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The Cardiac Function in the Beach Chair Position under General Anesthesia

Arthroscopic or open shoulder surgeries are often performed in the beach chair position (BCP) or the lateral decubitus position. Regional or general anesthesia may be utilized in conjunction with the BCP; however, under general anesthesia, the BCP is associated with an increased risk of neurological complications, including stroke, spinal cord ischemia, and transient loss of vision. The pathophysiology of these events has not been completely determined, but it has been suggested to be related to cerebral or upper spinal cord hypoperfusion due to improper blood pressure (BP) management. Then, the systemic arterial blood pressure (BP) must be increased to prevent cerebral hypoperfusion. However, it is not clear how the cardiac function is affected when BP is increased to maintain cerebral perfusion pressure in anesthetized patients.

In this study, an analysis was performed using the data from 13 patients. The authors prepared a parallel circuit using a FloTrac Sensor transducer and an arterial BP transducer. Following the transfer of the patient to the BCP under general anesthesia, the FloTrac Sensor transducer was placed at the level of the fourth intercostal space, the arterial BP transducer was placed at the external auditory meatus level. Then they selected two points before surgery (120 s apart), during which the mean arterial BP (mABP) at the level of the brain was stable and at which the values in the supine position and the BCP were within 5 mmHg. 

The results demonstrated that while the patients were in the supine position, the mean mABP at the mid-axillary level was 65.7 mmHg. In the BCP, the mean mABP was 66.5 mmHg at the external auditory meatus and 80.7 mmHg at the fourth intercostal space. The cardiac index changed from 2.2 (supine position) to 2.5 l/min/m2 (BCP). The stroke volume index was significantly increased from 35.8 to 42.3 ml/m2 (P = 0.003). The heart rate changed from 63.0 to 58.6 beats/min. The stroke volume variation was significantly decreased from 12.4% to 8.8% (P = 0.024). 

In conclusion, it is important to maintain the cerebral blood flow when a patient is in the BCP. And in order to ensure patient safety, close attention should be paid to the systemic cardiovascular changes that occur when the BP is increased. Besides, further studies are needed to determine optimal method for maintaining the BP that avoids both cerebral desaturation and the over-loading to the heart in anesthetized patients in the BCP.

Article by Kumiko Tanabe, et al, from Gifu University Graduate School of Medicine, Gifu, Japan.

Full access: http://mrw.so/2UN9JG
Image by priyank patel, from Flickr-cc.

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