1、高流量氧疗的生理效应高流量氧疗的生理效应 Physiological Effect of High Flow Nasal Cannula(HFNC)Therapy1COI statementThe author has no conflict of interest to declare.2High Flowan interesting oxygenation method-novel -magic-gentle and moderate3HFNC shines during RSIPut the big cannulae into your patients nose and letr ri
2、p.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
3、hes given up.You remember,though,the days of the giants.When being regarded as a skilled laryngoscopist meant something.When the word airwaymade internists scatter like mice.When it wasnt so easy to save a life.http:/ has promoted oxygen therapy1891-E.Bonnaire described O2 inhalations in the newborn
4、1963 Patrick Bouvier Kennedy dies of respiratory distress syndrome(RDS),34 weeks gestation,birthweight 2100 gms.1963 Maria Delivoria-PapadopoulosFirst successful ventilation of a preterm infant with hyaline membrane disease(Assistedventilationinterminalhyalinemembranedisease.Arch.Dis.Child.,39:481-4
5、84,19641971GregoryUse of continuous positive airway pressure(CPAP)for respiratory distress syndrome(RDS)5Oxygen therapy&oxygen delivery devicesOxygenTherapyLow flow systemsHigh flow systemsNasalcannulaFace tentO2 tentVenturi maskPRBMNRBMNIV(CPAP)ET tubeSimplemaskHFNC6The role of HFNC in respiratory
6、therapy7What is HFNC?l a“new”methods of oxygen therapyl air/oxygen applied to patient at high flow ratesl air/oxygen run through a nasal cannulal air/oxygen is well conditioned by sufficient warmth and humidification -so called heated,humidifiedhigh-flownasalcannula(HHHFNC)therapy2-70 L/min8Mechanis
7、ms of action for HFNClWashout of nasopharyngeal dead spacelReduction of inspiratory resistance(work of breathing)by providing adequate flowlImproved mechanics by supplying adequately warmed and humidified gaslReduction in the metabolic cost of gas conditioninglProvision of distending pressure9Washou
8、t of nasopharyngeal dead spaceThe 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.10Dead space washout improves ventilationlanatomical dead space in adults 30%of tidal volume in neonates 50%of
9、 tidal volume lchange the gas composition in nasopharyngeal spacelreduce rebreathing expired CO2 lincrease the fraction of inspired O2lincrease alveolar ventilation efficiencyMV=(VT VD)x RR PaCO2=PeCO2/(1 VD/VT)PaO2=(PBO2 PH2O)x FiO2 PaCO2/R PA-aO211CO2 washout during HFNC with different flow ratesN
10、HF rates 0 L/min 30 L/min 60 L/minMidwaythroughexpiration(t=1.2 s)End ofexpiration(t=2.2 s)VanHoveSC,etal.AnnBiomedEng(2016)44:3007-3019.12High flow and high velocity increase alveolar ventilation efficiencyl likely minimize the inspiratory resistance associated with the nasopharynx by providing nas
11、opharyngeal gas flows that match or exceed a patients peak inspiratory flowl Coanda effect occuring in the nasopharyngeal region during expiration potentially assist expiratory effortsl bring about a decrease in work of breathing and respiratory ratel create more turbulent energy for more effective
12、washout l flush the expiratory gas from the upper airway quickly during the exhalation phase of breathing,which is critical in patients with rapid breathing 13Ventilatory Responses to HFNC MndelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:1058106514Mucoc
13、iliary transport systemHealth ciliated epithelium Damaged ciliated epithelium缺乏湿度缺乏湿度增加感染危险加重呼吸负担小气道闭合细胞损伤https:/ functions dependent on inspired humidityWilliams,RB.RespireCareClinNAm1998Jun;4(2):215-2816Temperature and humidityl Low temperature does mean insufficient humidity.l Enough water supple
14、ment does not always mean sufficient humidity.l An adult may require approximately 150 calories/min(10kcal/h)for conditioning inspiratory air from ambient to BTS.KacmarekRM,etal.EgansFundamentalsofRespiratoryCare.St.Louis,MO:Elsevier/Mosby,2013.17Inspired gas needs conditioningl Respiration with amb
15、ient gas,not warmed or humidified,induced bronchoconstriction response,and resulted in a significant decrease in both pulmonary compliance.l The nasal air passages expend quite a few energy to warm and humidity inspiratory air from ambient to BTS.l Studies from the 1990s demonstrated the negative ef
16、fects of using non-warmed,non-humidified gas to support respiration.18Flow and Pressure fundamentalsHFNCisintendedtobeanopensystem,withflowdeliveredtoapatientvianasalcannula,wherethecannulaprongsdonotoccludethenaresandwherethepatientsmouthisnotheldclosed.Inthisopensystem,thepressureineachcompartment
17、isafunctionoftheresistor(s)thatlieinseriesdownstreamfromthatcompartment.Inthisregard,circuitpressureswillalwaysbesubstantiallygreaterthanpressureinthenasopharynx.19Factors determin nasopharyngeal pressure l the flow settingl the patients unique anatomical dimensionsl the leak out of the nose around
18、the prongs and out of the mouth(OD of cannula prong vs.ID of nares)20Mechanisms of Action:HFNC Differs from CPAPMndelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:1058106521Effects of flow on airway pressure during HFNCl Higher flow rate creates higher ai
19、rway pressure.l Pressure is different when mouth closed or open.l Only moderate positive airway pressure(10cmH2O)can be generated by HFNC.ParkeR,etal.RespirCare2011;56(8):11511155.22Positive airway pressure is not the principle mechanism of HFNCl The basic flow setting is meant fundamentally to exce
20、ed normal inspiratory flow rates so as to eliminate entrainment of room air,and enhance nasopharyngeal washout effects.l Excessive flows in an attempt to generate substantial distending pressures should not be utilized.l To accomplish the actions of dead space washout,selecting nasal prongs should h
21、ave an outside diameter no more than 50%of the inside diameter of the patients nares.l Thus,only moderate nasopharyngeal pressure can be expected.23Summary of HHHFNCHigh flow inpiratory flow ratesEliminate entrainment of room airWashout of the nasopharyngeal dead spaceNasal cannulaOpen air-supply system with high velocityWashout of dead spaceCreate positive airway pressureHeater&humidifierCondition inspiratory air from ATS to BTSProtect the functions of mucociliary transport systemReduce respiratory resistanceSave energy to condition inspiratory gasComfort patient during high flow therapy2425
