Airway Management During Cardiopulmonary Resuscitation in Filipinos a New Perspective - Page 109

7/27/2019 Airway Management During Cardiopulmonary Resuscitation in Filipinos a New Perspective - Page 109

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AIRWAY MANAGEMENT DURINGCARDIOPULMONARY RESUSCITATIONIN FILIPINOS: A NEW PERSPECTIVE

Ma. Minerva Patawaran-Calimag. M.D.*Julieta Canlas-Paiarillo, M.D. *

Endotracheal intubation may be a life saving procedure. In fact it remains the method of choice in maintaining an airway in advanced cardiac life support . Indeed, the cuffed tracheal tube has proven i tsel f to be aninvaluable tool during cardiopulmonary resuscitation.In the hands of the inexperienced, however, it can be aharbinger of disaster. The choice of the correct size andtype of tube is only one aspect in the management ofthe compromised airway. The length of the airway isas lmportant in so far as ignorance of this fact can leadto inadvertent endobronchial intubation with consequenthypoxemia. This study therefore aims to establish standards for determining tracheal tube length in Filipinoadults with the use of several anthroprometric data. Afterstudying ninety-eight randomly selected Filipino adults,the following conclusions were reached: I) The average'optimal orotracheal tube length were 22.13 ern,.SD1.02 cm for males and 21.17 em, SD1.74 ern forfemales; 2) There are significant statistical correlationsbetween optimal orotracheal tube length and the considered factors, namely height, cricoid to xiphoid tipdistance and length of the third finger; 3) The maximumsafe length of orotracheal tube in adult Filipinos can bepredicted as follows: Orotracheal tube - cricoid toxiphoid distance minus 2 ern, or three times the lengthof the third fmger minus I em. Nasotracheal tube cricoid to xiphoid tip distance, or three times thelength of the third fmger plus I ern.In the last quarter of the century, advances in thebasic understanding, techniques, teaching and practiceof cardiopulmonary resuscitation have resulted insaving countless lives. Initial measures to establishartificial ventilation and circulation are the same, whether performed by physicians or lay rescuers, andwhether performed in a hospital or in any other locations.In most instances, respiration stops before circulation. Since any other measures will be ineffective inthe absence of pulmonary ventilation, respirationshould always be checked. first.Because of the difficulties, delays and cornplications in the proper placement of an endotracheal tube,its use during cardiopulmonary resuscitation is restric-ted mainly to medical personnel or professional healthpersonnel who are highly trained in the said procedure."Santo Tomas University Hospital. Section of Anesthesia,Division of SurgeryJMMSI Vol. XXII No.4-6 April-8eptember, 1986

Even among the experienced, misconceptions stillabound as to the choice of the proper type, size andlength of the endotracheal tube to use in a given patient.Ignorance of important anatomical considerationscan lead to immediate or delayed complications. TheNational Conference on Cardiopulmonary Resuscitation ani! Cardiac Care (1979)1 in affirming the recommendations set forth by its Steering Committee in

19742 has stated that 8.0-8.5 mm LD. endotrachealtubes be used for women and 8.5-9.0 mm LD. tubes formen. Since then, several foreign authors have shownevidence that the above recommendations are too largein many cases even for Caucastans.' Standards of sub-glottic and tracheal diameters have been set by one ofthe authors in two previous s t u d i e s . 4 ~ The choice ofthe correct size and type of endotracheal tube, however, is only one aspect in the management of thecompromised airway. The length of the airway from theteeth or nose through the mouth, pharynx and finallyinto the trachea has likewise been discussed in foreignl iterature but no mention of it has yet been publishedin the local literature.In an attempt therefore to set standards of endotracheal tube length among Filipinos, this s tudy wasundertaken aimed at estimating the distances from

the base of the nose, or from the upper anterior incisorteeth to just above the carina.The data on Filipino subglottio- and tracheal diameters and their anatomic correlates previously reported4,s will also be reproduced here to point outpossible dimensional interrelationships of the upper

airway. Aside from pure anthropometry, such inform-ation has potential applications to studies in pulrnonary resuscitative physiology and anesthesiology. Ifcertain critical dimensions and their interrelationshipsare known, and further if they can be used as a basisof prediction, many problems in the areas mentionedcan be more precisely defined for study. Of course,there is a certain general interest in the knowledge ofmeasurements of the human body for its own sake.MATERIALS ANDMETHODS'The data for this study were obtained from ninetyeight randomly selected adult patients scheduled foroperation under general anesthesia via the orotrachealor nasotracheal route at the Santo Tomas University

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FIG. I. Number of subjects by gender and age group.

TABLE I. Summary of th e data for Filipino subjects (N '" 981.

so

MEAN AGE - 35.7 vrs.,SO 14.6 VI'S.\ ,\\\

___ males_femalet

D 1 subject

40 00Age (years I

t,o \I 'o \I \

20

4

2

B

'0

"0 B

RESULTSFigure I depicts the number of subjects by genderand age group. The age range was 15 to 78 years with anoverall mean age of 35.7 years, SD14.6 years. A summary of the data and measurements obtained on 98Filipino adults are presented OnTable l.The mean optimal orotracheal tube length were 22.13ems, SD1.02 ems for the male subjects, and 21.17 ems,SD1.74 ems for the female subjects.

males and females separately. Regression lines werederived using the least squares method.P:7To determine what effect advanced age might have onthe observed differences between the distance from thesuperior border of the cricoid cartilage to the ti p of thexiphoid process and the orocarinal distance, data forsubjects aged 50 and below Were compared with thosefrom 51 years old and over. Student's "T" test was used.For all statistical analysis a p value less than 0.0 I was

considered significant.

Number Numt.r., ..Subj""rs Me.., S,D, Subjeo:u "I n S.D.

AgIt tv.. rtl " 36.69 1!d Clnllage10 Xiphoid TipObllnee (em) " 24.15 0.99 ee 22-1ll I 1,32Length 01the 7.73 0.45iddle Finger lem) ea es 7 .40 0.42OptlmelOrotrach.lTw e Llngth (eml .. 22.13 1.02 eo 21.11 1,74OpdmllNlIOtrach...1Tube Length (em) , 26.80 0.11 , 25.32 0.30

Hospital , Clinical Division, from February to March,1985.The study included fifty-two males and forty-sixfemales.All measurements were made with the patient lyingsupine on the operating table with the head in theneutral position. Before in tubation, the followingparameters were determined: height, cricoid to xiphoiddistance and length of the third finger. Measurementswere made to the nearest 0.5 em.Cricoid to xiphoid distance was measured along thebody surface from the superior border of the cricoidcartilage to the tip of the xiphoid process, using ameasuring tape.

Third finger length was measured on the palmarsurface of the hand from the metacarpophalangeal jointcrease to the finger tip.Prior to intuba tion , the endotracheal tube and itscuff were checked for defects. The tube is then lubricated with lidocaine jelly. Patients were preoxygenatedand general anesthesia induced with thiopental sodium,3-5 mgs/kg BW intravenously. After loss of eyelid reflex, 1-2 mgs/kg BW of succinylcholine is administeredto facilitate intubat ion. Intubat ion was then carriedou t with the appropr ia te size of tracheal tube.' Deliberate endobronchial intubation was done after whichthe tube was gradually withdrawn unt il breath soundsare equal in all areas of the lungfields. The cuff is theninflated to minimal occlusive (i.e. that cuff volumewhich is needed to produce an airtight seal betweentrachea and cuff).

The level of the tube was verified further by performing the following maneuvers: I) constant pressure isapplied to the pilot balloon of the inflated cuff by theindex finger and the thumb of one hand, while the otherhand palpates the trachea between the cricothyroidcartilage and the suprasternal notch, where a distinctincrease in pressure could be felt over the inflated cuff;2) injecting one milliliter of sterile saline into the pilotballoon and the balloon compressed and released gentlybetween the fingers and auscultating for the presenceof crepitus over the suprasternal notch at the approximate level of the cuff.These maneuvers indicate that the cuff of the endotracheal tube is located below the vocal cords and severalcentimeters above the carina. Added documentation isacquired in those patients requiring chest x-ray postoperatively, showing the exact position of the tip of theendotracheal tube with the head in neutral posit ion. .Being satisfied with the position of the tube an oralairway is inserted and the tube fixed into position bymeans of adhesive tape. The depth of tube insertion isdetermined by the centimeter markings on the tube atthe level of the upper incisors, or in edentulous patientsat the external surface of the upper gums. The lengthof the tube is then compared with the various anthropometric measurements obtained, i.e, height, thirdfinger length and cricoid cartilage to xiphoid tilldistance.Statistical analysis were done using the Pearsonproduct moment correlation coefficient matrices. Arnatix was computed for the entire popula tion and for110 JMMSI Vol. XXII No. 4-5 April-September. 1986


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FIG. 3. Correlations and regressions of orotraeheal tube lengthwith cricoid cartilage to xiphoid tip distance.

Figure 3 illustrates the opt imal tube length versuscricoid to xiphoid process distance for each of the subjects. The regression line for the entire population(N=84) was expressed by the equat ion Y = O.969X-1.42. The equations Y =O.706X +4.80 and Y=O.994X- 1.84 represented the regression lines for male andfemale subjects, respectively.

2642

REGRESSIONS

Cricoid - Xiphoid O!ltllnce

-- all melesand ferrel" IN 84)males IN -44)- ~ - females IN . 40)

20

o male.o females

18

28

18

24~} 22

..l 20!

Correlative and Predictive Factors of Optimal Endotracheal Tube Length.

Age. Age had a very low correlation with optimaltube length. When data from subjects aged 50 and belowwere compared with data from those aged 50 and overusing the Student's 'T' test, the p value obtained was notsignificant (p value> 0.50).Sex. There was a highly significant level of correlation between sex and optimal orotracheal tube length.Female subjects were shorter and required shortercodertracheal tubes than theirmalecounterparts.Height. The mean height for males was 160 .70 ems,SO5.87 ems (63.27 inches, SO2.3 inches), and forfemales, 155.62 ems, S06.54 ems (61.27 inches,SO2.57 inches) . A significant correlation was foundwhen the optimal tube length was compared with theheight. When broken down by sex however, the correlation was better for males than for females.Third "Inger Length The length of the middle fingercorrelated wei! with optimal tube length. The orotracheallube length was usually less than three times the lengthof the middle finger in centimeters.The mean differencewas 0.5 em in malesand 0.9 em in females.

Figure 2 plots the optimal tube length versus thirdfinger length for each of the subjects. The regressionline for the ent ire populat ion (N=84) was expressed bythe equat ion Y = 1.75X + 8.2. Regression lines wereplotted separately for male subjects (Y = 1.58X + 9.67)and female subjects (Y = 1.65X + 8.7).FIG. 2. Correlations and regressions of crorrecheat tube lengthwith length of the middle finger.

26

24

22

20

maleso females

REGRESSIONS-- all malesand femllleilN - 84).... - - males IN -44)-.- females (N . 40)

The correlation coefficients and the levels of significance between optimal endotracheal tube length and thevarious anthropometric measurements considered arelisted in Tables II and III.Because of the scarcity of patients subjected to naso-tracheal intubation during the study period, no significant s ta tist ical analysis can be done. Inspect ion of thedata obtained, however, revealed that on the average,nasotracheal tube length approximate the cricoid car-tilage to xiphoid tip distance.

TABLE II . Correlations of considered factors with oPtImalorotracheal tube length in 84 Filipino adults.

Cricoid Cartilage to Xiphoid Tip Distance. The meandistance from the superior border of the cricoid cartilageto the x iphoid process for the male subjects was 24.15ems. SD 0.99 ems, and for the female subjects, 22.98ems, SO1.32 ems.The orotracheal tube length was usually less than thedistance from the cricoid cartilage to the tip of theXiphoid process. The mean differences was 2.5 ems inmales and 2.0 ems. in females.JMMSI Vol . XXII No. 4-5 AprilSeptember.1986

Middlo Finger Length fern)

'8

6.5 7.0 7.5 8.0 8.5

Orotrachealtub81ength

Age O . ~Height 0.300

Length of Middle Finger 0.860"

Cricoid Cartilage toXiphoid TIp Distance 0.974Up value ( 0.001, highly 5.lgntficant"p value ( 0.01, significant

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TABLE III. Correlations of ~ o n s i d e r e d factors with optimalorotracheal tube length in Fi lipino male (N = 44 ) and femaleIN =40 ) subjects.

OrotrachealMALES tube length

Height 0.783-Length of Middle Finger 0.863'Crjcoid Cartilage toXiphoid Tip Distance 0.779'

OrotracheatFEMALES tube length

Height 0.580'Length of Middle Finger 0.575'Cricoid Cartilage toXiphoid Tip Distance 0.987-

"p value ( 0.001, highly significant

DISCUSSIONOpening the airway and restoring breathing are thefirst steps in artificial ventilation during cardiopulmonary resuscitation. Oxygenation of the lungs by simpleairway adjuncts should precede attempts at trachealintubation." Adequate lung inflations interposed between external chest compressions require high pharyngeal pressures. This factor promotes gastric distentionwhich elevates the diaphragm and interferes with adequate lung inflation. Gastric distention likewise promotes regurgitation with the potential hazard of aspiration of gastric contents into the lungs. Therefore, assoon as is practical, the trachea should be intubated.This isolates the airway, diminishes the chances ofaspiration and ensures the entry of a high concentrationof oxygen to the lungs. With a cuffed endotracheallube. it is easier to provide adequate ventilation duringcardiopulmonary resuscitation than with mouth-tomouth, mouth-to-mask, or bag-valve-mask technique,The indications for endotracheal intubation includethe following: I) inability of the rescuer to ventilate theunconscious patient with conventional methods, 2)inability of the patient to protect his own airway(coma,areflexia), or 3) the need for prolonged artificial ventilation.'Indeed, the cuffed endotracheal tube has proven itself to be an invaluable tool during cardiopulmonary reo

suscitation. In the hands of the inexperienced and the uninitiated, however, it can be a harbinger of disaster evenas soon as the choice of a specific type and size of endotracheal tube ismade.Many authors have reported on the complications ofendotracheal i n t u b a t i o n . ~ 1 O , 1 I 1 2 , 1 3 , 1 4 Too large a tubecan result in pressure necrosis most especially in thesubglottic region. The cricoid cartilage surroundingcompletely the subglottic region forestalls any externalexpansion of the swollen surfaces which can only expandinternally, giving rise to a dangerous airway obstruction.The cuff On the endotracheal tube poses yet anotherproblem. The high pressure, low volume cuffs havebeen

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unequivocally implicated as the cause of pressure neerosis in the trachea. During prolonged intubation, however, a discrepancy between tracheal size and endotracheal cuff size may result in increased trachealdamage even with the use of low pressure, high volumecuffs. Damage can Occur due to overinflation causingexcessive lateral tracheal wall pressure herniation of theredundant cuff over the end of the tubed Or actualcollapse of the endotracheal tube lumen with consequent airway obstruction. Underinflation of too largea CUff, on the other hand, can displace the tip of thetube towards one side of the trachea especially in noncircular tracheas wherein they cause noncircumferentialerosions. At times, floppy cuffs may be thrown intodouble folds, thus allowing aspiration by the channelingof liquids through the folds. This is especially true ofcuffs with thickness of more than 0.1 rum.18Aside from the problems associated with the externaldiameter of the tube and the cuff; another dreadedcomplication that can arise following intubation is theinadvertent insertion of the tube down to the levelof the carina or eveninto a mainstem bronchus. Often,an "airway" and ventilation. are established underemergency conditions by an efficient well-informedteam which disperses when the emergency is over. Whilethis team may be familiar with the complications.ofintubation - ventilation, those charged with subsequentcare of the patient are commonly less so. Or with ventilation apparently well controlled, attention may bediverted to other acute problems of the patient's care.When respiratory distress recurs some hours later, therole of the airway itself in producing the symptomsmay not be recognized. Endobronchial intubation oftencauses amoreorlesscompletetermination of ventilationin the opposite lung which is thus converted into agreat shunt unit. The shunting of venous blood throughthe poorly ventilated or nonventilated lung results insevere hypoxemia. When imposed on a serious cardiopulmonary dysfunction, time is of the essence and anydelays may lead to rapid deterioration and death. Accidental right mainstem bronchus intubation has beenimplicated as a cause of respiratory distress in about1025% of intubated patients. Complications notedwere left-sided atelectasis,19 ,20,21,22 right-sidedtensionpneumothorax, or right upper lobe atelectasis.23The tube may go down into a bronchus as a resultof the weight of the attachments or from frequentsuctioning if the tube is not firmly anchored. Also,change in the position during the emergency periodcan cause the tube to move up or down in the trachea.It has been demonstrated that after an accurateintubation of a patient in the supine position, a changeto the Trendelenburg tilt will result into an upwardshift of the carina with impairment of left lung ventilation. 24 Conrardy et a125 has shown that even flexionof the head may cause the tip of the tracheal tube tomove an average of 1.9 em. towards the carina, whileextension of the head may cause it to move 1.9 em.away from tlie carina, i.e., regardless of the route ofintubation (oral vs. nasal).Conversely, failure to place the tracheal tube severalcentimeters beyond the vocal cords may result ninadvertent extubation, vocal cord paralysis, laryngo-

JMMSI Vol. XXII No.4-6 April-September, 1986


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spasm and aspiration pneumonia. 9 , 24 , 2 5Determining proper tube location has been the subject of many thesis in the past. Among the recorn

mended maneuvers include I) placement of the endotracheal tube- under direct vision I to 2 ern. below thevocal cords.?" 2) confirmation by auscultation forequality uf breath sounds in all areas of the lungfields,273) technique of deliberate endobronchial intubationwith gradual withdrawal of the tube to 1 to 2 em. beyound the point at which breath sounds are bilaterallycqual,27 4) rapid inflation and deflation of the cuffwith palpation for a change in pressure on the tracheajust above the suprasternal notch,'S ,'9 ,30 5) applyinga constant pressure to the pilot balloon of the inflatedcu ff by the index finger and the thumb while the tracheais palpated,'S 6) injecting one I ml of sterile saline intothe partially inflated pilot balloon and listening forcrepitus at the level of the cuff in the trachea while thepilot balloon is being c 0 " i ~ r e s s e d between the fingers,307) chest roentgenogram, , ) j 8) using an eletromagnetic sensing device,32 9) detecting for chanfes in endtidal CO, by continuous mass spectrometry. 3 Some ofthese methods, however, are either complicated, inconvenient, expensive, invasive and impratical. In essencetherefore, it appears beneficial to utilize a combinationof common sense with simple methods to verify properpositioning of an endotracheal tube. The only ult imateguarantee of proper tube placement is the chest roentgenogram and whenever doubt exists, it should berequested. The maximum safe insertion of a tube inadults should not exceed beyond T, leveL"

In this world where nature creates nothing to a standard size. man since the earliest time has used his own

body as the basis for measurements. From hereon, theconcept of anatomic correlates and anthropometricmeasurements have evolved and the orocarinal andnasocarinal distances in man is no except ion. Severalauthors have noted the "correct" length of orotrachealand nasotracheal tubes to use in infants and children,34 ,35 ,36.37,38,39,40,41 and in adults.42 ,4 3As early as 1907, Jackson has reported the straightline distance from the upper anterior teeth to thecarina measured along a bronchoscope to be 27 em.in men and 23 em. in women. Hewer reported thepathway of inspired gas from the anterior teeth to thecarina to be 26 em. in length. Gillespie, in 1948, suggested that the length of an endotracheal tube beselected by placing the tube alongside the patient'sneck whereby its tip should not extend beyoml theangle of Louis, the anatomical landmark for the bifurcation of the trachea/"Schellinger, in 1964, determined airway length to thebifurcation of the trachea on patients for autopsy.He has noted a positive correlation between the distancefrom the superior border of the cricoid cartilage to the

tip of the xiphoid process with the orocarinal distance.Whereas the diameter of the criooid and the tracheacan be redicted accurate ly in fresh cadaver specimens3,', the same cannot be said of tracheal length.The trachea appears to . be longer in life than at postmortem, mainly because of the elastic recoil of the diaphragm making interpretation of these data difficult.Fearon and Whalen's study 3S with living subjects (1965)demonstrated the unreliabili ty of data obtained incadavers.

FIG. 4. An algorithm for airway management In the acutely injured patient.

i -ICAlCOTHYFlOlDOTOMylIi

r,,!i,I....,,-,....

I'\e NASOTRACH'"- INTU8ATION

:::7::' -6- BAO MASK CWvIQl /\ l E N ~ r L A T I O N --. .pl....a/T \Ia.::-:. -61 -L -_ "" : ' : ' : " : " ' . J - ,, ,.. - - - - =.::.. _19_

SUPPLEMENTALOXYGEN

Trwchal tr- .ct lonorHYlfW anteriorInjury

X"-Vttudl.. Qlal nlm c.rvk:IlqoIne

- ....o'll'\IuryIo I.e.... 01 conad ........o V.nllinianoO"Y....1ono Aff-.r _ _ I or

Imrni...nl

I TRACHEOSTOMY IJMMSI Vol. XXII No. 4-6 April-September, 1986 113


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FIG. 5, Factors to consider In airway management of the acutely injured F il ipino patient.

o Cricoid to Jdphofddi$unaJncm..

taller then 160 em(5'3'" - - - '. 0 mm 1.0.

BuIld onheight end "

Ieller Ihlln 145 em 14'9", 6.5 mm I.D.shorter then 145 em 14'9'" --- B.Omm I.D.

shorter then 160 em 15'3'" 6.5 mm 1.0.

Bned on Lllnglh of the Third Finger

USEAPPROPRIATE SIZEOFENOOTAACHEALTUBE

Mo'a

oLength of thi rd f inger Inem 1.0. of tutMl ln mm

ORAL ROUTEo Crl


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limited since the chest is often blocked by other resuscitators applying external chest compressions.In a previous study by one of the authors,' it wasfound that the third finger length has a high correlationwith the cricoid ring size, thus making it an invaluablereference in the choice of the proper size of endotracheal tube to use among Filipino adults. In an emergency, the length of the third finger in centimeterscorresponds well to the correc t tube size ( in ternal diameter) in millimeters, that a tube may be selected onthat basis. For example, if the third finger length is6.7 crn., then a 7 mm. internal diameter endotrachealtube should be used. In the present study, an attemptwas made to correlate this anthropometric measure-men t with the optimal orotracheal tube length. Theresults indicate that when one centimeter is subtractedfrom the product of three times the length of the thirdflnger, the value obtained corresponds well to theopt imal orot racheal tube depth calculated for eachpatient.CONCLUSIONS AND RECOMMENDAnONSOn the basis of the foregoing data; we can thereforeconclude that a significant statistical correlation wasobtained between optimal orotracheal tube length andthe considered anthropometric measurements namely,height, cricoid to xiphoid distance and the length of

the third finger, thus making them good predictorsof airway length in Filipino adults. The maximum safelength for endotracheal tubes in Filipino adults are asfollows:

Orotracheal tube:a) Cricoid to xiphoid distance (em) - 2 em.b) (Third finger length in em x 3) - I em.

Nasotracheal tube:a) Cricoid to xiphoid distance in em.b) (Third finger length in em x 3) + 1 em.Cognizant therefore of the standards set forth in thisstudy and those of two previous studies among Filipinos4,s a more rational approach to airway manage-ment during cardiopulmonary resuscitation canbe done.

SUMMARYA method for the predetermination of the maximumsafe length of orotracheal and nasotracheal tubes in Filipino adults is presented.Correlations of such factors, i.e. age., sex, height. cri-coid to xiphoid distance and third finger length withopt imal orotracheal or nasotracheal tube length werecomputed,andconclusionswere derived accordingly.A review of the literature on the complications asso-

ciated with inadvertent endobronchial intubationwere presented and the importance of predeterminationof the tube length in prolonged intubation is crnphasized.REFERENCESI. AHA/NAS-NRC: Standards and Guidelines forCardiopulmonary Resuscitation (CPR) and Erner-

JMMSI Vol. XXII No. 4-5 AprilSeptember, 1986

gency Cardiac Care (ECe). JAMA 244 (5): 453-508,\980.

2. AHA/NAS-NRC: Standards for CardiopulmonaryResuscitation (CPR) and Emergency Cardiac Care(ECe). JAMA 227 (Supp!) 833-868, 1974.

3. Koufman, JA, Fortson, JK, and Strong, MS: Predictive Factors of Cricoid Ring Size in Adults in Relat ion to Acquired Subglottic Stenosis. OtolaryngolHead Neck Surg. 91: 177-182,1983.

4. Patawaran-Calimag, MMV: Normative Data on Cricoid Ring Size Among Adult Filipinos in Relationto Acquired Subglottic Stenosis. Unpublished Thesispresented at the 19th Annual Convention of thePhilippine Society of Anesthesiologists, December,1984.5. Patawaran-Calimag,MMV:FilipinoTracheal Ci;cum

ferenceas an Index of Correct Cuff Size: A Studyon Volume-Pressure Relationships in InflatableCuffs. Unpublished Thesis presented at the 20thAnnual Convention of the Philippine Society ofAnesthesiologists, December 1965.6. Rohlf', FJ and Sokal, RR: Statistical Tables:W. H.Freeman and Co., San Francisco, 1969.7. Sokal, RR, and Rohlf, FJ: Biometry: The Principlesand Practice of Statistics in Biological Research.W.H. Freeman and Co., San Francisco, 1969.8. Don Michael, TA: Comparison of the EsophagealObturator 'Airway and Endotracheal lntubation inPrehospital Ventilation during CPR. Chest 87 (6):

814-818,1985.9. Blanc, V. F. and Tremblay, NAG: The Complications of Tracheal Intubation: A New Classificationwith a Review of the Literature. Anes Analg 53:

202-214,1974.10. Bryce, D.P., Briant, TOR and Pearson, FG: laryngeal and Tracheal Complications of Intubation.Ann 0101 Rhinol Laryngol 77: 442-461,1968.I I . McGovern, FH, FitzHugh, GS, and Edgemon, U:

The Hazards of Endotracheal Intubation. Ann 010180: 556-564,1971.

12. Peppard, SB and Dickens, JH: Laryngeal InjuryFollowing Short Term Intubation. Ann Otol RhinolLaryngol92: 327-330,1983.13. Stauffer , JB, Olson, DE and Petty , TL: Complications and Consequences of Endotracheal Intubationand Tracheostomy. AmJMed70: 65-76,1981.14. Vogelhut, MM, Downs, JB: Prolonged EndotrachealIntubation. Chest 76: 110-111, 1979.

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Nealon, TF: The Contribution of Cuff Volume andPressure in Tracheostomy Tube Damage. J. ThoracCardiovasc Surg 62(3): 402-410, 1971.16. Dobrin, P, Canfield, T: Cuffed Endotracheal Tubes:Mucosal Pressures and Tracheal Wall Blood How.

AmJ Surg 1333: 552568, 1977.17. Knowlson, GTG, Bassett, HFM: The PressuresExerted on the Trachea by Endotracheal InflatableCuffs.Dr.J Anesthesia 42:834-837,1970.18. Pavlin, EG, vanNimwegan, D., Hornbein, TF: Failure of a High compliance, Low Pressure Cuff toPrevent Aspiration. Anesthesiology 42(2): 216219,1975.19. Tisi, GM, Twigg, HL and Moser, KM: Collapse ofLeft Lung Induced by Artificial Airway. Lancet. i :791, Apr 1968.

20. Hamilton, W. and Steven, W.: Malpositioning ofEndotracheal Catheters.JAMA 198:1113, 1966.21. Alberti, J., Hanafa, W., Wilson, G., et al: Unsuspected Pulmonary collapse during NeuroradiologicProcedures Radiology 89:316320, 1967.22. Keane, WM, Rowe, LD, Dennesy, JC and Atkins,JP: Complications of Intubation. Ann Otol RhinalLaryngol91 :584.587,1982.23. Seta, K., Goto, H., Hacker, DC, Arakawa: RightUpper Lobe Atelectasis after- I n a ~ v e r t e n t RightMain Bronchial Intubation. Anes Analg 62:851-854,1983.24. Heinonen, J., Tammisto, T., and Takki, S.: Effect

of the Trendelenburg Tilt and Other Procedures onthe Position of Endotracheal Tubes. Lancet 1:850,1969.25. Conrardy, P., Goodman, L., Laing, F., Singer, M.:Alteration of Endotracheal Tube Position - Flexionand Extension of the Neck Crit Care Med 4:8.12,1976.26. Ripoll, I., Lindholm, CL, Carroll, R., and Grenwik,

A.: Spontaneous Dislocation of EndotrachealTubes. Anesthesiol49 :5052, 1978.27: Bendixen, HH, Egbert, LD, Hedley, et al.: "TheAirway" Respiratory Care. St. Louis, C.V. Mosby,1965, pp 111121.28. Downes, JJ , Raphaely, R.C.: Pediatric IntensiveCare AnesthesioI43:238250, 1975.29. Trincr. L : A Simple Maneuver to Verify Proper

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