Efficacy of Dexmedetomidine as an Adjunct in Aiding Video laryngoscope-Assisted Assessment of Vocal Cord Movements at Extubation Following Total Thyroidectomy.

BACKGROUND: Assessment of vocal cord movements following total thyroidectomy diagnoses recurrent laryngeal nerve injury. Use of videoscope along with sedatives may blunt hemodynamic responses seen with the conduct of direct laryngoscopy for assessing vocal cord mobility. AIMS: The primary objective of this study was to assess changes in mean arterial pressure (MAP) during vocal cord assessment following total thyroidectomy using video laryngoscope, with and without the use of dexmedetomidine as an adjunct. Secondary objectives included assessment of changes in heart rate (HR), patient reactivity score along with ease of laryngoscopy and vocal cord visibility. SETTINGS AND
DESIGN: This randomized, prospective, unblinded study was conducted in 54 patients at a tertiary care center.
MATERIALS AND METHODS: Group D received dexmedetomidine 0.5 μg/kg, once the thyroid was removed. Group S did not receive dexmedetomidine. Hemodynamic response at extubation, patient reactivity, ease of laryngoscopy, and ease of vocal cord assessment were noted. STATISTICAL ANALYSIS USED: Chi-square test and Independent t-test.
RESULTS: Baseline HR, systolic blood pressure (SBP), and MAP were comparable between the groups. However subsequently, Group D had significantly lower HR and SBP at the time of extubation and at 3 and 6 min later. MAP at extubation and at 3 min later was comparable, but at 6 min, Group D had significantly lower values. In both groups, patient reactivity scores, ease of laryngoscopy, and vocal cord visibility were comparable (P > 0.05).
CONCLUSION: Dexmedetomidine 0.5 μg/kg when used as an adjunct clinically improved conditions for assessing vocal cord mobility with significant attenuation of associated hemodynamic responses.

INTRODUCTION

Thyroidectomy is a common surgical procedure performed worldwide, and recurrent laryngeal nerve (RLN) injury remains as one of the major postoperative complications despite improvements in surgical techniques. Assessment of vocal cord movements conventionally is done at extubation, after reversing neuromuscular blockers, and very often the patients cough and gag making a proper assessment difficult. The act of traditional laryngoscopy, in patients who are no longer paralyzed and almost out of anesthesia, leads to intense sympathetic stimulation resulting in a rise in hemodynamic parameters. This may have deleterious effects in susceptible individuals. In this regard, if a videoscope is used to assess the vocal cord movements, the upward force required to align the oral, pharyngeal, and laryngeal axes to obtain glottic view can be reduced, as it provides an indirect view. Therefore, the use of videoscopes for this purpose attenuates the hemodynamic stress response associated with laryngoscopy. In addition, vocal cord movements can be recorded and stored as a medical document, and the surgeons will also be able to witness the same and formulate the plan of management in case a nerve injury has occurred. A sedated patient may tolerate laryngoscopy better at the time of extubation rather than a fully awake one. Although various sedatives have been tried, no drug has been recommended as the ideal one for this purpose following thyroidectomy.

The primary objective of the present study was to assess changes in mean arterial pressure (MAP), during vocal cord mobility assessment following total thyroidectomy, using video laryngoscope with and without the use of dexmedetomidine as an adjunct. Our secondary objectives included assessment of changes in heart rate (HR), patient reactivity score, along with ease of laryngoscopy and vocal cord visibility as assessed by the anesthesiologist.

MATERIALS AND METHODS

This prospective, randomized, unblinded study was conducted after obtaining approval from the hospital ethical committee and patients’ written informed consent. Fifty-four patients aged 18–60 years, of the American Society of Anesthesiologists (ASA) physical status classes 1–2 with euthyroid status and no vocal cord dysfunction before surgery were included in the study. Patients with hypertension on two or more drugs or uncontrolled hypertension, those with asthma or other reactive airway diseases, on beta-blockers and with Cormack–Lehane Grade 3 and 4 were excluded from the study.

They were randomly allocated into two groups (D and S) of 27 each using computer generated random sequence of numbers. Allocation concealment was ensured using sequentially numbered, opaque sealed envelopes. All patients were given general anesthesia according to the standard protocol. Propofol (2 mg/kg) as induction agent, fentanyl (2 μg/kg) as analgesic agent, and vecuronium (0.1 mg/kg) as muscle relaxant. Anesthesia was maintained with 40:60 of oxygen-nitrous oxide mixture with 1% isoflurane and intermittent doses of vecuronium. Intraoperatively, all patients received paracetamol 1 g and dexamethasone 4 mg intravenously. Patients in Group D received dexmedetomidine 0.5 μg/kg as an infusion over 10 min after removal of the thyroid gland. Isoflurane was replaced by 1.5% sevoflurane toward the end of surgery, 10 min before anticipated extubation in both groups.

After the completion of the skin sutures, nitrous oxide was turned off in both groups. Sevoflurane was stopped in Group D, but it was maintained at 1%–1.5% (end-tidal concentration) in oxygen in Group S till patients were extubated. Extubation was performed, after reversing the neuromuscular blockade with neostigmine 0.05 mg/kg and glycopyrrolate 0.01 mg/kg, following thorough oral suctioning. In both groups, extubation was performed under indirect vision using Storz® C MAC video laryngoscope (Karl Storz Endoskope 8403 ZX, Germany) with D blade. The mobility of the vocal cords was assessed immediately following extubation. Along with vocal cord assessment, patients were evaluated on the basis of change in hemodynamic parameters, patient reactivity scores, and anesthesiologist's satisfaction scores during extubation and cord assessment.

As there were no previous similar studies done, we conducted a pilot study with 20 patients, allotted equally into two groups (D and S). Using the MAP at the time of extubation as the primary variable, with a standard deviation of 12.5 versus 14.7 in Group D and S, with 95% confidence interval and 90% power, the estimated sample size per group was calculated as 27 to obtain statistically significant results.

Chi-square test was used to compare the gender, ASA physical status, patient reactivity score and anesthesiologists’ assessment score between Groups D and S. Independent t-test was used to compare age, weight, HR and MAP. Statistical analyses were done using SPSS Version 20.0 for Windows (IBM Corporation ARMONK, NY, USA).

RESULTS

Fifty-four patients were assessed for eligibility to be included in the study and no subjects dropped out [Table 1]. Both groups were comparable with respect to mean age and weight, distribution of sex and ASA physical status [Table 2]. The baseline HR, systolic blood pressure (SBP), and MAP's were comparable between the two groups. However, subsequently, Group D had a significantly lower HR and SBP at the time of extubation and at 3 and 6 min later [Table 3 and Figures 1, 2]. The diastolic blood pressure was significantly lower only at 6 min in Group D. MAP at extubation and at 3 min later were comparable, but at 6 min, Group D had significantly lower values [Table 3]. In both groups, the patient reactivity scores, ease of laryngoscopy, and vocal cord visibility were comparable (P > 0.05) [Table 4 and Figure 3].

Table 1

CONSORT flow chart

Table 2

Comparison of demographic data and American Society of Anesthesiologists physical status

Variables	Group D, n (%)		Group S, n (%)		P
ASA 1	11 (40.7)		14 (51.9)		0.413
ASA 2	16 (59.3)		13 (48.1)
Male	22 (81.5)		18 (66.7)		0.352
Female	5 (18.5)		9 (33.3)
Variables	Mean	SD	Mean	SD	P
Age	43.7	13.4	47.9	13.5	0.258
Weight	62.3	12.8	65.2	11.2	0.380

ASA=American society of anesthesiologists, SD=Standard deviation

Table 3

Comparison of haemodynamics

Time	Group D		Group S		P
	Mean	SD	Mean	SD
Comparison of HR
Baseline	82.2	9.7	84.2	15.0	0.555
During extubation	72.7	14.6	88.1	15.9	0.001
3 min after extubation	76.5	16.9	86.5	15.0	0.026
6 min after extubation	72.9	13.4	86.4	17.3	0.002
Comparison of SBP
Baseline	127.3	10.8	125.6	14.4	0.632
During extubation	114.0	17.2	126.3	19.8	0.019
3 min after extubation	118.7	18.0	132.0	20.5	0.014
6 min after extubation	119.8	12.7	133.7	17.6	0.002
Comparison of diastolic blood pressure
Baseline	78.4	7.8	77.6	11.0	0.755
During extubation	74.6	13.1	79.6	20.0	0.285
3 min after extubation	75.7	11.6	78.5	12.3	0.396
6 min after extubation	74.9	6.8	82.2	11.9	0.008
Comparison of MAP
Baseline	93.9	8.4	92.9	11.3	0.704
During extubation	88.1	12.9	95.3	19.5	0.116
3 min after extubation	89.6	12.9	96.6	14.8	0.070
w6 min after extubation	90.0	8.4	98.7	12.4	0.004

HR=Heart rate, SBP=Systolic blood pressure, MAP=Mean arterial pressure, SD=Standard deviation

Figure 1

Changes in heart rate

Figure 2

Changes in systolic blood pressure

Table 4

Patient reactivity score and anesthesiologist’s assessment score

	Group D, n (%)	Group S, n (%)	P
No grimace
No	14 (51.9)	15 (55.6)	0.785
Yes	13 (48.1)	12 (44.4)
Grimace
No	14 (51.9)	17 (63.0)	0.409
Yes	13 (48.1)	10 (37.0)
Head movement
No	26 (96.3)	25 (92.6)	1.000
Yes	1 (3.7)	2 (7.4)
Limb movement
No	27 (100.0)	26 (96.3)	1.000
Yes	-	1 (3.7)
Cough
No	27 (100.0)	25 (92.6)	0.491
Yes	-	2 (7.4)
Easy laryngoscopy
No	6 (22.2)	12 (44.4)	0.149
Yes	21 (77.8)	15 (55.6)
Slightly difficult laryngoscopy
No	21 (77.8)	17 (63.0)	0.371
Yes	6 (22.2)	10 (37.0)
Very difficult laryngoscopy
No	27 (100.0)	25 (92.6)	0.491
Yes	-	2 (7.4)
Vocal cords completely visible
No	4 (14.8)	7 (25.9)	0.501
Yes	23 (85.2)	20 (74.1)
Vocal cords partly visible
No	23 (85.2)	20 (74.1)	0.501
Yes	4 (14.8)	7 (25.9)
Vocal cords not visible
No	27 (100.0)	27 (100.0)	NA

NA=Not available

Figure 3

Easy laryngoscopy

DISCUSSION

Unilateral RLN injury can lead to hoarseness of voice whereas bilateral RLN injury can lead to airway obstruction and jeopardize the life of the patient.[1] The incidence varies between 1% and 2% even when performed by experienced neck surgeons, and with a higher incidence when performed by less experienced surgeons, or when done for malignant disease.[2] With the advent of video laryngoscope,[3] it has become possible to assess the vocal cords by both the anesthesiologist and the surgeon at the same time.

Complete or partial nerve transection, contusion, crush or traction and compromised blood supply are the main proposed mechanisms for RLN injury.[4] In unilateral RLN injury, the voice becomes husky. Bilateral nerve injury is much more serious, because both vocal cords may assume a median or paramedian position and cause airway obstruction and tracheostomy may be required.[5] Hence, early identification of vocal cord movements immediately following total thyroidectomy, using a video laryngoscope, helps to determine if an injury to RLN has occurred.[6]

The hemodynamic changes brought about by laryngoscopy are usually short-lived and well tolerated by normal patients. However in patients with cardiovascular disease, it may lead on to myocardial ischemia, ventricular dysrhythmias, ventricular failure, and pulmonary edema. It can also result in cerebrovascular accidents in those with cerebrovascular diseases.[7] Several drugs have been in use for blunting the pressor response that accompanies laryngoscopy and extubation, which includes short-acting opioids such as fentanyl, lignocaine, calcium channel blockers, short-acting beta-blockers, and gabapentin administered intravenously.[89]

In our study, we had used dexmedetomidine as an adjuvant to facilitate the performance of laryngoscopy following total thyroidectomy. The advantage of using dexmedetomidine was that it preserves spontaneous respiration even in a sedated state, which was important in the immediate postoperative period following extubation. Propofol, when used for this purpose, may make the patient too sedated, if adequate dose required to tolerate direct laryngoscopy was given. Moreover, the risk of the patient becoming apneic was also there with the use of a higher dose of propofol. Dexmedetomidine is a highly selective α2 agonist that has been shown to have sedative, analgesic, and anesthetic sparing effects.[10] The role of α2 agonists[11] in regulating the autonomic and cardiovascular responses is well understood, whereby they inhibit release of catecholamines (nor-epinephrine) from the sympathetic nerve terminals by augmentation of a vasoconstrictive effect.[12] It causes a dose-dependent decrease in arterial blood pressure and HR, associated with a decrease in serum nor-epinephrine concentration.[13]

Dexmedetomidine was well tolerated, and no serious side effects or adverse reactions occurred in the present study. We observed that in Group D, where 0.5 μg/kg dexmedetomidine was used, there was significant attenuation of the pressor response to laryngoscopy and extubation as evidenced by reduction in HR and mainly SBP. In Group S, where deep extubation was performed with oxygen and sevoflurane 1%, the pressor response to laryngoscopy and extubation was much higher as evidenced by increased HR, SBP and mean blood pressure.

Although the patients in Group D clinically appeared to tolerate the laryngoscopy procedure better than those in Group S, with none of the patients showing adverse reactions like limb movements and coughing, the difference among the groups was found to be statistically insignificant.

Dexmedetomidine due to its centrally mediated sympatholytic effect attenuates the hemodynamic responses to extubation, and the effect continues in the postoperative period. A calm patient with stable hemodynamics during emergence from anesthesia and the immediate postoperative period is ideal as it prevents the chances of bleeding from the surgical site and vocal cord movements can be assessed with ease and accuracy. The study results correlated well with a previous study which assessed hemodynamic responses to laryngoscopy and endotracheal intubation with intravenous dexmedetomidine.[14]

Various studies have used dexmedetomidine in doses ranging from 0.1 to 10 μg/Kg/h[1516] with not so much conclusive data but definitely associated with a significant incidence of bradycardia and hypotension in higher doses. We used dexmedetomidine in a dose of 0.5 μg/kg over 10 min and observed a moderate reduction in the MAP and HR to the extent of 10%–15% from the baseline values and the findings are very much similar to the observations of other studies and can be explained on the basis of markedly decreased central nervous system sympathetic activity.

There were a few limitations to our study. Time to awakening and transfer to the recovery room were not assessed in our study, and the study was not a blinded one. The study population involved ASA physical status Classes 1 and 2 patients, so usefulness in high-risk patients could not be elucidated from the present study. Extending the study in patients with severe cardiovascular diseases should only be undertaken with caution keeping in mind the hemodynamic effects of dexmedetomidine in these subsets of patients.

CONCLUSION

Dexmedetomidine 0.5 μg/kg when used as an adjunct clinically improved conditions for assessing vocal cord mobility using a video laryngoscope with significant attenuation of associated hemodynamic responses following total thyroidectomy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.