STOP-BANG SCORE AND MANDIBULOHYOID DISTANCE
IN PREDICTION OF DIFFICULT AIRWAY IN PATIENTS WHO COME FOR ELECTIVE
SURGERY REQUIRING ENDOTRACHEAL INTUBATION IN HOSPITAL USM
BY
DR LEE KOK TONG
Dissertation Submitted in Partial Fulfillment of The Requirement for the Degree of Master of Medicine
(ANAESTHESIOLOGY)
UNIVERSITI SAINS MALAYSIA
2017
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ACKNOWLEDGEMENT
I would like to take this opportunity to express my gratitude and sincere appreciation to all who has helped me into the success of this study.
Special thanks to Dr Rhendra Hardy Mohamad and Dr Mohd Erham Hassan, my supervisors and Co supervisor, for their guidance and teaching in carrying out this study. Their effort and time spent during this period has been most invaluable and priceless. Their abundance of experience shared with me were my blessing.
I would like to thank Dr Nik Munirah Nik Mahadi (Head of Radiology Department) and Dr. Chandran Nadarajan ( Radiologist) and their staffs for providing precious support in the conduct of the study. Theirs advice on radiographic technique has given me an in-depth knowledge on how an accurate technique vital to the results of my study. The compliance of the radiographers on the techniques was greatly appreciated.
I would like to thank Dr. Ramiza Ramza Ramli( ENT surgeon) for his advice on sleep study and STOP Bang Scoring in obstructive sleep apnea patient.
I would also like to thank Associate Professor Dr Wan Mohd Zahirruddin Bin Wan Mohammad of the Department of Community Medicine and Dr Kueh Yee Cheng of department of biostatistic for their valuable advice on research methodology and biostatistics.
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Many thanks to all my lecturers and colleagues who have contributed to the study and preparation of this dissertation in terms of ideas and moral support.
Last but not the least, to my beloved parents, wife, a big thank you for their unconditional patience and support, without which, the success of this study would not be possible.
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TITLE i
ACKNOWLEDGEMENT ii
TABLE OF CONTENTS iv
LISTS OF TABLES AND FIGURES vi
ABSTRAK viii
ABSTRACT x
LIST OF ABBREVIATIONS xii
1. INTRODUCTION 1 1.2 OBJECTIVE OF THE STUDY 3
1.2.1 GENERAL OBJECTIVE 3 1.2.2 SPECIFIC OBJECTIVES 3 2.0 BODY [MANUSCRIPT READY FOR SUBMISSION] CONTENT: 4 2.1 TITLE PAGE 4
2.1.1 ARTICLE TITLE 4 2.1.2 RUNNING HEAD 4 2.1.3 AUTHORS’ NAMES AND INSTITUTIONAL AFFILIATIONS 4 2.1.4 CORRESPONDING AUTHOR’S DETAILS 5 2.2 MAIN DOCUMENT 6 2.2.1 ABSTRACT (ENGLISH) 6 2.2.2 INTRODUCTION 8 2.2.3 METHODOLOGY 9 2.2.4 RESULT 12 2.2.5 DISCUSSION 15
2.2.7 CONCLUSION 19 2.2.7 FIGURE FOR MANUSCRIPT 21
2.2.8 TABLES FOR MANUSCRIPT 33
2.2.9 REFERENCES FOR MANUSCRIPT 41 2.3 GUIDELINES FOR AUTHORS; JOURNAL FORMAT (MJMS) 45 3.0 STUDY PROTOCOL 58
3.1 DOCUMENT SUBMITTED FOR ETHICAL APPROVAL 58
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4.0 APPENDICES 96
4.1. LITERATURE REVIEW 96
4.1.1 OBSTRUCTIVE SLEEP APNOEA (OSA) 96
4.1.2 ANAESTHETIC PROBLEM ASSOCIATED WITH OSA 102
4.1.3 OSA IS ASSOCIATED WITH DIFFICULT AIRWAY 104 4.1.4 ROLE OF IMAGING TECHNIQUES IN AIRWAY EVALUATION 106 4.1.5 THE MANDIBULOHYOID DISTANCE ON THE LATERAL
CEPHALOMETRY RADIOGRAPH AND ITS ROLE IN AIRWAY
EVALUATION 107 4.1.6 STOP-BANG SCORE IN PREDICITON OF DIFFICULT AIRWAY 108
4.2 MAIN REFERRENCES 109
4.3 CASE REPORT AND COLLECTION FORM 114
4.4 CONSENT FORM (MALAY) 115
4.5 CONSENT FORM (ENGLISH) 123
4.6 STOP-BANG QUESTIONNAIRE 131
4.7 EVIDENCE OF SUBMISSION 132
4.8 ETHICAL APPROVAL LETTER 134
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LISTS OF TABLES AND FIGURES : List of Tables
Table 1 The mean age , BMI, neck circumference, mallampati score, height, weight of the patients, and distribution of gender, prevalence of difficult laryngoscopy.
Table 2 :Comparison between Easy laryngoscopy and Difficult
laryngoscopy among participant’s age, BMI, neck circumference, mallampati , weight, height.
Table 3 Association between difficulties of laryngoscopy and gender.
Table 4 Participants characteristics and odds of difficult laryngoscopy (n=41)
Table 5 Area under the curve of ROC curve for STOP BANG score (n=41)
Table 6 Area under the curve of ROC curve for mandibulohyoid distance(mm) (n=41)
Table 7 Area under the curve of ROC curve for STOP BANG score and mandibulohyoid distance(mm). (n=41)
Table 8: Associated factors of difficult laryngoscopy by univariable and multiple logistic regression model
Table 9 :Predictive parameters for the mandibulohyoid distance(mm), STOP-BANG score and combined STOP-BANG score and mandibulohyoid distance(mm).
7 List of figures:
Figure 1 Lateral Cephalometry
MPH- mandibulohyoid distance
Figure 2 Lateral cephalometry
(mandibulohyoid distance in mm)-
Figure 3 Receiver operating characteristic curve of STOP BANG score (n=41)
Figure 4 Receiver operating characteristic curve of mandibulohyoid distance(mm) (n=41)
Figure 5 Receiver operating characteristic curve of STOP BANG score and mandibulohyoid distance(mm). (n=41)
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ABSTRAK (BM)
Pemarkahan STOP BANG dan Pengukuran Jarak Mandibulohyoid Dalam Meramalkan Kesukaran Laringoskopi Di Kalangan Pesakit Yang Datang Untuk Pembedahan Elektif Dan Memerlukan Intubasi Trakea Di Hospital USM.
Latar Belakang:
Pesakit OSA berkemungkinan untuk menghadapi kesukaran laringoskopi dan intubasi. Peramalan kesukaran laringoskopi sebelum menjalani pembiusan am akan dapat mengurangkan komplikasi pembiusan di kalangan pesakit yang mengalami OSA.
Tujuan:
Tujuan kajian ini adalah untuk mengenalpasti faktor-faktor yang mungkin wujud dalam meramalkan kesukaran laringoskopi dan intubasi di kalangan pesakit yang mengalami OSA (kombinasi atau tidak kombinasi, pemarkahan STOP-BANG dan pengukuran jarak mandibulohyoid dalam x ray ) .
Kaedah:
Kajian ini dibuat melalui pemerhatian, secara prospektif, keratan lintang dengan 41 orang pesakit yang memenuhi kriteria pemilihan. Saringan dibuat dengan menggunakan soal selidik STOP-BANG,pesakit yang memenuhi >3 markah dipilih . Pengukuran jarak mandibulohyoid melalui gambar sinar-X leher dijalankan sebelum pembiusan am. Kesukaran laringoskopi dicatatkan semasa pembiusan am. Cormach Lehance grad 3 dan 4 ditetapkan sebagai kesusahan laryngoskopi. Kemudian keputusan pengukuran dan pencatatan dianalisa secara statistik.
Keputusan:
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Didapati pemarkahan STOP-BANG , jarak mandibulohyoid (mm), index jisim badan, pengukuran lilitan leher (cm) dan pemarkahan Mallampati adalah lebih tinggi di kalangan pesakit yang berkemungkinan mengalami OSA. Pesakit yang besar kemungkinan mengalami OSA juga menghadapi kesukaran laringoskopi . Kita dapat mengesan perhubungan antara pemarkahan STOP-BANG dan pengukuran jarak mandibulohyoid dalam proses peramalan kesukaran laringoskopi . AUC (95% CI) ,0.86 (0.74,0.97). Untuk STOP BANG sahaja,sensitivity dan spesifikasi (85.71, 66.7%
masing-masing).Untuk pengukuran jarak mandibulohyoid sahaja, sensitivity dan spesifikasi (77.8%, 69.6% masing-masing) . Kombinasi pemarkahan STOP-BANG dan pengukuran jarak mandibulohyoid telah menunjukkan peningkatan dari segi spesifikasi dan sensitiviti (77.3% and 84.2% masing-masing) dalam proses peramalan kesukaran laringoskopi.
Kesimpulan:
Pemarkahan STOP-BANG dan pengukuran jarak mandibulohyoid terbukti memainkan peranan penting dalam peramalan kesukaran laringoskopi di kalangan pesakit yang berkemungkinan mengalami OSA. Keberkesanan peramalan kesukaran laringoskopi adalah lebih tinggi apabila kombinasi pemarkahan STOP-BANG dan jarak mandibulohyoid(mm) telah digunakan dalam proses peramalan. Pesakit OSA mempunyai kemungkinan yang lebih besar untuk menghadapi kesukaran laringoskopi.
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ABSTRACT (ENGLISH)
Background:
Incidence of difficult laryngoscopy and difficult intubation are higher among patients with obstructive sleep apnoea (OSA). Precision in making the diagnosis and predicting difficult laryngoscopy preoperatively may help to reduce anaesthetic complications. This study was designed to evaluate the diagnostic performance of combined and non-combined radiological parameter (mandibulohyoid distance) and STOP-BANG questionnaire as screening tool.
Methodology:
Total of Forty-one subjects who score >3 using STOP-BANG questionnaire screening were recruited during admission (STOP BANG score >3 indicate the subject at risk for OSA). Lateral cephalometry( lateral head and neck x ray) was done to measure for mandibulohyoid distance and other radiological parameters. Evaluation for difficult laryngoscopy was carried out during general anaesthesia. Cormarch Lehance view of grade 3 and 4 were considered as difficult intubation, grade 1 and grade 2 were considering not difficult intubation. Result analysed using multiple logistic regression to look for association between STOP-BANG score and mandibulohyoid distance with difficult intubation in OSA patients.
Result:
STOP-BANG score, mandibulohyoid distance (mm) , were higher in the OSA group. OSA patients had a higher incidence of difficult laryngoscopy and intubation.
There was association between STOP-BANG score and mandibulohyoid distance with difficult intubation in OSA patients. AUC (95% CI) ,0.86 (0.74,0.97). In prediction of airway difficulty, for STOP BANG alone, sensitivity and specificity ( 85.71% ,66.7%
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respectively), for mandibulohyoid alone , sensitivity and specificity(77.8%, 69.6%
respectively). Combination of STOP-BANG score and mandibulohyoid distance had improved the specificity and sensitivity of the screening tool to predict difficult airway.(77.3% and 84.2% respectively).
Conclusion:
The STOP-BANG score and mandibulohyoid distance proved to be useful in the preoperative diagnosis of difficult laryngoscopy and intubation. The performance of the diagnostic tool improved when combined both STOP-BANG score and mandibulohyoid distance (mm) .OSA patients were more prone to difficult laryngoscopy.
12 ABBREVIATIONS
AHI Apnea /hypopnea index
ASA American Society of Anesthesiology AUC Area under curve
BMI Body Mass Index BP Blood Pressure ETT Endotracheal tube
HUSM Hospital Universiti Sains Malaysia HR Heart Rate
IV Intravenous
MAC Minimal alveolar concentration MHD /MPH Mandibulohyoid distance OSA Obstructive Sleep Apnea SBP Systolic Blood Pressure
SPSS Statistical Package for the Social Science STOP BANG Name of the screening questionnaire TOF Train of four (neuromuscular monitoring)
13 1. INTRODUCTION
There is a strong association between difficult intubation and Obstructive Sleep Apnea (OSA). These are two major problems for anaesthetists, which may contribute to perioperative morbidity and mortality because both are associated with upper airway abnormalities(1). About 20% of Obstructive Sleep Apnea patient have difficult intubation according to a retrospective study published in International Anesthesia Research Society (2).
Obstructive Sleep Apnea (OSA) is a potentially serious sleep disorder in which breathing repeatedly stops and starts during sleep. It has a prevalence of 2% for women and 4% for men in the general population(3). For anesthetist, the significant feature of OSA is the occurrence of perioperative respiratory adverse events , whereas one major consequences of OSA is the risk of difficult intubation(4).
Despite the frequency of difficult intubation in the general surgical populations is not extremely high , poor management of difficult airways account for 35% of all anesthesia related death(5).
Previous studies have suggested that OSA patients are at higher risk of difficult intubation than are control patients(2, 6). For that reason, the identification of OSA patient during preoperative assessment would prevent adverse events(1). A recent study also showed that 69% of the surgical patients had OSA and while 60% of the patients with moderate to severe OSA were not diagnosed preoperatively by
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anesthetist(7). Therefore, the ASA recommended routine screening of OSA by anesthetist preoperatively.
The are several screening tools for OSA, the STOP-BANG questionnaire is the most easy to use and proven validity(8). Beside , STOP-BANG ≥3 also predictive of potential difficult airway(9). There is no single airway test can provide a high index of sensitivity and specificity for the prediction of difficult airway. Therefore, it has to be a combination of multiple tests(10).
Radiological methods of prediction of difficult airway by using lateral cephalometry may increase the sensitivity and specificity of the models in prediction of difficult airway. This idea was supported by two studies done previously(11, 12).
In this study, firstly, we would like to define the association between STOP- BANG score, cephalometry; secondly, to determine the social demographic , clinical measurement , STOP-BANG score and cephalometric measurement in predicting difficult intubation in patients with Obstructive Sleep Apnea . Thirdly, we would like to assess whether combination of STOP-BANG score and lateral cephalometry measurement (mandibulohyoid distance) will improved the sensitivity and specificity of the models in prediction of difficult airway. Difficult airway can be divided into three parts, difficult mask ventilation, difficult laryngoscopy and difficult intubation. In our study, we will be assessing difficult laryngoscopy as part of difficult airway.
15 1.2 OBJECTIVE OF THE STUDY
1.2.1 GENERAL OBJECTIVE
To determine the association of STOP-BANG scores, cephalometric measurement with difficult intubation in patients at risk of Obstructive Sleep Apnea who come for elective surgery requiring endotracheal intubation.
1.2.2 SPECIFIC OBJECTIVES
1. To compare STOP-BANG scores between patients at risk of Obstructive Sleep Apnea in difficult and easy laryngoscopy groups who come for elective surgery requiring endotracheal intubation.
2. To compare Mandibulohyoid distance (cephalometric measurements) between patients at risk of Obstructive Sleep Apnea in difficult and easy laryngoscopy groups who come for elective surgery requiring endotracheal intubation.
3. To determine the correlation of STOP-BANG score and Mandibulohyoid distance (cephalometric measurement)in predicting difficult airway in patients at risk of OSA .
4. To determine the social demographic , clinical measurement , in prediction of difficult laryngoscopy in patients at risk of Obstructive Sleep Apnea who come for elective surgery required endotracheal intubation.
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2.0 BODY [MANUSCRIPT READY FOR SUBMISSION] CONTENT:
2.1 TITLE PAGE
2.1.1 ARTICLE TITLE
STOP-BANG SCORE AND MANDIBULOHYOID DISTANCE
IN PREDICTION OF DIFFICULT AIRWAY
IN PATIENT WHO COME FOR ELECTIVE SURGERY REQUIRING ENDOTRACHEAL INTUBATION IN HOSPITAL USM
2.1.2 RUNNING HEAD
STOP-BANG SCORE AND MANDIBULOHYOID DISTANCE
IN PREDICTION OF DIFFICULT AIRWAY
2.1.3 AUTHORS’ NAMES AND INSTITUTIONAL AFFILIATIONS
Kok Tong LEE
1, Rhendra Hardy MOHAMAD ZAINI
2School of Medicine, Department of Anaesthesia and Intensive Care, Universiti Sains Malaysia, 16150, Kota Bharu
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2.1.4 CORRESPONDING AUTHOR’S DETAILS
Dr Lee Kok Tong, MD (USM) Dr Rhendra Hardy Mohammad Zaini
School of Medicine, Department of Anaesthesia and Intensive Care, Universiti Sains Malaysia, 16150, Kota Bharu, Kelantan.
09-767 3000/3858/3859 ktong1984@gmail.com rhendra@gmail.com
18 2.2 MAIN DOCUMENT
STOP-BANG SCORE AND MANDIBULOHYOID DISTANCE IN PREDICTION OF DIFFICULT AIRWAY
IN PATIENT WHO COME FOR ELECTIVE SURGERY
REQUIRING ENDOTRACHEAL INTUBATION IN HOSPITAL USM
Kok Tong LEE
1, Rhendra Hardy MOHAMAD ZAINI
2School of Medicine, Department of Anaesthesia and Intensive Care, Universiti Sains Malaysia, 16150, Kota Bharu, Kelantan.
Keywords : airway assessment , difficult airway, lateral cephalometry, predictive test ,mandibulohyoid distance
Acknowledgements:I would like to thank staffs of Operation Theatre Hospital Universiti Sains Malaysia who have made completion of this study into reality.The manuscript has not been published elsewhere or submitted elsewhere for publication.The results of this study have not been presented in another form such as aposter or abstract, or at a symposium.There is no conflict of interest and no source of financial support in this study.
2.2.1 ABSTRACT (ENGLISH)
Background:
Incidence of difficult laryngoscopy and difficult intubation are higher among patients with obstructive sleep apnoea (OSA). Precision in making the diagnosis and predicting difficult laryngoscopy preoperatively may help to reduce anaesthetic complications. This study was designed to evaluate the diagnostic performance of combined and non-combined radiological parameter (mandibulohyoid distance) and STOP-BANG questionnaire as screening tool.
Methodology:
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Total of Forty-one subjects who score >3 using STOP-BANG questionnaire screening were recruited during admission (STOP BANG score >3 indicate the subject at risk for OSA). Lateral cephalometry( lateral head and neck x ray) was done to measure for mandibulohyoid distance and other radiological parameters. Evaluation for difficult laryngoscopy was carried out during general anaesthesia. Cormarch Lehance view of grade 3 and 4 were considered as difficult intubation, grade 1 and grade 2 were considering not difficult intubation. Result analysed using multiple logistic regression to look for association between STOP-BANG score and mandibulohyoid distance with difficult intubation in OSA patients.
Result:
STOP-BANG score, mandibulohyoid distance (mm) , were higher in the OSA group. OSA patients had a higher incidence of difficult laryngoscopy and intubation.
There was association between STOP-BANG score and mandibulohyoid distance with difficult intubation in OSA patients. AUC (95% CI) ,0.86 (0.74,0.97). In prediction of airway difficulty, for STOP BANG alone, sensitivity and specificity ( 85.71% ,66.7%
respectively), for mandibulohyoid alone , sensitivity and specificity(77.8%, 69.6%
respectively). Combination of STOP-BANG score and mandibulohyoid distance had improved the specificity and sensitivity of the screening tool to predict difficult airway.(77.3% and 84.2% respectively).
Conclusion:
The STOP-BANG score and mandibulohyoid distance proved to be useful in the preoperative diagnosis of difficult laryngoscopy and intubation. The performance of the diagnostic tool improved when combined both STOP-BANG score and mandibulohyoid distance (mm) .OSA patients were more prone to difficult laryngoscopy
20 2.2.2 INTRODUCTION
There is a strong association between difficult intubation and Obstructive Sleep Apnoea (OSA). These are two major problems for anaesthetist, which may contribute to perioperative morbidity and mortality because both are associated with upper airway abnormalities(1) . About 20% of Obstructive Sleep Apnoea patient have difficult intubation according to a retrospective study published in International Anesthesia Research Society(2) .
OSA is a potentially serious sleep disorder in which breathing repeatedly stops and starts during sleep. It has a prevalence of 2% for women and 4% for men in the general population(3). For anaesthetist, the significant feature of OSA is the occurrence of perioperative respiratory adverse events. One of the major concern is the risk of difficult intubation(4) .Even though difficult intubation do not occurs very commonly, poor management of difficult airways account for 35% of all anaesthesia related death(5) .
Previous studies suggested that OSA patients are at higher risk of difficult(2, 6).
Thus the identification of OSA patient during preoperative assessment would prevent adverse events(1). A recent study showed that 69% of the surgical patients had OSA while 60% of the moderate to severe OSA were undiagnosed preoperatively. Therefore, the ASA recommended routine screening of OSA by anaesthetist preoperatively. There are several screening tools for OSA. The STOP BANG questionnaire is the easiest to use and has a proven validity(7) . A score of ≥3 predicts difficult airway(8) .
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So far, there is no single airway test which can provide a high index of sensitivity and specificity for the prediction of difficult airway. A combination of multiple tests produced better predictive result(9) . Radiological methods by using lateral cephalometry (lateral head and neck x ray) may increase the sensitivity and specificity in prediction of difficult airway(10, 11).
2.2.3 METHODOLOGY
After approval obtained from Research Ethics Committee (Human) (JEPeM) of Universiti Sains Malaysia, 41 ASA class I and II patients, aged between 18 to 75 year old, who undergone operation requiring general anaesthesia and fulfil the STOP-BANG score of > 3 were chosen for this study.
A STOP-Bang score of ≥ 3 was chosen as it has a very high sensitivity and high negative predictive value for moderate to severe OSA, and had been suggested as a good cutoff value for high OSA prevalence among surgical populations such as bariatric patients (12).
Patients who were pregnant, not fasted for at least 6 hours, or those with GERD(
gastric oesophageal reflux disease ) were excluded. Written consents were obtained from all the patients before the study.
The patient’s age, gender, ASA status (American Society of Anaesthesiologist classification of physical status, only I to IV), height, weight, BMI (body mass index), thyromental distance, and neck circumference, and modified Mallampati scores were recorded.
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Modified Mallampati Test (Samsoon and Young) divides the visible airway structures into 4 classes:
→ Class I : the fauces, soft palate, the uvula and the anterior and posterior tonsillar pillars are visible.
→ Class II : all the class I structures are visible except for the tonsillar pillars.
→ Class III: only the base of the uvula is visible.
→ Class IV: the uvula cannot be seen and only the soft palate is visible.
After clinical assessment, Lateral Cephalometry (lateral head and neck x-ray) was taken in a neutral head position. Mandibular-hyoid distance was measured. Lateral head and neck x ray was not part of the standard pre-anaesthetics practice before elective surgery, but was taken for measurement of the mandibular hyoid distance in this study.
Patients were well fasted before the operation. No sedative premedication was given. Standard monitoring was applied before induction of anaesthesia. i.e. ECG, non- invasive blood pressure monitoring and a pulse oximeter.
Anaesthesia was performed by a skilled anaesthesiologist who was not the investigator for this study, and the cephalometric measurement and STOP-BANG scores of the patients. After preoxygenation, IV Fentanyl 1.5-2mcg per kg and IV Propofol 1-2mg per kg, were administrated in titration. 0.9 mg/kg IV Rocuronium (a muscle relaxant) was given after patient’s loss of consciousness. When the state of, paralysis was achieved guided by TOF nerve stimulator, patient’s head was placed in
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the sniffing position to facilitate intubation. Then a size 3 curved laryngoscopy was use to maximize the glottis exposure. Without pressing the thyroid cartilage, the airway was evaluated and graded following Cormack and Lehane’s grading system:
→ Grade I is when the epiglottis and vocal cords are completely exposed.
→ Grade II is when only rear of the vocal cords can be seen.
→ Grade III is when only the epiglottis is exposed.
→ Grade IV is when only the soft palate can be seen.
The patient was subsequently intubated using videolaryngoscope and with appropriate-sized ETT. After intubation, mechanical ventilation was conducted with volume control ventilation, at tidal volume of 8-9ml/kg IBW, rate of 12 breaths per minute. Anaesthesia was maintained with inhalational agent Sevoflurane with the MAC of 1. After operation, all patients were reversed using Sugammadex.
The Statistical Package for the Social Sciences (SPSS) version 22 software (with valid license for the institution) was used for data entry and analysis. Group A for whom the intubation is easy, is limited to the patients with a Cormack Lehance grade of 1 and 2 Group B for whom the intubation is difficult would comprise of patients given a Cormack Lehance grade of 3 and grade 4. All of the values are shown as mean ± SDs and as percentages. Independent sample t-test , cross-tabulation and chi square test were used to compare the two groups. A comprehensive evaluation is done by binary logistic regression analysis and a multivariate test to see the effects of each independent variable on the dependent variables.P<0.05 is considered statistically significant.
24 2.2.4 RESULT
We evaluated 41 patients, participants characteristics were evenly distributed, 22(53.7%) are females and 19(46.3%) are males. Difficult laryngoscopy was observed in 21 of 41 patients. STOP-BANGs score , mandibulohyoid distance , age, BMI, neck circumference, Mallampati, height, weight, submandibular angle and mandibular angle were checked for normality by using histogram, all are approximately to normal distribution.
The incidence of difficult intubation was 51.22% for patient at risk of OSA. The distribution of participants based on Cormack-Lehane grading system was shown in table 5.7 , 13 participants(31.75) were graded Class I, 7 participants(17.1%) in Class II, 16 participants (39%) in Class III and only 5 participants(12.2%) has Class IV laryngeal view. Cormach –Lehane class III and classes IV were considered difficult laryngoscopy.
By using STOP-BANG score model alone, out of 41 participants, 14 (34.2%) participants were forecasted to be difficult and 27 (65.9%) participants were deemed easy. The area under the curve covered was 0.81 (0.68,0.95), AUC(95%CI) as shown in figure 5.3. Tables 5.4 showed the diagnostic values of STOP BANG score, sensitivity was 85.7% and specificity was 66.7%. Positive likelihood ratio from the study was only 2.57 with a false positive rate of 33.4%. The false negative rate was in this study was as much as 14.3%. Accuracy was only 73.2%. The diagnostic odd ratio was marginally adequate at 3.46.
By using Mandibulohyoid distance (mm) model alone, out of the total 41 participants18 (43.9%) participants were forecasted to be difficult and 23 (56.1%)
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participants were deemed easy. The area under the curve covered 0.79 (0.64,0.94) ,AUC(95% CI) as shown in figure 5.5. Tables 5.6 showed the diagnostic values of mandibulohyoid distance (mm), sensitivity was 77.8% and specificity was 69.6%.
Positive likelihood ratio from the study was only 2.56 with a false positive rate of 22.2%. The false negative rate was in this study was as much as 30.4%. Accuracy was only 73.2%. The diagnostic odd ratio was marginally adequate at 1.26.
When combined STOP-BANG score and Mandibulohyoid distance (mm) model was used, Out of the total 41 participants 19 (46.3%) participants were forecasted to be difficult and 22 (53.7%) participants were deemed easy. The area under the curve covered was 0.86 (0.74,0.97) ,AUC(95%CI) as shown in figure 5.7. Table 5.7 showed the diagnostic values of STOP BANG score and mandibulohyoid distance (mm), sensitivity was 84.2% and specificity was 77.3%. Positive likelihood ratio from the study was only 3.71 with a false positive rate of 15.8%. The false negative rate was in this study was as much as 22.7%. Accuracy was only 80.5%.
A simple logistic regression analysis was done on patient characteristics to look for their association with difficulty laryngoscopy. The results were shown on table 5.13.
The BMI, weight, neck circumference, mallampati score had significant association with difficult laryngoscopy. The age, height and gender were not a significant predictor for difficulties of laryngoscopy.
By using Independent t test, Table 5.3 showed that Mandibulohyoid distance was significant larger in difficult laryngoscopy group ( 25.60+/- 5.46 mm) as compared to easy laryngoscopy group (19.95+/- 4.28 mm ) , p value = 0.001. STOP-BANG score
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was also statistically higher in difficult laryngoscopy group(5.76+/- 1.14) compare to easy laryngoscopy group(4.40+/- 0.94 ), p value = <0.001.
Associated factors of difficult laryngoscopy by univariable and multiple logistic regression models were showed in Table 5.9. Similar analyses were done on participant’s characteristics to evaluate their association with STOP BANG score and Mandibulohyoid distance. None of them were found to be confounding factors. STOP BANG score and mandibulohyoid distance were likely to be independent factor to difficult laryngoscopy.
Correlation between STOP-BANG score and mandibulohyoid distance (mm) was tested using Pearson correlation test (r = 0.421 with p value= 0.006.)
27 2.2.5 DISCUSSION
Our aim of the study was to develop more predictive models for difficulty in laryngoscopic intubation in patient at risk of obstructive sleep apnoea (OSA). Many assessment criteria had been incorporated, but do not consistently produce accurate evaluation of the risk of failed intubation (13, 14). Direct laryngoscopy is the gold standard for tracheal intubation. There is no single definition of difficult intubation.
Difficult glottic view on direct laryngoscopy is the most common cause of difficult intubation. Therefore our study outcome was based on difficult laryngoscopy with vocal cord visualization.
Our study major findings were STOP-BANGs score alone had a good sensitivity, and accuracy to predict difficult airway. However, with combined STOP- BANG score and mandibulohyoid distance (mm), the overall diagnostic performance had improved.
The study found that age, height and gender did not show significant differences between the easy laryngoscopy and difficult laryngoscopy group. On the other hand, BMI and weight had shown to have significant differences between the easy laryngoscopy and difficult laryngoscopy groups, these were correlating with the previous study(2) . Mallampati classification has been reported to be a good predictor by many but found to be of limited value by others (15-19). An important factor in achieving a reliable score for Mallampati classification is ensuring that the patient opens the mouth and protrudes the tongue maximally. Failure to do this is a major pitfall when
28
performing the assessment. Mallampati class may be affected if the patient inadvertently phonates during the assessment(20). Our study findings’ where mallampati had significant value in predicting difficult laryngoscopy, also consistent with findings shown in study done in 13380 obstetric patients (21). A recorded mallampati score and score > 1 was still a significant independent predictor for difficult airway in obstetric population(22) .However, Modified Mallampati score was inadequate as a stand-alone test of difficult laryngoscopy or tracheal intubation(23, 24) .Neck circumference had great influence in laryngoscopy, the greater it is , the higher the score by Cormack Lehane classification(14) . This finding was comparable to our study result.
We also found that the diagnostic performance of combined model was characteristically better than STOP BANG score model alone and Mandibulohyoid distance (mm) alone. It showed that specificity and sensitivity of each test is not perfect, but when we used these tests together, specificity and sensitivity will increase (24).
The STOP-BANG questionnaire appears to promise a good diagnostic performance in predicting difficult laryngoscopy. In the study, it showed high sensitivity and high accuracy and reasonable specificity. STOP-BANG questionnaire is quite easy to use, very cost effective. The severity of OSA increases linearly as the score increases from 3 to 8(12) . Our study findings were consistent with this. From practical point of view, we were actually killing two birds with one stone, by using the STOP-BANG questionnaire; we were detecting OSA and predicting possibility of difficult laryngoscopy .False positive rate was slight higher and the positive likelihood
29
ration is slightly lower. To improve the quality of it diagnostic performance, we decided to combine another parameter with diagnostic value.
Cephalometry has provided us substantial insight into the pathophysiology of OSA, identifying the most significant craniofacial characteristics associated with this disease. The increased in Mandibulohyoid distance (mm) was found to be significantly associated with large neck circumference and therefore OSA. Studies on lateral cephalometry on OSA patient showed that, there was association between changes of mandibulohyoid distance (mm) with difficult laryngoscopy and tracheal intubation. It showed that increased in mandibulohyoid distance in OSA patient has increased risk of difficult laryngoscopy(10) .Therefore, we decided to combine STOP BANG score and Mandibulohyoid distance to form a screening tool The finding was, the sensitivity remained relatively unchanged i.e. >80%. However, there was a significant improvement in specificity as much as 10 %. Accuracy had increased as much as 7% to 80.5%. Nevertheless, the positive likelihood ratio, had increased from 2.5 to 3.7. The positive predictive value had increased from 57% to 79%, whereas the negative predictive value remained static. There was also reduction in false positive rate about 50% from the initial value (33% to 15%). Overall, the diagnostic performance of the new model which combined STOP BANG score and MHD (mm) had improved compared to STOP BANG score alone.
The measurement of the radiographic parameters are electronically done, it does not depend on the skill of assessor thus preventing inter assessor variability. Our experience noted the mandibulohyoid distance (mm) was easily measured electronically
30
on a computerized radiographic system such as the picture archiving and communicating system (PACS) used in this institution. Results were accurate and could easily be retrieved for re-examination. In addition, a single cephalometry has the benefits of revealing other radiographic parameters.
The mandibulohyoid distance technique, however, is limited by the need of the lateral cephalometry. Risk of additional ionizing radiation is always a consideration.
According to the biological Effects of Ionizing radiation Committee VII (BEIR VII) reports, the risk of cancer death is 0.8% per rem doses of radiation received acutely and 0.04% per rem for doses received over a long period. The amount of radiation from a lateral cephalometry is 1.1 to 1.7 mSV(25) . Since 1 rem equals to 10mSV, therefore the risk of developing a fatal cancer from a single exposure from lateral cephalometry is only very minimal. Clearly the benefits of a single exposure of cephalometry with the aim of assessing ease of laryngoscopy outweighed the risk, given the risk of death from difficult airway management was as high as 40%.
In this study there were some limitations, Cormach Lehance grading system as outcome measure may not be as accurate as other classification system such as ASA Intubation Difficult score, repeated Intubation Attempt, Cook’s grading system. The grading system is operator dependent. Difficult mask ventilation was not assessed in our study, and yet it is part of the predictor of difficult intubation. The present study only involved patients who were at risk of obstructive sleep apnoea, therefore, the predictive value of difficult airway may not be practical in general population. The sample size of 41 candidates was a bit small, a larger population study is vital to validate results. This
31
study, attempts to direct the course of a larger work, and also hopes to fill the lacunae which currently exist where airway management in HUSM Operation room is concerned. Factors such as duration of laryngoscopy attempts, the number, and seniority of airway managers involved, though described as markers of difficult intubation, have not been included in this study because of their many confounding factors. These may, however be assessed in further studies. The study was conducted in an institution with patients who are mainly Asian. This group of patients are known to have higher incidence of difficult laryngoscopy. Therefore, it may not representative of other population worldwide .In order to obtain a diagnosis of OSA and Apnoea- hypopnoea index, sleep study must be performed prior to operation for all the participants. STOP- BANG score may not be as accurate as sleep study as the indicators of severity of obstructive sleep apnoea. STOP-BANG score may not discriminate those patients in whom difficult laryngoscopy is caused by limited head and neck mobility in the OSA patients. This cannot be detected using both STOP-BANG score and mandibulohyoid distance.
2.2.7 CONCLUSION
Mandibulohyoid distance and STOP-BANG score have significant association in predicting of difficult laryngoscopy.
A conclusion could be drawn that the combined STOP-BANG score and Mandibulohyoid distance (mm) can improved the overall diagnostic performance of the model to predict difficult laryngoscopy. This model had high sensitivity, higher specificity, higher accuracy, higher positive predictive value and negative predictive
32
value, higher positive likelihood ratio, and lower false positive rate when compared to STOP-BANG score alone as a screening model.
The technique provides relatively easy, reproducible and objective judgement that assessor can safely trust in order to make decision on patient’s ease of laryngoscopy.
The technique is limited only by the need of a lateral cephalometry, which subject patient to additional ionizing radiation but the benefits of a conclusive test as such may outweigh the risk that was evidently found to be low.
This study confirmed that incidence of difficult laryngoscopy in OSA patients is not negligible and suggest the use combined STOP-BANG score and mandibulohyoid distance (mm) as a predictive score to improve patient safety.
.
33 2.2.7 FIGURE FOR MANUSCRIPT
The Cormack-Lehane Classification
Class I =
Visualization of the entire laryngeal aperture
Class II =
Visualization of parts of the laryngeal aperture or the arytenoids
Class III =
No part of the glottis can be seen except the epiglottis
Class IV =
Not even the epiglottis can be seen
Figure 1 The Cormack-Lehane Classification
34
Modified Mallampati Classification
Class I =
soft palate, fauces, uvula and pillars seen
Class II =
soft palate, fauces, and uvula seen
Class III =
soft palate and base of uvula seen
Class IV =
soft palate not visible
Figure 2 The Modified Mallampati Classification
35
Figure 3 The diagram of Lateral Cephalometry, MPH (Mandibulohyoid distance in mm)
36
Figure 4 The Lateral Cephalometry, MPH (Mandibulohyoid distance in mm) arrow.
37 Figure 5.1. Enrolment stages of participants
Participants recruited (n=41)
Participants assessed for eligibility
Preoperative evaluation (n=41)
Inclusion and exclusion criteria
Laryngoscopy (n=41)
Withdrawn prior to laryngoscopy(n=0)
Withdrawn after laryngoscopy(n=0) Included in data analysis
(n=41)
38
Figure 5.2 Ease of laryngoscopy as predicted by STOP-BANG score (n=41) Easy
Laryngoscopy 65.9% (n=27)
Difficult Laryngoscopy
34.2% (n=14)
39
Figure 5.3 Receiver operating characteristic curve of STOP-BANG score (n=41)
40
Figure 5.4 Ease of laryngoscopy as predicted by mandibulohyoid distance(mm) (n=41) Easy
Laryngoscopy 56.1% (n=23) Difficult
Laryngoscopy 43.9% (n=18)
41
Figure 5.5 Receiver operating characteristic curve of mandibulohyoid distance(mm) (n=41)
42
Figure 5.6 Ease of laryngoscopy as predicted by STOP BANG score and mandibulohyoid distance(mm) (n=41)
Easy Laryngoscopy
53.7% (n=22) Difficult
Laryngoscopy 46.3% (n=19)
43
Figure 5.7 Receiver operating characteristic curve of STOP-BANG score and mandibulohyoid distance(mm). (n=41)
44
Figure 5.8 The proportion of participants with difficult and easy laryngoscopy based on Cormack-Lehane grading system (n=41)
Easy Laryngoscopy 48.78% (n=20) Difficult
Laryngoscopy 51.22% (n=21)
45 2.2.8 TABLES FOR MANUSCRIPT
Table 5.0 The mean age , BMI, neck circumference, mallampati score, height, weight of the patients, and distribution of gender, prevalence of difficult laryngoscopy.
Mean (SD)
Age (years) 49.59(13.32)
BMI(kg/m2) 33.04(6.23)
Neck circumference(cm) 44.37(4.71)
Mallampati 2.24(0.54)
Height (cm) 159.10(7.92)
Weight (kg) 83.66(16.28)
Gender n(%)
Female 22(53.66%)
Male 19(46.34%)
Easy laryngoscopy n(%)
Difficult laryngoscopy n(%)
Incidence 19(48.8%) 21(51.2%)
46
Table 5.1 :Comparison between Easy laryngoscopy and Difficult laryngoscopy among participant’s age, BMI, neck circumference, mallampati , weight, height.
Variables
Easy laryngoscopy Difficult larygoscopy
t-value df p-value
Mean (SD) Mean ( SD)
Age (years) 51.65(12.96) 47.62(13.67) 0.968 (39) 0.339 BMI(kg/m2) 30.15(5.51) 35.78(5.71) -3.209 (39) 0.003 Neck
circumference(cm)
42.20(2.61) 46.43(5.35) -3.289 (39) 0.003
Mallampati 2.05(0.22) 2.43(0.68) -2.382 (39) 0.022
Weight (kg) 76.19(12.81) 90.79(16.27) -3.182 (39) 0.003 Height (cm) 159.25(8.44) 158.95(7.59) 0.119 (39) 0.906
Table 5.2 Association between difficulties of laryngoscopy and gender.
variable
Easy laryngoscopy Difficult laryngoscopy
n(%) n(%)
Female Male
11(50.0%) 9(47.4%)
11(50.0%) 10(52.6%)
value df p value
Pearson’s chi square
0.028 (1) 0.867
47
Table 5.3 Comparison between easy laryngoscopy and difficult laryngoscopy among STOP –BANG score and Mandibulohyoid distance
Variables
Easy
Laryngoscopy
Difficult laryngoscopy
t value df p value Mean (SD) Mean ( SD)
Mandibular hyoid distance(mm)
19.95(4.28) 25.60(5.46) -3.676 (39) 0.001 STOPBANG
score
4.40(0.94) 5.76(1.14) -4.170 (39) <0.001
Table 5.4 Diagnostic values of STOP-BANG score (n=41)
Ease of Laryngoscopy*
Difficult Easy
Prediction of Laryngoscopy
Difficult 12 9
Easy 2 18
*Based on Cormack-Lehane Classification
Se (%)
Sp (%)
PPV (%)
NPV (%)
LR+ LR- FPR (%)
FNR
(%) Accuracy (%)
Prevalence
(%) OR
85.7 66.7 57.1 90.0 2.57 0.21 33.4 14.3 73.2 34.1 3.46 Se = Sensitivity, Sp = Specificity, PPV = Positive Predictive Value, NPV = Negative Predictive Value, LR+ = Positive Likelihood Ratio, LR- = Negative Likelihood Ratio, FPR = False Positive Rate, FNR = False Negative Rate, OR = Odd Ratio
48
Table 5.5 Area under the curve of ROC curve for STOP-BANG score (n=41)
AUC (95% CI)
STOP BANG score on Cormack-
Lehane Grading (Gold-standard) 0.81 (0.68,0.95)
Table 5.6 Diagnostic values of mandibulohyoid distance(mm) (n=41) Ease of Laryngoscopy*
Difficult Easy
Prediction of Laryngoscopy
Difficult 14 4
Easy 7 16
*Based on Cormack-Lehane Classification
Se (%)
Sp (%)
PPV (%)
NPV (%)
LR+ LR- FPR (%)
FNR
(%) Accuracy (%)
Prevalence
(%) OR
77.8 69.6 66.7 80.0 2.56 0.32 22.2 30.4 73.2 43.9 1.26
Se = Sensitivity, Sp = Specificity, PPV = Positive Predictive Value, NPV = Negative Predictive Value, LR+ = Positive Likelihood Ratio, LR- = Negative Likelihood Ratio, FPR = False Positive Rate, FNR = False Negative Rate, OR = Odd Ratio
49
Table 5.7 Area under the curve of ROC curve for mandibulohyoid distance(mm) (n=41)
AUC (95% CI)
Mandibulohyoid distance(mm) on Cormack-Lehane Grading (Gold- standard)
0.79 (0.64,0.94)
Table 5.8 Diagnostic values of STOP-BANG score and mandibulohyoid distance(mm) (n=41)
Ease of Laryngoscopy*
Difficult Easy
Prediction of Laryngoscopy
Difficult 16 3
Easy 5 17
*Based on Cormack-Lehane Classification
Se (%)
Sp (%)
PPV (%)
NPV (%)
LR+ LR- FPR (%)
FNR
(%) Accuracy (%)
Prevalence (%) 84.2 77.3 79.2 85.0 3.71 0.20 15.8 22.7 80.5 46.3
Se = Sensitivity, Sp = Specificity, PPV = Positive Predictive Value, NPV = Negative Predictive Value, LR+ = Positive Likelihood Ratio, LR- = Negative Likelihood Ratio, FPR = False Positive Rate, FNR = False Negative Rate.
50
Table 5.9 Area under the curve of ROC curve for STOP-BANG score and mandibulohyoid distance(mm). (n=41)
AUC (95% CI)
STOP-BANG score and
Mandibulohyoid distance(mm) on Cormack-Lehane Grading (Gold- standard)
0.86 (0.74,0.97)
51
Table 5.10: Associated factors of difficult laryngoscopy by univariable and multiple logistic regression model
Table 5.11 Predictive parameters for the mandibulohyoid distance(mm), STOP-BANG score and combined STOP-BANG score and mandibulohyoid distance(mm).
Mandibular hyoid distance(mm)
STOP-BANG score
Combined STOP- BANG score and Mandibulohyoid distance (mm)
Sensitivity 77.8% 85.71% 84.2%
Specificity 69.6% 66.7% 77.3%
Prevalence 43.9% 34.1% 46.34%
Positive predictive value
66.7% 57.1% 79.2%
Negative
predictive value
80.0% 90.0% 85.0%
False positive rate 22.2% 33.4% 15.8%
False negative rate 30.4% 14.28% 22.7%
Positive likelihood ratio
2.56 2.57 3.71
Negative likelihood ratio
0.32 0.21 0.20
accuracy 73.2% 73.2% 80.5%
variable
Simple Logistic Regression
Multiple Logistic Regression Crude
OR(95%CI)
p Adjusted
OR(95%CI)
p Mandibular hyoid
distance(mm) STOP-BANG score
1.26(1.08,1.46) 0.003 1.19(1.00,1.40) 0.048
3.46(1.54,7.79) 0.003 2.65(1.18-5.95) 0.018
52
Table 5.12 Distribution of laryngeal view based on Cormack-Lehane classification (n=41)
Cormack-Lehane Grading
System Frequency Proportion (%)
Class I 13 31.7
Class II 7 17.1
Class III 16 39.0
Class IV 5 12.2
Class I and II considered easy laryngoscopy
Class III and class IV considered difficult laryngoscopy
Table 5.13 Participants characteristics and odds of difficult laryngoscopy (n=41)
Variable Regression coefficient(b)
Crude odds ratio(95%CI)
Wald statistic
p-value
Age (years) -0.02 0.98(0.93,1.03) 0.94 0.332
BMI(kg/m2) 0.19 1.21(1.05,1.38) 6.95 0.008
Weight (kg) 0.07 1.08(1.02,1.14) 6.64 0.010
Height (cm) -0.01 1.00(0.92,1.08) 0.02 0.903
Neck
circumference(cm)
0.27 1.31(1.06,1.62) 6.36 0.012
Mallampati score 1.70 1.26(1.08,1.46) 8.53 0.003
Gender
Woman 0 1
Man 0.11 1.11(0.33,3.80) 0.03 0.887
53 2.2.9 REFERENCES FOR MANUSCRIPT
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57
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