‘lume 7 Number1 January 1991
`
`JAN 17 1991
`
`CLINICAL SCIENCES CENTER LIBR
`UNIVERSITY OF WISCONSIN
`600 HIGHLAND AVE.; MADISON, WI 537
`
`Original Articles
`
`
`
`and K. Maurer, Prof Dr tied
`
`EFULNESS
`
`A. POTENTIAL
`OMA SURGERY
`
`
`Nikolaus Gravenstein, MD, and Robert H. Blackshear, MD
`vi
`erhebl ANE
`i
`UAIT
`iF
`VO MEASUREMENT
`y.“Medelin,BPhD, er M.th: McGinn, MSec_
` ATERAlf
`" PRESSUF
`SURENrn I
`Michael S. Gorback, ‘MD, Timothy J. Quill, MD,
`and Michael L. Lavine, PhD
`DUR IN
`Case iecouOF
`
`IDURALLY EVOKE
`Takato Morioka,“MD, Kivonka Puli, MD,
`Shozo Tobimatsu, MD, Masashi Fukui, MD,
`and Yoshiro Sakaguchi,MD
`
`
`S. K. Gandhi, MD, FFARCS, Charul A. Munshi, MD,
`Robert Coon,PhD, and AnnaesMD
`YW
`uy
`DIDEL I
`OXYGEN PIPEL!
`Wayne R., Audercin, MD,"iidToh Gy Brock- Utne, FEA(SA)
`releNotes
`Michael|J. Belman,MD,andRezaShadmehr,MS _
`iS BY A ON OF FAI
`‘SH GAS FLOW
`49 RE
`IAGLE-h
`G cIRCUN -
`BAIK
`BREATHIN
`AOD!
`0D
`Toh Bernard Valdrighi, MD,and Patrick Newland Nance, MD
`
`SvanYourb Manitoriag Bouipmctts
`|
`Mapiaid Ramsey IH, MD, PhD
`Correspondence
`Books
`
`35
`
`a0
`
`42
`
`~ 56
`
`68
`
`70
`
`71
`
`83
`
`102
`
`ILURE:
`
`STRATEG
`
`TLATORY MUSCLE
`
`ED OSCILLOMETRIC
`
`leTERIZATION
`AGEMENT
`John H. Eichhorn, MD, and David W. Edsall,MD
`Abstracts of Scientific Papers
`TENTH
`DICAL MONITORINE
`OLOGY CONFEREMC!
`
`ARM
`i
`ESTE
`
`MEETING OF THE SOCIET)
`
`Hi
`
`CHROLOG
`
`Announcements
`
`FICIAL JOURNAL OF THE SOCIETY
`R TECHNOLOGYINANESTHESIA
`
`A-10
`A-15
`A-16 \ND
`
`1
`
`APPLE 1011
`
`1
`
`APPLE 1011
`
`

`

`Volume 7 Number 1 January 1991
`
`ae——_$_$_$___—_1—|.—aEmrSSS——Oe
`
`JAN 1 7 9991
`OFFICIAL JOURNAL OF THE SOCIETY FOR TECHNOLOGY IN ANESTHESIA
`EDITORIAL BOARD
`EDITORS
`Paul G. Barash, MD, New Haven, Connecticut
`N. Ty Smith, MD
`Charlotte Bell, MD, New Haven, Connecticut
`University of California, San Diego
`VA Medical Center
`Jan E. W. Beneken, PhD, Eindhoven, The Netherlands
`San Diego, California
`Casey D, Blitt, MD, Tucson, Arizona
`J. S. Gravenstein, MD
`Jerry M. Calkins, MD, PhD, Phoenix, AZ
`University of Florida College of Medicine
`Henry Casson, MD, Portland, Oregon
`Gainesville, Florida
`Jeffrey B. Cooper, PhD, Boston, Massachusetts
`Allen K. Ream, MD
`D. Daub, MD, Karlsruhe, Germany
`Stanford University School of Medicine
`
`Edward Deland, MD, Los Angeles, California
`Stanford, California _
`Peter C. Duke, MD, Winnipeg, Manitoba, Canada
`BOOK REVIEW AND TELECOMMUNICATIONS EDITOR
`
`John H. Eichhorn, MD, Boston, Massachusetts
`Frank E. Block, Jr, MD, Columbus, Ohio
`Erich Epple, PhD, Tubingen, Germany
`ADMINISTRATIVE EDITOR
`
`A. Dean Forbes, Palo Alto, California
`Robert K. Kalwinsky
`Wesley T. Frazier, MD, Atlanta, Georgia
`PUBLISHER
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`Betty L. Grundy, MD, Gainesville, Florida
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`Carl C. Hug, Jr, MD, Atlanta, Georgia
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`Kazuyuki Ikeda, MD, PhD, Hamamatsu, Japan
`Journal ofClinical Monitoring. ISSN 0748-1977. Published four times a year, in
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`Copyright © 1991 by Little, Brown and Company (Inc). All rights reserved.
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`Except as authorized in the accompanying statement, no part of the Journal of
`Michael L. Quinn, PhB, San Diego, California
`Clinical Monitoring may be reproduced in any form or by anyelectronic or
`mechanical means, including information storage and retrieval systems, with-
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`out the publisher's written permission. Authorization to photocopy items for
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`internal use, or the internal or personal use ofspecific clients, is granted by
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`the Copyright Clearance Center Transactional Reporting Service, provided
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`ted by Sections 107 or 108 of the U.S. Copyright Law. The code fee for this
`John W. Severinghaus, MD, San Francisco, California
`journal is 0748-1977/91 $1.50. This authorization docs not extend to other
`kinds of copying, such as copying for general distribution, for advertising or
`Lewis B. Sheiner, MD, SanFrancisco, California
`
`promotional purposes, for creating new collective works, or for resale.
`David B. Swedlow, MD, Hayward, California
`The authors, editors, and publisher have exerted every effort to ensure that
`drug selection and dosage, as well as the description of instruments and rec-
`Richard Teplick, MD, Boston, Massachusetts
`ommendations for their use, set forth in all articles appearing in the Journal of
`Kevin K. Tremper, PhD, MD, Orange, California
`Clinical Monitoring are in accord with current recommendations and practice
`Max H. Weil, MD, Chicago,Illinois
`at the time of publication. However, many considerations necessitate caution
`in applying in practice information reported in any article appearing in the
`Arnold M. Weissler, MD, Denver, Colorado
`Journal. These include ongoing research, changes in government regulations,
`
`Variations in standards among different countries, the possibility that original
`Karel H. Wesseling, PhD, Amsterdam, Holland
`research as reported in the Journal may differ from standard practice, and the
`constant flow of information relating to drug therapy and drug reactions, as
`well as the principles of monitoring, application of instruments, and differ-
`ences in instruments among manufacturers. The reader is advised to check
`the package inserts for each drug for changein indication and dosage, and the
`descriptions provided by instrument manufacturers for added warnings and
`Precautions. This caution is particularly important when the recommended
`
`drug or instrument is new or infrequently employed.
`The Journal of Clinical Monitoring is indexed in Index Medicus, Current
`Contents/Clinical Practice, Excerpta Medica, and Current Awareness in
`
`Bioloyical Sciences.
`
`
`
`JOURNAL OF CLINICAL MONITORING
`
`Sa
`
`2
`
`

`

`JOURNAL OF CLINICAL MONITORING
`Volume 7 Number 1 January 1991
`
`
`
`A-2
`
`|
`
`\
`
`Original Articles
`IN VITRO EVALUATION OF RELATIVE PERFORATING POTENTIAL
`OF CENTRAL VENOUS CATHETERS: COMPARISON OF
`MATERIALS, SELECTED MODELS, NUMBER OF LUMENS, AND
`ANGLES OF INCIDENCE TO SIMULATED MEMBRANE
`Nikolaus Gravenstein, MD, and Robert H. Blackshear, MD
`SKIN REFLECTANCE PULSE OXIMETRY:
`IN VIVO MEASUREMENTS
`FROM THE FOREARM AND CALF
`Y. Mendelson, PhD, and M. J. McGinn, MSc
`|
`THE RELATIVE ACCURACIES OF TWO AUTOMATED
`WONINVASIVE ARTERIAL PRESSURE MEASUREMENT DEVICES
`Michael S. Gorback, MD, Timothy J. Quill, MD,
`and Michael L. Lavine, PhD
`ELECTROENCEPHALOGRAPHIC MAPPING DURING ISOFLURANE
`AHESTHESIA FOR TREATMERT OF MENTAL DEPRESSION
`W. Engelhardt, Dr med, G. Carl, Dr Med,
`T. Dierks, Dr med, and K. Maurer, Prof Dr med
`Case Reports
`USEFULNESS OF EPIDURALLY EVOKED CORTICAL POTENTIAL
`MONITORING QURING CERVICOMEDULLARY GLIOMA SURGERY
`Takato Morioka, MD, Kiyotaka Fujii, MD,
`Shozo Tobimatsu, MD, Masashi Fukui, MD,
`
`and Yoshiro Sakaguchi, MD
`CAPNOGRAPHY FOR DETECTION OF ENDOBRONCHIAL
`MIGRATION OF AN ENDOTRACHEAL TUBE
`S. K. Gandhi, MD, FFARCS, Charul A. Munshi, MD,
`Robert Coon, PhD, and Ann Bardeen-Henschel, MD
`OXYGEN PIPELINE SUPPLY FAILURE: A COPING STRATEGY
`Wayne R. Anderson, MD, and John G. Brock-Utme, FFA(SA)
`Technical Notes
`A TARGET FEEDBACK DEVICE FOR VENTILATORY MUSCLE
`TRAINING
`Michael J. Belman, MD, and Reza Shadmehr, MS
`REDUCTION OF FRESH GAS FLOW REQUIREMENTS BY A
`CIRCLE-MODIFIED BAIN BREATHING CIRCUIT
`John Bernard Valdrighi, MD, and Patrick Newland Nance, MD
`Knowing Your Monitoring Equipment
`BLOOD PRESSURE MONITORING: AUTOMATED OSCILLOMETRIC
`DEVICES
`Maynard Ramsey I, MD, PhD
`Correspondence
`LOW PERFUSION PRESSURE OR INTERRUPTION OF BLOOD FLOW
`SUPPRESSES ELECTROENCEPHALOGRAPHIC ACTIVITY?
`Jorge Urzua, MD
`REPLY
`Mark S. Scheller and Brian R. Jones
`MEASUREMENT OF ARTERIAL OXYGEN TENSION IN THE
`HYPERBARIC ENVIRONMENT
`Lindell K. Weaver, MD
`REPLY
`Dr. G. Litscher
`Books
`CAPHOGRAPHY IM CLINICAL PRACTICE
`J. S. Gravenstein, MD, David A. Paulus, MD, MS, and
`Thomas J. Hayes, BS
`B, Smalhout, MD, PhD
`
`5
`
`13
`
`23
`
`30
`
`35
`
`39
`
`42
`
`49
`
`56
`
`68
`
`68
`
`68
`
`69
`
`70
`
`Contents continued on page A-4
`
`3
`
`

`

`Contents continued from page A-2
`
`Workshop
`71 COMPUTERIZATION OF ANESTHESIA INFORMATION
`MANAGEMENT
`John H. Eichhera, MD, and David W. Edsall, MD
`Abstracts of Scientific Papers
`83 TENTH MEDICAL MONITORING TECHNOLOGY CONFERENCE
`102 FIRST ANNUAL MEETING OF THE SOCIETY FOR TECHNOLOGY IN
`
`ANESTHESIA
`
`A-16 Announcements
`34 NOTICE FROM THE EDITORS
`
`A-10 INFORMATION FOR CONTRIBUTORS
`
`A+15 THE SOCIETY FOR TECHNOLOGY IN ANESTHESIA
`
`A-16 INDEX TO ADVERTISERS
`
`A-4
`
`4
`
`

`

`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`5
`
`

`

`8 Journal of Clinical Monitoring Vel 7 No 1 January 1991
`
`company, are better feliability in critical care situations
`such as peripheral circulatory shutdown, less interfer-
`ence from ambient light, and better accuracy because
`measurement fromthe forehead is relatively unsuscep-
`tible to motion artifacts.
`Currently,
`there are no commercially available re-
`flectance pulse oximeters for monitoring SaQ, from lo-
`cations other than the forehead. Therefore, the objective
`of this work was to investigate the feasibility of moni-
`toring SaO, with a skinreflectance pulse oximeter from
`two alternative and convenient locations on the body:
`the ventral side of the forearm and the dorsalside of the
`calf. Besides extending the clinical application of pulse
`oximetry, it appearsalso that reflectance pulse oximetry
`from peripheraltissues may have potential advantagein
`the assessment of local blood oxygenation after skin
`transplantation and regeneration following microvascu-
`lar surgery.
`In this article, we describe preliminary in vivo evalua-
`tion of a new optical reflectance sensor for noninvasive
`monitoring of SaO» with a modified commercial trans-
`mittance pulse oximeter. We present the experimental
`evaluation of this sensor in a group of 10 healthy adult
`volunteers and compare SaQ2 measured with the reflec-
`tance pulse oximeter sensor, SpOs2(r), with SaQz mea-
`sured noninvasively from the finger by a standard trans-
`mittance pulse oximeter sensor, SpO2(t).
`
`REFLECTANCE PULSE OXIMETRY
`
`The principle of reflectance, or backscatter, pulse ox-
`imetry is generally similar to that of transmittance pulse
`oximetry. Both techniques are based on the change in
`light absorptionoftissue caused by the pulsating arterial
`blood during the cardiac cycle. The pulsating arterioles
`in the vascular bed, by expanding and relaxing, mod-
`ulate the amount oflight absorbed by the tissue. This
`rhythmic change produces characteristic photoplethys-
`mographic waveforms, two of which are used to mea-
`sure SaQ> noninvasively.
`Recently, we showed that accurate noninvasive mea-
`surements of SaQ, from the forehead can be made with
`an unheated reflectance pulse oximeter sensor [1]. The
`major practical limitation of reflectance pulse oximetry
`is the comparatively low-level photoplethysmograms
`recorded from low-density vascular areas of the skin.
`Therefore,
`the feasibility of reflectance pulse oximetry
`dependson the ability to design an optical reflectance
`sensor that can reliably detect sufficiently strong reflec-
`tance photoplethysmograms from various locations on
`the skin,
`In order to partially overcome this limitation, we
`have developed an optical
`reflectance sensor that
`in-
`
`
`
`
`
`e3ooSoeCHDi?+,
`bat!fe%‘ “
`“>+,
`<>5s
`*<>So -“45
`43
`4
`55
`os
`LS
`
`es
`
`RG IR LEDs
`OPTICAL SHIELD
`
`PHOTODIODES
`PHOTODIODES
`
`BRASS RING
`OPTICALLY
`
`CLEAR EPOXY
`
`
` Ree
`pbbVK
`
`
`
`THERMOFOIL
`HEATER
`
`B
`
`Fig 1. (A) Frontal and (B) side views ofthe heated skin reflec-
`tance pulse oximeter sensor. See text for explanation. R & IR
`LEDs = red and infrared light-emitting diodes.
`
`cludes an array of six identical photodetectors arranged
`symmetrically in a hexagonal configuration surround-
`ing two pairs of red (peak emission wavelength, 660
`nm) and infrared (peak emission wavelength, 930 nm)
`light-emitting diodes (LEDs)
`[1].
`In another related
`study, we showedthat by locally heating the skin under
`the sensor to a temperature above 40°C,it is possible to
`achieve a four- to fivefold increase in the magnitude of
`the pulsatile componentdetected from the forearm, and
`thus significantly improve the detectionreliability of the
`reflectance photoplethysmograms [2]. The new optical
`reflectance sensor designed for this study combines the
`two features described above.
`
`
`SENSOR DESIGN
`
`reflectance sensor
`The temperature-controlled optical
`used in this study is shown in Figure 1. The major fea-
`ture of the optical layout design is the multiple photo-
`diode array, which is arranged concentric with the
`LEDs, This arrangement maximizes the amount of
`backscattered light that is detected by the sensor. The
`technical details related to the design and geometric
`
`6
`
`

`

`Mendelson and McGinn: Skin Reflectance Pulse Oximetry
`
`9
`
`configuration of the optical components were described
`recently by Mendelson etal [1].
`The heater consists of a ring-shaped (dimensions:
`30-mm outside diameter; 15-mm inside diameter)
`thermofoil resistive heating element (Ocean State Ther-
`motics, Smithfield, RD. The thermofoil heater was
`mounted between the surface of the optically clear
`epoxy, which was used to seal the optical components
`of the reflectance sensor, and a thin (0.005 mm) match-
`ing brass ring, which facilitates better thermal conduc-
`tion to the skin. A miniature (dimensions: 2 * 5
`x | mm) solid-state temperature transducer (AD 590,
`Analog Devices, Wilmington, MA) was mounted on
`the outer surface of the brass ring with the thermally
`sensitive surface facing the skin. The entire sensor as-
`sembly was potted in room-temperature vulcanizing
`silicone rubber to minimize heat losses to the surround-
`ing environment. The assembled sensor weighs approx~
`imately 65 g. The sensor measures approximately 38
`mmin diameter and is 15 mmthick. The heater assem-
`bly was separately interfaced to a temperature controller
`that was used to vary the temperature of the skin be-
`tween 35 and 45°C in 1 + 0.1°C steps.
`
`
`SUBJECTS AND METHODS
`
`Data Acquisition
`
`Each of the two heated optical reflectance sensors were
`separately interfaced to a temperature controller and a
`commercially available ACCUSAT (Datascope Corp,
`Paramus, NJ) pulse oximeter [3].
`Two of the three ACCUSAT pulse oximeters were
`modified to function as reflectance pulse oximeters. The
`modification, which was described in a separate study
`[1], included the adjustment ofthe red and infrared LED
`intensities in the reflectance sensors so that the reflec-
`tance photoplethysmograms were approximately equal
`to transmittance photoplethysmograms measured by a
`standard transmittance sensor froman averagesize adult
`finger tip.
`The third ACCUSAT transmittance pulse oximeter
`was used as a reference to measure SpO(t) from the
`finger tip. The specified accuracy of this transmittance
`pulse oximeter is +2.0% and +4,0% for SaQ, values
`ranging between 70 and 100%and 60 and 70%, respec-
`tively [3]. The three pulse oximeters were adapted to
`provide continuous digital readouts of the AC and DC
`components of the red and infrared photoplethysmo-
`grams,
`Readings from each ofthe three pulse oximeters were
`acquired every 2 seconds through a standard RS-232C
`
`serial port interface using an AT&T 6300 personal com-
`puter. The conversions of the reflectance red/infrared
`(R/IR) ratios measured by the tworeflectance pulse ox-
`imeters to SpO.(r) were performed by using the cali-
`bration algorithm obtained in a previous calibration
`study in which measurements were made with a similar
`nonheated sensor fromthe forehead [1].
`
`In Vivo Study
`
`The ability to measure SpO:(r) from the forearm and
`calf was investigated in vivo during progressive steady-
`state hypoxia in humans.
`Measurements were acquired from 10 healthy non-
`smoking male adult volunteers of different ages and skin
`pigmentations. The study was performed in compliance
`with the University of Massachusetts Medical Center's
`review guidelines on human experimentation. Each
`volunteer was informed of the complete procedure as
`well as the possible risks associated with breathing hy-
`poxic gas levels. Each volunteer received monetary
`compensation for participation in this study. The sub-
`ject distribution included 1 East Indian, 3 Asians, and 2
`darkly tanned and 4 lightly tanned Caucasians. Their
`ages ranged from 22 to 37 years old (mean + SD, 27.5
`+ 4,9 years). Measured blood hematocrits were in the
`range of 40 to 50.5% (mean + SD, 45.7 + 3.2%).
`All instruments were allowed to warmupforatleast
`30 minutes before the study. The transmittance sensor
`of the pulse oximeter was attached to the index finger.
`The reflectance sensors were attached to the ventral side
`of the forearm and the dorsalside of the calf by using a
`double-sided transparent adhesive ring. In cases where
`an abundance of hair prevented intimate contact be-
`tween the sensors and the skin,
`the contact was im-
`proved by loosely wrapping the sensor and the limb
`with an elastic strap. The temperature of each reflec-
`tance sensor was set to 40°C and remained unchanged
`throughout the entire study.
`A standard lead-I electrocardiogram and end-tidal
`carbon dioxide levels were continuously monitored by
`a Hewlett-Packard 78345A patient monitor (Hewlett-
`Packard, Andover, MA). Each subject was placed in a
`supine position. A face mask wastightly fitted over the
`subject’s nose and mouth, and the subject was instructed
`to breathe spontaneously while we administered differ-
`ent gas mixtures of nitrogen and oxygen. The inspired
`gas mixture was supplied by a modified Heidbrink anes-
`thesia machine (Ohio Medical Products, Madison, WI).
`The breathing circuit of the anesthesia machine was
`equipped with a carbon dioxide scrubber (soda lime).
`The inspired oxygen concentration was adjusted be-
`tween 12 and 100%and was monitored continuously
`
`nine
`
`7
`
`

`

`10
`
`Journal of Clinical Monitoring Vol 7 No 1 January 1991
`
`throughout the study with an IL 408 (Instrumentation
`Laboratories, Lexington, MA) oxygen monitor, which
`was inserted in the inspiratory limb of the breathing
`circuit.
`Steady-state hypoxia was gradually induced by low-
`ering the inspired fraction of oxygen in the breathing
`gas mixture. Initially,
`the inspired oxygen concentra-
`tion was changed in step decrements, each step pro-
`ducing approximately a 5% decrease in SpOa(t) as
`determined from the display of the ACCUSAT
`transmittance pulse oximeter. The inspired oxygen was
`maintained at each level for at least 3 minutes until the
`pulse oximeter readings reached a steady level (i-c.,
`SaQ> fluctuations ofless than +3%). When the inspired
`oxygen level reached 12%,
`the process was reversed.
`Thereafter, the inspired oxygen level was increased in a
`similar stepwise manner to 100%. Data were recorded
`during both desaturation and reoxygenation.
`All subjects tolerated the procedure well without ad-
`verse reactions. None ofthe subjects showedelectrocar-
`diographic abnormalities before or after the study. Each
`subject was studied for approximately | hour.
`
`Data Analysis
`
`To avoid operator biases, the data from each pulse ox-
`imeter were acquired automatically by the computer
`and later subjected to the samestatistical tests.
`For each step change in inspired oxygen, readings
`from the three pulse oximeters were averaged consecu-
`tively over a period of 20 seconds, Averaged readings
`from the 10 subjects were pooled and a least-squares
`linear regression analysis was performed. Student's f test
`determined the significance of each correlation; p <
`0.001 was considered significant.
`Although the correlation coefficient of the linear re-
`gression (r) provides a measure of association between
`the SpO,(r) and SpO2(t) measurements,it does not pro-
`vide an accurate measure of agreement between the two
`variables. Therefore, the measurement accuracy was es-
`timated on the basis of the meanand standard deviations
`of the difference between the readings from the trans-
`mittance and reflectance pulse oximeters. The mean of
`the difference between the pulse oximeter measure-
`ments, which is often referred to as the bias, was used to
`assess whether there was a systematic over- or underes-
`timation of one method compared with the other. The
`standard deviation of the bias, whichis often reférred to
`as the precision, represents the variability or random
`error. Finally, we computed the meanerrors and stan-
`dard deviations of each measurement. The mean error
`is defined as the absolute bias divided by the corre-
`sponding SpO.(t) values.
`
`Y = 0.87x + 0.04
`
`ORARM
`Y = 1.02% - 0,05
`CALF
`
`
`
`R/IRREFLECTANCERATIO
`
`0
`
`0.4 .
`
`0.8
`
`hee
`
`1.6
`
`R/IR TRANSMITTANCE RATIO
`
`tance pulse oximeter (y axis) and SpO.(t) readings mea-
`
`Fig 2. Comparison of red/infrared (R/IR) ratios measured by the
`modified reflectance pulse oximeter (y axis) and the standard trans-
`mittance pulse oximeter (x axis) during progressive steady-state
`hypoxia in 10 healthy subjects. The solid line represents the best-
`Sitted linear regression line for the forearm measurements, The bro-
`ken line represents the best-fitted linear regression line for the calf
`measurements.
`
`
`
`RESULTS
`
`Normalized R/IR ratios and SpOa.(r) values measured
`by the reflectance pulse oximeters fromthe forearm and
`calf of the 10 subjects were compared with the nor-
`malized R/IR ratios and SpO.(t) values measured simul-
`taneously by the transmittance pulse oximeter from the
`finger. A total of91 and 93 pairs ofdata points measured
`simultaneously from the forearm and calf, respectively,
`were used in the regressionanalysis, which provided the
`estimated slopes and intercepts ofthe linear regression
`lines. Eachpair of data points represents a different hy-
`poxic level.
`Regression analysis of the normalized R/IR ratios
`measured from the reflectance pulse oximeters from the
`forearm and calf (y axis) versus the normalized R/IR
`ratios measured simultaneously by the transmittance
`pulse oximeter from the fingertip (x axis) is shownin
`Figure 2. The equations for the best-fitted linear regres-
`sion lines were y = — 0.05 + 1.02x (r = 0.94, SEE =
`0.08, p <.0.001) for the forearm and y = 0.04 + 0.87x
`(r = 0.88, SEE = 0.11, p < 0.001) for the calf.
`A comparison of SpO2(r) readings from the reflec-
`
`8
`
`

`

`Mendelson and McGinn: Skin Reflectance Pulse Oximetry
`
`11
`
`100
`
`90
`
`
`
`REFLECTANCESpO>(%)
`
`
`
`FOREARM
`y = 1,09x - 7,06
`CALF
`¥ = 0,93x + 7.78
`
`70
`80
`90
`TRANSMITTANCE SpO5 (%)
`
`i100
`
`70
`
`80
`90
`TRANSMITTANCE SpO5 (%)
`
`100
`
`Fig 3, Comparison ofpercent arterial hemoglobin oxygen satura-
`tion (SpO2) measurements obtained from the modified reflectance
`pulse oximeter (y axis) and SpOz values measured by a standard
`transmittance pulse oximeter (x axis) during progressive steady-
`state hypoxia in 10 healthy subjects. The solid line represents the
`best-fitted linear regression line for the forearm measurements. The
`broken line represents the best-fitted linear regression line for the
`calf measurements.
`
`oO
`
`DIFFERENCES
`
`70
`
`90
`80
`TRANSMITTANCE SpO9 (%)
`
`100
`
`Fig 4. Meandifferences between arterial hemoglobin oxygen sat-
`uration (SpO2) measured from the forearm by the modified reflec-
`tance pulse oximeter and the standard transmittance pulse oximeter
`measurements from the finger tip.
`
`Fig 5. Mean differences betweenarterial hemoglobin oxygen sat-
`uration (SpOz) measured fromthe calf by the modified reflectance
`pulse oximeter and the standard transmittance pulse oximeter mea-
`surements from the finger tip.
`
`Statistical Analysis of Arterial Oxygen Saturation (SaQ2) Levels
`Measured from the Forearm and Calf by the Modified Reflectance
`Pulse Oximeters
`
`Location/
`% SaQr
`
`No. of
`Data Points
`
`Mean Value (SD)
`
`Difference
`
`% Error
`
`Forearm
`90-100
`80-89
`70-79
`Calf
`90-100
`80-89
`70-79
`
`42
`Sy
`12
`
`43
`33
`17
`
`1.25 (2.55)
`0.52 (2.85)
`—0.82 (1.96)
`
`2.47 (1.66)
`2.35 (2.45)
`2.42 (1.20)
`
`3.36 (3.06)
`1.57 (4.00)
`3.45 (4.12)
`2.22 (4.00)
`
`1.95 (2.42) 2.97 (2.75)
`
`sured simultaneously from the transmittance pulse ox-
`imeter (x axis) is shown in Figure 3. The equations for
`the best-fitted linear regression lines were y = — 7.06
`+ 1.09x (r = 0.95, SEE = 2.62, p < 0.001) for the
`forearm and y = 7.78 + 0.93x (r = 0.88, SEE = 3.73,
`p < 0.001) for the calf.
`Figures 4 and 5 showthe percent differences between
`SpO.(r) and SpO>(t), that is, SpOa(r) — SpO2(t), ob-
`tained from the forearm and calf data plotted in Figure
`3, respectively. The corresponding means and standard
`deviations of the differences and errors for the forearm
`and calf measurements are summarized in the Table.
`
`9
`
`

`

`12
`
`Journal of Clinical Monitoring Vol 7 No 1 January 1991
`
`Data were summarized for three different ranges of
`SpO,(t) values between 70 and 100%.
`
`DISCUSSION
`
`Commercially available transmittance sensors can be
`used ononly a limited numberof peripheral locations of
`the body. Brinkman and Zijlstra [4] and Cohen and
`Wadsworth [5] showed that instead of tissue transil-
`lumination, noninvasive monitoring of SaO.z can be
`performed based on skin
`reflectance
`spectropho-
`tometry. More recently, we described an improved
`optical reflectance sensor that was used for measuring
`SaQ, from the forehead with a modified commercial
`transmittance pulse oximeter[1].
`Measuring large reflectance photoplethysmograms
`fromsparsely vascularized areas of the skin is challeng-
`ing. Differences in capillary densities between various
`locations on the body are knownto affect the magnitude
`and quality of the reflected photoplethysmograms. For
`example, estimated average capillary density of the hu-
`man forehead is approximately 127 to 149 loops/mm?,
`whereas the capillary densities of the forearm and calf
`are approximately 35 to 51 and 41 loops/mm’, respec-
`tively [6,7]. Furthermore, the frontal bone of the fore-
`head provides a highly reflective surface that signifi-
`cantly increases the amount of light detected by the
`reflectance sensor, Therefore,
`reflected photoplethys-
`mograms recorded from the forehead are normally
`larger than those recorded from the forearm and calf.
`Local skin heating could be used as a practical method
`for improving the signal-to-noise ratio of the reflected
`photoplethysmograms from the forearm or calf areas
`and thus reduce the measurement errors in reflectance
`pulse oximetry.
`The approach presented in this article demonstrated
`that SaOs can be estimated by using a heated skin
`reflectance sensor from the forearm and calf over a rela-
`tively wide range of SaQ> values. This technique may
`provide a clinically acceptable alternative to currently
`available transmittance pulse oximeters. In a previous
`study [2], we found that the ability to measure accurate
`SaQz values with a reflectance skin oximeteris indepen-
`dent of the exact skin temperature. We noticed, how-
`ever,
`that a minimum skin temperature of approxi-
`mately 40°C is generally sufficient to detect adequately
`stable photoplethysmograms. Furthermore, our experi-
`ence in healthy adults also has shown that at this’skin
`temperature, the heated sensor can remain in the same
`location without any apparent skin damage.
`Note that despite the proven advantage oflocal skin
`heating to increase skin blood flow, reflected photo-
`plethysmogramsrecorded fromthe forearm andthe calf
`are considerably weaker than those recorded from the
`
`the mean errors for the SpOs(r)
`forehead. Therefore,
`measurements from the forearm andcalfare higher than
`the corresponding errors for similar SpOs(r) measure-
`ments made with an unheated reflectance sensor from
`the forehead. For comparison, relative to SaQz mea-
`sured with a noninvasive transmittance pulse oximeter,
`the SEE for SpO2(r) measurements obtained from the
`forehead using a similar unheated optical reflectance
`sensor were 1.82% [1]. The SEE obtained in this study
`using the heated reflectance sensor were 2.62% for the
`forearm and 3.73% for the calf measurements. Despite
`those differences, it is apparent that the degree of corre-
`lation obtained in this preliminary study is encouraging
`and in selected clinical applications may be acceptable.
`We conclude that reflectance pulse oximetry from the
`forearm and calf may provide a possible alternative to
`conventional transmittance pulse oximetry and reflec-
`tance pulse oximetry from the forehead. Further stud-
`ies, however, are needed in order to compare our
`reflectance pulse oximeter against SaOQ2 measurements
`obtained directly from arterial blood samples. Addi-
`tional work to investigate the source of variability in
`reflectance pulse oximetry is in progress.
`
`Financial support for this study was provided in part by the
`Datascope Corporation and NIH Grant R15 GM36111-01A1.
`The authors would like to acknowledgetheclinical assistance
`of Albert Shahnarian, PhD, Gary W. Welch MD, PhD, and
`Robert M. Giasi, MD, Department of Anesthesiology, Uni-
`versity of Massachusetts Medical Center, Worcester, MA.
`We also thank Paul A. Nigroni, Datascope Corporation,
`Paramus, NJ, and Kevin Hines, Semiconductor Division,
`Analog Devices, Wilmington, MA,
`fortechnical assistance.
`Theskillful art work by Yi Wangis also greatly appreciated.
`
`1. Mendelson Y, Kent JC, Yocum BL,Birle MJ. Design and
`evaluation of a new reflectance pulse oximeter sensor.
`Biomed Instrum Technol 1988;22(4):167-173
`2. Mendelson Y, Ochs BD. Noninvasive pulse oximetry
`utilizing skin reflectance photoplethysmography. LEEE
`Trans Biomed Eng 1988;35(10):798-—805
`3. Mendelson Y, Kent JC, ShahnarianA, et al. Evaluation of
`the ‘Datascope ACCUSAT pulse oximeter
`in healthy
`adults. J Clin Monit 1988;4:59-63
`4, Brinkman R, Zijlstra WG. Determination and continuous
`registration of the percentage oxygen saturationinclinical
`conditions. Neth J Surg 1949;1:177—183
`5. Cohen A, Wadsworth N. A light emitting diode skin
`reflectance oximeter. Med Biol Eng Comput 1972;10:385—
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`6. Moretti G. Handbuch der Haut- und Geschlechtskran-
`kheiten. Berlin: Springer-Verlag, 1968:491—623
`7. Rothman §. Physiology and biochemistry of the skin.
`Chicago: University of Chicago Press, 1954:685
`
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