July - August 2023

Canadian Journal of Anaesthesia

Submitted September 2023 by Dr Marlene Johnson

Read by 143 Journal Watch subscribers

Summary
This Canadian study was a prospective, observational study of 33 healthy volunteers aged between 2-14. It examined residual gastric volume using ultrasound, after patients were given 250mL of clear fluid. A baseline ultrasound was performed prior to clear fluids, and then at 30, 60, 90 and 120 minutes after fluid consumption. The primary outcome was the time to achieve a gastric volume of less than 1.5mL/kg.

Results were as follows:
Baseline 0.51 mL/kg (95%CI 0.46-0.57)
30 min 1.55 mL/kg (95%CI 1.36-1.75)
60 min 1.17 mL/kg (95%CI 1.01-1.33)
90 min 0.76 mL/kg (95%CI 0.67-0.85)
120 min 0.58 mL/kg (95%CI 0.52-0.65)

Individual results were not reported in the paper.

Take Home Message
This study adds further support to liberal (1 hour) clear fluid guidelines for healthy, elective paediatric patients. By 60 minutes, patients had gastric volumes of less than 1.5mL/kg. The authors argue that previous papers have shown 1.5mL/kg confers “negligible risk for significant aspiration”. By 120 minutes, gastric volumes returned to normal.

Limitations to this study include small sample size, a fixed volume of clear fluid for all participants (rather than weight based), and no discussion on the sensitivity or specificity of the formula used to estimate gastric volume. Of note, there were two “outlier” participants with higher than expected volumes at 60 and 90 minutes, highlighting the variable nature of gastric emptying.

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British Journal of Anaesthesia

Submitted September 2023 by Dr Rory Walsh

Read by 220 Journal Watch subscribers

Summary:
The Pediatric Difficult Intubation (PeDI) Registry is a large, multicentre international registry that collects data on paediatric patients where difficult intubation is identified. The authors performed a retrospective, observational cohort analysis of the registry with the following aims:

Primary aim:
Identify the physical characteristics and anaesthetic factors associated with difficult or impossible mask ventilation (MV).

Secondary aims:
i) Compare the incidence of complications between patients with difficult intubation AND difficult or impossible MV vs those with difficult intubation alone.
ii) Determine whether difficult MV was worsened or improved after neuromuscular blocking agents.
iii) Determine the efficacy of supraglottic airway devices as a rescue ventilation technique.

The analysis included cases between 2011 to 2021 across 36 institutions in seven countries. 5453 difficult intubation cases were ultimately included.

Given that the combination of both difficult intubation AND difficult MV is a potential crisis situation, identifying factors associated with difficult MV may help clinicians avoid ‘can’t intubate, can’t oxygenate’ scenarios. Similarly investigating the effectiveness of supraglottic airways and neuromuscular blocking agents in the context of difficult MV is also important.

While predictors of difficult MV and the effects of neuromuscular blocking agents on ventilation have been well studied in adults, there is a relative lack of paediatric-specific studies in these areas.

Findings:
The incidence of difficult or impossible MV in children with difficult intubation was 9% (difficult 8%, impossible 1%). As a comparison previously published data suggests that difficult MV occurs in up to 6% of children in the general population.

Patient factors associated with difficult/impossible MV:
• Age <1y
• Increased weight
• Low weight (<5th percentile for age)
• Treacher Collins Syndrome
• Glossoptosis
• Limited mouth opening

Anaesthetic factors associated with increased risk of difficult or impossible MV:
• Intravenous induction
• Tracheal intubation attempt in ICU

Anaesthetic factors associated with decreased risk of difficult impossible MV:
• Inhalational induction
• Opioid administration

The incidence of complications (including hypoxaemia, major airway trauma & cardiac arrest) was higher in patients with difficult or impossible MV than those with easy MV.

Supraglottic airway placement improved ventilation in 71% of patients with difficult MV, and 48% with impossible MV.

In patients with difficult or impossible MV, the use of neuromuscular blocking agents was more frequently associated with improvement or no change in ventilation (90%), than worsening (10%).

The main strength of this study is that it utilises a very large international, multicentre registry across a ten-year time frame. The main limitation of the study, as acknowledged by the authors, is that the analysis was limited to MV in patients with difficult intubation only. The findings cannot be generalised to patients who are not difficult to intubate.

The PeDI registry is large. This study analysed data from over 5000 difficult intubations collected from 36 institutions across seven countries (including the USA, Canada, and Australia). It can be reasonably inferred that the findings from such a large analysis are applicable to Australian and New Zealand paediatric practice.

Take Home Message/Commentary
Unsurprisingly the combination of difficult or impossible MV AND difficult intubation puts children at greater risk of complications.

In children that are difficult to intubate there are certain patient and anaesthetic factors that are associated with difficult or impossible MV. These factors should be considered when planning the airway management of children with known or suspected difficult intubation.

Supraglottic airways frequently improve ventilation when MV is difficult or impossible. A supraglottic airway should always be considered for rescue ventilation.

In some cases the administration of neuromuscular blocking agents will worsen MV. However, this analysis suggests that the use of these agents more often either improve or have no effect on MV.

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Pediatric Anesthesia

Submitted September 2023 by Dr David Pachter

Read by 255 Journal Watch subscribers

Summary:
Balancing the risk between pulmonary aspiration of gastric contents, and the adverse consequences of prolonged fasting times is one of the age-old conundrums of paediatric anaesthesia. This article summarises some of the recent updates in fasting guidelines that have been published by various anaesthesia societies around the world.

The general trend has been an adoption of more liberal strategies towards clear fluid consumption prior to theatre, notably a widely adopted reduction from 2 hours to 1 hour for clear fluid consumption prior to theatre. More recently, further liberalisation of fasting strategies to allow sips of clear fluids right up until the child is brought to theatre, so called “sips until send", or "6-4-0” have been introduced in centres in Europe, a point only briefly alluded in this review. The harms associated with prolonged fasting times, both psychological (eg distress resulting from thirst and hunger) and physiological (eg glycaemic and haemodynamic disturbance) are considered in detail by the authors. The final section of the article focuses on strategies aimed at improving tolerance of fasting, including the use of carbohydrate drinks and chewing gum to increase satiety, areas in which the evidence in paediatric populations is limited.

Take home messages:
In recent times there has been a trend towards strategies aimed at reducing perioperative fasting times. Reasons for this include
• The incidence of significant morbidity in children due to pulmonary aspiration is extremely low
• Excessive fasting remains common, and is associated with significant levels of distress and physiological derangement

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