Transcutaneous monitoring during high-frequency jet ventilation

Simultaneous transcutaneous PO2 (PtcO2) and PCO2 (PtcCO2) recordings, done on a patient during high-frequency jet ventilation (HFJV) in thoracic surgery, reflected exactly PaO2 and PaCO2 changes induced by surgical manipulation and by ventilator setting alterations. PtcO2 and PtcCO2 monitoring with a single sensor was valuable during HFJV for the early detection of acute changes in the efficacy of gas exchange and for the correction of the ventilator setting.     

Transcutaneous PO2 monitoring during sodium nitroprusside infusion

To determine the effect of vasodilator-induced hypotension on the relationship between transcutaneous PO2 (PtcO2) and PaO2, six mongrel dogs and 20 patients were monitored before and during infusion of sodium nitroprusside (SNP), with PtcO2 sensors heated to 45 degrees C. First, SNP infusion was used to lower the mean arterial pressure (MAP) of anesthetized dogs, in steps of approximately 25%, to 49 +/- 3 (SD) mm Hg. There were no significant changes in cardiac output, oxygen consumption, PtcO2, PaO2, or PtcO2 index (PtcO2/PaO2). Twenty patients were monitored during general anesthesia. Fifteen patients were being treated for acute hypertension with SNP, and in five patients hypotension was induced with SNP to minimize blood loss. There was a significant decrease in MAP, PaO2, and PtcO2, and a significant increase in alveolar-arterial PO2 difference during SNP infusion. PtcO2 index did not change significantly from its preinfusion value in either group.     

Transcutaneous and liver surface PO2 during hemorrhagic hypotension and treatment with phenylephrine

Transcutaneous PO2 (PtcO2) and liver surface PO2 (PIO2) were measured in six mongrel dogs during hemorrhagic shock, normotensive shock, and volume resuscitation. Normotension was produced during extreme hypovolemia by an infusion of phenylephrine. PtcO2 and PlO2 were compared to each other and to hemodynamic and oxygen transport variables. PtcO2 and PlO2 correlated well with cardiac index (CI) r = .71 and .86, respectively; n = 60) and with each other (r = .79; n = 60). Heart rate, mean arterial pressure (MAP), and PaO2) correlated less with PtcO2 or PlO2. During the normotensive shock period, PtcO2, PIO2, CI, oxygen delivery (DO2), and oxygen consumption (VO2) were all severely decreased, while PaO2 and MAP were normal and lactic acid concentrations were elevated. It was concluded that PtcO2 follows changes in PlO2 during hypotensive and normotensive low cardiac output shock in mongrel dogs. Low PtcO2 values are associated with low values of PlO2, DO2, VO2, and rising lactic acid concentrations in dogs. These animal data imply that low PtcO2 values encountered in clinical monitoring during anesthesia and surgery may correspond to decreased blood volume, blood flow, and PlO2.     

Use of transcutaneous O2 monitoring in the intraoperative management of severe peripheral vascular disease

Transcutaneous O2 (PtcO2) and CO2 (PtcCO2) monitoring has been used in infants, in critically ill adults, and more recently, in peripheral vascular disease. The present report compares values of centrally placed chest (PtcO2 and PtcCO2) sensors with values of peripherally placed calf (Ptc'O2 and Ptc'CO2) sensors in a patient with severe peripheral vascular disease during performance of an axillofemoral bypass graft. The calf Ptc'O2 values may be expressed as a ratio of their corresponding PaO2 values or as a percentage of the chest PtcO2, i.e., calf Ptc'O2/chest PtcO2 X 100. The ratio reflects local tissue perfusion in the face of fluctuating PaO2 and central PtcO2 values. The data demonstrate that PtcO2 sensors reflect tissue blood flow and oxygenation and, therefore, are useful measures of tissue perfusion, especially during limb revascularization.     

Noninvasive PtcO2 initial slope index and invasive PtcO2 arterial index as diagnostic criterion of the state of peripheral circulation

Transcutaneous PO2 (PtcO2), PaO2, PtcO2 arterial index (ARI; PtcO2/PaO2), and the initial slope index (ISI; [delta PO2/min]/starting PtcO2) were measured in 42 healthy volunteers, 12 patients with stable circulation and respiratory insufficiency, and ten patients with insufficient peripheral circulation in cardiogenic shock in order to investigate whether ARI and ISI can be used to detect insufficient circulation. The ISI was measured by placing a PtcO2 electrode on the forearm and interrupting blood flow by inflating a cuff until the PtcO2 dropped to zero. After releasing the cuff pressure, the initial slope of the PtcO2 trace was determined in order to calculate the ISI. In the PtcO2 range between 40 and 100 torr, the ARI and ISI did not depend on the PtcO2 magnitude. In all groups, the ISI behaved similarly to the ARI. We conclude that the noninvasive ISI and invasive ARI are able to differentiate between stable and insufficient peripheral circulation (ISI less than 0.75, ARI less than 0.8; p less than .001).     

Comparison of arterial blood gas with continuous intra-arterial and transcutaneous PO2 sensors in adult critically ill patients

We compared the partial pressure of oxygen directly via a continuous intra-arterial probe (PiaO2) and indirectly using a transcutaneous device (PtcO2) with simultaneously obtained arterial blood PaO2. The PiaO2 values were measured using a bipolar oxygen sensor placed through an 18-ga arterial catheter. The PtcO2 values were measured using a transcutaneous O2-CO2 sensor placed on the abdomen. Seven critically ill, hemodynamically stable, ventilator-dependent adult patients were studied. Measurements were obtained at varying concentrations (0.25 to 1.0) of inspired oxygen after a 10-min stabilization. A total of 78 simultaneous values were obtained; by linear regression: PiaO2 = 0.91 PaO2 + 1.39 (r = .98, standard errors of the estimate [SEE] = 18.6); PtcO2 = 0.39 PaO2 + 36.2 (r = .89, SEE = 14.1). To assess these instruments as trend monitors, we compared the changes in simultaneous PaO2, PiaO2, and PtcO2 values; by linear regression: delta PiaO2 = 0.90 delta PaO2 + 3.88 (r = .96, SEE = 27.7); delta PtcO2 = 0.43 delta PaO2 + 5.6 (r = .94, SEE = 15.2). We conclude that, although these instruments correlate highly with the PaO2, the SEE was substantial and therefore may limit their clinical reliability in adults. Any acute or clinically significant change in PiaO2 or PtcO2 should be confirmed with a blood gas PaO2.     

Transcutaneous oxygen monitoring beyond the neonatal period

Transcutaneous O2 (PtcO2) tensions were compared with PaO2 measurements in 57 infants and children (age range 2 wk to 15.5 yr) using electrode temperatures of 43 degrees and 44 degrees C. At both temperatures, the relationships between PtcO2 and PaO2 were linear over the whole range of data (PaO2 39.75 to 120 torr) although mean PtcO2/PaO2 fell from 44 degrees to 43 degrees C. Skin stripping by repeated applications of adhesive tape immediately before electrode placement did not improve these relationships. In an additional 20 children with a mean age of 2.4 yr (range 0.08 to 15.85) who were being investigated for sleep-disordered breathing, the mean PaO2/PtcO2 ratio of 1.22 at 44 degrees C was used as a correction factor during air calibration for PtcO2. This resulted in a mean PtcO2/PaO2 of 0.99 (range 0.83 to 1.15) provided blood flow is not impaired. Extending the monitoring period from 4 to 8 h between site changes did not result in any burns or persisting erythema. In hemodynamically stable infants and children, and at electrode temperatures of 44 degrees C and 43 degrees C, PtcO2 is linearly related to PaO2 over a wide range of PaO2 values. At an electrode temperature of 44 degrees C, PtcO2 can be arterialized effectively by allowing for transepidermal O2 loss during air calibration; at this electrode temperature, intervals between site changes can be extended safely up to 8 h.     

Circulatory support with sympathetic amines in brain death

In 12 cases of brain death, the cardiovascular effects and changes of transcutaneous PO2 (PtcO2) during infusion of various sympathomimetic amines were determined. The larger amounts of vasopressors were necessary to maintain the blood pressure at more than 100 mmHg. With norepinephrine and dopamine, marked increase in blood pressure, cardiac output, systemic vascular resistance and also PtcO2 were observed. On the other hand, dobutamine was not an effective pressor agent in those situations. Even with more than 10 times the routinely used concentration of dobutamine, difficulties were encountered in keeping the blood pressure above 100 mmHg in many cases studied. With the infusion of dobutamine, a marked increase in cardiac output and heart rate were observed with a decrease in systemic vascular resistance and a fall in PtcO2 values in many occasions. In brain death, norepinephrine and dopamine will be recommended as the pressor agents in clinical practice. The changes of PtcO2 closely followed the changes of arterial blood pressure and did not parallel the changes of cardiac output or of heart rate.     

Factors influencing transcutaneous oxygen and carbon dioxide measurements in adult intensive care patients

Transcutaneous PO2 (PtcO2) is suggested to reflect tissue oxygenation in intensive care patients, whereas transcutaneous PCO2 (PtcCO2) is advocated as a noninvasive method for assessing PaCO2. In 24 critically ill adult patients (mean Apache II score 14.2, SD 4.7) we investigated the impact of variables that are commonly thought to determine PtcO2 and PtcCO2 measurements. A linear correlation was found between PtcO2 and PaO2 (r = 0.6; p less than or equal to 0.0001) and between PtcO2 and mean arterial blood pressure (MAP; r = 0.42; p less than or equal to 0.003). Cardiac index (CI) correlated with tc-index (PtcO2/PaO2; r = 0.31; p less than or equal to 0.03). There was no relationship between PtcO2 and hemoglobin concentration (Hb) and the position of the oxygen dissociation curve (ODC). Stepwise multiple regression analysis demonstrated a significant influence of PaO2 and MAP on PtcO2. The contribution of CI, Hb and the ODC was not significant. Only 40% of the variability of a single PtcO2 measurement could be explained by PaO2 and MAP. A significant linear correlation was demonstrated between PtcCO2 and PaCO2 (r = 0.76; p less than or equal to 0.0001) but not between PtcCO2 and CI, MAP and arterial base excess (BEa). Stepwise multiple regression analysis revealed an influence of PaCO2 and of CI on PtcCO2; 66% of the variability of a single PtcCO2-value could be explained by PaCO2 and CI. Our data demonstrate that transcutaneous derived gas tensions result from complex interaction between hemodynamic, respiratory and local factors, which can hardly be defined in ICU-patients.     

Laser Doppler velocimetry as a monitor of cardiac output changes in dogs

Cutaneous blood flow may be measured utilizing a continuous, noninvasive technique, laser Doppler velocimetry (LDV). Monitoring of cutaneous blood flow by LDV might be a useful method to monitor cardiac output. To test this hypothesis, sequential measurements of cardiac output, LDV, and transcutaneous oxygen (PtcO2) were made on 10 anesthetized dogs during experimental shock. There was significant correlation between LDV and cardiac output, while PtcO2 reflected cardiac output only at low flow states. These results show that, in the animal model, cutaneous LDV is a sensitive and specific method for monitoring cardiac output changes.     

Factors affecting heated transcutaneous PO2 and unheated transcutaneous PO2 in preterm infants

The authors evaluated transcutaneous PCO2 (PtcCO2) and PO2 (PtcO2) electrodes in 25 infants. Their diagnosis were severe hyaline membrane disease (HMD) (18), aspiration syndrome (3), severe hydrops, (3) persistent fetal circulation (6), and the others, congenital pneumonia, congenital plural effusion, pulmonary hemorrhage. In most all, the cardiovascular system was compromised, i.e., PDA with congestive heart failure and shock. PtcO2 electrode was heated to 43.5 degrees C while PtcCO2 electrode was not heated. Simultaneous arterial blood pressure (ABP), pH, arterial blood gases were obtained with the transcutaneous gas measurements. The data were analyzed first dividing all the paired arterial and transcutaneous gas tensions into those with and without cardiovascular drugs (dopamine, isoproterenol), and second, the paired values were divided into those taken (a) during severe acidosis (pH less than 7.25), (b) hypotension (less than 2 SD) of normal, and (c) hypotension and acidosis. These data show: (1) the unheated PtcCO2 and heated PtcO2 accurately correlated with the simultaneous arterial measurements: (2) PtcCO2 reflects tissue PCO2; (3) drugs affect both the PtcCO2 and PtcO2; (4) elevated PtcCO2 dissociating from the simultaneous PaCO2 in neonates with cardiovascular compromise results from decreased tissue perfusion. These data suggest that transcutaneous gas sensors perform dual functions; first, as gas monitors in patients without cardiovascular alterations, and second, in patients with cardiovascular compromise, PtcCO2 reflected tissue perfusion and PtcCO2 monitored oxygen delivery to the tissues.     

Continuous conjunctival and transcutaneous oxygen tension monitoring during resuscitation in a patient

Conjunctival (PcjO2) and transcutaneous (PtcO2) oxygen tensions were serially measured in a patient with multiple stab wounds. Even though blood pressure was normal, severe hypovolemia due to hemorrhage was detected in the emergency department by abnormally low PcjO2/PaO2 and PtcO2/PaO2 ratios. The adequacy of resuscitation was established by return of these ratios to normal values. The conjunctival sensor stabilized more rapidly than the transcutaneous sensor and is of greater utility in the emergency setting. It was found that conjunctival and transcutaneous oxygen sensors can play an important role in monitoring clinical state and resuscitation of trauma patients.     

The significance of hypoxemia with low inspired O2 fraction before extubation

Arterial and transcutaneous O2 (PtcO2) and CO2 (PtcCO2) tensions, arterial O2 saturations (SaO2) and P50 values were measured in 47 patients before extubation. In order to unmask ventilation to perfusion (VA/Q) inequality, all variables were obtained without CPAP and with FIO2 of 0.40 as well as with CPAP of 5 cm H2O and FIO2 of 0.40, 0.35, 0.30, 0.25, and 0.21. Eighty to 90% of the patients had PaO2/FIO2 lower than 300 torr and no significant difference in PaO2 or SaO2 was found between those who were successfully extubated (group S, n = 38) and those who required reintubation (group R, n = 9). On the other hand, the patients in group R had significantly lower P50 values, and their PtcO2 values decreased at a greater incline with the lowering of FIO2 than those in group S. Pulmonary dysfunction does not solely explain the need for reintubation in group R. It is obvious that arterial hypoxemia may become more dangerous when the patient has a low P50, anemia, or hypermetabolism. Because PtcO2 seems to uncover these factors, it is a valuable method for predicting the patient's condition before extubation.     

The transcutaneous oxygen challenge test: a noninvasive method for detecting low cardiac output in septic patients

The transcutaneous partial pressure of oxygen (PtcO?) index has been used to detect low-flow state in circulatory failure, but the value of the transcutaneous oxygen challenge test (OCT) to estimate low cardiac output has not been thoroughly evaluated. The prospective observational study examined 62 septic patients requiring PiCCO-Plus for cardiac output monitoring. Simultaneous basal blood gases from the arterial, central venous catheters were obtained. Cardiac indices were measured by the transpulmonary thermodilution technique at the same time, then the 10-min inspired 1.0 fractional inspired oxygen concentration (FIO?) defined as the OCT was performed. Transcutaneous partial pressure of oxygen was measured continuously by using a noninvasive transcutaneous monitor throughout the test. The values for arterial pressure of oxygen (PaO?) were examined on inspired of 1.0 FIO?. We calculated the PtcO? index = (baseline PtcO?/baseline PaO?), 10-min OCT (10 OCT) = (PtcO? after 10 min on inspired 1.0 O?) - (baseline PtcO?), and the oxygen challenge index = (10 OCT) / (PaO? on inspired 1.0 O? - baseline PaO?). Patients were divided into two groups: a normal cardiac index (CI) group with CI of greater than 3 L/min per m (n = 41) and a low CI group with CI of 3 L/min per m or less (n = 21). The 10 OCT and the oxygen challenge index predicted a low CI (≤ 3 L/min per m) with an accuracy that was similar to central venous oxygen saturation, which was significantly better than the PtcO? index. For a 10 OCT value of 53 mmHg, sensitivity was 0.83; specificity, 0.86; a positive predictive value, 0.92; and a negative predictive value, 0.72 for detecting CI of 3 L/min per m or less. We propose that the OCT substituted for the PtcO? index as an accurate alternative method of PtcO? for revealing low CI in septic patients.     

Changes in cardiac output after acute blood loss and position change in man

Thoracic bioimpedance cardiac output (Qtbi) was measured at 1-min intervals in 27 volunteers before, during, and after withdrawing 500 ml (3.7 to 8.5 ml/kg; mean 5.8) of blood. The effects of passive leg raising (PLR) and standing on Qtbi were measured before and after blood withdrawal. Arterial oxygen saturation (SaO2), transcutaneous oxygen tension (PtcO2), mean arterial BP (MAP), and heart rate (HR) were also measured before and after blood withdrawal. Thoracic bioimpedance cardiac index (CI) decreased 18% (0.8 +/- 0.1 L/min.m2, p less than .0001) and stroke volume index (SI) decreased 22% (14.8 +/- 2.7 ml/beat.m2, p less than .0001) after blood withdrawal. HR, MAP, SaO2, and PtcO2 were not significantly different after blood withdrawal. Before blood withdrawal PLR increased CI 6.8% (0.3 +/- 0.1 L/min.m2, p less than .0001); after blood withdrawal PLR increased CI 11.1% (0.4 +/- 0.1 L/min.m2, p less than .0001). PLR can increase stroke volume and cardiac output in hypovolemic humans.     

A prospective randomized trial comparing oxygen delivery versus transcutaneous pressure of oxygen values as resuscitative goals

Transcutaneous pressure of oxygen (PtcO2) correlates with arterial pressure of oxygen (PaO2) in nonshock states, but in shock states, PtcO2 approximates cardiac output with no response to increasing fraction of inspired oxygen (FiO2) and PaO2. An incremental change of more than 21 mmHg in PtcO2 in response to an FiO2 of 1.0 (identified as the oxygen challenge test [OCT]) implies adequate tissue perfusion, and lack of response has been associated with mortality. Patients with severe sepsis and septic shock requiring pulmonary artery catheters were randomized to two groups: the oxygen delivery (DO2) group was treated to a DO2 and mixed venous oxygen saturation goals, and the PtcO2 group was treated to achieve an OCT value of 40 mmHg or more. The DO2 (n = 30) and PtcO2 (n = 39) groups were similar in baseline characteristics. Mortality rate was 12 (40%) of 39 for the DO2 group and 5 (13%) of 39 for the PtcO2 group (P = 0.02). Logistic regression analysis of the statistically significant variables between survivors and nonsurvivors demonstrated that inability to reach the PtcO2 goal at 24 h after resuscitation (T24) and a positive cardiac history are associated with mortality (P < 0.001). The area under the receiver operating curve was 0.824 for the OCT at T24. The best OCT value was 25 mmHg at T24 with positive and negative predictive values of 87% and 90%, respectively. Treating patients with severe sepsis/septic shock to an OCT value of 25 mmHg or more may provide a specific end point of resuscitation that may be associated with better survival than resuscitating to the central hemodynamic parameters of DO2 and mixed venous oxygen saturation.     

Early diagnosis of shock due to pericardial tamponade using transcutaneous oxygen monitoring

The early diagnosis of traumatic pericardial tamponade may be difficult. The transcutaneous oxygen (PtcO2) monitor has been shown to be a useful indicator of low-flow shock. In the case presented, PtcO2 monitoring was the earliest indicator of shock due to pericardial tamponade and led to successful early therapy before other signs of physiologic decompensation were evident. In the management of acutely traumatized patients, PtcO2 monitoring is useful both in identifying patients who are in shock and in helping to guide therapy.     

Evaluation of noninvasive measurements of oxygenation in stable infants

The accuracy with which transcutaneous measurements of oxygen tension reflect PaO2 in older infants has recently been questioned. We therefore examined the effect of maturation, i.e., age or skinfold thickness, on the accuracy of transcutaneous oxygen tension (PtcO2) and oxygen saturation (StcO2) measurements in 19 infants (age 1 to 61 wk) undergoing elective cardiac catheterization. Twenty-seven simultaneous arterial and transcutaneous measurements revealed a good correlation between PtcO2 and PaO2 (r = .91, slope .77, intercept 3.23 torr). The mean arterial-transcutaneous PO2 difference of 10 torr (range - 15 to 35) was independent of age but was significantly correlated with skinfold thickness (r = .45, p less than .05). There was also a good correlation between StcO2 and SaO2 (r = .95, slope .65, intercept 27.8%). The mean arterial-transcutaneous oxygen saturation of 1.4% (range - 17.3 to 14) was unaffected by age or skinfold thickness. However, neither PtcO2 or StcO2 measurements were accurate in patients with severe hypoxemia; StcO2 consistently overestimated the SaO2 when the SaO2 was below 70%. Thus, in this study the discrepant PtcO2 measurements in older infants were due to increasing skinfold thickness rather than age. PtcO2 monitoring still has an important role in oxygen monitoring and together with StcO2 provides valuable information on oxygenation.     

Continuous transcutaneous oxygen monitoring during an intraoperative cardiac arrest

A transcutaneous oxygen sensor was used continuously during surgical management of a ruptured abdominal aortic aneurysm. Closed chest compression initiated for intraoperative cardiac arrest gave an inadequate cardiac output on the basis of falling PtcO2 despite transmitted femoral pulses and an excellent PaO2. This discordance provided a rationale for open cardiac massage, which increased the cardiac output and tissue perfusion (PtcO2) needed for successful resuscitation. The PtcO2 sensor provides immediate, non-invasive, and continuous information regarding tissue oxygenation. It reflects the PaO2 in hemodynamically stable patients as well as providing a sensitive indicator for inadequate cardiac output during shock. In patients undergoing cardiopulmonary resuscitation, a falling PtcO2 with an acceptable PaO2 indicates poor tissue perfusion and, in select circumstances, may warrant open cardiac massage.