High PCO2 in Rat Kidney

It is a puzzling fact that PCO2 in the superficial renal cortex is much higher than in renal venous blood. Using a newly developed PCO2 electrode, the authors found the highest level of PCO2 in the first portion of the proximal tubule and concluded that this peak is caused by rapid bicarbonate reabsorption in this part of the tubule. To account fully for the large elevation in cortical PCO2, they postulate a countercurrent CO2 exchange between the arteries and veins in the kidney.

Unpredictable fluctuations in transcutaneous pCO2 from capillary blood gas determinations.

Transcutaneous pCO2 electrode response time was optimized by use of a new electrode filling solution composed of NaCl/NaHCO3 electrolyte buffer (100 and 20 mmol/L, respectively) in an equivolume mixture of glycerol and water. The 95% response time to a step change in pCO2 was 49.9 +/- 2.8 s (mean +/- SD) when there was no spacer between the membrane and glass of the electrode. Use of this filling solution during monitoring of severely ill premature infants with cardiopulmonary disease allowed identification of large, unpredictable transient changes in transcutaneous pCO2, and therefore presumably in arterial pCO2, that occurred during capillary blood gas sampling. The changes, which occurred in 19 of 20 samplings, ranged from -1.06 + 2.53 kPa (-8 to +19 Torr). The maximum relative change observed was +29%. These results indicate that the standard protocol for capillary blood collection induces significant transient fluctuations in blood gas tensions. We believe these fluctuations decrease the reliability of capillary pCO2 values for use in clinical management in patient populations similar to ours.

A combined transcutaneous PO2-PCO2 electrode with electrochemical HCO3- stabilization

Combined transcutaneous PO2-PCO2 electrodes are described in which the interaction between the two electrodes due to OH- production at the O2 cathode has been eliminated. An anode of either anodized aluminum or platinum has been driven at a current equal to cathode current to force stoichiometric consumption of OH- at its rate of production. The AgCl reference electrode operates at zero current. O2 sensitivity was not significantly altered by electrolyte pH variation from 6.7 to 9.0 with variations by PCO2. These electrodes have been found stable both with and without spacers, and with electrolytes dissolved in 50–100% ethylene glycol. In 22 anesthetized patients, with electrode temperature of 43 degrees C (s refers to skin surface, a to arterial blood); PsO2 = 0.52PaO2 + 15 (range 54–300) (r = 0.66; Sy . x = 29.6; n = 46); and PsCO2 = 1.39PaCO2 + 2.1 (range 24–98) (r = 0.99; Sy . x = 2.28; n = 48).

Role of neural afferents from working limbs in exercise hyperpnea

To determine the role of reflex discharge of afferent nerves from the working limbs in the exercise hyperpnea, 1.5- to 2.5-min periods of phasic hindlimb muscle contraction were induced in anesthetized cats by bilateral electrical stimulation of ventral roots L7, S1, and S2. Expired minute ventilation (VE) and end-tidal PCO2 (PETCO2) were computed breath by breath, and mean arterial PCO2 (PaCO2) was determined from discrete blood samples and, also in most animals, by continuous measurement with an indwelling PCO2 electrode. During exercise VE rose progressively with a half time averaging approximately 30 s, but a large abrupt increase in breathing at exercise onset typically did not occur. Mean PaCO2 and PETCO2 remained within approximately 1 Torr of control levels across the work-exercise transition, and PaCO2 was regulated at an isocapnic level after VE had achieved its peak value. Sectioning the spinal cord at L1-L2 did not alter these response characteristics. Thus, reflex discharge of afferent nerves from the exercising limbs was not requisite for the matching of ventilation to metabolic demand during exercise.

Skin Surface Carbon Dioxide Tension in Sick Infants

Skin surface Pco2 (Psco2) was measured at 44 C in 17 sick infants using a Radiometer surface Pco2 electrode. Values obtained for Psco2 were compared with simultaneous values for arterial Pco2 (Paco2). Psco2 was found to be linearly related to Paco2 by a regression line with a slope 1.37. Paco2 could be predicted from Psco2 to within 6 torr in all instances. The relationship was not affected by the patient's gestational age, postnatal age, weight, or blood pressure. This electrode is a valuable clinical tool in the management of sick infants.

Measurement of myocardial PCO2 with a microelectrode: its relation to coronary sinus PCO2

A micro-PCO2 electrode, with dimensions of 1 x 10 mm, and a 63% response time of 14 s was inserted into the left ventricular myocardium of the pentobarbital-anesthetized dog. Continuous recordings were made of myocardial PCO2 (PmCO2), arterial PCO2 (PaCO2), and coronary sinus PCO2 (CSPCO2) during variation of respiratory rate. PmCO2 and CSPCO2 were compared at varying coronary flow. PmCO2 was similar to and closely followed changes in CSPCO2. The difference between PmCO2 and CSPCO2 was -0.52 +/- 3.63 (SD) mmHg, and PmCO2 exceeded PaCO2 by 20.69 +/- 5.12 mmHg. After coronary occlusion, PmCO2, rose promptly, but CSPCO2 was only slightly elevated until the occlusion was released, when a CO2 efflux into the coronary sinus occurred. It is concluded that the electrode measures extracellular PCO2 and that extracellular and myocardial PCO2 are essentially equal. PmCO2 rises rapidly following coronary occlusion.