David K. Harrison

Tissue oxygen saturation, measured by near‐infrared spectroscopy, and its relationship to surgical‐site infections

Surgical‐site infections (SSIs) are common after major abdominal and groin bypass surgery. Tissue oxygen tension has been shown to predict these infections accurately. This study assessed whether a non‐invasive measurement of tissue oxygenation, tissue oxygen saturation as measured by spectrophotometry, was as accurate.

INTRAOPERATIVE MEASUREMENT OF COLONIC OXYGENATION DURING BOWEL RESECTION

Recently lightguide spectrophotometry (LGS) has been investigated for assessing bowel mucosal oxygenation and may prove helpful in the diagnosis of bowel ischaemia. This pilot study explores the use of LGS and laser Doppler flowmetry (LDF) to measure SO2 and perfusion in the bowel during key stages of colon surgery. SO2 and perfusion in the mucosal and serosal layers of the rectum, sigmoid and descending colon were measured in 7 patients by LGS (Whitland Research, UK) and LDF (Moor Instruments, UK) respectively at four stages (baseline, after mobilisation of the sigmoid, after ligation of the inferior mesenteric artery (IMA) and after complete devascularisation of the sigmoid). The sigmoid mucosal SO2 and LDF values were significantly lower than the baseline after the ligation of IMA and devascularisation. Mean (SD) baseline sigmoid mucosal SO2 (73%) decreased to 55% after ligation of IMA and to 39% after complete devascularisation. The sigmoid serosal SO2 did not show any change after ligation of IMA and showed only 7% decrease after devascularisation. There was no difference in baseline SO2 and LDF values in different parts of the bowel but the mean mucosal baseline SO2 (75%) was significantly lower than that in the serosa (87%). In conclusion, mucosal SO2 measurements can accurately diagnose bowel ischaemia but serosal SO2 does not reflect mucosal ischaemia.

Assessment of oxygenation and perfusion in the tongue and oral mucosa by visible spectrophotometry and laser Doppler flowmetry in healthy subjects

UNLABELLED Use of Visible Light Spectrophotometry (VLS) and Laser Doppler Flowmetry (LDF) is currently being studied by the authors to assess the viability of tissue margins in colon resection and to assess mucosal oxygenation in the colon. Thus, as a preliminary study it was necessary to evaluate whether there is any systematic inter-probe variability of the measurements by VLS and LDF. The oral mucosa was used as a model. METHODS SO2 with VLS (Whitland Research RM200) and blood flow with LDF (Moor Instruments DRT4) were measured at 10 sites each on the tongue and oral mucosa of 10 healthy volunteers at 0, 6 and 24 hours using 3 different probes for VLS and 2 probes for LDF. RESULTS The results showed that the SO2 measurements by VLS using the different probes on the tongue and mucosa were significantly correlated (P < 0.05). SO2 values at 6 hours were significantly higher than at 0 and 24 hours (P < 0.05) in all but one case. SO2 measurements were not correlated with LDF. LDF measurements by the 2 probes were correlated significantly (P < 0.05) but the standard deviations were very large. CONCLUSIONS SO2 measurements on the oral mucosa are reproducible. Due to the large variations in LDF, VLS is likely to be the more clinically useful tool for identifying mucosal ischaemia.

Prediction Of Surgical Site Infections After Major Surgery Using Visible And Near-Infrared Spectroscopy

Final results of an investigation into whether oxygen saturation of tissues (StO2, measured by spectrophotometry) could predict surgical site infections (SSI) after major abdominal surgery are presented. StO2 was measured on the arm and wound site pre-operatively and then at 12, 24 and 48 hours post-operatively. A Whitland Research RM200 was employed as the visible lightguide spectrophotometer. StO2 measurements using this machine were designated SSO2 (skin SO2). A Hutchinson Inspectra Model 325 was used for the near infrared spectroscopy (NIS) measurements. StO2 measurements using this machine were designated MSO2 (muscle SO2). Of 59 patients (38 males, 21 females), 42 healed uneventfully and 17 developed SSI. The overall infection rate was 28.8%. No significant differences were seen in wound SSO2 between outcome groups at any stage. At 12 hours there was a significant difference between the two groups with respect to mean wound MSO2 (A = 58.3 +/- 21.6%, B = 42.2 +/- 16.6%, p = 0.005, 95% confidence interval = 5.26, 26.98). A receiver operating characteristic curve showed that when a wound MSO2 of 53% was chosen as the threshold to classify potential infection a sensitivity of 71% and a specificity 73% (chi-squared test, p = 0.002) was achieved. The use of the near-infrared spectrophotometry as a tool to predict wound infections should be further evaluated and advocated.

Prediction of Surgical Site Infections Using Spectrophotometry: Preliminary Results

Wound infections occur in approximately 5% of operations. These infections cost the U.K. National Health Service up to £65 million per year and lower patient quality of life. If wound infections could be predicted there would be potential for prevention and a reduction in cost and morbidity would ensue. Work has previously been carried out to predict when these infections will occur, and attempts have been made to create scoring systems for patients undergoing operations. The most simple of these is to classify the type of operation into one of the four following groups:

Physiological oxygen measurements using oxygen electrodes.

It was the development by Clark in 1956 of the membrane-covered “integral” electrode that opened the field for truly physiological in vivo - and indeed clinical - measurements of oxygen partial pressure in blood and tissue. Since then, much of our knowledge about oxygen transport to tissue has been gained by the use of polarographic oxygen (and hydrogen) electrodes — many of them of the Clark-type. It is not possible in this paper to examine all of these applications and the reader is referred to a comprehensive review by Ltibbers.

Capillary blood flow and cutaneous uptake of oxygen from the atmosphere

In 1 987 Baurngartl, using needle electrodes to measure P02 in skin, demonstrated that a minimum P02 value could be observed between the surface and the capillary bed. This indicated that there is an 02 flux through the epidermis supplying the upper layers of the skin. The recent development of a fluorescence-based 02-fluxoptode for measuring oxygen flux has meant that the phenomenon could be studied directly. More recently Stucker et. al. showed, using simultaneous measurement of oxygen flux, transcutaneous P02 and laser Doppler perfusion, that the epidermal oxygen uptake from the atmosphere is in balance with the blood-borne (haematogenic) oxygen supply. These measurements of oxygen flux and previous measurements of P02 profiles indicated that capillary blood flow in skin at normal skin temperature may not contribute to the oxygen supply of the superficial layers. In order to investigate this further, in the present study the transcutaneous hydrogen clearance technique was applied at various skin temperatures between 33°C and 40°C. Laser Doppler flowmetry (LDF), transcutaneous oxygen flux, and tsanscutaneous oxygen measurements were also carried at the same site. The inability to detect hydrogen at the skin surface at 33°C confirms the minimal contribution of capillary blood flow to the oxygen supply to superficial layers

Relationships between muscle SO2, skin SO2 and physiological variables

In 1995 we introduced the technique of lightguide spectrophotometry for the measurement of tissue oxygen saturation (SO2) to predict healing viability of below-knee skin flaps in lower limb amputation for critical ischaemia. This technique, using a Photal MCPD 1000 (Otsuka Electronics, Osaka) spectrophotometer, has been applied to the routine assessment of patients at the University Hospital of North Durham since 1999. Since then a healing rate of 94% has been achieved with a below knee to above knee amputation ratio of 9:2. In a study to investigate the possible cause of the high infection rate in groin wounds following vascular bypass surgery Raza et al. used the Erlangen microlightguide spectrophotometer (EMPHO, BGT-Medizintechnik, Überlingen) to measure SO2 in the groin skin medially and laterally to the incision sites in patients undergoing femoropopliteal or femorodistal bypass operations prior to and at 2 and 7 days post-operatively. The equivalent contralateral sites were used as controls. The results showed a significant difference (p < .01) between the medial and lateral SO2 values post operatively. On this basis, it was postulated that a disruption of blood supply may be responsible for the high incidence of infection in such surgical wounds. The experience using lightguide spectrophotometry in the visible wavelength range to measure skin SO2 (SSO2) as a possible predictor of healing viability or infection of surgical wounds led to the study described elsewhere in this volume. In addition, it was proposed that infrared spectroscopy should be used in the clinical study on the premise that muscle SO2 may be a better predictor of wound infections emanating from deeper lying tissues than skin. The present study was therefore carried out in order to define the

Tissue spectrophotometry and thermographic imaging applied to routine clinical prediction of amputation level viability

About 5% of British males over 50 years develop peripheral arterial occlusive disease. Of these about 2% ultimately require lower limb amputation. In 1995 we proposed a new technique using lightguide spectrophotometry to measure the oxygen saturation level of haemoglobin (SO2) in the skin as a method for predicting tissue viability. This technique, in combination with thermographic imaging, was compared with skin blood flow measurements using the I125)4- Iodoantipyrine (IAP) clearance technique. The optical techniques gave a sensitivity and selectivity of 1.0 for the prediction of successful outcome of a below knee amputation compared with a specificity of 93% using the traditional IAP technique at a below knee to above knee amputation ratio (BKA:AKA) of 75%. The present study assesses the routine clinical application of these optical techniques. The study is ongoing, but the data to date comprises 22 patients. 4 patients were recommended for above knee amputation (AKA) and 18 patients for below knee amputation on the basis of thermographic and tissue SO2 measurements. All but one of the predicted BKA amputations healed. The study to date produces evidence of 94% healing rate (specificity) for a BKA:AKA ratio of 82%. This compares favorably with the previous figures given above.

Optical Measurements of Tissue Oxygen Saturation in Lower Limb Wound Healing

This review has highlighted the role of oxygen in wound healing and in the mechanism of preventing infection. Optical measurements of tissue SO2 in wounds can provide valuable information, not only about the inflammatory state of the wound, but also about healing potential in ulcers and critical limb ischaemia. The technique is fast, non-invasive and can be used without the necessity for contact with the skin.