Chat with us, powered by LiveChat Assignment #1; Using uploaded article 13 Write a one page annotated bibliography using APA format . | Max paper
  

Assignment #1; Using uploaded article 13

Write a one page annotated bibliography using APA format .

Assignment #2;  

Write a 2 page paper on how COVID-19 has impacted the world, strategies healthcare organizations implemented, treatments provided, and what are key factors you learned about COVID-19. You must include 3-4 references in your paper. Please utilize the articles from the course for your references. 

Using Anesthesia Machines as Critical Care Ventilators During the
COVID-19 Pandemic

Paul N Austin and Richard D Branson

Somewhere between 30% and 89% of patients with COVID-19 admitted to a critical care unit require

invasive mechanical ventilation. Concern over the lack of adequate numbers of critical care ventilators

to meet this demand led the U.S. Food and Drug Administration to authorize the use of anesthesia

machines as critical care ventilators. The use of anesthesia machines for ventilating patients with

COVID-19 is overseen by an anesthesia provider, but respiratory therapists may encounter their use.

This article reviews the fundamental differences between anesthesia machines and critical care ventila-

tors, as well as some common problems encountered when using an anesthesia machine to ventilate a

patient with COVID-19 and steps to mitigate these problems. Key words: COVID-19; anesthesia; me-
chanical ventilation; critical care. [Respir Care 2021;66(7):1184–1195. © 2021 Daedalus Enterprises]

Introduction

Somewhere between 30% and 89% of patients with

COVID-19 who are admitted to a critical care unit require

invasive mechanical ventilation.1 Concern over the lack of

adequate numbers of critical care ventilators to meet this

demand led the U.S. Food and Drug Administration to author-

ize the use of anesthesia machines (sometimes termed anesthe-

sia workstations) as critical care ventilators.2 This may occur

by repurposing operating rooms as intensive care areas or by

relocating anesthesia ventilators to the ICU. In both cases, the

stated simplicity belies the important technical differences in

devices and skills required for safe and effective operation.

Anesthesia machines are multi-component devices in-

tended to deliver oxygen (O2) and other gases (eg, nitrous ox-

ide and air) along with volatile inhaled anesthetic agents. The

anesthesia machine often includes a physiologic monitor, cap-

nograph, anesthetic gas monitor, and additional monitors. A

mechanical ventilator is integrated into the anesthesia machine

as one of these components. Anesthesia machines may effec-

tively ventilate critically ill patients but differ significantly

from critical care ventilators both in design and operation.3,4

Anesthesia providers (eg, certified registered nurse anesthetists

or physician anesthesiologists) should oversee the use of anes-

thesia machines for patients with COVID-19,3 but respiratory

therapists are likely to be involved in their monitoring and use

in the critical care unit.

This article provides critical care respiratory therapists

with a review of the fundamental differences between anesthe-

sia machines and critical care ventilators. Also examined are

the common problems encountered when using an anesthesia

machine to ventilate a COVID-19 patient and steps to mitigate

these problems. Volatile anesthetics are sometimes adminis-

tered to patients with severe asthma5 and seizure disorder6 in

critical care units. A discussion of this practice is beyond the

scope of this article. This information is not intended to

replace formal training or manufacturer instructions. Like crit-

ical care ventilators, there are many manufacturers and models

of anesthesia machines, and readers must follow manufacturer

instructions and other guidelines. Readers are referred else-

where for detailed directions on how to use an anesthesia

machine as a critical care ventilator.2-4

Fundamental Differences Between Critical Care

Ventilators and Anesthesia Machines

Critical care ventilators deliver breaths containing a vari-

able O2 concentration (FIO2), typically set from 0.21 to 1.0.

Depending on the ventilation mode selected, the flow of gas

Dr Austin is affiliated with Texas Wesleyan University, Fort Worth,

Texas. Mr Branson is affiliated with the Division of Trauma and Critical

Care, Department of Surgery, University of Cincinnati Medical Center,

Cincinnati, Ohio.

Mr Branson is Editor-in-Chief of RESPIRATORY CARE. He discloses

relationships with Mallickrodt Pharmaceuticals, Pfizer, Ventec Life

Systems, Vyaire, and Zoll Medical. Dr Austin has no conflicts to

disclose.

Correspondence: Paul N Austin PhD CRNA, 14311 Harvest Moon Rd,

Boyds, MD 20841. E-mail: [email protected]

DOI: 10.4187/respcare.08799

1184 RESPIRATORY CARE � JULY 2021 VOL 66 NO 7

from the ventilator can be triggered by patient effort, by set-

tings controlled by the operator (eg, delivering a specified

number of breaths per minute), or a combination of these 2

options. A critical care ventilator is capable of a number of

modes of ventilation as well as volume, pressure, and adapt-

ive pressure breaths. The critical care ventilator also delivers

PEEP and allows control of inspiratory flow, inspiratory

time, rise time, and flow termination criteria. Critical care

ventilators include a dizzying array of alarms and displays of

monitored variables based on airway pressure and flow.

An anesthesia machine delivers oxygen and other gases

such as air and nitrous oxide (an analgesic that has some an-

esthetic properties) along with volatile (also called “inhala-

tional”) anesthetics (Fig. 1). Patients may also breathe

spontaneously with no ventilatory support. A positive pres-

sure breath can be delivered either manually by squeezing a

breathing bag that is part of the machine or by using the

integrated mechanical ventilator. The ventilator may range

from a simple bellows-in-a-box device to one approaching

the sophistication of a critical care ventilator and deliver

patient-triggered breaths. The anesthesia machine may con-

tain a gas and anesthetic monitor, analyzing the inspiratory

and expiratory concentrations of O2, CO2, and the volatile

anesthetic as well as a physiologic vital signs monitor.

Unlike the critical care ventilator, the anesthesia machine is

intended to be operated with an anesthesia provider in

attendance at all times.

Two of the 5 major differences between critical care and

anesthesia machine ventilators are related: potential for

rebreathing of exhaled gases and CO2 absorption. The third

major difference is the use of a scavenging system to pre-

vent pollution of the room with inhaled anesthetics. The

fourth major difference is that FIO2 may be set using gas

flow meters on older anesthesia machine, while FIO2 is

directly set on a critical care ventilator or newer anesthesia

ventilator. The final major difference is that manual and

mechanical ventilation can be delivered using the anesthe-

sia machine.7 Table 1 contains a summary of these and

other differences between an anesthesia machine and a crit-

ical care ventilator. These 5 major differences are discussed

further below.

Non-, Partial, and Complete Rebreathing

The critical care ventilator operates as a non-rebreathing

system where exhaled gases are vented to the atmosphere.

The anesthesia machine can operate as a non-rebreathing

(also called an open) system where all of the exhaled gases

are vented to the scavenging system, as a partial rebreathing

(also called semi-closed) system where a portion of the

exhaled gases are recycled, or a complete rebreathing (also

called a closed) system where all of the exhaled gases are

recycled. The anesthesia machine is rarely used as a com-

plete rebreathing system in the operating room; in that

Fig. 1. A modern anesthesia machine (Aisys, GE Healthcare). There are many design variations.

ANESTHESIA MACHINES FOR CRITICAL CARE

RESPIRATORY CARE � JULY 2021 VOL 66 NO 7 1185

setting, the anesthesia machine is often used as a partial

rebreathing system to help conserve volatile anesthetics, to

reduce costs, and to conserve heat and moisture.7 When

used as a partial rebreathing system, the fresh gas flow (ie,

the amount of gas in L/min continuously entering the

breathing circuit set by the operator, not the flow of gas

during inhalation) is less than the patient’s minute ventila-

tion, and the CO2 contained in the portion of the patient’s

exhaled breath is chemically removed by the CO2 absorb-

ent.7 In contrast, the anesthesia machine is used as a non-

rebreathing system when used with patients with COVID-

19. This is primarily done to mitigate problems resulting

from excess moisture buildup in the inspiratory limb of the

breathing circuit when the anesthesia machine is used with

these patients.3,4 This is discussed further below.

Factors or controls determining whether the anesthesia

machine is operating as a complete, partial, or non-

rebreathing system include the fresh gas flow, adjustment

of the adjustable pressure-limiting valve if the patient is

breathing spontaneously or being manually ventilated (or

analogous valve located with the integrated mechanical

ventilator), use of one-way inspiratory and expiratory

valves, and the presence of the CO2 absorber.
7 Table 2

contains an explanation of terms used when discussing the

anesthesia machine and rebreathing. Fresh gas flow and the

circle system are discussed further below.

Fresh Gas Flow. Oxygen and other gases such as air and ni-

trous oxide are supplied from central pipeline sources or

tanks mounted on the anesthesia machine. The anesthesia

machine is disabled if there is a loss of the O2 supply pres-

sure. This is a safety system to prevent hypoxic gas mixtures

being delivered in the absence of an O2 supply. Regulators in

the anesthesia machine reduce the pressure of the supplied

gases prior to delivery. The flow of gases (O2, nitrous oxide,

air) to the patient are regulated by the anesthesia provider

directing setting the flows of the gases on flow meters or by

setting variables such as total flow and FIO2.
7 This gas flow

is termed the fresh gas flow and is the amount of new gas

added to the breathing circuit each minute.

High fresh gas flow is associated with minimal rebreath-

ing. High fresh gas flows (ie, greater than the patient’s mi-

nute ventilation) are used when the anesthesia machine is

operated as a non-rebreathing system, which is recom-

mended for patients with COVID-19 to help minimize ex-

cessive moisture production in the breathing circuit.3,4

Table 1. Important Differences Between an Anesthesia Machine and a Critical Care Ventilator

Anesthesia Machine Critical Care Ventilator

Major differences

Can operate as a non-rebreathing, a partial rebreathing, or a complete

rebreathing system by using a circle breathing system where exhaled gases

can be recycled and reintroduced with fresh gas flow

Operates as a non-rebreathing system; does not use a circle system

Equipped with a CO2 absorber (if depleted, may result in increased inspira-

tory CO2 and hypercapnia)

No need for a CO2 absorber

Can deliver manual or mechanical ventilation Delivers only mechanical ventilation

FIO2 determined by settings on the gas flow meters or an FIO2 control The operator directly sets the FIO2
Equipped with a scavenger system that prevents pollution of room with

anesthetics

No need for a scavenger system

Other differences

Operated by a continuously present anesthesia provider, maintained by an

anesthesia provider or anesthesia technician

Operated and maintained by a respiratory therapist

Delivers O2 and other gases such as air and nitrous oxide as well as volatile

(inhaled) anesthetics (eg, isoflurane, sevoflurane, desflurane)

Typically delivers only O2 and air

Requires an operator in attendance at all times Does not require an operator to be with the device at all times

Designed for intermittent use during a single day with multiple patients Designed for continuous use for days with the same patient

Alarm volume may not be loud enough to be heard in the critical care unit Alarm volume designed to be heard in a critical care unit

Alarms do not interface with the hospital nurse call alarm system Alarms may generate alerts in the hospital nurse call alarm system

May contain residual amounts of anesthetic agents in the breathing system

(remote risk of malignant hyperthermia)

Does not contain residual amounts of anesthetic agents

Often has an integrated gas and anesthetic monitor May contain or interface with a gas monitor

May have a physiologic monitor Typically does not have an integrated physiologic monitor

May interface with an electronic anesthesia record (that ultimately

becomes part of the patient record) but not directly with the patient elec-

tronic medical record

May interface directly with the patient electronic medical record

Rarely used with a heated humidifier Commonly used with a heated humidifier

From References 2-4,7.

ANESTHESIA MACHINES FOR CRITICAL CARE

1186 RESPIRATORY CARE � JULY 2021 VOL 66 NO 7

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ANESTHESIA MACHINES FOR CRITICAL CARE

RESPIRATORY CARE � JULY 2021 VOL 66 NO 7 1187

More rebreathing occurs as the fresh gas flow is decreased.7

To emphasize, fresh gas flow is the amount of gas in L/min

continuously entering the breathing circuit set by the opera-

tor and not the flow of gas mixture provided by the me-

chanical ventilator during inspiration. The flow of the gas

mixture from the mechanical ventilator during inspiration

is determined by the settings on the ventilator.

If desired by the anesthesia provider, the fresh gas flow

may pass through vaporizers before entering the breathing

circuit. These vaporizers convert the liquid volatile anes-

thetics to a vapor. The vaporizers allow delivery of the an-

esthetic at the desired concentration. Vaporizers should be

removed or drained on anesthesia machines repurposed as

critical care ventilators for patients with COVID-19.3,4 The

fresh gas flow then flows directly into the circle system.7

Circle System. The circle system is designed to permit

rebreathing of exhaled gases while chemically absorbing

exhaled CO2. The flow of gas to the patient circuit is con-

tinuous (ie, the fresh gas flow). The simplified patient cir-

cuit or circle system includes the adjustable pressure-

limiting valve, breathing bag, CO2 absorber, one-way

inspiratory and expiratory valves, breathing circuit (usually

22-mm corrugated tubing), and a Y-connector with a heat

and moisture exchanging filter (HMEF) (Fig. 2). The ad-

justable pressure-limiting valve prevents pressure buildup

in the system if fresh gas flow significantly exceeds the ox-

ygen consumption of the patient. An analogous valve on

the integrated mechanical ventilator performs this function

if the patient is mechanically ventilated.7

CO2 Absorption

There is no need for CO2 absorption with a critical care

ventilator as no portion of the exhaled gases are recycled.

Exhaled gases containing CO2 can be recycled using an anes-

thesia machine. The CO2 in the exhaled breath must be

removed to prevent hypercapnia. CO2 is removed using an ab-

sorbent material often soda lime. This commonly used CO2
absorbent contains primarily calcium hydroxide along with

small amounts of additional chemicals such as sodium hy-

droxide. The exhaled breath passes through the granular ab-

sorbent before returning to the patient.7

The absorbent does not soak up CO2 like a sponge.

Rather, CO2 is chemically removed by converting it to cal-

cium carbonate in a series of chemical reactions. These

reactions produce heat and water (Table 3). This water pro-

duction may be excessive in patients with COVID-19 due,

High
pressure
gas
source

Flow meters O2,
air, N2O or FIO2
control

Fresh gas
flow inlet

Anesthetic
vaporizer

CO2
absorber

Inspiratory
limb

Inspiratory
one-way
valve

Expiratory one-
way valve

To
scavenger

APL
valve

Breathing
bag

Bag/vent
selector

Ventilator

Expiratory
limb

Ventilator
outflow
valve

To
scavenger

Y-piece

Gas
monitor

Gas
sample
tubing

HMEF

ETT
and
patient

Fig. 2. A simplified drawing of the anesthesia machine circle system. APL ¼ adjustable pressure-limiting; ETT ¼ endotracheal tube; HMEF ¼
heat-and-moisture exchanging filter.

Table 3. Series of Chemical Reactions to Remove CO2 From

Exhaled Breaths by Soda Lime

CO2 + H2O ! H2CO3
H2CO3 + NaOH ! NaHCO3 + H2O
NaHCO3 + Ca(OH)2 ! CaCO3 + H2O + NaOH + Heat

Note that water and heat are by-products of these reactions. From Reference 8.

H2CO3 ¼ carbonic acid
NaOH ¼ sodium hydroxide
NaHCO3 ¼ sodium bicarbonate
Ca(OH)2 ¼ calcium hydroxide
CaCO3 ¼ calcium carbonate

ANESTHESIA MACHINES FOR CRITICAL CARE

1188 RESPIRATORY CARE � JULY 2021 VOL 66 NO 7

in part, to an increased minute ventilation and elevated CO2
production. The granules of the CO2 absorbent typically

contain an indicator. This enables the granules to change

color (such as from white to blue or purple) when the

absorbent’s capacity has been exhausted. The life of the ab-

sorbent is highly variable, depending on factors including

the type of absorbent, manufacturer, minute ventilation,

patient CO2 production, and the fresh gas flow.
7,8

Ability to Deliver Manual and Mechanical Ventilation

The critical care ventilator only delivers mechanical

breaths. If required, manual ventilation is accomplished

using a separate, manual resuscitator. A non-self-inflating

bag is part of the anesthesia machine. This bag is kept

inflated by the fresh gas flow. Closing the adjustable pres-

sure-limiting valve and squeezing the bag delivers a manual

breath to the patient via endotracheal tube or face mask. An

O2 flush valve is present in the anesthesia machine and,

when depressed, delivers 100% O2 into the patient circuit at

a flow of 35–70 L/min. This high flow of O2 helps when

manually ventilating a patient using the anesthesia machine

with a face mask in the presence of leaks. The anesthesia

machine does not initiate mechanical ventilation automati-

cally.7 The breathing bag/ventilator switch and ventilator

controls must be set correctly before mechanical ventilation

will begin.

Setting the FIO2

Anesthesia machines used as critical care ventilators

must be able to deliver air due to the consequences of pro-

longed breathing of 100% O2. The FIO2 is directly set on

the critical care ventilator. This may be done directly on

more modern anesthesia machines, but some anesthesia

machines require the use of settings on the flow meters to

determine the FIO2. For instance, if 1 L/min each of O2 and

nitrous oxide are delivered, the FIO2 is 0.5. If there is a flow

meter for air, then setting the O2 and air flow meters will

control the FIO2 (Table 4, Table 5).

FIO2 is continuously monitored using an O2 analyzer

with high and low alarms. Modern anesthesia machines are

designed to make it difficult to deliver hypoxic gas mix-

tures if the system is properly functioning.7 It is neverthe-

less possible to unknowingly change the FIO2 setting. This

underscores the need for the operator to be near the anesthe-

sia machine.

Scavenging System

There is no need for a scavenging system with a critical

care ventilator as the device does not deliver inhaled anes-

thetics. With an anesthesia machine, exhaled gases that are

not rebreathed when operating as a partial or open system

exit the circle system. These exhaled gases exit the circle

system via the adjustable pressure-limiting valve or another

analogous valve in the integrated mechanical ventilator

through a system that directs these gases out of the room, as

chronic exposure to personnel may be toxic.7 The scaveng-

ing hose leading from the anesthesia machine to the wall

should be removed if the anesthesia machine is used to ven-

tilate a patient with COVID-19 unless the machine will not

function properly without it attached to a wall suction

source.3

Excessive Water Production With Rebreathing

Partial rebreathing with lower fresh gas flows, often

done in the operating room, requires the CO2 absorbent to

chemically remove CO2 from the portion of the exhaled

breath that is rebreathed. In the operating room, this side

effect of CO2 absorption increases the temperature and hu-

midity of inspired gases. Water and heat are by-products of

the reactions of the chemicals in the absorbent and CO2.
7,8

This water production is a major problem in patients with

COVID-19 because they are often hypermetabolic (ie, high

CO2 production) and thus require a high minute ventilation.

Large amounts of water are produced, which can occlude

the patient circuit and interfere with flow sensors in the

Table 4. Basic Principles for Determining FIO2 Using Air and O2
Flow Meter Settings on an Anesthesia Machine

Basic Principles

Flow meter settings are used on some anesthesia machines to determine

the FIO2 .*

Fresh gas flow is the total flow per min of all gases (eg, O2 and N2O, or

O2 and air).

21% of air is O2.

If only air is used, the FIO2 will be 0.21.

FIO2 is calculated as follows when using air and O2:

FIO2 ¼ Air flow � 0:21
ð Þ þ O2 flow � 1:0ð Þ

Fresh gas flow
.

* For an adult patient with COVID-19, fresh gas flow should be equal to or higher than the

patient’s minute ventilation. See the manufacturer recommendations.9 Some have reported using

a fresh gas flow of 150% of minute ventilation or 10 L/min with these patients.3

N2O ¼ nitrous oxide

Table 5. Air and O2 Flow Meter Settings With Resultant FIO2 Using

a Fresh Gas Flow of 10 L/min

O2 Flow Meter

Setting, L/min

Air Flow Meter

Setting, L/min

O2 Content of Air

at This Flow Meter

Setting, L/min

FIO2

9 1 0.21 0.92

5 5 1.05 0.61

4 6 1.26 0.53

1 9 1.89 0.29

ANESTHESIA MACHINES FOR CRITICAL CARE

RESPIRATORY CARE � JULY 2021 VOL 66 NO 7 1189

anesthesia machine.3 The anesthesia machine should be

operated as a non-rebreathing (open) system to mitigate

the problem of excess water production from the CO2
absorbent.3,4

Fresh gas flows greater than the patient’s minute ventila-

tion (such as 1.5 times higher) are recommended for

patients with COVID-19. Manufacturers and others offer

guidance on setting the fresh gas flow (Fig. 3). Some

rebreathing may occur even with high fresh gas flows, and

the CO2 absorbent should be monitored for color change

indicating depletion and replacement as needed. Using a

capnograph to detect excess inspiratory CO2 may help

determine whether there is unwanted CO2 rebreathing.
3,4,7

Heated Humidifiers, HMEFs, and the

Anesthesia Machine

Heated humidifiers are rarely used with anesthesia

machines. It may not be possible to attach a heated humidi-

fier to an anesthesia machine because the moisture produced

may interfere with its operation. Therefore, an HMEF is

placed between the endotracheal tube and the patient connec-

tor to help conserve heat and moisture (Fig. 4). Importantly,

when using an anesthesia machine with a COVID-19 patient,

a heat-and-moisture exchanger with an integrated bacterial

and viral filter should be used. This positioning helps protect

the anesthesia machine from contamination with COVID-19

and from excessive moisture that can affect flow sensors in

the machine. This positioning also protects the small-bore

sample tubing leading to the gas monitor, thus helping pro-

tect the monitor from contamination. The HMEF may

become occluded due to copious secretions or by the added

moisture from the process of CO2 absorption. This may

result in a slow increase in resistance. The HMEF should be

routinely inspected and replaced as needed. Protection of the

anesthesia machine is also facilitated by placing a filter on

the end of expiratory limb where it connects to the anesthesia

machine. Decontamination of the anesthesia machine is

described in the manufacturer’s instructions.3,4

United States Food and Drug Administration
Ventilator Supply Mitigation Strategies: Letter to Health Care Providers
https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency
use-authorizations-medical-devices/ventila tors-and-ve ntilator-accessories-euas

Manufacturers
Dräger Medical
Letter
https://www.draeger.com/Library/Content/Draeger Customer Letter-COVID-19-
Usage of Anesthesia devices for long term ventilation-2020-03-18.pdf

COVID-19 general information
https://www.draeger.com/en-us us/Home/novel-coronavirus-outbreak#anesthesia

GE Healthcare
Letter
https://www.gehealthcare.com/-
nssmedia/3c655c83bd6b427 e9824994c12be0da5.pdf?la=en-us

COVID-19 general information
https://www.gehealthcare.com/corporate/covid-19

Anesthesia machines
https://www.gehealthcare.com/products/Anesthesia-Delivery-Systems-User-Resources

Mindray
COVID-19 general information
https://www.mi nd raynorthameri ca.com/covid-19-response/

Getinge
General information
https://www.getinge.com/dam/hospitaVdocuments/markeling-sales/customer
letters/enqlish/mcv00103387 reva covid-
19 customer letter long term ventilation with flow-en-us.pd!

Professional Organizations
American Association for Respiratory Care
COVID-19 News & Resources

COVID-19 News & Resources

American Association of Nurse Anesthetists …

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