MECHANICAL VENTILATION –

KEEP IT SIMPLES.Dial

Rounds 2020

Ventilation

■ Brain

■ Nerves

■ Rib cage

■ Respiratory muscles

■ Ventilators can replace the

function of these parts of

the respiratory system

The functional lung unit

Gas exchangeMixed

venous

Inspired air

Arterial blood

Expired air

Alveolus

O2

CO2

Rate of exchange

determined by

metabolic rate

High flow nasal cannula

■ Humidification improves tolerance of high flows

■ Nasal cannula- better tolerated than full face mask – patients

can speak and eat

■ The high flows delivered results in less dilution by room air in

patients with high flows

■ Systems – Vapotherm, AIRVO, Ventilator, Optiflo

Critical Care 2016: 20:109 Roca et al

Respiratory Medicine 2009: 103, 1400 -1405

AIRVO HFNC

A – 3

En

glish

AIRVO 2 AND ACCESSORIES

OXYGEN

INLET PORT

HEATER

PLATE FINGER

GUARD

AUTO-FILL W ATER

CHAMBER (MR290 )

(w ith adapt er fi t t ed)

Heated

b reat hing

t ube

Wat er chamber

Pat ient

int erface

Cleaning and Disinf ection

90 0 PT60 0 Disinfect ion Kit

90 0 PT60 1 Disinfect ion Filt er (2-Pack)

90 0 PT60 2 Cleaning Sponge-St ick (20 -Pack)

90 0 PT60 3 Clean Storage Cover (20 -Pack)

Miscellaneous

90 0 PT40 5 Pole mount ing t r ay

90 0 PT421 Hospital stand

90 0 PT422 Oxygen inlet extension kit

90 0 PT912 Filt er holder

90 0 PT913 Air fi lt er (2-Pack)

OPT0 12 W igglepads (OPT316/ OPT318)

(20 -pack)

OPT0 14 Oxygen Tubing (Opt iflow Junior)

Tube & chamber kits and pa tient interfaces

Tube & chamber kit Interfaces

90 0 PT531 Heated breathing tube,

MR290 aut o-fi ll chamber and

adapter (10 -Pack)

àOPT316 Nasal Cannula - Inf ant (20 -Pack)

OPT318 Nasal Cannula - Pediat ric (20 -Pack)

90 0 PT50 1

Heated breathing tube,

MR290 aut o-fi ll chamber and

adapter (10 -Pack)

à

OPT842 Nasal Cannula - Small (20 -Pack)

OPT844 Nasal Cannula - Medium (20 -P ack)

OPT846 Nasal Cannula - Lar ge (20 -Pack)

OPT870 Tracheostomy Direct Connect ion (20 -Pack)

RT0 13 Mask Int erface Adapter - 22mm (20 -Pack)

DISPLAY

AIRVO 2

HEATED BREATHING TUBE

CONNECTION PORT

CHAMBER PORTS

MEA SUREMENT POINT OF

DISPLAYED DEW POINT

TEMPERATURE

SERIAL PORT

AIR FILTER

FILTER COVERPOW ER CORD

and

CONNECTOR (PT10 1AZ/

PT10 1UK)

A – 3

En

glish

AIRVO 2 AND ACCESSORIES

OXYGEN

INLET PORT

HEATER

PLATE FINGER

GUARD

AUTO-FILL WATER

CHAMBER (MR290 )

(w ith adapt er fi t t ed)

Heated

breat hing

t ube

Water chamber

Pat ient

int erface

Cleaning and Disinf ection

90 0 PT60 0 Disinfect ion Kit

90 0 PT60 1 Disinfect ion Filt er (2-Pack)

90 0 PT60 2 Cleaning Sponge-St ick (20 -Pack)

90 0 PT60 3 Clean Storage Cover (20 -Pack)

Miscellaneous

90 0 PT40 5 Pole mount ing t r ay

90 0 PT421 Hospital stand

90 0 PT422 Oxygen inlet extension kit

90 0 PT912 Filt er holder

90 0 PT913 Air fi lt er (2-Pack)

OPT0 12 W igglepads ( OPT316/ OPT318)

(20 -pack)

OPT0 14 Oxygen Tubing (Opt iflow Junior)

Tube & chamber kits and pa tient interfaces

Tube & chamber kit Interfaces

90 0 PT531 Heated breathing tube,

MR290 aut o-fi ll chamber and

adapt er (10 -Pack)

àOPT316 Nasal Cannula - Inf ant (20 -Pack)

OPT318 Nasal Cannula - Pediat ric (20 -Pack)

90 0 PT50 1

Heated breathing tube,

MR290 aut o-fi ll chamber and

adapt er (10 -Pack)

à

OPT842 Nasal Cannula - Small (20 -P ack)

OPT844 Nasal Cannula - Medium (20 -P ack)

OPT846 Nasal Cannula - Lar ge (20 -Pack)

OPT870 Tracheostomy Direct Connect ion (20 -Pack)

RT0 13 Mask Interface Adapter - 22mm (20 -Pack)

DISPLAY

AIRVO 2

HEATED BREATHING TUBE

CONNECTION PORT

CHAMBER PORTS

MEA SUREMENT POINT OF

DISPLAYED DEW POINT

TEMPERATURE

SERIAL PORT

AIR FILTER

FILTER COVERPOW ER CORD

and

CONNECTOR (PT10 1AZ/

PT10 1UK)

Physiologic mechanisms of action of HFNC

■ Washout of nasopharyngeal dead space – the expired air is

replaced by a fresh source of air with a lower pCO2 and higher

FIO2

■ Decreases the resistance of the upper airway on inspiration –

prevents potential narrowing related to negative intra-luminal

pressure

■ Warm humidified air improves conductance and pulmonary

compliance

■ Humidification of air through the nasopharynx uses energy –

therefore saves energy

Physiologic mechanisms

■ Provides PEEP which is

dependent on the flow

■ Drying out of the mucosa

can cause damage which

interferes with muco-

ciliary clearance, this

increases the risk of

infections and atelectasis

– the humidification of

HFNC is thought to

decrease these risksMouth opening only decreases PEEP effect

on expiration

Not as bad as you think, nebulizer –clean particles, not patient

What they did in China

Other ways to give high O2

■ You can add a filter to the

end of this

■ Filter

CPAP

What does CPAP do

■ Increase FRC

■ Bigger lung = bigger surface area for gas exchange

– Recruit partially collapsed alveoli

■ Improve compliance

CPAP effect on compliance

Ventilation

0 Brain

0 Nerves

0 Rib cage

0 Respiratory muscles

0 Ventilators can replace the function of these parts of the respiratory system

Positive pressure

Plateau pressure measurements

Plateau pressure

Positive pressure and PEEP

0 PEEP

PEEP

= 10

What do you order

■ RR - Respiratory rate = 12 – 24

■ Vt or Tidal volume = 4 – 8 ml /kg

■ PEEP – 5 – 24 ? Average on COVID = 10

■ This is a recipe that has been used to which I have some

reservations – treatment arm outcome was no different than

controls

VILI

■ Volutrauma or baro – likely combination of both

– Physiology – think of upper and lower inflexion points

Some terminology

■ How does the ventilator when the patient is inspiring = trigger

■ Tidal volume ?= you tell it how much to give or you provide a pressure and the Vt can vary (Pressure support of pressure control)

■ How fast is the tidal volume delivered = flow

■ How does machine know when to stop delivering the breath = cycle

Hypercarbia

Clinically elevations in the pCO2 are more likely to

be a consequence of decreases in the alveolar

ventilation than increased production

Alveolar ventilation (VA ) = Total minute ventilation

– dead space ventilation

Dead space = non perfused alveoli – larger airways

VE = frequency of respiration(breaths/minute) x

tidal volume (Vt).

Decreases in alveolar ventilation can occur either

from a decrease in the total minute ventilation or

an increase in the dead space ventilation or both.

Alveolar ventilation

■ VA = f (Vt - Vd)

■ Effect of breathing pattern

– 12 x (600-150) = 5400ml/min

– 24 x (300 – 150) = 4200ml/min

■ Effect of machine added dead space

– 12 x (600 – (150anat + 100apparatus )) = 4200

ml/min

Relation between minute ventilation and pCO2

pCO2

Alveolar

ventilation

At higher pCO2 values, smaller changes in alveolar

ventilation result in large increases in pCO2

Prone positioning

Proning – PROSEVA trial -ARDS

■ You turn the patient on

their stomach and leave

them for 12-16 hours of

the day

■ There are videos on how

to do it – NEJM

■ https://www.nejm.org/do

i/full/10.1056/NEJMoa1

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