- Email: [email protected]
Massive Venous Air Embolism during Cardiopulmonary Bypass
Massive Venous Air Embolism during Cardiopulmonary Bypass Winfield J. Wells, M.D., and Quentin R. Stiles, M.D. ABSTRACT A massive bolus of oxygen was forced into the right atrium and venous system of a patient during cardiopulmonary bypass using a Bentley BOS-10 oxygenator. The unique design of the oxygenator canister provides an explanation for the event. Methods are outlined to avoid this type of venous embolism.
The presence of air in the venous drainage system can interfere with cardiopulmonary bypass and disturb the operating surgeon. The air can come from lacerations in the right atrium, from around atrial pursestring sutures, from imperfect exclusion of the venous drainage cannula from an opened chamber on the right side of the heart, from a loose connector or laceration in the venous drainage tubing, or from the introduction of air through an indwelling venous catheter. The sudden appearance of a completely air-filled venous drainage system in conjunction with a rapidly expanding heart is a unique situation to be encountered by the cardiac surgeon. The description and possible cause of such an event, the response in the operating room to the problem, and the final clinical result are presented in this report. A 58-year-old businessman with a short history of rapidly progressive angina pectoris, demonstrated triple-vessel coronary artery obstruction at angiography. In August, 1979, he underwent aortocoronary saphenous vein bypass grafting. The cardiopulmonary bypass circuit employed a single 42 mm venous cannula, which drained by gravity into a Bentley BOS-10 bubble oxygenator. A 24 mm Argyle aortic perfusion cannula was introduced into
From the Division of Thoracic and Cardiovascular Surgery, University of Southern California School of Medicine, Los Angeles, CA. Accepted for publication Feb 28, 1980. Address reprint requests to Dr. Wells, 1136 W Sixth St, Los Angeles, CA 90017.
the Lscending aorta for arterial return. The left heart was vented using an Argyle-Ferguson left ventricular catheter (18F) introduced through the right superior pulmonary vein, and a single cardiotomy sucker was used. Both the vent and cardiotomy sucker drained into separate Bentley cardiotomy reservoirs (model Q-120) maintained at a negative pressure of 30 to 60 cm of water by wall suction. Blood from each cardiotomy reservoir was returned to the oxygenator through separate pump heads (Fig 1). Of major importance was the presence of a polyvinyl tube attached to the gas vent port of the Bentley oxygenator. This tubing ran from the oxygenator, along the floor of the operating room, and into the room air exhaust. The purpose was to scavenge anesthetic gases passed through the oxygenator system in compliance with recent standards of practice. Cardiopulmonary bypass progressed normally through the initial phases of the procedure, during which four distal saphenous veincoronary artery anastomoses were fashioned. A partial occlusion clamp was placed on the proximal ascending aorta, and two 5 mm aortotomies were made for proximal saphenous vein anastomoses. As the first of the proximal anastomoses was in progress, the pump technician reported a sudden massive air lock and loss of venous return. Visual inspection revealed no blood in the venous system and a rapidly distending heart. The infusion of blood was immediately discontinued, and inflow and return tubings were clamped with the exception of the left ventricular vent. The pump technician, in an attempt to eliminate all potential sources of the problem, disconnected the tubing from the gas vent outlet of the oxygenator. The heart was compressed manually to decrease its size. The patient was placed in deep Trendelenburg position, and the ascending aorta was vented at multiple sites with a large slotted needle. Because of the presence of the partially occluding clamp controlling the two aortotomies in the as-
86 0003-4975/81/010086-04$01.25 @ 1980 by The Society of Thoracic Surgeons
87 Case Report: Wells and Stiles: Venous Air Embolism during CPB
Fig 1 . The authors' technique for cardiotomy and left ventricular vent return. The occlusive roller head is positioned between the oxygenator canister and the cardiotomy reservoir. As a result, positive pressure within the oxygenator can escape only through the venous return line.
cending aorta, it was technically difficult to cross-clamp the aorta. Attempts were made to identify the site of air entry into the venous system. Cannula position appeared ideal, and no laceration of the atrium or slackening of the atrial pursestring suture could be identified. During this time the left ventricular vent remained open, and a substantial aliquot of the patient's blood volume returned to the reservoir. Only a small amount of air was obtained from the root of the aorta. This appeared in a retrograde fashion in the aortic perfusion line and was aspirated easily through the stopcock connector at the proximal end of the aortic cannula. Then volume was returned to the patient from the oxygenator reservoir, and the venous cannula was reprimed and opened. Initially a large amount of air was returned from the right atrium and vena cava.
This was followed by considerable froth, and, after two or three minutes, a normal pattern of venous return was obtained. The proximal anastomoses were completed and the heart recovered. This allowed the patient to be weaned from cardiopulmonary bypass. The patient awakened in the operating room with no evidence of neurological deficit. Recovery was uneventful, and he was discharged on the ninth postoperative day.
Comment We believe that the unusual, sudden appearance of air in the venous system was the result of oxygen delivered under positive pressure through the venous return cannula into the patient's right atrium. The Bentley BOS-10 oxygenator is unique in that its canister is a closed system. With a bypass circuit such as the one described, the gas vent port is the only outlet for positive pressure other than the venous inlet. We presume a sudden buildup of positive pressure occurred in the oxygenator secondary to occlusion of the polyvinyl tubing used to evacuate gas from the canister (Fig 2). This
88 The Annals of Thoracic Surgery Vol 31 No 1 January 1981
89
Case Report: Wells and Stiles: Venous Air Embolism during CPB
gas vent obstruction removed the source of the embolic problem. Any surgeon using the Bentley oxygenator should be aware of this potential problem. Obstruction of the gas vent in any system used to scavenge exhaust must be avoided. This can be accomplished by placing a relief valve in the Fig 3 . The Bentley BOS-10 oxygenator. The 1/z inch (1.27 cm) open Luer-Lok connector in the gas vent tubline to prevent positive pressure developing ing will prevent the buildup of positive pressure in the within the canister if the tube should become oxygenator canister should the tubing become obstructed. obstructed (Fig 3). With these adjustments, we have found the Bentley oxygenator to be very event was transient and may have been caused satisfactory. by someone standing on the tubing. The buildInstructions for the Bentley oxygenator warn up of pressure in the canister was sudden at the against potential mismanagement of the gas oxygen flow of 8 liters per minute. The venous vent system. It is recommended that a l/z inch return in the drainage tubing was quickly dis- (1.27 cm) open Luer-Lok connector be placed in placed with oxygen and was responsible for the line to prevent occurrence of a “vacuum” in rapid distention of the heart. Ultimately, oxy- the canister by a negative pressure source. gen also was forced far into the venous system. These warnings are directed at avoiding excesThe long duration of frothy venous return after sive negative pressures being applied, but do resumption of cardiopulmonary bypass sug- not warn of the consequences of positivegests this. A potentially fatal massive venous pressure buildup if this outlet becomes oxygen embolus was averted by rapidly obstructed. It is our understanding that further clamping the venous return line. Relief of the warnings are planned. Fig 2 . The Bentley BOS-70 oxygenator. The gas vent, which is the only available outlet, has become obstructed (large arrow). Positive pressure (smaller arrows) within the sealed canister finds the least resistance by escaping through the venous return line into the patient’s right atrium and venous system. (LV = leff ventricular.)
The presence of air in the venous drainage system can interfere with cardiopulmonary bypass and disturb the operating surgeon. The air can come from lacerations in the right atrium, from around atrial pursestring sutures, from imperfect exclusion of the venous drainage cannula from an opened chamber on the right side of the heart, from a loose connector or laceration in the venous drainage tubing, or from the introduction of air through an indwelling venous catheter. The sudden appearance of a completely air-filled venous drainage system in conjunction with a rapidly expanding heart is a unique situation to be encountered by the cardiac surgeon. The description and possible cause of such an event, the response in the operating room to the problem, and the final clinical result are presented in this report. A 58-year-old businessman with a short history of rapidly progressive angina pectoris, demonstrated triple-vessel coronary artery obstruction at angiography. In August, 1979, he underwent aortocoronary saphenous vein bypass grafting. The cardiopulmonary bypass circuit employed a single 42 mm venous cannula, which drained by gravity into a Bentley BOS-10 bubble oxygenator. A 24 mm Argyle aortic perfusion cannula was introduced into
From the Division of Thoracic and Cardiovascular Surgery, University of Southern California School of Medicine, Los Angeles, CA. Accepted for publication Feb 28, 1980. Address reprint requests to Dr. Wells, 1136 W Sixth St, Los Angeles, CA 90017.
the Lscending aorta for arterial return. The left heart was vented using an Argyle-Ferguson left ventricular catheter (18F) introduced through the right superior pulmonary vein, and a single cardiotomy sucker was used. Both the vent and cardiotomy sucker drained into separate Bentley cardiotomy reservoirs (model Q-120) maintained at a negative pressure of 30 to 60 cm of water by wall suction. Blood from each cardiotomy reservoir was returned to the oxygenator through separate pump heads (Fig 1). Of major importance was the presence of a polyvinyl tube attached to the gas vent port of the Bentley oxygenator. This tubing ran from the oxygenator, along the floor of the operating room, and into the room air exhaust. The purpose was to scavenge anesthetic gases passed through the oxygenator system in compliance with recent standards of practice. Cardiopulmonary bypass progressed normally through the initial phases of the procedure, during which four distal saphenous veincoronary artery anastomoses were fashioned. A partial occlusion clamp was placed on the proximal ascending aorta, and two 5 mm aortotomies were made for proximal saphenous vein anastomoses. As the first of the proximal anastomoses was in progress, the pump technician reported a sudden massive air lock and loss of venous return. Visual inspection revealed no blood in the venous system and a rapidly distending heart. The infusion of blood was immediately discontinued, and inflow and return tubings were clamped with the exception of the left ventricular vent. The pump technician, in an attempt to eliminate all potential sources of the problem, disconnected the tubing from the gas vent outlet of the oxygenator. The heart was compressed manually to decrease its size. The patient was placed in deep Trendelenburg position, and the ascending aorta was vented at multiple sites with a large slotted needle. Because of the presence of the partially occluding clamp controlling the two aortotomies in the as-
86 0003-4975/81/010086-04$01.25 @ 1980 by The Society of Thoracic Surgeons
87 Case Report: Wells and Stiles: Venous Air Embolism during CPB
Fig 1 . The authors' technique for cardiotomy and left ventricular vent return. The occlusive roller head is positioned between the oxygenator canister and the cardiotomy reservoir. As a result, positive pressure within the oxygenator can escape only through the venous return line.
cending aorta, it was technically difficult to cross-clamp the aorta. Attempts were made to identify the site of air entry into the venous system. Cannula position appeared ideal, and no laceration of the atrium or slackening of the atrial pursestring suture could be identified. During this time the left ventricular vent remained open, and a substantial aliquot of the patient's blood volume returned to the reservoir. Only a small amount of air was obtained from the root of the aorta. This appeared in a retrograde fashion in the aortic perfusion line and was aspirated easily through the stopcock connector at the proximal end of the aortic cannula. Then volume was returned to the patient from the oxygenator reservoir, and the venous cannula was reprimed and opened. Initially a large amount of air was returned from the right atrium and vena cava.
This was followed by considerable froth, and, after two or three minutes, a normal pattern of venous return was obtained. The proximal anastomoses were completed and the heart recovered. This allowed the patient to be weaned from cardiopulmonary bypass. The patient awakened in the operating room with no evidence of neurological deficit. Recovery was uneventful, and he was discharged on the ninth postoperative day.
Comment We believe that the unusual, sudden appearance of air in the venous system was the result of oxygen delivered under positive pressure through the venous return cannula into the patient's right atrium. The Bentley BOS-10 oxygenator is unique in that its canister is a closed system. With a bypass circuit such as the one described, the gas vent port is the only outlet for positive pressure other than the venous inlet. We presume a sudden buildup of positive pressure occurred in the oxygenator secondary to occlusion of the polyvinyl tubing used to evacuate gas from the canister (Fig 2). This
88 The Annals of Thoracic Surgery Vol 31 No 1 January 1981
89
Case Report: Wells and Stiles: Venous Air Embolism during CPB
gas vent obstruction removed the source of the embolic problem. Any surgeon using the Bentley oxygenator should be aware of this potential problem. Obstruction of the gas vent in any system used to scavenge exhaust must be avoided. This can be accomplished by placing a relief valve in the Fig 3 . The Bentley BOS-10 oxygenator. The 1/z inch (1.27 cm) open Luer-Lok connector in the gas vent tubline to prevent positive pressure developing ing will prevent the buildup of positive pressure in the within the canister if the tube should become oxygenator canister should the tubing become obstructed. obstructed (Fig 3). With these adjustments, we have found the Bentley oxygenator to be very event was transient and may have been caused satisfactory. by someone standing on the tubing. The buildInstructions for the Bentley oxygenator warn up of pressure in the canister was sudden at the against potential mismanagement of the gas oxygen flow of 8 liters per minute. The venous vent system. It is recommended that a l/z inch return in the drainage tubing was quickly dis- (1.27 cm) open Luer-Lok connector be placed in placed with oxygen and was responsible for the line to prevent occurrence of a “vacuum” in rapid distention of the heart. Ultimately, oxy- the canister by a negative pressure source. gen also was forced far into the venous system. These warnings are directed at avoiding excesThe long duration of frothy venous return after sive negative pressures being applied, but do resumption of cardiopulmonary bypass sug- not warn of the consequences of positivegests this. A potentially fatal massive venous pressure buildup if this outlet becomes oxygen embolus was averted by rapidly obstructed. It is our understanding that further clamping the venous return line. Relief of the warnings are planned. Fig 2 . The Bentley BOS-70 oxygenator. The gas vent, which is the only available outlet, has become obstructed (large arrow). Positive pressure (smaller arrows) within the sealed canister finds the least resistance by escaping through the venous return line into the patient’s right atrium and venous system. (LV = leff ventricular.)