the following description and drawings are illustrative and are not to be construed as limiting . numerous specific details are described to provide a thorough understanding of the disclosure . however , in certain instances , well - known or conventional details are not described in order to avoid obscuring the description . reference in this specification to “ one embodiment ” or “ an embodiment ” means that a particular feature , structure , or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure . the appearances of the phrase “ in one embodiment ” in various places in the specification are not necessarily all referring to the same embodiment , nor are separate or alternative embodiments mutually exclusive of other embodiments . moreover , various features are described which may be exhibited by some embodiments and not by others . similarly , various features are described which may be included in some embodiments but not other embodiments . the terms used in this specification generally have their ordinary meanings in the art , within the context of the disclosure , and in the specific context where each term is used . certain terms in this specification may be used to provide additional guidance regarding the description of the disclosure . it will be appreciated that a feature may be described more than one - way . alternative language and synonyms may be used for any one or more of the terms discussed herein . no special significance is to be placed upon whether or not a term is elaborated or discussed herein . synonyms for certain terms are provided . a recital of one or more synonyms does not exclude the use of other synonyms . the use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only , and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term . fig1 a - 2b show an embodiment of an appliance 100 that includes ( i ) a fitting 110 for receiving an electromagnetic spectrum sensor 1000 , which senses if fluid is infusing perivascular tissue around cannula 20 ; ( ii ) a frame 120 for distributing forces acting on appliance 100 to the epidermis e ; and ( iii ) a body 130 for covering fitting 110 and frame 120 with a soft haptic surface . appliance 100 preferably couples electromagnetic spectrum sensor 1000 with the epidermis e proximate the insertion site s . preferably , appliance 100 positions sensor face 1000 a relative to the epidermis e within approximately 10 centimeters of the insertion site s and preferably approximately one centimeter to approximately five centimeters away from the insertion site s . electromagnetic spectrum sensor 1000 preferably aids in diagnosing infiltration or extravasation . preferably , electromagnetic radiation 1002 is emitted via a sensor face 1000 a of electromagnetic spectrum sensor 1000 and electromagnetic radiation 1004 is received via sensor face 1000 a . emitted electromagnetic radiation 1002 passes through the epidermis e into the perivascular tissue p . referring to fig1 c , the perivascular tissue p in the vicinity of a blood vessel v preferably includes the cells or interstitial compartments that may become unintentionally infused , e . g ., infiltrated or extravasated by fluid from cannula 20 . received electromagnetic radiation 1004 is at least a portion of emitted electromagnetic radiation 1002 that is reflected , scattered , diffused , or otherwise redirected from the perivascular tissue p through the epidermis e to sensor face 1000 a . emitted and received electromagnetic radiations 1002 and 1004 are preferably in the near - infrared portion of the electromagnetic spectrum . as the terminology is used herein , “ near infrared ” refers to electromagnetic radiation having wavelengths between approximately 1 , 400 nanometers and approximately 700 nanometers — proximate the nominal edge of red light in the visible light portion of the electromagnetic spectrum . these wavelengths correspond to a frequency range of approximately 215 terahertz to approximately 430 terahertz . preferably , emitted and received electromagnetic radiations 1002 and 1004 are tuned to a common peak wavelength . according to one embodiment , emitted and received electromagnetic radiations 1002 and 1004 each have a peak centered at approximately 950 nanometers . according to other embodiments , emitted electromagnetic radiation 1002 includes a wavelength profile in a band between a relatively low wavelength and a relatively high wavelength , and received electromagnetic radiation 1004 encompasses at least the band between the relatively low and high wavelengths . according to still other embodiments , received electromagnetic radiation 1004 is tuned to a wavelength profile in a band between relatively low and high wavelengths and emitted electromagnetic radiation 1002 encompasses at least the band between the relatively low and high wavelengths . the possibility of fluid infusing the perivascular tissue p preferably is indicated by analyzing received electromagnetic radiation 1004 . according to one embodiment , discrete pulses of emitted electromagnetic radiation 1002 cause corresponding pulses of received electromagnetic radiation 1004 . preferably , a processor ( not shown ) or another suitable device analyzes changes over time in received electromagnetic radiation 1004 for providing an indication of fluid infusing the perivascular tissue p . electromagnetic spectrum sensor 1000 may be coupled to the processor via a lead 1010 . according to some embodiments , electromagnetic spectrum sensor 1000 and the processor may be coupled to the processor wirelessly rather than via lead 1010 , or electromagnetic spectrum sensor 1000 may incorporate the processor . electromagnetic spectrum sensor 1000 preferably includes an anatomic sensor . as the terminology is used herein , “ anatomic ” preferably refers to the structure of an animalia body and an “ anatomic sensor ” preferably is concerned with sensing a change over time of the structure of the animalia body . by comparison , a physiological sensor is concerned with sensing the functions and activities of an animalia body , e . g ., pulse , at a point in time . electromagnetic spectrum sensor 1000 may be coupled to the epidermis e separately from typical contamination barriers ( not shown in fig1 a - 2b ). typical contamination barriers may ( i ) protect the insertion site s ; and ( ii ) allow the insertion site s to be observed . preferably , appliance 100 and a contamination barrier are coupled to the epidermis e separately , e . g ., at different times or in different steps of a multiple step process . according to one embodiment , a contamination barrier that overlies the insertion site s may also overlie portions of the cannula c and / or appliance 100 . according to another embodiment , a contamination barrier may overlie the insertion site s and be spaced from appliance 100 . appliance 100 preferably includes different arrangements that permit electromagnetic spectrum sensor 1000 to be reused with a plurality of appliances 100 . as the terminology is used herein , “ arrangement ” preferably refers to a relative configuration , formation , layout or disposition of appliance 100 and electromagnetic spectrum sensor 1000 . preferably , appliance 100 includes a fitting 110 that provides two arrangements with respect to electromagnetic spectrum sensor 1000 . referring to fig2 a , a first arrangement of fitting 110 preferably retains electromagnetic spectrum sensor 1000 relative to appliance 100 for monitoring infiltration or extravasation during an infusion with cannula 20 . referring to fig2 b , a second arrangement of fitting 110 preferably releases electromagnetic spectrum sensor 1000 from the first arrangement . accordingly , electromagnetic spectrum sensor 1000 may be decoupled from appliance 100 in the second arrangement of fitting 110 , e . g ., during patient testing or relocation , and subsequently recoupled in the first arrangement of fitting 110 such that sensor 1000 has approximately the same relationship to the epidermis e and the perivascular tissue p . relative movement between electromagnetic spectrum sensor 1000 and appliance 100 preferably is constrained between the first and second arrangements . preferably , fitting 110 includes a chute 112 that extends along an axis a between a first end 114 and a second end 116 . according to one embodiment , chute 112 preferably is centered about axis a , which preferably is obliquely oriented relative to the epidermis e . chute 112 and electromagnetic spectrum sensor 1000 preferably are cooperatively sized and shaped so that ( i ) electromagnetic spectrum sensor 1000 can be inserted in first end 114 in only one relative orientation ; and ( ii ) relative movement between the first and second arrangements is constrained to substantially only translation along axis a . as the terminology is used herein , “ translation ” refers to movement without rotation or angular displacement . electromagnetic spectrum sensor 1000 preferably does not rub the epidermis e during translation along axis a . accordingly , forces that may tend to distort the epidermis e preferably are prevented or at least minimized while moving electromagnetic spectrum sensor 1000 between the first and second arrangements of fitting 110 . it is believed that reducing distortion of the epidermis e reduces distortion of subcutaneous tissue including the perivascular tissue p and the blood vessel v , and therefore also reduces the likelihood of displacing cannula 20 while moving electromagnetic spectrum sensor 1000 between the first and second arrangements of fitting 110 . appliance 100 preferably includes a latch 118 for retaining electromagnetic spectrum sensor 1000 in the first arrangement of fitting 110 . preferably , latch 118 is resiliently biased into engagement with a cooperating feature on electromagnetic spectrum sensor 1000 in the first arrangement . according to one embodiment , latch 118 preferably includes a cantilever 118 a that has a recess or aperture 118 b for cooperatively receiving a projection 1000 b of electromagnetic spectrum sensor 1000 in the first arrangement . in the second arrangement , latch 118 may be manipulated to alter the nominal form of cantilever 118 a for releasing projection 1000 b from recess or aperture 118 a so that electromagnetic spectrum sensor 1000 may be withdrawn from chute 112 though first end 114 . preferably , latch 118 provides a positive indication , e . g ., a tactile or audible notification , that electromagnetic spectrum sensor 1000 is in at least one of the first and second arrangements . according to other embodiments , latch 118 may include snaps , a cap , or another suitable device that , in the first arrangement , retains electromagnetic spectrum sensor 1000 in fitting 110 and , in the second arrangement , releases electromagnetic spectrum sensor 1000 from fitting 110 , e . g ., allowing electromagnetic spectrum sensor 1000 to separate from appliance 100 . fitting 110 preferably permits reusing electromagnetic spectrum sensor 1000 . the first and second arrangements of fitting 110 preferably permit electromagnetic spectrum sensor 1000 to be decoupled and recoupled with appliance 100 , or decoupled from a first patient &# 39 ; s appliance 100 and coupled to a second patient &# 39 ; s appliance 100 . thus , fitting 110 preferably permits reusing electromagnetic spectrum sensor 1000 with a plurality of appliances 100 that are individually coupled to patients &# 39 ; epidermises . appliance 100 also preferably maintains electromagnetic spectrum sensor 1000 in a substantially consistent location relative to the perivascular tissue p . preferably , chute 112 delimits movement of electromagnetic spectrum sensor 1000 such that sensor face 1000 a of electromagnetic spectrum sensor 1000 is disposed proximate second end 116 of fitting 110 in the first arrangement . according to one embodiment , electromagnetic spectrum sensor 1000 projects from appliance 100 such that sensor face 1000 a preferably is disposed beyond second end 116 toward the epidermis e for substantially eliminating or at least minimizing a gap between sensor face 1000 a and the epidermis e . thus , appliance 100 in the first arrangement of fitting 110 preferably maintains a substantially consistent relative position between sensor face 1000 a and the epidermis e for sensing over time if fluid from cannula 20 is infusing the perivascular tissue p . appliance 100 preferably resists forces that tend to change the position of electromagnetic spectrum sensor 1000 relative to the perivascular tissue p . pulling or snagging lead 1010 is one example of the forces that frame 120 distributes over a larger area of the epidermis e than the areas overlaid by sensor face 1000 a or by fitting 110 . frame 120 therefore preferably enhances maintaining a substantially consistent relative position between sensor face 1000 a and the epidermis e for sensing over time if fluid from cannula 20 is infusing the perivascular tissue p . appliance 100 preferably includes a relatively rigid skeleton and a relatively supple covering . preferably , the skeleton includes fitting 110 for interacting with electromagnetic spectrum sensor 1000 , as discussed above , and frame 120 for distributing to the epidermis e forces acting on fitting 110 . frame 120 preferably includes a hoop 122 coupled with fitting 110 by at least one arm ( four arms 124 a - 124 d are indicated in fig1 a ). according to one embodiment , hoop 122 preferably includes an uninterrupted annulus disposed about fitting 110 . according to another embodiment , hoop 122 preferably includes a plurality of segments disposed about fitting 110 . the composition and dimensions of the skeleton preferably are selected so that forces acting on appliance 100 are distributed to the epidermis e . according to one embodiment , fitting 110 and frame 120 preferably are formed as a single independent component , e . g ., integrally molded with a substantially homogeneous chemical compound . according to another embodiment , fitting 110 and frame 120 may be composed of more than one compound and / or may include an assembly of a plurality of pieces . appliance 100 may be subjected to a variety of forces , for example , due to pulling or snagging lead 1010 , and preferably the dimensions of hoop 122 and arms 124 a - 124 d are selected for reacting to these forces . according to one embodiment , the dimensions of frame 120 preferably include arm 124 a being relatively more robust than arms 124 b - 124 d , arms 124 c and 124 d being relatively the least robust , and arm 124 b being relatively less robust than arm 124 a and relatively more robust than arms 124 c and 124 d . thus , according to this embodiment , appliance 100 reacts to forces , e . g ., an approximately eight - pound force pulling lead 1010 away from the epidermis e , that may tend to move electromagnetic spectrum sensor 1000 by ( i ) distributing a compression force to a first area of the epidermis e proximate arm 124 a ; and ( ii ) distributing a tension force to a second area of the epidermis proximate arm 124 b . the first and second areas preferably are larger than a third area of the epidermis e that the sensor face 1000 a and / or fitting 110 overlie . similarly , arms 124 c and 124 d preferably distribute compression and tension forces to fourth and fifth areas of the epidermis in response to , e . g ., torsion forces acting on lead 1010 . appliance 100 therefore preferably resists changes to the relative position between sensor face 1000 a and the epidermis e by distributing over relatively large areas of the epidermis e the forces that may tend to move electromagnetic spectrum sensor 1000 in the first arrangement of fitting 110 . the relatively supple covering of appliance 100 preferably includes a body 130 that presents a soft haptic exterior surface overlying the skeleton . preferably , body 130 has a relatively lower hardness as compared to fitting 110 and frame 120 . according to one embodiment , body 130 preferably consists of a first homogeneous chemical compound , fitting 110 and frame 120 preferably consist of a second homogeneous chemical compound , and the first homogeneous chemical compound has a lower hardness than the second homogeneous chemical compound . the first homogeneous chemical compound preferably includes silicone or another material having a relatively low durometer , e . g ., approximately shore a 10 to approximately shore a 60 , and the second homogeneous chemical compound preferably includes polyurethane or another material having a relatively higher durometer , e . g ., approximately shore d 30 to approximately shore d 70 . accordingly , the skeleton including fitting 110 and frame 120 preferably provides a structure for distributing forces applied to appliance 100 , and body 130 provides a soft haptic exterior surface that imparts to appliance 100 a desirable tactile feel , which may be characterized as soft rather than hard to the touch . preferably , fitting 110 includes a polypropylene homopolymer ( e . g ., pro - fax 6523 , manufactured by lyondellbasell industrial holdings , b . v ., rotterdam , the netherlands ) and body 130 includes a thermoplastic elastomer ( e . g ., versaflex ™ from polyone corporation , avon lake , ohio , usa ). a process for manufacturing appliance 100 preferably includes covering the skeleton with the soft haptic exterior surface . according to one embodiment , appliance 100 is molded in a multiple step process . preferably , one step includes molding fitting 110 and frame 120 in a mold , another step includes adjusting the mold , and yet another step includes molding body 130 over fitting 110 and frame 120 in the adjusted mold . an apparatus for molding fitting 110 , frame 120 and body 130 preferably includes a common mold portion , a first mold portion cooperating with the common mold portion for molding fitting 110 and frame 120 , and a second mold portion cooperating with the common mold portion for over - molding body 130 . preferably , the common and first mold portions receive a first shot of material to mold fitting 110 and frame 120 , the mold is adjusted by decoupling the first mold portion from the common mold portion and coupling the second mold portion with the common mold portion , and the common and second mold portions receive a second shot of material to mold body 130 . fitting 110 and frame 120 preferably remain in the common mold portion while decoupling the first mold portion and coupling the second mold portion . accordingly , appliance 100 is preferably molded in a two - shot process with a skeleton including fitting 110 and frame 120 being subsequently covered with a soft haptic exterior surface including body 130 . appliance 100 may be wholly biocompatible and / or include a biocompatible layer for contacting the epidermis e . as the terminology is used herein , “ biocompatible ” preferably refers to compliance with standard 10993 promulgated by the international organization for standardization ( iso 10993 ) and / or class vi promulgated by the united states pharmacopeial convention ( usp class vi ). other regulatory entities , e . g ., national institute of standards and technology , may also promulgate standards that may additionally or alternatively be applicable regarding biocompatibility . referring particularly to fig1 c , a foundation 150 preferably ( 1 ) couples appliance 100 and the epidermis e ; and ( 2 ) separates the rest of appliance 100 from the epidermis e . preferably , foundation 150 includes a panel 152 that is coupled to an undersurface of appliance 100 confronting the epidermis e ( shown in fig2 a ). according to one embodiment , panel 152 is adhered to the undersurface of appliance 100 . panel 152 preferably includes polyurethane and occludes second end 116 for providing a barrier between the epidermis e and sensor face 1000 a in the second arrangement . according to other embodiments , body 130 preferably includes panel 152 . for example , a substantially homogeneous material may be used for integrally molding body 130 and panel 152 . preferably , panel 152 is biocompatible according to iso 10993 and / or usp class vi . foundation 150 preferably includes an adhesive coating 154 for adhering appliance 100 to the epidermis e . adhesive 154 preferably includes an acrylic adhesive or another medical grade adhesive that is biocompatible according to iso 10993 and / or usp class vi . according to one embodiment , adhesive 154 may be applied to all or a portion of panel 152 on the surface that confronts the epidermis e . according to other embodiments , panel 152 may be omitted and adhesive 154 may directly adhere body 130 and / or fitting 110 to the epidermis e . adhesive 154 preferably may be adjusted to vary the bond strength between appliance 100 and the epidermis e . preferably , stronger or more adhesive 154 may be used for coupling appliance 100 to relatively robust skin , e . g ., adult skin , and weaker or less adhesive 154 may be used for coupling appliance 100 to relatively delicate skin , e . g ., pediatric skin . preferably , appliance 100 permits viewing the epidermis e with visible light and generally rejects interference by ambient sources with emitted and received electromagnetic radiation 1002 and 1004 . as the terminology is used herein , “ visible light ” refers to energy in the visible portion of the electromagnetic spectrum , for example , wavelengths between approximately 380 nanometers and approximately 760 nanometers . these wavelengths correspond to a frequency range of approximately 400 terahertz to approximately 790 terahertz . preferably , body 130 is transparent or translucent to visible light for viewing the epidermis e under at least a portion of appliance 100 . according to one embodiment , fitting 110 and frame 120 preferably are also transparent or translucent to visible light . according to other embodiments , fitting and / or frame 120 may be generally opaque to visible light . according to still other embodiments , body 130 may be generally opaque to visible light or fitting 110 and / or frame 120 may be may be transparent or translucent to visible light . preferably , fitting 110 , frame 120 and body 130 , but not foundation 150 , absorb or block electromagnetic radiation with wavelengths that approximately correspond to emitted and received electromagnetic radiation 1002 and 1004 , e . g ., radiation in the near - infrared portion of the electromagnetic spectrum . accordingly , appliance 100 preferably permits visible light viewing of the epidermis e and minimizes ambient source interference with emitted and received electromagnetic radiation 1002 and 1004 . appliance 100 preferably is advantageous at least because ( i ) the location of a patient monitor , e . g ., electromagnetic spectrum sensor 1000 , is not linked by appliance 100 to cannula 20 or to an iv dressing for the insertion site s ; ( ii ) appliance 100 is interchangeably useable with typical dressings for the iv insertion site s ; and ( iii ) minimal stress and strain is transferred by appliance 100 to the epidermis e when changing between the first and second arrangements of fitting 110 . as the terminology is used herein , “ link ” or “ linking ” preferably refers to at least approximately fixing the relative locations of at least two objects . fig3 - 5b show an embodiment of an appliance 200 that preferably includes ( i ) a fitting 210 for receiving electromagnetic spectrum sensor 1000 , which senses if fluid is infusing perivascular tissue around cannula 20 ; ( ii ) a frame 220 for distributing forces acting on appliance 200 to the epidermis e ; and ( iii ) a body 230 for covering fitting 210 and frame 220 with a soft haptic surface . as compared to appliance 100 ( fig1 a - 2b ), the location of cannula 20 is linked by appliance 200 to electromagnetic spectrum sensor 1000 . appliance 200 preferably positions sensor face 1000 a relative to the epidermis e within approximately five centimeters of the insertion site s and preferably approximately one centimeter to approximately three centimeters away from the insertion site s . appliances 100 and 200 preferably include some features and advantages that are comparable . as the terminology is used herein , “ comparable ” refers to similar , if not identical , compositions , constructions , properties , functions or purposes , and preferably combinations thereof . preferably , features of appliances 100 and 200 that are comparable include ( i ) fittings 110 and 210 ; ( ii ) chutes 112 and chute 212 ; ( iii ) latches 118 and 218 ; ( iv ) hoops 122 and 222 ; and ( v ) arms 124 and 224 . appliance 200 may also include a foundation 250 , which is comparable to foundation 150 , for separating and coupling the rest of appliance 200 with respect to the epidermis e . additional descriptions of comparable features or advantages may be found herein and may not be repeated in their entirety . appliance 200 preferably includes one or more wings 240 in addition to at least some of the features and advantages of appliance 100 . preferably , individual wings 240 ( i ) link electromagnetic spectrum sensor 1000 with respect to cannula 20 ; ( ii ) separate cannula 20 from the epidermis e ; ( iii ) provide resistance to forces that tend to change relative to the perivascular tissue p ; and / or ( iv ) stabilize the positions of cannula 20 and electromagnetic spectrum sensor 1000 relative to the epidermis e . each wing 240 preferably is coupled with fitting 210 , frame 220 or body 230 and includes a first surface 242 for contiguously engaging cannula 20 and a second surface 244 for contiguously engaging the epidermis e . according to one embodiment , individual wings 240 include portions of frame 220 and body 230 . appliance 200 preferably includes plural locating options for linking electromagnetic spectrum sensor 1000 with respect to cannula 20 . according to one embodiment , individual wings 240 preferably extend in two generally opposite lateral directions with respect to axis a of fitting 210 . accordingly , a footprint of appliance 200 on the epidermis e preferably is approximately tee - shaped or approximately wye - shaped and cannula 20 may be located on either one of the wings 240 on opposite sides of electromagnetic spectrum sensor 1000 . according to other embodiments , a single wing 240 preferably extends in one lateral direction with respect to axis a of fitting 210 . accordingly , a footprint of appliance 200 on the epidermis e preferably is approximately ell - shaped with cannula 20 being located on wing 240 extending to one side of electromagnetic spectrum sensor 1000 . preferably , individual appliances 200 with single wings 240 that extend on different sides of electromagnetic spectrum sensor 1000 may be included in a set . accordingly , one or another of appliances 200 in the set preferably is selected to provide the most suitable locating option for linking electromagnetic spectrum sensor 1000 with respect to cannula 20 . the most suitable locating option preferably is selected based on one or more factors including : ( i ) the location on the patient of the insertion site s ; ( ii ) the orientation of cannula 20 relative to the insertion site ; ( iii ) minimizing movement of cannula 20 or electromagnetic spectrum sensor 100 due to pulling or snagging tubing 32 or lead 1010 ; and ( iv ) comfort of the patient . a single wing 240 may make appliance 200 more compact and plural wings 240 on a single appliance 200 may provide additional options for locating electromagnetic spectrum sensor 1000 relative to cannula 20 . further , appliance 200 may include perforations or shear line indicators for separating , e . g ., tearing - off or cutting , at least one wing 240 from the rest of appliance 200 . accordingly , the size of appliance 200 may be compacted and / or appliance 200 may be made wingless in the manner of appliance 100 . thus , an advantage of each of the aforementioned embodiments is increasing the options for how an anatomical sensor may be located on a patient relative to the insertion site s . appliance 200 preferably separates cannula 20 from the epidermis e . according to one embodiment , wing 240 includes a thickness 246 between first surface 242 and second surface 244 . preferably , thickness 246 provides a spacer that prevents or at least minimizes contiguous engagement between the epidermis e and hub 20 a of cannula 20 . wing 240 therefore preferably eliminates or at least reduces epidermal inflammation or breakdown , e . g ., chafing or blistering , caused by cannula 20 . wing ( s ) 240 preferably supplement the ability of appliance 200 to resist forces that tend to change the positions of electromagnetic spectrum sensor 1000 and cannula 20 relative to the epidermis e and the perivascular tissue p . preferably , a skeleton of appliance 200 includes fitting 210 , frame 220 , and at least one wing rib 248 . fitting 210 preferably interacts with electromagnetic spectrum sensor 1000 in a manner comparable to fitting 110 discussed above . preferably , frame 220 includes a hoop 222 coupled with fitting 210 by at least one arm 224 . thus , frame 220 may be comparable to frame 120 at least insofar as preferably contributing to distributing to the epidermis e the forces that act on fitting 210 . appliance 200 preferably resists changes to the relative position between sensor face 1000 a and the epidermis e by distributing over relatively large areas of the epidermis e the forces that may tend to move electromagnetic spectrum sensor 1000 in the first arrangement of fitting 210 . individual wing ribs 248 preferably enlarge the area of the epidermis e over which frame 220 distributes forces acting on fitting 210 . according to one embodiment , individual wing ribs 248 preferably include a cantilever having a base coupled with frame 220 and a tip disposed in a corresponding wing 240 . according to other embodiments , more than one wing rib 248 may be disposed in a corresponding wing 240 , individual wing ribs 248 may include a bifurcated cantilever , and / or individual cantilevers may include one or more branches . the skeleton of appliance 200 therefore preferably enhances maintaining a substantially consistent relative position between electromagnetic spectrum sensor 1000 and the perivascular tissue p for sensing over time if fluid from cannula 20 is infusing the perivascular tissue p . appliance 200 preferably is sufficiently flexible to conform to the approximate contours of the epidermis e . for example , frame 220 may include one or more lines of weakness disposed on hoop 222 , arm ( s ) 224 and / or wing rib ( s ) 248 . as the terminology is used herein , “ lines of weakness ” preferably refers to living hinges or other suitable features for increasing flexibility at a particular location of the skeleton of appliance 200 . body 230 preferably presents a soft haptic exterior surface overlying the relatively rigid skeleton of appliance 200 . in a manner comparable to body 130 discussed above , body 230 is relatively supple , e . g ., has a relatively lower hardness , and may be molded over fitting 210 , frame 220 and wing rib ( s ) 248 . according to one embodiment , body 230 preferably includes first surface 242 , at least a portion of second surface 244 , and a large portion of thickness 246 . the remaining portions of second surface 244 and thickness 246 preferably are occupied by wing rib ( s ) 248 . accordingly , an individual wing 240 preferably is primarily composed of the relatively supple material of body 230 with wing rib ( s ) 248 included for force distribution and / or structural reinforcement . preferably accompanying appliance 200 may be at least one independent contamination barrier 260 for overlying the epidermis e and at least a portion of cannula 20 while allowing visual inspection of the insertion site s . fig3 shows an exploded view with contamination barrier 260 displaced from appliance 200 . contamination barrier 260 preferably is biocompatible according to iso 10993 and / or usp class vi and may include a polyurethane membrane 262 with a coating of medical grade acrylic adhesive 264 . examples of typical contamination barriers include tegaderm ™, manufactured by 3m ( st . paul , minn ., usa ), reactic ™, manufactured by smith & amp ; nephew ( london , uk ), and other transparent or translucent polymer films that are substantially impervious to solids , liquids , microorganisms and / or viruses . preferably , contamination barrier 260 is supplied as a separate piece to appliance 200 — both pieces may be included in a kit — and the two pieces are independently coupled to the epidermis e at different times or in different steps . appliance 200 and contamination barrier 260 preferably include form factors that cooperate with one another . according to one embodiment , body 230 preferably includes a form factor such as a flange 232 that covers hoop 222 and arm ( s ) 224 . preferably , flange 232 includes a top surface 232 a to which adhesive 264 may adhere membrane 262 when appliance 200 and contamination barrier 260 are used in combination . according to one embodiment , a set of individual contamination barriers 260 preferably accompanies each appliance 200 . each of the contamination barriers 260 in the set preferably includes a notch 266 or another form factor having a peripheral edge that is sized and / or shaped to correspond with at least a portion of flange 232 and / or wing 240 on one or the other side of axis a . accordingly , one or another of contamination barriers 260 in the set preferably is selected to apply to the epidermis e on the side of axis a that cannula 20 is located . according to other embodiments , contamination barrier 260 preferably includes a symmetrical shape that may be turned or otherwise reoriented to cooperatively engage appliance 200 on either side of axis a that cannula 20 is located . a method of using appliance 200 to monitor if fluid is infusing perivascular tissue around cannula 20 preferably includes ( i ) coupling appliance 200 to the epidermis e ; ( ii ) coupling electromagnetic spectrum sensor 1000 in the first arrangement of fitting 210 ; and ( iii ) coupling cannula 20 with one wing 240 . preferably , appliance 200 is coupled with the epidermis e by adhesive included in foundation 250 or by another suitable epidermal fastener . electromagnetic spectrum sensor 1000 preferably is translated along axis a to the first arrangement of fitting 210 and securely latched . preferably , one wing 240 underlays cannula 20 and an adhesive strip 270 ( see fig4 ) secures cannula 20 to wing 240 . according to one embodiment , cannula 20 is inserted in the blood vessel v and then one wing 240 is positioned under cannula 20 before adhering appliance 200 to the epidermis e . adhesive strip 270 subsequently overlies and couples cannula 20 with respect to wing 240 before coupling electromagnetic spectrum sensor 1000 in the first arrangement of fitting 210 . according to other embodiments , electromagnetic spectrum sensor 1000 is coupled in the first arrangement of fitting 210 before positioning one wing 240 under cannula 20 and adhering appliance 200 to the epidermis e . adhesive strip 270 subsequently overlies and couples cannula 20 with respect to wing 240 . each of the aforementioned embodiments may also include adhering contamination barrier 260 with top surface 232 a of flange 232 , as well as with the epidermis e . preferably , electromagnetic spectrum sensor 1000 may be moved between the first and second arrangements of fitting 210 without decoupling appliance 200 from the epidermis e , without decoupling cannula 20 or adhesive strip 270 from wing 240 , and without decoupling contamination barrier 260 from the epidermis e . appliance 200 preferably is advantageous at least because ( i ) appliance 200 may be physically associated with a dressing for the iv insertion site s ; ( ii ) appliance 200 links electromagnetic spectrum sensor 1000 and cannula 20 ; ( iii ) appliance 200 includes a plurality of locating options for linking electromagnetic spectrum sensor 1000 with respect to cannula 20 ; ( iv ) appliance 200 maintains a substantially consistent relative position between electromagnetic spectrum sensor 1000 and the perivascular tissue p for sensing over time if fluid from cannula 20 is infusing the perivascular tissue p ; and ( v ) appliance 200 eliminates or at least reduces epidermal inflammation or breakdown caused by cannula 20 . appliance 200 preferably also is advantageous insofar as preventing or minimizing forces that tend to distort the epidermis e while moving between the first and second arrangements of fitting 210 . it is believed that reducing distortion of the epidermis e reduces distortion of subcutaneous tissue including the perivascular tissue p and the blood vessel v , and therefore also reduces the likelihood of displacing cannula 20 while moving between the first and second arrangements of fitting 210 . fig6 and 7 show an embodiment of an appliance 300 that includes ( i ) a fitting 310 for receiving electromagnetic spectrum sensor 1000 , which senses if fluid is infusing perivascular tissue around cannula 20 ; ( ii ) a frame 320 for distributing forces acting on appliance 300 to the epidermis e ; and ( iii ) a body 330 for covering fitting 310 and frame 320 with a soft haptic surface . as compared to appliances 100 and 200 ( fig1 a - 5b ), a first arrangement of fitting 310 preferably is an alternate to the first arrangements of fittings 110 and 210 ; however , the second arrangements of fittings 110 , 210 and 310 preferably are similar insofar as releasing electromagnetic spectrum sensor 1000 from the respective first arrangements . preferably , other features and advantages of appliances 100 , 200 and 300 are comparable including ( i ) frames 120 , 220 and 320 ; ( ii ) wings 240 and 340 ; ( iii ) wing ribs 248 and 348 ; ( iv ) bodies 130 , 230 and 330 ; ( v ) foundations 150 , 250 and 350 ; ( vi ) contamination barriers 260 and 360 ; and ( vii ) adhesive strips 270 and 370 . appliance 300 preferably positions sensor face 1000 a relative to the epidermis e within approximately five centimeters of the insertion site s and preferably approximately one centimeter to approximately three centimeters away from the insertion site s . the first arrangement of fitting 310 preferably includes sets of pegs for constraining relative movement between electromagnetic spectrum sensor 1000 and appliance 300 . as the terminology is used herein , “ peg ” preferably refers to a projecting piece or portion of a surface that is used as a support or boundary . according to one embodiment , fitting 310 includes a first set of pegs 312 disposed proximate sensor face 1000 a and a second set of pegs 314 disposed proximate lead 1010 . preferably , a cage of appliance 300 includes first and second sets of pegs 312 and 314 . the cage preferably defines a pocket for receiving electromagnetic spectrum sensor 1000 and constrains relative movement between electromagnetic spectrum sensor 1000 and appliance 300 in the first arrangement of fitting 310 . preferably , first set of pegs 312 — two pegs are shown in fig7 — preferably includes a form factor that generally conforms to the contours of electromagnetic spectrum sensor 1000 to define a first portion of the cage . individual pegs 312 preferably include a cantilever extending between a base 312 a and a tip 312 b . preferably , base ( s ) 312 a are coupled to frame 320 and tip ( s ) 312 b at least slightly overlie electromagnetic spectrum sensor 1000 to constrain movement away from the epidermis e in the first arrangement of fitting 310 . according to one embodiment , individual pegs 312 preferably are bifurcated at base 312 a and converge at tip 312 b . second set of pegs 314 — two pegs are shown in fig7 — preferably are disposed on opposite sides of electromagnetic spectrum sensor 1000 to define a second portion of the cage . individual pegs 314 preferably include cantilevers extending between a base 314 a and a tip 314 b . preferably , bases 314 a are coupled to frame 320 and a portion of electromagnetic spectrum sensor 1000 proximate lead 1010 is received between tips 314 b to constrain relative angular movement and / or provide strain relief for electromagnetic spectrum sensor 1000 in the first arrangement of fitting 310 . other embodiments of appliance 300 may have sets including different numbers , locations and shapes of pegs 312 and pegs 314 . for example , the first set may include more or less than two pegs 312 ; the second set may include more than a single peg 314 located on each side of electromagnetic spectrum sensor 1000 ; and / or tip 314 b of at least one peg 314 may include a bump or other projection for retaining electromagnetic spectrum sensor 1000 in the first arrangement of fitting 310 . body 330 preferably presents a soft haptic exterior surface overlying the relatively rigid fitting 310 and frame 320 of appliance 300 . in a manner comparable to bodies 130 and 230 discussed above , body 330 is relatively supple , e . g ., has a relatively lower hardness , and may be molded over fitting 310 , frame 320 and wing rib ( s ) 348 . appliance 300 preferably includes a link between electromagnetic spectrum sensor 1000 and cannula 20 . preferably , appliance 300 includes at least one wing 340 coupled with at least one of fitting 310 , frame 320 , and body 330 . individual wings 340 preferably are comparable to individual wings 240 of appliance 200 at least insofar as ( i ) locating electromagnetic spectrum sensor 1000 with respect to cannula 20 ; ( ii ) separating cannula 20 from the epidermis e ; and / or ( iii ) providing resistance to forces that tend to change the position of electromagnetic spectrum sensor 1000 relative to the perivascular tissue p . individual wings 340 of appliance 300 preferably separate cannula 20 from the epidermis e , and preferably supplement the ability of appliance 300 to resist forces that tend to change the position of electromagnetic spectrum sensor 1000 relative to the perivascular tissue p . preferably , wing 340 includes a thickness 346 that eliminates or at least reduces epidermal inflammation or breakdown caused by cannula 20 . preferably , a skeleton of appliance 300 includes fitting 310 , frame 320 , and at least one wing rib 348 to distribute to the epidermis e the forces that act on fitting 310 . further , appliance 300 preferably resists changes to the relative position between sensor face 1000 a and the epidermis e by distributing over relatively large areas of the epidermis e the forces that may tend to move electromagnetic spectrum sensor 1000 in the first arrangement of fitting 310 . accordingly , appliance 300 is comparable at least in this regard to appliances 100 and 200 individual wing ribs 348 preferably enlarge the area of the epidermis e over which frame 320 distributes forces acting on fitting 310 . the skeleton of appliance 300 therefore preferably enhances maintaining a substantially consistent relative position between electromagnetic spectrum sensor 1000 and the perivascular tissue p for sensing over time if fluid from cannula 20 is infusing the perivascular tissue p . appliance 300 preferably is comparable to appliance 200 insofar as including plural locating options for linking electromagnetic spectrum sensor 1000 with respect to cannula 20 . factors for selecting the most suitable locating option are discussed above with regard to appliance 200 . appliance 300 also therefore includes the advantage of having more than one choice for how an anatomical sensor may be located on a patient relative to the insertion site s . a process for implementing appliance 300 to sense if fluid is infusing perivascular tissue around cannula 20 preferably includes ( i ) coupling appliance 300 to the epidermis e ; ( ii ) coupling electromagnetic spectrum sensor 1000 in the first arrangement of fitting 310 ; and ( iii ) coupling cannula 20 with one wing 340 . a process for coupling electromagnetic spectrum sensor 1000 with appliance 300 preferably includes ( i ) orienting electromagnetic spectrum sensor 1000 obliquely with respect to frame 320 ; ( ii ) slipping electromagnetic spectrum sensor 1000 under tip ( s ) 312 a ; and ( iii ) pivoting electromagnetic spectrum sensor 1000 between peg ( s ) 314 . accordingly , the cage including first and second sets of pegs 312 and 314 preferably constrains relative movement between electromagnetic spectrum sensor 1000 and appliance 300 . preferably , the cage of appliance 300 includes . preferably , the second arrangement of fitting 310 includes reversing the above process for coupling electromagnetic spectrum sensor 1000 with appliance 300 . decoupling electromagnetic spectrum sensor 1000 in the second arrangement of fitting 310 accordingly permits reusing electromagnetic spectrum sensor 1000 in the same or a different appliance 300 . while the present invention has been disclosed with reference to certain embodiments , numerous modifications , alterations , and changes to the described embodiments are possible without departing from the sphere and scope of the present invention , as defined in the appended claims . for example , appliances 100 , 200 and 300 preferably are devoid of materials , e . g ., metal , that may harm a patient or damage diagnostic equipment during magnetic resonance imaging , computerized axial tomography , x - rays , or other procedures that use electromagnetic radiation . advantageously , appliances 200 and 300 may be comparable to appliance 100 at least insofar as being also interchangeably useable with typical dressings for the iv insertion site s . accordingly , it is intended that the present invention not be limited to the described embodiments , but that it has the full scope defined by the language of the following claims , and equivalents thereof .