Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study.

BACKGROUND: Hypoxaemia during general anaesthesia can cause harm. Apnoeic oxygenation extends safe apnoea time, reducing risk during airway management. We hypothesised that low-flow nasal oxygenation (LFNO) would extend safe apnoea time similarly to high-flow nasal oxygenation (HFNO), whilst allowing face-mask preoxygenation and rescue. METHODS: A high-fidelity, computational, physiological model was used to examine the progression of hypoxaemia during apnoea in virtual models of pregnant women in and out of labour, with BMI of 24-50 kg m-2. Subjects were preoxygenated with oxygen 100% to reach end-tidal oxygen fraction (FE'O2) of 60%, 70%, 80%, or 90%. When apnoea started, HFNO or LFNO was commenced. To simulate varying degrees of effectiveness of LFNO, periglottic oxygen fraction (FgO2) of 21%, 60%, or 100% was configured. HFNO provided FgO2 100% and oscillating positive pharyngeal pressure. RESULTS: Application of LFNO (FgO2 100%) after optimal preoxygenation (FE'O2 90%) resulted in similar or longer safe apnoea times than HFNO FE'O2 80% in all subjects in labour. For BMI of 24, the time to reach SaO2 90% with LFNO was 25.4 min (FE'O2 90%/FgO2 100%) vs 25.4 min with HFNO (FE'O2 80%). For BMI of 50, the time was 9.9 min with LFNO (FE'O2 90%/FgO2 100%) vs 4.3 min with HFNO (FE'O2 80%). A similar finding was seen in subjects with BMI ≥40 kg m-2 not in labour. CONCLUSIONS: There is likely to be clinical benefit to using LFNO, given that LFNO and HFNO extend safe apnoea time similarly, particularly when BMI ≥40 kg m-2. Additional benefits to LFNO include the facilitation of rescue face-mask ventilation and ability to monitor FE'O2 during preoxygenation.

Effect of variable pre-oxygenation endpoints on safe apnoea time using high flow nasal oxygen for women in labour: a modelling investigation.

BACKGROUND: Studies of pulmonary denitrogenation (pre-oxygenation) in obstetric populations have shown high flow nasal oxygen therapy (HFNO) is inferior to facemask techniques. HFNO achieves median end-tidal oxygen fraction (FE'O2) of 0.87 after 3 min. As HFNO prolongs safe apnoea times through apnoeic oxygenation, we postulated that HFNO would still extend safe apnoeic times despite the lower FE'O2 after pre-oxygenation. METHODS: The Interdisciplinary Collaboration in Systems Medicine simulation suite, a highly integrated, high-fidelity model of the human respiratory and cardiovascular systems, was used to study the effect of varying FE'O2 (60%, 70%, 80%, and 90%) on the duration of safe apnoea times using HFNO and facemask techniques (with the airway open and obstructed). The study population consisted of validated models of pregnant women in active labour and not in labour with BMI of 24, 35, 40, 45, and 50 kg m-2. RESULTS: HFNO provided longer safe apnoeic times in all models, with all FE'O2 values. Labour and increased BMI reduced this effect, in particular a BMI of 50 kg m-2 reduced the improvement in apnoea time to 1.8-8.5 min (depending on the FE'O2), compared with an improvement of more than 60 min in the subject with BMI 24 kg m-2. CONCLUSIONS: Despite generating lower FE'O2, HFNO provides longer safe apnoea times in pregnant subjects in labour. Care should be taken when used in patients with BMI ≥50 kg m-2 as the extension of the safe apnoea time is limited.

Effect of Apneic Oxygenation on Tracheal Oxygen Levels, Tracheal Pressure, and Carbon Dioxide Accumulation: A Randomized, Controlled Trial of Buccal Oxygen Administration.

BACKGROUND: Apneic oxygenation via the oral route using a buccal device extends the safe apnea time in most but not all obese patients. Apneic oxygenation techniques are most effective when tracheal oxygen concentrations are maintained >90%. It remains unclear whether buccal oxygen administration consistently achieves this goal and whether significant risks of hypercarbia or barotrauma exist. METHODS: We conducted a randomized trial of buccal or sham oxygenation in healthy, nonobese patients (n = 20), using prolonged laryngoscopy to maintain apnea with a patent airway until arterial oxygen saturation (SpO2) dropped <95% or 750 seconds elapsed. Tracheal oxygen concentration, tracheal pressure, and transcutaneous carbon dioxide (CO2) were measured throughout. The primary outcome was maintenance of a tracheal oxygen concentration >90% during apnea. RESULTS: Buccal patients were more likely to achieve the primary outcome (P < .0001), had higher tracheal oxygen concentrations throughout apnea (mean difference, 65.9%; 95% confidence interval [CI], 62.6%-69.3%; P < .0001), and had a prolonged median (interquartile range) apnea time with SpO2 >94%; 750 seconds (750-750 seconds) vs 447 seconds (405-525 seconds); P < .001. One patient desaturated to SpO2 <95% despite 100% tracheal oxygen. Mean tracheal pressures were low in the buccal (0.21 cm·H2O; SD = 0.39) and sham (0.56 cm·H2O; SD = 1.25) arms; mean difference, -0.35 cm·H2O; 95% CI, 1.22-0.53; P = .41. CO2 accumulation during early apnea before any study end points were reached was linear and marginally faster in the buccal arm (3.16 vs 2.82 mm Hg/min; mean difference, 0.34; 95% CI, 0.30-0.38; P < .001). Prolonged apnea in the buccal arm revealed nonlinear CO2 accumulation that declined over time and averaged 2.22 mm Hg/min (95% CI, 2.21-2.23). CONCLUSIONS: Buccal oxygen administration reliably maintains high tracheal oxygen concentrations, but early arterial desaturation can still occur through mechanisms other than device failure. Whereas the risk of hypercarbia is similar to that observed with other approaches, the risk of barotrauma is negligible. Continuous measurement of advanced physiological parameters is feasible in an apneic oxygenation trial and can assist with device evaluation.

A case series of severe symptomatic peripartum hyponatraemia.

This single centre case series describes the presentation and management of six cases of peripartum hyponatraemia in women who were otherwise deemed low-risk at delivery. It highlights presenting symptoms such as fatigue, confusion and seizures as well as the effects on the neonate. It also focuses on areas of interest such as fluid intake, hormonal effects of ADH and oxytocin and the association with birthing pools for future research.

Feasibility of a RCT of techniques for managing an impacted fetal head during emergency caesarean section: the MIDAS scoping study.

Background: Second-stage caesarean sections, of which there are around 34,000 per year in the UK, have greater maternal and perinatal morbidity than those in the first stage. The fetal head is often deeply impacted in the maternal pelvis, and extraction can be difficult. Numerous techniques are reported, but the superiority of one over another is contentious and there is no national guidance. Objective: To determine the feasibility of a randomised trial of different techniques for managing an impacted fetal head during emergency caesarean. Design: A scoping study with five work packages: (1) national surveys to determine current practice and acceptability of research in this area, and a qualitative study to determine acceptability to women who have experienced a second-stage caesarean; (2) a national prospective observational study to determine incidence and rate of complications; (3) a Delphi survey and consensus meeting on choice of techniques and outcomes for a trial; (4) the design of a trial; and (5) a national survey and qualitative study to determine acceptability of the proposed trial. Setting: Secondary care. Participants: Health-care professionals, pregnant women, women who have had a second-stage caesarean, and parents. Results: Most (244/279, 87%) health-care professionals believe that a trial in this area would help guide their practice, and 90% (252/279) would be willing to participate in such a trial. Thirty-eight per cent (98/259) of parents reported that they would take part. Women varied in which technique they thought was most acceptable. Our observational study found that impacted head is common (occurring in 16% of second-stage caesareans) and leads to both maternal (41%) and neonatal (3.5%) complications. It is most often treated by an assistant pushing the head up vaginally. We designed a randomised clinical trial comparing the fetal pillow with the vaginal push technique. The vast majority of health-care professionals, 83% of midwives and 88% of obstetricians, would be willing to participate in the trial proposed, and 37% of parents reported that they would take part. Our qualitative study found that most participants thought the trial would be feasible and acceptable. Limitations: Our survey is subject to the limitation that, although responses refer to contemporaneous real cases, they are self-reported by the surgeon and collected after the event. Willingness to participate in a hypothetical trial may not translate into recruitment to a real trial. Conclusions: We proposed a trial to compare a new device, the fetal pillow, with a long-established procedure, the vaginal push technique. Such a trial would be widely supported by health-care professionals. We recommend that it be powered to test an effect on important short term maternal and baby outcomes which would require 754 participants per group. Despite the well-known difference between intent and action, this would be feasible within the UK. Future work: We recommend a randomised controlled trial of two techniques for managing an impacted fetal head with an in-built internal pilot phase and alongside economic and qualitative substudies. Study registration: This study is registered as Research Registry 4942. Funding: This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 27, No. 6. See the NIHR Journals Library website for further project information.

Text: One-quarter of UK pregnant women have a caesarean section. Most of these procedures are straightforward, but in a small number of cases unexpected complications can make the birth difficult. One complication, an impacted fetal head, may happen when caesarean sections are done in the second 'pushing' stage of labour. If the baby's head is low and wedged in the woman's pelvis, lifting it can be difficult, which can result in damage to the mother's womb and vagina, and to her baby. Occasionally, babies die. There are different techniques doctors and midwives can use to make these births easier, but there is uncertainty around which is best. To plan a trial to test these techniques, we needed to know how often impacted head happens, what techniques are used to manage it and whether or not research is acceptable to parents and health-care professionals. We surveyed doctors and midwives to find out which techniques they use and what training they need. We surveyed parents and pregnant women and interviewed women who had experienced a second-stage caesarean. We collected information from UK hospitals to find out how common this is and the impact on women and babies. We found out the following. List: • Around 7% of caesareans take place in second stage, and impacted fetal head occurs in 16% of these births. List: • One-third of women would consent to take part in a trial, if the complication happened to them. List: • Nearly all midwives and doctors thought that this research was important and would be willing to take part. Text: Using all of the information we collected, we designed a clinical trial. We wanted to compare two techniques for managing an impacted fetal head. The first is the vaginal push technique, where the doctor or midwife puts their hand into the mother's vagina to push her baby's head up, and the second is the fetal pillow, a device inserted into the mother's vagina before the operation starts to dislodge the baby's head upwards.

Managing an impacted fetal head at caesarean section: a UK survey of healthcare professionals and parents.

OBJECTIVE(S): To understand current practice, expertise and training requirements for management of an impacted fetal head (IFH) at caesarean section (CS) in the UK, and whether a clinical trial of techniques to manage an IFH is acceptable. STUDY DESIGN: Five hundred and thirty-eight online surveys were completed by obstetricians (n = 206), obstetric anaesthetists (n = 38), midwives (n = 35) and parents (n = 259). Data was collected on incidences of CS and IFH, current use of techniques, and acceptability of a clinical trial to manage an IFH from health care professionals. Information on incidences of CS and recollection of an IFH, acceptability of techniques, and likelihood of taking part in a clinical trial were sought from parents. RESULTS: The most common technique used by obstetricians (84%) and midwives (69%) was the 'push technique'. Eighty-seven percent of health care professionals would be willing to participate in a clinical trial, with 89% confirming that results would guide their clinical practice. Most parents expressed reluctance regarding participation in a clinical trial during labour (62%), due to preferring a doctor to adopt the technique they felt most comfortable with (63%). CONCLUSION(S): Given the lack of national guidance on appropriate techniques, no formal training, and no consensus on best practice for the management of an IFH during emergency CS, it is perhaps not surprising that the majority of heath care professionals would be willing to participate in a clinical trial, where results will guide their clinical practice. The future development of clinical trials, involving relevant stakeholders in the design of such trials, is crucial to improve upon the guidance and training provided to staff who may encounter an IFH.

Differences in dopaminergic neuroprotective effects of estrogen during estrous cycle.

Previous studies suggest that estrogen treatment protects nigrostriatal dopaminergic neurons, but have not examined whether the changes in estrogen levels during estrous cycle can influence the susceptibility of these neurons to neurotoxins. Here we show that the loss of dopaminergic neurons in the substantia nigra was greater in animals lesioned at diestrus (low estrogen) using 6-hydroxydopamine or buffered iron chloride, when compared with animals lesioned at proestrus (high estrogen). Lesioning at diestrus with 6-hydroxydopamine reduced the striatal dopamine content, whereas the dopamine content was preserved in animals lesioned at proestrus. The density of the dopamine transporter, upon which 6-hydroxydopamine toxicity is dependent, was lower when circulating estrogen was high. These results thus support a neuroprotectory role for estrogen.