Air embolism in the sitting position

Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position

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.

Use of spontaneous ventilation to monitor the effects of posterior fossa surgery in the sitting position

We describe the successful excision, guided by spontaneous ventilation, of a cervico-medullary hemangioblastoma in a 22-year-old female in the sitting position. A balanced anesthesia technique comprising an oxygen, nitrous oxide, sevoflurane, fentanyl and vecuronium mixture was used. Apart from routine monitors, electroencephalographic spectral entropy monitoring was used to determine the depth of anesthesia and transesophageal echocardiography for detection of venous air embolism. The patient remained in spontaneous ventilation for 235min during tumor excision. The intraoperative and postoperative course were uneventful. The patient recovered without any major neurological deficit.

Gas Embolism: Part I. Venous Gas Emboli

Gas emboli syndromes occur in many different settings, and their medical significance ranges from being life-threatening emergencies to being totally innocuous. We discuss venous gas embolization in Part I of this review, and it can result from a variety of traumatic, diagnostic, therapeutic, and surgical interventions. The pathophysiological consequences depend on where the gas bubbles impact and obstruct the circulation—by creating an “air lock” in the right ventricle, by obstruction of pulmonary arterioles, and sometimes with passage into the arterial circulation (so called paradoxical emboli). Various monitoring techniques are available and are known to be useful in high-risk patients. Nevertheless, the diagnosis can be difficult to establish. Myriad and generally nonspecific clinical manifestations may be present; the patient may often exhibit signs and symptoms suggestive of other acute cardiopulmonary or central nervous system events. The classically described “mill-wheel murmur” is actually a rare finding, and it is transient at best. There are no specific diagnostic tests available, and clinicians, must depend on a high level of suspicion in the appropriate settings. Rapid identification of the problem, with prevention of further gas entry into the venous circulation, should be a routine measure. The left lateral decubitus position, administration of 100% oxygen, and hyperbaric oxygenation should all be considered, and they have been shown to be effective treatment modalities.

Controlled neck compression in neurosurgery. Studies on venous air embolism in upright sheep

Bilateral compression of the jugular veins to raise temporarily cerebral venous pressure, is a manoeuvre recommended frequently in the immediate management of venous air embolism during neurosurgery. One method of compressing the neck veins is to inflate a pneumatic cuff secured around the neck with adhesive tape. This method of neck vein compression had been assessed in upright anaesthetised sheep and found to be an easily controlled and efficient way to raise the cerebral venous pressure. Advantages, dangers and potential problems associated with the use of an inflatable cuff in the clinical situation are discussed.

Air embolism during craniotomy in the seated position: a comparison of methods for detection

A case of air embolism sufficient to cause cardiovascular collapse is reported. This occurred during biopsy of the trigeminal nerve with the patient in the seated position. The use of an end-tidal carbon-dioxide monitor was a better indicator than a precordial doppler of the embolic problem. It allowed rapid detection and prompt resuscitation to be carried out. Air embolism is a significant and potentially fatal problem in clinical practice. It has been widely reported during neurosurgical, head and neck, and gynaecological procedures, and increasingly during laparoscopic procedures where carbon dioxide or air may be embolized systemically. A discussion of the incidence and pathophysiology as well as a review of the methods of diagnosis and management follows.

Air embolism associated with wounds from a pin-type head-holder. Case report

✓ A case of intraoperative air embolism during posterior fossa surgery performed with the patient in the sitting position is reported. The entry site was through a comminuted fracture and scalp laceration resulting from faulty application of a pin-type head-holder. The possible role played by a large tension pneumocephalus in the ingress of venous air is also discussed. Simple precautions regarding the use of the pin-type head-holder are suggested to lessen the possibility of air embolism through the puncture wounds.

Air embolism from wounds from a pin-type head-holder as a complication of posterior fossa surgery in the sitting position. Case report

✓ The authors report an unusual case of intraoperative air embolism during posterior fossa surgery in the sitting position. The source of air was one of the wounds made by the pin-type skull fixation device. We suggest that the patients should not be released from such device until they are in the supine position.

Detection of venous air embolism. A clinical report using end-tidal carbon dioxide monitoring during neurosurgery

A clinical report on the detection of venous air embolism during neurosurgery is presented. The use of end-tidal CO2 monitoring is described.

Venous air embolism during neurosurgery. A comparison of various methods of detection in man

A comparison of the various methods available for the detection of air embolus has been carried out in patients undergoing posterior fossa exploration in the sitting position. A group of 17 patients (Group A) was comprehensively monitored by a central venous catheter, an infra-red carbon dioxide analyser and a Doppler ultrasonic flow transducer in addition to more traditional clinical methods. Group B (19 patients) was monitored by commonly used clinical methods consisting of continuous palpation of the radial pulse, intermittent blood pressure measurement, the use of an oesophageal stethoscope and the electrocardiograph. In Group A the detection of air embolus varied from 6% using an oesophageal stethoscope to 58% by the Doppler method. In Group B air embolus was diagnosed in 10% of patients. One patient in each group died from air embolus; one patient had a paradoxical embolus to the coronary arteries. It is concluded that comprehensive monitoring for air embolus, including the use of Doppler ultrasound, is an essential part of the management of these patients, for both diagnosis and treatment.

Anesthetic management of posterior fossa surgery in the sitting position

From the surgical aspect, the sitting position gives good surgical access to the operative site, improves venous drainage, gives a better view of facial area for monitoring evoked responses from cranial nerve stimulation and allows for better ventilation. Conversely, the sitting position can present complications such as air emboli, postural hypotension and serious cardiac arrhythmias due to surgical stimulation of cranial nerves and brainstem. This paper presents our clinical experience in 180 neurosurgical procedures on the posterior fossa in the sitting position. The standardized anesthetic technique consisted of narcotic, muscle relaxant, nitrous oxide and controlled ventilation. All patients were monitored with ECG, direct arterial and venous pressure, discontinuous blood gases, and expiratory CO2 and urinary output. Air embolism was detected via Doppler ultrasonic detector and evacuated through a right atrial catheter. Air was detected, visualized and aspirated in 45 cases for an incidence of 25%, with most episodes occurring early in the procedure. In 11 cases (6%) air was detected on closure. There were no deaths in this series. Fifty-eight patients (32%) had a 10-20 mmHg drop in blood pressure on reaching the sitting position, 19 became temporarily hypertensive (10.5%), and the remainder were normotensive. In 46 patients (25%), bradycardia developed during retraction-manipulation-stimulation of structures on or adjacent to brainstem as well as to cranial nerves. Surgical stress also accounted for the 13 patients (7%) having frequent premature ventricular extrasystoles. One case of profound hypotension and another case of virtual cardiac standstill were noted during the use of the bipolar electrocautery at or near the fifth nerve exit from brainstem. Additional hemodynamic data, the physiopathology, diagnosis and treatment of air embolism is discussed.

Evaluation of catheter placement in the treatment of venous air embolism

Venous air embolism is a potential complication of many surgical, therapeutic, and diagnostic procedures. Aspiration of air via a catheter placed in the superior vena cava or right atrium or placed in the pulmonary outflow tract and pulled through the right heart chambers had been advocated for the treatment of venous air embolism. In this study, three catheter positions were analyzed to determine which was best for removal of gas after induction of massive venous air embolism in dogs. In 18 dogs, 9 of which were suspended by their forelegs to simulate the sitting position used in posterior fossa exploration and 9 of which were supine, a Swan-Ganz catheter was placed in the right atrium, right ventricle, or pulmonary artery. A measured amount of air was injected into the left jugular vein and syringe aspiration of the air was attempted through the catheter. In the group with the catheter in the pulmonary artery, aspiration was continuous while the catheter was withdrawn through the right heart chambers. The amount of air aspirated varied widely among the three catheter positions, and no one catheter position proved superior to the other two.

Acute pulmonary edema following venous air embolism during a neurosurgical procedure. Case report

✓ A case of venous air embolism during a procedure in the sitting position is reported in which the patient developed fulminant pulmonary edema within 2 hours of the embolus. Possible cause and effect relationships are discussed.

Paediatric neurosurgical and neuroradiological anaesthesia

Summary Anaesthesia for paediatric neurosurgery and neuroradiology involves all the problems pertinent to

(i) management of infants and small children during procedures which may be relatively protracted;

(ii) avoidance or correction of disturbances of intracranial pressure and cerebral perfusion;

(iii) assessment of patients with depression of consciousness or of other neurological functions;

(iv) adoption of unusual positions for the conduct of procedures with special risks and limited access for the anaesthetist;

(v) providing optimum conditions for radiologists and avoiding radiation risks.

Embolia gasosa em neurocirurgia

São relatados três casos em que ocorreram embolias gasosas e êxito letal em pacientes submetidos à intervenções neurocirúrgicas em posição sentada. As medidas preventivas e os métodos de diagnóstico e tratamento são comentados.