Characterization and clinical application of the "significance band" for acute respiratory alkalosis

Acute renal response to changes in carbon dioxide in mechanically ventilated female pigs

Kidney response to acute and mechanically induced variation in ventilation associated with different levels of PEEP has not been investigated. We aimed to quantify the effect of ventilatory settings on renal acid-base compensation. Forty-one pigs undergoing hypo- (<0.2 Lkg-1 min-1, PEEP 25 cmH2O), intermediate (0.2-0.4 Lkg-1 min-1 with either PEEP 5 or 25 cmH2O), or hyper-ventilation (>0.4 Lkg-1 min-1, PEEP 5 cmH2O) for 48 h were retrospectively included. The decrease in pH paralleled the decrease in plasma strong ion difference (SID) in hyper- and intermediately ventilated groups with lower PEEP. In contrast, the plasma SID remained nearly constant in hypo- and intermediately ventilated groups with higher PEEP. Changes in plasma chloride concentration accounted for the changes in plasma SID (conditional R2 = 0.86). The plasma SID changes were paralleled by mirror changes in urinary SID. Higher PEEP (25 cmH2O), compared to lower PEEP (5 cmH2O) dampened or abolished the renal compensation through its effect on hemodynamics (higher central venous and mean pulmonary pressures), irrespective of minute ventilation. During mechanical ventilation, the compensatory renal response to respiratory derangement is immediate and progressive but can be dampened by high PEEP levels.

Combining the Physical-Chemical Approach with Standard Base Excess to Understand the Compensation of Respiratory Acid-Base Derangements: An Individual Participant Meta-analysis Approach to Data from Multiple Canine and Human Experiments

BACKGROUND

Several studies explored the interdependence between Paco2 and bicarbonate during respiratory acid-base derangements. The authors aimed to reframe the bicarbonate adaptation to respiratory disorders according to the physical-chemical approach, hypothesizing that (1) bicarbonate concentration during respiratory derangements is associated with strong ion difference; and (2) during acute respiratory disorders, strong ion difference changes are not associated with standard base excess.

METHODS

This is an individual participant data meta-analysis from multiple canine and human experiments published up to April 29, 2021. Studies testing the effect of acute or chronic respiratory derangements and reporting the variations of Paco2, bicarbonate, and electrolytes were analyzed. Strong ion difference and standard base excess were calculated.

RESULTS

Eleven studies were included. Paco2 ranged between 21 and 142 mmHg, while bicarbonate and strong ion difference ranged between 12.3 and 43.8 mM, and 32.6 and 60.0 mEq/l, respectively. Bicarbonate changes were linearly associated with the strong ion difference variation in acute and chronic respiratory derangement (β-coefficient, 1.2; 95% CI, 1.2 to 1.3; P < 0.001). In the acute setting, sodium variations justified approximately 80% of strong ion difference change, while a similar percentage of chloride variation was responsible for chronic adaptations. In the acute setting, strong ion difference variation was not associated with standard base excess changes (β-coefficient, -0.02; 95% CI, -0.11 to 0.07; P = 0.719), while a positive linear association was present in chronic studies (β-coefficient, 1.04; 95% CI, 0.84 to 1.24; P < 0.001).

CONCLUSIONS

The bicarbonate adaptation that follows primary respiratory alterations is associated with variations of strong ion difference. In the acute phase, the variation in strong ion difference is mainly due to sodium variations and is not paralleled by modifications of standard base excess. In the chronic setting, strong ion difference changes are due to chloride variations and are mirrored by standard base excess.

EDITOR’S PERSPECTIVE

Natural high ambient temperature-induced respiratory hypocapnia without activation of the hypothalamic-pituitary-adrenal axis in lactating goats

Background and Aim

Activation of breathing, the hypothalamic-pituitary-adrenal (HPA) axis, and plasma antioxidant defense are adaptive mechanisms in lactating dairy goats fed during the summer season. However, an excess of these responses can interfere with the gas exchange. This study aimed to investigate the effect of natural high ambient temperature (HTa) on blood gas parameters and their relation to the HPA axis and antioxidant defense.

Materials and Methods

Six mid-lactating goats were included in this study and were fed in individual pens for 2 weeks. The data on ambient conditions, physiological responses, and blood chemistry were measured for two sampling days (D7 and D14), 1 week apart during the late summer season. On this two-sampling day, the main physiological responses to HTa, including respiration rate (RR), rectal temperature (Tr), blood gas, and blood chemistry, were measured in the morning and afternoon.

Results

Goats from both D7 and D14 increased RR and Tr significantly according to morning and afternoon periods. In addition, goats were at the hypocapnia stage during afternoon panting without a change in blood pH and bicarbonate levels. Interestingly, HTa-induced hypocapnia was not accompanied by an increase in plasma cortisol levels. Finally, ΔTa was negatively correlated with changes in glutathione peroxidase activity.

Conclusion

The natural HTa (ΔTa; 5-8°C) in this study activated evaporative heat dissipation and was high enough to induce respiratory hypocapnia. Importantly, this ΔTa did not activate the HPA axis but was correlated with a change in antioxidant defense. Therefore, under natural HTa in tropical conditions, respiratory hypocapnia is the first line of physiological response in goats within a specific range of natural ΔTa (5-8°C).

What's Old Is New Again: Harnessing the Power of Original Experiments to Learn Renal Physiology

Although medical schools across the United States have updated their curricula to incorporate active learning techniques, there has been little discussion on the nature of the content presented to students. Here, we share detailed examples of our experience in using original experiments to lay the groundwork for foundational concepts in renal physiology and pathophysiology. We believe that this approach offers distinct advantages over standard case-based teaching by (1) starting with simple concepts, (2) analyzing memorable visuals, (3) increasing graphical literacy, (4) translating observations to "rules," (5) encouraging critical thinking, and (6) providing historical perspective to the study of medicine. Although we developed this content for medical students, we have found that many of these lessons are also appropriate as foundational concepts for residents and fellows and serve as an excellent springboard for increasingly complex discussions of clinical applications of physiology. The use of original experiments for teaching and learning in renal physiology harnesses skills in critical thinking and provides a solid foundation that will help learners with subsequent case-based learning in the preclerkship curriculum and in the clinical arena.

Clinical Approach to Assessing Acid-Base Status: Physiological vs Stewart

Evaluation of acid-base status depends on accurate measurement of acid-base variables and their appropriate assessment. Currently, 3 approaches are utilized for assessing acid-base variables. The physiological or traditional approach, pioneered by Henderson and Van Slyke in the early 1900s, considers acids as H⁺ donors and bases as H⁺ acceptors. The acid-base status is conceived as resulting from the interaction of net H⁺ balance with body buffers and relies on the H₂CO₃/HCO₃^- buffer pair for its assessment. A second approach, developed by Astrup and Siggaard-Andersen in the late 1950s, is known as the base excess approach. Base excess was introduced as a measure of the metabolic component replacing plasma [HCO₃^-]. In the late 1970s, Stewart proposed a third approach that bears his name and is also referred to as the physicochemical approach. It postulates that the [H⁺] of body fluids reflects changes in the dissociation of water induced by the interplay of 3 independent variables-strong ion difference, total concentration of weak acids, and PCO₂. Here we focus on the physiological approach and Stewart's approach examining their conceptual framework, practical application, as well as attributes and drawbacks. We conclude with our view about the optimal approach to assessing acid-base status.

Stewart analysis unmasks acidifying and alkalizing effects of ionic shifts during acute severe respiratory alkalosis

PURPOSE

Although both the Henderson-Hasselbalch method and the Stewart approach can be used to analyze acid-base disturbances and metabolic and respiratory compensation mechanisms, the latter may be superior in detecting subtle metabolic changes.

MATERIALS AND METHODS

We analyzed acid-base disturbances using both approaches in six healthy male volunteers practicing extreme voluntary hyperventilation. Arterial blood gas parameters were obtained during a breathing exercise consisting of approximately 30 cycles of powerful hyperventilation followed by breath retention for approximately 2 min.

RESULTS

Hyperventilation increased pH from 7.39 ± 0.01 at baseline to 7.74 ± 0.06, PaCO₂ decreased from 34.1 ± 1.1 to 12.6 ± 0.7 mmHg, PaO₂ increased from 116 ± 4.6 to 156 ± 4.3 mmHg. Baseline apparent strong ion difference was 42.3 ± 0.5 mEq/L, which decreased to 37.1 ± 0.7 mEq/L following hyperventilation. The strong ion gap significantly decreased following hyperventilation, with baseline levels of 10.0 ± 0.9 dropping to 6.4 ± 1.1 mEq/L.

CONCLUSIONS

Henderson-Hasselbalch analysis indicated a profound and purely respiratory alkalosis with no metabolic compensation following extreme hyperventilation. The Stewart approach revealed metabolic compensation occurring within minutes. These results challenge the long-held axiom that metabolic compensation of acute respiratory acid-base changes is a slow process.

Low noncarbonic buffer power amplifies acute respiratory acid-base disorders in patients with sepsis: an in vitro study

Patients with sepsis have typically reduced concentrations of hemoglobin and albumin, the major components of noncarbonic buffer power (β). This could expose patients to high pH variations during acid-base disorders. The objective of this study is to compare, in vitro, noncarbonic β of patients with sepsis with that of healthy volunteers, and evaluate its distinct components. Whole blood and isolated plasma of 18 patients with sepsis and 18 controls were equilibrated with different CO₂ mixtures. Blood gases, pH, and electrolytes were measured. Noncarbonic β and noncarbonic β due to variations in strong ion difference (β_SID) were calculated for whole blood. Noncarbonic β and noncarbonic β normalized for albumin concentrations (β_NORM) were calculated for isolated plasma. Representative values at pH = 7.40 were compared. Albumin proteoforms were evaluated via two-dimensional electrophoresis. Hemoglobin and albumin concentrations were significantly lower in patients with sepsis. Patients with sepsis had lower noncarbonic β both of whole blood (22.0 ± 1.9 vs. 31.6 ± 2.1 mmol/L, P < 0.01) and plasma (0.5 ± 1.0 vs. 3.7 ± 0.8 mmol/L, P < 0.01). Noncarbonic β_SID was lower in patients (16.8 ± 1.9 vs. 24.4 ± 1.9 mmol/L, P < 0.01) and strongly correlated with hemoglobin concentration (r = 0.94, P < 0.01). Noncarbonic β_NORM was lower in patients [0.01 (-0.01 to 0.04) vs. 0.08 (0.06-0.09) mmol/g, P < 0.01]. Patients with sepsis and controls showed different amounts of albumin proteoforms. Patients with sepsis are exposed to higher pH variations for any given change in CO₂ due to lower concentrations of noncarbonic buffers and, possibly, an altered buffering function of albumin. In both patients with sepsis and healthy controls, electrolyte shifts are the major buffering mechanism during respiratory acid-base disorders.NEW & NOTEWORTHY Patients with sepsis are poorly protected against acute respiratory acid-base derangements due to a lower noncarbonic buffer power, which is caused both by a reduction in the major noncarbonic buffers, i.e. hemoglobin and albumin, and by a reduced buffering capacity of albumin. Electrolyte shifts from and to the red blood cells determining acute variations in strong ion difference are the major buffering mechanism during acute respiratory acid-base disorders.

Mobilizing Carbon Dioxide Stores. An Experimental Study

Rationale: Understanding the physiology of CO₂ stores mobilization is a prerequisite for intermittent extracorporeal CO₂ removal (ECCO₂R) in patients with chronic hypercapnia.Objectives: To describe the dynamics of CO₂ stores.Methods: Fifteen pigs (61.7 ± 4.3 kg) were randomized to 48 hours of hyperventilation (group "Hyper," n = 4); 48 hours of hypoventilation (group "Hypo," n = 4); 24 hours of hypoventilation plus 24 hours of normoventilation (group "Hypo-Baseline," n = 4); or 24 hours of hypoventilation plus 24 hours of hypoventilation plus ECCO₂R (group "Hypo-ECCO₂R," n = 3). Forty-eight hours after randomization, the current [Formula: see text]e was reduced by 50% in every pig.Measurements and Main Results: We evaluated [Formula: see text]co₂, [Formula: see text]o₂, and metabolic [Formula: see text]co₂ ([Formula: see text]o₂ times the metabolic respiratory quotient). Changes in the CO₂ stores were calculated as [Formula: see text]co₂ - metabolic V̇co₂. After 48 hours, the CO₂ stores decreased by 0.77 ± 0.17 l kg^-1 in group Hyper and increased by 0.32 ± 0.27 l kg^-1 in group Hypo (P = 0.030). In group Hypo-Baseline, they increased by 0.08 ± 0.19 l kg^-1, whereas in group Hypo-ECCO₂R, they decreased by 0.32 ± 0.24 l kg^-1 (P = 0.197). In the second 24-hour period, in groups Hypo-Baseline and Hypo-ECCO₂R, the CO2 stores decreased by 0.15 ± 0.09 l kg^-1 and 0.51 ± 0.06 l kg^-1, respectively (P = 0.002). At the end of the experiment, the 50% reduction of [Formula: see text]e caused a Pa_CO2 rise of 9.3 ± 1.1, 32.0 ± 5.0, 16.9 ± 1.2, and 11.7 ± 2.0 mm Hg h^-1 in groups Hyper, Hypo, Hypo-Baseline, and Hypo-ECCO₂R, respectively (P < 0.001). The Pa_CO2 rise was inversely related to the previous CO₂ stores mobilization (P < 0.001).Conclusions: CO₂ from body stores can be mobilized over 48 hours without reaching a steady state. This provides a physiological rationale for intermittent ECCO₂R in patients with chronic hypercapnia.

Sensitive Wearable Temperature Sensor with Seamless Monolithic Integration

Accurate temperature field measurement provides critical information in many scientific problems. Herein, a new paradigm for highly sensitive, flexible, negative temperature coefficient (NTC) thermistor-based artificial skin is reported, with the highest temperature sensing ability reported to date among previously reported NTC thermistors. This artificial skin is achieved through the development of a novel monolithic laser-induced reductive sintering scheme and unique monolithic structures. The unique seamless monolithic structure simultaneously integrates two different components (a metal electrode and metal oxide sensing channel) from the same material at ambient pressure, which cannot be achieved by conventional heterogeneous integration through multiple, complex steps of photolithography or vacuum deposition. In addition to superior performance, electronic skin with high temperature sensitivity can be fabricated on heat-sensitive polymer substrates due to the low-temperature requirements of the process. As a proof of concept, temperature-sensitive artificial skin is tested with conformally attachable physiological temperature sensor arrays in the measurement of the temperatures of exhaled breath for the early detection of pathogenic progression in the respiratory system. The proposed highly sensitive flexible temperature sensor and monolithic selective laser reductive sintering are expected to greatly contribute to the development of essential components in various emerging research fields, including soft robotics and healthcare systems.

Disorders of Acid-Base Balance: New Perspectives

BACKGROUND

Disorders of acid-base involve the complex interplay of many organ systems including brain, lungs, kidney, and liver. Compensations for acid-base disturbances within the brain are more complete, while limitations of compensations are more apparent for most systemic disorders. However, some of the limitations on compensations are necessary to survival, in that preservation of oxygenation, energy balance, cognition, electrolyte, and fluid balance are connected mechanistically.

SUMMARY

This review aims to give new and comprehensive perspective on understanding acid-base balance and identifying associated disorders. All metabolic acid-base disorders can be approached in the context of the relative losses or gains of electrolytes or a change in the anion gap in body fluids. Acid-base and electrolyte balance are connected not only at the cellular level but also in daily clinical practice. Urine chemistry is essential to understanding electrolyte excretion and renal compensations.

KEY MESSAGES

Many constructs are helpful to understand acid-base, but these models are not mutually exclusive. Electroneutrality and the close interconnection between electrolyte and acid-base balance are important concepts to apply in acid-base diagnoses. All models have complexity and shortcuts that can help in practice. There is no reason to dismiss any of the present constructs, and there is benefit in a combined approach.

Assessing Acid-Base Status: Physiologic Versus Physicochemical Approach

The physiologic approach has long been used in assessing acid-base status. This approach considers acids as hydrogen ion donors and bases as hydrogen ion acceptors and the acid-base status of the organism as reflecting the interaction of net hydrogen ion balance with body buffers. In the physiologic approach, the carbonic acid/bicarbonate buffer pair is used for assessing acid-base status and blood pH is determined by carbonic acid (ie, Paco₂) and serum bicarbonate levels. More recently, the physicochemical approach was introduced, which has gained popularity, particularly among intensivists and anesthesiologists. This approach posits that the acid-base status of body fluids is determined by changes in the dissociation of water that are driven by the interplay of 3 independent variables: the sum of strong (fully dissociated) cation concentrations minus the sum of strong anion concentrations (strong ion difference); the total concentration of weak acids; and Paco₂. These 3 independent variables mechanistically determine both hydrogen ion concentration and bicarbonate concentration of body fluids, which are considered as dependent variables. Our experience indicates that the average practitioner is familiar with only one of these approaches and knows very little, if any, about the other approach. In the present Acid-Base and Electrolyte Teaching Case, we attempt to bridge this knowledge gap by contrasting the physiologic and physicochemical approaches to assessing acid-base status. We first outline the essential features, advantages, and limitations of each of the 2 approaches and then apply each approach to the same patient presentation. We conclude with our view about the optimal approach.

Homeostasis, the milieu intérieur, and the wisdom of the nephron

The concept of homeostasis has been inextricably linked to the function of the kidneys for more than a century when it was recognized that the kidneys had the ability to maintain the "internal milieu" and allow organisms the "physiologic freedom" to move into varying environments and take in varying diets and fluids. Early ingenious, albeit rudimentary, experiments unlocked a wealth of secrets on the mechanisms involved in the formation of urine and renal handling of the gamut of electrolytes, as well as that of water, acid, and protein. Recent scientific advances have confirmed these prescient postulates such that the modern clinician is the beneficiary of a rich understanding of the nephron and the kidney's critical role in homeostasis down to the molecular level. This review summarizes those early achievements and provides a framework and introduction for the new CJASN series on renal physiology.

Acid-base patterns in acute severe asthma

BACKGROUND AND OBJECTIVES

Acid-base status in acute severe asthma (ASA) remains undefined; some studies report complete absence of metabolic acidosis, whereas others describe it as present in one fourth of patients or more. Conclusion discrepancies would therefore appear to derive from differences in assessment methodology. Only a systematic approach centering on patient clinical findings can correctly establish true acid-base disorder prevalence levels.

METHODS

This study examines acid-base patterns in ASA (314 patients), taking into account both natural history of disease and treatment, in patients free of other diseases altering acid-base status. Data were collected from patients admitted for ASA without prior history of chronic bronchitis, emphysema, kidney or liver disease, heart failure, uncontrolled diabetes mellitus or gastrointestinal illness. Informed consent was obtained for all patients, after study protocol approval by the Institutional Review Board.

RESULTS

Arterial blood gases, plasma electrolytes, lactate levels, and FEV(1) were measured on arrival. Severe airway obstruction was found with FEV(1) values of 25.6 ± 10.0%, substantial hypoxemia (PaO(2) 66.1 ± 11.9 mmHg) and increased A-a O(2) gradient (39.3 ± 12.3 mmHg) breathing room air. While respiratory alkalosis occurred in patients with better preservation of FEV1, respiratory acidosis was observed with more severe airway obstruction, as was increased lactate in the majority of patients, independent of PaO(2) and PaCO(2) levels.

CONCLUSIONS

Predominant acid-base patterns observed in ASA in this patient population included primary hypocapnia, or less frequently, primary hypercapnia. Lactic acidosis occurred in 11% of patients and presented consistently as a mixed acid-base disorder. These findings suggest lactic acidosis results from the combined effects of both ASA and medication-related sympathetic effects.

Secondary responses to altered acid-base status: the rules of engagement

Each of the four canonical acid-base disorders expresses as a primary change in carbon dioxide tension or plasma bicarbonate concentration followed by a secondary response in the countervailing variable. Quantified empirically, these secondary responses are directional and proportional to the primary changes, run a variable time course, and tend to minimize the impact on body acidity engendered by the primary changes. Absence of an appropriate secondary response denotes the coexistence of an additional acid-base disorder. Here we address the expected magnitude of the secondary response to each cardinal acid-base disorder in humans and offer caveats for judging the appropriateness of each secondary response.

Exaggerated compensatory response to acute respiratory alkalosis in panic disorder is induced by increased lactic acid production

BACKGROUND

In acute respiratory alkalosis, the severity of alkalaemia is ameliorated by a decrease in plasma [HCO(3)(-)] of 0.2 mEq/L for each 1 mmHg decrease in PaCO(2). Although hyperventilation in panic disorder patients is frequently encountered in outpatients, the drop in plasma [HCO(3)(-)] sometimes surpasses the expectation calculated from the above formula. The quantitative relationship between reduced PaCO(2) and plasma [HCO(3)(-)] in acute respiratory alkalosis has not been studied in panic disorder patients. Our objective was to provide reference data for the compensatory metabolic changes in acute respiratory alkalosis in panic disorder patients.

METHODS

In 34 panic disorder patients with hyperventilation attacks, we measured arterial pH, PaCO(2), plasma [HCO(3)(-)] and lactate on arrival at the emergency room.

RESULTS

For each decrease of 1 mmHg in PaCO(2), plasma [HCO(3)(-)] decreased by 0.41 mEq/L. During hypocapnia, panic disorder patients exhibited larger increases in serum lactate levels (mean +/- SD; 2.59 +/- 1.50 mmol/L, range; 0.78-7.78 mmol/L) than previously reported in non-panic disorder subjects. Plasma lactate accumulation was correlated with PaCO(2) (P < 0.001).

CONCLUSIONS

These results suggest that the compensatory metabolic response to acute respiratory alkalosis is exaggerated by increased lactic acid production in panic disorder patients. Here, we call attention to the diagnosis of acid-base derangements by means of plasma [HCO(3)(-)] and lactate concentration in panic disorder patients.

Clinical acid-base pathophysiology: disorders of plasma anion gap

The plasma anion gap is a frequently used parameter in the clinical diagnosis of a variety of conditions. The commonest application of the anion gap is to classify cases of metabolic acidosis into those that do and those that do not leave unmeasured anions in the plasma. While this algorithm is useful in streamlining the diagnostic process, it should not be used solely in this fashion. The anion gap measures the difference between the unmeasured anions and unmeasured cations and thus conveys much more information to the clinician than just quantifying anions of strong acids. In this chapter, the significance of the anion gap is emphasized and several examples are given to illustrate a more analytic approach to using the clinical anion gap; these include disorders of low anion gap, respiratory alkalosis and pyroglutamic acidosis.

Respiratory effects in humans of a 5-day elevation of end-tidal PCO2 by 8 Torr

The aims of this study were to determine 1) whether ventilatory adaptation occurred over a 5-day exposure to a constant elevation in end-tidal Pco2 and 2) whether such an exposure altered the sensitivity of the chemoreflexes to acute hypoxia and hypercapnia. Ten healthy human subjects were studied over a period of 13 days. Their ventilation, chemoreflex sensitivities, and acid-base status were measured daily before, during, and after 5 days of elevated end-tidal Pco2 at 8 Torr above normal. There was no major adaptation of ventilation during the 5 days of hypercapnic exposure. There was an increase in ventilatory chemosensitivity to acute hypoxia (from 1.35 ± 0.08 to 1.70 ± 0.07 l/min/%; P < 0.01) but no change in ventilatory chemosensitivity to acute hypercapnia. There was a degree of compensatory metabolic alkalosis. The results do not support the hypothesis that the ventilatory adaptation to chronic hypercapnia would be much greater with constant elevation of alveolar Pco2 than with constant elevation of inspired Pco2, as has been used in previous studies and in which the feedback loop between ventilation and alveolar Pco2 is left intact.

Accuracy of base excess--an in vitro evaluation of the Van Slyke equation

OBJECTIVES

To evaluate the precision, bias and CO2 invariance of base excess as determined by the Van Slyke equation over a wide P(CO2) range at normal and low hemoglobin concentrations.

DESIGN

Prospective in vitro study.

SETTING

University research laboratory.

SUBJECTS

Normal human blood, both undiluted and diluted with plasma.

INTERVENTIONS

Two experiments were conducted. In the first, blood unmodified or after adding HCl or sodium bicarbonate was rendered hypercarbic (P(CO2) >70 torr) by gas equilibration. Rapid Pco2 reduction in > or =10 steps to a final P(CO2) < or =20 torr was then performed. In the second experiment, blood unmodified or diluted to a hemoglobin concentration of approximately 4 G% was mixed anaerobically (9:1, vol:vol) with varying concentrations of lactic acid in saline (0-250 mmol/L).

MEASUREMENTS AND MAIN RESULTS

In the first experiment, blood gas analysis at each step during the progressive P(CO2) reduction revealed that base excess remained nearly constant (SD all specimens < or =0.6 mmol/L) whereas P(CO2) changed by >80 torr. In the second experiment, simultaneous blood gas and plasma lactate analyses showed that changes in base excess correlated closely with changes in both plasma and whole blood lactate concentrations (r2 > or = 0.91) despite concurrent P(CO2) elevations as great as 200 torr. Quantification by base excess of change in whole blood lactate concentration was precise with slight negative bias (mean negative bias, 1.1+/-1.9 mmol/L) in both diluted and undiluted blood. There was significant underestimation of change in plasma lactate concentration in undiluted blood, presumably because base excess is a whole blood variable.

CONCLUSIONS

Base excess calculated using the Van Slyke equation accurately quantifies metabolic (nonrespiratory) acid-base status in blood in vitro. This accuracy is little affected by large simultaneous alterations in P(CO2), or by very low hemoglobin concentrations similar to that used to calculate standard base excess.

Marked hyperlactatemia associated with severe alkalemia in a patient with thrombotic thrombocytopenic purpura

This report describes a case of severe alkalemia associated with a blood lactate level greater than 13 mEq/L in a patient without evidence of hypotension or hypoxemia. The patient, who had the clinical manifestations of thrombotic thrombocytopenic purpura (TTP), developed the alkalemia from an acute respiratory alkalosis superimposed on an existing metabolic alkalosis. Profound alkalemia may impair oxygen delivery because of stronger hemoglobin-oxygen affinity, vasoconstriction, and alterations in the redox potential of cytochrome c. We suggest that the synergistic effects of a sudden, extreme alkalemia and the localized tissue hypoxia that resulted from extensive microvascular thrombi secondary to TTP caused the patient's hyperlactatemia.

Human PaCO2 and standard base excess compensation for acid-base imbalance

OBJECTIVES

Renal and respiratory acid-base regulation systems interact with each other, one compensating (partially) for a primary defect of the other. Most investigators striving to typify compensations for abnormal acid-base balance have reported their findings in terms of arterial pH, PaCO2, and/or HCO3-. However, pH and HCO3- are both altered by both respiratory and metabolic changes. We sought to simplify these relations by expressing them in terms of standard base excess (SBE in mM), which quantifies the metabolic balance and is independent of PaCO2.

DESIGN

Meta-analysis.

SETTING

Historical synthesis developed via the Internet.

PATIENTS

Arterial pH, PaCO2, and/or HCO3- data sets were obtained from 21 published reports of patients considered to have purely acute or chronic metabolic or respiratory acid-base problems.

INTERVENTIONS

We used the same data to compute the typical compensatory responses to imbalances of SBE and PaCO2. Relations were expressed as difference (delta) from normal values for PaCO2 (40 torr [5.3 kPa]) and SBE (0 mM).

MEASUREMENTS AND MAIN RESULTS

The data of patient compensatory changes conformed to the following equations, as well as to the traditional PaCO2 vs. HCO3- or H+ vs. PaCO2 equations: Metabolic change responding to change in PaCO2: Acute deltaSBE = 0 x deltaPaCO2, hence: SBE = 0, Chronic deltaSBE = 0.4 x deltaPaCO2. Respiratory change responding to change in SBE: Acidosis deltaPaCO2 = 1.0 x deltaSBE, Alkalosis deltaPaCO2 = 0.6 x deltaSBE.

CONCLUSION

Data reported by many investigators over the past 35 yrs on typical, expected, or "normal" human compensation for acid-base imbalance may be expressed in terms of the independent variables: PaCO2 (respiratory) and SBE (metabolic).

Acid-base disorders in medicine

The practice of internal medicine involves daily exposure to abnormalities of acid-base balance. A wide variety of disease states either predispose patients to develop these conditions or lead to the use of medications that alter renal, gastrointestinal, or pulmonary function and secondarily alter acid-base balance. In addition, primary acid-base disease follows specific forms of renal tubular dysfunction (renal tubular acidosis). We review the acid-base physiologic functions of the kidney and gastrointestinal tract and the current understanding of acid-base pathophysiologic conditions. This includes a review of whole animal and renal tubular physiologic characteristics and a discussion of the current knowledge of the molecular biology of acid-base transport. We stress an approach to diagnosis that relies on knowledge of acid-base physiologic function, and we include discussion of the appropriate treatment of each disorder considered. Finally, we include a discussion of the effects of acidosis and alkalosis on human physiologic functions.

Plasma potassium response to acute respiratory alkalosis

Acute respiratory alkalosis (hyperventilation) occurs in clinical settings associated with electrolyte-induced complications such as cardiac arrhythmias (such as myocardial infarction, sepsis, hypoxemia, cocaine abuse). To evaluate the direction, magnitude and mechanisms of plasma potassium changes, acute respiratory alkalosis was induced by voluntary hyperventilation for 20 (18 and 36 liter/min) and 35 minutes (18 liter/min). The plasma potassium response to acute respiratory alkalosis was compared to time control, isocapnic and isobicarbonatemic (hypocapnic) hyperventilation as well as beta- and alpha-adrenergic receptor blockade by timolol and phentolamine. Hypocapnic hypobicarbonatemic hyperventilation (standard acute respiratory alkalosis) at 18 or 36 liter/min (delta PCO2-16 and -22.5 mm Hg, respectively) resulted in significant increases in plasma potassium (ca + 0.3 mmol/liter) and catecholamine concentrations. During recovery (post-hyperventilation), a ventilation-rate-dependent hypokalemic overshoot was observed. Alpha-adrenoreceptor blockade obliterated, and beta-adrenoreceptor blockade enhanced the hyperkalemic response. The hyperkalemic response was prevented under isocapnic and isobicarbonatemic hypocapnic hyperventilation. During these conditions, plasma catecholamine concentrations did not change. In conclusion, acute respiratory alkalosis results in a clinically significant increase in plasma potassium. The hyperkalemic response is mediated by enhanced alpha-adrenergic activity and counterregulated partly by beta-adrenergic stimulation. The increased catecholamine concentrations are accounted for by the decrease in plasma bicarbonate.

A hyperventilation interpretation of the termination of panic attacks: a reply to van den Hout, de Jong, Zandbergen and Merckelbach

This paper summarizes the brief publication history of how a hyperventilatory positive-feed-back-loop theory of panic attacks explains the termination of panic attacks. A cautionary note is suggested when interpreting generalizations pertaining to panic attacks in panic-disorder sufferers in the everyday world made from laboratory findings based on healthy asymptomatic subjects.

Understanding serum electrolytes. How to avoid mistakes

Serum electrolyte levels by themselves may be difficult to interpret. For example, an abnormal serum potassium concentration cannot be understood without taking into account the patient's history, other serum electrolyte values, and possibly results of other laboratory tests. Knowledge of the principles of serum electrolyte concentrations, therefore, is an important adjuvant to understanding their implications.

Chronic respiratory alkalosis. The effect of sustained hyperventilation on renal regulation of acid-base equilibrium

BACKGROUND

In normal subjects, chronic hyperventilation lowers plasma bicarbonate concentration, primarily by inhibiting the urinary excretion of net acid. The quantitative relation between reduced arterial carbon dioxide tension (PaCO2) and the plasma bicarbonate concentration in the chronic steady state has not been studied in humans, however, and the laboratory criteria for the diagnosis of chronic respiratory alkalosis therefore remain undefined. We wished to provide such reference data for clinical use. Moreover, because chronic hyperventilation paradoxically lowers blood pH still further in dogs with metabolic acidosis, we desired to study the effect of chronic hypocapnia on the plasma bicarbonate concentration (and blood pH) in normal human subjects in whom acidosis had been induced with ammonium chloride.

METHODS

Under metabolic-balance conditions, we used altitude-induced hypobaric hypoxia to produce chronic hypocapnia in nine normal young men, five of whom received ammonium chloride daily to cause metabolic acidosis (the mean [+/- SE] steady-state plasma bicarbonate level in these five was 12.0 +/- 0.5 mmol per liter).

RESULTS

For each decrease of 1 mm Hg (0.13 kPa) in the PaCO2, the plasma bicarbonate concentration decreased by 0.41 mmol per liter in the subjects who started with a normal plasma bicarbonate concentration and by 0.42 mmol per liter in the subjects with acidosis. In contrast to the findings in previous studies of dogs, hypocapnia increased blood pH similarly in both groups; the blood hydrogen ion concentration decreased by about 0.4 nmol per liter for every decrease of 1 mm Hg (0.13 kPa) in PaCO2.

CONCLUSIONS

These results provide reference data for the diagnosis of chronic respiratory alkalosis in humans. Although chronic hypocapnia decreased plasma bicarbonate levels similarly in normal subjects with acidosis and without acidosis, the percent reduction in PaCO2 was always greater than the corresponding percent reduction in the plasma bicarbonate concentration. Therefore, as was not true of the response in dogs, the subjects' blood pH always increased with hyperventilation, regardless of the initial plasma bicarbonate concentration.

Acid-base disturbances in acute asthma

The clinical features, arterial blood gases, and acid-base profile were examined in 229 consecutive episodes of acute asthma in 170 patients who required hospitalization. A simple respiratory alkalosis was the most common acid-base disturbance, occurring in 48 percent of the episodes. Metabolic acidosis, either alone or as part of a mixed disturbance, was noted in 28 percent. Of 60 episodes presenting with respiratory acidosis, 37 (62 percent) had a coexistent metabolic acidosis. Metabolic acidosis was more likely to occur in male subjects and in patients with evidence of more severe airflow obstruction. Patients with metabolic acidosis had an average anion gap of 15.8 mEq/L; these patients were more hypoxemic than those without metabolic acidosis and there was a significant inverse correlation between the anion gap and the degree of hypoxemia. We conclude that metabolic acidosis is a common finding in acute, severe asthma and suggest that the pathogenesis of lactic acidosis is multifactorial and includes contributions from lactate production by respiratory muscles, tissue hypoxia, and intracellular alkalosis.

Clinical indices to predict simple and mixed acid-base disturbances

We propose that in any acid-base disturbance there is a predictable mathematical relationship between the changes in the individual serum anionic concentrations of chloride, bicarbonate and the unmeasured anion gap. Two indices were developed, from the ratios of the changes in these anionic concentrations, that are useful in predicting the presence of an acid-base disturbance. Based on recent experimental evidence we determined the mathematical values of these 2 indices, alpha and beta, in 17 acid-base disturbances. By utilizing the paired values of these indices, the 17 disturbances including simple, metabolic plus respiratory and triple disorders were subcategorized into 7 groups. It is suggested that the use of these indices will facilitate the diagnosis of complicated mixed acid-base disorders.

Postoperative metabolic alkalosis following general surgery: its incidence and possible etiology

A prospective clinical study was performed on 293 patients, in order to elucidate the abnormalities in acid-base balance following general surgery. Six arterial blood gas and pH determinations were taken from each patient before surgery and on postoperative days zero, one, three, five and seven. A total of 1699 determinations were obtained. Although the majority of patients (87.5 per cent) had a normal acid-base balance before surgery, a postoperative metabolic alkalosis was seen in 50.5 per cent of the patients. However, there was an extremely low incidence of other postoperative acid-base abnormalities, apart from a transient increase in metabolic acidosis on the operative day. A significantly high mortality rate (32.3 per cent) was observed in 31 patients who had continuous metabolic alkalosis during the postoperative period. An excessive bicarbonate load resulting from the administration of fresh frozen plasma following surgery was strongly suggested as one of the major causes of postoperative metabolic alkalosis. Further investigation is required to elucidate the mechanism of the generation of metabolic alkalosis induced by the postoperative bicarbonate load in surgical patients.

Development of acidosis in human beings during closed-chest and open-chest CPR

We studied the development of acidosis, as measured by blood gases, in a convenience sample of 16 patients undergoing five minutes of closed-chest CPR (CC-CPR) followed by five minutes of open-chest CPR (OC-CPR). To eliminate the influence of variable pCO2 on serum pH, all blood gas values were adjusted to a pCO2 of 40 mm Hg. Adjusted pH fell a mean of 0.09 U (SEM +/- 0.03, P = .02) with five minutes of CC-CPR and then 0.05 U (SEM +/- 0.02, P = .05) with five minutes of OC-CPR. The decline in adjusted pH during CC-CPR was statistically comparable to the decline that occurred during OC-CPR. The development of acidosis as measured by blood gases does not appear to be significantly different for patients undergoing five minutes of CC-CPR versus five minutes of OC-CPR when OC-CPR follows CC-CPR.

Mineralocorticoid-stimulated renal acidification: the critical role of dietary sodium

Recent in vitro studies of isolated distal nephron segments have demonstrated that mineralocorticoid hormone stimulates H+ secretion by both Na+-dependent and Na+-independent mechanisms, and the Na+-independent acidification mechanism has a greater capacity. These in vitro data suggest that mineralocorticoid administration in vivo might increase renal acid excretion when an augmentation in distal Na+ reabsorption is precluded by rigid restriction of dietary Na+; under these circumstances, virtually all Na+ delivered to the distal nephron is reabsorbed in the basal state. In the present studies, prolonged (12 days) administration of DOC (15 mg/day) was undertaken in both Na+-fed and rigidly Na+-restricted dogs with chronic HCl acidosis. Na+-fed animals responded to DOC administration with a large increment in net acid excretion and complete correction of metabolic acidosis. Marked hypokalemia and significant kaliuresis also occurred. Na+-restricted dogs experienced no changes in renal acid excretion, systemic acid-base equilibrium, plasma [K+] or K+ balance. These results suggest that both renal H+ and K+ excretory responses to prolonged mineralocorticoid hormone administration in vivo are critically dependent on the availability for reabsorption of surplus Na+ within the distal nephron; this requirement is met when the diet, and hence the final urine, contains Na+ but cannot be satisfied when dietary Na+ is rigidly restricted.

A computerized system for rapid interpretation of acid/base disorders

Rapid and correct interpretation of arterial blood gas results is necessary in the operating room or intensive care unit. However, manual calculation and interpretation is tedious and prone to error. A computer system consisting of two programs written in BASIC has been created to address these problems. The program uses a series of decisions to arrive at a conclusion. Data generated by the Interpreter may be used by a subsequent program, the Manager, in determining ventilation parameters.

Diagnosis of complex acid-base disorders: physician performance versus the microcomputer

Patients with acid-base disturbances that are often complex frequently present to the emergency department. The sometimes hectic nature of the ED can preclude the appropriate quantitative analysis required by these disorders, especially when mixed disturbances are present. A computer program using generally accepted acid-base and electrolyte formulae was developed for use on the Apple II+ or IBM-PC microcomputer. Each of a series of 35 acid-base disturbances incorporating single, double, and triple disorders was correctly identified by the computer in less than 45 seconds. Problem sets based on the same 35 disturbances were presented to 21 physician-subjects at various levels of training from the emergency medicine, internal medicine, pediatrics, surgery, and family practice specialties. Although the physicians were given unlimited time and the necessary formulae to reach a diagnosis, they were requested to perform their analyses in the same fashion used in the ED. Although times varied widely, no physician spent more than five minutes on any problem. The physician correct response rates were 86%, 49%, and 17% for single, double, and triple disorders, respectively. The primary disorder correct response rate was 89% for double disorders and 94% for triple disorders. The primary and secondary disorder correct response rate was 58% for triple disorders. The data suggest that the microcomputer may be beneficial in the rapid assessment of complex disorders.

[Practical approach to complex acid-base disorders using a slide rule]

Diagnosis of mixed acid-base disturbances is often difficult. Nowadays it depends on biochemical and statistical interpretation, coupled with clinical data. The acid-base slide-rule is a useful tool to carry out this five step procedure, which it simplifies, giving rapidly at the patient's bed-side an objective support for the diagnosis of acid-base disturbances.

Lactic acidosis in severe asthma

Twelve patients with severe asthma in whom lactic acidosis developed are presented. All had an arterial blood pH level lower than that expected for the measured partial pressure of arterial carbon dioxide, all had an abnormally large anion gap, and the blood lactate level exceeded 2.8 mmol/liter. Respiratory acidosis subsequently developed in eight patients, and six required intubation. Lactic acidosis can develop in patients with severe asthma. Such patients are in danger of the development of respiratory failure and must be treated vigorously and observed closely.

Clinical approach to patients with acid-base disorders

Simple relationships that hold during compensation for metabolic or respiratory acid-base disturbances have been emphasized. When considered by the physician, they should allow for the interpretation and diagnosis of both simple and mixed disturbances. Since the correct diagnosis of an acid-base disturbance is central to initiation of correct therapy, these considerations are not merely academic exercises but are essential steps to follow in careful management. Table 6 summarizes the stepwise approach to diagnosis of an acid-base disorder. Application of these principles in a routine fashion combined with a careful history and physical examination often results in the successful diagnosis of complicated disturbances. Understanding of the pathophysiologic derangements in each specific disorder is necessary for full appreciation of acid-base balance in disease.

[Acid-base equilibrium and vascular exclusion of the liver: study of 30 extensive hepatectomies]

The acid-base disorders after hepatic vascular exclusion (HVE) were studied in 30 major liver resections. HVE included portal triad clamping and occlusion of the inferior vena cava below and above the liver, without venous shunt nor cooling. Clamping of the supra-coeliac abdominal aorta (AoC) was associated with HVE in 12 patients. HVE lasted 18 to 65 min (mean 37 min). Liver ischemia and splanchnic blood pooling resulted in metabolic acidosis and hyperlactatemia. In order to prevent his acidosis, prophylactic administration of NaHCO23 was used during the first 19 cases. This induced significant metabolic alkalosis during HVE and the early postoperative period; increasing experience made us reduce the amount of NaHCO3. After the release of the clamps, Paco2 increased 25% following HVE without AoC (p less than 0.001) and 53% following HVE with AoC (p less than 0.001). In an attempt to distinguish between the effects of the metabolic acidosis and the rise of Paco2 in the fall of pH which occurred after removal of the clamps, NAaHCO3 was deliberately not given in the last 11 patients. Acidosis appeared to be greater with AoC than without and mainly related to the rise of Paco2. A fall of Paco2 to its initial value was always followed by the return of pH to the normal range. This study demonstrated the human ability to correct spontaneously the acidosis which followed HVE. The need for NaHCO3 after HVE reflected a poor hemodynamic state after major liver resection rather than a metabolic consequence of hepatic ischaemia.

Failure of increased sodium avidity to facilitate renal acid excretion in dogs fed sulfuric acid

Previous studies have suggested that the increment in renal acid excretion caused by sulfuric acid feeding is mediated solely by an interplay between the sulfate-induced increase in distal sodium delivery and the gradual augmentation of distal sodium reabsorption that occurs as sodium losses accumulate. This hypothesis predicts that if distal sodium reabsorption were stimulated sufficiently prior to the administration of sulfuric acid, excretion of the hydrogen ion load would occur promptly, thus obviating the fall in plasma bicarbonate or loss of cation that normally occurs. To test this prediction, we fed sulfuric acid (7 mEq of H+/kg/day) to dogs in which distal sodium avidity had been enhanced prior to acid feeding either by diuretic-induced sodium depletion (N = 6) or by deoxycorticosterone acetate 7.5 mg, twice a day and a low-sodium diet (N = 8). Contrary to expectation, over the first 3 days of acid feeding there was a significant fall in plasma bicarbonate (7.1 and 7.5 mEq/liter) and an increase in urinary sodium excretion (48 mEq in both groups). Moreover, changes in both plasma bicarbonate and urinary sodium excretion were similar to those observed previously (5.9 mEq/liter and 46 mEq, respectively) in normal dogs fed the same dose of sulfuric acid.

Mixed acid base disturbances: a clinical approach

The analysis of a mixed acid-base disturbance begins with the history and physical examination from which data can be derived that make the clinician suspect a specific disturbance(s). The electrolytes are then evaluated with emphasis on the meaning of the values for serum bicarbonate, potassium and chloride concentration and on the level of the anion gap. Other laboratory data such as serum creatinine or glucose concentrations, blood cultures, and so forth, should also be reviewed for further clues to a possible disturbance(s). When it is clinically indicated, values for pH and Pco2 are obtained by blood gas determination. If the evidence up to this point indicates the presence of at least one disturbance, the data are examined to see if compensation for this disturbance is appropriate. If not, a mixed disturbance must be present. A normal pH in the setting of an abnormal serum HCO3(-) concentration or Pco2 also suggests a mixed disturbance since compensation rarely corrects the pH back to normal. Of course, a pH deviated in the opposite direction than that expected for a known primary disturbance makes the diagnosis of a mixed disturbance certain. The diagnosis of a mixed acid-base disturbance is therefore based on an analysis of all the clinical data and not just the blood gas measurements. Treatment of the disorders should be directed at maintaining a normal or near normal pH. Some combined acid-base disorders are important to recognize because they can result in a severe deviation in blood pH that demands immediate, specific therapy. Other mixed disturbances result in a pH which is near normal but are important to recognize since they can alert the clinician to the possibility of certain clinical derangements such as septic shock or drug ingestion. Careful analysis of mixed acid-base disturbances in this way is not peutic information to be used in caring for his (her) patients.