In this randomised controlled study the investigators intended to compare the analgesic effects of EMLA and\or nitrous oxide in children submitted to lumbar puncture.

It is a randomized controlled clinical trial, double blinded, with the purpose to compare the use of EMLA - local anesthetic (lidocaine and prilocaine), and or nitrous oxide at 50% in oxygen (Livopan®) to prevent and treat pain in pediatric patients aged four to 16 years old submitted to lumbar puncture for intrathecal chemotherapy. Pain was assessed using the Wong Baker faces scale and the visual numeric scale during six observational periods: baseline; three minutes after gas administration and before the first attempt of lumbar puncture; during the first lumbar puncture attempt; during the chemotherapy administration; during needle remove and three minutes after gas interruption. All the studied procedures will have clinical indication and will not be held by the researcher. The children was random divided within three groups A, B and C as follow: Group A (n=16)EMLA + Livopan; Group B (n=19)EMLA + gas placebo (oxygen); Group C (n=17) Livopan® + placebo cream.

Primary outcome was the detection of a difference of 20% or more in the visual numeric scale between the three treatment groups during the first attempt of lumbar puncture.

Inclusion Criteria:

• Age between four and 14 years;
• Not present cognitive disabilities;
• Necessity to perform the clinical procedure;
• Accordance in participating in the study.

Exclusion Criteria:

• Continuity skin lesion in the procedure site;
• Metahemoglobinemia;
• Neuromuscular disability;
• Presence of pneumothorax, emphysema, intra-abdominal infection, cranioencephalic traumatism, otitis media, sinusitis and intracranial hypertension;
• Vitamin B12 known deficits;
• Urgency for the procedure;
• Disagreement in participating of the project;
• Patients in use of Dapsone.