Pupillometry - Future of Objective Pain Reaction Measurement While Unconscious

Laryngoscopy and tracheal intubation are associated with a sympathetic discharge caused by stimulation of the upper respiratory tract. Venous lidocaine is the agent most used to attenuate the hemodynamic response to laryngoscopy and intubation. Hemodynamic response might be masked by the drugs the patient is taking and its status (ex. sepsis). There's a need for an objective pain assessment method while the patient is unconscious, to maintain a proper level of analgesia and to control the hemodynamic response in order to decrease systemic repercussions.

This single-blind, randomized, single center, prospective study was approved by the Bioethics Committee of the University of Warmia and Mazury under the report number 11/2019 21st of February 2019.

Patients scheduled for elective surgery under general anesthesia with tracheal intubation were divided into three groups:

Group 1: anaesthetic induction with standard doses iv was performed (fentanyl 3mcg/kg, propofol 2mg/kg, rocuronium 0,6mg/kg).

Group 2: same as in group 1 + lidocaine 1,5mg/kg w 100ml 0,9% NaCl 10 min before intubation.

Group 3 (placebo group): same as group 1 + 100ml 0,9% NaCl 10 min before intubation

The values for blood pressure (NIBP), heart rate (HR), Train of four (TOF) and bispectral index (BIS) were measured in all groups during the whole time of the protocol. PRD (Pupillary Reflex Dilation) was measured in the exact time of intubation. Additionally, after intubation PPI (Pupillary Pain Index) was checked.

During the whole protocol BIS value was maintained to be equal to or less than 50, if this value was not reached, a venous increment of 1mg/kg of propofol was administered.

Hypertension was considered when the BP values were 20% above baseline values or if Systolic Blood Pressure (SBP) > 140 mmHg. Hypotension was considered when the Blood Pressure (BP) values were 20% below baseline values or if SBP > 90 mmHg. Tachycardia was considered when the Heart Rate (HR) values were 20% above baseline values or if HR > 100 mmHg. Bradycardia was considered for HR values under 50 bpm.

Inclusion criteria

• Physical State 1 or 2 of the American Society of Anesthesiology (ASA)
• Electively scheduled for surgery requiring general anesthesia
• Age >18 years

Exclusion criteria

• Difficult airway
• Unanticipated difficult airway based on the previous history of difficult intubation
• Urgently scheduled for surgery requiring general anesthesia
• Ophthalmologic pathology precluding pupillometry, ex. Horner's syndrome, Sjogrens syndrome
• Anisocoria
• History of opioid abuse
• Subjects who are or may be pregnant
• Unable to converse in Polish
• History of psychiatric/cognitive disease
• Patients who do not give informed consent
• Patients with contraindications or history of hypersensitivity to lidocaine
• Patients with coronary ischemic disease
• Patients with atrioventricular block at any grade
• Patients with diagnosed cardiac arrhythmias
• Patients with heart failure
• Patients who are taking drugs influencing the pupil size
• Patients with pacemaker
• Patients younger than 18 years of age
• History of chronic pain, chronic opioid use (> 3 months)