FiO2 Group Research Articles

Effects of oxygen concentration and exposure time on cultured human airway epithelial cells

To distinguish the direct effects of oxygen dose and exposure time on human airway epithelial cells. We hypothesized that progressive oxygen exposure would induce cell dysfunction and inflammation in a dose-dependent manner. Interventional laboratory study. An academic medical research facility in the northeastern United States. Calu-3 human airway epithelial cell culture. Cells were cultured at a gas-liquid interface with the cells fed basolaterally with medium and grown to full confluence. The apical surfaces were then exposed to gas containing 21%, 40%, 60%, or 80% oxygen, 5% CO2, and balance nitrogen for 24 or 72 hrs. The effects of oxygen concentration and time-induced cellular change were examined by measuring transepithelial resistance of monolayers, cell viability by trypan blue exclusion, basolateral lactate concentration, histology of monolayer cross-sections, and cytospin slides, plus interleukin (IL)-6 and IL-8 secretion in apical surface fluid. Transepithelial resistance decreased in a dose- and time-dependent manner (p < .001), whereas cell viability was reduced only at 72 hrs and in all hyperoxic groups (p < .05). IL-6 secretion was elevated in all hyperoxic groups at 24 hrs (p < .001), and both IL-6 and IL-8 levels were greater in the 40% FiO2 group compared with all other groups at 72 hrs (p < .01). In this model, airway epithelial cells demonstrate profound concentration and time-dependent responses to hyperoxic exposure with respect to cell physiology, viability, histology, and secretion of inflammatory mediators. This model might be a valuable tool for preliminary analysis of potentially protective therapies against hyperoxia-induced airway epithelial injury.

Hyperoxia to Reduce Surgical Site Infection?

Hospital General Universitario de Elche, Elche, Alicante, Spain. gtorcam@hotmail.comI read with interest the review article of Dr. Mauermann and Dr. Nemergut1about the anesthesiologist's role in preventing surgical site infection (SSI).The authors deal with hypothermia and write, “The incidence of SSI was 5.8% in the normothermic group and 18.8% in the hypothermic group. The patients who developed SSIs required hospital stays nearly 1 week longer than those who did not develop a SSI, indicating that these were clinically significant complications ” (italics added).They also review the role of hyperoxia to reduce SSI and write, “Both of these studies found statistically significant reductions in the rates of SSIs in the 0.8 fraction of inspired oxygen (Fio2) group versus the 0.3 Fio2group.” They correctly cite the two studies2,3that found that 80% oxygen could halve surgical site infection versus 30% oxygen; they also cite another study4that found that 80% oxygen increased surgical site infection versus 35%. But surprisingly, they do not report whether the impressive reduction in SSI using 80% oxygen found in those two studies reduced clinically significant complications.Greif et al. 2report a 54% relative risk reduction of SSI using 80% versus 30% oxygen. However, patients who received 80% oxygen had 12.2 days of hospitalization versus 11.9 days among those who received 30% oxygen. Moreover, no difference was found for time to first solid food intake or staples removed.Belda et al. 3report a 39% relative risk reduction of SSI using 80% versus 30% oxygen. Again, consistently with the lack of clinically significant benefit, there was no difference in days of hospitalization, time to solid food intake, or staples removed.The authors conclude that “… high inspired oxygen levels in the perioperative period confers some benefit in reducing the incidence of SSIs.” They do not report, however, the lack of clinically significant benefit.In contrast with these results, Pryor et al. 4did find clinically significant harm among patients who received 80% oxygen (longer hospital stay, higher reoperation rate). This study, the lack of clinical benefit in the other two studies, and the inexistence of data evaluating more moderate oxygen concentrations (45–60%)5should prevent anesthesiologists from accepting 80% as the ideal perioperative oxygen concentration to improve surgery outcomes.Hospital General Universitario de Elche, Elche, Alicante, Spain. gtorcam@hotmail.com

Supplemental Perioperative Oxygen and the Risk of Surgical Wound Infection&lt;SUBTITLE&gt;A Randomized Controlled Trial&lt;/SUBTITLE&gt;

Supplemental perioperative oxygen has been variously reported to halve or double the risk of surgical wound infection. To test the hypothesis that supplemental oxygen reduces infection risk in patients following colorectal surgery. A double-blind, randomized controlled trial of 300 patients aged 18 to 80 years who underwent elective colorectal surgery in 14 Spanish hospitals from March 1, 2003, to October 31, 2004. Wound infections were diagnosed by blinded investigators using Centers for Disease Control and Prevention criteria. Baseline patient characteristics, anesthetic treatment, and potential confounding factors were recorded. Patients were randomly assigned to either 30% or 80% fraction of inspired oxygen (FIO2) intraoperatively and for 6 hours after surgery. Anesthetic treatment and antibiotic administration were standardized. Any surgical site infection (SSI); secondary outcomes included return of bowel function and ability to tolerate solid food, ambulation, suture removal, and duration of hospitalization. A total of 143 patients received 30% perioperative oxygen and 148 received 80% perioperative oxygen. Surgical site infection occurred in 35 patients (24.4%) administered 30% FIO2 and in 22 patients (14.9%) administered 80% FIO2 (P=.04). The risk of SSI was 39% lower in the 80% FIO2 group (relative risk [RR], 0.61; 95% confidence interval [CI], 0.38-0.98) vs the 30% FIO2 group. After adjustment for important covariates, the RR of infection in patients administered supplemental oxygen was 0.46 (95% CI, 0.22-0.95; P = .04). None of the secondary outcomes varied significantly between the 2 treatment groups. Patients receiving supplemental inspired oxygen had a significant reduction in the risk of wound infection. Supplemental oxygen appears to be an effective intervention to reduce SSI in patients undergoing colon or rectal surgery. Trial Registration ClinicalTrials.gov Identifier: NCT00235456.

Hyperoxic ventilation reduces 6-hour mortality at the critical hemoglobin concentration.

Acute normovolemic hemodilution reduces the circulating erythrocyte mass and, thus, the hemoglobin concentration. After extreme acute normovolemic hemodilution to the critical hemoglobin concentration (Hbcrit), oxygen demand of the tissues is no longer met by oxygen supply, and death occurs with increasing oxygen debt. The aim of the current study was to investigate whether ventilation with 100% oxygen (fraction of inspired oxygen [FiO2] = 1.0; hyperoxic ventilation) initiated at Hbcrit could restore adequate tissue oxygenation and prevent death. Fourteen anesthetized pigs ventilated with room air (FiO2 = 0.21) were hemodiluted by exchange of whole blood for 6% hydroxyethyl starch (200,000:0.5) until the individual Hbcrit was reached. Hbcrit was defined as the onset of oxygen supply dependency of oxygen consumption and was identified with indirect calorimetry. For the next 6 h, animals were either ventilated with an FiO2 of 0.21 (n = 7) or an FiO2 of 1.0 (n = 7). All animals in the 0.21 FiO2 group died within the first 3 h at Hbcrit (i.e., 6-h mortality 100%). Death was preceded by an increase of serum concentrations of lactate and catecholamines. In contrast to that, six of the seven animals of the 1.0 FiO2 group survived the complete 6-h observation period without lactacidosis and increased serum catecholamines (i.e., 6-h mortality 14%; FiO2 0.21 vs. FiO2 1.0, P < or = 0.05). After 6 h at Hbcrit, the FiO2 was reduced from 1.0 to 0.21, and five of the six animals died within the next 3 h. In anesthetized pigs submitted to lethal anemia, hyperoxic ventilation enabled survival for 6 h without signs of circulatory failure.

Effect of changes in oscillatory amplitude on Paco2 and Pao2 during high frequency oscillatory ventilation

AIMSTo describe the relation between oscillatory amplitude changes and arterial blood gas (ABG) changes in preterm infants receiving high frequency oscillatory ventilation, using a multiparameter intra-arterial sensor (MPIAS).METHODSContinuous MPIAS ABG...

Idiopathic pulmonary fibrosis and anesthesia: The possible risk of oxygen administration

We studied the effects of a low oxygen concentration (less than 50%) during the induction of and the emergence from general anesthesia on the postoperative course of patients with idiopathic pulmonary fibrosis (IPF). Fifteen of 30 patients who had open lung biopsies between May 1990 and March 1994 were anesthetized with a low FIO2 (<0.50) (Group A), while the other 15 patients received 100% oxygen (Group B). To evaluate the postoperative state, we used the ratio of the postoperative to the preoperative serum level of lactate dehydrogenase (post/pre LDH) and the number of days oxygen assistance was needed after operation. In addition, the following risk factors were also considered: age over 60 years, heavy smoking (a smoking index of more than 600), and a serum level of preoperative LDH higher than 400IU/I. The post/pre LDH was similar in the two groups (Group A 1.060±0.148; Group B 1.079±0.177, not significant). Group A patients needed fewer days of oxygen assistance after operation than did Group B patients (5.6±4.1vs 12.8±12.3;P=0.0426). The number of days using oxygen assistance after operation was: in the elderly, 5.0±1.7 in Group A, 11.8±2.0 in Group B (P=0.0236); in heavy smokers, 5.2±1.2 in Group A, 11.5±2.2 in Group B (P=0.0383); and in the high LDH groups, 4.7±1.1 in Group A, 19.0±7.5 in Group B (P=0.0483). We thus conclude that even such a short exposure to highly concentrated oxygen may affect the postoperative course. Therefore, anesthesia with low oxygen inhalation is recommended because it is simple and poses no risk to the patients.

REDUCTION OF INFARCT SIZE BY OXYGEN INHALATION FOLLOWING ACUTE CORONARY OCCLUSION

This study was carried out in order to determine the effects of the inspiration of O2-enriched air on the size of myocardial infarction. In 15 anesthetized dogs, epicardial electrograms were recorded from 10 to 14 sites on the anterior surface of the left ventricle before and after intermittent occlusion of the left anterior descending coronary artery or one of its major branches. In each dog, one occlusion was carried out while the fraction of inspired oxygen (FIO2) was 0.20 and the other while the FIO2 was 0.40. With an FIO2 of 0.20 the average ST-segment elevation (ST) was 4.0 +/- 0.6 mV (SEM) and the number of sites exhibiting ST-segment elevations exceeding 2 mV (NST) 15 minutes following occlusion was 6.2 +/- 0.7 sites; comparable values following occlusion with an FIO2 of 0.40 were 1.8 +/- 0.4 mV (P less than 0.01) and 2.7 +/- 0.7 sites (P less than 0;01), reflecting reduction in acute myocardial ischemic injury; An FIO2 of 1.0 did not decrease myocardial injury further. In 24 other dogs, occlusion was maintained for 24 hours. In nine dogs in which FIO2 was increased from 0.20 to 0.40 30 minutes after occlusion, myocardial creatine phosphokinase activity (CPK) was less depressed in sites having comparable levels of ST-segment elevation at 15 minutes than in dogs that respired an FIO2 of 0.20 during the entire 24 hours. All (54) sites with ST-segment elevations greater than 3 mV in the 0.20 FIO2 group showed early signs of myocardial infarction, while only 49% of such specimens showed infarction in the 0.40 FIO2 group. Thus it is concluded that 0.40 FIO2 following an experimental coronary artery occusion decreases acute ischemic injury and reduces the eventual development of necrosis, as evaluated by enzymatic and histological techniques.