This article reviews the phenomenon of opioid-induced hyperalgesia (OIH) and its implications for clinical anesthesia. The goal of this review is to give an update on perioperative prevention and treatment strategies, based on findings in preclinical and clinical research. ⋯ Since the immediate postoperative period is not ideal to initiate long-term treatment for OIH, the best strategy is to prevent its occurrence. A multimodal approach, including choice of opioid, dose limitations and addition of nonopioid analgesics, is recommended.
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."
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.summary
This massively-multicenter (235 hospitals, 24 countries; mainly Europe & N. America) cohort study investigated post-operative morbidity and mortality in those with confirmed SARS-CoV-2 infection.
Why is this significant?
Early data suggested that COVID-19 patients who underwent even minor elective surgery suffered worse post-operative outcomes, particularly higher mortality.
This large cohort study confirms these concerns and will assist decision making around the timing of surgery for COVID-19 patients and the process for re-commencing elective surgery in communities hardest hit by the pandemic.
What did they do?
Over a 3 month period in early 2020 the researchers analysed 1,128 patients who underwent emergency (74%) or elective (25%) surgery across 24 countries. Patients diagnosed with COVID seven days pre-op or 30 days post-op were included, although the majority of patients (74%) had SARS-CoV-2 infection diagnosed post-operatively.
And they found?
30-day mortality was extremely high (24%).
Pulmonary complications (pneumonia, ARDS or unexpected post-op ventilation) were very common (51%) and were associated with an even higher mortality (38%; and 83% of all deaths).
Mortality was unsurprisingly associated with older age ≥ 70 years, male sex, ASA ≥ 3, emergency surgery, major surgery, and malignancy.
Other interesting observations...
- Nonetheless 'lower-risk' groups still suffered significant 30-day mortality rates, eg. 30-49 year olds (6%), women (18%), ASA 1-2 (12%), no-comorbidities (7%).
- Being asymptomatic at admission did not have a significant protective effect (22% vs 27% mortality).
- Dyspnoea and/or sputum on admission were the only symptoms associated with worse outcomes.
- 20% of patients suffered ARDS, with a 63% mortality rate.
- Although emergency surgery was higher risk, elective surgery still carried a 19% mortality rate. Even minor surgery resulted in a 16% mortality rate!
- Even obstetrics (2% mortality) and gynaecology (5%) demonstrated orders of magnitude-higher mortality than expected.
- There was no statistically significant difference between local, regional or general anaesthesia.
- Pulmonary embolus was only seen in 2% at 30 days and when present did not appear to impact mortality.
Why such high post-operative COVID mortality?
The authors suggest this could be due to the combination of pro-inflammatory cytokine and immunosuppressive responses to surgery, and/or mechanical ventilation associated with general anaesthesia (although the later was not significantly associated with higher mortality).
Surgery for those with known or suspected COVID-19 should be avoided or delayed until after recovery from infection, as allowed by the underlying surgical pathology. When surgery cannot be delayed less-invasive surgery is preferable, and post-operative recovery should be closely monitored.
Keep in mind
Although RT-PCR testing was the main diagnostic test, in some settings clinical criteria (6%) and/or chest CT (7%) were instead used for diagnosis. Additionally, hospital data collection during a pandemic emergency carries higher risk of error, although this should not effect the broad validity of the research conclusions.summary
Why should I read this?
The cuffed vs non-cuffed ETT debate for children and neonates is largely settled, demonstrating the superiority of modern cuffed tubes over their historical, uncuffed forbears. Nevertheless, despite reliable evidence to the contrary, many general anaesthetists still prefer uncuffed tubes for children.
Give me the quick overview
Shah & Carlisle explore the accumulated evidence supporting the shift to cuffed endotracheal tubes by paediatric anaesthetists, both in neonates and older children.
They challenge historical airway anatomy & physiology myths that once encouraged the use of uncuffed ETTs in children, and the questionable reliability of the widely-used Cole formula for tube size prediction (size = age/4 + 4; correct in only 50-75%).
The development of Weiss et al.'s Microcuff™ tube represents a watershed moment in addressing concerns of paediatric airway trauma from cuffed ETTs, resulting in improved ETT function without any increase in stridor.
More recently, Chamber's 2018 RCT compared cuffed and uncuffed ETTs in children undergoing elective general anaesthesia, and found that cuffed tubes improved ventilation and reduced short-term post-operative respiratory complications, in addition to decreasing tube changes.
Addressing concern for increased work-of-breathing and higher inspiratory pressures when using a 0.5 mm smaller ID tube, Shah & Carlisle note Thomas et al.'s 2018 laboratory study showing any such effect is easily compensated for with pressure support and automatic tube compensation.
Similarly, the authors also note that there has been no demonstrated evidence of an increased incidence of subglottic stenosis in children using cuffed ETTs.
Finally, Shah & Carlisle report on their updated meta-analysis, showing that cuffed tracheal tubes in children result in fewer tube changes and less sore throat, but no difference in risk of laryngospasm.
Using a modern, Microcuff™ or equivalent cuffed ETT that is 0.5 mm smaller in size than an equivalent uncuffed tube, offers functional, ventilation and safety benefits.summary