rise (80.8 [11.5] mmHg) was observed at two minutes. There was a significant rise in MAP from the pre-stimulus value (73.2 [12.6] mmHg) at one, two, three, four and five minutes (P <0.05) following insertion of SLIPA[TM] and the maximum rise (86.9 [15.1] mmHg) was observed at three minutes. MAP rise was significantly higher (P <0.05) with SLIPA[TM] at two, three, four and five minutes compared to that with LMA[TM]. BIS rose significantly (P <0.05) at one, two, three, four and five minutes following insertion of the device in both the groups but the difference between the two groups was not significant. Peak BIS occurred at four minutes in the SLIPA[TM] group and at three minutes in the LMA[TM] group. Though HR did not change significantly in either of the groups following insertion of airway device, HR at five minutes was significantly higher (P=0.035) in the SLIPA[TM] group (82.8 [14.5] vs. 77.4 [10.6] bpm). Haemodynamic and BIS response to insertion are shown in Table 3. A subgroup analysis done to compare the rise in MAP in ASA I and II (hypertension) patients revealed no difference in these patients.
[FIGURE 3 OMITTED]
The rate of successful insertion of SLIPA[TM] on first attempt was 91.84% which is consistent with the previous reports, in which success rate was 85 to 98% (4,13,14). The slightly higher time taken for ventilation in the LMA[TM] group may be due to the additional time required to inflate the cuff. Time to ventilate in the SLIPA[TM] group in this study is consistent with a previous study (14) which has shown the median time to ventilate (with SLIPA[TM]) to be 20.4 seconds (range 12.6 to 109) and 24.8 seconds (range 8.2 to 82.5), in which insertion was performed by different persons. The lower rate of 'easy' insertion compared to an earlier study (14) may be due to the subjective nature of assessment done in this study and the difference in the prior experience of the investigator with the two devices. There was a short learning curve of about 13 cases for insertion of SLIPA[TM] (Figure 3). The investigator did not have any prior experience in inserting SLIPA[TM]. SLIPA[TM] provided adequate seal for positive pressure ventilation as evident by the oropharyngeal leak pressure of 23.4 (6) cm[H.sub.2]O which is similar to but slightly less than the values in previous studies (25 to 30 cm[H.sub.2]O) (4,13).
In a pilot study, we found that keeping a target of BIS 50 leads to higher incidence of patient movement during insertion of the device. Therefore, we had kept the target to BIS [approximately equal to] 40 at the time of insertion. Only one patient coughed and one patient gagged in response to insertion of SLIPA[TM], suggesting that the incidence of adverse airway reaction during insertion is low and confirms its clinical safety.
Higher peak MAP was seen in SLIPA[TM] group with comparable pre-stimulus values. The maximum rise of BIS was 10 [+ or -] 7 in the LMA[TM] group and 11.3 [+ or -] 9 in the SLIPA[TM] group. A previous study (11) has shown that BIS rises following insertion of the LMA[TM] and the maximum rise was 12 [+ or -] 11. The pre-stimulus BIS was higher (48 [+ or -] 7) compared to our study (43.1 [+ or -] 3.4) and the authors had studied these changes only until two minutes following insertion. These results show that SLIPA[TM] causes more blood pressure response following insertion than the LMA[TM] which is probably because of its preformed shape. These changes may not be clinically important.
Incidence of blood on the device was significantly higher with SLIPA[TM] (40%) compared with LMA[TM] (12%), suggesting that insertion of the former causes more trauma. Though there was no detectable trauma to the clinically visible part of the upper airway, the stiff part of the SLIPA[TM] ('toe') might have caused mucosal injury to the deeper pharyngeal structures. Previous report has shown the incidence of "blood on device" to be 23% (14). As the investigator gained experience in inserting the SLIPA[TM], the incidence of "blood on device" decreased. This indicates that early learners with these airway devices tend to cause some degree of trauma. At the same time, lack of serious upper airway injury in any patient is probably reassuring. Considering the very little clinical experience with SLIPA[TM] in the present anaesthetic practice, this complication rate can be expected to decrease once users gain sufficient experience with this new device.
Early "sore throat", assessed on arrival of the patient to the recovery room and two hours after, had only one patient in the SLIPA[TM] group complaining of sore throat (rated 30 on NRS scale of 101). This can be explained by the indirect questioning, since it is well recognised that the method of questioning is an important determinant of the incidence of sore throat (15). One patient in the LMA[TM] group complained of dysphagia and hoarseness postoperatively which may be due to rise in intra-cuff pressure, as [N.sub.2]O was used, duration of anaesthesia was 106 minutes and cuff pressure was not measured.
As bite-blocks were not used in any patient in the SLIPA[TM] group (bite-block used with LMA[TM]), it decreased the care required to maintain SLIPA[TM] in position, providing 'hands free' comfort. There was increased resistance felt during insertion when the bridge of the SLIPA[TM] was crossing the base of the tongue in the majority of cases as the prominent anterior surface of the device was coming in contact with the molars. It is felt that attempts could be made to reduce the height of the bridge so that insertion becomes much easier, at the same time taking care that the pharyngeal seal quality is not affected. This is prompted by the very "smooth" insertion in two edentulous patients. It is also felt that if the 'heel' is made more smoothly-curved, this will facilitate its insertion, avoiding injury to the soft palate and uvula, and probably decreasing the incidence of "blood on device". Since there was no case of regurgitation or aspiration in this study, and a laboratory model (3) has shown that SLIPA[TM] provides some degree of protection against aspiration, its role as an airway management device in emergency situations needs to be studied.
Finally, though we have not made any direct cost comparisons (not the aim of the study), a single use LMA[TM] and SLIPA[TM] cost about 80 [pounds sterling] and 2.80 [pounds sterling] in Europe, respectively. Reusable (up to 40 times) LMA[TM] is costlier and needs repeated autoclaving and other maintenance procedures which add to the overall cost associated with its usage.
A number of limitations exist regarding our study. First, the investigator who performed all airway insertions was experienced in LMA[TM] use, though had not performed any insertion of SLIPA[TM] prior to this study. This might have altered the outcome of the study, especially the incidence of "blood on device". Second, we acknowledge that the potential for bias exists, because it is impossible to blind the anaesthesiologist to the device being used. Third, our study does not have adequate power to detect the difference in complication rates like sore throat, dysphagia and hoarseness.
In conclusion, SLIPA[TM] causes significantly higher blood pressure response and more trauma to the airway mucosa following insertion though similar BIS response as compared to LMA[TM].
Our sincere thanks to Dr Donald M. Miller, Consultant Anaesthetist, Department of Anaesthetics, Guy's Hospital, London, (inventor of SLIPA[TM], has financial interest with the manufacturer) for providing free samples of SLIPA[TM] for the study from the manufacturer (Hudson RCI AB, Upplands Vasby, Sweden). None of the authors have received any financial support either from the inventor or from the manufacturer.
Accepted for publication on February 24, 2008.
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(10.) Versichelen L, Struys M, Krombez E, Fonck K, Mortier E, Rolly G. Haemodynamic and electroencephalographic response to insertion of a cuffed oropharyngeal airway: comparison with the laryngeal mask airway. Br J Anaesth 1998; 81:393-397.
(11.) Brain AU. The Intavent Laryngeal Mask. Instruction Manual, 2nd ed. s1993.
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G. D. PURI *, H. V. HEGDE ([dagger]), A. JAYANT ([double dagger]), I. BHUKAL ([section])
Department of Anaesthesia and Intensive Care Postgraduate Institute of Medical Education and Research, Chandigarh, India.
* M.D., Professor.
([dagger]) M.D., Junior Resident.
([double dagger]) M. D., Senior Resident.
([section]) M.D., Associate Professor.
Address for reprints: Dr. G. D. Puri, Professor, Department of Anaesthesia and Intensive Care, Postgraduate Institute of Medical Education and Research (PGIMER), Sector 12, Chandigarh 160012, India.
TABLE 1 Patient characteristics and anaesthesia times (no difference between the two groups) LMA[TM] (n=50) SLIPA[TM] (n=50) Age (years) * 47.70 (8.8) 46.6 (9.3) Gender (M/F) ** 3/47 4/46 ASA 1/11 ** 45/5 43/7 Height (cm) * 158.70 (4.9) 160.2 (5.9) Weight (kg) * 50.60 (11.3) 53.2 (10) BSA ([m.sup.2]) * 1.50 (0.15) 1.54 (0.14) BMI (kg/m2) * 20.37 (4.5) 20.73 (.9) MMP ** 1 16 17 2 24 22 3 10 11 Duration of anaesthesia 27 (13.5) 31 (28) (min) * Values are mean (SD) or number. BSA=body surface area, BMI=body mass index, MMP=Mallampati grade. * independent t-test. ** Chi-square test. TABLE 2 Performance of devices LMA- SLIPA- Pvalue Time taken for insertion 11.2(4.2) 10.5(6.7) 0.492 (sec) Time taken for ventilation 23.9(8) 20.3(10.3) 0.059 (sec) No of attempts (%) 1 40(81.6) 45(91.8) 2 8(16.3) 2(4.1) 3 1(2) 2(4.1) 0.121 Ease of insertion (%) Easy 38(76) 21(42) Moderate 11(22) 28(56) Difficult 1(2) 1(2) 0.002 Overall success rate (%) 49(98) 49(98) Failed case 1 1 OPLP (cm[H.sub.2]O 23.83(7.1) 23.4(6.0) 0.760 Airway reaction to insertion Coughing 0 1 Gagging 0 1 Removal reaction 1 (coughing) 1 (coughing) Blood on device (%) 6(12) 20(40) 0.001 Sore throat Arrival to recovery 0 1 At two hours 0 1 Dysphagia 1 0 Hoarseness 1 0 Values are mean (SD) or number (proportion). OPLP=oropharyngeal leak pressure. TABLE 3 Haemodynamic and BIS response to insertion (mean + or -] SD) Baseline Pre-stimulus 1 L MA [TM] HR (bpm) 95.5 (20.3) 80.4 (14.4) 82.5 (12.8) MAP (mm g) 102.1 (13.9) 73.8 (10.6) 79.9 (12.3) BIS 95.4 (3.6) 43.1 (3.4) 48.9 (6.9) * SL IPA [TM] HR (bpm) 97.2 (22.1) 82.7 (15.3) 84.9 (15.9) MAP (mm g) 97.5 (15.6) 73.2 (12.6) 84.2 (14.3) * BIS 95.4 (3.1) 42.9 (3.6) 49.9 (8.5) * 2 3 L MA [TM] HR (bpm) 80.8 (13.2) 80.3 (11.4) MAP (mm g) 80.8 (11.5) * 80.4 (10.1) * BIS 51.3 (6.7) * 53.1 (7) * SL IPA [TM] HR (bpm) 84.5 (16.3) 83.6 (16.8) MAP (mm g) 86.6 (17.3) * ([section]) 86.9 (15.1) * ([section]) BIS 52.8 (8.8) * 53.7 (9.4) * 4 5 L MA [TM] 78.8 (11.3) 77.4 (10.6) HR (bpm) 80.0 (10.4) 78.5 (10.5) MAP (mm g) 52.7 (7.2) * 52.7 (8.2) * BIS SL IPA [TM] 84.1 (15.9) 82.8 (14.5) ([section]) HR (bpm) 85.1 (15.6) * ([section]) 84.2 (14.9) * ([section]) MAP (mm g) 54.2 (9.0) * 53.85 (8.9) * BIS * Pre-stimulus-just before insertion; one, two, three, four and five=one, two, three, four and five minutes after insertion, respectively. HR=heart rate, MAP=mean arterial pressure, BIS=bispectral index. * Significant difference compared with pre-stimulus value (P <0.05) (ANOVA). ([section]) Significant difference compared with LMA group (P <0.05) (independent t-test).
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|Author:||Puri, G.D.; Hegde, H.V.; Jayant, A.; Bhukal, I.|
|Publication:||Anaesthesia and Intensive Care|
|Date:||May 1, 2008|
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