8. High flow nasal cannula
Traditionally small nasal cannula has been used for delivery
of oxygen. Varying flow rates have been used and a flow rate of
more than 1 L/minute is described as high flow oxygen delivery.
It was believed that high flows through nasal cannula
may not be feasible. However, for this mode to be effective the
inhaled gases should be heated and humidified (HHHFNC:
Heated Humidified High Flow Nasal Cannula). HHHFNC has
been shown to generate distending pressure or CPAP. However,
the amount of pressure generated varies with size of
nasal cannula and flow rates. The average external diameter
of binasal prongs to deliver CPAP is 3.7e4.6 mm. The
commonly used nasal cannula to deliver oxygen has an
external diameter of 1.5e2.4 mm. Some of the initial studies
did not find any significant benefit of HFNC possibly because
these used lower flow rates.34,35 The Cochrane review published
in 2011 did not find enough evidence in favor of efficacy
or safety of flow rates more than 1 L/minute to treat RDS in
preterm neonates.35
Nasal CPAP with binasal prong may be difficult to manage
for prolonged periods especially in active preterm infants. It is
also likely to be associated with nasal injury, occasionally
resulting in permanent disfigurement. Kaufman et al
described a nasal trauma score which is a good bedside
monitoring tool for early detection of nasal injury thus minimizing
the damage (Table. 6).36 More work with HHHFNC
showed that with varying degrees of nasal occlusion ranging
from 33% to 80% and flow rates more than 2e3 L/minute could
achieve significant distending pressures.37,38
Various studies comparing HHHFNC with nCPAP have
shown no difference in extubation failure rates in the first
week (Tables 7 and 8).39e42 With evidence emerging from more
RCTs in progress, if they are able to show equivalence of
HHHFNC with nCPAP, the nasal canula oxygen therapy is
likely to be more widely used especially in situations where
nCPAP is difficult to maintain or the risk of nasal trauma is
high. Most of these trials used a flow rates ranging from 3 to
8 L/minute.38 Klingenberg compared patient comfort in 20
preterm infants