Retrograde venous air embolism (RVAE) occurs when central venous pressure (CVP) is lower than atmospheric pressure, as is the case with deep inhalation, vertical positions above 45°, and hypovolaemia. The pressure gradient favours the entry of air into venous circulation, travelling to the right ventricle and pulmonary artery, and potentially even leading to an obstructive shock and right ventricular dysfunction. Some studies show that the air may retrogradely ascend to the cerebral venous circulation when the patient is in a vertical position, due to the lower specific weight of air in comparison with blood. This phenomenon will depend on the size of the bubble, the diameter of the vein, and the patient’s cardiac output. Causes of RVAE include trauma, vascular surgery, diving, barotrauma due to mechanical ventilation, and insertion and extraction of central venous catheters. Incidence is difficult to determine, ranging from 1.6% to 55.3%; it is an underestimated entity due to the difficulty of establishing a diagnosis, which requires presence of a known risk factor, compatible clinical signs, no right-to-left shunting in the echocardiography, and imaging studies showing the presence of air in the intravascular space. The most frequent neurological complications are altered level of consciousness, coma, stroke, and seizures. Patients may also present haemodynamic and respiratory alterations including dyspnoea, tachypnoea, chest pain, arterial hypotension, low cardiac output, and even obstructive shock and cardiorespiratory arrest. Electrocardiographic alterations include sinus tachycardia, right ventricular overload signs, non-specific changes in the ST segment/T-wave, and elevated markers of myocardial damage. Definitive diagnosis is established by head CT scan revealing air bubbles in the cerebral intravascular space and parenchyma, sometimes accompanied by diffuse cerebral oedema. In addition to symptomatic treatment with volume therapy, treatment for RVAE includes vasoactive amines, antiepileptics, oxygen therapy with high FiO2, and placing the patient in the left lateral decubitus position (Durant manoeuvre) or the Trendelenburg position. Hyperbaric oxygen therapy may be considered in severe cases.Reference:
Balboa S, Albillos R, Yano R, Escudero D. Position is important: Retrograde air embolism after central venous catheter removal. Neurologia (Engl Ed). 2022 Nov 16:S2173-5808(22)00180-8. doi: 10.1016/j.nrleng.2022.04.006. Epub ahead of print. PMID: 36402402.