Apple Inc.
`APL1017
`U.S. Patent No. 8,989,830
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`0001
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`
`/‘lnestliesioliniy
`
`THE JOURNAL or
`THE AMERICAN SOCIETY or ANESTHESIOLOGISTS, INC.
`Editor-in-Chief
`LAWRENCE]. SAIDMAN, M.D., San Diego. California
`Editors
`
`David E. Longnecker, M.D.
`julien F. Biebuyck, M.B., D.Phil.
`Philadelphia, Pennsylvania
`Hershey, Pennsylvania
`Dennis T. Mangano, Ph.D., M.D.
`john]. Downes, M.D.
`San Francisco, California
`Philadelphia, Pennsylvania
`Kai Rehder, M.D.
`H. Barrie Fairlcy, M.B., B.S.
`Rochester, Minnesota
`Stanford, California
`Donald R. Stanski, MD.
`Simon Gelman, M.D., Ph.D.
`Stanford, California
`Birmingham, Alabama
`Michael M. Todd, M.D.
`Carol A. Hirshman. M.D.
`Iowa City, Iowa
`Baltimore, Maryland
`Warren M. Zapol, M.D., Boston, Massachusetts
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`Associate Editors
`
`Charles W. Buffington, M.D.
`Pittsburgh, Pennsylvania
`David H. Chestnut, M.D.
`Iowa City, Iowa
`_[efi‘rey E. Cooper, Ph.D.
`Boston, Massachusetts
`Dennis M. Fisher. M.D.
`San Francisco. Callf01‘nia
`Thomas F. Hornbein, M.D.
`Seattle. Washington
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`Carl Lynch III, M.D., Ph.D.
`Charlottesville, Virginia
`Mervyn Maze, M.B., Ch.B.
`Stanford, California
`Henry Rosenberg, M.D.
`Philadelphia, Pennsylvania
`Gary R. Strichartz, Pli.D.
`Boston, Massachusetts
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`Tony L. Yaksh, Ph.D.
`San Diego, California
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`correspondence relating to editorial nianageiiient. and Letters to the Editor should be mailed to Lawrence
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`0002
`0002
`
`

`
`Jlnenfiesiollm
`
`January 1989
`
`CONTENTS
`
`EDITORIAL VIEWS
`
`A Change in Format for ANESTHESIOLOGY.
`Lawrence _]. Saidman
`
`Changing Perspectives in Monitoring Oxygenation
`H. Barrie Fairley
`
`Studies in Animals Should Precede Human Use of Spinally Administered Drugs
`Tony L. Yaltslz and j. G. Collins
`
`CLINICAL INVESTIGATIONS
`
`The Influence o
`
`Pipecuroniu
`Oxide.
`
`f Renal Failure on the Pharmacokinetics and Duration of Action of
`In Bromide in Patients Anesthetized with Halothane and Nitrous
`
`well, P. Claver Canjell, Kay P. Caszagnoli, Daniel P. Lynam Mark R
`James E. Cold
`Fahey, Dennis M. Fisher, and Ronald D. Miller
`Effect of Intercostal Nerve Blockade on Respiratory Mechanics and CO2 Chemosen-
`sitivity at Rest and Exercise.
`Bernice R. Heclzer, Robert Bjurstrom, and Robert B. Schoene
`mic, Electrocardiographic, Mechanical, and Metabolic In-
`Comparison of Hernodynative Myocardial Ischemia in Vascular Surgical Patients with
`dicators of Intraopera
`Coronary Artery Disease.
`r, Margarela Ostrnan, Arnold Friedman, George Diamond,
`Slfren Hdggmark, Per Hohne
`Edward Lowenstein, and Sebastian Rel:
`mall Doses of Sufentanil or Fentanyl: Dose Versus EEG
`d Thiopental Requirement.
`
`Induction of Anesthesia with S
`
`Relationship of Mivacurium Chloride in Humans during Nitrous
`The Dose-Response
`ide—Enflurane Anesthesia.
`Oxide—FentanyI or Nitrous Ox
`n B. Kills, Tom Heéer, Marl: R. Fahey, Daniel P. Lynam, and
`james E. Caldwell, joh
`Ronald D. Miller
`
`janlce Mei-Ll Wang, Donnell ]. Creel, and K. C. Wong
`
`(Gontinuetl on page 5)
`
` —
`
`0003
`
`

`
`January 1989—ANESTI-IESIOLOGY
`
`CONTENTS
`
`eal Contractility Predicts Movement during Skin Incision in Patients
`Lower Esophag
`h Halothane, but Not with Nitrous Oxide and Alfentanil.
`Anesthetized wit
`Daniel I. Sessler, Randi Swen, Christine 1. Olcfsson, and Franklin Chow
`
`42
`
`Determination of Intra-abdominal Pressure Using a Transurethral Bladder Catheter:
`Clinical Validation of the Technique.
`Thomas], mam‘, Charles E. Lieber, and Ernest Benjamin
`
`(Continued from page 3)
`
`LABORATORY INVESTIGATIONS
`
`Epidural Clonicline Analgesia in Obstetrics: Sheep Studies.
`james C. Eisenach, Maria I. Castro, David M. Dewan, andjames C. Rose
`
`The Enhancement of Proton/Hydroxyl Flow across Lipid Vesicles by Inhalation An-
`esthetics.
`
`Dgugfas E. Raine: and David S. Cafiso
`The Influence of Dextrose Administration on Neurologic Outcome after Temporary
`al Cord Ischemia in the Rabbit.
`Spin
`john C. Dzramanand and Suzanne S. Moore
`Tachyphylaxis to Local Anesthetics Does Not Result from Reduced Drug Effectiveness
`at the Nerve Itself.
`pm,» Lgpfgrz, Halger Halthnse
`Comparison of the Effects of I-Ialothane on Skinned Myocardial Fibers from Newborn
`and Adult Rabbit. I. Effects on Contractile Proteins.
`Elliot]. Ksrane andjudy 1’. 31%
`
`n, and joachirn 0. Anna:
`
`Effects of “Nitrendipine" on Nitrous Oxide Anesthesia, Tolerance, and Physical De-
`pendence.
`S. Dalin and H. LEW?
`
`MEDICAL INTELLIGENCE ARTICLE
`
`Pulse Oximetry.
`Kevin K. Tremper and Steven Bari???
`
`_
`
`(Cmllilillcd on page 7}
`
`0004
`
`

`
`.]'=1nu:lI‘y' I98£)—/\NES'I"l-IESI(')L()GY
`
`CONTENTS
`
`(Continued from page 5)
`
`LABORATORY REPORTS
`
`Laudanosine Does Not Displace Receptor-specific Ligands from the Benzodiazepinergic
`or Muscarinic Receptors.
`Yeshayahu Kat: and Masha Gavish
`
`Effects of Methemoglobinemia on Pulse Oxirnetry and Mixed Venous Oximetry
`Steven j. Barker, Kevin K. Trernper, and john Hyagg
`Hyperbilirubinemia Does Not Interfere with Hemoglobin Saturation Measured by Pulse
`Oximetry.
`Francis Veyckemans, Philippe Basie, ]. E. Guillaume, Eric Wiliems, Anm-‘g Roger; and
`Thierry Clerbaux
`
`Evaluation of a Blood G35 and Chemistry Monitor for Use during Surgery
`G. Bashein, Wesley K. Greydanns, and Margaret A. Kenny
`
`A Model for Determining the Influence of Hepatic Uptake of Nondepolarizing Muscie
`Relaxants in the Pig.
`Johann Motsch, Pim Hennis, Franz Alta Zimmermann, and Sander Agoszon
`Transtracheal Doppler: A New Procedure for Continuous Cardiac Output Measure-
`ment.
`
`jerome H. Abrams, Roland E. Weber, and Kenneth D. Holman
`
`CASE REPORTS
`
`tracranial Pressure during Hepatic Transp]an_
`
`D. Brajzbard, R. 1'. Parks, M. A. Ramsay,
`and G. B. Klintmalm
`Treatment of Isorhythmic A-V Dissociation during General Anesthesia with Propran-
`010].
`
`A. W. Paulsen, T. R. Vaiek, T. H. Swygerz,
`
`Russell F. Hill
`
`Fiberoptic Endobronchial Intubation for Resection ofan Anterior Mediastinal Mass.
`Dirk Yaunker, Randal! Clark, and Lewis Coveler
`
`o
`
`0005
`
`146
`
`(Continued on page 9)
`
`

`
`January 1989-AN ESTH F.SI(')[.OGY
`
`CONTENTS
`
`Caudal Epidural Anesthesia in an Infant with Epidermolysis Bullosa
`
`'
`
`((3ontiI1ned from page 7;
`
`149
`
`Lawffflfif L Yr‘-’€. joei B. Garner, and Charies B. Maniey
`
`Recurrent Respiratory Depression after Alfentanil Administration
`Rory S. jafe and Dennis Coaison
`
`1 ocame.
`Pain of Delayed Traumatic Splenic Rupture Masked by Intrapleural L.d
`.
`Gregory A. Weaver
`0’
`Omen” 8’ Slang H’ Thong’ James 31- Raflfldiak, and
`Wiiiiam W. Pond, Grego M. 3
`‘,5;
`r
`Dose-res onse Relationshi
`for S
`'
`1 h '
`-
`-
`.
`.
`LOVE Plasma Cholinegteraseuffdiiiiriiyfmne In a Patient with Geneu':allY Detemliflfid
`Charles E. Smith, Geraint Lewis, Francois Donati, and David R Bevan
`
`CORRESPONDENCE
`
`Determination of Decay Constants from Time-varying Pressure Data
`Charies Beat:-ie, Linda S. Humphrey, and Gary Mafugchak
`Reply. Ciifiird R. Swanson and Wiiiiarn W. Muir 11;
`
`IOU.
`Use Caution when Extrapolating from a Small Sample Size to the General Populat.
`David]. Benefiei, Edward A. Eisier, and Rodger Shepherd
`Reply. Irnad H. Abdul-Rasool, Daniel H. Sears, and Ronaid L. Katz
`
`Succinylcholine and Trismus.
`Frederic A. Berry and Carl Lynch HI
`
`An Infant Model to Facilitate Endotracheal Tube Fixation in the Pediatric ICU Patient
`Patrick K. Birmingham and Babette Horn
`
`An Alternative Method for Management of Accidental Dural Puncture for Labor and
`Delivery.
`Shani Cohen, Jonathan S. Daitch, and Paul L. Goidiner
`
`High-press
`Michae
`
`ure Uterine Displacement.
`i
`Dorsey and Waiter L. Miiiar
`
`Calculating the Potency of Mivacurium.
`Aaron F. Koprnan
`Reply. john]. Savarese
`
`166
`
`166
`
`(Continued on page 1 1)
`
`e_—
`
`0006
`
`

`
`january ]989——A N ICSTI-l ESIO LOGY
`
`CONTENTS
`
`Midazolam in a Malignant Hyperthermia-susceptible Patient.
`juliana H.j. Breaks
`
`(Cmitiliued from page 9)
`167
`
`Exchange Autotransfusion Using the Cell Saver during Liver Transplantation
`Mare R. Brown, Michael A. E. Ramsay, and Thomas H. Swygen:
`
`Air Entrainment Through a Multiport Injection System.
`Dean Gilbert, Theodore]. Sanford, _]r., and Brian L. Partridge
`Reply. Thelma Masada
`
`A Tracheal Tube Extension for Emergency Tracheal Reanastomosis.
`Robert S. Holzman
`
`The Relationship Between Malignant Hyperthernia and Neuroleptic Malignant Syn-
`drome.
`
`Haggai Hernzesh, Dov Aizenberg, Marga Lapidot, and Hanan Munit:
`Reply. Stanley N. Carefi Stephan C. Mann, Henry Rosenberg, jejfrey E. Ftetche-r, and Terry
`D. Heiman-Patterson
`
`Appropriate Facilitation of Intravenous Regional Techniques in RSD.
`Kevin Foley, Linda Schatz, and Randall L. Martin
`
`REPORT OF SCIENTIFIC MEETING
`
`ANNOUNCEMENT
`
`GU11)!-I 'l'(_) AU'I‘l'I()R5
`
`The Guide for Authors is published in the January and July issues. It may be found on page 33A of this
`issue.
`
`A N.'i.‘§.»!V it re rrirlur mm?!‘ ("rar.I'mI"J us.-'.r.I" try the (Ihe':'m'rnl' .-H1\'.'r(:rr .‘s'rr::fr:* tn iI'r!'m.".._",-‘j' HIP ;'nm'nal'.
`
`-
`
`0007
`
`

`
`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`0008
`
`

`
`Anesthesiology
`\"".l'0, No l,_]an 1989
`
`PULSE OXIMIETRY
`
`became a standard clinical and laboratory tool in pul-
`monary medicine. Although it was demonstrated to be
`accurate for intraoperative monitoring.” its size and ex-
`pense. and the cumbersome nature of the ear probe pre-
`vented its acceptance as a routine monitor. At this time.
`all oximeters produced various light source wavelengths
`by filtering white light. The filtered light was then trans—
`mitted to and from the tissue through fiberoptic cables.
`In the mid 1970s, Takuo Aoyagi. an engineer working
`for Nihon Kohden Corporation. made an ingenious dis-
`covery regarding oximetry. He was developing a tnethod
`to estimate cardiac output semi-noninvasively by detecting
`the washout curve of dye injected into a peripheral vein
`as it perfused the car. This washout curve was measured
`in the ear with a red and infrared light densitometer sim-
`ilar to the Millikan ear oximeter. He noticed that his
`
`washout curves contained pulsations due to the arterial
`pulse in the ear. To more easily analyze the dye washout
`curve, he subtracted these pulsations from the curve, and
`in doing so he discovered that the absorbance ratio of the
`pulsations at the two wavelengths changed with arterial
`hemoglobin saturation. He soon realized that he could
`build an ear oximeter that measured arterial hemoglobin
`saturation without heating the ear by analyzing pulsatile
`light absorbances.2 This first pulse oximeter, developed
`by Nihon Kohden, used filtered light sources similar to
`MiIlikan’s ear oximeter. The device was evaluated clini-
`cally in the mid 1970s and marketed with little success.2
`In the late 1970s. Scott Wilber in Boulder. Colorado,
`developed the first clinically accepted pulse oximeter by
`making two modifications of
`the Nihon Kohden
`method.“:{: First, he produced a lightweight sensor by
`using light emitting diodes (LEDs} as light sources and
`photodiodes as detectors. Consequently, the instrument
`was connected to its earciip sensor only by a small electrical
`cable. Wilber also improved the saturation estimates by
`using a digital microprocessor to store a complex calibra-
`tion algorithm based on human volunteer data”: This
`method will be discussed in more detail below. This device
`
`was developed by Biox Corporation of Boulder. Colorado,
`and was successfully marketed to pulmonary function lab-
`oratories in the early 1980s.
`The clinical utility of the noninvasive oximeter in the
`operating room was rediscovered in the 19805 by William
`New, an anesthesiologist at Stanford University. Realizing
`that a continuous, noninvasive monitor of oxygenation
`would be useful to anesthesiologists, New developed and
`marketed a pulse oximeter to this group.” The Nellcor
`model N100 had by 1985 become almost synonymous
`with the term "pulse oximeter.“
`
`i Wilber 5: Blood constituent measuring device and method. US
`Patent #4, 407. 290 April 1. 1981.
`
`%0‘sJt‘rt.mAr.«a,v
`
`FIG. 1. Thisfigure is from a 1951 article in ANES'I‘HESi0l.0GY. It
`reveals dramatic desaturation in a 4-yr-old patient during a tonsillec.
`‘°mY- Repmducfd from 3l¢3Ph€I1 RC. Slater HM. Johnson AL, Sekelj
`P: The oximeter—-A technical aid for the anesthesiologist. ANE.5THt-:-
`SIO1-OGV 125543 1951. Wlth permission.
`
`The Ph}’3iC3 and Physiology of Pulse Oximetry
`
`BEE.R’S Law
`
`In the 19305, Matthes used spectrophotometry to dc-
`termine hemoglobin oxygen saturation? This method is
`based on the Beer-Lambert law, which relates the con-
`centration ofa solute to the intensity oflight transmitted
`through a solution.
`
`I-trans = Iine-A
`
`A = DC:
`
`(1)
`
`(13)
`
`Where [trans = intensity oftransmitted light; I,,. = intensity
`of incident light; A = absorption; D = distance light is
`transmitted through the liquid (path length); (3 = Con-
`centration of solute (hemoglobin); e = extinction coeffi-
`cient of the solute (a constant for a given solute at a spec-
`ified wavelength). Thus, if a known solute is in a clear
`solution in a cuvette of known dimensions, the solute con.
`centration can be calculated from measurements of the
`incident and transmitted light intensity at a known wave.
`length. The extinction coefficient E is a property of light
`absorption for a specific substance at a specified wave-
`length. In a one-component system. the absorption A is
`the product of the path length, the concentration, and
`the extinction coefficient. equation la. If multiple solutes
`
`0009
`
`

`
`K. K. TREMPER AND S.
`
`BARKER
`
`Anesthesiolo
`v to, No 1. _]an 1939
`
`By the above definition of oxygen saturation, the two
`forms of hemoglobin that do not bind oxygen (C01-lb
`and MetHb) are not included. This is the origin of what
`is now referred to as “functional hemoglobin saturation,”
`defined as (Severinghaus JW, personal communication);
`
`O21-lb
`2
`Functional S2102 = 6—~l_-IE-;TI-6
`
`x 100%.
`
`(2)
`
`With the advent of multiwavelength oxitneters that can
`measure all four species of hemoglobin, “fractional sat-
`uration” has been defined as the ratio of oxyhemoglobin
`to total hemoglobin:
`
`HEMOGLOBIN EXTINCTION cu fives
`
`Infrpred
`I
`
`methemoglobin
`
`I i
`
`oxyhemoglobin
`nu.--.....,___.
`
`reduced
`hemoglobin
`
`IIIII
`
`
`
`ExtinctionCoeifieient
`
`sue am can 720
`
`160
`
`son
`
`aau
`
`530
`
`920
`
`sen
`
`Wavelength A (nm}
`
`Fractional S3102
`
`FIG. 2. Transmitted light absorbance spectra of four hemoglobin
`species: oxyhemogiobin. reduced hemoglobin, carboxyhemoglobin, and
`methemoglobin. Adapted from Barker 5] and Tremper KK: Pulse
`Oximetry: Applications and limitations, Advances in Oxygen Moni-
`toring. International Anesthesiology Clinics. Boston. Little, Brown and
`Company. 1987, pp. 155-175.
`
`are present, A is the sum of similar expressions for each
`solute. The extinction coefficient can vary dramatically
`with the wavelength of the light. The extinction coeffi-
`cients for various hemoglobin species in the red and in-
`frared wavelength range are shown in figure 2.
`Laboratory oximeters use this principle to determine
`hemoglobin concentration by measuring the intensity of
`light transmitted through a cuvette filled with a hemo-
`globin solution produced from lysed red blood cells.”
`For Beer's law to be valid, both the solvent and the cuvette
`
`must be transparent at the wavelength used, the light path
`length must be known exactly, and no absorbing species
`can be present in the solution other than the known solute.
`It is difficult to fulfill these requirements in clinical devices;
`therefore, each instrument theoretically based on Beer’s
`law also requires empirical corrections to improve accu-
`racy.
`
`HEMOGLOBIN SATURATION DEFINITIONS
`
`Adult blood usually contains four species of hemoglo-
`bin: oxyhernoglobin (OgHb), reduced hemoglobin (Hb),
`methemoglobin (MetHb), and carboxyhemoglobin (C0-
`Hb) (fig. 2). The last two species are in small concentra-
`tions, except in pathologic conditions. There are several
`definitions of hemoglobin saturation. Historically, “oxy-
`gen saturation” was first defined as the oxygen content
`expressed as a percentage of the oxygen capacity. The
`oxygen content (cc of oxygen per 100 cc of blood) was
`measured volumetrically by the method of Van Slylte and
`Neill (1924).15 The oxygen capacity was defined as the
`oxygen content after the blood sample had been equili-
`brated with room air (158 mmHg oxygen at sea level).
`
`O2Hb
`= :—————j x 100 .
`0211!: + Hb + COHb + MetHb
`%
`
`(3)
`
`The fractional hemoglobin saturation is also called the
`“oxyhemoglobin fraction,” or “oxyhemoglobin %.“”
`When oximetry is used to measure hemoglobin satu-
`ration, Beer‘s law must be applied to a solution containing
`four unknown species: O-gHb, Hb, COHb, and MetHb.
`Expanding equation 1a to a four-component system results
`in an absorption given by:
`
`A = D1C1€1
`
`‘l' Dgcgfg ‘l' D3_C3€3
`
`'l" D4C4E4.
`
`The subscripts 1 through 4 correspond to the four he-
`moglobin species. If the path lengths are the same, then
`D can be factored out:
`
`A = D(C1E1 ‘l’ C263 "l' C363 'l' C464).
`
`The extinction coeflicients £1 through 54 are constants at
`a given wavelength X (fig. 2). The absorption defined in
`equation 1c is determined from equation 1 by measuring
`the incident and transmitted light intensities. From equa-
`tion lc, we see that four wavelengths of light are needed
`to produce four equations to solve for the unknown con-
`centrations C1 through C4. If COHb and MetHb were
`not present, their contributions to the absorption would
`be zero and functional hemoglobin saturation could be
`determined by a two-wavelength oximeter (two equations
`and two unknowns). If two wavelengths existed for which
`the extinction coefficients for COHb and MetHb were
`
`zero, then these absorption terms would again be zero
`and a two-wavelength oximeter could measure functional
`saturation. Unfortunately, as illustrated in figure 2, the
`extinction coefficients for CO1-lb and MetHb are not zero
`
`in the red and infrared range, and their presence will,
`therefore, contribute to the absorption. Even though the
`definition of functional hemoglobin saturation involves
`only two hemoglobin species (O2Hb and Hb), when
`_ MetHb and C01-lb are present, four wavelengths are re-
`quired to determine either functional or fractional he-
`moglobin saturation.”
`
`0010
`
`

`
`Atiesibesiultigjr
`V 70. No |.]an 1989
`
`PULSE OxI:viF.'1‘Rv
`
`Noninvasive oximeters measure red and infrared light
`transmitted through a tissue bed, effectively using the fin-
`ger or ear as a cuvette containing hemoglobin. There are
`several technical problems in accurately estimating SaO2
`by this method. First, there are many absorbers in the
`light path other than arterial hemoglobin, including skin,
`soft tissue, and venous and capillary blood. The early ox-
`imeters subtracted the tissue absorbance by compressing
`the tissue during calibration to eliminate all the blood,
`and using the absorbance of bloodless tissue as the base-
`line. These oximeters also heated the tissue to obtain a
`
`signal related to arterial blood with minimum influence
`of venous and capillary blood.
`Pulse oximeters deal with the effects of tissue and ve-
`
`nous blood absorbances in a completely different way.
`Figure 3 schematically illustrates the series of absorbers
`in a living tissue sample. At the top of the figure is the
`pulsatile or AC. component, which is attributed to the
`pulsating arterial blood. The baseline or DC component
`represents the absorbances of the tissue bed, including
`venous blood, capillary blood, and nonpulsatile arterial
`blood. The pulsatile expansion of the arteriolar bed pro-
`duces an increase in path length (see equation lb), thereby
`increasing the absorbance. All pulse oxiineters assume that
`the only pulsatile absorbance between the light source
`and the photodetector is that of arterial blood. They use
`two wavelengths of light: 660 nanometers (red) and 940
`nanometers (near infrared). The pulse oximeter first de-
`termines the AC component of absorbance at each wave-
`length and divides this by the corresponding DC coin-
`ponent to obtain a “ptilse-added" absorbance that is in-
`dependent ofthe incident light intensity. it then calculates
`the ratio (R) of these pulse-added absorbances, which is
`empirically related to SaO2:
`
`_ Acsso/Dcaso
`R _
`AC940/DC940
`
`.
`
`4
`
`(
`
`)
`
`Figure 4 is an example of a pulse oximeter calibration
`curve.” The actual curves used in commercial devices
`
`are based on experimental studies in human volunteers.
`Note that when the ratio of red to infrared absorbance
`
`is one, the saturation is approximately 85%. This fact has
`clinical implications to be discussed later.
`It is a fortuitous coincidence of technology and phys-
`iology that allowed the development of solid-state pulse
`oximeter sensors.” Light emitting diodes (LEDs) are
`available over a relatively narrow range of the electro-
`magnetic spectrum. Among the available wavelengths are
`some that not only pass through skin but also are absorbed
`by both oxyhemoglobin and reduced hemoglobin. For
`best sensitivity, the difference between the ratios of the
`absorbances of OgHb and I-lb at the two wavelengths
`
`PULSI-I (JXIl~il“.‘l'RY
`
`101
`
`LightAbsorption
`
`Absorption due to pulsatile arterial blood
`Absorption due to noi'1—pulsaIile arterial blood
`Absorption clue to venous and capillary blood
`
`'
`
`as itititititiitifititi
`T‘?00O0O0O9O060'O O O A.
`0000000020
`AALL.LA.A. A
`Time
`
`masorptioii due to tissue
`
`FIG. 3. This figure schematically illustrates the light absorption
`through living tissue. Note that the AC signal is due to the pulsatile
`component of the arterial blood while the DC signal is comprised of
`all the nonpnlsatile absorbers in the tissue; nonpulsatile arterial blood,
`venous and capillary blood, and all other tissues. Adapted from Ohmedzi
`Pulse Oximcter Model 3700 Service Manual, 1986, p. 22.
`
`should be maximized. As we see in figure 2, at 660 nano-
`meters. reduced hemoglobin absorbs about ten times as
`mtich light as oxyhemoglobin. (Note that the extinction
`coefficients are plotted on a logarithmic axis.) At the in-
`frared wavelength of 940 nanometers, the absorption
`coefficient of Oglrlb is greater than that of Hb.
`
`Engineering Design and Physiologic Limitations
`
`‘ Although the theory on which pulse oximetry is based
`is relatively straightforward. the appiication of this theory
`to the production ofa clinically useful device involves a
`
`0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.0 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
`
`Fl : T
`A Cfifilig D C 560
`Ac9.io’lDc one
`
`FIG. 4. This is a typical pulse oximeter calibration curve. Note that
`the SaOg estimate is determined from the ratio (R) of the pulse-added
`red absorbance at 660 nanometers to pulse-added infrared absorbance
`at 940 nanometers. The ratios of red to infrared absorbances vary
`from approximately .4 at I00‘/'6 saturation to 3.4 at 0% saturation.
`Note that the ratio of red to infrared absorbance is one at a saturation
`
`of approximately 85%. This curve can be approximately determined
`on a theoretical basis but, for accurate predictions of SpOg. experi-
`mental data are required. Adapted from _]A Pologe: Pulse oitimetry:
`Technical aspects of machine design, International Anesthesiology
`Clinics, Advances in Oxygen Monitoring. Edited by Tremper 1-(K,
`Barker S]. Boston, Little. Brown and Company, 1987. p 142.
`
`0011
`
`

`
`102
`
`K. K. TREMPER AND S. J. BARKER
`
`Ancslhtsiology
`V '.l'(l.No1.jan19S9
`
`significant engineering effort. This section will present in
`general terms the clinical and physiologic problems of
`oximeter design and their engineering solutions. The dis-
`cussion is divided into four areas: dyshemoglobins and
`dyes, LED center wavelength variability, signal artifact
`management, and accuracy and response. The reader
`should be aware that these problems can interact with
`one another.
`
`DYSHEMOGLOBINS AND DYES
`
`Being two-wavelength devices, pulse oximeters can deal
`with only two hemoglobin species. As noted above, this
`would be adequate to measure functional SaOg if MetHb
`and COI-Ib did not absorb red or infrared light at the
`wavelengths used. Unfortunately, this is not the case, and
`therefore both MetHb and COHb will cause errors in the
`
`pulse oximeter reading. It is not intuitively obvious how
`a pulse oximeter will behave in the presence of dyshem-
`oglobins. With respect to carboxyhemoglobin, we can gain
`some insight from the extinction curves of figure 2. In
`the infrared range (940 nm), COHb absorbs very little
`light: whereas, in the red range (660 nm), it absorbs as
`much light as does 02Hb. This is clinically illustrated by
`the fact that patients with carboxyhemoglobinemia appear
`red. Therefore, to the pulse oximeter, COHb looks like
`O21-lb at 660 nm; while, at 940 nm COHb is relatively
`transparent. The effect of COI-Ib on pulse oximeter values
`has been evaluated experimentally in dogs.” In this study,
`the pulse oximeter saturation (SpOg) was found to be given '
`approximately by:
`
`4, an absorbance ratio of one corresponds to a saturation
`of 85% on the calibration curve. Pulse oximeter error
`
`during methemoglobinernia has also been confirmed in a
`clinical report.”
`In neonatal blood, a fifth type of hemoglobin is present,
`fetal hemoglobin (I-lbF). I-IbF differs from adult Hb in
`the amino acid sequences of two of the four globin sub.
`units. Adult Hb has two 0c- and two ,6-globin chains, while
`I-IbF has two at and two f chains. This difference in globin
`chains has little effect on the extinction curves and there-
`
`fore should not affect pulse oximeter readings.§'ll This is
`indeed fortunate because the fraction of HbF present in
`neonatal blood is a function of gestational age and cannot
`be accurately predicted. HlJF does produce a small error
`in in vitro laboratory oximeters; O«_;HbF may be inter-
`preted as consisting partially of COHb.2°
`The absorbance ratio R (equation 4) may be affected
`by any substance present in the pulsatile blood that absorbs
`light at 660 or 940 nm and was not present in the same
`concentration in the volunteers used to generate the cal-
`ibration curve (fig. 4). Intravenous dyes provide a good
`example of this principle.” '22 Scheller at all. evaluated the
`effects of bolus doses of methylene blue, indigo carmine,
`and indocyanine green on pulse oximeters in human vol-
`unteers.“ They found that methylene blue caused a fall
`in SpOg to approximately 65% for 1-2 min. Indigo car-
`mine produced a very small drop in saturation, while in-
`docyanine green had an intermediate effect. The detec-
`tion of intravenous dyes by pulse oximeters should not
`be surprising. because it was this effect that led Aoyagi
`to the invention of pulse oximetry.2
`
`SP0” :
`
` ra X ,,,,,%_
`total Hb
`
`(5)
`
`LED CENTER WAVELENGTH VARIABILITY
`
`The effects of methemoglobinemia on pulse oximetry
`are also partially predictable from the extinction curves
`(fig. 2). MetHb has nearly the same absorbance as reduced
`hemoglobin at 560 nm, while it has a greater absorbance
`than the other hemoglobins at 940 nm. This is consistent
`with the clinical observation that methemoglobinemia
`produces very dark, brownish blood. Thus, it would be
`expected to produce a large pulsatile absorbance signal
`at both wavelengths. The effect of Metl-Ib on pulse ox-
`imeter readings has also been measured in dogs.” As
`methemoglobin levels increased, the pulse oximeter sat-
`uration (SPO2) tended toward 85% and eventually became
`almost independent of the actual SaOg .13 In other words,
`in the presence of high levels of MetHb, SpOg is erro-
`neously low when S2102 is above 85%, and erroneously
`high when SaOg is below 85%. This may be explained by
`the fact that MetHb causes a large pulsatile absorbance
`at both wavelengths, thereby adding to both the numer-
`ator and denominator of the absorbance ratio R (equation
`4) and forcing this ratio toward unity. As shown in figure
`
`The LEDS used in pulse oximeter sensors are not ideal
`monochromatic light sources: there is a narrow spectral
`range over which they emit light. The center wavelength
`of the emission spectrum varies even among diodes of the
`same type from the same manufacturer. This variation
`can be $15 nanometers.” As seen in figure 2, a shift in
`LED center wavelength will change the measured ex-
`tinction coefficient and thus produce an error in the sat-
`uration estimate. This source wavelength effect will be
`greatest for the red (560 nm) wavelength, because the
`extinction curves have a steeper slope at this wavelength.
`Manufacturers have found two approaches to this prob-
`lem. Some test all the LEDs and reject those that are out
`of their specified wavelength range, e.g., 660 i 5 nano-
`meters. This is expensive due to the number of LEDs
`
`.
`
`§ Pologe _]A, Raley DM: Effects of fetal hemoglobin on pulse ox-
`imetry._I Perinat VII:324-525, 1987.
`ll Anderson _]V: The accuracy of pulse oximetry in neonates: Effects
`of fetal hemoglobin and bilirubin.] Perinat VII:323. 1987.
`
`0012
`
`

`
`Anesthesiology
`V 1'0. No|.]an1‘.IB9
`
`PULSE OXIMETRY
`
`103
`
`rejected; i.r., narrower acceptable range yields improved
`accuracy but also more rejected LEDs. Alternatively,
`other manufacturers program the pulse oximeter to ac-
`cept several ranges of LED center wavelengths for both
`the red and infrared, allowing the device to correct in-
`terna