Capture efficiency of CONTRAfluran absorbers for sevoflurane in a real-world scenario
Sebastian Gibb1,✉, Nadin Möller1, Falk von Dincklage1, and Stephan Knigge1
Please find details at https://github.com/umg-minai/vct-or.
Manuscript date: 2024-05-24 11:51; Version: 2ac7614
1 Department of Anesthesiology and Intensive Care Medicine, University Hospital Greifswald, Ferdinand-Sauerbruch-Straße, D-17475 Greifswald, Germany.
✉ Correspondence: Sebastian Gibb <mail@sebastiangibb.de>
1 Summary
Background: Volatile anaesthetics are potent greenhouse gases, but can be captured using active charcoal absorbers on the exhaust port of anaesthesia machines to reduce their negative climate impact. Previous studies investigating the capture efficiency of absorbers have been performed mostly under circumstances that differ from everyday clinical routine. Therefore, we here investigated the capture efficiency of the CONTRAfluranTM absorbers for sevoflurane in a ‘real-world’ scenario.
Methods: In this prospective single-centre study, we collected 20 consecutive CONTRAfluranTM absorbers from two different operating rooms (ORs) after they were saturated to their maximum saturation levels. After storage and transport, the sevoflurane was recaptured from the absorbers by the absorber manufacturer ZeoSys. To calculate the capture efficiency, we divided the amount of recaptured sevoflurane by the total sevoflurane consumption during the use of the absorbers, which was obtained by comparing the weight of the sevoflurane bottles before versus after refilling the vaporizers.
Results: We observed 738 balanced anaesthesia cases. A total of 14.2 kg sevoflurane was used and NA kg could be recovered, yielding a capture efficiency of NA %. The capture efficiencies differed significantly between the ORs, with NA % in the OR with shorter anaesthesia durations and frequently inhaled induction versus NA % in the OR with longer anaesthesia duration. We saw a weight loss over time of around 69 mg per day per absorber during storage.
Conclusions: If CONTRAfluranTM absorbers are used until they are fully saturated, almost half of the sevoflurane can be recaptured, but the capture efficiency depends on the fresh gas flow used and duration of anaesthesia.
Keywords: balanced anaesthesia, sevoflurane, vapour capture technology
2 Introduction
The anthropogenic climate crisis is the largest threat to global health [1]. However, the health-care sector itself is responsible for 5-10 % of greenhouse gas emissions [2]. A relevant part of these emissions are caused by volatile anaesthetics (VAs) used in anaesthesia and intensive care [2,3].
Active charcoal absorbers can be attached to the exhaust port of the anaesthesia machines to decrease these emssions and capture VAs. Using absorbers that allow the recapture of the VAs has the additional benefit of being able to reuse the substances.
A previous study by Hinterberg et al. [4], which investigated the efficiency of the CONTRAfluranTM (ZeoSys medical, Luckenwalde, Germany) vapour-capturing system for VAs in the operating room (OR), found that only 25 % of the vapourised desflurane could be recaptured. However, as Kalmar et al. pointed out [5], the desorption process to recapture the substances from the absorber is highly dependent on the saturation level of the CONTRAfluranTM anaesthetic gas canister (AGC), with a higher capture efficiency for full charcoal absorbers. Therefore, it can be assumed that a higher efficiency could be obtained, when AGCs are used to a higher saturation level than the 15 % in the study by Hinterberg et al. [4,5]. This might be one reason why Gandhi et al. reported a significantly higher capture efficiency of 43-51 % using SageTech Medical’s Volatile Capture Device (SageTech Medical, Paignton, UK) for sevoflurane, even though one would expect that the capture efficiency for sevoflurane would be lower in comparison to desflurane, due to the higher blood-gas coefficients and metabolism rate of sevoflurane [6]. Mulier et al. weighed the AGC before, during and after anaesthesia for laparoscopic surgery and determined an in vivo mass transfer (ratio of absorber weight gain to consumed weight of sevoflurane) of 45 % [7]. But as the system used by Gandhi et al. included an additional anaesthetic gas scavenging system (AGSS) to capture the VA and Mulier et al. did not report the results of the desorption process, it remains unknown how efficient vapour capture systems for sevoflurane without an AGSS connected can be when used to maximum saturation levels [6,7]. Therefore, we conducted this exploratory study to investigate the efficiency of passive vapour capture systems for sevoflurane and the entire recapture process when vapour capture systems for sevoflurane are used to higher saturation levels.
3 Methods
3.1 Ethics approval
The study was approved by the ethics committee of the University Medicine Greifswald (reference number: BB 102/23; approval date: 8 August 2023)
3.2 Setting
We collected a total of 20 consecutive CONTRAfluranTM AGCs in two different ORs in this prospective single-centre exploratory observational study.
We mostly took care of patients for ear, nose and throat surgery in the first OR (referred to as OR1). The first and second case each day were generally children, where we did inhaled inductions with a fresh gas flow in the range of the minute ventilation of the respective child. The following cases were mostly adults. We mostly used supraglottic airways. All cases, in median five cases per day, were inducted and emerged from anaesthesia in the OR.
We mostly took care of patients for neurosurgical spine surgery in the second OR (referred to as OR2). Here, the median number of cases was two per day and the patients were mostly adults who were intubated. The first case was always inducted in the OR, the following cases rarely in a special induction room where no AGC was installed. All cases emerged from anaesthesia in the OR.
All anaesthesia cases were performed at the discretion of the anaesthesiologist in charge in clinical routine according to our local standard operating procedures. Following these, a minimal or metabolic flow (< 0.5 l.min-1, mostly 0.3 l.min-1) was used during the steady state phase in all cases. We did recorded neither the patient data, the type of anaesthesia, the induction strategy nor the airway used because of the exploratory, pragmatic and anonymous character of the study.
We used the Draeger connect software (Draeger Medical Deutschland GmbH, Luebeck, Germany) to determine the number, duration and type of anaesthesia cases.
3.3 Consumption and weight measurement
Balanced anaesthesia with VAs was given using Draeger Perseus A500 anaesthesia machines equipped with bypass vaporizers of the type Draeger D-Vapor 3000 (Draeger Medicine Deutschland GmbH, Luebeck, Germany). The AGCs were connected to the exhaust port of the anaesthesia machines, which work in a passive mode, without an AGSS connected. We weighed the sevoflurane (SEVOrane, AbbVie Deutschland GmbH & Co. KG, Mainz, Germany) bottles before and after maximum filling of the vaporizer and used the difference in weight to record the sevoflurane consumption. The vaporizers were filled to the maximum before we attached the first CONTRAfluranTM AGC (ZeoSys medical, Luckenwalde, Germany) and started our recordings. During the study period, almost every day the two vaporizers were filled completely and the sevoflurane bottle weight difference measured by the study team, which was not involved in the anaesthesia.
In the case where a new bottle of sevoflurane was opened, it was initially attached to a non-study vaporizer to lose any excess pressure, and was weighed before the study vaporizer was filled.
Each AGC was only changed after it had been exhausted. This was made visible by a red LED and an acoustic warning signal of the SENSOfluran sensor unit (ZeoSys medical, Luckenwalde, Germany). Subsequently, we refilled the vaporizer to its maximum and measured the weight difference of the sevoflurane bottle, again. The weight difference was counted as consumption for the just exhausted AGC.
The weight gain of an AGC was determined by weighing the AGC before usage and after it had been exhausted to determine the in vivo mass transfer (ratio of absorber weight gain to consumed weight of sevoflurane). Each exhausted AGC was recapped and stored in a closed plastic zip-lock bag.
ZeoSys needs 20 AGCs for a single desorption process. We stored all consecutive AGCs at room temperature until the 20th AGC was exhausted. Before returning the AGCs to ZeoSys, we weighed all AGCs again to determine any potential weight loss.
All weight measurements were done with a precision scale (Kern PCB 2500-2; Kern&Sohn GmbH, Balingen-Frommern; Germany; maximum weight = 2500 g; d = 0.01 g).
ZeoSys stored all AGCs for a further four weeks at least, due to regulatory reasons before starting the desorption and recovery process. Afterwards, they sent us the information about the total amount of sevoflurane recovered from all 20 AGCs.
3.4 Outcome
The primary outcome was the amount of recovered sevoflurane reported by ZeoSys. The secondary outcomes were the difference between the in vivo mass transfer and the recapture rate reported by ZeoSys, the difference in the sevoflurane recovery between both ORs and the weight loss of the AGC during storage.
3.5 Data processing and statistical analysis
All data processing and statistical analyses were performed using R version 4.3.2 [8]. The two-sided Wilcoxon rank-sum test was used for statistical comparison. A p-value less than 0.05 was considered to be statistically significant. Summary tables were generated using the gtsummary package [9]. All data and analysis can be found at https://github.com/umg-minai/vct-or [10].
4 Results
| Characteristic | Operating rooms | p-value2 | |
|---|---|---|---|
| OR1 (ENT), N = 151 | OR2 (Neurosurgery), N = 51 | ||
| (A) Case summary | |||
| Total number of cases | 43.5 (37.0, 50.3) | 70.2 (59.6, 75.5) | 0.011 |
| Number of inhaled anaesthesia cases | 28.0 (26.3, 34.0) | 64.2 (55.6, 68.5) | 0.002 |
| Total duration of inhaled anaesthesia [h] | 32.1 (30.4, 36.3) | 168.0 (141.6, 191.0) | <0.001 |
| Average duration of inhaled anaesthesia [min] | 69.3 (62.2, 74.5) | 181.2 (178.6, 181.2) | <0.001 |
| (B) Sevoflurane consumption | |||
| Total sevoflurane weight used [g] | 524.9 (483.4, 559.2) | 1,261.4 (1,070.0, 1,271.3) | <0.001 |
| Average sevoflurane weight used per hour inhaled anaesthesia [g.h^-1^] | 15.8 (14.3, 17.5) | 7.5 (6.8, 7.8) | <0.001 |
| (C) Anaesthetic gas canister characteristics | |||
| Weight gain [g] | 399.0 (385.8, 415.7) | 381.0 (373.0, 384.5) | 0.13 |
| *In vivo* mass transfer [%] | 78.1 (72.0, 81.1) | 34.9 (27.5, 35.6) | <0.001 |
| Proportional sevoflurane captured [g] | NA (NA, NA) | NA (NA, NA) | |
| (Missing) | 15 | 5 | |
| Proportional capture efficiency [%] | NA (NA, NA) | NA (NA, NA) | |
| (Missing) | 15 | 5 | |
| 1 Median (IQR) | |||
| 2 Wilcoxon rank sum exact test; Wilcoxon rank sum test | |||
4.1 Sevoflurane consumption and capture efficiency
We observed a total of 968 anaesthesia cases during the 26 week study period, of which 76 % received VAs at a total duration of 1348 h.
A total of 14.2 kg sevoflurane was used and NA kg could be recaptured (capture efficiency NA %).
Comparing the two ORs, we found a large and significant difference in the total sevoflurane used, which is partly due to differences in the ratio of patients receiving VAs and the variations in the duration of anaesthesia (Table 4.1A and B).
While the median weight gain of the AGCs did not differ between the two ORs, we observed a large and significant difference in the in vivo mass transfer, which was at 78.1 % for OR1 and 34.9 % for OR2 due to the significantly different sevoflurane consumption in the two ORs (Table 4.1B and C). Thus, assuming the same proportion of sevoflurane could be accounted for the relative weight gain of each AGC, the proportional capture efficiency differed significantly between the two ORs, with NA % for OR1 and NA % for OR2 (Table 4.1C).
The details of each AGC can be found in Supplemental Table 9.1.
4.2 Weight loss
The 20 AGCs were stored for 69.0 (33.2, 120.0) days. in median (lower and upper quartile). Before sending all AGCs to ZeoSys, we weighed them again and found an almost linear decrease in weight over time of around 69 mg per day (Figure 4.1 and Supplemental Section 9.2)).
Figure 4.1: Weight loss of the anaesthetic gas canisters during storage. The dots represent the weight loss of each individual anaesthetic gas canister for the days after exhaustion. The dashed line is the linear fit.
5 Discussion
We demonstrated in this prospective single-center observational study that using active charcoal absorbers for sevoflurane until they reached their maximum saturation levels can yield a total capture efficiency of NA %. This represents a total amount of NA kg that can be recovered from a total of 14.2 kg sevoflurane used in our study cohort of 738 balanced anaesthesia cases.
Interestingly, we saw a large and significant difference in the proportional capture efficiencies in the two ORs, with NA % for OR1 and NA % for OR2. Despite the different disciplines and procedures, the inhaled induction and the duration of anaesthesia are observious differences. During an inhaled induction, even if done with a fresh gas flow in the range of the minute ventilation of the respective child, a large amount of sevoflurane is wasted and cannot be compensated by a following metabolic flow anaesthesia, as could be seen in the large difference in the average sevoflurane consumption per hour. However, a large wastage of VA yields a higher capture efficiency.
Another major determinant for the lower capture efficiency in OR2 may be the longer duration of anaesthesia. The slow compartments of the body, for example fat, have a huge capacity to store a large amount of VA. It takes hours to saturate the slow compartments due to the long time constant for sevoflurane [11]. However, the absolute amount of VA in the fat tissue, even before saturation, is much larger than in the fast compartments (e.g. brain, muscle) and the blood [11]. The fat tissue will also release the VA slowly during the emergence process, due to its small part in the total cardiac output and the low partial pressure. The longer the anaesthesia lasts, the more VA will be stored in the fat tissue and carried to the post anaesthesia care unit, where it is unable to be captured, resulting in a lower capture efficiency. This effect was relatively mild in a previous simulation study with a 9 % reduction of the capture efficiency from 82 % after one hour to 73 % after five hours anaesthesia with sevoflurane and a fresh gas flow of 0.5 l.min-1 [12]. Considering the large volume of fat tissue and the theoretical storage capacity, this seems significantly underestimated. Hinterberg et al. had also recognised a much lower capture efficiency in longer rather than shorter anaesthesia [4]. Interestingly, Mulier et al. had not seen any correlation between the in vivo mass transfer and duration of anaesthesia [7]. Their duration of anaesthesia, at around only 90 min, lasted about half as long as ours and may be too short for a relevant accumulation of sevoflurane in the fat tissue compared to the consumption during induction. This could be in line with the results of the simulation study, where the largest drop in capture efficiency for minimal-flow anaesthesia was found between one and two hours [12].
Our overall capture efficiency of NA % is very similar to the 43-51 % previously reported for the AGSS-dependent SageTech Medical’s Volatile Capture Device (SageTech Medical, Paignton, UK; [6]) or the 45 % in vivo mass transfer for CONTRAfluranTM during laparoscopic surgery [13]. Hinterberg et al. reported a much lower capture efficiency of just 25 % for desflurane [4]. They used a new AGC for every case, which produced underfilled AGCs with less than 15 % of their capacity, possibly yielding a relative higher contribution of water to the weight gain and insufficiencies in the desorption and recapture process [5]. By contrast, our study represents a ‘real-world’ usage of the AGCs until they were saturated.
Despite the difference in the overall capture efficiency, our results in the different ORs confirm that a longer duration of minimal-flow anaesthesia reduces the capture efficiency, as described and simulated previously [4,12]. However, the focus on the capture efficiency as a target is misleading as a higher fresh gas flow yields a higher capture efficiency due to an increased proportion of anaesthetic wasted and entering the AGC [14,15].
Beside the volatile agent, the AGC contains a varying proportion of water, acetone and, in the case of sevoflurane, compound A-E. The absorption of the volatile agent in the AGC is based on strong non-covalent interactions displacing water and the other components. In our study, NA % was attributable to sevoflurane (desorption efficiency). We believe that the complete saturation of our AGCs explains the higher proportion compared to the 70 % reported previously [4]. Perhaps a connected AGSS caused a dryer AGC, which could be a reason for the very high desorption efficiency of 95.5 % sevoflurane for SageTech’s AGSS-dependent volatile capture device [6].
Although we stored all AGCs in a zip lock bag, we surprisingly found a linear decrease in weight of around 69 mg per day during storage (Figure 4.1). A previous study reported a constant weight over time [4]. Because of the strong non-covalent interaction between the VA and the activated charcoal, and the hydrophobic character of the latter, we assume that a drying or evaporation process of the captured water could explain the weight loss. However, we recognised some rare exhausting alarms by SENSOfluran during minimal-flow total intravenous anaesthesia, which may be due to spontaneous desorption. Weight loss during high-flow total intravenous anaesthesia was already reported [7]. Thus spontaneous desorption, even without any flow, may be another explanation.
The weight loss and the difference in desorption efficiency illustrate that it is not possible to draw any conclusions about the overall capture efficiency of AGCs from the (in vivo) mass transfer alone.
5.1 Limitations
The primary limitation of our study is that we included only two ORs with a different number of patients and a variety of surgical and anaesthesia procedures. Due to the large number of patients per AGC and the pragmatic design, we were not able to analyse patient-related associations, fresh gas flows and other procedure-related factors in a meaningful way. Therefore, our findings should be regarded as exploratory, indicating a further need for research.
In contrast to previous studies that used a new AGC for every case or utilised the AGC only for select procedures to infer associations between capture efficiency and patient characteristics, we studied a day-to-day use, which is why our results can be compared easily to other settings.
Seven of 328 cases of OR2 were inducted in the separate induction room. This may overestimate the proportional capture efficiency of the AGCs in this OR because an external, unmeasured amount of sevoflurane was introduced. However, due to the small number of external inductions, the short duration and the need to fill the circuit in the OR, its effect should be negligible.
We did not record the intraoperative change of the carbon dioxide absorber. However, the influence should also be negligible due to the infrequent changes.
The gold standard to determine the consumption of VA is weighing the vaporizer before and after the observation period, typically a single anaesthesia case. Unfortunately, a scale that was precise enough to measure more than 9 kg with a precision of a few grams was not available. However, our approach, weighing the sevoflurane bottles, has small advantages in our scenario. According to the manual of the vaporizer, the Draeger D-Vapor 3000 loses small amounts of VAs (< 0.5 ml in 24 h; equals < 31 mg/h). While this loss is small and perhaps negligible, it can not be measured by weighing the vaporizer before and after each case. Ignoring such a loss would slightly overestimate the capture efficiency. We can easily measure all, possibly hidden, losses of VAs and determine the capture efficiency more accurately by weighing the bottles.
After the removal of the last exhausted AGC, CH0100012088, in OR2 the vaporizer was not refilled and the weight difference of the sevoflurane bottle not recorded. That is why we calculate the sevoflurane consumption data for the four last anaesthesia cases as described by Biro et al. (54.10 g; Supplemental Section 9.3) [16]. They described an overestimation of the sevoflurane consumption by 6.2 %. This would result in an error of 0.26 % for our AGC CH0100012088 and just slightly underestimate the in vivo mass transfer and proportional capture efficiency.
6 Conclusion
The capture efficiency of active charcoal absorbers (CONTRAfluranTM) may depend on the fresh gas flow used and duration of anaesthesia. It was higher than previously reported, when the absorbers were used until they reached their maximum saturation levels. Using metabolic flow, the proportional capture efficiencies were NA % and NA % , respectively, in the two ORs studied. However, focusing on capture efficiency is misleading. Further research and independent life cycle analyses are needed to understand the factors of different capture efficiencies and determine the carbon footprint of balanced anaesthesia with vapour-capture technology.
7 Declarations
7.1 Ethical approval
Research involving human subjects complied with all relevant national regulations and institutional policies, as well as the tenets of the Helsinki Declaration (as revised in 2013), and was approved by the ethics committee of the University Medicine Greifswald (reference number: BB 102/23; approval date: 8 August 2023)
7.2 Consent for publication
Not applicable.
7.3 Availability of data and materials
The datasets generated and/or analysed during the current study are available in the zenodo repository, [10].
7.4 Competing interests
All authors state no conflict of interest.
7.5 Funding
None.
7.7 Acknowledgements
We thank Marco Reinke and Steffen Suermann from Draeger Medical Deutschland GmbH for exporting the Draeger connect data, the Draeger Perseus’ logbooks and for helpful discussions about sevoflurane consumption, Christian Ewers, managing director of ZeoSys medical, for reporting the amount of recovered sevoflurane and information about the desorption process. Additionally, we would like to thank Linda Grüßer and Stephanie Snyder-Ramos for proofreading the manuscript.
8 References
9 Supplement
9.1 Table of anaesthetic gas canisters
| Id | OR | Wi | Wf | Wd | Wl | S | N | Nsev | D | Dsev | Davg | Csev | Cavg | MT |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CH0100009185 | OR1 | 1031.0 | 1456.8 | 425.8 | 9.0 | 102 | 52.0 | 41.0 | 3702 | 2842 | 69.3 | 610.7 | 12.9 | 69.7 |
| CH0100009250 | OR1 | 1065.5 | 1488.8 | 423.3 | 4.0 | 40 | 46.1 | 29.8 | 3802 | 1870 | 62.8 | 524.9 | 16.8 | 80.7 |
| CH0100009255 | OR2 | 1048.6 | 1433.2 | 384.5 | 2.1 | 18 | 81.9 | 76.9 | 14824 | 13932 | 181.2 | 1807.2 | 7.8 | 21.3 |
| CH0100009267 | OR1 | 1047.4 | 1472.9 | 425.6 | 4.5 | 53 | 39.1 | 27.0 | 2179 | 1485 | 55.0 | 543.4 | 22.0 | 78.3 |
| CH0100009273 | OR1 | 1047.6 | 1438.4 | 390.8 | 0.8 | 11 | 52.0 | 28.0 | 3155 | 1953 | 69.8 | 500.7 | 15.4 | 78.1 |
| CH0100012066 | OR1 | 1028.4 | 1415.2 | 386.8 | 9.5 | 131 | 49.5 | 34.0 | 2708 | 1928 | 56.7 | 471.1 | 14.7 | 82.1 |
| CH0100012067 | OR1 | 1028.7 | 1425.9 | 397.3 | 1.5 | 26 | 49.6 | 34.1 | 3207 | 2251 | 66.1 | 555.9 | 14.8 | 71.5 |
| CH0100012074 | OR1 | 1022.8 | 1407.2 | 384.4 | 8.1 | 119 | 51.0 | 35.0 | 3481 | 2218 | 63.4 | 584.1 | 15.8 | 65.8 |
| CH0100012076 | OR1 | 1029.3 | 1437.2 | 407.9 | 4.0 | 35 | 27.7 | 21.7 | 2225 | 1876 | 86.6 | 562.5 | 18.0 | 72.5 |
| CH0100012088* | OR2 | 1034.0 | 1383.6 | 349.5 | 0.0 | 4 | 70.2 | 64.2 | 12592 | 11458 | 178.6 | 1271.3 | 6.7 | 27.5 |
| CH0100012089 | OR1 | 1034.2 | 1415.2 | 381.0 | 10.6 | 159 | 35.0 | 27.0 | 2395 | 1913 | 70.9 | 514.1 | 16.1 | 74.1 |
| CH0100012091 | OR1 | 1024.6 | 1434.6 | 410.0 | 11.6 | 147 | 29.9 | 20.9 | 2437 | 1780 | 85.1 | 533.2 | 18.0 | 76.9 |
| CH0100012196 | OR1 | 1020.0 | 1404.9 | 384.9 | 8.6 | 168 | 31.6 | 19.6 | 2000 | 1194 | 60.8 | 473.3 | 23.8 | 81.3 |
| CH0100012198 | OR1 | 1022.2 | 1401.8 | 379.6 | 3.0 | 28 | 51.4 | 34.4 | 3637 | 2595 | 75.5 | 577.6 | 13.4 | 65.7 |
| CH0100022360 | OR1 | 1039.1 | 1438.1 | 399.0 | 6.0 | 76 | 39.0 | 29.0 | 3152 | 2132 | 73.5 | 493.5 | 13.9 | 80.8 |
| CH0100022366 | OR2 | 1028.4 | 1469.2 | 440.8 | 4.8 | 60 | 59.6 | 55.6 | 10767 | 10079 | 181.2 | 1261.4 | 7.5 | 34.9 |
| CH0100022367 | OR1 | 1040.0 | 1461.5 | 421.4 | 7.5 | 88 | 42.5 | 26.5 | 3303 | 1635 | 61.6 | 465.0 | 17.1 | 90.6 |
| CH0100022433 | OR2 | 1031.8 | 1404.8 | 373.0 | 7.0 | 123 | 75.5 | 68.5 | 9529 | 8497 | 124.0 | 957.6 | 6.8 | 38.9 |
| CH0100022435 | OR2 | 1043.8 | 1424.8 | 381.0 | 5.1 | 94 | 40.9 | 38.9 | 7685 | 7189 | 184.9 | 1070.0 | 8.9 | 35.6 |
| CH0100022442 | OR1 | 1034.9 | 1441.3 | 406.4 | 5.0 | 62 | 43.5 | 26.0 | 2721 | 2031 | 78.1 | 462.2 | 13.7 | 87.9 |
9.2 Weight lost during storage
After the AGCs were exhausted we stored them before shipping to ZeoSys. We weighed them again before shipping and recognised a nearly linear weight loss even though every AGC was stored in a zip-lock bag.
##
## Call:
## lm(formula = LostWeight ~ 0 + DaysStored, data = agc)
##
## Residuals:
## Min 1Q Median 3Q Max
## -3.0272 -0.2894 0.6678 1.1163 1.9567
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## DaysStored 0.069150 0.003041 22.74 3.05e-15 ***
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 1.251 on 19 degrees of freedom
## Multiple R-squared: 0.9646, Adjusted R-squared: 0.9627
## F-statistic: 517 on 1 and 19 DF, p-value: 3.054e-159.3 Estimation of sevoflurane consumption
After changing the last AGC CH0100012088 in OR25, the vaporizer was not refilled. Therefore, we retrospectively calculated the sevoflurane consumption for the last four anaesthesia cases utilising the user log entry provided by the Draeger Perseus anaesthesia machine. The calculation was done as described in [16].
| Case | Time since vaporizer opened [min] | Fresh gas flow [l.min-1] | Vaporizer setting [Vol%] | Duration [min] | Sevoflurane consumption [g] |
|---|---|---|---|---|---|
| 1 | 0 | 1.0 | 3.31 | 2 | 0.55 |
| 1 | 2 | 1.0 | 5.09 | 1 | 0.42 |
| 1 | 3 | 0.3 | 8.00 | 5 | 0.99 |
| 1 | 8 | 0.3 | 6.11 | 6 | 0.91 |
| 1 | 14 | 0.3 | 5.14 | 1 | 0.13 |
| 1 | 15 | 0.2 | 5.14 | 2 | 0.17 |
| 1 | 17 | 0.2 | 3.52 | 38 | 2.21 |
| 1 | 55 | 0.2 | 4.48 | 3 | 0.22 |
| 1 | 58 | 0.2 | 5.00 | 2 | 0.17 |
| 1 | 60 | 0.2 | 6.11 | 55 | 5.55 |
| 1 | 115 | 0.2 | 4.57 | 29 | 2.19 |
| 2 | 0 | 0.2 | 8.00 | 13 | 1.72 |
| 2 | 13 | 0.2 | 6.70 | 1 | 0.11 |
| 2 | 14 | 0.2 | 5.04 | 2 | 0.17 |
| 2 | 16 | 0.2 | 3.56 | 6 | 0.35 |
| 2 | 22 | 0.3 | 4.06 | 11 | 1.11 |
| 2 | 33 | 0.3 | 2.57 | 1 | 0.06 |
| 2 | 34 | 0.3 | 1.49 | 1 | 0.04 |
| 2 | 35 | 0.3 | 0.62 | 9 | 0.14 |
| 2 | 44 | 0.3 | 2.50 | 11 | 0.68 |
| 2 | 55 | 0.3 | 3.96 | 8 | 0.79 |
| 2 | 63 | 0.3 | 3.05 | 49 | 3.71 |
| 2 | 112 | 0.3 | 2.93 | 19 | 1.38 |
| 2 | 131 | 0.2 | 2.93 | 5 | 0.24 |
| 2 | 136 | 0.3 | 2.93 | 54 | 3.92 |
| 2 | 190 | 0.3 | 1.53 | 3 | 0.11 |
| 2 | 198 | 0.3 | 1.75 | 4 | 0.17 |
| 2 | 202 | 0.3 | 4.01 | 29 | 2.88 |
| 3 | 0 | 15.0 | 3.56 | 1 | 4.41 |
| 3 | 1 | 0.2 | 3.56 | 9 | 0.53 |
| 3 | 10 | 0.2 | 8.00 | 14 | 1.85 |
| 3 | 24 | 0.2 | 5.04 | 1 | 0.08 |
| 3 | 25 | 0.3 | 5.04 | 8 | 1.00 |
| 3 | 33 | 0.3 | 3.65 | 3 | 0.27 |
| 3 | 36 | 0.3 | 2.54 | 12 | 0.76 |
| 3 | 48 | 0.3 | 3.56 | 7 | 0.62 |
| 3 | 55 | 0.3 | 4.53 | 4 | 0.45 |
| 3 | 59 | 0.3 | 5.58 | 17 | 2.35 |
| 3 | 76 | 0.3 | 3.87 | 1 | 0.10 |
| 3 | 77 | 0.3 | 3.35 | 51 | 4.24 |
| 3 | 128 | 0.3 | 3.01 | 6 | 0.45 |
| 4 | 0 | 0.2 | 8.00 | 21 | 2.78 |
| 4 | 21 | 0.2 | 4.62 | 1 | 0.08 |
| 4 | 22 | 0.2 | 2.54 | 15 | 0.63 |
| 4 | 37 | 0.2 | 3.05 | 41 | 2.07 |
| 4 | 78 | 0.2 | 3.52 | 6 | 0.35 |
| Case | Total sevoflurane consumption [g] |
|---|---|
| 1 | 13.51 |
| 2 | 17.59 |
| 3 | 17.10 |
| 4 | 5.90 |
9.4 R session information
sessionInfo()## R version 4.3.2 (2023-10-31)
## Platform: x86_64-unknown-linux-gnu (64-bit)
## Running under: Debian GNU/Linux 12 (bookworm)
##
## Matrix products: default
## BLAS/LAPACK: /gnu/store/in3yw5xrghzmxn29i0mmz5zhpd748mas-openblas-0.3.20/lib/libopenblasp-r0.3.20.so; LAPACK version 3.9.0
##
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=de_DE.UTF-8
## [7] LC_PAPER=de_DE.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=C
##
## time zone: Europe/Berlin
## tzcode source: system (glibc)
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] lubridate_1.9.3 gtsummary_1.7.2 english_1.2-6
##
## loaded via a namespace (and not attached):
## [1] gt_0.10.1 sass_0.4.8 utf8_1.2.4
## [4] generics_0.1.3 tidyr_1.3.1 xml2_1.3.6
## [7] stringi_1.8.3 digest_0.6.34 magrittr_2.0.3
## [10] evaluate_0.23 timechange_0.3.0 bookdown_0.37
## [13] fastmap_1.1.1 rprojroot_2.0.4 broom.helpers_1.13.0
## [16] jsonlite_1.8.8 backports_1.4.1 purrr_1.0.2
## [19] fansi_1.0.6 viridisLite_0.4.2 bibtex_0.5.1
## [22] jquerylib_0.1.4 cli_3.6.2 rlang_1.1.3
## [25] commonmark_1.9.1 withr_3.0.0 cachem_1.0.8
## [28] yaml_2.3.8 tools_4.3.2 dplyr_1.1.4
## [31] forcats_1.0.0 broom_1.0.5 vctrs_0.6.5
## [34] R6_2.5.1 lifecycle_1.0.4 stringr_1.5.1
## [37] pkgconfig_2.0.3 pillar_1.9.0 bslib_0.6.1
## [40] glue_1.7.0 xfun_0.42 tibble_3.2.1
## [43] tidyselect_1.2.0 highr_0.10 knitr_1.45
## [46] htmltools_0.5.7 rmarkdown_2.25 compiler_4.3.2
## [49] markdown_1.129.5 Git commit hash
## [1] "Git commit revision: 2ac76148bb48c051f311a1da8fce875da9d04976"