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|Year : 2016
: 19 | Issue : 2 | Page
|Tricks, tips, and literature review on the adapted vaporize system to deliver volatile agents during cardiopulmonary bypass
Caetano Nigro Neto1, Francesco De Simone2, Luigi Cassara2, Carlos Gustavo Dos Santos Silva1, Thiago Augusto Almeida Maranhão Cardoso1, Francesco Carco2, Alberto Zangrillo3, Giovanni Landoni3
1 Department of Surgery and Anesthesia, Dante Pazzanese Institute of Cardiology, São Paulo, Italy
2 Department of Anesthesia and Intensive Care, IRCCS San Raffaele Scientific Institute, Milan, Italy
3 Department of Anesthesia and Intensive Care, IRCCS San Raffaele Scientific Institute; Department of Anesthesia and Intensive Care, Vita-Salute San Raffaele University, Milan, Italy
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|Date of Submission||01-Oct-2015|
|Date of Acceptance||25-Feb-2016|
|Date of Web Publication||1-Apr-2016|
| Abstract|| |
Background: Recently, evidence of cardio-protection and reduction in mortality due to the use of volatile agents during cardiac surgery led to an increase in their use during cardiopulmonary bypass (CPB). These findings seem to be enhanced when the volatile agents are used during all the surgical procedure, including the CPB period. Aims: Since the administration of volatile agents through CPB can be beneficial to the patients, we decided to review the use of volatile agents vaporized in the CPB circuit and to summarize some tricks and tips of this technique using our 10-year experience of Brazilian and Italian centers with a large volume of cardiac surgeries. Study Setting: Hospital. Methods: A literature review. Results: During the use of the volatile agents in CPB, it is very important to analyze all gases that come in and go out of the membrane oxygenators. The proper monitoring of inhaled and exhaled fraction of the gas allows not only monitoring of anesthesia level, but also the detection of possible leakage in the circuit. Any volatile agent in the membrane oxygenator is supposed to pollute the operating theater. This is the major reason why proper scavenging systems are always necessary when this technique is used. Conclusion: While waiting for industry upgrades, we recommend that volatile agents should be used during CPB only by skilled perfusionists and physicians with the aim to reduce postoperative morbidity and mortality.
Keywords: Anesthesia; Cardiac surgery; Cardiopulmonary bypass; Sevoflurane; Volatile anesthetic
|How to cite this article:|
Nigro Neto C, De Simone F, Cassara L, Dos Santos Silva CG, Maranhão Cardoso TA, Carco F, Zangrillo A, Landoni G. Tricks, tips, and literature review on the adapted vaporize system to deliver volatile agents during cardiopulmonary bypass. Ann Card Anaesth 2016;19:240-4
|How to cite this URL:|
Nigro Neto C, De Simone F, Cassara L, Dos Santos Silva CG, Maranhão Cardoso TA, Carco F, Zangrillo A, Landoni G. Tricks, tips, and literature review on the adapted vaporize system to deliver volatile agents during cardiopulmonary bypass. Ann Card Anaesth [serial online] 2016 [cited 2020 Jul 2];19:240-4. Available from: http://www.annals.in/text.asp?2016/19/2/240/179592
| Introduction|| |
The use of volatile anesthetic agents during cardiopulmonary bypass (CPB) was described for the 1 st time about 40 years ago.  Originally, volatile agents were vaporized and administered in the early-generation bubble oxygenators. Today, most cardiac surgery interventions are performed with standard membrane oxygenators. Unfortunately, the newest CPB machines are not equipped routinely for the use of these anesthetic agents, and this means that we still need to adapt anesthetic vaporizers in the bypass circuit.
Some studies showed an evidence of cardioprotection and reduction in mortality due to the use of volatile agents during cardiac surgery. ,,,, These findings seems to be enhanced when the volatile agents are used during all the surgical procedure, including the period of CPB. 
Since the administration of volatile agents through CPB can be beneficial to the patients, we decided to review the use of volatile agents vaporized in the CPB circuit and to summarize some tricks and tips of this technique in our 10-year experience of Brazilian and Italian centers with a large volume of cardiac surgeries.
[Table 1] summarizes the problems that we found in our extensive experience that can be related to the use of volatile agents vaporized in the CPB circuit. All these problems are associated to the vaporizer and to the analysis of the exhaled gases from the membrane oxygenator.
|Table 1: Tricks and tips for the adapted vaporize system using volatile agents during cardiopulmonary bypass based on the 10 years' experience of two teaching hospitals (one in Italy and one in Brazil) |
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Until now, the technique of the use of volatile agents during CPB is an adaptation which includes the volatile agent vaporized into the circuit of the CPB machine mixed with the fresh gas flow (oxygen and compressed air) delivered from the blender. At first, the fresh gas flow from the blender enters into the calibrated vaporizer and is mixed with a desired concentration of the volatile agent. After that, the fresh gas flow, now mixed with a vaporized volatile agent, and enters into the circuit of the membrane oxygenator [Figure 1]. Many companies fail to mention that vaporizers can be included in their circuit and that the volatile agents can be used with standard membrane oxygenators. ,
|Figure 1: Schematic representation of the use of volatile agents adapted to cardiopulmonary bypass machine|
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During the use of the volatile agents in CPB, it is very important to analyze all gases that come in and go out of the membrane oxygenators. The proper monitoring of inhaled and exhaled fraction of the gas allows not only the monitoring of anesthesia level, but also to detect possible leakage in the circuit. Nevertheless, most current oxygenators have redundant venting systems that eliminate the hazards of potential over pressurization inside the oxygenator which makes it difficult to measure precisely the volatile anesthetic levels in the exhaust port. In a prospective observational study, changes in sevoflurane plasma concentrations (SPCs) and bispectral index values during CPB were evaluated together with patient temperature, hemodilution, oxygenator fresh gas flow, and sevoflurane concentration in the exhaust gas from the oxygenator.  This study evidenced that SPCs were higher during hypothermia and with an increased fresh gas flow in oxygenator, while were lower with hemodilution. No correlation was found between SPCs and the concentration of sevoflurane in the oxygenator exhaust port gas, suggesting that leakages occurred from the main port during measurements. Moreover, most scavenging system devices used during this technique to evacuate the volatile gases from the operating room could be the cause of the reading line failure during monitoring.
Any volatile agent in the membrane oxygenator is supposed to pollute the operating theater. This is the major reason why proper scavenging systems are always necessary when this technique is used. The exposure limit for halogenated anesthetics is on average 2 parts per million (ppm), and it slightly changes according to the average over the period of anesthetic administration. It is important to mention that the olfactory thresholds typically is much higher than the 2 ppm. 
Recently, Nigro Neto et al. described in a systematic review that the most serious accidents associated to the use of volatile agents during CPB are pollution of the room and cracks in the polycarbonate shell of the extracorporeal circuit components caused by spilled liquid volatile agent. Awareness is rare and seems to be associated to the type of membrane oxygenator used. Currently, there are two groups of hollow-fiber membrane oxygenators used in clinical practice [Table 2].  The first type includes hollow-fiber membranes, primarily composed of microporous polypropylene, which is widely for standard CPB without having performances affected by the use of volatile agents.  The second type (diffusion plasma-resistant oxygenators) has the basic membrane compounded primarily of poly-(4-methyl-1-pentene). This type is increasingly used for extracorporeal life support or extracorporeal membrane oxygenation, and might increase the risk of intraoperative awareness during CPB by lowering the transfer of the volatile agent to the blood. , To avoid this undesirable event, it is important to monitor the consciousness depth by monitoring systems such as bispectral index scale or by extrapolating plasma concentration from measured end-tidal anesthetic gas concentrations.  Moreover, proper scavenging system is utmost important along with strict patient monitoring during the delivery of these agents. Unlike bubble oxygenators (which rely on direct contact of blood and bubbles for gas exchange and are designed to separate undissolved gas from blood before the blood exits the oxygenator), membrane oxygenators are not designed to separate blood and bubbles of undissolved gas. Consequently, if large volumes of undissolved gas enter into the blood or are generated by back pressure in the membrane oxygenator, these will flow out of the oxygenator with blood. The potential for gas embolism exists if the outlet gas vent port of these oxygenators becomes either partially or totally occluded. Gas scavenging systems for these oxygenators must not cause the application of positive or negative pressures in the gas jackets as this may be dangerous. The American National Standards Institute (ANSI) standard (ANSI Z79.11) addressing scavenging systems for anesthetic gases apply to oxygenators as well as to anesthesia machines. This standard states that scavengers must not generate positive pressures exceeding 10 cm of water (7.4 mmHg) or negative pressures exceeding 0.5 cm of water (0.37 mmHg). 
|Table 2: Difference in the hollow - fiber membrane oxygenators and their variability in transmembrane passage of volatile agents |
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| Conclusion|| |
While waiting for industry upgrades, we recommend that volatile agents should be used during CPB only by skilled perfusionists and physicians with the aim to reduce postoperative morbidity and mortality.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
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Department of Anesthesia and Intensive Care, IRCCS San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milan
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]