Department of Critical Care Medicine
Kovai Medical Center and Hospital
MONITORING OF MECHANICALLY
VENTILATED PATIENT
DR.T.GOPINATHAN MD., IDCCM.,EDIC
Consultant Intensivist
Kovai Medical Center and Hospital
GOALS OF MECHANICAL VENTILATION
 Decrease the WOB and improve patient comfort
 Maintain adequate gas exchange to keep body in
relative homeostasis
OBJECTIVE
Monitoring : monere - meaning ‘to warn’
Goals of continuous monitoring :
 Baseline measurement – initial plan, reference for
future
 follow real time specific physiological values that
changes rapidly – alerts for adverse events
 Assessment of therapeutic intervention
RESPIRATORY


Monitoring gas exchange
•
Oxygenation
•
Ventilation
Monitoring lung and chest wall mechanics
•
Pressure
•
Volume
•
Flow
•
Compliance
•
Resistance
GAS EXCHANGE

Clinical signs and symptoms - Nonspecific, late

ABG

PULSE OXYMETRY

CAPNOGRAPHY

The clinical significance of hypoxia/hypercapnia
depends on Chronicity of Compensatory
mechanisms and tolerance of vital organs
PULSE OXYMETRY

Pulsatile signal generated by
arterial blood

Difference in the absorption spectra
of oxyHb and Hb.

Determines O2 saturation by
absorption spectrophotometry
PULSE OXYMETRY
 Advantages:
• Inexpensive
• Accuracy - Spo2 below 80%
• Direct measurement
• Continuous
• Non-invasive
• Pleth variability index
LIMITATIONS OF PULSE OXYMETRY
 Shape of oxygen dissociation curve
 False alarms
 Dyshemoglobinemia
 Motion artifact
 Dyes
 Skin pigmentation
 Nail polish
 Low perfusion state
 Ambient light
ABG
Advantages:
• Direct measurement of PaO2 and PaCO2
• Also gives values for acid-base status and electrolytes
Disadvantages:
• Not specific or sensitive
• Calculates saturation
• Requires invasive procedure
• Intermittent sampling - miss events
ABG
Factors influencing values:
PaO2 varies
• Age
• Altitude
• Sampling techniques: air bubble, heparin
PaCO2 remains relatively constant
OXYGENATION
Efficacy of oxygen exchange
• Alveolar gas equation
 PAO2 = PIO2 – (PaCO2/R)
• AaDO2 = PAO2 – PaO2
• Oxygenation index : PaO2/(FiO2 X Paw)
• PaO2/FiO2
VENTILATION
• PaCO2 is directly measured in blood.
• PaCO2 is a measure of ventilation - CO2 elimination
• Increased PaCO2
.
PaCO2 = VCO2/ ( Vt –Vd ) RR
CAPNOGRAPHY
•
Between ETT and expiratory limb of vent tubing
•
Expired CO2 against time
•
Healthy subjects, V/Q ≈
•
Information about RR and rhythm
•
ETT placement (obstr, discon, kinking)
•
Determine dead space, CO and PE
•
Best PEEP, PaCO2 – PET CO2 difference
1, EtCO2 ≈PaCO2
CAPNOGRAPHY
ABNORMAL EtCO2 WAVEFORMS
ASTHMA/ COPD
ABNORMAL EtCO2 WAVEFORMS
Hypoventilation
Hyperventilation
OBJECTIVES OF VENTILATOR GRAPHICS
• Describe how to use graphics to more appropriately adjust
the patient ventilator interface.
• Identify adverse complications of mechanical
ventilation.
EQUATION OF MOTION
Muscle pressure + ventilator pressure =flow
resistance pressure +Elastic recoil pressure
Pmus + PrS =
(R x Flow) + V/C
SCALARS & LOOPS
SCALARS
• Pressure vs. Time
• Flow vs. Time
• Volume vs. Time
LOOPS
• Pressure vs Volume
• Flow vs volume
MODE OF VENTILATION -> USEFUL
WAVEFORMS
Mode of
ventilation
Independent
variables
Dependent
variables
Waveforms that will be
useful
Waveforms that
normally remain
unchanged
Volume
Control/
AssistControl
Tidal volume,
RR, Flow rate,
PEEP, I/E ratio
Paw
Pressure-time:
Changes in Pip, Pplat
Flow-time (expiratory):
Changes in compliance
Pressure-volume loop:
Overdistension, optimal PEEP
Volume-time
Flow time (inspiratory)
Flow-volume loop
Pressure
Control
Paw, Inspiratory
time (RR), PEEP
and I/E ratio
Vt, flow
Volume-time and flowtime: Changes in Vt and
compliance
Pressure-volume loop:
Overdistension, optimal PEEP
Pressure-time
Pressure
support/
CPAP
PS and PEEP
Vt,and RR,
flow, I/E
Ratio
Volume- time
Flow- time
(for Vt and VE)
PRESSURE TIME
PRESSURE TIME
20
Pressure Ventilation
Volume Ventilation
Paw
cmH2O
Sec
1
2
3
4
5
6
flow
pressure
pressure
HIGH AIRWAY RESISTANCE
time
timetime
HIGH FLOW RATE
pressure
Paw(peak) = Flow x Resistance + Volume x 1/compliance + PEEP
time
INADEQUATE FLOW - VCV
30
Adequate flow
Paw
Flow set too low
cmH2O
1
-10
2
3
Time (s)
pressure
DECREASED COMPLIANCE
time
FLOW - TIME
120
INSP
Inspiration
PIFR
.
Vt
V
LPM
Te
Ti
SEC
1
2
3
4
5
6
Expiration
PEFR
120
EXH
CHANGING FLOW WAVEFORM IN VCV:
EFFECT ON INSPIRATORY TIME
120
.
V
SEC
LPM
1
-120
2
3
4
5
6
EXPIRATORY FLOW RATE AND CHANGES IN
EXPIRATORY RESISTANCE
120
.
SEC
V
LPM
-120
1
2
3
4
5
6
DETECTING AUTOPEEP
120
.
V
SEC
LPM
1
120
2
3
4
5
6
The transition from expiratory to inspiratory
occurs without the expiratory flow returning
to zero
VOLUME Vs TIME CURVE
800 ml
Vt
Inspiration
Expiration
VT
SEC
1
Ti
2
Te
3
4
5
6
LEAKS
1.2
A
VT
Liters
SEC
Leak Volume
1
2
3
-0.4
A = exhalation that does not return to zero
4
5
6
MEASUREMENT OF AUTOPEEP
800 ml
Inspiration
VT
Expiration
End Expiratory Hold
PEEP i
SEC
PEEP e
1 Ti
2 Te
3
4
5
6
LOOPS
Pressure-Volume Loop
PV Loops
VT
Volume
(mL)
Paw (cm H2O)
PIP
Flow-Volume Loop
Inspiration
Volume (ml)
Expiration
FV Loops
ASSISTED BREATH
spontaneous breath
Assisted breath
controlled breath
Expiration
Inspiration
Paw
v
cmH2O -60
40
20
0
20
40
60
PV LOOP-INCREASED RESISTANCE
PCV
DECREASED COMPLIANCE
WORK OF BREATHING
Work of Breathing
Volume (ml)
A: Resistive Work
B: Elastic Work
B
A
Pressure (cm H2O)
Essentials of Ventilator Graphics
©2000
RespiMedu
COPD
LEAK
OVERDISTENSION
VT
A = inspiratory pressure
LITERS
B = upper inflection point
0.6
C = lower inflection point
A
0.4
B
0.2
C
Paw
cmH2O
-60
-40
-20
0
20
40
60
NORMAL FLOW-VOLUME LOOPS
FV LOOP – VOLUME CONTROL
Tidal Volume
Peak Inspiratory Flow
Peak Expiratory Flow
Inspiration
Volume
Expiration
ETT OR CICUIT LEAKS
AUTOPEEP
BRONCHODILATOR RESPONSE
BEFORE
AFTER
3
3
INSP
2
2
1
1
V
LPS
V
LPS
1
1
2
2
3
3
.
.
VT
EXH
USES
• Identify mode
• Detect auto-PEEP
• Determine patient-ventilator synchrony
• Assess and adjust trigger levels
• Measure the work of breathing
• Adjust tidal volume and minimize overdistension
• Assess the effect of bronchodilator admn.
USES
• Detect equipment malfunctions
• Determine appropriate PEEP level
• Evaluate adequacy of inspiratory time in pressure control
ventilation
• Detect the presence and rate of continuous leaks
• Determine appropriate Rise Time
No monitoring device, no matter how
simple or complex, invasive or noninvasive, inaccurate or precise will
improve outcome unless coupled to a
treatment, which itself improves
outcome
Thank you