CAD is a manifestation of AIHA. In CAD, IgM autoantibodies agglutinate erythrocytes in response to low temperatures and simultaneously activate the complement system, leading to extravascular hemolysis as erythrocytes are engulfed by reticuloendothelial cells expressing C3b receptors [1, 2]. Clinical manifestations include anemia due to erythrocyte agglutination and peripheral circulatory failure that can lead to life-threatening thrombotic complications due to microvascular occlusion [3]. It has been postulated that patients with CAD may be at risk for sudden death due to hemolysis or thrombotic events if they become hypothermic during surgery.

Anti-cold agglutinin antibody therapy may be an option to prevent thrombosis in CAD patients. Rituximab, an anti-CD20 monoclonal antibody, is used to suppress B cells that produce cold agglutinin antibody [7], and sutimlimab, an anti-C1s complement antibody, directly suppresses classical complement pathway-mediated hemolysis in patients by inhibiting the cleavage of C1s to C4 [8]. Moreover, plasma exchange may also be effective for red blood cell aggregation by cold agglutinin to remove IgM autoantibodies from plasm a [9]. However, these therapies have side effects of immunosuppression and extracorporeal circulation-induced hemolysis, and the procedure entails risks; it is crucial to consider the suitability of the method on a case-by-case basis.

While several case reports have detailed the anesthetic management of patients with CAD [4,5,6, 10, 11], particularly during cardiac surgery, most emphasize the importance of maintaining body temperature above 37 °C to avoid complications. The use of forced-air warming devices has been shown to be the most effective method of preventing hypothermia [12, 13]. Additionally, brain surgery allows for efficient maintenance of systemic warmth, as forced-air warming devices can cover the entire body. The patient’s core temperature was maintained by elevating the room temperature and employing forced-air warming systems, with no evidence of hemolysis. However, thrombosis occurred at the site of vascular anastomosis. In this case, irrigation with room-temperature saline may have induced anastomotic occlusion due to thrombus formation. This emphasizes the necessity of maintaining both systemic and local irrigation fluids at normothermic levels (37–38 °C).

In abdominal and thoracic surgery, peritoneal and pleural lavages are commonly performed with warmed saline to prevent hypothermia. There are also reports that adjusting the temperature of peritoneal lavage fluid can induce hypothermia [14] and accelerate recovery from hypothermia [15]. On the other hand, saline and buffer solutions used for local lavage of the brain surface during brain surgery are usually administered through an infusion line, so even if they are warmed, the temperature at the brain surface is equivalent to room temperature. In addition, from the perspective of brain protection, the brain surface temperature may be lower than body temperature, so they are often used without warming. Mechanical interruption of blood flow during anastomosis can cause thromboembolism. Although it is difficult to distinguish between CAD-induced and surgically induced thrombus formation, mechanical interruption of blood flow has not caused thrombus formation at the anastomosis site in previous STA-MCA bypass procedures performed at our institution. Therefore, it can be speculated that CAD was the main cause of thrombus formation in this case. However, in cases where there is a risk of thrombus formation when exposed to a low-temperature environment anywhere with blood flow, such as in this case, more careful consideration was required, such as using the brain surface lavage fluid in a warmed state. Furthermore, brain surface temperature monitoring, occasionally used in cases of severe head trauma, may prove beneficial in regulating the temperature of the surgical field to prevent cold agglutination, as observed in this case.