Association of lactate level with nocturnal hypoxemia and pulmonary hypertension in patients with idiopathic pulmonary fibrosis

Background: Nocturnal hypoxemia, exertional desaturation and pulmonary hypertension have a negative impact on the prognosis of idiopathic pulmonary fibrosis (IPF). Searching for markers for early detection of these three comorbid conditions will contribute positively to the prognosis of the disease. In our study, we investigated the relationship between arterial blood gas (ABG) lactate level and nocturnal hypoxemia, exertional desaturation, and pulmonary hypertension. Method: In our cross-sectional study, IPF cases without hypoxemic respiratory failure, who were followed up in the ITF Chest Diseases Interstitial Pulmonary Diseases Outpatient Clinic between 2019 and 2020, who were diagnosed according to current guidelines, were included. Age, gender, body mass index, comorbidities and duration of symptoms of the cases were recorded. Spirometry, diffusion capacity measurement, daytime arterial blood gas analysis, 6-minute walking test (6MWT), transthoracic echocardiography, nocturnal oximetry and / or polysomnography were performed in all cases. (EthicNo: 2019/1440). Results: Twenty-five IPF cases without daytime hypoxemia were included in our study. Pulmonary hypertension (PH) was detected in seven patients (26.9%). The time when saturation was less than 90% in three of the cases was more than 20% of the time spent asleep, 17 (85%) were diagnosed with obstructive sleep apnea (9 mild, 3 moderate, 5 severe). Lactate levels of 7 patients with PH did not differ from the others. The lactate level in daytime ABG was higher in 9 patients with exertional desaturation (lactate level in daytime ABG: 1.42 ± 0.38mmol vs. 1.16 ± 0.87mmol p = 0.049, lactate level in ABG after sleep: 1.38 ± 0.68mmol vs. 1.08. ± 0.44mmol p = 0.379). In IPF cases, lactate level in ABG taken during the day was correlated with lactate level in ABG after sleep (Rs = 0.604, p = 0.002) and desaturation in 6MWT (Rs = 0.401, p = 0.047). Lactate level in ABG after sleep and minimum saturation during sleep (Rs =-0.490, p = 0.015), percentage of nocturnal desaturation (Rs = 0.445, p = 0.029), apnea hypopnea index (Rs = 0.537, p = 0.018) and oxygen the desaturation index (Rs = -0.674, p = 0.002) was correlated. In the multiple regression analysis of the model created with nocturnal hypoxemia parameters, exertional desaturation and the presence of pulmonary hypertension, lactate level was found to be independently associated only with nocturnal hypoxemia (p = 0.034). Conclusion: In our study, it was shown that lactate level in daytime arterial blood gas increased in patients with exertional desaturation, Lactate level in ABG after sleep was associated with nocturnal hypoxemia, and there was a relationship between nocturnal hypoxemia and pulmonary hypertension. Keywords: Idiopathic pulmonary fibrosis, lactate, pulmonary hypertension, nocturnal hypoxemia, exertional desaturation