Anesthesia Management During Cardiopulmonary

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AUTHOR'S PROOF

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Article Title

Anesthesia Management During Cardiopulmonary Bypass: Volatile v s. Intrav enous Drugs

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Springer Science+Business Media, LLC 2017 (This w ill be the copyright line in the final PDF)

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Current Anesthesiology Reports

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Corresponding Author

Neto Caetano Nigro

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Dante Pazzanese Institute of Cardiology

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Anesthesiology Department

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Av. Dr. Dante Pazzanese, 500, Sao Paulo

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[email protected]

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Landoni

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Giov anni

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Vita-Salute San Raffaele University

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San Raffaele Scientific Institute

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Milan

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[email protected]

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Bezerra

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Author

Francisco José Lucena

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e-mail

[email protected]

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Maranhão

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Particle

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[email protected]

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Gustav o

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Thiago

Carlos

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[email protected]

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Stahlschmidt

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Adriene

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[email protected]

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Abstract

Anesthetic management during cardiopulmonary bypass (CPB) is challenging in many aspects. Evidence of mortality reduction due to the use of volatile agents during cardiac surgery has led to their increased use in CPB. Partly because of the difficulty to administer volatile agents during CPB, total intravenous anesthesia (TIVA) has become the most popular technique used by cardiac anesthetists throughout this critical period. The aim of this review is to provide an overview of volatile agents’ administration to ensure maintenance of adequate depth of anesthesia during CPB and weighting risks and benefits of this technique compared to TIVA.

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Keywords separated by ' - '

Cardiopulmonary bypass - Inhalational anesthesia - Volatile agents - Awareness - Oxygenator - Cardiac anesthesia - Air pollution Myocardial protection - TIVA - Desflurane - Isoflurane - Sevoflurane - Propofol

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Foot note information

This article is part of the Topical Collection on Cardiovascular Anesthesia

AUTHOR'S PROOF

JrnlID 40140_ArtID 222_Proof# 1 - 16/06/2017

Curr Anesthesiol Rep DOI 10.1007/s40140-017-0222-9

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Anesthesia Management During Cardiopulmonary Bypass: Volatile vs. Intravenous Drugs Caetano Nigro Neto 1 & Giovanni Landoni 2 & Francisco José Lucena Bezerra 1 & Thiago Maranhão 1 & Carlos Gustavo 1 & Adriene Stahlschmidt 1

# Springer Science+Business Media, LLC 2017

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Abstract Anesthetic management during cardiopulmonary bypass (CPB) is challenging in many aspects. Evidence of mortality reduction due to the use of volatile agents during cardiac surgery has led to their increased use in CPB. Partly because of the difficulty to administer volatile agents during CPB, total intravenous anesthesia (TIVA) has become the most popular technique used by cardiac anesthetists throughout this critical period. The aim of this review is to provide an overview of volatile agents’ administration to ensure maintenance of adequate depth of anesthesia during CPB and weighting risks and benefits of this technique compared to TIVA.

This article is part of the Topical Collection on Cardiovascular Anesthesia

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* Caetano Nigro Neto [email protected]

Giovanni Landoni [email protected] Francisco José Lucena Bezerra [email protected] Thiago Maranhão [email protected] Carlos Gustavo [email protected] Adriene Stahlschmidt [email protected] Q1

Keywords Cardiopulmonary bypass . Inhalational anesthesia . Volatile agents . Awareness . Oxygenator . Cardiac anesthesia . Air pollution . Myocardial protection . TIVA . Desflurane . Isoflurane . Sevoflurane . Propofol

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Introduction

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Anesthetic management during cardiopulmonary bypass (CPB) is challenging in many aspects. The choice of the hypnotic agent that can safely be administered without causing adverse effects like hypotension and post-CPB cardiac depression is the most obvious goal and deserves special attention. Possible differences in clinically relevant outcomes due to pharmacological properties have to be considered as well. In 1974, the use of volatile anesthetic agents (VAA) during CPB was described for the first time [1], and its role has been expanding since then. Over the last two decades, evidence of mortality reduction due to VAA use in cardiac surgery [2] has increased their utilization during CPB. This is mainly due to the fact that their cardioprotective properties might be related to its administration modalities [3]. Originally, in the bubble oxygenators’ early generation, VAA were vaporized and administered mixed with oxygen [4]. Nowadays, most cardiac interventions are performed with standard membrane oxygenators. Partly because of these agents’ administration difficulties during CPB, total intravenous anesthesia (TIVA) has become a popular technique used by cardiac anesthetists over this period [5••]. Nowadays, several hundred thousand heart surgeries with CPB are performed every year around the world. However, administering and ensuring anesthesia with VAA during CPB is still a challenge. First of all, the administration through lungs is prevented by their exclusion from circulation. In addition, the main clinical signs of anesthesia depth, including

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CARDIOVASCULAR ANESTHESIA (J FASSL, SECTION EDITOR)

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Anesthesiology Department, Dante Pazzanese Institute of Cardiology, Av. Dr. Dante Pazzanese, 500, Sao Paulo, Brazil

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San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy

AUTHOR'S PROOF


Curr Anesthesiol Rep

Volatile Agents and Cardiopulmonary Bypass

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First of all, it is important that all anesthetists who want to vaporize volatile agents during CPB to be aware that this technique is under development; therefore, caution and knowledge of every step are of the utmost importance. One should consider three major points that require special attention when administering VAA during CPB: vaporizers, membrane oxygenators, and scavenging systems.

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Vaporizers

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Until now, vaporizers are still adapted to CPB machine circuit to deliver volatile agents. Generally, they are positioned between the blender and the oxygenator. At first, fresh gas flow from blender enters the vaporizer in the inlet position in order to be mixed with a desired VAA concentration. After that, the gas flow, now enriched with VAA, goes out in the outlet position of the vaporizer and flows into the membrane oxygenator (Fig. 1). Many companies fail to mention that vaporizers can be included in their circuit and that VAA can be used with standard membrane oxygenators [8, 9••]. Vaporizers’ choice is probably unimportant, but they must always be calibrated, regardless of the model. Whichever vaporizer is placed on CPB machine, it needs to be readily accessible in case it becomes exhausted and additional anesthetic agent should be filled in. Care should be taken to position the vaporizer on the CPB machine where it is clearly visible so that its filling level can be observed to ensure that it contains enough agent. In order to prevent awareness, vaporizers should be full and with the desired concentration set up on the dial before patient is placed on CPB. Additionally, incorrect mounting of the gas inlet and outlet on vaporizer’s back bar can result in sweep gas loss before it enters the oxygenator, resulting not only in inadequate depth of anesthesia and patient awareness, but also in hypoxia and hypercapnia [5••, 9••, 10] (Figs. 2 and 3). Filling a vaporizer on a CPB machine is not free of hazard. Spillage of isoflurane onto the oxygenator, for instance, can cause cracking of the polycarbonate casing as reported by some authors [11]. Thus, it is essential to position the

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Membrane Oxygenators

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Membrane oxygenators are an important part of the current technological components of extracorporeal circulation circuits. Gas exchange through oxygenators into the blood represents a fundamental step in heart surgery with CPB. This ensures adequate oxygen supply to the tissues, removing CO2 and also provides adequate maintenance of anesthesia throughout perfusion, which can also have direct impact on the mortality, as suggested by some authors [13••, 14••, 15]. Basically, there are two groups of membrane oxygenators used in clinical practice: diffusion and hollow-fiber membranes (Table 1). The basic membrane compound of diffusion oxygenators is poly-(4-methyl-1-pentene). They have been increasingly used for extracorporeal life support or extracorporeal membrane oxygenation, with durability of more than 6 hours, but interfere directly in the VAA exchange, causing reduction on blood levels. The hollow-fiber membranes, which the basic compound is semi-porous polypropylene (PPL) are the standard oxygenators used in cardiac surgery with CPB. They offer excellent O2 exchange and CO2 removal and guarantee the efficient transport of VAA to the blood.

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vaporizer away from the oxygenator and to remove the vaporizer from the CPB machine while filling it with anesthetic agent to reduce the risk of damage from potential spillages (Fig. 4). During the use of volatile agents in CPB, it is very important to analyze all gases that come in and out of the membrane oxygenators. In many cases, the percentage displayed on the vaporizer does not correspond to the VAA blood levels. Parts of these situations were described in a recent article about the correct adaptation of vaporizers to CPB circuits and how to avoid its most frequent problems [9••]. The proper monitoring of inhaled and exhaled gas fraction allows not only to monitor anesthesia level, but also to detect possible leakage in the circuit. Nevertheless, most current oxygenators have redundant venting systems that eliminate hazards of potential over pressurization inside the oxygenator, which makes it difficult to precisely measure VAA levels in the main exhaust port. In a prospective observational study, changes in sevoflurane plasma concentrations (SPC) and bispectral index values during CPB were evaluated together with patient temperature, hemodilution, oxygenator fresh gas flow, and sevoflurane concentration in oxygenator’s exhaust gas [12]. This study evidenced that SPC were higher during hypothermia and with increased fresh gas flow in oxygenator, while they were lowered by hemodilution. No correlation was found between SPC and sevoflurane concentration in the oxygenator exhaust port gas, suggesting that leakages occurred from the main port during measurements. Moreover, most scavenging system devices used to evacuate VAA from the OR could be the cause of a wrong reading line during monitoring (Fig. 5).

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heart rate, respiratory drive, and systemic blood pressure, are useless during CPB. Moreover, there are issues regarding pollution of the operating room (OR) by VAA administration during CPB, such as staff occupational exposure and depletion of atmospheric ozone, contributing to greenhouse effect [6, 7]. The aim of this review is to provide an overview of volatile agents’ administration to ensure maintenance of adequate depth of anesthesia during CPB, weighting risks, and benefits of this technique compared to TIVA.

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Fig. 1 Schematic representation of the use of volatile agents adapted to CPB machine. Adapted from [9]

that halogenated agents should only be used with PPL-based oxygenators.

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However, manufacturers’ guidelines specify that, above concentrations of 1.3 and 2.6% for isoflurane and sevoflurane, respectively, adjustments of inspired oxygen concentration and gas flow rates may be needed to achieve the desired gas transfer performance [9••, 16]. There are few reports of recall in more than 40 years of applicability of VAA during CPB. Nigro Neto et al. [11], evaluating the adverse events of this technique, recommended

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Fig. 2 Front view of vaporizer’s connections of the gas inlet (from blender) and outlet (to the oxygenator)

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Scavenging Systems

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There are several ways to reduce pollution in the OR: TIVA technique can be chosen to anesthetize the patient, use exposure controls guided by institutional guidelines and protocols (such as engineering department, administrators, and environment practice controls), and use of personal protective equipment. Engineers can be responsible for proper managing of scavenging systems (gas removal, deactivation), ventilation and key filler devices for vaporizers, besides monitoring the air quality. Administration can play an important role through education and offering medical surveillance. Clinicians can include the use of closed system and low-flow anesthesia in their practice, check for leaks in gas lines, and start anesthetic gas flow only after mask or airway device are applied to the patient [17].

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Fig. 3 Back view of vaporizer’s connections of the gas inlet (from blender) and outlet (to the oxygenator)

AUTHOR'S PROOF



was connected to the hospital’s central scavenging system, providing suction flow of 60 L/min and a negative pressure of 0.6 bar. To avoid negative pressure being transmitted to the oxygenator, an evacuation system has been used to reduce the suction flow to 20 L/min. Three-eighths inch PVC tube was placed on the outlet of the oxygenator and advanced into the suction tubing, leaving a circumference of 0.5 cm to provide pressure balance with atmospheric air and prevent damage to the oxygenator [20]. Care needs to be taken with such systems as excessive negative pressures can be generated and may produce a negative pressure gradient across membrane oxygenators, which might result in oxygenator’s membrane damage. Therefore, it has been recommended that this pressure gradient should be monitored and, since no specific proprietary equipment exists for these purposes, scavenging systems need to be constructed individually, bearing in mind the potential risks of using such systems [9••]. Nowadays, a new gas waste scavenging system, which consists of an activated charcoal filter, is under development and has been tested ex vivo being efficient in adsorbing the inhalational gas with no interference in the oxygenator’s performance [21•].

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Risks During CPB: Volatile Agents X Total Intravenous Anesthesia

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The choice of TIVA technique during CPB seems to be free of potential risks. However, hypotension and awareness are not unusual undesirable effects that can occur when only intravenous anesthetic agents are used, especially when cerebral monitoring is not properly used. Moreover, in a recent randomized controlled trial, a sevoflurane-based anesthesia was suggested to be associated with better short-term postoperative cognitive performance in on-pump cardiac surgery, compared to propofol [22].

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The most important factor to avoid environmental pollution in the OR seems to be the use of an efficient air conditioning and waste gas scavenging system. In this respect, keeping the air exchange rate of >10 per hour can provide concentrations of volatile anesthetics up to 75% lower when compared to OR’s where air exchange rate is