This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2018. Authors present a systematic review of the HFNC for adult patients. One of the issues addresed is the rol of high flow in patients undergoing bronchoscopy. Here you can see what the article says about it.
The HFNC has been studied as an adjunct to airway instrumentation during manipulation of the airway (e.g., bronchoscopy, intubation) in patients with both low and high risk (i.e., hypoxemia, morbid obesity).
Simon et al. randomized hypoxemic patients (PaO2/FiO2 < 300) undergoing bronchoscopy in the critical care setting to HFNC or NIV (20 patients per group). The FiO2 was set initially to 1.0 and then adjusted to achieve SaO2 of above 90%. The HFNC was set to deliver 50 l/min and NIV was set to a PEEP of 3–10 cmH2O and a pressure support of 15–20 cmH2O. The authors found that the HFNC was inferior to NIV for maintenance of oxygenation during bronchoscopy of critical care patients with moderate to severe hypoxemia .
Lucangelo et al. compared delivery of 50% oxygen before and during bronchoscopy using either a HFNC (40 or 60 l/min) or a Venturi mask in stable patients (SaO2 > 90% while breathing room air) undergoing bronchoscopy. Fifteen patients in each group contributed data at baseline (while breathing room air), at the end of bronchoscopy (during which they had received 50% oxygen using the assigned treatment modality) and 10 min after bronchoscopy (at which time they were receiving 35% oxygen through a Venturi mask). Patients receiving 60 l/min via HFNC maintained higher PaO2 values, higher arterial-alveolar oxygen tensions and higher PaO2/FiO2 ratios both during and after the procedure. In an attempt to explain their findings, the authors measured airway pressures in healthy volunteers; at a flow rate of 60 l/min the median pressure measured was 3.6 cmH2O whereas at a flow rate of 40 l/min, the median pressure measured was 0 cmH2O. Although interesting, this finding does not necessarily mean that HFNC at 60 l/min must be used to maintain oxygenation during bronchoscopy in patients with mild respiratory dysfunction as suggested by the authors .
Induction of sedation/anesthesia for intubation requires (ideally) pre-oxygenation followed by administration of medications (sedatives and/or neuromuscular blockers). The resultant apnea provides better conditions for vocal cord visualization  but at the same time may be accompanied by downward spiraling hypoxemia . Although oxygenating face masks must be removed for intubation, the HFNC may be left in place, theoretically maintaining CPAP and thereby prolonging the non-hypoxemic apnea time. Vourc’h et al. assigned adult patients with respiratory failure (PaO2/FiO2 < 300, respiratory rate > 30) in six ICUs to one of two groups during intubation: either 100% FiO2/60 l/min delivered by HFNC (n = 63) or 15 l/min O2 delivered by a face mask (n = 61). The HFNC was kept in place during intubation whereas the face mask was removed after induction of general anesthesia. Pre-oxygenation parameters, the duration of the intubation procedure and the quality of airway visualization were similar in the two groups. Despite randomization, the two groups had similar “lowest SaO2s” and mortality rates. The authors therefore concluded that “using HFNC without discontinuation during an apneic period was not more effective than face mask in preventing desaturation regardless of the severity of respiratory distress” .
Jaber et al. randomized hypoxemic patients undergoing intubation in a single ICU (hypoxemia defined as SaO2 < 90% on 0.5 FiO2, respiratory rate > 30, PaO2/FiO2 < 300 within the four hours before inclusion) to pre-oxygenation with either a combination of NIV and HFNC (n = 25) or NIV alone (n = 24). The time from induction to secure airway was 120 and 60 s for the intervention and control groups, respectively (calculated as non significant). The outcome was assessor-blinded. No differences were observed between the groups in intubation-related complications. However, during intubation, peripheral capillary oxygen saturation (SpO2) remained constant at 100% with combination treatment but decreased to 96% with NIV alone . Although this difference was statistically significant, its clinical importance is doubtful.
Simon et al. also randomized patients with hypoxemic respiratory failure who required intubation to pre-oxygenation with either a HFNC with 50 l/min of 100% oxygen (n = 20) or a bag-valve-mask with 10 l/min of 100% oxygen (n = 20). In the 1 min of apnea after induction of anesthesia, saturation dropped significantly more in the bag-valve-mask group than with the HFNC . The authors observed that only patients that had not been pre-treated with HFNC or NIV prior to pre-oxygenation demonstrated an increase in SpO2. This led them to conclude that pre-oxygenation with a HFNC prior to intubation should be considered only in patients with mild-moderate hypoxemia. In contrast to other authors who have published on this topic, these authors also calculated the power required to detect a 3% difference in SpO2 between the groups and concluded that their study had been underpowered to detect the difference they had sought.
Obese patients have a particularly low functional residual capacity (FRC), which increases the likelihood and severity of hypoxemia during apnea when compared to other patients . Heinrich et al. randomized obese patients (BMI > 35) undergoing intubation for bariatric surgery to receive FiO2 1.0 in one of three modes (11 per group): HFNC (flow 50 l/min), face mask connected to an anesthesia ventilator (flow 12 l/min) and CPAP (7 cmH2O). PaO2 increased significantly in all the groups within one minute of initiating pre-oxygenation. However, after five minutes, patients treated with a HFNC had a significantly higher PaO2 than those treated with a face mask and, after intubation (at 8.5 min), SpO2decreased significantly with the face mask and CPAP but not with the HFNC .
To summarize, HFNCs may have a role in decreasing apneic hypoxemia during airway instrumentation but multicenter trials that include a greater number of patients are required to establish this claim."