In vivo effects of hypothermia on the microcirculation during extracorporeal circulation.
OBJECTIVE
Induced hypothermia has been shown to be protective during cardiac surgery, but also in traumatic, ischemic, burn, and neurological injury. In previous in vivo animal experiments, we documented increased leukocyte/endothelial (L/E) cell interaction following normothermic extracorporeal blood circulation (ECC). This study was carried out to investigate whether reduced core temperature during ECC affects the damage to the microcirculation as evidenced by leukocyte adherence and edema formation.


METHODS
Intravital fluorescence microscopy was used on the dorsal skinfold chamber preparation in Syrian golden hamsters. ECC was introduced via a micro-rollerpump (1 ml/min) and a 60 cm silicon tube (1mm inner diameter) shunted between the carotid artery and the jugular vein after application of 300IE Heparin/kg per body weight. Experiments were performed in chronically instrumented, awake animals (age 10-14 weeks, weight 65-75 g). Animals of the experimental group were cooled to 18 degrees C body temperature while ECC, followed by a rewarming period (n=7), controls experienced ECC under normothermia (37 degrees C, n=7).


RESULTS
30 min ECC at 18 degrees C resulted in a decrease of rolling and adherent leucocytes (stickers) in postcapillary venules after 1, 4 and 8h compared with the control group (119+/-46 vs. 274+/-113 n/mm2, P<0.05, mean+/-SD; n=7 in each group). Functional capillary density was significantly reduced during hypothermia (80+/-16 vs. 148+/-16 cm/cm2, P<0.05), but restored after rewarming. In contrast, edema formation was markedly increased during hypothermia.


CONCLUSIONS
Hypothermia during ECC significantly reduced L/E cell interaction in the early post-ECC period. Hypothermia markedly reduced microvascular perfusion, but was completely restored upon rewarming. Despite a reduced number of adherent leukocytes, no protection of endothelial barrier function was seen as a consequence of induced hypothermia.
Kamler
Markus
M
Department of Thoracic and Cardiovascular Surgery, West German Heart Center Essen, University Hospital Essen, 45147 Essen, Germany. markus.kamler@uni-essen.de
Goedeke
Jan
J
Pizanis
Nikolaus
N
Milekhin
Vitaliy
V
Schade
Fritz-Ulrich
FU
Jakob
Heinz
H
D000818:Animals; D001160:Arterioles / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D002199:Capillary Permeability / Q000502:physiology; D002448:Cell Adhesion / Q000502:physiology; D006224:Cricetinae; D004487:Edema / Q000503:physiopathology; D042783:Endothelial Cells / Q000502:physiology; D005112:Extracorporeal Circulation / Q000379:methods*; D006400:Hematocrit / Q000379:methods; D006439:Hemodynamics / Q000502:physiology; D007036:Hypothermia, Induced / Q000379:methods*; D007962:Leukocytes / Q000502:physiology; D008297:Male; D008647:Mesocricetus; D008833:Microcirculation / Q000502:physiology*; D008856:Microscopy, Fluorescence / Q000379:methods; D010314:Partial Thromboplastin Time; D011897:Random Allocation; D012867:Skin / Q000098:blood supply