Abstract :
Background:
Childhood acute lymphoblastic leukemia (ALL) treatment requires numerous
lumbar punctures (LPs) with intrathecal (IT) chemotherapy to prevent and
treat central nervous system disease. Historically, LPs in this setting
are performed using propofol sedation. At our institution, LPs are often
alternatively performed under nitrous oxide (N2O). To
date, there have been no large scale assessments comparing these
sedation methods for this purpose.
Procedures:
Retrospective cohort study of patients aged 0-31 years with ALL treated
between 1/1/2013-12/31/2018 at the Children’s Minnesota Cancer and Blood
Disorders Center, including all therapeutic LPs performed in the clinic
setting under either propofol or N2O.
Results:
Among 215 patients and 2677 therapeutic LPs, 56.6% (n = 1515) occurred
under N2O with 43.3% (n = 93) of patients using
exclusively N2O with all LPs. The incidence of traumatic
LPs (RBC ≥ 10 cells/µL) were similar between both treatments (27.3% vs
30.2). Successful IT chemotherapy delivery (99.7% N2O
vs 99.8% propofol) did not differ between sedation types. Experiencing
a traumatic LP under N2O was associated with a sedation
switch for the subsequent LP (aOR 2.40, p=0.002) while older age (aOR
1.08, p<0.0001) and higher BMI percentile (aOR 1.01, p=0.009)
were associated with increased likelihood for undergoing a traumatic LP.
Conclusion:
N2O is an effective sedation option for therapeutic LPs
in children with ALL with noninferiority to propofol in terms of IT
chemotherapy administration and traumatic LP incidence. For many
patients, N2O can effectively replace propofol during LP
procedures, which has important safety and quality-of-life implications.
Introduction :
Conventional treatment for B-lineage and T-lineage childhood acute
lymphoblastic leukemia (ALL) and lymphoma includes anywhere from 16-30
lumbar punctures (LPs) with intrathecal (IT) chemotherapy in order to
prevent and/or treat central nervous system (CNS)
leukemia1-4. Historically, LPs in children are
performed using propofol as a sedative-hypnotic agent, which has a
strong and lengthy record of attaining deep sedation with rapid onset in
the clinic setting5-7, but is unfortunately limited by
requiring a nil per os (NPO) status and, due to the small but not
insignificant risk of hypotension and respiratory depression, entails
management by a provider skilled in airway management. Each of these
caveats can result in timing, patient quality-of-life, and safety
limitations.
At our institution, many outpatient LPs alternatively incorporate
inhaled nitrous oxide (N2O) as a sedation
agent8,9. The decision to provide N2O
or propofol is ultimately made by a patient’s care team during a visit
prior to the actual sedation and based on a variety of real-world
factors, including patient age, patient anatomy (body-mass index (BMI),
scoliosis), patient temperament, patient and parent preference, and
prior experience with the various sedation methods. N2O
has a well-established, safe history of alleviating pain and anxiety
with rapid onset in children undergoing various procedures, including
LPs, although with the unfortunate caveat of providing only moderate
sedation and carrying the possible hazards of provider drug exposure and
SARS-CoV-2 aerosolization in presymptomatic or asymptomatic
patients8-12. N2O does not carry the
same cardiopulmonary risks and can be administered regardless of NPO
status.
To date, there have been no large scale assessments comparing these
sedation methods for the purpose of performing therapeutic LPs in
children with leukemia. The primary aim of this retrospective study was
to assess the patterns of use of N2O and propofol as
sedation methods when conducting LPs with IT chemotherapy administration
in children with ALL. Secondary aims included comparing the
effectiveness of N2O and propofol sedation for this
purpose and identifying factors associated with selection of one
sedation agent over the other, switching from one sedation agent to the
other, and obtaining a traumatic LP under a given sedation
choice.
Methods :
Study design and population:
We conducted a retrospective cohort study of patients with ALL treated
between 1/1/2013-12/31/2018 at the Children’s Minnesota Cancer and Blood
Disorders Center, including all LPs performed in the clinic setting. LPs
performed in conjunction with bone marrow aspirations/biopsies or
diagnostic LPs without the intent of providing IT chemotherapy were
excluded from the dataset. Our study population included patients who
had undergone a minimum of 5 LPs to allow for adequate within-subject
data to better characterize sedation trajectories over time. Patients
who received > 2 of their LPs under an alternative sedation
regimen (e.g. midazolam monotherapy) were excluded from this analysis.
Any sedated LP using a sedation regimen other than N2O
or propofol were removed from the dataset. Subjects were considered
N2O or propofol-predominant if they underwent
> 90% of all clinic LPs under that particular sedation
agent. Subject data was collected from the data warehouse and electronic
health records. The study was approved by the Children’s Minnesota
Institutional Review Board.
Study variables:
For the purpose of assessing efficacy, each individual LP was evaluated
as a discrete event. Demographic data (age, sex, race/ethnicity,
language, BMI), encounter-specific data (sedation choice, concurrent
midazolam administration, child life involvement), and outcomes
(successful IT chemotherapy administration, CSF (cerebrospinal fluid)
RBCs (red blood cells), number of LP attempts) were abstracted. A
’traumatic’ LP was defined as any LP with a CSF RBC value ≥ 10 cells/µL.
BMI was presented as a percentile based on age and gender appropriate
WHO growth charts and included weight-for-length percentiles as a
substitute in children < 2 years of age.
Statistical methods:
Comparisons between N2O and propofol sedated patients
were made using ANOVA, two-sample T tests, χ2 tests,
and Fisher’s exact tests where appropriate. Random effects logistic
regression was used to model associations with two outcomes: switching
sedation agents and obtaining a traumatic LP. Clinically relevant
factors included in the model were sedation agent used, number of
previous LPs, description of previous LP (i.e. traumatic LP, child life
involvement), age, BMI, language, and race/ethnicity. Outcomes from a
patient’s first LP were not included because the models incorporated
information from the previous LP. Random effects for patients were used
to account for within-patient correlation. Results are reported as
adjusted odds ratios (aOR) with 95% confidence intervals (CI).
Results :
There were a total of 215 subjects (Figure 1) who received 2677 clinic
LPs, 56.6% (n = 1515) of which were performed under N2O
sedation and 43.4% (n = 1162) under propofol sedation. Midazolam was
used as an anxiolytic in conjunction with 5.5% (n = 84) of all
N2O LPs and 2.6% (n = 30) of all propofol LPs.
N2O was exclusively used for all LPs in 43.3% (n = 93)
of patients compared to propofol for 22.3% (n = 48). The plurality of
patients (45.1%, n = 97) were N2O-predominant whereas
29.8% (n = 64) and 25.1% (n = 54) were propofol-predominant or had no
overwhelming sedation preference, respectively (Table 1).
IT chemotherapy was unable to be given in only 0.2% (n = 6) of all LPs,
of which 4 were under N2O and 2 under propofol. A
traumatic LP was obtained in 28.6% (n = 760) of all LPs. This occurred
30.2% of the time (n = 348) under propofol sedation and 27.3% of the
time (n = 412) under N2O sedation.
The mean BMI percentile was significantly higher among the
propofol-predominant patients when compared to nitrous-predominant
patients and those with no sedation preference (65.8% vs 50.7% vs
52.3%, p = 0.01). There were no statistically significant differences
in these groups in terms of gender, age at first LP, or race/ethnicity
(Table 1). Twenty-five percent (n = 29) of the 0-5.99 year old group
were propofol-predominant, compared to 34.6% (n = 18) and 36.2% (n =
17) of the 6-12.99 and 13-30.99 year old groups (p = 0.38). Among the
Hispanic patients, 56.3% (n = 9) were propofol-predominant compared to
30.3% (n = 43), 27.3% (n = 3), 35.3% (n = 6) of white, black, and
Asian patients (p = 0.06).
N2O was the sedation agent of choice in 72.1% (n = 155)
of the first clinic LPs performed, however this proportion declined with
subsequent LPs, including 66.1% (n = 142) of second and 47.9% (n =
103) of final clinic LPs (Figure 2). Among those patients who received
N2O for their first clinic LP, 11.6% (n = 18) switched
to propofol for the subsequent LP. Among those patients, 88.9% (n = 16)
never reattempted N2O. Child life was present for 40.2%
(n = 1075) of total procedures, including 18.8% of propofol procedures
(n = 218) and 56.6% of N2O procedures (n = 857).
A multivariate model demonstrated that switching sedation agents with
the subsequent LP is primarily associated with the previous sedation
agent used and the previous LP outcome, with patients switching from
N2O to propofol more often than vice versa, and in
particular when the previous LP was traumatic (Table 2). Specifically,
the odds of switching after an atraumatic LP was 0.37 (95% CI:
0.16-0.84) times lower for propofol than N2O while after
a traumatic LP, the odds were 0.13 (95% CI: 0.04-0.39) times lower for
propofol than N2O. A prior traumatic LP did not change
the odds of switching under a previous propofol sedation (aOR 0.82, 95%
CI: 0.28-2.42), but it did change the odds of switching after a previous
N2O sedation (aOR 2.40, 95% CI: 1.39-4.15). As an
example of these associations, we considered the probability of
switching sedation agents after an LP. The probability of switching to
propofol after a prior N2O LP was 0.05 if the LP was
atraumatic and 0.11 if the LP was traumatic. In contrast, the
probability of switching to N2O if the prior LP was
under propofol was the same at 0.02, whether or not the LP was
traumatic. The number of previous LPs a subject had undergone was
associated with a reduced likelihood of switching to the alternate
sedation with the next LP (aOR 0.89, 95% CI: 0.83-0.95).
A multivariate model demonstrated that the odds of a traumatic LP are
comparable for propofol and N2O sedations (Table 3; aOR
0.99, 95% CI 0.76-1.28). Older age (aOR 1.08, 95% CI 1.05-1.10),
higher BMI percentile (aOR 1.01, 95% CI 1.00-1.01), and midazolam use
with the prior LP (aOR 2.23, 95% CI 1.38-3.63) were significantly and
independently associated with an increased likelihood for experiencing a
traumatic LP.
Discussion :
In this large retrospective assessment of sedation methods for the
purpose of performing LPs with IT chemotherapy in children with ALL, we
report that N2O has been adopted as the most commonly
used sedation option in our clinic. We undertook the creation of an
N2O program at the request of our patients, families,
and providers to address a variety of quality-of-life considerations. It
serves as the sedation agent of choice in the majority of all
therapeutic LPs and nearly 3 in 4 first clinic LPs while a plurality of
patients use N2O exclusively for all clinic LPs.
Moreover, it has been shown to be highly effective and equivalent to
propofol in terms of successful IT chemotherapy administration and
traumatic LP incidence.
While patients in our cohort were not randomly assigned to one sedation
method or another, a difference in discretionary sedation selection is
evident. Our demographic data supports a preference for providing
propofol to patients with elevated BMIs. This suggests a set of
unmeasured criteria (e.g. patient temperament, parent interest, provider
comfort) that may underlie the initial sedation allocation. A
significant proportion of patients (40%) trialed N2O
initially in the treatment course but ultimately transitioned
permanently to propofol sedation for reasons to be determined. Once a
patient has set forth on a particular sedation route for the remainder
of therapy, the likelihood of persevering with that sedation for the
next LP relies predominantly on the number of prior LPs the patient has
undergone, the sedation choice that was used for the most recent LP, and
if they received N2O, whether a traumatic LP occurred
with the most recent LP. This collective data complements those factors
associated with successful LPs cited in the pediatric literature, such
as local anesthetic use, child life involvement, hypnosis, and virtual
reality13-16.
In terms of limitations, there is certainly a subjective aspect to the
patient, parent, and provider experience during an LP that is not
addressed here in the data, as intimated above. Additionally, as is
inherent to retrospective studies in general, there may be critical
measurable variables and confounders that were not represented.
N2O is a frequently used, highly effective sedation
option for therapeutic LPs in children at our institution. It appears to
be comparable to propofol in terms of successful IT chemotherapy
administration and traumatic LP incidence and, for many patients, can
effectively replace propofol during most if not all LP procedures, which
has important implications from a quality-of-life and safety standpoint.
Future analyses will focus on further defining patient-related factors
supporting N2O use early in the treatment course,
assessing patient, provider, and parent experience, evaluating safety
events by sedation type, and comparing encounter costs in lieu of
sedation used.
Acknowledgments: The authors thank the 215 children, adolescents, and
young adults with ALL whose treatment and sedation experiences
contributed to the information gained in this study.
Disclosures: The authors have no financial relationships to disclose.
Grant support: None
Figure Legends:
FIGURE 1: Diagram of initial and subsequent sedation selection
(N2O, propofol) among children with a minimum of 5
therapeutic LPs performed in the outpatient setting. ALL, acute
lymphoblastic leukemia; LP, lumbar puncture; IT, intrathecal;
N2O, nitrous oxide.
FIGURE 2: Bar chart detailing the trajectories of sedation selection
across the first, second, third, penultimate, and final therapeutic LPs
in children with ALL in the outpatient setting; LP, lumbar puncture;
N2O, nitrous oxide.
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* The dataset on which this paper is based is too large to be retained
or publicly archived with available resources, however they can be made
available by contacting the author at Children’s Minnesota.