Transcutaneous Oximetry Does Not Reliably Predict Wound-healing Complications in Preoperatively Radiated Soft Tissue Sarcoma.

BACKGROUND: Surgical wound-healing complications after tumor resections in tissue that has been preoperatively radiated are a major clinical problem. Most studies have reported that complications occur in more than 30% of patients undergoing such resections in the lower extremity. There is currently no available method to predict which patients are likely to have a complication. Transcutaneous oximetry has been identified in preliminary studies as potentially useful, but the available evidence on its efficacy for this application thus far is inconclusive. QUESTIONS/PURPOSES: (1) Does transcutaneous oximetry measurement below 25 mmHg at any location in the surgical wound bed predict a wound-healing complication? (2) Does recovery (increase) in transcutaneous oxygen measurement during the rest period between the end of radiation and the time of surgery protect against wound-healing complications? METHODS: A prospective, multi-institution study was coordinated to measure skin oxygenation at three timepoints in patients undergoing surgery for a lower extremity soft tissue sarcoma after preoperative radiation. Between 2016 and 2020, the five participating centers treated 476 patients for lower extremity soft tissue sarcoma. Of those, we considered those with a first-time sarcoma treated with radiation before limb salvage surgery as potentially eligible. Based on that, 21% (98 of 476) were eligible; a further 12% (56 of 476) were excluded because they refused to participate or ultimately, they were treated with a flap, amputation, or skin graft. Another 1% (3 of 476) of patients were lost because of incomplete datasets or follow-up less than 6 months, leaving 8% (39 of 476) for analysis here. The mean patient age was 62 ± 14 years, 62% (24 of 39) of the group were men, and 18% (7 of 39) of patients smoked cigarettes; 87% (34 of 39) of tumors were intermediate/high grade, and the most common histologic subtype was undifferentiated pleomorphic sarcoma. In investigating complications, a cutoff of 25 mmHg was chosen based on a pilot investigation that identified this value. All patients were assessed for surgical wound-healing complications, which were defined as: those resulting in a return to the operating room, initiation of oral or IV antibiotics, intervention for seroma, or prolonged wound packing or dressing changes. To answer the first research question, we compared the proportion of patients who developed a wound-healing complication between those patients who had any reading below 25 mmHg (7 of 39) and those who did not (32 of 39). To answer the second question, we compared the group with stable or decreased skin oxygenation (22 of 37 patient measurements [two patients missed the immediate postoperative measurement]) to the group that had increased skin oxygen measurement (15 of 37 measurements) during the period between the end of radiation and the surgical procedure; again, the endpoint was the development of a wound-healing complication. This study was powered a priori to detect an unadjusted odds ratio for wound-healing complications as small as 0.71 for a five-unit (5 mmHg) increase in TcO 2 between the groups, with α set to 0.05, ß set to 0.2, and a sample size of 40 patients. RESULTS: We found no difference in the odds of a wound-healing complication between patients whose transcutaneous oxygen measurements were greater than or equal to 25 mmHg at all timepoints compared with those who had one or more readings below that threshold (odds ratio 0.27 [95% confidence interval (CI) 0.05 to 1.63]; p = 0.15). There was no difference in the odds of a wound-healing complication between patients who had recovery of skin oxygenation between radiation and surgery and those who did not (OR 0.63 [95% CI 0.37 to 5.12]; p = 0.64). CONCLUSION: Transcutaneous oximetry cannot be considered a reliable test in isolation to predict wound-healing complications. This may be a function of the fact that transcutaneous oximetry samples a relatively small portion of the landscape in which a wound-healing complication could potentially arise. In the absence of a reliable diagnostic test, clinicians must still use their best judgment regarding surgical timing and work to address modifiable risk factors to avoid complications. The unanswered question that remains is whether there is a skin perfusion or oxygenation issue at the root of these complications, which seems likely. Alternative approaches that can assess the wound more broadly and in real time, such as fluorescent probes, may be deserving of further investigation. LEVEL OF EVIDENCE: Level II, diagnostic study.

Transcutaneous Carbon Dioxide Monitoring with Reduced-Temperature Probes in Very Low Birth Weight Infants.

Background Obtaining blood gases in very low birth weight (VLBW) infants is an invasive procedure. Studies using transcutaneous carbon dioxide (tcPCO2) have reported variable skin complications with high-temperature probes. No enough data available on tcPCO2 monitoring using reduced-temperature probes (41°C). Objective The objective of this study was to assess reliability and safety of tcPCO2 monitoring at reduced-temperature probe in VLBW infants. Design and Methods A prospective study was conducted on VLBW infants. tcPCO2 was monitored for 12 hours. Default skin probe temperature was adjusted at 41°C. Blood gases were done as clinically indicated. Arterial partial pressure of CO2 (PaCO2) as well as capillary CO2 were compared with simultaneous tcPCO2. Results A total of 124 data points were identified from 50 patients (gestational age [GA] = 28.1 ± 2.4 weeks and birth weight [BW] = 1,035 ± 291 g). Patients were supported with continuous positive airway pressure (40%), noninvasive positive pressure ventilation (16%), mechanical ventilation (18%), and high-frequency oscillation ventilation (24%). PaCO2 was measured using either capillary (58%) or arterial (42%) samples. Mean CO2 did not differ between tcPCO2 (51.3 ± 16) and PaCO2 (49.1 ± 13.7) mm Hg. tcPCO2 showed positive correlation with partial pressure of CO2 (r = 0.6, p < 0.001). This correlation continued to be significant after controlling for GA, postmenstrual age, type of sample, and pH. No skin complications were reported. Conclusion tcPCO2 monitoring using a temperature of 41°C is feasible and reliable in VLBW infants.

Does gastric tonometry work? No.

Gastrointestinal tonometry is supposed to diagnose gut mucosal hypoxia using gastric luminal PCO2 and arterial bicarbonatemia, which are substituted in a modified Henderson-Hasselbach equation. This article reviews some of the problems inherent to the multiple assumptions underlying this technique. Tonometry is influenced by several local factors and by systemic acid-base imbalances that are unrelated to oxygenation. Tonometry is a rather crude and cumbersome method of gut capnometry, a technology that may provide valuable information regarding visceral perfusion, but not necessarily oxygenation.

Local skin hyperthermia due to transcutaneous electrode heat.

The hypothesis that a transcutaneous monitor electrode can heat skin beyond the electrode edge was tested. This heating would cause a skin thermistor probe, if placed too close to the transcutaneous electrode, to transduce an artifactually high skin temperature. In a skin servo control system, this might result in a cooler environment than desired. Eight premature newborns in humidified incubators were tested once each between one and five days of age. Mean skin temperatures at 0.5 cm, 1.5 cm, and 2.5 cm from the electrode edge were significantly higher after electrode placement, although there were virtually no temperature changes in two of the subjects. Transcutaneous monitor electrodes can heat the surrounding skin. This may affect environment temperature in a skin servo control system if the skin probe is placed too close to the transcutaneous electrode.