The relation of conjunctival PO2 to capillary bed PO2

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.

The relationship of conjunctival and arterial blood gas oxygen measurements

Conjunctival oxymetry (CjO2) measures peripheral tissue oxygen at the conjunctival level. CjO2 changes can indicate pulmonary or circulatory conditions leading to shock. Literature review does not define 'normal' CjO2/ABG PaO2 ratios. We designed a study to measure these ratios. Twenty-two healthy patients undergoing cardiac catheterization had simultaneous PcjO2 and PaO2 measurements completed. The range of conjunctival oxygen measurements was from 34 to 68 mmHg with a mean of 50.5 mmHg. The PaO2 readings ranged from 65 to 93 mmHg with a mean of 77.1 mmHg. The average PcjO2/PaO2 ratio was 0.656 with a range of 0.47-0.93. Thus the PcjO2 is on average 66% of the arterial blood gas PaO2. This ratio of 0.66 can serve as a base for further clinical studies in which PcjO2 is looked at in patients with pulmonary or circulatory illnesses or injuries.

Continuous conjunctival oxygen tension (PcjO2) monitoring for assessment of cerebral oxygenation and metabolism during carotid artery surgery

The clinical value of noninvasive continuous monitoring of conjunctival oxygen tension for assessment of cerebral perfusion during carotid endarterectomy performed under general anaesthesia has been evaluated. The patients (n = 17; mean age 62.5 +/- 1.7 years) were monitored as follows: conjunctival oxygen tension (PcjO2); internal jugular venous oxygen tension at the skull base level (PcijvO2); arterial blood pressure; arterial and internal jugular venous blood gases; acid-base data and lactate, pyruvate levels; end-tidal CO2 concentration. The mean preanaesthetic PcjO2 level of 4.86 +/- 0.40 kPa was significantly lower than PaO2(PcjO2)/PaO2 ratio of 0.48). Following anaesthesia, a larger PcjO2-PaO2 gradient (ratio 0.32) was seen in spite of the hyperoxic situation (FiO2 = 0.40) due to vasoconstriction induced by slight hypocapnia (reduction of PaCO2 from 5.13 +/- 0.08 to 4.64 +/- 0.10 kPa). The carotid artery crossclamping resulted in a rapid and pronounced decrease of PcjO2, while PcijvO2 remained unchanged. No relationship between PcjO2 and stump pressure was found, while a significant correlation (P less than 0.02) between PcjO2 and lactate in effluent venous blood from the brain was demonstrable. It is concluded that PcjO2 monitoring seems a clinically useful trend indicator of cerebral perfusion in the individual patient. Due to large interindividual variations in basal PcjO2 readings and in PcjO2 changes during carotid artery clamping, however, transconjunctival oxygen tension monitoring does not seem to allow early and accurate recognition of impending cerebral ischaemia during carotid endarterectomy, and its routine use therefore seems of limited value.

Conjunctival oxygen tension monitoring in experimental septic shock

Continuous non-invasive monitoring of conjunctival oxygen tension (PcjO2) versus 'conventional' invasive hemodynamic and oxygen transport variables was evaluated in a porcine model of septic shock induced by a continuous i.v. infusion of E. coli endotoxin over 2 hours. Seventeen pigs under ketamine anesthesia and breathing air spontaneously were investigated. PcjO2, which reflects local oxygen tension at tissue level, correlated significantly at baseline and throughout the septic course with mixed venous oxygen saturation and oxygen utilization coefficient. All these correlations were significant at the 1% level. The corresponding correlations between PcjO2 and cardiac output were significant at the 5% level. A finding of great importance was that changes in PcjO2 preceded major changes in the intermittently measured physiological variables such as SvO2 and cardiac output. We conclude that PcjO2 monitoring is a valuable non-invasive method and which can provide a continuous assessment of the hemodynamic and oxygenation status in experimental septic shock.

Conjunctival oxygen tension monitoring in emergency department patients

Conjunctival oxygen tension (PcjO2) was sequentially monitored in 96 medical and surgical patients admitted to the emergency department resuscitation suite during a 6-month period. There were 28 patients with cardiac arrest, 44 with major trauma, and 24 with severe medical problems. A total of 2,392 PcjO2 data points were collected in these patients. In patients with cardiac arrest, PcjO2 showed changes in physiological condition as early as or earlier than measurement of vital signs. Measurement of PcjO2 and the finding of a PcjO2 index (PcjO2/PaO2) less than .5 in normotensive multiple trauma patients allowed rapid detection of hemorrhagic hypovolemia. In critically ill medical patients, low values for PcjO2 were found with hypoxemia as well as in conditions associated with decreased cardiac output and tissue oxygen delivery. These two conditions could be distinguished by measuring PaO2 and calculating the PcjO2 index; a PcjO2 index less than .5 was associated with diminished peripheral perfusion and cardiac output, and a PcjO2 index greater than .5 indicated hypoxemia without any compromise in cardiac output. In the group of critically ill surgical and medical patients included in this study, conjunctival oxygen monitoring provided clinically useful information not available from vital signs and permitted identification of physiological instability associated with abnormalities in peripheral tissue perfusion and oxygenation as early as or earlier than conventional monitoring methods.

[Conjunctival oxygen pressure in patients with acute cerebral infarct]

Conjunctival oxygen tension and arterial blood gases were measured in 20 patients with acute ischaemic stroke and compared to values obtained in a reference group. The conjunctival capillary bed is perfused by the ophthalmic artery and, thus, reflects the oxygen delivery to the areas supplied by the internal carotid artery. Patients with acute ischaemic stroke showed especially on the ipsilateral side, i.e. the side of the infarction, and to a lesser extent on the other side a lowered conjunctival oxygen tension and a reduced ratio of conjunctival to arterial oxygen tension. These findings indicate disturbances of the blood fluidity, of the cerebrovascular autoregulation and of brain microperfusion. Monitoring of conjunctival oxygen tension is simple and safe. This method allows the assessment of oxygen tension in a tissue bed vascularized by the internal carotid artery. It appears to yield an objective criterion of the effectiveness of therapeutic procedures aiming at an improvement of cerebral perfusion and oxygen supply in patients with acute ischaemic stroke.

Postoperative monitoring of conjunctival oxygen tension and temperature

To define the utility of conjunctival temperature (Tcj) and conjunctival oxygen tension (PcjO2) monitoring during rewarming in the postoperative period, we measured serial Tcj, PcjO2 and PcjO2 index (PcjO2/PaO2) values in 10 patients after cardiac surgery. PcjO2 and PcjO2 index were markedly depressed at the low conjunctival temperatures recorded during the immediate postoperative period. As the patients' core and conjunctival temperatures increased, there was a concomitant, linear increase in PcjO2 and PcjO2 index for Tcj less than 33.5 degrees C. Two patients showed deviation from this temperature-related rise in PcjO2 and PcjO2 index, and both of these patients demonstrated physiologic deterioration associated with cardiac arrest or hypotension. These results indicate that monitoring of PcjO2 and Tcj can provide a continuous assessment of the adequacy of peripheral perfusion and oxygenation in the postoperative period.

Deterioration of conjunctival PO2 after CPR

An 82-year-old man was resuscitated following cardiac arrest suffered outside the hospital. Conjunctival oxygenation (PcjO2), as measured by a conjunctival PO2 monitor, increased in the immediate post-resuscitation period (60 min) and neurologic status improved. The PcjO2 steadily declined over the next three hours. During the period of declining PcjO2, the systolic blood pressure tended to remain stable (104 mm Hg +/- 18), the arterial PO2 (PaO2) was greater than or equal to 103 mm Hg, and the PcjO2/PaO2 ratio initially increased, while the PcjO2/arterial oxygen content (CaO2) ratio and neurologic status declined. The rise and subsequent fall of PcjO2 in this patient paralleled the neurologic status and may be consistent with the cerebral reperfusion/hypoperfusion phenomena observed in experimental preparations of resuscitation from circulatory arrest.

Closed-lid factors influencing human corneal oxygen demand

A micropolarographic system was used to measure the flux of oxygen crossing the tear-epithelial interface of the human cornea just following stabilization of four lid closure conditions. In all, 215 oxygen flux measurements were made on the corneas of 6 young healthy subjects, including 2 reference conditions: the normal open eye and anterior surface oxygen deprivation. When compared with the temperatures associated with certain of those conditions, oxygen demands greater than those predicted by a previous Q10 measurement were found. Proportional contributions of the non-temperature factor are presented, and the nature of its components suggested.

Human corneal oxygen demand: the closed-eye interval

A micropolarographic system was used to measure the flux of oxygen crossing the tear epithelial interface of the human cornea just following lid-closure periods of 0-15 min, and just following a series of brief lid openings (0.2-0.3 s) of frequencies from 0 to 30 times/min. In all, 462 measurements spanning those two formats were made on the corneas of seven young healthy subjects. In the extended-closure format the average rate increased over the first 5 min, then stabilized at 2.51 times the oxygen-uptake rate under normal open-eye conditions. In the brief lid-opening format, frequencies of 30 openings/min reduced the oxygen uptake rate to 70% of that of the stabilized closed eye. Individual differences noted among subjects may influence their relative success in extended contact lens wear, and natural lid and eye movements during sleep may have at least transient effects on corneal oxygen supply and demand during those periods.

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.

Continuous monitoring of critically ill patients with transcutaneous oxygen and carbon dioxide and conjunctival oxygen sensors

Transcutaneous (PtcO2) and conjunctival (PcjO2) oxygen tensions and transcutaneous (PtcCO2) carbon dioxide tension were serially measured in 31 critically ill patients. Sixteen patients maintained a normal or greater blood pressure and 15 patients were severely hypotensive (MAP less than 60 mm Hg) or suffered cardiac arrest while in the emergency department. In hemodynamically stable patients, the correlations between PtcO2 and PaO2, PcjO2 and PaO2, and PtcCO2 and PaCO2 were significant, with correlation coefficients (r values) of 0.62, 0.48, and 0.73, respectively. In hemodynamically unstable patients, there was poor correlation between PtcO2, PcjO2, PtcCO2, and arterial blood gas values. In the severely hypotensive patients, however, PtcO2 and PcjO2 were sensitive real-time monitors of peripheral perfusion and tissue oxygen delivery. Increases in PcjO2 and PtcO2 occurred within three minutes in patients who regained a palpable blood pressure from a pulseless baseline. PtcO2 fell one to five minutes after the loss of blood pressure in patients whose clinical condition deteriorated in the emergency department. Decreases in PcjO2 from previously stable levels occurred over three to four minutes before loss of blood pressure. Transcutaneous and conjunctival sensors can be used as continuous monitors of respiratory status in hemodynamically stable patients. In severely hypotensive patients and during cardiopulmonary resuscitation, these sensors no longer accurately reflect arterial blood gases, but act as sensitive real-time monitors of cardiac function and peripheral perfusion. PcjO2 can detect deterioration of clinical state before alterations in blood pressure occur.

Conjunctival and transcutaneous oxygen monitoring during resuscitation

Conjunctival (PciO2) and transcutaneous (PtcO2) oxygen tensions were serially measured during cardiopulmonary resuscitation (CPR). Changes in cardiac function and arterial oxygen content were reflected accurately by alterations in PciO2 and PtcO2. PciO2 showed more rapid responses to changes in physiologic state than did PtcO2. Conjunctival and transcutaneous oxygen sensors gave continuous information with respect to oxygen delivery during CPR, and provided real-time assessment of the effectiveness of CPR in terms of peripheral perfusion and tissue oxygenation.