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The Price of Therapeutic Artificial Ventilation
1161
THE LANCET
The Price of
Therapeutic Artificial
Ventilation INTERMITTENT positive-pressure ventilation demands an airtight seal between the ventilator and the patient’s respiratory passages. Endotracheal and tracheostomy tubes, with their inflatable cuffs, can be damaging. Endotracheal tubes damage the larynx rather than the trachea, producing, not infrequently, paralysis of the small muscles of the larynx in patients who have been intubated for some time 1,22 and, more rarely, vocal-cord granuloma.1,3 Fixation of the arytenoid cartilages is another occasional sequel to prolonged intubation.4 PAEGLE et awl. have lately recorded the necropsy appearances in patients intubated for different periods, revealing a possible sequence of events. When a tube has been in position for twelve hours, ciliated epithelium is lost over the tracheal rings. Shortly afterwards the submucosa shows early necrosis with congestion and capillary thrombosis. Within twenty-four hours the erosions reach the cartilage in the central portion of the rings; and after three to five days the inflammatory reaction has usually extended to the margins of the tracheal rings, with early necrosis of cartilage. Some patients survived long enough for scarring to begin at the site of the damage. Where epithelium regenerated it was quite often stratified-the loss of ciliary activity in such areas predisposes, of course, to retention of tracheobronchial secretions. Simple pressure is not the only factor which has been blamed for tracheal necrosis; some believe that residues of ethylene oxide, used to sterilise tubes, diffuse into the tracheal lining, where ethylene glycol and ethylene chlorhydrin (2-chloroethanol)-both profoundly irritant-are formed. 6, In addition to ulceration of the trachea, tubes may give rise to tracheomalacia with progressive dilatation of the trachea 8,9-and even to tracheocesophageal fistula. 10 Occasionally a tracheostomy Elbrond, L. Dan. med. Bull. 1964, 9, 134. Dan, W., Zwergius, E. Nord. Med. 1952, 48, 1095. Lindholm, C. E. Acta anœsth. scand. 1969, 33, suppl. p. 33. McClelland, R. M. A. Proc. R. Soc. Med. 1972, 65, 401. Paegle, R. D., Ayres, S. M., Davis, S. Archs Surg. 1973, 106, 31. Little, K., Parkhouse, J. Lancet, 1962, ii, 857. Stetson, J. B., Guess, W. L. Anesthesiology, 1970, 33, 635. Feldman, S. A., Deal, C. W., Urquhart, W. Lancet, 1966, i, 954. Robbie, D. S., Feldman, S. A. Br. J. Anœsth. 1963, 35, 771. 10. Muck, O., Kristensen, H. S., Larssen, H. C. A. Lancet, 1961, i, 66. 1. 2. 3. 4. 5. 6. 7. 8. 9.
tube ulcerates right through the tracheal wall into the innominate artery, with disastrous haemorrhage.ll Damage to tracheal mucosa is much diminished by the use of low-pressure cuffs In the United Kingdom the Radcliffe tube, with its latex inflatable cuff, has been employed for many years. These, however, are not completely foolproof and they can be inflated, even at minimum occluding volume, to the point at which the pressure on the tracheal mucosa is at least equal to the blood-pressure at the arterial end of the normal capillary.13 Little wonder, then, that tracheal damage is accentuated in patients who are hypotensive for any length of time. 14 For a time similar cuffs were popular in the United States.15 They too produced an airtight seal with quite low pressures within the cuff and between the cuff and the tracheal wall. Now, however, most U.S. anaesthetists prefer plastic tubes to the latex-rubber cuffed tracheostomy tubes, possibly because reactions to rubber are feared. Such plastic cuffs have a very low compliance indeed, and injection into them of very little more than 2 ml. of air can produce an intra-cuff pressure of up to 300 mm. Hg. Of course, not all this pressure within the cuff is transmitted to the tracheal wall, but with such a poorly compliant cuff the margin between the lowest pressure required-for an airtight seal and the pressure which converts the cuff into a stone-like object producing excessive pressure on the tracheal wall is very narrow indeed.6 Herein may lie the explanation for BASSETT’s observation 14 that all his cases of tracheal stenosis developed while such tubes were being used in his hospital. In the U.S.A. it is now customary to prestretch the plastic cuff of the tracheostomy tube. Larger low-pressure cuffs are also available, and with these tracheal damage associated with intermittent positive-pressure respiration is considerably reduced.17 These large-volume, lowpressure cuffs will also relieve the anxieties of those who worry about overstretching cuffs and producing cuff herniation over the end of the tube with consequent acute respiratory obstruction. The most dramatic sequel to treatment by intermittent positive-pressure respiration is tracheal stenosis. In some clinics this has the disturbingly high incidence of 15%.18 In the Massachusetts General Hospital, however, around 1% of patients treated by mechanical ventilation for more than 24 hours have required surgical resection and reconstruction of the trachea because of stenosis and tracheomalacia.19 11. Garland, H. Proc. R. Soc. Med. 1959, 52, 877. 12. Grillo, H. C., Cooper, J. D., Geffin, B., Pontoppidan, H. J. cardiovasc. Surg. 1971, 62, 898. 13. Knowlson, G. I. G., Bassett, H. F. M. Br. J. Anœsth. 1970, 42, 834. 14. Bassett, H. F. M. Proc. R. Soc. Med. 1971, 64, 890. 15. Adriani, J., Phillips, M. Anesthesiology, 1957, 18, 1. 16. Geffin, B., Pontoppidan, H. ibid. 1969, 31, 462. 17. Ching, N. P., Ayres, S. M., Paegle, R. D., Linden, J. M., Nealon, T. F., Jr. J. cardiovasc. Surg. 1971, 62, 402. 18. Pearson, F. E., Goldberg, M., Da Silva, A. J. Archs Surg. 1968, 19.
97, 380. Pontoppidan, H., Geffin, B., Lowenstein, 1972, 287, 799.
E. New
Engl. J. Med.
1162
Some
of stenosis undoubtedly result from the of an inflated cuff on the tracheal wall. pressure Here the main presenting symptom is stridor at rest, often with dyspnoea on exertion. Symptoms usually appear within three months of extubation, but may be delayed as long as eighteen months. It seems that for a stricture to give rise to symptoms the diameter of the tracheal lumen must be reduced by 50% or more, and diameters as small as 5 mm. are quite common. This group of strictures represent rather less than 50°of those which present for surgical treatment. 20 Tracheal stenosis at the site of the stoma is rather commoner. In one retrospective study of 50 patients who had been treated for chest injury by intermittent positive-pressure respiration, all but 2 showed some narrowing of the trachea 21; with 2 exceptions the narrowing was at the site of the tracheostome and not at the site of the cuff. Therefore surgical trauma to the trachea is apparently an even more potent cause of the subsequent narrowing than is cuff pressure. Presumably the most serious stenoses at this site are due to surgical misjudgment: those who do tracheostomies on patients who are to have artificial ventilation ought to be fully aware of the possible complications and sequelae. Finally, there is yet another site at which tracheal stenosis may occur. BASSETT has noted a fibrogranulomatous diaphragm going into the trachea and obstructing it.14 Such a lesion may appear at the stoma,19 but it can also appear at the level of the tip of the tracheostomy tube-also, of course, the point at which the tracheostomy tube is liable to ulcerate its way into the innominate artery. This type of lesion is believed to be most likely where an airtight seal between the tracheal wall and the ventilator is secured by inflation of a spherical cuff, for a spherical object in the trachea (or indeed anywhere else in the cylindrical tube) can rotate in any direction. No doubt when such tubes are in position the traction on the hoses attaching the patient to the breathingmachine pulls the tube round until its end digs into the tracheal mucous membrane. There is therefore a great deal to be said for using a tracheostomy tube with a long cuff: not only does this spread the pressure over a considerable area but it also prevents the end from being pushed against the tracheal wall. Some forms of tracheal stenosis, particularly the fibrogranulomatous variety, respond well to dilatation. The other forms, however, require resection-an operation with a substantial mortality. 2Stomal stenosis can be avoided by judicious surgery. Low-pressure cuffs will go far to prevent stenosis at the site of the cuff. Substitution of long cuffs for those which become spherical when inflated will eliminate damage to the tracheal wall by the hard tip of the tracheostomy tube.
Mycoplasmas
cases
in Human
Infertility
be isolated from a human THE first mycoplasma being came from a Bartholin’s abscess.1 Since that time interest has been focused on the relation between the various mycoplasma species found in the genitourinary tract and disease. Three species of mycoplasma have been isolated from this siteMycoplasma hominis and M. fermentans (both of which are " classic " mycoplasmas which form typical " fried egg " colonies on suitable solid culture media), and the T-strain mycoplasmas which form tiny colonies on solid media. M. fermentans is not often isolated from the genitourinary tract and its import is unknown. M. hominis is commonly found in adults and may from time to time give rise to local sepsis such as bartholinitis, salpingitis,2 and even pelvic peritonitis,3 as well as being isolated from the blood of patients with post-partum or postoperative pyrexia.3,4 T-strain mycoplasmas, of which there appear to be many different serotypes,5 are commonly found in the genitourinary tract of adults, and their prevalence seems to be related to sexual activity. 6,7 Although there has been much controversy over the role of T-strain mycoplasmas in genitourinary-tract disease, especially in relation to nonspecific urethritis, there is still no clearcut evidence that these organisms play a pathogenic role.6-8 to
Lately, interest has centered on the possible relation between mycoplasmas and reproductive failure. KLEIN et a1.,9 working with neonates, reported an association between isolation of M. hominis and of T-strain mycoplasmas and low birth-weight, while KUNDSIN and DRISCOLL 10 isolated mycoplasmas more frequently from pregnant women with previous reproductive failure (or with a poor prognosis for the current pregnancy) and from the fetal membranes of aborted fetuses or premature babies than from normal pregnant women and normal full-term babies. They also reported 11 that women with a history of spontaneous abortions and with mycoplasmas in their cervical secretions had successful pregnancies after erythromycin or tetracycline treatment of both husband and wife. Since then GNARPE and FRIBERG 12 1. 2. 3. 4. 5.
6. 7. 8. 9. 10.
Dienes, L., Edsall, J. Proc. Soc. exp. Biol. Med. 1937, 36, 740. Stokes, E. J. Lancet, 1955, i, 276. Russell, F. E., Fallon, R. J. ibid. 1970, i, 1295. Tully, J. G., Brown, M. S., Sheagren, J. N., Young, V. M., Wolff, S. M. New Engl. J. Med. 1965, 273, 648. Purcell, R. H., Chanock, R. M., Taylor-Robinson, D. in The Mycoplasmatales and the L-phase of Bacteria (edited by L. Hayflick); p. 254. Amsterdam, 1969. McCormack, W. M., Braun, P., Lee, Y-H., Klein, J. O., Kass, E. H. New Engl. J. Med. 1973, 288, 78. McCormack, W. M., Almeida, P. C., Bailey, P. B., Grady, E. M., Lee, Y-H. J. Am. med. Ass. 1972, 221, 1375. Lancet, 1970, i, 876. Klein, J. D., Buckland, D., Finland, M. New Engl. J. Med. 1969, 280, 1025. Kundsin, R. B., Driscoll, S. G. Ann. N.Y. Acad. Sci. 1970, 174, 794.
Andrews, M. J., Pearson, F. G. Br. J. Surg. 1973, 60, 208. Davidson, I. A., Cruickshank, A. N., Duthie, W. H., Bargh, W., Duncan, J. G. Proc. R. Soc. Med. 1971, 64, 886. 22. Grillo, H. C. Ann. Surg. 1965, 162, 374. 20. 21.
11.
12.
Kundsin, R. B., Driscoll, S. G., Praznick, J. in Mycoplasma Diseases of Man (edited by M. Sprossig and W. Witzleb); p. 141. Jena, 1969. Gnarpe, H., Friberg, J. Nature, 1973, 242, 120.
THE LANCET
The Price of
Therapeutic Artificial
Ventilation INTERMITTENT positive-pressure ventilation demands an airtight seal between the ventilator and the patient’s respiratory passages. Endotracheal and tracheostomy tubes, with their inflatable cuffs, can be damaging. Endotracheal tubes damage the larynx rather than the trachea, producing, not infrequently, paralysis of the small muscles of the larynx in patients who have been intubated for some time 1,22 and, more rarely, vocal-cord granuloma.1,3 Fixation of the arytenoid cartilages is another occasional sequel to prolonged intubation.4 PAEGLE et awl. have lately recorded the necropsy appearances in patients intubated for different periods, revealing a possible sequence of events. When a tube has been in position for twelve hours, ciliated epithelium is lost over the tracheal rings. Shortly afterwards the submucosa shows early necrosis with congestion and capillary thrombosis. Within twenty-four hours the erosions reach the cartilage in the central portion of the rings; and after three to five days the inflammatory reaction has usually extended to the margins of the tracheal rings, with early necrosis of cartilage. Some patients survived long enough for scarring to begin at the site of the damage. Where epithelium regenerated it was quite often stratified-the loss of ciliary activity in such areas predisposes, of course, to retention of tracheobronchial secretions. Simple pressure is not the only factor which has been blamed for tracheal necrosis; some believe that residues of ethylene oxide, used to sterilise tubes, diffuse into the tracheal lining, where ethylene glycol and ethylene chlorhydrin (2-chloroethanol)-both profoundly irritant-are formed. 6, In addition to ulceration of the trachea, tubes may give rise to tracheomalacia with progressive dilatation of the trachea 8,9-and even to tracheocesophageal fistula. 10 Occasionally a tracheostomy Elbrond, L. Dan. med. Bull. 1964, 9, 134. Dan, W., Zwergius, E. Nord. Med. 1952, 48, 1095. Lindholm, C. E. Acta anœsth. scand. 1969, 33, suppl. p. 33. McClelland, R. M. A. Proc. R. Soc. Med. 1972, 65, 401. Paegle, R. D., Ayres, S. M., Davis, S. Archs Surg. 1973, 106, 31. Little, K., Parkhouse, J. Lancet, 1962, ii, 857. Stetson, J. B., Guess, W. L. Anesthesiology, 1970, 33, 635. Feldman, S. A., Deal, C. W., Urquhart, W. Lancet, 1966, i, 954. Robbie, D. S., Feldman, S. A. Br. J. Anœsth. 1963, 35, 771. 10. Muck, O., Kristensen, H. S., Larssen, H. C. A. Lancet, 1961, i, 66. 1. 2. 3. 4. 5. 6. 7. 8. 9.
tube ulcerates right through the tracheal wall into the innominate artery, with disastrous haemorrhage.ll Damage to tracheal mucosa is much diminished by the use of low-pressure cuffs In the United Kingdom the Radcliffe tube, with its latex inflatable cuff, has been employed for many years. These, however, are not completely foolproof and they can be inflated, even at minimum occluding volume, to the point at which the pressure on the tracheal mucosa is at least equal to the blood-pressure at the arterial end of the normal capillary.13 Little wonder, then, that tracheal damage is accentuated in patients who are hypotensive for any length of time. 14 For a time similar cuffs were popular in the United States.15 They too produced an airtight seal with quite low pressures within the cuff and between the cuff and the tracheal wall. Now, however, most U.S. anaesthetists prefer plastic tubes to the latex-rubber cuffed tracheostomy tubes, possibly because reactions to rubber are feared. Such plastic cuffs have a very low compliance indeed, and injection into them of very little more than 2 ml. of air can produce an intra-cuff pressure of up to 300 mm. Hg. Of course, not all this pressure within the cuff is transmitted to the tracheal wall, but with such a poorly compliant cuff the margin between the lowest pressure required-for an airtight seal and the pressure which converts the cuff into a stone-like object producing excessive pressure on the tracheal wall is very narrow indeed.6 Herein may lie the explanation for BASSETT’s observation 14 that all his cases of tracheal stenosis developed while such tubes were being used in his hospital. In the U.S.A. it is now customary to prestretch the plastic cuff of the tracheostomy tube. Larger low-pressure cuffs are also available, and with these tracheal damage associated with intermittent positive-pressure respiration is considerably reduced.17 These large-volume, lowpressure cuffs will also relieve the anxieties of those who worry about overstretching cuffs and producing cuff herniation over the end of the tube with consequent acute respiratory obstruction. The most dramatic sequel to treatment by intermittent positive-pressure respiration is tracheal stenosis. In some clinics this has the disturbingly high incidence of 15%.18 In the Massachusetts General Hospital, however, around 1% of patients treated by mechanical ventilation for more than 24 hours have required surgical resection and reconstruction of the trachea because of stenosis and tracheomalacia.19 11. Garland, H. Proc. R. Soc. Med. 1959, 52, 877. 12. Grillo, H. C., Cooper, J. D., Geffin, B., Pontoppidan, H. J. cardiovasc. Surg. 1971, 62, 898. 13. Knowlson, G. I. G., Bassett, H. F. M. Br. J. Anœsth. 1970, 42, 834. 14. Bassett, H. F. M. Proc. R. Soc. Med. 1971, 64, 890. 15. Adriani, J., Phillips, M. Anesthesiology, 1957, 18, 1. 16. Geffin, B., Pontoppidan, H. ibid. 1969, 31, 462. 17. Ching, N. P., Ayres, S. M., Paegle, R. D., Linden, J. M., Nealon, T. F., Jr. J. cardiovasc. Surg. 1971, 62, 402. 18. Pearson, F. E., Goldberg, M., Da Silva, A. J. Archs Surg. 1968, 19.
97, 380. Pontoppidan, H., Geffin, B., Lowenstein, 1972, 287, 799.
E. New
Engl. J. Med.
1162
Some
of stenosis undoubtedly result from the of an inflated cuff on the tracheal wall. pressure Here the main presenting symptom is stridor at rest, often with dyspnoea on exertion. Symptoms usually appear within three months of extubation, but may be delayed as long as eighteen months. It seems that for a stricture to give rise to symptoms the diameter of the tracheal lumen must be reduced by 50% or more, and diameters as small as 5 mm. are quite common. This group of strictures represent rather less than 50°of those which present for surgical treatment. 20 Tracheal stenosis at the site of the stoma is rather commoner. In one retrospective study of 50 patients who had been treated for chest injury by intermittent positive-pressure respiration, all but 2 showed some narrowing of the trachea 21; with 2 exceptions the narrowing was at the site of the tracheostome and not at the site of the cuff. Therefore surgical trauma to the trachea is apparently an even more potent cause of the subsequent narrowing than is cuff pressure. Presumably the most serious stenoses at this site are due to surgical misjudgment: those who do tracheostomies on patients who are to have artificial ventilation ought to be fully aware of the possible complications and sequelae. Finally, there is yet another site at which tracheal stenosis may occur. BASSETT has noted a fibrogranulomatous diaphragm going into the trachea and obstructing it.14 Such a lesion may appear at the stoma,19 but it can also appear at the level of the tip of the tracheostomy tube-also, of course, the point at which the tracheostomy tube is liable to ulcerate its way into the innominate artery. This type of lesion is believed to be most likely where an airtight seal between the tracheal wall and the ventilator is secured by inflation of a spherical cuff, for a spherical object in the trachea (or indeed anywhere else in the cylindrical tube) can rotate in any direction. No doubt when such tubes are in position the traction on the hoses attaching the patient to the breathingmachine pulls the tube round until its end digs into the tracheal mucous membrane. There is therefore a great deal to be said for using a tracheostomy tube with a long cuff: not only does this spread the pressure over a considerable area but it also prevents the end from being pushed against the tracheal wall. Some forms of tracheal stenosis, particularly the fibrogranulomatous variety, respond well to dilatation. The other forms, however, require resection-an operation with a substantial mortality. 2Stomal stenosis can be avoided by judicious surgery. Low-pressure cuffs will go far to prevent stenosis at the site of the cuff. Substitution of long cuffs for those which become spherical when inflated will eliminate damage to the tracheal wall by the hard tip of the tracheostomy tube.
Mycoplasmas
cases
in Human
Infertility
be isolated from a human THE first mycoplasma being came from a Bartholin’s abscess.1 Since that time interest has been focused on the relation between the various mycoplasma species found in the genitourinary tract and disease. Three species of mycoplasma have been isolated from this siteMycoplasma hominis and M. fermentans (both of which are " classic " mycoplasmas which form typical " fried egg " colonies on suitable solid culture media), and the T-strain mycoplasmas which form tiny colonies on solid media. M. fermentans is not often isolated from the genitourinary tract and its import is unknown. M. hominis is commonly found in adults and may from time to time give rise to local sepsis such as bartholinitis, salpingitis,2 and even pelvic peritonitis,3 as well as being isolated from the blood of patients with post-partum or postoperative pyrexia.3,4 T-strain mycoplasmas, of which there appear to be many different serotypes,5 are commonly found in the genitourinary tract of adults, and their prevalence seems to be related to sexual activity. 6,7 Although there has been much controversy over the role of T-strain mycoplasmas in genitourinary-tract disease, especially in relation to nonspecific urethritis, there is still no clearcut evidence that these organisms play a pathogenic role.6-8 to
Lately, interest has centered on the possible relation between mycoplasmas and reproductive failure. KLEIN et a1.,9 working with neonates, reported an association between isolation of M. hominis and of T-strain mycoplasmas and low birth-weight, while KUNDSIN and DRISCOLL 10 isolated mycoplasmas more frequently from pregnant women with previous reproductive failure (or with a poor prognosis for the current pregnancy) and from the fetal membranes of aborted fetuses or premature babies than from normal pregnant women and normal full-term babies. They also reported 11 that women with a history of spontaneous abortions and with mycoplasmas in their cervical secretions had successful pregnancies after erythromycin or tetracycline treatment of both husband and wife. Since then GNARPE and FRIBERG 12 1. 2. 3. 4. 5.
6. 7. 8. 9. 10.
Dienes, L., Edsall, J. Proc. Soc. exp. Biol. Med. 1937, 36, 740. Stokes, E. J. Lancet, 1955, i, 276. Russell, F. E., Fallon, R. J. ibid. 1970, i, 1295. Tully, J. G., Brown, M. S., Sheagren, J. N., Young, V. M., Wolff, S. M. New Engl. J. Med. 1965, 273, 648. Purcell, R. H., Chanock, R. M., Taylor-Robinson, D. in The Mycoplasmatales and the L-phase of Bacteria (edited by L. Hayflick); p. 254. Amsterdam, 1969. McCormack, W. M., Braun, P., Lee, Y-H., Klein, J. O., Kass, E. H. New Engl. J. Med. 1973, 288, 78. McCormack, W. M., Almeida, P. C., Bailey, P. B., Grady, E. M., Lee, Y-H. J. Am. med. Ass. 1972, 221, 1375. Lancet, 1970, i, 876. Klein, J. D., Buckland, D., Finland, M. New Engl. J. Med. 1969, 280, 1025. Kundsin, R. B., Driscoll, S. G. Ann. N.Y. Acad. Sci. 1970, 174, 794.
Andrews, M. J., Pearson, F. G. Br. J. Surg. 1973, 60, 208. Davidson, I. A., Cruickshank, A. N., Duthie, W. H., Bargh, W., Duncan, J. G. Proc. R. Soc. Med. 1971, 64, 886. 22. Grillo, H. C. Ann. Surg. 1965, 162, 374. 20. 21.
11.
12.
Kundsin, R. B., Driscoll, S. G., Praznick, J. in Mycoplasma Diseases of Man (edited by M. Sprossig and W. Witzleb); p. 141. Jena, 1969. Gnarpe, H., Friberg, J. Nature, 1973, 242, 120.