When the gas embolism enters the systemic arterial circulation, it may cause transient arterial obstruction with subsequent ischaemia and reperfusion injuries resulting in neurological or myocardial damage. Cerebral arterial air embolism can arise when air is directly introduced in the arterial circulation between the heart and brain, for example during left-sided cardiac catheterisation, lung surgery, cardiac surgery or carotid surgery.[8]

In our patient, there was air in both the systemic arterial and venous circulation, and in the pulmonary circulation without the presence of a right to left shunt. A possible explanation could be that both the pulmonary and systemic venous circulation were punctured during biopsy.

Symptoms
Air embolism can present in many ways. Embolisms can occur in every organ system, but the effects are particularly profound in the cerebral or coronary circulation.[9] The severity of symptoms depends on the patient’s position, the volume and type of gas, the size of the bubbles and the rapidity of gas entry into the arteries.[3,6,7]

Cerebral ischaemia can occur when embolisms lodge in the arterioles of the brain. This resembles solid embolisms, as gas can lead to endothelial damage with an inflammatory response.[8] Neurological symptoms include motor symptoms (hemiparesis, tetraplegia), seizures, and altered consciousness. Although the prevalence of cerebral arterial air embolism is low (5.7/100,000 hospital admissions), the neurological sequelae and mortality rates are severe.[8]

Cardiopulmonary symptoms are also frequent, and sometimes even proceed and potentially mask neurological symptoms.[3,6] Entrapment of venous bubbles in the pulmonary micro-circulation may also lead to cellular injury and lung oedema, resulting from the release of vasoactive mediators following pulmonary vascular obstruction.[6]

Diagnostics
The diagnosis is made clinically when sudden neurological, pulmonary or cardiac abnormalities occur during invasive procedures.[2] In the early stages, the diagnosis can be difficult if a small amount of gas is involved or if the patient is anaesthetised or sedated.[9] CT can be used to confirm air embolism, however a normal CT scan does not rule out air embolism.[8] Literature shows that gas embolisms up to 1 cm3 may not be visualised via any imaging modality once diffusely distributed.[5] More subtle cases may be diagnosed by echocardiography and transcranial Doppler, while electro-encephalography and transcranial oximetry can be useful in the diagnostic process.[2,8]

Treatment
The mainstay of acute management is rapid recognition and termination of further entrainment of air.[5,8,9] Further treatment consists of supportive care.[8] Administration of 100% oxygen is important to treat hypoxaemia and improve the oxygenation of affected tissues but also to decrease air bubble size by establishing a diffusion gradient that favours the elimination of gas from the bubbles by lowering the arterial nitrogen pressure.[3,6] If intubated, airway pressures should be limited to prevent a persistent airway-to-vein-pressure differential.[5]

Hyperbaric oxygen in a recompression chamber should be considered in all patients with (probable) air embolism, especially in case of severe neurological or circulatory symptoms.[8-10] Hyperbaric oxygen therapy is suppletion of 100% oxygen at a high ambient pressure. The air bubble volume may be reduced by the high pressure and by inducing blood denitrogenation.[2] Hyperbaric oxygen raises the arterial oxygen pressure up to 1500 mmHg, leading not only to a favourable gradient and diffusion of nitrogen, but also higher oxygen pressure in the brain. Lastly, hyperbaric oxygen therapy has anti-inflammatory features.

Potential disadvantages of hyperbaric oxygen therapy include risks associated with the transport of critically ill patients, hyperoxic seizures, claustrophobic reactions and barotrauma.[2] An absolute contraindication is a pneumothorax, because of the possible evolution to a tension pneumothorax when the ambient pressure decreases at the end of the treatment. Therefore, a chest tube will be placed upfront in cases of lung injury.[11,12] A relative contraindication is delay between the onset of symptoms and the start of treatment. A clear time cut-off is not exactly known, but previous literature suggests unfavourable outcomes after seven hours due to irreversible damage.[11,13] Amsterdam UMC maintains a 24-hour limit. Other relative contraindications are difficulty in equalising ear pressure (a paracentesis will be performed before treatment), recent eye surgery when a gas or air bubble is still present in the eye and devices in general (e.g. pacemakers, neurostimulators, epidural pumps) which might malfunction due to altered pressure.[12] Pulmonary comorbidity is also a relative contraindication because hyperbaric oxygen can lead to alveolar inflammation and subsequent decreased oxygenation.[12] In patients with chronic obstructive pulmonary disease, an increased oxygen saturation can lead to oxygen-induced hypoventilation and increased ventilation/perfusion mismatch.[12]

In the Netherlands, hyperbaric oxygen treatment is possible at the Antonius Hypercare Center in the Antonius Hospital in Sneek, and at Amsterdam UMC.[11] During office hours hyperbaric oxygen treatment is also provided at the Admiraal de Ruyter Hospital in Goes.[11] Patients on mechanical ventilation can only be treated in Amsterdam UMC.[10,11] Referrals can be made by attending physicians (mostly intensive care physicians and pulmonologists) after telephone consultation with the on call specialist of the hyperbaric treatment department.[10,11]

In our patient the Trendelenburg position was used to prevent air ascending to the aorta and brain because of the large amount of air in the apex of the left ventricle. Also the patient had been moved into the supine position after biopsy while vomiting, leading to possible embolisation. However, recent literature suggests that air embolisms are too small to overcome the blood pressure and that the Trendelenburg position can have negative effects on intracranial pressure.[9] Further cerebral damage should be prevented by maintaining normocapnia, normotension, hypothermia and treatment of possible epileptic seizures.[9]

Outcomes
Little is known about the morbidity and mortality associated with iatrogenic gas embolism, because the diagnosis may be difficult in conditions other than high-risk surgery.[2] Full recovery of neurological complications varies in the literature from 7% to 77%;[8] also the range of described mortality is wide from 5% to 23%.[2]

Conclusion
Air embolism is an uncommon, but life-threatening complication of lung biopsy. Healthcare workers should be especially attentive to neurological and cardiopulmonary symptoms after procedures with a high inherent risk of embolisation. In all cases of proven or suspected arterial gas embolism, a hyperbaric facility should be consulted immediately.

Disclosures
All authors declare no conflict of interest. No funding or financial support was received. Written informed consent was obtained from the patient’s relatives for the publication of this case report and the accompanying images.