A prospective, up-down sequential allocation study investigating the effectiveness of vital capacity breaths using high-flow nasal oxygenation versus a tight-fitting face mask to pre-oxygenate term pregnant women

Anesthetic challenges of pregnant obesity women

Obesity causes significant morbidity and increases the mortality risk for both mother and fetus. With an increasing projected prevalence, it is vital that the obstetric anesthetist is equipped with the knowledge and tools to manage these women. A multi-disciplinary team approach and early planning is required. Neuraxial analgesia for labor helps to negate the need for general anesthesia, which is associated with increased risk in this subset of women. Catheter techniques for neuraxial anesthesia allow for titration, manipulation, and prolongation of the anesthetic block to reduce the risk of conversion to general anesthesia.

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.

Emergencies in obstetric anaesthesia: a narrative review

We conducted a narrative review in six areas of obstetric emergencies: category-1 caesarean section; difficult and failed airway; massive obstetric haemorrhage; hypertensive crisis; emergencies related to neuraxial anaesthesia; and maternal cardiac arrest. These areas represent significant research published within the last five years, with emphasis on large multicentre randomised trials, national or international practice guidelines and recommendations from major professional societies. Key topics discussed: prevention and management of failed neuraxial technique; role of high-flow nasal oxygenation and choice of neuromuscular drug in obstetric patients; prevention of accidental awareness during general anaesthesia; management of the difficult and failed obstetric airway; current perspectives on the use of tranexamic acid, fibrinogen concentrate and cell salvage; guidance on neuraxial placement in a thrombocytopenic obstetric patient; management of neuraxial drug errors, local anaesthetic systemic toxicity and unusually prolonged neuraxial block regression; and extracorporeal membrane oxygenation use in maternal cardiac arrest.

Peri-intubation oxygenation for Caesarean delivery: is there an optimal technique?

Peri-intubation oxygen administration to the pregnant patient during induction of general anaesthesia is critical to avoiding hypoxaemia and harm to the mother and fetus. Recent modelling comparing low-flow with high-flow nasal oxygen in simulated term pregnant women of varying body habitus, taken together with previous work, suggests that face mask preoxygenation with the use of low-flow or high-flow nasal oxygen during the period of apnoea prolongs the safe apnoea period, with the benefit varying by body habitus. Low-flow compared with high-flow nasal oxygen may be easier to combine with face mask preoxygenation and is readily available in all operating theatres, although future improvements in high-flow nasal oxygen delivery systems may improve ease of use for this indication.

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.