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1、高流量氧疗的生理效应,Physiological Effect of High Flow Nasal Cannula(HFNC)Therapy,1,COI statement,The author has no conflict ofinterest to declare.,2,High Flow,an interesting oxygenation method,-novel-magic-gentle and moderate,So cool,3,HFNC shines during RSI,Put the big cannulae into your patients nose and l
2、etr 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
3、 when hes given up.,You remember,though,the days of the giants.When being regarded as a skilled laryngoscopist meant something.When the wordairwaymade internists scatter like mice.When it wasnt so easy to save a life.http:/,4,Pediatrician has promoted oxygen therapy,5,Oxygen therapy&oxygen delivery
4、devices,HFNC,6,The role of HFNC in respiratory therapy,7,What is HFNC?,a“new”methods of oxygen therapyair/oxygen applied to patient at high flow ratesair/oxygen run through a nasal cannulaair/oxygen is well conditioned by sufficient warmth and humidification-so called heated,humidified high-flow nas
5、al cannula(HHHFNC)therapy,2-70 L/min,8,Mechanisms of action for HFNC,Washout of nasopharyngeal dead spaceReduction of inspiratory resistance(work of breathing)by providing adequate flowImproved mechanics by supplying adequately warmed and humidified gasReduction in the metabolic cost of gas conditio
6、ningProvision of distending pressure,9,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.,10,Dead space washout improves ventilation,anatomical dead spac
7、ein adults 30%of tidal volume in neonates 50%of tidal volume change the gas composition in nasopharyngeal spacereduce rebreathing expired CO2increase the fraction of inspired O2increase alveolar ventilation efficiency,MV=(VT VD)x RR PaCO2=PeCO2/(1 VD/VT)PaO2=(PBO2 PH2O)x FiO2 PaCO2/R PA-aO2,11,CO2 w
8、ashout during HFNC with different flow rates,NHF rates 0 L/min 30 L/min 60 L/minMidwaythroughexpiration(t=1.2 s)End ofexpiration(t=2.2 s),Van Hove SC,et al.Ann Biomed Eng(2016)44:3007-3019.,12,High flow and high velocity increase alveolar ventilation efficiency,likely minimize the inspiratory resist
9、ance associated with the nasopharynx by providing nasopharyngeal gas flows that match or exceed a patients peak inspiratory flowCoanda effect occuring in the nasopharyngeal region during expiration potentially assist expiratory effortsbring about a decrease in work of breathing and respiratory ratec
10、reate 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,13,Ventilatory Responses to HFNC,Mndel T et al.Mechanisms of nasal high ow on ventilation during w
11、akefulness and sleepJ Appl Physiol,2013.114:10581065,14,Mucociliary transport system,Health ciliated epithelium Damaged ciliated epithelium,https:/,15,Mucosal functions dependent on inspired humidity,Williams,RB.Respire Care Clin N Am 1998 Jun;4(2):215-28,16,Temperature and humidity,Low temperature
12、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
13、.,17,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 BT
14、S.Studies from the 1990s demonstrated the negative effects of using non-warmed,non-humidified gas to support respiration.,18,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 w
15、here 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.,19,Factors deter
16、min nasopharyngeal pressure,the flow settingthe patients unique anatomical dimensionsthe leak out of the nose around the prongs and out of the mouth(OD of cannula prong vs.ID of nares),20,Mechanisms of Action:HFNC Differs from CPAP,Mndel T et al.Mechanisms of nasal high ow on ventilation during wake
17、fulness and sleepJ Appl Physiol,2013.114:10581065,21,Effects of flow on airway pressure during HFNC,Higher flow rate creates higher airway pressure.Pressure is different when mouth closed or open.Only moderate positive airway pressure(10cmH2O)can be generated by HFNC.,Parke R,et al.Respir Care 2011;
18、56(8):11511155.,22,Positive airway pressure is not the principle mechanism of HFNC,The basic flow setting is meant fundamentally to exceed normal inspiratory flow rates so as to eliminate entrainment of room air,and enhance nasopharyngeal washout effects.Excessive flows in an attempt to generate sub
19、stantial distending pressures should not be utilized.To accomplish the actions of dead space washout,selecting nasal prongs should have an outside diameter no more than 50%of the inside diameter of the patients nares.Thus,only moderate nasopharyngeal pressure can be expected.,23,Summary of HHHFNC,24,Thanks！,25,
