Abstract:
An intravenous infiltration detection apparatus for monitoring intravenous failures, which applies an optical method coupled with fiber optics and algorithms for tissue optics to provide a means for noninvasive detection of intravenous infiltration surround the site of IV injection. In the invention, the tissue surrounding the injection site is exposed to a single-wavelength of electromagnetic radiation, and light is collected with only one detector. Changes in the relative intensity of the radiation reflected, scattered, diffused or otherwise emitted provide a means for monitoring infiltration. The invention provides routine, automated, continuous, and real-time monitoring for patients undergoing IV therapy.

Description:
BACKGROUND OF THE INVENTION 
     In the United States, approximately 80% of hospital patients require intravenous (IV) therapy and approximately 50% of the IV lines fail due to infiltration, a clot in the cannula, an inflammatory response of the vein, or separation of the cannula from the vein. IV infiltration is usually accompanied by pain, erythema, and/or swelling at the cannula tip or the insertion site. Severe infiltration may lead to necrosis requiring skin debridement, skin grafting, or amputation. One common area of malpractice lawsuits filed against physicians and nurses involves infiltration. The leakage of cytotoxic drugs, intravenous nutrition, solutions of calcium, potassium, and bicarbonate, and even 10% dextrose outside the vein into which they are delivered is known to cause tissue necrosis and to precipitate significant scarring around joints. An infiltration rate of 0.1-1% has been reported in cases where contrast agents were used in medical imaging procedures. Early detection of infiltration prevents the occurrence of serious incidents that may require surgical correction. 
     It has been postulated that there are six predictors of infiltration—catheter material, age of patients, anatomic insertion site, hyperalimentation, the use of furosemide, and the use of dopamine. The age of patient is a very important factor for the risk of infiltration. Because the amount of connective tissue is limited in elderly patients as well as the very young, they are prone to extensive diffusion of infiltrated fluid. The patient&#39;s osmotic balance is another important consideration. Obese patients or patients with low albumin or edema may not have normal tissue responses to pressure. 
     Infiltration may develop in different ways: (a) the steel needle or plastic cannula may pierce the wall of the vein, allowing fluid to flow into the interstitial space; (b) a clot distal to the cannula may develop, causing narrowing of the vein wall, blocking blood flow, increasing backpressure, and infiltration at the needle insertion site; (c) certain IV fluids may cause change in blood pH and constriction of veins with increasing pressure and subsequent infiltration; (d) the IV cannula or the infused solution may cause an inflammatory reaction, increasing permeability of the vein and allowing fluid to leak into surrounding tissues; and (e) the cannula may be dislodged from the vein. The extent of tissue damage caused by infiltration depends on the drug, the dosage, the site of IV administration, and the exposure duration. Injuries due to infiltration of cytotoxic drug infusions range from 0.1-0.7%. Severe infiltration injuries often require surgical treatment and even amputation. One study reported that infiltration results in skin loss in 0.24% of the peripheral lines. 
     There are several methods currently existing for detecting infiltration: visual and tactile examinations; monitoring IV line pressure; checking for blood return; and electromagnetic radiation detection. 
     Visual and tactile examinations of IV sites are the most widely used methods for detecting infiltrations. The infiltrated site may appear swollen or puffy. In this case erythema may also be present. Infiltrations may also appear as a pale area where the infiltrate has pooled below the skin. The skin may feel cooler than the surrounding area due to rapid entrance of the IV fluid into the tissue before it can be warmed to body temperature. The visual and tactile examination technique is ineffective in detecting infiltration, since by the time infiltration is detected, tissue damage has already occurred. 
     IVs are administered either by gravity control or infusion pumps. For gravity control, the solution head height, defined as the vertical distance from the fluid meniscus to the IV site, generates the pressure necessary to infuse IV fluid. In theory, gravity control would stop fluid infusion when sufficient fluid accumulates in the interstitial space. Once the fluid flow stops, an alarm alerts the nurse to check the IV site. For gravity control IV, the solution reservoir can be lowered to below IV sites. If blood flows toward the lowered reservoir, infiltration is less likely to occur. However, this technique cannot reliably detect infiltration. 
     Infusion pumps provide volumetric and timed delivery of IV fluids under conditions of increased resistance to flow. The occlusion pressure can be as high as 25 psi (1293 mm Hg). The disadvantage of maintaining a high pressure is that a potential hazard to patients exists should infiltration occur. Studies of the performance of low, non-variable pressure infusion pumps in alerting the nurses to infiltrations, show that while 64% of IV sites show clinical evidence of infiltration, no alarm occurs. It has been reported that infiltration may be detected by monitoring the IV pressure, one measures either the in-line IV pressure or the in-line IV pressure dissipation after a brief pressure increase. However, both pressure monitoring methods have proven unreliable, since there is limited predictability of change in in-line pressure following infiltration. Perfusion, diffusion, and metabolic processes occurring in living tissue and intra- and inter-patient differences render the use of pressure monitoring for infiltration detection ineffective. 
     Another method of checking for infiltration is to look for a blood return. Removing the positive pressure caused by the infusion controller (either gravity or infusion pump) checks for the presence of a blood return. While the lack of a blood return indicates infiltration, the presence of a blood return cannot be construed as the absence of an infiltration. 
     One commercial device, the Venoscope® uses transillumination to locate the patient&#39;s peripheral venous network. It employs two movable optical fibers to illuminate the skin. The veins appear as dark areas beneath the skin. Detection of veins is by visual inspections. The Venoscope® must be used in a dimly lit room in order to have sufficient contrast to locate the venous network. It has been claimed that the Venoscope® can be used to detect IV infiltration. However, the detection is performed by subjective visual inspections. 
     Another method of detecting infiltration is described in U.S. Pat. No. 4,877,034 (Atkins). The Atkins invention teaches an IV monitoring technique that allows detection of tissue infiltration by exposing tissue surrounding the site of intravenous injection to a plurality of wavelengths of electromagnetic radiation. Changes in the relative levels of the detected radiation at each wavelength as compared to a baseline reading obtained when no infiltration is occurring indicate tissue infiltration. Electromagnetic radiation sources of at least two different wavelengths of radiation are used to direct electromagnetic radiation at the tissue surrounding the intravenous insertion site. The amount of radiation reflected, scattered and absorbed under certain conditions depends on the wavelength of the electromagnetic radiation and local tissue properties. The intensities of the detected radiation at the two wavelengths change when infiltration occurs, and these changes are different for different wavelengths. That is, infiltration affects the intensity of the detected electromagnetic radiation at one wavelength more than that of the second wavelength, allowing the difference to be used to indicate infiltration. While Atkins teaches a noninvasive method of detecting tissue infiltration, it is unnecessarily complex. 
     U.S. Pat. No. 6,487,428 (Culver) describes an IV monitoring apparatus for detecting IV infiltration by monitoring light transmitted through the tissue of the patient in proximity to a site at which fluid is being injected. Light is irradiated from a plurality of light sources in an encoded manner into the body part at the site at which the fluid is injected and the light that is reflected, scattered, diffused or otherwise emitted from the body part is detected individually by a plurality of light detectors. Signals representative of the detected light are collected and, prior to injection of the fluid, references are developed against which measurements made during injection of the fluid are compared. Like Atkins, the Culver invention is unnecessarily complex. 
     To solve the shortcomings in the existing systems, a need exists for a simple, reliable, inexpensive, and noninvasive method of monitoring IV sites for early detection of infiltration. 
     SUMMARY OF THE INVENTION 
     The present invention solves the shortcomings of existing systems by providing a device and method:
     (1) That is potentially sensitive and robust against false alarms. Using the present invention on simulated infiltrations, the minimally detectable fluid volume is about 0.1 ml when a syringe is used to inject the fluid and it is about 0.02 ml when either a syringe pump or an infusion pump is used to infuse the fluid. The sensitivity, specificity, positive and negative predictive values of the present invention are calculated to be 97%.   (2) That monitors both the insertion site and any infiltration that may occur without direct attention of medical personnel, providing continuous monitoring of the IV site.   (3) That eliminates the subjectivity of observer-based visual inspections. It applies optical technology as compared with pressure monitoring using infusion pumps.   (4) That may be incorporated into existing IV systems to provide an alarm signal to alert the patient and/or healthcare personnel of potential infiltrations.   (5) That can detect small amounts of infiltrate well before a skilled observer detects the infiltration.   (6) That uses a single light source and a single detector making the present invention less complex and more reliable than any prior art devices.   

     An intravenous infiltration detection apparatus according to the present invention includes a light source, a power supply, two light guides, a detector, an electronics unit, a skin-contact sensor, and an indicator. The power supply provides power to the light source, the detector, the electronics unit, and the indicator. The light source provides illumination to the infusion site. The first light guide delivers incident electromagnetic radiation to the infusion site, its proximal end is optically coupled to the light source and its distal end is embedded in a skin-contact sensor placed near the IV infusion site of a patient. The second light guide collects the electromagnetic radiation reflected, scattered, diffused or otherwise emitted from the tissue near the infusion site and delivers the collected radiation to the detector. The proximal end of the second light guide is optically coupled to the detector and, like the first light guide, its distal end is embedded in the skin-contact sensor. The distal ends of both the illumination (first) light guide and the collection (second) light guide are flush with the skin-contact side of the skin-contact sensor. The distance between the distal ends of the two light guides in the skin-contact sensor is approximately a few millimeters. The skin-contact sensor can be made of different materials, including, but not limited to, wood and plastics. The skin-contact sensor is attached to the skin via a securing device such as, but not limited to, a piece of surgical tape. A detector at the proximal end of the second light guide receives the collected electromagnetic radiation from the tissue. An electronics unit connected to the detector analyzes the collected radiation. The information on the occurrence of IV infiltration is exhibited on the indicator. In one example of the present invention, the indicator may display normal infusion (no infiltration), possible infiltration, and infiltration. 
     The electronics unit further comprises (a) a power module enclosing a power source, (b) a driver module for regulating the light source, (c) a detector module for adjusting the gain and offset of the detector, receiving signals from the photodetector, and sending the received signals to an analyzer module, (d) an analyzer module for analyzing the received signals, and (e) an indicator module for triggering the alarms. 
     The present invention is also directed toward a method of monitoring tissue infusion site for the detection of infiltration during IV infusion. The method comprises means for controlling the intensity of the light source; means for directing light onto tissue near an IV site; means for collecting light from the tissue near the IV site; means for delivering the collected light to a photon detection device; means for developing, prior to injection of the IV fluid, baseline signals associated with the light source and light detector and against which measurements made during the injection of IV fluid are compared; means for comparing signals collected during IV injection/infusion with the associated baseline signals, means for determining the alarm levels, means for triggering the alarms, and means for indicating the alarms. 
     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram depicting the insertion of the needle into a vein and the placement of a skin-contact sensor on the skin. 
         FIG. 2  is a diagram showing the collected optical signals from a skin surface at four different wavelengths as a function of time. 
         FIG. 3  is a graph showing the effect of antiseptics on the collected optical signals from skin as a function of wavelength. 
         FIG. 4  is a graph showing the collected optical signals from skin as a function of time for an infiltration occurring at about 510 s. 
         FIG. 5  is a schematic block diagram of the optical infiltration detection apparatus of the present invention. 
         FIG. 6  is a schematic diagram showing a configuration of a 5-fiber skin-contact sensor consisting of one illumination fiber and four collection fibers. 
         FIG. 7  is a schematic diagram showing a side view of the skin-contact sensor. 
         FIG. 8  is a schematic diagram showing the side and end views of the flanged skin-contact sensor. 
         FIG. 9  is a schematic block diagram showing the electronics unit of the optical infiltration detection apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , when a beam of optical radiation impinges on skin  300  near an IV infusion site, the radiation reflected, scattered, diffused or otherwise emitted from the skin can be measured. As shown in the figure, an optical fiber bundle  270  comprises an illumination light guide  50  that provides illumination to the infusion site and a collection light guide  80  that collects the electromagnetic radiation reflected from the infusion site. The ends of the light guides  50  and  80  are embedded in a skin-contact sensor  200  that is secured onto the skin  300 . A needle  540  is inserted through the skin  300  into a vein  560  for infusion of IV fluids. 
     When IV fluid infiltrates the interstitial tissue space, optical density of tissue changes. This change can be measured as follows. First, the infusion site is illuminated using a beam of electromagnetic radiation with certain wavelength. Before energizing the illumination source, the radiation collected after insertion of the needle  540  establishes an ambient signal which is continuously monitored and recorded to provide a running ambient signal value, and this value is subtracted from subsequent radiation values collected when the illumination source is energized. In a preferred embodiment of the invention, a light-emitting diode (LED) is employed as the illumination source. The LED can be controlled to operate in a predefined on-off mode. For example, it can be energized for a predefined duration such as 1 s, de-energized and stay so for a predefined duration such as 4 s, and re-energized again. When the illumination source is energized, the optical signals are again collected from the infusion site, recorded, and averaged to establish a baseline R 0 . During IV infusion, optical signals (R) are continuously collected at predefined intervals. The R values are averaged over a predefined duration to minimize the effects of motion artifacts caused by the patient&#39;s movements and/or the action of tactile examination. 
     When an IV fails and the IV fluid infiltrates the interstitial space, the values of the collected signals from the infusion site change considerably. In one embodiment of the invention, this change is used to infer the presence of infiltrated fluid in subcutaneous tissue  580  using the expression:
 
 F= 1 −R/R   0   Equation 1
 
     The fractional change F is continuously recalculated. The present invention provides a means to interpret the conditions of infusion such as normal infusion, potential infiltration, and definitive infiltration, from the value of F. A suitable choice of F can be used as the alarm threshold for setting a trigger signal to an alarm. The use of the relative change in the collected radiations from infusion site minimizes the effects caused by patients with different skin color, shade, and/or texture. The time required to detect IV infiltration depends on factors such as the infusion rate, diffusivity of tissue, osmotic properties of the infused fluid, and the location of the skin-contact sensor  200  relative to the infusion site. 
     Referring to  FIG. 1 , the optical fiber bundle  270  is attached to the IV line via a securing mechanism, such as a clamp  600 , and the location of the clamp  600  is chosen such that it allows easy attachment of a skin-contact sensor  200  to the IV infusion site on the skin  300  via a securing mechanism, such as surgical tapes. The skin-contact sensor  200  is secured onto the skin  300  near the intravenous insertion site. 
     The selection of the operating wavelength of the illumination source depends on several factors such as the photon penetration depth, the available light sources and detectors, and the absorptions of tissue. The photon penetration depth, defined as the distance at which the intensity of radiation is reduced to 1/e of its initial value, is smaller for shorter wavelength radiations. In one embodiment of the invention, LEDs with a wavelength of 850 nm are the preferred light source. The 850 nm LEDs have a deep photon penetration depth (approximately 1.3 mm) and high intensity, suitable detectors are readily available, and at this wavelength, plastic optical fibers have acceptable transmission, and water and common chromophores have low absorptions. 
     The present invention provides a method for determining the optimal wavelengths for an intravenous infiltration detection apparatus. The method includes means for conducting simulated infiltrations by injecting subcutaneously IV fluids into tissue, means for illuminating the infusion site with only a one-wavelength light source, means for sequentially and separately energizing the single, one-wavelength light source, means for collecting radiations reflected, scattered, diffused or otherwise emitted from the infusion site with only one light source energized, means for bundling multiple illumination fibers and collection fibers, and means for analyzing the collected radiations. 
       FIG. 2  shows an example of a graph developed to assist in the wavelength selection process, depicting the radiations collected near the infusion site from the skin using four different light sources emitting 660, 735, 850, and 940 nm wavelength radiations as a function of infusion time. The data shown in  FIG. 2  are obtained with a 5-fiber skin-contact sensor consisting of one collection fiber coupled to a photon detection device and four illumination fibers coupled to four different light sources such as the LEDs. The intensity of the 660 nm LED is about 70% of the other three LEDs. The flow rate of the IV fluid injected into tissue is controlled with an infusion pump. Referring to  FIG. 2 , at T=50 s, the infusion pump is turned on and IV fluid is pumped into tissue at a rate of 10 ml/hr. The decrease in the collected signals R can be clearly seen at all four wavelengths. At T=400 s, a minor weal starts to form, resulting a gradual increase of R. The pump is stopped at T=528 s. As clearly shown in  FIG. 2 , the near-infrared LED (850 nm) provides the highest signals. 
     Another important factor affecting the wavelength selection is the effect of antiseptics on the signal strengths of the collected radiation from the injection site. Isopropyl alcohol and betadine (povidone-iodine) are commonly used to cleanse the injection site. The effect of these antiseptics is investigated by measuring the collected radiation from the injection site as a function of wavelength for (a) untreated injection site, (b) injection site treated with isopropyl alcohol, (c) injection site treated with betadine and followed with alcohol, and (d) injection site treated with betadine and allowing the skin to dry. 
       FIG. 3  shows an example of the graph depicting the relative intensities of radiations collected from a sampling site on the skin for the above-described conditions as a function of wavelength, using a broadband light source for illuminating the skin. As shown in  FIG. 3 , the measurements on the skin for the fourth condition (d) (shown as the lower curve) show weaker signals below 720 nm than the measurements for the other three conditions, due to the absorption of Betadine at shorter wavelength, whereas the signals for the first three conditions (a-c) are indistinguishable (shown as the upper curve), indicating that alcohol has negligible effect on the collected signals and it wipes out the effect of betadine, and most importantly, for wavelengths longer than around 720 nm, there shows no effect of the commonly used antiseptics on the collected signals. In a preferred embodiment of the invention, a single LED emitting at around 850 nm is selected as the light source. The 850 nm radiation is especially effective in humans, since the absorptions of melanin and water are relatively low at that wavelength. Melanin is the dominant absorber in the epidermis of human skin; the absorption coefficient of melanin is highest in the UV spectral region (200-400 nm) and falls exponentially for wavelengths greater than 400 nm. 
     The present invention also provides a method for determining the number of wavelengths required for an intravenous infiltration detection apparatus. The method includes means for conducting induced infiltrations by injecting IV fluids into a vein and inducing the infiltration by either pushing the injection needle through the vein or by pulling the needle out of the vein. 
       FIG. 4  shows an example of the graph depicting the signals collected near the injection site as a function of time at a single wavelength. As shown in  FIG. 4 , the infusion starts at T=0 s (in this example, it is 7 min after the needle was inserted into the vein). At T=485 s, an induced infiltration is initiated. A 10% decrease in R is observed over a period of 20 s. At T=755 s, infusion is stopped and the signal begins to increase gradually. The occurrence of infiltration is clearly seen in  FIG. 4 . Light sources with different wavelengths are used and the results compared. One very important aspect of the invention is that unlike prior arts, only one wavelength from one light source is needed to accurately detect IV infiltration. 
       FIG. 5  is a schematic diagram of a preferred embodiment of the invention. The optical IV infiltration detection apparatus utilizes a power supply  20 , which may be any power supply known to those of average skill in the art. The power supply  20  is connected to an electromagnetic radiation source  40 . In a preferred embodiment of the invention, the electromagnetic radiation source  40  is a light-emitting diode (LED). An LED with a wavelength of 850 nm has been found effective due to its deep photon penetration depth, high intensity, acceptable transmission of plastic optical fibers at this wavelength, and the availability and suitability of the LEDs and detectors. Additionally, water and common chromophores have low absorptions at 850 nm. A first light guide  50 , which contains an optical fiber or multiple fibers, has a proximal end  60 , which is optically coupled, to the light source  40  via a connector, such as an SMA connector. The incident electromagnetic radiation is delivered from the light source  40  through the light guide  50  to a distal end  70  of the same light guide. The first light guide  50  provides illumination to the infusion site. The distal end  70  of the first light guide  50  is embedded in a skin-contact sensor  200  that is mounted near the IV infusion site of a patient. A second light guide  80  which contains an optical fiber or multiple fibers is used to collect the electromagnetic radiation reflected, scattered, diffused or otherwise emitted from the infusion site and deliver the collected radiation to a light detection device  120 . A distal end  100  of the second light guide  80  is also embedded in the skin-contact sensor  200 . In a preferred embodiment of the present invention, the light detection device  120  is a GaAlAs photodiode encased in a TO-5 housing, with a 5-mm 2  sensing area. The GaAlAs photodiodes have good gain and low noise. An electronics unit  140  receives the detected signals from the light detection device  120  and analyzes the detected signals, stores the analyzed signals, and sends the analyzed results to an indicator (alarm) device  160 . The indicator device  160  triggers an alarm signal when the analyzed results reach a certain level. The alarm signals such as audible signals, flashing lights, signals displayed on monitors in the nurses&#39; stations provide warnings to medical staffs of potential occurrence of IV failures. A proximal end  90  of the second (collection) light guide  80  is connected to the detector via a connector such as an SMA connector. Both ends of the light guides are polished with polishing laps, ending with a 0.1 μm lap. 
     In a preferred embodiment of the invention, the light guides  50  and  80  are jacketless plastic optical fibers made of polymethyl methacrylate (PMMA), with a 500 μm core diameter. In the visible region, plastic optical fibers have about 10-15% lower transmission than glass fibers. At the near-infrared (NIR) region, plastic fibers have moderate attenuation. However, since the fiber lengths are 2-m or less, the loss in transmission is immaterial. Plastic fibers are more flexible and cost less than glass fibers. 
     In one embodiment of the invention, the first and second light guides,  50  and  80 , each contains a single optical fiber and the distal ends,  70  and  100 , of these fibers are embedded in a skin-contact sensor  200  for attachment to the skin of the patient. In an alternate embodiment of the invention, the first light guide  50  is a single optical fiber and the second light guide  80  comprises multiple optical fibers having multiple distal ends spaced around the distal end  70  of the first light guide  50 . 
       FIG. 6  illustrates an end face  400  of the skin-contact sensor  200 : the second light guide  80  contains four (4) optical fibers having four (4) distal ends  102 ,  104 ,  106 , and  108  spaced around the distal end  70  of the first light guide  50 . In this configuration, the proximal ends of the multiple light collection fibers are severally connected to multiple detectors. The fiber core diameter and the distances between the distal ends  102 ,  104 ,  106 , and  108  of the collection light guide  80  and the distal end  70  of the illumination light guide  50  have insignificant effect on the performance of the infiltration sensor. Small-diameter fibers and short distances between various distal ends of the light guides allow the fabrication of smaller skin-contact sensor  200  that covers smaller sensing areas, allowing easier examination of the IV infusion site. A larger skin-contact sensor  200  facilitates easier attachment of the skin-contact sensor  200  to the skin. In another embodiment of the invention, the second light guide  80  is a single optical fiber and the first light guide  50  comprises multiple optical fibers having multiple distal ends spaced around the distal end  100  of the second light guide  80 . In this configuration, the illumination light guide provides more evenly distributed electromagnetic radiation to the infusion site. In yet another embodiment of the invention, both the illumination and collection light guides  50  and  80  contain multiple optical fibers. 
     In one embodiment of the invention, the distal ends  70  and  100  of the illumination and collection light guides  50  and  80 , respectively, are embedded in the skin-contact sensor  200  and are flush with the skin-contact side of the sensor. The skin-contact sensor  200  can be made of different materials, and in the present invention, both wood and plastics are used. The distance between the distal ends  70  and  100  is a few millimeters. In another embodiment of the invention, the ends of the illumination and collection light guides  50  and  80 , respectively, are embedded in a wood or plastic base plate  220  which is secured to a foam pad  240  using an adhesive such as epoxy  260 , as shown in  FIG. 7 . The foam pad  240  has an opening in the center that provides optical access to the skin  300 . In this configuration, the skin-contact sensor  200  consists of a base plate  220 , a foam pad  240 , the interfacing medium, epoxy,  260 , and the distal ends  70  and  100  of the light guides  50  and  80 . In the present embodiment of the invention, the base plate  220  and the foam pad  240  have about the same lengths and widths, whereas the thickness of the foam pad  240  (˜2-3 mm) is smaller than that of the base plate  220  (˜5-10 mm), and the distal ends  70  and  100  of the light guides  50  and  80 , respectively, extend beyond the epoxy interface between the base plate  220  and the foam pad  240 . In this configuration, the effects of ambient light on the collected signals may be reduced, since the foam pad, when secured with a securing medium such as surgical tapes to the skin  300 , may provide better light shields than a rigid skin-contact sensor  200  made of wood or plastic, as described previously. 
     In a preferred embodiment of the invention, referring to  FIG. 7 , the illumination light guide  50  and the collection light guide  80  are threaded through a 20-gauge black polyvinyl chloride (PVC) tubing  280  to reduce ambient light. The PVC tubing  280  that contains light guides  50  and  80  is secured to the base plate  220  with a securing medium such as epoxy. The distance between the distal ends  70  and  100  is about a few millimeters. 
     In yet another embodiment of the invention shown in  FIG. 8 , the distal ends  70  and  100  of the first and second light guides  50  and  80 , respectively, are embedded in an adaptor  320  that can be secured via a locking mechanism to an adaptor such as a flange  350 , and the flange  350  is secured to the skin  300  near the infusion site via a securing mechanism. The flange can be of any shape that is compatible with the skin-contact sensor  200 .  FIG. 8  shows one example of the end view of a circular-shaped flange. The flange  350  can be made of biocompatible materials that are acceptable for use in clinical settings; it can be either disposable or reusable. Use of an adaptor may reduce the effect of motion artifacts and provide strain relief from the IV line. 
       FIG. 9  shows the schematic diagram of the electronics unit  140  of the IV infiltration detection apparatus. In one embodiment of the invention, the proximal ends  60  and  90  of the illumination and collection light guides  50  and  80 , respectively, are connected to the electronics unit  140  via SMA connectors,  65  and  95 , respectively. The electronics unit  140  consists of a driver module  420 , a power module  440 , a detector module  460 , an analyzer module  480 , and an indicator module  500 . The driver module  420  controls the light source  40 , providing a stable illumination to the sensing site on the skin. The power module  440  controls input power to the driver module  420 , detector module  460 , analyzer module  480 , and indicator module  500 . In the present invention, a light source such as an LED is enclosed in the electronics unit  140  which has an internally adjustable gain mounted on a circuit board for controlling the voltage applied to the LED. For alignment purposes, the LED can also be controlled manually. The detector module  460  consists of an amplifier with adjustable gain and offset. It receives signals from the photodetector  120  and sends the signals to the analyzer module  480 . In one embodiment of the invention, a band pass filter centered at 850 nm is mounted in front of the photodetector to increase the signal to noise ratio (SNR). In an alternate embodiment of the invention, a long-pass filter with a cut-on wavelength of around 850 nm is used. The analyzer module  480  stores and analyzes the signals received from the detector module  460  and sends the analyzed signals to the indicator module  500 . The indicator module  500  triggers an alarm signal when the analyzed results reach a pre-selected level; it also comprises an optional shut-off feature allowing the interruption of the flow of IV fluid upon the detection of IV infiltration. In an advanced embodiment of the invention, the electronics unit  140  can be a circuit board incorporated into an infusion pump or a standalone monitor. 
     Referring to  FIG. 9 , in one embodiment of the invention, the electronics unit  140  is powered either by a 9-volt DC battery contained in the unit or an AC source. When using the AC source, an AC-to-DC converter is required to convert the AC power to DC and the DC power is delivered to the electronics unit  140  through a DC port  510 . The power module  440  provides 5-volt DC to the LED  40  and 12-volt DC to the detector module  460 . The driver module  420  contains a voltage divider circuitry for adjusting the voltage across the LED  40  to control its intensity. The electronics unit  140  integrates the collected signals and stores the integrated data. A computer equipped with a data acquisition board with a sampling rate of 40 kHz is interfaced to the electronics unit  140  through the communication port  520  for programming the microprocessor inside the electronics unit  140 , receiving data from the microprocessor, and transferring the data to a disk file or other storage devices such as memory chips and/or flash cards. The microprocessor performs limited functions such as data collection, integration, setting the alarm threshold, setting the detector gain, and initiation of the measurement. In the present invention, specially designed and developed software programs are used to control the operating parameters. 
     While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.