Retrospective Analysis of Arterial Carbon Dioxide Level and Arterial pH Level at the Time of Initiation of Respiratory ECMO and Outcome
Authors: Oza Pranay , Umbarkar Rajendra , Goyal Venkat , Shukla Pranali 
Published: September 2022

Introduction Respiratory extracorporeal membrane oxygenation (ECMO) is well established and its popularity has increased during coronavirus disease 2019 (COVID-19) time. The efficacy of ECMO has been proved in refractory respiratory failure with varied etiology. More than 85,000 respiratory ECMO cases (neonatal, pediatric, adult) registered as per Extracorporeal Life support Organization (ELSO) statistics April 2022 report, with survived to discharge or transfer ranging from 58 to 73%. Early initiation of ECMO is usually associated with shorter ECMO run and better outcome. Many patient factors have been associated with mortality while on ECMO. Pre-ECMO patient pH and arterial partial pressure of carbon dioxide (paCO2) have been associated with poor outcome. We designed a retrospective study from a single tertiary care center and analyzed our data of all respiratory ECMO (neonatal, pediatric, and adult) to understand the effect of pre ECMO, paCO2, and arterial pH to ECMO outcome.

Methods It is a retrospective analysis of data collected of patients with acute respiratory failure managed on ECMO from January 2010 to December 2021. Pre-ECMO (1–6 hours before initiation), paCO2, and arterial pH level were noted and analyzed with primary and secondary outcome. Primary outcome goal was survivor and discharged home versus nonsurvivor, while secondary goal was the number of ECMO days and incidence of neurological complications. The statistical analysis was done for primary outcome and incidences of neurological complications and p-value obtained by using chi-squared method. Meta-analysis was done by classifying the respiratory ECMO cases in three major category—COVID-19, H1N1 non-COVID-19, and H1N1 respiratory failure.

Results The total 256 patients of respiratory failure were treated with ECMO during specified period by Riddhi Vinayak Multispecialty Hospital ECMO team. Data analysis of 251 patients (5 patients were transferred for lung transplant, hence been not included in study) done. Patients were divided on the basis of pH level less than 7.2 and more than 7.2 and analyzed for primary and secondary outcome. Similarly, patients were divided on the basis of paCO2 level of less than 45 and more than 45.

Patient with pre-ECMO pH level more than 7.2 has statistically better survived extracorporeal life support (ECLS) (p-value: 0.008) and survival to discharge home (p-value: 0.038) chances. Pre-ECMO paCO2 level of less than 45 also showed better survival chance of survived ECLS (46.67 vs. 36.02) and survived to discharge home (42.22 vs. 31.06) but not statistically significant (p-value: 0.15 and 0.18, respectively). There was no significant difference in average number of ECMO days in patient survived to discharge home with paCO2 less than 45 and more than 45 (15.7 vs. 11.1 days), and also in pH more than 7.2 and pH less than 7.2 (15.8 vs. 11.6). The incidence of neurological complications was also found lower in patient with pH more than 7.2 (7.5 vs. 17.3%, p-value: 0.034) and in paCO2 level of less than 45 (4.4 vs. 12.65, p-value: 0.15).

Conclusion Pre-ECMO arterial pH of more than 7.2 (statistically significant) and paCO2 of less than 45 (statistically not significant) have definitely better survival chances and have lesser incidences of neurological complications. There was no significance difference in the number of ECMO days in either group. Authors recommends early initiation of ECMO for mortality and morbidity benefits.