Critical haemoglobin concentration in anaesthetized dogs: comparison of two plasma substitutes

Abstract

We have explored systemic and regional tolerance to haemodilution during anaesthesia with two different synthetic colloids. Eighteen dogs undergoing mechanical ventilation during anaesthesia with ketamine were submitted to progressive normovolaemic haemodilution with either gelatin (GEL; n = 9) or hydroxyethylstarch (HES; n = 9) administered on a 1:1 ratio. Systemic oxygen delivery was calculated from measurement of thermodilution cardiac output and arterial oxygen content, while systemic oxygen consumption was determined from expired gas analysis. Mesenteric oxygen delivery and consumption were determined using ultrasonic flow measurements, and arterial and mesenteric venous oxygen contents. The critical haemoglobin concentration (i.e. the haemoglobin value below which oxygen consumption becomes oxygen delivery dependent) was mean 3.6 (SD 0.8) g dl-1 in the GEL and 3.5 (1.5) g dl-1 in the HES group. The mesenteric critical oxygen extraction ratio (O2ER) (GEL 50.1 (12.1)%; HES 48.5 (13.4)%) was significant lower than the systemic critical O2ER (GEL 66.1 (8.4)%; HES 67.7 (7.1)%). There were no significant differences between the GEL and HES groups for any of these variables, or in the amount of colloid administered. During the study, oxygen delivery decreased almost linearly with reduction in haemoglobin, indicating a lack of cardiac output response to anaemia during ketamine anaesthesia.

NT-ProBNP and cardiac troponin I in virulent canine babesiosis

“…Several animal studies have indicated that at a hematocrit of 0.1-0.15-l/l tissue oxygenation is maintained (Weisekopf, 1995). The critical value of hemoglobin at which oxygen delivery is equal to oxygen utilization has been shown to occur at a hematocrit of approximately 10% (van der Linden et al, 1998). Below these levels of critical oxygen delivery, signs of circulatory collapse and shock develop.…”

Buffer capacity of 4% succinylated gelatin does not provide any advantages over acidic 6% hydroxyethyl starch 130/0.4 for acid-base balance during experimental mixed acidaemia in a porcine model

“…The latter was in confirmation with the findings of Van der Linden and colleagues who explored systemic tolerance to haemodilution in dogs during anaesthesia comparing the two colloids 3% modified gelatin and 6% HES 200/0.5. In their dog experiments, the DO 2 decreased almost linearly with the reduction of Hb concentration [15]. Furthermore, in a former study on the impact of colloids on the biocompatibility of CVVH, we already found that GEL infusion leads to a decrease in red blood cell counts in healthy pigs [6].…”

Acute Normovolemic Hemodilution in Cardiac Surgery

“…This so-called "critical" hemoglobin value has been demonstrated in several experimental studies. 17,18 Van Woerkens et al studied a Jehovah's Witness patient who died from extreme hemodilution and they observed a critical hemoglobin concentration of 4 g/dL. 19 The efficacy of the mechanisms preserving tissue O 2 delivery when the O 2 carrying capacity of the blood is reduced depends primarily on the maintenance of an adequate circulating blood volume.…”