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Biochemical tissue monitoring during hypoxia and reoxygenation
Stephan Klaus1, Matthias Heringlake, Jan Gliemroth
1Department of Anaesthesiology, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany. stephan.klaus@epost.de
Abstract:
Oxygen deficiency during critical illness may cause profound changes in cellular metabolism and subsequent tissue and organ dysfunction. Clinical treatment in these cases targets rapid reoxygenation to avoid a prolonged impaired synthesis of cellular high-energy phosphates (ATP). However, the effect of this therapeutic intervention on tissue metabolism has not been determined yet. Thus the present study was designed to determine the effects of hypoxia and reoxygenation with either room air or 100% oxygen on variables of interstitial metabolism in different tissues using in vivo microdialysis. Twenty-seven adult, male CD-rats (407-487 g; Ivanovas, Kisslegg, Germany) were studied during general anesthesia. Following preparation and randomization, rats were normoventilated for 45 min (FiO(2) 0.21), followed by induction of hypoxia (FiO(2) 0.1, 40 min) and reoxygenated for 50 min either with FiO(2) 1.0 (group 1, n=10) or FiO(2) 0.21 (group 2, n=10). Control animals (n=7) were ventilated with 21% oxygen during the observation period. Additional to invasive haemodynamic parameters, biochemical tissue monitoring was performed using CMA 20 microdialysis probes, inserted into muscle, subcutaneous space, liver, and the peritoneal cavity allowing analyses of lactate and pyruvate at short intervals. Hypoxia induced a significant reduction in mean arterial pressure (MAP) in group 1 and 2 compared with the control group (P<0.05) without any significant differences between both treatment groups. This was accompanied by a significant increase in blood lactate (10.5+/-3.1 mM (group 1) and 12.3+/-4.1 mM (group 2) vs. 1.5+/-0.3 mM (control); P<0.05) and severe metabolic acidosis (base excess (BE): -18.3+/-5 mM (1) and -17.3+/-7 mM (2) vs. -2.6+/-1.8 mM (control), P<0.05). During hypoxia, the interstitial lacate/pyruvate ratio in groups 1 and 2 increased to 455+/-199% (muscle), 468+/-148% (intraperitoneal), 770+/-218% (hepatic) and 855+/-432% (subcutaneous) (P<0.05 vs. control, respectively). No significant inter-organ or inter-group differences in interstitial dialysates were observed in the treatment groups, neither during hypoxia nor during reoxygenation. Our data suggest, that hypoxia induces comparable metabolic alterations in various tissues and that reoxygenation with 100% oxygen is not superior to 21% oxygen in restoring tissue metabolism after critical hypoxia.
Insights
Hypoxia during critical illness causes metabolic changes. Reoxygenation with 100% oxygen or room air showed no difference in restoring tissue metabolism, suggesting room air is sufficient after critical hypoxia.
Area of Science:
- Physiology
- Biochemistry
- Critical Care Medicine
Background:
- Oxygen deficiency (hypoxia) in critical illness leads to cellular dysfunction and impaired energy production (ATP synthesis).
- Rapid reoxygenation is a clinical goal, but its impact on tissue metabolism remains unclear.
- Understanding metabolic responses to hypoxia and reoxygenation is crucial for optimizing critical care interventions.
Purpose of the Study:
- To investigate the effects of hypoxia and subsequent reoxygenation with room air (21% oxygen) versus 100% oxygen on interstitial metabolism.
- To compare the efficacy of different reoxygenation strategies in restoring tissue metabolism.
- To analyze metabolic changes in muscle, subcutaneous tissue, liver, and peritoneal cavity.
Main Methods:
- In vivo microdialysis was used to monitor interstitial lactate and pyruvate levels in rats.
- Rats were subjected to normoventilation, followed by hypoxia (10% oxygen), and then reoxygenated with either 100% oxygen (FiO(2) 1.0) or room air (FiO(2) 0.21).
- Hemodynamic parameters and biochemical tissue monitoring were performed throughout the experiment.
Main Results:
- Hypoxia significantly reduced mean arterial pressure and caused severe metabolic acidosis in both reoxygenation groups compared to controls.
- Interstitial lactate/pyruvate ratios increased significantly in all tissues during hypoxia, indicating impaired cellular metabolism.
- No significant differences in interstitial metabolic markers were observed between the 100% oxygen and room air reoxygenation groups.
Conclusions:
- Hypoxia induces significant and comparable metabolic alterations across various tissues.
- Reoxygenation with 100% oxygen offers no discernible advantage over room air in restoring tissue metabolism following critical hypoxia.
- These findings suggest that standard room air may be adequate for reoxygenation in certain critical care scenarios, potentially simplifying treatment protocols.