Anaesthesia for Neurosurgery in the Sitting Position: A Practical Approach

Abstract

Neurosurgery in the sitting position offers advantages for certain operations. However, the approach is associated with potential complications, in particular venous air embolism. As the venous pressure at wound level is usually negative, air can be entrained. This air may follow any of four pathways. Most commonly it passes through the right heart into the pulmonary circulation, diffuses through the alveolar-capillary membrane and appears in expelled gas. It may pass through a pulmonary-systemic shunt such as a probe patent foramen ovale (paradoxical air embolism); it may collect at the superior vena cava-right atrial junction. Rarely it may traverse through lung capillaries into the systemic circulation. Many monitors, such as the precordial Doppler, capnography, pulmonary artery catheter, transoesophageal echocardiography are useful for venous air embolism detection, with transoesophageal echocardiography being today's gold standard. Various manoeuvres, including neck compression and volume loading, are also useful in reducing the incidence of venous air embolism. Volume loading, in particular, is very helpful as it reduces the risk of hypotension. Other particular concerns to the anaesthetist are airway management, avoidance of pressure injuries, and the risk of pneumocephalus, oral trauma, and quadriplegia. Newer anaesthetic agents have made the choice of anaesthetic technique easier. An appreciation of the implications of neurosurgery in the sitting position can make the procedure safer.

Comparative incidence of cardiovascular changes during venous air embolism as detected by transesophageal echocardiography alone or in combination with end tidal carbon dioxide tension monitoring

“…12 However, it has not become widely used in neurosurgery due to the aforementioned reasons. In a survey conducted by the Neuroanesthesia Research Group of the German Society of Anesthesia and Intensive Care Medicine in 1997, it was found that only 38% of all responding hospitals use TEE monitoring for detection of VAE during neurosurgery with the patient in the sitting position.…”

“…11 In addition to the early detection of VAE, TEE is also helpful for the preoperative detection of a patent foramen ovale, for assisting with optimal positioning of a right atrial catheter, and for the detection of air in the left side of the heart. 12 Despite these advantages, TEE has not become a popular monitoring approach for detection of VAE because of its high cost, its invasiveness, and the potential for serious morbidity associated with its use. [13][14][15][16] Moreover, TEE monitoring can fail to detect some VAE incidents.…”

The role of eustachian valve and patent foramen ovale in sudden death

“…23,[39][40][41][42] Although the term decompression illness is used classically for describing decompression disorders with gas bubbles as the initiator, 39 an alternative pathway for venous gas embolism to be transferred to the systemic arterial side consists of an intra-atrial shunt due to an atrial septal defect or a PFO. 40 Also air embolism may occur during neurosurgical operations in the sitting or semi-sitting position [43][44][45][46][47][48] or tracheal extubation in patients with PFO. 49 Although recent case reports have clearly shown that paradoxical brain fat embolism can occur in the setting of long bone fractures and joint arthroplasties in patients who have PFO, [50][51][52] Colonna et al, suggests that large numbers of fat emboli are able to rapidly traverse the pulmonary circulation (in less than 4 h) in the setting of total hip arthroplasty, even in the absence of a PFO.…”

Carbon dioxide field flooding reduces the hemodynamic effects of venous air embolism occurring in the sitting position

“…Transesophageal echocardiography (TEE), analysis of carbon dioxide arterial partial pressure (PaCO 2 ), and capnography (endtidal CO 2 , ETCO 2 ) are the standard systems to directly or indirectly detect air embolism during neurosurgical procedures in the sitting position. However, also this sophisticated monitoring as many other more traditional maneuvers and tricks may not be sufficient once the air emboli entered the venous system [3,5,7,11,19].…”