Intranasal dexmedetomidine sedation for paediatric MRI by radiology personnel
A retrospective observational study
June 2023 by Dr Jon Stacey
This Scandinavian study adds to the evidence base around needle-free sedation techniques for paediatric imaging, itself the subject of a recent systematic review (https://www.bjanaesthesia.org/article/S0007-
0912(22)00517-7/fulltext), summarised elegantly by Dr Burton in the January-February edition of this forum (Needle-free pharmacological sedation techniques in paediatric patients for imaging procedures: a systematic review and meta-analysis - SPANZA).
The authors identify access to paediatric anaesthetic services as a common rate-limiting step for the timely provision of paediatric MRI, and moreover suggest an alternative model that is both largely needle- and anaesthetist-free.
Over a period of 4 years, 1091 appropriately-triaged children of mean age 34 months and ASA 1 or 2 received nasal dexmedetomidine alone as sedation for MRI scans of predicted duration less than one hour, administered by radiology staff in the absence of an anaesthetist. The initial dose was of 4mcg/kg, with a subsequent 2mcg/kg if the child was deemed ‘not sedated enough’.
Within the limits of the study design, the results seem appealing; 93% of scans commenced were completed as planned with adequate image acquisition.
The mean time from first administration of dexmedetomidine to scan readiness is not clear, nor the time at which a second dose (required in 36% of children) was adjudged to be required or effective. Further, there is a poorly-defined cohort of children in whom adequate sedation was never achieved despite repeat dosing, and who do not appear in the subsequent analysis.
The safety data is confusingly presented but appears re-assuring (especially given the dexmedetomidine protocol did not mandate any pre-procedural fasting); 4 children had minor de-saturations requiring only brief supplemental oxygen, and 5 had bradycardias below the 1st centile for age, with none requiring intervention. Closer inspection however suggests that agreed indications for seeking anaesthetic input were not always followed by radiology staff, and moreover blood pressure was not measured at any point during the period of sedation.
In the discussion the authors argue their results support the safety and efficacy of nasal dexmedetomidine for paediatric MRI, thereby enabling radiology departments to take greater ownership of the process, including those previously lacking the opportunity. They go on to extrapolate that paediatric anaesthetists need not be part of the process beyond a consultative role.
Whilst no doubt an interesting study, I’m not sure their findings yet support their confidence.
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Comparison of intravenous and inhalation anesthesia on postoperative behavior changes in children undergoing ambulatory endoscopic procedures
A randomized clinical trial
June 2023 by Dr Priya Sreedharan
This randomized, parallel, double-blinded clinical trial performed in an outpatient endoscopic clinic between October 2018 and December 2021 was designed to determine if intravenous anaesthesia was effective at reducing post operative behavioural changes in children undergoing ambulatory endoscopic procedures when compared to inhalational anaesthesia.
164 children between the ages of 1-12 yrs , ASA I -III, undergoing endoscopic day surgery procedures, were included and analysed in the study and randomised to receive either inhalational or intravenous maintenance of anaesthesia post induction. All children received inhalational induction with sevoflurane. The intravenous group was then maintained with propofol post placement of a peripheral intravenous cannula.
All children were assessed using a modified Yale Preoperative Anxiety Scale (mYPAS) and the parental anxiety preoperatively assessed using a 100mm Visual analog scale (VAS-anx). Post procedure emergence delirium was assessed using Paediatric Anaesthesia Emergence Delirium (PAED) scale whilst pain was assessed using FLACC scale. Severe emergence delirium (ED) was treated with a bolus of propofol (1mg/kg) and severe pain was treated with fentanyl (1ug/kg).
On days 1,7 and 14 post procedure, the parents were contacted by telephone, and the child’s behaviour was evaluated using the Post Hospitalisation Behaviour Questionnaire for Ambulatory Surgery (PHBQ-AS). The PHBQ-AS is a slightly abbreviated version of the PHBQ with 11 items including anxiety, regression, sleep and eating disorders, aggression and apathy.
They recorded a 19% incidence of ED in the intravenous group and 41% in the inhalational group in the first minute post wake up. This difference did not persist to the 5th and 10th minute post wake up with FLACC pain scores being comparable. There were no differences of note in the preoperative children’s or parental anxiety scores. They did not find any differences in the adverse behavioural outcome between the inhalational and intravenous group post procedure on day one, seven and fourteen as per the PHBQ-AS questionnaire. They did find a moderate co-relation between the occurrence of emergence delirium and the number of negative postoperative behaviours on day 7 but this was across both groups.
Take home message: ED and prolonged negative behavioural changes post procedure is a topic of much interest in the paediatric anaesthetic world and data to date suggests that the cause is multifactorial, with no magical single intervention to prevent their occurrence. Several studies have looked into the effect of the two anaesthetic techniques on post operative delirium and found that there may be benefits in the incidence of emergence delirium with intravenous techniques but the effects on prolonged post operative behavioural changes is less clear. This study found an early reduction in ED with the intravenous technique but no differences between inhalational and intravenous maintenance techniques for negative behaviours in the days following.
The did note that many of their patients were “frequent flyers” and may have exhibited less preoperative anxiety but the co-relation between ED and post procedural negative behaviour was reinforced regardless of technique.
Extrapolation of the findings in this study to the general “anxious” paediatric population undergoing painful procedures must be carefully made.
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Ultrasound Assessment of Gastric Fluid Volume in Children Scheduled for Elective Surgery After Clear Fluid Fasting for 1 Versus 2 Hours
A Randomized Controlled Trial
June 2023 by Dr David Stoeter
This small randomized single-blinded controlled trial is the second such trial comparing gastric fluid volumes after a 1-hour versus a 2-hour clear fluid fast in children undergoing general anaesthesia for elective surgery. It is the first utilising ultrasound. The authors (from a major university hospital in Cairo, Egypt) postulated that a 1-hour fast would result in significantly higher gastric volumes. They did indeed demonstrate that the volumes roughly doubled, and suggest that a 1-hour fast may result in an unsafe stomach. The questions the reader is specifically interested in, however, are: Is there a gastric fluid volume at which the risk of aspiration is significantly increased? Does a 1-hour fluid fast lead to a significantly greater proportion of patients having gastric volumes above this threshold?
The former question has as yet not been clearly answered. It would require a study of 10,000-20,000 patients in order to reliably demonstrate an increase in aspiration rates above baseline levels. What we do have is attempts to define a normal distribution of gastric volumes in small (ranging 34 to 538 patients) observational studies of both adults and children with and without risk factors for regurgitation or aspiration events. These normal distributions seem to demonstrate that around 95% of children have volumes less than 1.5ml/kg and that there are always small groups of outliers with larger volumes occupying the remaining 5% who have volumes greater than this regardless of clear fluid fasts of 2, 5 or 6-hours. This study demonstrates that whether a 1 or 2-hour fast is enforced, a child’s gastric volume never lies above this 1.5ml/kg threshold. Other risk thresholds of 1.25ml/kg and 0.8ml/kg (as mentioned by the authors) seem to be based on an arbitrary grading system that has not been related to aspiration risk nor to a normal distribution of the population of interest.
Strengths of the study included a robust overall design, a fairly well powered sample size, standardisation of quantity and caloric content to a maximum of 3ml/kg and 0.42kcal/ml respectively in keeping with standard practices in many countries and international recommendations. They did not comment on exactly how successful they were at enforcing the precise 1 and 2-hour fasts. It would also have been helpful to have some more parameters reported such as mean, standard deviation and range in order to establish the nature of the normal distribution in each sample. Their reference to several difference risk thresholds (0.8ml/kg, 1.25ml/kg and 1.5ml/kg) is likely confusing for practical application.
In summary, this study shows that whilst gastric volumes are higher after a 1-hour versus a 2-hour fast, this does not seem to place patients outside of the normal distribution of what is understood to be a fasted stomach and would, contrary to the authors conclusions, support a 1-hour minimum fast given that we know that most patients who apply this rule in practice fast longer than 1 hour. It would be helpful in the future to better define the normal distribution of gastric volumes in fasted children for the sake of studies like this one since some of the statistical reporting in existing studies is not always crystal clear on this point. A multicentre study is likely necessary to generate the numbers needed to relate this to aspiration risk.
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What we know and what we don't know about the perioperative use of methadone in children and adolescents
June 2023 by Dr Sorcha Evans
This review article looks at methadone use in the paediatric perioperative population summarising the benefits and risks.
A brief description of the pharmacokinetics and pharmacodynamics is presented, along with potential benefits of using methadone perioperatively and the unknowns in this population. The article deduces that dosing strategies would likely be similar to that of adults. However, they also state that the minimal effective analgesic concentration has still not been ascertained in children.
The article goes on to review several retrospective and prospective studies of methadone use in posterior spinal fusion, cardiac and pectus excavatum surgery. They suggest intraoperative use of methadone reduces opioid requirements intraoperatively and postoperatively with similar or maybe less adverse effects and potentially reduced hospital stay. However, the studies were small, heterogenous and some with complex multifaceted pain protocols making interpretation difficult. Examples of potential perioperative dosing protocols including PRN dosing and infusions are given.
Proposals for future development included procedure specific protocols, research into the use of methadone in routine paediatric surgery and safety and efficacy of methadone as a primary opioid for pain management. Additionally, they highlighted the lack of studies comparing opioid PCA vs methadone PRN dosing or methadone PCA in the paediatric population.
Take home message
Methadone is a potential suitable and safe alternative to standard opiates in paediatric patients undergoing surgery, especially those with neuropathic pain. However, there remains gaps in knowledge regarding this area despite methadone being around since World War II.
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Videolaryngoscopy in neonates
A narrative review exploring the current state of the art
June 2023 by Dr Ashton Speed
This article is a narrative review exploring the utility, benefits and pitfalls of the use of videolaryngoscopy in children with a specific focus on the current practice of neonatal tracheal intubation. The authors conducted a Medline search on all published articles between 2010 and 2022 and ultimately included 20 articles in their narrative review including randomised control trials, observational studies, review articles, meta-analyses and editorials.
The authors concluded that in neonates and or children with expected difficult intubation the routine use of a videolaryngoscope (VL) compared to standard direct laryngoscopy (SDL) as first device for tracheal intubation is associated with higher first attempt tracheal intubation and reduced intubation related complications. This conclusion is supported by data from the Paediatric Difficult Intubation registry (PEDI) and the multicentre RCT Videolaryngoscopy in Small Infants (VISI) trial:
• The PEDI trial found initial tracheal intubation success rate in <18yo paediatric patients with a suspected difficult intubation to be 53% with VL group compared to 4% w SDL
• The VISI trial found that VL compared with SDL improved first pass intubation in neonates and infants <6.5kg by 5%.
The Neonate and Children adult of Anaesthesia practise in Europe (NECTARINE) observational cohort study of critical events during anaesthesia in neonates and infants found that two-thirds of difficult intubations were unexpected and that the use of VL as first device for tracheal intubation was only used when difficult intubation was expected. In that study, VL was associated with reduced intubation attempts, improved first pass tracheal intubation and reduced intubation related complications. Hence, Bonfiglio and Grief have asked the question as to whether anaesthetic clinicians should be using VL as first devices for tracheal intubation in all neonates and infants less than 1yo of age – especially given the majority of difficult intubations are unexpected and VL improves first pass intubation in both neonates and children with difficult intubation.
However, the authors’ contention has not been reflected in Cochrane reviews by Lingappan et al (2018) and Abdelgadir et al (2017) which concluded that there is insufficient evidence to support the routine use of VL for neonatal intubation. Bonfiglio and Grief surmise that these findings are likely due to the heterogeneity of studies included in the Cochrane reviews and that more recent evidence in the PEDI, NECTARINE, VISI and OPTIMISE studies favour the use of VL to improve tracheal intubation management in neonates and infants with difficult intubations. This study further recommends that routine VL use might accelerate the laryngoscopy learning curve to improve clinician skillset when conducting both routine and difficult VL neonatal intubation.
There is a paucity of evidence for recommending specific VL brands and blade type when performing neonatal intubation. In children with difficult intubation, the PEDI trial found that the use hyper-angulated blades were associated with a high tracheal intubation success rate compared with VL standard blades (Miller or MAC). However, after multi-variable logistic regression analysis in patients <5kg without an expected difficult intubation, the PEDI trial found that the use of standard VL blades (MAC, MILLER) resulted in improved initial tracheal intubation success. Hence, Bonfiglio and Grief recommend the use of standard VL blades (MAC/MILLER) over hyper-angulated blades for routine neonatal tracheal intubation.
Due to lack of evidence and recommendations from paediatric and neonatal difficult airway societies the authors have not provided specific suggestions with regards to what specific VL brand should be used when conducting both routine and difficult neonatal and infant intubation. This narrative review has highlighted the potential benefit of video-laryngoscopy when managing neonatal and infant intubation and children with a difficult intubation. The authors have discussed the potential benefits of routine use of VL for neonatal intubation, namely:
• Improved first pass tracheal intubation
• Reduced intubation related complications
• Improved safety when training novice intubators
• Improved airway team situational awareness and performance
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Rapid sequence induction in Paediatric Anaesthesia
A narrative review
June 2023 by Dr Christoher Dawson
Bronchial aspiration - dangerous for our patients and medico-legally and morally dangerous for providers. This narrative review presents an overview of rapid sequence induction (RSI) as it pertains to paediatric patients.
Few large studies have examined the incidence of pulmonary aspiration in children and its risk factors. The Near 4 Kids trial found a 4% incidence of regurgitation during intubation, with 0.7% incidence of clinical aspiration, with age >8 and haemodynamic instability among the risk factors. The APRICOT study found 0.1% of their patients had aspiration, with roughly 50% at induction and 50% at emergence / maintenance.
There is a large heterogeneity of RSI techniques in the paediatric literature beyond the classically described pre-oxygenate + muscle relaxant + cricoid pressure + no ventilation. One large survey described in this review noted only 24% of respondents performed cricoid pressure during RSI and nearly a third performed low pressure ventilation. In the APRICOT study half the patients were ventilated and half were not, and 90% of them had muscle relaxants. (Notably in a recent ANZCA survey [Mistry et al, Anaesthesia and Intensive Care 2021] the numbers were closer to 75% amongst those who use cricoid).
The article presents several risk factors for aspiration/indications for RSI in children which would be near identical to a list for adults. Some more information around specific risk factors that might be more unexpected in children versus adults and why may have been useful for the occasional paediatric anaesthetist.
In terms of fasting the authors note that European recommendations on preoperative fasting in children suggest assessing gastric contents with ultrasound in children before emergency surgery, which may present challenges depending on operator skill and patient compliance.
The article presents a preparation checklist for equipment for RSI. Again, no real surprises here but it may be a useful checklist to have to hand in a crisis. They suggest use of video laryngoscopy as first choice where available, noting there is evidence in infants that it improves first pass success and reduces complications.
Skating delicately over the huge area of controversy that is use of cricoid pressure, the authors state "many paediatric anaesthetists wonder whether cricoid is performed as a ritual", noting the potential issues relating to cricoid pressure in children - smaller cricoid size, application of correct pressure and potential for decrease in lower oesophageal sphincter tone leading to aspiration.
They note that several European paediatric anaesthesia societies no longer recommended use of cricoid pressure during RSI, and that the Near 4 Kids trial showed an increased incidence of aspiration with the use of cricoid - though this was not significant after adjusting for patient and practice factors. Notably cricoid pressure can help prevent gastric insufflation when ventilating children <1 year old. As always - more RCTs are needed! The authors’ final opinion is not to recommend cricoid pressure.
The authors give a concise summary of a suggested standard operating procedure for RSI in children. Mostly sensible stuff that fits with local practice. Injecting opioids or atracurium slowly and use of thiopentone might raise eyebrows.
The planning and equipment as described in this article assumes that all patients will have an IV placed as part of the preparation for RSI. This is all well and good, but discussion around use of sedatives and adjuncts (eg N2O) and their safety (or lack thereof) would be helpful for the children who would not tolerate IV placement.
With regards to oxygenation the authors note the difficulty in pre-oxygenating smaller, non-compliant children. They suggest a number of strategies to achieve a “controlled RSI” which have been demonstrated to have improved outcomes:
• gentle ventilation - <8mL/kg, APL at 10cm, which appears to only cause gastric insufflation in children <1 year old
• maintain FRC by fixing APL at 10cm and applying “manual high frequency tiny ventilation”
• nasal oxygenation via standard nasal prongs during intubation
The authors do not describe how nasal oxygenation could be achieved smoothly without interfering with effective mask ventilation, if desired.
For the child in whom does aspiration occur the authors give a nice summary of management techniques - head down, suction, bronchoscopy if large pieces obstruct. Use PEEP, more suction and bronchodilators depending on the clinical picture. Systematic bronchial-alveolar lavage, chest XR and steroids are not routinely required. Handy disposition suggestions are also provided - asymptomatic patients can be sent to their pre-planned destination (home / ward) after two hours of observation, while symptomatic patients should go to the ward, and those requiring ventilatory support or if SaO2 cannot be maintained over 90% should go to ICU.
Finally, a timely reminder of the use of capnography and consideration of human factors in confirmation of tracheal intubation, particularly in the light of recent publicised tragic events: no trace = wrong place.
This review gives a succinct summary of the issues surrounding RSI in children and the important steps to consider, with useful discussion of some specific techniques that can be applied.
It could have used a little more depth as to the evidence base for some of their recommendations, or more included more recommendations from international societies where the evidence base is weak. It would be useful to know more about which risk factors for pulmonary aspiration are more prevalent in children and why, in order to better prevent these events.
Some more real-world consideration of management of the non-compliant child without an IV who requires an RSI would be helpful.
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The effect of hyperventilation versus normoventilation on cerebral oxygenation using near infrared spectroscopy in children undergoing posterior fossa tumor resection
A randomized controlled cross-over trial
June 2023 by Dr Rosalyn Boyd
This study examined the effects of hyperventilation versus normoventilation on cerebral oxygenation in children undergoing posterior fossa surgery.
Fifty children were enrolled and randomised into two groups; an early hyperventilation group (ETCO2 target: 26-30 mmHg) and an early normoventilation group (ETCO2 target: 31-35 mmHg). The study was a cross-over trial, so after 30 minutes in the prescribed ventilation strategy (phase 1) the patient was then switched to the alternative ventilation strategy for a further 30 minutes (phase 2). Near infrared spectroscopy (NIRS) was used to assess cerebral oxygen saturation with measurements taken at baseline and then every 5 minutes until then end of phase 2. Other measurements collected were: three intracranial pressure (ICP) measurements and a neurosurgical score of brain relaxation at the end of phase 1.
During the study period blood pressure (BP) was kept within 20% of baseline. If BP dropped below this a 10-20 ml/kg fluid bolus was administered. Any patients requiring vasopressors during the study were excluded.
The results demonstrated that cerebral oxygen saturation was significantly lower in the hyperventilation phase compared to the corresponding normoventilation phase. Linear regression showed that for every 1 mmHg decrease in ETCO2 there was a 1.4% reduction in NIRS values. There was no statistically significant difference in brain relaxation score or ICP measurements between the groups.
This study helps to clarify the utility of different ventilation strategies during neuro anaesthesia. Hyperventilation has historically been used as a strategy to emergently reduce ICP through its effect on cerebral vasoconstriction and decreased cerebral blood flow. This study demonstrates the reduction on cerebral oxygenation associated with hyperventilation but without significant beneficial effects on brain relaxation or ICP. The results are in keeping with other studies showing a variable reduction in NIRS with hyperventilation in adult and adolescent populations undergoing non neurosurgical procedures.
A limitation of this study is that patients who had significant mass effect or oedema on their preoperative MRI were excluded, suggesting the patients who arguably would most likely benefit from hyperventilation may not be represented within this cohort. Another limitation is that there was no study into the post operative outcomes of patients undergoing hyperventilation and a reduction in cerebral oxygenation. Other studies in cardiac and non-cardiac surgery have, however, demonstrated long term cognitive delay and post operative behavioural changes associated with drops in cerebral oxygenation suggesting it is not a benign finding.
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