Non-invasive support in hypoxemic patients: nasal high

flow, helmet CPAP or NIV?

Tommaso Mauri University of Milan

Non-invasive respiratory support in hypoxic ARF

Rationale:

• Maintain physiologic spontaneous breathing vs. un-physiologic passive positive pressure ventilation

• Avoid complications of invasive mechanical ventilation: sedation, paralysis, poor clearance of secretions, infections, delirium, muscles weakness

• Avoid VILI??? Mauri T Annals Transl Med 2017

Mascheroni Intensive Care Med 1988 Brochard AJRCCM 2017

Hyperventilation

Healthy sheep, pharmacologic-induced hyperventilation causes hypoxic lung injury.

P-SILI: VILI during spontaneous breathing.

Ventilation-induced lung injury during spontaneous breathing

Physiologic effects of ideal non-invasive support

Given the rationale, the ideal non-invasive support should:

• Improve oxygenation

• Increase CO2 clearance

• Decrease work of breathing

• Limit the risk of PSILI: decrease lung stress, strain, heterogeneity

• Be associated with high patient comfort

What is nasal high flow?

High-flow nasal cannula (HFNC): 30-60 l/min of heated and humidified mix of air and oxygen at desired set FiO2.

HFNC is not a lot of oxygen!

Papazian L Intensive Care Med 2016

Mauri T AJRCCM 2017 Ou X CMAJ 2017 (meta-analysis)

HFNC improves oxygenation and decreases the respiratory rate

40 l/min 40 l/min

Moller W J Appl Phys 2017

At the same FiO2, HFNC delivers more oxygen to distal airways

Matching between set and alveolar FiO2

PEEP effect by NHF

Parke R Respir Care 2011

PEEP is between 2 and 5 cmH2O with mouth closed, 1-3 cmH2O with mouth open, fluctuations of PEEP level are intrinsic to HFNC support

CO2 wash-out from the upper airways

Moller W J Appl Physiol 2017

Krypton scintigraphy ≈

CO2 scintigraphy

Healthy volunteers: disappearance of Krypton from the nasal, pharyngeal and tracheal airways during HFNC.

During HFNC, the system clear CO2 out more efficiently. Mechanisms: • Decreased CO2

rebreathing by washout? • Decreased CO2

production by reduced respiratory effort?

• Maybe both?

Mauri T AJRCCM 2017

Improved CO2 clearance by nasal high flow

MVcorr= MV * actual PaCO2/40 mmHg

0

1

2

3

4

5

6

7

8

9

10

1

DPLcm

H2O

ΔP

L cm

H2O

Decreased lung stress

HFNC Venturi

Chiumello AJRCCM 2008 Mauri T AJRCCM 2017

ΔPL

End-inspiratory driving transpulmonary pressure is decreased during HFNC (improved mechanics?)

Lung stress = driving transpulmonary pressure (ΔPL)

PEEP effect decreases lung strain

Bellani AJRCCM 2011 Mauri T AJRCCM 2017

Unchanged tidal volume Increased EELV

Lung strain = Vt/EELV

HFNC decreases ventilation heterogeneity

20

30

40

50

60

70

80

1

Globalin

homogeneity%

HFNC Venturi

Cressoni AJRCCM 2015 Mauri T AJRCCM 2017

Ventilation heterogeneity measured by EIT

HFNC decreases ventilation heterogeneity (PEEP + more physiologic effort?)

Mauri T Crit Care Med 2013

What is helmet CPAP?

PEEP

PEEP PEEP

Continuous flow of humidified gas delivered within a sealed helmet. Gas outlet is connected to a PEEP valve. Continuous application of 5-15 cmH2O of PEEP

Bellani G Minerva Anest 2008

Helmet CPAP improves oxygenation

Cammarota ICM 2011 Isgrò ICM 2010 Cosentini Chest 2010

In patients with acute respiratory failure, helmet CPAP improves oxygenation both by increased correspondence between set and alveolar FiO2 and by PEEP

Helmet CPAP and CO2 rebreathing

Taccone CCM 2004 Patroniti ICM 2003

Patient breaths inside a “small room” flushed by continuous flow but still some CO2 accumulates. The higher the flow the better. Helmet CPAP increases the dead space and decreases CO2 clearance

Helmet

Face mask

Helmet CPAP and WOB

L’Her AJRCCM 2005 Elliott Anaesthesia 1994

CPAP

Decreased hypoxic drive and PEEP should decrease patient’s effort, but probably due to CO2 rebreathing, effort and WOB are not decreased by helmet CPAP

Helmet CPAP and lung stress

Elliott Anaesthesia 1994

CPAP

In the absence of positive pressure during inspiration, the lung stress is the Pes deflection and if they remain stable , the stress is not decreased

Helmet CPAP decreases lung strain

Patroniti ICM 2003 Elliott Anaesthesia 1994

Helmet CPAP increases the end expiratory lung volume (due to PEEP +/- recruitment) with unchanged tidal volume. Vt/EELV ratio will be decreased.

Helmet CPAP and heterogeneity

Mauri T CCM 2013

No data on heterogeneity measured during helmet CPAP but higher PEEP decreased heterogeneity in intubated patients undergoing stable PSV, maybe the effect could be similar…

Comfort during helmet CPAP

Brambilla ICM 2014

Chiumello Crit Care 2008

Cavaliere Acta Anest Scand 2008

Helmet CPAP can be noisy and uncomfortable, use HME at the inlet might decrease noise

What is Face mask NIV?

Sealed mask that directly connects the airways to a ventilator, which usually delivers PSV or BIPAP Face mask NIV is different from high flow and helmet CPAP because it is inspiratory positive pressure ventilation!!!!

García-de-Acilu M Curr Opin Crit Care 2019

Face mask NIV improves oxygenation

Face mask NIV improves oxygenation mostly because of the high PEEP level applied

L’Her AJRCCM 2005

Face mask NIV and CO2 rebreathing

Patroniti ICM 2003

Helmet

Face mask

Inside the face mask CO2 accumulates, albeit less than within the helmet. Face mask increases the dead space

Face mask NIV decreases WOB

Navalesi ICM 2007

Fraticelli CCM 2009 Vanpee Chest 2002

Face mask NIV decreases the WOB as the work is done in part by the ventilator

Face mask NIV and lung stress

L’Her AJRCCM 2005

Face mask NIV usually increases the tidal volume and the decrease in esophageal pressure swing is compensated by positive pressure ventilation, thus NIV usually increases stress

Chiumello Crit Care 2008

Face mask NIV and lung strain

Patroniti ICM 2003

Face mask NIV increases EELV similarly to helmet CPAP, however the tidal volume is decreased and the decrease in lung strain will be less pronounced

Face mask NIV and heterogeneity

Mauri T CCM 2013

No data on heterogeneity measured during Face mask NIV but higher PSV increased heterogeneity in intubated patients undergoing PSV, maybe the effect could be similar…

Comfort during face mask NIV Cavaliere Acta Anesth Scand 2008

Frat NEJM 2015

Comfort duting face mask NIV is better than during helmet CPAP but worse than with nasal high flow

Paw

∆Pes

∆PL

SB NHF H-CPAP NIV CMV

NHF and NIV decrease effort but only NHF decreases effort AND transpulmonary pressure. Helmet CPAP provides higher PEEP and preserves SB.

What to choose?

EFFECTS ON: HFNC HELMET CPAP

FACE MASK NIV

Oxygenation ++ +++ +++

CO2 clearance +++ -- +

Decrease WOB ++ - +++

Lung stress ++ - --

Lung strain + +++ +

Heterogeneity + ++? -?

Comfort +++ - +

There is no ideal non-invasive support Each has pro and cons

Healthy volunteers, HFNC+CPAP to obtain high stable PEEP + CO2 washout. Mauri AJRCCM 2018

HFNC+HELMET: a new highly effective support?

Variable

Set PEEP: 3 cmH2O

n=5

Set PEEP: 5 cmH2O

n=5

Set PEEP: 8 cmH2O

n=5

P-value

Pawm, cmH2O 3.2 [2.8-3.5] 5.4 [5.4-6.0] 8.2 [8.1-8.5]* <0.001

ΔPaw, cmH2O 1.0 [0.7-1.1] 0.8 [0.6-1.1] 0.7 [0.4-1.0] 0.522

Helmet + HFNC might be the best option?

EFFECTS ON: HFNC HELMET CPAP

FACE MASK NIV

HELMET+HFNC

Oxygenation ++ +++ +++ +++

CO2 clearance +++ -- + +++

Decrease WOB ++ - +++ ++

Lung stress ++ - -- ++

Lung strain + +++ + +++

Heterogeneity + ++? -? ++

Comfort +++ - + +/-

HFNC vs. standard oxygen

High Flow Nasal Cannula Compared with Conventional Oxygen Therapy for Acute Hypoxemic Respiratory Failure: A Systematic Review and Meta-analysis. Rochwerg B, Granton D, Wang DX, Helviz Y, Einav S, Frat JP, Mekontso-Dessap A, Schreiber A, Azoulay E, Mercat A, Demoule A, Lemiale V, Pesenti A, Riviello ED, Mauri T, Mancebo J, Brochard L, Burns K.

Intensive Care Med, 2019

Metanalysis of published trials comparing HFNC vs. stabdard oxygen. 9 trials, >1700 hypoxemic patients No effect on mortality, but significantly decreased intubation rate and need for escalation of therapy (from HFNC to NIV to intubation; from oxygen to HFNC, NIV, intubation).

HFNC vs. standard oxygen

Intensive Care Med, 2019

Effects of HFNC on intubation

Effects of HFNC on the need of escalation of therapy

Helmet vs. standard oxygen

81 patients with pneumonia in the ED PF ratio 140-150, RR 32-34 15% vs. 63% of patients meeting criteria for intubation, mostly because of respiratory distress or severe desaturation.

RR >25 b/min; PaO2/FiO2 ≤300, PaCO2 ≤45 mmHg

SpO2 ≥92%, NIV ≥8 h/d

HFNC vs. NIV

Primary endpoint: lower intubation rate

Secondary endpoints: lower intubation in pts with p/f ≤200 and survival in the whole population

Helmet vs. NIV

83 ARDS patients NIV PEEP 5 PS 11 Helmet PEEP 8 PS 8 Helmet decreased intubation rate and mortality.

Helmet vs. HFNC

NO DATA

Conclusions

Physiologic approach:

• HFNC decreases WOB and PL but has limited PEEP effect

• Helmet has higher PEEP effect

• NIV decreases WOB and can deliver high PEEP but increases PL

Evidence-based approach:

• HFNC and Helmet better than oxygen alone

• HFNC and Helmet better than NIV

• Helmet vs. HFNC???????