Comparison of postoperative sore throat following laryngoscopy conducted by Miller and Macintosh laryngoscope blades

doi:10.4236/health.2011.310105

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Vol.3, No.10, 623-625 (2011)

doi:10.4236/health.2011.310105

Health

Comparison of postoperative sore throat following

laryngoscopy conducted by Miller and Macintosh

laryngoscope blades

Khosro Barkhordari, F arhad Ete zadi, R eza Shariat Mo harari , Mohammad Re za Khaj avi*

Tehran University of Medical Sciences, Sina Hospital, Tehran, Iran; *Corresponding author: [email protected]

Received 6 January 2011; revised 1 June 2011; accepted 15 June 2011.

ABSTRACT

BACKGROUN D: Post operative sore throat (PST)

is one of the most common complaints after

tracheal intubation. In this study we compared

the effects of curved and straight laryngoscope

blades on severity and incidence of PST. METH-

OD: In this prospective randomized clinical trial

we evaluated incidence and severity of PST in

147 ASA physical status I–II, aged 18 – 62 y

(group Miller, n = 71), (group Macintosh, n = 76)

following intubation with Miller and Macintosh

laryngoscope blades by using Visual Analog

Scale (VAS). RESULTS: The overall incidence of

PST in our study was 35.4% (Macintosh group =

39.5% and in Miller group = 31% and P = 0.829).

The incidence of PST was not statistically differ-

ent between two kinds of laryngoscope blades

and the mean rank of pain score was not statisti-

cally different in recovery room and up to 48

hours after surgery. CONCLUSIONS: Our study

showed these types of laryngoscope blade had

not association with incidence and severity of

PST.

Keywords: Post Operative Sore Throat;

Tracheal Incubation; Laryngoscope Blades

1. INTRODUCTION

Post operative sore throat (PST) is one of the most

frequent complaints after tracheal intubation and its in-

cidence varies between 14% - 50% [1-4]. Mucosal injury,

stretch of ligaments and muscles of throat, prolonged

surgery, changing position of patients during surgery

have been implicated in the pathogenesis of PST [4].

Chandler’s study showed that pressure trauma is very

important to induce PST and he found an association

between mechanical forces and PST [4].

Our hypothesis was that straight blade (Miller) gener-

ates less pressure on pharyngeal wall, muscles and liga-

ments of pharynx than curved blade (Macintosh). Hast-

ings et al showed that the use of Miller laryngoscope

blade required less force and head extension than Mac-

intosh one [5]. We didn’t find any study comparing se-

verity of pain produced by these two common blades

used for laryngoscopy.

The aim of our study was to compare the incidence

and severity of PST with Macintosh and Miller laryngo-

scope blades during normal intubating attempts.

2. METHODS

After Institutional Ethics Committee app roval, written

informed consent was obtained for all patients. We pro-

spectively studied 147 consecutive adult patients (18 -

64 years old) with ASA physical status I–II receiving

general anesthesia with tracheal intu bation. Using a com-

puter generated sequence of numbers, patients were

randomly allocated to be in tubated using either a straight

blade laryngoscope (n = 71) or a curved blade, (n = 76).

Failure to tracheal intubation in the first attempt, posi-

tive history of sore throat, use of NSAIDS, head and

neck surgery, smoking, Mallampati class greater than 2

were our exclusions criteria. After establishing IV access

and use of standard monitoring, midazolam 0.05 mg/kg,

fentanyl 2 µg/kg injected as premedication, thiopental

Na 5 mg/kg, and atracurium 0.4 mg/kg were used for

induction of anesthesia. An anesthesiologist with three

years of continuous practice performed all endotracheal

intubation gently. Size of tracheal tubes were adjusted

for age and body size of patients, and miller no 2 and

Macintosh no 3 blades were used. Endotracheal tubes

(ETT) were lubricated with sterile water. ETT cuffs were

inflated at the safe occlusive volume so initial Cuff

pressure was fixed at 20 cm H2O (Mallinckrodt, Seel-

scherf 1, Germany). Anesthesia was maintained by: air/

N2O (50%/50%), isoflurane (1% to 1.2%) a nd inter mittent

injection of fentanyl as was necessary.

When tracheal extubation criteria were met (return of

neuromuscular function confirmed using train-of-four

K. Barkhordari et al. / Health 3 (2011) 623-625

624

peripheral nerve stimulation, ability to follow verbal

commands, r egular spontaneou s ventilation), tracheal ex-

tubation was performed just after gentle suctioning at the

discretion of anesthesiologist who was a member of an-

esthesia team. Another anesthesiologist who was blin-

ded to the study evaluated th e PST w ith a Visual Analog

Scale (VAS, 0 - 10 score) in the postoperative period (at

0, 3, 6, 12, 24 and 48 hours after surgery). Sample-size

was calculated based on our pilot stud y with 70 patients.

In order to permit 5% of type 1 error enrollment of 73

patients in each group was required. Demographic char-

acteristics and incidence of pain in both groups were

com- pared by using chi-square and Student’s t-test. VAS

scores were analyzed using Wilcoxon rank sum test.

Medians and their confidence intervals were calculated

using binomial interpretation. Statistical sign ificance was

defined as P < 0.05. Data were analyzed using SPSS

version 13 and Intercooled STATA version 9.1.

3. RESULTS

One Hundred Forty Seven patients were enrolled in

the study. Two cases in Miller group were exclud ed from

the study because first intubation attempt was failed. At

the baseline, there were no statistically significant dif-

ferences between groups regar ding sex , age, Mall ampatti

class, and ASA class and operation time between two

groups (Table 1). The overall incidence of PST in our

study was 35.4% (Macintosh group = 39.5% and in

Miller group = 31% and P = 0.829) and the highest mean

VAS score was observed at third post operative hour in

both groups (Figure 1).

The assumption for performing parametric test did not

met; therefore we used Wilcox, rank sum test to compare

VAS scores in the study groups. The assumption for per-

Table 1. Patient characteristics and demographic data.

Group A: Macintosh

blade (n = 76) Group B: Miller

blade (n = 71) P value

Sex; n (%)

Male 26 (34.2%) 19 (27.7%) P = 0.33

Female 50 (66%) 52 (73.2%)

Mallampatti

class n (%)

I 74 (97.3%) 70 (98.6%) P = 0.33

II 2 (2.7%) 1(1.4%)

ASA class

I 71 (93.4%) 69 (97%) P = 0.74

II 5 (6.6%) 2 (2.8%)

Mean Age (yr) 33.4 ± 12.8 29.6 ± 10.4 P = 0.47

Operation time

(min) 52 ± 9.7 51.9 ± 8.7 P = 0.829

ASA: American Society of Anesthesiologists.

Figure 1. Incidence of sore throat in different time after opera-

tion.

forming parametric test did not met; therefore we used

Wilcox, rank sum test to compare VAS scores in the

study group s.

4. DISCUSSION

In our country, curved blade laryngoscope are more

commonly used than straight blades especially in our

hospital, because the laryngoscopic views obtained with

curved blades are better than straight blades [10]. How-

ever, there are many studies regarding severity and

higher incidence of PST in patients who were intubated

with curved blades [6-9]. Skills of intubator, history of

smoking, lung disease, and pressure of cuff and opera-

tion time have been implicated to be the factors which

are associated with PST [3,6-9]. Chandler ’s study show-

ed that mechanical trauma is an important factor in path-

ogenesis of PST and he found a positive assosiation be-

tween mechanical forces and PST (they studied on me-

chanical models) [4]. We didn’t find any study in litera-

ture for comparing incidence and severity of PST with

these two kinds of laryngoscope blades during tracheal

intubation. However, One study showed that force,

torque and head extension were 30% less with Miller

blade compared to Macintosh blade [5].

Our impression was that mechanical trauma plays

more important role in producing PST than other prob-

able factors. We thought that reducing stretch forces

during intubation by using straight blade may decrease

the rate of PST. But our study showed that PST rate in

recovery room and during first 48 hours after surgery

was not statistically different between Macintosh and

Miller blade. Our study has several limitations. One of

those was medications that we had to give to the patients

because of surgical pain in postoperative period. We

administered equivalent doses of morphine 0.1 mg/kg

for reducing postoperative surgical pain to both groups

of the patients. Another limitation was difficulty in ob-

K. Barkhordari et al. / Health 3 (2011) 623-625

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taining VAS score immediately after awakening from

anesthesia in some patients because of residual effect of

anesthetics. Other limitation of our study is enrollment

of only class 1 airway patients and excluding patients

with mallampatti class 3 and 4, therefore we suggest new

studies for finding probable association between difficult

intubation a n d occurrence of PST.

Openly accessible at

In conclusion, we didn’t find statistically significant

differences in the incidence and severity of PST between

curved and straight laryngoscope blades during uncom-

plicated attempts of intubation.

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