1	Evidence Based Interpretation of Transcutaneous Oximetry (TcPO₂) Studies
2	Common Uses of TcPO₂ Prediction of healing Non-invasive vascular screening Amputation level prediction Response to revascularization Predicting benefit of HBOT
3	Methods Expert Panel: Convened with participants from the transcutaneous oximetry workshop held June 13, 2007, in Maui, Hawaii. Literature Review: Results circulated to all participants Delphi Approach: Consensus issues circulated among the 6 participants Modified until concurrence was achieved on the wording of each point. Literature consulted when questions or conflicts occurred Paper Submitted to Undersea and Hyperbaric Medicine
4
5	"Survival without Diabetes" Survival without Diabetes: 1 year:70.8% (AKA 50.6%/BKA 74.5%) 5 year: 50.1% (AKA 22.5%/BKA 37.8%) Survival in Diabetics: I year: 69.4% 5 year:30.9% (p=0.002) Survival in Renal Failure: 1 year: 51.9% 5 year: 14.4%
6	Non-Invasive Screening in Wound Patients There is Level 1 evidence that suspicion of arterial disease in the context of a patient with a lower extremity ulcer should prompt referral to a vascular specialist Guidelines recently published by the Wound Healing Society (WHS) state that all patients with lower extremity ulcers should be assessed for arterial disease. The ideal way to perform non-invasive vascular screening by the primary care or wound care clinician has not been defined by clinical research. A variety of clinical options exist.
7	Non-Invasive Vascular Testing MACRO Circulation ABI (Ankle-Brachial Index) PVR (Pulse Volume Recordings) Segmental Pressures MICRO Circulation TcPO2 (TCOM) (Trans-cutaneous Oxygen)
8
9	ABI (Ankle Brachial Index) Ankle Systolic Pressure 　Brachial Systolic Pressure Technically Easy BP cuff + Handheld Doppler Required 15-20min Required 0.9 or Lower = Vasc med/surg referral ABI Interpretation: 0.96 or More = Normal 0.71 – 0.96 = Mild Obstruction 0.31 – 0.71 = Moderate Obstructions 0.30 or Lower = SEVERE Obstructions
10	Incompressible Vessels 223 consecutive arterial leg ulcer patients Mean Ankle Systolic Pressure (ASP) = 88 mm Hg (range 18-130) Mean ABI = 0.6 (0.15-0.86) Concluded most arterial leg ulcers do not meet the criteria of chronic critical limb ischemia (ASP < 50 mm Hg), due to incompressible vessels. Hafner, J. et al. J Am Acad Dermatol 2000 43(6):1001-8
11	ABI & Wound Healing Predictions ABI vs. Wound Healing is not correlated in DM & CRF pts
12	TcPO₂ Electrode Lead Heating element & sensor Gas permeable membrane Electrolyte solution
13	Physiological Basis of TcPO₂: Measures Oxygen MOLECULES (PO₂), not saturation! Modified Clark electrode Gold cathode, silver anode When constant polarizing voltage applied to cathode, silver in anode becomes oxidized by chloride ions to form silver chloride Reaction generates electrons Oxygen molecules at cathode become reduced Current is generated in proportion to the number of oxygen molecules in solution
14	TcPO₂: Measures PO2 Before Pulse Oximetry was available, TCOM was used as a surrogate for arterial PO2 in neonates. Still being used in a variety of ways to monitor patients with sleep apnea, post operatively, and neonates. Pulse oximetry and transcutaneous oxygen tension for detection of hypoxemia in critically ill infants and children. J Pediatr. 1985 Sep;107(3):362-6. Fanconi S, Doherty P, Edmonds JF, Barker GA, Bohn DJ. Home monitoring of transcutaneous oxygen tension in the early detection of hypoxaemia in infants and young children CF Poets, MP Samuels, JP Noyes, KA Jones and DP Southall Department of Paediatrics, National Heart and Lung Institute, Royal Brompton Hospital, London. Archives of Disease in Childhood, Vol 66, 676-682, Copyright © 1991 by Archives of Disease in Childhood. Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor *. Critical Care Medicine. 33(10):2203-2206, October 2005. Bendjelid, Karim MD, MS; Schutz, Nicolas MD; Stotz, Martin MD; Gerard, Isabelle MD; Suter, Peter M. MD, FCCM, FCCP; Romand, Jacques-Andre MD, FCCM
15
16	Definition of Hypoxia with TcPO₂: What are “Normal” values? On the foot, while breathing air, the average PtcO2 in healthy subjects is > 50 mmHg Thirty-eight studies since 1982 suggest that hypoxia is defined as PtcO2 < 40 mmHg.
17
18	TcPO2 is More Reliable than Doppler for Healing Prediction Fifteen studies (1137 patients) have demonstrated that PtcO2 provides better overall predictive capability than Doppler studies ABI, segmental pressures, or laser fluximetry.
19	TcPO₂ & Wound Healing Predictions (Padberg et al. J Surg research.1996)
20	TcPO₂ and Healing Prediction Prediction of Healing Because hypoxia is often the final common denominator for wound failure, it is easier to find a value below which a wound will NOT heal than to find a value above which a wound is reliably predicted TO heal. This is because wound healing may be impaired by many factors other than hypoxia, including venous hypertension, pressure, infection, steroids or other immunosuppressants, inadequate nutrition, etc. Sea level air PtcO2 values can be used to predict which wounds will not heal spontaneously.
21	TcPO₂ and Arterial Disease Arterial Disease: Patients with critical limb ischemia, (rest pain, gangrene, or an arterial ulcer) will almost always have PtcO2 <30 mmHg and usually less than 20 mm Hg. However, low AIR values may be caused by a diffusion barrier such as edema, excess consumption caused by inflammation, or reversible vasoconstriction caused by cold exposure, dehydration, or pain. Sea level air PtcO2 values need to be evaluated in conjunction with the clinical history and conditions present at the time of testing.
22	Factors Potentially Affecting TcPO₂: Bony prominence Callous (other skin disease, eg scleroderma) Edema Infection Arterial oxygen concentration Tissue oxygen consumption Blood flow around electrode Perfusion pressure Room temperature Hydration state BODY POSITION!!!! Technician
23	Factors Potentially Affecting TcPO₂ It is also possible that low air values are caused by microvascular disease such as seen in diabetes. Isolated low values in peri-wound tissue (with normal distal values) may be caused by local vasoconstriction or lack of angiogenesis, or some other process confined to the wound.
24	Overcoming the Diffusion Barrier 100% oxygen via a non-re-breather face mask (flow usually set at 15 liters per minute). In normal subjects, TcPO2 values on the extremity always increase to a value > 100 mmHg. Such an oxygen response indicates that significant macrovascular disease is unlikely. A TcPO2 < 30 mmHg is consistent with severe arterial disease
25	TcPO₂ in assessing healing potential
26	What would you say about this TcPO₂ study? Chest reference and L AKA values Borderline low Medial and Lateral BK values normal Dorsal and lateral foot VERY low
27	Adding an Oxygen Challenge in an Edematous Patient Chest reference and L AKA values on Oxygen Normal response Medial and Lateral BK values on Oxygen Normal response Dorsal and lateral foot Normal Response
28	TcPO₂ for Healing potential and arterial status
29	What would you say about this TcPO₂ study with regard to the likelihood of wound healing? Medial thigh on air and Oxygen: Normal Right lateral thigh, calf and foot on air: Low Lateral thigh, calf and foot on Oxygen: Poor Interpretation: Spontaneous healing of wounds unlikely Poor oxygen response confirms severe PVD
30	Angiogram on this patient
31
32	Decreases in TcPO₂ with Increasing Inspired Oxygen Levels No change or decrease in TcPO₂ when going from 1 ATA air breathing to oxygen breathing occurred in 51 pts (10%) Failure to benefit from HBO (71.7%) False negative rate (26%) No clear explanation but oxygen related vasoconstriction is a possible explanation
33
34	Summary Statements on Oxygen Challenge and Arterial Disease In normal subjects breathing 100% oxygen at sea level, TcPO2 values on the extremity always increase to a value > 100 mmHg. Such an oxygen response indicates that significant macrovascular disease is unlikely. The sea level oxygen challenge is the best way to determine whether low air values are due to a reversible diffusion barrier, such as edema or inflammation or to macrovascular arterial disease. TcPO2 < 30 mmHg on air and >100 mmHg on 100% oxygen suggests adequate arterial inflow but a local barrier to oxygen diffusion. A TcPO2value obtained by breathing 100% oxygen at sea level that is < 30 mmHg is consistent with severe arterial disease.
35	TcPO₂ to predict amputation level A sea level air PtcO2 < 40 mmHg is associated with a lower than normal likelihood of amputation healing. (10 references) If the baseline PtcO2 increases < 10 mmHg while breathing 100% sea level oxygen, this is at least 68% accurate in predicting failure of healing after an amputation in patients in whom no attempt is made nor is possible to increase wound oxygenation (e.g., revascularization or HBO2T).
36
37	Assessing Response to Revascularization
38	Patient in 1992 Cachectic BF Non-healing wound L groin (s/p bypass) Painful non-healing wound lateral R leg Cold R foot + Femoral pulses (no DP or PT)
39	Patient in 1992
40
41
42	Arroyo Patients with severe foot ischemia, TcPO₂ < 30 mmHg, (11 pts) Co-morbidities: 11 HTN 7 DM 7 Smokers Protocol: All pts had vascular bypass surgery Doppler assured bypass patency Excluded post-op complications or mortalities Compared TcPO₂ on post-op days 1, 2, and 3
43	TcPO₂ on post-op days 1, 2, and 3
44	Caselli Successful (23) 100% limb salvage Unsuccessful (20) Major amputation (19) or died after PTA
45	TcPO₂ Response to Percutaneous Transluminal Angioplasty (PTCA)
46	Predicting Response to Revascularization An absolute increase in TcPO₂of > 30 mmHg during air breathing after revascularization (by surgery or endovascular procedure) is a significant improvement, and is usually associated with subsequent wound healing. TcPO₂values can continue to increase for as long as 28 days after revascularization. The literature suggests that postrevascularization TcPO₂ studies should not be performed until at least 3 days following the procedure, and preferably more than a week.
47	Predicting Response to Hyperbaric Oxygen Therapy
48	TcPO₂: What are “Normal” values in the Chamber?
49	Fife, et al. The predictive value of TcPO₂ in diabetic lower extremity ulcers treated with HBO₂: a retrospective analysis of 1144 patients. Wound Rep Reg 2002;10:198-207. How reliable are TcPO₂ values in predicting outcomes of HBO₂-treated diabetic lower extremity wounds? Inclusion: Retrospective analysis of 774 standard care diabetic patients treated in 6 facilities Exclusion: Patients who received Procuren were excluded from final analysis because they received significantly more HBO despite higher initial TCOMS (had a poorer outcome). Outcome Categories: 1) healed, 2) partially healed, 3) no apparent healing, 4) amputated, 5) died
50	Fife, et al. The predictive value of TcPO₂ in diabetic lower extremity ulcers treated with HBO₂ Results: Overall 75.6% improved after HBO Improved: 34 treatments (mean) Not improved: 24 treatments (mean) Baseline TcPO₂ (air 1 ATA) has almost no predictive value- multiple cut-off scores analyzed Single best discriminator of success or failure - TcPO₂ during HBO₂ > 200 mm Hg Reliability 74% Positive Predictive Value (PPV)- 58% (221 pts)
51	Can a 1 ATA Oxygen Challenge be used to predict response to HBO? MYTH: If the TcPO2 triples then the patient is a good candidate for HBO: A tripling of absolute TcPO₂ on (air 1 ATA) is only 54% reliable in predicting good HBOT outcome. There is no sea level oxygen value or ratio which can be used to predict response to HBOT
52	Failure Rate of HBOT Compared to the Percent Increase in TcPO₂ (Air 1 ATA)
53	Grolman RE, et al. TcPO₂ measurements predict a beneficial response to HBO₂ in patients with nonhealing wounds and critical limb ischemia. The American Surgeon Nov 2001; 67(11):1072-80. 36 patients Non-reconstructible (50%) vascular disease Failed prior revascularization attempts Non-healing even after successful revascularization HBO₂at 2-2.5 ata X 90 min
54	Grolman Hypothesis: change in TcPO₂ of > 10 mmHg from air to 100% O₂-breathing is predictive of healing with adjunctive HBO, and a change of <10 mm Hg predicts failure of healing with HBO Previously used-skin flaps, amputation level Group A (change < 10 mmHg) Group B (change > 10 mmHg) HBO continued until healing, or until further use of HBO could not be justified
55	Grolman D < 10 mmHg D > 10 mmHg Patients 9 27 # HBO₂ 25.9 28.2 Air baseline 5.8 + 1.6 torr 16.0 + 2.5* 100% O₂ 6.5 + 2.4 torr 75.9 + 11* D TcPO₂ 0.7 + 1.5 torr 59.9 + 10* Pts healed 11% (1/9) 70% (19/27)** (p < 0.05) *(p < 0.01)
56	HBOT and TcPO₂ Sea level air PtcO2 values alone cannot be used to predict benefit of subsequent HBO2T. This is because patients with very low sea level air values, even as low as 5 mm Hg, have subsequently healed with HBO2T, and because HBO2T has been shown to progressively correct hypoxia in ischemic tissue.58 Several published cases since 1977, using both PtcO2 and invasive oxygen tension measurements in a variety of wound types (e.g. radiation and diabetes), have shown that baseline air oximetry values increase in response to HBO2T. To date, however, an increase in PtcO2 breathing air during a course of hyperbaric oxygen treatments has not been evaluated as a predictor of clinical HBO2T success.
57	Diabetic foot ulcers and TCPO₂ If the ulcer is hypoxic while breathing air, and a TCPO2 > 200 mmHg is achieved breathing HBO2T, this is a predictor for success of subsequent HBO2T for diabetic foot ulcers. This test is 75% reliable. Conversely, in-chamber TcPO2 values < 100 mmHg are closely associated with failure of HBO2T in diabetic foot ulcers (reliability 89%). Although several studies have suggested that an ulcer with a TcPO₂ of less than 200 mmHg obtained while breathing hyperbaric oxygen is unlikely to heal, due to the variety of etiological and treatment modalities used in these studies, a definitive statement regarding healing prediction cannot be made based on in-chamber TcPO₂ alone.
58
59	Practical use of TcPO₂ in patient selection for HBO₂ therapy; A Step wise process Perform baseline air TcPO₂ to evaluate whether tissue hypoxia exists Perform vascular evaluation on patients with low TcPO₂ . Patients whose values increase dramatically upon respiring sea level oxygen are unlikely to have large vessel disease. Patients with a poor sea level oxygen response warrant anatomical studies. Repeat TcPO₂ after re-vascularization; those with values still low consider for HBOT if an appropriate indication exists. In-chamber TcPO₂ data should be utilized as a guide to patient selection for HBO₂ therapy when possible (>200 mmHg cut-off)
60	Best Practice Suggestions (not based on Evidence) A thorough assessment of the patient must be done prior to acceptance for HBO2T and the decision to treat should not be based on TCPO2 alone. Even in patients with in-chamber values < 100 mmHg (and thus a low likelihood of HBO2T benefit), the reliability of this test is still only 76%. Thus, a trial of HBO2T continues to be a reasonable approach. A reasonable trial of HBO2T is regarded as 15-20 treatments. There are some data to suggest that leg elevation might be a better indicator of vascular disease than failure to respond to sea level oxygen. However, since sea level oxygen is useful for other things, such as predicting amputation healing and confirming that arterial disease is not present, and there is nothing to suggest that adding limb elevation adds to/enhances TcPO2 data, one might argue that sea level oxygen it is a more versatile test. TcPO2 measurements should be made with the patient at rest, in a supine or recumbent position, in a comfortably warm room, with the extremity covered by a sheet or blanket. Measurements conducted with legs at an angle to the body are likely to results in values that cannot be compared to supine position.
61	Best Practice Suggestions When breathing oxygen, this portion of the test should last at least 10 minutes. The standard temperature setting for the thermistor is 45ºC. However, this temperature can result in skin blistering, particularly in ischemic patients. Due to issues of safety and comfort, some facilities use 44ºC. However, even this one degree reduction in the thermistor temperature can result in PtcO2 values that are 2%-3% lower than those taken at 45ºC.93 This difference translates to about a 1 mm Hg difference at 40 mm Hg tissue PO2 and about 6 mm Hg at 200 mm Hg tissue PO2. A “best practice” would be to check oxygen saturation at the time of PtcO2 testing in all patients to ensure they do not have arterial hypoxia. A combination of technologies might be useful in diagnosing the cause of a low TcPO2 (eg: Skin perfusion pressure).
62	www.intellicure.com