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Neonates experience significant moderate and severe postoperative pain. Effective postoperative pain management in neonates is required to minimize acute and long-term effects of neonatal pain. Protecting the developing nervous system from persistent sensitization of pain pathways and developing primary hyperalgesia is essential. Opioids and acetaminophen are commonly analgesics used for pain control. Regional anesthesia provides adequate intraoperative and postoperative analgesia in neonates. It decreases exposure to opioids, reduces adverse drug effects, and facilitates early extubation. It suppresses the stress response and can prevent long-term behavioral responses to pain. The most common blocks performed in neonates are neuraxial blocks. Using ultrasound increased the number of peripheral nerve blocks performed in neonates. Recently, various peripheral nerve blocks (paravertebral, transverse abdominis plane, rectus sheath, quadratus lumborum, erector spinae plane blocks) were safely used. Many studies support analgesic efficacy but highlight neonates' unpredictability and variability of fascial blocks.

A sacrococcygeal teratoma and a sacral agenesis represent a contraindication to a caudal block. We report two cases where the optimal use of ultrasound helped place a sacral intervertebral catheter in two neonates. Radiological and ultrasound studies of the sacrum and spine should be available before performing the procedure.

Adequate perioperative analgesia for pediatric abdominal transplant surgery is essential for patient recovery. However, the risks of commonly used medications such as hepatotoxicity, nephrotoxicity, bleeding concerns, and poor graft results with opioids limit pain management in this population. Thoracic epidural, continuous erector spinae plane, and type-1 quadratus lumborum blocks (QLBs) have been described and utilized in the adult population in this setting. The safety and benefits of regional anesthetic techniques in pediatrics have been widely documented for different types of procedures except pediatric abdominal transplantation, where data remains scarce. Our primary goal was to determine if QLBs provided adequate perioperative analgesia when part of a multimodal approach. Secondary objectives were to examine complications and effects on the intensive care unit (ICU) and hospital stay.We performed a retrospective, observational study of pediatric patients who underwent abdominal transplant surgeries at the University of Pittsburgh Medical Center Children's Hospital of Pittsburgh from January 2015 to July 2021 and received a single injection QLB for pain control. Data collected included: demographics, nerve block characteristics, perioperative opioid consumption, use of non-opioid analgesia, daily pain scores, and hospital and ICU stay.Forty-two patients met the inclusion criteria for our study. Our results suggest that QLBs decrease opioid consumption, facilitate early extubation, prevent reintubation in the ICU, and reduce ICU and hospital stay.QLB is feasible and can be used as a multimodal approach for postoperative pain control in pediatric solid organ transplantation.

Intravenous administration of acetaminophen is an alternative to the oral and rectal routes, which may be contraindicated in particular clinical settings. This randomized, placebo‐controlled study of intravenous acetaminophen (Ofirmev, Mallinckrodt Pharmaceuticals, Bedminster, New Jersey) in neonate and infant patients with acute postoperative pain assessed pharmacokinetics (PK) and safety, in addition to efficacy and pharmacodynamics of repeated doses administered over 24 hours. Neonate and infant patients (

Chronic chest pain is a debilitating condition that is poorly treated, resulting in opioid dependence and significantly decreased quality of life. In this case report, we describe the successful use of 266 mg of liposomal bupivacaine for 4 rounds of left-sided multilevel intercostal nerve blocks performed to treat chronic chest pain of a 21-year-old woman (150 kg, 163 cm). The sensory blockade duration was up to 7 days, analgesia lasted 2 months, and was described superior to that with ropivacaine intercostal blockade. The treatment improved satisfaction with pain control and quality of life.

Study objective The primary goal of this study was to determine if the addition of clonidine to ropivacaine prolonged periumbilical numbness compared to ropivacaine alone in pediatric patients receiving ultrasound guided rectus sheath nerve blocks for laparoscopic appendectomy. The secondary goals were to evaluate differences in perioperative pain scores, analgesic consumption, sedation, anxiolysis, and hemodynamic effects from clonidine. Design This was a single center, randomized, double-blinded prospective study. Setting This study was conducted within the pediatric operating rooms at the Children’s Hospital of Pittsburgh, a large university-based academic medical center. Patients Fifty pediatric patients (ages 10-17 years old) without pre-existing cognitive impairment, developmental delay or chronic pain undergoing laparoscopic appendectomy during weekday hours were enrolled and randomized to control versus intervention groups. Intervention Ultrasound guided rectus sheath nerve block injections were performed at the beginning of surgery with either ropivacaine 0.5% plus normal saline or ropivacaine 0.5% plus clonidine (2 mcg/kg, maximum of 100 mcg). Measurements The duration of periumbilical numbness, Numeric Pain Rating Scale scores, University of Michigan Sedation Scale, State-Trait Anxiety Inventory for Children, analgesic consumption, heart rate, blood pressure, and mean arterial pressures, were recorded for each patient at several time points in the perioperative setting. Main results There were no significant differences in demographic characteristics between groups. The median duration of periumbilical numbness did not significantly differ between the ropivacaine only and the ropivacaine plus clonidine groups 540.0 minutes [360.0 -1015.0] (median [interquartile range (IQR)]) versus 823.5 minutes [509.5- 1080.0], p = 0.451. There were no significant differences in perioperative analgesic consumption, pain and anxiety scores, PACU sedation, or hemodynamic instability. Conclusions The addition of clonidine did not significantly prolong rectus sheath nerve block duration and was well tolerated in pediatric patients. Perioperative analgesia, hemodynamics, anxiety, and PACU sedation did not differ between groups. Trial registration Clinical Trials NCT02439281

To the Editor After carefully reading the report by Hartzell and colleagues[1][1] on the use of dexmedetomidine for rectus sheath blockade in pediatric umbilical hernia repair, I have a few comments regarding the clinical significance of this study. The authors reported a statistically significant

Abdominal wall nerve blocks have been gaining popularity for the treatment of perioperative pain in children. Our aim was to compare a technique of surgeon-performed, laparoscopic abdominal wall nerve blocks to anesthesia-placed, ultrasound-guided abdominal wall nerve blocks and the current standard of local wound infiltration.After institutional review board approval was obtained, a retrospective chart review was performed of pediatric patients treated at a single institution during a 2-year period. Statistics were calculated using analysis of variance with post-hoc Bonferonni t tests for pair-wise comparisons.Included in this study were 380 patients who received ultrasound-guided abdominal wall nerve blocks (n = 125), laparoscopic-guided abdominal wall nerve blocks (n = 88), and local wound infiltration (n = 117). Groups were well matched for age, sex, and weight. There was no significant difference in pain scores within the first 8 hours or narcotic usage between groups. Local wound infiltration demonstrated the shortest overall time required to perform (P .0001). Patients who received a surgeon-performed abdominal wall nerve block demonstrated a shorter duration of hospital stay when compared to the other groups (P = .02).Our study has demonstrated that laparoscopic-guided abdominal wall nerve blocks show similar efficacy to ultrasound-guided nerve blocks performed by pain management physicians without increasing time in the operating room.

A quadratus lumborum block associated complication is a rare event. We report two cases of hematoma following the performance of quadratus lumorum blocks in two patients. Performing this block requires additional consideration of abdominal wall anatomy and patient coagulation status.

Elective laparoscopic cholecystectomy (LC) pediatric patients in our institution have historically been admitted for an overnight hospital stay (OHS). The purpose of this study was to implement an ERAS protocol for elective LC in pediatric patients to promote same-day discharge (SDD) while maintaining excellent outcomes.An ERAS protocol for elective LC was implemented encompassing pre-, peri-, and postoperative management. A retrospective review of prospectively collected data from patients before (BI) and after implementation (AI) of the protocol was performed.A total of 250 patients (BI 105, AI 145) were included in the study. The AI group had significantly higher rate of SDD compared to BI (77.2% vs. 1.9%, p 0.01) and significantly decreased opioid use (morphine equivalents mg/kg AI 0.36 vs. BI 0.46, p 0.001). There were also no significant differences in the rate of total 30-day emergency department visits (BI 11.4% vs. AI 9.7%, p = 0.52) or surgery-related 30-day emergency department visits (BI 7.6% vs. AI 8.3%, p = 0.53). Factors that predisposed patients to an OHS after LC included higher ASA, later surgery start times, and longer operative times.The ERAS protocol significantly increased the rate of SDD after elective LC in pediatric patients without an associated increase in emergency department visits or readmissions.III.

Acute Interventional Perioperative Pain Service consultants have routinely placed paravertebral nerve block (PVB) catheters for the continuous release of ropivacaine following stage I microtia reconstruction with costal cartilage graft at our institution since 2010. A retrospective chart review from July 2006 was performed to compare the length of hospital stay, median pain score (0-10 scale), and opioid use of patients receiving PVB with those of historical controls. Statistical analysis included t, Mann-Whitney U, and Fisher's exact tests. A total of 15 stage I microtia surgeries were included, 10 with PVB and 5 without. Patients with and without PVB had high peak pain scores (8.4 vs 7.8), remained in the hospital for 3.5 and 3.8 days, and consumed 0.69 and 0.36 mg/kg morphine equivalents, respectively. These findings highlight the feasibility of PVB, but larger studies are needed to optimize pain relief in this population.

Effective analgesia is necessary for optimal recovery after surgery, but children often do not attain adequate postoperative pain control. This review examines the current trends in paediatric regional anaesthesia.Better pain assessment and therapeutic regimens are needed for our patients. Trunk blocks such as paravertebral, transversus abdominis plane, rectus sheath and ilioinguinal/iliohypogastric are becoming a popular means of providing analgesia for thoracic and abdominal procedures. The introduction of ultrasound guidance improves accuracy, efficacy, and safety of regional anaesthesia, and also decreases the amount of local anaesthetic injected. Single injection nerve blocks have a limited duration and the patients can benefit from adding an adjunct to local anaesthetic or placing a catheter. The use of adjuncts is reasonable, but it is difficult to find a medication with both minimal side-effects and the ability to combat pain for extended periods of time. More peripheral nerve block catheters are used in the paediatric inpatient and outpatient settings and recent data support the feasibility and efficacy of ambulatory peripheral nerve catheters.By using a multimodal approach that includes regional anaesthesia, paediatric pain management should aim to reduce patients' pain to an acceptable level without compromising their degree of mobilization. Undoubtedly, peripheral nerve blocks improve analgesia, but future large prospective studies should be conducted to further delineate their effectiveness, duration and safety.

BACKGROUND: Single-injection paravertebral nerve blocks (PVBs) provide effective postoperative analgesia after adult laparoscopic cholecystectomy (LC). We sought to compare PVBs with local anesthetic injections at laparoscopic port sites in a pediatric population. METHODS: Eighty-three patients (8–17 years old) scheduled for LC were randomized prospectively to 2 treatment groups: the PVB group received ropivacaine 0.5% injected in the paravertebral space and normal saline injections at laparoscopic instrument sites, and the port infiltration group received normal saline in the paravertebral space and ropivacaine 0.5% at instrument sites. Postoperative analgesia was provided with hydromorphone via patient-controlled analgesia for up to 12 hours, followed by oxycodone and hydromorphone. The total amount of analgesic, serial visual analog scale scores for pain and subject pain control satisfaction, type and characteristics of pain, and complications were recorded for 24 hours. RESULTS: The intraoperative fentanyl requirement (ng/kg/min) was lower in the PVB group than in the port infiltration group (12.81 vs 16.57, P = 0.007). Total postoperative analgesic consumption and mean visual analog scale scores were not different between the groups. Baseline pain recorded before surgery correlated with self-reported postoperative pain scores only in the port infiltration group. The rate of complications was low and similar between groups. There was no difference in incidence of patient-reported incisional, visceral, or gas pain. Shoulder pain, however, was 49% less (95% confidence interval, 0.269–0.893) in the port infiltration group. CONCLUSIONS: PVBs did not reduce postoperative pain associated with pediatric LC but decreased intraoperative fentanyl requirements.

Background Bilateral rectus sheath blocks have proven to be superior to local anesthetic infiltration for umbilical incisions and have been gaining popularity for the treatment of perioperative pain in children. We aim to develop a technique of surgeon performed rectus sheath blocks under laparoscopic-guidance alone. Methods In phase I, we observed the laparoscopic appearance of a rectus sheath block. The pain management team performed an ultrasound-guided rectus sheath nerve block as we visualized the posterior rectus sheath with the laparoscope. In phase II, after completion of the laparoscopic procedure, we performed a rectus sheath nerve block. Ultrasound was used to identify where the local anesthetic had been injected. Results Nineteen patients were included in this study, accounting for 38 rectus sheath blocks. In phase I, we observed with the laparoscope the delivery of ten ultrasound-guided rectus sheath blocks. In phase II, 28 laparoscopic-guided rectus sheath blocks were completed with immediate ultrasound confirmation of correct placement. Conclusions We have demonstrated that the rectus sheath nerve block can be performed reliably under laparoscopic-guidance alone. The efficacy of the laparoscopic-guided nerve block compared to the ultrasound-guided approach will need further study in a prospective, randomized trial. Type of study Retrospective review. Level of evidence 3.

Outpatient pain management after iliac crest bone harvesting can be challenging. We report the use of home L2 paravertebral nerve block catheter (L2PVBC) in a series of five children. The pain scores were low, and analgesic medication consumption was minimal. No complications were reported related with these catheters, and the patients reported very high pain control satisfaction scores. Outpatient L2PVBC can be beneficial as part of a multimodal analgesia strategy in selected pediatric patients.

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To the Editor, Having read carefully the report by Moore and colleagues[1][1] on the novel use of continuous erector spinae plane (ESP) blockade for postoperative analgesia after pediatric liver transplant and being very familiar with both pediatric pain management and liver transplantation, I have

Summary Pain management in small infants and children is challenging. We report the use of unilateral transversus abdominis plane (TAP) catheters for analgesia following single-sided open lower abdominal surgery when epidural analgesia was undesirable in a series of six low-weight children. Data collection was done via a retrospective chart review. All catheters attempted were successfully placed with resultant low pain scores and the minimal use of rescue analgesic medications. No complications were reported related to these catheters. TAP catheters, although technically challenging, are feasible for the provision of analgesia for surgeries involving the lower abdominal wall in very small patients.

Regional anesthesia techniques commonly utilized in post-operative pain management are often considered contraindicated in coagulopathic patients. We report on successful postoperative pain control utilizing peripheral nerve blockade after exploratory laparotomy with small bowel resection in a mildly coagulopathic patient. In our case, complicated by abnormal PT, PTT and INR, a thromboelastogram (TEG) was performed before the procedure and found to be normal. An ultrasound-guided bilateral paravertebral blockade with continuous paravertebral catheters was then performed in this pediatric patient without complications. The patient expressed satisfaction with his pain control. More studies are needed to evaluate the validity of TEG in the prediction of bleeding risk and the safety of this regional technique in a mildly coagulopathic patients.

Children often experience significant postoperative pain and effective analgesia is necessary for optimal recovery. By simultaneously improving analgesia and reducing side effects from opioid use, a multimodal approach that includes ultrasound guided peripheral nerve blocks (PNBs) is a better therapeutic regimen than the standard of care. In addition, PNBs, a form of regional analgesia, improves quality of care, increases satisfaction and saves health care costs. Furthermore, ultrasound technology improves accuracy and efficacy, decreases the amount of local anesthetic, and offers additional safety benefits. This chapter covers ultrasound guided single injections PNBs for thoracic and abdominal surgeries.

Different transversus abdominis plane blocks techniques cause variations in postoperative analgesia characteristics. We report the use of unilateral quadratus lumborum catheter for analgesia following colostomy closure. The catheter was placed under direct ultrasound visualization and had good outcomes: low pain scores and minimal use of rescue analgesic medication. No complications were reported in this pediatric patient. More studies are needed to evaluate the effectiveness and safety of this regional anesthesia technique.

Background: Placement of a thoracic paravertebral nerve block catheter (PVBC) is a safe and effective method for providing postoperative analgesia for pediatric patients undergoing thoracotomy. The PVBC can be misplaced despite accurate needle placement. Case Presentation: An 8 year old girl with a history of right lower extremity osteosarcoma and a right lung nodule underwent thoracotomy and wedge resection of the right lung. A T7 paravertebral nerve block catheter (PVBC) was placed under ultrasound guidance for postoperative pain relief. The patient reported satisfactory analgesia at thoracic incision without side effects throughout postoperative anesthesia care unit stay and postoperative day 1 (POD1). On POD2, the patient reported a droopy left eyelid and disclosed blurry vision since POD1. The physical exam revealed left partial Horner’s syndrome and numbness along the left T5-7 dermatome. The PVBC insertion depth was unchanged. The ptosis and miosis resolved completely one hour after stopping the ropivacaine infusion. The infusion was restarted after the catheter was pulled back by 2 cm and bloused with 5 ml of ropivacaine 0.2%. Patient reported that her pain was relieved with no recurrence of her symptoms. Discussion: This is the first case report of a patient who developed contralateral Horner’s syndrome from the placement of a PVBC. The PVBC can reach the contralateral paravertebral space via inter vertebral foramina or prevertebral space. Conclusion: The paravertebral catheter depth in children may need to be individualized.

Summary Background Ambulatory continuous peripheral nerve blocks (CPNBs) are feasible for pediatric patients. We sought to evaluate the efficacy of CPNBs in a pediatric population. Methods This retrospective report of 33-month prospectively collected data investigates patient, parent, and nurse pain control satisfaction score (PCSS), the incidence and severity of pain, daily analgesic consumption following discharge home with various CPNBs and On-Q pumps, and any complications and side effects related to CPNBs. Results Four hundred and three patients (403; aged 5–22) were discharged home with 410 CPNBs (brachial and lumbar plexus, femoral, sciatic, and paravertebral); 76.7% on the day of surgery. The median/interquartile range (IQR) ropivacaine continuous infusion via On-Q pump was 0.24 (0.20–0.30) mg·kg−1·hr−1, and the median/IQR duration was 72 (48–72) h. The median/IQR home PCSS was 10 (9–10). Median Postoperative Ambulatory Care Unit (PACU)/IQR pain control satisfaction scores were 10 (8–10) for the patient, 10 (9–10) for the parent, and 10 (9–10) for the nurse. Thirty-three (10.0%) patients did not report any pain at home, and median maximum home/IQR pain score was 4 (2–6). In the PACU, 126 (31.3%) patients did not report any pain and median/IQR pain score was 1 (0–3). No opioids were administered at home for 12 (4.3%) patients and in the PACU for 150 (37.4%). Sixty-three (14.4%) complications and side effects for 58 patients were reported. We report 93.1% ambulatory efficacy of CPNBs. Conclusion Our patients and their caregivers were very satisfied with ambulatory CPNBs. When combined with oral analgesics, CPNBs provided effective home postoperative analgesia.

Study Objective: It is to compare continuous thoracic paravertebral blockade and thoracic epidural catheters for postoperative pain after VATS and chemical pleurodesis in children. Design: Case series, retrospective chart review. Setting: Children’s Hospital of University of Pittsburgh Medical Center. Patients: We studied seventeen (17) pediatric patients who underwent VATS with chemical pleurodesis. Interventions: Fourteen children (14) had continuous thoracic paravertebral blockade and three children (3) had thoracic epidural catheters. Measurements and main results: Postoperative pain scores and consumption of analgesics were compared during the first 48 hours after surgery. Total length of hospital stay and complications secondary to analgesics and regional analgesia were analyzed and compared. Median pain scores were similar with P-values ranging from P = 0.13-0.76. Opioid consumption was not significantly different, with P-values for opioid morphine equivalency ranging from P= 0.13-0.96. Length of stay was significantly shorter for thoracic paravertebral group (3.86, SD±0.77) than for thoracic epidural group (5.00, SD±1.00) (P= 0.04). The rate of complications was low; frequency of nausea /emesis (P= 0.16) and itching (P= 0.60) was similar between groups.

SummaryBackground Paravertebral perineural blocks are used to prevent pain in the thoracoabdominal dermatomes. Traditionally, a landmark-based technique is used in children, while ultrasound-guided (UG) techniques are being employed in adult patients. Objective To describe an UG technique for placement of thoracic paravertebral nerve block (TPVNB) catheters in pediatric patients. Methods Retrospective chart review of a series of 22 pediatric patients' ages 6 months to 17 years with weights from 6.25 kg to 135 kg using a transverse in-plane technique. Catheters were placed both bilateral and unilateral for a variety of thoracic and abdominal procedures. A linear ultrasound transducer was used in all cases with frequency of oscillation and transducer length chosen based on individual patient characteristics of age, weight, and BMI. Results The median pain scores at 12, 24, 36, and 48 h were 1.2 (interquartile range, 4.5), 0.84 (interquartile range 3.0), 1.6 (interquartile range 2.9), and 0.83 (interquartile range 1.74), respectively. The median dose of opioid expressed as morphine equivalents consumed during the first 24 h after surgery was 0.14 mg·kg−1 (interquartile range, 0.78 mg·kg−1) and from 24 to 48 h the median dose was 0.11 mg·kg−1 (interquartile range 0.44 mg·kg−1). No complications were noted, and catheters were left an average of 3 days with a range of 1–5 days with good pain relief. Conclusion This technical description demonstrates the feasibility of placing PVNB catheters using a transverse in-line ultrasound-guided technique in a wide range of pediatric patients.

Mutations in the ryanodine receptor type 1 gene (RYR1) that encodes the skeletal muscle-specific intracellular calcium (Ca(2+)) release channel are a cause of malignant hyperthermia (MH). In this study, we examined RYR1 mutations in a large number of North American MH-susceptible (MHS) subjects without prior genetic diagnosis.RYR1 was examined in 120 unrelated MHS subjects from the United States in a tiered manner. The α-1 subunit of the dihydropyridine receptor gene (CACNA1S) was screened for 4 variants in subjects in whom no abnormality was found in ≥ 100 exons of RYR1.Ten known causative MH mutations were found in 26 subjects. Variants of uncertain significance in RYR1 were found in 36 subjects, 16 of which are novel. Novel variants in both RYR1 and CACNA1S were found in the 1 subject who died of MH. Two RYR1 variants were found in 4 subjects. Variants of uncertain significance were found outside and inside the hotspots of RYR1. Maximal contractures in the caffeine-halothane contracture test were greater in those who had a known MH mutation or variant of uncertain significance in RYR1 than in those who did not.The identification of novel RYR1 variants and previously observed RYR1 variants of uncertain significance in independent MHS families is necessary for demonstrating the significance of these variants for MH susceptibility and supports the need for functional studies of these variants. Continued reporting of the clinical phenotypes of MH is necessary for interpretation of genetic findings, especially because the pathogenicity of most of these genetic variants associated with MHS remains to be elucidated.

Pain management in small infants and children is challenging. We report the use of unilateral transversus abdominis plane (TAP) catheters for analgesia following single-sided open lower abdominal surgery when epidural analgesia was undesirable in a series of six low-weight children. Data collection was done via a retrospective chart review. All catheters attempted were successfully placed with resultant low pain scores and the minimal use of rescue analgesic medications. No complications were reported related to these catheters. TAP catheters, although technically challenging, are feasible for the provision of analgesia for surgeries involving the lower abdominal wall in very small patients.

Regional anesthesia techniques commonly utilized in post-operative pain management are often considered contraindicated in coagulopathic patients. We report on successful postoperative pain control utilizing peripheral nerve blockade after exploratory laparotomy with small bowel resection in a mildly coagulopathic patient. In our case, complicated by abnormal PT, PTT and INR, a thromboelastogram (TEG) was performed before the procedure and found to be normal. An ultrasound-guided bilateral paravertebral blockade with continuous paravertebral catheters was then performed in this pediatric patient without complications. The patient expressed satisfaction with his pain control. More studies are needed to evaluate the validity of TEG in the prediction of bleeding risk and the safety of this regional technique in a mildly coagulopathic patients.

The time between the beginning of anesthetic administration and recognition of the first sign of malignant hyperthermia (MH) (MH onset time) could differ among anesthetic drugs.We examined the time of the first signs of suspected MH, anesthetic drugs administered, subject age, and year of event in Adverse Metabolic/Musculoskeletal Reaction to Anesthesia reports in the North American Malignant Hyperthermia Registry. Inclusion criteria were judgment by the reporting clinician that the event was possible or fulminant MH, documentation of the time when anesthetic administration began, and the time when the first MH sign was noted. Descriptive statistics, Kruskal-Wallis analysis, and nonparametric correlation were used to assess the difference in MH onset times under different conditions.Four hundred seventy-seven cases met inclusion criteria; 58.5% were possible MH and 41.5% fulminant MH. Inhaled anesthetic and succinylcholine were given in 53.9% of cases, inhaled anesthetic only in 41.7%, and succinylcholine without inhaled anesthetics in 2.9%. No causative anesthetic drugs were reported in 7 MH cases. In 394 patients exposed to only 1 of the 4 inhaled anesthetics, without regard for subject age, MH onset time was shorter in the presence of halothane than any of the other anesthetics and shorter after succinylcholine in all anesthetics. If succinylcholine was not given, MH onset was shorter during sevoflurane anesthesia than during desflurane or isoflurane. In 322 cases, 1 rather than multiple first signs of MH were reported with masseter spasm as the earliest MH sign. In 339 cases in which masseter spasm was not reported, there was no difference in MH onset time with or without succinylcholine. In 146 cases in which masseter spasm was not reported and succinylcholine was not given, MH onset was shorter during halothane anesthesia, than during exposure to desflurane, or isoflurane. MH onset time during sevoflurane was shorter than during desflurane or isoflurane. MH was reported later in the course of anesthesia after 1998, when halothane and succinylcholine were less often reported. MH occurred after succinylcholine administration in the absence of inhaled anesthetics. We could not separate an effect of age from that of other variables.The onset of MH has been observed later during desflurane and isoflurane anesthesia than during exposure to sevoflurane. Since 1998, MH signs have more often appeared later, in the second or third hour of anesthesia, than they did before 1998.