Neuromuscular Blockade with Rocuronium Bromide Increases the Tolerance of Acute Normovolemic Anemia in Anesthetized Pigs

Abstract

Background: The patient’s individual anemia tolerance is pivotal when blood transfusions become necessary, but are not feasible for some reason. To date, the effects of neuromuscular blockade (NMB) on anemia tolerance have not been investigated. Methods: 14 anesthetized and mechanically ventilated pigs were randomly assigned to the Roc group (3.78 mg/kg rocuronium bromide followed by continuous infusion of 1 mg/kg/min, n = 7) or to the Sal group (administration of the corresponding volume of normal saline, n = 7). Subsequently, acute normovolemic anemia was induced by simultaneous exchange of whole blood for a 6% hydroxyethyl starch solution (130/0.4) until a sudden decrease of total body O₂ consumption (VO₂) indicated a critical limitation of O₂ transport capacity. The Hb concentration quantified at this time point (Hb_crit) was the primary endpoint of the protocol. Secondary endpoints were parameters of hemodynamics, O₂ transport and tissue oxygenation. Results: Hb_crit was significantly lower in the Roc group (2.4 ± 0.5 vs. 3.2 ± 0.7 g/dl) reflecting increased anemia tolerance. NMB with rocuronium bromide reduced skeletal muscular VO₂ and total body O₂ extraction rate. As the cardiac index increased simultaneously, total body VO₂ only decreased marginally in the Roc group (change of VO₂ relative to baseline –1.7 ± 0.8 vs. 3.2 ± 1.9% in the Sal group, p < 0.05). Conclusion: Deep NMB with rocuronium bromide increases the tolerance of acute normovolemic anemia. The underlying mechanism most likely involves a reduction of skeletal muscular VO₂. During acellular treatment of an acute blood loss, NMB might play an adjuvant role in situations where profound stages of normovolemic anemia have to be tolerated (e.g. bridging an unexpected blood loss until blood products become available for transfusion).

The choice of the intravenous fluid influences the tolerance of acute normovolemic anemia in anesthetized domestic pigs

“…Several authors found Hb crit at values between 1.6 and 3.0 g/dL [10,12,14-21]. In detail, Hb crit was reduced by 1) hypothermia (moderate reduction of body core temperature reduces total body O 2 demand [15]); 2) hyperoxemia (bioavailability of physically dissolved O 2 is excellent in profound anemia [12,16,17]); 3) infusion of norepinephrine (stabilization of coronary perfusion pressure during hemodilution [19]); 4) artificial O 2 carriers (maintenance of arterial oxygen content despite reduced hematocrit [18,22]), and 5) con-tinuous neuromuscular blockade (lowering skeletal muscular O 2 demand [23]).…”

The Limit of Anemia Tolerance during Hyperoxic Ventilation with Pure Oxygen in Anesthetized Domestic Pigs

“…In particular, a reduction of Hb crit could be achieved by hypothermia (moderate reduction of body core temperature reduces total body O 2 demand [18]), infusion of norepinephrine (stabilization of CPP during hemodilution [19]), infusion of artificial O 2 carriers (maintenance of CaO 2 despite reduced hematocrit [20,21]) and continuous NMB (lowering skeletal muscular O 2 demand [22]). …”

Evidence Base for Restrictive Transfusion Triggers in High-Risk Patients

“…In anesthetized pigs, cellular signs of hypoxia in the kidney and skeletal muscle developed at significantly higher Hb concentrations than in the heart, brain, and liver [17]. Last but not least, anesthetic measures such as deep neuromuscular blockade [18], application of norepinephrine to treat severe arterial hypotension [19], and induction of hypothermia [20] can increase anemia tolerance. From a physiologic point of view, anemia tolerance thus is quite remarkable.…”