Säure-Base-Haushalt aus der Perspektive von P. Stewart

[Acid-base balance and Stewart concept : Guide to routine daily use]

In 1981 the Canadian Peter Stewart presented a new concept for the interpretation of the acid-base balance. Rehm et al. published the first German language article on this topic. In 2007 the works of Deetjen and Lichtwarck-Aschoff as well as Funk presented both the physiological and clinical foundations of the Stewart concept as well as algorithms to interpret the acid-base status more precisely. Furthermore, since 2004 many other publications on the Stewart concept have been published, which have sometimes been controversially discussed and has not yet found its way into the everyday interpretation of blood gas analysis. This gap is intended to be filled by this work. It introduces a simple, practical algorithm and provides an approach to understanding the acid-base balance and the Stewart concept, which assumes that the plasma ions determine the pH value and the base excess (BE) in the plasma.

[Blood gas analysis in dogs in veterinary practice. A review]

Blood gas analysis is useful to obtain information about acid-base state and gas exchange of the lung. Interpretation is based on the Henderson-Hasselbalch equation. This approach has its limitations especially in interpretation of complex disturbances of acid-base status and has been complemented by base excess and anion gap. Peter Stewart described a model of quantitative approach to the acid-base disturbances which has been further developed and is known as the strong ion approach. This model differs from the traditional approach in the assessment of metabolic disorders of acid base status. Both models complement each other but also have their advantages and disadvantages. For simple disorders of the acid-base state the Henderson-Hasselbalch approach can be used, however in complex disturbances of acid-base balance, especially with abnormalities of serum albumin and phosphate concentrations, the strong ion approach is recommended. With the understanding of both models and of the clinical presentation of blood gas abnormalities, optimal case management and therapy can be provided.

Importance of the effective strong ion difference of an intravenous solution in the treatment of diarrheic calves with naturally acquired acidemia and strong ion (metabolic) acidosis

BACKGROUND

The effect of sodium bicarbonate on acid-base balance in metabolic acidosis is interpreted differently by Henderson-Hasselbalch and strong ion acid-base approaches. Application of the traditional bicarbonate-centric approach indicates that bicarbonate administration corrects the metabolic acidosis by buffering hydrogen ions, whereas strong ion difference theory indicates that the co-administration of the strong cation sodium with a volatile buffer (bicarbonate) corrects the strong ion acidosis by increasing the strong ion difference (SID) in plasma.

OBJECTIVE

To investigate the relative importance of the effective SID of IV solutions in correcting acidemia in calves with diarrhea.

ANIMALS

Twenty-two Holstein-Friesian calves (4-21 days old) with naturally acquired diarrhea and strong ion (metabolic) acidosis.

METHODS

Calves were randomly assigned to IV treatment with a solution of sodium bicarbonate (1.4%) or sodium gluconate (3.26%). Fluids were administered over 4 hours and the effect on acid-base balance was determined.

RESULTS

Calves suffered from acidemia owing to moderate to strong ion acidosis arising from hyponatremia and hyper-D-lactatemia. Sodium bicarbonate infusion was effective in correcting the strong ion acidosis. In contrast, sodium gluconate infusion did not change blood pH, presumably because the strong anion gluconate was minimally metabolized.

CONCLUSIONS

A solution containing a high effective SID (sodium bicarbonate) is much more effective in alkalinizing diarrheic calves with strong ion acidosis than a solution with a low effective SID (sodium gluconate). Sodium gluconate is ineffective in correcting acidemia, which can be explained using traditional acid-base theory but requires a new parameter, effective SID, to be understood using the strong ion approach.

Alterations of acid-base balance, electrolyte concentrations, and osmolality caused by nonionic hyperosmolar contrast medium during pediatric cardiac catheterization

OBJECTIVE

This prospective clinical observational study was conducted to investigate the effects of contrast medium on acid-base balance, electrolyte concentrations, and osmolality in children.

BACKGROUND

For pediatric cardiac catheterization, high doses of nonionic hyperosmolar contrast medium are widely used.

METHODS

Forty pediatric patients (age 0-16 years) undergoing cardiac angiography with more than 3 ml·kg(-1) of nonionic hyperosmolar contrast medium (Iomeprol) were enrolled, and the total amount of the contrast agent given was documented. Before and after contrast medium administration, a blood sample was collected to analyze electrolytes, acid-base parameters, osmolality, hemoglobin, and hematocrit.

RESULTS

After cardiac catheterization, pH, hemoglobin, hematocrit, bicarbonate, base excess, sodium, chloride, calcium, anion gap and strong ion difference decreased, whereas osmolality increased significantly (base excess -1.8 ± 1.8 vs -3.4 ± 2.3, sodium 138 ± 2.9 vs 132 ± 4.1 mm, osmolality 284 ± 5.7 vs 294 ± 7.6 mosmol·kg(-1), P < 0.01). Seventy-eight percent of the children developed hyponatremia (sodium <135 mm). No changes were seen in pCO(2) , lactate, and potassium levels.

CONCLUSIONS

Regarding the differential diagnosis of metabolic disturbances after pediatric cardiac catheterization, low-anion gap metabolic acidosis and hyponatremia should be considered as a possible side effect of the administered contrast medium.

Alteration of anion gap and strong ion difference caused by hydroxyethyl starch 6% (130/0.42) and gelatin 4% in children

BACKGROUND

Synthetic colloid administration is a common practice for preventing perioperative hypovolemia and consecutive circulatory failure in children. This prospective, randomized study was conducted to investigate the effects of two different unbalanced synthetic colloid solutions on acid-base equilibrium in children.

METHODS

Fifty pediatric patients (aged 0-12 years) scheduled for major pediatric surgery were randomized to receive either 10 ml x kg(-1) of 6% hydroxyethyl starch solution 130/0.42 (HES) or 4% modified fluid gelatin (GEL) to maintain adequate systemic hemodynamics. Before and after colloid administration, a blood sample was collected to analyze hemoglobin, hematocrit, electrolytes, and acid-base parameters. The anion gap and the strong ion difference (SID) were calculated using standard formulas.

RESULTS

Both HES and GEL administration caused a significant increase in plasma chloride concentration (P < 0.01) and an accompanying decrease in SID (P < 0.01). In the HES group, the anion gap decreased significantly (P < 0.01) whereas the anion gap remained stable in the GEL group. In both groups, initial actual base excess and pH did not change significantly after colloid administration.

CONCLUSIONS

Moderate intraoperative plasma replacement with unbalanced synthetic colloids HES and GEL leads to a decrease in SID and, in the case of HES, to a significant decrease in the anion gap in children. These alterations may result in a possible misinterpretation when the anion gap and SID are used for differential diagnosis of metabolic disturbances during major pediatric surgery.