Intracerebral laser Doppler blood flow measurements compared to blood flow in porcine internal carotid artery

Revised resuscitation guidelines: Adrenaline versus adrenaline/vasopressin in a pig model of cardiopulmonary resuscitation—A randomised, controlled trial

BACKGROUND

Synergistic effects of adrenaline (epinephrine) and vasopressin may be beneficial during cardiopulmonary resuscitation. However, it is unknown whether either adrenaline alone or an alternating administration of adrenaline and vasopressin is better for restoring vital organ perfusion following basic life support (BLS) according to the revised algorithm with a compression-to-ventilation (c/v) ratio of 30:2.

MATERIAL AND METHODS

After 4min of ventricular fibrillation, and 6min of BLS with a c/v ratio of 30:2, 16 pigs were randomised to receive either 45microg/kg adrenaline, or alternating 45microg/kg adrenaline and 0.4U/kg vasopressin, respectively.

RESULTS

Coronary perfusion pressure (mean+/-S.D.) 20 and 25min after cardiac arrest was 7+/-4 and 5+/-3mm Hg after adrenaline, and 25+/-2 and 14+/-3mm Hg after adrenaline/vasopressin (p<0.001 and <0.01 versus adrenaline), respectively. Cerebral perfusion pressure was 23+/-7 and 19+/-9mm Hg after adrenaline, and 40+/-10 and 33+/-7mm Hg after adrenaline/vasopressin (p<0.001 and <0.01 versus adrenaline), and cerebral blood flow was 30+/-10 and 27+/-11% of baseline after adrenaline, and 65+/-40 and 50+/-31% of baseline after adrenaline/vasopressin (p<0.05 versus adrenaline), respectively. Return of spontaneous circulation (ROSC) did not differ significantly between the adrenaline group (0/8) and the adrenaline/vasopressin group (3/8).

CONCLUSION

Adrenaline/vasopressin resulted in higher coronary and cerebral perfusion pressures, and cerebral blood flow, while ROSC was comparable.

Post-hypoxic hypoperfusion is associated with suppression of cerebral metabolism and increased tissue oxygenation in near-term fetal sheep

Secondary cerebral hypoperfusion is common following perinatal hypoxia-ischaemia. However, it remains unclear whether this represents a true failure to provide sufficient oxygen and nutrients to tissues, or whether it is simply a consequence of reduced cerebral metabolic demand. We therefore examined the hypothesis that cerebral oxygenation would be reduced during hypoperfusion after severe asphyxia, and further, that the greater neural injury associated with blockade of the adenosine A(1) receptor during the insult would be associated with greater hypoperfusion and deoxygenation. Sixteen near-term fetal sheep received either vehicle or 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) for 1 h, followed by 10 min of severe asphyxia induced by complete occlusion of the umbilical cord. Infusions were discontinued at the end of the occlusion and data were analysed for the following 8 h. A transient, secondary fall in carotid artery blood flow and laser Doppler flow was seen from approximately 1-4 h after occlusion (P < 0.001), with no significant differences between vehicle and DPCPX. Changes in laser Doppler blood flow were highly correlated with carotid blood flow (r(2)= 0.81, P < 0.001). Cortical metabolism was suppressed, reaching a nadir 1 h after occlusion and then resolving. Cortical tissue P(O(2)) was significantly increased at 1, 2 and 3 h after occlusion compared to baseline, and inversely correlated with carotid blood flow (r(2)= 0.69, P < 0.001). In conclusion, contrary to our initial hypothesis, delayed posthypoxic hypoperfusion was associated with suppression of cerebral metabolism and increased tissue P(O(2)), and was not significantly affected by preceding adenosine A1 blockade. These data suggest that posthypoxic hypoperfusion is actively mediated and reflects suppressed cerebral metabolism.

Cerebral nitric oxide concentration and microcirculation during hypercapnia, hypoxia, and high intracranial pressure in pigs

Intracerebral nitric oxide (NO) concentration was measured to establish the technique and to investigate the response of the NO concentration to CO(2)variations, hypoxia, and reduced cerebral perfusion pressure. An intracerebral nitric oxide sensor was used in 10 pigs. Cerebral microcirculation was measured by laser Doppler flowmetry. Five pigs received 40 mg/kg nitro-1-arginine methyl ester (L-NAME). Baseline NO concentration was 246 +/- 42 nM. Hypercapnia increased cerebral microcirculation (P< 0.05) and NO concentration (P< 0.05). Hypoxia decreased NO concentration (P< 0.05). During high intracranial pressure, cerebral microcirculation decreased (P< 0.05) before the NO concentration decreased (P< 0.05), and after normalisation of the intracranial pressure the NO concentration increased, but more slowly than the cerebral microcirculation. L-NAME caused a decrease in cerebral microcirculation (P< 0.05) and NO concentration (P< 0.05) to a new steady state, and L-NAME attenuated the changes in NO concentration after hypoxia (P< 0.05) and high intracranial pressure (P< 0.05). In conclusion, the electrochemical sensor appears to reliably detect changes in localised intracerebral NO concentration and seems to be a promising tool for direct measurement of this chemically unstable substance.