The world is in the middle of a pandemic with a new coronavirus, SARS-CoV-2, which has a high mortality in the elderly and people with co-morbidities such as hypertension, chronic heart disease and diabetes. The clinical course is biphasic [1] , first a viral infection in the upper or/and lower respiratory tract sometimes followed by a dysregulated inflammatory response ("cytokine storm") with severe inflammation in the lungs which often require several weeks of mechanical ventilation. It is unclear what triggers the dysregulated inflammatory response which is a clinical feature much more commonly seen than in severe influenza pneumonia, and one suggestion is that it is the viral interaction with its human receptor, the acetylcholinesterase2, ACE2, molecule that could be an explanation [2] . A characteristic of the SARS-CoV-2 infection is lymphopenia and especially a low CD4+ T cell count [3] and the potential to infect CD4+ T cells [4] . It is generally assumed that the mortality is due to lung failure, but here we describe a patient who developed a strong inflammatory response with high C-reactive protein, very high IL-6 and white blood cells (WBC) and went into an irreversible metabolic acidosis.
A 72-year-old man with diabetes mellitus and G-6PD deficiency presented with 10-day history of fever, dry cough, shortness of breath and nasal congestion. At admission his oxygen saturation was 95% on 3 liters of oxygen. Hemoglobin concentration was 13.6 g/dL(normal range: 11.5-15.5), 2), renal function test was normal and chest radiograph revealed right lung ground glass opacities. Nasopharyngeal swab for SARS-CoV-2 RNA was positive. He was started on ceftriaxone 2 gm once daily and azithromycin 500 mg once daily according to national guidelines.
On day 12 of his illness (2 nd day after admission), his hypoxia worsened. Arterial blood gas showed a pH of 7.48, PaCO2 31mmHg, PaO2 60mmHg, bicarbonate 23mmol/L, lactate 1.5 mmol/L and a Creactive protein of 237 mg/L ( Figure A) . He was intubated and started on mechanical ventilation.
Hydroxychloroquine, beta interferon and lopinavir/ritonavir were added according to national guidelines. Post intubation, the patient was kept on volume-controlled ventilation and lung protective mode with a tidal volume of 6 mL/kg of predicative body weight (PBW) and positive end expiratory pressure (PEEP) between 16-18 cmH2O. The sedation was maintained with intravenous fentanyl and midazolam with additional intermittent doses of cisatracurium. CO2 accumulation was significant with a pCO2 of 70-80 mmHg . This was attributed to acute lung injury due to SARS-CoV2 and the use of protective lung ventilation strategy. Therefore PEEP was lowered and tidal volume raised. Fraction of inspired oxygen (FiO2) was also successfully weaned to 0.5 with targeted partial pressure of oxygen (PO2) above 60 mmHg. Over the next few days, the metabolic acidosis progressed despite CVVHD with pH of 6.9, PaO2 68mmHg, PCO2 33mmHg,Na 134mmol/L, CL 102mmol/L, lactate reaching 19.6 mmol/L, and the WBC increased to 59500/uL with neutrophils of 35000/u L, ALT increased to more than 3300 IU/L, and interleukin-6 level was 262.7 pg/mL (normal range < 16.4 ) eventually leading to cardiopulmonary arrest and death.
IL-6 is a strong predictor of respiratory failure [5] . During the energy producing metabolism that takes place in the cytoplasm of cells, glucose is transformed into pyruvate molecules generating 2 ATP molecules. During this glycolysis process, no oxygen is utilized. If the tissue oxygenation is regular, pyruvate molecules enters the mitochondria where they undergoes a series of enzymatic processes generating ATP, as well as CO2 and H2O molecules. In a situation of tissue hypoxia py-J o u r n a l P r e -p r o o f ruvate molecules cannot enter the mitochondria but are converted to lactic acid and in this process ATP is released maintaining the energy production. The lactic acid is removed mainly through the process of gluconeogenesis that takes place in the liver and kidney cortex, but also through the oxidation process in various organs. The lactic acid accumulation is the result of increased production and/or its decreased removal [6] . On 18th day of the patient's illness, the lactic acid levels started to increase significantly but levels of pCO2 were acceptable, it was concluded that he was in metabolic acidosis. It is possible that dysregulated inflammatory response (cytokine storm) caused the metabolic acidosis.This has been described in severe bacterial sepsis [7] .
Another reason could be extensive microvascular thrombosis causing the tissue hypoxia which has been described in COVID-19 patients [8] . Significant contribution to high lactic acid levels probably also comes from the high WBC count [9] . However, there is also the possibility of mitochondrial toxicity caused by lopinavir and ritonavir treatment although this is less likely to occur in short treatment duration [10] .
Consent to publish this case report was obtained from the patient's family and the copy of the consent is available for the journal on request.