the metablog

Tylenol, Tyranny, and Misogyny

Fri, 26 Sep 2025 04:49:00 +0000

The Misogyny of MAHA and the Politics of Health

Wrapped up in the near-incoherent warning against the use of paracetamol (Tylenol/acetaminophen) in pregnancy reveals the real story of the Make America Healthy Again project: misogyny dressed up as health advice.

This is a broader project of bad science weaponised to undermine trust and weaken the very institutions that exist to support health and wellbeing.

Let's start with the evidence: while there has been more than a decade of concern about possible associations between paracetamol use in pregnancy and neurodevelopment consequences in children, particularly ADHD and autism spectrum disorder, the best and most recent evidence is reassuring:

"Acetaminophen use during pregnancy was not associated with children's risk of autism, ADHD, or intellectual disability in sibling control analysis." – Ahlqvist et al. 2024

Science as a punching bag

Despite this, we are treated to the absurd spectacle of a brain-wormed conspiracy peddler teaming up with a carnival barker unable to even pronounce acetaminophen. Together they issue sweeping advice in direct opposition to medical organisations across the world reaffirming the safety of appropriate paracetamol use in pregnancy.

What's revealing is not the bad science itself, but who bears the consequences of these pronouncements: this is not primarily about paracetamol. It’s about a particularly regressive worldview.

“If you’re telling parents or telling society that someone should be doing this work of keeping kids safe, what you’re really saying is women should be doing this work, especially mothers. ... RFK Jr is weaponizing the supermom myth – the false idea that moms are the only ones who can keep kids safe from harm.” – Prof. Jessica Calarco (2025)

Wrapped up together with the just-asking-questions bad faith anti-vax arguments, the distracting focus on food-dyes, fructose and food-purity¹, and now the "just tough it out" advice for pregnant women with pain and fever, is exposure of this movement's misogyny. The weight of navigating decisions on food, vaccines and now, paracetamol, falls disproportionately on women, and the consequences of making the wrong decision will be to be judged by MAHA as a bad mother.² Women bear all the responsibility and blame, but get little help and support.

The burden falls on women

The rhetoric is always the same: choices, responsibility, discipline. Pregnant women are told to carry the moral weight of every decision, bearing responsibility without support, risk without remedy, and blame without resources. The politics of American healthcare is quick to blame, slow to protect.

Condemning parents for childhood nutritional shortfalls while slashing $1 billion in funding for programs bringing fresh fruits and vegetables to schools and food banks; limiting vaccine access while fanning the flames of measles outbreaks; limiting reproductive health access while doing nothing for US maternal mortality rates more than double other wealthy countries; providing no mandated maternity leave (the only high-income country without such protection) or ready access to affordable childcare; and repeatedly refusing to address the scourge of childhood exposure to gun violence, are all unforgivable moral failings. Advising pregnant women to avoid paracetamol while offering no alternative is more of the same.

Misogyny, medicine, and power

The logic here is not accidental. By shifting responsibility onto the individual while dismantling institutions that help, MAHA’s ideology performs a double trick: it leaves people unsupported, and then discredits those institutions – medical, public health, government – that would normally step in.³ The state fails, blames the individual, and then demands more power. The moralistic thread tying these ideologies together both ignores the importance of institutions in addressing these issues, and then further disempowers them.

Anesthesiologists and other clinicians must defend access to safe and effective pain relief, a basic human right. Paracetamol is cheap, effective, and globally accessible. Pretending otherwise is not just bad science, it’s political theatre designed to keep women in pain, institutions weakened, and power concentrated. Beyond the drug, the real fight is recognising when science is being twisted to advance ideological goals, when those goals reinforce sexism and inequity, and then weaponise this sexism to hollow out the very institutions that sustain public health.

The misogyny of MAHA is not an accident. It’s the point.

Yes, some food dyes are harmful and yes, high-fructose corn syrup has helped fuel the obesity epidemic. But this simplistic, reductionist thinking ignores the many real social, cultural, economic and political causes of America's abysmal health outcomes. Switching Coke to cane sugar and using natural dye in Froot Loops is branding, not public health policy. ↩
Don't get me started on this essentialist obsession with the primary role of women in society, reducing them to wombs, caregivers, and homemakers, with little value beyond reproduction. Fifty percent of the population written off as support staff... ↩
Institutions are undermined in two ways: directly, through defunding, contradiction, and performative attacks; and indirectly, by corroding the very idea of expertise. When public figures spew bad science, it doesn’t just damage trust in them—it erodes trust in any medical authority. That’s the point: if no one believes experts, institutions themselves lose their power. ↩

Opioid-free, AF anaesthesia and LMA atelectasis

Thu, 14 Nov 2024 10:37:00 +0000

Three interesting recent studies looking at specific choices around anaesthetic technique. In the Canadian Journal of Anesthesia, da Silveira reviews the benefits of opioid-free laparoscopic surgery; in the Journal of Cardiothoracic and Vascular Anesthesia, Ford goes deep on the pros and cons of different anaesthetic techniques for AF ablation procedures; and finally in the JCA, Liu reports on a single-centre RCT investigating the beneficial effects of LMAs on atelectasis.

Opioid-Free Laparoscopic Surgery: Less Nausea, Similar Pain Control

An interesting meta-analysis from da Silveira et al. explores whether we can effectively manage minimally invasive abdominal surgery without using opioids - an important question given how common opioid-related side effects are.

This was a comprehensive systematic review and meta-analysis of 26 randomised controlled trials, including 2,025 patients. The researchers specifically compared opioid-free versus opioid-containing anesthesia in minimally invasive abdominal surgeries. They were particularly interested in looking at side effects like PONV and bradycardia, as well as pain control and recovery times.

The results were quite interesting. The authors found that opioid-free anaesthesia:

Reduced PONV by 45% (from 24% to 13% / RR CI 0.40 to 0.74).
Led to slightly lower immediate postoperative pain scores (though not clinically significant).
Required less postoperative opioid use in the first 2 hours.
Showed no difference in recovery room length of stay.
Showed no increase in bradycardia, a previously noted concern when using intraoperative dexmedetomidine.

These findings are consistent with previous meta-analysis, but unique to this study, focus only on laparoscopic surgery, excluding orthopaedics and head & neck surgery included in past analyses.

"Opioid-free anesthesia showed a significant reduction in PONV and a decrease in opioid consumption during the first 2 hr postoperatively, suggesting it can be an alternative to opioid anesthesia in minimally invasive abdominal surgeries."

The (small) reduction in postop pain scores and opioid consumption is particularly notable, supporting the idea that intraoperative opioid may induce acute tolerance postoperatively. (We know this happens with remifentanil above a certain dose)

"A multimodal analgesic approach avoiding opioids with the use of lidocaine, magnesium, and ketamine suppresses impulses from injured nerve fibres and transmission of nociceptive stimuli, and may be able to promote analgesia in the first 24 hr after surgery, while reducing opioid consumption in the early postoperative period. ... Additionally, a2-agonists such as dexmedetomidine may replace opioids in terms of sympathetic stabilization, especially during major surgeries."

While the study captured a large sample size and robust statistical analysis, the authors acknowledge limitations related to study heterogeneity, "the included RCTs used different opioid-free anesthesia strategies and medication regimens".

Da Silveira and team make a strong argument for the possible superiority of opioid-free anaesthesia for laparoscopic surgery, it's worth noting that successful use of the technique requires expertise in using alternative agents like dexmedetomidine, ketamine, and regional techniques. The benefits, particularly in reducing post-operative nausea and vomiting, may be worth the learning curve.

Modern Anaesthesia and AF Ablation: What's Best?

This narrative review by Ford et al. examines the impact of anaesthetic technique on the success of catheter ablation for atrial fibrillation (AF), particularly ventilation strategies. It has relevance given that AF's is the most common arrhythmia, leading to a surge in ablation procedures.

The authors examine three key areas: general anaesthesia (GA) vs conscious sedation, high-frequency jet ventilation (HFJV), and high-frequency low tidal volume ventilation (HFLTV).

They show that GA appears superior to conscious sedation, with one study showing 88% vs 69% arrhythmia-free rates at 17 months. The GA group also experience a lower rate of pulmonary vein reconnection and shorter procedural and fluoroscopy times.

Both HFJV and HFLTV show promise in improving catheter stability and procedural outcomes. The authors note:

"GA has been shown to decrease the movement of catheter tips compared to conscious sedation, enabling better stability and lesion formation."

Though they acknowledge that HFJV faces practical challenges:

"While HFJV is known for its positive impact on catheter stability, its implementation faces challenges such as high costs, the need for additional training to use the ventilator, and the inability to measure end-tidal CO2."

HFLTV might thus offer a practical middle ground between conventional ventilation and HFJV, potentially providing similar benefits without the extra cost and training demands.

The benefits of GA, HFJV and HFLTV arise from reduced respiratory variability, leading to:

Minimising left atrial movement.
Better catheter stability, improving procedural accuracy.
More effective lesion formation.

The main weakness of the review is the lack of direct comparative data between the different ventilation strategies, which the authors acknowledge, calling out the need for randomised controlled trials comparing these strategies.

Nevertheless, the review makes a compelling argument for the use of an anaesthetic technique that avoids ventilation variability – and the less variability, the better.

Less is more: Do laryngeal masks reduce atelectasis compared to endotracheal tubes?

Liu and colleagues investigated whether laryngeal mask airway (LMA) use reduces atelectasis formation during general anaesthesia, compared to endotracheal tubes (ETT) – relevant given that ~90% of patients develop some degree of atelectasis after induction.

This was a single-centre, double-blind RCT of 180 patients undergoing non-laparoscopic surgery under 2 hours, with intention-to-treat analysis. They used lung ultrasound (LUS) scoring to assess atelectasis at various timepoints (15 min post-induction, pre-emergence and 30 min after extubation) along with oxygenation. All patients were induced with sufentanil, propofol and rocuronium, and maintained with propofol/remifentanil TIVA. Ventilation was volume controlled with TV 6-8 mL/kg and PEEP 5 cmH2O, I:E 1:1.5, RR 12-20 and FiO2 40%.

Surprisingly the LMA group showed significantly lower LUS scores at all three timepoints, along with better oxygenation and fewer postoperative pulmonary complications.

The authors propose several mechanisms to explain the superiority of LMAs:

Faster Airway Insertion

Shorter apnea time during airway placement (41 vs 95 seconds).
Less time for oxygen absorption in preoxygenated alveoli to cause absorptive atelectasis.
As they note: "Prolonged ventilation pause during this period can easily lead to excessive absorption of oxygen in the alveoli, causing absorptive atelectasis".

Reduced Airway Irritation

Less manipulation of the throat.
Reduced stimulation of airway reflexes.
Lower risk of bronchospasm and secretions.
Less risk of small airway obstruction.
Better preserved mucociliary clearance rates.

Lower Muscle Relaxant Requirements

"After anesthesia induction and administration of muscle relaxants, the weakening of inspiratory muscle tension in patients leads to a relative increase in intra-abdominal pressure. The relaxed diaphragm moves cephalad, reducing the cross-sectional area of the chest, thereby altering the geometry of the thoracic cavity and increasing chest wall pressure, subsequently compressing lung tissue and causing compressive atelectasis."

Reduced Anaesthetic Requirements

Lower doses of sufentanil and rocuronium for induction.
Lower maintenance doses of propofol and remifentanil.
Better preserved respiratory function.

Particularly relevant in this study, "the majority of surgeries in both groups being endoscopic procedures, resulting in minimal demand for anesthetic drugs. Therefore, the increase in the required dose of anesthetic drugs to attenuate cough reflex during endotracheal intubation becomes more significant." Thus the effect could be more about depth of anaesthesia and muscle relaxation than airway choice per se.

The authors note: "Compared to endotracheal intubation, laryngeal masks effectively reduce atelectasis formation and progression in gynecological, urological non-laparoscopic, and orthopedic limb surgeries."

The study is mainly limited by the lack of neuromuscular monitoring and the restriction to relatively healthy patients having shorter (mainly endoscopic!) procedures – arguably the group that atelectasis is least clinically important for!

Nonetheless, the results suggest that when appropriate, using an LMA rather than ETT may reduce atelectasis formation. The authors acknowledge this may not apply to longer procedures, laparoscopic surgery, or higher-risk patients; and naturally the risk-benefit balance of an unprotected airway versus an ETT needs to be considered.

"Rapid insertion and less airway irritation are key factors contributing to the LMA's ability to decrease the formation of absorptive atelectasis."

Mentioned studies:

CAB da Silveira, ACD Rasador, HJS Medeiros et al. Opioid-free anesthesia for minimally invasive abdominal surgery: a systematic review, meta-analysis, and trial sequential analysis. Can J Anaesth. 2024 Nov 5.
Ford P, Cheung AR, Khan MS et al. Anesthetic Techniques for Ablation in Atrial Fibrillation: A Comparative Review. J. Cardiothorac. Vasc. Anesth. 2024 Nov 1; 38 (11): 275427602754-2760.
Liu B, Wang Y, Li L et al. The effects of laryngeal mask versus endotracheal tube on atelectasis after general anesthesia induction assessed by lung ultrasound: A randomized controlled trial. J Clin Anesth. 2024 Nov 1; 98: 111564111564.

COVID research mid-year round up

Thu, 07 Jul 2022 03:50:00 +0000

We are now two and a half years into the COVID pandemic, and just beginning to see yet another case surge with the arrival of the BA.5 Omicron sub-variant. The good news just keeps coming! 😉

Along with new variants, 30 months has also given us a lot of research and data. Metajournal alone has indexed almost 39,000 COVID-related publications relevant to anaesthesia, pain, critical care and emergency medicine.

Of course that's a crazy volume of research to manage, with a pretty low signal-to-noise ratio. Sifting through that for quality and relevant studies is exactly what metajournal was designed for.

Here's a quick round-up of interesting COVID-related research...

RAT tests & infectiousness

As good quality, locally validated RAT tests become increasingly available, we are also collecting more data showing they are a good indicator of individual infectiousness at the moment in time the test is performed.

The article collection 'Does a COVID RAT-negative result mean non-infectious?' explores several of these studies, suggesting that a negative RAT is likely a reliable indicator of being non-infectious.

The bottom line...

A correctly-performed adequately-validated RAT, is likely a sensitive indictor of individual infectiousness at that specific moment in time. The reliability of a negative RAT will be improved if using the same manufacturer and technique as a previously positive test, and more so if there are several subsequent negative RATs.

Return to exercise after COVID?

A recent J Sci Med Sport editorial (Hughes 2022) from Australian elite sport, exercise medicine and sports cardiology experts, provides reassuring encouragement when returning to exercise after COVID recovery.

The authors first note that:

"...with over 6 million cases recorded in Australia & NZ in the first 4 months of 2022, and few reports of serious adverse outcomes with exercise, the approach to return to exercise has become more pragmatic."

The authors' experience has been that most vaccinated elite athletes achieve pre-morbid fitness levels by day 7-14 post COVID recovery. Recreational athletes are recommended to pursue a more conservative course, but nonetheless they suggest:

"...a quick return to moderate exercise with a more cautious return to higher intensity exercise."

For those with no or minimal symptoms, the authors describe a graduated approach of exercise return over 6 days (days 1-3, 50% intensity for 15-30 min, then days 4-6, 75% intensity for 30 min), culminating in return to normal activity on day 7, if the graduation is well tolerated.

Interestingly these guidelines are very similar to Jewson's 2020 roadmap for return to activity after COVID infection, developed by the Australasian College of Sport and Exercise Physicians.

Jewson (2020) described three risk categories:

Low: Under 50 years with mild illness resolving within 7 days.
Intermediate: prolonged symptoms (>7d); persistent SOB or chest pain; pre-existing comorbidities; elite/endurance athletes.
High: hospitalised with COVID; SOB or chest pain at rest; cardiac abnormalities.

Jewson's graduated return to physical activity:

Begin after 10 days of rest and when 7 days symptom-free.
Begin with 15 minutes of light activity, with gradual increase guided by lack of fatigue with activity.
🚩 Red flag symptoms: chest pain, palpitations, severe dyspnoea. STOP & medical review.

Key takeaway

For those with mild or asymptomatic COVID infections, a careful graduated return to exercise can begin soon after recovery from COVID, while monitoring for excessive fatigue and cardiorespiratory symptoms.

Which N95/P2 respirators most often pass Fit Tests?

Ng and co. out of Australia's Royal Melbourne Hospital published excellent audit data answering this very question after Fit Testing 2,161 healthcare workers.

Why is this important?

Many healthcare workers and significantly, the general public, may not have access to formal Fit Testing. We also know that as face shape varies among individuals, so does the effectiveness of protection for different mask types – this is particularly significant for women who have more difficulty in finding suitably-fitting N95 respirators. (Notably 73% of Fit Tested staff in this study were women.)

The results of this study may allow individuals to make educated choices on suitable masks even when they do not have access to Fit Testing, as well as guiding institutional mask purchases.

What did they find?

Three-panel flat-fold N95 masks performed best (3M Aura 9320A+) both for fit test (96% pass) and wearer comfort and usability.

The other three tested designs were not as performant:

Semi-rigid cup type (3M 1860 or 1860S): 65% FT pass.
Duckbill type: (BSN ProShield or Halyard Fluidshield): 59% FT pass.
Flat-fold cup type: (BYD Care DE2322): 32% FT pass.

Final word?

Three-panel flat-fold N95 masks performed best for both fit test (96% pass) and wearer comfort and usability.

Novavax vs Omicron

Nuvaxoid (NVX-CoV2373), the protein-subunit COVID vaccine developed by Novavax, was already shown to be safe and 90% effective against the Alpha (B.1.1.7) SARS-CoV-2 variant – but now we have early release data showing similar efficacy against Omicron and it's various sub-variants (including the surging BA.5).

"...the data indicates a booster shot of Novavax’s vaccine generates neutralizing antibody responses to Omicron variants comparable to what was seen against the original strain of SARS-CoV-2 at the peak of its initial Phase 3 trial."

It is thought that Nuvaxoid's protein subunit structure provides much broader cross-neutralising antibodies than mRNA vaccines, such as from Moderna and Pfizer.

Interesting, animal studies show that the original Nuvaxoid vaccine results in similar neutralising titres to BA.5 as does a new, Omicron BA.1-specific formulation.

Bottom-line...

The current Nuvaxoid vaccine could make for a good booster option for populations where BA.5 is surging.

Pre-print hoopla: COVID-associated neurodegeneration & Risks of subsequent infections

Two pre-prints generated a lot of attention recently.

Outcomes of SARS-CoV-2 Reinfection (Al-Aly, Bowe, Xie)

A large cohort study using US Dep. of Veterans Affairs data looked at the mortality and morbidity associations between first infections, re-infections and the non-infected.

This data found that re-infection was associated with further increases in mortality, hospitalisation and morbidity, regardless of vaccination status.

While this was erroneously reported as 'subsequent infections are worse' it appears more accurately to show that there is (likely) a cumulative health burden to reinfection with COVID. This should not surprise us. However we should temper our concern by noting that this says nothing about the 219,000 study participants (85%) who did not suffer a reinfection, or about those who were unknowingly reinfected, but for whatever reason were not tested.

Retrospective cohort studies like this, even when very large, are acutely sensitive to confounders. Arguably this study selected those with re-infections and symptoms, as these were the group most likely to present for care. Additionally 90% of subjects were men - so take it all with a pinch of salt.

Regardless, you should try hard to avoid any COVID infection, whether it is your first or your third. There is no COVID infection that it better than non-infection!

COVID and neurodegenerative risk (Zarifkar)

The second pre-print to get us all hot & bothered was Danish data presented by Zarifkar at the recent European Academy of Neurology (EAN) Congress.

Among over 35,000 COVID-positive patients there was an associated increased relative risk for Alzheimer's (RR, 3.5, 95% CI 2.2-5.5), Parkinson's (RR 2.6, 95% CI 1.7-4.0), ischaemic stroke (RR 2.7, 95% CI, 2.3-3.2), and intracerebral haemorrhage (RR 4.8, 95% CI 1.8-12.9).

Buuuuut, and here's the problem, for all of those morbid end-points (except ischaemic stroke) a similar association was seen for influenza infection or "after other common respiratory tract infections".

Clearly COVID (or Influenza) is not causing Alzheimer's disease (a progressive chronic disease usually occuring over decades), but it is feasible that a systemic inflammatory insult could hasten progression of existing neurodegeneration. There may also be confounding factors, such that the same comorbidities associated with neurodegeneration are also associated with infection, severe COVID illness, or simple seeking out a test.

These large-population observational studies are clearly interesting, but we need to be careful to avoid rushing straight down the causation-highway. Remember that before falling in with the crazy COVID-minimiser crowd (🙄), legendary meta-researcher Dr John Ioannidis' published landmark research showing that 80% of conclusions from observational studies were later disproven.

Food for thought.

xkcd.com

Some more COVID reading...

Despite the 39,000 COVID-related publications indexed by metajournal, it's easy to drill down into more relevant research and seperate the signal from the noise.

Click on Search... and then Reviews to narrow the COVID results to only the Latest COVID Review Articles.

Case in point, the latest edition of Critical Care Clinics has a big COVID focus, including reviews of COVID critical illness post-sequalae, COVID and acute kidney injury, the role of thrombus in COVID-19, Multisystem inflammatory syndrome in children, and COVID in the critically ill pregnant patient.

Of course, don't worry, plenty more COVID research still to come...

Does doctor gender impact patient outcome?

Tue, 18 Jan 2022 00:00:00 +0000

A very interesting study in JAMA Surgery from Wallis et al. received a lot of press coverage. The research team showed that female patients treated by male surgeons not only more commonly experienced post-operative complications, but also suffered a higher mortality, than when treated by female surgeons.

What did they do?

This big-data study covered 12 years of the 20-most-common surgical procedures performed in Ontario, Canada. Wallis and team investigated how patient-surgeon sex discordance correlated to a composite for adverse postoperative outcomes. (A deeper investigation of the earlier Wallis 2017 study).

And they found?

While ~15% of all patients experienced an adverse post-operative outcome, female patients treated by a male surgeon experienced significantly higher odds of a composite of adverse events (OR 1.15 [1.10-1.20]), 30-day complications (OR 1.16 [1.11-1.22]), readmissions (OR 1.11 [1.04-1.19]), and death (OR 1.32 [1.14-1.54]) compared to when treated by female surgeons.

Yet male patients treated by female surgeons experienced either lower odds (death 0.87 [0.78-0.97]) or statistically-similar odds of complications (composite end-point, readmission or post-op complications).

The hot-take

Women once again receive the metaphorical short-end of the medical-stick. Whether societal or elsewhere in the health industry value-chain, long established gender inequity reveals itself in worse surgical outcomes for female patients.

Hang on a sec…

But this cannot just be written off as a consequence of existing social gender inequity, but rather a disquieting causal loop between this as a cause and the result then perpetuating further inequity.

If some part of a surgeon’s ’professional success’ is wrapped-up in the ability to achieve positive outcomes for patients while minimising the adverse, then male surgeons are failing their female patients when compared to either female surgeons, or to the care they provide their male patients.

And yet the same discordance cost is not true for female surgeons.

The take-away

If you are a male surgeon interested in successful patient outcomes (surely that’s every surgeon?), then this should make you very, very uncomfortable. At the very least it should make male surgeons stop and consider whether their female colleagues conduct any aspects of their practice differently – particularly when treating female patients.

The negative consequences of patient-physician sex-discordance on outcomes has been observed before, notably Greenwood, Carnahah & Laura Huang found in 2018 that female heart-attack patients were less likely to survive when treated by a male physician than a female physician. Offering a causal glimpse, they also found that this mortality burden lessened when care either occurred in EDs with more female physicians, or from male physicians with more experience treating female patients.

Sun, et al’s 2021 article explored the triad of gender discordance between surgeon, anaesthesiologist and patient for cardiac surgery. Although less conclusive than Wallis’ work, they did show that care from male surgeons and anaesthesiologists (together or alone!) was associated with longer lengths of stay.

Certainly there is a lot of potential for confounders among these studies, although through subgroup analysis and cohort matching, the association between gender-discordance and outcome is arguably robust.

Researching essential (kinda-) immutable characteristics of doctors and how they impact patient care is not new. Tsugawa & Newhouse, et al. (2017) showed that patients treated by older physicians suffered a higher 30-day mortality. Interestingly the difference disappeared for high-volume physicians, suggesting a very believable link between clinical volume and quality maintenance.

More recently, and this time reassuring for old male surgeons (😉), Satkunasivam, et al. (2020) found in a retrospective cohort study of 1.1 million Canadian patients that increasing surgeon age was almost linearly associated with decreases in death, readmission & complications.

Clearly there are some foundational contributors to medical care that we need to understand better. These outcome disparities are not just a failing for the impacted patient groups, but rather a deeper and more concerning failure for our wider practice of medicine.

Referenced articles can be found in the metajournal knowledge collection, Effect of doctor gender & age on patient outcomes.

Does a GA CS increase PPD risk? Plus LMA studies & COVID vaccine optimism

Thu, 22 Jul 2021 02:04:00 +0000

GA caesarean section & post-partum depression

This large study (Guglielminotti 2020) of 428,204 New York caesarean section records (2006-2013), including 34,356 general anaesthetics (8%), investigated the association between mode of anaesthesia and post-partum depression (PPD). Other studies have shown an association between caesarean section (emergency > elective) and PPD. (Sun 2021, Xu 2017, and others), though this is the first to look specifically at general anaesthesia as a PPD risk factor.

Guglielminotti and Li found that general anaesthesia increased the odds of severe PPD by 54% (aOR 1.54, 1.21-1.95), and suicidal ideation by a massive 91% (aOR 1.91, 1.12-3.25), though not a significant increase in anxiety or PTSD.

The researchers discuss many potential causative factors, particularly known associations between GA CS & poor pain control, and subsequent pain & PPD – while also acknowledging the obvious potential for confounders. Of note patients receiving GA were older, more often non-Caucasian, had more co-morbidities, neonatal complexity, and lower socio-economic levels – also all independently associated with PPD risk.

In order to quantify the potential confounding contribution of emergency vs elective status, the researchers employed the novel E value:

To assess the impact of emergent cesarean delivery on our results, we calculated the E value associated with the aOR for the risk of PPD and suicidality. This relatively new metric takes into consideration 2 associations: (1) that between the confounder (emergent cesarean delivery) and the outcome (PPD); and (2) the association between the confounder (emergent cesarean delivery) and the exposure (general anesthesia).

An E value of 1.7 for the unmeasured confounder emergent cesarean delivery indicates that to explain away the association between general anesthesia and depression, either: (1) emergent cesarean delivery increases the risk of depression by at least 70%; or (2) emergent cesarean delivery is at least 70% more prevalent among general anesthesia than among neuraxial anesthesia. Either association is clinically plausible.

Keep it in perspective...

We already know that general anaesthesia for CS is suboptimal: it compromises both maternal experience and safety, but it should (hopefully) only ever be a chosen mode of anaesthesia when there is a true contraindication to regional anaesthesia – even at the modestly-high 8% GA rate among this New York cohort.

Looking at it from the other end, bear in mind that the modestly-faster time-to-incision for GA over regional is also of questionable neonatal benefit.

The take-home:

Just another reason to avoid GA CS when possible – but you already knew that, right?

"...general anesthesia is a potentially modifiable risk factor for PPD. This finding provides further supporting evidence favoring neuraxial over general anesthesia in cesarean delivery whenever possible."

Supraglottic airway training and manikins

Interesting prospective simulation & equipment study by way of the University of Freiburg. Schmutz et al. investigated how effective five different second generation supraglottic airway devices (SADs) performed in two common airway manikins: the TruCorp AirSim® and the crowd favourite, Laerdal's Resusci Anne® Airway Trainer™.

While ventilation was achieved in all SAD-manikin combinations, the Resusci Anne® Airway Trainer™ was associated with better and more consistent performance for SAD position, participant subjective assessment and ease of gastric tube insertion for most of the SADs. The TruCorp AirSim® did however achieve better leak pressures across most of the SADs (LMA® Supreme™, Ambu® AuraGain™, i-gel®, KOO™-SGA & LTS-D™).

But then, what are the implications for airway simulation training? The researchers correctly note that:

The most important quality of a manikin is the ability to simulate the real-world conditions and thus to give the trainee an authentic feedback.

The bottom line for SAD manikins?

While considering how manikin choice and SAD availability match with your aims for simulation training, the bigger picture is that the primary goal of any manikin-SAD coupling is real-life fidelity – and for that reason, participant subjective assessment is king. And so in this study at least, the Resusci Anne® Airway Trainer™ wins.

Head-rotation to improve LMA leak pressure?

Another interesting little airway study, this time out of Sapporo, Japan (Chaki 2021). A neat little randomised but-not-blinded study of the effect of head rotation on the oropharyngeal leak pressure of both the i-gel and LMA Supreme 2nd generation supraglottic airways.

The researchers investigated the leak pressure (OPLP) of the i-gel and LMA Supreme in paralysed patients with the head: 1. neutral, 2. rotated 30°, and 3. rotated 60°. They found that rotation of the head through 30° and 60° progressively increased OPLP by a clinically-significantly amount (0° vs 60° 5.5 cmH₂O (3.3-7.8) & 6.5 cmH₂O (5.1-8.0) respectively).

Before you get too excited...

The result however may not be reliably applicable to all populations, notably the study subjects were overwhelmingly small (x̄ ~160cm & 60kg) Japanese women (71%), receiving a TIVA muscle-relaxant anaesthetic (propofol, remifentanil, rocuronium). How well this improvement-with-rotation holds up among, for example, spontaneously ventilating large Caucasian males, is unclear.

Bottom-line

When using an i-gel or LMA Supreme 2nd generation supraglottic airway, careful head rotation to 60° may increased oropharyngeal leak pressure and so assist with ventilation troubleshooting. However head and neck rotation of anaesthetised, paralysed patients should be performed gently and cautiously – you are after all, not a chiropractor!

COVID mRNA vaccines and immune persistence

A great Good News study just published in Nature by researchers from Wash U Med investigated persisting COVID immunity following the Pfizer mRNA vaccination (BNT162b2). Turner et al. looked at the presence of not only circulating antibody-secreting B cells, but also germinal centre B cells found in the axillary lymph nodes of 14 study volunteers.

While the persistence of mRNA-vaccine induced immunity to SARS-CoV-2 has already been demonstrated to last at least 6 months, and likely 12 months, we do not yet know if or when vaccine boosters will be required beyond that.

Turner's study is particularly exciting because they found spike-protein binding B cells in the germinal centre of draining lymph nodes in all 14 post-immunisation participants for the full 15 weeks of the study. The germinal centre response was so vigorous and persistent that the researchers believe this could represent COVID-protection lasting for years.

"Ellebedy said the immune response observed in his team’s study appears so robust and persistent that he thinks that it could last for years. The researcher based his assessment on the fact that germinal centre reactions that persist for several months or longer usually indicate an extremely vigorous immune response that culminates in the production of large numbers of long-lasting immune cells, called memory B cells. Some memory B cells can survive for years or even decades..." – Dr Francis Collins, NIH Directors Blog

This study builds on the same team's earlier work (Turner 2021 May) looking at bone marrow plasma cells in those who have recovered from mild COVID infection, also showing a long-lived immune response.

COVID persistent immunity takeaway:

Although COVID-19 and developed vaccines have been circulating for only 12-18 months, these immune-response studies give some hope that the miracle of mRNA vaccines may not only be in their efficacy, but also in the longevity of protection.

Mentioned studies:

Guglielminotti J Li G. Exposure to General Anesthesia for Cesarean Delivery and Odds of Severe Postpartum Depression Requiring Hospitalization. Anesth. Analg. 2020 Nov 1; 131 (5): 1421-1429.
Schmutz A, Bohn E, Spaeth J et al. Comprehensive evaluation of manikin-based airway training with second generation supraglottic airway devices. Ther Clin Risk Manag. 2019 Jan 1; 15: 367-376.
Chaki T, Tachibana S, Kumita S et al. Head Rotation Reduces Oropharyngeal Leak Pressure of the i-gel and LMA® Supreme™ in Paralyzed, Anesthetized Patients: A Randomized Trial. Anesth. Analg. 2021 Mar 1; 132 (3): 818-826.
Turner JS, O'Halloran JA, Kalaidina E et al. SARS-CoV-2 mRNA vaccines induce persistent human germinal centre responses. Nature. 2021 Jun 28.