European Journal of Cardiovascular Medicine

Chronic Obstructive Pulmonary Disease (COPD) is a leading cause of global morbidity and mortality, with acute exacerbations (AECOPD) contributing significantly to disease progression, hospital admissions, and healthcare burden. These exacerbations are frequently triggered by respiratory infections or environmental pollutants, causing sudden deterioration in respiratory function. Accurate evaluation of a patient’s ventilatory and acid-base status during such episodes is essential for timely intervention and effective management.

Arterial Blood Gas (ABG) analysis remains the gold standard for assessing pH, partial pressures of oxygen (PaO₂) and carbon dioxide (PaCO₂), and bicarbonate (HCO₃⁻) levels. It is vital for determining the severity of respiratory compromise and guiding therapeutic strategies like oxygen supplementation and ventilation. However, ABG sampling is invasive, painful, technically demanding, and associated with complications such as hematoma, arterial spasm, and infection. Repeated arterial sampling is often impractical, particularly in elderly or critically ill patients.1

Venous Blood Gas (VBG) analysis offers a less invasive alternative, with emerging evidence indicating strong correlation between venous and arterial values of pH, pCO₂, and HCO₃⁻. While VBG cannot reliably reflect PaO₂, it shows promise in evaluating ventilation and acid-base status. Likewise, pulse oximetry (SpO₂) provides non-invasive, real-time monitoring of arterial oxygen saturation, although its accuracy may be influenced by factors such as poor perfusion and skin pigmentation.2-3

Despite several international studies exploring VBG and SpO₂ as substitutes for ABG in AECOPD, results remain inconsistent, and data from the Indian population are scarce. Therefore, this study aims to assess the correlation of VBG parameters and SpO₂ readings with ABG values in patients with AECOPD. The findings may help determine whether VBG and pulse oximetry can serve as reliable, less invasive alternatives to ABG in initial assessments and ongoing monitoring of these patients.4-5

Aims and Objectives

This study aims to evaluate the correlation between venous blood gas (VBG) values and arterial blood gas (ABG) values in patients presenting with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). To assess the reliability of pulse oximetry (SpO₂) as a non-invasive alternative to arterial oxygen saturation (SaO₂) obtained from ABG in the same patient population.

This was a cross sectional and analytical study will start after approval given by IEC till 1 year in Shyam Shah Medical College and Sanjay Gandhi hospital Rewa M.P. The Present study was performed on patients with acute exacerbation of chronic obstructive pulmonary disease in ICU of Medicine department SGMH Rewa.

Inclusion of patients was done after obtaining informed consent from the patient or their relative. Keeping patient data confidential and publishing findings anonymously was among other measures for ethical conduct in this study.

Sample size:

Daniel et al (2021) in their study shown a prevalence of Chronic Obstructive Pulmonary Disease patients at 7.4%

So, according to the formula:

n = 4pq/l2   (where p = 7.4%, q = 100-p, l = 5%)

= 4x22x92.8/5x5 = 110

The sample size will be 110 patients.

Inclusion Criteria:

• Patients who are known or newly diagnosed case of chronic obstructive pulmonary disease.
• Age more than 18 years.
• Those who are consenting for the study.

Exclusion criteria:

• Those who did not give consent for the study.
• Collagen vascular disorder.
• Post cardiac arrest patients.
• Interval of more than 10 min between arterial and venous sampling and inappropriate sample transfer to the laboratory.
•  
• Contraindication (infection/ fistula at the injection site).

Procedure Plan:

 Patients satisfying inclusion criteria were included in the study and a written consent were obtained from each patient. Patients were eligible if the on-duty emergency physician decided to obtain an ABG sample for the initial assessment. After having the study explained, written consent was obtained from the patient or the relative, and patients were sampled for arterial and venous blood with minimum delay (always, <10 min) between the samples. For arterial samples (0.5-1 ml). A notionally heparinised plastic syringe with 24 G needle was used to puncture the radial artery / femoral artery. For venous sampling, blood will be obtained at the time of intravenous cannula placement or using peripheral vene-puncture. The two samples were taken as close as possible in time and before the initiation of any form of treatment. The samples were analyzed as quickly as possible using the blood gas analyzer located in the ED.

Data Collection

Data collection was collected by using a pre-designed proforma including demographic data (age, sex), laboratory findings, vital signs, level of consciousness, diagnosis, and finally, the outcome of patients (death, renal failure, liver failure, need for mechanical ventilation etc.).

Sample Collection

• Performed arterial blood sampling from the radial artery under aseptic conditions using heparinized syringes for ABG analysis.
• Collected venous blood samples from a peripheral vein simultaneously for VBG analysis.
• Measured oxygen saturation (SpO₂) using a standard pulse oximeter at the time of blood sample collection.

Laboratory Analysis

• Analyzed arterial and venous blood samples immediately using a blood gas analyzer to determine pH, partial pressure of carbon dioxide (PaCO₂/PvCO₂), and arterial oxygen saturation (SaO₂).
• Calibrated the blood gas analyzer regularly according to the manufacturer's instructions to ensure accuracy.

Statistical Analysis:

Statistical analysis was done for all the recorded data. After compilation and tabulation of data, appropriate test was applied.

Table 1: Demographic Characteristic feature of COPD cases

The majority of COPD cases were from rural areas (55.46%). Most patients were aged between 61–70 years (47.06%), followed by 71–80 years (27.73%). Males constituted 64.71% of the study population. Farmers (32.77%), housewives (27.73%), and labourers (25.21%) made up the largest occupational groups. A significant proportion (76.47%) belonged to the lower socioeconomic class. (Table-1)

Table 2: Distribution of cases according to Co-Morbidities and Addiction (n=119)

                Among the 119 cases, 62.18% had COPD without other comorbidities, while 24.37% had COPD with hypertension. COPD with both type 2 diabetes mellitus (T2DM) and hypertension was observed in 12.61% of patients, and 0.84% had COPD with T2DM alone. Regarding addiction, 43.69% were smokers, 15.97% had both smoking and alcohol addiction, and 40.34% had no history of addiction.(Table-2)

Table 3: Comparison correlation of ABG and VBG Mean Value (n=119)

In the comparison between ABG and VBG values among 119 patients, a strong positive correlation was observed for all parameters. The mean arterial pH was 7.32±0.08, while venous pH was 7.31±0.07, with a correlation coefficient of 0.88 (p<0.0001). Arterial and venous pCO₂ showed a correlation of 0.79, with mean values of 39.87±13.65 mmHg and 41.78±14.96 mmHg, respectively. The correlation for pO₂ was lower at 0.64, with ABG and VBG means of 93.03±17.17 mmHg and 54.97±13.33 mmHg. The strongest correlation was seen in HCO₃ values, with ABG at 24.19±4.37 mmol/L and VBG at 23.78±4.79 mmol/L (r=0.90, p<0.0001). (Table-3)

Table 4: Comparison of Pulse Oximetry Value to Arterial PO2 Value (n=119)

Among 119 cases, 20.16% had SpO₂ <80% with a mean saturation of 92.62±1.73% and arterial PO₂ of 97.62±7.29 mmHg (p=0.0020). In 79.84% with SpO₂ >80%, mean saturation was 93.14±6.32% and PO₂ was 93.76±16.16 mmHg (p=0.7280). Overall, no significant correlation was found between pulse oximetry and arterial PO₂ (p=0.3050). (Table-4)

Table 5: Mortality of cases according to co-morbidities and Addiction (n=119)

Among patients with COPD alone, mortality was 10.81%, while it was 3.44% in those with COPD and hypertension, and 26.66% in those with COPD, T2DM, and hypertension. No deaths occurred in the single case with COPD and T2DM. Mortality was 8.33% in patients with no addiction, 7.69% in smokers, and highest at 26.31% in those with both smoking and alcohol addiction. (Table-5)

In the present study, a higher proportion of COPD patients belonged to the rural population (55.46%) as compared to the urban (44.54%), indicating a probable association between rural exposure and COPD. This could be due to increased exposure to biomass fuel and poor access to healthcare. Similar findings were reported by Salvi et al. (2012)6, who observed a higher prevalence of COPD in rural areas of India, especially among women exposed to household air pollution from traditional cooking fuels

Age-wise distribution showed that the majority of the patients were in the age group of 61–70 years (47.06%), followed by 71–80 years (27.73%) and >80 years (15.97%). Only 2.52% of the patients were ≤50 years. This reflected the chronic nature of the disease and its cumulative exposure-related etiology. A study by Jindal et al. (2012)7 also documented a peak incidence in the 6th to 7th decade of life, supporting the notion that COPD is primarily a disease of older adults

Regarding gender distribution, males constituted 64.71% of the study population while females accounted for 35.29%. The predominance of males could be linked to higher rates of tobacco use and occupational exposure. These findings were consistent with the study by Mohan et al. (2016)8, who reported male predominance among COPD cases, attributing it to smoking habits and occupational risks among men.

Occupationally, farmers (32.77%) and housewives (27.73%) formed the largest groups, followed by labourers (25.21%). This trend points toward increased exposure to dust, chemicals, and biomass fuel smoke in these occupational categories. Koul et al. (2017)9 similarly found that farming and domestic exposure to biomass smoke were significantly associated with COPD in the Kashmir valley.

In terms of socioeconomic status, a majority of the patients (76.47%) belonged to the lower class, suggesting a strong association between low socioeconomic status and COPD. This might be due to poor nutrition, inadequate access to healthcare, and high exposure to environmental pollutants. Bhardwaj et al. (2021)10 also demonstrated a similar trend, where most COPD patients were from low-income backgrounds.

In the our study, among 119 COPD patients, 62.18% had COPD alone, 24.37% had COPD with hypertension, 12.61% had COPD with both type 2 diabetes mellitus (T2DM) and hypertension, and 0.84% had COPD with T2DM. Regarding addiction, 43.69% were smokers, 15.97% had both smoking and alcohol addiction, and 40.34% reported no addiction history.

These findings align with a systematic review by Dos Santos NC et al. (2022)11, which analyzed data from 20 studies involving 447,459 COPD subjects. They reported that hypertension was present in 17% to 64.7% of COPD patients, and diabetes in 10.2% to 45%, indicating a significant prevalence of these comorbidities among COPD patients. 

Similarly, a study conducted in Kashmir by Bhat AH (2022)12 found that among COPD patients, 56.7% had hypertension and 24.3% had diabetes. These results further support the high prevalence of hypertension and diabetes as comorbidities in COPD patients. 

 Furthermore, a comprehensive study by Ghafil NY et al. (2023)13 in Iraq reported that COPD patients had a significantly higher prevalence of T2DM, atherosclerotic cardiovascular diseases (ASCVD), hypertension, and dyslipidemia compared to non-COPD individuals. The study highlighted that the prevalence of these comorbidities increased with the severity of COPD. 

Regarding addiction, the current study's finding that 43.69% of COPD patients were smokers aligns with the well-established role of smoking as a primary risk factor for COPD. The additional 15.97% of patients with both smoking and alcohol addiction highlights the need for comprehensive addiction history assessments in COPD management.

In the present study involving 119 patients, arterial blood gas (ABG) and venous blood gas (VBG) analyses were compared, yielding the following mean values and correlations:

·         pH: ABG 7.32±0.08, VBG 7.31±0.07, correlation coefficient 0.88, p < 0.0001

·         pCO₂: ABG 39.87±13.65 mmHg, VBG 41.78±14.96 mmHg, correlation coefficient 0.79, p < 0.0001

·         pO₂: ABG 93.03±17.17 mmHg, VBG 54.97±13.33 mmHg, correlation coefficient 0.64, p < 0.0001

·         HCO₃⁻: ABG 24.19±4.37 mmol/L, VBG 23.78±4.79 mmol/L, correlation coefficient 0.90, p < 0.0001

 These findings suggest strong correlations between ABG and VBG measurements for pH, pCO₂, and HCO₃⁻, with a moderate correlation for pO₂.

Similar results were reported by Prasad A et al. (2019)14, who conducted a study on 100 critically ill patients. They found a mean pH difference of 0.04 (p < 0.0001) with a correlation coefficient of 0.832, and a pCO₂ mean difference of approximately 5.7 mmHg (p < 0.0001) with a correlation coefficient of 0.916. The HCO₃⁻ values showed a mean difference of 1.22 mmol/L (p < 0.001) with a correlation coefficient of 0.960. However, the pO₂ values demonstrated poor correlation, with a mean difference of 55.191 mmHg (p < 0.0001) and a correlation coefficient of 0.166.

In another study by Malatesha G et al. (2007)15, involving 95 patients with diverse medical conditions, the 95% limits of agreement between arterial and venous values were narrow for pH (0.13 to -0.1), bicarbonate (4.3 to -5.8), and pCO₂ (6.8 to -7.6), indicating acceptable agreement. However, the agreement in pO₂ measurements was poor, with 95% limits of agreement ranging from 145.3 to -32.9. 

Furthermore, a study by Malatesha et al. (2007)15 assessed 95 patients in an emergency department setting. They reported Pearson correlation coefficients of 0.874 for pH, 0.835 for pCO₂, and 0.768 for HCO₃⁻, indicating strong correlations. The pO₂ values showed a weaker correlation, with a coefficient of 0.287.

In the present study involving 119 patients, the comparison between pulse oximetry (SpO₂) and arterial partial pressure of oxygen (PaO₂) revealed that among patients with SpO₂ <80%, the mean saturation was 92.62±1.73%, and the mean PaO₂ was 97.62±7.29 mmHg (P=0.0020). For those with SpO₂ >80%, the mean saturation was 93.14±6.32%, and the mean PaO₂ was 93.76±16.16 mmHg (P=0.7280). Overall, the total mean saturation was 93.04±5.70%, with a mean PaO₂ of 94.54±14.86 mmHg (P=0.3050). These findings suggest a statistically significant discrepancy between SpO₂ and PaO₂ measurements, particularly in patients with lower SpO₂ values.

Similar observations were reported by Garnet B et al. (2023)16, who evaluated the accuracy of pulse oximetry in assessing the need for long-term oxygen therapy (LTOT) in stable outpatients with chronic obstructive pulmonary disease (COPD). They found that relying solely on SpO₂ measurements led to a 10% false-negative rate in detecting severe resting hypoxemia (PaO₂ ≤55 mm Hg), with 2.5% of patients exhibiting occult hypoxemia (SpO₂ >92% with PaO₂ ≤55 mm Hg). The study concluded that SpO₂ alone might not be sufficient for accurate LTOT assessment, particularly in active smokers, and recommended arterial blood gas (ABG) analysis for precise evaluation. 

In terms of mortality associated with comorbidities and addiction, the current study reported that among patients with COPD alone, the mortality rate was 10.81%. Those with COPD and hypertension had a mortality rate of 3.44%, while patients with COPD, type 2 diabetes mellitus (T2DM), and hypertension exhibited a higher mortality rate of 26.66%. Regarding addiction, patients with no addiction had a mortality rate of 8.33%, smokers had a mortality rate of 7.69%, and those with both smoking and alcohol addiction had the highest mortality rate at 26.31%. These findings underscore the impact of multiple comorbidities and combined addictions on mortality in COPD patients.

In our study, evaluated the correlation between venous blood gas (VBG), pulse oximetry (SpO₂), and arterial blood gas (ABG) in acute exacerbation of COPD (AECOPD) patients. Results showed a strong correlation between venous and arterial pH and pCO₂, supporting VBG as a feasible alternative to ABG for assessing acid-base status. However, venous pO₂ did not reliably reflect arterial oxygenation, emphasizing the continued importance of ABG in evaluating hypoxemia. Pulse oximetry moderately correlated with arterial oxygen saturation but may be influenced by external factors. VBG, along with SpO₂, can aid initial evaluation, but ABG remains essential in critical cases.

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