Research Article
Using Entropy in the General Anesthesia Managements
Elif Büyükerkmen, Remziye Gül Sivaci and Elif Doğan Baki*
Departement of Anesthesiology and Reanimation, Afyon Kocatepe University, Afyonkarahisar, Turkey
*Corresponding author: Elif Doğan Baki, Departement of Anesthesiology and Reanimation, Afyon Kocatepe University, Campus of Ali Çetinkaya, Afyon-İzmir Karayolu, 8 km, Afyonkarahisar, 03200, Turkey
Published: 07 Jul 2017
Cite this article as: Büyükerkmen E, Sivaci RG, Baki
ED. Using Entropy in the General
Anesthesia Managements. Clin Surg.
2017; 2: 1549.
Abstract
Purpose: We aimed to investigate the effects of three general anesthesic management on depth of
anesthesia, anesthesic quality, agent consumption and postoperative recovery.
Materials and Methods: 90 patients scheduled for elective tympanoplasty and septoplasty surgery
with American Society of Anesthesiologist (ASA) pysical status between I-III were included
in this study. Neuromuscular transmission (NMT), surgical pleth index (SPI) and entropy were
monitorized in addition to standart monitoring. Entropy was recorded as state entropy (SE) and
response entropy (RE). After standart anesthesia induction, patients were divided into three groups
according to maintenance of anesthesia using a sealed envelope system. Propofol 3-5 mg/kg/h
iv infusion was performed to Group 1 (Group P, n=30), Desflurane 1MAC was used to Group 2
(Group D, n=30) and Sevoflurane to Group 3 (Group S, n=30). Also, rocuronium and remifentanyl
infusion were used in maintenance. While desflurane and sevoflurane consumption were recorded
from the anesthesia directly, propofol consumption was calculated through the consumption of
perfusors and recorded at the end of the surgery. Total cost of anesthetics that used were calculated
by multiplying the unit price with their consumption. Apart from these, hemodynamic values of
all patients, recovery time, alertness levels in the recovery room (according to Ramsey Scale) were
recorded.
Results: Significant differences were found between the three groups in terms of cost. While the cost
of propofol was significantly lower, it was significantly higher in desfluane group. Also awareness
and postoperative hemodynamics were observed to be more stable in propofol and sevoflurane
group patients.
Conclusıon: We concluded that propofol anesthesia decreased the cost significantly.
Keywords: Propofol; Desflurane; Sevoflurane; Entropy; Cost; Recovery
Introduction
The evaluation of anesthetic depth during general anesthesia is an ongoing problem and quite a
complex issue [1,2]. Conventionally, anesthetic depth is evaluated according to clinical symptoms
such as eyelash and corneal reflexes, pupil size and reaction to light, blood pressure, pulse rate, and
respiratory depth and rythym [3]. However, all these clinical findings may not always suffice in
showing the anesthetic depth. Awareness of the under- or over-dosage of anesthetics used, as well as
the related economic loss, have led to the increased use of different new techniques and devices for
determining the anesthetic depth [4].
One of the monitorization techniques used for assessing the degree of anesthetic hypnosis
is entropy monitoring [5,6]. Entropy relies on a method of assessing the degree of irregularity,
complexity and uncertainty in electroencephalogram (EEG) signals [7]. The principle is based on
calculation of the spectral entropy of raw EEG and frontal electromyelographic (EMG) data [8].
Entropy monitors produce two numbers (RE: Response Entropy and SE: State Entropy), which are
related to the frequency bandpass used [9]. Entropy is the measurement of EEG signal irregularity.
The irregularity within an EEG signal decreases with increasing brain levels of anaesthetic drugs.
If we relate the irregularity to the entropy within the signal, then an entropy scale can be assigned
[10]. There are only a few studies in the literature on the effect of entropy monitoring on anesthetic
depth, consumption of anesthetic agent, and postoperative recovery. The purpose of this study was
to assess the effects of three general anesthesia methods on anesthetic depth and quality, anesthetic
agent consumption, and postoperative recovery, using the entropy monitoring.
Material and Methods
This study was carried out in the operation rooms of the Medical Faculty Hospital of Afyon Kocatepe University after acquiring the approval of the Faculty
Ethics Committee (approval date, 15 August 2013; approval number,
2013/10-60) and informed written consent of the patients included in
the study. A total of 90 adult patients with an age range between 18
and 70 were included in the study. Elective surgery had been planned
for the patients who were in the I-III risk group of ASA (American
Society of Anesthesiologists), and the patients had undergone
tympanoplasty and septoplasty surgery lasting between 60 and 240
min.
The criteria for exclusion from the study were the following:
ASA IV risk group, postoperative intensive care, need for ventilation,
pregnancy, age of under 18, inappropriate psychiatric state for giving
consent, and refusal of consent.
After anesthesizing the patients with the standard anesthetic
technique, the patients were divided into three groups according to
anesthetic maintenance. The groups were randomly determined using
the sealed envelope method. Group 1 (Group P) received propofol
3-5 mg/kg/h i.v. infusion; Group 2 (Group D) received Desflurane
1MAC, and Group 3 (Group S) received Sevoflurane 1 MAC.
Protocol of study
1. For hemodynamic follow-up; electrocardiography (EKG),
non-invasive systolic arterial pressure (SAP), diastolic arterial
pressure (DAP), mean arterial pressure (MAP), and peripheral
oxygen saturation (SpO2) were monitorized.
2. The anesthetic depth was monitorized with entropy
(Carescape Monitor B650 GE Healthcare, Finland). For this purpose,
SE and RE values measured via a forehead-mounted sensor were
noted. After cleansing the skin with alcohol, the entropy sensor was
placed on the fronto-temporal region and pressed for 5 seconds to
provide skin-sensor contact. Since RE is affected by response of facial
muscles, whereas SE reflects the effect of the hypnotic agent on the
brain, the SE values were noted as essential values.
3. Neuromuscular monitorization (NMT) was performed by
exciting the ulnar nerve at about 2 cm proximal to the volar wrist
joint and observing the response of the m. adductor pollicis.
Vascular access was established with a 20 gauge-intraket, and
after calculating the hourly fluid requirement, crystalloid solution
infusion was started.
For induction; midozolam 0.01 mg/kg, fentanyl 2 mcg/kg,
lidocaine 1 mg/kg, propofol 2 mcg/kg, and rocuronium 0.6 mg/kg
were used. The patients were pre-oxygenated with a face mask using
O2 100% 4 L/min. Following a 2-min controlled mask ventilation,
the patients were intubated with an orotracheal intubation tube
appropriate for age and weight. For anesthetic maintenance; 2 lt/min
fresh gas flow with O2/air 50/50%, the vaporizer was set at 2% for
Group S, at 6% for Group D, and at propofol 5 mcg/kg/h infusion
for Group P. Remifentanyl 0.1 mcg/kg/min infusion was started
after induction, and, as myorelaxant, rocuronium 0.1 mg/kg/h was
administered to all three groups. During surgery, the quantities of
desflurane, sevoflurane, and propofol were decreased or increased so
as to maintain RE and SE values between 40 and 60. Ventilation with
tidal volume 8-10 ml/kg and frequency of 12/min was started. The
end-tidal CO2 levels in all patients were continuously monitorized
during surgery and kept between 35 and 40 mmHg.
The following values of the patients at pre-induction (T1), postintubation
(T2), and at hours 1st (T3), 2nd (T4), pre-extubation (T5),
and post-extubation (T6) were noted: Systolic pressure, diastolic
pressure, mean arterial pressure, pulse rate, saturations, SPI value,
NMT value, and RE and SE values. At the end, desflurane and
sevoflurane consumptions were directly calculated over the used
anesthesia device (Datex-Ohmeda Avance Config, 3030 Ohmeda
Drive USA) and the propofol consumption was calculated over
the perfusor. Subsequently, the total cost of anesthetic agents was
calculated by multiplying the unit price of each agent with the quantity
used. Furthermore, the total anesthesia and surgery durations and the
Ramsey scores at post-extubation minute 1 and post-op min 30 of all
patients were noted.
Statistical analyses
For the statistical evaluation of the obtained data, the SPSS 20.0
Program (Statistical Package for the Social Sciences Inc, Chicago, IL,
USA) was used. The Kolmogorov-Simirnov test was performed for
the control of normal distribution of the data. The frequency analysis
was performed to assess the gender distribution in the groups. The continuous variables according to their normal distribution were
expressed as mean ± standard deviation or as median (minimummaximum).
The difference analysis of the categorical variables
between groups was performed using the chi-square test. The
difference analysis of continuous variables according to the normal
distribution between the groups was performed using the One-Way
ANOVA or the Kruskal-Wallis test. The Post-Hoc Tukey test was
performed to determine the group with variables causing a significant
difference.
The Spearman’s or the Pearson’s correlation analyses were
performed in terms of distribution of the total cost, the quantity of
consumed anesthetic agent, BMI, and RE and SE entropies within
each group. A p value of < 0.05 was accepted as statistically significant.
Table 1
Table 2
Table 3
Table 4
Results
A total of 90 adult patients who had undergone tympanoplasty and septoplasty surgery lasting between 60 and 240 minutes completed the study. There was no significant difference between the groups in terms of gender, age, weight, BMI, duration of anesthesia, and duration of surgery (p>0.05) (Table 1). Pre-extubation SPI values of Group P were significantly lower than Group D (p< 0.05) (Table 2). There was no significant difference in neuromuscular transmission (NMT) values between the three groups (p>0.05) (Table 3). The Ramsey scores of the study groups at post-extubation at minute 1st and 30th minute in the recovery room were seen in Table 4, no significance was seen between them. There was a significant and positive correlation between the duration of anesthesia and total consumption of the anesthetic agents in all groups (p< 0.05). And there was a significant and positive correlation between the body mass index (BMI) and the cost (r=0.256, p=0.015). There was a positive and significant correlation between the duration of anesthesia and cost, too (r=0.962, p< 0.05). The cost of the propofol group was significantly lower than the other groups (p< 0.05). MAP measured before and just after extubation were significantly lower in Group P than the others (p< 0.05) (Table 5).
Discussion
Measurement of anesthetic depth is a critical issue in routine
anesthesia pratice. EEG is used for measurement of the anesthetic
depth, that is, to follow the electrical activity of brain; however,
application and interpretation of EEG during anesthesia is quite
difficult. Newly developed monitorization techniques like EEG,
BIS, and entropy have been introduced into routine use. Entropy is
a monitorization technique used to follow-up the anesthetic depth,
which presents EEG measurements in a simple, easy, non-invasive
and numerical manner. Entropy allows the easy follow-up of
anesthetic maintenance of the patient by momentary measurements.
Hence, a correlation between entropy and anesthetic agents can be
made. Using entropy monitoring, we assessed the effects of three
general anesthesia methods on the anesthetic depth and quality,
consumption of anesthetic agent, and post-operative recovery. In
our study were the following the most important findings: 1) The
cost of propofol was significantly lower than the cost of inhalation
anesthetics, 2) propofol and sevoflurane provided a better postoperative
hemodynamic stability and awareness than dessflurane.
Rapidly increasing health expenditures and high costs of modern
inhalation anesthetics have reviewed cost control in anesthesia [10].
Several studies on the cost comparison of inhalation anesthetics and
propofol, some have reported TIVA (total intravenous anesthesia)
to be more expensive and some have reported no cost difference in
between. It has been reported that depending on the used volatile
agent and fresh gas flow, TIVA is about 2 to 6 times more expensive
than inhalation anesthesia and therefore, should be used only for
short surgical interventions [11]. It has been determined that the cost
of the new anesthetic desflurane or sevoflurane combined with fresh
gas flow 2 L/min is similar to that of sufentanyl infusion, thus TIVA
is more expensive [12,13]. In their study on application of O2 100%
with desflurane or propofol infusion 100-200 μg/kg/min, Rosenberg
et al. [14] have found that TIVA with propofol is more expensive
than anesthesia with desflurane. Another study [15] compared TIVA using propofol and remifentanyl with that using desflurane and
fentanyl plus high fresh gas flow in long surgical interventions and
reported that in the desflurane-fentanyl group, the recovery time was
shorter and the anesthesia cost wass lower, and that in both groups,
the return of cognitive functions and the duration of stay in postsurgery
unit were similar time-wise. Consistent with the findings
of our study, in septorhinoplasty cases, no significant difference in
terms of cost and recovery profiles was determined between TIVA
using propofol and remifentanyl and anesthesia with desflurane and
remifentanyl infusion applied with high rate of fresh gas flow [16].
In the study [17] they compared the cost of remifentanyl combined
with propofol with the cost of sevoflurane and desflurane applied
with fresh gas flow 6 L/min used in total abdominal hysterectomy
operations and found no significant difference in between. When we
compare our study with the above-mentioned two studies, we think
that the lower consumption of propofol could be due to the use of
entropy monitoring in our study.
When we evaluated the hemodynamic data, we determined that
hemodynamically, propofol anesthesia is a safe and stable method.
We observed no increase in the mean values of arterial blood
pressure when compared with the control values. Smith et al. [18]
have reported that the post-induction mean arterial pressure was
lower in patients under propofol anesthesia than in those under
sevoflurane anesthesia. Özköze et al. [19] have determined that the
post-induction mean arterial pressure was significantly lower in the
propofol group than in the sevoflurane and isoflourane groups. In our
study, there was an elevation in the pre- and post-extubation MBP
values in all three groups; however, this elevation was significantly
lower in the propofol group (MBP 5; p< 0.038, MBP 6; p< 0.007).
There was no difference between the three groups in terms of preintubation,
post-intubation, and intra-operative pulse values; the
pulse values were found to be higher than the pre-extubation basal
values, however, but this increase showed no difference between the
propofol and desflurane groups, whereas it was significantly high in
the sevoflurane group (p< 0.029).
Various tests have been used to assess the patients’ hypnotic
status and cognitive functions during the recovery period [20]. In our
study, in order to determine the level of consciousness, we used the
Ramsey scale at post-extubation minutes 1 and 30. The Ramsey score
at minute 1 was 2 in 60% of the patients in Group S, in 50% in Group
D, and in 23% in Group P. The Ramsey score(s) at minute 30 were 2
in all patients in Groups P and S; and in Group D, 2 in 26 patients and
3 in 4 patients. This meant that in the postoperative period, patients
in Groups S and D were more conscious, and patients in Group P
were more sedatized and tranquil. However, there was no significant
difference in the level of consciousness at minute 30 between all
patients of the three groups.
The surgical pleth index (SPI) has been developed to numerically
express the nociceptive physiological responses during general
anesthesia. The index has a scoring system between 0 and 100. High
scores are associated with high stress. The optimal score has not been
determined yet, however, when balanced with nociceptive and antinosciceptive
factors, 50 is considered as the average stress score [21].
In our study, when compared with the basal values, the extubation SPI
values decreased in all three groups. Intraoperatively, the propofol
group had a more stable course, but this was statistically insiginificant.
However, while the pre-extubation SPI values increased in all groups,
this increase was significantly lower in the propofol group (p<0.009).
There was no significant difference between the three groups in terms
of pre-extubation and post-extubation NMT values.
Entropy monitoring is based on the irregularity of EEG waves
caused by different frequencies [22]. When the patient loses
conciousness, EEG waves tend to be more regular and provide
continuous data on the hypnosis level during anesthesia [23]. The
EMG of facial muscles coincides with classical EEG frequencies. This
coincidence causes problems in the analysis of the cortical activity.
The EMG waves of facial muscles change with the consciuosness level
of the patient and use of myorelaxant agent. In the entropy module
first developed by Datex-Ohmeda, EEG waves are evaluated by SE
and EMG waves are evaluated by RE. Both SE and RE values increase
as the patient is relieved of the effect of myorelaxant and starts to gain
consciousness. Balcı et al. [24] have reported that entropy monitoring
can be safely used to follow-up the hypnosis level during anesthesia
and the recovery period. In our study, we also used the SE and RE
levels to determine the anesthetic level in all of our patients. There
was no significant difference between the three study groups in terms
of SE and RE values.
Table 5
Conclusion
With anesthetic depth kept fixed by entropy in all groups, there
was a significant difference in anesthesia cost between the groups. We
think that entropy and SPI are good alternatives to BIS in measuring
the anesthetic depth.
1. The cost of propofol anesthesia was clearly low, whereas the
cost of desflurane anesthesia was significantly high.
2. The patients in the propofol group were more stable in
terms of hemodynamics and post-operative conciousness level.
For more reliable and significant results, studies on larger patient
populations are required.
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