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Noninvasive Tissue Oxygen Monitoring in Surgical and Critical Care Medicine
Symposium on Critical Care
Noninvasive Tissue Oxygen Monitoring in Surgical and Critical Care Medicine Harry B. Kram, M.D.*
Scientists and clinicians have long sought to quantitate tissue oxygenation as a means to evaluate tissue perfusion. Although indirect methods for assessing tissue perfusion, such as Doppler ultrasonography and fluorescein angiography, provide valuable information, they do not specifically address the adequacy of 0 2 delivery. Invasive 0 2 monitoring techniques using platinum needle electrodes, on the other hand, accurately measure tissue oxygenation, but their invasive nature precludes routine clinical use. During the past decade, the polarographic 0 2 sensor has emerged as a noninvasive technique for assessing tissue perfusion and oxygenation. The polarographic principle, however, is not a new idea; Heyrovsky in 1925 demonstrated that by applying a proper voltage to a mercury electrode, a current was produced that was proportional to the 0 2 tension in the surrounding liquid. By 1950, scientists were using platinum electrodes to measure the 0 2 tension of living tissues. Although the use of a platinum cathode was well regarded by scientists of that period, it quickly became apparent that the platinum surface was changed by direct exposure to tissue fluids, producing a gradual loss in sensitivity. Furthermore, it was found that if there was motion at the cathode surface, the current generated artifactually increased because of diffusion phenomena and cathode 0 2 consumption. In 1954, Leland Clark, Jr.9 developed a new polarographic electrode in which the platinum cathode was covered with a semipermeable membrane to produce a more uniform 0 2 diffusion layer. This membrane also served as a barrier to the entrance of unwanted tissue substances that might affect the cathode surface. The following historical perspective is an excerpt written by Dr. Clark: 8 I will never forget the day when I assembled some glass, platinum and silver wire, a drop of KCl solution, and a bit of polyethylene film to see if it would work as an oxygen electrode. It was late in the day on October 4, 1954. The circuit was a *Fellow in Trauma, Department of Surgery, Hollywood Presbyterian Medical Center, Los Angeles, California
Surgical Clinics of North America-Yo!. 65, No. 4, August 1985
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flashlight battery, two resistors, and a string spotlight galvanometer from an old Evelyn colorimeter. The total cost of the electrode and the circuit was under a dollar. First, there was a current which settled at a few microamperes. Next, I squirted oxygen at the tip of the electrode and the galvanometer spot took off. It returned to the air current when the oxygen stream was removed. I squirted gas from a nearby Bunsen burner and the current decreased rapidly to near zero. Although I had hoped it might work, I was really surprised when it did. I have had this feeling of elation a few times since then .... After my new electrode worked, I measured the Po2 in everything I could find: blood, plasma, urine, coke, beer, honey, oil, liver homogenate, acids, alkali, etc.
METHODS FOR MEASURING TISSUE OXYGENATION TRANSCUTANEOUS Po 2 SENSOR
The development of the Clark Po 2 electrode stimulated further interest in the measurement of tissue oxygenation. In 1972, Huch and colleagues2I and Eberhard and associatesi 2 reported on the use of heated Clark electrodes as a practical method to monitor skin surface (transcutaneous) Po 2. These instruments were first applied clinically in neonates and subsequently in adults. In the former, transcutaneous 0 2 tensions (Ptco2) were found to approximate Pao 2 values closely. However, it was belatedly realized that this principle was not valid in infants with circulatory problems. 48, 70 Furthermore, when used in adults, the Ptco2 value was found to underestimate Pao 2 values variably. 4 • re, 40 • 52 , 54 • 57 Circulatory compromise caused even greater discrepancies between the Ptco 2 and Pao2 . Tremper and coworkers68 showed that when blood flow was adequate, Ptco2 values tracked Pao2 , but when blood flow was compromised, Ptco2 values tracked flow; throughout both of these conditions, Ptco2 reflected local 0 2 delivery. The fact that Ptco2 values reflect local 0 2 delivery has led to its use in monitoring systemic, as well as regional, perfusion. CoNJUNCTIVAL Po2 SENSoR
Measurement of palpebral conjunctival Po2 (Pcjo2) was first reported by Kwan and Fatt39 in 1970. Unlike Ptco2 monitoring, this method of measuring tissue perfusion and oxygenation does not require tissue heating because the conjunctiva lacks the stratum corneum layer and has a capillary bed only four to six cell layers beneath its mucous membrane surface. The Pcjo2 sensor system also measures tissue temperature. More importantly, the conjunctival capillary bed is perfused by the same arterial circulation as the brain, namely the internal carotid artery. This method may be applied in carotid arterial surgery and neurosurgery, as well as in the intensive care setting.29, eo ORGAN SURFACE OXIMETRY
Recently, Kram and colleagues 3I. 33 reported on the use of a nonheated, miniature Clark electrode to measure organ surface Po 2 in experimental and clinical conditions. When used intraoperatively, this method
NONINVASIVE TISSUE OXYGEN MONITORING
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allows noninvasive assessment of organ perfusion and viability in cases of suspected tissue ischemia, for example, cerebral and intestinal vascular disease and testicular torsion. CLINICAL APPLICATIONS CARDIOPULMONARY RESUSCITATION
Nowhere in the management of acute illness is the maintenance of tissue perfusion and oxygenation more important than during cardiopulmonary resuscitation (CPR). Monitoring of Ptco 2 has been shown to be extremely helpful in assessing the adequacy of tissue 0 2 transport during CPR. 44 • 65, 67 Although chest Ptco2 values reflect Pao2 during respiratory failure, they reflect cardiac output during cardiac failure and 0 2 delivery during both conditions (Fig. 1). Furthermore, chest Ptco 2 values below those of the simultaneously measured mixed venous Po2 tension were found to predict cardiac arrest by an average of 43 ± 28 minutes in patients in a preterminal stage of illness who were monitored continuously before cardiac decompensation and circulatory collapse. 67 Conjunctival 0 2 monitoring has also been used noninvasively to monitor tissue perfusion and oxygenation during CPR. 1• 2 Because the conjunctival Po 2 sensor does not use tissue heating, valid measurements are obtained more rapidly after placement than with the Ptco 2 sensor, which requires 10 to 15 minutes for stabilization. This feature has obvious advantages in the acute cardiopulmonary arrest situation. ACUTE TRAUMA
Transcutaneous 0 2 monitoring has been shown to be useful in the management of acutely ill traumatized patients in the emergency room setting. Depressed Ptco2 values obtained from severely ill emergency room patients were found to correlate well with the need for aggressive resuscitation; patients with an initial chest Ptco 2 value of less than 60 torr were subsequently found to have more difficult clinical courses and poorer outcomes than those with significantly greater Ptco2 values. 71 A chest Ptco2 value of less than 60 torr implies a deficit in either arterial oxygenation or local perfusion; these can be differentiated by an arterial blood gas analysis. Thus, Ptco2 monitoring may be a valuable method for triaging and evaluating emergency department patients in a major trauma center. Sensors for monitoring Ptco 2 have also been used to aid in the diagnosis and management of major peripheral arterial injury in patients with limb trauma. 32, 36 By placing Ptco2 sensors bilaterally on both the injured and the uninjured (contralateral) limb, Kram and Shoemaker were able to develop a transcutaneous 0 2 Bilateral Perfusion Index (BPI) to quantify circulatory deficits in comparison with the uninjured limb (Fig. 2).32 Thus BPI= Injured limb Ptco2 Uninjured limb Ptco 2
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Figure l. Sequential transcutaneous (PtcoJ and arterial (Pao 2) oxygen tensions (upper section), Ptco 2 and cardiac output (middle section), and Ptco 2 and 0 2 delivery (lower section) in a patient during respiratory failure, cardiac decompensation, cardiac arrest, and cardiopulmonary resuscitation. Note that Ptco2 values follow Pao2 during respiratory failure (hypoxia), cardiac output during cardiac decompensation (low flow), and 0 2 delivery during both conditions. (From Tremper, K. K., Waxman, K., Bowman, R., et al.: Continuous transcutaneous oxygen monitoring during respiratory failure, cardiac decompensation, cardiac arrest, and CPR. Crit. Care Med., 8:377-381, 1980; with permission.)
Use of the BPI allows adequate assessment of relative limb perfusion, regardless of differences in arterial 0 2 content and peripheral vasoconstriction between patients. Monitoring of Ptco2 may prove to have certain advantages over conventional Doppler ultrasonographic techniques in the diagnosis of major peripheral arterial trauma (Fig. 3). This advantage is largely because the pulse wave may be transmitted through short obstructions, such as intimal flaps; via collateral vessels; and through areas of fresh, soft clot. 49 Regional Ptc02 tension, on the other hand, is affected when there is reduced flow secondary to arterial narrowing, bleeding, occlusion from thrombosis, in-
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Uninjured Limb Ptco2 Figure 2. Transcutaneous oxygen (Ptco2) values of the injured limb versus Ptco 2 values of the uninjured (contralateral) limb in 33 suspected major peripheral arterial injuries. The Bilateral Perfusion Index (BPI) is the ratio of the injured limb Ptco2 to the uninjured limb Ptc02 • The diagonal line represents a BPI of 0.90. (From Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:776-780, 1984; with permission.)
tramural dissection, or external compression. In addition, limb Ptco 2 monitoring in patients with concomitant peripheral nerve injuries alk>ws evaluation of tissue perfusion when neurologic function cannot be used as a measure of limb anoxia. 32 Continuous limb Ptco2 monitoring during surgical operations for peripheral arterial trauma allows continuous, real-time assessment of limb perfusion, as well as immediate evidence of a successful surgical result (Fig. 4). 36 Nevertheless, the absence of abnormalities in measured limb Ptco2 values should not interdict arteriography if it is indicated to rule out arterial injury. In addition, low values may also be seen in patients with peripheral vascular disease, significant prior surgery, and certain compartment syndromes.
INTENSIVE CARE
Critically ill patients in the intensive care unit very often suffer from disturbances in tissue perfusion. These episodes of inadequate tissue 0 2 transport may be sudden, unheralded by symptoms, and allowed to pro-
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DIAGNOSTIC FINDINGS IN 36 SUSPECTED MAJOR PERIPHERAL ARTERIAL INJURIES '% DIAGNOSTIC YIELD HR)100 SYSTOLIC BP(100 PALLOR SIGNIFICANT HEMATOMA BRUIT COOLNESS NEUROLOGIC DEFICIT PULSE DEFICIT
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Figure 3. Diagnostic findings and positive diagnostic yield (percentage) in 36 suspected major peripheral arterial injuries. Transcutaneous oxygen monitoring was performed in 33 of the suspected injuries. Note that a transcutaneous 0 2 Bilateral Perfusion Index (BPI) of less than 0. 90 was associated with an 80 per cent positive diagnostic yield. (From Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:77&-780, 1984; with permission.)
gress unnoticed. Variables conventionally used to monitor cardiopulmonary performance include cardiac and respiratory rate, arterial and central venous blood pressures, temperature, urinary output, and color of the extremities; although useful, these parameters provide only a qualitative assessment of tissue perfusion. Monitoring of Ptco 2 has proved helpful in detecting unexpected cardiac or respiratory decompensations in critically ill patients. 52, 53, 57, 65, 66, 67 In a published series 66 of 106 critically ill adults monitored with the Ptco2 sensor and intermittent conventional invasive hemodynamic and 0 2 transport variables, Ptco 2 values in patients with low-flow shock responded quickly to blood flow changes with a 95 per cent response time of approximately 1 minute; the patients not in shock responded to changes in inspired 0 2 concentration (F10 2) with Ptco2 changes in about 2 minutes.
lOll
NONINVASIVE TISSUE OXYGEN MONITORING
Noninvasive conjunctival and Ptco 2 monitors have increased the safety and simplicity of managing patients on mechanical ventilation and during extubation. 30, 45, 57, 63, 66, 69, 74 In a study conducted on mechanically ventilated patients immediately before extubation, Ptco 2 monitoring was helpful in predicting which patients would eventually require reintubation. 63 This is largely because measured Ptco 2 values depend on factors that include the P50 , hemoglobin concentration, Pao 2 , and cardiac output; patients who require reintubation usually have conditions present that reduce one or more of these variables. Continuous Ptco 2 monitoring has also been helpful in estimating the patient's condition during the different stages of ventilator weaning. 63 Because polarographic 0 2 sensors applied to tissue surfaces will track local 0 2 delivery during hypoxic and low-flow conditions, they are especially useful as continuous monitors during therapeutic interventions that may cause abrupt changes in Pao 2 or cardiac output-for example, endotracheal tube suctioning or positive end-expiratory pressure (PEEP) therapy. During PEEP therapy, a sudden drop in measured transcutaneous or conjunctival 0 2 tension may be secondary to a life-threatening complication, such as hypoxemia, low cardiac output, or pneumothorax. Continuous
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Figure 4. Perioperative transcutaneous (Ptco 2) and arterial (Pao 2) oxygen tensions in a patient with unilateral occlusion of the external iliac and popliteal arteries secondary to blunt trauma. Note that the injured limb Ptco 2 correlated best with uninjured (contralateral) limb Ptco2 values after restoration of normal blood flow to the leg (r = 0. 97). (From Kram, H. B., Wright, J., Shoemaker, W. C., et a!.: Perioperative transcutaneous 0 2 monitoring in the management of major peripheral arterial trauma. J. Trauma, 24:443-445, 1984; with permission.)
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conjunctival 0 2 monitoring during PEEP optimization in a hemodynamically stable patient with severe adult respiratory distress syndrome (ARDS) is illustrated in Figure 5.
ARTERIAL OCCLUSIVE DISEASE
Noninvasive tissue 0 2 monitoring techniques have been evaluated extensively as adjuncts in the diagnosis and management of peripheral arterial occlusive disease (PAOD). Sensors for monitoring Ptco 2 appear to be especially useful in the management of patients with atherosclerotic disease of the lower extremity. The Ptco2 sensor may be used to assess limb perfusion during the preoperative, intraoperative and postoperative period, as well as to help predict the success of wound healing after amputation. Measured limb Ptco 2 values usually show appreciable differences when patients with symptomatic PAOD are compared with healthy, control subjects. 7• 10• 14• 20· 28 · 35• 42 • 43 • 47 • 73 However, the overlap is sufficiently large that there is less than complete confidence in the diagnostic accuracy. Methods to improve diagnostic sensitivity and specificity include 0 2 inhalation, 47 positional changes, 18• 64 exercise testing, 20. 47 temporary cuff occlusion, 7, 14, 28,35 and comparing limb Ptco 2 values with those obtained on other body surface areas. 18 · 20• 32 • 34 • 36• 47 Of these, only exercise testing and temporary cuff occlusion (ischemia) significantly increase local 0 2 demand. However, exercise testing causes muscular contractions that may hinder local blood flow and thereby markedly reduce the Ptco 2 reading. Moreover, when subjected to treadmill testing, patients with associated coronary atherosclerosis have a low but definite risk of myocardial infarction. 22
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TIME Figure 5. Sequential conjunctival, arterial, and mixed venous oxygen tensions during optimization of PEEP therapy in a hemodynamically stable patient with severe adult respiratory distress syndrome. Note that when cardiac output is normal, as in this patient, conjunctival Po2 values track arterial Po2 values. (From Kram, H. B., Chen, B., Lee, T. S., et al.: Conjunctival oxygen monitoring in postoperative respiratory failure and shock. Int. J. Clin. Monit. Comput., 1:165, 1984; with permission.)
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NONINVASIVE TISSUE OXYGEN MONITORING
Increasing limb 0 2 demand is an important diagnostic maneuver because many patients, particularly those with intermittent claudication, manifest tissue hypoxia only when limb 0 2 demand is increased. The use of 0 2 inhalation or limb elevation results in significant changes in limb 0 2 supply but does not greatly increase 0 2 demand. Patients distinguishable by the latter tests already have severe disease with minimal or no circulatory reserve and may not be candidates for vascular reconstruction. The transcutaneous 0 2 recovery half-time (TORT), defined as the time required to recover half of the decrease in the limb-to-chest Ptco 2 ratio caused by temporary limb ischemia induced by cuff occlusion, was found to (I) increase greatly the diagnostic accuracy of Ptco 2 measurements to differentiate normal limbs versus those with PAOD and (2) determine successful versus unsuccessful results of surgical therapy (Figs. 6 and 7). 28 When measured on the dorsum of the foot, TORT values correlated well with the severity of symptoms (Fig. 8)35; this permitted quantitation of functional disability and comparison with the patient's symptoms. Furthermore, TORT can be performed simultaneously with measurement of the
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Figure 6. Effect of temporary limb ischemia for 4 minutes by a standard pneumatic blood pressure cuff on calf and foot transcutaneous oxygen (PtcoJ tensions expressed as a percentage of the simultaneously recorded chest Ptco2 • This is shown for four groups: normal volunteer subjects, patients with symptomatic peripheral vascular disease (PVD), patients who had successful operative therapy, and patients who had unsuccessful therapy. Values are represented as mean ± SEM. Note that the postocclusive Ptco2 recovery is significantly delayed in limbs with symptomatic PVD or following unsuccessful therapy. (From Kram, H. B., Appel, P. L., White, R. A., et al.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg., 1:628, 1984; with permission.)
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Figure 7. Postocclusive transcutaneous oxygen recovery half-time (TORT) of the calf and foot in normal volunteer subjects, patients with symptomatic peripheral vascular disease (PVD), patients who had successful operative therapy, and patients who had unsuccessful therapy. The TORT is the time required to recover half of the decrease in the limb Ptco.-to-chest Ptco2 ratio caused by temporary limb ischemia induced by cuff occlusion. Values are mean ± SEM. Note that TORT values of limbs with successful operative therapy were similar to those of normal subjects. (From Kram, H. B., Appel, P. L., White, R. A., et a!.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg., 1:628, 1984; with permission.)
5
toe pulse reappearance time, an already well-accepted, noninvasive vascular diagnostic modality; this practice reduces the additional time and monitoring personnel needed. Monitoring of Ptco 2 has also been used to help predict wound healing success after amputation. A Ptco 2 value of greater than 35 to 45 torr measured on the anterior skin surface of the pretibial area has been correlated with successful wound healing after below-knee amputations, although there is significant variability among published reports. 6, 14, 24, 42, 43, 51, 72, 73 This variability may be due to differences in Pao 2 values, sensor location, and monitoring technique. Continuous limb Ptco 2 monitoring during vascular operations is informative because it provides immediate evidence of improved blood flow in the lower extremity, thereby demonstrating a satisfactory operative result before the termination of surgery. 34 · 36 Conjunctival 0 2 monitoring during carotid arterial surgery has recently been shown to be beneficial in that conjunctival Po2 values were reduced in association with systemic hypotension, carotid artery manipulation, carotid artery clamping, and obstruction and clamping of the carotid shunt (Fig. 9).29, oo Because the conjunctival Po 2 sensor monitors tissue oxygenation in a capillary bed perfused by the internal carotid artery, it may prove valuable in refining the criteria for operative intervention in patients with asymptomatic carotid bruits, as well as in indicating the need for prompt intervention in patients with deteriorating perfusion before the onset of life-threatening cerebral ischemia.
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Time {minutes) Figure 8. Postocclusive transcutaneous oxygen recovery half-time (TORT) values, measured on the dorsum of the foot, in 90 limbs classified according to symptoms. Values are mean ± SEM. Note that foot TORT values correlated well with the severity of symptoms.
PLASTIC AND RECONSTRUCTIVE SURGERY
Monitoring of Ptco2 has been gaining increasing popularity in plastic and reconstructive surgery. Because Ptco 2 values reflect local tissue perfusion, they may be used to assess continuously the circulatory status of skin flaps, 3• 25. 27, 58 skin grafts, 26 replanted fingers or hands, 41 • 62 and free tissue transfers. 62 A provocative test involving the skin flap Ptco 2 response to increased F10 2 has potential use for qualitatively judging tissue perfusion and viability. 3, 25-27, 58, 62 A lack of increase in Ptco 2 after a substantial increase in the patient's FI0 2 suggests circulatory compromise of the tissue being monitored. Further investigations involving the use of this maneuver in conjunction with other noninvasive tissue 0 2 monitoring techniques may prove to be useful. Skin flap Ptco 2 values may also be compared with simultaneously measured chest Ptco 2 values to assess more accurately relative flap perfusion in the postoperative period (Fig. 10). 58 Use of this method may lead to the earlier detection of tissue ischemia, which may threaten skin flap survival, thereby allowing timely therapeutic maneuvers to improve flap circulation.
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INTRAOPERATIVE MONITORING
The value of noninvasive tissue 0 2 monitoring has been examined in virtually all types of surgical operations. Continuous Ptco 2 monitoring has been used to assess the adequacy of 0 2 transport during general, 44 • 46· 50• 55. 66 thoracic, 15. 19• 46 cardiac, 19· 55 • 59 and vascular surgery, 34 · 36 neurosurgery, 5o and oral surgery. 5, 37, 38 In a series 46 of high-risk surgical patients monitored intraoperatively with Ptco 2 sensors, decreases in cardiac output, 0 2 delivery, and 0 2 consumption were the earliest warning signs of impending circulatory deterioration; these hemodynamic and bulk 0 2 transport variables were paralleled by decreases in measured Ptco 2 values. In this series, the heart rate and mean arterial pressures had highly variable and frequent changes unrelated to alterations in blood flow and 0 2 transport. Monitoring of Ptco 2 may also be beneficial immediately after surgery when frequent changes in cardiopulmonary status are common secondary to hypothermia, extubation, and recovery from anesthesia. During the period after cardiopulmonary bypass in cardiac surgery, hemodynamic instability may require pharmacologic support; low chest Ptco 2 values related
NONINVASIVE TISSUE OXYGEN MONITORING
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to Pao2 during this period were correlated with the judgment of the anesthesiologist regarding the need for pharmacologic support to improve cardiorespiratory function. 59 Severe hypoventilation may occur during procedures that involve the airway or thorax; the efficacy of Ptco2 monitoring to detect these hypoxic periods has been well documented.17, 19, 44, 50 During vascular reconstruction, Ptco2 sensors applied to the extremity provide continuous measurements that reflect the adequacy of limb 0 2 transport. 34• 36 Noninvasive conjunctival 0 2 monitoring may similarly be employed to assess carotid 0 2 transport during carotid arterial surgery. 29· 60 Conjunctival 0 2 monitoring during surgery may also be used as an early warning device of sudden compromise in systemic 0 2 delivery (Fig. ll). Although many clinicians have expressed concern regarding the effects of inhalational anesthesia on values obtained from tissue Po2 sensors incorporating a membrane-covered polarographic electrode, these effects do not appear to limit the clinical utility or efficacy of the sensors.ll, 16, 50, 56
ORGAN SURFACE
Po2 MONITORING
Recently, a miniature Po2 sensor consisting of a Clark-type polarographic electrode with a platinum cathode and polypropylene oxygen-
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1 & 2 ~ hours postoperot1ve Figure 10. Postoperative transcutaneous oxygen (TcPo2) tensions measured on a vascularized latissimus dorsi musculocutaneous flap and on the chest (control) in a patient who underwent pelvic reconstruction for carcinoma of the vulva. Note the decrease in flap TcPo 2 on the seventh postoperative day; a significant wound infection became clinically apparent 2 days later. Adequate drainage and appropriate selection of systemic antibiotics resulted in eventual total survival of the flap, which was reflected by recovery of the TcPo2 tension. (From Serafin, D., Lesesne, C. B., Mullen, R. Y., et al.: Transcutaneous Po, monitoring for assessing viability and predicting survival of skin flaps: Experimental and clinical correlations. J. Microsurg., 2:165-178, 1981; with permission.)
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permeable membrane was used to measure "noninvasively" organ surface 0 2 tension in experimental animals. 31 The miniature Po 2 sensor is diagrammatically illustrated in Figure 12. Like transcutaneous and conjunctival Po2 values, measured organ surface 0 2 tensions track Pao 2 during hypoxia
Figure 12. Diagram of the miniature polarographic oxygen sensor used to measure organ surface Po2 • (1 =platinum cathode; 2 =thermistor; 3 =silver-silver chloride anode; 4 = polypropylene membrane; 5 =oxygen electrode; 6 =nylon mesh spacer; 7 =snap-on ring; 8 = polymethylmethacrylate plate; 9=cable; 10=connector.) (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
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Figure 13. A, Conjunctival and organ surface Po2 tensions and sequential hemodynamic and oxygen transport variables during normoxia, hyperoxia, and hypoxia in an anesthetized dog. Note that conjunctival and organ surface Po2 tensions track Pao2 during hyperoxia and hypoxia, provided that blood flow is adequate. B, Conjunctival and organ surface Po2 tensions and sequential hemodynamic and oxygen transport variables during hemorrhagic shock and resuscitation in an anesthetized dog. Note that conjunctival and organ surface Po2 tensions tracked blood flow (cardiac output) during the low flow state; the Po2 remained relatively stable.
and local blood flow during shock (Fig. 13), reflecting tissue 0 2 delivery during both conditions. The potential experimental uses for this new method include many areas of research. The miniature Po 2 sensor has also been used intraoperatively in patients to aid the surgeon in the determination of tissue perfusion and viability in suspected organ ischemia (Fig. 14) and during certain procedures, 31 · 33 for example, clipping of cerebral arterial aneurysms and
Figure 14. Intestinal surface Po2 measured using the miniature oxygen sensor in a patient with suspected gangrenous bowel. (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
1020
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HEPATIC SURFACE OXYGEN TENSION
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Figure 15. Sequential hepatic surface, arterial, and mixed venous oxygen tensions are shown in a hemodynamically stable patient during performance of an end-to-side portacaval shunt. (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
TESTICULAR SURFACE OXYGEN TENSION DURING TORSION 20
0 I
Control TORSION
15
MINUTES
Figure 16. Sequential testicular surface oxygen tension Pso2 values during varying degrees of unilateral torsion. Values are mean ± SD.
NONINVASIVE TISSUE OXYGEN MONITORING
1021
portacaval shunting (Fig. 15). Measurements were easily obtained on the surfaces of the brain, liver, kidney, gallbladder, small intestine, colon, and testicle (Fig. 16) in experimental and clinical conditions.
CONCLUSION Noninvasive tissue 0 2 monitoring using polarographic electrodes is a valuable method for assessing tissue perfusion and oxygenation in surgical and critically ill patients. The values obtained from electrodes applied to tissue surfaces are dependent upon both arterial 0 2 content and blood flow and reflect the balance between local 0 2 supply and demand. These sensors provide a unique means to assess systemic, regional, and organ surface 0 2 transport in clinical and experimental conditions.
REFERENCES l. Abraham, E., and Ehrlich, H.: Conjunctival and transcutaneous oxygen monitoring during resuscitation. Ann. Emerg. Med., 12:287, 1984. 2. Abraham, E., Smith, M., and Silver, L.: Conjunctival and transcutaneous oxygen moni-
toring during cardiac arrest and cardiopulmonary resuscitation. Crit. Care Med., 12:419, 1984. 3. Achauer, B. M., Black, K. S., and Litke, D. K.: Transcutaneous Po2 in flaps: A new method of survival protection. Plast. Reconstr. Surg., 65:738, 1980. 4. Armstrong, J. R., Kreps, T. W., and Conway, W. A.: The non-value of monitoring transcutaneous oxygen tension in patients with chronic renal failure (abstract). Crit. Care Med., 9:270, 1981. 5. Beech, A. D., and Lyttle, J. J.: Continuous transcutaneous oxygen tension monitoring during ultralight general anesthesia for oral surgery. J. Oral MaxillofilC. Surg., 40:559, 1982. 6. Burgess, M. E., Watsen, F. A., Wyss, C. R., eta!.: Segmental transcutaneous measurements of Po2 in patients requiring below-the-knee amputation for peripheral vascular insufficiency. J. Bone Joint Surg., 64:378, 1982. 7. Cina, C., Katsamouris, A., Megerman, J., eta!.: Utility of transcutaneous oxygen tension measurements in peripheral arterial occlusive disease. J. Vase. Surg., 2:362, 1984. 8. Clark, L. C., Jr.: Measurement of oxygen tension: A historical perspective. Crit. Care Med., 9:690, 1981. 9. Clark, L. C., Jr.: Monitor and control of blood and tissue oxygen tensions. Trans. Am. Soc. Artif. Intern. Organs, 2:41, 1956. 10. Clyne, C. A. C., Ryan, J., Webster, J. H. H., et a!.: Oxygen tension of the skin of ischemic legs. Am. J. Surg., 143:315, 1982. ll. Eberhard, P., and Mindt, W.: Interference of anesthetic gases at skin surface sensors for oxygen and carbon dioxide. Crit. Care Med., 9:717, 1981. 12. Eberhard, P., Mindt, W., and Hammacher, K.: Perkutane Messing des Sauerstoff partaldnuckes: Methodik und Anwendungen. Stuttgart, Proc. Medizin-Technik, May 16, 1972. 13. Fink, S., Ray, C. W., McCartney, S., eta!.: Oxygen transport and utilization in hyperoxia and hypoxia. Crit. Care Med., 12:943, 1984. 14. Franzeck, V. K., Talke, P., Bernstein, E. T., eta!.: Transcutaneous Po2 measurements in health and peripheral arterial occlusive disease. Surgery, 91:156, 1982. 15. Gothgen, I., Degn, H., Jacobsen, E., et a!.: Transcutaneous oxygen measurement during thoracic anaesthesia. Acta Anaesthesiol. Scand., 24:491, 1980. 16. Gothgen, I., and Jacobsen, E.: Transcutaneous oxygen tension measurements. I. Age, variation and reproducibility. II. The influence of halothane and hypotension. Acta Anaesthesiol. Scand., 67[Suppl.]:66, 1978.
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17. Hamik, E., Kukzycki, L., and Gomes, M. N.: Transcutaneous oxygen monitoring during bronchoscopy and washout for cystic fibrosis. Anesth. Analg. (Cleve.), 62:357, 1983. 18. Hauser, C. J., Appel, P., and Shoemaker, W. C. : Pathophysiologic classification of peripheral vascular disease by positional changes in regional transcutaneous Po2 • Surgery, 95:689, 1984. 19. Hauser, C. J., and Harley, D. P.: Transcutaneous gas tension monitoring in the management of intraoperative apnea. Crit. Care Med., 11:830, 1983. 20. Hauser, C. J., and Shoemaker, W. C.: Use of a transcutaneous Po2 regional perfusion index to quantify tissue perfusion in peripheral vascular disease. Ann. Surg., 197:337, 1983. 21. Huch, A., Huch, R., Menzer, K., et a!.: Eine Schuelle, behizte proberlachenelektrode zur kontinuier lichen iiberwache ung des Po 2 beim Menschen. Elektrodenautbau undeigen schaften. Stuttgart, Proc. Medizin-Technik, May 16, 1972. 22. Hummel, B. W., Hummel, B. A., Mowbry, A., eta!.: Reactive hyperemia vs. treadmill exercise testing in arterial disease. Arch. Surg., 113:95, 1979. 23. Hutchinson, D. C. S., Rocca, G., and Honeybourne, D.: Estimation of arterial oxygen tension in adult subjects using a transcutaneous electrode. Thorax, 36:473, 1981. 24. Katsamouris, A., Brewster, D. C., Megerman, J., eta!.: Transcutaneous oxygen tension in selection of amputation level. Am. J. Surg., 147:510, 1984. 25. Keller, H. P., and Klaue, P.: Objective control of pedule flaps with transcutaneous Po 2 measurements (abstract). Eur. Soc. Surg. Res., 13:77, 1978. 26. Keller, H. P., Klaue, P., and Lubbers, D. W.: Transcutaneous Po2 measurements for evaluating the oxygen supply of skin allo- and autografts. Eur. Surg. Res., 10:272, 1978. 27. Knote, V. G., and Bohmert, H.: Zur Bestimmung der Uberlebensfahigkeit Nekrosegefahrdeter Hautareale: Mittele transkutaner polarographischen Sauererstoffdruck-messung. Fortschr. Med., 95:640, 1977. 28. Kram, H. B., Appel, P. L., White, R. A., et a!.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg. 1:628, 1984. 29. Kram, H. B., Bratanow, N., White, R. A., eta!.: Conjunctival and transcutaneous oxygen monitoring during carotid arterial surgery. (submitted) 30. Kram, H. B., Chen, B., Lee, T. S., et a!.: Conjunctival oxygen monitoring in postoperative respiratory failure and shock. Int. J. Clin. Manit. Comput. 1:165, 1984. 31. Kram, H. B., Fukunaga, A., Chen, B., eta!.: Method for measuring organ surface oxygen tension in experimental and clinical conditions (abstract). Crit. Care Med., 12:298, 1984. 32. Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:776, 1984. 33. Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984. 34. Kram, H. B., and Shoemaker, W. C.: Use of transcutaneous 0 2 monitoring in the intraoperative management of severe peripheral vascular disease. Crit. Care Med., 11:482, 1983. 35. Kram, H. B., Tabrisky, J., eta!.: Transcutaneous oxygen recovery and toe pulse reappearance time to assess peripheral vascular disease. Circulation. In press. 36. Kram, H. B., Wright, J., Shoemaker, W. C., eta!.: Perioperative transcutaneous 0 2 monitoring in the management of major peripheral trauma. J. Trauma, 24:443, 1984. 37. Kraut, R. A.: Transcutaneous oxygen monitoring of patients undergoing surgical removal of wisdom teeth. Anesth. Prog., 29:70-1, 1982. 38. Kraut, R. A.: Transcutaneous oxygen monitoring of patients undergoing surgical removal of wisdom teeth utilizing general anesthesia. Anesth. Prog., 29:132, 1982. 39. Kwan, M., and Fatt, I.: A noninvasive method of continuous arterial oxygen tension estimation from measured palpebral conjunctival oxygen tension. Anesthesiology, 35:309, 1970. 40. Lofgren, 0.: Transcutaneous oxygen measurement in adult intensive care. Acta Anaesthesia!. Scand., 23:534, 1979. 41. Matsen, F. A., Bach, A. W., Wyss, C. R., eta!.: Transcutaneous Po 2 : A potential monitor of the status of replanted limb parts. Plast. Reconstr. Surg., 65:732, 1980. 42. Matsen, F. A., Wyss, C. R., Pedegana, L. R., et a!.: Transcutaneous oxygen tension measurement in peripheral vascular disease. Surg. Gynecol. Obstet., 150:525, 1980. 43. Mustapha, N. M., Redhead, R. G., Jain, S. K., eta!.: Transcutaneous partial oxygen
I'
~
NONINVASIVE TISSUE OXYGEN MONITORING
44. 45. 46.
t
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II
49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60.
61. 62. 63.
64. 65. 66.
67.
68. 69.
1023
pressure assessment of the ischemic lower limb. Surg. Gynecol. Obstet., 156:582, 1983. Nichter, L. S., Bryant, C. A., Tremper, K. K., et al.: Continuous transcutaneous oxygen monitoring during an intraoperative cardiac arrest. Resuscitation, 10:213, 1983. Nikke, P., Rasanen, J., Tahvanainen, J., et al.: Ventilatory pattern in respiratory failure arising from acute myocardial infarction. II. Ptco2 and Ptcco2 compared to Pao2 and Paco2 during IMV4 vs. IPPV 12 and PEEP0 vs. PEEP10 . Crit. Care Med., 10:79, 1982. Nolan, L., and Shoemaker, W. C.: Transcutaneous 0 2 and C0 2 monitoring of high risk surgical patients during the perioperative period. Crit. Care Med., 10:762, 1982. Ohgi, S., Ito, K., and Mori, T.: Quantitative evaluation of the skin circulation in ischemic legs by transcutaneous measurement of oxygen tension. Angiology, 32:833, 1981. Peabody, J. L., Willis, M. M., Gregory, G. A., et al.: Clinical limitations and advantages of transcutaneous oxygen electrodes. Acta Anaesthesiol. Scand., 68[Suppl.):76, 1978. Perry, M. 0.: The Management of Acute Vascular Injuries. Baltimore, The Williams and Wilkins Co., 1981, pp. 13-20. Rafferty, T. D., Marrero, 0., Nardi, D., et al.: Transcutaneous Po 2 as a trend indicator of arterial Po2 in normal anesthetized adults. Anesth. Analg. (Cleve.), 61:252, 1982. Ratliff, D. A., Clyne, C. A. C., Chant, A. D. B., et al.: Prediction of amputation wound healing: The role of transcutaneous Po2 assessment. Br. J. Surg., 71:219, 1984. Reineke, H.: Measurement of the Po2 transcutaneously with an oximeter: A new method for patients in intensive care. Resuscitation, 6:21, 1978. Rithalia, S. V. S., George, R. J. D., and Tinker, J.: Continuous tissue pH and transcutaneous Po 2 measurement as an index of tissue perfusion in critically ill patients. Resuscitation, 9:67, 1981. Rooth, G., Hedstrand, V., Tyden, H., et al.: The validity of the transcutaneous oxygen tension method in adults. Crit. Care Med., 4:162, 1976. Samra, S. K.: Comparison of Teflon and polypropylene membranes for transcutaneous oxygen monitoring during anesthesia. Crit. Care Med., 11:46, 1983. Samra, S. K.: Halothane interference with transcutaneous oxygen monitoring: In vivo and in vitro. Crit. Care Med., 11:612, 1983. Schachter, E. N., Rafferty, T. D., Knight, C., et al.: Transcutaneous oxygen and carbon dioxide monitoring: Use in adult surgical patients in an intensive care unit. Arch. Surg., 116:1193, 1981. Serafin, D., Lesesne, C. B., Mullen, R. Y., et al.: Transcutaneous Po2 monitoring for assessing viability and predicting survival of skin flaps: Experimental and clinical correlations. J. Microsurg., 2:165, 1981. Shibutani, K., Komatsu, T., Kumar, Y. N., et al.: Use of transcutaneous oxygen sensor as a monitor of coming off bypass (abstract). Crit. Care Med., 10:226, 1982. Shoemaker, W. C., and Lawner, P.: Method for continuous conjunctival oxygen monitoring during carotid artery surgery. Crit. Care Med., 11:946,1983. Shoemaker, W. C., and Vidyasagar, D.: Physiological and clinical significance of Ptco2 and Ptcco 2 measurements. Crit. Care Med., 9:689, 1981. Smith, A. R., Sonneveld, G. J., Kort, W. J., et al.: Clinical application of transcutaneous oxygen measurements in replantation surgery and free tissue transfer. J. Hand Surg., . 8:139, 1983. Tahvanainen, J., and Nikki, P.: The significance of hypoxemia with low inspired 0 2 fraction before extubation. Crit. Care Med., 11:708, 1983. Tonnesen, K. H.: Transcutaneous oxygen tension in imminent foot gangrene. Acta Anaesthesiol. Scand., 68[Suppl.):107, 1978. Tremper, K. K., Shoemaker, W. C.: Continuous CPR monitoring with transcutaneous oxygen and carbon dioxide sensors. Crit. Care Med., 9:417, 1981. Tremper, K. K., and Shoemaker, W. C.: Transcutaneous oxygen monitoring of critically ill adults, with and without low flow shock. Crit. Care Med., 9:706, 1981. Tremper, K. K., Waxman, K., Bowman, R., et al.: Continuous transcutaneous oxygen monitoring during respiratory failure, cardiac decompensation, cardiac arrest, and CPR. Crit. Care Med., 8:377, 1980. Tremper, K. K., Waxman, K., and Shoemaker, W. C.: Effects of hypoxia and shock on transcutaneous Po2 values in dogs. Crit. Care Med., 7:526, 1979. Tremper, K. K., Waxman, K., and Shoemaker, W. C.: Use of transcutaneous oxygen sensors to titrate PEEP. Ann. Surg., 193:206, 1981.
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70. Versmold, H. T., Linderkamp, 0., Holzmann, M., et al.: Limits oftcPo 2 monitoring in sick neonates: Relation to blood pressure, blood volume, peripheral blood flow and acid base status. Acta Anaesthesia!. Scand., 68[Suppl.]:88, 1978. 71. Waxman, K., Sadler, R., Eisner, M. E., et al.: Transcutaneous oxygen monitoring of emergency department patients. Am. J. Surg., 146:35, 1983. 72. White, R. A., Nolan, L., Harley, D., et al.: Noninvasive evaluation of peripheral vascular disease using transcutaneous oxygen tension. Am. J. Surg., 144:68, 1982. 73. Wyss, C. R., Watsen, F. A., Simmons, C. W., et al.: Transcutaneous oxygen tension measurements on limbs of diabetic and nondiabetic patients with peripheral vascular disease. Surgery, 95:339, 1984. 74. Yelderman, M.: Transconjunctival oxygen measurements in critical care medicine. Letter to the Editor. Anesthesiology, 59:266, 1983. Department of Surgery Hollywood Presbyterian Medical Center Los Angeles, CA 90027
Noninvasive Tissue Oxygen Monitoring in Surgical and Critical Care Medicine Harry B. Kram, M.D.*
Scientists and clinicians have long sought to quantitate tissue oxygenation as a means to evaluate tissue perfusion. Although indirect methods for assessing tissue perfusion, such as Doppler ultrasonography and fluorescein angiography, provide valuable information, they do not specifically address the adequacy of 0 2 delivery. Invasive 0 2 monitoring techniques using platinum needle electrodes, on the other hand, accurately measure tissue oxygenation, but their invasive nature precludes routine clinical use. During the past decade, the polarographic 0 2 sensor has emerged as a noninvasive technique for assessing tissue perfusion and oxygenation. The polarographic principle, however, is not a new idea; Heyrovsky in 1925 demonstrated that by applying a proper voltage to a mercury electrode, a current was produced that was proportional to the 0 2 tension in the surrounding liquid. By 1950, scientists were using platinum electrodes to measure the 0 2 tension of living tissues. Although the use of a platinum cathode was well regarded by scientists of that period, it quickly became apparent that the platinum surface was changed by direct exposure to tissue fluids, producing a gradual loss in sensitivity. Furthermore, it was found that if there was motion at the cathode surface, the current generated artifactually increased because of diffusion phenomena and cathode 0 2 consumption. In 1954, Leland Clark, Jr.9 developed a new polarographic electrode in which the platinum cathode was covered with a semipermeable membrane to produce a more uniform 0 2 diffusion layer. This membrane also served as a barrier to the entrance of unwanted tissue substances that might affect the cathode surface. The following historical perspective is an excerpt written by Dr. Clark: 8 I will never forget the day when I assembled some glass, platinum and silver wire, a drop of KCl solution, and a bit of polyethylene film to see if it would work as an oxygen electrode. It was late in the day on October 4, 1954. The circuit was a *Fellow in Trauma, Department of Surgery, Hollywood Presbyterian Medical Center, Los Angeles, California
Surgical Clinics of North America-Yo!. 65, No. 4, August 1985
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flashlight battery, two resistors, and a string spotlight galvanometer from an old Evelyn colorimeter. The total cost of the electrode and the circuit was under a dollar. First, there was a current which settled at a few microamperes. Next, I squirted oxygen at the tip of the electrode and the galvanometer spot took off. It returned to the air current when the oxygen stream was removed. I squirted gas from a nearby Bunsen burner and the current decreased rapidly to near zero. Although I had hoped it might work, I was really surprised when it did. I have had this feeling of elation a few times since then .... After my new electrode worked, I measured the Po2 in everything I could find: blood, plasma, urine, coke, beer, honey, oil, liver homogenate, acids, alkali, etc.
METHODS FOR MEASURING TISSUE OXYGENATION TRANSCUTANEOUS Po 2 SENSOR
The development of the Clark Po 2 electrode stimulated further interest in the measurement of tissue oxygenation. In 1972, Huch and colleagues2I and Eberhard and associatesi 2 reported on the use of heated Clark electrodes as a practical method to monitor skin surface (transcutaneous) Po 2. These instruments were first applied clinically in neonates and subsequently in adults. In the former, transcutaneous 0 2 tensions (Ptco2) were found to approximate Pao 2 values closely. However, it was belatedly realized that this principle was not valid in infants with circulatory problems. 48, 70 Furthermore, when used in adults, the Ptco2 value was found to underestimate Pao 2 values variably. 4 • re, 40 • 52 , 54 • 57 Circulatory compromise caused even greater discrepancies between the Ptco 2 and Pao2 . Tremper and coworkers68 showed that when blood flow was adequate, Ptco2 values tracked Pao2 , but when blood flow was compromised, Ptco2 values tracked flow; throughout both of these conditions, Ptco2 reflected local 0 2 delivery. The fact that Ptco2 values reflect local 0 2 delivery has led to its use in monitoring systemic, as well as regional, perfusion. CoNJUNCTIVAL Po2 SENSoR
Measurement of palpebral conjunctival Po2 (Pcjo2) was first reported by Kwan and Fatt39 in 1970. Unlike Ptco2 monitoring, this method of measuring tissue perfusion and oxygenation does not require tissue heating because the conjunctiva lacks the stratum corneum layer and has a capillary bed only four to six cell layers beneath its mucous membrane surface. The Pcjo2 sensor system also measures tissue temperature. More importantly, the conjunctival capillary bed is perfused by the same arterial circulation as the brain, namely the internal carotid artery. This method may be applied in carotid arterial surgery and neurosurgery, as well as in the intensive care setting.29, eo ORGAN SURFACE OXIMETRY
Recently, Kram and colleagues 3I. 33 reported on the use of a nonheated, miniature Clark electrode to measure organ surface Po 2 in experimental and clinical conditions. When used intraoperatively, this method
NONINVASIVE TISSUE OXYGEN MONITORING
1007
allows noninvasive assessment of organ perfusion and viability in cases of suspected tissue ischemia, for example, cerebral and intestinal vascular disease and testicular torsion. CLINICAL APPLICATIONS CARDIOPULMONARY RESUSCITATION
Nowhere in the management of acute illness is the maintenance of tissue perfusion and oxygenation more important than during cardiopulmonary resuscitation (CPR). Monitoring of Ptco 2 has been shown to be extremely helpful in assessing the adequacy of tissue 0 2 transport during CPR. 44 • 65, 67 Although chest Ptco2 values reflect Pao2 during respiratory failure, they reflect cardiac output during cardiac failure and 0 2 delivery during both conditions (Fig. 1). Furthermore, chest Ptco 2 values below those of the simultaneously measured mixed venous Po2 tension were found to predict cardiac arrest by an average of 43 ± 28 minutes in patients in a preterminal stage of illness who were monitored continuously before cardiac decompensation and circulatory collapse. 67 Conjunctival 0 2 monitoring has also been used noninvasively to monitor tissue perfusion and oxygenation during CPR. 1• 2 Because the conjunctival Po 2 sensor does not use tissue heating, valid measurements are obtained more rapidly after placement than with the Ptco 2 sensor, which requires 10 to 15 minutes for stabilization. This feature has obvious advantages in the acute cardiopulmonary arrest situation. ACUTE TRAUMA
Transcutaneous 0 2 monitoring has been shown to be useful in the management of acutely ill traumatized patients in the emergency room setting. Depressed Ptco2 values obtained from severely ill emergency room patients were found to correlate well with the need for aggressive resuscitation; patients with an initial chest Ptco 2 value of less than 60 torr were subsequently found to have more difficult clinical courses and poorer outcomes than those with significantly greater Ptco2 values. 71 A chest Ptco2 value of less than 60 torr implies a deficit in either arterial oxygenation or local perfusion; these can be differentiated by an arterial blood gas analysis. Thus, Ptco2 monitoring may be a valuable method for triaging and evaluating emergency department patients in a major trauma center. Sensors for monitoring Ptco 2 have also been used to aid in the diagnosis and management of major peripheral arterial injury in patients with limb trauma. 32, 36 By placing Ptco2 sensors bilaterally on both the injured and the uninjured (contralateral) limb, Kram and Shoemaker were able to develop a transcutaneous 0 2 Bilateral Perfusion Index (BPI) to quantify circulatory deficits in comparison with the uninjured limb (Fig. 2).32 Thus BPI= Injured limb Ptco2 Uninjured limb Ptco 2
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Figure l. Sequential transcutaneous (PtcoJ and arterial (Pao 2) oxygen tensions (upper section), Ptco 2 and cardiac output (middle section), and Ptco 2 and 0 2 delivery (lower section) in a patient during respiratory failure, cardiac decompensation, cardiac arrest, and cardiopulmonary resuscitation. Note that Ptco2 values follow Pao2 during respiratory failure (hypoxia), cardiac output during cardiac decompensation (low flow), and 0 2 delivery during both conditions. (From Tremper, K. K., Waxman, K., Bowman, R., et al.: Continuous transcutaneous oxygen monitoring during respiratory failure, cardiac decompensation, cardiac arrest, and CPR. Crit. Care Med., 8:377-381, 1980; with permission.)
Use of the BPI allows adequate assessment of relative limb perfusion, regardless of differences in arterial 0 2 content and peripheral vasoconstriction between patients. Monitoring of Ptco2 may prove to have certain advantages over conventional Doppler ultrasonographic techniques in the diagnosis of major peripheral arterial trauma (Fig. 3). This advantage is largely because the pulse wave may be transmitted through short obstructions, such as intimal flaps; via collateral vessels; and through areas of fresh, soft clot. 49 Regional Ptc02 tension, on the other hand, is affected when there is reduced flow secondary to arterial narrowing, bleeding, occlusion from thrombosis, in-
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Uninjured Limb Ptco2 Figure 2. Transcutaneous oxygen (Ptco2) values of the injured limb versus Ptco 2 values of the uninjured (contralateral) limb in 33 suspected major peripheral arterial injuries. The Bilateral Perfusion Index (BPI) is the ratio of the injured limb Ptco2 to the uninjured limb Ptc02 • The diagonal line represents a BPI of 0.90. (From Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:776-780, 1984; with permission.)
tramural dissection, or external compression. In addition, limb Ptco 2 monitoring in patients with concomitant peripheral nerve injuries alk>ws evaluation of tissue perfusion when neurologic function cannot be used as a measure of limb anoxia. 32 Continuous limb Ptco2 monitoring during surgical operations for peripheral arterial trauma allows continuous, real-time assessment of limb perfusion, as well as immediate evidence of a successful surgical result (Fig. 4). 36 Nevertheless, the absence of abnormalities in measured limb Ptco2 values should not interdict arteriography if it is indicated to rule out arterial injury. In addition, low values may also be seen in patients with peripheral vascular disease, significant prior surgery, and certain compartment syndromes.
INTENSIVE CARE
Critically ill patients in the intensive care unit very often suffer from disturbances in tissue perfusion. These episodes of inadequate tissue 0 2 transport may be sudden, unheralded by symptoms, and allowed to pro-
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DIAGNOSTIC FINDINGS IN 36 SUSPECTED MAJOR PERIPHERAL ARTERIAL INJURIES '% DIAGNOSTIC YIELD HR)100 SYSTOLIC BP(100 PALLOR SIGNIFICANT HEMATOMA BRUIT COOLNESS NEUROLOGIC DEFICIT PULSE DEFICIT
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Figure 3. Diagnostic findings and positive diagnostic yield (percentage) in 36 suspected major peripheral arterial injuries. Transcutaneous oxygen monitoring was performed in 33 of the suspected injuries. Note that a transcutaneous 0 2 Bilateral Perfusion Index (BPI) of less than 0. 90 was associated with an 80 per cent positive diagnostic yield. (From Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:77&-780, 1984; with permission.)
gress unnoticed. Variables conventionally used to monitor cardiopulmonary performance include cardiac and respiratory rate, arterial and central venous blood pressures, temperature, urinary output, and color of the extremities; although useful, these parameters provide only a qualitative assessment of tissue perfusion. Monitoring of Ptco 2 has proved helpful in detecting unexpected cardiac or respiratory decompensations in critically ill patients. 52, 53, 57, 65, 66, 67 In a published series 66 of 106 critically ill adults monitored with the Ptco2 sensor and intermittent conventional invasive hemodynamic and 0 2 transport variables, Ptco 2 values in patients with low-flow shock responded quickly to blood flow changes with a 95 per cent response time of approximately 1 minute; the patients not in shock responded to changes in inspired 0 2 concentration (F10 2) with Ptco2 changes in about 2 minutes.
lOll
NONINVASIVE TISSUE OXYGEN MONITORING
Noninvasive conjunctival and Ptco 2 monitors have increased the safety and simplicity of managing patients on mechanical ventilation and during extubation. 30, 45, 57, 63, 66, 69, 74 In a study conducted on mechanically ventilated patients immediately before extubation, Ptco 2 monitoring was helpful in predicting which patients would eventually require reintubation. 63 This is largely because measured Ptco 2 values depend on factors that include the P50 , hemoglobin concentration, Pao 2 , and cardiac output; patients who require reintubation usually have conditions present that reduce one or more of these variables. Continuous Ptco 2 monitoring has also been helpful in estimating the patient's condition during the different stages of ventilator weaning. 63 Because polarographic 0 2 sensors applied to tissue surfaces will track local 0 2 delivery during hypoxic and low-flow conditions, they are especially useful as continuous monitors during therapeutic interventions that may cause abrupt changes in Pao 2 or cardiac output-for example, endotracheal tube suctioning or positive end-expiratory pressure (PEEP) therapy. During PEEP therapy, a sudden drop in measured transcutaneous or conjunctival 0 2 tension may be secondary to a life-threatening complication, such as hypoxemia, low cardiac output, or pneumothorax. Continuous
1.0
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Thrombectomy End of and Embolectomy Operation Coml)leted Postoperative Day 1
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Figure 4. Perioperative transcutaneous (Ptco 2) and arterial (Pao 2) oxygen tensions in a patient with unilateral occlusion of the external iliac and popliteal arteries secondary to blunt trauma. Note that the injured limb Ptco 2 correlated best with uninjured (contralateral) limb Ptco2 values after restoration of normal blood flow to the leg (r = 0. 97). (From Kram, H. B., Wright, J., Shoemaker, W. C., et a!.: Perioperative transcutaneous 0 2 monitoring in the management of major peripheral arterial trauma. J. Trauma, 24:443-445, 1984; with permission.)
1012
HARRY
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KRAM
conjunctival 0 2 monitoring during PEEP optimization in a hemodynamically stable patient with severe adult respiratory distress syndrome (ARDS) is illustrated in Figure 5.
ARTERIAL OCCLUSIVE DISEASE
Noninvasive tissue 0 2 monitoring techniques have been evaluated extensively as adjuncts in the diagnosis and management of peripheral arterial occlusive disease (PAOD). Sensors for monitoring Ptco 2 appear to be especially useful in the management of patients with atherosclerotic disease of the lower extremity. The Ptco2 sensor may be used to assess limb perfusion during the preoperative, intraoperative and postoperative period, as well as to help predict the success of wound healing after amputation. Measured limb Ptco 2 values usually show appreciable differences when patients with symptomatic PAOD are compared with healthy, control subjects. 7• 10• 14• 20· 28 · 35• 42 • 43 • 47 • 73 However, the overlap is sufficiently large that there is less than complete confidence in the diagnostic accuracy. Methods to improve diagnostic sensitivity and specificity include 0 2 inhalation, 47 positional changes, 18• 64 exercise testing, 20. 47 temporary cuff occlusion, 7, 14, 28,35 and comparing limb Ptco 2 values with those obtained on other body surface areas. 18 · 20• 32 • 34 • 36• 47 Of these, only exercise testing and temporary cuff occlusion (ischemia) significantly increase local 0 2 demand. However, exercise testing causes muscular contractions that may hinder local blood flow and thereby markedly reduce the Ptco 2 reading. Moreover, when subjected to treadmill testing, patients with associated coronary atherosclerosis have a low but definite risk of myocardial infarction. 22
PEEP
em H20
20 15
150 10 100 5
50 0
0 0
20
40
60
80
120 100 minutes
140
TIME Figure 5. Sequential conjunctival, arterial, and mixed venous oxygen tensions during optimization of PEEP therapy in a hemodynamically stable patient with severe adult respiratory distress syndrome. Note that when cardiac output is normal, as in this patient, conjunctival Po2 values track arterial Po2 values. (From Kram, H. B., Chen, B., Lee, T. S., et al.: Conjunctival oxygen monitoring in postoperative respiratory failure and shock. Int. J. Clin. Monit. Comput., 1:165, 1984; with permission.)
1013
NONINVASIVE TISSUE OXYGEN MONITORING
Increasing limb 0 2 demand is an important diagnostic maneuver because many patients, particularly those with intermittent claudication, manifest tissue hypoxia only when limb 0 2 demand is increased. The use of 0 2 inhalation or limb elevation results in significant changes in limb 0 2 supply but does not greatly increase 0 2 demand. Patients distinguishable by the latter tests already have severe disease with minimal or no circulatory reserve and may not be candidates for vascular reconstruction. The transcutaneous 0 2 recovery half-time (TORT), defined as the time required to recover half of the decrease in the limb-to-chest Ptco 2 ratio caused by temporary limb ischemia induced by cuff occlusion, was found to (I) increase greatly the diagnostic accuracy of Ptco 2 measurements to differentiate normal limbs versus those with PAOD and (2) determine successful versus unsuccessful results of surgical therapy (Figs. 6 and 7). 28 When measured on the dorsum of the foot, TORT values correlated well with the severity of symptoms (Fig. 8)35; this permitted quantitation of functional disability and comparison with the patient's symptoms. Furthermore, TORT can be performed simultaneously with measurement of the
CALF
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successful therapy
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/
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' T~~t~i~j
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.
-
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/
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-
unsuccessful therapy
2
3
4
5
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Figure 6. Effect of temporary limb ischemia for 4 minutes by a standard pneumatic blood pressure cuff on calf and foot transcutaneous oxygen (PtcoJ tensions expressed as a percentage of the simultaneously recorded chest Ptco2 • This is shown for four groups: normal volunteer subjects, patients with symptomatic peripheral vascular disease (PVD), patients who had successful operative therapy, and patients who had unsuccessful therapy. Values are represented as mean ± SEM. Note that the postocclusive Ptco2 recovery is significantly delayed in limbs with symptomatic PVD or following unsuccessful therapy. (From Kram, H. B., Appel, P. L., White, R. A., et al.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg., 1:628, 1984; with permission.)
1014
HARRY
B. KRAM
TORT I P
_j
I
Calf
P
I P
_j Group
I
Group II
0
normal
~ peripheral vascular disease
Group
ma 0
successful therapy
Group
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unsuccessful therapy
l
P
_j
I
Foot
P
_j
l 0
3 4 2 TIME (minutes)
Figure 7. Postocclusive transcutaneous oxygen recovery half-time (TORT) of the calf and foot in normal volunteer subjects, patients with symptomatic peripheral vascular disease (PVD), patients who had successful operative therapy, and patients who had unsuccessful therapy. The TORT is the time required to recover half of the decrease in the limb Ptco.-to-chest Ptco2 ratio caused by temporary limb ischemia induced by cuff occlusion. Values are mean ± SEM. Note that TORT values of limbs with successful operative therapy were similar to those of normal subjects. (From Kram, H. B., Appel, P. L., White, R. A., et a!.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg., 1:628, 1984; with permission.)
5
toe pulse reappearance time, an already well-accepted, noninvasive vascular diagnostic modality; this practice reduces the additional time and monitoring personnel needed. Monitoring of Ptco 2 has also been used to help predict wound healing success after amputation. A Ptco 2 value of greater than 35 to 45 torr measured on the anterior skin surface of the pretibial area has been correlated with successful wound healing after below-knee amputations, although there is significant variability among published reports. 6, 14, 24, 42, 43, 51, 72, 73 This variability may be due to differences in Pao 2 values, sensor location, and monitoring technique. Continuous limb Ptco 2 monitoring during vascular operations is informative because it provides immediate evidence of improved blood flow in the lower extremity, thereby demonstrating a satisfactory operative result before the termination of surgery. 34 · 36 Conjunctival 0 2 monitoring during carotid arterial surgery has recently been shown to be beneficial in that conjunctival Po2 values were reduced in association with systemic hypotension, carotid artery manipulation, carotid artery clamping, and obstruction and clamping of the carotid shunt (Fig. 9).29, oo Because the conjunctival Po 2 sensor monitors tissue oxygenation in a capillary bed perfused by the internal carotid artery, it may prove valuable in refining the criteria for operative intervention in patients with asymptomatic carotid bruits, as well as in indicating the need for prompt intervention in patients with deteriorating perfusion before the onset of life-threatening cerebral ischemia.
1015
NONINVASIVE TISSUE OXYGEN MONITORING
TORT
l plOS
D Normal r:J Asymptomatic
limb
~:'?a Intermittent claudication !!§Rest pain
l~ p
J 0
2
3
4
5
Time {minutes) Figure 8. Postocclusive transcutaneous oxygen recovery half-time (TORT) values, measured on the dorsum of the foot, in 90 limbs classified according to symptoms. Values are mean ± SEM. Note that foot TORT values correlated well with the severity of symptoms.
PLASTIC AND RECONSTRUCTIVE SURGERY
Monitoring of Ptco2 has been gaining increasing popularity in plastic and reconstructive surgery. Because Ptco 2 values reflect local tissue perfusion, they may be used to assess continuously the circulatory status of skin flaps, 3• 25. 27, 58 skin grafts, 26 replanted fingers or hands, 41 • 62 and free tissue transfers. 62 A provocative test involving the skin flap Ptco 2 response to increased F10 2 has potential use for qualitatively judging tissue perfusion and viability. 3, 25-27, 58, 62 A lack of increase in Ptco 2 after a substantial increase in the patient's FI0 2 suggests circulatory compromise of the tissue being monitored. Further investigations involving the use of this maneuver in conjunction with other noninvasive tissue 0 2 monitoring techniques may prove to be useful. Skin flap Ptco 2 values may also be compared with simultaneously measured chest Ptco 2 values to assess more accurately relative flap perfusion in the postoperative period (Fig. 10). 58 Use of this method may lead to the earlier detection of tissue ischemia, which may threaten skin flap survival, thereby allowing timely therapeutic maneuvers to improve flap circulation.
1016
torr
300
250
HARRY
Carotid Endarterectomy
Control Neck Dissection
KRAM
Wound Closed
•
•
I
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~
Cuotid clamped
•
l
200
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Shunt
\ •\ • •\ ./ 1
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Shunt
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\
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•
50
I 0
10
I 20
I 30
I 40
50
I 60
70
TIME (minutes.) Figure 9. Intraoperative conjunctival Po, monitoring in a hemodynamically stable patient undergoing carotid endarterectomy. Note that the conjunctival Po2 decreased with carotid artery manipulation and clamping. The Flo, was kept constant at 1.0.
INTRAOPERATIVE MONITORING
The value of noninvasive tissue 0 2 monitoring has been examined in virtually all types of surgical operations. Continuous Ptco 2 monitoring has been used to assess the adequacy of 0 2 transport during general, 44 • 46· 50• 55. 66 thoracic, 15. 19• 46 cardiac, 19· 55 • 59 and vascular surgery, 34 · 36 neurosurgery, 5o and oral surgery. 5, 37, 38 In a series 46 of high-risk surgical patients monitored intraoperatively with Ptco 2 sensors, decreases in cardiac output, 0 2 delivery, and 0 2 consumption were the earliest warning signs of impending circulatory deterioration; these hemodynamic and bulk 0 2 transport variables were paralleled by decreases in measured Ptco 2 values. In this series, the heart rate and mean arterial pressures had highly variable and frequent changes unrelated to alterations in blood flow and 0 2 transport. Monitoring of Ptco 2 may also be beneficial immediately after surgery when frequent changes in cardiopulmonary status are common secondary to hypothermia, extubation, and recovery from anesthesia. During the period after cardiopulmonary bypass in cardiac surgery, hemodynamic instability may require pharmacologic support; low chest Ptco 2 values related
NONINVASIVE TISSUE OXYGEN MONITORING
1017
to Pao2 during this period were correlated with the judgment of the anesthesiologist regarding the need for pharmacologic support to improve cardiorespiratory function. 59 Severe hypoventilation may occur during procedures that involve the airway or thorax; the efficacy of Ptco2 monitoring to detect these hypoxic periods has been well documented.17, 19, 44, 50 During vascular reconstruction, Ptco2 sensors applied to the extremity provide continuous measurements that reflect the adequacy of limb 0 2 transport. 34• 36 Noninvasive conjunctival 0 2 monitoring may similarly be employed to assess carotid 0 2 transport during carotid arterial surgery. 29· 60 Conjunctival 0 2 monitoring during surgery may also be used as an early warning device of sudden compromise in systemic 0 2 delivery (Fig. ll). Although many clinicians have expressed concern regarding the effects of inhalational anesthesia on values obtained from tissue Po2 sensors incorporating a membrane-covered polarographic electrode, these effects do not appear to limit the clinical utility or efficacy of the sensors.ll, 16, 50, 56
ORGAN SURFACE
Po2 MONITORING
Recently, a miniature Po2 sensor consisting of a Clark-type polarographic electrode with a platinum cathode and polypropylene oxygen-
•-control a-flop
10
o~--~~--~~--~~--~~--~----~----~~~~~·----~·
~I
2
1
12
29
1 & 2 ~ hours postoperot1ve Figure 10. Postoperative transcutaneous oxygen (TcPo2) tensions measured on a vascularized latissimus dorsi musculocutaneous flap and on the chest (control) in a patient who underwent pelvic reconstruction for carcinoma of the vulva. Note the decrease in flap TcPo 2 on the seventh postoperative day; a significant wound infection became clinically apparent 2 days later. Adequate drainage and appropriate selection of systemic antibiotics resulted in eventual total survival of the flap, which was reflected by recovery of the TcPo2 tension. (From Serafin, D., Lesesne, C. B., Mullen, R. Y., et al.: Transcutaneous Po, monitoring for assessing viability and predicting survival of skin flaps: Experimental and clinical correlations. J. Microsurg., 2:165-178, 1981; with permission.)
1018
HARRY
B.
KRAM
ANESTHESIA INDUCTION torr
mmHg
300 000\ 250
200 150
100
\{Y•~'/ohyc/• \ \ I1 I'0
\
/\
1 •
.
o-:-o
V,;!j0
1100
o_..
o
.]150
o
'"
0
I
Figure 11. Conjunctival oxygen (Pcjo2) tension and systolic blood pressure (BP) in a patient who suffered abrupt hypotension during the induction of general anesthesia. Note the rapid drop in Pcjo2 values during the hypotensive periods. The Flo 2 was 1.0.
•
50 0
5
10
15
20
25
TIME (minutes)
permeable membrane was used to measure "noninvasively" organ surface 0 2 tension in experimental animals. 31 The miniature Po 2 sensor is diagrammatically illustrated in Figure 12. Like transcutaneous and conjunctival Po2 values, measured organ surface 0 2 tensions track Pao 2 during hypoxia
Figure 12. Diagram of the miniature polarographic oxygen sensor used to measure organ surface Po2 • (1 =platinum cathode; 2 =thermistor; 3 =silver-silver chloride anode; 4 = polypropylene membrane; 5 =oxygen electrode; 6 =nylon mesh spacer; 7 =snap-on ring; 8 = polymethylmethacrylate plate; 9=cable; 10=connector.) (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
NONINVASIVE TISSUE OXYGEN MONITORING Control HyperOIUO
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Figure 13. A, Conjunctival and organ surface Po2 tensions and sequential hemodynamic and oxygen transport variables during normoxia, hyperoxia, and hypoxia in an anesthetized dog. Note that conjunctival and organ surface Po2 tensions track Pao2 during hyperoxia and hypoxia, provided that blood flow is adequate. B, Conjunctival and organ surface Po2 tensions and sequential hemodynamic and oxygen transport variables during hemorrhagic shock and resuscitation in an anesthetized dog. Note that conjunctival and organ surface Po2 tensions tracked blood flow (cardiac output) during the low flow state; the Po2 remained relatively stable.
and local blood flow during shock (Fig. 13), reflecting tissue 0 2 delivery during both conditions. The potential experimental uses for this new method include many areas of research. The miniature Po 2 sensor has also been used intraoperatively in patients to aid the surgeon in the determination of tissue perfusion and viability in suspected organ ischemia (Fig. 14) and during certain procedures, 31 · 33 for example, clipping of cerebral arterial aneurysms and
Figure 14. Intestinal surface Po2 measured using the miniature oxygen sensor in a patient with suspected gangrenous bowel. (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
1020
HARRY
B.
KRAM
HEPATIC SURFACE OXYGEN TENSION
~~JAL
torr 250iCONTROL
ARTERIAL 225
AFTER I PORTACAVAL SI-IJNT ~
PORTAL VEIN CLAMPED
MPED
.
HEPATIC ARTERY CLAMPED
/'•""'""'
-·-·-·--·-.__,....-
··-·-·-·-·--
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z
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z
~
75
~
50
1---.. MIXED VENOUS
25
0 I 0
I •-'
I
4
8
,,..
minutes
I
160
TIME
Figure 15. Sequential hepatic surface, arterial, and mixed venous oxygen tensions are shown in a hemodynamically stable patient during performance of an end-to-side portacaval shunt. (From Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984; with permission.)
TESTICULAR SURFACE OXYGEN TENSION DURING TORSION 20
0 I
Control TORSION
15
MINUTES
Figure 16. Sequential testicular surface oxygen tension Pso2 values during varying degrees of unilateral torsion. Values are mean ± SD.
NONINVASIVE TISSUE OXYGEN MONITORING
1021
portacaval shunting (Fig. 15). Measurements were easily obtained on the surfaces of the brain, liver, kidney, gallbladder, small intestine, colon, and testicle (Fig. 16) in experimental and clinical conditions.
CONCLUSION Noninvasive tissue 0 2 monitoring using polarographic electrodes is a valuable method for assessing tissue perfusion and oxygenation in surgical and critically ill patients. The values obtained from electrodes applied to tissue surfaces are dependent upon both arterial 0 2 content and blood flow and reflect the balance between local 0 2 supply and demand. These sensors provide a unique means to assess systemic, regional, and organ surface 0 2 transport in clinical and experimental conditions.
REFERENCES l. Abraham, E., and Ehrlich, H.: Conjunctival and transcutaneous oxygen monitoring during resuscitation. Ann. Emerg. Med., 12:287, 1984. 2. Abraham, E., Smith, M., and Silver, L.: Conjunctival and transcutaneous oxygen moni-
toring during cardiac arrest and cardiopulmonary resuscitation. Crit. Care Med., 12:419, 1984. 3. Achauer, B. M., Black, K. S., and Litke, D. K.: Transcutaneous Po2 in flaps: A new method of survival protection. Plast. Reconstr. Surg., 65:738, 1980. 4. Armstrong, J. R., Kreps, T. W., and Conway, W. A.: The non-value of monitoring transcutaneous oxygen tension in patients with chronic renal failure (abstract). Crit. Care Med., 9:270, 1981. 5. Beech, A. D., and Lyttle, J. J.: Continuous transcutaneous oxygen tension monitoring during ultralight general anesthesia for oral surgery. J. Oral MaxillofilC. Surg., 40:559, 1982. 6. Burgess, M. E., Watsen, F. A., Wyss, C. R., eta!.: Segmental transcutaneous measurements of Po2 in patients requiring below-the-knee amputation for peripheral vascular insufficiency. J. Bone Joint Surg., 64:378, 1982. 7. Cina, C., Katsamouris, A., Megerman, J., eta!.: Utility of transcutaneous oxygen tension measurements in peripheral arterial occlusive disease. J. Vase. Surg., 2:362, 1984. 8. Clark, L. C., Jr.: Measurement of oxygen tension: A historical perspective. Crit. Care Med., 9:690, 1981. 9. Clark, L. C., Jr.: Monitor and control of blood and tissue oxygen tensions. Trans. Am. Soc. Artif. Intern. Organs, 2:41, 1956. 10. Clyne, C. A. C., Ryan, J., Webster, J. H. H., et a!.: Oxygen tension of the skin of ischemic legs. Am. J. Surg., 143:315, 1982. ll. Eberhard, P., and Mindt, W.: Interference of anesthetic gases at skin surface sensors for oxygen and carbon dioxide. Crit. Care Med., 9:717, 1981. 12. Eberhard, P., Mindt, W., and Hammacher, K.: Perkutane Messing des Sauerstoff partaldnuckes: Methodik und Anwendungen. Stuttgart, Proc. Medizin-Technik, May 16, 1972. 13. Fink, S., Ray, C. W., McCartney, S., eta!.: Oxygen transport and utilization in hyperoxia and hypoxia. Crit. Care Med., 12:943, 1984. 14. Franzeck, V. K., Talke, P., Bernstein, E. T., eta!.: Transcutaneous Po2 measurements in health and peripheral arterial occlusive disease. Surgery, 91:156, 1982. 15. Gothgen, I., Degn, H., Jacobsen, E., et a!.: Transcutaneous oxygen measurement during thoracic anaesthesia. Acta Anaesthesiol. Scand., 24:491, 1980. 16. Gothgen, I., and Jacobsen, E.: Transcutaneous oxygen tension measurements. I. Age, variation and reproducibility. II. The influence of halothane and hypotension. Acta Anaesthesiol. Scand., 67[Suppl.]:66, 1978.
1022
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KRAM
17. Hamik, E., Kukzycki, L., and Gomes, M. N.: Transcutaneous oxygen monitoring during bronchoscopy and washout for cystic fibrosis. Anesth. Analg. (Cleve.), 62:357, 1983. 18. Hauser, C. J., Appel, P., and Shoemaker, W. C. : Pathophysiologic classification of peripheral vascular disease by positional changes in regional transcutaneous Po2 • Surgery, 95:689, 1984. 19. Hauser, C. J., and Harley, D. P.: Transcutaneous gas tension monitoring in the management of intraoperative apnea. Crit. Care Med., 11:830, 1983. 20. Hauser, C. J., and Shoemaker, W. C.: Use of a transcutaneous Po2 regional perfusion index to quantify tissue perfusion in peripheral vascular disease. Ann. Surg., 197:337, 1983. 21. Huch, A., Huch, R., Menzer, K., et a!.: Eine Schuelle, behizte proberlachenelektrode zur kontinuier lichen iiberwache ung des Po 2 beim Menschen. Elektrodenautbau undeigen schaften. Stuttgart, Proc. Medizin-Technik, May 16, 1972. 22. Hummel, B. W., Hummel, B. A., Mowbry, A., eta!.: Reactive hyperemia vs. treadmill exercise testing in arterial disease. Arch. Surg., 113:95, 1979. 23. Hutchinson, D. C. S., Rocca, G., and Honeybourne, D.: Estimation of arterial oxygen tension in adult subjects using a transcutaneous electrode. Thorax, 36:473, 1981. 24. Katsamouris, A., Brewster, D. C., Megerman, J., eta!.: Transcutaneous oxygen tension in selection of amputation level. Am. J. Surg., 147:510, 1984. 25. Keller, H. P., and Klaue, P.: Objective control of pedule flaps with transcutaneous Po 2 measurements (abstract). Eur. Soc. Surg. Res., 13:77, 1978. 26. Keller, H. P., Klaue, P., and Lubbers, D. W.: Transcutaneous Po2 measurements for evaluating the oxygen supply of skin allo- and autografts. Eur. Surg. Res., 10:272, 1978. 27. Knote, V. G., and Bohmert, H.: Zur Bestimmung der Uberlebensfahigkeit Nekrosegefahrdeter Hautareale: Mittele transkutaner polarographischen Sauererstoffdruck-messung. Fortschr. Med., 95:640, 1977. 28. Kram, H. B., Appel, P. L., White, R. A., et a!.: Assessment of peripheral vascular disease by postocclusive transcutaneous oxygen recovery time. J. Vase. Surg. 1:628, 1984. 29. Kram, H. B., Bratanow, N., White, R. A., eta!.: Conjunctival and transcutaneous oxygen monitoring during carotid arterial surgery. (submitted) 30. Kram, H. B., Chen, B., Lee, T. S., et a!.: Conjunctival oxygen monitoring in postoperative respiratory failure and shock. Int. J. Clin. Manit. Comput. 1:165, 1984. 31. Kram, H. B., Fukunaga, A., Chen, B., eta!.: Method for measuring organ surface oxygen tension in experimental and clinical conditions (abstract). Crit. Care Med., 12:298, 1984. 32. Kram, H. B., and Shoemaker, W. C.: Diagnosis of major peripheral arterial trauma by transcutaneous oxygen monitoring. Am. J. Surg., 147:776, 1984. 33. Kram, H. B., and Shoemaker, W. C.: Method for intraoperative assessment of organ perfusion and viability using a miniature oxygen sensor. Am. J. Surg., 148:404, 1984. 34. Kram, H. B., and Shoemaker, W. C.: Use of transcutaneous 0 2 monitoring in the intraoperative management of severe peripheral vascular disease. Crit. Care Med., 11:482, 1983. 35. Kram, H. B., Tabrisky, J., eta!.: Transcutaneous oxygen recovery and toe pulse reappearance time to assess peripheral vascular disease. Circulation. In press. 36. Kram, H. B., Wright, J., Shoemaker, W. C., eta!.: Perioperative transcutaneous 0 2 monitoring in the management of major peripheral trauma. J. Trauma, 24:443, 1984. 37. Kraut, R. A.: Transcutaneous oxygen monitoring of patients undergoing surgical removal of wisdom teeth. Anesth. Prog., 29:70-1, 1982. 38. Kraut, R. A.: Transcutaneous oxygen monitoring of patients undergoing surgical removal of wisdom teeth utilizing general anesthesia. Anesth. Prog., 29:132, 1982. 39. Kwan, M., and Fatt, I.: A noninvasive method of continuous arterial oxygen tension estimation from measured palpebral conjunctival oxygen tension. Anesthesiology, 35:309, 1970. 40. Lofgren, 0.: Transcutaneous oxygen measurement in adult intensive care. Acta Anaesthesia!. Scand., 23:534, 1979. 41. Matsen, F. A., Bach, A. W., Wyss, C. R., eta!.: Transcutaneous Po 2 : A potential monitor of the status of replanted limb parts. Plast. Reconstr. Surg., 65:732, 1980. 42. Matsen, F. A., Wyss, C. R., Pedegana, L. R., et a!.: Transcutaneous oxygen tension measurement in peripheral vascular disease. Surg. Gynecol. Obstet., 150:525, 1980. 43. Mustapha, N. M., Redhead, R. G., Jain, S. K., eta!.: Transcutaneous partial oxygen
I'
~
NONINVASIVE TISSUE OXYGEN MONITORING
44. 45. 46.
t
47. 48.
II
49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60.
61. 62. 63.
64. 65. 66.
67.
68. 69.
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