The effect of nitrous oxide on cerebral blood flow velocity in children anesthetized with propofol

Nitrous oxide intoxication: systematic literature review and proposal of new diagnostic possibilities

Background

Nitrous oxide (N2O), also called “laughing gas,” is the most commonly used inhalation anesthetic in dentistry. The N2O is no longer used, because of the long-term neurologic and cardiovascular sequelae. Due to its sedative and euphoric properties, N2O is often used for recreational use or in some erotic activities. Accidental deaths are mainly associated with the uses of N2O: death can occur from sudden cardiac arrhythmia or, most commonly, acute asphyxiation due to hypoxia. This paper aims to study the literature concerning deaths due to N2O intoxication and highlight pathological findings useful for diagnosis when the crime scene investigation does not reveal any evidence.

Materials and methods

The authors conducted the literature search by PubMed and Scopus databases, searching for articles from 1 January 1970 to 1 March 2020 using the key terms: “Nitrous oxide,” “Laughing gas,” “Hypoxic damage,” “Nitrous oxide anesthesia,” and “Nitrous oxide death.”

Results and discussion

A total of 244 articles were collected. Only 26 articles were included in the systematic review. Most of the deaths from intoxication are due to asphyxiation; the diagnosis is often difficult and immunohistochemistry could be helpful. Nitrous oxide increases the intracellular adhesion molecule expression, E- and P-Selectin (markers of the early inflammatory response), and HIF-1 α (indicative of oxidative stress during ischemia-reperfusion).

Conclusion

The macroscopic and microscopic signs of N2O intoxication are non-specific, but N2O has been proven to cause hypoxic damage to the brain. The suspicion of the presence of the gas in the environment should guide the pathologist. Tissue analyzes provide important information; immunohistochemical stains can confirm hypoxic damage through the use of markers such as HIF-1 α, E-Selectin, and P-Selectin.

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.

Is nitrous oxide use appropriate in neurosurgical and neurologically at-risk patients?

PURPOSE OF REVIEW

To address controversial issues surrounding the use of nitrous oxide as a component of anesthesia in neurosurgical and neurologically at-risk patients.

RECENT FINDINGS

Nitrous oxide has been used as a component of general anesthesia for over 160 years and has contributed to countless apparently uneventful anesthetics in neurologically at-risk patients. Avoidance of nitrous oxide in specific circumstances, such as pre-existing pneumocephalus, during acute venous air embolism, and in patients with disorders of folate metabolism, is warranted. However, various controversies exist regarding the use of this drug in the general neurosurgical population. Specifically, some suggest a possible association between nitrous oxide and the postoperative development of tension pneumocephalus despite lack of data to support this notion. Additionally, data describing alterations of cerebral hemodynamics and metabolism and exacerbation of ischemic neurologic injury by nitrous oxide are inconsistent. Recent data derived from humans having cerebral aneurysm clipping failed to show any long-term adverse effect from the use of nitrous oxide on gross neurologic or cognitive function.

SUMMARY

Except in a few specific circumstances, there exists no conclusive evidence to support the dogmatic avoidance of nitrous oxide in neurosurgical patients.

Impact of anesthetic agents on cerebrovascular physiology in children

The role of the pediatric neuroanesthetist is to provide comprehensive care to children with neurologic pathologies. The cerebral physiology is influenced by the developmental stage of the child. The understanding of the effects of anesthetic agents on the physiology of cerebral vasculature in the pediatric population has significantly increased in the past decade allowing a more rationale decision making in anesthesia management. Although no single anesthetic technique can be recommended, sound knowledge of the principles of cerebral physiology and anesthetic neuropharmacology will facilitate the care of pediatric neurosurgical patients.

Transcranial Doppler and anesthetics

Transcranial Doppler (TCD) is widely used to investigate the effects of anesthetic drugs on cerebral blood flow. Its repeatability and non-invasivity makes it an ideal, first choice method. Anesthesia providers are required to be conscious of the cerebral hemodynamic effects of drugs given in their practice, especially in neurosurgery and in subjects with impaired brain functions. The purpose of this review is to present the basic concepts of the TCD technique and the effects on cerebral hemodynamics of the most popular anesthetic drugs evaluated using TCD ultrasonography.

Remifentanil Requirements During Propofol Administration to Block the Somatic Response to Skin Incision in Children and Adults

BACKGROUND

During sevoflurane administration, children require a remifentanil infusion rate twofold higher than adults to block responses to skin incision. Similar data concerning remifentanil requirements are unavailable during total IV anesthesia.

METHODS

We prospectively determined the infusion rate (IR) of remifentanil necessary to block the somatic response to skin incision in 50% (IR50) of adults (n = 20, aged 20-60 yr) and children (n = 20, aged 3-11 yr) during propofol anesthesia. In each patient undergoing lower abdominal surgery, a remifentanil infusion was initiated, followed by target-controlled infusion of propofol set at a plasma concentration of 6 mug/mL. After tracheal intubation, propofol was reduced to 3 microg/mL until the end of the study. Remifentanil IR was determined according to Dixon's up-and-down method, with the first patient in each group receiving 0.2 microg x kg(-1) x min(-1) followed by the consecutive patient receiving 0.02 microg x kg(-1) x min(-1) modifications according to the response of the previous patient. The remifentanil IR was kept unchanged for at least 20 min before surgery. At the beginning of surgery, only the skin incision was performed, and the somatic response was observed. If there was any gross movement of extremity the response was considered positive.

RESULTS

The IR50 (CI(95%)) was 0.08 (0.06-0.12) microg x kg(-1) x min(-1) in adults and 0.15 (0.13-0.17) microg x kg(-1) x min(-1) in children (P < 0.001).

CONCLUSION

These results demonstrate that, similar to sevoflurane anesthesia, during total IV anesthesia with propofol, children require a remifentanil IR almost twofold higher than adults to block the somatic response to skin incision.

Effect site concentrations of propofol producing hypnosis in children and adults: comparison using the bispectral index

BACKGROUND

No study has determined the concentration of propofol producing a degree of hypnosis compatible with anaesthesia in children. As a result, concentrations determined in adults are recommended for children. As this can result in an inadequate depth of anaesthesia, we determined the predicted effect site concentration (C(e)) of propofol necessary to obtain a bispectral index (BIS) of 50 in 50% (EC(e50)) of children and adults.

METHODS

Twenty adults (aged 33-44 years) and 20 children (aged 3-11 years) undergoing surgery under general anaesthesia were studied. All were monitored with a BIS monitor, and a target controlled infusion of propofol aiming for a constant C(e) value was started. After 10 min, patients were evaluated using a sedation scale, and the last 5 min was used to determine the mean BIS for this C(e) value. The C(e) value of propofol was defined using the up-and-down method of Dixon and Massey. The first patient in each group received C(e)= 6 microg/ml; thereafter, it was modified in 0.5 microg/ml decrements/increments with positive or negative responses, respectively. A positive response was BIS < 50 and a negative response was BIS > or = 50. The EC(e50) value was compared using unpaired Student's t-test. The prediction probability (P(K)) was used to study the association between BIS and the sedation score.

RESULTS

The mean EC(e50) (95% confidence interval) values were 3.75 microg/ml (2.97-4.75 microg/ml) in adults and 3.65 microg/ml (3.36-3.96 microg/ml) in children (not significant). All patients with BIS < 50 were unarousable with tactile stimulation. The P(K) value was 0.99 in both groups.

CONCLUSIONS

The predicted C(e) value of propofol resulting in BIS = 50 was similar in adults and children aged 3-11 years. The predicted C(e) value of propofol producing hypnosis in adults also seems to be useful in this paediatric population.

The effect of nitrous oxide on cerebral blood flow velocity in children anaesthetised with sevoflurane

To determine the effects of nitrous oxide on middle cerebral artery blood flow velocity (CBFV) during sevoflurane anaesthesia in children, CBFV was measured using transcranial Doppler sonography in 16 ASA I or II children. Anaesthesia consisted of 1.0 MAC sevoflurane in 30% oxygen with intermittent positive pressure ventilation maintaining FEco2 at 38 mmHg (5.0 kPa) and a caudal epidural block using 0.25% bupivacaine 1.0 ml.kg-1. The remainder of the inspired gas was varied in one of two sequences either air/nitrous oxide/air or nitrous oxide/air/nitrous oxide. The results showed that CBFV decreased when nitrous oxide was replaced by air (p = 0.03) and returned to its initial value when nitrous oxide was reintroduced. CBFV increased when air was replaced by nitrous oxide (p = 0.04) and returned to its initial value when air was reintroduced. Mean heart rate and blood pressure remained constant. We conclude that nitrous oxide increases cerebral blood flow velocity in healthy children anaesthetised with 1.0 MAC sevoflurane.

Effect of nitrous oxide on cerebrovascular reactivity to carbon dioxide in children during sevoflurane anaesthesia

BACKGROUND

Sevoflurane and nitrous oxide have intrinsic cerebral vasodilatory activity. To determine the effects of nitrous oxide on cerebrovascular reactivity to carbon dioxide (CCO(2)R) during sevoflurane anaesthesia in children, middle cerebral artery blood flow velocity (V(mca)) was measured over a range of end-tidal carbon dioxide concentrations (E'(CO(2))), using transcranial Doppler (TCD) ultrasonography.

METHODS

Ten children aged 1.5-6 yr were anaesthetized with sevoflurane and received a caudal block. Patients were allocated randomly to receive either air-nitrous oxide or nitrous oxide-air. Further randomization determined the sequence of E'(CO(2)) (25, 35, 45, and 55 mm Hg) and sevoflurane (1.0 then 1.5 MAC or 1.5 then 1.0 MAC) concentrations. Once steady state had been reached, three measurements of V(mca), mean arterial pressure (MAP), and heart rate (HR) were recorded.

RESULTS

Cerebrovascular carbon dioxide reactivity was reduced in the 25-35 mm Hg E'(CO(2)) range on the addition of nitrous oxide to 1.5 MAC, but not 1.0 MAC sevoflurane. A plateau in CCO(2)R of 0.4-0.6% per mm Hg was seen in all groups between E'(CO(2)) values of 45 and 55 mm Hg. Mean HR and MAP remained constant throughout the study period.

CONCLUSIONS

Cerebrovascular carbon dioxide reactivity is reduced at and above an E'(CO(2)) of 45 mm Hg during 1.0 and 1.5 MAC sevoflurane anaesthesia. The addition of nitrous oxide to 1.5 MAC sevoflurane diminishes CCO(2)R in the hypocapnic range. This should be taken into consideration when hyperventilation techniques for reduction of brain bulk are being contemplated in children with raised intracranial pressure.