Article Notes
-
Local COVID PPE guidelines were used: face-shield, goggles/glasses, mask, gown & gloves. ↩
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.
Daniel Jolley
Also relevant to read is Duggan's 2019 CJA editorial: The MacGyver bias and attraction of homemade devices in healthcare
Daniel Jolley
Leff & Finucane's (JAMA 2008) 'gizmo idolatry' commentary is also related, and well worth a read. The human love of bells and whistles...
Daniel Jolley
Why the interest?
The combination of a deadly contagion (COVID-19) and recognition that endotracheal intubation is a high risk procedure for the airway technician has lead to the development of novel medical equipment. One such innovation is the clear-perspex 'intubating box' designed to contain viral-aerosols released during intubation. There has been limited prior evaluation of the safety or efficacy of such devices, despite their promotion.
What did they do?
Begley et al. conducted 36 simulated intubations with twelve PPE-adorned1 anaesthetists, with and without intubating boxes. They primarily aimed to quantify the effect on time to intubation.
Investigators tested both a first-generation and newer generation device. Each of twelve senior anaesthesiologists performed three block-randomised intubations: no box, original, and latest-design box. The airway manikin tongue was inflated to simulate a grade 2A airway.
And they found...
Intubation time was significantly increased by both the older and newer box designs (x̄=48s and x̄=28s longer respectively, though with wide confidence intervals). More relevantly there were frequent prolonged-duration intubations with the box (58% >1 minute, 17% >2 min), but none without the box.
Most worrying, there were eight breaches of PPE caused by box use, seven occurring with the newer, more advanced design.
"PPE breaches often seemed to go unrecognised by participants, potentially increasing their risk further."
Reality check
Despite the superficial appeal of an intubation box, this simulation study warns that such devices fail both to support safe and timely intubation and to protect the clinician – the very arguments used to advocate for its use.
These failings occur before even considering the actual effectiveness in reducing viral exposure, the box's impact on emergent airway rescue, or the practicality of cleaning a reusable device now coated with viral particles.
The intubating aerosol box appears dead on arrival.
Bonus biases
Begley notes the appeal of such novel devices may be partly driven by 'gizmo idolatry' (Leff 2008) and 'MacGyver bias' (Duggan 2019), blinding clinicians to consider unknown consequences of box use and discounting resultant hazards.
Daniel Jolley
The main premise of Duggan's argument is that our MacGyver bias is grounded in an overweighting of the perceived benefits of MacGyvered 'workarounds' to medical problems, with discounting or even ignoring of unknowns, risks and newly introduced hazards.
This bias is rooted in the satisfaction and enjoyment of solving a problem, the chance to "showcase one's creativity" and to be solutions oriented.
"The danger is that a workaround is so culturally appealing that it circumvents the level of scientific scrutiny that we would expect from any other equipment that we use. Novelty, immediacy, ownership, and ease of use can increase our propensity to bias and wilful blindness." – Duggan et al.
Daniel Jolley