Evidence-based practice paper

Evidence-based practice paper Critique of a research article related to physical assessment/preoperative evaluation in anesthesia: Comparison of Mallampati test with lower jaw protrusion Margin, font, and page specification: 3 pages, 12-point font, 1” margins, double spacing, APA format Introduction •    the topic of the article clearly and concisely introduced •    the introduction include a clear and concise summary statement •    the information should forecast the remainder of the article critique for the reader Body of the paper •    Provide a brief synopsis of the article and provide a critical summary of the research drawn upon •     What is the study problem? What is the study purpose? •    Synthesize the material reviewed into a few main points •    Provide excellent background, context and idea development •    What are the study design, results, and conclusions •    Critique the strengths and weaknesses of the article •    What are the limitations of the study, if they are identified by the researcher •     Discussion regarding implications for anesthesia practice •    What suggestions are made for further studies? Conclusion (a brief summary of what has been discussed) References Journal of Anaesthesiology Clinical Pharmacology | July-September 2013 | Vol 29 | Issue 3 313 Background: Failure to maintain a patent airway is one of the commonest causes of anesthesia -related morbidity and mortality. Many protocols, algorithms, and different combinations of tested methods for airway assessment have been developed to predict difficult laryngoscopy and intubation. The reported incidence of a difficult intubation varies from 1.5% to 13%. The objective of this study was to compare Mallampati test   (MT) with lower jaw protrusion   (LJP) maneuver in predicting difficult laryngoscopy and intubation. Materials and Methods: Seven hundred and sixty patients were included in the study. All the patients underwent MT and LJP maneuver for their airway assessment. After a standardized technique of induction of anesthesia, primary anesthetist performed laryngoscopy and graded it according to the grades described by Cormack and Lehane. Sensitivity, specificity, accuracy, and positive predictive value   (PPV) and negative predictive value   (NPV) were calculated for both these tests with 95% confidence interval   (CI) using conventional laryngoscopy as gold standard. Area under curve was also calculated for both, MT and LJP maneuver. A P < 0.05 was taken as significant. Results: LJP maneuver had higher sensitivity  (95.9% vs. 27.1%), NPV   (98.7% vs. 82.0%), and accuracy   (90.1% vs. 80.3%) when compared to MT in predicting difficult laryngoscopy and intubation. Both tests, however, had similar specificity and PPV. There was marked difference in the positive and negative likelihood ratio between LJP and MT. Similarly, the area under the curve favored LJP maneuver over MT. Conclusion: The results of this study show that LJP maneuver is a better test to predict difficult laryngoscopy and tracheal intubation. We recommend the addition of this maneuver to the routine preoperative evaluation of airway. Key words:  Airway, difficult intubation, lower jaw protrusion maneuver, Mallampati test Comparison of Mallampati test with lower jaw protrusion maneuver in predicting difficult laryngoscopy and intubation Muhammad Irfan Ul Haq, Hameed Ullah Department    of     Anesthesiology,     Aga    Khan    University     Hospital,    Stadium    Road,    Karachi,    Pakistan Address for correspondence:  Dr.  Muhammad Irfan Ul Haq, Department of Anesthesiology, Aga Khan University Hospital, Stadium Road, PO Box 3500, Karachi 74800, Pakistan. E‑mail:  [email protected] Introduction Unanticipated difficult laryngoscopy and tracheal intubation always remain a primary concern for the anesthesiologist, as the failure to maintain a patent airway after the induction of general anesthesia is one of the most common cause of anesthesia -related morbidity and mortality. [1] Difficult laryngoscopy and tracheal intubation can cause soft -tissue damage, [2,3] bronchial intubation, laryngospasm, bronchospasm, inability to ventilate or intubate, hypoxic brain injury, and even death. [1,4,5] The reported incidence of a difficult laryngoscopy and tracheal intubation varies     from      1.5%     to      13%      in      patients      undergoing     elective surgery. [6] Because of potentially serious consequences of failed tracheal intubation, considerable attention has been focused on attempts to predict patients in whom laryngoscopy and intubation might be difficult, [5,7] and in this regard combination of different test and scores are developed, but none of them have proven to be totally reliable. [5,8,9] Although difficult intubation is defined in a number of ways, but visualization obtained during laryngoscopy remains the mainstay of definition. [10] Cormack and Lehane defined the grade of laryngoscopic view and they are widely used to label the difficulty of tracheal intubation. [11,12] Modified Mallampati test [13] (MT) is the most widely used tool in the armamentarium of an anesthesiologist for the assessment and prediction of difficult airway. The pitfalls associated with this MT are its low sensitivity [14,15] and poor interobserver reliability. [7,9,16] Abstract Access this article online Quick Response Code: Website: www.joacp.org DOI: 10.4103/0970-9185.117059 Original Article Haq and Ullah: Comparison of mallampati with lower jaw protrusion 314 Journal of Anaesthesiology Clinical Pharmacology | July-September 2013 | Vol 29 | Issue 3 Lower jaw protrusion  (LJP) maneuver is a well -established simple bedside maneuver for predicting difficult airways in number of studies. It has a relatively simple grading system in which patients were graded depending on the extent to which they could translate their temporo -mandibular joint to approximate their superior to inferior incisors. [17 -19] Although the importance of jaw thrust during laryngoscopy has been described    some     100    years     back, [20] there are number of studies published in the last decade recommending the addition of LJP maneuver in the routine evaluation of airway examination. The objective of our study was to compare the sensitivity and specificity of MT with LJP maneuver in predicting difficult laryngoscopy and tracheal intubation using Cormack and Lehane’s criteria of intubation as the gold standard. Materials and Methods After obtaining approval from Ethics Review Committee of the hospital     (reference     number     703-Ane/ERC -07)    and    obtaining informed     consent,     760    patients     were     enrolled     in     the    prospective observational study, which was conducted at preoperative clinic, preoperative waiting area, and operating rooms of a tertiary care     hospital.    ASA    I-III     patients     aged     above    18    years     of     either sex who were scheduled for elective surgeries under general anesthesia requiring tracheal intubation were included in the study. Patients who were bed bound, edentulous, having oral pathology,      obesity      [body     mass      index      (BMI)      >     28     Kg/m 2 ], previous history of difficult intubations, Glasgow Coma Scale (GCS)     14    or     below,    those     undergoing    obstetric    or     emergency procedures, and those who refused consent were excluded from the study. Patient’s airway was assessed by the principal investigator at either of the above -mentioned areas. Cormack and Lehane’s criteria of laryngoscopy were taken as gold standard and MT and LJP maneuvers as under study methods. The MT was performed with the patient in the sitting position, head neutral, mouth wide open, tongue protruded to its maximum, and patient not phonating. Classification was assigned into one     of      the     four      grades     [Table      1].     Out     of      the     four      grades     of modified MT, grades I and II were considered as predictors of “Easy” laryngoscopy and intubation, while grades III and IV as predictors of “Difficult” laryngoscopy and tracheal intubation. The LJP maneuver was performed by asking the patient to protrude his or her lower jaw as much as possible beyond the upper jaw. Patient was then assigned to one of the three grades of mandibular protrusion [16] [Table     2].    LJP grade A was considered as predictor of “Easy” and grade  B and C as predictors of “Difficult” laryngoscopy and tracheal intubation. Cormack and Lehane’s classification of difficult intubation was also classified as “Easy”  (grades I and II) or “Difficult”   (grades III and IV). All this information was recorded in a prescribed proforma. Biometric patient data including age, sex, weight, height, BMI, ASA status, and surgical specialty was also noted. Patient was then transferred to operating room and head ring was placed below the head with routine monitors [Electrocardiography (ECG), Non Invasive Blood Pressure (NIBP), Pulse Oximetry (SpO 2 )]      were      applied. After obtaining baseline readings, an intravenous access was maintained with Lactated Ringer’s solution. Patient was preoxygenated     with     100%     oxygen      for     3      min.     Anesthesia was     induced      with     fentanyl      2     µg/kg,      propofol     2     mg/kg,     and atracurium     0.5    mg/kg.    Patients’    were     then     manually    ventilated for 3   min using circle system; during this period, anesthesia was    maintained    with    50%     N 2 O in O 2 and    isoflurane     (≤0.5-1%).     An    anesthetist     with    an     experience     of     more     than     2    years, blinded to the result of LJP maneuver, was asked to perform laryngoscopy and intubation. This was graded according to Cormack and Lehane’s criteria and was documented on a separate form along with the duration of laryngoscopy and number of attempts to successful tracheal intubation. For laryngoscopy, Macintosh blade of size 3 was used, while tracheal intubation was done using polyvinylchloride orotracheal     tube      of      size      7-mm     ID     and     8-mm     ID     for     females and males, respectively. Sample     size     was    calculated     in     order     to     obtain    a    power    of     80% and    level     of     significance    of     5%    using     area     under    curve     (AUC) between     0.55      to      0.90      and     a     difference      of      0.1     in      the     area considering     the     difficulty     of      10%.     All     the     relevant      data      were analyzed     by      using      SPSS     version      14.0.     Percentages     were generated for qualitative variable like gender and compared by Chi-square test. For quantitative variables like age, height, weight, and gender, mean and standard deviation were computed and compared by using t-test. Sensitivity, specificity, accuracy, and positive and negative predictive values were calculated     for    MT    and    LJP    maneuver    with    95%     confidence Table  1: Modified Mallampati test [5,6] Grade I Visualization of the soft palate, fauces; uvula, anterior and the posterior pillars Grade II Visualization of the soft palate, fauces and uvula Grade III Visualization of soft palate and base of uvula Grade IV Only hard palate is visible. Soft palate is not visible at all Table  2: Lower jaw protrusion maneuver [16] Grade A Lower incisors can be brought anterior to the upper incisors Grade B Lower incisors can only be protruded edge to edge with upper incisors Grade C Lower incisors cannot be protruded edge to edge with upper incisors Haq and Ullah: Comparison of mallampati with lower jaw protrusion Journal of Anaesthesiology Clinical Pharmacology | July-September 2013 | Vol 29 | Issue 3 315 interval  (CI) using laryngoscopic view as gold standard. AUC was also computed by receiving operative curve  (ROC). A P    <    0.05     was    taken     as     significant. Results Seven hundred and sixty patients were enrolled and completed the study. There was a predominance of female participant     (55.5%     vs.     44.5%).    The    mean     values    of     weight, height, and BMI of study patients were within normal range with no significant effect on airway examination. Other biometric details are shown in Table 3. More     than     90%     of     participants     had    an     “Easy”     grade     of     Mallampati, while     nearly    9%    have     a    “Difficult”     Mallampati    grade.    Similarly, 69.6%     of      the     patients      enrolled      in      the     study      had     “Easy”      grade of     LJP    test    and    30.4%    patients     as     “Difficult”     grade     [Table    4]. There was no grade IV intubation. The mean intubation time in     our    study     was    21.08    ±    7.57     s. When the “Easy” grades of Mallampati were compared with Cormack    and    Lehane’s    grades,     there     were     17.9%     participants who have actually difficult laryngoscopic grades, i.e.,  grades III     and    IV    of     Cormack    and    Lehane,    while     out    of     71    patients that were predicted by MT as having difficult grades of laryngoscopy     and    intubation,     only     32.2%     found    to     have     easy grade    of     Cormack    and    Lehane     [Table     4]. Similarly, when “Easy” grades of LJP were compared with Cormack     and     Lehane’s     grades      of      intubation,     only      1.3% were found to have difficult grades of intubation, while out of 231     patients      that      were      predicted     to      have      difficult      intubation grades,     nearly    29.4%    of     patients     were     actually     found    to     have     easy grade according to Cormack and Lehane, as shown in Table 4. Statistical measures used to describe the predictive values for LJP maneuver and MT in predicting difficult intubations are shown     in     Table    5. Using     McNemar’s     test      and     with     a      95%      CI,     statistically significant differences were observed between these two predictive tests  ( P      <      0.05)     showing     higher      level      of sensitivity     (95.9%)    and    accuracy    (90.1%)    for    LJP    maneuver than     MT,    which    has    a    sensitivity     and    accuracy    of     27.1%     and 80.3%,     respectively. Discussion Prediction of difficult laryngoscopy and tracheal intubation has been the primary focus of many research papers and many time tested methods have been developed to avoid difficult intubation and its related complications. [6,13] Problems with tracheal intubation can range from minor complications as mild soft-tissue damage, transient, and uncomplicated hypoxia to more severe effects leading to severe airway damage [5] to hypoxic brain injury and death. [1,4,5] Because of these potentially serious consequences of failed tracheal intubation, considerable attention has been focused on attempts to predict patients in whom laryngoscopy and intubation will be difficult. [15-19] Difficult intubation is defined in a number of ways, but an unanticipated poor laryngoscopic view is mainstay of definition. [10] Although many advances have been made and many time -tested methods, for example MT, sternomental distance, interincisor gap, upper lip bite test, thyromental distance alone or in combination, have been used to overcome the conundrum of an unanticipated difficult laryngoscopy and tracheal intubation but none of them are totally reliable. [8,9,14] Objective of our study was to compare the sensitivity and specificity of MT with LJP maneuver in predicting difficult Table  3: Demographic and anesthetic observations of the patients ( n=760) Variables Overall statistics Cormack and Lehane’s P values Easy (I and II) n=590 Difficult (III and IV) n=170 Age  (years) 43.44±14.93 40.97±14.22 52.03±14.18 0.0005 Weight (kg) 65.04±10.74 65.04±10.94 65.06±10.03 0.98 Height  (cm) 163.01±8.69 163.40±8.73 161.63±8.44 0.019 BMI  (kg/m 2 ) 24.38±2.86 24.26±2.91 24.81±2.63 0.025 Duration of laryngoscopy  (min) 21.08±7.57 17.73±4.11 32.69±4.83 0.0005 Gender † (%) Male 338  (44.5) 268  (45.4) 70 (41.2) 0.326 Female 422  (55.5) 322  (54.6) 100  (58.8) Number of attempts † (%) 1 705  (92.8) 586  (99.3) 119  (70) 0.0005 2 53 (7) 4 (0.7) 49 (28.8) 3 02 (0.3) 0 (0) 2 (1.2) Data are presented as mean±SD or number (%), † Chi‑square test used for qualitative, Independent t ‑test used for quantitative observation, BMI=Body mass index Haq and Ullah: Comparison of mallampati with lower jaw protrusion 316 Journal of Anaesthesiology Clinical Pharmacology | July-September 2013 | Vol 29 | Issue 3 laryngoscopy and intubation using Cormack and Lehane’s criteria of intubation as a gold standard. We could not find any study in which MT has been compared with LJP maneuver in nonobstetric and nonobese South Asian population. The reported incidence of a difficult laryngoscopy and endotracheal     intubation     varies    from     1.5%    to     13%     in     patients undergoing surgery. [6] This variation in incidence might be due to different reference standard for difficult intubation among studies which were based on Cormack and Lehane’s intubation grades, number of laryngoscopic attempts, and use of backward upward rightward pressure  maneuver. [6] In      our     study,     we     examined      the     airway      of      760      patients      who required general anesthesia and elective intubation and found the     incidence      of      difficult      intubation      to      be      22.4%,      which     is higher compared to previous studies. The probable reasons for this may be the use of more strict criteria for difficult intubation, as described by intubation grades III and IV of Cormack and Lehane’s grading rather than using only grade   IV as difficult intubation or relying upon Cook’s modification of Cormack and Lehane’s grading. [11] Another reason for this higher incidence could be the avoidance of external pressure during     intubation.      Majority     of      intubations     (82.2%)     in      our study were done by an anesthetist with an experience of more than four years and none by an anesthetist with less than two years experience. Nevertheless, our reported incidence is quite comparable to the one reported by Bergler  et   al. , i.e.,     20.2%. [12] The high incidence of difficult LJP observed in our study can be attributed to the different classification used in our study wherein we collated grade B and grade C as difficult contrary to the classification used by Eberhart  et   al . [9] However if we also translate difficult as per Ebehart et  al ’s classification, the incidence      of      difficult      LJP     in      our     study      would     also      be      8.2% which is very similar to Eberhart et  al . [9] . The    sensitivity     of     MT    in     our    study    is     22.4%     which    is     quite comparable to that demonstrated by Vani  et   al. [14] who found    it     to     be     25%.    Siddiqui    et  al. [21] found the sensitivity of     MT    to     be     higher    (42%)     in     his    study,    while    other     authors have found even higher sensitivities. This shows the wide interobserver variability, an issue which has been confirmed by Hilditch et   al., [7] Eberhart  et   al ., [9] and      Karkouti et   al . [15] who have shown poor interobserver reliability for MT. Sensitivity of LJP maneuver in our study was very high      (95.6%),      which     is      in      contradiction     with      the     work by James  et   al . [17] and Sava et   al . [18] who have found the sensitivity     to     be     14.9%     and    29.4%,     respectively.     This     wide variation can also be attributed to interobserver variability and needs further evaluation. The accuracy of both tests is high and unchanged by their combination, similar to James  et  al . [17] By    assessing    the    AUC,    Table    5,     LJP    comes out to be a better predictor of difficult laryngoscopy and tracheal intubation. The main strength of our study was that the LJP maneuver and MT were performed for the assessment of airway by primary investigator, which reduced the risks of interobserver variation and increased the reliability of the tests. We have not evaluated obstetric patients in our study where the incidence of unanticipated difficult intubation was quite high as compare to general population and as such there is a need to develop a more reliable predictive test in future in that specific specialty. In conclusion, MT is the most commonly used test for the prediction of difficult laryngoscopy and tracheal intubation but with limited accuracy. We, therefore, recommend the addition of LJP maneuver to the routine preoperative evaluation of airway. Table  4: Laryngoscopic view of all patients with respect to Mallampati, LJP and Cormack (n=760) Predictors Cormack and Lehane’s Total (%) Easy Difficult I n=522 II n=68 III n=170 Mallampati I Easy 317 25 43 385  (50.7) II 191 32 81 304  (40) III Difficult 14 10 39 63 (8.3) IV 0 1 7 8 (1.1) Lower jaw protrusion grade A Easy 490 32 7 529  (69.6) B Difficult 32 32 105 169  (22.2) C 0 4 58 62 (8.2) Cormack and Lehane’s grade IV, not observed in patients. TP=46, FP=25, FN=124, TN=565 for Mallampati, TP=163, FP=68, FN=7, TN=522 for LJP Grade, LJP=Lower jaw protrusion Table  5: Predictive values for MMT and LJP and their combinations to predict the difficult laryngoscopy and tracheal intubation Mallampati LJP Sensitivity 27.06% (20.94, 34.19) 95.88% (91.75, 97.99) Specificity 95.76% (93.82, 97.11) 88.47% (85.65, 90.81) PPV 64.79% (53.18, 74.88) 70.56% (64.39, 76.07) NPV 82%  (79.96, 84.69) 98.56% (97.29, 99.36) Accuracy 80.39% (77.42, 83.06) 90.13% (87.81, 92.05) Likelihood ratio  (+) 6.38  (5.26, 7.74) 8.32  (8.08, 8.57) Likelihood ratio  (–) 0.76  (0.74, 0.77) 0.046 (0.035, 0.061) Area under the curve 61.4%  (0.56 to 0.66) 92.2%  (0.89 to 0.95) 95% confidence interval was computed by Wilson method, LJP=Lower jaw protrusion, PPV=Positive predictive value, NPV=Negative predictive value, MMT=Modified mallampati test Haq and Ullah: Comparison of mallampati with lower jaw protrusion Journal of Anaesthesiology Clinical Pharmacology | July-September 2013 | Vol 29 | Issue 3 317 References 1.   Gannon  K. 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Br J Anaesth 1994;73:49-53. 19.  Kheterpal  S, Han   R, Tremper   KK, Shanks   A, Tait   AR, O’Reilly  M. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006;105:885-91. 20.  Defalque  RJ, Wright  AJ. Who invented the “jaw thrust”? Anesthesiology 2003;99:1463-4. 21.  Siddiqui  R, Kazi WA. Predicting difficult intubation, a comparison between Mallampati classification and Wilson Risk -Sum. J  Coll Physician Surg Pak 2005;15:253-6. How to cite this article: Ul Haq MI, Ullah H. Comparison of Mallampati test with lower jaw protrusion maneuver in predicting difficult laryngoscopy and intubation. J Anaesthesiol Clin Pharmacol 2013;29:313-7. Source of Support: Nil, Conflict of Interest: None declared. Staying in touch with the journal 1)   Table of Contents (TOC) email alert Receive an email alert containing the TOC when a new complete issue of the journal is made available online. 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