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THE RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS
Brit. J. Anaesth. (1963), 35, 498 THE RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS BY A. M. C. JENNINGS
The London Hospital, Whitechapel, London SUMMARY
Corrugated rubber endotracheal catheter mounts additional information of consequence would result have recently been introduced. These tubes can from testing a pulsating flow rather than a steady be occluded by twisting but not by bending. The flow, and this view was followed by Orkin, Siegel advantages over parallel-sided mounts are the and Rovenstine (1957) in their work on expiratory greater manoeuvrability and the reduced risk of valves. Smith (1961b), testing endotracheal tubes and their mounts and connections, produced rekinking by bending. However, we heard of a patient in another sults which support this view. For this reason it hospital who was being ventilated by a volume- was thought unnecessary to perform a more comregulated mechanical ventilator whilst connected plicated experiment. to the machine by one of these mounts. Despite pressures of 25 to 30 cm H,O, and at times even METHOD more, adequate ventilation was not obtained. The catheter mount was replaced by a parallel-sided The apparatus used was similar to that used by one and immediately the pressure dropped to 15 Galloon (1957) except that a T-piece was used to 17 cm H 2 O. A suggested explanation was that instead of a Y-piece. Galloon used a cylinder to the irregular lumen of the corrugated tube caused deliver gas via a flowmeter at a steady rate of 25 increased turbulence and a greater resistance. l./min to a Y-piece, a water manometer being fixed However, the second mount was much shorter to another limb of the Y-piece and the various than the first so that it would be unwise to draw connections under investigation being attached to definite conclusions from this case. The sugges- the other limb. tion was plausible, though, because Macintosh, Air was driven by a compressor into a large Mushin and Epstein (1958) have stressed that oil drum out of which a steady flow emerged. This "irregularities of the inner wall of a tube and flow was controllable and passed via a flowmeter sudden alterations in the bore of tubes and con- to one horizontal limb of the T-piece. The flownections are frequent offenders causing a change meter was graduated from 15 to 150 l./min at from laminar to turbulent flow". Orkin, Siegel intervals of 5 l./min. The catheter mount being and Rovenstine (1954), and Smith (1961b) stress tested was attached to the other horizontal limb the same point and it seemed, therefore, desirable of the T-piece and a water manometer to the verto test this possibility. tical limb (fig. 1). The metal part of the catheter A simple experiment was performed to measure mount was fixed at the beginning and not disthe pressure needed to drive various steady flows turbed until all the readings with the tubes lying through catheter mounts of both types. Hunt straight had been taken. It was confirmed that with (1955), discussing the properties of expiratory this apparatus pressure-flow readings were reprovalves, stated that it would be unlikely that any ducible. 498
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
Observations made on a patient who was being artificially ventilated suggested that the newer type of corrugated rubber endotracheal catheter mounts might have a higher resistance than the older straight-sided ones. This possibility was verified using steady flows of air with the catheter mount straight. In these circumstances the difference between the two is small. However, corrugated tubes are designed to be flexible and when they are bent through 180 degrees the resistance increases sharply, being doubled.
499
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS RESULTS
l cm.
m
r
I
FIG. 1 Diagram of apparatus used for measuring pressureflow characteristics of catheter mounts. cm. Catheter mount being tested f. Flowmeter m. Manometer t. T piece
Four catheter mounts were used, all of which are in clinical use in the London Hospital. Their sizes were: (1) Corrugated, (2) Straight sided, (3) Corrugated, (4) Straight sided,
length length length length
143 mm, 138 mm, 89 mm, 91 mm,
diameter diameter diameter diameter
9 mm. 9 mm. 10£ mm. 91 mm.
Measurements were made on each of these tubes in three different conditions with the mounts lying straight. (1) With the catheter mount discharging directly into the atmosphere. (2) With the mount connected to a size 7 endotracheal tube via a Magill oral connection and discharging into the atmosphere. (3) With the mount connected to the same endotracheal tube via a Cobb connection and discharging into the atmosphere. Flows from 15 to 150 l./min were used. A test was now made of the effects of bending the long corrugated mount through 180 degrees. A size 10 endotracheal tube with a Magill oral connection was tested for steady flows of 20 to 100 l./min. The corrugated mount 143 mm long was then added, lying quite straight in clamps, and another set of readings taken. Without disturbing the apparatus in any other way the catheter mount was then bent through 180 degrees, clamped, and another set of readings taken, its patency apparently unaltered by the bending.
TABLE I
Increase in resistance due to using a corrugated instead of a straight catheter mount.
Flow rate (l./min) 15 20 25 30 35 40 45 50 55 60 65 70
Pressure with corrugated mount minus pressure with straight mount (mm ]H2O) Short catheter Long iatheter mount mount Cobb Magill Magill Cobb 0 -1 0 -1 -1 0
2
0
+3 +7 +6 +6
0 +1 -1 +1 +2 +2 +5 +3 +3 +4 +6 +4
! +1
+
+H +1 +2 +4 +5 +7 +8 +8 +8 + 10
+1 0 0 J 0 +1 +3 +2 +3 +4 +5 +6
TABLE II
Increase in resistance due to using a Cobb connector in place of a Magill connector. Pressure with Cobb connector minus pressure with Magill connector (mm H2O) Flow rate (l./min) 15 20
25 30 35 40 45 50 55 60 65 70
Long catheter mount
Short catheter mount
Corrugated
Straight
Corrugated
Straight
2 3 7 7 9 11 6 14 23
2 5 6 9 12 13 13 17 23 25' 32 36
21 6 8 9 10 12 15 20 24 28 31 37
3 5 7 7 8 9 13 15 19 24 28 33
28 32 38
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
COMPRESSOR and DRUM
The increased resistance of the corrugated mount when lying straight is clearly shown in figures 2 and 3, but the importance of this is perhaps better appreciated by comparing the differences due to using a corrugated mount, rather than a straight one, at various flows, with the differences due to using a Cobb connector rather than a Magill in otherwise identical conditions. This is shown in tables I and II and in figure 4.
250n
200-
Q,
A
FIG. 2 Pressure-flow curves of long catheter mounts, corrugated and straight sided.
E 150E
O Corrugated ) m o u n t • Straight sided j only
A O
g
50-
A •
0
20
40
60 80 100 Flow (l./min)
120
140
D Corrugated | •• c. • L J J /mount • Straight sided J with Cobb and endotracheal tube A Corrugated ) _ •L / mount e. V .Straight / w i t h Magill and endotracheal tube
250 200FIG. 3 Pressure-flow curves of short catheter mounts, corrugated and straight sided.
O Corrugated • Straight sided
q E
O
mount only to (/>
• _ •
Corrugated | _ . , . , , }mount Straight sided j w i t h Cobb and endotracheal tube A Straight T Corrugated m u n t
A
150-
100o
0) Q_
o
50-
j °
Magill and endotracheal tube
0
20
40
60 80 100 Flow (l./min)
120
-1 140
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
I 100
501
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS
40-i
+
t 30-
+ +
FIG. 4 Comparison of increased resistance due to corrugation with increased resistance due to use of Cobb connector.
I 10-1
4
• t
+
+ Increase in pressure due to using a Cobb connection rather than a Magill (from table II).
Q_
i
0 •
-5
60
20 40 Flow (l./min) Figure 5 shows the striking effect of bending the catheter mount through 180 degrees. The extra resistance due to attaching the endotracheal catheter mount to the tube is almost exactly doubled if the mount is bent (see also table III). Comparing the results in table III with those in table II, and with Smith's results using a size 10 endotracheal tube (Smith, 1961b), it appears that the effect of bending the mount is about half the effect of substituting a Cobb for a Magill connector.
200-,
o 100-
Pressure (mm H2O)
Flow rate (l./min) 20 40 60 80 100
Endotracheal Endotracheal tube with tube with long corru- long corrugated mount gated mount Endotracheal lying bent tube only straight through 180° 6 16 32 54 83
6i 23 49 86 134
9 30 68 120 190
+
50
TABLE III
Increase in resistance due to attaching the corrugated mount when this is both straight and bent
+ o
0
420
i 40
60 80 Flow (l./min)
FIG.
100
120
5
Pressure-flow curves of long catheter mount, straight and bent through 180 degrees. # Endotracheal tube. + Magill connection. + Endotracheal tube + Magill + corrugated mount straight. O Endotracheal tube + Magill + corrugated mount bent.
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
# Increase in pressure due to using a corrugated catheter mount rather than a straight sided mount (from table I).
20-
BRITISH JOURNAL OF ANAESTHESIA
502 DISCUSSION
ACKNOWLEDGMENTS
These measurements were made in the Research Department of Anaesthetics in the Royal College of Surgeons and I am grateful to Dr. D. W. Hill for allowing me to work in his laboratory and to Drs. A. I. Parry Brown, B. R. J. Simpson and W. D. A. Smith for help and advice.
REFERENCES
Galloon, S. (1957). The resistance of endotracheal connections. Brit. J. Anaesth., 29, 160. Hunt, K. H. (1955). The resistance of expiratory valves and canisters. Aneslhesiology, 16, 190. Macintosh, Sir Robert R., Mushin, W. W., and Epstein, H. G. (1958). Physics for the Anaesthetist, 2nd ed., p. 175. Oxford: Blackwell. Mushin, W. W., Rendell-Baker, L., and Thompson, P. W. (1959). Automatic Ventilation of the Lungs, 1st ed., p. 15. Oxford: Blackwell. Orkin, L. R., Siegel, M., and Rovenstine, E. A. (1954). Resistance to breathing by apparatus used in anesthesia. Curr. Res. Anesth., 33, 217. (1957). Resistance to breathing by apparatus used in anesthesia. Anesth. Analg. curr. Res., 36, 19 (March—April). Smith, W. D. A. (1961a). The effects of external resistance to respiration. Part I: General review. Brit. 1. Anaesth., 33, 549. (1961b). The effects of external resistance to respiration. Part II: Resistance to respiration due to anaesthetic apparatus. Brit. J. Anaesth., 33, 610.
LA RESISTANCE DES SONDES ENDOTRACHfiALES EN CAOUTCHOUC STRIfi SOMMAIRE
L'auteur a remarqu^ chez un patient ventil6 artificiellement que le nouveau type de sonde en caoutchouc strie semblait presenter au passage de l'air une resistance plus grande que les anciennes sondes lisses. II proce'da a une verification et constata, que tant que le courant d'air passa par la sonde maintenue droite, la difference entre sondes lisses et sondes striees £tait insignifiante. Cependant les sondes strides — crepes ainsi pour etre plus flexibles — presentment, une fois courbees a 180 degres, une resistance brusquement augmentee et qui
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
The four tubes were of different diameters and lengths. Poiseuille's law cannot be applied exactly to these tubes but it is reasonable to use it as a rough guide to what might be expected. It would seem that the difference between the lengths of the long mounts might cause a slight apparent increase in the resistance of the corrugated tube, but in the case of the short mounts the bias would be very much in the opposite direction, since the corrugated tube is both wider and shorter. The apparatus available did not allow flow rates greater than 150 l./min to be measured. Orkin, Siegel and Rovenstine (1954), quoting other workers, state that the normal maximum flow in healthy adults ranges from 30 to 50 l./min, although maximum flow in tachypnoea and hyperpnoea may reach 90 l./min, and in coughing much higher flow rates occur. Mushin, RendellBaker and Thompson (1959) describe 40 to 80 l./min as a high flow rate in speaking of mechanical ventilators. Although Galloon (1957) has recorded 400 l./min, this seems to be exceptional, and measurements up to 150 l./min would appear to cover a wide enough range for practical purposes. The effects of increasing airway resistance have been discussed by Smith (1961a) who reviews experimental work in conscious and anaesthetized man and dogs. Most ill effects appear to occur when the airway pressure rises above 10 cm H,O. The results presented indicate that the airway pressure increase due to using one of the newer catheter mounts is likely to be small in comparison with the pressures which might harm the patient, provided the mount is straight. However, the advantage of these mounts lies in their flexibility and, as soon as use is made of this, the price has to be paid in terms of a considerably higher resistance. The bend of 180 degrees tested is perhaps more than would often be used, but the impossibility of kinking by bending invites the anaesthetist to do this if convenient to him. Smith (1961b) has condemned the use of the Cobb connection because of its higher resistance. The corrugated catheter mounts are open to the same objection if they are going to be bent. If they are not, and if the mount will be accessible to the anaesthetist throughout the operation, there seems no reason to use them.
It may be arguable that when there is a risk that the catheter mount might become kinked in an inaccessible site during operation, the increased resistance is acceptable. The possibility of occlusion by twisting must, however, not be forgotten. If they are to be used, it is important for the anaesthetist to be aware of the increased resistance and alert to its possible ill effects.
BRITISH JOURNAL OF ANAESTHESIA
502 DISCUSSION
ACKNOWLEDGMENTS
These measurements were made in the Research Department of Anaesthetics in the Royal College of Surgeons and I am grateful to Dr. D. W. Hill for allowing me to work in his laboratory and to Drs. A. I. Parry Brown, B. R. J. Simpson and W. D. A. Smith for help and advice.
REFERENCES
Galloon, S. (1957). The resistance of endotracheal connections. Brit. J. Anaesth., 29, 160. Hunt, K. H. (1955). The resistance of expiratory valves and canisters. Aneslhesiology, 16, 190. Macintosh, Sir Robert R., Mushin, W. W., and Epstein, H. G. (1958). Physics for the Anaesthetist, 2nd ed., p. 175. Oxford: Blackwell. Mushin, W. W., Rendell-Baker, L., and Thompson, P. W. (1959). Automatic Ventilation of the Lungs, 1st ed., p. 15. Oxford: Blackwell. Orkin, L. R., Siegel, M., and Rovenstine, E. A. (1954). Resistance to breathing by apparatus used in anesthesia. Curr. Res. Anesth., 33, 217. (1957). Resistance to breathing by apparatus used in anesthesia. Anesth. Analg. curr. Res., 36, 19 (March—April). Smith, W. D. A. (1961a). The effects of external resistance to respiration. Part I: General review. Brit. 1. Anaesth., 33, 549. (1961b). The effects of external resistance to respiration. Part II: Resistance to respiration due to anaesthetic apparatus. Brit. J. Anaesth., 33, 610.
LA RESISTANCE DES SONDES ENDOTRACHfiALES EN CAOUTCHOUC STRIfi SOMMAIRE
L'auteur a remarqu^ chez un patient ventil6 artificiellement que le nouveau type de sonde en caoutchouc strie semblait presenter au passage de l'air une resistance plus grande que les anciennes sondes lisses. II proce'da a une verification et constata, que tant que le courant d'air passa par la sonde maintenue droite, la difference entre sondes lisses et sondes striees £tait insignifiante. Cependant les sondes strides — crepes ainsi pour etre plus flexibles — presentment, une fois courbees a 180 degres, une resistance brusquement augmentee et qui
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
The four tubes were of different diameters and lengths. Poiseuille's law cannot be applied exactly to these tubes but it is reasonable to use it as a rough guide to what might be expected. It would seem that the difference between the lengths of the long mounts might cause a slight apparent increase in the resistance of the corrugated tube, but in the case of the short mounts the bias would be very much in the opposite direction, since the corrugated tube is both wider and shorter. The apparatus available did not allow flow rates greater than 150 l./min to be measured. Orkin, Siegel and Rovenstine (1954), quoting other workers, state that the normal maximum flow in healthy adults ranges from 30 to 50 l./min, although maximum flow in tachypnoea and hyperpnoea may reach 90 l./min, and in coughing much higher flow rates occur. Mushin, RendellBaker and Thompson (1959) describe 40 to 80 l./min as a high flow rate in speaking of mechanical ventilators. Although Galloon (1957) has recorded 400 l./min, this seems to be exceptional, and measurements up to 150 l./min would appear to cover a wide enough range for practical purposes. The effects of increasing airway resistance have been discussed by Smith (1961a) who reviews experimental work in conscious and anaesthetized man and dogs. Most ill effects appear to occur when the airway pressure rises above 10 cm H,O. The results presented indicate that the airway pressure increase due to using one of the newer catheter mounts is likely to be small in comparison with the pressures which might harm the patient, provided the mount is straight. However, the advantage of these mounts lies in their flexibility and, as soon as use is made of this, the price has to be paid in terms of a considerably higher resistance. The bend of 180 degrees tested is perhaps more than would often be used, but the impossibility of kinking by bending invites the anaesthetist to do this if convenient to him. Smith (1961b) has condemned the use of the Cobb connection because of its higher resistance. The corrugated catheter mounts are open to the same objection if they are going to be bent. If they are not, and if the mount will be accessible to the anaesthetist throughout the operation, there seems no reason to use them.
It may be arguable that when there is a risk that the catheter mount might become kinked in an inaccessible site during operation, the increased resistance is acceptable. The possibility of occlusion by twisting must, however, not be forgotten. If they are to be used, it is important for the anaesthetist to be aware of the increased resistance and alert to its possible ill effects.
503
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS atteignit presque le double de celle offerte par la sonde striee maintenue droite.
CORRESPONDENCE
DER LUFTWIDERSTAND VON GEWELLTEN ANSATZSTUCKEN FOR ENDOTRACHEALKATHEDER
Sir,—I read with interest the article "Estimation of blood loss with particular reference to cardiac surgery" by Dr. J. A. Thornton et al. (Brit. J. Anaesth., 35, 91) but was surprised to see no reference made to the machine developed in Aberdeen (Roe, Gardiner and Dudley, 1962). This machine also utilizes the colorimetric method; it has an overall accuracy of 3 per cent and incorporates a spin-drier through which the swabs are finally put. This both facilitates the swab count and avoids change in the volume of the bath contents.
ESTIMATION OF BLOOD LOSS
ZUSAMMENFASSUNG
W. N. ROLLASON
Aberdeen REFERENCE
Roe, C. F., Gardiner, A. J. S., and Dudley, H. A. F. (1962). A simple instrument for rapid, continuous determination of operative blood loss. Lancet, 1, 672.
BOOK REVIEW The Obstetrician, the Anaesthetist and the Paediatrician in the Management of Obstetric Problems. Edited by Trevor Barnett and John Joyce Foley. Published by Pergamon Press, Oxford and London. Pp. 188. Price 50s. The Obstetric Unit at Portsmouth is well known to all anaesthetists due to the excellent work carried out there by the late Dr. Hamer Hodges and his colleagues. In November 1961 a conference was organized in that city by the South Western Obstetrical and Gynaecological Society, and attended by leading members of the profession. The book is a record of the papers
presented at the five half-day sessions and of the discussion that followed. The subjects considered were Unstable Presentation, Obstetric Anaesthesia, the Place of the General Practitioner in Obstetrics, Asphyxia Neonatorum, and Management of the Third Stage. Anaesthetists will find points of interest in every section, but the most challenging is that on Asphyxia Neonatorum, epitomized in Professor Ian Donald's opening phrase as "not a diagnosis but an emergency". This is a valuable work, containing many useful statements of fact and intention. It is not, nor is it intended to be, comprehensive, but anyone with an interest in obstetric anaesthesia should be aware of its contents. W. D. Wylie
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
Beobachtungen an einem Patienten, der kiinstlich beatmet wurde, lieflen vermuten, dafi die neuere Art der Ansatzstiicke fiir Endotrachealkatheder aus gewelltem Gummi einen hoheren Widerstand hat als die alteren mit geraden Seiten. Dies wurde mittels eines kontinuierlichen Luftstroms bei geradem Kathederansatzstilck bestatigt. Unter diesen Umstanden ist der Unterschied zwischen den beiden gering. Gewellte Schlauche sind aber entworfen, um biegsam zu sein, und wenn sie um 180 Grad gebogen werden, steigt der Widerstand stark an; er wird tatsachlich verdoppelt.
The London Hospital, Whitechapel, London SUMMARY
Corrugated rubber endotracheal catheter mounts additional information of consequence would result have recently been introduced. These tubes can from testing a pulsating flow rather than a steady be occluded by twisting but not by bending. The flow, and this view was followed by Orkin, Siegel advantages over parallel-sided mounts are the and Rovenstine (1957) in their work on expiratory greater manoeuvrability and the reduced risk of valves. Smith (1961b), testing endotracheal tubes and their mounts and connections, produced rekinking by bending. However, we heard of a patient in another sults which support this view. For this reason it hospital who was being ventilated by a volume- was thought unnecessary to perform a more comregulated mechanical ventilator whilst connected plicated experiment. to the machine by one of these mounts. Despite pressures of 25 to 30 cm H,O, and at times even METHOD more, adequate ventilation was not obtained. The catheter mount was replaced by a parallel-sided The apparatus used was similar to that used by one and immediately the pressure dropped to 15 Galloon (1957) except that a T-piece was used to 17 cm H 2 O. A suggested explanation was that instead of a Y-piece. Galloon used a cylinder to the irregular lumen of the corrugated tube caused deliver gas via a flowmeter at a steady rate of 25 increased turbulence and a greater resistance. l./min to a Y-piece, a water manometer being fixed However, the second mount was much shorter to another limb of the Y-piece and the various than the first so that it would be unwise to draw connections under investigation being attached to definite conclusions from this case. The sugges- the other limb. tion was plausible, though, because Macintosh, Air was driven by a compressor into a large Mushin and Epstein (1958) have stressed that oil drum out of which a steady flow emerged. This "irregularities of the inner wall of a tube and flow was controllable and passed via a flowmeter sudden alterations in the bore of tubes and con- to one horizontal limb of the T-piece. The flownections are frequent offenders causing a change meter was graduated from 15 to 150 l./min at from laminar to turbulent flow". Orkin, Siegel intervals of 5 l./min. The catheter mount being and Rovenstine (1954), and Smith (1961b) stress tested was attached to the other horizontal limb the same point and it seemed, therefore, desirable of the T-piece and a water manometer to the verto test this possibility. tical limb (fig. 1). The metal part of the catheter A simple experiment was performed to measure mount was fixed at the beginning and not disthe pressure needed to drive various steady flows turbed until all the readings with the tubes lying through catheter mounts of both types. Hunt straight had been taken. It was confirmed that with (1955), discussing the properties of expiratory this apparatus pressure-flow readings were reprovalves, stated that it would be unlikely that any ducible. 498
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
Observations made on a patient who was being artificially ventilated suggested that the newer type of corrugated rubber endotracheal catheter mounts might have a higher resistance than the older straight-sided ones. This possibility was verified using steady flows of air with the catheter mount straight. In these circumstances the difference between the two is small. However, corrugated tubes are designed to be flexible and when they are bent through 180 degrees the resistance increases sharply, being doubled.
499
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS RESULTS
l cm.
m
r
I
FIG. 1 Diagram of apparatus used for measuring pressureflow characteristics of catheter mounts. cm. Catheter mount being tested f. Flowmeter m. Manometer t. T piece
Four catheter mounts were used, all of which are in clinical use in the London Hospital. Their sizes were: (1) Corrugated, (2) Straight sided, (3) Corrugated, (4) Straight sided,
length length length length
143 mm, 138 mm, 89 mm, 91 mm,
diameter diameter diameter diameter
9 mm. 9 mm. 10£ mm. 91 mm.
Measurements were made on each of these tubes in three different conditions with the mounts lying straight. (1) With the catheter mount discharging directly into the atmosphere. (2) With the mount connected to a size 7 endotracheal tube via a Magill oral connection and discharging into the atmosphere. (3) With the mount connected to the same endotracheal tube via a Cobb connection and discharging into the atmosphere. Flows from 15 to 150 l./min were used. A test was now made of the effects of bending the long corrugated mount through 180 degrees. A size 10 endotracheal tube with a Magill oral connection was tested for steady flows of 20 to 100 l./min. The corrugated mount 143 mm long was then added, lying quite straight in clamps, and another set of readings taken. Without disturbing the apparatus in any other way the catheter mount was then bent through 180 degrees, clamped, and another set of readings taken, its patency apparently unaltered by the bending.
TABLE I
Increase in resistance due to using a corrugated instead of a straight catheter mount.
Flow rate (l./min) 15 20 25 30 35 40 45 50 55 60 65 70
Pressure with corrugated mount minus pressure with straight mount (mm ]H2O) Short catheter Long iatheter mount mount Cobb Magill Magill Cobb 0 -1 0 -1 -1 0
2
0
+3 +7 +6 +6
0 +1 -1 +1 +2 +2 +5 +3 +3 +4 +6 +4
! +1
+
+H +1 +2 +4 +5 +7 +8 +8 +8 + 10
+1 0 0 J 0 +1 +3 +2 +3 +4 +5 +6
TABLE II
Increase in resistance due to using a Cobb connector in place of a Magill connector. Pressure with Cobb connector minus pressure with Magill connector (mm H2O) Flow rate (l./min) 15 20
25 30 35 40 45 50 55 60 65 70
Long catheter mount
Short catheter mount
Corrugated
Straight
Corrugated
Straight
2 3 7 7 9 11 6 14 23
2 5 6 9 12 13 13 17 23 25' 32 36
21 6 8 9 10 12 15 20 24 28 31 37
3 5 7 7 8 9 13 15 19 24 28 33
28 32 38
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
COMPRESSOR and DRUM
The increased resistance of the corrugated mount when lying straight is clearly shown in figures 2 and 3, but the importance of this is perhaps better appreciated by comparing the differences due to using a corrugated mount, rather than a straight one, at various flows, with the differences due to using a Cobb connector rather than a Magill in otherwise identical conditions. This is shown in tables I and II and in figure 4.
250n
200-
Q,
A
FIG. 2 Pressure-flow curves of long catheter mounts, corrugated and straight sided.
E 150E
O Corrugated ) m o u n t • Straight sided j only
A O
g
50-
A •
0
20
40
60 80 100 Flow (l./min)
120
140
D Corrugated | •• c. • L J J /mount • Straight sided J with Cobb and endotracheal tube A Corrugated ) _ •L / mount e. V .Straight / w i t h Magill and endotracheal tube
250 200FIG. 3 Pressure-flow curves of short catheter mounts, corrugated and straight sided.
O Corrugated • Straight sided
q E
O
mount only to (/>
• _ •
Corrugated | _ . , . , , }mount Straight sided j w i t h Cobb and endotracheal tube A Straight T Corrugated m u n t
A
150-
100o
0) Q_
o
50-
j °
Magill and endotracheal tube
0
20
40
60 80 100 Flow (l./min)
120
-1 140
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
I 100
501
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS
40-i
+
t 30-
+ +
FIG. 4 Comparison of increased resistance due to corrugation with increased resistance due to use of Cobb connector.
I 10-1
4
• t
+
+ Increase in pressure due to using a Cobb connection rather than a Magill (from table II).
Q_
i
0 •
-5
60
20 40 Flow (l./min) Figure 5 shows the striking effect of bending the catheter mount through 180 degrees. The extra resistance due to attaching the endotracheal catheter mount to the tube is almost exactly doubled if the mount is bent (see also table III). Comparing the results in table III with those in table II, and with Smith's results using a size 10 endotracheal tube (Smith, 1961b), it appears that the effect of bending the mount is about half the effect of substituting a Cobb for a Magill connector.
200-,
o 100-
Pressure (mm H2O)
Flow rate (l./min) 20 40 60 80 100
Endotracheal Endotracheal tube with tube with long corru- long corrugated mount gated mount Endotracheal lying bent tube only straight through 180° 6 16 32 54 83
6i 23 49 86 134
9 30 68 120 190
+
50
TABLE III
Increase in resistance due to attaching the corrugated mount when this is both straight and bent
+ o
0
420
i 40
60 80 Flow (l./min)
FIG.
100
120
5
Pressure-flow curves of long catheter mount, straight and bent through 180 degrees. # Endotracheal tube. + Magill connection. + Endotracheal tube + Magill + corrugated mount straight. O Endotracheal tube + Magill + corrugated mount bent.
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# Increase in pressure due to using a corrugated catheter mount rather than a straight sided mount (from table I).
20-
BRITISH JOURNAL OF ANAESTHESIA
502 DISCUSSION
ACKNOWLEDGMENTS
These measurements were made in the Research Department of Anaesthetics in the Royal College of Surgeons and I am grateful to Dr. D. W. Hill for allowing me to work in his laboratory and to Drs. A. I. Parry Brown, B. R. J. Simpson and W. D. A. Smith for help and advice.
REFERENCES
Galloon, S. (1957). The resistance of endotracheal connections. Brit. J. Anaesth., 29, 160. Hunt, K. H. (1955). The resistance of expiratory valves and canisters. Aneslhesiology, 16, 190. Macintosh, Sir Robert R., Mushin, W. W., and Epstein, H. G. (1958). Physics for the Anaesthetist, 2nd ed., p. 175. Oxford: Blackwell. Mushin, W. W., Rendell-Baker, L., and Thompson, P. W. (1959). Automatic Ventilation of the Lungs, 1st ed., p. 15. Oxford: Blackwell. Orkin, L. R., Siegel, M., and Rovenstine, E. A. (1954). Resistance to breathing by apparatus used in anesthesia. Curr. Res. Anesth., 33, 217. (1957). Resistance to breathing by apparatus used in anesthesia. Anesth. Analg. curr. Res., 36, 19 (March—April). Smith, W. D. A. (1961a). The effects of external resistance to respiration. Part I: General review. Brit. 1. Anaesth., 33, 549. (1961b). The effects of external resistance to respiration. Part II: Resistance to respiration due to anaesthetic apparatus. Brit. J. Anaesth., 33, 610.
LA RESISTANCE DES SONDES ENDOTRACHfiALES EN CAOUTCHOUC STRIfi SOMMAIRE
L'auteur a remarqu^ chez un patient ventil6 artificiellement que le nouveau type de sonde en caoutchouc strie semblait presenter au passage de l'air une resistance plus grande que les anciennes sondes lisses. II proce'da a une verification et constata, que tant que le courant d'air passa par la sonde maintenue droite, la difference entre sondes lisses et sondes striees £tait insignifiante. Cependant les sondes strides — crepes ainsi pour etre plus flexibles — presentment, une fois courbees a 180 degres, une resistance brusquement augmentee et qui
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
The four tubes were of different diameters and lengths. Poiseuille's law cannot be applied exactly to these tubes but it is reasonable to use it as a rough guide to what might be expected. It would seem that the difference between the lengths of the long mounts might cause a slight apparent increase in the resistance of the corrugated tube, but in the case of the short mounts the bias would be very much in the opposite direction, since the corrugated tube is both wider and shorter. The apparatus available did not allow flow rates greater than 150 l./min to be measured. Orkin, Siegel and Rovenstine (1954), quoting other workers, state that the normal maximum flow in healthy adults ranges from 30 to 50 l./min, although maximum flow in tachypnoea and hyperpnoea may reach 90 l./min, and in coughing much higher flow rates occur. Mushin, RendellBaker and Thompson (1959) describe 40 to 80 l./min as a high flow rate in speaking of mechanical ventilators. Although Galloon (1957) has recorded 400 l./min, this seems to be exceptional, and measurements up to 150 l./min would appear to cover a wide enough range for practical purposes. The effects of increasing airway resistance have been discussed by Smith (1961a) who reviews experimental work in conscious and anaesthetized man and dogs. Most ill effects appear to occur when the airway pressure rises above 10 cm H,O. The results presented indicate that the airway pressure increase due to using one of the newer catheter mounts is likely to be small in comparison with the pressures which might harm the patient, provided the mount is straight. However, the advantage of these mounts lies in their flexibility and, as soon as use is made of this, the price has to be paid in terms of a considerably higher resistance. The bend of 180 degrees tested is perhaps more than would often be used, but the impossibility of kinking by bending invites the anaesthetist to do this if convenient to him. Smith (1961b) has condemned the use of the Cobb connection because of its higher resistance. The corrugated catheter mounts are open to the same objection if they are going to be bent. If they are not, and if the mount will be accessible to the anaesthetist throughout the operation, there seems no reason to use them.
It may be arguable that when there is a risk that the catheter mount might become kinked in an inaccessible site during operation, the increased resistance is acceptable. The possibility of occlusion by twisting must, however, not be forgotten. If they are to be used, it is important for the anaesthetist to be aware of the increased resistance and alert to its possible ill effects.
BRITISH JOURNAL OF ANAESTHESIA
502 DISCUSSION
ACKNOWLEDGMENTS
These measurements were made in the Research Department of Anaesthetics in the Royal College of Surgeons and I am grateful to Dr. D. W. Hill for allowing me to work in his laboratory and to Drs. A. I. Parry Brown, B. R. J. Simpson and W. D. A. Smith for help and advice.
REFERENCES
Galloon, S. (1957). The resistance of endotracheal connections. Brit. J. Anaesth., 29, 160. Hunt, K. H. (1955). The resistance of expiratory valves and canisters. Aneslhesiology, 16, 190. Macintosh, Sir Robert R., Mushin, W. W., and Epstein, H. G. (1958). Physics for the Anaesthetist, 2nd ed., p. 175. Oxford: Blackwell. Mushin, W. W., Rendell-Baker, L., and Thompson, P. W. (1959). Automatic Ventilation of the Lungs, 1st ed., p. 15. Oxford: Blackwell. Orkin, L. R., Siegel, M., and Rovenstine, E. A. (1954). Resistance to breathing by apparatus used in anesthesia. Curr. Res. Anesth., 33, 217. (1957). Resistance to breathing by apparatus used in anesthesia. Anesth. Analg. curr. Res., 36, 19 (March—April). Smith, W. D. A. (1961a). The effects of external resistance to respiration. Part I: General review. Brit. 1. Anaesth., 33, 549. (1961b). The effects of external resistance to respiration. Part II: Resistance to respiration due to anaesthetic apparatus. Brit. J. Anaesth., 33, 610.
LA RESISTANCE DES SONDES ENDOTRACHfiALES EN CAOUTCHOUC STRIfi SOMMAIRE
L'auteur a remarqu^ chez un patient ventil6 artificiellement que le nouveau type de sonde en caoutchouc strie semblait presenter au passage de l'air une resistance plus grande que les anciennes sondes lisses. II proce'da a une verification et constata, que tant que le courant d'air passa par la sonde maintenue droite, la difference entre sondes lisses et sondes striees £tait insignifiante. Cependant les sondes strides — crepes ainsi pour etre plus flexibles — presentment, une fois courbees a 180 degres, une resistance brusquement augmentee et qui
Downloaded from http://bja.oxfordjournals.org/ at University of Illinois at Urbana-Champaign on March 12, 2015
The four tubes were of different diameters and lengths. Poiseuille's law cannot be applied exactly to these tubes but it is reasonable to use it as a rough guide to what might be expected. It would seem that the difference between the lengths of the long mounts might cause a slight apparent increase in the resistance of the corrugated tube, but in the case of the short mounts the bias would be very much in the opposite direction, since the corrugated tube is both wider and shorter. The apparatus available did not allow flow rates greater than 150 l./min to be measured. Orkin, Siegel and Rovenstine (1954), quoting other workers, state that the normal maximum flow in healthy adults ranges from 30 to 50 l./min, although maximum flow in tachypnoea and hyperpnoea may reach 90 l./min, and in coughing much higher flow rates occur. Mushin, RendellBaker and Thompson (1959) describe 40 to 80 l./min as a high flow rate in speaking of mechanical ventilators. Although Galloon (1957) has recorded 400 l./min, this seems to be exceptional, and measurements up to 150 l./min would appear to cover a wide enough range for practical purposes. The effects of increasing airway resistance have been discussed by Smith (1961a) who reviews experimental work in conscious and anaesthetized man and dogs. Most ill effects appear to occur when the airway pressure rises above 10 cm H,O. The results presented indicate that the airway pressure increase due to using one of the newer catheter mounts is likely to be small in comparison with the pressures which might harm the patient, provided the mount is straight. However, the advantage of these mounts lies in their flexibility and, as soon as use is made of this, the price has to be paid in terms of a considerably higher resistance. The bend of 180 degrees tested is perhaps more than would often be used, but the impossibility of kinking by bending invites the anaesthetist to do this if convenient to him. Smith (1961b) has condemned the use of the Cobb connection because of its higher resistance. The corrugated catheter mounts are open to the same objection if they are going to be bent. If they are not, and if the mount will be accessible to the anaesthetist throughout the operation, there seems no reason to use them.
It may be arguable that when there is a risk that the catheter mount might become kinked in an inaccessible site during operation, the increased resistance is acceptable. The possibility of occlusion by twisting must, however, not be forgotten. If they are to be used, it is important for the anaesthetist to be aware of the increased resistance and alert to its possible ill effects.
503
RESISTANCE OF CORRUGATED ENDOTRACHEAL CATHETER MOUNTS atteignit presque le double de celle offerte par la sonde striee maintenue droite.
CORRESPONDENCE
DER LUFTWIDERSTAND VON GEWELLTEN ANSATZSTUCKEN FOR ENDOTRACHEALKATHEDER
Sir,—I read with interest the article "Estimation of blood loss with particular reference to cardiac surgery" by Dr. J. A. Thornton et al. (Brit. J. Anaesth., 35, 91) but was surprised to see no reference made to the machine developed in Aberdeen (Roe, Gardiner and Dudley, 1962). This machine also utilizes the colorimetric method; it has an overall accuracy of 3 per cent and incorporates a spin-drier through which the swabs are finally put. This both facilitates the swab count and avoids change in the volume of the bath contents.
ESTIMATION OF BLOOD LOSS
ZUSAMMENFASSUNG
W. N. ROLLASON
Aberdeen REFERENCE
Roe, C. F., Gardiner, A. J. S., and Dudley, H. A. F. (1962). A simple instrument for rapid, continuous determination of operative blood loss. Lancet, 1, 672.
BOOK REVIEW The Obstetrician, the Anaesthetist and the Paediatrician in the Management of Obstetric Problems. Edited by Trevor Barnett and John Joyce Foley. Published by Pergamon Press, Oxford and London. Pp. 188. Price 50s. The Obstetric Unit at Portsmouth is well known to all anaesthetists due to the excellent work carried out there by the late Dr. Hamer Hodges and his colleagues. In November 1961 a conference was organized in that city by the South Western Obstetrical and Gynaecological Society, and attended by leading members of the profession. The book is a record of the papers
presented at the five half-day sessions and of the discussion that followed. The subjects considered were Unstable Presentation, Obstetric Anaesthesia, the Place of the General Practitioner in Obstetrics, Asphyxia Neonatorum, and Management of the Third Stage. Anaesthetists will find points of interest in every section, but the most challenging is that on Asphyxia Neonatorum, epitomized in Professor Ian Donald's opening phrase as "not a diagnosis but an emergency". This is a valuable work, containing many useful statements of fact and intention. It is not, nor is it intended to be, comprehensive, but anyone with an interest in obstetric anaesthesia should be aware of its contents. W. D. Wylie
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Beobachtungen an einem Patienten, der kiinstlich beatmet wurde, lieflen vermuten, dafi die neuere Art der Ansatzstiicke fiir Endotrachealkatheder aus gewelltem Gummi einen hoheren Widerstand hat als die alteren mit geraden Seiten. Dies wurde mittels eines kontinuierlichen Luftstroms bei geradem Kathederansatzstilck bestatigt. Unter diesen Umstanden ist der Unterschied zwischen den beiden gering. Gewellte Schlauche sind aber entworfen, um biegsam zu sein, und wenn sie um 180 Grad gebogen werden, steigt der Widerstand stark an; er wird tatsachlich verdoppelt.