Correlation between capillary and arterial blood gas parameters in an ED

Bone metabolism during strict head-down tilt bed rest and exposure to elevated levels of ambient CO2

Astronauts on the International Space Station are exposed to levels of atmospheric carbon dioxide (CO₂) above typical terrestrial levels. We explored the possibility that increased levels of ambient CO₂ further stimulate bone resorption during bed rest. We report here data from 2 ground-based spaceflight analog studies in which 12 male and 7 female subjects were placed in a strict 6° head-down tilt (HDT) position for either 30 days at 0.5% ambient CO₂ or 60 days with nominal environmental exposure to CO₂. Bone mineral density (BMD) and bone mineral content (BMC) were determined using dual-energy X-ray absorptiometry (DXA). Blood and urine were collected before and after HDT for biochemical analysis. No change was detected in either BMD or BMC, as expected given the study duration. Bone resorption markers increased after bed rest as expected; however, elevated CO₂ had no additive effect. Elevated CO₂ did not affect concentrations of minerals in serum and urine. Serum parathyroid hormone and 1,25-dihydroxyvitamin D were both reduced after bed rest, likely secondary to calcium efflux from bone. In summary, exposure to 0.5% CO₂ for 30 days did not exacerbate the typical bone resorption response observed after HDT bed rest. Furthermore, results from these strict HDT studies were similar to data from previous bed rest studies, confirming that strict 30-60 days of HDT can be used to evaluate changes in bone metabolism. This is valuable in the continuing effort to develop and refine efficacious countermeasure protocols to mitigate bone loss during spaceflight in low-Earth orbit and beyond.

Review of pediatric hypercarbia and intraoperative management

PURPOSE OF REVIEW

Hypercarbia in pediatric patients is an important component of intraoperative management. Despite marked advances in medicine and technology, it is uncertain what the physiological CO2 range in neonates, infants and small children. This data is extrapolated from the adult population. We are going to review advantages and disadvantages of CO2 measurement techniques, causes and systemic effects of hypercarbia. We are going to discuss how to approach management of intraoperative hypercarbia.

RECENT FINDINGS

Although physiological range in this patient population may not be fully understood, it is known that any rapid change from a child's baseline increases risks of complications. Any derangements in CO2 are further compromised by hypoxia, hypotension, hypothermia, anemia, all of which may occur in a dynamic operating room environment.

SUMMARY

Pediatric anesthesiologists and their teams must remain vigilant and anticipate these developments. Care must be taken to avoid any rapid changes in these vulnerable patients to minimize risks of adverse outcomes.

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.

Agreement between Arterial and Capillary pH, pCO2, and Lactate in Patients in the Emergency Department

Background

Blood gas analysis (BGA) is a frequent painful procedure in emergency departments. The primary objective of the study was a quantitative analysis to assess the mean difference and 95% confidence interval of the difference between capillary and arterial BGA for pH, pCO₂, and lactate. Secondary objective was to measure the sensitivity and specificity of capillary samples to detect altered pH, hypercarbia, and lactic acidosis. Adults admitted to the ED were screened for inclusion. We studied the agreement between the two methods for pH, pCO₂, and lactate with Bland-Altman bias plot analysis and receiver operating characteristic curves.

Results

One hundred ninety-seven paired analyses were included. Mean difference for pH between arterial and capillary BGA was 0.0095, and 95% limits of agreement (LOA) were −0.048 to 0.067. For pCO₂, mean difference was −0.3 mmHg, and 95% LOA were −8.5 to 7.9 mmHg. Lactate mean difference was −0.93 mmol/L, and 95% LOA were −2.7 to 0.8 mmol/L. At a threshold of 7.34, capillary pH had 98% sensitivity and 97% specificity to detect acidemia; at 45.9 mmHg, capillary pCO₂ had 89% sensitivity and 96% specificity to detect hypercarbia. At a threshold of 3.5 mmol/L, capillary lactate had 66% sensitivity to detect lactic acidosis.

Conclusion

Capillary BGA cannot replace arterial BGA despite high concordance between the two methods for pH and pCO₂ and moderate concordance for lactate. Capillary measures had good accuracy when used as a screening tool to detect altered pH and hypercarbia but insufficient sensitivity and specificity when screening for lactic acidosis.

Agreement between arterial and non-arterialised fingertip capillary blood gas and acid-base values

Background: Arterial puncture is considered the gold standard for obtaining blood gas and acid-base values and facilitates the assessment of acutely and critically ill patients, as well as control of patients in long-term oxygen therapy (LTOT). Substitutional capillary sampling has been proposed, as researchers cite lower complication rates, physician independence, lower degree of invasiveness and higher degree of patient comfort. An arterialised earlobe is considered the method of choice to obtain capillary blood sampling, but in an acute setting, the need for vasodilating pastes may be time-consuming and impractical. The aim of this study is to examine whether accurate blood gas and acid-base measurements can be obtained using non-arterialised fingertip blood. Materials and methods: Consecutive arterial punctures and non-arterialised capillary blood samples were drawn from 62 patients with stable-phase chronic obstructive pulmonary disease (COPD), and subsequently analysed. Agreement between arterial and capillary blood gas values was compared using the method recommended by Bland and Altman. Results: Results show that limits of agreement (LoA) regarding PO₂ (LoA: -1.27-4.45 kPa); Base Excess (LoA: -1.35-0.55); lactate (LoA: -0.77-0.20 mmol/l) and SO₂ (LoA: -0.02-0.06) are wider than what would be applicable for clinical use. However, clinically acceptable LoA were obtained regarding PCO₂ (LoA: -0.64-0.38 kPa); pH (LoA: -0.02-0.03), and HCO₃ ^- (LoA: -1.06-0.55 mmol/l). Conclusion: LoA for PCO₂, pH and HCO₃ ^- indicate that measurement of these parameters in non-arterialised capillary blood may be useful in clinical practice/an acute setting. What this paper adds: Capillary blood sampling provides a fast, non-invasive means of obtaining blood gas-values;Traditionally, capillary blood sampling for blood gas analysis is obtained from the earlobe using arterialisation;The present study presents accurate measurements of PCO₂, HCO₃ ^- and pH using non-arterialised fingertip capillary blood;The present study is the first to show this in a population of stable-phase COPD patients.

Obesity Hypoventilation Syndrome: Early Detection of Nocturnal-Only Hypercapnia in an Obese Population

STUDY OBJECTIVES

Hypoventilation in obesity is now divided into five stages; stage 0 (pure obstructive sleep apnea; OSA), stages I/II (obesity-related sleep hypoventilation; ORSH) and stages III/IV (awake hypercapnia, obesity hypoventilation syndrome; OHS). Hypercapnia during the day may be preceded by hypoventilation during sleep. The goal of this study was to determine the prevalence and to identify simple clinical measures that predict stages I/II ORSH. The effect of supine positioning on selected clinical measures was also evaluated.

METHODS

Ninety-four patients with a body mass index > 40 kg/m² and a spirometric ratio > 0.7 were randomized to begin testing either in the supine or upright seated position on the day of their diagnostic sleep study. Arterialized capillary blood gases were measured in both positions. Oxygen saturation measured by pulse oximetry was also obtained while awake. Transcutaneous CO₂ monitoring was performed during overnight polysomnography.

RESULTS

Stages I/II ORSH had a prevalence of 19% in an outpatient tertiary hospital setting compared with 61%, 17%, and 3% for stages 0, III/IV, and no sleep-disordered breathing respectively. Predictors for sleep hypoventilation in this group were an awake oxygen saturation of ≤ 93% (sensitivity 39%, specificity 98%, positive likelihood ratio of 22) and a partial pressure of carbon dioxide ≥ 45 mmHg (sensitivity 44%, specificity 98%, positive likelihood ratio of 24) measured in the supine position.

CONCLUSIONS

ORSH has a similar prevalence to OHS. Awake oxygen saturation and partial pressure of carbon dioxide performed in the supine position may help predict obese patients with sleep hypoventilation without awake hypercapnia.

COMMENTARY

A commentary on this article appears in this issue on page 1455.

CLINICAL TRIAL REGISTRATION

Registry: Australian New Zealand Clinical Trials Registry, Identifier: ACTRN 12615000135516, URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=367493&isReview=true, Title: A cross-sectional study to identify obese patients who are at risk for developing obesity hypoventilation syndrome (OHS) by investigating the relationship between daytime measures (including supine hypercapnia, distribution of body fat and lung volumes) with the presence of hypoventilation during sleep.

Capillary blood for point-of-care testing

Clinically, blood sample analysis has been widely used for health monitoring. In hospitals, arterial and venous blood are utilized to detect various disease biomarkers. However, collection methods are invasive, painful, may result in injury and contamination, and skilled workers are required, making these methods unsuitable for use in a resource-limited setting. In contrast, capillary blood is easily collected by a minimally invasive procedure and has excellent potential for use in point-of-care (POC) health monitoring. In this review, we first discuss the differences among arterial blood, venous blood, and capillary blood in terms of the puncture sites, components, sample volume, collection methods, and application areas. Additionally, we review the most recent advances in capillary blood-based commercial products and microfluidic instruments for various applications. We also compare the accuracy of microfluidic-based testing with that of laboratory-based testing for capillary blood-based disease diagnosis at the POC. Finally, we discuss the challenges and future perspectives for developing capillary blood-based POC instruments.