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:

  1. 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.
  2. 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.
  3. 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.