REVIEW ARTICLE

David S. Warner, M.D., Editor

Home Noninvasive Ventilation

What Does the Anesthesiologist Need to Know?

Karen A. Brown, M.D.,* Gianluca Bertolizio, M.D.,† Marisa Leone, R.R.T.,‡ Steven L. Dain, M.D.§

ABSTRACT

Treatment of chronic respiratory failure with noninvasiveventilation (NIV) is standard pediatric practice, and NIVsystems are commonly used in the home setting. Althoughpractice guidelines on the perioperative management of chil-dren supported with home NIV systems have yet to be pub-lished, increasingly these patients are referred for consulta-tion regarding perioperative management. Just as knowledgeof pharmacology underlies the safe prescription of medica-tion, so too knowledge of biomedical design is necessary for

the safe prescription of NIV therapy. The medical devicedesign requirements developed by the Organization for In-ternational Standardization provide a framework to rational-ize the safe prescription of NIV for hospitalized patients sup-ported at home with NIV systems. This review articleprovides an overview of the indications for home NIV ther-apy, an overview of the medical devices currently available todeliver it, and a specific discussion of the management co-nundrums confronting anesthesiologists.

N ONINVASIVE ventilation (NIV) refers to a tech-nique of augmenting alveolar ventilation without the

requirement for an invasive artificial airway. The use of NIVin the home was introduced in the 1980s for the long-termtreatment of sleep apnea, and has more recently been used forthe management of chronic hypercapnic respiratory failure.Management of acute respiratory failure may also includeNIV, both to avoid invasive ventilation and to facilitateweaning from mechanical ventilation. Interested readers arereferred to a recent review in Lancet.1 This review focuses onthe use of NIV in the home for the management of chronicstable respiratory failure and/or obstructive sleep apnea.

Children with Duchenne muscular dystrophy wereamong the first patients to be managed with domiciliary NIVtherapy. Children currently represent 10% of patients man-aged in home ventilation programs.2 Children on home NIVtherapy are now presenting to anesthesiologists for diagnosticand surgical procedures. There are substantial questions con-cerning the optimal management of these children: Shouldthey be permitted the use of their own domiciliary NIVmedical devices? Are they eligible for ambulatory surgicalprograms? With respect to their own NIV medical devices,the ECRI Institute (formerly Emergency Care Research In-stitute) has cautioned hospitals against the use of patient-supplied medical equipment.3,4 The answers to the aboverequire a working understanding of the indications for homeNIV therapy, the medical devices used to deliver it, and theimpact of sedative and analgesic medications on NIV ther-apy. This review provides an overview of the indications forNIV therapy, an overview of the medical devices available to

* Professor, Division of Pediatric Anesthesia, McGill UniversityHealth Center Research Institute, Montreal Children’s Hospital,Montreal, Quebec, Canada, and Vice-Chair, Canadian AdvisoryCommittee for the International Organization for Standardization,Technical Committee 121, Subcommittee 3 Breathing Machines.† Clinical Fellow, Shriners Hospital for Children Pediatric AnesthesiaFellowship, McGill University, Montreal, Quebec, Canada. ‡ Assis-tant Chief Respiratory Therapist, Department of Pediatric Respira-tory Therapy, Montreal Children’s Hospital of the McGill UniversityHealth Center, Montreal, Quebec, Canada. § Associate Professor,Department of Anesthesia and Perioperative Medicine, SchulichMedicine and Dentistry, University of Western Ontario, London,Ontario, Canada, and Chair, Canadian Advisory Committee for theInternational Organization for Standardization, Technical Commit-tee 121, Subcommittee 3 Breathing Machines.

Received from the Division of Pediatric Anesthesia, McGill Uni-versity Health Center Research Institute, Montreal Children’s Hos-pital, Montreal, Quebec, Canada. Submitted for publication Novem-ber 23, 2011. Accepted for publication May 12, 2012. Dr. Brown issupported by the Queen Elizabeth Hospital of Montreal FoundationChair in Pediatric Anesthesia, McGill University, Montreal, Quebec,Canada, and Dr. Bertolizio was supported by the Shriners Hospitalfor Children Pediatric Anesthesia Fellowship, Montreal, Quebec,Canada. Figures 1, 4, 6, and 9 were created by Annemarie B.Johnson, C.M.I., Medical Illustrator, Wake Forest University Schoolof Medicine Creative Communications, Wake Forest UniversityMedical Center, Winston-Salem, North Carolina.

Address correspondence to Dr. Brown: Division of PediatricAnesthesia, McGill University Health Center/Montreal Children’sHospital, 2300 Tupper Street, Rm. C-1118, Montreal, Quebec H3H1P3 Canada. roula.cacolyris@muhc.mcgill.ca. This article may beaccessed for personal use at no charge through the Journal Web site,www.anesthesiology.org.

Copyright © 2012, the American Society of Anesthesiologists, Inc. LippincottWilliams & Wilkins. Anesthesiology 2012; 117:657–68

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deliver NIV therapy, and a specific discussion of manage-ment conundrums facing anesthesiologists. The discussionfocuses on children, because the use of NIV therapy in thepediatric patient exposes the limitations of NIV systems.However, these pediatric concerns may also be relevant tosmall adults and patients with poor respiratory musclestrength and reduced respiratory neural drive.

The technique of noninvasive ventilation has two uniquefeatures that distinguish it from invasive ventilation with aendotracheal tube. First, noninvasive ventilation employs anonhermetic technique, and the mask interface is deliber-ately designed to leak. Second, whereas invasive ventilationbypasses the upper airway with a endotracheal tube, the non-invasive ventilation system incorporates the upper airwayinto the breathing pathway.5 NIV modalities include contin-uous positive airway pressure (CPAP) and noninvasive posi-tive airway pressure ventilation (NIPPV), both of which de-liver a therapeutic positive airway pressure. NIPPV is alsoreferred to by the acronym NPPV (noninvasive positive pres-sure ventilation) and BiPAP (bilevel positive airway pres-sure), and BiPAP® is also the name of a NIV medical devicemanufactured by Philips Respironics (Murrysville, PA).

An Overview of the Indications for Domiciliary NIVMedical Indications for Home CPAP Therapy. In 1981,Colin Sullivan introduced CPAP therapy as a modality toreverse the symptoms of obstructive sleep apnea (OSA).6

CPAP therapy is currently widely prescribed for the manage-ment of OSA in adults and in children with OSA refractoryto adenotonsillectomy.7,8 During CPAP therapy, the posi-tive airway pressure acts as a pneumatic splint for the pha-ryngeal airway.9 It also increases lung volume (i.e., functionalresidual capacity).10 Both actions act to decrease the collaps-ibility of the upper airway and thereby mitigate obstructionof the pharyngeal airway, offset auto-positive end-expiratorypressure, reduce the load on respiratory muscles, and de-crease the work of breathing. In adult patients, CPAP levelsof 5 and 10 cm H2O may increase tidal volume by 80 ml and150 ml, respectively. CPAP therapy may also improve gasexchange.11 In patients with coexistent pulmonary diseaseand OSA, CPAP therapy may also improve lung function. Inpatients with coexistent heart failure and OSA, CPAP ther-apy may improve cardiac function.12

Prescription of home CPAP therapy in children is re-served for those with OSA refractory to adenotonsillectomy.Initiation of CPAP therapy usually involves a CPAP titrationstudy in a sleep laboratory. Once discharged home on CPAPdevices, children are followed in outpatient clinics, and theirmanagement requires periodic review with overnight poly-somnography. Preoperative consultation with the sleep phy-sician or respirologist is important.Medical Indications for Home NIPPV Therapy. In chronicrespiratory failure associated with neuromuscular disease and

morbid obesity, respiratory muscle weakness may lead tohypoventilation during both sleep and wakefulness. Hall-marks of hypoventilation during wakefulness are a chroniccompensated respiratory acidosis, i.e., daytime hypercapniawith an increased serum bicarbonate level, and a low oxygensaturation on room air during wakefulness. Management ofchronic hypercapnic respiratory failure with domiciliaryNIPPV in children with neuromuscular and chest wall dis-ease is now standard practice.12–19

NIPPV therapy aims to deliver a therapeutic pressureduring inspiration – the inspiratory positive airway pres-sure (IPAP) – and hold a positive pressure on exhalation –the expiratory positive airway pressure (EPAP). LikeCPAP therapy, bilevel airway pressure therapy aims tosplint the pharyngeal airway and preserve lung volume.18

During inspiration, NIPPV therapy further augments airwaypressure by increasing inspiratory airflow in order to provide aninspiratory assist to the muscles of respiration. Indeed, NIPPVtherapy in adult patients has been shown to improve tidal vol-ume and minute ventilation by 33% and 17%, respectively.18

The use of NIPPV therapy during sleep enhances gas exchangeand decreases the work of breathing.13,20 Both exercise toleranceand quality of life improve.21

As pulmonary function declines, respiratory supportduring wakefulness may also be indicated. In the past,children with deteriorating respiratory status were sup-ported with a succession of increasingly complex medicaldevices, culminating in tracheostomy and invasive venti-lation. Parents and children currently may prefer to con-tinue with NIPPV therapy, in order to avoid tracheos-tomy and thereby preserve phonation and swallowingfunctions important to their quality of life. Children whorequire both nocturnal and diurnal NIPPV are at veryhigh risk for respiratory complications, because their vitalcapacity is usually less than 25% predicted, and they havedifficulty handling secretions.13 Failure of home NIVtherapy occurs more often in these children.2

Children requiring domiciliary NIPPV therapy are sup-ported and managed in comprehensive home ventilation pro-grams. Medical supervision is provided by sleep physicians andrespirologists who provide periodic review, including scheduledovernight polysomnography studies. Therefore, preoperativeconsultation with these physicians is important, because theyform the liaison with the home ventilation program.

An Overview of the Medical Devices Available to DeliverDomiciliary NIV TherapyThe acronym NIV is frequently applied to both the therapyand the device that delivers the therapy. There are presentlymore than two dozen brands of medical devices to deliverNIV therapy,5 varying in biomedical design complexity fromsimple sleep apnea equipment to sophisticated home andcritical care ventilators with NIV capabilities.

Regulatory bodies classify medical devices by risk�. Class Imedical devices are not intended for use in sustaining or sup-

� http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri�CELEX:31993L0042:EN:HTML. Accessed April 30, 2012.

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porting life and do not present a risk for injury. Examples ofClass I medical devices are stethoscopes, hearing aids and wheel-chairs. Class II medical devices are intended to support life, arerequired to meet mandatory performance standards, are de-signed to perform without causing injury, and are subject topostmarket surveillance. Examples of Class II medical devicesare infusion pumps and ventilators. Medical devices to deliverNIV therapy include both Class I and Class II medical devices.(table 1) Class I medical devices are less expensive than Class IIventilators, a reality that renders them cost-effective for home use.

The Organization for International Standards (ISO) andthe International Electrotechnical Commission, both world-wide networks of national standards institutes, develop in-ternational standards that provide the requirements for basicsafety and performance of medical equipment. These designrequirements provide a framework to compare the availablemedical devices with those that deliver home NIV therapy(table 1). Class I NIV devices comply with the standard, ISO17510 Part 1.22 Class II ventilators with NIV capabilitiescomply with ISO 10651–623 or ISO 10651–2.24 For the

Table 1. Design Features of Class I and Class II Medical Devices Available for Home Noninvasive Ventilation

Sleep Apnea BreathingTherapy Equipment:Continuous Positive

Airway Pressure Device

Sleep Apnea BreathingTherapy Equipment:

BiLevel Positive AirwayPressure Device

Home-care VentilatorySupport Devices

Home-careVentilators for

Ventilator-dependantPatients

ISO standard ISO 17510–1: 2007 ISO 17510–1: 2007 ISO 10651–6: 2004 ISO 10651–2: 2004Medical devices

classificationClass I Class I Class II Class II

DesignIntended to deliver Positive airway pressure Positive airway pressures Positive airway pressure Positive airway pressure

and ventilationIntended for use duringspontaneous breathing

Yes Yes Yes Yes

Intended to be lifesupporting

No No No Yes

Intended for use duringapnea

No No No Yes

Intended for use with anonhermetic maskdesign

Yes Yes NIV mode option NIV mode option

Intended for use withtracheal tube

No No Invasive ventilation modeoption

Invasive ventilation modeoption

MonitorsAirway pressure Mandatory Mandatory Mandatory MandatoryVentilation Optional Optional Optional Mandatory: Expiratory tidal

volume or expiratoryminute ventilation orexpiratory end-tidalcarbon dioxide

Specified accuracyfor the expiratoryvolume monitor

No No If volume monitorprovided, accuracy �20% actual value

�20% actual value

Protection DevicesMeans to allowspontaneous breathingduring devicefailure

Mandatory Mandatory Mandatory Mandatory

Maximum NIV systempressure

40 cm H2O (40 hPa) 40 cm H2O (40 hPa) 60 cm H2O (60 hPa) 60 cm H2O (60 hPa)

Means to preventrebreathing

Mandatory Mandatory Mandatory Mandatory

Alarm conditionsHigh-inspiratory pressure Not required Not required Mandatory MandatoryContinuing positivepressure

Not required Not required Not required Mandatory

High and low expiratorytidal volume andminute ventilation

Not required Not required Not required Mandatory

Hypoventilation Not required Not required Not required MandatoryHigh and low end-tidalCO2

Not required Not required Not required If a capnometer present,alarms are mandatory

Purchase price (USD) Less than $1,000 $2,000–$5,000 $6,000 More than $15,000

ISO � Organization for International Standardization; USD � United States dollars.

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purpose of this discussion, NIV systems complying with ISO17510 Part 1 will be referred to as NIV devices. NIV systemscomplying with ISO 10651–6 or ISO 10651–2 will be re-ferred to as ventilators with NIV capabilities. The same ven-tilator may be equipped with both noninvasive and invasiveventilation modalities.

The essential components of NIV systems are the flowgenerator, the breathing circuit, and the NIV mask. (fig.1) All NIV systems are designed to deliver a therapeuticairway pressure and achieve a positive airway pressure bydirecting airflow into a mask equipped with a high-resis-tance exhaust port or expiratory valve. Whereas the drivingpressure for the flow generator in critical care ventilators is sup-plied from either pipelines, compressed gas, or air compressors,in home NIV systems, it is supplied by a servo-controlled aircompressor.

Two different circuits – double- and single-limb circuits –are available for use in NIV systems, as illustrated in figure2.5 In double-limb circuits, there are separate inspiratory andexpiratory breathing pathways and an expiratory valve (fig.2A). In single-limb circuits, the inspiratory and expiratorybreathing pathway share a common conduit. Single-limbcircuits lack an expiratory valve (figs. 2BC, BD), and insingle-limb circuits, the expiratory flow cannot be directlymeasured. In double-limb circuits, the expiratory flow canonly be measured directly if the spirometer is interposedbetween the expiratory valve and the patient (fig. 2A2).Single-limb circuits are the usual circuit used to deliverhome NIV therapy.

NIV systems lack a reservoir bag, a design feature thatfacilitates the delivery of a constant positive airway pressurethroughout the phases of the respiration. However, the ab-sence of a reservoir bag requires a design that ensures anadequate peak inspiratory flow rate. These design featuresinclude a high rate of gas flow and/or an alternate inspiratorypathway. In normal operation, the level of inspiratory gasflow delivered through the breathing tube ranges from 20 to60 l/min.

The NIV mask complies with ISO 17510 –2.25 TheNIV mask is used interchangeably with Class I NIV de-

vices and Class II ventilators with NIV capabilities. De-livery of NIV therapy relies on a nonhermetic techniqueand requires a high-resistance exhaust port/expiratoryvalve located on the mask or mask connection. The ex-haust port discharges a continuous intentional leak duringnormal operating conditions. In addition, the imperfectseal of the mask to the face is an additional source ofleakage: the unintentional leak. The magnitude of theunintentional leak varies with the phase of respiration,with shifts in the mask position and with changes in the

Fig. 1. Components of a single-limb circuit noninvasiveventilation system. The exhaust port may be located in thenoninvasive ventilation mask or mask connection. Pres-sure and flow sensors are housed in the flow generator,which also contains a pressure regulation valve. NIV �noninvasive ventilation.

Fig. 2. Essential components of noninvasive ventilation (NIV)systems using double (AA, AB) and single (BD, BC) circuits.In all systems, the flow generator directs a high rate of gasflow through the inspiratory pathway to a NIV mask equippedwith an expiratory valve interposed in the circuit (AA, AB) orexhaust port (BC, BD). When applied to the face, this resultsin an intentional leak and pressurizes the NIV system. Expi-ratory airflow is only measurable when the flow meter islocated between the patient and the expiratory valve (A2). Inthe three other configurations, expiratory airflow cannot bemeasured directly. NIV � noninvasive ventilation. Repro-duced with permission from Rabec et al.,5 modified fromPerrin C, Jullien V, Lemoigne F: Aspects pratiques et tech-niques de la ventilation non invasive. Rev Mal Respi 2004;21(3):556–66.

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compliance and resistance of the upper airway and respi-ratory system. Modern NIV devices are equipped withmicroprocessors and sophisticated proprietary algorithmsthat adjust the rate of gas flow to compensate for thevariable unintentional leak.

Although NIV systems will fit a 15 mm/22 mm connec-tor, they are not intended for use with tracheal tubes. Theleak around an invasive uncuffed tracheostomy tube is insuf-ficient to adequately discharge the high rate of inspiratory gasflow, in excess of 20 l/min, without injury. Home ventilatorsfor invasive ventilation are indicated in tracheostomizedpatients.23

NIV systems have three additional design features. First,all NIV devices are equipped with a pressure sensor located inthe flow generator to detect high airway pressure. Second, allNIV systems are equipped with a pressure regulation valve inthe flow generator and design features to limit the maximumpressure to 40 cm H2O in Class 1 NIV devices and to 60 cmH2O in Class II ventilators with NIV capabilities (table 1).And third, home NIV devices are intended for dedicated usein single patient and are not designed to function with in-linefilters.CPAP Devices. CPAP devices are designed to deliver acontinuous distending pressure throughout the patient’srespiratory cycle.26 The minimum performance for thedelivery of positive airway pressure is � 1.5 cm H2O ofthe set pressure.22,27

NIPPV Systems. NIPPV devices are designed to deliver acyclical application of two levels of positive pressure: IPAPand EPAP. This requires design features that sense the phaseof respiration8,26 and trigger the transitions between IPAPand EPAP.

The Inspiratory Trigger between EPAP and IPAPThe trigger for IPAP is initiated by the patient’s inspira-tory effort and is detected by a change in airway pressureor gas flow within the NIV system.5 Most modern NIVsystems achieve the transitions between IPAP and EPAPwith flow-based triggers. Sophisticated proprietary algo-rithms have been developed to detect phasic changes in gasflow, gas waveforms, and flow reversal(s). Asynchrony be-tween the child and NIV system during the inspiratorytrigger is common especially during sleep, and thereforesome homecare NIV protocols require a backup ventila-tion rate. The selected backup rate is often set at a ratehigher than the child’s spontaneous rate during sleep, ef-fectively instituting a controlled mode of ventilator sup-port.8 NIV devices, however, are not intended for use inapneic patients (table 1).

The Expiratory Trigger between IPAP and EPAPThe trigger for expiration may be either a function of time ora threshold decline in inspiratory flow.8 In children, a max-imum inspiratory time of 0.3–0.5 s is often used.

The sensitivity of the trigger function represents an im-portant limit to the use of NIPPV in small children, partic-ularly those with poor respiratory muscle strength,18,26,28

because their low rates of inspiratory flow may be insufficientto initiate the inspiratory trigger.8 This is one of the reasonsNIV devices are not intended for use in patients weighing lessthan 30 kg. For these children, ventilators with NIV capabil-ities offer a better option.

Pressure-targeted NIPPV SystemsMost bilevel pressure NIV systems achieve the IPAP level byincreasing the rate of gas flow during inspiration, until thepredefined positive airway pressure target is attained. It isbeyond the scope of this review to discuss all NIV modalities,and readers are directed to a comprehensive review in Tho-rax.5 The two basic NIV modalities are pressure-targetedNIPPV and volume-targeted NIPPV. The majority of homeNIV systems use pressure-targeted modalities.

The EPAP is titrated to eliminate obstructive airwayevents, and IPAP is titrated to attenuate hypercarbia duringsleep. The usual levels of IPAP and EPAP range from 10 to16 cm H2O and from 4 to 5 cm H2O, respectively. NIPPVdevices have less pressure-generating capacity than ventila-tors.7 The magnitude of inspiratory assist depends on thedifference between IPAP and EPAP.18 However, the NIVsystem–lung assembly does not behave as a single compart-ment model, because the upper airway presents a variableresistance. Increasing the airway pressure may not increasethe effective ventilation to the patient.5

Volume-targeted DevicesVolume-targeted NIPPV devices deliver a set flow to theairway for a defined time interval or until a preset volume isobtained. The presence of leaks at the mask interface requiresa design feature capable of delivering very large gas flowsduring the inspiratory phase of the respiratory cycle.8 Thesegas flow rates may exceed 150 l/min.

The Interface and the NIV MaskNIV therapy is delivered with a nasal or full-face mask. TheNIV mask design is deliberately nonhermetic, allowing themask to be adjusted to comfort. The mask must be soft andsecure and yet allow for sweating. Velcro straps applied tootightly to a full-face mask may displace the mandible back-ward, allowing the tongue to obstruct the upper airway.8 Inaddition, a tight, ill-fitted mask risks skin injury and ulcer-ation. Too tight a mask, worn over many years, may ad-versely affect the growth and development of facial bones.1

Although the patient connection port may be a 15 mm/22mm connector,22,25 NIV systems are not designed for usewith a endotracheal tube, tracheostomy tube, laryngealmask, or anesthesia mask. If the expiratory trigger failed andthe high inspiratory gas flow continued during expiration,the patient could become hyperinflated, risking barotraumaand injury.

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For children, nasal masks are preferred, in part to mini-mize the apparatus dead space and facilitate the trigger func-tions of the NIV systems. During normal operation, mouthbreathing increases the gas leakage, and parents may deviseways and means to ensure the mouth remains closed duringsleep (i.e., chin straps).

In pressure-targeted NIV systems, the magnitude of theinspiratory assist decreases during perturbations such as in-creased upper airway resistance, decreased lung compliance,or increased unintentional leak. Modern NIV systems offer a“volume guarantee” mode that will deliver a minimum levelof ventilation when such perturbations occur. The efficacy ofthe “volume guarantee” mode was recently tested in six NIVsystems.29 Perturbations sufficient to decrease tidal volume(VT) were determined. The ventilators were set in the “vol-ume guarantee” mode to deliver a minimum VT. The re-sponse to a perturbation was to increase IPAP (fig. 3). Withperturbations in airway resistance or lung compliance, five ofsix NIV systems achieved the guaranteed minimum VT.However, when the unintentional leak increased, only oneNIV system achieved it. Auto-triggering, or the delivery of a

breath cycle without the patient triggering a breath, occurredfrequently during large unintentional leaks. In addition, alarge unintentional leak may preclude attainment of the pre-set IPAP, and the NIV system may not cycle to EPAP,8,18

allowing the high rate of gas flow to continue even if thepatient ceases to inhale. This high gas flow rate will impedeexhalation, increasing the work of breathing and riskingbarotraumas, gastric insufflation, and aspiration of stomachcontents. Large unintentional leaks at the mask interface areparticularly common in children.

Rebreathing Potential in NIV DevicesAlthough the ECRI Institute considers the patient-suppliedNIV mask less hazardous than the NIV device, it is the designof the NIV mask that influences the risk of rebreathing.Washout of carbon dioxide is more efficient if the exhaustport is located within the mask.4,5

Dual-limb NIV systems mitigate the degree of rebreath-ing by using an expiratory valve and separating the inspira-tory and expiratory pathways.5 In a single-limb NIV system,the inspiratory and expiratory breathing pathway share a

Fig. 3. Representative tracing showing the response to a noninvasive ventilation system with a “minimum guarantee” mode toa perturbation. The inspiratory positive airway pressure increased in order to achieve the minimum guaranteed tidal volume. Theonset and offset response times ranged from 1 to 51 breaths. The tidal volume decreased transiently during the onset andincreased transiently during the offset. The specific responses to three types of perturbations are shown in the accompanyingtable. IPAP � inspiratory positive airway pressure; NIV � noninvasive ventilation; VT � tidal volume. Adapted from Fauroux etal.29 and reprinted with permission.

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common conduit (fig. 4). As the exhaust port purposely of-fers a high resistance, the expiratory pathway may include thelow-resistance breathing tube. A high rate of gas flow is re-quired to prevent rebreathing during normal use.30 The riskof rebreathing decreases with increasing airway pressure(higher gas flows). The NIV systems are designed such thatduring normal use, the time-weighted average for inspiredcarbon dioxide is 1%, a limit which harmonizes with thatallowed in occupational health exposure.25 A minimummandatory EPAP level of 3 or 4 cm H2O (gas flow around 20l/min) is needed to ensure adequate washout of exhaled car-bon dioxide.

The risk of rebreathing is maximal when inspiratory gasflow ceases. In the event of a power failure, the inspiredcarbon dioxide level will rise precipitously, coincident with afall in inspired oxygen (fig. 5). Although a battery reserveshould protect from electrical power failure, battery life isdifficult to predict and often brief. Class I medical devicesmay not be equipped with a battery backup. Therefore, thedesign of NIV equipment incorporates a means to allowspontaneous breathing in the event of a device failure. Thismay be accomplished by including an antiasphyxiation valvein the NIV mask. A nasal NIV mask should have less risk ofasphyxiation because the child can initiate mouth breathing.However, mouth breathing may not be possible if chin strapsare used. In NIV systems, the short-term exposure limit forinhaled carbon dioxide is 3% (about 22 mmHg), a limit thatassumes that the physiologic arousal response will be suffi-cient to rouse the patient.22,25

Inspired Oxygen ConcentrationDuring power failure, with cessation of gas flow, the re-breathing of exhaled gases will allow a hypoxic admixture toaccumulate in the breathing tube (fig. 5).30 In the event of apower failure, it is expected that the sleeping patient willrouse and remove the NIV mask.

During normal use, supplemental oxygen may be inten-tionally delivered into the breathing tube or the mask inter-face. Several factors influence the inspired oxygen concentra-

tion, including the NIV modality, the rate of gas flow rate,the minute ventilation, and the location at which oxygen isdelivered into the NIV system. In healthy volunteers on NIVtherapy, a maximum inspired oxygen concentration of 67% wasreported.31 However, the inspiratory oxygen concentrationachieved in patients on NIV devices is often less than 50%.

Perioperative Management Conundrums in PatientsSupported with Domiciliary NIVPatient Selection. The safe use of NIV to support ventila-tion following surgery requires selection of both appropri-ate patients and NIV systems, and a recognition that theclinical scenario in the hospital differs from that in thehome environment.

In hospitalized patients, eligibility criteria for NIV sup-port are the ability to call for help, to pass 15 min off NIVwithout respiratory decompensation, and to maintain oxy-gen saturation with modest inspired oxygen concentra-tions.1,32 Health Canada advises that patients who have alimited ability to adjust or remove the NIV mask should beattended at all times.# NIV therapy is contraindicated ifchildren are apneic, unable to protect their own airway, un-able to maintain the patency of the upper airway, have areduced level of consciousness, or have an unstable respira-tory status.33

Can Children Supported with Home NIV Systems BeManaged in Ambulatory Surgical Programs?Class I NIV devices and some Class II ventilators with NIVcapabilities are not intended to support life (table 1). These

# http://hc-sc.gc.ca/dhp-mps/medeff/advisories-avis/prof/_2012/index-eng.php. Accessed April 30, 2012.

Fig. 5. Rebreathing potential in noninvasive ventilation sys-tems. During normal use, elimination of exhaled carbon di-oxide depends on a high rate of gas flow. In the conventionalcontinuous positive airway pressure system (A), an electricalpower-off scenario results in rebreathing of exhaled gas.There is a rapid rise in inspired carbon dioxide and fall ininspired oxygen concentration. Design features that includenonrebreathing valves (B) mitigate the risk for rebreathing.NIV � noninvasive ventilation. Reproduced with permissionfrom Farre et al.30

Fig. 4. Gas pathway in noninvasive ventilation system using asingle-limb circuit. During normal use, the flow generatordirects air into the breathing tube, which contains an admix-ture of fresh and exhaled gas. The admixture of fresh andexhaled gas is designed to egress the system via the exhaustport (intentional leak) and noninvasive ventilation mask inter-face (unintentional leak).

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NIV systems rely on the patient’s reflex and arousal mecha-nisms to monitor the function of the NIV system. Sedativeand analgesic medication may blunt arousal and reflex de-fenses. Because the safe use of NIV systems is predicated onan intact physiologic defense system, children on domi-ciliary NIV systems should not be discharged home untilthese protective and defense mechanisms have returned13

(fig. 6). Children with continuous home NIPPV therapyhave a limited respiratory reserve and are at extreme riskfor respiratory complications following anesthesia andsurgery. These children are poor candidates for ambula-tory programs.13

Which Surgical Procedures?As NIV systems include the upper airway in the breathingpathway, compromise of nasopharyngeal airway patencymay limit the efficacy of NIV therapy. Surgeries associatedwith upper airway edema, bleeding, nasal congestion, andsurgical packings may obstruct the upper airway, and affectthe efficacy of NIV therapy. Pulmonary function may beaffected in the postoperative period, and supplemental oxy-gen may be required. In addition, the settings for the NIVsystem may require adjustment. IPAP levels of 10–16 cmH2O usually provide sufficient support. Children becomeuncomfortable if IPAP settings exceed 20 cm H2O.18 Themaximum IPAP for preadolescent children is 20 cm H2O,and for adolescents the maximum is 30 cm H2O.34 Higherlevels of IPAP may increase the gas leak, and the straps secur-ing the NIV mask may require adjustment.

Can NIV Be Safely Administered on Hospital Wards?Expertise of Healthcare Providers. The challenges of deliv-ering NIPPV therapy on hospital wards are illustrated by twopublished scenarios in patients with advanced cystic fibrosis.An adolescent on continuous NIPPV was found unrespon-sive on the floor, having removed the NIPPV system withoutnotifying his nurse. A young adult with chronic respiratoryfailure developed agitation because of respiratory acidosis.Trigger asynchrony was suspected, and she was treated with

intravenous sedation. The respiratory status further deterio-rated, requiring invasive ventilation.17

Because NIV devices are used in a home environment,their use on hospital wards might seem reasonable. However,mishaps during NIV therapy have been reported in hospital-ized patients. In one case, the CPAP device was misas-sembled.35 Another patient died because of NIV system fail-ure, and a third death was linked to NIV system-relatedinfection.3 Health Canada advises that medical staff caringfor patients supported by NIV systems should be knowledge-able of the capacities and limitations of NIV systems.# Thesafe use of NIV therapy on the wards requires the selection ofpatients with stable respiratory failure, the availability of ex-pert and adequately trained staff throughout a 24-h period,adequate monitoring, and immediate access to invasive ven-tilation in the event of respiratory deterioration.1,32

In addition, the settings for NIV systems that are ade-quate in the home environment may not be therapeutic inthe postoperative period, as illustrated in figures from threeconsecutive nocturnal NIV recordings (figs. 7 and 8). Figure7A is a representative baseline trace of internally logged datafrom a home NIV system; the set EPAP and IPAP levels of 4and 15 cm H2O, respectively, were achieved throughout13 h of use. During the majority of the record, there were nopatient-triggered breaths, and ventilation was supported en-tirely with the NIV system, at a backup rate of 25 breaths/min. The estimated tidal volume was 277 ml and the esti-mated minute ventilation was 6.8 l/min. Following surgery(fig. 7B), the set EPAP and IPAP levels were identical andachieved throughout 18 h of use. However, patient-triggeredbreaths are now present throughout the record, likely reflect-ing a combination of wakefulness and pain. The recordedtidal volume has decreased to 202 ml. During the followingnight (fig. 8), the set EPAP and IPAP levels were unchangedand achieved throughout the 22 h of use, but the recordedtidal volume has now decreased to 98 ml. The levels of pos-itive airway pressure, which were therapeutic in the homeenvironment, are now inadequate.

Monitoring and Alarms: Do NIV Systems MonitorVentilation?All NIV systems are required to measure airway pressure, andthe majority of modern NIV systems log parameters of airwaypressure for periodic review. However, a data log is not synon-ymous with a monitor. Class I medical devices are not designedto monitor patients, and patient well-being is the prime indica-tor that an NIV device is functioning. A feature that distin-guishes the Class II NIV systems from Class I NIV devices is therequirement, in the former, to monitor the ventilation of thepatient (table 1). Class II ventilators for ventilator-dependantpatients are intended to deliver both positive airway pressureand ventilation and are therefore designed appropriately.24

Home ventilation programs define ineffective ventilationby the failure to attain the set airway pressures, an excessive

Fig. 6. Discharge criteria for patients supported with homecontinuous positive airway pressure devices.

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unintentional leak, and frequent desaturation indices.36

Capnography is not used in the home environment. Somemanufacturers have developed sophisticated proprietary al-gorithms that assess gas flows and estimate the unintentionalleaks of the NIV system. In addition, there are proprietaryalgorithms that estimate the delivered minute ventilationand VT of the patient. However, the accuracy and clinicalrelevance of the reported physiologic parameters lack valida-tion. Recent bench studies suggest that VT is underesti-mated, especially at high IPAP pressures.37 In the home en-vironment, there is no need for bedside reporting of data,because the efficacy of the NIV therapy is assessed by patientwell-being and periodic review of the internally logged data.In hospitalized patients it may prove useful to review thisinternally logged data, but currently this feature is not readilyavailable at the bedside.

If Patients on Domiciliary NIV Are Not Being Monitoredat Home, Do They Need to Be Monitored While in theHospital?Unless the ventilation is being monitored at the bedside,changes in the ventilatory status may not be obvious.Health Canada advises that hospitalized patients supportedwith NIV systems must be monitored with oxygen saturationand vital signs.# Arterial or capillary blood gases may also beindicated. Although capnography is available in hospitals, itsaccuracy in NIV systems may be influenced by dead space,VT, and the high rate of gas flow. Transcutaneus measure-

ment of carbon dioxide may be more useful in the hospitalenvironment.36

Should Children Be Permitted the Use of Their OwnDomiciliary NIV Systems?Of the task force’s consultants charged with developingguidelines for the perioperative management of patients withOSA, 79% strongly agreed that patients should be restartedon their home NIV therapy as soon as feasible after surgery.38

Parents and children often request the use their own NIVsystem while in the hospital, citing differences among NIVsystems in leakage, trigger sensitivities, type of circuit, andposition of the exhaust port – all of which may affect thequality of ventilatory support.39–41 In the home environ-ment, the NIV systems are reported to be robust and reli-able,8,33,42 and this request may seem reasonable. However,whereas the use of patient-supplied NIV masks is condoned,the ECRI Institute cautions hospitals against the use of pa-tient-supplied NIV systems.3,4

Most countries lack a centralized database for reportingproblems with home NIV systems.2 The lack of reporting isnot evidence of safety, as Health Canada cautions that ratesfor spontaneously reported adverse incidents (with NIVsystems) are presumed to underestimate the risk.# A mul-ticenter evaluation of 22 conventional NIV systems re-ported significant differences between the set parametersand the actual values. In 17% of patients, the index ofventilator error exceeded 20%. In addition, home NIVsystems underperform when subjected to high-level re-

Fig. 7. Representative figures illustrating the limitations of a noninvasive positive pressure ventilation system in the hospitalenvironment. In both the home (A) and hospital (B) use scenarios, the set levels of inspiratory positive airway pressure andexpiratory positive airway pressure were identical. However, the efficacy of the ventilatory support differed. EPAP �expiratory positive airway pressure; IPAP � inspiratory positive airway pressure; NIPPV � noninvasive positive pressureventilation.

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quirements similar to those which may occur during thepostoperative period.43

Another major issue with patient-supplied NIV systems isthat the alarms have frequently been disabled, because most (i.e.,low VT) enunciate so frequently they constitute a nuisance anddisrupt sleep.33,43 A feature that distinguishes the Class II NIVsystems from Class I NIV devices is the requirement, in theformer, to enunciate alarm conditions intended to summonhelp (table 1). Disabling alarms on ventilators with NIV capa-bilities negates the safety design features that distinguish Class IIfrom Class I medical devices. In the postoperative period, when thepatient’s clinical state may change rapidly, ventilators with NIPPVcapabilities, which are designed for ventilator-dependant patients,may provide more reliable respiratory support. At some point be-fore discharge, transition to a domiciliary NIV system and liaisonwith the home ventilation program is required (fig. 9).

RecommendationsAnesthesiologists increasingly encounter children who aresupported on home NIV therapy and are asked for advice on

their perioperative management. The optimal transitionfrom sedation and/or general anesthesia to their home NIVsystem is an area of study, and practice guidelines for the safemanagement of patients supported with home NIV systemshave yet to be developed. Our recommendations are listed intable 2. As the intensive care unit is the only location in ourhospital with continuously available expertise in NIV sys-tems, all children requiring NIV therapy in the postoperativeperiod are initially admitted to the intensive care unit follow-ing anesthesia. Our caseload of the children on home NIVtherapy is small, and this requirement has not proven prob-lematic. Recovery of both defensive and protective reflexesand transition to the home NIV system should occur beforedischarge from hospital.

SummaryTreatment of refractory obstructive sleep apnea and chronicrespiratory failure with home NIV is now standard pediatricpractice. Anesthetic and analgesic medications induce apnea,depress respiratory drive, decrease compliance of the respira-

Fig. 8. Representative figure in a postoperative scenario showing the limitation of the same noninvasive positive pressure ventilationsystem illustrated in Fig. 7. The set levels of inspiratory positive airway pressure and expiratory positive airway pressure remainunchanged from those in figs. 7A and 7B; however, the level of ventilatory support is much lower. EPAP � expiratory positive airwaypressure; IPAP � inspiratory positive airway pressure; NIPPV � noninvasive positive pressure ventilation.

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tory system, increase the collapsibility of the upper airway,and alter the sensorium, thereby compromising NIV ther-apy. Just as knowledge of pharmacology underlies the safeprescription of medication, so too knowledge of biomedicaldesign underlies the safe prescription of NIV medical de-vices. The medical device design requirements developed bythe Organization for International Standardization provide aframework to rationalize our choice of the medical device tosupport ventilation in the postoperative patient who has beensupported with a domiciliary NIV system.

References1. Nava S, Hill N: Non-invasive ventilation in acute respiratory

failure. Lancet 2009; 374:250 –9

2. Simonds AK: Risk management of the home ventilator de-pendent patient. Thorax 2006; 61:369 –71

3. ECRI Institute: Hazard report. Using patient-supplied respi-ratory care equipment in hospitals. Health Devices 2009;38:417– 8

4. ECRI Institute: Guidance Article. Part 2. Managing the use ofpatient-supplied medical devices: Should patients be allowedtheir own medical devices in the hospital. Health Devices2007; 155– 64

5. Rabec C, Rodenstein D, Leger P, Rouault S, Perrin C, Gonza-lez-Bermejo J, SomnoNIV Group: Ventilator modes and set-tings during non-invasive ventilation: Effects on respiratoryevents and implications for their identification. Thorax 2011;66:170 – 8

6. Sullivan CE, Issa FG, Berthon-Jones M, Eves L: Reversal ofobstructive sleep apnea by continuous positive airway pres-sure applied through the nares. Lancet 1981; 1:862–5

7. Mehta S, Hill NS: Noninvasive ventilation. Am J Respir CritCare Med 2001; 163:540 –77

8. Nørregaard O: Noninvasive ventilation in children. Eur Re-spir J 2002; 20:1332– 42

9. Hoffstein V, Zamel N, Phillipson EA: Lung volume depen-dence of pharyngeal cross-sectional area in patients withobstructive sleep apnea. Am Rev Respir Dis 1984; 130:175– 8

10. Isono S, Shimada A, Utsugi M, Konno A, Nishino T: Compar-ison of static mechanical properties of the passive pharynxbetween normal children and children with sleep-disorderedbreathing. Am J Respir Crit Care Med 1998; 157:1204 –12

11. Andersson B, Lundin S, Lindgren S, Stenqvist O, OdenstedtHerges H: End-expiratory lung volume and ventilation distri-bution with different continuous positive airway pressuresystems in volunteers. Acta Anaesthesiol Scand 2011; 55:157– 64

12. Theerakittikul T, Ricaurte B, Aboussouan LS: Noninvasivepositive pressure ventilation for stable outpatients: CPAPand beyond. Cleve Clin J Med 2010; 77:705–14

13. Ward S, Chatwin M, Heather S, Simonds AK: Randomisedcontrolled trial of non-invasive ventilation (NIV) for noctur-nal hypoventilation in neuromuscular and chest wall diseasepatients with daytime normocapnia. Thorax 2005; 60:1019 –24

14. Laursen SB, Dreijer B, Hemmingsen C, Jacobsen E: Bi-levelpositive airway pressure treatment of obstructive sleep ap-noea syndrome. Respiration 1998; 65:114 –9

15. Guilleminault C, Pelayo R, Clerk A, Leger D, Bocian RC:Home nasal continuous positive airway pressure in infantswith sleep-disordered breathing. J Pediatr 1995; 127:905–12

16. Waters KA, Everett FM, Bruderer JW, Sullivan CE: Obstruc-tive sleep apnea: The use of nasal CPAP in 80 children. Am JRespir Crit Care Med 1995; 152:780 –5

17. Teague WG: Non-invasive positive pressure ventilation: Cur-rent status in paediatric patients. Paediatr Respir Rev 2005;6:52– 60

18. Fauroux B, Pigeot J, Polkey MI, Roger G, Boule M, ClementA, Lofaso F: Chronic stridor caused by laryngomalacia inchildren: Work of breathing and effects of noninvasive ven-tilatory assistance. Am J Respir Crit Care Med 2001; 164:1874 – 8

19. Edwards EA, Hsiao K, Nixon GM: Paediatric home ventilatorysupport: The Auckland experience. J Paediatr Child Health2005; 41:652– 8

20. Padman R, Lawless ST, Kettrick RG: Noninvasive ventilationvia bilevel positive airway pressure support in pediatricpractice. Crit Care Med 1998; 26:169 –73

21. Young AC, Wilson JW, Kotsimbos TC, Naughton MT: Ran-

Fig. 9. Decision tree for the selection of a medical device todeliver noninvasive positive pressure ventilation in the hos-pitalized postoperative patient. ISO � Organization for Inter-national Standardization; NIPPV � noninvasive positive pres-sure ventilation; NIV � noninvasive ventilation.

Table 2. Recommendations for the PerioperativeManagement of Children Supported with HomeNoninvasive Ventilation Therapy

Recommendations

1. Preoperative consultation with respiratory medicine.2. Postoperative admission to the intensive care unit.3. Support with the appropriate NIV system designed

to enunciate the relevant alarm conditions.4. Independent monitoring of the oxygen saturation

and the cardiorespiratory status of the patient.5. Transition to the home NIV system prior to

discharge home.6. Liaison with the home ventilation program or

responsible physician prior to discharge home.

NIV � noninvasive ventilation.

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domised placebo controlled trial of non-invasive ventilationfor hypercapnia in cystic fibrosis. Thorax 2008; 63:72–7

22. International Standard ISO-17510 –1: Sleep Apnoea TherapyPart 1. Geneva, Switzerland: International Organization forStandardization; 2007

23. International Standard ISO-10651– 6: Lung ventilators formedical use: Particular requirements for basic safety andessential performance. Part 6: Home-care ventilatory supportdevices. Geneva, Switzerland: International Organization forStandardization; 2004

24. International Standard ISO-10651–2: Lung ventilators formedical use: Particular requirements for basic safety andessential performance. Part 2: Home ventilators for ventila-tor-dependant patients. Geneva, Switzerland: InternationalOrganization for Standardization; 2004

25. International Standard ISO-17510 –2: Sleep Apnea TherapyPart 2: Masks and application accessories. Geneva, Switzer-land: International Organization for Standardization; 2007

26. Essouri S, Nicot F, Clement A, Garabedian EN, Roger G,Lofaso F, Fauroux B: Noninvasive positive pressure ventila-tion in infants with upper airway obstruction: Comparison ofcontinuous and bilevel positive pressure. Intensive Care Med2005; 31:574 – 80

27. Antonescu-Turcu A, Parthasarathy S: CPAP and bi-level PAPtherapy: New and established roles. Respir Care 2010; 55:1216 –29

28. Stucki P, Perez MH, Scalfaro P, de Halleux Q, Vermeulen F,Cotting J: Feasibility of non-invasive pressure support venti-lation in infants with respiratory failure after extubation: Apilot study. Intensive Care Med 2009; 35:1623–7

29. Fauroux B, Leroux K, Pepin JL, Lofaso F, Louis B: Are homeventilators able to guarantee a minimal tidal volume? Inten-sive Care Med 2010; 36:1008 –14

30. Farre R, Montserrat JM, Ballester E, Navajas D: Potentialrebreathing after continuous positive airway pressure failureduring sleep. Chest 2002; 121:196 –200

31. Samolski D, Anton A, Guell R, Sanz F, Giner J, Casan P:Inspired oxygen fraction achieved with a portable ventilator:Determinant factors. Respir Med 2006; 100:1608 –13

32. Elliott MW, Confalonieri M, Nava S: Where to perform non-invasive ventilation? Eur Respir J 2002; 19:1159 – 66

33. Samuels M, Bolt P: Non-invasive ventilation in children. Pae-diatr Child Health 2007; 17:167–73

34. Kushida CA, Chediak A, Berry RB, Brown LK, Gozal D, IberC, Parthasarathy S, Quan SF, Rowley JA, Positive AirwayPressure Titration Task Force, American Academy of Sleep

Medicine: Clinical guidelines for the manual titration of pos-itive airway pressure in patients with obstructive sleep ap-nea. J Clin Sleep Med 2008; 4:157–71

35. Hove LD, Steinmetz J, Christoffersen JK, Møller A, Nielsen J,Schmidt H: Analysis of deaths related to anesthesia in theperiod 1996 –2004 from closed claims registered by the Dan-ish Patient Insurance Association. ANESTHESIOLOGY 2007; 106:675– 80

36. Janssens JP, Borel JC, Pepin JL, SomnoNIV Group: Nocturnalmonitoring of home non-invasive ventilation: The contribu-tion of simple tools such as pulse oximetry, capnography,built-in ventilator software and autonomic markers of sleepfragmentation. Thorax 2011; 66:438 – 45

37. Contal O, Vignaux L, Combescure C, Pepin JL, Jolliet P,Janssens JP: Monitoring of noninvasive ventilation by built-insoftware of home bilevel ventilators: A bench study. Chest2012; 141:469 –76

38. Gross JB, Bachenberg KL, Benumof JL, Caplan RA, ConnisRT, Cote CJ, Nickinovich DG, Prachand V, Ward DS, WeaverEM, Ydens L, Yu S, American Society of AnesthesiologistsTask Force on Perioperative Management: Practice guide-lines for the perioperative management of patients withobstructive sleep apnea: A report by the American Society ofAnesthesiologists Task Force on Perioperative Managementof patients with obstructive sleep apnea. ANESTHESIOLOGY

2006; 104:1081–93

39. Schettino GP, Chatmongkolchart S, Hess DR, Kacmarek RM:Position of exhalation port and mask design affect CO2rebreathing during noninvasive positive pressure ventilation.Crit Care Med 2003; 31:2178 – 82

40. Fauroux B, Leroux K, Desmarais G, Isabey D, Clement A,Lofaso F, Louis B: Performance of ventilators for noninvasivepositive-pressure ventilation in children. Eur Respir J 2008;31:1300 –7

41. Bunburaphong T, Imanaka H, Nishimura M, Hess D, Kac-marek RM: Performance characteristics of bilevel pressureventilators: A lung model study. Chest 1997; 111:1050 – 60

42. Reiter K, Pernath N, Pagel P, Hiedi S, Hoffmann F, Schoen C,Nicolai T: Risk factors for morbidity and mortality in pediat-ric home mechanical ventilation. Clin Pediatr (Phila) 2011;50:237– 43

43. Farre R, Navajas D, Prats E, Marti S, Guell R, Montserrat JM,Tebe C, Escarrabill J: Performance of mechanical ventilatorsat the patient’s home: A multicentre quality control study.Thorax 2006; 61:400 – 4

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