DISCUSSION
In our study, HFNC was a proper respiratory management for patients
admitted to PICU because of asthma. We observed that there was no
difference in PS at admission between children which only received HNFC
or those with NIMV support. Children with only HNFC received less
pharmacological therapies and have fewer days of hospitalization.
Finally, they did not require escalating therapeutic measures the days
of PICU admission were lower. We observed that lower
SatO2/ FiO2 and higher
PCO2 at admission were related to the use of NIMV.
The HFNC delivers a flow of warm and humidified air, with a variable
oxygen fraction (between 0,21-1) and a flow between 2 and 60 litres.
From a theoretical point of view, the HFNC reduces the oropharyngeal
dead space, reduces CO2rebreathing26, improves
mucociliary clearance27and generate an end positive pressure in the airway up to 6
cmH2O during
expiration17,28,29.
The growing interest in the use of HFNC as respiratory support derives
from these properties added to a higher comfort for the
patient24,29.
It also does not need synchronisation with patient breathing and
requires less nursing care (versus a NIMV device). The HFNC would help
the respiratory muscles to overcome the auto-peep characteristic of
obstructive pathologies. Also, this constant flow may facility the
renewal of nasopharyngeal air that would contribute to improving
CO2 washing and
oxygenation17.
As previously said, asthma is one of the leading causes of PICU
admission. The evidence about the utility of HFNC as optimal respiratory
support is scarce. Recently, Ramnarayan et al. carried out a
pilot study to assess it through a multicenter and randomised clinical
trial. They found that it was common to switch treatment from HFNC to
CPAP. Also, HFNC patients experienced fewer ventilator-free days at day
2821. Added to this, an
observational study in 42 asthmatic children by Pilar et al.concluded that initial support with HFNC was no optimal and delay
support with NIMV20. In
our prospective observational study, the HFNC was the most frequent
respiratory assistance applied. In 74% of patients, the HFNC was their
first and only support. None of these children needs to escalate to
NIMV. In the rest cases, the HFNC was always used as de-escalation of
NIV.
About this absence of necessity to switch from HFNC to NIMV, we must do
some commentaries. As can be seen in our series children with higher
PCO2 and lower SatO2/
FiO2 received NIMV as first support. Furthermore, there
is a tendency to use HFNC in older patients (median age 25 versus 14
months in the case of NIV, p> 0.05). There were also
differences among groups regarding chest radiography, initiation of
empirical antibiotic therapy, administration of magnesium sulfate, and
continuous nebulisation of salbutamol. Although we did not find
differences in PS we thing that children with NIMV support were more
severe at PICU admission. As explained previously the management was not
protocolised. The attending experience influenced the respiratory
assistance chosen and act as a selection bias that for sure influences
our results.
About the days of PICU or hospital admission, they were no longer in
HNFC group that in others (Table 3). These findings are contrary to what
has been described in other
studies21. This
observation may be related to this selection bias in which HNFC will be
effective.
This study has several limitations. It is a single-centre study.
Patients under the age of two are included. Although those with acute
bronchiolitis diagnosis were excluded, this fact should be taken into
account. It is also observed that this was the age group in which the
need for non-invasive was higher. The choice between different
therapeutic options was influenced by the know-how of the physician in
charge of each patient. This non-protocolised approach influenced the
results through a selection bias about the utility of HFNC. It also
informs about the importance of clinical experience to ensure the
success of this respiratory approach.
In summary, in our study, the HFNC was a safe approach that did not
require escalation to NIV. It did not increase the length of hospital
admission. Initial blood gases and the absence of high oxygen
requirements on admission could be helpful to select children that will
be good responders to HNFC. The external validation of our results is
complex. Randomised and multicenter clinical trials are needed to verify
this data.