Effects of hypercapnia on BP in hypoalbuminemic and nagase analbuminemic rats

Study objective: To determine if animals with abnormally low albumin levels are more susceptible to the effects of hypercapnia on BP compared to normal animals. Design: Prospective, controlled laboratory experiment. Setting: University research laboratory. Animals: Eighteen male Sprague-Dawley rats: 6 rats 10 to 12 weeks old (young Sprague-Dawley [YSD]), 6 rats 6 to 9 months old (old Sprague-Dawley [OSD]), and 6 rats 10 to 12 weeks old (Nagase analbuminemic mutant Sprague-Dawley [NAR]). Methods: Under general anesthesia and paralysis, we varied the PaCO2 by changing the respiratory rate on mechanical ventilation. Mean arterial pressure (MAP) was monitored in a continuous fashion. We obtained arterial blood for blood gas and electrolyte analysis, and nitric oxide (NO) production. Results: OSD rats had reduced serum albumin, while NAB rats were analbuminemic. Although NAB animals had a decreased buffer capacity compared to age-matched control animals (0.010 vs 0.013, p < 0.05), the MAP decreased in an identical fashion in all three groups. NO production increased with hypercapnia but was similar in all three groups. However, NAB rats had consistently higher plasma strong ion gap (2.8 to 4.1 mEq/L greater) compared to either YSD or OSD rats (p < 0.01), and baseline strong ion difference (mean +/- SD) was significantly lower in NAB rats (28.7 +/- 2.1 mEq/L) compared to either YSD rats (33.0 +/- 5.1 mEq/L) or OSD rats (31.2 +/- 5.1 mEq/L) [p < 0.05]. Conclusions: These findings suggest that analbuminemic or hypoalbuminemic rats are not more susceptible to hypercapnia-induced hemodynamic instability. Baseline values for apparent strong ion difference are lower in NA rats consistent with a reduced buffer base resulting from analbuminemia.