Anaesthesia 2014, 69, 1287–1297
addition, we also wished to use methods that are less dependent on patient positioning, which is one potential limitation of sternomental distance measurement. For instance, it has been shown that sternomental distance may change depending on when the measurement is taken; that is, before (sitting, conscious) or after (supine, unconscious) induction of general anesthesia [6]. Regardless of the assessment method used, predicting a difficult airway is highly subjective. Indeed, various factors, including patient anatomy and co-morbidities, technical skill and experience of the assessor, and medications administered (e.g. neuromuscular blocking drugs), influence the degree to which a difficult airway can be predicted with accuracy. In any case, these methods are merely used to prepare oneself for the possibility of a difficult airway – the true test comes at the time of intubation. As has been stated before with respect to physical examination methods, no screening test is 100% sensitive and 100% specific [5]. Similarly, we anticipate that ultrasonography will not predict difficult intubation all the time. Thus, I believe that ultrasound and physical methods should be used in combination to obtain the best idea of how difficult intubation will be for a given case. B. C. H. Tsui Stollery Children’s Hospital/ University of Alberta Hospital, Edmonton, Canada Email: [email protected] No external funding and no conflict of interest declared. Previously 1290
Correspondence
posted on the Anaesthesia correspondence website: www.anaesthe siacorrespondence.com.
References 1. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: A meta-analysis of bedside screening test performance. Anesthesiology 2005; 103: 429–37. 2. Hui CM, Tsui BC. Sublingual ultrasound as an assessment method for predicting difficult intubation: a pilot study. Anaesthesia 2014; 69: 314–9. 3. Adhikari S, Zeger W, Schmier C, et al. Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Academic Emergency Medicine 2011; 18: 754–8. 4. Kundra P, Mishra SK, Ramesh A. Ultrasound of the airway. Indian Journal of Anaesthesia 2011; 55: 456–62. 5. Savva D. Prediction of difficult tracheal intubation. British Journal of Anaesthesia 1994; 73: 149–53. 6. Choi J, Kang H, Park HJ, Park SJ. The changes of the sternomental distance under general anesthesia and with increasing age. Anesthesiology and Pain Medicine 2009; 4: 183–6. doi:10.1111/anae.12864
Intrathecal opioids and fetal heart rate abnormalities Patel et al. observed a significant increase in the incidence of abnormal fetal heart rate patterns following neuraxial (combined spinal-epidural (CSE) or epidural only) analgesia [1]. The authors noted that deterioration in the fetal heart rate pattern has a multifactorial causation, but is usually transient, resolving spontaneously or following intrauterine fetal resuscitative measures, including the reduction or discontinuation of oxytocin before initiation of analgesia, fluid administration, and/or reducing the
dose of intrathecal opioids [2, 3]. However, the authors do not justify their use of a low dose of intrathecal fentanyl (5 lg) in the present study, when most published literature supports the use of intrathecal fentanyl ≥ 15 lg for analgesia [4], which may explain why 32% of parturients in the CSE group had ineffective analgesia. The authors’ technique cannot be supported for wider clinical practice, as a result, particularly as rescue analgesia was not administered for a further 30 min. Also, although 15–23% of patients received oxytocin in this study, it is not clear what stage of labour these patients had reached or whether they showed fetal heart rate deterioration. The authors found no association between hypotension and fetal heart rate abnormalities, and concluded “fetal heart rate abnormalities increase after institution of neuraxial analgesia and oxytocin rather than hypotension may be an important associated factor”. Could the authors please clarify whether blood pressure was recorded every 2–3 min, as is usual, or only ‘at baseline immediately before neuraxial block and at 15 and 30 min after neuraxial block’, as stated in their methods, between which times maternal hypotension may have gone unobserved? There is no strong evidence to support the routine use of either CSE or epidural over the other for initiation of neuraxial analgesia. Nevertheless, since intrathecal opioids are reported to be associated with fetal heart rate changes, further research is needed to clarify whether opioidfree intrathecal injectates provide acceptable maternal analgesia within
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Correspondence
Anaesthesia 2014, 69, 1287–1297
5 min of administration and for more than 30 min, and decrease the incidence of hypotension without altering uterine tone. Co-administration of epidural opioid within 30 min of intrathecal analgesia may reduce the incidence of breakthrough pain with fewer side-effects [2]. K. A. Swini K. Jain J. K. Makkar R. Bagga Post Graduate Institute of Medical Education and Research, Chandigarh, India Email: [email protected] No external funding and no conflicts of interest declared. Previously posted on the Anaesthesia correspondence website: www.anaesthesiacorrespon dence.com.
References 1. Patel NP, El-Wahab N, Fernando R, et al. Fetal effects of combined spinal-epidural vs epidural labour analgesia: a prospective, randomised double-blind study. Anaesthesia 2014; 69: 458–67. 2. Van de Velde M. Neuraxial analgesia and fetal bradycardia. Current Opinion in Anesthesiology 2005; 18: 253–6. 3. Loubert C, Hinova A, Fernando R. Update on modern neuraxial analgesia in labour: a review of the literature of the last 5 years. Anaesthesia 2011; 66: 191–212. 4. Wong CA, Scavone BM, Slavenas JP, et al. Efficacy and side effect profile of varying doses of intrathecal fentanyl added to bupivacaine for labor analgesia. International Journal of Obstetric Anesthesia 2004; 13: 19–2. doi:10.1111/anae.12833
A reply We thank Jain et al. for their interest in our paper [1], and for the
discussion points raised. We decided to use 2.5 ml premixed bupivacaine 0.1%/fentanyl 2 lg.ml 1 because this is used at our hospitals for combined spinal-epidural (CSE) anaesthesia, and so was familiar to anaesthetists. Clearly, our results cannot be generalised to other dosing regimens. We believe that this dose is adequate since it has been shown that the ED50 of plain bupivacaine with 5 lg fentanyl in the first stage of labour is 0.69 mg [2], and that the addition of doses of fentanyl greater than 5 lg do not confer an advantage with respect to quality of analgesia, though duration of analgesia is increased in a dosedependent manner [2]. Importantly, the use of higher doses of fentanyl is not associated with a bupivacaine dose-sparing effect. The ED95 for plain bupivacaine with 15 lg fentanyl is 1.66 lg [3]. Since the dose we used was significantly above both ED50 and ED95, we do not believe that this easily explains why a proportion of parturients in the CSE group experienced ineffective analgesia. Fourteen percent of the epidural group also experienced ineffective analgesia following the initial injection. It is well recognised that maximal analgesia following either CSE or epidural in labour is never achieved in 100% of women initially, although the proportion of ineffective blocks in our study is higher than documented previously [4]. In our study, rescue analgesia was deferred until assessment 30 min after injection, because this is a time point that has been used previously in similar studies
© 2014 The Association of Anaesthetists of Great Britain and Ireland
and allows the maximal effect of injection to be attained. This time period also reflects both our hospitals’ normal clinical practice and National Institute for Health and Care Excellence (NICE) guidelines, which recommend an interval of 30 min following epidural top-up before an anaesthetist is called to provide rescue analgesia [5]. Nine (15%) parturients in the CSE group and 12 (23%) of those in the epidural group received an oxytocin infusion during the first stage of labour. Subgroup analysis using Generalised Cochran-MantelHaenszel tests revealed the presence of suspicious or pathological fetal heart rate (FHR) patterns in 9 (41%) of those receiving oxytocin compared with only 10 (11%) without oxytocin. We conclude that the use of oxytocin is associated with a significant increase in FHR abnormalities (p = 0.004). Maternal blood pressure was measured at baseline and then at 5-min intervals for the first 15 min following neuraxial block by the midwife looking after the patient, as is standard care. This is in line with departmental and NICE guidelines [5]. For the purpose of the study, blood pressure was recorded 15 min and 30 min after neuraxial injection by the third anaesthetist who was blinded to the procedure performed. It is therefore conceivable that brief periods of hypotension may have gone unnoticed. We agree that further research is warranted in order to determine the optimal dosing regimen for
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addition, we also wished to use methods that are less dependent on patient positioning, which is one potential limitation of sternomental distance measurement. For instance, it has been shown that sternomental distance may change depending on when the measurement is taken; that is, before (sitting, conscious) or after (supine, unconscious) induction of general anesthesia [6]. Regardless of the assessment method used, predicting a difficult airway is highly subjective. Indeed, various factors, including patient anatomy and co-morbidities, technical skill and experience of the assessor, and medications administered (e.g. neuromuscular blocking drugs), influence the degree to which a difficult airway can be predicted with accuracy. In any case, these methods are merely used to prepare oneself for the possibility of a difficult airway – the true test comes at the time of intubation. As has been stated before with respect to physical examination methods, no screening test is 100% sensitive and 100% specific [5]. Similarly, we anticipate that ultrasonography will not predict difficult intubation all the time. Thus, I believe that ultrasound and physical methods should be used in combination to obtain the best idea of how difficult intubation will be for a given case. B. C. H. Tsui Stollery Children’s Hospital/ University of Alberta Hospital, Edmonton, Canada Email: [email protected] No external funding and no conflict of interest declared. Previously 1290
Correspondence
posted on the Anaesthesia correspondence website: www.anaesthe siacorrespondence.com.
References 1. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: A meta-analysis of bedside screening test performance. Anesthesiology 2005; 103: 429–37. 2. Hui CM, Tsui BC. Sublingual ultrasound as an assessment method for predicting difficult intubation: a pilot study. Anaesthesia 2014; 69: 314–9. 3. Adhikari S, Zeger W, Schmier C, et al. Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Academic Emergency Medicine 2011; 18: 754–8. 4. Kundra P, Mishra SK, Ramesh A. Ultrasound of the airway. Indian Journal of Anaesthesia 2011; 55: 456–62. 5. Savva D. Prediction of difficult tracheal intubation. British Journal of Anaesthesia 1994; 73: 149–53. 6. Choi J, Kang H, Park HJ, Park SJ. The changes of the sternomental distance under general anesthesia and with increasing age. Anesthesiology and Pain Medicine 2009; 4: 183–6. doi:10.1111/anae.12864
Intrathecal opioids and fetal heart rate abnormalities Patel et al. observed a significant increase in the incidence of abnormal fetal heart rate patterns following neuraxial (combined spinal-epidural (CSE) or epidural only) analgesia [1]. The authors noted that deterioration in the fetal heart rate pattern has a multifactorial causation, but is usually transient, resolving spontaneously or following intrauterine fetal resuscitative measures, including the reduction or discontinuation of oxytocin before initiation of analgesia, fluid administration, and/or reducing the
dose of intrathecal opioids [2, 3]. However, the authors do not justify their use of a low dose of intrathecal fentanyl (5 lg) in the present study, when most published literature supports the use of intrathecal fentanyl ≥ 15 lg for analgesia [4], which may explain why 32% of parturients in the CSE group had ineffective analgesia. The authors’ technique cannot be supported for wider clinical practice, as a result, particularly as rescue analgesia was not administered for a further 30 min. Also, although 15–23% of patients received oxytocin in this study, it is not clear what stage of labour these patients had reached or whether they showed fetal heart rate deterioration. The authors found no association between hypotension and fetal heart rate abnormalities, and concluded “fetal heart rate abnormalities increase after institution of neuraxial analgesia and oxytocin rather than hypotension may be an important associated factor”. Could the authors please clarify whether blood pressure was recorded every 2–3 min, as is usual, or only ‘at baseline immediately before neuraxial block and at 15 and 30 min after neuraxial block’, as stated in their methods, between which times maternal hypotension may have gone unobserved? There is no strong evidence to support the routine use of either CSE or epidural over the other for initiation of neuraxial analgesia. Nevertheless, since intrathecal opioids are reported to be associated with fetal heart rate changes, further research is needed to clarify whether opioidfree intrathecal injectates provide acceptable maternal analgesia within
© 2014 The Association of Anaesthetists of Great Britain and Ireland
Correspondence
Anaesthesia 2014, 69, 1287–1297
5 min of administration and for more than 30 min, and decrease the incidence of hypotension without altering uterine tone. Co-administration of epidural opioid within 30 min of intrathecal analgesia may reduce the incidence of breakthrough pain with fewer side-effects [2]. K. A. Swini K. Jain J. K. Makkar R. Bagga Post Graduate Institute of Medical Education and Research, Chandigarh, India Email: [email protected] No external funding and no conflicts of interest declared. Previously posted on the Anaesthesia correspondence website: www.anaesthesiacorrespon dence.com.
References 1. Patel NP, El-Wahab N, Fernando R, et al. Fetal effects of combined spinal-epidural vs epidural labour analgesia: a prospective, randomised double-blind study. Anaesthesia 2014; 69: 458–67. 2. Van de Velde M. Neuraxial analgesia and fetal bradycardia. Current Opinion in Anesthesiology 2005; 18: 253–6. 3. Loubert C, Hinova A, Fernando R. Update on modern neuraxial analgesia in labour: a review of the literature of the last 5 years. Anaesthesia 2011; 66: 191–212. 4. Wong CA, Scavone BM, Slavenas JP, et al. Efficacy and side effect profile of varying doses of intrathecal fentanyl added to bupivacaine for labor analgesia. International Journal of Obstetric Anesthesia 2004; 13: 19–2. doi:10.1111/anae.12833
A reply We thank Jain et al. for their interest in our paper [1], and for the
discussion points raised. We decided to use 2.5 ml premixed bupivacaine 0.1%/fentanyl 2 lg.ml 1 because this is used at our hospitals for combined spinal-epidural (CSE) anaesthesia, and so was familiar to anaesthetists. Clearly, our results cannot be generalised to other dosing regimens. We believe that this dose is adequate since it has been shown that the ED50 of plain bupivacaine with 5 lg fentanyl in the first stage of labour is 0.69 mg [2], and that the addition of doses of fentanyl greater than 5 lg do not confer an advantage with respect to quality of analgesia, though duration of analgesia is increased in a dosedependent manner [2]. Importantly, the use of higher doses of fentanyl is not associated with a bupivacaine dose-sparing effect. The ED95 for plain bupivacaine with 15 lg fentanyl is 1.66 lg [3]. Since the dose we used was significantly above both ED50 and ED95, we do not believe that this easily explains why a proportion of parturients in the CSE group experienced ineffective analgesia. Fourteen percent of the epidural group also experienced ineffective analgesia following the initial injection. It is well recognised that maximal analgesia following either CSE or epidural in labour is never achieved in 100% of women initially, although the proportion of ineffective blocks in our study is higher than documented previously [4]. In our study, rescue analgesia was deferred until assessment 30 min after injection, because this is a time point that has been used previously in similar studies
© 2014 The Association of Anaesthetists of Great Britain and Ireland
and allows the maximal effect of injection to be attained. This time period also reflects both our hospitals’ normal clinical practice and National Institute for Health and Care Excellence (NICE) guidelines, which recommend an interval of 30 min following epidural top-up before an anaesthetist is called to provide rescue analgesia [5]. Nine (15%) parturients in the CSE group and 12 (23%) of those in the epidural group received an oxytocin infusion during the first stage of labour. Subgroup analysis using Generalised Cochran-MantelHaenszel tests revealed the presence of suspicious or pathological fetal heart rate (FHR) patterns in 9 (41%) of those receiving oxytocin compared with only 10 (11%) without oxytocin. We conclude that the use of oxytocin is associated with a significant increase in FHR abnormalities (p = 0.004). Maternal blood pressure was measured at baseline and then at 5-min intervals for the first 15 min following neuraxial block by the midwife looking after the patient, as is standard care. This is in line with departmental and NICE guidelines [5]. For the purpose of the study, blood pressure was recorded 15 min and 30 min after neuraxial injection by the third anaesthetist who was blinded to the procedure performed. It is therefore conceivable that brief periods of hypotension may have gone unnoticed. We agree that further research is warranted in order to determine the optimal dosing regimen for
1291
