British journal of anaesthesia
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High-flow, heated, and humidified nasal oxygen therapy (HFNO) is frequently used in critical care and perioperative settings for a range of clinical applications. Much of the benefit of HFNO is attributed to generation of modest levels of positive airway pressure. Concern has been raised that this positive airway pressure may cause gastric insufflation, potentially increasing the risk of regurgitation and aspiration in an unprotected airway. ⋯ NCT03134937.
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We hypothesised that Calabadion 1, an acyclic cucurbit[n]uril molecular container, reverses fentanyl-induced respiratory depression and dysfunction of the CNS. ⋯ Calabadion 1 selectively and dose dependently reversed the respiratory system and CNS side-effects of fentanyl.
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High ventilatory frequencies increase static lung strain and possibly lung stress by shortening expiratory time, increasing intrathoracic pressure, and causing dynamic hyperinflation. We hypothesised that high intraoperative ventilatory frequencies were associated with postoperative respiratory complications. ⋯ High intraoperative ventilatory frequency was associated with increased risk of postoperative respiratory complications, and increased postoperative healthcare utilisation.
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LMA and Caesarean – why should I care?
There is a small attitude change underway in the use of supraglottic airway devices (SGA) in obstetric anaesthesia. While there is already an appreciation of their role in obstetric airway rescue, we now see a shift in some countries to use an SGA as the primary airway choice for Caesarean section under general anaesthesia.
Anaesthesiologists need to be aware of this attitudinal shift, and importantly appreciate the inherent compromises and uncertainties driving it.
In this editorial, Metodiev & Mushambi review changing attitudes toward obstetric airway preference, the realities of maternal aspiration risk, and several large studies suggesting acceptable safety when using a SGA for Caesarean GA.
The tension between airway and aspiration
It is well accepted that regional anaesthesia for Caesarean section is overwhelmingly the best choice, driven first by the historical experience of maternal general anaesthesia risk. The very features that underline this safety improvement are also those in tension when considering endotracheal intubation or SGA: risk of failed intubation versus aspiration.
Studies showing safety
Several retrospective, prospective and randomised studies totalling more than 8,000 patients have concluded that in these populations, SGA use (mainly 2nd generation devices, such as ProSeal™ or LMA Supreme™) was not associated with any greater risk of aspiration. This includes both the single largest study investigating 3,000 women (Halaseah 2010), and two RCTs (Yao 2019 & Li 2017), none of which identified any cases of aspiration (although there was a single regurgitation).
So on the surface, SGA use appears arguably safe, particularly with careful patient selection. Among the studies, generally obese patients and those with reflux were excluded, muscle relaxants were frequently used, an orogastric tube was inserted, and cricoid pressure was used at least for some periods of airway intervention.
And yet we do know from NAP4 (2011) that aspiration is a real danger, accounting for 50% of anaesthesia-related deaths.
Is gastric ultrasound the answer?
No. Next question... 😉
While gastric ultrasound shows some utility in quantifying residual gastric volume, it is 1. Not possible to equate this to aspiration risk in pregnant patients, 2. Technically difficult in the pregnant patient.
They conclude that...
"...there is insufficient evidence to recommend universal or selective replacement of tracheal tubes with SGA devices during general anaesthesia for Caesarean delivery. Aspiration remains the main concern."
Be smart
And before you get too excited by the lack of observed aspiration in these large studies, as Metodiev & Mushambi note, many of the studied populations were Asian and Middle Eastern, having different diets and obesity prevalence than Europe, Oceania and North America.
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