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Mechanical Ventilator/Patient
Monitoring Part II
RET 2264C
Prof. J.M. Newberry
Dr. J.B. Elsberry
Special Thanks to
Sean Chambers , J. Cairo and Jeff Davis
Physiological Monitoring
• Physiological data are useful in managing patients on
ventilatory support in respect to oxygenation, ventilation,
ventilatory mechanics (Use Loops), and hemodynamic
monitoring…
Hemodynamics
Physics of Blood flow in the
circulation
Circulatory System
Circulation Schematic
Left Side of Heart
Pulmonary Vein
A
Aorta
V
Aortic Valve
Mitral Valve
Tissues
Lungs
Tricuspid Valve
Pulmonary Valve
V
Pulmonary Artery
A
Right Side of Heart
Sup. & Inf. Vena Cava
Heart Valves
• Atrioventricular (A-V) valves - separate
Atria from Ventricles
• Bicuspid (Mitral) - Left Side
• Tricuspid - Right Side
• Semi-Lunar Valves - separate ventricles
from Arteries
Opening, Closing of Valves - Depends on Pressure
differences between blood
in adjacent areas
Heart Sounds
• ‘Lubb’ (1st sound) - Closure of A-V valves
• ‘Dupp’ (2nd sound) - Closure of S-L valves
Caused by Turbulence on closing.
Anything extra ’Murmur’ (swishing of blood)
Could be due to:
Increases
• Stenosis of Valves (calcification)
Pressure on
• Valves not closing properly
heart
(Incompetence, Insufficiency)
Blood Vessels
• Arteries
• Capillaries
• Veins
Systemic Pathway:
Left Ventricle
of Heart
Venules
Aorta
Arteries
Arterioles
Capillaries
Veins
Right Atrium
of Heart
Blood
• Composition:
– Approx 45% by Vol. Solid Components
» Red Blood Cells (12m x 2 m)
» White Cells
» Platelets
– Approx 55% Liquid (plasma)
» 91.5% of which is water
» 7% plasma proteins
» 1.5% other solutes
Blood Functions
• Transportation
of blood gases, nutrients, wastes
• Homeostasis (regulation)
of pH, Body Temp, water content
• Protection
• Viscosity of Blood = 3 3.5 times of water
• Blood acts as a non-newtonian fluid in
smaller vessels (including capillaries)
Cardiac Output
• Flow of blood is usually measured in l/min
• Total amount of blood flowing through the
circulation = Cardiac Output (CO)
Cardiac Ouput = Stroke Vol. x Heart Rate
or SV1 + SV2 + …+ SVn = C.O. l/min
Influenced by Blood Pressure & Resistance
Force of blood
against vessel wall
 with water retention
 with dehydration, hemorrage
•Blood viscosity
•Vessel Length
•Vessel Elasticity
•Vasconstriction / Vasodilation
Overall
• Greater Pressure  Greater Blood
Differences
Flow
• Greater Resistance  Lesser Blood Flow
HEART
(PUMP)
REGULATION
CARDIOVASCULAR
SYSTEM
VESSELS
(DISTRIBUTION SYSTEM)
AUTOREGULATION
NEURAL
HORMONAL
RENAL-BODY FLUID
CONTROL SYSTEM

Blood Pressure
Driving force for blood flow is pressure
created by ventricular contraction
Elastic arterial walls expand and recoil
continuous blood flow
ARTERIES (LOW COMPLIANCE)
HEART
DIASTOLE
VEINS
CAPACITY
VESSELS
80 mmHg
120 mmHg
SYSTOLE
CAPILLARIES
Blood pressure is highest in the arteries
(Aorta!) and falls continuously . . .
Systolic pressure in Aorta: 120 mm Hg
Diastolic pressure in Aorta: 80 mm Hg
Diastolic pressure in ventricle: ?? mm Hg
Ventricular pressure difficult to measure
arterial blood pressure assumed to indicate
driving pressure for blood flow
Arterial pressure is pulsatile
useful to have single value for driving pressure:
Mean Arterial Pressure
MAP = diastolic P + 1/3 pulse pressure
Pulse Pressure = systolic pressure - ??
= measure of amplitude of blood pressure
wave
MAP influenced by
• Cardiac output
• Peripheral resistance

MAP
CO x Rarterioles
• Blood volume
– fairly constant due to homeostatic mechanisms
(kidneys!!)
BP too low:
• Driving force for blood flow unable to
overcome gravity
O2 supply to brain 
 Symptoms?
BP too high:
• Weakening of arterial walls - Aneurysm
Risk of rupture & hemorrhage
Cerebral hemorrhage: ?
Rupture of major artery:
Principles of Estimated Sphygmomanometry
Cuff inflated until brachial artery compressed and blood
flow stopped
what kind of sound?
Slowly release pressure in cuff:
turbulent flow
Pressure at which . . .
. . . sound (= blood flow) first heard:
. . . sound disappeared:
• Pressure can be stated in terms of column of
fluid.
mm Hg
50
100
200
300
400
Pressure Units
cm H2O
PSI
68
136
272
408
544
0.9
1.9
3.8
5.7
7.6
ATM
0.065
0.13
0.26
0.39
0.52
Pressure = Height x Density
or
P = gh
Density of blood
= 1.035 that of water
If Right Atrial pressure = 1 cm H2O in an open
column of blood
 Pressure in feet = 140 cm H2O
 Rupture
Incompetent venous valves
 Varicosities
 Venous Valves
Actual Pressure in foot
= 4-5 cm H2O
Pressures in the Circulation
Review
• Pressures in the arteries, veins and heart
chambers are the result of the pumping
action of the heart
• The right and left ventricles have similar
waveforms but different pressures
• The right and left atria also have similar
waveforms with pressures that are similar
but not identical
How do we Continuously Monitor Left
and Right Heart Pressures
Hemodynamic Function
Summarized in these
Wiggers Diagrams from
Pilbeam-Cairo
3. As blood enters the
aorta, the aortic pressure
begins to rise to form the
systolic pulse
4. As the LV pressure falls
in late systole the aortic
pressure falls until the LV
pressure is below the aortic
diastolic press.
2. Pressure rises until the
LV pressure exceeds the
aortic pressure
5. Then the aortic valve
closes and LV pressure falls
to LA pressure
 The blood begins to
move from the ventricle
to the aorta
1. The LV pressure begins
to rise after the QRS wave
of the ECG
•The first wave of atrial pressure (the A wave) is due to atrial
contraction
•The second wave of atrial pressure (the V wave) is due to
ventricular contraction
Normal Pressures
• RV and pulmonary systolic pressures are
15-25 mm Hg
• Pulmonary diastolic pressure is 5-12 mm Hg
• LA pressure is difficult to measure because access
to the LA is not direct
AS produces a
pressure gradient
between the aorta
and LV
i.e. For blood to move
rapidly through a
narrowed aortic valve
orifice, the pressure
must be higher in the
ventricle
• The severity of AS is determined by the pressure drop across the aortic
valve or by the aortic valve area
• The high velocity of blood flow through the narrowed valve causes
turbulence and a characteristic murmur AS can be diagnosed with a
stethoscope
Pressure Measurement
• Accurate pressure measurements are essential to
understanding the status of the circulation
• In 1733 Steven Hales connected a long glass tube
directly to the left femoral artery of a horse and
measured the height of a column of blood (8 feet,
3 inches) to determine mean BP
• Direct pressure measurements are made frequently
in the cardiac catheterization laboratory, the ICU
and the OR
• A tube is inserted into an artery and connected to
an electrical strain gauge that converts pressure
into force that is sensed electrically
• The output of the transducer is an electrical signal
that is amplified and recorded on a strip chart
• For correct pressure measurements the cannula
and transducer must be free of air, the cannula
should be stiff and short
Cardiac Output (CO)Measurement
• The measurement of blood flow through the
circulation is usually done clinically using either
the Fick method or Thermodilution
• The Fick method states that the cardiac output is
equal to the oxygen consumption divided by the
arterial-venous oxygen difference
CO = Oxygen consumption / A-V O2
MEASUREMENT OF CARDIAC OUTPUT
THE FICK METHOD:
VO2 = ([O2]a - [O2]v) x Flow
Spirometry or nomogram (250 ml/min)
VO2
Flow =
[O2]a - [O2]v
Pulmonary Artery Blood (15 ml%)
Arterial Blood (20 ml%)
CARDIAC OUTPUT
PULMONARY BLOOD FLOW
VENOUS RETURN
PERIPHERAL
BLOOD FLOW
.
VO2
CARDIAC OUTPUT (Q) = [O ] - [O ]
2 a
2 v
=
250 ml/min
20 ml% - 15 ml%
= 5 L/min
.
Q = HR x SV
.
Q
SV =
HR
.
Q
CARDIAC INDEX = m2 body surface
area
5 L/min
70 beats/min
= 0.0714 L or 71.4 ml
=
= 5 L/min
1.6 m2
= 3.1 L/min/m2
Oxygen Delivery to the Tissues
It’s simple but very important
.
DO2 = CaO2 x Qc
• The measurement is done by determining the
oxygen consumption using respiratory gas
measurements and the O2 content of arterial and
mixed venous blood
• The mixed venous blood sample is obtained from
a PA with a catheter
• The arterial sample can be drawn from any artery
Indications & Contraindications for
Arterial Cannulation
Arterial Cannulation
• Continuous BP, frequent ABG’s
• Complications—hemorrhage, infection,
ischemia (embolus, thrombus, arterial
spasm)
Indications & Contraindications for
Venous Cannulation
Central Venous Catheter:
• Fluid admin., nutritional support, CVP
measurements/monitoring
• Complications: pneumothorax, embolus &
thrombus formation, infection
Pulmonary Artery Catheter:
• PCWP measurements, Cardiac Output and mixed
venous blood gases
• Complications: pneumothorax, arrhythmias,
embolus & thrombus formation, infection and
cardiovascular injury
Hemodynamic Pressures that Can
be Measured Directly
• Heart Rate: 60-90/min
• Systemic (Arterial) BP:
90-140/60-90 torr
• CVP 2-6 torr
• PAP: 15-35/5-15 torr
• PCWP: 5-12 torr
.
• C.O. (Q): 4-8 l/min.
- • PvO2 : 40 torr
- • PaO2 : 80-100 torr
Next PA Monitoring
Angles 45°
30°
0°
• Supine
• O to 60 degrees from
horizontal
Components of Hemodynamic
Pressure Monitoring
• The invasive catheter
and the high pressure
tubing connecting the
patient to the
transducer
• The transducer
• The flush system
• The bedside monitor
IDENTIFY PHLEBOSTATIC
AXIS
 Intersection of the 4th ICS and ½ the anterior-
posterior diameter of the chest
AACN PAP Measurement Practice Alert
McHale DL, Carlson KK.
AACN Procedure Manual for Critical Care 4th ed
WB Saunders: Philadelphia, Pa 2001 (479)
With permission from Elsevier
LEVELING
– Eliminates effects of hydrostatic forces
on the observed hemodynamic pressures
– Ensure air-fluid interface of the
transducer is leveled before zeroing
and/or obtaining pressure readings
– Phlebostatic axis:
• Level of left atrium
• 4th ICS & ½ AP diameter
• Mark the chest with washable felt pen
AACN PAP Measurement Practice Alert
UNDER DAMPED SYSTEM
OVER DAMPED SYSTEM
– Sluggish, artificially
rounded & blunted
appearance
– SBP erroneously low; DBP
erroneously high
– Causes: large air bubbles
in system, ostial lesion,
compliant tubing,
loose/open connections,
low fluid level in flush bag
AACN PAP Measurement Practice Alert
Reprinted from Darovic GO. Hemodynamic Monitoring:
Invasive and Noninvasive Clinical Application 2nd ed.
Philadelphia,Pa: WB Saunders Co;1995;161-162
Used with permission from Elsevier
AO Pressure
Damped AO Pressure
PAP DOCUMENTATION
• Measure at end expiration
• Measure pressures from a graphic tracing
• Measure pulmonary capillary wedge
pressure at end-expiration using the mean
of the a wave
– a wave indicates atrial contraction and falls
within the P – QRS interval of the
corresponding ECG complex
AACN PAP Measurement Practice Alert
RESPIRATORY COMPONENT
 Changes in intrathoracic
pressure during respiration
change PAP readings
AACN PAP Measurement Practice Alert
 Record and trend pressure
readings at end expiration
Used with permission of PACEP Collaborative
AACN PAP Measurement Practice Alert
AACN PAP Measurement Practice Alert
Used with permission of PACEP Collaborative
Accurate Measurement
•
•
•
•
Regular zero check
Open transducer to room air
Hit balance button on monitor
Zero in Ft. Myers does not = zero in Denver
Effect of air in line
Effect of long line
Troubleshooting
• What can we do to reduce damping thus
ensuring the best frequency response?
– Short, stiff tubing
– No blood, contrast or air in line
Correctable Sources of Artifact
Review
• Loss of frequency response
– Air, blood, contrast
• Improper zero
– Phlebostatic axis
• Improper calibration
– Hg if valve case