Although pain management in intensive care units and intensive care units has improved since the DOLOREA study, research into therapies and techniques to optimise analgesia is still needed. The many adverse effects of morphine are well known, and it has been observed that excessive sedation during the first 48 hours is associated with an increase in mortality and length of stay. Multimodal analgesia protocols, preferably including non-morphine analgesics, could improve the comfort of critical care patients.

Comfort is a central element of critical care and perioperative management, as demonstrated by Patients-Reported Outcomes (PRO), new assessment tools that take into account the patient as a whole. The (Inconfort of REAnimation Patients) IPREA questionnaire, a specific scale for assessing the comfort of critical care patients, is an example of a PRO.

Lidocaine is a voltage-dependent sodium channel blocker, used as a local anaesthetic and antiarrhythmic agent, whose intravenous administration produces analgesic effects, particularly on hyperalgesia. The widely demonstrated clinical benefits in scheduled and major surgery (reduced post-operative pain, reduced doses of anaesthetic agents and opiates, reduced post-operative nausea and vomiting) have led to recommendations for its use. Furthermore, adverse events associated with lidocaine in continuous infusion are minimal.

Based on the early Comfort using Analgesia (eCASH), minimal Sedative and maximal Human care) concepts, the recent PADIS (Pain, Agitation, Delirium, Immobility, Sleep deprivation) recommendations, which determine levels of evidence and research avenues for improving the quality of care, conclude that intravenous lidocaine may be beneficial, but there is a lack of data.

The investigators are therefore proposing a randomised placebo-controlled clinical trial to assess the effectiveness of lidocaine infused continuously for 48 hours on the perceived comfort of post-operative critical care patients, as assessed by the IPREA score.

IPREA, an 18-item score exploring PADIS, is a direct, relevant, objective and reproducible assessment criterion for evaluating algorithms for improving the quality of care. The data on sources of discomfort reveal the importance of pain, dyspnoea, thirst and sleep deprivation, which are all influenced by the analgesia-sedation protocol. Incorporating lidocaine with anti-hyperalgesic properties into the protocol should reduce discomfort in critical care patients.

The choice of analgesia protocol will be left to the discretion of the clinician between MORPHINE CHLORHYDRATE, SUFENTANIL and REMIFENTANIL for objectives of Behavioral Pain Scale (BPS) (3 to 5) or pain visual analogue scale (VAS) < 4.

The use of co-analgesics intraoperatively (Paracetamol, Nefopam, NSAIDs (nonsteroidal anti-inflammatory drugs) such as Ketoprofen or Ibuprofen, Ketamine) is authorised (data not collected).

If a hypnotic is required intraoperatively, the choice of agent is left to the discretion of the clinician.

Once the sedation-analgesia protocol has been discontinued, pain relief is left to the clinician's discretion.

Patients are monitored from randomisation until discharge from the critical care unit or until a maximum of 30 days post-operatively.

In the event of an adverse reaction linked to lidocaine (see list in § 8.2.), the doctor stops administration of the product.

The blind is lifted (see § 9.2 'Insu (or blinding)'). If the patient is in the lidocaine group, the lidocaine plasma concentration is measured to check for a toxic plasma concentration (see § 5.6 'Management of biological samples').

It should be noted that the completion of an assay or discontinuation of treatment does not result in the patient's withdrawal from the clinical trial. Patient follow-up continues until the end of the trial.

If the patient is discharged from critical care before the 30th post-operative day, the patient's vital status on the 30th post-operative day will be collected.

Inclusion Criteria:

1. Patient over 18
2. Patient admitted immediately post-operatively in critical care (scheduled or emergency admission, e.g. post-operative exploratory laparotomy, cardiac surgery, major orthopaedic surgery such as polytrauma patients, vascular surgery at risk of complications such as open aortic surgery)
3. Anticipated length of stay in critical care ≥ 48h
4. Membership of a social security scheme
5. Informed consent signed by the patient or by a close relative or legal representative or, failing this, the emergency procedure

Non-inclusion Criteria:

1. Weight over 100 kg
2. Hypersensitivity to one of the active substances used for anaesthesia or to one of the excipients.
3. Known acute porphyria,
4. Pregnant or breast-feeding women
5. Patients who have received or are about to receive peri-medullary analgesia intra-operatively or post-operatively.
6. Patient who has received or will receive loco-regional analgesia intra-operatively or post-operatively.
7. Severe head injury, open cephalic neurosurgery, interventional neuroradiology
8. Recovered cardiorespiratory arrest
9. Noradrenaline doses > 0.5 μg/kg/min
10. Stage IV/V chronic renal failure, not on dialysis
11. Severe hepatocellular insufficiency at inclusion (Child-Pugh C)
12. Bradycardia < 50 bpm on antiarrhythmic drugs
13. Clinical convulsive seizure at inclusion
14. Predictable inability to answer the questionnaire (cognitive impairment, non-Francophone)
15. Known participation in another interventional research study (RIPH1 or RIPH2)
16. Known situation of deprivation of liberty or legal protection (safeguard of justice, guardianship or curatorship)

Exclusion Criteria:

Patients under court protection will be excluded as soon as the investigator is aware of their status.

The syringes are prepared by a 'friendly' service (not involved in the patient's follow-up) and are of identical format whatever the experimental treatment, in order to maintain blindness. The randomisation arm is not known to the doctor in charge of the patient.