Central Venous Access via Supraclavicular Approach to the Subclavian Vein

Overview

First described by Aubaniac in 1952, central venous catheterization, or central line placement, is a time-honored and tested technique of quickly accessing the major venous system. Benefits over peripheral access include greater longevity without infection, line security in situ, avoidance of phlebitis, larger lumens, multiple lumens for rapid administration of combinations of drugs, a route for nutritional support, fluid administration, and central venous pressure monitoring. Central vein catheterization is also referred to as central line placement.

The image below depicts central line equipment.

Central venous catheter equipment. Image courtesy of Wikimedia Commons.

Overall complication rates range up to 15%,[1, 2, 3, 4] with mechanical complications reported in 5-19% of patients,[5, 6, 7] infectious complications in 5-26%,[1, 2, 4] and thrombotic complications in 2-26%.[1, 8] These complications are all potentially life-threatening and, invariably, consume significant resources to treat. Placement of a central vein catheter is a common procedure, and house staff require substantial training and supervision to become facile with this technique. A physician should have a thorough foreknowledge of the procedure and its complications before placing a central vein catheter.

The supraclavicular approach was first put into clinical practice in 1965 and is an underused method for gaining central access. It offers several advantages over the infraclavicular approach to the subclavian vein. At the insertion site, the subclavian vein is closer to the skin, and the right-sided approach offers a straighter path into the subclavian vein. Also, this site is often more accessible during CPR and during active surgical cases. Lastly, in patients who are obese, this anatomic area is less distorted.

Nevarre et al published a review of the literature and his own series of 178 supraclavicular line placements. He reported 1 pneumothorax, 1 malposition, and 2 instances of inability to thread the wire. The overall complication rate was 0.56%. This site is likely among the safest approaches for central venous access (but note that an experienced surgeon performed the procedures reported by Nevarre).[5]

A study by Muhm et al of 208 supraclavicular lines in 168 hemodialysis patients focused on large bore catheters such as may be needed for hemodialysis or resuscitation of patients with trauma or sepsis. Complications included 1 pneumothorax, 7 arterial punctures, and 2 thoracic duct punctures without sequelae. Catheter malpositions occurred only sporadically (1%). Thus, even with large bore catheters, the supraclavicular approach may be a preferable route of placement.[6]

Czarnik et al published a study demonstrating a high overall success rate (92%) of the supraclavicular approach in 370 patients. Most of the patients (78.4%) were mechanically ventilated during the procedure and the overall complication rate was 1.7%, including 3 subclavian artery punctures and 3 contralateral subclavian vein catheterizations. No life-threatening complications occurred. The authors noted this approach to be another viable site for venous access, even in those being mechanically ventilated.[9]

These studies are encouraging, especially considering that a large percentage of the studied patients represented a situation in which the line placement was complicated or difficult. However, the number of patients included is still small, and the operators were experienced with this technique.

While ultrasonographic guidance has proved to be a useful adjunct for internal jugular cannulation, its use for subclavian routes has been infrequently studied. Given the anatomy of the supraclavicular approach, there is little room to effectively position the transducer while manipulating the needle. Using an ultrasound transducer to locate and superficially mark the vessel prior to needle insertion remains an option.[10]

NextIndicationsVolume resuscitationEmergent venous accessNutritional supportAdministration of caustic medications (eg, vasopressors)Central venous pressure monitoringTransvenous pacing wire introductionHemodialysisPulmonary artery catheterizationPreviousNextContraindicationsAbsolute contraindications to central venous access Distorted anatomy (eg, vascular injury, prior surgery, radiation history)Infection at insertion siteRelative contraindications to central venous access Presence of anticoagulation or bleeding disorderPatient who is excessively underweight or overweightUncooperative patientCurrent or possible thrombolysisAbsolute contraindications to the supraclavicular approach Trauma to ipsilateral clavicle, neck, or subclavian vesselsCoagulopathy (Direct pressure to stop bleeding can not be applied to the subclavian vein or artery due to their location beneath the clavicle.) Relative contraindications to the supraclavicular approach Chest wall or neck deformityChronic obstructive pulmonary disease (COPD)PreviousNextAnesthesiaLocal anesthesia using 1% lidocaine is required.For more information, see Local Anesthetic Agents, Infiltrative Administration.PreviousNextEquipmentCentral venous catheter tray (line kit)Sterile glovesAntiseptic solution with skin swabsSterile drapes or towelsSterile gownSterile saline flush, approximately 30 mLLidocaine 1% (obtain additional vial of lidocaine 1%, if needed)GauzeDressingScalpel, No. 11PreviousNextPositioningPlace the patient in the supine position.If possible, the bed should be raised to a comfortable height for the operator so bending over is unnecessary.Needle insertion site options include the following: One centimeter lateral to the lateral border of the clavicular head of the sternocleidomastoid muscle and one centimeter superior to the clavicle (The needle approach should bisect the angle of the muscle border and the clavicle.) One centimeter medial and one centimeter superior to the midpoint of the clavicle (Direct the introducer needle to the ipsilateral sternoclavicular joint.)[11] Just posterior to the clavicle at the middle/medial third junction of the clavicle (Direct the needle toward the ipsilateral sternoclavicular joint with the needle oriented parallel to the coronal plain.)[12] Options for directing the needle include the following: Contralateral nipple: The contralateral nipple may be used as a target for directing the introducer needle.Sternal notch: A point just superior and posterior to the sternal notch may be used as a target for directing the introducer needle. PreviousNextTechniqueExplain the procedure, benefits, risks, and complications and obtain signed informed consent.Position the patient.Identify landmarks.Open the line kit, and position the equipment within easy reach. One may want to retract the J-wire into the plastic loop sheath for easy directing into the introducer needle. Also, uncap the distal lumen, which is typically the brown lumen. Prepare the insertion site with the iodine or alcohol solution provided in the kit. This amount of preparation is often inadequate, and a wide area around the insertion site should be liberally prepared with 4 x 4 cm gauze soaked in a povidone iodine solution (eg, Betadine). Prepare the neck as well, in case the initial approach fails and another approach must be attempted. Put on sterile mask, gown, and gloves.Drape the patient in a sterile fashion with the insertion site exposed.Using a generous amount of lidocaine, infiltrate the skin and subcutaneous tissue.Position the bevel of the introducer needle in line with the numbers on the syringe. Upon insertion, orient the bevel to open caudally so as to facilitate the caudal progression of the guide wire down the vein toward the right atrium. While continuing to aspirate with the syringe, insert the introducer needle along the 45° bisection of the approximately 90° angle formed by the superior aspect of the clavicle and the lateral border of the sternocleidomastoid muscle. The needle should be virtually parallel to the chest wall in the coronal plane. If the vein is difficult to locate, remove the introducer needle, flush it clean of clots, and try again. Change insertion sites after 3 unsuccessful passes with the introducer needle. When venous blood is freely aspirated, disconnect the syringe from the needle, immediately occlude the lumen to prevent air embolism, and reach for the guide wire. Insert the guide wire through the needle into the vein.Advance the wire until it is mostly in the vein or until ectopy is seen on the cardiac monitor. Then, retract the wire a 3-4 cm. Holding the wire in place, withdraw the introducer needle and set aside.Use the tip of the scalpel to make a small stab just against the wire to enlarge the catheter entry site.Thread the dilator over the wire and into the vein with a firm and gentle twisting motion while maintaining control of the wire. Holding the wire in place, remove the dilator. To estimate the distance from the insertion site to the subclavian vein just over the atrium, the catheter can be held over the patient’s chest. Thread the catheter over the wire; then, thread the wire out of the distal (brown) lumen and grasp the wire. Continue to thread the catheter into the vein to the desired length. Hold the catheter in place, remove the wire, and occlude the open lumen.Attach a syringe with some saline in it to the hub and aspirate blood. Take needed samples and then flush the line with saline and recap. Repeat this step with all lumens. Verify line placement with chest radiograph. The catheter should end in the vena cava at the manubriosternal angle, not in the right atrium. Suture the catheter in place. For patient comfort, the clinician may need to anesthetize this area with lidocaine first.Apply a clean dressing.PreviousNextPearlsThe key to a successful line placement is meticulous preparation and setup before starting or donning sterile garb. This includes consideration of what equipment may be needed if complications arise. Use the same preparation technique every time this procedure is performed.Prepare a sterile field from the jaw to several fingerbreadths below the clavicle.The amount of lidocaine provided in most kits is often inadequate. The authors recommend supplementing the kit with a 10-mL syringe and a bottle of 1% lidocaine without epinephrine. In the technique first described by Yoffa in 1965, the needle is directed at an angle of 45 º from the sagittal plane and 15 º anterior from the coronal plane. Newer literature using 3-dimensional CT have shown higher success rates by placing the needle at the clavisternomastoid angle and directing the needle 10 º from the sagittal plan and 35 º posteriorly from the coronal plane. This change allows for the shortest distance to the target vessel and for the first rib to act as a physical barrier to reduce the risk of pneumothorax.[13] If the wire does not pass easily through the needle down the vein, remove the wire, reattach the syringe, and confirm that the needle is still in the lumen of the vein before reattempting the procedure. Beware a return of red or pulsatile blood. If this occurs, the wire is in an artery.Beware aspirating air bubbles through the probing introducer needle. This indicates a pneumothorax. (For details, see Medscape Reference article Tube Thoracostomy.) Anesthetize the suture site as well as the insertion site.Some clinicians find it useful to remove the contents of the line kit and lay them out in the order and configuration that they will be used. Never place equipment on a patient.Antibiotic ointments are contraindicated. Transparent dressings are not necessary.PreviousNextComplications

Complication rates for the various approaches are shown in the table below.

Table. Complication Rates of Central Venous Catheterization[5, 6, 7, 9, 14, 15] (Open Table in a new window)

Internal JugularSubclavianFemoralSupraclavicularArterial puncture6.3-9.13.1-4.99.0-15.00.8-3.36Hematoma1.2-2.13.8-4.4N/AHemothoraxN/A0.1-0.6N/AN/APneumothorax1.5-3.1N/A0.48-0.56Thrombosis7.61.921.5N/ALocal site or systemic infection: Multiple studies have shown lower infection rates with the use of maximal sterile-barrier precautions, including mask, cap, sterile gown, sterile gloves, and large sterile drape. This approach has been shown to reduce the rate of catheter-related bloodstream infections and to save an estimated $167 per catheter inserted.[6] Arterial puncture: As in other central venous catheter approaches, lacerating the subclavian artery is theoretically possible. Also, the subclavian vein cannot be compressed; therefore, this approach should be avoided in patients who are anticoagulated. Hematoma: A hematoma usually requires monitoring only.Hemothorax: Check the chest radiograph for evidence of a hemothorax. If evidence is found, consult a surgeon immediately, and consider tube thoracostomy. Pneumothorax: Check a chest radiograph when finished or before switching to the contralateral side after failed insertion on one side. Catheter-related thrombosis: This complication might lead to pulmonary embolism.Air embolism: An air embolism is caused by negative intrathoracic pressure, with inspiration drawing air into an open line hub. Be sure the line hubs are always occluded, and note that placing the patient in the Trendelenburg position lowers this risk. If air embolism occurs, the patient should be placed in the Trendelenburg position with a left lateral decubitus tilt, which may prevent the movement of air into the right ventricle and onward. One hundred percent oxygen should be administered to speed the resumption of air. If a catheter is located in the heart, aspiration of air should be attempted. Dysrhythmias: Dysrhythmia is due to cardiac irritation by the wire or catheter tip. Placing a central venous catheter without a cardiac monitor is unwise. Atrial wall puncture: This complication leads to pericardial tamponade.Lost guide wire: If the clinician is not conscientious about maintaining control of the guide wire, it may be lost into the vein and require retrieval by interventional radiology. Anaphylaxis: Patients who are allergic to antibiotics may experience anaphylaxis upon insertion of an antibiotic-impregnated catheter. Catheter tip too deep: Check for this complication on the postprocedure chest radiograph, and pull the line back if the tip disappears into the cardiac silhouette. Catheter in the wrong vessel: When the subclavian catheter is not in the correct position, it usually deviates cranially up the internal jugular instead of down the subclavian vein. This complication is rare with the supraclavicular approach. Chylothorax: This complication is possible on the left side.Previous, Central Venous Access via Supraclavicular Approach to the Subclavian Vein

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Central Venous Access via Subclavian Approach to the Subclavian Vein

Overview

First described in 1952, central venous catheterization, or central line placement, is a time-honored and tested technique of quickly accessing the major venous system. Its benefits over peripheral access include greater longevity without infection, line security in situ, avoidance of phlebitis, larger lumens, multiple lumens for rapid administration of combinations of drugs, a route for nutritional support, fluid administration, and central venous pressure monitoring.

Central line equipment is depicted in the image below.

Central venous catheter equipment. Image courtesy of Wikimedia Commons.

Overall complication rates range up to 15%,[1, 2, 3, 4] with mechanical complications reported in 5-19% of patients,[5, 6, 7] infectious complications in 5-26%,[1, 2, 4] and thrombotic complications in 2-26%.[1] These complications are all potentially life-threatening and, invariably, consume significant resources to treat. Placement of a central vein catheter is a common procedure, and house staff require substantial training and supervision to become facile with this technique. A physician should have a thorough foreknowledge of the procedure and its complications before placing a central vein catheter.

Compared to femoral site access, internal jugular or subclavian access has been associated with a lower risk of catheter-related bloodstream infections in earlier studies, but newer studies (2008-2010) indicate that there is no difference in the rate of catheter-related bloodstream infections between these three sites.[8]

The advent of bedside ultrasonography has changed the overall technique of the placement of central venous catheters in both the internal jugular and femoral veins, but the subclavian approach remains the most commonly used blind approach. Its advantages include consistent landmarks, increased patient comfort, and lower potential for infection or arterial injury compared with other sites of access. The physician’s experience and comfort level with the procedure, however, are the main determinants as to the success of the line placement in cases with no other patient-related factors that may increase the incidence of complications.

NextIndicationsVolume resuscitationEmergent venous accessNutritional supportAdministration of caustic medications (eg, vasopressors)Central venous pressure monitoringTransvenous pacing wire introductionHemodialysisPulmonary artery catheterizationPreviousNextContraindicationsAbsolute contraindications to central venous access Distorted local anatomy (eg, vascular injury, prior surgery, radiation history)Infection at insertion siteRelative contraindications to central venous access Presence of anticoagulation or bleeding disorderPatient who is excessively underweight or overweightUncooperative patientCurrent or possible thrombolysisAbsolute contraindications to the subclavian approach Trauma to the ipsilateral clavicle, anterior proximal rib, or subclavian vesselsCoagulopathy (Direct pressure to stop bleeding cannot be applied to the subclavian vein or artery due to their location beneath the clavicle.) Relative contraindications to the subclavian approach Chest wall deformityChronic obstructive pulmonary disease (COPD)PreviousNextAnesthesiaLocal anesthesia using 1% lidocaine is required.For more information, see Local Anesthetic Agents, Infiltrative Administration.PreviousNextEquipmentCentral venous catheter tray (line kit)Sterile glovesAntiseptic solution with skin swabSterile drapes or towelsSterile gownSterile saline flush, approximately 30 mLLidocaine 1% (obtain additional vial of lidocaine 1% if needed)GauzeDressingScalpel, No. 11PreviousNextPositioningPlace the patient in the supine position.If possible, the bed should be raised to a comfortable height for the operator so bending over is unnecessary.Do not place towels between the shoulder blades or turn the head, as this has been shown to decrease the size of the subclavian vein.[5] Place the patient in 15 º of Trendelenburg position to reduce the risk of air embolism. Increasing this angle does not improve vessel distention as the subclavian vein is fixed within surrounding tissue. Needle insertion site options include the following: One centimeter inferior to the junctions of the middle and medial third of the clavicleInferior to the clavicle at the deltopectoral grooveJust lateral to the midclavicular line, with the needle perpendicular along the inferior lateral clavicleOne fingerbreadth lateral to the angle of the clavicleSternal notch: Direct the insertion needle toward this target in the coronal plane.PreviousNextTechniqueExplain the procedure, benefits, risks, and complications and obtain a signed informed consent.Position the patient.Identify landmarks.Open the line kit, and position the equipment so it is easy to reach. One may want to retract the curved J-tip wire into the plastic loop sheath for easy directing into the introducer needle. Also, uncap the distal lumen, which is commonly the brown lumen. Prepare the insertion site with the iodine or alcohol solution provided in the kit. This amount of preparation is often inadequate, and a wide area around the insertion site should be liberally prepared with 4 x 4 cm gauze soaked in a povidone iodine solution (e.g., Betadine). Prepare the neck as well, in case the subclavian approach fails and another approach must be attempted. Put on sterile mask, gown, and gloves.Drape the patient in a sterile fashion, with the insertion site exposed.Using a generous amount of lidocaine 1%, infiltrate the skin, subcutaneous tissue, and, possibly, the clavicular periosteum.Position the bevel of the introducer needle in line with the numbers on the syringe. Upon insertion, orient the bevel to open caudally, which facilitates smooth caudal progression of the guide wire down the vein toward the right atrium. Insert the introducer needle at the desired landmark while gently withdrawing the plunger of the syringe. Advance the needle under and along the inferior border of the clavicle, making sure the needle is virtually horizontal to the chest wall. Once under the clavicle, the needle should be advanced toward the suprasternal notch until the vein is entered. If the vein is difficult to locate, remove the introducer needle, flush it clean of clots, and try again. Change insertion sites after 3 unsuccessful passes with the introducer needle. When venous blood is freely aspirated, disconnect the syringe from the needle, immediately occlude the lumen to prevent air embolism, and reach for the guide wire. Insert the guide wire through the needle into the vein with the J-tip directed caudally to improve successful placement into the subclavian vein. If using a kit that allows for the wire to be placed directly through a port on the syringe, then it is not necessary to disconnect the syringe. Beware that disconnecting the syringe gives the added benefit of allowing verification of nonpulsatile flow of venous blood. Advance the wire until it is mostly in the vein or until ectopy is seen on the cardiac monitor. Then, retract the wire 3-4 centimeters. Holding the wire in place, withdraw the introducer needle and set aside.Use the tip of the scalpel to make a small stab just against the wire to enlarge the catheter entry site.Thread the dilator over the wire and into the vein with a firm and gentle twisting motion while maintaining constant control of the wire. After the introducer is inserted, hold the wire in place and remove the dilator. Thread the catheter over the wire until it exits the distal (brown) lumen and grasp the wire as it exist the catheter. Continue to thread the catheter into the vein to the desired length. Hold the catheter in place and remove the wire. After the wire is removed, occlude the open lumen.Attach a syringe with some saline in it to the hub and aspirate blood. Take needed samples and then flush the line with saline and recap. Repeat this step with all lumens. Verify line placement with chest radiograph. The tip of the line should end in the vena cava at the manubriosternal angle, not in the right atrium. Suture the catheter in place. For patient comfort, the clinician may need to infiltrate this area prior to suturing.Apply a clean dressing.PreviousNextPearlsThe key to a successful line placement is meticulous preparation and setup before starting or donning sterile garb.Prepare a sterile site from the jaw to several fingerbreadths below the clavicle.The amount of lidocaine provided in most kits is often inadequate. The authors recommend supplementing the kit with a 10-mL syringe and a bottle of 1% lidocaine. If the wire does not pass easily through the needle down the vein, remove the wire, reattach the syringe, and confirm that the needle is still in the lumen of the vein before reattempting. Beware a return of red pulsatile blood. If this occurs, the wire is in an artery.Beware aspirating air bubbles through the probing introducer needle. This indicates a pneumothorax. (For details, see Medscape Reference article Tube Thoracostomy.) Anesthetize the suture site as well as the insertion site.Some clinicians find it useful to remove the contents of the line kit and lay them out in the order and configuration that they will be used. Never place equipment on a patient.Antibiotic ointments are contraindicated. Transparent dressings are not beneficial.Choose the central line with the fewest number of lumens required; increasing the number of lumens has been shown to increase infection rates.[9] To date, ultrasonographic guidance has mainly been used in a "mark & go" fashion to identify points of insertion and in this usage may not improve the overall success rate of placement as it does for both the femoral and internal jugular vessels. However, a ICU-based prospective, randomized study suggested that real-time ultrasonographic guidance in sedated and ventilated patients was useful for the subclavian approach in the hands of experienced operators.[10] Further studies are needed to confirm these results and to evaluate the success of educational methods for learning this technique. PreviousNextComplications

The table below shows complication rates for the various approaches.

Table 1. Complication Rates of Central Venous Catheterization Approaches[6, 11, 7] (Open Table in a new window)

Internal Jugular Subclavian Femoral Arterial puncture6.3-9.13.1-4.99.0-15.0Hematoma1.2-2.13.8-4.4HemothoraxN/A0.1-0.6N/APneumothorax1.5-3.1N/AThrombosis7.61.921.5Total6.3-11.86.2-10.712.8-19.4Local site or systemic infection: Multiple studies have shown lower infection rates with the use of maximal sterile-barrier precautions, including mask, cap, sterile gown, sterile gloves, and large sterile drape. This approach has been shown to reduce the rate of catheter-related bloodstream infections and to save an estimated $167 per catheter inserted.[6] Arterial puncture: Lacerating the subclavian artery is theoretically possible, but the risk of this complication is higher with other approaches. The subclavian artery cannot be compressed; so, the subclavian approach should be avoided in anticoagulated patients. Hematoma: A hematoma usually requires monitoring only.Hemothorax: Check the chest radiograph for evidence of a hemothorax. If evidence is found, consult a surgeon immediately.Pneumothorax: Check a chest radiograph when finished or before switching to the contralateral side after failed insertion on one side. Catheter-related thrombosis: This complication may lead to pulmonary embolism.Air embolism: An air embolism may be caused by negative intrathoracic pressure, with inspiration by the patient drawing air into an open line hub. Be sure the line hubs are always occluded. Placing the patient in the Trendelenburg position lowers the risk of this complication. If air embolism occurs, the patient should be placed in Trendelenburg position with a left lateral decubitus tilt, which may prevent the movement of air into the right ventricle and onward into the left side of the heart. One hundred percent oxygen should be administered to speed the resorption of the air. If a catheter is located in the heart, aspiration of the air should be attempted. Dysrhythmias: Dysrhythmia is due to cardiac irritation by the wire or catheter tip. This can usually be terminated by simply withdrawing the line into the superior vena cava. Placing a central venous catheter without a cardiac monitor is unwise. Atrial wall puncture: This complication leads to pericardial tamponade.Lost guide wire: If the clinician is not conscientious about maintaining control of the guide wire, it may be lost into the vein and require retrieval by interventional radiology. Anaphylaxis: Patients who are allergic to antibiotics may experience anaphylaxis upon insertion of an antibiotic-impregnated catheter. Catheter tip too deep: Check for this complication on the postprocedure chest radiograph, and pull the line back if the tip disappears into the cardiac silhouette. Catheter in the wrong vessel: When the subclavian catheter is not in the correct position, it most often deviates cranially up the internal jugular instead of down the subclavian vein. Flushing 10 mL of saline through the distal port and palpating the neck for a thrill can help to detect misplaced subclavian venous catheters into the ipsilateral internal jugular.[12] Chylothorax: This complication is possible on the left side.PreviousNextCommon Errors in Technique

Kilbourne and colleagues analyzed failed subclavian catheter placement attempts by resident physicians in an effort to describe common technical errors and to direct future teaching strategies. Subclavian cannulations were videotaped. Analysis of 86 patients revealed 6 common errors in technique that occurred in the following frequencies over 277 attempts.[13]

Table 2. Common Errors in Technique (Open Table in a new window)

Error Percent of Failures (n = 277) Inadequate landmark identification14.7Improper insertion position32.3Insertion of needle through periosteum21.9Taking too shallow a trajectory with needle16.1Aiming the needle too cephalad7.5Failure to keep needle in place for wire passage7.5Previous, Central Venous Access via Subclavian Approach to the Subclavian Vein

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Venous Air Embolism

Background

Venous air embolism (VAE), a subset of gas embolism, is an entity with the potential for severe morbidity and mortality. Venous air embolism is a predominantly iatrogenic complication[1, 2] that occurs when atmospheric gas is introduced into the systemic venous system[3] . In the past, this medical condition was mostly associated with neurosurgical procedures conducted in the sitting position.[4, 5] More recently, venous air embolism has been associated with central venous catheterization,[3, 6, 7] penetrating and blunt chest trauma,[8, 9] high-pressure mechanical ventilation,[3] thoracocentesis,[1] hemodialysis,[3, 7] and several other invasive vascular procedures.

Venous air embolism (VAE) has also been observed during diagnostic studies, such as during radiocontrast injection for computerized tomography.[10, 11] The use of gases such as carbon dioxide and nitrous oxide during medical procedures and exposure to nitrogen during diving accidents can also result in VAE.[2] Many cases of VAE are subclinical with no adverse outcome and thus go unreported. Usually, when symptoms are present, they are nonspecific, and a high index of clinical suspicion of possible venous air embolism is required to prompt investigations and initiate appropriate therapy.

NextPathophysiology

Two preconditions must exist for venous air embolism to occur: (1) a direct communication between a source of air and the vasculature and (2) a pressure gradient favoring the passage of air into the circulation.[12, 4]

The key factors determining the degree of morbidity and mortality in venous air emboli are related to the volume of gas entrainment, the rate of accumulation, and the patient’s position at the time of the event.[1, 6, 11]

Generally, small amounts of air are broken up in the capillary bed and absorbed from the circulation without producing symptoms. Traditionally, it has been estimated that more than 5 mL/kg of air displaced into the intravenous space is required for significant injury (shock or cardiac arrest) to occur.[1] However, complications have been reported with as little as 20 mL of air[7] (the length of an unprimed IV infusion tubing) that was injected intravenously. The injection of 2 or 3 mL of air into the cerebral circulation can be fatal.[13] Furthermore, as little as 0.5 mL of air in the left anterior descending coronary artery has been shown to cause ventricular fibrillation.[13, 9] Basically, the closer the vein of entrainment is to the right heart, the smaller the lethal volume is.[1]

Rapid entry or large volumes of air entering the systemic venous circulation puts a substantial strain on the right ventricle, especially if this results in a significant rise in pulmonary artery (PA) pressures. This increase in PA pressure can lead to right ventricular outflow obstruction and further compromise pulmonary venous return to the left heart. The diminished pulmonary venous return will lead to decreased left ventricular preload with resultant decreased cardiac output and eventual systemic cardiovascular collapse.[1, 4, 6]

With venous air embolism (VAE), resultant tachyarrhythmias are frequent, but bradyarrhythmias can also occur.[4, 2]

The rapid ingress of large volumes of air (>0.30 mL/kg/min) into the venous circulatory system can overwhelm the air-filtering capacity of the pulmonary vessels, resulting in a myriad of cellular changes.[3] The air embolism effects on the pulmonary vasculature can lead to serious inflammatory changes in the pulmonary vessels; these include direct endothelial damage and accumulation of platelets, fibrin, neutrophils, and lipid droplets.[1]

Secondary injury as a result of the activation of complement and the release of mediators and free radicals can lead to capillary leakage and eventual noncardiogenic pulmonary edema.[1, 7, 3]

Alteration in the resistance of the lung vessels and ventilation-perfusion mismatching can lead to intra-pulmonary right-to-left shunting and increased alveolar dead space with subsequent arterial hypoxia and hypercapnea.[1, 4, 11]

Arterial embolism as a complication of venous air embolism (VAE) can occur through direct passage of air into the arterial system via anomalous structures such as an atrial or ventricular septal defect, a patent foramen ovale, or pulmonary arterial-venous malformations. This can cause paradoxical embolization into the arterial tree.[1, 4, 9, 2, 3] The risk for a paradoxical embolus seems to be increased during procedures performed in the sitting position.[1, 5]

Air embolism has also been described as a potential cause of the systemic inflammatory response syndrome (case report), triggered by the release of endothelium derived cytokines.[12]

PreviousNextEpidemiologyFrequencyUnited States

The nonspecific nature of the signs and symptoms of venous air embolism (VAE) as well as the difficulty in documenting the diagnosis does not allow the true incidence of VAE to be known. Interventional radiology literature reports an incidence of venous air embolism of 0.13% during the insertion and removal of central venous catheters despite using optimal positioning and techniques.[14] The frequency of venous air embolism with central venous catheters based on a reported case series has also ranged from 1 in 47 to 1 in 3000.[15, 2] The neurosurgical procedure-related complications of venous air embolism have been estimated to be between 10-80%.[16, 2, 17] Reports of venous air embolism in the setting of severe lung trauma have been estimated between 4-14%.[13, 8, 9, 18, 17]

Mortality/Morbidity

The potentially life-threatening and catastrophic consequences of venous air embolism (VAE) are directly related to its effects on the affected organ system where the embolus lodges. VAE may be fatal and frequently carries high neurologic, respiratory, and cardiovascular morbidity. Catheter-associated VAE mortality rates have reached 30%.[2] In a case series of 61 patients with severe lung trauma, the mortality rate associated with concomitant VAE was 80% in the blunt trauma group and 48% in the penetrating trauma group.[8, 18, 17] The morbidity and mortality associated with traumatic VAE, as with nontraumatic VAE, depends not only on associated injuries but also on the volume and rate of air entry, underlying cardiac condition, and the patient's position.

Race

No racial predilection exists for venous air embolism.

Sex

No gender predilection exists for venous air embolism.

Age

No specific age predilection exists for venous air embolism.

PreviousProceed to Clinical Presentation , Venous Air Embolism

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