Phrenic Nerve Injury Following Cardiac Surgery, with Emphasis on the Role of Topical Hypothermia

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Abstract
Phrenic nerve dysfunction that develops after cardiac surgery has generally been attributed to the topical hypothermia used for myocardial preservation and protection. Although studies relying on postoperative radiographic findings to establish the diagnosis reveal an incidence as high as 73%, investigations employing electrophysiological assessment indicate a 10% incidence. Most patients who sustain phrenic injury during cardiac surgery do not suffer major respiratory morbidity; those who do generally recover. In addition to the role of topical hypothermia as a major etiological factor, physical trauma or compromise of the vascular supply to the phrenic nerve and diaphragm may also be important factors. Although a number of measures have been advocated to lower the incidence of the problem, none have been evaluated in a prospective, randomized study using electrophysiological techniques. This review focuses on the incidence, underlying mechanisms, and clinical and electrophysiological recognition of phrenic nerve dysfunction following cardiac surgery.