Department of Critical Care MedicineKovai 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

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

OBJECTIVE

Monitoring gas exchange

• Oxygenation

• Ventilation

Monitoring lung and chest wall

mechanics

• Pressure

• Volume

• Flow

• Compliance

• Resistance

RESPIRATORY

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

GAS EXCHANGE

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

PULSE OXYMETRY

Shape of oxygen dissociation

curve

Dyshemoglobinemia

Dyes

Nail polish

Ambient light

LIMITATIONS OF PULSE OXYMETRY

False alarms

Motion artifact

Skin pigmentation

Low perfusion state

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

ABG

Efficacy of oxygen exchange

• Alveolar gas equation

PAO2 = PIO2 – (PaCO2/R)

• AaDO2 = PAO2 – PaO2

• Oxygenation index : PaO2/(FiO2 X Paw)

• PaO2/FiO2

OXYGENATION

• PaCO2 is directly measured in blood.

• PaCO2 is a measure of ventilation - CO2

elimination

• Increased PaCO2

PaCO2 = VCO2/ ( Vt –Vd ) RR

VENTILATION

.

• Between ETT and expiratory limb of vent

tubing

• Expired CO2 against time

• Healthy subjects, V/Q ≈ 1, EtCO2

≈PaCO2

• Information about RR and rhythm

• ETT placement (obstr, discon, kinking)

• Determine dead space, CO and PE

• Best PEEP, PaCO2 – PET CO2 difference

CAPNOGRAPHY

CAPNOGRAPHY

ABNORMAL EtCO2 WAVEFORMS

ASTHMA/ COPD

Hypoventilation

ABNORMAL EtCO2 WAVEFORMS

Hyperventilation

• Describe how to use graphics to more

appropriately adjust the patient ventilator

interface.

• Identify adverse complications of mechanical

ventilation.

OBJECTIVES OF VENTILATOR GRAPHICS

Pmus + PrS = (R x Flow) + V/C

Muscle pressure + ventilator pressure =flow resistance pressure +Elastic recoil

pressure

EQUATION OF MOTION

LOOPS

• Pressure vs

Volume

• Flow vs volume

SCALARS

• Pressure vs.

Time

• Flow vs. Time

• Volume vs. Time

SCALARS & LOOPS

Mode of ventilation

Independent variables

Dependent variables

Waveforms that will be useful

Waveforms that normally remain unchanged

Volume Control/ Assist-Control

Tidal volume,

RR, Flow rate, PEEP, I/E ratio

PawPressure-time:Changes in Pip, Pplat

Flow-time (expiratory): Changes in compliancePressure-volume loop: Overdistension, optimal PEEP

Volume-timeFlow time (inspiratory)Flow-volume loop

Pressure Control

Paw, Inspiratory time (RR), PEEP and I/E ratio

Vt, flowVolume-time and flow-time: Changes in Vt and compliancePressure-volume loop: Overdistension, optimal PEEP

Pressure-time

Pressure support/CPAP

PS and PEEP Vt,and RR, flow, I/E Ratio

Volume- timeFlow- time(for Vt and VE)

MODE OF VENTILATION -> USEFUL WAVEFORMS

PRESSURE TIME

1 2 3 4 5 6

20

Sec

Paw

cmH2O

Pressure VentilationVolume Ventilation

PRESSURE TIME

time

pres

sure

time

flow

time

pres

sure

HIGH AIRWAY RESISTANCE

time

pres

sure

Paw(peak) = Flow x Resistance + Volume x 1/compliance + PEEP

HIGH FLOW RATE

30

Time (s)

-10

1 2

awPcmH2O

Adequate flow

Flow set too low3

INADEQUATE FLOW - VCV

time

pres

sure

DECREASED COMPLIANCE

1 2 3 4 5 6

SEC

120

120EXH

INSP

Expiration

V

.LPM

Inspiration

PIFR

PEFR

Ti

Te

Vt

FLOW - TIME

1 2 3 4 5 6

SEC

120

-120

V

.LPM

CHANGING FLOW WAVEFORM IN VCV: EFFECT ON INSPIRATORY TIME

1 2 3 4 5 6

SEC

120

-120

V

.LPM

EXPIRATORY FLOW RATE AND CHANGES IN EXPIRATORY RESISTANCE

The transition from expiratory to inspiratory occurs without the expiratory flow returning to zero

1 2 3 4 5 6

SEC

120

120

V

.LPM

DETECTING AUTOPEEP

Expiration

SEC

800 ml

2 3 4 5 61

VT

Inspiration

Vt

Ti Te

VOLUME Vs TIME CURVE

1 2 3 4 5 6

SEC

1.2

-0.4

VT

Liters

A

A = exhalation that does not return to zero

Leak Volume

LEAKS

Expiration

SEC

800 ml

2 3 4 5 61

VT

Inspiration

Ti Te

End Expiratory Hold

PEEP i

PEEP e

MEASUREMENT OF AUTOPEEP

PV Loops

FV Loops

Flow-Volume Loop

Volume (ml)

Inspiration

Expiration

Pressure-Volume Loop

Volume (mL)

PIP

VT

Paw (cm H2O)

LOOPS

Inspiration

Expiration

v0 20 40 602040-60

Paw

cmH2O

Assisted breath

controlled breath

spontaneous breath

ASSISTED BREATH

PV LOOP-INCREASED RESISTANCE

PCV

DECREASED COMPLIANCE

Essentials of Ventilator Graphics ©2000 RespiMedu

Work of Breathing

B

A

A: Resistive WorkB: Elastic Work

Pressure (cm H2O)

Volume (ml)

WORK OF BREATHING

COPD

LEAK

B

A

0 20 40 60-20-40-60

0.2

0.4

0.6

LITERS

Paw

cmH2O

C

A = inspiratory pressure

B = upper inflection point

C = lower inflection point

VT

OVERDISTENSION

NORMAL FLOW-VOLUME LOOPS

Flow

Volume

Peak Expiratory Flow

Peak Inspiratory Flow

Tidal Volume

Inspiration

Expiration

FV LOOP – VOLUME CONTROL

ETT OR CICUIT LEAKS

AUTOPEEP

2

1

1

2

3

3

VLPS

.VT

INSP

EXH

BEFORE AFTER

2

1

1

2

3

3

VLPS

.

BRONCHODILATOR RESPONSE

• 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

USES

No monitoring device, no matter how

simple or complex, invasive or non-

invasive, inaccurate or precise will

improve outcome unless coupled to a

treatment, which itself improves

outcome

Thank you