Effects of different inspired oxygen fractions on lipid peroxidation during general anaesthesia for elective Caesarean section

Effects of perioperative oxygen concentration on oxidative stress in adult surgical patients: a systematic review

Background

The fraction of inspired oxygen (FiO₂) administered during general anaesthesia varies widely despite international recommendations to administer FiO₂ 0.8 to all anaesthetised patients to reduce surgical site infections (SSIs). Anaesthetists remain concerned that high FiO₂ administration intraoperatively may increase harm, possibly through increased oxidative damage and inflammation, resulting in more complications and worse outcomes. In previous systematic reviews associations between FiO₂ and SSIs have been inconsistent, but none have examined how FiO₂ affects perioperative oxidative stress. We aimed to address this uncertainty by reviewing the available literature.

Methods

EMBASE, MEDLINE, and Cochrane databases were searched from inception to March 9, 2020 for RCTs comparing higher with lower perioperative FiO₂ and quantifying oxidative stress in adults undergoing noncardiac surgery. Candidate studies were independently screened by two reviewers and references hand-searched. Methodological quality was assessed using the Cochrane Collaboration Risk of Bias tool.

Results

From 19 438 initial results, seven trials (n=422) were included. Four studies reported markers of oxidative stress during Caesarean section (n=328) and three reported oxidative stress during elective colon surgery (n=94). Risk of bias was low (four studies) to moderate (three studies). Pooled results suggested high FiO₂ was associated with greater malondialdehyde, protein-carbonyl concentrations and reduced xanthine oxidase concentrations, together with reduced antioxidant markers such as superoxide dismutase and total sulfhydryl levels although total antioxidant status was unchanged.

Conclusions

Higher FiO₂ may be associated with elevated oxidative stress during surgery. However, limited studies have specifically reported biomarkers of oxidation. Given the current clinical controversy concerning perioperative oxygen therapy, further research is urgently needed in this area.

Anesthesia for Urgent Cesarean Section

Cesarean section (CS) is a common surgical procedure worldwide. The anesthesiologist is responsible, together with obstetrician and neonatologist, for safe perioperative management. A continuum of risk exists for urgent CS. The decision-to-delivery interval is an important audit tool, to ensure international standards are upheld and good outcomes for mother and neonate are achieved. Urgent CS may be performed under either GA or RA, with benefits and risks attributable to each. Specific clinical scenarios require an individualized approach to anesthesia, including hemorrhage, hypertensive disorders, cardiac disease, the difficult airway and fetal compromise. Ongoing training is integral to the provision of safe anesthesia.

Newborn Resuscitation in Settings Without Access to Supplemental Oxygen

Low- and middle-income countries and resource-limited regions are major contributors to perinatal and infant mortality. Oxygen is widely used for resuscitation in high- and middle-income settings. However, oxygen supplementation is not available in resource-limited regions. Oxygen supplementation for resuscitation at birth has adverse effects in human/animal model studies. There has been a change with resultant recommendations for restrictive oxygen use in neonatal resuscitation. Neonatal resuscitation without supplemental oxygen decreases mortality and morbidities. Oxygen in resource-limited settings for neonatal resuscitation is ideal as a backup for selected resuscitations but should not be a limiting factor for implementing basic life-saving efforts.

Oxygen and oxidative stress in the perinatal period

Fetal life evolves in a hypoxic environment. Changes in the oxygen content in utero caused by conditions such as pre-eclampsia or type I diabetes or by oxygen supplementation to the mother lead to increased free radical production and correlate with perinatal outcomes. In the fetal-to-neonatal transition asphyxia is characterized by intermittent periods of hypoxia ischemia that may evolve to hypoxic ischemic encephalopathy associated with neurocognitive, motor, and neurosensorial impairment. Free radicals generated upon reoxygenation may notably increase brain damage. Hence, clinical trials have shown that the use of 100% oxygen given with positive pressure in the airways of the newborn infant during resuscitation causes more oxidative stress than using air, and increases mortality. Preterm infants are endowed with an immature lung and antioxidant system. Clinical stabilization of preterm infants after birth frequently requires positive pressure ventilation with a gas admixture that contains oxygen to achieve a normal heart rate and arterial oxygen saturation. In randomized controlled trials the use high oxygen concentrations (90% to 100%) has caused more oxidative stress and clinical complications that the use of lower oxygen concentrations (30-60%). A correlation between the amount of oxygen received during resuscitation and the level of biomarkers of oxidative stress and clinical outcomes was established. Thus, based on clinical outcomes and analytical results of oxidative stress biomarkers relevant changes were introduced in the resuscitation policies. However, it should be underscored that analysis of oxidative stress biomarkers in biofluids has only been used in experimental and clinical research but not in clinical routine. The complexity of the technical procedures, lack of automation, and cost of these determinations have hindered the routine use of biomarkers in the clinical setting. Overcoming these technical and economical difficulties constitutes a challenge for the immediate future since accurate evaluation of oxidative stress would contribute to improve the quality of care of our neonatal patients.

Controlled moderate hypovolaemia in healthy volunteers is not associated with the development of oxidative stress assessed by plasma F2-isoprostanes and isofurans

Hypovolaemia can be associated with substantial morbidity, particularly when it occurs in the setting of trauma and in patients with comorbid diseases. Hypovolaemia and inflammation such as occur in the setting of trauma and surgery, are associated with systemic oxidative stress and free-radical injury. Free-radical injury that results from hypovolaemia-induced organ reperfusion may further augment inflammatory processes. It is unknown exactly what proportion of free-radical injury is associated with isolated hypovolaemia as opposed to the contribution from inflammation from surgery or trauma. In the first human study of its kind, we exposed 8 adult male volunteers to venesection-induced hypovolaemia in progressive aliquots of 5% of total blood volume until 20% had been removed. This blood was subsequently reinfused. Plasma F2-isoprostanes and isofurans, markers of in vivo lipid oxidation, were measured by gas chromatography-mass spectrometry at each 5% aliquot venesected and at each 5% reinfused. Between baseline and maximal blood loss there was a minor fall in haemoglobin concentration from 143.9g/l to 138.8g/l (p=0.004, 95% CI 2.2, 8.0g/L). No significant change from baseline occurred in the concentrations of either plasma F2-isoprostanes or isofurans during venesection (p=0.116 and p=0.152, respectively) or blood reinfusion (p=0.553 and p=0.736, respectively). We can conclude that in healthy adult volunteers, isolated hypovolaemia to 20% total blood volume loss is not associated with detectable systemic oxidative stress. The free-radical injury identified in surgical and trauma patients may represent the effects of tissue damage and inflammation, with an uncertain contribution from tissue ischemia as may occur with hypovolaemia.

Assessment of fetal antioxidant and oxidant status during different anesthesia techniques for elective cesarean sections

Background:

We aimed to investigate the effects of general, spinal and epidural anesthesia on fetal total antioxidant status (TAS) and total oxidant status (TOS), and oxidative stress index (OSI) during elective cesarean section in this study.

Materials and Methods:

Forty-seven parturients scheduled for elective cesarean section were randomly allocated into three groups: Group spinal (n = 15), group epidural (n = 17), and group general (n = 15), This prospective randomized study was performed in Faculty of Medicine, Turgut Ozal University, Turkey. After the baby was delivered; TAS, TOS levels, and arterial blood gases parameters were analyzed in an umbilical arterial blood sample. OSI values are calculated by a ratio of TOS to the TAS.

Results:

The levels of TAS and TOS in umbilical arterial blood sample were not statistically different among three. However, OSI values were significantly different among the three groups (P = 0.042). Median OSI values is 24 (interquartile range [IQR], 2-37) in group spinal, 19 (IQR, 4-44) in group epidural, and 8 (IQR, 4-36) in group general. There was no significant difference in OSI values in the comparison of group spinal with group general and group epidural, but it was significantly lower in group general when compared with group epidural with Bonferroni correction (P = 0.017). Umbilical cord arterial blood gas values (pH, PaCO₂, PaO₂, SaO₂, HCO₃, and CtO₂), glucose, lactate, and hemoglobin levels were similar in three groups.

Conclusion:

General anesthesia may be more favorable than epidural in those undergoing cesarean section when fetal oxidative status gains importance.

Comparative Evaluation of Remifentanil and Dexmedetomidine in General Anesthesia for Cesarean Delivery

Background

Use of remifentanil and dexmedetomidine in general anesthesia for cesarean section have been described. This study was designed to evaluate the effects of remifentanil and dexmedetomidine on maternal hemodynamics and bispectral index, and neonatal outcomes in elective caesarean delivery.

Material/Methods

Forty-four women undergoing elective cesarean delivery with ASA I or II and term or near-term singleton pregnancies were randomly assigned to receive remifentanil at a loading dose of 2 μg/kg over 10 min followed by a continuous infusion of 2 μg/kg/h until about 6 min before fetal delivery (Group REM), or dexmedetomidine at a loading dose of 0.4 μg/kg over 10 min followed by a continuous infusion of 0.4 μg/kg/h until about 6 min before fetal delivery (Group DEX). Maternal hemodynamics and BIS values were recorded. Neonatal effects were assessed using Apgar scores and umbilical cord blood gas analysis.

Results

Mean arterial pressure (MAP) increased after intubation in both groups, and the change magnitude of the MAP was higher in Group DEX (P<0.05). Patients in Group DEX had a lower BIS value at recovery and consumed less propofol during surgery (P<0.05). The incidences of neonatal resuscitation at 1 min were 81.8% in Group REM and 54.5% in Group DEX (P=0.052). There was no significant difference in either group in Apgar scores at 1 and 5 min and umbilical cord blood gas values.

Conclusions

Both remifentanil and dexmedetomidine are effective to blunt hemodynamic responses to intubation and also seem safe for neonates at the administrated doses, but remifentanil still has the potential to cause neonatal transient respiratory depression.

Extracorporeal life support for massive pulmonary embolism during pregnancy

Massive pulmonary embolism is a leading cause of death during pregnancy. While the prevention of thromboembolic disease during the peripartum period is codified, there is no consensus regarding its treatment. We report two cases of pregnant women who had massive pulmonary embolisms (PE) and shock treated with veno-arterial extracorporeal life support (ECLS) and heparin therapy.

Haemodynamic and oxygenation parameters were rapidly restored. The patients completely recovered and the pregnancies continued. The patients did not develop pulmonary hypertension. ECLS can be considered as a successful treatment option of massive pulmonary embolism during pregnancy.

Current concepts of oxygen therapy in neonates

Use of high oxygen concentrations in treating neonatal illness has been challenged in the past few decades. In the face of evidence suggesting adverse outcomes (both clinical and biochemical) with use of high oxygen concentrations, the current guidelines appear to favour use of the lowest possible concentrations of oxygen for the shortest time to treat ill neonates. Current delivery room guidelines recommend using room air when initiating positive pressure ventilation during resuscitation. Targeting appropriate oxygen saturation when delivering supplemental oxygen, both in the delivery room and neonatal intensive care unit (NICU), are now the new emerging standards in neonatal care. Investments in good quality pulse oximeters and oxygen blenders in neonatal care units is now seen as critical to improve newborn survival.

Effects of sevoflurane and desflurane on oxidative stress during general anesthesia for elective cesarean section

BACKGROUND

Anesthetic agents might considerably influence maternal-fetal oxidative stress and antioxidants during cesarean section (CS). The aim of this study was to investigate the effects of desflurane and sevoflurane on oxidative stress parameters both in mothers and newborns undergoing elective CS.

MATERIALS AND METHODS

Eighty ASA physical status I-II, term parturients undergoing elective CS under general anesthesia were randomized to desflurane (Group D) and sevoflurane (Group S) groups. Blood samples were collected from mothers before operation and postoperatively and umbilical artery samples were obtained at delivery. Total oxidant status (TOS), total antioxidant capacity (TAC) status, lipid hydroperoxide (LOOH), and free sulfhydryl (-SH) levels were measured and oxidative stress index was calculated. Secondary outcomes included maternal hemodynamics.

RESULTS

Preoperative LOOH, TOS, OSI, TAC, and -SH levels were similar among groups. Postoperative maternal serum LOOH, TOS, and OSI levels were significantly increased in Group D compared to Group S (p = 0.003, p = 0.005, p = 0.04; respectively). Postoperative umbilical artery LOOH, TOS, OSI levels were also significantly increased in Group D compared to Group S (p = 0.04, p = 0.02, p = 0.01; respectively). Postoperative TOS (p = 0.001, < 0.001 respectively) and OSI (p = 0.003, < 0.001 respectively) levels in both Group D and Group S were statistically significantly decreased compared to preoperative levels. Postoperative LOOH and -SH levels in Group S (p = 0.04, 0.029 respectively) were statistically significantly decreased compared to preoperative levels. There were no significant differences in TAC and -SH levels among groups (p = nonsignificant [n.s.]). Maternal perioperative mean blood pressure and heart rate were similar among groups (p = n.s.).

CONCLUSION

Oxidative stress indices might be modified with preferred anesthetic agent and sevoflurane showed more favorable effects than desflurane in view of oxidative stress.

[Caesarean sections under regional anesthesia: pros and cons of supplementary oxygen]

The routine administration of supplemental oxygen to women undergoing elective caesarean section under regional anesthesia in order to optimize oxygen supply to the fetus is common anesthetic practice in many German hospitals. However, this practice has been controversially discussed in the non-German literature for many years. This review presents and discusses the pros and cons of routinely providing supplemental oxygen to a parturient during caesarean section on the basis of the literature published over the last 30 years. Proponents of routine oxygen administration point to potential and unforeseeable risks of caesarean sections and consider the prophylactic administration of oxygen based on physiological considerations to be advantageous in terms of patient safety. Interestingly, data regarding the effects of an increased maternal FIO2 on improvement of fetal oxygenation are inconsistent, therefore, no unambiguous recommendation concerning which FIO2 to choose can be given. Opponents of routine oxygen supplementation allude above all to an increase in free radical activity in both mother and fetus; however, data in this respect are not consistent either. As supplemental oxygen to patients undergoing elective caesarean section without any risk factors under regional anesthesia is associated with potential risks while no advantage has so far been demonstrated, routine administration of oxygen has to be challenged and is no longer considered to be indicated by many. On the contrary, in cases of emergency with a concomitant risk of hypoxia for mother and fetus, administration of oxygen is indispensable in the light of present data.

Cord blood 8-isoprostane in the preterm infant

BACKGROUND

Cord blood 8-isoprostane (8-IP) is a marker of lipid peroxidation in the peripartum period. The independent association with degree of prematurity is not well-described.

OBJECTIVE

To identify patterns of lipid peroxidation among early, moderate and late preterm infants, and to understand how cord blood 8-IP varies with gestational age (GA) and related covariates.

STUDY DESIGN

Mother-infant pairs from 237 preterm births were studied as part of a longitudinal birth cohort study. GA subgroups were defined as extremely (≤28w), moderately (29-33w), and late (34-36w) preterm. Cord blood 8-IP was measured using EIA. Elevated 8-IP (4th quartile) was the primary outcome for multivariate logistic regression models, which were adjusted for maternal age/race, multiple gestation and infant gender, as well as other relevant covariates.

RESULTS

Elevated 8-IP was associated with extremely preterm birth (OR=4.31; 95% CI=1.90, 9.76), and was inversely associated with increasing GA (OR=0.88; 95% CI=0.80, 0.97). Elevated 8-IP was also associated with decreasing birth weight (BW), clinical chorioamnionitis, fetal inflammatory response of the placenta (FIR), and signs of perinatal depression. The GA on 8-IP association appeared to be modified by several maternal disease and fetal-infant factors. Lastly, the indirect associations between log-transformed 8-IP, GA and BW appeared to be most prominent for GA<30w and for BW<2000g.

CONCLUSION

Lipid peroxidation in preterm birth, and the relative influence of accompanying peripartum factors, varies according to degree of prematurity. These findings have important implications for the developmental regulation of antioxidant defense and its impact on neonatal outcomes.

Oxygen saturation targets for preterm infants in the delivery room

Fetal life evolves in a low oxygen milieu as compared to the extra-uterine. In the fetal to neonatal transition rapid changes in the oxygen content of the newly born infant occur within a brief period of time. Delivery room care givers should be aware of the slow transition regarding oxygenation, and supply oxygen as needed trying to avoid damage caused by hyper-and-hypoxia. In this regard, titrating oxygen inspiratory fraction against oxygen saturation as measured by pulse oximetry following recent nomogram ranges is a valid method.

The use and misuse of oxygen during the neonatal period

This article describes aerobic metabolism, oxygen free radicals, antioxidant defenses, oxidative stress, inflammatory response and redox signaling, the fetal to neonatal transition, arterial oxygen saturation, oxygen administration in the delivery room, oxygen during neonatal care in the NICU, evolving oxygen needs in the first few weeks of life, and complications that can occur when infants go home from the hospital on oxygen.

Short courses of mechanical ventilation with high-O2 levels in elderly rat lungs

PURPOSE

To evaluate the effects of mechanical ventilation (MV) of high-oxygen concentration in pulmonary dysfunction in adult and elderly rats.

METHODS

Twenty-eight adult (A) and elderly (E), male rats were ventilated for 1 hour (G-AV1 and G-EV1) or for 3 hours (G-AV3 and G-EV3). A and E groups received a tidal volume of 7 mL/kg, a positive end-expiratory pressure of 5 cm H2O, respiratory rate of 70 cycles per minute, and an inspiratory fraction of oxygen of 1. We evaluated total protein content and malondialdehyde in bronchoalveolar lavages (BAL) and performed lung histomorphometrical analyses.

RESULTS

In G-EV1 animals, total protein in BAL was higher (33.0±1.9 µg/mL) compared with G-AV1 (23.0±2.0 µg/mL). Upon 180 minutes of MV, malondialdehyde levels increased in elderly (G-EV3) compared with adult (G-AV3) groups. Malondialdehyde and total proteins in BAL after 3 hours of MV were higher in elderly group than in adults. In G-EV3 group we observed alveolar septa dilatation and significative increase in neutrofiles number in relation to adult group at 60 and 180 minutes on MV.

CONCLUSION

A higher fraction of inspired oxygen in short courses of mechanical ventilation ameliorates the parameters studied in elderly lungs.