Discussion
Most chlorine poisoning onsets in where chlorine-containing disinfectants are used, such as chemical plants and swimming pools. The treatment mainly includes conjunctival cleaning, high PEEP mechanical ventilation, bronchiectasis drugs inhalation, glucocorticoid administration and so on. Rare patients need ECMO support. The prognosis is usually good with few sequelae [1, 2]. The case we described has the following characteristics: ①Complicated with shock and acute renal injury. ②VA-ECMO was established instead of the common chosen veno-venous ECMO (VV-ECMO).
Shock develops in 23-50% of severe ARDS patients due to acute corpulmonale (ACP) [5, 6]. In a large-scale prospective study by Mekontso et al.[7], the four independent risk factors for ACP in ARDS were ARDS caused by pneumonia, driving pressure>18 cmH2O, PaO2/FiO2<150 mmHg and PaCO2>48 mmHg. The main pathogenic mechanisms is a sharp rising in pulmonary arterial pressure and pulmonary circulatory resistance caused by hypoxic/hypercapnia pulmonary vasoconstriction, interstitial edema compression on pulmonary vessels, high PEEP ventilation and so on. Clinically, acute right heart failure can occur due to high right ventricular after load, followed by a decrease in pulmonary blood flow that aggravates hypoxia and hypercapnia, and leads to a significant decrease in blood pressure. Bedside echocardiography is very important in the early diagnosis of ACP and the continuous monitoring of cardiac function in children [8, 9]. Transthoracic echocardiography is non-invasive, but sometimes can hardly get clear images in obese and mechanically ventilated patients. Transesophageal echocardiography is invasive, but the image is clear. The child we discussed had high risk factors for ACP, while no pathophysiological basis of distributed shock or hypovolemic shock; after VA-ECMO, his pulse pressure difference was normal, and the cardiac ultrasound proved normal left ventricular function, his troponin was normal too, so cardiogenic shock could be excluded; chest X-ray and coagulation test could also exclude tension pneumothorax and pulmonary embolism. Therefore, we considered as obstructive shock caused by ACP. Unfortunately, transthoracic ultrasound before VA-ECMO failed to get clear images, and our ICU was not equipped with transesophageal probe, so objective evidence for the diagnosis of ACP caused by ARDS hadn’t been obtained.
ECMO should be considered in patients with ACP caused by ARDS who can’t be maintained by routine treatment. VV-ECMO can improve oxygenation and acidosis, reduce carbon dioxide, and then reduce pulmonary circulatory resistance, several reports have reported successful application of it on patients with ACP caused by ARDS duetoacute poisoned gasinhalation [1, 10]. VA-ECMO can significantly reduce blood flow in pulmonary circulation, which is more beneficial to reduce pulmonary exudation during ARDS, and can immediately reduce the pre- and after load of right ventricular during ACP so as to improve hemodynamics. But VA-ECMO will affect left cardiac function, reduce coronary oxygen supply, and cause different limb and cerebral perfusion according to the location of arterial catheterization. Morbidities are relatively more, and may cause myocardial injury when used for a long time. The ECMO support time required for ARDS is generally longer, so VV-ECMO is more commonly used. For this patient, VA-ECMO was chosen because the possibility of cardiogenic shock couldn’t be excluded before ECMO establishment and the existence of extremely unstable hemodynamics. The severe hypotension and hypoxia were corrected quickly after VA-ECMO so as the circulatory condition. Acute kidney injury occurred a few hours after hypotension due to insufficient perfusion, but returned to normal in 2 days, which may also be related to the rapid correction of hemodynamic abnormalities by VA-ECMO. For patients with ARDS complicated with ACP, it suggests that the duration of lung injury caused by the primary disease is expected to be short and complicated with severe hemodynamic disturbance, VA-ECMO might be considered first. Temporary aggravation of pulmonary exudation after withdrawal of VA-ECMO suggests that in children with ARDS treated by VA-ECMO, the PEEP and volume load should be properly adjusted before a dafter weaning.
Chlorine inhalation can cause chemical aspiration pneumonia. Severe ARDS, even shock can occur in the acute stage, but the prognosis is mostly good. Therefore, if conventional treatment is ineffective and patients do not have severe underlying diseases, ECMO should be considered promptly. Transesophageal probe had better be equipped in advanced ICUs to facilitate the completion of bedside cardiacultrasound in special patients.