Anaesthesia 2014, 69, 1051–1064 insertion guide in a porcine phantom model. Anaesthesia 2013; 68: 826–9. 3. Kopac DS, Chen J, Tang R, Sawka A, Vaghadia H. Comparison of a real time Sonix GPS needle tracking ultrasound technique with traditional ultrasound for vascular access in a phantom gel model. Journal of Vascular Surgery 2013; 58: 735–41. 4. Wong SW, Niazi AU, Chin KJ, Chan VW. Real-time ultrasound-guided spinal anesthesia using the SonixGPS needle tracking system: a case report. Canadian Journal of Anesthesia 2013; 60: 50–3. doi:10.1111/anae.12820
The effect of general anaesthesia on memory in children We read with interest the recent article by Yin et al. [1], comparing memory changes between children undergoing general anaesthesia with propofol or sevoflurane, and we agree that this is a very important topic that merits intense and thorough research. However, we have some questions about the methodology and data interpretation that we would like the authors to address. Firstly, the sample size calculation was based on the assumption that a difference in scores of more than one SD was considered significant, but without publication of the pilot study data, we are uncertain whether this calculation is based on sufficiently rigorous evidence. In addition, the eight components of the memory testing score appear to vary in scale and dimension, meaning that a single SD difference could have different absolute effects on each result presented, but no information is provided about 1062
Correspondence
whether significance was adjusted for multiple-testing effects. The conclusion that propofol impairs memory would require comparison with a control group that was not anaesthetised. Secondly, we question the propofol infusion scheme described. The authors infused propofol 1% at rate of 5–10 lg.kg 1.min 1, providing a maximum blood concentration of less than 2 lg.ml 1, which is normally insufficient for maintaining anaesthesia in children. If this is a typographic error and the authors infused at 50–100 lg.kg 1.min 1, then the concentration would be too high. In addition, there was no attempt to ensure equipotency of the anaesthetic drugs used when comparing the techniques, which constitutes a significant weakness in the study design. Finally, we think that the authors have misinterpreted the study by Jacob et al. [2], which found that higher cerebral concentrations of lactate and taurine in children anaesthetised with sevoflurane compared with propofol infusion correlated with higher scores for emergence agitation and delirium. This may be a sign of deleterious effects of sevoflurane on the brain, rather than a sign of earlier recovery of normal brain function, as Yin et al. claim. There is considerable concern about the possibility that general anaesthesia might damage the developing human brain [3]. We urge caution in accepting the conclusions of this study without the authors’ addressing our concerns about whether the study was correctly powered.
F. A. Lobo J. Guimar~aes Centro Hospitalar do Porto, Porto, Portugal S. Schraag Golden Jubilee National Hospital, Glasgow, UK F. Engbers Leiden University Hospital, Leiden, The Netherlands E-mail: [email protected] No external funding or competing interests declared. Previously posted on the Anaesthesia correspondence website: www.anaesthesiacorrespon dence.com. No reply provided by the authors.
References 1. Yin J, Wang SL, Liu XB. The effects of general anaesthesia on memory in children: a comparison between propofol and sevoflurane. Anaesthesia 2014; 69: 118–23. 2. Jacob Z, Li H, Makaryus R, Zhang S, et al. Metabolomic profiling of childrens brains undergoing general anesthesia with sevoflurane and propofol. Anesthesiology 2012; 117: 1062–71. 3. SmartTots. www.smarttots.org (accessed 17/05/2014). doi:10.1111/anae.12779
Driving advice after isoflurane anaesthesia Changes to the Summary of Product Characteristics (SPC) for isoflurane in August 2013, state that “patients should be advised that performance of activities requiring mental alertness, such as operating a motor vehicle or hazardous machinery, may be impaired for 2–4 days after anaesthesia with isoflurane” [1]. Previously, the SPC stated that driving or working machinery should be avoided for at least 24 hours. The
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Correspondence
reason for this change is listed as “Marketing Authorisation Holder details changed to reflect the company change from Abbott to AbbVie.” [2]. It is unclear on what justification the change to the SPC was made. In contrast, the SPC information for sevoflurane states “patients should be advised that performance of activities requiring mental alertness, such as operating a motor vehicle or hazardous machinery, may be impaired for some time after general anaesthesia” [3]. Propofol’s SPC also opts for the more vague “Patients should be advised that performance at skilled tasks, such as driving and operating machinery, may be impaired for some time after general anaesthesia”[4]. Desflurane’s SPC states that “patients should be advised that the ability to perform tasks such as driving or operation of machinery may be impaired after general anaesthesia, and it is advisable to avoid such tasks for a period of 24 hours” [5]. At present in our hospital, we advise patients not to drive/cook/ operate machinery for 24 hours after anaesthesia. We are very concerned that this change to the SPC of isoflurane has not been well publicised and has potentially serious medicolegal implications for anaesthetists, should a patient, for example, be involved in a traffic collision when driving three days after surgery. The Royal College of Anaesthetists website states “current advice is that it is not usually safe to drive or drink alcohol until at least 24 hours after a general anaesthetic” [6]. The Association of Anaesthestists of Great Britain and Ireland
Anaesthesia 2014, 69, 1051–1064
states “advice should be given not to drink alcohol, operate machinery or drive for 24 h after a general anaesthetic” [7], which is based on previously published work [8]. We are uncertain as to whether we should review our advice to patients and urge both the AAGBI and the Royal College to issue new statements that take into consideration the revised isoflurane SPC advice.
www.rcoa.ac.uk/patients-and-relatives/ common-concerns-and-faqs (accessed 17/06/2014). 7. Verma R, Alladi R, Jackson I, et al. Day case and short stay surgery: 2. Anaesthesia 2011; 66: 417–34. 8. Chung F, Kayumov L, Sinclair DR, Edward R, Moller HJ, Shapiro CM. What is the driving performance of ambulatory surgical patients after general anesthesia? Anesthesiology 2005; 103: 951–6.
A. Pollard R. Marr The Royal Victoria Infirmary, Newcastle upon Tyne, UK E-mail: [email protected]
Problem with Portex ‘loss of resistance’ syringes
No external funding and no competing interests declared.
References 1. Electronic Medicines Compendium, Summary of product characteristics of Isoflurane. Updated 6/9/2013. http://www. medicines.org.uk/emc/medicine/41/ SPC/Isoflurane+(inhalation+anaesthe)/ (accessed 17/06//2014). 2. Electronic Medicines Compendium, Summary of product characteristics of Isoflurane. Updated 6/9/2013. http:// beta.medicines.org.uk/emc/history/41 (accessed 17/06/2014). 3. Electronic Medicines Compendium, Summary of product characteristics of Sevoflurane. Updated 19/4/2013. http://www. medicines.org.uk/emc/medicine/49/spc#CLINICAL_PRECAUTIONS (accessed 17/ 06/2014). 4. Electronic Medicines Compendium Summary of product characteristics of Diprivan 1%. Updated 26/1/2012. https:// www.medicines.org.uk/EMC/medicine/ 2275/SPC/Diprivan+1/ (accessed 17/ 06/2014). 5. Medicines and Healthcare products Regulatory Agency, Summary of product characteristics of Desflurane. Updated 22/11/2011. http://www.mhra.gov.uk /home/groups/spcpil/documents/spcpil/con1364186700072.pdf (accessed 17/06/2014). 6. The Royal College of Anaesthetists, Common concerns and FAQs. http://
© 2014 The Association of Anaesthetists of Great Britain and Ireland
doi:10.1111/anae.12809
We would like to highlight a problem we have found with recent batches of Portex (Smiths Medical, Ashford, Kent) ‘loss of resistance’ epidural syringes, which, when left half-filled with air or saline for 5 s or more, developed initial resistance when depressing the plunger, requiring a surprisingly large amount of force to overcome. Such resistance might be misinterpreted as indicating the position of the Tuohy needle’s tip within a ligament, increasing the likelihood of dural puncture. We used a transducer (Force Measurement Systems, Glasgow, UK. Load Indicator-Model: GM7464, Force Transducer-Model: GM74-570) to measure the force needed to disengage the syringe plunger in a randomised sample of 15 Portex epidural syringes from different manufacturing dates, taking six readings from each syringe (three when filled with 8 ml air and then three when filled with 8 ml saline). Each reading was taken after a 5-s
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The effect of general anaesthesia on memory in children We read with interest the recent article by Yin et al. [1], comparing memory changes between children undergoing general anaesthesia with propofol or sevoflurane, and we agree that this is a very important topic that merits intense and thorough research. However, we have some questions about the methodology and data interpretation that we would like the authors to address. Firstly, the sample size calculation was based on the assumption that a difference in scores of more than one SD was considered significant, but without publication of the pilot study data, we are uncertain whether this calculation is based on sufficiently rigorous evidence. In addition, the eight components of the memory testing score appear to vary in scale and dimension, meaning that a single SD difference could have different absolute effects on each result presented, but no information is provided about 1062
Correspondence
whether significance was adjusted for multiple-testing effects. The conclusion that propofol impairs memory would require comparison with a control group that was not anaesthetised. Secondly, we question the propofol infusion scheme described. The authors infused propofol 1% at rate of 5–10 lg.kg 1.min 1, providing a maximum blood concentration of less than 2 lg.ml 1, which is normally insufficient for maintaining anaesthesia in children. If this is a typographic error and the authors infused at 50–100 lg.kg 1.min 1, then the concentration would be too high. In addition, there was no attempt to ensure equipotency of the anaesthetic drugs used when comparing the techniques, which constitutes a significant weakness in the study design. Finally, we think that the authors have misinterpreted the study by Jacob et al. [2], which found that higher cerebral concentrations of lactate and taurine in children anaesthetised with sevoflurane compared with propofol infusion correlated with higher scores for emergence agitation and delirium. This may be a sign of deleterious effects of sevoflurane on the brain, rather than a sign of earlier recovery of normal brain function, as Yin et al. claim. There is considerable concern about the possibility that general anaesthesia might damage the developing human brain [3]. We urge caution in accepting the conclusions of this study without the authors’ addressing our concerns about whether the study was correctly powered.
F. A. Lobo J. Guimar~aes Centro Hospitalar do Porto, Porto, Portugal S. Schraag Golden Jubilee National Hospital, Glasgow, UK F. Engbers Leiden University Hospital, Leiden, The Netherlands E-mail: [email protected] No external funding or competing interests declared. Previously posted on the Anaesthesia correspondence website: www.anaesthesiacorrespon dence.com. No reply provided by the authors.
References 1. Yin J, Wang SL, Liu XB. The effects of general anaesthesia on memory in children: a comparison between propofol and sevoflurane. Anaesthesia 2014; 69: 118–23. 2. Jacob Z, Li H, Makaryus R, Zhang S, et al. Metabolomic profiling of childrens brains undergoing general anesthesia with sevoflurane and propofol. Anesthesiology 2012; 117: 1062–71. 3. SmartTots. www.smarttots.org (accessed 17/05/2014). doi:10.1111/anae.12779
Driving advice after isoflurane anaesthesia Changes to the Summary of Product Characteristics (SPC) for isoflurane in August 2013, state that “patients should be advised that performance of activities requiring mental alertness, such as operating a motor vehicle or hazardous machinery, may be impaired for 2–4 days after anaesthesia with isoflurane” [1]. Previously, the SPC stated that driving or working machinery should be avoided for at least 24 hours. The
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Correspondence
reason for this change is listed as “Marketing Authorisation Holder details changed to reflect the company change from Abbott to AbbVie.” [2]. It is unclear on what justification the change to the SPC was made. In contrast, the SPC information for sevoflurane states “patients should be advised that performance of activities requiring mental alertness, such as operating a motor vehicle or hazardous machinery, may be impaired for some time after general anaesthesia” [3]. Propofol’s SPC also opts for the more vague “Patients should be advised that performance at skilled tasks, such as driving and operating machinery, may be impaired for some time after general anaesthesia”[4]. Desflurane’s SPC states that “patients should be advised that the ability to perform tasks such as driving or operation of machinery may be impaired after general anaesthesia, and it is advisable to avoid such tasks for a period of 24 hours” [5]. At present in our hospital, we advise patients not to drive/cook/ operate machinery for 24 hours after anaesthesia. We are very concerned that this change to the SPC of isoflurane has not been well publicised and has potentially serious medicolegal implications for anaesthetists, should a patient, for example, be involved in a traffic collision when driving three days after surgery. The Royal College of Anaesthetists website states “current advice is that it is not usually safe to drive or drink alcohol until at least 24 hours after a general anaesthetic” [6]. The Association of Anaesthestists of Great Britain and Ireland
Anaesthesia 2014, 69, 1051–1064
states “advice should be given not to drink alcohol, operate machinery or drive for 24 h after a general anaesthetic” [7], which is based on previously published work [8]. We are uncertain as to whether we should review our advice to patients and urge both the AAGBI and the Royal College to issue new statements that take into consideration the revised isoflurane SPC advice.
www.rcoa.ac.uk/patients-and-relatives/ common-concerns-and-faqs (accessed 17/06/2014). 7. Verma R, Alladi R, Jackson I, et al. Day case and short stay surgery: 2. Anaesthesia 2011; 66: 417–34. 8. Chung F, Kayumov L, Sinclair DR, Edward R, Moller HJ, Shapiro CM. What is the driving performance of ambulatory surgical patients after general anesthesia? Anesthesiology 2005; 103: 951–6.
A. Pollard R. Marr The Royal Victoria Infirmary, Newcastle upon Tyne, UK E-mail: [email protected]
Problem with Portex ‘loss of resistance’ syringes
No external funding and no competing interests declared.
References 1. Electronic Medicines Compendium, Summary of product characteristics of Isoflurane. Updated 6/9/2013. http://www. medicines.org.uk/emc/medicine/41/ SPC/Isoflurane+(inhalation+anaesthe)/ (accessed 17/06//2014). 2. Electronic Medicines Compendium, Summary of product characteristics of Isoflurane. Updated 6/9/2013. http:// beta.medicines.org.uk/emc/history/41 (accessed 17/06/2014). 3. Electronic Medicines Compendium, Summary of product characteristics of Sevoflurane. Updated 19/4/2013. http://www. medicines.org.uk/emc/medicine/49/spc#CLINICAL_PRECAUTIONS (accessed 17/ 06/2014). 4. Electronic Medicines Compendium Summary of product characteristics of Diprivan 1%. Updated 26/1/2012. https:// www.medicines.org.uk/EMC/medicine/ 2275/SPC/Diprivan+1/ (accessed 17/ 06/2014). 5. Medicines and Healthcare products Regulatory Agency, Summary of product characteristics of Desflurane. Updated 22/11/2011. http://www.mhra.gov.uk /home/groups/spcpil/documents/spcpil/con1364186700072.pdf (accessed 17/06/2014). 6. The Royal College of Anaesthetists, Common concerns and FAQs. http://
© 2014 The Association of Anaesthetists of Great Britain and Ireland
doi:10.1111/anae.12809
We would like to highlight a problem we have found with recent batches of Portex (Smiths Medical, Ashford, Kent) ‘loss of resistance’ epidural syringes, which, when left half-filled with air or saline for 5 s or more, developed initial resistance when depressing the plunger, requiring a surprisingly large amount of force to overcome. Such resistance might be misinterpreted as indicating the position of the Tuohy needle’s tip within a ligament, increasing the likelihood of dural puncture. We used a transducer (Force Measurement Systems, Glasgow, UK. Load Indicator-Model: GM7464, Force Transducer-Model: GM74-570) to measure the force needed to disengage the syringe plunger in a randomised sample of 15 Portex epidural syringes from different manufacturing dates, taking six readings from each syringe (three when filled with 8 ml air and then three when filled with 8 ml saline). Each reading was taken after a 5-s
1063
