Effects of increased oxygen breathing in a volume controlled hemorrhagic shock outcome model in rats

Cardiac Effects of Hyperoxia During Resuscitation From Hemorrhagic Shock in Swine

Hyperoxia (ventilation with FIO2 = 1.0) has vasoconstrictor properties, in particular in the coronary vascular bed, and, hence, may promote cardiac dysfunction. However, we previously showed that hyperoxia attenuated myocardial injury during resuscitation from hemorrhage in swine with coronary artery disease. Therefore, we tested the hypothesis whether hyperoxia would also mitigate myocardial injury and improve heart function in the absence of chronic cardiovascular comorbidity.After 3 h of hemorrhage (removal of 30% of the calculated blood volume and subsequent titration of mean arterial pressure to 40 mm Hg) 19 anesthetized, mechanically ventilated, and instrumented pigs received FIO2 = 0.3(control) or hyperoxia(FIO2 = 1.0) during the first 24 h. Before, at the end of and every 12 h after shock, hemodynamics, blood gases, metabolism, cytokines, and cardiac function (pulmonary artery thermodilution, left ventricular pressure-conductance catheterization) were recorded. At 48 h, cardiac tissue was harvested for western blotting, immunohistochemistry, and mitochondrial respiration.Except for higher left ventricular end-diastolic pressures at 24 h (hyperoxia 21 (17;24), control 17 (15;18) mm Hg; P = 0.046), hyperoxia affected neither left ventricular function cardiac injury (max. Troponin I at 12 h: hyperoxia:9 (6;23), control:17 (11;24) ng mL; P = 0.395), nor plasma cytokines (except for interleukin-1β: hyperoxia 10 (10;10) and 10 (10;10)/control 14 (10;22), 12 (10;15) pg mL, P = 0.023 and 0.021 at 12 and 24 h, respectively), oxidation and nitrosative stress, and mitochondrial respiration. However, hyperoxia decreased cardiac tissue three-nitrotyrosine formation (P < 0.001) and inducible nitric oxide synthase expression (P = 0.016). Ultimately, survival did not differ significantly either.In conclusion, in contrast to our previous study in swine with coronary artery disease, hyperoxia did not beneficially affect cardiac function or tissue injury in healthy swine, but was devoid of deleterious side effects.

Hyperoxia or Therapeutic Hypothermia During Resuscitation from Non-Lethal Hemorrhagic Shock in Swine

We previously demonstrated beneficial effects of 22 h of hyperoxia following near-lethal porcine hemorrhagic shock, whereas therapeutic hypothermia was detrimental. Therefore, we investigated whether shorter exposure to hyperoxia (12 h) would still improve organ function, and whether 12 h of hypothermia with subsequent rewarming could avoid deleterious effects after less severe hemorrhagic shock.Twenty-seven anesthetized and surgically instrumented pigs underwent 3 h of hemorrhagic shock by removal of 30% of the blood volume and titration of the mean arterial blood pressure (MAP) to 40 mm Hg. Post-shock, pigs were randomly assigned to control, hyperoxia (FIO2 100% for 12 h) or hypothermia group (34°C core temperature for 12 h with subsequent rewarming). Before, at the end of shock, after 12 and 23 h of resuscitation, data sets comprising hemodynamics, blood gases, and parameters of inflammation and organ function were acquired. Postmortem, kidney samples were collected for immunohistochemistry and western blotting.Hyperoxia exerted neither beneficial nor detrimental effects. In contrast, mortality in the hypothermia group was significantly higher compared with controls (67% vs. 11%). Hypothermia impaired circulation (MAP 64 (57;89) mm Hg vs. 104 (98; 114) mm Hg) resulting in metabolic acidosis (lactate 11.0 (6.6;13.6) mmol L vs. 1.0 (0.8;1.5) mmol L) and reduced creatinine clearance (26 (9;61) mL min vs. 77 (52;80) mL min) compared to the control group after 12 h of resuscitation. Impaired kidney function coincided with increased renal 3-nitrotyrosine formation and extravascular albumin accumulation.In conclusion, hyperoxia proved to be safe during resuscitation from hemorrhagic shock. The lacking organ-protective effects of hyperoxia compared to resuscitation from near-lethal hemorrhage suggest a dependence of the effectiveness of hyperoxia from shock severity. In line with our previous report, therapeutic hypothermia (and rewarming) was confirmed to be detrimental most likely due to vascular barrier dysfunction.

Effects of Hyperoxia and Mild Therapeutic Hypothermia During Resuscitation From Porcine Hemorrhagic Shock

OBJECTIVE

Hemorrhagic shock-induced tissue hypoxia induces hyperinflammation, ultimately causing multiple organ failure. Hyperoxia and hypothermia can attenuate tissue hypoxia due to increased oxygen supply and decreased demand, respectively. Therefore, we tested the hypothesis whether mild therapeutic hypothermia and hyperoxia would attenuate postshock hyperinflammation and thereby organ dysfunction.

DESIGN

Prospective, controlled, randomized study.

SETTING

University animal research laboratory.

SUBJECTS

Thirty-six Bretoncelles-Meishan-Willebrand pigs of either gender.

INTERVENTIONS

After 4 hours of hemorrhagic shock (removal of 30% of the blood volume, subsequent titration of mean arterial pressure at 35 mm Hg), anesthetized and instrumented pigs were randomly assigned to "control" (standard resuscitation: retransfusion of shed blood, fluid resuscitation, norepinephrine titrated to maintain mean arterial pressure at preshock values, mechanical ventilation titrated to maintain arterial oxygen saturation > 90%), "hyperoxia" (standard resuscitation, but FIO2, 1.0), "hypothermia" (standard resuscitation, but core temperature 34°C), or "combi" (hyperoxia plus hypothermia) (n = 9 each).

MEASUREMENTS AND MAIN RESULTS

Before, immediately at the end of and 12 and 22 hours after hemorrhagic shock, we measured hemodynamics, blood gases, acid-base status, metabolism, organ function, cytokine production, and coagulation. Postmortem kidney specimen were taken for histological evaluation, immunohistochemistry (nitrotyrosine, cystathionine γ-lyase, activated caspase-3, and extravascular albumin), and immunoblotting (nuclear factor-κB, hypoxia-inducible factor-1α, heme oxygenase-1, inducible nitric oxide synthase, B-cell lymphoma-extra large, and protein expression of the endogenous nuclear factor-κB inhibitor). Although hyperoxia alone attenuated the postshock hyperinflammation and thereby tended to improve visceral organ function, hypothermia and combi treatment had no beneficial effect.

CONCLUSIONS

During resuscitation from near-lethal hemorrhagic shock, hyperoxia attenuated hyperinflammation, and thereby showed a favorable trend toward improved organ function. The lacking efficacy of hypothermia was most likely due to more pronounced barrier dysfunction with vascular leakage-induced circulatory failure.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.

Hyperoxia may be beneficial

The current practice of mechanical ventilation comprises the use of the least inspiratory O2 fraction associated with an arterial O2 tension of 55 to 80 mm Hg or an arterial hemoglobin O2 saturation of 88% to 95%. Early goal-directed therapy for septic shock, however, attempts to balance O2 delivery and demand by optimizing cardiac function and hemoglobin concentration, without making use of hyperoxia. Clearly, it has been well-established for more than a century that long-term exposure to pure O2 results in pulmonary and, under hyperbaric conditions, central nervous O2 toxicity. Nevertheless, several arguments support the use of ventilation with 100% O2 as a supportive measure during the first 12 to 24 hrs of septic shock. In contrast to patients without lung disease undergoing anesthesia, ventilation with 100% O2 does not worsen intrapulmonary shunt under conditions of hyperinflammation, particularly when low tidal volume-high positive end-expiratory pressure ventilation is used. In healthy volunteers and experimental animals, exposure to hyperoxia may cause pulmonary inflammation, enhanced oxidative stress, and tissue apoptosis. This, however, requires long-term exposure or injurious tidal volumes. In contrast, within the timeframe of a perioperative administration, direct O2 toxicity only plays a negligible role. Pure O2 ventilation induces peripheral vasoconstriction and thus may counteract shock-induced hypotension and reduce vasopressor requirements. Furthermore, in experimental animals, a redistribution of cardiac output toward the kidney and the hepato-splanchnic organs was observed. Hyperoxia not only reverses the anesthesia-related impairment of the host defense but also is an antibiotic. In fact, perioperative hyperoxia significantly reduced wound infections, and this effect was directly related to the tissue O2 tension. Therefore, we advocate mechanical ventilation with 100% O2 during the first 12 to 24 hrs of septic shock. However, controlled clinical trials are mandatory to test the safety and efficacy of this approach.

Effects of arterial oxygen content on oxidative stress during resuscitation in a rat hemorrhagic shock model

OBJECTIVE

To examine whether reactive oxygen species (ROS) production is affected by arterial oxygen content (CaO(2)) in attempted resuscitation to restore blood pressure from hemorrhagic shock (HS) or not.

METHODS

Under light anesthesia and spontaneous beating, 16 rats underwent HS for 80min, during which 3.0mL/100g of blood was withdrawn, followed by resuscitation attempt for 70min. At 80min, rats were randomized into a high-CaO(2) group (Group 1, transfusion under fractional inspired oxygen (F(I)O(2)) of 1.0, n=8) or a low-CaO(2) group (Group 2, fluid administration under F(I)O(2) of 0.21, n=8). In each group, either blood or lactate Ringer's (LR) solution was infused to maintain mean arterial pressure ≥75mmHg under each F(I)O(2) concentration. CaO(2), O(2) utilization coefficient (UC) and plasma %CoQ9 were compared between groups.

RESULTS

Mean infused volume for attempted resuscitation was 7.6±1.0mL of blood in Group 1, and 31.4±5.5mL of LR solution in Group 2. At the end of resuscitation, CaO(2) was 18.5±1.2 vol% in Group 1, almost double the 9.1±0.8 vol% in Group 2 (P<0.01). O(2) UC and %CoQ9 in all rats increased from baselines of 0.25±0.12 and 7.6±1.8% to 0.44±0.13 and 9.7±1.8% after resuscitation, respectively (P<0.05 vs. baseline for each), but did not differ significantly between the groups.

CONCLUSION

In a rat HS model, attempted resuscitation to restore blood pressure increased O(2) UC as well as %CoQ9. However, the magnitude of %CoQ9 increase that represents ROS production is not affected by CaO(2) during resuscitation from HS.

Effects of various concentrations of inhaled oxygen on tissue dysoxia, oxidative stress, and survival in a rat hemorrhagic shock model

OBJECTIVE

To test the hypothesis that a fractional inspired oxygen (F(I)O(2)) of 1.0 compared to 0.4 during hemorrhagic shock (HS) and fluid resuscitation (FR): mitigates tissue dysoxia; however, enhances the oxidative stress; therefore, offsets the benefit on survival.

METHODS

Thirty rats underwent: HS for 75min, during which 3.0mL/100g of blood was withdrawn, followed by FR for 75min, during which 1.0mL/100g of shed blood and 3.0mL/100g of crystalloid solution were infused. Ten rats were randomized into one of three F(I)O(2) (0.21 vs. 0.4 vs. 1.0) groups, and observed for survival until 72h in each group. Hemodynamics, liver tissue PO(2) (P(T)O(2)), and, plasma antioxidants levels were also monitored.

RESULTS

Oxygen inhalation increased mean arterial pressure (MAP) and decreased heart rate (HR) during HS and FR. Liver P(T)O(2) was less than 10Torr in all groups throughout HS; while it increased to average 26-35Torr in oxygen groups during FR, it remained at 10Torr with F(I)O(2) 0.21 (P<0.01). MAP, HR, and P(T)O(2) did not differ significantly between oxygen groups. Plasma antioxidants levels did not differ among the three groups. All rats treated with oxygen, but eight of 10 rats with F(I)O(2) 0.21 survived up to 72h (NS).

CONCLUSIONS

Supplemental oxygen does not mitigate tissue dysoxia during HS, but does reduce tissue dysoxia without enhancing oxidative stress during subsequent FR. Increased F(I)O(2) appears to prolong survival. These beneficial effects of supplemental oxygen do not differ between an F(I)O(2) of 0.4 and 1.0.

Neuronal damage in rat brain and spinal cord after cardiac arrest and massive hemorrhagic shock*

OBJECTIVE

Severe global ischemia often results in severe damage to the central nervous system of survivors. Hind-limb paralysis is a common deficit caused by global ischemia. Until recently, most studies of global ischemia of the central nervous system have examined either the brain or spinal cord, but not both. Spinal cord damage specifically after global ischemia has not been studied in detail. Because the exact nature of the neuronal damage to the spinal cord and the differences in neuronal damage between the brain and spinal cord after global ischemia are poorly understood, we developed a new global ischemia model in the rat and specifically studied spinal cord damage after global ischemia. Further, we compared the different forms of neuronal damage between the brain and spinal cord after global ischemia.

DESIGN

Randomized, controlled study using three different global ischemia models in the rat.

SETTING

University research laboratory.

SUBJECTS

Male, adult Sprague-Dawley rats (300 g).

INTERVENTIONS

Animals were divided into three experimental groups, group A (n = 6, survived for 7 days), 12 mins of hemorrhagic shock; group B (n = 6, survived for 7 days), 5 mins of cardiac arrest; or group C (n = 6, each for 6 hrs, 12 hrs, 1 day, 3 days, and 7 days), 7 mins of hemorrhagic shock and 5 mins of cardiac arrest. Motor deficit of the hind limbs was studied 6 hrs to 7 days after resuscitation. Also, nonoperated animals (n = 6) were used as the control. Histologic analysis (hematoxylin and eosin, Fluoro-Jade B, terminal deoxynucleotidyl transferase- mediated dUTP end-labeling [TUNEL], Klüver-Barrera) and ultrastructural analysis using electron microscopy were performed on samples from the CA1 region of the hippocampus and lumbar spinal cord. Demyelination of the white matter of the lumbar spinal cord was analyzed semiquantitatively using Scion Image software.

MAIN RESULTS

No paraplegic animals were observed in either group A or B. All group C animals showed severe hind-limb paralysis. Severe neuronal damage was found in the CA1 region of the hippocampus in all groups, and the state of delayed neuronal cell death was similar among the three groups. Neuronal damage in the lumbar spinal cord was detected only in group C animals, mainly in the dorsal horn and intermediate gray matter. Demyelination was prominent in the ventral and ventrolateral white matter in group C. A significant difference was observed between control and group C rats with Scion Image software. Ultrastructural analysis revealed extensive necrotic cell death in the intermediate gray matter in the lumbar spinal cord in group C rats.

CONCLUSION

The combination in the global ischemia model (i.e., hemorrhagic shock followed by cardiac arrest) caused severe neuronal damage in the central nervous system. Thereby, hind-limb paralysis after global ischemia might result from spinal cord damage. These results suggest that therapeutic strategies for preventing spinal cord injury are necessary when treating patients with severe global ischemia.

Cardiovascular responses to oxygen inhalation after hemorrhage in anesthetized rats: hyperoxic vasoconstriction

Oxygen inhalation is recommended for the initial care of trauma victims. The improved survival seen in early hemorrhage is normally associated with an increase in blood pressure. Although clinical use of oxygen can occur late after hemorrhage, the effects of late administration have not been specifically examined. Anesthetized rats were studied using an isobaric hemorrhage model with target pressures of either 70 or 40 mmHg. At various times after hemorrhage, the feedback control of the blood pressure was stopped and the inspired gas was changed from room air to 100% oxygen. The results show that shortly after hemorrhage to 70 mmHg, oxygen inhalation results in an increase in mean arterial blood pressure of 60 +/- 3 mmHg, which is associated with a large increase in total peripheral resistance from 0.89 +/- 0.05 to 1.25 +/- 0.1 peripheral resistance units. The blood pressure response is essentially unchanged with time, and it is not altered by a 10-min exposure to N(G)-nitro-l-arginine methyl ester. At a target pressure of 40 mmHg, the initial blood pressure response to oxygen is the same, but it gradually decreases as the animal develops a lactic acidosis. We conclude that the therapeutic value of oxygen needs to be separately evaluated for late hemorrhage.

The physiological changes of cumulative hemorrhagic shock in conscious rats

Hemorrhagic shock is a common cause of death in emergency rooms. Current animal models of hemorrhage encounter a major problem that the volume and the rate of blood loss cannot be controlled. In addition, the use of anesthesia obscures physiological responses. Our experiments were designed to establish an animal model based on the clinical situation for studying hemorrhagic shock. Hemorrhagic shock was induced by withdrawing blood from a femoral arterial catheter. The blood volume withdrawn was 40% of the total blood volume for group 1 and 30% for group 2 and 3. Group 3 was anesthetized with sodium pentobarbital (25 mg/kg, i.v.) at the beginning of blood withdrawal. Our data showed that the survival rate was 87.5% at 48 h in the conscious group and 0% at 9 h in anesthetic group after hemorrhage. The levels of mean arterial pressure, heart rate, white blood count, TNF-alpha, IL1-beta, CPK, and LDH after blood withdrawal in the anesthetic group were generally lower than those in conscious groups. These results indicated that anesthetics significantly affected the physiology of experimental animals. The conscious, unrestrained and cumulative volume-controlled hemorrhagic shock model was a good experimental model to investigate the physical phenomenon without anesthetic interfernce.

HYPEROXIC VENTILATION REDUCES SIX-HOUR MORTALITY AFTER PARTIAL FLUID RESUSCITATION FROM HEMORRHAGIC SHOCK

Ventilation with 100% oxygen (Fio(2) 1.0; hyperoxic ventilation; HV) as an alternative to red blood cell transfusion enables survival in otherwise lethal normovolemic anemia. The aim of the present study was to investigate whether HV as a supplement to fluid infusion therapy could also restore adequate tissue oxygenation and prevent death in otherwise lethal hemorrhagic shock. In 14 anesthetized pigs ventilated on room air (Fio(2) 0.21), hemorrhagic shock was induced by controlled withdrawal of blood (target mean arterial pressure 35-40 mmHg) and maintained for 1 h. Subsequently, the animals were partially fluid-resuscitated (i.e., replacement of lost plasma volume) either with hydroxyethyl starch (6% HES, 200/0.5) alone (G 0.21) or with HES supplemented by HV (G 1.0). After completion of partial fluid resuscitation, all animals were followed up for the next 6 h. Five of seven animals of G 0.21 died within the 6-h observation period (i.e., 6-h mortality 71%). Death was preceded by a continuous increase of the serum concentrations of arterial lactate and persistent tissue hypoxia. In contrast to that, all animals of G 1.0 survived the 6-h observation period without lactic acidosis and with improved tissue oxygenation (i.e., 6-h mortality 0%; G 0.21 versus G 1.0 P < 0.05). In anesthetized pigs submitted to lethal hemorrhagic shock, the supplementation of partial fluid resuscitation with HV improved tissue oxygenation and enabled survival for 6 h.

Extending the golden hour of hemorrhagic shock tolerance with oxygen plus hypothermia in awake rats. An exploratory study

In a previous study of volume-controlled hemorrhagic shock (HS) in awake rats, without fluid resuscitation, either breathing of 100% oxygen or moderate hypothermia while breathing air, increased survival time. We hypothesized that combining oxygen and hypothermia can maximally extend the "golden hour" of HS from which resuscitation can be successful in terms of survival rate. Rats were prepared under light general anesthesia, breathing spontaneously via face mask, and then awakened for 2 h. Then, 3.25 ml arterial blood/100 g were withdrawn over 20 min. At the end of HS of 30, 60, 90 or 180 min duration, the shed blood was reinfused. Breathing was spontaneous. Survival endpoint was 24 h or earlier death. HS of 30 or 60 min was used for preliminary experiments; HS of 90 or 180 min for 35 definitive experiments. Control groups A-1 and B-1 had normothermia (rectal temperature 37.5 degrees C) and were breathing air. Treatment groups A-2 and B-2 had total body surface cooling during HS to rectal temperature 32 degrees C and were breathing 100% O(2). Arterial pressure during HS was higher in the hypothermia-O(2) groups. With HS of 90 min, in the normothermia-air group A-1 (n=10), none of the 10 rats survived to 3 h; while in the hypothermia-O(2) group A-2 (n=5), all rats survived to 24 h (P<0.001). With HS of 180 min, in the normothermia-air group B-1 (n=10), three of 10 rats survived to 3 h and 24 h (hypotension during HS in these three survivors was less severe than in the non-survivors); and in the hypothermia-O(2) group B-2 (n=10) all 10 rats survived to 24 h (P<0.003). We conclude that moderate hypothermia (32 degrees C) plus 100% oxygen inhalation during volume-controlled HS in awake rats mitigates hypotension and increases the chance of survival. It enables survival even after 3 h of moderate HS.

Prolonged general anesthesia in MR studies of rats

RATIONALE AND OBJECTIVES

Magnetic resonance (MR) imaging of laboratory animals may require general anesthesia to minimize body movements over many hours. The anesthetization technique should allow physiologic parameters to remain as close to normal as possible, permit fast recovery, allow safe, repeated use, and avoid attachment of ferrous metal components to the animal. The purpose of this study was to evaluate an anesthetization technique that was developed to meet each of these qualifications.

MATERIALS AND METHODS

In 15 rats (280-483-g body weight), general anesthesia was induced (with intramuscular ketamine hydrochloride, xylazine hydrochloride, acepromazine maleate, and atropine), a tail vein catheter was inserted, and preimaging surgical procedures were performed. A face mask was applied, the animal was positioned in a dorsal recumbent position on an acrylic board, and an isothermal heating pad was placed on the ventral aspect of the abdominal wall. The rat, on the board, was then inserted into a trough that contained a custom-built, linearly polarized birdcage head coil and placed in the bore of a 4.7-T horizontal-bore magnet. The face mask was connected to a non-rebreathing gaseous anesthetic system, and anesthesia was maintained with 1.5-2.0 L/min oxygen and 0.25%-1.50% isoflurane. Oxygen saturation, heart rate, and rectal temperature were continuously monitored.

RESULTS

The duration of intramuscular anesthesia was 110 minutes +/- 12, and the duration of gaseous anesthesia was 106 minutes +/- 43. The monitoring equipment permitted display of vital signs.

CONCLUSION

The method appeared safe, was easy to perform, maintained a stable physiologic state for the parameters monitored, and could be used for repeated anesthesia in the same animal.