Correlation of PaCO2 and ETCO2 in COPD Patients with Exacerbation on Mechanical Ventilation.

Introduction: Chronic obstructive pulmonary disease (COPD) patients in hypercapnic respiratory failure require multiple arterial blood gas (ABG) analysis for monitoring. It is a painful, invasive, and expensive investigation. This study was aimed at finding an agreement between end-tidal carbon dioxide (ETCO2, a noninvasive modality) and arterial carbon dioxide (PaCO2) in COPD patients with acute exacerbation on mechanical ventilation. Materials and methods: A prospective observational study was conducted in COPD patients who required mechanical ventilation. ETCO2 was recorded by mainstream capnography along with ABG analysis. An agreement between PaCO2 and ETCO2 was assessed. The effect of various factors on correlation was also studied. Results: A total of 100 patients with COPD in hypercapnic respiratory failure were included. Seventy-three percentage of patients were managed on invasive mechanical ventilation (IMV). The mean ETCO2 and PaCO2 were 48.66 ± 15.57 mm Hg and 75.52 ± 21.9 mm Hg, respectively. There was a significant correlation between PaCO2 and ETCO2 values (r = 0.82, 95% confidence interval of r = 0.78-0.86, p <0.0001). The Bland-Altman analysis shows the mean bias as -19.4 (95% limits of agreement = -40.0-1.1). Pearson's correlation coefficient was 0.84 in intubated patients and 0.58 in patients on noninvasive ventilation (NIV). Pearson's correlation coefficient between PaCO2 and ETCO2 in subjects with consolidation, cardiomegaly, hypotension, and raised pulmonary artery pressures was 0.78, 0.86, 0.85, and 0.86, respectively. Conclusion: Mainstream ETCO2 measurement accurately predicts the PaCO2 in COPD patients on IMV. However, for patients on NIV, ETCO2 is insufficient in monitoring PaCO2 levels due to weak correlation. Clinical significance: ETCO2 can be used as a noninvasive modality in intensive care unit for monitoring the PaCO2 in COPD patients on IMV. This can reduce the requirement of arterial blood sampling to a minimum number, in turn, reducing the cost of the treatment and discomfort to the patients. How to cite this article: Tyagi D, Govindagoudar MB, Jakka S, Chandra S, Chaudhry D. Correlation of PaCO2 and ETCO2 in COPD Patients with Exacerbation on Mechanical Ventilation. Indian J Crit Care Med 2021;25(3):305-309.

Failure of methanol detoxification in pests confers broad spectrum insect resistance in PME overexpressing transgenic cotton.

Methanol is noxious to insect pests, but most plants do not make enough of it to shield themselves from encroaching insects. Methanol emission is known to increase in the instance of herbivory. In the current study, we showed that Aspergillus niger pectin methylesterase over-expression increases methanol emission and confers resistance to polyphagous insect pests on transgenic cotton plants by impeding the possible methanol detoxification pathways. Transgenic plants emitted ∼11 fold higher methanol displaying insect mortality of 96% and 93% in Helicoverpa armigera and Spodoptera litura, respectively. The larvae were unable to survive and finish their life cycle and the surviving larvae exhibited severe growth retardation. Insects try to detoxify methanol via catalase, carboxylesterase and cytochrome P450 monooxygenase enzymes, amongst which cytochrome P450 plays a major role in oxidizing methanol to formaldehyde and formaldehyde to formic acid, which is broken down into carbon dioxide and water. In our study, catalase and esterase enzymes were found to be upregulated, but cytochrome P450 monooxygenase levels were not much affected. Leaf disc assays and In-planta bioassays also showed 50-60% population reduction in the sap sucking pests, such as Bemisia tabaci and Phenacoccus solenopsis. These findings imply that elevated methanol emissions confer resistance in plants against chewing and sap-sucking pests by tampering the methanol detoxification pathways. Such mechanism will be useful in imparting expansive resistance against pests in plants.