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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