Acid-base Evaluation Research Articles

Independent variables of pH: Ten Knights of the Hydrogen Ion Kingdom-Part I. A prospective observational study.

CO2, HCO3, SID, and total weak acids have been defined as pH's independent variables. However, according to Gamble, HCO3 should be equal to the difference between the sum of cations and the sum of anions besides HCO3. Therefore, if this mathematical expression is substituted for HCO3 in the Henderson-Hasselbalch equation, all independent variables of pH can be demonstrated. Our aim is to test this theory in this study. This prospective observational study was conducted between 2019 and 2020. All admitted patients to the intensive care unit who were >18 years old were included. Demographic data, blood gas parameters, albumin, magnesium, and inorganic phosphorus levels, and outcomes were recorded twice (at admission and at the 24th hour). The multivariate linear regression model was used to determine pH's independent variables. In the multivariate linear regression model, pH was significantly increased by each unit increase in Na, K, Ca, and Mg (mmol L-1). In contrast, pH was significantly decreased by each unit increase in CO2, Cl, lactate, albumin (g dL-1), inorganic phosphorus (mg dL-1), and the strong ion gap. Ten independent variables can accurately predict the changes in pH. For this reason, all ten independent variables should be separately evaluated when interpreting the acid-base status. With this understanding, all algorithms regarding acid-base evaluation may become unnecessary.

Non-carbonic buffer power of whole blood is increased in experimental metabolic acidosis: An in-vitro study.

Non-carbonic buffer power (βNC) of blood is a pivotal concept in acid-base physiology as it is employed in several acid-base evaluation techniques, including the Davenport nomogram and the Van Slyke equation used for Base excess estimation in blood. So far, βNC has been assumed to be independent of metabolic acid-base status of blood, despite theoretical rationale for the contrary. In the current study, we used CO2 tonometry to assess βNC in blood samples from 10 healthy volunteers, simultaneously analyzing the electrolyte shifts across the red blood cell membrane as these shifts translate the action of intracellular non-carbonic buffers to plasma. The βNC of the blood was re-evaluated after experimental induction of metabolic acidosis obtained by adding a moderate or high amount of either hydrochloric or lactic acid to the samples. Moreover, the impact of βNC and pCO2 on the Base excess of blood was examined. In the control samples, βNC was 28.0 ± 2.5mmol/L. In contrast to the traditional assumptions, our data showed that βNC rose by 0.36mmol/L for each 1 mEq/l reduction in plasma strong ion difference (p < 0.0001) and was independent of the acid used. This could serve as a protective mechanism that increases the resilience of blood to the combination of metabolic and respiratory acidosis. Sodium and chloride were the only electrolytes whose plasma concentration changed relevantly during CO2 titration. Although no significant difference was found between the electrolyte shifts in the two types of acidosis, we observed a slightly higher rate of chloride change in hyperchloremic acidosis, while the variation of sodium was more pronounced in lactic acidosis. Lastly, we found that the rise of βNC in metabolic acidosis did not induce a clinically relevant bias in the calculation of Base excess of blood and confirmed that the Base excess of blood was little affected by a wide range of pCO2.

QUESTIONING THE RELEVANCE OF SOLUTION pH CALCULATION

A brief discussion on the unnecessary calculation of pH in solution was done, as the historical reasons for this need before the invention of commercial pH meter was widely diffused. An alternative approach for acid-base equilibrium evaluation was proposed, without approximation or need of application only for simple solutions. The central aspect for the new approach is the determination of equilibrium concentration of all chemical species in solution, including the strong acid or base concentration for adjusting of pH of solutions. Therefore, the proposed method allowed the calculation in a mixture, including several polyprotic systems. Two detailed examples were presented. The effective electrical charge parameter was formally defined.

Arterial Partial Pressures of Carbon Dioxide Estimation Using Non-Invasive Parameters in Mechanically Ventilated Children.

We aim to create a predictive model capable of giving a noninvasive, immediate and reliable estimate of the arterial partial pressure of carbon dioxide (PaCO2) in mechanically ventilated children with a better reliability than its estimation from end-tidal CO2 (PetCO2) and minute ventilation volume (Vmin) evolution. We collected data from the Intensive Care Unit (ICU) database of Sainte-Justine University Hospital (Montreal, Canada) and used the multilayer perceptron (MLP) to estimate the PaCO2. Input data were (1) Arterial blood gas (ABG) at a previous time to calibrate the model, (2) mechanical ventilator parameters and (3) pulse oximetry. The data were divided into four groups depending on the time gap between previous ABG and its prediction: [0 h, 2 h], [2h, 6h], [6h, 12h] and [12 h, 24 h]. We included 17,329 ABGs collected from 527 patients between May 2015 and October 2018. Median age was 6.7 months (interquartile range 1-60) and female proportion was 45%. Patients had a median of 13 ABGs per patient (IQR 5-34). The accuracy of the models in the four groups was 18%, 18%, 19% and 25% higher than the minute volume models and the PetCO2 models (4% to 11%, respectively). Our model based on noninvasive parameters was able to better estimate the PaCO2 in mechanically ventilated children when compared to the traditional techniques. ABG analysis is very important in ICU; it is the gold standard in respiratory and acid-base evaluation. ABG is invasive, painful and risky. Our approach, noninvasive and reliable, is an alternative for optimizing mechanical ventilator settings, thus providing better care for patients.

Acid-base evaluation of chitosan-ferulic acid conjugate by a free radical grafting method

Chitosan-ferulic acid conjugate has been synthesized based on the free radical-mediated grafting reaction. This study investigated the application of potentiometric titration to evaluate the free radical grafting method of ferulic acid on chitosan. The synthesis was done by hydrogen peroxide/ascorbic acid induced free radical reaction to conjugate ferulic acid with chitosan. The conjugate product of ferulic acid-chitosan was characterized by FTIR, UV-Vis spectrophotometry, potentiometric titration, and SEM images. Evaluation of the grating ratio of the ferulic acid-g-chitosan was determined by Folin–Ciocalteu method. The chitosan-ferulic acid conjugate gave 84% in yield with total phenolic showed the value was 92 .53 mg per gram of dry polymers and the conjugate product only soluble at pH around 6. The antioxidant activity of chitosan was increased after functionalized with ferulic acid.

Strong ion gap in cardiogenic shock—the calculation seems wrong

These formulae are erroneous and lead to predictably grossly wrong results. The authors find SIG values of mean -14 mEq/l in the non-survivors' and -10 mEq/l in the survivors' group. ' According to our data the SIG approach does not seem to add further information to usual parameters in acid-base evaluation or early risk stratification in cardiogenic shocks patients.'

Strong ion gap is associated with mortality in pediatric burn injuries.

Severe burn injury produces significant tissue damage, resulting in metabolic acidosis. Current methods of acid-base evaluation are based on dependent variables that may not be accurate after burn injury. The strong ion method of acid-base evaluation is based on independent variables and may accurately predict outcomes in severely burn-injured patients. The authors hypothesize that an increased strong ion gap present on admission will be associated with mortality in severely burn-injured pediatric patients. A retrospective chart review was performed of burn-injured pediatric patients with a TBSA 20% or greater. Data collected included age, TBSA burn injury, mechanism of injury, survival, ventilator days, hospital length of stay, intensive care unit length of stay, and admission laboratory values. Apparent and effective strong ion difference (SIDa, SIDe) were calculated. The strong ion gap (SIG) was determined as the difference between SIDa and SIDe. A total of 48 patients were included in the study. Mean age (years) and TBSA were 7.9 ± 0.8 years and 56.8 ± 2.6%. Eleven patients (23%) died. Mean TBSA for survivors (54.2 ± 2.9%) did not significantly differ from that of nonsurvivors (65.7 ± 5.34%). Ten patients suffered inhalation injury, which was associated with an odds ratio of 10.1* for mortality. Mean SIDa was 44.2 ± 3.2 for the entire study population. Survivors had a significantly lower SIDa (36.6 ± 0.5) than nonsurvivors (59.7 ± 13*). Mean SIDe for all patients was (25 ± 0.7) and did not differ significantly between survivors (24.7 ± 0.7) and nonsurvivors (25.8 ± 2). SIG for nonsurvivors (33.91 ± 14*) was significantly higher than for survivors (14.9 ± 0.3). Controlling for both TBSA and inhalation injury, death was associated with both an increased SIDa (B = 19.3*) and SIG (B = 17.3*). SIG is increased in severely burn-injured pediatric patients, indicating the presence of metabolic acidosis. Furthermore, an increased SIG is significantly associated with mortality. (*P <.05.).

Strong-ion gap approach in patients with cardiogenic shock following ST-elevation myocardial infarction

Assess if acid-base evaluation by Stewart's approach had a clinical role in cardiogenic shock (CS) following ST-elevation myocardial infarction (STEMI). There are three widely used approaches to investigate metabolic acidosis: base excess (BE), anion gap (AG) and the Stewart's approach or strong ion gap (SIG). Available studies suggest the usefulness of SIG in sepsis and trauma. No data are so far available in CS. We enrolled 63 consecutive patients with CS following STEMI submitted to Percutaneous Coronary Intervention (PCI). On admission, the APACHE II (Acute physiology and chronic health evaluation II) score and HOMA (Homeostasis model assessment) index were assessed together with glomerular filtration rate (eGFR), quantitative BE, AG, lactate values and 12 h lactate clearance. Non-survivors showed a higher incidence of PCI failure, higher APACHE II score, lower LVEF, lower eGFR, lower 12 h lactate clearance; a higher admission lactate and more negative BE. No difference was detectable in AG and SIG. Only 3 patients exhibited pathological values of SIG (≥ 2) and only 1 of these patients died. According to our data the SIG approach does not seem to add further information to usual parameters in acid-base evaluation or early risk stratification in CS patients.

Mode of delivery is associated with different hematological profiles in the newborn calf

Several studies on babies have shown that the type of delivery can influence the hematological and immune status of the newborn. In bovine medicine, some authors reported the hematological pattern of the newborn calf, but never related it with the calving process or other perinatal factors. The purpose of the present study was to evaluate the hematological profile in newborn calves in relation to the type of delivery. A total of 41 healthy calves were enrolled; 16 Friesian calves which were born by vaginal delivery without assistance (VD), and 25 Belgian Blue calves that were born by elective Caesarean section (CS). As soon as the calves were born, a complete clinical examination was performed to verify viability and maturity. At 10 min after birth, 2 mL venous blood was collected to perform the blood gas and acid-base evaluation. Blood samples were subsequently collected from the jugular vein within 30 min after birth, and at 1, 2, 3, 7, and 14 days of age. An automatic analyzer was used to determine hemoglobin concentration (Hb), hematocrit (Ht), and red and white blood cell counts, while differential leukocyte count was performed microscopically. Statistical analysis was applied to assess differences between the groups and within the group for all parameters between each sampling time (P ≤ 0.05). All the calves were born alive, viable, and mature. There were no acidotic calves, but statistical analysis revealed many differences, as higher pH, base excess (BE) (P ≤ 0.05), PO2 (P < 0.001), and sO2 (P < 0.0001) in the VD group. Levels of hemoglobin concentration, hematocrit, and red blood cell number were constantly higher in CS calves (P < 0.001). In comparison with the VD calves, white blood cell and neutrophil absolute number were higher at birth and at 14 days of age in the CS group (P < 0.001 and P ≤ 0.05). The mode of delivery, therefore, seems to have an influence on the oxygenation levels and on the hematological and nonspecific immunity profile of the newborn calf.

Beyond the unmeasured anions: the clinics

We thank Dr Berend for his kind suggestions. Beyond the discussion and comparison between different types of fruits, the aim of our investigation was to assess, on a clinical ground, the prognostic values of base excess in uncomplicated ST elevation myocardial infarction. Two considerations arises from this. Firstly, despite the universal controversy on the diagnostic power of different methodological approaches for the evaluation of acid–base disorders [1, 2] (diagnostic target), the assessment of acidosis also retains a prognostic significance in different clinical settings [3–5] (prognostic target). In this context, recently, in acute myocardial infarction, anion gap (though its ‘‘diagnostic’’ limits) proved to provide important incremental information for initial risk stratification. In agreement with these findings, and despite the scarcity of data on acute cardiac patients on this topic, we documented that the presence of low base excess was an independent predictor for intra-ICCU complications (represented by acute pulmonary edema and arrhythmias) in uncomplicated ST elevation myocardial infarction submitted to percutaneous interventions. Secondly, the available literature dealing with the diagnostic significance of ‘‘acid–base parameters’’ stems mainly from studies in critically ill patients. A recent growing body of evidence [3–5] strongly supports the notion that HCO3, base excess and anion gap (corrected for hypoalbuminemia, when needed) remain the most appropriate for clinical usage. In our investigation we enrolled consecutive uncomplicated STEMI patients, mirroring the real world scenario. These patients do not show hypoalbuminemia and hence anion gap correction is not necessary. In our opinion, the strength of our investigation is represented by the fact that easily available parameters (such as base excess) proved to help clinicians in optimizing risk stratification in the early phase of STEMI patients, even if uncomplicated. Like Dr Berend, we agree that Cl/Na deserves further studies in a larger cohort of patients in order to better clarify its clinical significance since it is a very feasible parameter, and that is what we have expressed in the section ‘‘limit of the study’’. We are very grateful for the suggestions and challenges posed by Dr Berend. Yet we are convinced that in the dialectic reasoning on acid–base evaluation, the clinical significance of parameters should also be taken into account, bearing in mind the recent evidence.

Buffy Coat and Serum Concentration of Potassium Related to the Acid-base Status in Dogs Following Induced Hypokalemia

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Acid-base evaluation of umbilical cord blood: relation to delivery mode and Apgar scores

Acid-base status of umbilical artery and vein blood was measured immediately after delivery in 300 cases. A slight acidosis of mixed respiratory/metabolic type was found in newborns delivered following a second stage of 10–30 min duration. After a second stage of more than 30 min the metabolic contribution to the acidosis was predominating. With Apgar scores lower than 10 the pH was found to decrease and carbon dioxide tension to increase. Induction or augmentation of labor by oxytocin did not influence the acid-base status of umbilical cord blood. Delivery by vacuum extraction or low forceps resulted in lower pH and higher carbon dioxide tension in umbilical cord blood, but the changes were associated with the indication for instrumental delivery and not with mode of delivery. A large arterio-venous difference between the acid-base parameters was usually connected to vigorous newborns and a small difference to depressed infants. The carbon dioxide tension was usually increased in newborns with decreased pH, and a close correlation between these parameters was found. No case of acidosis (pH below 7.15) was found in this population at carbon dioxide tensions below 7.2 kPa; at higher P co 2 values only 25% of the newborns were acidotic. A P co 2 level of 7.7 kPa might be used at transcutaneous carbon dioxide monitoring during labor, although the sensitivity and specificity of this parameter will have to be decided in a prospective study.

Paracervical block with 2-chloroprocaine.

Thirty healthy term gravidas in active labor received a paracervical block (PCB) with the ester-type local anesthetic, 2-chloroprocaine (2CP). Good to excellent pain relief resulted in all but 1 case. The duration of action was short (mean 38.9 min), requiring repeat blocks in 6/30 cases. Fetal heart rate and uterine contractions were electronically monitored, and fetal acid-base status was periodically checked by fetal scalp pH measurements. PCB-related fetal bradycardia was observed in 3 cases, but in only 1 case was PCB the only cause for the bradycardia. Fetal acidosis was not observed. No instance of neonatal depression or acidosis as expressed by the 1- and 5-minute Apgar scores and cord blood acid-base evaluation was observed. No maternal complications were observed. It is concluded that paracervical block using 2CP is an effective though short-acting method of pain relief which, when properly monitored, is safe for both mother and fetus.

Significance of meconium during labor

Continuous fetal heart rate (FHR) monitoring and routine fetal scalp blood sampling was utilized in the evaluations of 366 fetuses during labor. One hundred and six patients had meconium in the amniotic fluid at some time during labor. A total of 26,110 uterine contractions were monitored during these 366 labors. The incidence of FHR patterns as a percentage of uterine contractions was calculated for the meconium and nonmeconium groups. Although there was a 3½ increase in the incidence of low five-minute Apgar scores (less than 7) in the meconium group, signs of fetal distress were, with rare exception, not significantly different from those in the nonmeconium group. The presence of meconium in the amniotic fluid without signs of fetal asphyxia (late decelerations and acidosis) is not a sign of fetal distress and need not be an indication for active intervention. The combination of fetal asphyxia and meconium staining of the amniotic fluid, however, does enhance the potential for meconium aspiration and a poor neonatal outcome. Universal fetal heart rate monitoring and appropriate fetal acid-base evaluation is recommended for following patients with meconium in the amniotic fluid during labor.