Transesophageal echocardiography and transcutaneous O2 and CO2 monitoring for detection of venous air embolism

The sensitivities of current monitoring methods for detection of air embolism were compared in eight anesthetized dogs. Air was infused at controlled rates of 0.001 and 0.005 ml X kg-1 X min-1 for 1 min; 0.01, 0.05, 0.1, 0.2, and 0.4 ml X kg-1 X min-1 for 6 min; and 5 ml X kg-1 bolus injection. Based on the mean quantity of air infused to elicit a positive response, the monitors could be placed into three significantly different sensitivity groups. Transesophageal echocardiography (TEE) and precordial Doppler ultrasound were the most sensitive monitoring methods detecting 0.19 and 0.24 ml X kg-1 of air, respectively. TEE detected air during six infusions in which the Doppler failed to do so. The next most sensitive group of monitoring methods included pulmonary artery pressure (PAP), end-tidal CO2 (PETCO2), arterial oxygen tension (PaO2), and transcutaneous oxygen tension (PtcO2). The mean quantity of air infused to elicit a positive response in this group of monitors ranged from 0.61 to 0.76 ml X kg-1. The response of PtcO2, PaO2, PETCO2, and PAP equally reflected the quantity of air infused. The least-sensitive group of methods included arterial and transcutaneous carbon dioxide tension and systemic arterial blood pressure. These data indicate that TEE is more sensitive than Doppler ultrasound and that PAP, PETCO2, and PtcO2 are equally sensitive in detecting venous air embolism in the dog.     

Dialysis-induced hypoxemia. Continuous monitoring of blood oxygen and carbon dioxide tension in children

We report our experience with continuous, transcutaneous monitoring of capillary oxygen and carbon dioxide tension (PtcO2, PTlcCO2 ) during the entire length of hemodialysis treatment in 8 pediatric patients. The relative changes in PtcO2 and PtcCO2 observed with this method were in accordance with those reported in the literature, obtained with frequent arterial blood sampling. There was a temporary fall of PtcO2, averaging 26.2% after 2h of dialysis, with a concomitant rise of PtcCO2 of 9.9%. The noninvasive, transcutaneous measurement of PtcO2 and PtcCO2 is a reliable and valuable adjunct for the monitoring of the dialysis patient who is prone to develop hypoxemia. It is particularly useful in the very young.     

Value of transcutaneous blood gas monitoring in fiberoptic bronchoscopy in intensive care patients

Transcutaneous carbon dioxide and oxygen tensions (PtcCO2 and PtcO2) were monitored in seven critically ill patients under mechanical ventilation during fiberoptic bronchoscopy. In these conditions, both PtcO2 and PaO2 and PtcCO2 and PaCO2 correlated, with correlation coefficients of 0.964 and 0.793 respectively. Fiberoptic bronchoscopy induced an average fall in PtcO2 of 42 +/- 2.57 mmHg and an average increase in PtcCO2 of 12.1 +/- 1.89 mmHg; these two parameters returned quickly to their initial values after the procedure. Holter monitoring showed an arrhythmia in five of the seven patients. Continuous measurement of PtcO2 and PtcCO2 was a safe and reliable method for monitoring mechanically ventilated patients undergoing fiberoptic bronchoscopy.     

Measurement of transcutaneous P±o2, Pco2 and skin blood flow at different probe temperatures using mass spectrometry

Transcutaneously measured partial pressures of oxygen and carbon dioxide (PtcO2, PtcCO2) approximate the corresponding arterial values at a probe temperature of 44 degrees C. The temperature-dependent increase of PtcO2 and PtcCO2 is caused by an increased skin perfusion, a decrease in the mean diffusion path, a change of skin metabolism, a decrease of tissue solubility of oxygen and carbon dioxide and a right shift of the oxygen and carbon dioxide binding curves of blood. Seven healthy volunteer test subjects participated in the study. A transcutaneous probe connected to a mass spectrometer was placed on the earlobe of the test subject. Four measurements of the transcutaneous PO2, PCO2 and skin blood flow (from the washout kinetics of argon) were determined on each test subject. The first measurement was made with a transcutaneous probe temperature of 37 degrees C. The probe temperature was then increased to 44 degrees C before the next determination. Finally, two determinations were made at 37 degrees C, separated by a time interval of 1 h. The PtcO2 and skin blood flow increased when the probe temperature increased from 37 degrees C to 44 degrees C. However, when the probe temperature was decreased again from 44 degrees C to 37 degrees C, the estimated skin blood flow returned to the initial value while the PtcO2 remained unchanged. It required a further 1 h before the PtcO2 returned to the initial value at 37 degrees C. The most likely explanation of the experimental results is that heating of the skin to 44 degrees C causes a reversible decrease in the skin metabolism.     

Intracranial pressure responses during hyperbaric oxygen therapy.

The responses of intracranial pressure (ICP) to hyperbaric oxygen (HBO) therapy and arterial gas pressures were investigated. ICP was measured through a ventricular or spinal drainage catheter in patients with brain tumor or cerebrovascular disease. Changes in ICP, heart rate (HR), arterial blood pressure (ABP), and transcutaneous partial pressure of carbon dioxide (PtcCO2) or oxygen (PtcO2) were recorded continuously during air or 100% O2 breathing at 1 and 2.5 atmospheres absolute (ATA). HR and PtcCO2 decreased and mean ABP was unchanged during HBO inhalation. ICP was reduced at the beginning and tended to increase gradually during HBO inhalation. The change from air to O2 without altering respiratory frequency and volume caused a gradual increase of ICP and PtcCO2 with a transient ICP reduction in an artificially respirated patient. Intentionally reduced respiration to maintain PtcCO2 at the value at 2.5 ATA with air caused the ICP to return to near the value at 2.5 ATA with air even during HBO inhalation. These findings suggest that reduced ICP is initially due to direct cerebral vasoconstriction caused by hyperoxia and is maintained mainly by induced hypocapnia during HBO inhalation. Care is required when giving HBO therapy to patients with a high ICP and/or who are respirated artificially.     

Transcutaneous Monitoring of Blood Gas Tensions in Patients on Intermittent Peritoneal Dialysis

A relative contraindication to intermittent peritoneal dialysis (IPD) is chronic lung disease. To evaluate whether the instillation of 2 L of fluid into the peritoneal cavity affects respiratory function, five IPD patients were studied in the supine position during the first 4 h of a routine IPD session. Blood gas tensions were monitored transcutaneously throughout the study period. At the onset of dialysis, mean transcutaneous blood oxygen tension (PtcO2) was 70.6 +/- 9.1 mm Hg. It decreased to 55 +/- 9.9 mm Hg (22% change from basal values) during the instillation of dialysate. Upon drainage, PtcO2 returned to baseline. This sequence of events repeated itself on subsequent exchanges, although with decreasing decrements of PtcO2 with each consecutive exchange (decrease to 58.6 +/- 7.05, 61 +/- 6.5, 63.8 +/- 5.2 mm Hg corresponding to 16%, 12.7%, and 9.6%, respectively, during the second to fourth exchanges). Transcutaneous blood carbon dioxide tension, PtcCO2, showed a very mild increase during the study (33 +/- 7.1 to 38 +/- 6.0 mm Hg). In two patients, the same study protocol was performed during the last 4 h of an IPD session. In these two patients, there was only a 5% variation of PtcO2 from baseline values. These results suggest that an adaptive response to the hypoxemia induced by dialysate instillation rapidly occurs in IPD patients.     

Outcome prediction by a mathematical model based on noninvasive hemodynamic monitoring

BACKGROUND: The aims are to apply a mathematical search and display model based on noninvasive hemodynamic monitoring, to predict outcome early in a consecutively monitored series of 661 severely injured patients. METHODS: A prospective observational study by a previously designed protocol in a Level I trauma service in a university-run inner city public hospital was conducted. The survival probabilities were calculated at the initial resuscitation on admission and at subsequent intervals during their hospitalization beginning shortly after admission to the emergency department. Cardiac function was evaluated by cardiac output (CI), heart rate (HR), and mean arterial blood pressure (MAP), pulmonary function by pulse oximetry (SapO2), and tissue perfusion function by transcutaneous oxygen indexed to FiO2, (PtcO2/FiO2), and carbon dioxide (PtcCO2) tension. RESULTS: The survival probability (SP) averaged 89 +/- 0.4% for survivors and 75.7 +/- 1.6% (p < 0.001) for nonsurvivors in the first 24-hour period of resuscitation. The CI, MAP, SapO2, PtcO2, and PtcO2/FiO2 were significantly higher in survivors than in nonsurvivors in initial resuscitation, whereas HR and PtcCO2 were higher in nonsurvivors. CONCLUSIONS: During the initial resuscitation period, misclassifications were 102 of 661 or 15%. The SP provided early objective criteria to evaluate hospital outcome and to track changes throughout the hospital course based on a large database of patients with similar clinical-hemodynamic states.     

Transcutaneous carbon dioxide and oxygen measurement in patients undergoing microlaryngosurgery with high frequency jet ventilation

BACKGROUND: High frequency jet ventilation (HFJV) via thin tracheal tube is a convenient method of ventilation in microlaryngosurgery, but the problem of the assessment of oxygen and carbon dioxide status during HFJV is yet to be studied. METHODS: Fifteen patients undergoing microlaryngosurgery under total intravenous anesthesia with HFJV were studied. The combined transcutaneous carbon dioxide (PtcCO2) and oxygen (PtcO2) levels were compared with arterial blood gas values (PaCO2, PaO2). RESULTS: The PtcCO2 values demonstrated a high degree of correlation with PaCO2 before intubation (r = 0.97), during HFJV (r = 0.96), and after anesthesia (r = 0.93). The PaO2 values demonstrated a generally good correlation with PaO2 before intubation (r = 0.78) and during HFJV (r = 0.83), but not after anesthesia (r = 0.54). CONCLUSION: Capnography values are invalid during HFJV, and an arterial catheter is not always indicated and feasible in microlaryngoscopy. The transcutaneous devices provide an effective method for non-invasive monitoring of PaCO2 in situations where continuous and precise control of CO2 levels is desired such as in perioperative period of microlaryngosurgery with HFJV.     

Hyperventilation reduces transcutaneous oxygen tension and skin blood flow

Transcutaneous oxygen tension (PtcO2) is often used to monitor neonates and infants in special care units and the operating room. The transcutaneous index (TCI = PtcO2/arterial oxygen tension [PaO2]) is known to depend both on age and on cardiac index but is assumed to be independent of other physiologic variables. In this study we have shown that TCI also depends upon arterial carbon dioxide tension (PaCO2). Five young pigs were anesthetized and paralyzed and their lungs mechanically ventilated while they were monitored with PtcO2 electrodes and serial arterial blood gas analyses. For a 45 degrees C PtcO2 sensor, the mean TCI during normocapnia was 0.78, whereas during hyperventilation (PaCO2 = 20 mmHg) the mean TCI was reduced 65%, to 0.27. The corresponding TCI values for a 43 degrees C sensor were 0.33 and 0.065, representing an 80% decrease in TCI during hyperventilation. Hypoventilation had little effect upon TCI as long as hypoxemia was avoided. Twelve awake adult volunteers with radial artery cannulas were monitored with PtcO2 sensors at several body sites and two sensor temperatures. For a 44 degrees C sensor on the chest, the mean TCI decreased from 0.77 at normocapnia to 0.60 at a PaCO2 of 17 mmHg, a 22% change. For the same sensor on the foot, TCI decreased from 0.63 to 0.32, a 49% change. For a 42 degrees C sensor under the same conditions, the corresponding TCI decreases were 51 and 64%. Six of the volunteers were also monitored with laser-Doppler skin blood flow probes located on the chest, hand, and foot.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hemodynamic patterns of blunt and penetrating injuries

BACKGROUND: The aims of this prospective observational study were to describe early hemodynamic patterns of blunt and penetrating truncal injury and to evaluate outcomes prediction using noninvasive hemodynamic monitoring with a mathematical model tested against actual in-hospital outcomes. The hypothesis was that traumatic shock is a circulatory disorder that can be monitored by noninvasive hemodynamic parameters that reflect cardiac, pulmonary, and tissue perfusion functions. STUDY DESIGN: The cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), pulse oximetry (SapO(2)), transcutaneous oxygen tension indexed to FiO(2) (PtcO(2)/FiO(2)), and carbon dioxide (PtcCO(2)) tensions were monitored beginning shortly after emergency department admission in 657 emergency patients with severe blunt and penetrating chest, abdominal, and extremity trauma. Of these, 113 patients had associated head injury, and these patients also were analyzed separately. A search and display mathematical model, with a decision support program, was based on continuous online, real-time, noninvasive hemodynamic monitoring. RESULTS: There were similar patterns in the blunt and penetrating injuries; the cardiac index, mean arterial pressure, pulse oximetry, transcutaneous oxygen tension indexed to FiO(2), and survival probability values of the survivors were significantly higher (p < 0.01) than the corresponding values of those who died, although heart rate and carbon dioxide tension were higher in the nonsurvivors during the first 24 hours after their emergency department admission. These patterns occurred more rapidly in patients with penetrating injuries. After initial resuscitation in the emergency department, results were correlated with actual outcomes at hospital discharge and found to be 88% correct. CONCLUSIONS: Early noninvasive hemodynamic monitoring with a computerized information system provided a feasible pattern recognition program for outcomes prediction and therapeutic decision support.     

Perioperative transcutaneous oxygen monitoring in thoracic anaesthesia

Transcutaneous oxygen tension (PtcO2) was measured in 30 patients scheduled for elective pulmonary resection requiring one-lung ventilation during anaesthesia. Simultaneous PtcO2 and arterial oxygen tension (PaO2) measurements were taken preoperatively (preop), intraoperatively during two-lung endotracheal (ET) and one-lung endobronchial ventilation (EB), and postoperatively (postop). There was a significant correlation (r) between PtcO2 and PaO2 at all time periods: 0.97 (preop); 0.91 (ET); 0.83 (EB); 0.81 (postop). There were no significant differences among the transcutaneous oxygen indices (tcO2 index = PtcO2/PaO2) in the preop (0.69 +/- 0.09), ET (0.68 +/- 0.10) and postop (0.71 +/- 0.12) time period. The tcO2 index was significantly lower during one-lung anaesthesia (0.61 +/- 0.14). The PtcO2 was consistently lower than the corresponding PaO2 measurement, thus providing a continuous estimation of the "minimum" PaO2 level throughout anaesthesia and recovery. In four patients a marked drop in PtcO2 occurred just after the initiation of one-lung ventilation. In three, this was associated with arterial hypoxaemia and in one, haemodynamic compromise. In all four cases the PtcO2 was the first monitored parameter to change. As there is a substantial risk of developing hypoxaemia during thoracic anaesthesia, PtcO2 monitoring provides valuable early warning of impending hypoxaemia or haemodynamic compromise, thereby facilitating early therapeutic intervention.     

Transcutaneous carbon dioxide monitoring during prolonged apnoea with high-flow nasal oxygen

Background

The duration of apnoeic oxygenation with high-flow nasal oxygen is limited by hypercapnia and acidosis and monitoring of arterial carbon dioxide level is therefore essential. We have performed a study in patients undergoing prolonged apnoeic oxygenation where we monitored the progressive hypercapnia with transcutaneous carbon dioxide. In this paper, we compared the transcutaneous carbon dioxide level with arterial carbon dioxide tension.

Methods

This is a secondary publication based on data from a study exploring the limits of apnoeic oxygenation. We compared transcutaneous carbon dioxide monitoring with arterial carbon dioxide tension using Bland–Altman analyses in anaesthetised and paralysed patients undergoing prolonged apnoeic oxygenation until a predefined limit of pH 7.15 or PCO₂ of 12 kPa was reached.

Results

We included 35 patients with a median apnoea duration of 25 min. Mean pH was 7.14 and mean arterial carbon dioxide tension was 11.2 kPa at the termination of apnoeic oxygenation. Transcutaneous carbon dioxide monitoring initially slightly underestimated the arterial tension but at carbon dioxide levels above 10 kPa it overestimated the value. Bias ranged from −0.55 to 0.81 kPa with limits of agreement between −1.25 and 2.11 kPa.

Conclusion

Transcutaneous carbon dioxide monitoring provided a clinically acceptable substitute for arterial blood gases but as hypercapnia developed to considerable levels, we observed overestimation at high carbon dioxide tensions in patients undergoing apnoeic oxygenation with high-flow nasal oxygen.     

Oxygen Tension Monitoring in Uremic Patients During Hemodialysis Treatment

The aim of this study was to evaluate the influence on cerebral and cutaneous vascular regions of PaO2 reduction during acetate dialysis, by monitoring conjunctival oxygen tension (PcjO2) and transcutaneous oxygen tension (PtcO2) during hemodialysis (HD) treatment. The study was performed on 23 patients with end-stage renal disease in chronic HD. All patients underwent dialytic treatment with cuprophan membranes and acetate containing dialysate. PcjO2 and PtcO2 were recorded and PaO2 and arterial carbon dioxide tension (PaCO2) were also measured. Results of the study show that hypoxemia during acetate dialysis with cuprophan membranes is not accompanied by changes of PcjO2 and therefore by changes in cerebral oxygenation. Moreover, PtcO2 remains constant during dialysis treatment. Furthermore, maintenance of normal oxygen tension at the conjunctival level is not obtained at the expense of the peripheral region of the skin.     

Use of transcutaneous oxygen sensors to titrate PEEP.

The relationship of transcutaneous oxygen tension (PtcO2) to arterial oxygen tension (PaO2), pulmonary shunt (Qsp/Qt), mixed venous oxygen tension (PVO2), and O2 delivery was determined in patients with respiratory failure in order to explore the possible usefulness of PtcO2 to titrate the level of positive end expiratory pressure (PEEP). Transcutaneous oxygen sensors were applied to the chest of surgical ICU adult patients who were in acute postoperative respiratory failure. The patients had mechanical ventilation with volume ventilators and an intermittent mandatory ventilation (IMV) rate, which allowed normal pH and arterial CO2 tension ventilation (PacO2). Swan-Ganz and arterial catheters were inserted. The blood volume was measured by iodinated I-125-serum albumin and brought into the normal range, before the study began, with appropriate volume therapy. Serial cardiorespiratory data were taken before and after PEEP was increased from zero to 20 cm H2O, in 5 cm increments. PtcO2 correlated well with PaO2 and PV-O2; it was inversely correlated with Qsp/Qt. PtcO2 correlated with O2 delivery in only seven severely ill patients mean alveolar-arterial oxygen tension difference [A-aDO2] was 380 mmHg and the pulmonary shunt was 37%). For the eight other patients, variations in the greatly elevated cardiac output associated with hypoxemia led to poor correlations between PtcO2 and O2 delivery. There was no significant depression of cardiac output in any of the studies. We conclude that the continuous noninvasive nature of PtcO2 monitoring greatly increased the safety and simplicity of PEEP optimization and respiratory management of adult patients with respiratory failure.     

Correlation of hemodynamic variables with transcutaneous PO2 measurements in critically ill adult patients

Transcutaneous oxygen (PtcO2) monitoring with miniaturized heated electrodes has been shown to continuously track arterial oxygen tension (PaO2) noninvasively in stable infants. However, the correlation between the two is less marked in unstable adults, and PtcO2 appears to be additionally influenced by perfusion. The ability of PtcO2 to detect alterations in cardiac index (CI) was evaluated in 19 critically ill adult patients. The PtcO2 was found to be influenced by the PaO2, the CI, and local vascular tone, with a rapid response time to changes in these variables. All instances of improvement in PtcO2 readings were associated with improvement in PaO2 or hemodynamic status. Because of its high sensitivity, continuous noninvasive PtcO2 monitoring should allow reduction in routine PaO2 and CI determinations. However, a decrease in PtcO2 requires immediate in-depth evaluation of the patient's PaO2 and CI because of its lack of specificity.     

Transcutaneous PO2 measurement

Transcutaneous PO2 sensors have been developed over the past ten years from the same basic electrodes used in conventional blood gas machines. The skin is heated to enable the skin surface sensors to respond quickly to the gas tensions beneath them. PtcO2 is a variable which reflects the PO2 in the peripheral tissue. PtcO2 has its own range of normal values and it responds to cardiopulmonary changes which affect tissue oxygenation. In the majority of patients, those without decreased cardiac output, PtcO2 follows the trend of the arterial gas tension, and the PtcO2 value decreases relative to PaO2 with increasing patient age (Table II). When there is severely reduced cardiac output and peripheral perfusion, the PtcO2 values will deviate from their relationship with the arterial tensions and become blood flow dependent, thus providing quantitative information regarding blood flow. It is likely that the technique of transcutaneous PO2 monitoring will gain wider acceptance because it is a noninvasive and continuous monitor which provides useful information regarding tissue oxygenation.     

Hemodynamic patterns preceding circulatory deterioration and death after trauma

OBJECTIVE: To describe the sequence of hemodynamic changes associated with sudden circulatory deterioration compared with those of terminal patients to identify the earliest signs warning of shock and death. METHODS: This is a prospective observational study of 89 patients with thermodilution cardiac index and continuous noninvasive hemodynamic monitoring who had episodes of circulatory deterioration. These data were compared with the data of a second group of 24 patients in their terminal stage just before death. RESULTS: The earliest indications of impending collapse were decreased cardiac index, and tissue perfusion reflected by decreased transcutaneous O2 tension (PtcO2). This was followed by reduced blood pressure, tachycardia, reduced arterial hemoglobin saturation, and increased transcutaneous CO2 tension (PtcCO2). This pattern of changes was more pronounced in the nonsurvivors and was seen in exaggerated form in terminal patients. CONCLUSION: Sequential hemodynamic patterns revealed reduced blood flow and poor tissue perfusion as the earliest warning signs in both circulatory deterioration and death. These were followed by reduced mean arterial pressure, tachycardia, and low values of pulse oximetry. Adequate blood flow and even distribution of flow are needed for tissue perfusion.     

Pulmonary embolism during laparoscopic cholecystectomy detected by sudden decrease in end-tidal carbon dioxide pressure

We report a case of intraoperative pulmonary embolism, detected by a sudden decrease in end-tidal carbon dioxide pressure (PETCO2). The patient was a 56-year-old female without any history of pulmonary disease. The patient was intubated and ventilated manually during the operation under anesthesia with sevoflurane, nitrous oxide, and vecuronium. The percutaneous oxygen saturation (SpO2) and PETCO2 were monitored continuously. Twenty minutes after starting the laparoscopic procedure, PETCO2 decreased suddenly from values between 34 and 38 mmHg to 24 mmHg, and SpO2 decreased from 99% to 95%. Nitrous oxide was discontinued. Removal of the drape revealed profound subcutaneous emphysema. Postoperative pulmonary scanning revealed areas with reduced pulmonary perfusion (Fig. 2). An intravenous bolus of heparin (3000 IU) was given immediately, followed by 10,000 IU heparin over the next 24 hours. The patient was discharged on the fifteenth postoperative day without any sequelae. Although monitoring pulmonary arterial pressure is generally considered a more reliable method for the early detection of pulmonary embolism, an invasive monitoring procedure, such as the insertion of a Swan-Ganz catheter, is usually not indicated in laparoscopic surgery. For the early detection of pulmonary embolism, we therefore recommend the continuous monitoring of PETCO2 during laparoscopic surgery.     

A capnography and transcutaneous CO2 profile of bariatric patients during early postoperative period after opioid-sparing anesthesia

BackgroundNoninvasive monitoring of partial pressure of carbon dioxide can be accomplished indirectly with capnography (P_ETCO₂) or with transcutaneous carbon dioxide monitoring (P_TCCO₂). The use of capnography has been shown to offer an advantage over pulse oximetry alone in the early detection of adverse respiratory events when supplemental oxygen is administered. Furthermore, capnography allows for the monitoring of various respiratory measures, including end-tidal carbon dioxide, respiratory rate, tidal volume, and changes in breathing patterns. Transcutaneous CO₂ also closely approximates arterial CO₂ values, but is not as easy to monitor for prolonged periods. The purpose of this study was to examine the usefulness of capnography and of transcutaneous carbon dioxide monitoring in patients recovering from obesity surgery at high risk of developing postoperative obstructive sleep apnea.MethodsIn a prospective observational study, 64 bariatric surgery patients at risk of developing obstructive sleep apnea were monitored in the postanesthesia care unit (PACU) with either capnography alone (31 patients) or capnography plus transcutaneous carbon dioxide monitoring (33 additional patients) every 3–5 minutes for the duration of their recovery. Primary endpoints included end-tidal and transcutaneous carbon dioxide, peripheral oxygen saturation, respiratory rate, pain scores, and incidence of adverse respiratory events.ResultsAlthough no adverse pulmonary events were observed, capnography detected several patients who experienced short periods of respiratory apnea while maintaining pulse oximetry readings within normal limits. Transcutaneous values were slow to change and averaged 4.5 ± 5.5 mm Hg (P < .05) higher than corresponding end-tidal measurements.ConclusionsThese results indicate the capabilities of both these noninvasive techniques for postoperative monitoring. Capnography acutely monitors changes in respiration, whereas transcutaneous monitoring more accurately reflects arterial CO₂ levels.     

Intraoperative transcutaneous oxygen tension criteria for completion arteriography

During the past three years, we studied the value of transcutaneous oxygen monitoring in 28 lower extremity vascular bypass procedures. In 21 reconstructions, a rapid rise in the transcutaneous oxygen tension following reperfusion was indicative of a patent graft and patent runoff vessels. Inadequate revascularization was identified in three of four patients in whom transcutaneous oxygen tension failed to rise following femorodistal arterial bypass (positive predictive value 75%). A normal intraoperative transcutaneous oxygen tension study following femorodistal bypass had a negative predictive value of 95%. The overall accuracy was 91%. Transcutaneous oxygen tension monitoring during lower extremity vascular bypass procedures is useful in assessing the success of revascularization and may be used to select which patients should undergo completion arteriography as opposed to those in whom an arteriogram is not essential.