Management of air embolism in dialysis
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Air emboli can cause iatrogenic stroke during a procedure when air has an opportunity to enter blood vessels. This is a rare occurrence that should be considered when a person who has had a procedure suddenly develops acute stroke symptoms. Clinical suspicion can help to identify stroke vs cerebral air embolism,1,2 which is important because the recommended treatment for air emboli is hyperbaric oxygen therapy (HBOT), not intracranial procedures.3 Show EtiologyStrokes from air emboli can be caused by air in the cerebral venous or arterial circulation and most commonly have iatrogenic causes,4,5 including but not limited to neurosurgery with the patient in a sitting position, fluid infusion, trauma, using positive end-expiratory pressure on a ventilator, hemodialysis, thoracentesis, intraoperative procedures, and deep-water dives.6,7 Venous air emboli (VAE) arise from air entering the venous circuitry and traveling through the right side of the heart into the pulmonary system.8 These can turn into an arterial air embolus when gas paradoxically enters the arterial circulation either through a pulmonary arteriovenous malformation, patent foramen ovale (PFO), or cardiac septal defects.8-10
 For VAE to form, there must firstly be air-to-vessel communication. Secondly, the individual must be upright (usually sitting) during the procedure.5,11 For patients who undergo regular hemodialysis, the first condition is created to bypass the capillary bed and establish a direct connection from an artery to a vein. Gaseous particulates from the dialysis machine may enter the arteriovenous fistula without initiating the machine’s alarm system if a bubble is less than 50 mcL in diameter, or the flow rate is below the standard pump rate for infusion and dialysis.10 This air can travel to the cerebral vasculature because air has lower specific gravity than blood. As described in the case report, a paradoxical VAE can occur when air enters the atrial circulation via a PFO. The prevalence of PFO in the adult population is approximately 20% to 25%, but prevalence rises to 40% to 50% in individuals who have had a stroke from uncertain causes, also termed cryptogenic.9,12 Individuals who experienced a cryptogenic stroke should be evaluated for PFO with transthoracic/transesophageal echocardiogram or contrast-enhanced transcranial Doppler (bubble-TCD).13 The route for the air emboli from the venous circulation via a PFO is from the right to left atrial cardiac shunt into the aorta and into the arterial circulation. Because of the lower specific gravity of air compared with blood, an air bubble will rise and can cause occlusion of the arterial cerebral vasculature.5,10 The air emboli in the vessel can also cause damage to the surrounding tissue via inflammation and platelet aggregation, which further contributes to the stroke.14 Clinical Presentation and DiagnosisIndividuals experiencing VAE have symptoms that range from subtle headache to tachyarrhythmias, stroke symptoms, and unresponsiveness.5,10 Air emboli can go unnoted because there may be no symptoms. A high index of suspicion should be maintained for anyone with acute stroke symptoms who has just had a procedure or hemodialysis.
The differential diagnosis of an acute neurologic change begins with acute stroke and also includes seizure, migraine, toxic and metabolic causes (eg, hyper- or hypoglycemia), infection, tumor, and migraine. Acute ischemic stroke may be from ischemic causes including venous, arterial, or hemorrhagic. Individuals with end-stage renal disease (ESRD) are more prone to hemorrhagic stroke because of the increased risk of bleeding from frequent use of heparin for dialysis and impaired platelet function from uremia.15 Diagnosis is made with head and brain CT and is indicated by hyperlucency that appears the same on both brain and bone windows (see Figure). Accurate diagnosis is essential because treatment of air emboli is time dependent as described in the case and following section.
TreatmentTreatment of air emboli is 100% oxygen followed by immediate transfer to a facility with HBOT.3,16 There are no guidelines for using HBOT in people who have cerebral air embolic strokes, although several case reports and case series suggest HBOT is associated with better outcomes. Administration of 100% oxygen reduces nitrogen content of air bubbles to, in turn, reduce or compress the size of the bubbles.4,5,17 HBOT improves oxygenation to the cerebral tissue and reduces cerebral edema and thus, intracranial pressure.5 If no hyperbaric chamber is available, it is recommended to transport the patient to a facility with HBOT. Treatment should begin within 6 hours.3 Resolution of neurologic damage from air embolus is highly associated with initiating HBOT as early as possible.18 Full neurologic recovery has been seen when HBOT was initiated with 3 to 5 hours of the inciting incident, whereas after a delay of 9 to 20 hours, only 1 of the 8 individuals had full neurologic recovery.18 In another case series, 75% of individuals treated within 5 hours had little to no disability at 6-month follow-up.19
PreventionIntraoperative maneuvers such as lowering the head during a procedure may reduce the risk of venous air emboli because of the lower specific gravity of air vs blood, making it less likely that an embolism will rise to the cerebral vasculature. In some surgical procedures, pericardial Doppler may be used to detect VAE; however, proper placement of the probes and close attention to the event by an anesthesiologist can be challenging.20,21 Air emboli often lead to hemodynamic instability because of the resulting strain on the cardiopulmonary systems that may result in hypoxia, hypercapnia, and even a decrease in cardiac output.5 SummaryCerebral air embolism can occur during a routine hemodialysis procedure through an arteriovenous graft and is an emergency. Hemodialysis should be immediately stopped. Once stabilized, the patient should be transferred urgently to a facility with HBOT available. HBOT should be started within 6 hours. In the case presented, the individual with cerebral air embolism had HBOT for 6 hours, which reduced his NIHSS score from 14 to 6 with subsequent resolution of all symptoms except residual left arm weakness. KM, AV, and BM report no disclosures How should you manage an air embolism in a dialysis patient?Treatment. Prevent further air entry by clamping and disconnecting the circuit (2–4). Flat supine position may be better over traditionally advocated left lateral (Duran's position) and Trendelenburg position (2–4). Oxygen with FiO2 100% (4). Hyperbaric oxygen (prevents cerebral edema) (4,5). What should be done to manage air embolism?Treating an air or gas embolism caused by diving
They'll need to lie in the hyperbaric chamber for several hours, breathing a mixture of gases and oxygen in a pressurised environment. The high pressure restores normal blood flow and oxygen to the body's tissues, and reduces the size of the air bubbles in the body.
How is venous air embolism treated?Treatment of air embolism includes discontinuation of nitrous oxide, aspiration through a right heart catheter, adequate supplementation of inspired oxygen, and prevention of further air entry into the circulation (flooding the field with saline, jugular compression and lowering the head in neurosurgical cases).
How do you reverse air embolism?If the air embolism has been caused by diving, the only choice is immediate recompression treatment in a hyperbaric chamber. The diver will lie vertically and breathe a mixture of gases at high pressure. This will restore normal blood flow and reduce the size of the embolism.
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