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Query: UMLS:C0242706 (hyperoxia)
5,219 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study was designed to compare the effect of intraoperative administration of 100% oxygen (F1O2 = 1.0) with 50% O2 (air-O2 mixture, F1O2 = 0.5) on cardiovascular and respiratory parameters in adults undergoing coronary artery surgery. Nineteen patients were assigned to receive either F,O2 = 1.0 (group A) or F1O2 = 0.5 (group B) in a randomized fashion. Anesthesia was induced with fentanyl (15 microg/kg) and diazepam (0.1 to 0.2 mg/kg) and maintained with fentanyl (total dose 50 microg/kg) and isoflurane. A bubble oxygenator (F1O2 = 1.0) was used during cardiopulmonary bypass (CPB) in both groups. Hemodynamic and respiratory profiles were determined at specific intervals prior to incision, following CPB, and postoperatively. Patients ventilated with F1O2 = 0.5 were well oxygenated at measured intraoperative intervals (PaO2 range 90 to 268 mmHg, saturation 95% to 99%), with adequate mixed venous O2 levels (PvO2 range 35 to 65 mmHg, saturation 63% to 89%). Compared with patients receiving F1O2 = 1.0, those receiving F1O2 = 0.5 had significantly greater increases in cardiac index (CI) (mean +/- SEM B: 87% +/- 18% v A: 26% +/- 12%) and stroke index (B: 10% +/- 5% increase vA: 14% +/- 7% decrease), and a larger decrease in peripheral resistance (B: 38% +/- 7% v A: 4% +/- 12%) at postoperative day 1 relative to preincision values (P < 0.05). At postoperative day 1, both groups had an elevated alveolar-to-arterial O2 gradient (A: 55% +/- 19% v B: 48% +/- 17% increase) and shunt fraction (A: 58% +/- 28% v B: 99% +/- 35% increase). Although O2 consumption increased similarly in both groups at postoperative day 1 relative to preincision values (A: 91% +/- 23% v B: 113% +/- 16%), O2 delivery was enhanced more in group B than in group A (67% +/- 17% v 20% +/- 13% increase, respectively, P < 0.05). The data suggest that significant hemodynamic derangements may occur with hyperoxia and that intraoperative administration of 50% O2 may be more appropriate during coronary artery surgery.
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PMID:Effects of inspired oxygen tension on hemodynamics and pulmonary gas exchange in patients undergoing coronary artery surgery. 1717 54

Hyperoxia is present in many anaesthesia protocols used in animal blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. However, little data exist on the influence of hyperoxia on the magnitude of stimulus-induced relative changes in BOLD fMRI signal (DeltaBOLD%). No study to date has investigated these effects in a time-resolved manner, although cerebral vasoregulation offers sites for a time-dependent interaction of hyperoxia and DeltaBOLD%. Here we investigated time-dependent effects of an inspiratory oxygen fraction of 90%. We tightly clamped end tidal CO(2) and body temperature and recorded physiological parameters relevant to rCBF in (fentanyl/isoflurane) anaesthetized monkeys while using visual stimulation to elicit DeltaBOLD%. To clarify whether changes in DeltaBOLD% arose from changes in baseline blood oxygenation or rather altered neuronal or vascular reactivity, we directly measured changes in rCBV using monocrystalline ion oxide nanoparticles (MION) as contrast agent. In visual cortex we found a biphasic modulation of stimulus-induced DeltaBOLD% under hyperoxia: We observed first a significant decrease in DeltaBOLD% by -24% for data averaged over the time interval of 0-180 min post onset of hyperoxia followed by a subsequent recovery to baseline. rCBV response amplitudes were decreased by 21% in the same time interval (0-180 min). In the LGN, we neither found a significant modulation of DeltaBOLD% nor of MION response amplitude. The cerebrovascular effects of hyperoxia may, therefore, be regionally specific and cannot be explained by a deoxyhemoglobin dilution model accounting for plasma oxygenation without assuming altered neuronal activity or altered neurovascular coupling.
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PMID:Time-dependent effects of hyperoxia on the BOLD fMRI signal in primate visual cortex and LGN. 1732 59

The mechanism by which hyperoxia decreases blood flow is still not understood. Hyperoxemia-induced vasoconstriction is known to occur in many organs, including brain and retina, skeletal muscle, and myocardium. Whether this also occurs in skin is unknown. This study was conducted in healthy volunteers exposed intermittently to 100% oxygen (F(I)O(2) 1.0). Perfusion of forearm skin was measured by laser Doppler imaging (LDI). In series 1, it was measured in 7 subjects before, during, and after 15 min of oxygen breathing. In series 2, flow was measured, also during air and O(2) breathing, after perfusion was raised by (a) sympathetic blockade (induced by a topically applied local anesthetic) (n=9) and by (b) current-induced vasodilation (n=8). In normal unperturbed skin, there was no significant change with hyperoxia. When basal perfusion was raised by topical anesthesia or by current, there was also no change in mean perfusion overall with hyperoxia. However, areas with the highest perfusion (upper decile) showed a significant perfusion decrement with hyperoxia (-30% and -20%, respectively; p<0.001). Vasoconstriction with hyperoxia has been demonstrated in human skin. The fact that it is observed only when flow is increased above basal levels and then only in high-flow vessels suggests that cutaneous blood flow control is primarily regulated by variables other than oxygen.
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PMID:Hyperoxia decreases cutaneous blood flow in high-perfusion areas. 1745 53

Cortical spreading depression (CSD), a transient neuronal and glial depolarization that propagates slowly across the cerebral cortex, is the putative electrophysiological event underlying migraine aura. It negatively impacts tissue injury during stroke, cerebral contusion and intracranial hemorrhage. Susceptibility to CSD has been assessed in several experimental animal models in vivo, such as after topical KCl application or cathodal stimulation. Various combinations of anesthetics and ambient conditions have been used by different laboratories making comparisons problematic and differences in data difficult to reconcile. We systematically studied CSD susceptibility comparing commonly used experimental anesthetics (isoflurane, alpha-chloralose, and urethane) with or without N(2)O or normobaric hyperoxia (100% O(2) inhalation). The frequency of evoked CSDs, and their propagation speed, duration, and amplitude were recorded during 2 h topical KCl (1 M) application. We found that N(2)O reduced CSD frequency when combined with isoflurane or urethane, but not alpha-chloralose; N(2)O also decreased CSD propagation speed and duration. Urethane anesthesia was associated with the highest CSD frequency that was comparable to pentobarbital. Inhalation of 100% O(2) did not alter CSD frequency, propagation speed or duration in combination with any of the anesthetics tested. Our data show anesthetic modulation of CSD susceptibility in an experimental model of human disease, underscoring the importance of proper study design for hypothesis testing as well as for comparing results between studies.
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PMID:The impact of anesthetics and hyperoxia on cortical spreading depression. 1850 48

Anesthesia may be an important factor in maximizing the success of microsurgery by controlling the hemodynamics and the regional blood flow. The intraanesthetic basic goal is to maintain an optimal blood flow for the vascularized free flap by: increasing the circulatory blood flow, maintaining a normal body temperature to avoid peripheral vasoconstriction, reducing vasoconstriction resulted from pain, anxiety, hyperventilation, or some drugs, treating hypotension caused by extensive sympathetic block and low cardiac output. A hyperdynamic circulation can be obtained by hypervolemic or normovolemic hemodilution and by decrease of systemic vascular resistance. The importance of proper volume replacement has been widely accepted, but the optimal strategy is still open to debate. General anesthesia combined with various types of regional anesthesia is largely preferred for microvascular surgery. Maintenance of homeostasis through avoidance of hyperoxia, hypocapnia, and hypovolemia (all factors that can decrease cardiac output and induce local vasoconstriction) is a well-established perioperative goal. As the ischemia-reperfusion injury could occur, inhalatory anesthetics as sevoflurane (that attenuate the consequences of this process) seem to be the anesthetics of choice.
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PMID:Anesthesia for free vascularized tissue transfer. 1894 83

Based on previous observations in hyperbaric hyperoxia, we hypothesized that normobaric hyperoxia, often used during general anaesthesia and resuscitation, might also induce a neuromuscular excitability. In healthy volunteers, we studied the consequences of a 50 min period of pure oxygen breathing on the neuromuscular conduction time (CT), the amplitude of the compound evoked muscle potential (M-wave), the latency and amplitude of the Hoffman reflex (H reflex) and the electromyographic tonic vibratory response (TVR) of the flexor digitorum superficialis muscle to explore the proprioceptive reflex loop. Hyperoxia-induced oxidative stress was measured by the changes in blood markers of lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and antioxidant response (reduced ascorbic acid, RAA). During hyperoxia, the M-wave amplitude increased, both CT and H reflex latency were shortened, and the H reflex amplitude increased. By contrast, TVR significantly decreased. Concomitantly, an oxidative stress was assessed by increased TBARS and decreased RAA levels. This study shows the existence of dual effects of hyperoxia, which facilitates the muscle membrane excitability, nerve conduction and spinal reflexes, but reduces the gain of the proprioceptive reflex loop. The activation of the group IV muscle afferents by hyperoxia and the resulting oxidative stress might explain the TVR depression.
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PMID:The changes in neuromuscular excitability with normobaric hyperoxia in humans. 1968 94

To investigate whether the established reductions in heart rate and cardiac output with hyperoxia in humans are primary effects or secondary to increases in systemic vascular resistance, we paced the hearts of nine patients with permanent pacemakers at a fixed rate when breathing either medical air (inspired O(2) fraction 0.21) or oxygen (inspired O(2) fraction 0.80) in a randomised, double-blind fashion. A thoracic bio-impedance machine was used to measure heart rate, stroke volume and blood pressure and calculate cardiac index and systemic vascular resistance index. Oxygen caused no change in cardiac index (p = 0.18), stroke index (p = 0.44) or blood pressure (p = 0.52) but caused a small (5.5%) increase in systemic vascular resistance index (p = 0.03). This suggests that hyperoxia has no direct myocardial depressant effects, but that the changes in cardiac output reported in previous studies are secondary to changes in systemic vascular resistance.
Anaesthesia 2010 Feb
PMID:The cardiovascular effects of normobaric hyperoxia in patients with heart rate fixed by permanent pacemaker. 2000 16

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.
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PMID:Hyperoxia may be beneficial. 2116 98

The mechanism of oxygen toxicity for central nervous system and hyperbaric oxygen (HBO) seizure has not been clarified. Noradrenergic cells in the brain may contribute to HBO seizure. In this study, we defined the activation of noradrenergic cells during HBO exposure by c-fos immunohistochemistry. Electroencephalogram electrodes were pre-implanted in all animals under general anesthesia. In HBO seizure animals, HBO was induced with 5 atm of 100% oxygen until manifestation of general tonic convulsion. HBO non-seizure animals were exposed to 25 min of HBO. Control animals were put in the chamber for 120 min without pressurization. All animals were processed for c-fos immunohistochemical staining. All animals in the HBO seizure group showed electrical discharge on EEG. In the immunohistochemistry, c-fos was increased in the A1, A2 and A6 cells of the HBO seizure group, and in the A2 and A6 cells of the HBO non-seizure group, yet was extremely low in all three cell types in the control group. These results suggest the participation of noradrenaline in HBO seizure, which can be explained by the early excitement of A1 cells due to their higher sensitivity to high blood pressure, hyperoxia, or by the post-seizure activation of all noradrenergic cells.
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PMID:The excitement of multiple noradrenergic cell groups in the rat brain related to hyperbaric oxygen seizure. 2170 13

Head injury is one of the major causes of trauma-related morbidity and mortality in all age groups in the United Kingdom, and anaesthetists encounter this problem in many areas of their work. Despite a better understanding of the pathophysiological processes following traumatic brain injury and a wealth of research, there is currently no specific treatment. Outcome remains dependant on basic clinical care: management of the patient's airway with particular attention to preventing hypoxia; avoidance of the extremes of lung ventilation; and the maintenance of adequate cerebral perfusion, in an attempt to avoid exacerbating any secondary injury. Hypertonic fluids show promise in the management of patients with raised intracranial pressure. Computed tomography scanning has had a major impact on the early identification of lesions amenable to surgery, and recent guidelines have rationalised its use in those with less severe injuries. Within critical care, the importance of controlling blood glucose is becoming clearer, along with the potential beneficial effects of hyperoxia. The major improvement in outcome reflects the use of protocols to guide resuscitation, investigation and treatment and the role of specialist neurosciences centres in caring for these patients. Finally, certain groups are now recognised as being at greater risk, in particular the elderly, anticoagulated patient.
Anaesthesia 2011 Nov
PMID:Early hospital care of severe traumatic brain injury. 2195 Jun 89


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