Negative pressure [Neurosurgery Wiki]

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====== Negative pressure ======

A negative value of a [[pressure]] variable.

[[Air embolism]] is a potentially fatal [[complication]] of any [[operation]] when an opening to [[air]] occurs in a non-collapsible vein (e.g. [[diploic vein]] or a [[dural sinus]]) when there is a negative pressure in the [[vein]] (e.g. when the [[head]] is elevated above the [[heart]])
((Grady MS, Bedford RF, Park TS. Changes in Superior Sagittal Sinus Pressure in Children with Head Elevation, Jugular Venous Compression, and PEEP. J Neurosurg. 1986; 65:199–202)).

[[Air]] is entrained in the [[vein]] and can become trapped in the right atrium of the heart, which may impair venous return, causing [[hypotension]]. May also produce cardiac arrhythmias. Paradoxical [[air embolism]] can occur in the presence of a patent [[foramen ovale]]
((Black S, Cucchiara RF, Nishimura RA, et al. Parameters Affecting Occurrence of Paradoxical Air Embolism. Anesthesiology. 1989; 71:235–241)) 
or pulmonary AV fistula, and may produce ischemic [[cerebral infarction]].

Greater negative pressures occur in the [[sitting position]] due to the extreme elevation of the head, but AE can occur in any operation with the head elevated higher than the heart. Incidence: a wide range has been quoted in the literature, and depends on the monitoring method used: ≈ 7–25% incidence with the sitting position using Doppler monitoring is an estimate
((Standefer MS, Bay JW, Trusso R. The Sitting Position in Neurosurgery. Neurosurgery. 1984; 14:649–658)).

[[Negative pressure wound therapy]]