Intensive Care Medicine journal , online early access articles March 2013
Predicting non invasive ventilation failure in children from the SpO2/FiO2 ratio
Brief summary and comments:
– Spanish and Portuguese paediatric ICU study, 390 episodes over 12 months.
– goal was to validate use of SpO2/FiO2 ratio as NIV outcome predictor & develop a NIV failure prediction model.
-NIV was defined as CPAP, BiPAP, via face mask, nasal devices with initial settings EPAP( expiratory positive airway pressure ) 5cm H2O, IPAP(inspiratory pressure) 6-8cm, FiO2 variable but target SpO2 93-98%.
-Interesting point in that sedation was used as deemed necessary and in fact was given in 49.2% of cases. Midazolam was the sedation most often given. Why not ketamine? The authors do not comment on that but write that it was deemed non of the NIV failures were due to sedation. AS far as I can tell this was a clinician’s opinion alone.
– Most common indication for NIV was bronchiolitis
– NIV was successful in about 80% of cases
-NIV failure was defined as clinician’s opinion , SpO2 65mmHg , with maximal NIV settings of IPAP >25cm, EPAP>12cm
– What did they find ? Sp02/FiO2 ratio ( SF ratio) at 1 hr after NIV initiation was predictive of failure. The authors suggest the SF cutoff value of 193 at 1 hr of NIV.
HOW DO YOU CALCULATE THE SF RATIO?
SPO2 % VALUE / FIO2 DECIMAL = SF RATIO
EXAMPLE : SpO2 88% / FiO2 0.6 = 146
MY TAKE HOME MESSAGE FROM THIS STUDY :
SF ratio is simple to calculate when using NIV on a child. At 1 hr mark this study gives SOME validity into using SF ratio to highlight children who will likely fail NIV. Useful potentially in the prehospital and retrieval setting. Arterial blood gases are not fun in anyone , especially children. VBGs can give you the indicator of PCO2 and pH but they do not always correlate with NIV success or failure dependinng on when they are done in relation to NIV initiation. NIV was 80% successful in this study so its a useful modality in sick kids with acute respiratory failure. Identifying those who will be in the 20% who fail NIV early is potentially helpful information!
Nice work from our Spanish and Portuguese colleagues! Still not sure why they did not try ketamine sedation for the NIV..
Prehospital and Retrieval Medicine - THE PHARM dedicated to the memory of Dr John Hinds 
What is an acceptable ratio? What am I missing?
Matt
Greater than 193 at 1 hr
Ketamine has some disadvantages when used in infants with respiratory tract infections. It increases the production of airway secretions and lowers the trigger threshold for laryngospasm.
Pharyngeal secretions can induce laryngospasm under Ketamine sedation.
In small infants Ketamine can also cause apnoea when given fast or in higher doses.
A much more promising sedative drug for NIV is Dexmedetomidine.
Johann
thanks Johann! makes sense theoretically..would you use midazolam in a kid with resp failure for NIV tolerance?
Yes, I would use it. NIV is often not tolerated without sedation. And sometimes it is even not tolerated with sedation.
Another usefull drug to improve NIV-tolerance is Nalbuphine.It has analgesic and sedative properties but does not depress respiratory drive. I think it is safer than Midazolam.