Opioid sparing during endotracheal intubation using mccoy laryngoscope in neurosurgical patients: The comparison of haemodynamic changes with macintosh blade in a randomized trialPrabhat Tewari1, D Gupta1, A Kumar1, U Singh2
1 Department of Anaesthesiology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raibarely Road, Lucknow, India
2 Department of Biostatistics, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raibarely Road, Lucknow, India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 16388166
Source of Support: None, Conflict of Interest: None
Background: There is conflicting data in literature to show that the McCoy laryngoscope is less stressful and opioids can actually be avoided during laryngoscopy and intubation with the use of this laryngoscope. Aim: A comparison of hemodynamic changes with McCoy vs Macintosh laryngoscope.. Settings and Design: 180 ASA I and II neurosurgical patients undergoing elective surgery for space occupying lesions were recruited. The study was was prospective, randomized and blinded in the setting of neurosurgical perioperative services. Methods and Materials: The patients were divided into four groups (Gr.1 McCoy and fentanyl; Gr. 2 McCoy and no fentanyl; Gr. 3 Macintosh and fentanyl; Gr. 4 Macintosh and no fentanyl). In Gr. 2 and 4 equivalent volume of saline was given in place of fentanyl as placebo. Heart rate, systolic and diastolic blood pressure were measured after laryngoscopy, after intubation and subsequently every minute for the next five minutes. The incidence of cough due to fentanyl treatment was observed. Statistical Analysis: Haemodynamic changes were compared between and within groups using oneway ANOVA and repeated measures ANOVA. All analysis included 95% CI at 5% significance. The Mann Whitney U test was used for comparing incidence of cough. Results: No difference was found between McCoy laryngoscopy when done with or without fentanyl pretreatment (HR p =0.848, sys BP p =0.229 and diastolic blood pressure p =0.981). Significant changes in haemodynamic parameters were seen between Macintosh and McCoy laryngoscopy without fentanyl pretreatment ( p <0.001) whereas changes were blunted with fentanyl pretreatment in Macintosh laryngoscopy ( p <0.05). Conclusions: McCoy laryngoscope blade is less stressful and fentanyl pretreatment is not necessary to attenuate haemodynamic responses with its use in ASA I and II patients.
Keywords: Analgesics opioids, cardiovascular, fentanyl, haemodynamics, laryngoscopy, Macintosh, McCoy
The haemodynamic responses to laryngoscopy and tracheal intubation are well described. Apart from other drugs, opioids seem to be good agents to suppress the enhanced haemodynamic responses to laryngoscopy and intubation. Fentanyl has high potency but a short half-life and thus is a reasonably good agent to suppress these haemodynamic perturbations in patients undergoing surgical procedures., However, fentanyl also has adverse effects, which include inconsistency in obtunding the laryngoscopy and intubation response, hypotension and coughing.,, In neurosurgical patients, coughing may further increase intracranial pressure, apart from the haemodynamic response of laryngoscopy and intubation, which can compromise the total blood flow to the brain and jeopardize its functions.
Since its introduction in 1993, the McCoy levering laryngoscope has been reported to enable several otherwise difficult intubations. The McCoy laryngoscope incorporates a modification of the Macintosh blade for better viewing of larynx. Use of this blade had been shown to be less stressful as haemodynamic variations are less though the number of patients in this trial were less. We hypothesized that if McCoy laryngoscope is used for endotracheal intubation, then there would be fewer haemodynamic changes and consequently less fentanyl use. This formed the rationale of the study.
After institutional ethical approval and written informed consent out of 200 screened participants 180 elective ASA 1 and 2 prospective patients, in the age range 18-50 years, with intracranial space occupying lesions, reporting to the neurosurgical department were included in this study. The study was carried out from January 2002 to 2003. The trial profile is given in [Figure - 1]. Exclusion criteria were patients with airway problems, hypertension, diabetes, any other metabolic disease, cardiovascular disease, preoperative signs of intracranial hypertension or those known to have cerebral aneurysms. A sample size of 40 in each group has a 95% power to detect a difference of 8.14 mmHg blood pressure between means with McCoy and Macintosh laryngoscope with a significance level (alpha) of 0.05 (two tailed) according to a previous trial. The patients were randomly assigned to one of the following four groups according to the computer-generated table of random numbers. The randomization was done by independent statisticians and by people not directly involved with the clinical study in the peri-operative period in the neurosurgical wards.
Group 1: McCoy laryngoscope with fentanyl pretreatment (McC+F).
Group 2: McCoy laryngoscope without fentanyl pretreatment (McC+NF).
Group 3: Macintosh laryngoscope without fentanyl (Mk+NF).
Group 4: Macintosh laryngoscope with fentanyl pretreatment (Mk+F).
Once the patient was wheeled in the operation theatre, two peripheral venous lines, a left radial arterial line and a triple lumen central venous pressure (CVP) line in right internal jugular vein were placed under local anaesthesia. The other intraoperative monitoring included real time ECG, pulse oximetry, capnography, core temperature, urine output and train-of-four ratio for muscle relaxant activity on Myotest (Biometer, Denmark). One of the anesthesiologists, who was blinded to the type of laryngoscope used gave all the drugs. This anesthesiologist was given an unmarked similar volume syringe, which either contained fentanyl or saline. Fentanyl pretreatment was done with 2 mg/kg, intravenously, in designated groups (Group 1 and Group 4) and same volume of saline was given in the no fentanyl group (Group 2 and Group 3). The drug was given 5 min prior to the start of induction. Another anaesthesiologist took note of the heart rate and blood pressure at different point of times (assessor blind). He was blinded for the drug and the device and he marked all the events on the trend graph of the monitor. The third anesthesiologist who was blinded to the drugs and the haemodynamic parameters did the laryngoscopy and intubation. Laryngoscopy technique was standardized with the head lifted on a pillow in all the cases. All the three anaesthesiologists were same for all the cases and followed the same protocol. Induction was done with intravenous midazolam (0.05 mg/kg), priming dose of vecuronium bromide (0.015 mg/kg) followed with thiopentone sodium. At the loss of eyelash reflex rest of vecuronium bromide (total dose 0.1 mg/kg) was given to achieve muscle relaxation. The remaining dose of thiopentone sodium was given to the total dose (5 mg/Kg) according to the protocol. At this point nitrous oxide was added so as to make 60% inhaled mixture in oxygen. The laryngoscopy was done immediately after two minutes once 90% block on Train-of-Four nerve stimulation was achieved. The McCoy laryngoscope was used with full lever on and it was never used as Macintosh laryngoscope. Once the vocal cords were visualized, the intubation was done. The laryngoscopy and intubation was done in single attempt and when ever more than one attempt was used or laryngeal pressure from outside was used, such patients were excluded.. The heart rate (HR), systolic blood pressure (SBP), and the diastolic blood pressure (DBP) were noted at different time points- baseline, after visualization of vocal cords, immediately after intubation, and subsequently at one-minute interval after intubation. These events were marked on the trend graphics on the monitor and the values were noted down afterwards. Thus haemodynamic data was collected for all the patients at eight time points. Provision for rescue by beta blockade using intravenous esmolol 150 mg stat (11) to check unusual haemodynamic responses after laryngoscopy to critical levels (rise of HR > 30%; SBP > 60% of basal value) was kept in the protocol. Once the data was collected the study protocol ended and all the patients were managed as per neurological OT anesthesia services protocol with fentanyl as analgesic. The haemodynamic data, the drugs used, the device used, patient profile and the incidence of cough was sealed in different envelopes by a person not associated with the study and all was sent to the statistician. They were opened for analysis once the trial was over.
For statistical analysis SPSS version 9 (SPSS corporation, USA) was used. The demographic data was compared by one-way anova. The number of females was presented as percentage and the ratio compared with Chi square test. Data for heart rate, systolic and diastolic blood pressure was presented as mean and standard deviation. Within group comparisons were done using repeated measures anova. Differences among the groups were analyzed using a one-way anova. A Tukey's test post hoc test was used when a significant difference seen with anova. Incidence of cough in patients was analysed using non parametric Mann-Whitney test. All analysis were done at 5% significance (degree of freedom 10.8, 95% confidence interval).
One hundre and sixty patients completed the study. Two patients were found to have difficult intubation. In 10 patients McCoy blade was used in a Macintosh style and outside laryngeal pressure was applied. Four patients in Group 3 needed rescue and other measures to control severe hypertension and in 4 patients there was episode of severe hypotension after fentanyl treatment needing posture change to Trendlenbergh position and other measures. Thus all of them were omitted from the result compilation as they did not confirm to the laid protocol. Demographic details are summarized in [Table - 1]. There was no significant difference among the groups in age, weight, and preoperative haemodynamics. The haemodynamic data of the four groups is summarized in [Table - 2], [Table - 3], [Table - 4].
Heart rate showed insignificant change at all points ( P =0.848) in Gr. 1 and Gr. 2 where McCoy laryngoscope was used (maximum attained was 88 beats/min in both the groups). Macintosh laryngoscope significantly increased heart rate in Grs. 3 (maximum 103 bpm/73 bpm baseline) and 4 ( P <0.001 maximum 96 bpm/72 bpm baseline). Fentanyl treatment significantly reduced heart rate ( P =0.048) with Macintosh laryngoscope in Gr. 4 as compared to Gr. 3. This significant change was noted post laryngoscopy, after intubation and after 1 minute. In fact the changes in pulse rate were significantly higher ( P <0.001) at all time points in Gr. 4 where fentanyl was used with Macintosh as compare to Gr. 2 where McCoy blade was used without fentanyl pretreatment.
The systolic blood pressure showed no significant rise with usage of McCoy alone or along with fentanyl (Gr. 1 and 2 P =0.229). Maximum in Gr. 1 was 124 mmHg/119 mmHg baseline and in Gr. 2 was 129 mmHg/121 mmHg baseline. The comparison of Gr. 1 with Gr. 3 ( P <0.001 maximum 150 mmHg/121 mmHg baseline) and Gr. 4 ( P <0.001 maximum 141 mmHg/ 122 mmHg baseline) and that of Gr.2 with Gr. 3 ( P <0.001) and 4 ( P <0.001) were highly significant showing increase in systolic blood pressure from baseline with Macintosh blade either with or without fentanyl treatment. Fentanyl pretreatment did not show any significant difference in systolic blood pressure in Gr. 3 as compared to Gr. 4 ( P =0.456) as blood pressure remained significantly high from baseline in both the groups (with in the group significance P =0.04). The blood pressure rise was maximum in Gr. 3 immediately after intubation ( P <0.001) when compared to the same point of time in Gr. 4. Afterwards both the groups have similar high blood pressures with insignificant difference.
Diastolic blood pressure also shows no significant difference in the McCoy groups (Gr. 1 and 2 P =0.981). Similarly with in the group changes were non significant in Gr.1 and 2with maximum rising to 78 and 80 mmHg. It rises significantly in Macintosh groups as compared to McCoy ( P <0.001 maximum 96 mmHg from baseline of 75 mmHg). Fentanyl pretreatment in Macintosh group significantly reduces the diastolic pressure after intubation ( P <0.001 maximum 86 mmHg) and keeps so till one minute afterwards ( P <0.05). After one minute the diastolic change reaches to non-significant level.
The incidence of cough at the time of intravenous injection of fentanyl is shown in [Table - 5]. In Gr. 1 (12/40) and Gr. 4 (14/40) achieved significant incidence ( P <0.001, CI 95%) when compared to Gr. 2 and Gr. 3, respectively.
This study shows that McCoy blade can spare the usage of narcotics during the time of laryngoscopy and intubation as it gives stable haemodynamic response even when fentanyl is not used. Thus the common complications of fentanyl usage can be potentially avoided.
The McCoy levering laryngocope differs from a usual curved Macintosh blade in four respects. It has a hinged tip, a lever at the proximal end, a spring-loaded drum and a connecting shaft. The hinged tip blade controlled by a lever on the handle of laryngoscope allows elevation of epiglottis while decreasing overall laryngoscpic movement. This unique design has shown two advantages over Macintosh laryngoscope. First the use of McCoy laryngoscope results in less force being applied during laryngoscopy and thus stress response is reduced. Secondly, difficult laryngoscopic visualization may be improved by lifting the epiglottis. This laryngoscope can improve the laryngeal view especially in the patients with neck fixed in the neutral position or patient suspected cervical spine injury with cervical collar.
It is known that the major cause of cardiovascular response during laryngoscopy and intubation is the tissue tension induced by the laryngoscopic blade in the supraglottic region. These nociceptive signals are conducted to the brain through glossopharyngeal nerve and vagus nerve. The pressor response to laryngoscopy and intubation is mediated via sympathetic nerves. Laryngoscopy with McCoy blade required only 53% of the force (10.1 N) in order to obtain a clear view of vocal cord as compared to Macintosh blade (18.9 N). The reason could be the hinged tip elevates the epiglottis rather than forward displacement of the attached structures by curved blade. Increase in plasma noradrenaline level with use of Macintosh blade and absence of significant change in plasma noradrenaline level with the McCoy blade is again a reflection of very less pressure response and tachycardia after laryngoscopy. A positive correlation has been demonstrated between force exerted at laryngoscopy and patient's height, weight, body mass index (BMI) and presence of maxillary incisors but it was seen that effect of these factors on force exerted with the McCoy blade is not as important as with Macintosh blade.
In space occupying lesions in neurosurgical patients effective haemodynamic control is required during laryngoscopy and intubation, as any rise in these parameters may increase the already raised intracranial pressure and thus jeopardize the brain function. Various drugs are used to subdue or attenuate this response. Intravenous fentanyl given before laryngoscopy and intubation has shown to decrease the haemodynamic response but complications of hypotension and cough many a times may not make it a good agent. Secondly, in neurosurgical patients lesser use of narcotics in the intraoperative period may help surgeon to better evaluate the patient in immediate postoperative period. Though this study does not address this issue directly but an effort towards reduction in narcotics at any given point of time may help especially where the drugs have a cumulative effect. Researchers have used remifentanyl-guided by its short lived action-to attenuate the noxious stimuli of orotracheal intubation but significant bradycardia and hypotension have resulted in the use of additional medications in the form of glycopyrrolate thus can not be an optimal choice.
The present study had several limitations. First, we conducted our study on ASA I and II patients with normal airways. In hypertensive patients these responses may get exaggerated. Secondly normal duration of laryngoscopy in difficult airways may produce different response as compared to having normal airway. These patients may then need protection for hypertensive response even with McCoy laryngoscope. It has been shown by Cook et al . that the laryngoscopic view with McCoy laryngoscope suffers when neck is extended. Though Tuckey et al . have emphatically supported that once the laryngoscopic view with McCoy in neutral position is attained there is no need for further manipulation. These manipulations may add unnecessary haemodynamic upheavals, needing medications. Familiarity and learning of correct use of McCoy laryngoscope is fundamental as even with its lever in "on position" one may get tempted to easily use it as Macintosh laryngoscope. As the study was restricted to the period around laryngoscopy and intubation we could not take into account the total dose of narcotics used in the four groups therefore we can not comment on the total opioid requirement during the surgery. Pin manipulation in neurosurgical patients is always done under local anaesthetics. Other limitations include non measurement of plasma levels of the induction agent. In such study proper blinding of the personnel and procedures poses a real problem.
In conclusion, the present study shows the usefulness of McCoy laryngoscope in maintaining the haemodynamics near baseline and the use of fentanyl can be avoided. This corollary may further be extended to minimize the usages of other drugs to attenuate the haemodynamic responses to laryngoscopy and intubation. The findings of this study need to be confirmed by more prospective studies.
[Figure - 1][Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]