E Letters to the Editor Blocks of the Anterior Abdominal Wall: Local and Systemic Effect? To the Editor
W
e read with interest the meta-analysis by De Oliveira et al.1 and subsequent Letter to the Editor by Groudine,2 which suggest that the analgesic effect of the transversus abdominis plane (TAP) block may be related to both the local neural blockade and a systemic effect of absorbed local anesthetics. We believe this is likely, as only 3 to 3.75 nerves are typically blocked after classic TAP block, and only 5.5 nerves are blocked after subcostal TAP block.3 The mean number of blocked nerves corresponds to the mean number of dermatomes blocked.4–6 Børglum et al.6,7 reported that 7 nerves and dermatomes could be blocked with a combined classic and subcostal technique but with an overall higher efficacy rate in the lower dermatomes.5–7 Not only is block extent limited but there is also a great variability between techniques and in the spread of local anesthetic between muscular fascias.8 Only a few studies report dermatomal assessment as a measure of block effectiveness. Most studies report analgesic consumption. Moreover, dermatomal anesthesia has not been correlated with analgesic consumption. Latzke et al.8 found conflicting results about local anesthetic concentrations in the injected site and noninjected sites as underscored by Groudine.2 While they provided support for neural blockade mechanism, they did not assess dermatomal anesthesia in the injection site and noninjected sites, and their study cannot support a systemic effect of TAP block. Pharmacokinetic data may suggest a systemic mechanism. The terminal half-life of local anesthetics after injection into the abdominal wall is longer than that after IV administration,6 possibly because the terminal half-life is determined by slow absorption from the tissue depot and flip-flop pharmacokinetics. This may explain the longlasting plasma levels observed in patients. Pettersson et al.9 reported a high variability in peak concentration times and terminal half-life times, suggesting a marked variation in absorption rates after abdominal blocks. These investigators reported that patients with a longer terminal half-life of ropivacaine asked for their first postoperative analgesic later than patients with a shorter terminal half-life. Because both local and systemic effects of local anesthetics may contribute to the analgesic response, we believe that pharmacokinetic findings should be correlated to sensory outcomes and analgesic consumption to understand the role of systemically absorbed drugs. Zhirajr Mokini, MD Department of Anesthesia University of Medicine, State University of Tirana Tirana, Albania [email protected]
1428 www.anesthesia-analgesia.org
Giovanni Vitale, MD Department of Anesthesia San Gerardo University Hospital Monza, Italy REFERENCES 1. De Oliveira GS Jr, Castro-Alves LJ, Nader A, Kendall MC, McCarthy RJ. Transversus abdominis plane block to ameliorate postoperative pain outcomes after laparoscopic surgery: a meta-analysis of randomized controlled trials. Anesth Analg 2014;118:454–63 2. Groudine S. Transversus abdominis plane blocks and systemic absorption. Anesth Analg 2014;119:1002 3. Milan Z, Tabor D, McConnell P, Pickering J, Kocarev M, du Feu F, Barton S. Three different approaches to transversus abdominis plane block: a cadaveric study. Med Glas 2011;8:181–4 4. Lee TH, Barrington MJ, Tran TM, Wong D, Hebbard PD. Comparison of extent of sensory block following posterior and subcostal approaches to ultrasound-guided transversus abdominis plane block. Anaesth Intensive Care 2010;38:452–60 5. Mitchell AU, Torup H, Hansen EG, Petersen PL, Mathiesen O, Dahl JB, Rosenberg J, Møller AM. Effective dermatomal blockade after subcostal transversus abdominis plane block. Dan Med J 2012;59:A4404 6. Børglum J, Jensen K, Christensen AF, Hoegberg LC, Johansen SS, Lönnqvist PA, Jansen T. Distribution patterns, dermatomal anesthesia, and ropivacaine serum concentrations after bilateral dual transversus abdominis plane block. Reg Anesth Pain Med 2012;37:294–301 7. Børglum J, Maschmann C, Belhage B, Jensen K. Ultrasoundguided bilateral dual transversus abdominis plane block: a new four-point approach. Acta Anaesthesiol Scand 2011;55:658–63 8. Latzke D, Marhofer P, Kettner SC, Koppatz K, Turnheim K, Lackner E, Sauermann R, Müller M, Zeitlinger M. Pharmacokinetics of the local anesthetic ropivacaine after transversus abdominis plane block in healthy volunteers. Eur J Clin Pharmacol 2012;68:419–25 9. Pettersson N, Emanuelsson BM, Reventlid H, Hahn RG. Highdose ropivacaine wound infiltration for pain relief after inguinal hernia repair: a clinical and pharmacokinetic evaluation. Reg Anesth Pain Med 1998;23:189–96 DOI: 10.1213/ANE.0000000000000715
Longer Times to Reanesthetization with Longer Anesthetic Duration? To the Editor
L
eeson et al.1 address an important clinical problem. The authors simulated 1, 2, 4, and 6 hours of inhalation of isoflurane, sevoflurane, and desflurane at concentrations of 0.75, 1.0, and 1.5 minimum alveolar concentration (MAC). After the simulated inhalation, they reduced the inspired anesthetic concentration to zero and ventilated the simulated subjects with 4.0 L/min until the anesthetic concentration in the vessel-rich group (i.e., brain) decreased to 0.33 MAC, simulating awakening. They then simulated hypoventilation by reducing the minute ventilation to 0 and 0.1 L/min and looked at the time for the anesthetic concentration in the vessel-rich group to exceed 0.5 MAC. They analyzed the times to reanesthetization as a function of minute ventilation, duration of
June 2015 • Volume 120 • Number 6
Copyright © 2015 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.
Letters to the Editor
anesthesia, dose of anesthetic, and sequestered anesthetic concentrations in various tissues. One finding seems improbable. Table 2 shows1 that at 1.5 MAC, longer anesthetic duration produces shorter times to reanesthetization. This is expected because of higher sequestration of anesthetic in peripheral tissues. However, close scrutiny of reanesthetization times in 1 MAC group shows unexpectedly paradoxical values. The 6-hour administration shows longer times to reanesthetization compared with 4-hour administration. As expected, Table 4 shows1 a higher concentration of anesthetic in the muscle and fat at 6 hours compared with 4 hours. It is inconceivable that the release of inhaled anesthetic from these tissues would be slower with higher concentration gradients between muscle and vessel-rich tissues. Dhritiman Chakrabarti, MBBS, MD Venkatapura J. Ramesh, MBBS, MD Department of Neuroanaesthesia National Institute of Mental Health and Neuro Sciences Bangalore, Karnataka, India [email protected] REFERENCE 1. Leeson S, Roberson RS, Philip JH. Hypoventilation after inhaled anesthesia results in reanesthetization. Anesth Analg 2014;119:829–35 DOI: 10.1213/ANE.0000000000000718
Questions on Prevention of Newborn Hypothermia After Cesarean Delivery To the Editor
N
eonatal hypothermia is a common problem worldwide. There are many published methods to prevent neonatal hypothermia after vaginal birth, but little research has explored the incidence and prevention of neonatal hypothermia after caesarean section. The article by Horn et al.1 helps fill this void, but several aspects merit comment. First, the upper body of the women in the active warming group was covered with a forced-air warming blanket set at 44°C, completely covering the newborn (see Fig. 2 in Horn et al.1). This could cause hyperthermia and its associated complications in the newborn. The 19 babies who received this treatment had an average core temperature of 37°C. The proportion who became hyperthermic at any time is unspecified. Second, the ambient room temperature during the study was “near 23°C.” This deviates from the World Health Organization guidelines, which recommend that the operating room temperature during delivery should be a minimum of 25°C for term babies and 26 to 28°C for preterm babies.2 Maintaining the room temperature during delivery at 25°C or more is an essential intervention to prevent neonatal hypothermia.3 We suggest that the safety of forced-air warming blankets during skin-to-skin contact following cesarean delivery
June 2015 • Volume 120 • Number 6
is not sufficiently investigated to merit widespread adoption without further research on the risk of hyperthermia. Aliona Vilinsky, BSc, RM, MSc Theatre Department Rotunda Hospital Dublin, Ireland [email protected] Conan McCaul, MB BCH, BAO, FFARCSI, MD Department of Anesthesiology Theatre Department Rotunda Hospital Dublin, Ireland REFERENCES 1. Horn EP, Bein B, Steinfath M, Ramaker K, Buchloh B, Höcker J. The incidence and prevention of hypothermia in newborn bonding after cesarean delivery: a randomized controlled trial. Anesth Analg 2014;118:997–1002 2. World Health Organization. Thermal Protection of the Newborn: A Practical Guide. Maternal and Newborn Health/ Safe Motherhood Unit, Division of Reproductive Health. Geneva: WHO, 1997 3. Vilinsky A, Sheridan A. Hypothermia in the newborn: an exploration of its cause, effect and prevention. Br J Midwifery 2014;22:557–62 DOI: 10.1213/ANE.0000000000000761
In Response: Vilinsky and McCaul1 raise several important questions about our recently published article on neonatal warming after cesarean delivery. We agree that hypothermia in neonates born by cesarean delivery is a serious problem, and research data, especially from randomized trials, are scarce. We also agree that overheating of newborns has to be avoided. In our study, core temperature in actively warmed neonates decreased from 37.5°C ± 0.2°C at birth to 37.0°C ± 0.2°C after 20 minutes of bonding. By using the forced-air device set to 44°C, air temperature was safe. Mothers and neonates tolerated the procedure well. None of the 19 neonates showed overheating (Table 1). Core temperature was not higher in any newborn at any time during bonding or later when compared with their birth temperature. These results are consistent with the practical experiences in our department, where during a period of 10 years, any mature neonate born by cesarean delivery was actively warmed using the described procedure. None of the >3000 neonates showed signs of overheating. Forced-air warming is recommended by guidelines for adults, children, and infants as an efficient and safe method to prevent perioperative hypothermia.2,3 Guidelines recommend operating room temperatures of not
W
e read with interest the meta-analysis by De Oliveira et al.1 and subsequent Letter to the Editor by Groudine,2 which suggest that the analgesic effect of the transversus abdominis plane (TAP) block may be related to both the local neural blockade and a systemic effect of absorbed local anesthetics. We believe this is likely, as only 3 to 3.75 nerves are typically blocked after classic TAP block, and only 5.5 nerves are blocked after subcostal TAP block.3 The mean number of blocked nerves corresponds to the mean number of dermatomes blocked.4–6 Børglum et al.6,7 reported that 7 nerves and dermatomes could be blocked with a combined classic and subcostal technique but with an overall higher efficacy rate in the lower dermatomes.5–7 Not only is block extent limited but there is also a great variability between techniques and in the spread of local anesthetic between muscular fascias.8 Only a few studies report dermatomal assessment as a measure of block effectiveness. Most studies report analgesic consumption. Moreover, dermatomal anesthesia has not been correlated with analgesic consumption. Latzke et al.8 found conflicting results about local anesthetic concentrations in the injected site and noninjected sites as underscored by Groudine.2 While they provided support for neural blockade mechanism, they did not assess dermatomal anesthesia in the injection site and noninjected sites, and their study cannot support a systemic effect of TAP block. Pharmacokinetic data may suggest a systemic mechanism. The terminal half-life of local anesthetics after injection into the abdominal wall is longer than that after IV administration,6 possibly because the terminal half-life is determined by slow absorption from the tissue depot and flip-flop pharmacokinetics. This may explain the longlasting plasma levels observed in patients. Pettersson et al.9 reported a high variability in peak concentration times and terminal half-life times, suggesting a marked variation in absorption rates after abdominal blocks. These investigators reported that patients with a longer terminal half-life of ropivacaine asked for their first postoperative analgesic later than patients with a shorter terminal half-life. Because both local and systemic effects of local anesthetics may contribute to the analgesic response, we believe that pharmacokinetic findings should be correlated to sensory outcomes and analgesic consumption to understand the role of systemically absorbed drugs. Zhirajr Mokini, MD Department of Anesthesia University of Medicine, State University of Tirana Tirana, Albania [email protected]
1428 www.anesthesia-analgesia.org
Giovanni Vitale, MD Department of Anesthesia San Gerardo University Hospital Monza, Italy REFERENCES 1. De Oliveira GS Jr, Castro-Alves LJ, Nader A, Kendall MC, McCarthy RJ. Transversus abdominis plane block to ameliorate postoperative pain outcomes after laparoscopic surgery: a meta-analysis of randomized controlled trials. Anesth Analg 2014;118:454–63 2. Groudine S. Transversus abdominis plane blocks and systemic absorption. Anesth Analg 2014;119:1002 3. Milan Z, Tabor D, McConnell P, Pickering J, Kocarev M, du Feu F, Barton S. Three different approaches to transversus abdominis plane block: a cadaveric study. Med Glas 2011;8:181–4 4. Lee TH, Barrington MJ, Tran TM, Wong D, Hebbard PD. Comparison of extent of sensory block following posterior and subcostal approaches to ultrasound-guided transversus abdominis plane block. Anaesth Intensive Care 2010;38:452–60 5. Mitchell AU, Torup H, Hansen EG, Petersen PL, Mathiesen O, Dahl JB, Rosenberg J, Møller AM. Effective dermatomal blockade after subcostal transversus abdominis plane block. Dan Med J 2012;59:A4404 6. Børglum J, Jensen K, Christensen AF, Hoegberg LC, Johansen SS, Lönnqvist PA, Jansen T. Distribution patterns, dermatomal anesthesia, and ropivacaine serum concentrations after bilateral dual transversus abdominis plane block. Reg Anesth Pain Med 2012;37:294–301 7. Børglum J, Maschmann C, Belhage B, Jensen K. Ultrasoundguided bilateral dual transversus abdominis plane block: a new four-point approach. Acta Anaesthesiol Scand 2011;55:658–63 8. Latzke D, Marhofer P, Kettner SC, Koppatz K, Turnheim K, Lackner E, Sauermann R, Müller M, Zeitlinger M. Pharmacokinetics of the local anesthetic ropivacaine after transversus abdominis plane block in healthy volunteers. Eur J Clin Pharmacol 2012;68:419–25 9. Pettersson N, Emanuelsson BM, Reventlid H, Hahn RG. Highdose ropivacaine wound infiltration for pain relief after inguinal hernia repair: a clinical and pharmacokinetic evaluation. Reg Anesth Pain Med 1998;23:189–96 DOI: 10.1213/ANE.0000000000000715
Longer Times to Reanesthetization with Longer Anesthetic Duration? To the Editor
L
eeson et al.1 address an important clinical problem. The authors simulated 1, 2, 4, and 6 hours of inhalation of isoflurane, sevoflurane, and desflurane at concentrations of 0.75, 1.0, and 1.5 minimum alveolar concentration (MAC). After the simulated inhalation, they reduced the inspired anesthetic concentration to zero and ventilated the simulated subjects with 4.0 L/min until the anesthetic concentration in the vessel-rich group (i.e., brain) decreased to 0.33 MAC, simulating awakening. They then simulated hypoventilation by reducing the minute ventilation to 0 and 0.1 L/min and looked at the time for the anesthetic concentration in the vessel-rich group to exceed 0.5 MAC. They analyzed the times to reanesthetization as a function of minute ventilation, duration of
June 2015 • Volume 120 • Number 6
Copyright © 2015 International Anesthesia Research Society. Unauthorized reproduction of this article is prohibited.
Letters to the Editor
anesthesia, dose of anesthetic, and sequestered anesthetic concentrations in various tissues. One finding seems improbable. Table 2 shows1 that at 1.5 MAC, longer anesthetic duration produces shorter times to reanesthetization. This is expected because of higher sequestration of anesthetic in peripheral tissues. However, close scrutiny of reanesthetization times in 1 MAC group shows unexpectedly paradoxical values. The 6-hour administration shows longer times to reanesthetization compared with 4-hour administration. As expected, Table 4 shows1 a higher concentration of anesthetic in the muscle and fat at 6 hours compared with 4 hours. It is inconceivable that the release of inhaled anesthetic from these tissues would be slower with higher concentration gradients between muscle and vessel-rich tissues. Dhritiman Chakrabarti, MBBS, MD Venkatapura J. Ramesh, MBBS, MD Department of Neuroanaesthesia National Institute of Mental Health and Neuro Sciences Bangalore, Karnataka, India [email protected] REFERENCE 1. Leeson S, Roberson RS, Philip JH. Hypoventilation after inhaled anesthesia results in reanesthetization. Anesth Analg 2014;119:829–35 DOI: 10.1213/ANE.0000000000000718
Questions on Prevention of Newborn Hypothermia After Cesarean Delivery To the Editor
N
eonatal hypothermia is a common problem worldwide. There are many published methods to prevent neonatal hypothermia after vaginal birth, but little research has explored the incidence and prevention of neonatal hypothermia after caesarean section. The article by Horn et al.1 helps fill this void, but several aspects merit comment. First, the upper body of the women in the active warming group was covered with a forced-air warming blanket set at 44°C, completely covering the newborn (see Fig. 2 in Horn et al.1). This could cause hyperthermia and its associated complications in the newborn. The 19 babies who received this treatment had an average core temperature of 37°C. The proportion who became hyperthermic at any time is unspecified. Second, the ambient room temperature during the study was “near 23°C.” This deviates from the World Health Organization guidelines, which recommend that the operating room temperature during delivery should be a minimum of 25°C for term babies and 26 to 28°C for preterm babies.2 Maintaining the room temperature during delivery at 25°C or more is an essential intervention to prevent neonatal hypothermia.3 We suggest that the safety of forced-air warming blankets during skin-to-skin contact following cesarean delivery
June 2015 • Volume 120 • Number 6
is not sufficiently investigated to merit widespread adoption without further research on the risk of hyperthermia. Aliona Vilinsky, BSc, RM, MSc Theatre Department Rotunda Hospital Dublin, Ireland [email protected] Conan McCaul, MB BCH, BAO, FFARCSI, MD Department of Anesthesiology Theatre Department Rotunda Hospital Dublin, Ireland REFERENCES 1. Horn EP, Bein B, Steinfath M, Ramaker K, Buchloh B, Höcker J. The incidence and prevention of hypothermia in newborn bonding after cesarean delivery: a randomized controlled trial. Anesth Analg 2014;118:997–1002 2. World Health Organization. Thermal Protection of the Newborn: A Practical Guide. Maternal and Newborn Health/ Safe Motherhood Unit, Division of Reproductive Health. Geneva: WHO, 1997 3. Vilinsky A, Sheridan A. Hypothermia in the newborn: an exploration of its cause, effect and prevention. Br J Midwifery 2014;22:557–62 DOI: 10.1213/ANE.0000000000000761
In Response: Vilinsky and McCaul1 raise several important questions about our recently published article on neonatal warming after cesarean delivery. We agree that hypothermia in neonates born by cesarean delivery is a serious problem, and research data, especially from randomized trials, are scarce. We also agree that overheating of newborns has to be avoided. In our study, core temperature in actively warmed neonates decreased from 37.5°C ± 0.2°C at birth to 37.0°C ± 0.2°C after 20 minutes of bonding. By using the forced-air device set to 44°C, air temperature was safe. Mothers and neonates tolerated the procedure well. None of the 19 neonates showed overheating (Table 1). Core temperature was not higher in any newborn at any time during bonding or later when compared with their birth temperature. These results are consistent with the practical experiences in our department, where during a period of 10 years, any mature neonate born by cesarean delivery was actively warmed using the described procedure. None of the >3000 neonates showed signs of overheating. Forced-air warming is recommended by guidelines for adults, children, and infants as an efficient and safe method to prevent perioperative hypothermia.2,3 Guidelines recommend operating room temperatures of not
