Some Nasal Background
For years, proponents of rapid sequence intubation have tried to identify the most reliable way to prevent desaturation. Pre-oxygenation is an important part of the RSI strategy, and avoidance of hypoxia in the head injured patient predicts an adverse outcome. RSI fundamentalists believe that NO positive pressure ventilation should take place during an RSI attempt. Positive pressure ventilation theoretically increases the risk for emesis and may cause gastric insufflation. Recently, the strategy\ of high flow oxygen via nasal cannula (HFNC) at flow rares in excess of 15 lpm has emerged as a feasible strategy for passive oxygenation. In patients undergoing RSI, the application of HFNC has been shown to increase "safe apnea time."
Dr. Rich Levitan, a nationally recognized (and emergency medicine trained) airway expert has published on the "NO-DESAT" protocol. This protocol advocates for HFNC in addition to the usual measures can prevent and perhaps maintain oxygen saturation during rapid sequence intubation.
Nice summary of "NO-DESAT" here:
http://www.epmonthly.com/archives/features/no-desat-/
THE PREOXYFLOW TRIAL
A recent study published in Intensive Care Medicine looks more specifically at the use of HFNC in hypoxic patients. The study randomized patients to either high flow oxygen via face mask or high flow (>60 lpm!) nasal cannula. The primary outcome of interest was the lowest saturation of oxygen measured by pulse oximetry.
The study randomized over 120 ***sick*** adult patients. These patients exhibited respiratory failure as evidenced by a high Fi02 requirement, tachypnea, or hypoxia. The study results did not establish the superiority of the HFNC technique, and both patient groups (HFFM and HFNC) experienced significant medical complications.
Does this study urge practitioners to back off the cannula?
Should HFNC be abandoned for patients exhibiting significant respiratory distress?
Before attempting to summarize this trial, we've got to remember that when talking about HFNC, we're still comparing oral airways to king LTs. That is to say, there's quite a lot of difference between the use of HFNC as an adjunct and the use of HFNC as a primary strategy for avoidance of hypoxia. Also, this study uses nasal cannulae specifically designed to accommodate high flow rates. Can the ordinary oxygen regulators supply flow rates in excess of 60 lpm? Probably not. Given peri-intubation hypoxia's association with adverse outcomes, it makes sense that airway practitioners should try to maximize a patients oxygen reserve. Sustaining normoxic values in distressed patients is always a challenging endeavor, and emergency medicine regularly encounters patients at risk for desaturation. Whether its poor respiratory mechanics, morbid obesity, acute blood loss, or baseline pulmonary disease, there are many threats to address in the pre-intubation phase of RSI. Furthermore, its pretty clear that a higher preintubation oximetry reading is linked to that precious "safe apnea" time... that wonderful interval prior to the obnoxious cascade of alarms that herald impending doom.
BOTTOM LINE:
-The PREOXYFLOW trial (HFNC vs HFFM) is NOT an indictment o the NO-DESAT protocol and does not mean that HFNC is bad for patients
-Hypoxia is, in general, something to avoid during RSI
-Use HFNC to complement preoxygenation efforts
-Severely hypoxemic patients may require more active measures to increase and maintain a satisfactory pre-oxygenation level
-In patients with respiratory failure, HFNC as a "stand alone" hypoxia prevention strategy may not represent best practice
Keep the high flow flowing!
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