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Monocrystalline antimony electrodes can be used as pH sensors for continuous monitoring in vivo.The electric potential of the electrodes stems from a corrosion reaction in which antimony metal dissolution constitutes the anodic reaction. In this study the amount of antimony which leaves a monocrystalline antimony sensor, when monitoring pH in thermostatically controlled sterile human heparinized plasma, was determined by neutron activation analyses. From these results the toxicity hazard of using such electrodes in vivois assessed. It is concluded that the amount of antimony released from a monocrystalline pH sensor, when used in a biological medium, is small compared with the amount of antimony accepted for administration as a medical therapeutic. Thus it should be safe from the toxicological point of view to use monocrystalline antimony electrodes for in vivopH monitoring.

The membranes of the pO2 sensor in a conventional blood gas analyser and a commercially available catheter pO2electrode were coated with a glutardialdehyde stabilized heparin layer. It was analysed whether or not the "non-thrombogenic" heparin surface could improve the accuracy of in vitro pO2 registration and continuous in vivo paO2 monitoring. The in vivo experiments were performed on anaesthetized and non-anticoagulated dogs. Two identical blood gas analysers were used, one furnished with a heparin coated pO2 membrane and the other with a standard pO2 membrane. In vitro pO2 determinations exhibited - when simultaneously analysing the same blood sample - identical mean values. For repeated pO2 determinations, however, the standard deviation was significantly lower on the analyser furnished with a heparinized membrane. The non-heparinized catheter pO2 electrode showed a marked deterioration in accuracy with time as compared with blood-gas analysis on reference blood samples. Falsely low paO2 values were presented. The heparinized catheter electrode monitored values in full agreement with those of the conventional blood gas analyser using standard membranes.It is concluded that the heparin surface on the oxygen diffusible membranes diminishes the variability of the diffusion characteristics both at contact with anticoagulated blood in vitro and during in vivo paO2 monitoring. The "non-thrombogenic" heparin surface prevents diffusion impeding clot formations when an arterial catheter pO2 sensor is used.

Continuous intra-arterial pH-monitoring was performed on anaesthetized and artificially ventilated dogs. The pH sensor consisted of monocrystalline antimony. The sensor was placed on the tip of a catheter, length approximately 35 cm and diameter 0.8 mm. No anticoagulation was undertaken. The pH range studied was 7.01-7.53, the pH being changed by infusion of sodium bicarbonate or ammonium chloride. Arterial reference blood samples for in vitro blood gas analyses were taken under stable monitoring conditions and analysed with a minimal delay. The millivolt signal from the antimony sensor was found to be a linear function of the pH of the reference blood samples in the intra-arterial pH range studied. The sensitivities of the different antimony sensors were closely correlated but not identical. When the antimony sensor was used completely uncalibrated, the standard deviation of the registered potential corresponds to 0.06 pH units. After single point calibration a standard deviation of 0.03 pH units was obtained. These standard deviations include a suspected influence of minor changes in the partial pressure of oxygen during the experiments.

Surface-heparinized catheter Po2electrodes were used for continuous intraarterial monitoring in non-heparinized dogs. During one-day experiments the read-out of the electrode monitoring unit was compared with that of conventional blood gas analysis. Furthermore, the electrodes were studied after long-term implantation. The intra-arterial Po2electrodes have previously been reported to be linear in the gas phase, water phase and in heparinized blood. The present study demonstrates that the catheter electrodes remain linear after surface heparinization. As compared with the conventional blood gas analysis it was found that the desk analyser in the range Pao2> 18 kPa underestimated the actual Pao2as compared to the invasively monitored Pao2, but in the range below 7 kPa the desk analyser overestimated the Pao2. Surface-heparinized Po2catheter electrodes were studied after up to 23 days of implantation. No coagulation phenomenon was found around the catheters, neither macroscopically nor by scanning electron microscopy. The electrical function withstood 7 days of implantation. After more extended periods the electrical leads were broken without any damage to the catheter itself. When compared with acutely implanted surface-heparinized electrodes, there was no difference in monitoring characteristics between the acutely implanted and the long-term implanted Po2electrodes.

Surface-heparinized catheter Po2 electrodes were used for continuous intraarterial monitoring in non-heparinized dogs. During one-day experiments the read-out of the electrode monitoring unit was compared with that of conventional blood gas analysis. Furthermore, the electrodes were studied after long-term implantation. The intra-arterial Po2 electrodes have previously been reported to be linear in the gas phase, water phase and in heparinized blood. The present study demonstrates that the catheter electrodes remain linear after surface heparinization. As compared with the conventional blood gas analysis it was found that the desk analyser in the range Pao2 > 18 kPa underestimated the actual Pao2 as compared to the invasively monitored Pao2, but in the range below 7 kPa the desk analyser overestimated the Pao2. Surface-heparinized Po2 catheter electrodes were studied after up to 23 days of implantation. No coagulation phenomenon was found around the catheters, neither macroscopically nor by scanning electron microscopy. The electrical function withstood 7 days of implantation. After more extended periods the electrical leads were broken without any damage to the catheter itself. When compared with acutely implanted surface-heparinized electrodes, there was no difference in monitoring characteristics between the acutely implanted and the long-term implanted Po2 electrodes.

Monocrystalline antimony catheter electrodes were studied intra-arterially in non-heparinized dogs. The sensitivity for variations in arterial Po2(Pao2) was evaluated for this kind of metal-metal oxide pH sensor. The influence of Pao2compensation on a previous pH sensitivity estimate was calculated. When the mV signal from the antimony sensor, after compensation for pH and temperature variations, was expressed as a function of log10Pao2, a non-linear relation was found for the Pao2range studied, 2.9–50 kPa. After calculations this range was divided into a lower and a higher sub-range. A first-order linear approximation was applied for these subranges. The sensitivity for oxygen was 70 mVlog10Pao2in the range 2.9 kPa < Pao2< 10 kPa, and 20.7 mVlog10Pao2in the range 10 kPa < Pao2< 50 kPa. The non-logarithmic sensitivity for intra-arterial oxygen is contradictory to results from in vitrostudies in test solutions. The present study indicates that the monocrystalline antimony pH sensor has a sensitivity for Pao2variations which is closely correlated to the haemoglobin-oxygen dissociation function. When compensation for Pao2variations was performed on an earlier evaluated study over a wide pH range but limited Pao2range, the pH sensitivity previously found was not influenced.