Transcript Slide 1

LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
LOW FLOW ANESTHESIA
Dr. Paul Zilberman
Israel, 2010
[email protected]
…or the long way of the oxygen from its
discovery till our patients…
JOSEPH PRIESTLEY
1733-1804
On August 1, 1774, he produced the “dephlogisticated
air”, known later as OXYGEN
A SHORT HISTORY
Inhalational anesthesia and closed system anesthesia are
almost the same age. Almost/closed anesthesia systems
have been in use since 1850. At that time the anesthetic
agent was cloroform, administrated via a closed system,
where KOH was utilized as a CO2 absorber. However, that
kind of CO2 absorption did not gain acceptance. Later, a
quick and effective method of CO2 absorption was developed
when the first soda-lime absorber was introduced in 1917.
A SHORT HISTORY (con’t…)
In the mid 50’s, when HAL was brought forth, the use of LFA
and closed system anesthesia diminished significantly.
This was largely due to the inherent problem of the first
generation HAL vaporizers, which was the unreliable delivery
of vapor at low FGF.
A SHORT HISTORY (con’t…)
Introduction of ISO in the early 1980’s gave way to a
renewed interest in LFA and closed circuit anesthesia. It
was further enhanced by the fact that anesthetic agents
are atmospheric pollutants, especially N2O, HAL, ENF,
and to some extent ISO.
The introduction of new low solubility agents, like DES and
SEVO, have initiated a renaissance in the use of LFA,
in order to contain costs associated with adapting FGF to
patient demand.
A FEW DEFINITIONS…
Low Flow Anesthesia (LFA) has been variously defined as an
inhalation technique in which a circle system with absorbent is used with a
fresh gas inflow of :
- less than the patient’s alveolar minute volume
- less than 1-1.5 l/min
- 3 l/min or less
- 0.5 – 2 l/min
- less than 4 l/min
- 500 – 1000 ml/min
- 0.5 – 1 l/min
Closed System Anesthesia is a form of LFA in which the FGF =
uptake of anesthetic gases and oxygen by the patient and gas sampling.
No gas is vented by the APL valve.
Dorsch and Dorsch
Understanding Anesthesia Equipment
A FEW DEFINITIONS (con’t)…
LFA:
Anesthesia delivery, where FGF is below 1.5 l/min, but maintained slightly
above the uptake of the patient. In addition, there is a low flow of excess
gas that leaves the circuit through the excess gas valve.
Closed Circle Anesthesia:
Anesthesia whereby FGF matches patient gas uptake and there is no
excess gas leaving the circuit by way of excess gas valve.
Minimal Flow Anesthesia:
Anesthesia whereby FGF is 0.5 l/min.
www.clinicalwindow.net
Ola Stenqvist MD. PhD
Anest. And Intensive Care
Goteborg, Sweden,
Sponsored by GE Health Care
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Professor Samuel Brody
The kind of laboratory used by Prof. Brody. It seems that
excellent minds can extract a lot from apparently little.
Graph relating metabolism to body size
“Bioenergetics and growth” 1945
Brody Formula for Oxygen
Uptake
VO2 = 10 x KG [kg] 3/4 [mL/min]
Where BW is body weight in kilograms
However, for clinical purposes, oxygen
consumption can be more easily calculated
as:
VO2 = 3.5 x BW [ml/min]
John W. Severinghaus
UPTAKE OF NITROUS OXIDE
VN2O = 1000 t-1/2 [mL/min]
Having 70% in N2O, with a BW of 70 kg.
That gives a – 1st minute uptake of 1000mL
- 200 mL/min uptake after 25 minutes
- 140 mL/min uptake after 50 minutes
- 90 mL/min uptake after 2 hours (120 minutes)
Source: Severinghaus JW, The rate of uptake
of nitrous oxide in man. J. Clin. Invest 1954
UPTAKE OF INHALATIONAL
AGENTS
Independent of the agent employed uptake can be
calculated using Lowe’s formula:
Van= f * MAC * λB/G * Q * t-1/2
[mL/min]
f = factor that defines the inhalation concentration that is
sufficient for unresponsive skin incision at ~MAC 1.3
λB/G = blood/gas partition coefficient
Q = cardiac output
t = time
Reproduced with permission from “Low
Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
THE REBREATHING SYSTEMS
REBREATHING describes a technique in which
non-consumed gases, contained in the exhaled air
are partially or completely re-routed back to the
patient during the following inspiration, purified from
CO2 AND admixed with a certain amount of fresh
gas.
THE REBREATHING SYSTEMS
Semi-open: VF ≥ MV
Semi-closed: MV > VF > Uptake
Closed:
VF = Uptake
Where:
VF = FGF
MV = Minute Ventilation
Uptake = Total gas uptake of the patient
THE “CATCH”
Using a FGF of 5 LPM and a vaporizer setting
of 1%, we give to the patient:
5000mL/min x 0.01 = 50 mL/min
What would be the vaporizer setting if we
would use a FGF of 1 LPM for the same 50 mL
to be delivered?
1000mL/min X ? = 50 mL/min
? = ……
? = 0.05
That means that the vaporizer should be
opened to 5%!
Sounds bizarre, isn’t it! It really does, because
we are not used to it! And yet, mathematics is
all what it is about!
Under these circumstances the patient
receives EXACTLY the same amount of gas,
in fact the same amount of MEDICINE! This is
called : BIOAVAILABILITY!
All over the world 5 X 1 =
=1 X 5
TECHNICAL ASPECTS
In LFA there are a few technical requirements. Typically
they are rather generic and more or less independent of
anesthesia machines used.
1. Circle rebreathing system with CO2 absorption
2. Accurate flow meters for adjustments of FGF below
1L/min
3. Gas tight breathing system. Recommended test leakage
should be below 150 mL/min at 30 cm H2O test pressure.
4. Ascending bellows, not rising up to the top of the bellows
chamber may indicate breathing system leakage. The
same is true for other alarms (LOW PRESSURE,
spirometry loop).
5. The breathing system should have minimal internal
volume and a minimum number of components and
connections.
6. Continuous gas monitoring MUST be employed. From
the clinical standpoint the measurement of expiratory
gas concentrations close to the Y-piece is of crucial
importance. That information is essential in controlling
the patient’s alveolar gas concentrations, whereas Fi
reflect the adequacy of gas concentrations into the
breathing circuit.
Hey! Does it sound very familiar with our usual anesthesia
machine?
“Introduction to low flow anesthesia” ppt. 2004, author unreachable
ADVANTAGES OF THE LFA
1. QUALITY OF PATIENT CARE
Anesthetic gases delivered using high FGF are
usually dry and cold. Reducing FGF makes gases
recirculating in the circle system more humid and
warmer.
With low FGF the gases repeatedly circulate through
the CO2 absorber. Consequently more heat and
humidity is produced through the chemical CO2
absorption process.
Breathing warm and humid gases is beneficial for
the patient because they help maintaining body heat,
prevent postoperative shivering and airway and
bronchial drying during ETT use.
Tracheal intubation bypasses the upper airways, thus,
eliminating the main effect of the inhaled gases : warming
and humidification. In the spontaneously breathing patient
the isothermic saturation boundary of the inspiratory
mixture (the point where the gases reach 370C and 100%
humidity) is located at the 4-5th generation of bronchi.
After tracheal intubation, as a consequence of the upper
airway bypass, this isothermic point is shifted down about
10cm in a bronchial region not suited to deal with dry and
cold gases and not suited to physiologically condition the
respiratory mixture (do you think now about the LMA in a
new way?).
2. ECONOMIC BENEFITS
Over 80% of anesthetic gases are wasted when flows of 5
L/min are used.
Several studies also prove that the use of low and minimal
flow anesthesia techniques can dramatically reduce the
(annual) costs of volatile anesthetics. Typically the reduction
of FGF from 3 L/min to 1 L/min results in savings of about
50% of the total consumption of any volatile agent.
clinicalwindow.net
Total cost of anesthesia depend on complex interactions
between anesthesia providers, patients, payers, technology and facility. Money makes the world go round!?
These costs comprise direct, indirect and intangible costs.
Direct costs, the ones that can be influenced by the anesthesia provider represent 3-5% of the total healthcare costs in
the US. (1993). If we consider the PACU expenses related
to the anesthesia process than the costs may go up to
10%.
While it is difficult to measure exactly the volatile agent cost
(mL/hour, different producers, vapor/mL liquid, delivery in
excess of uptake) as opposed to IV drugs, a larger survey
demonstrated that economies in volatile use going up to
90% can be achieved.
Pharmacoeconomics 2000,
June 17(6), 585-590
Definitions of different types of costs
Type of cost
Definition
Costs
Irreversible use of a resource
Direct costs
Costs of the material and labor
used for production
Fixed
Costs that remain the same no
matter many goods or services are
produced
Variable
Costs that change with the number
of goods or services that are produced
Indirect costs
Costs related to the consequences of
an event to society or an individual
Intangible costs
Costs of pain and suffering as a result
of illness or treatment
This is where unused gases ($,€,£,¥,etc.),
including O2, N2O go…
Copyright 1984-2011, James H Philip, all rights reserved
3. ENVIRONMENTAL BENEFITS
High flow anesthesia inevitably results in pollution of the
environment. N2O, for example, is a significant “green
house gas”, and is estimated to be responsible for about
10% of this effect. Hmmm, not so green after all…
Reduced FGF releases a lower amount of anesthetic
agents into the environment, resulting in less pollution.
All gases delivered from the anesthesia machines are lost to
the atmosphere. HAL, ENF, ISO contain chlorine. They are
believed to have significant ozone (O3) depleting potential.
The stability of these molecules permits their passage to the
stratosphere where increasing UV radiation causes dissociation to liberate free chlorine, which acts as a catalyst in the
break down of O3. This reaction is the major cause of destruc
tion of the O3 layer, especially over the South Pole.
N2O is also a catalyst in an analogous reaction.
While anesthetists thus have a clear duty to minimize the
use (release) of these chemicals, it has to be admitted that
our practice’s contribution to the global release is minimal.
DES and SEV contain no chlorine and appear to have no
greenhouse gas effects.
THE OTHER SIDE OF THE COIN
Disadvantages of LFA:
1.Limitations of currently used vaporizers:
Modern vaporizers are little different from those used
in the ’60s. They are designed for use with high FGF
with a consequent requirement for high thermal
capacity, temperature compensation and high accuracy. The use of LFA makes these characteristics
unnecessary but it also introduces the problem of
delivering an adequate quantity of volatile agent into
the breathing system.
2.Accumulation of unwanted gases into the
breathing system:
If you put little gas into the breathing system, little (or none)
will come out. As a result of this failure to flush gases out of
the system, any gases introduced which are not taken up
by the patient or absorbed chemically will tend to accu
mulate.
Such gases may be exhaled by the patient, be a contaminant of the medical gases or result from a reaction with the
chemical agents used for CO2 absorption.
Substances exhaled by the patient:
- Alcohol
- Acetone
- CO
- CH4
Therefore the use of LFA is contraindicated in patients
who are intoxicated, in uncompensated diabetic states or
who are suffering from CO intoxication.
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Specific safety features of anesthetic
techniques with reduced FGF
1. Improved equipment maintenance
2. The long time constant: sometimes the “good is
imbedded in the bad”!
3. Improved knowledge of the theory and practice of
inhalational anesthesia.
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
SO, HOW DO WE DO “IT”?
PRACTICALLY!
HOW TO ADJUST FGF AT
DIFFERENT PHASES OF LFA
Premedication, pre-oxygenation and induction of
sleep are performed according to the usual
practice. Concerning adjustment of FGF
anesthesia can be divided into 3 phases:
1. Initial HIGH flow
2. Low flow
3. Recovery
1.Initial HIGH flow phase
At the beginning of anesthesia high FGF of 5-6
LPM is necessary to wash out nitrogen (N2) from
the patients body tissues.
High initial flow facilitates the filling of the breathing
system with the desired gas composition which in
turn influences patient uptake and distribution of
the anesthetic agents. (Remember the formulas in
the beginning? The patient takes , after all, what
he/she needs, provided the provider is providing
enough!)
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
2. Low flow phase
After the high flow phase of 5-15 min, or when the target
gas concentrations has been achieved FGF can be
reduced at the desired low flow level. The lower the FGF the
greater the difference between the vaporizer setting and
inspired concentration of the anesthetic agent in the breathing
circuit will be.
With low FGF, time to reach the desired concentration in the
inspiratory gas will be prolonged.
Hence, monitoring of oxygen and anesthetic agent
concentration is essential and necessary in LFA.
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger
machines” by Prof.J.A.Baum
If the flow provided is too small for the patient’s
needs the bellow will gradually go down, down
down...
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Reproduced with permission from “Low Flow Anesthesia with Draeger machines”
by Prof.J.A.Baum
Low Fresh Gas Flow
Oxygen and Agent Considerations
JAMES H. Philip MEE MD CCE
Anaesthesiologist and Director of Bioengineering
Department of Anaesthesiology, Perioperative and Pain
Medicine Brigham and Woman’s Hospital
Medical Liaison for Anesthesia
Department of Anaesthesia
Harvard Medical School
Author of GasMan® and President of MedMan Simulations Inc., a
charitable Organization distributing gas man
http://gasmanweb.com
The following X slides have been added with the author’s permission
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
Copyright 1984-2011, James H Philip, all rights reserved
3. Recovery phase
At the end of anesthesia high FGF, usually 100% O2, is
necessary, to facilitate the washout of the anesthetic agent
from the patient and to remove the agent to the scavenging
system.
SOME COMMENTS…
Today, LFA is such a safe and simple procedure that
there are no reasons not to use it routinely. It can be
even argued that the use of unnecessary FGF
should be regarded as inappropriate. However, it is
still possible to find anesthesia departments where
LFA is not used in special situations (prone position,
thoracic surgery) or simply not at all.
The most common misconception about is that it
cannot be used in spontaneous breathing patients or
with those having an LMA. There is, however, no
rationale for such a view. The LMA has been shown
to be effective both in pediatric and adult LFA.
www.clinicalwindow.net
The majority of anesthesiologists, during their clinical practice
usually avoid working with FGF < 1 LPM due to their cultural
and practical beliefs including:
- requirement of in depth knowledge on gas laws and physics
applied to clinical anesthesia (oof, learn again?)
- pharmacokinetic and pharmacodynamic features of haloge
nated agents used until the mid 90’s
- lack of accuracy, expense and limited performance of anes
thesia machines utilized in anesthesia up to the end of the
90’s.
In 1994, in the United States, 90% of anesthesiologists utilized
2-5 l/min of FFG and only 12% of physicians used an FFG infe
rior to 1l/min.
The recent introduction on the market of low solubility halogenated agents and the technological development of high- performing
anesthesia ventilators, supplied with feed-back control systems
and high precision monitoring systems, make LFA/CSA safe and
feasible on a daily basis. This occurrence represents a great
advantage as far as clinical practice, cultural, environmental,
pharmacological, technological and cost savings concerns.
As with any other anaesthetic technique, LFA has its relative
and absolute contraindications, and anaesthetists have to
know the risks and limitations of this method. The potential
risks associated with low-flow anaesthesia are accidental
hypoxia, hypercapnia, inadequate depth of anaesthesia
and the accumulation of potentially toxic trace gases. A
basic knowledge of the uptake and distribution of anaesthetic gases and appropriate patient monitoring such as pulse
oxymetry, capnometry, inspired oxygen monitoring and
anaesthetic gas analysis are required for safely delivering
general anaesthesia with low fresh gas flows.
The extent of patient monitoring, however, is similar to that
for any other anaesthetic technique. Sounds familiar again?
Awareness during
anesthesia
“It can’t be! You should be sleeping!”
The end? Not quite…A few
answers from…
FINLAND, Dr. Riku Aantaa
MD, DMedSci
former President of the Finnish Society of Anesthesiologists
“…I have the understanding (we even did a survey some 5
years ago) that low flow (FGF 0.5-1.5 LPM) is standard
care throughout my country”.
USA, Dr. Jerrold Lerman
Jerrold Lerman MD,
Clinical Professor of Anesthesia
Women and Children's Hospital of Buffalo, SUNY at Buffalo, and
University of Rochester, Rochester, New York
“I use flows about 1-1.5 LPM”
NORWAY, Dr. Per Meinich
President
The Norwegian Society of Anaesthesiology
“…has approximately 50 surgical hospitals, and
with the exception of some small, private clinics,
they all perform gas anesthesia. Each hospital
decides on which machines they want to use, and
each hospital has its own guidelines. To my
knowledge, all hospital which utilize gas
anesthesia do so in close loop, low flow systems”.
SOUTH KOREA, Dr. Hong Seuk Yang :
MD, Department of Anesthesiology and Pain Medicine, Asan Medical
Center, College of Medicine, University of Ulsan
“Low flow anesthesia technique is more popular in Korea
from 5 years ago, after the introduction of SEVO and DES.
Flow rate is maintained at 2LPM (O2: N2O 1:1). Usually we
don’t decrease the flow rate below 2 LPM”
CANADA, Dr. Glenn McGuire
Department of Anesthesia
Toronto Western Hospital
“The circuit is checked at the beginning of the day for
leaks (leak must be under 180mL/min). I use DES with N2O
and O2 at a total flow of 1 LPM for both mechanical
ventilation and spontaneous breathing.
Years ago anesthetists used to turn up the flows for
spontaneous breathing. This is an outdated concept and is
no longer practical. Of course, with spontaneous breathing
I always use CPAP”
UNITED KINGDOM,
Dr. Andrew McHutchon
MB ChB FRCA,
Anesthesia & Intensive Care.
Northumbria Healthcare , UK .
In my hospital we have a very strict approach to gas economy. The
reason for no recent publications is that virtually all the information we
need is already known. Anyone who uses high flows is wasting money
and polluting the environment without any benefit to patients. If we
need more information we should ask the question:" what happens to
inhalational agents in the upper atmosphere?” A similar question for
TIVA, “what substances do the manufacturers of Propofol and
Remifentanil release into the environment?”
If the anesthetist understands the kinetics of his system, the patient
gets a good anesthetic with enough agent.
ITALY, Dr. Amato del Monte:
Dr. Amato De Monte
Director of Anaesthesia & I.C.U. Department
Azienda Ospedaliero Universitaria
S. M. Misericordia – Udine
“The breaking method to introduce closed system anesthesia in my
hospital was the implementation of our anesthesia machines with the
ZEUS…This fact obliged my colleagues to face the topic. I can’t give
[you] an answer of the penetration [of LFA] in Italy. Anyway, the
majority of a small group, 400 anesthesiologists, interviewed with the
simple question considered low flow a FGF of 3 LPM”.
It’s up to you
If you want to be
Like the guy in the figure
All the time
With the finger on the
trigger…
Or enjoy a cozy sleep
While the machine does gently “beep”…
In a simple way, we can say…
The LFA is the mathematical art of volatile
anesthesia…
Questions anyone?