Comparison of tissue oxygen-tension measurements by different devices. An experimental study in pigs

Human cardiovascular dose-response to supplemental oxygen

AIM

The aim of the study was to examine the central and peripheral cardiovascular adaptation and its coupling during increasing levels of hyperoxaemia. We hypothesized a dose-related effect of hyperoxaemia on left ventricular performance and the vascular properties of the arterial tree.

METHODS

Oscillometrically calibrated arterial subclavian pulse trace data were combined with echocardiographic recordings to obtain non-invasive estimates of left ventricular volumes, aortic root pressure and flow data. For complementary vascular parameters and control purposes whole-body impedance cardiography was applied. In nine (seven males) supine, resting healthy volunteers, aged 23-48 years, data was collected after 15 min of air breathing and at increasing transcutaneous oxygen tensions (20, 40 and 60 kPa), accomplished by a two group, random order and blinded hyperoxemic protocol.

RESULTS

Left ventricular stroke volume [86 +/- 13 to 75 +/- 9 mL (mean +/- SD)] and end-diastolic area (19.3 +/- 4.4 to 16.8 +/- 4.3 cm(2)) declined (P < 0.05), and showed a linear, negative dose-response relationship to increasing arterial oxygen levels in a regression model. Peripheral resistance and characteristic impedance increased in a similar manner. Heart rate, left ventricular fractional area change, end-systolic area, mean arterial pressure, arterial compliance or carbon dioxide levels did not change.

CONCLUSION

There is a linear dose-response relationship between arterial oxygen and cardiovascular parameters when the systemic oxygen tension increases above normal. A direct effect of supplemental oxygen on the vessels may therefore not be excluded. Proximal aortic and peripheral resistance increases from hyperoxaemia, but a decrease of venous return implies extra cardiac blood-pooling and compensatory relaxation of the capacitance vessels.

Evaluation of subcutaneous tissue gases and pH during induction of acidosis and alkalosis. An experimental study in pigs

Peripheral tissue oxygen utilization was studied during hypoxic-induced acidosis and sodium bicarbonate-induced alkalosis in 8 domestic pigs by measurements of subcutaneous oxygen tension (PscO2), carbon dioxide tension (PscCO2) and pH (pH(sc)) in relation to central hemodynamic parameters and oxygenation. Hypoxic-induced acidosis resulted in a decrease in P(sc)O(2) [corrected] and arterial oxygen tension (P(a)O(2)) to one third of baseline values (p < 0.05), an increase in PscCO2 and arterial carbon dioxide tension (PaCO2) from 41 to 55 and 34 to 39 mm Hg, respectively (p < 0.05), and a decrease in pH(sc) from 7.47 to 7.30 (p < 0.05). PscO2 and PaO2 increased during reversal of hypoxia and infusion of bicarbonate (p < 0.05), without reaching baseline values. In parallel PscCO2 decreased and pH(sc) increased but changes lagged behind changes in blood gases. Alkalosis established by further infusion of bicarbonate resulted in a decrease in PaO2 to 62 mm Hg whereas PscO2 remained below baseline values (p < 0.05). Correction of oxygen utilization in the subcutaneous tissue as measured by the markers PscCO2 and pH(sc) is slower than indicated by changes in tissue oxygen tension, blood gases and pH. Overcompensation of acidosis with bicarbonate resulting in alkalosis impairs oxygenation.

Influence of positive end-expiratory pressure ventilation on peripheral tissue perfusion evaluated by measurements of tissue gases and pH. An experimental study in pigs with oleic acid lung injury

Measurements of subcutaneous oxygen tension (PscO(2)), subcutaneous carbon dioxide tension (PscCO(2)) and subcutaneous pH (pHsc) were used for evaluation of peripheral oxygenation in pigs subjected to oleic acid-induced lung injury during ventilation with increasing levels of positive end-expiratory pressure (PEEP). Lung injury resulted in a decrease of arterial oxygen tension (PaO(2)) from 93 to 37 mm Hg (p<0.01) with maintained cardiac output. PscO(2) decreased from 45 to 17 mm Hg (p<0.01) and pHsc from 7.47 to 7.39 (p<0.05), and PscCO(2) increased from 46 to 59 mm Hg (p<0.05). Increase of PEEP level between 5 and 20 cm H(2)O resulted in a continuous increase of PaO(2) from 45 to 145 mm Hg and a decrease of cardiac output from 4.1 to 2.0 liters/min (p<0.01). PscO(2) increased up to a PEEP level of 15 cm H(2)O, reaching 26 mm Hg. Further increase of PEEP level up to 20 cm H(2)O resulted in an increase of PscCO(2) from 65 to 71 mm Hg (p<0.05) and a decrease of pHsc from 7.31 to 7.29 (p<0.05).

IN CONCLUSION

measurements of tissue gases and pH can be used to evaluate optimum peripheral tissue oxygenation during titration of PEEP level. Whether these measurements can be used as the only indicator to guide therapy in an individual case remains to be studied.

A new method of intrathecal PO2, PCO2, and pH measurements for continuous monitoring of spinal cord ischemia during thoracic aortic clamping in pigs

BACKGROUND

Impaired spinal cord circulation during thoracic aortic clamping may result in paraplegia. Reliable and fast responding methods for intraoperative monitoring are needed to facilitate the evaluation of protective measures and efficiency of revascularization.

METHODS

In 11 pigs, a multiparameter PO2, PCO2, and pH sensor (Paratrend 7, Biomedical Sensors Ltd, United Kingdom) was introduced into the intrathecal space for continuous monitoring of cerebrospinal fluid (CSF) oxygenation during thoracic aortic cross-clamping (AXC) distal to the left subclavian artery. A laser-Doppler probe was inserted into the epidural space for simultaneous measurements of spinal cord flux. Registrations were made before and 30 minutes after clamping and 30 and 60 minutes after declamping. The same measuring points were used for systemic hemodynamic and metabolic data acquisition.

RESULTS

The mean CSF PO2 readings of 41 mm Hg (5.5 kPa) at baseline decreased within 3 minutes to 5 mm Hg (0.7 kPa) during AXC (P < .01). Spinal cord flux measurement responded immediately in the same way to AXC. Both methods indicated normalization of circulation during declamping. Significant (P < .01) changes were also observed in the CSF metabolic parameters PCO2 and pH.

CONCLUSIONS

In this experimental model of spinal ischemia by AXC, online monitoring of intrathecal PO2, PCO2, and pH showed significant changes and correlated well with epidural laser-Doppler flowmetry (P < .01).