高流量氧疗的生理效应,Physiological Effect of High Flow Nasal Cannula (HFNC) Therapy,上海交通大学第一人民医院急诊与危重病科 俞康龙,COI statement,The author has no conflict of interest to declare.,High Flow,an interesting oxygenation method,- novel - magic - gentle and moderate,So cool,HFNC shines during RSI,Put the big cannulae into your patients nose and letr rip. Add a face mask or NIV or whatever your preoxygenation pleasure, then push your meds and laugh to yourself as the saturation rises during apnea. Whistle sweetly as the intern illuminates every inch of the soft palate with great determination. Hell, go see another patient and tell him to call you when hes given up.,You remember, though, the days of the giants. When being regarded as a skilled laryngoscopist meant something. When the word airway made internists scatter like mice. When it wasnt so easy to save a life. http:/emupdates.com/2012/03/01/the-high-flow-nasal-cannula-in-the-emergency-department/,Pediatrician has promoted oxygen therapy,Oxygen therapy & oxygen delivery devices,HFNC,The role of HFNC in respiratory therapy,What is HFNC?,a “new” methods of oxygen therapy air/oxygen applied to patient at high flow rates air/oxygen run through a nasal cannula air/oxygen is well conditioned by sufficient warmth and humidification -so called heated, humidified high-flow nasal cannula (HHHFNC) therapy,2-70 L/min,Mechanisms of action for HFNC,Washout of nasopharyngeal dead space Reduction of inspiratory resistance (work of breathing) by providing adequate flow Improved mechanics by supplying adequately warmed and humidified gas Reduction in the metabolic cost of gas conditioning Provision of distending pressure,Washout of nasopharyngeal dead space,The high volumetric flows pouring from a small bore cannula cause high velocity flows which create turbulent energy to flush the upper airway of expiratory gas.,Dead space washout improves ventilation,anatomical dead space in adults 30% of tidal volume in neonates 50% of tidal volume change the gas composition in nasopharyngeal space reduce rebreathing expired CO2 increase the fraction of inspired O2 increase alveolar ventilation efficiency,MV = (VT VD) x RR PaCO2 = PeCO2 / (1 VD/VT) PaO2 = (PBO2 PH2O) x FiO2 PaCO2 / R PA-aO2,CO2 washout during HFNC with different flow rates,NHF rates 0 L/min 30 L/min 60 L/min Midway through expiration (t =1.2 s) End of expiration (t =2.2 s),Van Hove SC, et al. Ann Biomed Eng (2016) 44: 3007-3019.,High flow and high velocity increase alveolar ventilation efficiency,likely minimize the inspiratory resistance associated with the nasopharynx by providing nasopharyngeal gas flows that match or exceed a patients peak inspiratory flow Coanda effect occuring in the nasopharyngeal region during expiration potentially assist expiratory efforts bring about a decrease in work of breathing and respiratory rate create more turbulent energy for more effective washout flush the expiratory gas from the upper airway quickly during the exhalation phase of breathing, which is critical in patients with rapid breathing,Ventilatory Responses to HFNC,Mndel T et al. Mechanisms of nasal high ow on ventilation during wakefulness and sleepJ Appl Physiol , 2013. 114: 10581065,Mucociliary transport system,Health ciliated epithelium Damaged ciliated epithelium,https:/www.fphcare.com/files/images/hospital/respiratory-care-continuum/full-width/mucociliary-disfunction-table/,Mucosal functions dependent on inspired humidity,Williams, RB. Respire Care Clin N Am 1998 Jun; 4 (2): 215-28,Temperature and humidity,Low temperature does mean insufficient humidity. Enough water supplement does not always mean sufficient humidity. An adult may require approximately 150 calories/min (10kcal/h) for conditioning inspiratory air from ambient to BTS.,Kacmarek RM, et al. Egans Fundamentals of Respiratory Care. St. Louis, MO: Elsevier/Mosby, 2013.,Inspired gas needs conditioning,Respiration with ambient gas, not warmed or humidified, induced bronchoconstriction response, and resulted in a significant decrease in both pulmonary compliance. The nasal air passages expend quite a few energy to warm and humidity inspiratory air from ambient to BTS. Studies from the 1990s demonstrated the negative effects of using non-warmed, non-humidified gas to support respiration.,Flow and Pressure fundamentals,HFNC is intended to be an open system, with flow delivered to a patient via nasal cannula, where the cannula prongs do not occlude the nares and where the patients mouth is not held closed. In this open system, the pressure in each compartment is a function of the resistor(s) that lie in series downstream from that compartment. In this regard, circuit pressures will always be substantially greater than pressure in the nasopharynx.,Factors determin nasopharyngeal pressure,the flow setting the patients unique anatomical dimensions the leak out of the nose around the prongs and out of the mouth (OD of cannula prong vs. I