Acid-base patterns in acute severe asthma

Prevalence of hyperventilation in patients with asthma

OBJECTIVE

Asthma is frequently accompanied by dysfunctional breathing of which hyperventilation has been recognized as a subtype. The prevalence of hyperventilation in stable asthma has been scantily studied using blood gas analysis. Hence, a reliable estimate of its prevalence is lacking. It is unknown whether the Nijmegen Questionnaire (NQ) is a useful screening tool for hyperventilation in asthma. Therefore, the primary aim of this study was to determine the prevalence of hyperventilation in a large sample of patients with asthma in a stable state of disease. Secondary aims were to compare the clinical characteristics between patients with and without hyperventilation, and, to examine the concurrent validity of the NQ to detect hypocapnia in patients with asthma.

METHODS

A real-world, observational, multicenter study was conducted. Capillary blood gas analysis was performed in adults with a confirmed diagnosis of stable asthma. A subset of patients completed the NQ.

RESULTS

A blood gas analysis was obtained in 1006 patients. In 17% of the patients an acute hyperventilation was found, and in another 23% a chronic hyperventilation was uncovered. Patients with a chronic hyperventilation blood gas were more often female, were younger and had a better spirometric outcomes. The NQ appeared not to correlate with PCO2.

CONCLUSION

Hyperventilation is common in patients with stable asthma. Chronic hyperventilation is more often found in females of younger age and with the best spirometric outcomes compared to patients without hyperventilation. The NQ is not a suitable screening tool for the presence of hyperventilation in stable asthmatics.

Acid-Base Disturbances in Patients with Asthma: A Literature Review and Comments on Their Pathophysiology

Asthma is a common illness throughout the world that affects the respiratory system function, i.e., a system whose operational adequacy determines the respiratory gases exchange. It is therefore expected that acute severe asthma will be associated with respiratory acid-base disorders. In addition, the resulting hypoxemia along with the circulatory compromise due to heart–lung interactions can reduce tissue oxygenation, with a particular impact on respiratory muscles that have increased energy needs due to the increased workload. Thus, anaerobic metabolism may ensue, leading to lactic acidosis. Additionally, chronic hypocapnia in asthma can cause a compensatory drop in plasma bicarbonate concentration, resulting in non-anion gap acidosis. Indeed, studies have shown that in acute severe asthma, metabolic acid-base disorders may occur, i.e., high anion gap or non-anion gap metabolic acidosis. This review briefly presents studies that have investigated acid-base disorders in asthma, with comments on their underlying pathophysiology.

Lactic acid suppresses IgE-mediated mast cell function in vitro and in vivo

Mast cells have functional plasticity affected by their tissue microenvironment, which greatly impacts their inflammatory responses. Because lactic acid (LA) is abundant in inflamed tissues and tumors, we investigated how it affects mast cell function. Using IgE-mediated activation as a model system, we found that LA suppressed inflammatory cytokine production and degranulation in mouse peritoneal mast cells, data that were confirmed with human skin mast cells. In mouse peritoneal mast cells, LA-mediated cytokine suppression was dependent on pH- and monocarboxylic transporter-1 expression. Additionally, LA reduced IgE-induced Syk, Btk, and ERK phosphorylation, key signals eliciting inflammation. In vivo, LA injection reduced IgE-mediated hypothermia in mice undergoing passive systemic anaphylaxis. Our data suggest that LA may serve as a feedback inhibitor that limits mast cell-mediated inflammation.

Intercostal muscle oxygenation during expiratory load breathing at rest

BACKGROUND

During acute bronchial obstruction, despite a higher work of breathing, blood supply and oxygen availability may be reduced in intercostal muscles because of mechanical constraints. This hypothesis was assessed in healthy subjects breathing with and without expiratory load (ETL).

METHODS

Eleven men (24 ± 2 years) breathed at rest for 5 min in unloaded condition and for 20 min through a 20-cmH₂O ETL. Tissue saturation index (TSI) and changes (Δ) in concentration of total and oxy-haemoglobin ([tHb] and [O₂Hb]) were measured in the seventh intercostal space by near-infrared spectroscopy.

RESULTS

[tHb] and [O₂Hb] decreased with ETL (-5.16 μM and -3.54 μM; p < 0.05). TSI did not vary. Negative correlations were observed between Δ[O₂Hb] and changes in expiratory flow rate (ΔVt/Te) and between ΔTSI and Δ V˙E (r = -0.78 and -0.74; p ≤ 0.01).

CONCLUSION

Despite decreases in Hb concentrations, saturation in oxygen was not reduced with ETL in intercostal muscles, suggesting a satisfactory ventilatory and/or hemodynamic arrangement.

Clinical use of plasma lactate concentration. Part 1: Physiology, pathophysiology, and measurement

OBJECTIVE

To review the current literature with respect to the physiology, pathophysiology, and measurement of lactate.

DATA SOURCES

Data were sourced from veterinary and human clinical trials, retrospective studies, experimental studies, and review articles. Articles were retrieved without date restrictions and were sourced primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Lactate is an important energy storage molecule, the production of which preserves cellular energy production and mitigates the acidosis from ATP hydrolysis. Although the most common cause of hyperlactatemia is inadequate tissue oxygen delivery, hyperlactatemia can, and does occur in the face of apparently adequate oxygen supply. At a cellular level, the pathogenesis of hyperlactatemia varies widely depending on the underlying cause. Microcirculatory dysfunction, mitochondrial dysfunction, and epinephrine-mediated stimulation of Na⁺ -K⁺ -ATPase pumps are likely important contributors to hyperlactatemia in critically ill patients. Ultimately, hyperlactatemia is a marker of altered cellular bioenergetics.

CONCLUSION

The etiology of hyperlactatemia is complex and multifactorial. Understanding the relevant pathophysiology is helpful when characterizing hyperlactatemia in clinical patients.

Blood gas tensions in adult asthma: a systematic review and meta-regression analysis

OBJECTIVE

The last half-century has seen substantial changes in asthma treatment and care. We investigated whether arterial blood gas parameters in acute and non-acute asthma have changed historically.

METHODS

We performed a systematic search of the literature for studies reporting P(aO2) , P(aCO2) and forced expiratory volume in 1 s, percentage of predicted (FEV1%). For each of the blood gas parameters, meta-regression analyses examined its association with four background variables: the publication year, mean FEV1%, mean age and female fraction in the respective studies.

RESULTS

After screening, we included 43 articles comprising 61 datasets published between 1967 and 2013. In studies of habitual-state asthma, mean P(aO2) was positively associated with the publication year (p = 0.001) and negatively with mean age (p < 0.01). Mean P(aCO2) showed a positive association with publication year (p = 0.001) and a negative association with female fraction (p < 0.05). In acute asthma studies, blood gas levels were unassociated with publication year and mean age, mean P(aO2) was positively associated with FEV1% (p < 0.05) whereas mean P(aCO2) showed a negative association with FEV1% (p < 0.05) for studies with mean FEV1% <40. In neither acute nor habitual-state studies was mean arterial pH associated with any of the predictor variables.

CONCLUSIONS

In studies of habitual-state asthma, mean reported P(aO2) and P(aCO2) levels were found to have increased since 1967. In acute asthma studies, mean P(aO2) and P(aCO2) were associated with mean FEV1% but not with either publication year or patient age.