P. D. Wimberley

HYPERTENSIVE PEAKS IN THE PATHOGENESIS OF INTRAVENTRICULAR HEMORRHAGE IN THE NEWBORN. ABOLITION BY PHENOBARBITONE SEDATION

ABSTRACT. Mean arterial blood pressure (MABP) was measured continuously for 3 to 5 days after birth in 27 premature infants with a birth weight under 1500 g, and who required umbilical artery catheterisation. All had respiratory distress syndrome (RDS). Intraventricular hemorrhage (IVH) occurred in 9 infants (33%), diagnosed by computered tomography (CT). IVH was more common in infants of lower gestational age, in infants delivered vaginally and in infants with perinatal asphyxia. Variable increases in MABP over the resting value occurred in all infants associated with increases in both active and passive motor activity. In 6 infant pairs matched for birth weight, gestational age, mode of delivery and severity of perinatal asphyxia, the infants who developed IVH had higher peak MABP valued compared to matched controls. Resting and minimum MABP values were not different in the two groups. We conclude that the large increases in arterial blood pressure which occur with both spontaneous motor activity and in association with nursing procedures, are an important cause of development of IVH in very low birth weight infants. An example is given to show that pressure peaks can be abolished by phenobarbitone sedation.

Are sodium bicarbonate and potassium bicarbonate fully dissociated under physiological conditions

In solutions containing 160 mmol/l Na+ and K+, respectively, measurements with an ion-selective electrode system (KNA1, Radiometer), showed apparent falls in the respective Na+ and K+ concentrations when C1- was replaced by HCO3-. After correction for the change in liquid junction potential, the fall was 9.2 mmol/l for Na+ and 7.3 mmol/l for K+. On the basis of these findings we conclude that sodium bicarbonate and potassium bicarbonate are not fully dissociated in solution, and that NaHCO3(0) and KHCO3(0) do exist as chemical components with association constants of 0.72 and 0.55, respectively. Using these association constants, normal plasma will contain 1.2 mmol/l NaHCO3(0) and 0.03 mmol/l KHCO3(0). Thus NaHCO3(0) accounts for virtually the same amount of CO2 as the physically dissolved fraction. A review of all the currently known CO2 species in plasma suggests that there may be a residue of about 2 mmol/l of unknown CO2 species in normal plasma.

Arterial oxygen status determined with routine pH/blood gas equipment and multi-wavelength hemoximetry: Reference values, precision, and accuracy

We measured pH, pCO2, pO2, oxygen saturation, total hemoglobin concentration, and fractions of carboxy- and methemoglobin in arterial blood samples from 35 healthy adults. We used a new algorithm to calculate active hemoglobin concentration, total oxygen concentration, actual half-saturation tension, 2,3-diphosphoglycerate concentration, estimated functional shunt, oxygen extraction tension px (for extracting 2.3 mmol of oxygen per liter of blood, values below 4.5 kPa indicating risk of tissue hypoxia), and the oxygen compensation factor Qx (the factor by which the cardiac output should rise to maintain a normal mixed venous pO2 of 5.0 kPa, factors above 1.5 indicating an extra burden on the heart). Analytical precision was evaluated by duplicate determinations. The accuracy of the half-saturation tension was evaluated by comparison with values for simultaneously drawn venous blood, the accuracy of the calculated concentration of 2,3-diphosphoglycerate by comparison with direct enzymatic measurements. We conclude that all the variables may be determined with sufficient accuracy and precision in healthy adults, provided the oxygen saturation is less than 0.97 and the measurements are performed according to the highest state of the art.

Relation between pH and ionized calcium in vitro and in vivo in man

We investigated the in vitro and in vivo relation between pH and ionized calcium during acute respiratory pH changes. The in vitro slope delta 1gcCa2+/delta pH determined in 20 healthy volunteers after equilibration at two different pCO2 values was -0.22 +/- 0.04 (mean +/- 2 SD) for whole blood and -0.24 +/- 0.04 (mean +/- SD) for serum. The in vivo slope delta 1gcCa2+/delta pH during acute respiratory changes in 10 healthy volunteers was -0.17 +/- 0.04 (mean +/- 2 SD) for capillary blood. A mathematical formula which describes the relation between pH and ionized calcium is presented.

Hemoglobin Hafnia: α2(β116 (G18)His→Gln)2; a new hemoglobin variant mistaken for glycated hemoglobin

Abstract Isoelectric focusing of hemolysate from patients with diabetes mellitus is routinely performed to measure their level of HbA 1c (glycated hemoglobin). For a 6 year old boy with diabetes mellitus this analysis showed an HbA 1c , fraction of approx. 50%, which is very unlikely to occur. The possibility of a hemoglobin variant was considered, and by HPLC-separation the presence of two different β-chains was shown. One tryptic fragment was found to deviate from the normal, and amino-acid analysis and sequence determination revealed the following amino-acid substitution: β116 His→Gln. It is the first reported mutation at this position. Functional studies showed almost normal behaviour, consistent with the fact that the affected persons are without any symptoms. In a family survey we found five nondiabetic members with an abnormality similar to the proband. For the variant we chose the name Hafnia, which is Latin for Copenhagen.

Evaluation of a Transcutaneous Oxygen and Carbon Dioxide Monitor in a Neonatal Intensive Care Department

Transcutaneous‐Po2; (tc‐Po2 (tc‐Pco2) at 44oC and transcutaneous‐Pco2) at 38, 42, 43 and 44oC were measured with a currently available monitoring system (TCM222, Radiometer, Copenhagen) in 64 newborn infants with severe respiratory insufficiency during the first five days of life. Tc‐Pco2 at all four temperatures correlated better with arterial blood‐Pco2 (aB‐Pco2)> than tc‐Po2 with aB‐Po2. However, the sensitivity and specificity of tc‐Po2 and tc‐Pco2 were similar with regard to maintaining aB‐Po2, and aB‐Pco2 within specified limits. Tc‐Pco2 increased relatively with increasing electrode temperature by a factor which was similar to the anaerobic temperature coefficient of Po2, in blood. The coefficient of variation of duplicate measurements was 10 % for tc‐Po2 and 5 % for tc‐Pco2. Electrode drift after an average of 3 hours patient monitoring was 2%±6% (1SD) for tc‐Pco2, and ‐3 %±6 % for tc‐Pco2‐ We conclude that tc‐Po2 and tc‐Pco2 are a valuable supplement to arterial blood gas measurements, but the variable correlation with arterial blood gas values and the electrode drifts which may occur, mean that they cannot fully replace arterial sampling.

Guidelines for routine measurement of blood hemoglobin oxygen affinity: International Federation of Clinical Chemistry (IFCC)

Two methods for the routine determination of blood hemoglobin oxygen affinity are described. Both methods use whole blood and do not require special equipment, tonometry or special gas mixtures. The first method consists of a one-point determination of p50, and requires only 200 μL to 400 μL of whole blood, therefore making it suitable for the pediatric population. The second method uses multiple points, thereby establishing both the shape and position of the hemoglobin oxygen equilibrium curve between 10 and 99 % oxygen saturation. Interpretation of p50 is discussed in relation to evaluation of patients with hemoglobinopathies and as a parameter in estimating availability of oxygen to the tissues.

Evaluation of the Gas-STAT® fluorescence sensors for continuous measurement of pH, pCO2 and pO2 during cardiopulmonary bypass and hypothermia

Continuous measurement of pH, pCO2 and pO2 during extracorporeal circulation has become feasible using disposable fluorescence sensors (optodes). We have evaluated a commercial system: Gas-STAT (American Bentley) by reference to in-vitro measurements on discrete samples using conventional electrochemical sensors (BMS-3, Radiometer). The Gas-STAT measures at the actual temperature of the blood in the extracorporeal circuit. The reference measurements were performed at two fixed temperatures of 25 and 37 °C with interpolation of the values to the actual temperature of the Gas-STAT.10 patients undergoing coronary artery bypass grafting during hypothermic extracorporeal circulation with hemodilution were monitored in the venous as well as the arterial line with the Gas-STAT with 6–9 samplings of arterial and venous blood from each patient, a total of 136 samples.The comparisons revealed a large scatter which was due partly to inter-optode partly to intra-optode variation and partly to a memory effect which re...

Hb Volga [β27(B9)Ala→Asp], A possible de novo mutation in a Danish Person

A 20-year-old Danish male with severe hemolytic anemia was shown to have Hb Volga, which is a rare unstable hemoglobin (Hb) variant (1-5)

THE INFLUENCE OF CHANGES IN ARTERIAL BLOOD PRESSURE ON TRANSCUTANEOUS OXYGEN TENSION (tcPO2) IN THE NEWBORN

ABSTRACT. The possible artefacts in transcutaneous oxygen tension (tcPO2) induced by fluctuations in arterial blood pressure were investigated in ten newborn babies. We mounted one tcPO2 electrode on the foot and another on the chest, and the local arterial blood pressure under the foot electrode was reduced 0.6‐2.0 kPa (9‐15 mmHg) by elevating the foot 11‐19 cm above the heart level. In five mature newborns the tcPO2 of the foot decreased significantly (p=0.015) during elevation by a mean valve of 0.029 kPa (0.22 mmHg) per mmHg decrease in mean arterial blood pressure. In five premature newborns the artefact was insignificant (p=0.62). We conclude therefore that, in contrast to adults, the artefacts induced by minor fluctuations in arterial blood pressure in newborns are hardly of clinical importance.