Control of hyperpnoea and pulmonary gas exchange during prolonged exercise: The role of group III/IV muscle afferent feedback.

It remains unclear whether feedback from group III/IV muscle afferents is of continuous significance for regulating the pulmonary response during prolonged (>5 min), steady-state exercise. To elucidate the influence of these sensory neurons on hyperpnoea, gas exchange efficiency, arterial oxygenation and acid-base balance during prolonged locomotor exercise, 13 healthy participants (4 females; 21 (3) years, V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ : 46 (8) ml/kg/min) performed consecutive constant-load cycling bouts at ∼50% (20 min), ∼75% (20 min) and ∼100% (5 min) of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ with intact (CTRL) and pharmacologically attenuated (lumbar intrathecal fentanyl; FENT) group III/IV muscle afferent feedback from the legs. Pulmonary responses were continuously recorded and arterial blood (radial catheter) periodically collected throughout the exercise. Pulmonary gas exchange efficiency was evaluated using the alveolar-arterial P O 2 ${{P}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ difference ( A - a D O 2 ${\mathrm{A - a}}{{D}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ). There were no differences in any of the variables of interest between conditions before the start of the exercise. Pulmonary ventilation was up to 20% lower across all intensities during FENT compared to CTRL exercise (P < 0.001) and this hypoventilation was accompanied by an up to 10% lower arterial P O 2 ${{P}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and a 2-4 mmHg higher P C O 2 ${{P}_{{\mathrm{C}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ (both P < 0.001). The exercise-induced widening of A - a D O 2 ${\mathrm{A - a}}{{D}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ was up to 25% larger during FENT compared to CTRL (P < 0.001). Importantly, the differences developed within the first minute of each stage and persisted, or further increased, throughout the remainder of each bout. These findings reflect a critical and time-independent significance of feedback from group III/IV leg muscle afferents for continuously regulating the ventilatory response, gas exchange efficiency, arterial oxygenation and acid-base balance during human locomotion. KEY POINTS: Feedback from group III/IV leg muscle afferents reflexly contributes to hyperpnoea during short duration (i.e. <5 min) locomotor exercise. Whether continuous feedback from these sensory neurons is obligatory to ensure adequate pulmonary responses during steady-state exercise of longer duration remains unknown. Lumbar intrathecal fentanyl was used to attenuate the central projection of group III/IV leg muscle afferents during prolonged locomotor exercise (i.e. 45 min) at intensities ranging from 50% to 100% of V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ . Without affecting the metabolic rate, afferent blockade compromised pulmonary ventilation and gas exchange efficiency, consistently impairing arterial oxygenation and facilitating respiratory acidosis throughout exercise. These findings reflect the time-independent significance of feedback from group III/IV muscle afferents for regulating exercise hyperpnoea and gas exchange efficiency, and thus for optimizing arterial oxygenation and acid-base balance, during prolonged human locomotion.

Influence of arterial blood gases on the renal arterial resistive index in intensive care unit.

BACKGROUND: Renal artery Doppler sonography with resistive index (RI) determination is a noninvasive, fast, and reliable diagnostic tool increasingly used in the intensive care unit (ICU) to predict and assess the reversibility of acute kidney injury (AKI). However, interpreting the RI can be challenging due to numerous influencing factors. While some studies have explored various confounding factors, arterial blood gases have received limited attention. Therefore, our study aims to evaluate the impact of arterial blood gases on the RI in the ICU setting. METHODS: This prospective observational study enrolled ICU patients who required blood gas analysis and had not experienced significant hemodynamic changes recently. The RI was measured using standardized Doppler ultrasound within an hour of the arterial blood gases sampling and analysis. RESULTS: A total of sixty-four patients were included in the analysis. Univariate analysis revealed a correlation between the RI and several variables, including PaCO2 (R = 0.270, p = 0.03), age (R = 0.574, p < 0.0001), diastolic arterial pressure (DAP) (R = - 0.368, p = 0.0028), and SaO2 (R = - 0.284, p = 0.0231). Multivariate analysis confirmed that age > 58 years and PaCO2 were significant factors influencing the RI, with respective odds ratios of 18.67 (p = 0.0003) and 1.132 (p = 0.0267). CONCLUSION: The interpretation of renal arterial RI should take into account thresholds for PaCO2, age, and diastolic arterial pressure. Further studies are needed to develop a comprehensive scoring system that incorporates all these cofactors for a reliable analysis of RI levels. Trial registration This observational study, registered under number 70-0914, received approval from local Ethical Committee of Toulouse University Hospital.

The reduction in arterial pH with increased temperature is not affected by hyperoxia in toads (Rhinella marina) and pythons (Python molurus).

It is well established that arterial pH decreases with increased temperature in amphibians and reptiles through an elevation of arterial PCO2, but the underlying regulation remains controversial. The alphastat hypothesis ascribes the pH fall to a ventilatory regulation of protein ionisation, but the pH reduction with temperature is lower than predicted by the pKa change of the imidazole group on histidine. We hypothesised that arterial pH decreases at high, but not at low, temperatures when toads (Rhinella marina) and snakes (Python molurus) are exposed to hyperoxia. In toads, hyperoxia caused similar elevations of arterial PCO2 at 20 and 30°C, indicative of a temperature-independent oxygen-mediated drive to breathing, whereas PCO2 was unaffected by hyperoxia in snakes at 25 and 35°C. These findings do not support our hypothesis of an increased oxygen-mediated drive to breathing as body temperature increases.

Arterial Blood Gases in Normal Subjects at 2240 Meters Above Sea Level: Impact of Age, Gender, and Body Mass Index.

Background: The values of arterial blood gases (ABG) change with altitude above sea level; empirical verification is essential because ventilatory acclimatization varies with ethnicity and a population's adaptation. Objective: The aim of the study was to describe ABG in a healthy population residing at 2,240 meters above sea level, to identify the mean level of alveolar ventilation (PaCO2), and to know whether a progressive increase in PaCO2 occurs with age and the impact of increasing body mass index (BMI). Methods: We conducted a cross-sectional study in a referral center for respiratory diseases in Mexico City. Associations among variables with correlation coefficient and regression models of PaO2, SaO2, and P(A-a)O2 as dependent variables as a function of age, BMI, minute ventilation, or breathing frequency were explored. Results: Two hundred and seventeen healthy subjects were evaluated with a mean age of 40 ± 15 years, mean of the PaO2 was 71 ± 6 mmHg, SaO2 94% ± 1.6%, PaCO2 30.2 ± 3.4 mmHg, HCO3 20 ± 2 mmol/L, BE-2.9 ± 1.9 mmol/L, and the value of pH was 7.43 ± 0.02. In a linear regression, the main results were PaO2 = 77.5-0.16*age (p < 0.0001) and with aging P(A-a)O2 tended to increase 0.12 mmHg/year. PaCO2 in women increased with age by 0.075 mmHg/year (p = 0.0012, PaCO2 =26.3 + 0.075*age). SaO2 and PaO2 decreased significantly in women with higher BMI 0.14% and 0.52 mmHg per kg/m2, (p = 0.004 and 0.002 respectively). Conclusion: Mean PaCO2 was 30.7 mmHg, implying a mean alveolar ventilation of around 30% above that at sea level.

Decision-based learning for teaching arterial blood gas analysis.

OBJECTIVES: This case study explored implementation of a Decision-Based Learning (DBL) tool for teaching arterial blood gas (ABG) analysis to nursing students. METHODS: For this mixed-methods study, ABG problems in a DBL model were solved by nursing students. Students answered a survey about their experience with DBL. Quantitative survey results are reported with descriptive statistics. Open-ended questions and instructor and student interview data were qualitatively analyzed. RESULTS: Students had a positive experience with DBL and gained self-efficacy regarding ABG analysis. The tool was engaging, simple to use, and not overly time-consuming. CONCLUSIONS: DBL can be a useful tool for teaching ABG analysis to nursing students. Implications for an international audience nursing students everywhere benefit from understanding ABG analysis. DBL is a promising tool that can be used in any location with digital resources.

Respiratory failure and bioelectrical phase angle are independent predictors for long-term survival in acute heart failure.

Background. The assessment of long-term mortality in acute decompensated heart failure (ADHF) is challenging. Respiratory failure and congestion play a fundamental role in risk stratification of ADHF patients. The aim of this study was to investigate the impact of arterial blood gases (ABG) and congestion on long-term mortality in patients with ADHF. Methods and results. We enrolled 252 patients with ADHF. Brain natriuretic peptide (BNP), blood urea nitrogen (BUN), phase angle as assessed by means of bioimpedance vector analysis, and ABG analysis were collected at admission. The endpoint was all-cause mortality. At a median follow-up of 447 d (interquartile range [IQR]: 248-667), 72 patients died 1-840 d (median 106, IQR: 29-233) after discharge. Respiratory failure types I and II were observed in 78 (19%) and 53 (20%) patients, respectively. The ROC analyses revealed that the cut-off points for predicting death were: BNP > 441 pg/mL, BUN > 1.67 mmol/L, partial pressure in oxygen (PaO2) ≤69.7 mmHg, and phase angle ≤4.9°. Taken together, these four variables proved to be good predictors for long-term mortality in ADHF (area under the curve [AUC] 0.78, 95% CI 0.72-0.78), thus explaining 60% of all deaths. A multiparametric score based on these variables was determined: each single-unit increase promoted a 2.2-fold augmentation of the risk for death (hazard ratio [HR] 2.2, 95% CI 1.8-2.8, p< .0001). Conclusions. A multiparametric approach based on measurements of BNP, BUN, PaO2, and phase angle is a reliable approach for long-term prediction of mortality risk in patients with ADHF.

Wearable Transcutaneous CO2 Monitor Based on Miniaturized Nondispersive Infrared Sensor.

Transcutaneous oxygen and carbon dioxide provide the status of pulmonary gas exchange and are of importance in diagnosis and management of respiratory diseases. Though significant progress has been made in oximetry, not much has been explored in developing wearable technologies for continuous monitoring of transcutaneous carbon dioxide. This research reports the development of a truly wearable sensor for continuous monitoring of transcutaneous carbon dioxide using miniaturized nondispersive infrared sensor augmented by hydrophobic membrane to address the humidity interference. The wearable transcutaneous CO2 monitor shows well-behaved response curve to humid CO2 with linear response to CO2 concentration. The profile of transcutaneous CO2 monitored by the wearable device correlates well with the end-tidal CO2 trend in human test. The feasibility of the wearable device for passive and unobstructed tracking of transcutaneous CO2 in free-living conditions has also been demonstrated in field test. The wearable transcutaneous CO2 monitoring technology developed in this research can be widely used in remote assessment of pulmonary gas exchange efficiency for patients with respiratory diseases, such as COVID-19, sleep apnea, and chronic obstructive pulmonary disease (COPD).

Dyspnea, effort and muscle pain during exercise in lung transplant recipients: an analysis of their association with cardiopulmonary function parameters using machine learning.

BACKGROUND: Despite improvement in lung function, most lung transplant (LTx) recipients show an unexpectedly reduced exercise capacity that could be explained by persisting peripheral muscle dysfunction of multifactorial origin. We analyzed the course of symptoms, including dyspnea, muscle effort and muscle pain and its relation with cardiac and pulmonary function parameters during an incremental exercise testing. METHODS: Twenty-four bilateral LTx recipients were evaluated in an observational cross-sectional study. Recruited patients underwent incremental cardio-pulmonary exercise testing (CPET). Arterial blood gases at rest and peak exercise were measured. Dyspnea, muscle effort and muscle pain were scored according to the Borg modified scale. Potential associations between the severity of symptoms and exercise testing parameters were analyzed using a Forest-Tree Machine Learning approach, which accomplishes for a ratio between number of observations and number of screened variables less than unit. RESULTS: Dyspnea score was significantly associated with maximum power output (WR, watts), and minute ventilation (VE, L/min) at peak exercise. In a controlled subgroup analysis, dyspnea score was a limiting symptom only in LTx recipients who reached the higher levels of WR (≥ 101 watts) and VE (≥ 53 L/min). Muscle effort score was significantly associated with breathing reserve as percent of maximal voluntary ventilation (BR%MVV). The lower the BR%MVV at peak exercise (< 32) the higher the muscle effort perception. Muscle pain score was significantly associated with VO2 peak, arterial [HCO3-] at rest, and VE/VCO2 slope. In a subgroup analysis, muscle pain was the limiting symptom in LTx recipients with a lower VO2 peak (< 15 mL/Kg/min) and a higher VE/VCO2 slope (≥ 32). CONCLUSIONS: The majority of our LTx recipients reported peripheral limitation as the prevalent reason for exercise termination. Muscle pain at peak exercise was strictly associated with basal and exercise-induced metabolic altered pathways. The onset of dyspnea (breathing effort) was associated with the intensity of ventilatory response to meet metabolic demands for increasing WR. Our study suggests that only an accurate assessment of symptoms combined with cardio-pulmonary parameters allows a correct interpretation of exercise limitation and a tailored exercise prescription. The role and mechanisms of muscle pain during exercise in LTx recipients requires further investigations.

Impaired pulmonary gas exchange efficiency, but normal pulmonary artery pressure increases, with hypoxia in men and women with a patent foramen ovale.

NEW FINDINGS: What is the central question of this study? Do individuals with a patent foramen ovale (PFO+ ) have a larger alveolar-to-arterial difference in PO2 ( A-aDO2 ) than those without (PFO- ) and/or an exaggerated increase in pulmonary artery systolic pressure (PASP) in response to hypoxia? What is the main finding and its importance? PFO+ had a greater A-aDO2 while breathing air, 16% and 14% O2 , but not 12% or 10% O2 . PASP increased equally in hypoxia between PFO+ and PFO- . These data suggest that PFO+ may not have an exaggerated acute increase in PASP in response to hypoxia. ABSTRACT: Patent foramen ovale (PFO) is present in 30-40% of the population and is a potential source of right-to-left shunt. Accordingly, those with a PFO (PFO+ ) may have a larger alveolar-to-arterial difference in PO2 ( A-aDO2 ) than those without (PFO- ) in normoxia and with mild hypoxia. Likewise, PFO is associated with high-altitude pulmonary oedema, a condition known to have an exaggerated pulmonary pressure response to hypoxia. Thus, PFO+ may also have exaggerated pulmonary pressure increases in response to hypoxia. Therefore, the purposes of the present study were to systematically determine whether or not: (1) the A-aDO2 was greater in PFO+ than in PFO- in normoxia and mild to severe hypoxia and (2) the increase in pulmonary artery systolic pressure (PASP) in response to hypoxia was greater in PFO+ than in PFO- . We measured arterial blood gases and PASP via ultrasound in healthy PFO+ (n = 15) and PFO- (n = 15) humans breathing air and 30 min after breathing four levels of hypoxia (16%, 14%, 12%, 10% O2 , randomized and balanced order) at rest. The A-aDO2 was significantly greater in PFO+ compared to PFO- while breathing air (2.1 ± 0.7 vs. 0.4 ± 0.3 Torr), 16% O2 (1.8 ± 1.2 vs. 0.7 ± 0.8 Torr) and 14% O2 (2.3 ± 1.2 vs. 0.7 ± 0.6 Torr), but not 12% or 10% O2 . We found no effect of PFO on PASP at any level of hypoxia. We conclude that PFO influences pulmonary gas exchange efficiency with mild hypoxia, but not the acute increase in PASP in response to hypoxia.

Standard factors predicting success of Non-invasive ventilation are useful in treating Patients with POST Tuberculosis sequel.

OBJECTIVE: The aim was to access the effectiveness of Bilevel Positive Airway Pressure (BiPAP) in patients with type II respiratory failure secondary to Post Tuberculosis (TB) sequelae and determine the factors that can predict its success. PostTB pulmonary sequelae are complications after healing of TB and type II respiratory failure is frequently encountered in this group. . METHODS: This prospective study was carried out in the department of Chest Medicine, Jinnah Postgraduate Medical Center Karachi. (JPMC) Total 78 patients, between 20-80 years of age having hypercapnic respiratory failure, were included. Patients were given BiPAP along with standard treatment. RESULTS: Among 78 patients, 45 (56.3%) were males and 33 (43.7%) were females. Patients mean age was 50.6 } 15.76 years. The BiPAP success rate was 70.5% (55/78). There is significant difference in age (p=0.008), duration of disease (p=0.021), baseline pH (p=0.00), PaCO2 (p=0.004), Glasgow Coma Score (p=0.031), Chest X-ray (p<0.05) and systolic blood pressure (p=0.007) between responders and non-responders. Improvement in Abgs and vitals was observed among responders following 3 hours of therapy while pH drops significantly at 3 hours in non-responders. CONCLUSIONS: This study reveals that BiPAP is also efficacious method in patients with Type II respiratory failure post TB sequelae. Potential non responders can be identified relatively early in course of treatment and considered for ventilator.

Outcome of early use of non-invasive positive pressure ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease.

OBJECTIVE: To determine the outcome of early use of non-invasive positive pressure ventilation (NIPPV) in Pakistani patients with acute exacerbation of chronic obstructive pulmonary disease. METHODS: This descriptive study was conducted at Shifa International Hospital Islamabad from April 2015 to January 2017. A total of 120 patients with acute exacerbation of chronic obstructive pulmonary disease receiving NIPPV alongside standard therapy were included in the study. The patients were clinically assessed before starting on NIPPV. The parameters of respiratory rate, pH and paCO2 were monitored and NIPPV was given for six hours to evaluate clinical outcomes and analyze the factors predicting failure (requirement of mechanical ventilation and mortality). Frequency and percentages were calculated for qualitative variables while Mean and Standard Deviation for quantitative variables. Chi-square and t-test were used to see differences in pre and post NIPPV arterial blood gases. RESULTS: Patients' mean age was 58.88±10.09 years. Males were 88 (73.3%) and females were 32 (26.7%). The mean respiratory rate was 24±1.45 per minute before and 17.96±1.35 per minute after NIPPV (p < 0.00001). The mean pH before NIPPV was 7.27±0.04 and afterwards 7.38±0.02 (p < 0.00001). The mean pCO2 was 61.87±9.60 mm of Hg before and 57.46±6.79 mm of Hg after NIPPV (P < 0.0003). Twenty Four (20%) patients required invasive ventilation of which 19 (15.8%) patients could not survive. CONCLUSIONS: There was remarkable improvement in the arterial blood gases after NIPPV. However, the high mortality rate and significant number of COPD patients requiring mechanical ventilation necessitates further investigation into our population.

Effective thiafentanil immobilization and physiological responses of free-ranging moose (Alces alces) in northern Sweden.

OBJECTIVE: To evaluate clinical and physiological responses in moose to thiafentanil administration for immobilization. STUDY DESIGN: Cross-sectional clinical study. ANIMALS: Eleven (six males and five females) free-ranging adult moose (Alces alces). METHODS: Each moose was darted from a helicopter with 7.5 mg thiafentanil during March 2014 in northern Sweden. Physiological evaluation included vital signs and blood gases. Arterial blood was collected after induction and again after 10 minutes of intranasal oxygen administration and analyzed immediately with an i-STAT analyzer. A total of 10 mg naltrexone per milligram of thiafentanil was administered to all animals for reversal. Data were analyzed using descriptive statistics. RESULTS: All moose were sufficiently immobilized with a single dart injection. Induction occurred within 3 minutes in 10 of 11 moose. One individual became recumbent while crossing a river and naltrexone was immediately administered. Animals maintained sternal recumbency with their head raised and vital signs were stable. Nine of 10 moose were hypoxemic before oxygen administration, with seven becoming markedly hypoxemic [partial pressure of arterial oxygen (PaO2) between 40 and 59 mmHg (5.3-7.9 kPa)]. The PaO2 increased significantly between samples, but six moose remained hypoxemic despite therapy. Hypercapnia was seen in all moose, with eight having marked hypercapnia [partial pressure of arterial carbon dioxide (PaCO2) > 60 mmHg (>8.0 kPa)]. All moose were acidemic, with nine showing marked acidemia (pH < 7.20). The pH increased significantly with time and lactate decreased. Recoveries were rapid and uneventful, and all moose were living 6 months after capture. CONCLUSIONS: Thiafentanil provided rapid and sufficient immobilization of moose and its effects were rapidly reversed with naltrexone. As with other opioids, moose showed hypoxemia and varying degrees of respiratory and metabolic acidosis. Arterial oxygenation of moose improved following intranasal oxygen, but hypoxemia was not fully resolved despite therapy. CLINICAL RELEVANCE: Thiafentanil (7.5 mg per adult) is effective for immobilization of free-ranging moose. Supplemental oxygen may be of benefit when using this regimen; however, further investigation is required to confirm these results.

Initial size of unilateral pleural effusion determines impact of thoracocentesis on oxygenation.

BACKGROUND: There have been contradicting reports in the literature regarding the impact of pleural fluid aspiration on patients' oxygenation. The aim of this study was to assess the role of the initial size of effusion on post-drainage oxygenation. METHODS: We studied 122 patients, aged (mean±SD) 61.2±16.8 years, with unilateral pleural effusion and no remarkable parenchymal lesion, by determining PaO2, PaCO2 and [A-a] PaO2 just before thoracocentesis (T1), 30 min after its completion (T2) and 48 hours after the procedure (T3). Patients were divided into group A (75 patients) with small and moderate sized effusions and group B (47 patients) with large and massive effusions. The position of the meniscus line on the posteroanterior film, being arbitrarily set at just above the upper costal margin of the sixth anterior rib, was used to divide the two groups. Patients were studied at rest, breathing room air in the sitting position. Repeated measures ANOVA (related samples) and the Friedman test when the normality assumption was violated were used. RESULTS: In group A, at T3, PaO2(mm Hg) showed a statistically significant increase versus T1 (p<0.001) and T2 (p=0.002), while [A-a] PaO2 displayed a statistically significant decrease compared with T1 (p<0.001) and T2 (p=0.001). In group B, at T2, PaO2 presented significant decrease versus T1 (p<0.001) and T3 (p<0.001), while [A-a] PO2 was found to be significantly increased compared with both T1 and T3 (p<0.001). CONCLUSION: Patients with smaller effusions showed a small improvement in their oxygenation 48 hours post-thoracocentesis (T3). Patients with larger effusions exhibited a transient reduction in their oxygenation immediately after fluid removal (T2).

Caudwell Xtreme Everest: An Overview.

The Caudwell Xtreme Everest (CXE) expedition in the spring of 2007 systematically studied 222 healthy volunteers as they ascended from sea level to Everest Base Camp (5300 m). A subgroup of climbing investigators ascended higher on Everest and obtained physiological measurements up to an altitude of 8400 m. The aim of the study was to explore inter-individual variation in response to environmental hypobaric hypoxia in order to understand better the pathophysiology of critically ill patients and other patients in whom hypoxaemia and cellular hypoxia are prevalent. This paper describes the aims, study characteristics, organization and management of the CXE expedition.

Are transcutaneous oxygen and carbon dioxide determinations of value in pulmonary arterial hypertension?

BACKGROUND: We hypothesized that transcutaneous gas determinations of O2 and CO2 (TcPO2 and TcPCO2 ) are associated with the severity of PAH. METHODS: In this cross-sectional study, we included consecutive patients with PAH (group 1 PH; n = 34). Transcutaneous gas determinations were compared to those of age- and gender-matched healthy controls (n = 14), nongroup 1 PH (n = 19) or patients with high estimated RVSP on echocardiography but without hemodynamic evidence of PH (n = 12). RESULTS: In patients with PAH, TcPO2 , and TcPCO2 were significantly associated with PaO2 (R = 0.44, p = 0.03) and PaCO2 (R = 0.77, p < 0.001), respectively. TcPO2 /FiO2 (mean difference: -65.0 [95% CI: -121.3, -8.7]) and TcPCO2 (mean difference: -7.4 [95% CI: -11.6, -3.1]) were significantly lower in patients with PAH than healthy controls. TcPCO2 was useful in discriminating PAH patients from other individuals (AUC: 0.74 [95% CI: 0.62, 0.83]). TcPO2 /FiO2 ratio was significantly associated with mean PAP, TPG, PVR, CI, SVI, DLCO, six-minute walk distance and components of the CAMPHOR questionnaire. CONCLUSIONS: Transcutaneous pressure of CO2 was lower in patients with PAH. Transcutaneous pressure of O2 over inspired fraction of O2 ratio was inversely associated with severity of disease in patients with PAH.

Predictors for PaO2 and hypoxemic respiratory failure in COPD-A three-year follow-up.

BACKGROUND: Knowledge about predictors for developing hypoxemia in the course of chronic obstructive pulmonary disease (COPD) progression is limited. The objective of the present study was to investigate predictors for overall PaO2, for a potential change in PaO2 over time, and for first occurrence of hypoxemia. METHODS: 419 patients aged 40-76 years with COPD GOLD stages II-IV underwent clinical and pulmonary function measurements, including repeated arterial blood gases over three years. Airway obstruction, lung hyperinflation, markers of systemic inflammation and cardiovascular health, exacerbation frequency, smoking habits, and body composition were tested as possible predictors of PaO2 and first episode of hypoxemia. RESULTS: In multivariate adjusted longitudinal analyses, forced expiratory volume in 1 second, total lung capacity and functional residual capacity (all in% predicted), resting heart rate and fat mass index were all associated with overall PaO2 (all P < 0.005). We found no change in PaO2 over time (ρ = 0.33), nor did we find evidence that any of the tested variables predicted change in PaO2 over time. In multivariate adjusted survival analyses, functional residual capacity and resting heart rate were predictors of episodic hypoxemia (both ρ < 0.005). CONCLUSIONS: This longitudinal study identified pulmonary, cardiac and metabolic risk factors for overall PaO2 and episodic hypoxemia, but detected no change in PaO2 over time.

Effects of expiratory ribcage compression before endotracheal suctioning on arterial blood gases in patients receiving mechanical ventilation.

AIM AND OBJECTIVES: To investigate the effects of expiratory ribcage compression (ERCC) before endotracheal suctioning on the arterial blood gases (ABG) in patients receiving mechanical ventilation. BACKGROUND: Endotracheal suctioning is one of the most frequently used methods for airway clearance in patients receiving mechanical ventilation. Chest physiotherapy techniques such as ERCC before endotracheal suctioning can be used as a means to facilitate mobilizing and removing airway secretions and improving alveolar ventilation. DESIGN: A prospective, randomized, controlled cross-over design. METHODS: A randomized controlled cross-over trial with a convenience sample of 70 mechanically ventilated patients was conducted from 2006 to 2007. The patients received endotracheal suctioning with (experiment-period) or without (control-period) an antecedent 5-min expiratory ribcage. All the patients experienced both periods with at least a 3-h washed-out interval between the two periods. ABG were measured 5 min before and 25 min after endotracheal suctioning. RESULTS: The statistical tests showed that the levels of partial pressure of oxygen (PaO2 )/fraction of inspired oxygen (FiO2 ), partial pressure of carbon dioxide (PaCO2 ) and arterial oxygen saturation (SaO2 ) in the experimental period at 25 min after the intervention were significantly different from the control period. The tests also revealed that the levels of these variables at 25 min after suctioning were also significantly different from baseline values. However, these differences were clinically significant only for PaO2 /FiO2 . CONCLUSION: By improving the levels of PaO2 /FiO2 , ERCC can reduce the patients' need for oxygen and hence it can at least reduce the side effects of oxygen therapy. RELEVANCE TO CLINICAL PRACTICE: Improving PaO2 /FiO2 levels means less need for oxygen therapy. Hence, by applying ERCC we can at least minimize the side effects of oxygen therapy.

Effects of the thoracic block technique on vital signs, blood gases, and lung compliance in children with atelectasis.

Objectives: This study was aimed at examining the effects of the thoracic block technique on vital signs, arterial blood gases, and lung compliance in children with unilateral atelectasis receiving mechanical ventilation. Methods: Forty-four boys and girls with unilateral atelectasis and receiving mechanical ventilation, ranging in age from 4 months to 4 years, were recruited from the Abo El-Reesh Hospital intensive care unit at Cairo University. They were assigned to control and study groups: group A included 22 children receiving chest physical therapy, and group B included 22 children receiving the same chest physical therapy program as well as the thoracic block technique. Electrocardiography, mechanical ventilation, and blood gas analysis were conducted to assess the respiratory and heart rates, dynamic compliance, and arterial blood gases, respectively. Results: Respiratory rate and heart rate were significantly lower in the study group than the control group (p = 0.03). PaO2 and SaO2 increased in both groups, and the increase was more significant (p = 0.01 and 0.001, respectively) in group B than group A. A significant decrease in PaCO2 was observed in both groups, and the decrease was more significant in group B than group A (p = 0.02). A significant increase in dynamic lung compliance was observed in both groups, and the increase was more significant in group B than group A (p = 0.01). Conclusions: Applying the thoracic block technique rather than chest physical therapy techniques alone in children with atelectasis receiving mechanical ventilation may lead to improvements in arterial blood gases and dynamic lung compliance, and has no negative effects on heart rate and respiratory rate.

Venous blood gases in the assessment of respiratory failure in patients undergoing sleep studies: a randomized study.

STUDY OBJECTIVES: Venous blood gases (VBGs) are not consistently considered suitable surrogates for arterial blood gases (ABGs) in assessing acute respiratory failure due to variable measurement error. The physiological stability of patients with chronic ventilatory failure may lead to improved agreement in this setting. METHODS: Adults requiring ABGs for sleep or ventilation titration studies had VBGs drawn before or after each ABG, in a randomized order. Veno-arterial correlation and agreement were examined for carbon dioxide tension (PCO2), pH, oxygen tension (PO2), and oxygen saturation (SO2). RESULTS: We analyzed 115 VBG-ABG pairs from 61 patients. Arterial and venous measures were correlated (P < .05) for PCO2 (r = .84) and pH (r = .72), but not for PO2 or SO2. Adjusted mean veno-arterial differences (95% limits of agreement) were +5.0 mmHg (-4.4 to +14.4) for PCO2; -0.02 (-0.09 to +0.04) for pH; -34.3 mmHg (-78.5 to +10.0) for PO2; and -23.9% (-61.3 to +13.5) for SO2. VBGs obtained from the dorsal hand demonstrated a lower mean PCO2 veno-arterial difference (P < .01). A venous PCO2 threshold of ≥ 45.8 mmHg was > 95% sensitive for arterial hypercapnia, so measurements below this can exclude the diagnosis without an ABG. A venous PCO2 threshold of ≥ 53.7 mmHg was > 95% specific for arterial hypercapnia, so such readings can be assumed diagnostic. The area under the receiver operating characteristic curve of 0.91 indicated high discriminatory capacity. CONCLUSIONS: A venous PCO2 < 45.8 mmHg or ≥ 53.7 mmHg would exclude or diagnose hypercapnia, respectively, in patients referred for sleep studies, but VBGs are poor surrogates for ABGs where precision is important. CLINICAL TRIAL REGISTRATION: Registry: Australian New Zealand Clinical Trials Register; Name: A comparison of arterial and blood gas analyses in sleep studies; URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=372717; Identifier: ACTRN12617000562370. CITATION: Lindstrom SJ, McDonald CF, Howard ME, et al. Venous blood gases in the assessment of respiratory failure in patients undergoing sleep studies: a randomized study. J Clin Sleep Med. 2024;20(8):1259-1266.

Relative hypoxemia at depth during breath-hold diving investigated through arterial blood gas analysis and lung ultrasound.

Pulmonary gas exchange in breath-hold diving (BHD) consists of a progressive increase in arterial partial pressures of oxygen ([Formula: see text]) and carbon dioxide ([Formula: see text]) during descent. However, recent findings have demonstrated that [Formula: see text] does not consistently rise in all subjects. This study aimed at verifying and explaining [Formula: see text] derangements during BHD analyzing arterial blood gases and searching for pulmonary alterations with lung ultrasound. After ethical approval, 14 fit breath-hold divers were included. Experiments were performed in warm water (temperature: 31°C). We analyzed arterial blood gases immediately before, at depth, and immediately after a breath-hold dive to -15 m of fresh water (mfw) and -42 mfw. Signs of lung interstitial edema and atelectasis were searched simultaneously with a marinized lung ultrasound. In five subjects (-15 mfw) and four subjects (-42 mfw), the [Formula: see text] at depth seems to decrease instead of increasing. [Formula: see text] and lactate showed slight variations. At depth, no lung ultrasound alterations were seen except in one subject (hypoxemia and B-lines at -15 mfw; B-lines at the surface). Lung interstitial edema was detected in 3 and 12 subjects after resurfacing from -15 to -42 mfw, respectively. Two subjects developed hypoxemia at depth and a small lung atelectasis (a focal pleural irregularity of triangular shape, surrounded by thickened B-lines) after resurfacing from -42 mfw. Current experiments confirmed that some BH divers can experience hypoxemia at depth. The hypothesized explanation for such a discrepancy is lung atelectasis, which could not be detected in all subjects probably due to limited time available at depth.NEW & NOTEWORTHY During breath-hold diving, arterial partial pressure of oxygen ([Formula: see text]) and arterial partial pressure of carbon dioxide ([Formula: see text]) are believed to increase progressively during descent, as explained by theory, previous end-tidal alveolar gas measurements, and arterial blood gas analysis in hyperbaric chambers. Recent experiments in real underwater environment found a paradoxical [Formula: see text] drop at depth in some divers. This work confirms that some breath-hold divers can experience hypoxemia at depth. The hypothesized explanation for such a discrepancy is lung atelectasis, as suggested by lung ultrasound findings.