Comparison of hemodynamic responses to intubation: Flexible fiberoptic bronchoscope versus McCoy laryngoscope in presence of rigid cervical collar simulating cervical immobilization for traumatic cervical spine.

BACKGROUND: Intubation is known to cause an exaggerated hemodynamic response in the form of tachycardia, hypertension, and dysrhythmias. In cervical spine instability, intubation has to be performed using cervical immobilization to prevent exacerbation of spinal cord injuries. Application of rigid cervical collar may reduce cervical spine movements, but it hinders tracheal intubation with a standard laryngoscope. The aim of this study was to compare the hemodynamic responses to fiberoptic bronchoscope (FOB) and McCoy laryngoscope in patients undergoing elective surgery under general anesthesia with rigid cervical collar simulating cervical spine immobilization in the situation of cervical trauma.
METHODS: Thirty-two patients in the age range 20-50 years, of American Society of Anaesthesiologist I-II, and of either sex undergoing elective surgery under general anesthesia were randomly allocated into each group. There were two groups according to the technique used for intubation: Group A (flexible FOB) and Group B (McCoy laryngoscope). Systolic blood pressure, diastolic blood pressure, mean arterial blood pressure and heart rate (HR) were recorded at baseline, intraoperatively, immediately before and after induction, and immediately after intubation. Thereafter, every min for next 5 min. STATISTICAL ANALYSIS: Intergroup comparison of categorical data was done by Chi-square test. P < 0.05 was considered statistically significant. Intergroup comparison of quantitative data was done by the parametric test (unpaired t-test), and probability was considered to be significant if <0.05.
RESULTS: Due to intubation response, HR and blood pressure increased significantly (P < 0.05) above preoperative values in McCoy group as compared to the fiberoptic group.
CONCLUSION: We suggest that the flexible FOB is an effective and better method of intubation in a situation like traumatic cervical spine injury and provides stable hemodynamics.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

In anesthesia, intubation is an essential artistry for an anesthesiologist during airway management. With the use of the conventional approach of intubation, exaggerated hemodynamic response occurs which is due to forces exerted by laryngoscope blade for visualization of glottic opening. These hemodynamic changes manifest as increase in heart rate (HR), arterial blood pressure, and arrhythmias which can cause detrimental cardiovascular and neurological effects specially in vulnerable patients e.g., those with ischemic heart disease, cerebrovascular disease, etc.[1] Any technique for intubation requires lesser lifting force would proportionally reduce the sympathetic discharge, and hence changes in HR and blood pressure.[2] For obtundation of this hemodynamic response, various interventions (pharmacological[34] and nonpharmacological[56]) have been tried.

During intubation in cervical spine trauma victims, adequate cervical immobilization (in the form of manual inline axial stabilization or application of rigid cervical collar) is prime and foremost task to avoid devastating neurological outcomes.[7] Intubation in these patients is a significant challenging task for an experienced anesthesiologist. In cervical spine instability, sufficient laryngeal exposure during intubation requires movement of cervical vertebrae in form of flexion of cervical spine and extension of atlanto-occipital joint, but to prevent aggravation of cord injury, intubation has to be performed with cervical immobilization, hence both objectives are contradictory.[8] Use of rigid cervical collar may reduce cervical spine movement, but it significantly reduces the mouth opening, making laryngoscopy difficult and also lifts up the chin and tips the larynx anteriorly.[910]

Devices such as fiberoptic bronchoscope (FOB) and McCoy laryngoscope are very useful in such difficult intubation situations and obtund hemodynamic response of intubation.

In the situation of difficult intubations, flexible FOB is considered as gold standard.[11] With the help of flexion-deflexion movement of distal flexi tip, the operator can visualize the airway structures nearly at 360° along with the rotational movement of fiberscope. It reduces the stress response to intubation due to less mechanical stimulation of laryngeal surface. Many studies have compared the cardiovascular response to laryngoscopy and fiberoptic intubation.[1213141516]

McCoy laryngoscope (Penlon Ltd., Abingdon, England) is a modified Macintosh laryngoscope, introduced in 1993[17] as an aid for difficult tracheal intubations.[18] With the help of lever on the back of the handle, hinged tip of McCoy blade allows elevation of the epiglottis which ultimately reduces the amount of force required and improves the view of glottis.[19] It was found as a very useful tool of laryngoscopy in limited neck extension in several studies.[202122]

The primary objective of this clinical study was to investigate whether there is clinically significant difference between the hemodynamic response to orotracheal intubation, guided by either of the devices (flexible FOB and McCoy laryngoscope) in patients undergoing elective surgery under general anesthesia with rigid cervical collar simulating cervical spine immobilization in the situation of cervical trauma, in terms of: Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and HR. The secondary objectives were to compare intubation duration and glottic visualization with the use of either of the two devices.

METHODS

This hospital-based randomized comparative interventional type of study was conducted between February 1, 2014 and January 31, 2015. After obtaining approval of the Institution Ethical Committee and written informed consent from the patient, 64 American Society of Anaesthesiologist (ASA) physical status I and II patients of either gender between 20 and 50 years of age scheduled for elective procedures under general anesthesia and required endotracheal intubation were included in this study. Exclusion criteria included patient's refusal, ASA physical status III, IV, V, anticipated difficult intubation (Mallampatti grade 4, thyromental distance <6 cm, sternomental distance <12 cm, mentohyoid distance <5 cm, neck circumference >42 cm), a history of reactive airway disease, gastro-esophageal reflux, hypertension, dysrhythmia, cervical spine pathology, airway distortion or trauma, morbid obesity, major organ dysfunction and use of medication that affect blood pressure and HR. Patients were divided into two groups of 32 each according to the technique used for intubation: Group A - Flexible FOB (n = 32) and Group B - McCoy laryngoscope (n = 32). Patients were assigned randomly into these two groups using chit in box method.

All the patients were examined on the day before surgery with routine investigations under the institutional protocol and explained about the anesthetic technique and perioperative course. Preoperatively, all the patients were fasted adequately (8 h fasting) and were normothermic. In the operation theater, the rigid cervical collar was applied, and intravenous (i.v.) lines with 18/20 gauge cannula were secured. Standard monitoring included noninvasive arterial pressure, electrocardiography, oxygen saturation, end tidal carbon dioxide (EtCO2), and measurement of volatile anesthetic levels. After 15 min of stabilization period, baseline readings of HR, SBP, DBP, and MAP were recorded.

Premedication with glycopyrrolate (0.005 mg/kg i.v.) and fentanyl citrate (2 µg/kg i.v.) was given along with preoxygenation for 5 min. Patients were induced with propofol 2 mg/kg infused i.v. slowly over 1 min, followed by injection of neuromuscular blocking agent-rocuronium 1 mg/kg i.v. after checking the adequacy of mask ventilation. Patients were ventilated with face mask with 1% isoflurane in oxygen for 2 min. If any difficulty was encountered in mask ventilation, the patient was excluded from the study.

After 2 min of the administration of muscle relaxant, tracheal intubation was performed with endotracheal tube (ETT) (male - 8.0 mm ID, female - 7.5 mm ID) either by flexible FOB or by McCoy laryngoscope. While using FOB for oral intubation, modified Berman's airway was used as an aid and the tip of the bronchoscope was not advanced too deep into the trachea to avoid stimulation of the carina. Tube position was checked by auscultation and confirmed by EtCO2 tracings. After successful tracheal intubation, the lungs were mechanically ventilated for the duration of the procedure and anesthesia was maintained with isoflurane in a mixture of N2O and O2.

All values of HR and BP (SBP, DBP, and MAP) were recorded before induction of anesthesia, immediately after induction, just after intubation, and thereafter, every minute for next 5 min. No other medications were administered, or manipulations (including any movement of the head and neck and preparation of the operative field) were performed during the 5 min data collection period after tracheal intubation. The duration of the tracheal intubation procedure was noted. The duration of the intubation attempt is defined as the time taken from insertion of the blade/fiberoptic cord between the teeth until the ETT is placed through the vocal cords, as evidenced by visual confirmation by the anesthesiologist. Glottic view was categorized as: (i) Complete glottis (ii) posterior glottis only (iii) epiglottis only (iv) no glottis and epiglottis. All the intubations were performed by a single anesthesiologist who was familiar and trained with intubation using McCoy laryngoscope and FOB. Any patient who required more than one attempt to achieve successful intubation was excluded from the study. Due to the nature of the study, only single blinding was possible; however, the person recording the hemodynamic parameters was unconnected to the study.

Statistical analysis

A pilot study on 20 patients, 10 in each group, was conducted after obtaining approval of the Institution Ethical Committee and written informed consent from the patient. The results were analyzed with the aid of a statistician, and a sample size of 32 in each group was calculated with alpha error 0.05 and power 80%. Analysis of the statistical data obtained from the study was carried out by statistical programming software Statistical Package for the Social Sciences - SPSS Statistics version 17.0.0 (SPSS Inc., Chicago, Illinois, USA). SPSS is a statistical tool used to analyze and correlate social data. Categorical data (sex, ASA grade, Mallampati grade and glottic view) are presented as numbers and intergroup comparison of these was done by Chi-square test. P < 0.05 was considered statistically significant. Quantitative data, that is, age, weight, airway parameters, intubation duration, and hemodynamic variables (HR, SBP, DBP, and MAP) are presented as mean value and standard deviation. Intergroup comparison of continuous data was done by the parametric test (unpaired t-test), and statistical significance was considered at P < 0.05.

RESULTS

The demographic data and airway characteristics of patients were insignificantly (P > 0.05) different between Group A (FOB) and Group B (McCoy) as shown in Table 1. While intubation duration shown in Figure 1 was significantly (P < 0.05) higher in Group A in comparison to Group B and glottic view shown in Figure 2 was significantly (P < 0.05) less clear in Group B as compared to Group A.

Table 1

Intergroup comparison of demographic data, airway characteristics and intubation duration

Figure 1

Intubation durations (in seconds) with flexible fiberoptic bronchoscope and McCoy laryngoscope

Figure 2

Glottic view with flexible fiberoptic bronchoscope and McCoy laryngoscope

Hemodynamic parameters are shown in Table 2. HR and blood pressure (SBP, DBP and MAP) were comparable at baseline in both groups (P > 0.05). Figure 3 shows the mean of the SBP, DBP, and MAP of the patients at preinduction, postinduction, just after intubation and thereafter, every minute for next 5 min. It shows that in McCoy group, SBP, DBP, and MAP increases significantly (P < 0.05) after intubation and lasts up to 5 min as compared to the fiberoptic group. Figure 4 shows the HR of patients at preinduction, postinduction, just after intubation and thereafter, every minute for next 5 min. The increase in HR was statistically significant (P < 0.05) in McCoy group as compared to FOB group up to 1 min after intubation.

Table 2

Comparison of hemodynamic parameters in between fiberoptic group (FOB) and McCoy group (McCoy) at different time points

Figure 3

Blood pressure (in mmHg) response to intubation with flexible fiberoptic bronchoscope and McCoy laryngoscope at various time points

Figure 4

Heart rate (in beat per min) response to intubation with flexible fiberoptic bronchoscope and McCoy laryngoscope at various time points

The endotracheal intubation was successfully performed in a single attempt in all the patients without any failure. There was no esophageal intubation with both devices. There was no incidence of dental or more severe airway laceration or any other complications with the use of both the devices.

DISCUSSION

Efforts to blunt circulatory response to tracheal intubation in situations such as cervical immobilization have prompted the development of several alternative methods, with more focus on pharmacological methods as compared to nonpharmacological methods. In this study, we aimed to evaluate the relative efficacy of flexible FOB and McCoy laryngoscope when used by experienced anesthesiologist in the clinical setting of simulation of cervical immobilization using rigid cervical collar, in terms of cardiovascular response to intubation.

According to study of McCoy et al.[19] use of McCoy laryngoscope reduces the force required for better laryngoscopy by lifting epiglottis and ultimately reduces the stress response to laryngoscopy. Nishiyama et al.,[5] Tewari et al.,[23] and Haidry and Khan[24] compared McCoy and Macintosh blades and showed that the use of McCoy blade resulted in a lesser change in HR and BP. On other side, some studies[252627] did not find any significant difference in the circulatory response between McCoy blade and Macintosh blade.

Adachi et al.[1213] and Barak et al.[14] compared fiberoptic intubation with conventional direct laryngoscopy and found stable hemodynamics with the fiberoptic group. While Shibata et al.[16] found that the cardiovascular responses to oral fiberoptic intubation are less severe than those to the nasal approach and recommended oral approach, especially in patients with coronary artery disease, taking into consideration the cardiovascular responses to fiberoptic intubation and similarly Cook et al.[28] also reported hemodynamic stability and less morbidity with fiberoptic oral intubation.

We have demonstrated that both flexible FOB and McCoy laryngoscope offer high success rates when difficult airways are simulated by the application of a rigid cervical collar. Our study demonstrated that with the use of flexible FOB, there was a significantly lesser change in HR and all kind of pressure readings (SBP, DBP, MAP) due to intubation in comparison to McCoy blade group. Although in McCoy group significant increase in pressure readings lasts for at least 5 min, significant increase of HR only lasts for 1–2 min. With better centralization of FOB's distal flexi-tip, we can minimize the stimulation of the laryngeal surface and as a result of this minimal change in cardiovascular variables. Less sympathetic stimulation with FOB can be of clinical benefit as less dose of drugs will be required to attenuate this response thereby decreasing the side effects associated with drugs like potent narcotics.

In patients where neck is stabilized in a neutral position, the McCoy laryngoscope improves the view of glottic opening.[202122] While fiberoptic provides a nearby complete view of the larynx. Our study demonstrated that in McCoy group, full glottic view was presented in 56% of group population and only posterior glottis was visible in 44% of group population while with fiberoptic, complete view of glottis was seen in 100% of group population. In our study, we also found that intubation duration was significantly less in McCoy group (17.9 s ± 3.07) as compared to fiberoptic group (40 s ± 7.28). Various studies of McCoy[2824] and FOB[1429] showed variability in terms of intubation duration as it depends on the skill of specialist.

We did experience some difficulty during railroading of ETT over insertion cord during oral intubation. Asai et al.,[30] Katsnelson et al.,[31] and Schwartz et al.[32] reported the same problem in their studies. We solved this problem by 90° anticlockwise rotation of the tube over cord or keeping Murphy's eye anteriorly. Several studies[323334] have confirmed that 90° anticlockwise rotation of the tube decreases the difficulty in railroading of tube over fiberoptic cord. Although we were concerned that view through fiberoptic might become obstructed by secretion or fogging, neither problem was observed.

CONCLUSION

We conclude that although, with McCoy laryngoscope, intubation can be performed more swiftly in situation of emergency as compared to fiberscope, but in a situation of cervical immobilization which is utmost priority to avoid further neurological injury or fracture instability in cervical trauma, as far as stable hemodynamic response to intubation and glottis visualization are concerned, FOB is superior device over McCoy laryngoscope, if available.