ReliableClinicalMonitoringusingWirelessSensorNetworks:ExperiencesfromaStep‐downHospitalUnit
OctavChipara,ChenyangLuThomasBailey*,Gruia‐CatalinRomanComputerScience&Engineering,SchoolofEngineering
*DepartmentofMedicine,SchoolofMedicine
MoAvaAon
ClinicaldeterioraDoninhospitalizedpaDents 4‐17%sufferfromadverseeventssuchascardiacorrespiratoryarrest.
Upto70%ofsucheventscouldhavebeenprevented.
EarlydetecDonofclinicaldeterioraDonbasedonvitalsigns clinicaldeterioraDonisoOenprecededbychangesinvitals
Real‐DmepaDentmonitoringisrequired wiredpaDentmonitoringequipmentinIntensiveCareUnits mostgeneralhospitalunitscollectvitalsmanually wirelesstelemetrysystemstooexpensiveforwideadopDon
2
Goal:reliablewirelessclinicalmonitoringforgeneralhospitalunits
OurApproach
1. Buildaclinicalmonitoringsystemusingsensornetworks.2. Deployitinageneralhospitalunitover7months.
3. Clinicaltrialwith46hospitalizedpaDents.
4. HolisDcsystemreliabilitystudy:networkandsensor.
5. DemonstratepotenDalforclinicaleventdetecDon.
3
SystemArchitecture
BasestaDon• LaptopconnectedtoWi‐Fi
Relays• Pluggedintowalloutlets• Redundantdeployment
coverage faulttolerance
Portablepulseoximeter• pulseoximeter+microcontroller+
radio
• ba`eryoperated
4
ReliableNetworkArchitecture
Problem:PaDentsingeneralhospitalunitsareambulatory.SoluDon:Two‐Derarchitectureforend‐to‐enddatadelivery.
1 DynamicRelayAssociaDonProtocol(DRAP):PaDent‐>1strelay DynamicallyassociatethepaDentnodewitharelay
Single‐hopprotocolhandlespaDentmobility SimplifypowermanagementinpaDentnodes(sendonly)
2 StaDonaryrelaynetwork:1strelay‐>…‐>basestaDon ReusewelltestedmeshrouDngprotocol:CTP
IsolatedfrompaDentmobility
Wall‐plugged=>noneedtoworryaboutenergy
5
ClinicalDeployment
Step‐downcardiaccareunit• 16paDentrooms,1200m2
Network• 18relays:redundantnetwork• Longestpath:3‐4hops• Channel26ofIEEE802.15.4
PulseandoxygenaDoncollectedevery30or60seconds
46paDentsenrolled• >41daysofmonitoring
• 2‐68hoursperpaDent• 5paDentsexcludedfromanalysis• Upto3paDentsataDme
6
PotenAalforDetecAngClinicalDeterioraAon
!"
#$%&
7
Bradycardia
!"
#$%&
Pulmonaryedema
!"
#$%&
Sleepapnea
SystemReliability
Networkreliability>95%forallpaDents. EffecDvenessofDRAP+CTP
Mediansensingreliability>80%. But29%ofpaDentswithsensingreliability<50%
Systemreliabilitydominatedbysensingreliability.
8
NetworkReliability Time‐to‐failure
TimeintervalduringwhichasystemconDnuouslyoperateDllafailureoccurs.
Time‐to‐recovery TimeintervalfromtheoccurrenceofafailureDllwhenthesystemrecovers.
9
Recoverfrom90%offailureswithin2min=>Quickrecoveryfromfailure
CDFofAme‐to‐failure CDFofAme‐to‐recovery
MedianCmetofailure=19min
SensingReliability Failuresarecommon:medianDme‐to‐failure<2min
Recoverfrom90%ofsensingfailureswithin4min Transientfailurescausedbyhumanmovement
Long‐taileddistribuDonforDme‐to‐recovery SensordisconnecDon
10
90%ofoutages<4min
Longtail
CDFofAme‐to‐failure CDFofAme‐to‐recovery
RelaxSamplingRates
Increaserequiredsamplingperiodto5,10,15min Oversampleat1‐2reading/min Consideredasuccessifonevalidmeasurementperrequiredsamplingperiod
SDllordersofmagnitudehigherratethanmanualmeasurement
Higherreliabilityatasamplingperiodof5min Diminishingreturnatlongersamplingperiods
11
Sensingreliabilityatdifferentsamplingrates
SensorDisconnecAonAlarms
AutomaDcallynoDfynurseaOerreceivingnodataforaDmeoutthreshold
15minDmeoutbalances#alarmsvs.reliabilitygain Infrequentalarms:1.55intervenDonsperpaDent,perday Similarreliabilityto5and10minDmeouts
12
SensingreliabilitywithdifferentAmeouts #alarmsperday
PuLngthemtogether
DisconnecDonalarmsandoversamplingarecomplementary.• DisconnecDonalarms=>handlessensordisconnecDon• Oversampling=>handlesintermi`entfailurescausedbymovement
88%ofpaDentswith>70%sensingreliabilitywith5minsamplingperiodand15minDmeout
13
WirelessSensorNetworksvs.Wi‐Fi
MoreenergyefficientthanWi‐Fiatlowdatarate Commonvitalsignshavelowdatarate. Nursesaretoobusytochangeba`eries!
Lowdeploymentcost Meshnetworkswithoutwiredinfrastructure.
EaseadopDon(e.g.,fieldhospitals,ruralareas). EvenmajorhospitalsmaynotguaranteefullWi‐Ficoverage.
Sufficientreliability Mediannetworkreliability>99%inourclinicaltrial. Evenawirednetworkwouldimprovereliabilityonlymarginally.
14
Relatedprojects
Assistedliving:ALARM‐NET
Disasterrecovery:AID‐N,CodeBlue,WIISARD
Emergencyroom:MEDISN,SMART
MoDonanalysis:Mercury
Commercialwirelesstelemetry(Phillips,Cisco,GE)• WiFi=>single‐hopwireless,wiredbackbone• adopDonlimitedtospecializedhospitalunits
15
Conclusion
Wirelessclinicalmonitoringforgeneralhospitalunits. Clinicaltrialinastep‐downhospitalunit
• Highlyreliablenetwork
• Systemreliabilitydominatedbypulseoximetersensors Oversampling
DisconnecDonalarms
• PotenDalfordetecDngclinicaldeterioraDon
On‐going:real‐DmeclinicaleventdetecDon IntegraDonwithelectronicmedicalrecords EventdetecDonbasedonmachinelearning
AutomaDcalarmsforearlyintervenDon LargerclinicaltrialofeventdetecDonsystem
16