Erratic breathing pattern Petechial rash (but with normal platelets and coagulation)
Fear is of raised intracranial pressure, leading to coning. Abnormal respiratory pattern eg Cheynes Stokes is one sign, focal neurological signs esp pupil abnormalities and decerebrate/decorticate posturing are other indicators. Double vision would only be a contraindication if there was impairment of eye movements suggesting a cranial nerve palsy, or fixed deviation. In meningococcal septicaemia (suggested by a petechial rash), the yield from cultures is higher for blood/skin scraping culture and PCR, and lumbar puncture does not add much (but if meningitis is the predominant clinical symptom, then LP would be indicated). Cardiovascular instability eg hypotension demands resuscitation and stabilization prior to LP, as the procedure itself may increased oxygen demand. Impaired conscious level is not an absolute contraindication, but if there is progressive deterioration in coma score then raised intracranial pressure should be suspected and LP deferred. If comatose (ie GCS less than 8), then clinical assessment is of limited value and CT should be done first.