Maquet FLOW-I User manual

POCKET GUIDE
FLOW-i version 2.1
MODES OF VENTILATION
POCKET GUIDE
FLOW-i
WAVEFORMS AND LOOPS

Table of contents
4|Introduction
1
7|Background and basic concepts
2
15|Waveforms and loops
3
26|Capnogram, end-tidal CO2 monitoring
4
30|Other factors
5
53|References and suggested reading
6
3
1.1
EMPTY

Scope
This document is intended to function as a guide when working with
the FLOW-i anesthesia system. The main focus lies on understanding
and analyzing waveforms and loops presented on the control panel.
Other pocket guides describe other aspects of the FLOW-i system.
This pocket guide only covers selected topics and cannot r eplace
the user’s manual. For detailed information, please always r efer to
the latest corresponding version of the user's manual.
4
1.1
INTRODUCTION

Waveforms and loops
Waveforms and loops are used to visually display the curr ent lung
status of the patient. Their appearances are based on real-time values
and are continuously updated.
Specifically, this pocket guide will provide the user with the following:
A background on the real-time values used primarily to illustrate
the breathing cycle; pressure, flow, volume and CO2-level.
A review of the ventilation modes and the associated waveforms
and loops.
A review of external factors affecting the appearance of waveforms
and loops.
5
1.1
INTRODUCTION

Breathing
Breathing is a complex process, neurally controlled by a specialized
centre in the brain stem, located just under the brain. The brain stem
comprises, together with the brain and spinal cord, the central
nervous system (CNS).
The breathing center automatically regulates the rate and depth of
breathing; specific organs regularly provide feedback pertaining to
the metabolic requirements of the body.
When the breathing process is compromized, e.g. during general
anesthesia, breathing function is maintained by delivering air into
the lungs using an increase in the external pressure.
Operators of the FLOW-i system control ventilation by having the
system deliver gas using pressure. This pressure can either be set
directly to create a flow into the lungs (pressure control), or indirectly
so by defining a target volume to be administered with every breath
(volume control). Other automatic breathing modes are variants or
combinations of pressure control and volume control. FLOW-i, when
fully equipped, supports the following ventilation modes:
Pressure Control
Volume Control
PRVC
Pressure Support
SIMV (PC) + PS
SIMV (VC) + PS
AFGO
Manual ventilation
6
1.1
INTRODUCTION

Estimated values and set parameters
This chapter describes three important estimated values that are
used to generate waveforms and loops on the contr ol panel:
Pressure
Flow
Volume
Pressure
Volume Flow
Pressure(dierences)
generate a ow by
causing a displacement
of gas.
Flow over time is the
administered volume.
Increasing lung pressure
causes volume expansion.
This is referred to as
compliance.
Note: The CO2 waveform, the capnogram, is treated in a seperate
section later in this guide.
7
1.1
BACKGROUND AND BASIC CONCEPTS

Linear and exponential change
Linear change
A linear type increase, or decrease, is characterized by a straight
line in a graphical diagram (A). The change is constant irr espective
of the current value.
This is the case with the volume waveform in volume contr ol. The
increase in volume is constant when comparing any section of the
inspiratory phase.
Exponential change
An exponential type increase, or decrease, is characterized by a
parabolic (arched) line in a graphical diagram (B). The rate of change
is dependant on the current value.
The gas flow during expiration can be used to illustrate this. At the
start of expiration the lungs are filled with gas. When the expiratory
valve opens, the large pressure difference causes gas to rapidly flow
from the lungs.
At the end of expiration, the pressure difference causing the flow is
small, and flow is consequently lower. Flow is thus dependant on
the current value of pressure.
AB
22
11
33
8
1.1
BACKGROUND AND BASIC CONCEPTS

Pressure
Pressure, in the context of ventilation, refers to the compression of
gas. A mechanical ventilation system uses pressure to create a
pressure gradient resulting in the displacement, movement, of gas
into the lungs. This movement of gas is r eferred to as 'flow'.
The pressure waveform on the control panel describes the external
pressure used to deliver gas to the patient. It is measur ed inside the
FLOW-i.
9
1.1
BACKGROUND AND BASIC CONCEPTS

Pressure control - pressure waveform
In pressure control, pressure is constant during the entire inspiration.
Volume control - pressure waveform
In volume control, pressure increases during inspiration, thus always
maintaining a pressure gradient between delivery pressure and lung
pressure.
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1.1
BACKGROUND AND BASIC CONCEPTS

Flow
Flow, or movement of gas, is the r esult of a pressure gradient. The
value of flow is proportional to the pressure difference. As the
difference, i.e. pressure gradient, approaches zero, flow decreases.
The flow waveform on the control panel describes the amount of
gas per unit of time that moves into, or out of, the patient. Common
units are l/min and ml/sec.
By convention, inspiratory flow is positive and expiratory flow is
negative.
15
10 20
25
5
1
15
10 20
25
5
1
5
Flow
Delivery pressure Lung pressure
11
1.1
BACKGROUND AND BASIC CONCEPTS

Pressure control - flow waveform
In pressure control, the numeric value for flow is highest at the
beginning of inspiration and at the beginning of expiration. This is
when the pressure gradient is largest. Inspiration and expiration can
both be described by an exponential function.
Volume control - flow waveform
In volume control, flow is made constant during inspiration by
continuously increasing the pressure used when delivering gas. This
section is described by a linear function.
Expiratory flow in volume control can be described by an exponential
function.
12
1.1
BACKGROUND AND BASIC CONCEPTS

Volume
The delivered volume is either specified by setting the tidal
volume/minute volume in volume control mode, or is a subsequent
effect of setting the pressure level above PEEP in pressure control
mode. In pressure control, lung and thorax characteristics such as
resistance and compliance effect the final delivered volume.
13
1.1
BACKGROUND AND BASIC CONCEPTS

Pressure control - volume waveform
Delivered volume increases exponentially in pressure control, slowing
down as the pressure gradient becomes smaller. There is no
inspiratory pause, expiration follows immediately after inspiration.
Volume control - volume waveform
Delivered volume increases linearly in volume control. The inspiratory
pause is evident from the plateau between inspiration and expiration.
14
1.1
BACKGROUND AND BASIC CONCEPTS

Waveforms
Waveforms allow for a quick assessment of how ventilation
parameters interact and how patient dependant factors contribute
to their appearance.
Changes in resistance and compliance are immediately reflected in
the waveform (and loop) appearance.
15
1.1
WAVEFORMS AND LOOPS

Pressure control, waveform example
b
e
a
c
d
f
h
i
j
k
l
m
n
o
g
xz
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1.1
WAVEFORMS AND LOOPS

Pressure-Time waveform. Points and regions of interest
a. Start of Inspiration
b. Early inspiratory pressure
c. End inspiratory pressure
d. Early expiratory pressure
e. End expiratory pressure
x. Inspiration
z. Expiration
Flow-Time waveform. Points and regions of interest
f. Peak inspiratory flow
g. Decelerating flow
h. Peak expiratory flow
i. The slope represents the decreasing
flow from the patient during expiration
j. End expiratory flow
x. Inspiration
z. Expiration
Volume-Time waveform. Points and regions of interest
k. Start of inspiration
l. The slope represents current delivery
of inspiratory tidal volume
m. End inspiration
n. The slope represents current patient
delivery of expiratory tidal volume
o. End expiration
x. Inspiration
z. Expiration
17
1.1
WAVEFORMS AND LOOPS

Volume control, waveform example
xy z
b
e
a
c
df
h
i
j
k
l
m
n
o
p
q
g
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1.1
WAVEFORMS AND LOOPS

Pressure-Time waveform. Points and regions of interest
a. Start of Inspiration
b. Inspiratory rise time
c. Peak inspiratory pressure
d. Early inspiratory pause pressure
e. End inspiratory pause pressure
f. Early expiratory pressure
g. End expiratory pressure
x. Inspiration
y. Pause time
z. Expiration
Flow-Time waveform. Points and regions of interest
h. Peak inspiratory flow
i. Zero flow phase
j. Peak expiratory flow
k. The slope represents the decreasing
flow from the patient during expiration
l. End expiratory flow
x. Inspiration
y. Pause time
z. Expiration
Volume-Time waveform. Points and regions of interest
m. Start of inspiration
n. The slope represents current delivery
of inspiratory tidal volume
o. End inspiration
p. The slope represents current patient
delivery of expiratory tidal volume
q. End expiration
x. Inspiration
y. Pause time
z. Expiration
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1.1
WAVEFORMS AND LOOPS

Pressure control - summary
P
V
V
time (s)
time (s)
time (s)
PressureFlowVolume
Inspiration
phase
Expiration
phase
Inspiratory
volume
Expiratory
volume
Pressure remains constant during the inspiratory phase. Expiration
starts when the valves open, removing the delivery pressure.
Flow decreases exponentially during inspiration and expiration.
The rate is dependant on the pressure difference between the
system and lungs.
The delivered volume is an estimated parameter, it depends on
the inspiratory pressure and the bio-mechanical properties of the
lung (compliance, resistance etc.).
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1.1
WAVEFORMS AND LOOPS