Non-invasive assessment of cardiovascular autonomic activity induced by brief exposure to 50% nitrous oxide in children

Autonomic cardiac regulation after general anesthesia in children

BACKGROUND

General anesthesia dramatically decreases the activity of the autonomic nervous system. Most of the hypnotic agents used to induce anesthesia inhibit sympathetic cardiovascular regulation and baroreflex control in a dose-dependent manner, lowering cardiac adaptability during the operation. The consequence of this effect in children during and after surgery has never been studied to date.

AIM

The aim of this study was to follow the variations in autonomic cardiac indices in children younger than 8 years old after general anesthesia (6-24 hours) in programmed surgery.

METHOD

A prospective descriptive monocentric study of 44 children under 8 years old who underwent scheduled surgery at our hospital center (Saint-Étienne University Hospital, France) was performed between June 1, 2016 and November 1, 2016. Heart rate variability was monitored for 24 hours using Holter-ECG devices and the resulting data were interpreted using linear and nonlinear analyses.

RESULTS

Compared to baseline thresholds before surgery, all heart rate variability indices decreased dramatically during general anesthesia. After awakening, a slight reduction in sympathetic activity persisted 6 hours after surgery, but all measurements of sympathetic and parasympathetic activity had returned to baseline thresholds 12 hours after the operation. Twenty-four hours after surgery, some parameters had increased above the corresponding baseline levels.

CONCLUSION

Autonomic nervous function normalizes rapidly (within 12 hours) in prepubertal children. This study indicates that general anesthesia does not seem to increase the long-term risk of autonomic dysfunction in these patients.

Nitrous oxide myelopathy in a pediatric patient

OBJECTIVE

Nitrous oxide myelopathy is rare in children. We report a 16-year-old girl who presented at the pediatric emergency department with progressive ascending numbness in 4 limbs for 1 week and sensory ataxia for 4 days. The patient had frequently inhaled nitrous oxide for recreation over the preceding 3 months. Her serum vitamin B12, homocysteine, and folate levels were within normal ranges. Magnetic resonance imaging of the spinal cord T2-weighted images series showed hyperintensities in the central and dorsal cervical spinal cord section over C1 to C6 and suspicious of hyperintensities in the thoracic spinal section over T7 and T8.

CONCLUSIONS

Myelopathy due to nitrous oxide should be considered in a differential diagnosis when adolescents develop neurologic symptoms after nitrous oxide inhalation abuse.

Applications of nitrous oxide for procedural sedation in the pediatric population

OBJECTIVE

The objective of this review was to provide a general descriptive account of the physical properties, end-organ effects, therapeutic applications, and delivery techniques of nitrous oxide (N2O) as used in the arena of procedural sedation.

DATA SOURCE

A computerized bibliographic search regarding the applications of nitrous for provision of sedation and analgesia during procedures with an emphasis on the pediatric population was performed.

RESULTS

The end-organ effects of N2O have been well described in the operating room setting. Aside from its effects on the central nervous system of sedation and analgesia, N2O may alter intracerebral dynamics and alter cerebral blood flow and intracranial pressure especially in patients with altered intracranial compliance. Effects on ventilation include a dose-related depression of ventilatory function and control of upper airway patency. These effects are generally limited in the absence of comorbid diseases and potentiated by other sedative and analgesic agents. The more clinically significant respiratory effect of N2O on ventilatory function is a dose-dependent depression of the ventilatory response to hypoxemia. Hemodynamic effects include a mild direct depressant effect on myocardial function, which in the absence of comorbid cardiac disease is generally compensated by stimulation of the sympathetic nervous system. Nitrous oxide may potentially aggravate pulmonary hypertension. Additional physiologic effects on neurologic and hematologic function may result in inactivation of the enzyme, methionine synthetase. Recent concern has also been raised regarding the potential effects of N2O on immune function and its relationship to perioperative surgical site infections. Given differences in the solubility, N2O will diffuse into and significantly expand gas-filled cavities. Chronic exposure of health care works to N2O is also a concern. Although there are limited data in the literature to clearly substantiate concerns regarding the reproductive toxicity of occupational exposure to N2O, appropriate scavenging and use of other techniques are mandatory. Nitrous oxide has been shown to be effective for a variety of minor surgical procedures such as venipuncture, intravenous cannula placement, lumbar puncture, bone marrow aspiration, laceration repair, dental care, and minor dermatologic procedures. It is generally as effective as midazolam, with several studies demonstrating it to be more effective. However, its utility is not as great in severely painful procedures such as fracture reduction. Demonstrated advantages to parenteral sedation include a more rapid onset and a shorter recovery time with the majority of patients preferring it to over other agents or agreeing to its use for subsequent procedures. The literature also suggests increased success rates with simple procedures such as intravenous cannula placement when compared with placebo. In general, life-threatening adverse events have not been reported. Most common adverse effects include dysphoria and vomiting. For more painful procedures, combination with another agent may be used, and in all cases, topical or infiltrative local anesthesia is recommended.

CONCLUSIONS

In general, N2O is a useful adjunct for procedural sedation. Given the variety of procedures performed in the pediatric patient, ongoing research is required to identify the most appropriate and effective use of this agent. This may be particularly relevant when evaluating its use for procedures associated with significant pain. In these scenarios, the combination of N2O with other agents needs to be evaluated. Given the potential for adverse effects, strict adherence to published guidelines regarding procedural sedation and monitoring is suggested.

A review of the safety of 50% nitrous oxide/oxygen in conscious sedation

Few studies into conscious sedation with 50% nitrous oxide/oxygen premix (50% N2O/O2) have been conducted in accordance with Good Clinical Practice in Clinical Trials. Of the 140 articles retained in this review, the incidence of adverse events (AEs) varied in the range of 0-68% according to the indications. When other drugs and/or local anaesthesia were used concomitantly, the relative risk for nausea and vomiting increased whereas it decreased for vertigo or hallucinations. Only one study examined potential causal relationship between serious AEs and the 50% N2O/O2 gas itself, giving a risk for a serious AE directly due to the gas of 3/10,000 administrations. No analysis of the effect of the method of administration was possible, nor could conclusions be drawn relating to the risk of occupational exposure.

The circulatory responses to tracheal intubation in children: a comparison of the oral and nasal routes

The circulatory responses to laryngoscopic tracheal intubation in 62 healthy children undergoing surgery requiring tracheal intubation were studied. They were randomly assigned to receive either the oral or nasal route for intubation. Baseline non-invasive blood pressure and heart rate were recorded following induction of anaesthesia, at intubation and then every minute for 5 min. The percentage changes of systolic blood pressure and heart rate during the measurement period were calculated. The results demonstrated that intubation time was significantly longer in the nasal group. Both oral and nasal intubation caused significant increases in blood pressure and heart rate compared to baseline and postinduction values. However, there were no significant differences found between the two groups in relation to blood pressure and heart rate. The two groups were similar with respect to the percentage changes of systolic blood pressure and heart rate during the observation period. It is concluded that oral and nasal intubation using a direct laryngoscopy can result in a similar circulatory response in anaesthetised children.

Noninvasive investigation of autonomic activity after carotid stenting or carotid endarterectomy

OBJECTIVE

Carotid artery stenting (CAS) has been introduced as an alternative to carotid endarterectomy (CEA) for the treatment of carotid artery stenosis. Both techniques seem to be associated with postoperative hemodynamic lability. Both may induce baroreceptor dysfunction, possibly leading to transient impairment of cardiovascular autonomic activity and resulting in hemodynamic instability. This instability might contribute to postoperative morbidity. To elucidate these phenomena, we studied the cardiac baroreflex and autonomic cardiovascular control after CAS and CEA.

METHOD

In 20 patients scheduled for CAS (n = 10) or CEA (n = 10), intra-arterial pressures and electrocardiograms were recorded during 10 minutes before and 8 and 24 hours after the procedure. Spontaneous cardiac baroreflex sensitivity was assessed using the sequence method and cross-spectral analysis. In addition, cardiovascular autonomic activity was investigated using spectral analysis of heart rate variability and systolic arterial pressure variability.

RESULTS

After CAS, we demonstrated an increase of the spontaneous baroreflex sensitivity median (interquartile range) from 5.6 (5.1 to 6.2) ms/mm Hg before the procedure to 8.8 (6.8 to 10.5) ms/mm Hg and 7.7 (3.9 to 8.6) ms/mm Hg (P < .001), 8 and 24 hours after the procedure. This was consistent with the increase of the high frequency component of heart rate variability reflecting cardiac parasympathetic activity and a decrease of the low frequency of systolic arterial pressure variability reflecting sympathetic vascular activity. The postoperative period was also associated with decreased systolic arterial pressure from 173 (162 to 190) mm Hg at baseline to 122 (109 to 143) mm Hg and 136 (121 to 143) mm Hg at 8 and 24 hours after CAS (P < .001). No changes in baroreflex sensitivity or in autonomic activity were observed after CEA.

CONCLUSIONS

These preliminary data suggest that CAS is associated with parasympathetic predominance postoperatively and may probably explain the lower systolic arterial pressure observed after CAS.

Blood pressure and heart rate changes during fibreoptic orotracheal intubation: a comparison of children and adults

BACKGROUND AND OBJECTIVES

Autonomic circulatory regulation and airway anatomy in children are significantly different from those in adults. There is no available published data to compare whether there is a clinically relevant difference in the haemodynamic responses to fibreoptic orotracheal intubation (FOI) under the same conditions between children and adults. In this randomized clinical study, we compared the blood pressure (BP) and heart rate (HR) changes during FOI in 40 children aged 3.5-9 yr and 40 adults aged 21-57 yr, ASA 1 scheduled for elective plastic surgery under general anaesthesia requiring orotracheal intubation.

METHODS

Anaesthesia was induced with intravenous (i.v.) injection of fentanyl and propofol, and face mask inhalation of isoflurane before FOI. Noninvasive BP and HR were recorded before induction (baseline values), after induction (postinduction values), at intubation and for 5 min after intubation at 1-min intervals. The percentage changes of BP and HR at each time point were calculated.

RESULTS

In children and adults, HR at intubation and 1-3 min after intubation were significantly higher than baseline and postinduction values. In adults, BP at intubation increased significantly compared to the postinduction values but did not exceed baseline values. In children, BP at intubation and 1 min after intubation were significantly higher than postinduction and baseline values. As compared to adults, FOI caused a more significant pressor response in children. The percentage changes of BP at intubation and 1 min after intubation were larger in children than in adults. However, there was no significant difference in the percentage change of HR during the observation between children and adults.

CONCLUSIONS

Under general anaesthesia, FOI might cause a more significant pressor response in children than in adults.

Spontaneous baroreflex sensitivity in (pre)adolescents

OBJECTIVE

To present normal spontaneous baroreflex sensitivity (BRS) values and investigate the influence of posture, sex, age, pubertal stage, body mass index (BMI), and physical activity level on BRS in (pre)adolescents. BRS is a sensitive measure of both sympathetic and parasympathetic cardiovascular regulation that may help detect early subclinical autonomic dysfunction.

DESIGN

A cross-sectional cohort study in a large sample of 10-13-year-old Dutch (pre)adolescents from the general population.

METHODS

Short-term spontaneous BRS was determined non-invasively by Portapres in both the supine and standing position. BRS was calculated by power spectral analysis using the discrete Fourier method (frequency band 0.07-0.14 Hz). Univariate statistical methods and multiple regression analyses were applied.

RESULTS

BRS in a standing position was lower than in a supine position (9.0 +/- 4.9 versus 15.3 +/- 9.1 ms/mmHg; t = 27.8, P < 0.001). Girls had lower BRS values than boys in both postures (supine 14.3 +/- 8.7 versus 16.4 +/- 9.4 ms/mmHg, beta = 0.12, P < 0.001; standing 8.4 +/- 4.4 versus 9.5 +/- 5.4 ms/mmHg, beta = 0.08, P = 0.012), independent of age, pubertal stage, BMI, and physical activity. Lower limits (P2.5) for normal BRS values in supine and standing positions were for girls 3.6 and 2.2 ms/mmHg and for boys 3.9 and 2.5 ms/mmHg, respectively. BRS declined with age in the standing position (beta = -0.13, P < 0.001). In obese (pre)adolescents, BMI was negatively associated with BRS during standing (Kendall's tau = -0.26, P = 0.010).

CONCLUSION

The BRS of (pre)adolescents was negatively related to female sex, age, and obesity. A reduced BRS in obese (pre)adolescents might be a candidate predictor of future cardiovascular health, and therefore warrants further exploration.

[Premixed 50% nitrous oxide and oxygen: theoretical recalls and practical modalities]

The concept of premixed 50% nitrous oxide and oxygen dated back to 1961 in England, where it is commercialised under the name Entonox. In France, after a so marginal use, premixed 50% nitrous oxide and oxygen now knows such a revival since we first consider the pain provoked by the cure. To use correctly premixed 50% nitrous oxide and oxygen, we need to know the main properties of the nitrous oxide. The four commercial versions, now on the market, are presented (Kalinox, Medimix, Antasol, Oxynox. Except a few contraindications, these indications are large, as well at hospital as outside. In less than 10% of the cases, side effects are possible. Conditions of administration are given in details. The limits of the technic and the particular precautions of use are precised.

Effects of nitrous oxide on baroreflex gain and heart rate variability

BACKGROUND

Spontaneous baroreflex method allows continuous assessment of cardiovagal reflex function within resting blood pressure, but effects of nitrous oxide, per se, on the spontaneous baroreflex response remain unknown. This study was designed to determine the effects of nitrous oxide on spontaneous baroreflex gain and heart rate variability assessed by power spectral analysis in humans.

METHODS

Electrocardiogram and non-invasive blood pressure were monitored in 12 healthy volunteers before and during a 15-min inhalation of 67% nitrous oxide in oxygen, while spontaneous respiration was maintained. Least-square regression analysis relating R-R interval and systolic blood pressure was performed to obtain spontaneous baroreflex gains. Heart rate variability was analyzed using fast Fourier transformation.

RESULTS

Nitrous oxide did not significantly alter spontaneous baroreflex gains, which correlated well with high-frequency power (0.15-0.4 Hz) of heart rate variability before and during nitrous oxide inhalation.

CONCLUSION

Our results indicate that (a) cardiovagal reflex response is not affected by nitrous oxide, per se, and (b) spontaneous baroreflex responses closely reflect beat-to-beat dynamic modulation of the cardiac cycle by the parasympathetic nervous system during inhalation of 67% nitrous oxide.

Does Halothane Really Preserve Cardiac Baroreflex Better Than Sevoflurane? A Noninvasive Study of Spontaneous Baroreflex in Children Anesthetized with Sevoflurane Versus Halothane

Heart rate profiles during the induction of anesthesia differ markedly between the administration of sevoflurane and halothane. Previous investigations have shown that halothane preserves cardiac parasympathetic activity more than sevoflurane. Because vagal drive to the sinus node is the main effector of arterial baroreflex control of heart rate, halothane may preserve cardiac baroreflex better than sevoflurane. To investigate cardiac baroreflex in anesthetized children, we used two noninvasive methods providing different approaches to the arterial blood pressure (BP) and R-R interval (RRI) relationship: the sequence methods investigating beat-to-beat changes in BP and RRI (time domain) and the cross-spectral analysis investigating relationships between oscillations of BP and RRI (frequency domain). Children were randomly assigned to mask induction with sevoflurane in 100% oxygen, sevoflurane in 50% nitrous oxide/50% oxygen, or halothane in 50% nitrous oxide/50% oxygen. After tracheal intubation, the inspired fraction of volatile anesthetic was reduced to 1 minimum alveolar anesthetic concentration (MAC). The spontaneous baroreflex (SBR) sensitivity was calculated with the sequence method at baseline, during induction, and after intubation. The cardiac baroreflex was also estimated with cross-spectral analysis at baseline and at 1 MAC (stationary conditions). In the three groups, the induction of anesthesia was associated with a marked decrease of SBR sensitivity, which occurred earlier with sevoflurane than with halothane. Five minutes after intubation (1 MAC), the sequence method showed a similar decrease of the SBR sensitivity in the three groups. Similarly, the cross-spectral analysis between systolic blood pressure and RRI showed a decrease of the gain calculated in the low-frequency band, but the gain in the respiratory band was higher with halothane compared with sevoflurane. In children, the induction of anesthesia with halothane and sevoflurane is associated with a marked decrease of cardiac baroreflex activity. The persistence of respiratory RRI fluctuations under halothane might reflect reflex respiratory arrhythmia rather than efficient parasympathetic baroreflex activity.