Evaluation of intestinal viability is essential during colic surgery and includes the assessment of intestinal macro- and microcirculation. Visual evaluations of intestinal color, mesenteric pulsation, and intestinal motility remain the most commonly used methods but are also often subjective.1–3 Methods used to determine intestinal circulation in equids include surface oximetry,4,5 Doppler ultrasonography,6 sodium fluorescein dye fluorescence,6,7 and pulse oximetry.8
Doppler ultrasonography has variable efficacy in evaluation of intestinal circulation depending on the type of strangulation, being more useful for assessing tissue perfusion following venous strangulation and less useful than other techniques following arterial strangulation.6 Another limitation of Doppler ultrasonography is the inability to examine large areas of intestine.9 Also, Doppler ultrasonography can be used to assess macrocirculation but provides no quantitative assessment of microcirculation.10 Surface oximetry has a moderate to low sensitivity but high specificity for detecting nonviable intestines; horses with a surface oxygen tension < 20 mm Hg had a lower survival rate than those with higher surface oxygen tension.5 Pulse oximetry depends on the detection of pulsatile blood flow,11,12 and movement and environmental light can interfere with measurement accuracy.11
Micro-lightguide spectrophotometry represents a noninvasive method to determine tissue microperfusion and oxygen saturation.10 By combining Doppler fluxmetry and micro-lightguide spectrophotometry, microvascular blood flow and tissue oxygenation can be assessed with a single probe.13 Several systems of microlightguide spectrophotometry have been described. The micro-lightguide tissue spectrophotometer described by Frank et al14 and another commercially available micro-lightguide tissue spectrophotometer are the most commonly used in current experimental and clinical applications. Use of these methods has been described for human diabetic research10,13,15,16 and in microcirculatory examinations of the gastrointestinal tract of dogs,12 pigs,17,18 humans,19,20 and rabbits21; nervous system of humans22,23 and rats24; liver of mice25; lungs of rabbits26; eyes of rabbits27; wounds during healing of humans10,a; and tissues in transplantation medicine of rodents28 and humans.29 Reliability of measurements could be influenced by factors like external light sources30 and movement of the examined tissue.30
A commonly used commercially available microlightguide tissue spectrophotometer transmits monochromatic laser light (830 nm; 30 mW) and white light (500 to 800 nm; 20 W; resolution, 1 nm) into the tissue, where it is scattered, reflected, and detected again in the probe at the tissue surface. The collected light is first divided into its spectral components by a charge-coupled device array and afterward converted into an electrical signal.10,13
Laser light determines perfusion quantities in tissue (eg, the relative blood flow and the blood flow velocity).31 A laser Doppler shift is caused by the movement of erythrocytes.10 The principle of the Doppler effect is a change of the wavelength while being reflected from moving objects like cellular components of blood.9 This Doppler shift is analyzed and displayed as the blood flow velocity. The detected laser light also correlates with the number of moving erythrocytes.31 The product of the number of moving erythrocytes and the erythrocyte velocity is used for the calculation of relative blood flow.10,13
Hemoglobin variables (eg, oxygen saturation and the relative amount of hemoglobin) are detected with the use of white light. Blood color changes with the degree of hemoglobin saturation. By detecting the blood color, the degree of oxygen saturation of hemoglobin is calculated.31 The relative amount of hemoglobin is a variable of light absorption by the tissue.10,13 The greater the amount of blood in the measured volume, the more light is absorbed by hemoglobin and the less light will be detected by the sensor.31 Only vessels up to 100 μm in diameter are included in the measurements because during transit through larger vessels (> 100 μm), all light is absorbed and no light is reflected to the detector system in the probe.32
The purpose of the study reported here was to validate the use of micro-lightguide spectrophotometry in the evaluation of the microcirculation in the intestines of horses. We hypothesized that a micro-lightguide spectrophotometry system would be easy to use to quickly and reliably assess microcirculation in the intestinal tract of horses without gastrointestinal disease.
Intraclass correlation coefficient
Oxygen saturation as measured by pulse oximetry
Coerper S, Beckert S, Beckert HD. New method for measurement of ischemia in wounds—a pilot study (asbtr). 6th World Cong Trauma Shock Inflammation Sepsis Pathophysiol Immune Consequences Ther 2004;553.
Xylapan, Vetoquinol GmbH, Ravensburg, Germany.
Narketan, Vetoquinol GmbH, Ravensburg, Germany.
Midazolam ratiopharm (15 mg/3 mL), Ratiopharm GmbH, Ulm, Germany.
Isofluran CP, CP-Pharma GmbH, Burgdorf, Germany.
Dobutamin ratiopharm (250 mg), Trockensubstanz, Ratiopharm GmbH, Ulm, Germany.
Euthadorm 400, CP-Pharma GmbH, Burgdorf, Germany.
Flachsonde LF-2, LEA Medizintechnik GmbH, Gießen, Germany.
O2C, Oxygen to See, LEA Medizintechnik GmbH, Gießen, Germany.
Cardiocap/5, GE Healthcare, Helsinki, Finland.
SAS, version 9.3, SAS Institute Inc, Cary, NC.
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Protocol for spectrophotometric measurements (measuring conditions) in the small and large intestines.
|SI-1||Intestinal wall laid on the probe; room light|
|SI-2||Probe positioned on the intestinal wall; room light|
|SI-3||Probe positioned on the antimesenteric side of the intestinal wall; room light|
|SI-4||Probe positioned on the mesenteric side of the intestinal wall; room light|
|SI-5||Probe positioned between the mesenteric and antimesenteric intestinal walls; room light|
|SI-6||Probe positioned as in SI-5; surgical lights pointing at the measuring site|
|SI-7||Probe positioned as in SI-5; surgical lights pointing at the measuring site; probe covered by surgeon's hand|
|SI-8||Probe positioned as in SI-5; surgical lights off|
|SI-9||Probe positioned as in SI-5; intestine exteriorized just to the level of the laparotomy|
|SI-10||Probe positioned as in SI-5; intestine exteriorized as far as possible|
|SI-11||Probe positioned as in SI-5; intestine exteriorized without torsion|
|SI-12||Probe positioned as in SI-5; intestine exteriorized with 180° torsion|
|SI-13||Probe positioned as in SI-5; intestine returned to the abdomen and exteriorized again|
|SI-14||Probe positioned as in SI-5; intestine returned to the abdomen and exteriorized again|
|SI-15||Probe positioned as in SI-5; intestine returned to the abdomen and exteriorized again|
|LI-1||Intestinal wall laid on the probe; room light|
|LI-2||Probe positioned on the intestinal wall; room light|
|LI-3||Probe positioned on the antimesenteric side of the intestinal wall; room light|
|LI-4||Probe positioned on the mesenteric side of the intestinal wall; room light|
|LI-5||Probe positioned between the mesenteric and antimesenteric intestinal walls; room light|
|LI-6||Probe positioned as in LI-5; surgical lights pointing at measuring site|
|LI-7||Probe positioned as in LI-5; surgical lights pointing at measuring site; probe covered by surgeon's hand|
|LI-8||Probe positioned as in LI-5; surgical lights off|
|LI-9||Probe positioned as in LI-5; intestine exteriorized as far as possible; enterotomy tray at 0° relative to floor|
|LI-10||Probe positioned as in LI-5; intestine exteriorized as far as possible; enterotomy tray at 10° relative to floor|
|LI-11||Probe positioned as in LI-5; intestine exteriorized as far as possible; enterotomy tray at 20° relative to floor|
LI = Large intestine. SI = Small intestine.
Room light was a measuring condition with the surgical lights on but directed away from the intestine.