Suspected venous air embolism

To assess the relationship between the time period before hyperbaric oxygenation therapy (HBO) and clinical outcome in patients with iatrogenic cerebral air embolism. Retrospective study in a hyperbaric chamber and medical intensive care unit of a university hospital. All patients with air embolism from 1980 to 1999. We retrieved the cases of 86 patients who benefited from an identical HBO and analyzed the relationship between the time period before HBO and clinical outcome. Patients treated with HBO less than 6 h had a better outcome than those treated later. In patients treated within this delay the cause was venous air embolism in 84% and arterial air embolism in only 16% of cases. After this delay the cause was venous air embolism (53%) and arterial air embolism (47%). Patients with venous air embolism and recovery had a shorter delay than patients with sequelae or death (2 h 15 min vs. 4 h). Patients with venous air embolism treated less than 6 h had a better outcome than those treated later. In patients with arterial air embolism the time period before HBO was longer than in venous air embolism (8 h vs. 3 h) and the outcome worse (recovery in 35% vs. 67%). In patients with arterial air embolism no difference in the time period was found between patients with recovery and sequelae or death. We stress the beneficial effect of an early HBO in air embolism, the importance of an increased awareness of physicians concerned with this severe complication, and the need to develop techniques to detect air emboli in the cerebral circulation.

The benefit of the sitting position for surgery of the posterior fossa and cervical spine is still a matter of controversy. In our study we analyzed the outcome after sitting position surgery at our institution. We compared the incidence of venous air embolism (VAE) as recognized with different monitoring techniques and the severity of complications. We retrospectively analyzed 600 patients, who underwent surgery for different posterior fossa and cervical spine pathologies, respectively, in the sitting position at our institution from 1995 to 2011. Intraoperative monitoring for VAE included endtidal CO2 level, Doppler ultrasound or intraoperative transesophageal echocardiography (TEE). We defined VAE as a decrease of the endtidal CO2 levels by more than 4 mm Hg, a characteristic sound in the thoracic Doppler, or any sign of air in the TEE. We found an overall incidence of VAE in 19 % of all patients, whereas the rate of severe complications associated with VAE such as a decline of partial oxygen pressure (pO2) or a drop of blood pressure was only 3.3 % in all patients. Only three out of 600 operations had to be terminated because of non-controllable VAE (0.5 %). There was no mortality resulting from VAE in our series. We also found a difference in the incidence of VAE depending on the monitoring technique. The VAE rate as monitored with TEE was 25.6 % whereas the incidence of VAE in patients monitored with Doppler ultrasound was 9.4 %. The rate of a significant VAE was comparable in both methods 4.8 % vs. 1.2 %. All patients were preoperatively screened for persisting foramen ovale (PFO); 24 patients with clinically confirmed PFO were included in this series. There was no case of paradox air embolism. In our series, VAE was detected in 19 % of all patients in the sitting position. However, in only 0.5 % of cases a termination of the surgical procedure became necessary. In all other cases, the cause of air embolism could be found and eliminated during surgery. TEE was found to be the monitoring technique with the highest sensitivity. In our opinion, the sitting position is a safe positioning technique if TEE monitoring is used.

A venous air embolism can occur as a result of circumstances that include blunt head or chest trauma, thoracentesis, arterial catheterization, neurosurgery, cardiac surgery, and Caisson disease. The formation of a venous air embolism requires an air source, interaction between the air source and the vessel, and a pressure gradient supporting air migration into the vessel. Air enters through the impaired venous structure and travels to the right side of the heart and the pulmonary arteries, and depending on the amount of air, may occasionally be fatal. This report is the description of the case of a 3-year-old child who developed a fatal venous and cerebral embolism during neurosurgery for the treatment of skull fractures with epidural and subdural bleeding due to blunt head and chest trauma resulting from a television falling on her. The pathophysiology of death and notes regarding the medico-legal autopsy procedure in such cases are discussed. Meticulous autopsy techniques must be used to determine the presence of an air embolism in cases of blunt trauma, especially in patients with blunt trauma to the head who die during neurosurgery, and possible future malpractice claims should be kept in mind.

The physical properties of carbon dioxide (CO2) make it the most appropriate gas for the evaluation of body spaces. We report a serious, life-threatening complication that occurred during delineation of the hip joint in an infant despite the use of CO2. Case Report A 6.1-kg, 4-mo-old girl (ASA physical status I) with possible bilateral congenital hip dislocations was scheduled for hip arthrography. She had no history of allergies and no cardio-respiratory abnormalities. Anesthesia was induced with halothane. The trachea was intubated after 2.7 mg of rocuronium and maintained with N2 O/O2 and 1% halothane. Mechanical ventilation was adjusted to ETCO2 levels of 30-35 mm Hg. Her postinduction blood pressure was 110/56 mm Hg, heart rate was 130 bpm, and oxygen saturation (SpO2) was 100%. Twenty-gauge needles were inserted by the surgeons into each hip joint. Radiography showed that the tip of the needles were adjacent to the capital epiphysis on each side. Thirty milliliters of CO2 was injected by a syringe into each hip joint. On fluoroscopy, it was noted that some of the CO2 was tracked along the iliopsoas sheath. Attempts to remove the CO2 were made. Blood was aspirated from one of the joint spaces. A total of 3 mL of diatrizoate was injected but partially escaped around the joint space. During the procedure, a sudden onset of oxygen desaturation to 80% was detected, which resolved spontaneously within 30 s. Approximately 3 min later, another episode of oxygen desaturation occurred (SpO2 40%). N2 O was discontinued. The breathing circuit, the endotracheal tube, and the IV were checked. The breath sounds were equal on auscultation. On precordial auscultation, a millwheel murmur was detected, similar to "crunching of cornflakes." ETCO2 was approximately 3 mm Hg. A progressive decrease in blood pressure and pulse rate were noted. Atropine 0.1 mg and ephedrine 5 mg were given. Surgery was stopped. Manual hyperventilation with 100% O2 and placement of the child in the head-down (Trendelenburg) position eliminated the harsh millwheel murmur and improved her vital signs (SpO2 100%). The overall period of desaturation lasted approximately 7 min. Because adequate delineation of the hip joints were obtained, the procedure was terminated, and the residual neuromuscular blockade was antagonized with 0.3 mg of neostigmine and 0.1 mg of glycopyrolate. On awakening, the tracheal tube was removed, and the child was observed for an additional 30 min in the operating room. Forty-five minutes after the incident, the infant was completely awake, with no detectable neurological sequelae. She was discharged home the same day. Discussion Gas embolism is rare during orthopedic procedures. However, gases from several different sources and resulting from unexpected air emboli have been found in body tissues [1-3]. Because CO2 remains in circulation for a short time, it is used routinely whenever gas insufflation is required. However, rare but devastating complications caused by CO2 embolism have been reported during laparoscopic surgery [4]. Although air embolism has been reported among patients operated on in the sitting position, entrainment of gas also occurs during surgery in the lateral, supine, or prone positions [5,6]. Because CO2 has greater solubility in tissues than air, CO2 bubbles remain in circulation for less time. Thus, CO2 is safer if venous gas embolism were to occur. Judging from the rapidity of the cardiopulmonary decompensation in our patient, she undoubtedly suffered form the intravascular insufflation of a relatively large bolus of CO2 at a high flow rate. It was not possible to estimate the total volume of CO2 that entered the venous system. The primary pathophysiologic event in venous gas embolism is presumed to be the accumulation of gas in the right ventricle. However, recent studies in animals suggest that a combination of increased right ventricular afterload and arterial hypotension leading to ischemia are the primary mechanisms of cardiac dysfunction during venous gas embolism [6]. Gas may also pass through right-to-left intracardiac shunts, thereby gaining paradoxical access to the coronary, cerebral, and systemic circulations [5]. The signs and symptoms of venous air embolism are global chest wheezing, bradycardia, hypotension, cyanosis, and even cardiac arrest. The symptoms depend on the volume of the embolized gas and the rate at which it is released into the circulation. It is usually diagnosed by the presence of a cardiac murmur (mill-wheel), cardiac dysrhythmias, hypotension, a decrease in expired carbon dioxide, and the sudden appearance of vigorous spontaneous ventilation despite continuing mechanical ventilation. Small volumes of intravascular gas produce a ventilation-perfusion mismatch, which is reflected in a reduced ETCO2[7]. However, the most sensitive clinical method for detection of venous air embolism is the ultrasound detector [7-9]. The treatment of gas embolism is directed to prevent a further influx of gas and aspiration of air from the right atrial catheter (if present). Nitrous oxide is discontinued to prevent further expansion of embolized gas. The standard teaching is to put the patient in a head-down and left lateral decubitus position to help divert air away from the right ventricle [10]. However, the recent animal data do not support the above-mentioned recommendation [6,11]. Our patient improved with the supine, head-down position. We acknowledge, however, that the dog is a surrogate model for human cardiopulmonary physiology, and clinical correlates on the effect of position during venous gas embolism in humans needs to be evaluated. We report this case to alert practicing physicians that major complications from gas embolism can occur during a benign diagnostic procedure. The outcome of this case may have been different if it had been performed in the radiography suite with sedation and without appropriate monitoring and supervision.

Rationale:One of the catastrophic complications of surgical hysteroscopy is venous gas embolism (VGE), and this event could cause morbidity and in serious cases may even lead to death. However, in cases of VGE accompanied by refractory hypokalemia is rare and can significantly increase the difficulty of treatment and resuscitation. Here, we successfully treated a patient with fatal VGE during surgical hysteroscopy, accompanied by difficult resuscitation with refractory hypokalemia.Patient concerns:We report a rare case of sudden cardiac arrest due to VGE during surgical hysteroscopy, followed by difficult resuscitation with refractory hypokalemia.Diagnosis:VGE was diagnosed by a sudden decrease in EtCO2, a loud mill wheel murmur in the thoracic area, and a small number of air bubbles evacuated from the internal jugular catheter. And refractory hypokalemia was diagnosed by serum potassium levels dropping frequently to as low as 2.0 mmol/L within 36 hours of resuscitation after cardiac arrest.Interventions:Our vigilant anesthesiologist noticed the early sign of VGE with a sudden drop in EtCO2, and as the cardiac arrest occurred, interventional maneuvers were implemented quickly including termination of the surgical procedure, adjustment of the patient’s position, cardiac resuscitation, continuous chest compression, and correction of electrolyte disturbances, particularly refractory hypokalemia during the early stage of resuscitation.Outcomes:The patient regained consciousness 4 days after the cardiac arrest and was discharged 1 month later without any neurological deficits.Lessons:As a relatively simple procedure, surgical hysteroscopy may have catastrophic complications. This case demonstrates the full course of fatal gas embolism and difficult resuscitation during hysteroscopic surgery, and emphasizes the importance of early detection, prompt intervention, and timely correction of electrolyte disturbances, such as refractory hypokalemia.

The sitting position is routinely used in many centers, although its use remains controversial and appears to be diminishing because of the risk of venous air embolism (VAE). This is a retrospective analysis of 601 adult and 91 pediatric cases underwent neurosurgery from January 1995 through December 2010 in the sitting position. The incidence of VAE and other complications related to the sitting position has been determined. VAE was defined as a sudden and sustained decrease of end-tidal carbon dioxide (ETCO2) ≥0.7 kPa. The incidence of VAE in children and adults were found to be 26.3% (n=24) and 20.4% (n=123) consecutively but the difference was not significant. The incidence of positioning induced hypotension was more in adults (37.6%) compared to children (18.6%, p=0.00001). The presence of COPD (p=0.04) and ASA status (p=0.03) showed a correlation with 'hypotension with positioning'. There was no peroperative mortality. The study provides a significant body of data on neuroanesthesia for the sitting position and our results suggest that if the sitting position is a neurosurgical necessity it can be used with vigilant follow up throughout the procedure to detect any occurrence of VAE by ETCO2 monitoring if you do not have the chance to use more sensitive tools.

Professor of AnesthesiaUniversity of California, San Diego Medical CenterSan Diego, CaliforniaTo the Editor:—Drs. Ho and Ling's excellent Meeting Abstracts article, “Systemic Air Embolism after Lung Trauma,”1provides an important teaching service to the anesthesia community. However, one totally preventable and recurring cause of potentially fatal venous air embolism that was not mentioned in the article (particularly in the last section entitled, “Other Causes of Air Embolism in Nontraumatic and Traumatic Clinical Setting”) is externally pressurizing a reinfusion blood bag that has been filled with blood from a surgical field scavenging–blood processing system. In most of the Haemonetics blood scavenging–processing models (Cell-Saver; Haemonetics Corp., Braintree, MA), the unit sends an 80-ml column of air ahead of the first column of blood into the reinfusion blood bag. If the reinfusion blood bag, which contains air, is then externally pressurized, a venous air embolism may occur. The obvious, but life-saving, take-home message of these considerations is that reinfusion blood bags that have been filled with blood from an autotransfusion system should never be externally pressurized.The old warning on the Haemonetics Cell-Saver reinfusion bag of “Do Not Use With Pressure Cuff” was changed to “Do Not Use Pressure Cuff. The Use of Pressure Cuff May Lead to Fatal Infusion of Air” in 1995 for obvious reasons. However, I am aware that the practice of externally pressurizing Cell-Saver reinfusion blood bags is still common and widespread. Consequently, other additional solutions to minimize the risk of fatal venous air embolism appear to be desirable and necessary. The potential solutions include insertion of a air bubble detector with an audible alarm in the infusion line to the patient, routine use of a double reinfusion bag (transfer pack) system, redesign of the processing unit to exclude air from being sent to the reinfusion bag (mandatory use of a purge mechanism), and insertion of a nondependent air escape valve in the reinfusion bag. All these solutions involve an additional response to the problem by the manufacturer. Certainly any two in-series solutions (e.g. , the printed warning on the reinfusion bag plus one of the above suggestions) for the air in the reinfusion bag problem will greatly minimize the risk of venous air embolism.

During diagnostic and interventional radiological procedures, venous air embolism is seen as a nonfatal event. In this study, it was aimed to determine the frequency and localization of nonfatal venous air embolism in contrast enhanced computed tomography (CT). 1654 contrast-enhanced thorax computed tomography examinations performed in the Radiology Unit of our hospital between January 1, 2019 and December 31, 2019. The localization and size of the detected venous air emboli and from which side the contrast agent was administered were recorded. In this study, iatrogenic venous air embolism was seen in 3.1%. The most common localization is the main pulmonary artery (1.81%) and other localizations in order of frequency are left brachiocephalic vein (0.66%), left subclavian vein (0.36%), right brachiocephalic vein (0.30%), right subclavian vein (0.24%), right ventricle ( 0.18%) and right atrium (0.18%). Looking at the size of the venous air embolism, 2.5% small, 0.50% moderate and 0.12% large air embolism were seen. Radiologists should be aware of the possibility of vascular air embolism after contrast agent injection in CT scanning and should be careful.

OBJECTIVE The semisitting position of a patient confers numerous advantages in various neurosurgical procedures, but venous air embolism is one of the associated complications of this position. To date, no prospective studies of the relationship between the degree of head elevation and the rate and severity of venous air embolism for patients undergoing a procedure in this position have been performed. In this study, the authors compared changes in the severity of venous air embolism according to the degree of head elevation (30° or 45°) in patients undergoing an elective cranial neurosurgical procedure in the semisitting position. METHODS One hundred patients undergoing an elective infratentorial craniotomy in the semisitting position were included, and each patient was assigned to 1 of 2 groups. In Group 1, each patient's head was elevated 30° during surgery, and in Group 2, each patient's head elevation was 45°. Patients were assigned to their group according to the location of their lesion. During surgery, the standard anesthetic protocol was used with total intravenous anesthesia, and transesophageal echocardiography was used to detect air in the blood circulation. Any air embolism seen on the echocardiography screen was classified as Grade 0 to 4. If multiple events occurred, the worst graded attack was used for statistical analysis. During hemodynamic changes caused by emboli, fluid and vasopressor requirements were recorded. Surgical and anesthetic complications were recorded also. All results were compared statistically, and a p value of < 0.05 was considered statistically significant. RESULTS There was a statistically significant difference between groups for the total rates of venous air emboli detected on transesophageal echocardiography (22.0% [n = 11] in Group 1 and 62.5% [n = 30] in Group 2; p < 0.0001). The rate and severity of air embolism were significantly lower in Group 1 than in Group 2 (p < 0.001). The rates of clinically important venous air embolism (Grade 2, 3, or 4, venous air embolism with decreased end-tidal carbon dioxide levels and/or hemodynamic changes) were 8.0% (n = 4) in Group 1 and 50.0% (n = 24) in Group 2 (p < 0.0001). There was no association between the rate and severity of venous air embolism with patient demographics (p > 0.05). An association was found, however, between the rate of venous air embolism and the type of surgical pathology (p < 0.001); venous embolism occurred more frequently in patients with a meningioma. There were no major surgical or anesthetic complications related to patient position during the postoperative period. CONCLUSIONS For patients in the semisitting position, an increase in the degree of head elevation is related directly to a higher rate of venous air embolism. With a 30° head elevation and our standardized technique of positioning, the semisitting position can be used safely in neurosurgical practice.

Besides intracardiac shunts, such as a patent foramen ovale (PFO), that allow paradoxical embolization, emboli can bypass the pulmonary microcirculation via dynamic large intrapulmonary arterial‐venous anastomoses (IPAVAs). They are believed to be closed at rest but open with exercise. They allow venous gas emboli (VGE) to cross over to the arterial side of the circulation. Whether these arterial gas emboli (AGE) reach the cerebral circulation is not known. For this study we recruited twenty PFO negative SCUBA divers and conducted a field study with the aim to investigate the appearance of AGE in intracranial vessels. They performed a single dive to a depth of 18m sea water with a 47‐min bottom time and a direct ascent to the surface. Transthoracic echocardiography was used to grade VGE and AGE scores. Transcranial Doppler was used to visualize middle (MCA) and posterior cerebral (PCA) arteries and objective automated bubble counting was applied. Observations were conducted for 45 min post‐dive at rest, throughout an incremental cycle exercise test in the supine position until exhaustion and for 10 min of recovery. After surfacing all divers presented VGE (bubble grades from 1 to 4B) and arterializations were present in 3/20 divers. Incremental exercise increased only the incidence of arterializations at higher workloads but not the AGE grades. The total amount of AGE that reached the MCA and PCA was 2 at 60W, 3 at 90W, 5 at 120W, 7 at 150 W and 5 at 180W. Exercise‐induced IPAVA recruitment was not coupled with a parallel increase in bubble count in the MCA and PCA.

Venous air embolism (VAE) is a potential complication of all surgical procedures in which the operative field is vertically superior to the level of the heart. Although VAE may occur in a variety of surgical positions, this phenomenon is most associated with the sitting position [1]. The incidence of Doppler-detected VAE is as high as 45% in sitting craniectomy patients and 24% in sitting cervical surgeries. Losasso et al. [2] report Doppler-detected VAE in 7% of patients undergoing cervical spine surgery. Matjasko et al. [3] note an incidence of Dopplerdetected VAE of 8.2% (18/220 patients) during cervical foraminotomy. Cervical microdiscectomy is one type of cervical spine surgery which may or may not be performed using the sitting position and which requires a smaller incision (2 cm) than is used for cervical laminectomy. Because our experience with the microdiscectomy procedure in the sitting position suggested an incidence of Doppler-detected VAE of less than the 7% previously reported [2], we retrospectively examined 121 consecutive cervical microdiscectomies peformed in the sitting position. Methods In our review of 121 patients (January 1992-July 1995) who had undergone sitting cervical discectomies, those with known preoperative pulmonary disease (n = 4) were removed from consideration, leaving 117 patients for analysis. Anesthesia was induced intravenously (IV) with propofol in all patients, and the trachea was intubated after the IV administration of succinylcholine. Anesthesia was typically maintained with 50 nitrous oxide and oxygen, isoflurane or desflurane, fentanyl, and a nondepolarizing muscle relaxant. Patients were monitored with the usual monitors. A 20-gauge radial artery catheter was inserted and the transducer was positioned at the level of the external auditory meatus. In all patients, a multiorificed right atrial catheter was placed; correct position within the right atrium was confirmed by either pressure wave analysis as the catheter was withdrawn from the right ventricle, catheter electrocardiogram determination, or chest roentgenogram. A precordial Doppler ultrasound probe (Versatone model D8; Medsonics, Fremont, CA) was applied and its position confirmed through test saline injections via the central line. Ohmeda Rascal Trademark (Ohmeda, Salt Lake City, UT) gas monitors were used to assess gas exchange. Doppler sounds were monitored continuously in all cases by experienced neuroanesthesiologists familiar with sounds characteristic of VAE. Four neurosurgeons performed the procedures. Ventilation was controlled to maintain an end-tidal CO2 between 30 and 35 mm Hg. Positive end-expiratory pressure was not used. The incidence of VAE in the studied population was compared with that found in Matjasko's cervical foraminotomy subgroup [3]. This subgroup was chosen for comparison because for aminotomy, like microdiscectomy, involves a more limited surgical procedure than cervical laminectomy. We acknowledge that comparison of different groups from different institutions reduces the reliability of statistical comparisons. This comparison used Fisher's two-sided test. The confidence bounds were calculated using Hanley and Lippman-Hand's method [4]. Results Patient demographics are presented in Table 1. Microdiscectomies were performed at the following levels: C3-4 (n = 1); C4-5 (n = 4); C5-6 (n = 33); C6-7 (n = 68); C-7-T-1 (n = 11). The surgery averaged 142 min in duration (range, 60-270 min). No Doppler-detected incidents of VAE were reported. No decreases in end-tidal CO2 more than 1 to 2 mm Hg were recorded during the period of surgical exposure. Pressor support or changes in patient positioning were not required after the surgical incision in any procedure. No arrthymias were noted. All patients had an uneventful perioperative and recovery course. There were no complications from central line placement.Table 1: Patient/Surgical Site DemographicsConsidering our study alone and using statistical rules for interpreting zero numerators, the 95% confidence interval for VAE was 0%-3%, i.e., it is statistically unlikely that the incidence of VAE would exceed 3 patients per 100 [4]. Using Fisher's two-sided test, the rate of VAE in our population was significantly lower than in Matjasko's cervical foraminotomy surgery subgroup (P = 0.001). Discussion This analysis of 117 sitting cervical microdiscectomies demonstrated no apparent hemodynamically or Doppler-detected VAE. This reflects an incidence of VAE lower than the 7%-8% previously noted for cervical spine surgery [2,3]. Perhaps this difference can be accounted for in four ways. Firstly, microdiscectomy uses a smaller surgical field, thereby reducing the number of veins exposed. Secondly, using microsurgical techniques, the neurosurgeon can readily identify potential sites of air entrainment. Thirdly, these procedures were performed primarily on lower cervical disks, C5-6 and C6-7. As such, the distance between the operative site and the right atrium is decreased, lessening any potential pressure gradient. Finally, individual neurosurgical technique may influence the risk of VAE. Transesophageal echocardiography (TEE) may be a more sensitive measure than precordial Doppler in the detection of VAE [5]. Nevertheless, the sensitivity of the precordial Doppler compares favorably with TEE for air bubble detection [6]. Unfortunately, limited resources have prevented the routine use of TEE during sitting cervical microdiscectomies. Although our data suggest that the incidence of Doppler-detected VAE is minimal in sitting cervical microdiscectomies, this finding should be confirmed using Doppler and TEE detection in a prospective series. A multicentered trial might be required because of the low incidence of VAE in this population. Matjasko et al. [3] proposed that central line placement, if unsuccessful via the basilic vein, is not warranted in cervical foraminotomy if close monitoring and meticulous hemostasis are used. Our experience supports and strengthens this conclusion for sitting microdiscectomy patients. However, this analysis does not excuse anesthesiologists from taking all appropriate measures to detect and to respond to VAE in the seated cervical disk patient. Rather, it is to alert anesthesiologists, especially those who encounter the sitting position infrequently, that the incidence of VAE in this particular population would appear quite low. Should hemodynamic instability develop, the physician is advised to thoughtfully consider other differential diagnoses along with VAE in guiding therapeutic interventions. We wish to thank Professor Alan Zaslavsky, Department of Statistics, Harvard University, for statistical advice, and our neurosurgical colleagues for their help.

Isovolemic anemia results in improved gas exchange in rabbits with normal lungs but in relatively poorer gas exchange in rabbits with whole-lung atelectasis. In the current study, the authors characterized the effects of hemodilution on gas exchange in a distinct model of diffuse lung injury: venous gas embolization. Twelve anesthetized rabbits were mechanically ventilated at a fixed rate and volume. Gas embolization was induced by continuous infusion of nitrogen via an internal jugular venous catheter. Serial hemodilution was performed in six rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; six rabbits were followed as controls over time. Measurements included hemodynamic parameters and blood gases, ventilation-perfusion (V(A)/Q) distribution (multiple inert gas elimination technique), pulmonary blood flow distribution (fluorescent microspheres), and expired nitric oxide (NO; chemoluminescence). Venous gas embolization resulted in a decrease in partial pressure of arterial oxygen (PaO2) and an increase in partial pressure of arterial carbon dioxide (PaCO2), with markedly abnormal overall V(A)/Q distribution and a predominance of high V(A)/Q areas. Pulmonary blood flow distribution was markedly left-skewed, with low-flow areas predominating. Hematocrit decreased from 30+/-1% to 11+/-1% (mean +/- SE) with hemodilution. The alveolar-arterial PO2 (A-aPO2) difference decreased from 375+/-61 mmHg at 30% hematocrit to 218+/-12.8 mmHg at 15% hematocrit, but increased again (301+/-33 mmHg) at 11% hematocrit. In contrast, the A-aPO2 difference increased over time in the control group (P < 0.05 between groups over time). Changes in PaO2 in both groups could be explained in large part by variations in intrapulmonary shunt and mixed venous oxygen saturation (SvO2); however, the improvement in gas exchange with hemodilution was not fully explained by significant changes in V(A)/Q or pulmonary blood flow distributions, as quantitated by the coefficient of variation (CV), fractal dimension, and spatial correlation of blood flow. Expired NO increased with with gas embolization but did not change significantly with time or hemodilution. Isovolemic hemodilution results in improved oxygen exchange in rabbits with lung injury induced by gas embolization. The mechanism for this improvement is not clear.

VENOUS air embolism (VAE) has been reported in a wide variety of procedures. In most cases, signs of clinically significant VAE are present soon after the entry of air into the circulation. We present a case of urologic surgery in which no signs of VAE were recognized during surgery, but circulatory collapse occurred when the patient was transferred from the operating room bed to the transport stretcher. The presumptive diagnosis of VAE as the cause of circulatory collapse was made on aspiration of frothy blood from the central venous pressure (CVP) catheter and was confirmed with the immediate placement of a transesophageal echocardiography (TEE) probe.

The overall benefit of employing a sitting/semisitting position for neurosurgical procedures remains under criticism due to concerns for additional risk, especially the risk of intraoperative venous air embolism (VAE). The aim of this single-center cohort study was to evaluate the frequency and severity of VAEs and associated complications in patients undergoing neurosurgery in the lounging position. From 2010 to 2020, 1000 patients, including 172 patients with a patent foramen ovale, underwent surgery in the lounging position for different neurosurgical pathologies. All patients were monitored intraoperatively using continuous transesophageal echocardiography (TEE). The anesthesia team documented any observed incidences of VAEs and scored their severity according to the Tuebingen classification system (TCS) for VAE (TCS-VAE). The patients' clinical condition, radiological findings, and hospital course were subsequently analyzed to assess complications in a retrospective analysis of prospectively collected data. In the cohort of 1000 patients, 5 underwent cervical spine surgery and 995 underwent suboccipital craniotomy. VAE was detected by TEE in 51.4% (95% CI 48.4%-54.5%) of patients, with synchronous changes in end-tidal CO2 (grade 2-5 TCS-VAE) noted in 10.2% (95% CI 8.3%-12.3%). None of the patients presented with hemodynamic instability (grade 5 TCS-VAE). Patients with high-grade VAEs were significantly older (p = 0.02) and had lower BMIs (p = 0.001) than the respective mean value of the cohort. VAE grade was not associated with any of the outcome measures such as Karnofsky Performance Scale score, duration of ventilation, length of intensive care unit stay, and length of hospital stay. Postoperative acute respiratory distress syndrome (ARDS) was diagnosed in 0.3% (95% CI 0.0%-0.7%, n = 3) of all cases, and ARDS was associated with perioperative VAE grade (p = 0.001). No patient suffered a new permanent neurological deficit due to a paradoxical VAE. In this large cohort, the risk of an intraoperative VAE during neurosurgery in the lounging position was assessed, and contrary to the general perception in the field, no permanent sequelae or fatal adverse events attributable to VAEs were observed. Furthermore, the overall incidence of ARDS was very low. This study clearly establishes that experienced interdisciplinary teams can safely use the lounging position for neurosurgical procedures.

Nine days after a surgical intervention due to an injury of the left hind hoof capsule, a 9-y-old, 538-kg female Wielkopolski horse was found recumbent in its stall with an unplugged permanent intravenous catheter positioned in the left jugular vein. Despite immediate resuscitation attempts, the animal died within minutes. Suspecting venous air embolism, radiographic imaging and detailed postmortem examinations were performed. However, visualization of the heart by radiography was hindered by the animal's body mass and postmortem changes. The autopsy followed a modified Richter method, originally developed for diagnosing air embolism in humans. The horse was positioned in left lateral recumbency to allow in situ access to the atria and venous sinuses. Gas bubbles observed in the right atrium and ventricle confirmed venous air embolism as the cause of death. Venous air embolism is a rarely documented cause of death in veterinary pathology. We present here an autopsy protocol for diagnosis of venous air embolism in large animals, which is primarily a macroscopic diagnosis.