Safety and Efficacy of Dexmedetomidate vs. Midazolam for Procedural Sedation During Medical Thoracoscopy

Francis Richard Cruise was probably the first person to ever implement the idea of peeking into the pleural cavity with an endoscope, which he did back in 1865-1866 for examining an 11-year-old girl with tuberculous pleural effusion complicated by a pleurocutaneous fistula. However, Hans-Christian Jacobaeus was the first respiratory physician to meticulously explore the scope of diagnostic and therapeutic thoracoscopy and document it extensively as early as 1910(1). Medical thoracoscopy, so called because of the ability of the physicians to perform it under simple analgesia and conscious sedation without the need of intubation or general anaesthesia (as opposed to VATS), has come a long way since then and is currently one of the most important invasive diagnostic procedures performed by the respiratory physicians for diagnosis of pleural diseases. Mainly lauded for its high diagnostic accuracy for malignant pleural effusion (sensitivity of 97%) and pleural tuberculosis (99%)(2) after all other investigations have failed, medical thoracoscopy can also be used to evaluate and manage parapneumoic effusions, recurrent pneumothoraxes(3, 4), mediastinal disorders, diffuse lung diseases(5-7) and to perform therapeutic procedures such as adhesiolysis and pleurodesis (talc powdrage).

Medical thoracoscopy can be performed under procedural sedation (conscious sedation) in most of the cases. Procedural sedation is a state where the patient lies comfortably without much movement, does not feel pain and has a dissociative state (separation of mind and body)(8)8. Conscious sedation is preferred in this procedure because it can then be performed outside an operation theatre, and a continuous communication with the patients can be maintained. Proper level of conscious sedation is of paramount importance to perform the procedure swiftly and obtain the intended samples. British thoracic society recommends use of local anaesthesia with 1 or 2% lignocaine for local infiltration in conjunction with a benzodiazepine (midazolam) as sedative and an opioid (fentanyl) as analgesic. They point out that propofol may be an alternative in selected cases, but its administration requires presence of an anaesthesiologist(9). The NCCP-ICS joint consensus based clinical guideline on medical thoracoscopy also recommends the midazolam and fentanyl as a combination for procedural sedation(10). A survey of Indian practices on thoracoscopy found that 54.5% proceduralists use a combination of midazolam and fentanyl for procedural sedation and 1-7% use propofol or other agents in combination. Only 2% have used dexmedetomidine for this purpose(11). Although midazolam has been widely used for this purpose due to its quick onset and short duration of action, overall safety and availability of specific antidote, it is not without limitations. Midazolam does not have analgesic property and requires another opioid to be administered to relieve pain during the procedure. Boluses of midazolam are known to cause hypotensive episodes which may complicate the procedure. A recent study of gastrointestinal endoscopy also found hypoxia and failure of sedation as major adverse events associated with midazolam-induced procedural sedation(12). Dexmedetomidine, the active dextro-isomer of medetomidine, was first approved for short-term sedation in the ICU (<24 hours) in 1999. It has since gained prominence as an excellent agent for procedural sedation. It is a highly selective alpha-2 agonist (8 times the affinity of clonidine towards alpha2 receptor). It acts both pre- and post-synaptically, mainly on alpha2A-AR and alpha2C-AR isotypes. Its sedative properties are attributed to high concentration of these receptors in locus caeruleus of brainstem and the analgesic property is probably due to its action at the level of spinal cord (inhibitory action on nociceptive receptors in substantia gelatinosa of the dorsal horn). Dexmedetomidine has additional axiolytic properties. Its sympatholytic and vagomimetic actions are responsible for drop in heart rate and blood pressure, which make it an excellent agent in patients with tachycardia or hypertension. It has a distribution half-life of just 5 minutes, a plasma half-life of 2-2.5 hours and an elimination half-life of 2 hours, all of which translates into its faster onset of action and faster recovery from sedative effects. Its major side effects included hypotension and bradycardia, both of which could be promptly managed with ephedrine and atropine, respectively(13). Some studies have shown it to have some anti-inflammatory and bacterial clearance properties superior to GABA-agonists like benzodiazepines or propofol expected to improve clinical outcomes in ventilated patients with sepsis, although clinical trials failed to show any statistically significant difference in outcome measures(14-17). Moreover, there is a growing body of evidence that dexmedetomidine may reduce the risk of delirium in ICU, which has been a problem with currently used benzodiazepines like delirium. A 2019 meta-analysis (including 25 eligible papers) found that, in comparison to placebo, dexmedetomidine reduces the incidence of delirium (7.6% in dexmedetomidine group vs 18.5% in placebo group, OR 0.36, CI-95%, P<0.001) in ICU patients. This was concluded from 8 randomized clinical trials with low level of heterogeneity. 4 RCTs also pointed towards a lower level of agitation among patients receiving dexmedetomidine in comparison to placebo(18). Taking all this into consideration it appears logically sound to hypothesize that dexmedetomidine may be a better agent for procedural sedation in comparison to midazolam. A systematic review in 2017 found that dexmedetomidine sedation was associated with higher clinician and patient comfort and a higher degree of analgesia and sedation in comparison to midazolam(19). Among the procedures included in this meta-analysis, bronchoscopy was the most frequent (one study by Liao et al; n=198). Other procedures included dental and ophthalmological interventions and endoscopies. A 2021 randomized clinical trial performed in PGIMER, Chandigarh found that dexmedetomidine reduces the need of rescue sedation during EBUS-TBNA and allows for a faster post-procedure recovery albeit at the expense of slightly higher risk of hypotension and bradycardia(20). However, medical thoracoscopy should not be equated with bronchoscopy as it requires incision and insertion of the endoscope in an otherwise sterile cavity. It is associated with considerably higher degree of pain and discomfort. Henceforth the observations of this study may not be applicable in cases of medical thoracoscopy. There is very little body of evidence for comparison of dexmedetomidine and midazolam for procedural sedation in medical thoracoscopy. In 2021, a randomized clinical trial aimed at comparing midazolam-fentanyl with dexmedetomidine for procedural sedation during pluroscopy showed that although use of dexmedetomidine did not improve PF ratio during the procedure, it did have a significant advantage over midazolam-fentanyl in terms of smaller decrease in FEV1 after procedure, smaller consumption of rescue analgesics and accelerated recovery from sedation after completion of the procedure(21). A pilot RCT was done in 2022 that compared dexmedetomidine infusion and midazolam bolus for procedural sedation during medical thoracoscopy. They found that pulmonologist-rated procedural satisfaction VAS score was significantly higher and pulmonologist-rated cough VAS score, and patient-rated faces pain scale score were significantly lower in dexmedetomidine group in comparison to midazolam group. The patients in dexmedetomidine group also required lower dose of rescue analgesia(22). The problem with the study was that it had the clinicians' comfort as its primary outcome and used VAS score to compare it. The minimum clinically significant difference in VAS score is not known or validated, and hence question remains about the difference in comfort the proceduralist felt.

In view of the existing literature that has been laid out above, we hypothesize that use of dexmedetomidine for procedural sedation during medical thoracoscopy will improve the ease of performing the procedure, lower the consumption of rescue analgesics and risk of intra- and post-procedure complications, improve the yield, shorten the recovery period and reduce the post-procedure pain in comparison to midazolam. In this study we propose to show that procedural sedation with dexmedetomidine during medical thoracoscopy is more beneficial for both patient and the clinician in terms of yield and shorter procedure time in comparison with conventional midazolam-fentanyl combination.