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.