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ORIGINAL ARTICLE

Detection of postoperative sleep-disordered breathingusing a portable monitoring device

Ian D. Weir & Khaleel Mohammed Ahmed & Steve Korbuly & Anil Achaen &Mary OMalley & Ed OMalley & Christopher Manfredi & Dorothy B. Wakefield &Jonathan M. Fine & Stephen M. Winter

Received: 9 November 2010 /Revised: 18 August 2011 /Accepted: 5 September 2011 /Published online: 28 September 2011# Springer-Verlag 2011

AbstractPurpose Adverse surgical outcomes may occur morefrequently in patients with sleep-disordered breathing(SDB). Despite this concern, there have been no prospec-tive studies using objective measures of postoperative SDBto determine the scope of the problem. We designed aprospective study to determine the feasibility of identifyingSDB in elective postoperative patients by the use of a typeIV portable monitor (PM).Methods Patients >18 years old who presented for electivesurgery with at least one postoperative hospital night on anon-monitored unit were enrolled and wore a type IV

device that measured nasal flow, heart rate, and oxygensaturation on their first postoperative night. Respiratorydisturbance index (RDI) and oxygen desaturation index(ODI) were generated for each patient.Results Data sufficient for interpretation were collectedon 100/116 patients enrolled. SDB (RDI 5) wasobserved in 51% of the study group, and 17% had aRDI >15. An elevated ODI 5 was seen in 42%, while17% had an ODI 15. Device malfunction occurred in16% of the study participants.Conclusion A type IV PM can be employed in the postop-erative setting to detect and gauge the severity of SDB.

This paper is presented at the American Thoracic Society NationalMeeting 2008.

I. D. Weir :K. M. Ahmed : C. Manfredi : J. M. Fine :S. M. WinterSection of Pulmonary and Critical Care Medicine, InternalMedicine, Norwalk Hospital,Norwalk, CT, USA

K. M. Ahmede-mail: [email protected]

C. Manfredie-mail: [email protected]

J. M. Finee-mail: [email protected]

S. M. Wintere-mail: [email protected]

I. D. Weir :A. Achaen :M. OMalley : C. ManfrediSleep Section, Internal Medicine, Norwalk Hospital,Norwalk, CT, USA

A. Achaene-mail: [email protected]

M. OMalleye-mail: [email protected]

S. KorbulyInternal Medicine, Norwalk Hospital,Norwalk, CT, USAe-mail: [email protected]

E. OMalleyOptimal Sleep,Easton, CT, USAe-mail: [email protected]

D. B. WakefieldUniversity of Connecticut Health Center,Farmington, CT, USAe-mail: [email protected]

I. D. Weir (*)Norwalk Hospital Sleep Disorders Center,24 Stevens Street,Norwalk, CT 06854, USAe-mail: [email protected]

Sleep Breath (2012) 16:881886DOI 10.1007/s11325-011-0590-1

Keywords Obstructive sleep apnea . Sleep-disorderedbreathing . Portable monitoring . Oxygen . Postoperativecomplications

AbbreviationsOSA Obstructive sleep apneaSDB Sleep-disordered breathingRDI Respiratory disturbance indexAHI Apnea hypopnea indexODI Oxygen desaturation indexCPAP Continuous positive airway pressureBMI Body mass indexMEND Morphine equivalent narcotic dose

Background

Postoperative sleep-disordered breathing (SDB) hasgarnered major attention due to concern that this widelyunderdiagnosed disorder leads to postoperative compli-cations and is associated with difficult intubations [1].Screening tools have been proposed that depend on theidentification of recognized risk factors for SDB, includ-ing clinical signs such as hypertension, symptoms, andabnormal overnight oximetry [1]. Issues exist, however,concerning the validity of these screening tools foridentification of patients at risk for postoperative SDB.Missing from the traditional risk factors, for example, butpresent after surgery are the lingering effects of narcoticsand sedatives as well as the changes in rapid eyemovement sleep [2]. Validation of these screening tools,moreover, has relied on association with postoperativecomplications, which can be difficult to assign to SDBrather than to related comorbid conditions or on poly-somnography (PSG) prior to surgery. The underlyingassumption with the latter is that the identification ofSDB by polysomnography in the preoperative statesuffices to predict the occurrence of respiratory disturban-ces indicative of SDB in the immediate postoperativestate. To actually prove that this assumption is true,postoperative SDB must be identified, which would be adaunting task using the gold standard of PSG.

An alternative method to full-scale PSG for identifyingSDB is the use of a multichannel type IV portable testingdevices that detect respiratory disturbances characteristic ofSDB by measuring nasal air flow, oximetry, and heart rateand an actigraph to record movement as a surrogate forwakefulness. These type IV devices have been approved forhome testing and may be more workable in the postoper-ative environment because of ease of set up and minimalintrusiveness. A potential barrier to the use of type IV

devices, however, is that postoperative patients frequentlyreceive oxygen via nasal cannula, which could obscurethe measurement of nasal flow. This barrier could bepotentially overcome by employing a dual-lumen nasalcatheter for simultaneous delivery of oxygen and mea-surement of air flow, although this solution has not beenwell examined. In this study, we examine the feasibilityof using a type IV device, including dual-lumen nasalcatheters for patients receiving supplemental oxygen, inpostoperative patients to detect respiratory disturbancescharacteristic of SDB.

Methods

Study sample

The study was approved by the institutional review board atNorwalk Hospital. Over a 9-month period, we recruitedstable postsurgical patients older than 18 years old whopresented to a university-affiliated community teachinghospital for an elective surgery with an expected stay onthe general surgical floor of at least one postoperative night.Patients were excluded if they refused to participate, hadnasal packing or any other reason why nasal flow could notbe measured, were clinically unstable including requiring ahigher level of care postoperatively (telemetry or ICU), orwere currently on continuous positive airway pressure(CPAP) at home. Enrolled patients wore a Medcare(currently Embla) Compass type IV device (Reykjavik,Iceland) on the first postoperative night that measurednasal flow by a nasal pressure transducer, heart rate,and oxygen saturation. This device shares the internalcomponents of the Embletta X10 device and usesRemLogic software system. Patients were placed onoxygen by a respiratory therapist postoperatively ifoxygen saturation was

following morning. A total recording time of at least6 h was required for the study to be considered valid.The data collected were used to generate a respiratorydisturbance index (RDI) defined as the number ofapnea or hypopnea events per hour of recorded timeminus the movement time, and oxygen desaturationindex (ODI) defined as the number of oxygen desatu-ration events of greater or equal to 4% per hour ofrecorded time minus the movement time. Movementtime (estimated wake time) was detected by the use ofa built-in actigraph. Nasal flow, heart rate, and oxygensaturation data were prepared using Somologica soft-ware and scored by a physician with specialized trainingin sleep medicine using preestablished criteria [3].Apnea was defined as a greater than 90% reduction offlow from baseline for 10 s and hypopnea was defined as a30% reduction of flow for 10 s associated with a 4%oxygen desaturation. Because we did not measure sleepdirectly, we did not include respiratory effort-relatedarousals in the RDI. Postoperative sleep-disorderedbreathing was defined as a RDI 5 in accordance withpublished guidelines [4].

Patient characteristics

Patient data were collected from the medical record andincluded the following: patient demographics, personalhistory of OSA, family history of OSA, BMI, type ofanesthesia, type of surgical procedure, length of surgery,difficult intubation, oropharyngeal exam, neck circumfer-ence, Mallampati score, and past medical history includingcardiac and pulmonary disease. Also, abstracted was theanesthesiologist's impression of whether OSA was present.No formal screening tool was used. Sedative medicationsincluding narcotics and benzodiazepines given over 24 hfrom surgery were recorded. The morphine equivalentnarcotic dose (MEND) score, tabulated as milligrams ofmorphine equivalent over 24 h, was calculated for eachpatient.

Postoperative complications were assessed by the use ofelectronic chart review and discharge diagnosis Interna-tional Statistical Classification of Diseases and RelatedHealth Problems (ICD-9) codes. Electronic chart and ICD-9code review were blinded to the results of the portablemonitoring. A complication was said to occur if any oneof the following occurred during the hospitalization afterthe planned procedure: reintubation, acute hypercapnia(PaCO2>45), use of noninvasive ventilation, postoperativepneumonia, myocardial infarction or ischemia, cardiacarrhythmia, unplanned transfer to higher level of care(ICU or telemetry), or death. The association betweeneither RDI or ODI and patient characteristics was per-

formed by using the Pearson chi2 bivariate analysis or twosample t test with equal variances.

Results

Study sample and patient characteristics

A total of 214 outpatients were evaluated for inclusion inthe study. Ninety patients refused to participate in the study.Others were excluded because of device malfunction priorto initiation of data collection (n=3), concern for latexallergy (n=1), and device not available (n=4). No patientovertly refused to wear the device after being attached.Among the 116 patients tested, 16 patients (2 with the dualcannula) had a flow signal recording insufficient forinterpretation, resulting in 100 (86%) patients with ade-quate monitoring data for at least 6 h. Most were female(77%) and the mean SD for age was 5815.4 years(Table 1). Among the 100 patients included in the study, 44patients required oxygen postoperatively and were studiedwith a dual-lumen cannula with an average oxygen flowrate of 2.5 l/min. The average dose of midazolamadministered over 24 h was 2.31.4 mg. Only 4 of 100patients received midazolam in the post anesthesia care unitor surgical ward. Twenty-one patients were included in thestudy after undergoing laparoscopic banding proceduresand were not previously diagnosed with SDB or usingCPAP. The mean SD of RDI and ODI for all patients was8.812.3 and 7.710.1, respectively. The mean SD (inpercent) for time 5 and RDI >5 except for age (p=.001). Noassociation between MEND score and RDI was observed(p=0.43).

Fifty-one of the 100 patients evaluated had evidence ofSDB with an RDI 5, one third of whom had an RDI >15(Table 2). One patient had a personal history of OSA andwas not using CPAP. All 100 patients were screened forOSA by the anesthesiologist prior to surgery and 5 patientswere thought by the anesthesiologist to have OSA. Therewere four difficult intubations

No increase in the serious complication rate occurredamong patients with SDB compared with those withoutSDB. Five (5%) patients had postoperative complications,two of whom had evidence of SDB (RDI 5). Postoperativepneumonia was diagnosed in one patient with SDB and twopatients without SDB. One patient with SDB requiredreintubation the following day and one patient without SDBwas transferred to telemetry due to an arrhythmia. No

Sleep Breath (2012) 16:881886 883

complication was diagnosed during the recording period,and there were no deaths among the enrolled patients.

Discussion

These results show that the use of a type IVmonitoring deviceto detect respiratory disturbances suggestive of SDB isfeasible in postoperative patients, including those requiring

supplemental oxygen via nasal cannula. All patients agreeingto participate in the study tolerated wearing the cannula andactigraph, further supporting the use of this monitoring device.This method, therefore, appears suitable for monitoringpostoperative patients to determine whether the types ofcomplications reported are plausibly related to SDB and togive better estimates of the prevalence of this problem.

Although this was strictly a feasibility study, weobserved that among the selected patient population

Table 2 Postoperative sleep-disordered breathing and oxygenation

Classification All patients (n=100) No oxygen (n=56) Oxygen (n=44)

Sleep-disordered breathing

Respiratory disturbance index 5 (%) 51 62 36Respiratory disturbance index >15 (%) 17 20 14

Mean RDI SD 8.812.3 10.312.5 6.89.2

Oxygenation

Oxygen desaturation index 5 (%) 42 55 25Oxygen desaturation index >15 (%) 17 21 11

Mean ODI SD 7.710.1 7.511.3 4.97.5

Mean SD time class 2(mild systemic disease) (%)

25 19 32

884 Sleep Breath (2012) 16:881886

studied, 51% had an abnormal RDI and, among these, 33%had an RDI greater than 15. These rates are considerablyhigher than the prevalence estimate in the general outpatientpopulation [5]. Additionally, a recent study of patientspresenting for ambulatory surgery by Collop and colleaguesidentified only 4.8% of patients at high risk for OSA [6]. Ourpopulation of patients, however, may not be representative ofall non-critically ill postoperative patients because approxi-mately half of the eligible patients refused to participate. Nopostoperative complications, moreover, occurred among thepatients while they were being monitored. Nonetheless, theelevated prevalence rate noted raises concern that the firstpostoperative night surgical population comprises a high riskgroup for sleep-disordered breathing.

Flow measurement characteristics from the dual-lumencatheter were excellent. Although patients wearing the dual-lumen catheter had risk factors for SDB similar to thosewearing the single-lumen catheter, they were significantlyless likely to have an abnormal RDI. This finding is notsurprising given that the calculation of RDI is partiallydependent on oxygen saturation measurement. Whethersupplemental oxygen also provides a protective effect orsimply masquerades the apneas in this setting is unknown.Furthermore, it is possible that oxygen may prolong apneasby decreasing the arousal threshold and, thereby, worsenthe severity of the sleep-disordered breathing at the sametime that the RDI may be lowered.

Current recommendations from the American Society forAnesthesiologists call for identification of OSA usingtraditional risk factors, physical findings, and past medicalhistory and for the scoring of OSA severity based on PSG.PSG results, in concert with the type of surgery andpostoperative narcotic use, are recommended for postoper-ative risk stratification [1]. In our study, anesthesiologistspreoperatively identified only 5% of the patients found tohave postoperative SDB despite screening all patients,highlighting the poor predictive value of clinical impressionalone. The STOP-Bang scoring system has been proposedas a screening tool for preoperative patients and has beenvalidated for identifying OSA patients outside of thehospital setting with a negative predictive value of 83.6%for apnea hypopnea index (AHI) >5 and 92.9% for AHI>15%, among the 51% of patients agreeing to be studied[7]. Although plausible, these methods of screening andscoring have not been validated for the immediatepostoperative setting. The use of the type IV monitoringdevice would allow the reasonable determination ofwhether patients with SDB in the postoperative settingcan be accurately identified and their severity estimatedwith these screening methods. It is worth noting that noprospective study has shown that a screening programfollowed by the provision of positive airway pressurereduces the hazards associated with postoperative SDB.

Further studies are also needed to characterize the risk ofpostoperative complications in patients with SDB and todetermine the effect of postoperative positive airwaypressure. Given the very high prevalence of SDB found inour postoperative patients, we speculate that some of ourpatients had SDB associated only with the type ofphysiologic conditions associated with the postoperativestate and might not have had a diagnosis of SDB made withmeasurements in the preoperative period. Further, mostknown risk factors and MEND score were not associatedwith SDB in this study, although our patient populationmay have been underpowered to detect such associations.Follow-up PSG data were not collected on the studypatients and, therefore, the long-term health risks frompostoperative SDB are unclear. This potential group ofpatients with transient demonstration of SDB might notshare the same risk for postoperative complications as thosewith more chronic cardiovascular stress. Moreover, theabsence of chronic compensatory responses may place thispopulation at even greater risk. This is an importantquestion for future studies.

Limitations of this study include our inability todistinguish central from obstructive apneas because effortbelts could not be employed in this postoperative popula-tion. We, therefore, use the more general term of sleep-disordered breathing, accepting actigraphy as a validmethod of estimating sleep. It is also unclear if makingsuch a distinction between central and obstructive apneaswould be useful in assessing postoperative complicationrisk. Portable devices may also overestimate or underesti-mate the AHI when compared to overnight PSG. [8, 9]Although movement time was excluded, it is possible wecounted apneas or hypopneas that did not occur in sleep.More likely, however, we may have overestimated the totalsleep time and, as a result, may have underestimated theRDI. It should also be recognized that PM has not beenvalidated with PSG postoperatively and that setting specificvariables may affect the diagnostic reliability of PM. Anadditional caveat is the high refusal rate to participate inthe study, which is not surprising given the expecteddiscomfort experienced by these patients and is a likelyissue for any postoperative study. Inadequate duration ofstudy and device malfunction was observed in 19 of the 116patients agreeing to be studied, which is consistent with thefindings in other studies employing similar portable devices[10].

In conclusion, our pilot study shows that a type IVdevice can be employed in the postoperative setting todetect and gauge the severity of SDB. For patients requiringsupplemental oxygen via nasal cannula, a dual cannula canbe employed to detect flow; however, RDI may beartificially reduced by the prevention of oxygen desatura-tion by the supplemental oxygen. Further studies are

Sleep Breath (2012) 16:881886 885

feasible using such methods to determine the accuracy ofproposed postoperative SDB screening tools and to deter-mine what special risk factors for OSA that surgery mayimpose.

Disclosure There is no financial support, conflict of interest, andoff-label or investigational use to disclose.

References

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

c.11325_2011_Article_590.pdfDetection of postoperative sleep-disordered breathing using a portable monitoring deviceAbstractAbstractAbstractAbstractAbstractBackgroundMethodsStudy sampleMeasure of postoperative respiratory disturbance indexPatient characteristics

ResultsStudy sample and patient characteristics

DiscussionReferences

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