ventilatory strategies in the icu

Ventilatory strategies in the ICU


Need for mechanical ventilation

Modes of ventilation – VCV, PCV, DCV

Invasive vs Noninvasive ventilation

Weaning from mechanical ventilation

Extubation and failure to extubate

Respiratory distress RS:

• Mouth open

• Alae nasi flaring

• Pursed lips

• Tracheal tug

• Active accessory muscles

• Breathlessness

• Tachypnoea

• Cyanosis

• Paradoxical respiration

CVS:

• Cool extremities

• Rising pulse

• Falling BP

• Anxiety

• Drowsiness

• Restlessness

• Disorientation

• Picking bedclothes

CNS

“Inability to maintain either the normal

delivery of O2 to the tissues ± removal of

CO2 from the tissues”

Type I vs Type II

Respiratory failure

INDICATIONS FOR MECHANICAL VENTILATION

• Ventilation abnormalities - Respiratory muscle dysfunction

Respiratory muscle fatigue

Chest wall abnormalities

Neuromuscular disease

Decreased ventilatory drive

Increased airway resistance

• Oxygenation abnormalities - Refractory hypoxaemia

Need for PEEP

Excessive work of breathing

INDICATIONS FOR MECHANICAL VENTILATION

• Need for anaesthesia, sedation and/or

neuromuscular blockade

• Need to decrease systemic/myocardial

oxygen consumption, e.g., low cardiac

output states

• Use of hyperventilation to reduce

intracranial pressure

Oxygen delivery

Adequate alveolar ventilation

Restore acid-base balance

Reduce work of breathing

Minimal side-effects

Goals of ventilatory support

vs

Man

Machine

Inspiration

2 3

Expiration 41

SET TRIGGER1, Trigger

3, Cycling

4, Baseline P cmH2O

2, Limit

Time

Basic Modes of Ventilation

Volu

me

Pres

sure

Flow

Insp

Exp

Volume limitedConstant flow

Time

Volu

me

Pres

sure

Flow

Insp

Exp

Volume limitedConstant flow

Pressure limitedVolume controlled Pressure controlled

Time

Volume controlled vs Pressure controlled modes

COMPARISON VCV PCV

Volume Constant Varies

Effect of low compliance

Higher pressure Lower volume

Effect of high airway resistance

Higher pressure Lower volume

Peak airway pressure

High Lower

Mean airway pressure

Lower Higher

Case scenario 1

A 30 year old man, weighing 50 kg who had

undergone laparotomy the previous day was

complaining of pain at the incision. The

postgraduate prescribed morphine 50 mg and

phenergan 12.5 mg IM. The injections were given.

Fifteen minutes later, he becomes apnoeic.

Time-triggered, flow lim

ited and

volume-cycled

Case scenario 2

He was nicely settled on ventilator but now seems

to have some respiratory efforts

Patient-triggered, flow lim

ited

and volume-cycled

Mechanical Ventilation

Volume Controlled Ventilation

Pressure Controlled Ventilation

Pressure Control Ventilation - CMV

Pressure

Flow

Volume

0

30

Time-triggered, pressure-limited

and time-cycled

Time

Pressure Control Ventilation - SIMV

Pressure

Flow

Volume

0

30

Patient-triggered, pressure-limited

and time-cycled

Time

Case scenario 3

By 4 AM, the patient seems to be stable

and breathing a lot better than before. You

want to see whether you can encourage

his spontaneous breaths and wean him by

morning. What mode would you choose?

Pressure Support Ventilation (PSV)

Pressure Support Ventilation (PSV)P

r es s

ur e

Fl o

w

Vo

lum

e

Time

25 %

0

20

Patient triggered, pressure

controlled, flow cycled

ventilation

Time

Positive End-Expiratory Pressure (PEEP)

PEEP is not a mode of ventilation per se

0

+

PEEP with Mandatory breaths

Alv

eola

r pr

essu

re

Time

5

Baseline variable

Continuous Positive Airway Pressure (CPAP)

Appropriate for patients who have adequate

spontaneous ventilation but persistent

hypoxaemia due to physiological shunting

Pre

ssur

e (c

m H

2O

)

0

+

-Baseline

Ventilatory setting

Mode

Frequency

Tidal volume

I:E ratio

FIO2




Invasive vs Noninvasive ventilation


Invasive ventilation

Noninvasive Ventilation

Noninvasive Ventilation – Advantages

Reduced need for sedation

Preservation of airway reflexes

Avoidance of upper airway trauma

Decreased ventilator associated pneumonia

Improved patient comfort

Shorter length of stay in the ICU and hospital

Improved survival

Noninvasive Ventilation – Disadvantages

Claustrophobia

Facial/nasal pressure lesions

Unprotected airway

Inability to suction deep airway

Gastric distension with face mask

Delay in intubation

Noninvasive Ventilation - Contraindications

Cardiac or respiratory arrest

Haemodynamic instability

Patients unable to co-operate

Inability to protect airway

High risk for aspiration

Active upper GI bleed

Severe hypoxaemia

Facial trauma, surgery or burns

Case scenario 4

This patient was doing fine for two days

but developed abdominal distension,

vomited and aspirated. He had to be

reintubated and ventilated. He has stiff

lungs now.

Case scenario 4

ABG

FIO2 – 1

PaO2 – 100 mm Hg

PaCO2 – 45 mm Hg

pH – 7.3

SpO2 – 98%

Mode

Frequency

Tidal volume

I:E ratio

FIO2

PaO2PvO2P50

a

v

PO2 (mm Hg)

Hae

mog

lobi

n sa

tura

tion

(%)

Oxygenation status

PaO2/FIO2 ratio

³500 – Normal

250 – Good

100 – 250: Poor

100 - Critical

10% shunt

PaO

2 (m

mH

g)

10040 60 800 20

Air

600

400

200

Assume normal QT, VO2, Hb, C(a-v)O2

20% shunt

30% shunt40% shunt50% shunt

FIO2 (%)

Nunn JF: Oxygen. In Nunn JF (ed): Applied Respiratory Physiology, 3rd ed. London: Butterworths,1987,109

Normal

NormalShunt Dead space

Case Scenario 4 Mode - PCV

Frequency - Higher

Tidal volume - Lower

I:E ratio – 1:2 to 1:1 or

even inverse ratio ventilation

FIO2 – As required

PEEP

Avoid

• Barotrauma

• Volutrauma

• Atelectrauma

• Biotrauma

• Oxygen toxicity

Mean airway pressure

Increase mean airway pressure by Increasing peak airway pressure

Increasing plateau pressure

Increase duration of inspiration (I:E ratio)

Increase PEEP

Bilevel Positive Airway Pressure

Ventilation (BiPAP)


Volume Controlled Ventilation

Pressure Controlled Ventilation

Dual Controlled Ventilation

Dual control breath to breath

PRVC = Time or patient-triggered, Pressure-

limited, volume targeted and time-cycled

Case Scenario 5

A 20 year old man, known asthmatic, was

admitted to the Casualty with severe

wheeze. He is tachypnoeic, hypoxic and

restless. He was sedated and intubated but

his lungs are very stiff. What would you do?

Case scenario 5

Mode - PCV

Frequency - Slower

Tidal volume – 7 ml/kg

I:E ratio – Longer I:E

FIO2

ABG

FIO2 – 1

PaO2 – 250 mm Hg

PaCO2 – 50 mm Hg

pH – 7.3

Auto-PEEP Detection F

LO

W

INCREASED RESISTANCE NORMAL

TIME

LINEAR DECAY

EXPONENTIAL DECAY

Flow –time graph

Auto-PEEP Reduction

Low respiratory rate

Lower tidal volume

Large endotracheal tube

Higher inspiratory flow rate

Longer expiratory time

Permissive hypercapnia

Watch • Gas exchange

• Lung mechanics – Volumes,

pressures

• CVS

• The complete picture!




Noninvasive ventilation


“Weaning” is …

gradual discontinuation

of ventilatory support

When to wean?

Early withdrawal Vs

Premature discontinuation

Has there been a

significant improvement

or reversal

in the primary pathology ?

Step 1

Assessment of patients

Are they ready for weaning?

Step 2

Is the respiratory

function adequate?

FIO2 < 0.4 – 0.5

PaO2 (mmHg) > 60

SaO2 (%) > 90

SvO2 (%) > 60

PaO2/PAO2 ratio > 0.35

PaO2/FIO2 ratio > 350

Oxygenation

PaCO2 < 50 mmHg

pH > 7.35

Ventilation

Respiratory rate < 35.min-1

Minute volume < 10 L.min-1

Maximum inspiratory pressure

> - 20 cmH2O

Vital capacity > 10 ml.kg-1

VD / VT < 0.6

Rapid shallow breathing index (RSBI) *

* Yang KL, Tobin MJ. N Engl J Med 1991,324:1445-50

f / VT < 105 (b.min-1L-1)

Where,

f = Respiratory rate in breaths.min-1

VT = Tidal volume in Litres

Are his other systems

functioning adequately?

Spontaneous

Breathing Trial

(SBT)

Low levels of CPAP (e.g., 5 cmH2O)

Low levels of pressure support

(e.g., 5 – 7 cmH2O) or

Simply as “T-piece breathing”

Screening phase (5 min)

Assessment phase (30 – 120 min)Ref: MacIntyre NR. Chest 120, December 2001 375S – 395S

Monitoring during weaning

Monitors do not

substitute for an ever

vigilant clinician !

The patient

Oxygenation

Ventilation

Cardiovascular status

Failed Spontaneous

Breathing Trial (SBT)

Why ?

What next ?

The most common cause of

failure to wean is an

imbalance between

ventilatory capability and

ventilatory demand.

Patients who fail an SBT should

receive a stable, nonfatiguing,

comfortable form of ventilation

Attempts at weaning can continue

with once daily SBTs.

Twice daily SBTs offer no

advantage over once daily SBT.

The decision to discontinue

ventilatory support

must be distinct from the

decision to extubate !

Those who will be successfully extubated will have

i) the resolution of the disease

ii) haemodynamic stability

iii) absence of sepsis

iv) adequate oxygenation status

v) adequate ventilatory status…. etc, etc

and also will have….

the ability to maintain

patency of the airway

? Upper airway obstruction

? Excess respiratory secretions

? Inability to protect airway

? Cardiac failure or ischaemia

? Encephalopathy

? Respiratory failure

? GI bleeding, sepsis, seizures

Causes of

failure to

extubate

Maziak DE, Meade MO, Todd RJ. Chest 1998;114:605-9

Insufficient evidence exists to support the

idea that the timing of tracheotomy alters

the duration of mechanical ventilation in

critically ill patients.

ROLE OF TRACHEOSTOMY IN

WEANING

Thank you

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