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Measurement of Tidal Volume
COMMUNICATIONS TO THE EDITOR Lidocaine for Quinidine Syncope To the Editor: Kaplinsky and coworkers reported what they believed to be the first patient treated with lidocaine for quinidine syncope (Chest 62:764, 1972), noting a "dramatic response" and urging further trials of lidocaine in this clinical situation. However, in 1969 my associates and I described a patient in whom repeated boluses of 100 mg lidocaine failed to prevent recurrent ventricular tachycardia and fibrillation due to quinidine sensitivity. 1 Like Kaplinsky's patient, our patient developed syncope after two days of relatively low dose quinidine therapy ( 200 mg po, QID). Ultimately, pharmacologic overdriving was required to stabilize our patient's heart rhythm. Although I would no more seek to condemn lidocaine therapy for quinidine syncope on the basis of one unsuccessful case than they should want to endorse its use after one apparent success, nevertheless, the essentially self limited nature of quinidine syncope has been amply documented2 and the possibility of a fortuitous spontaneous recovery certainly should be considered in their patient. Leonard]. Lyon, M.D., Co-Director of Medical Education, Bergen Pines County Hospital, Paramus, New Jersey REFERENCES
1 Lyon LJ, Donoso E, Friedberg CK: Temporary control of ventricular arrhythmias by drug induced sinus tachycardia. Arch Int Med 123:436, 1969 2 Selzer A, Wray HW: Quinidine syncope. Paroxysmal ventricular fibrillation occurring during treatment of chronic atrial arrhythmias. Circulation 30:17, 1964
A New Suture Holder*
To the Editor: The large number of individual sutures needed in heart valve replacements has always presented the problem as to how they are best kept in order between being placed and tied. This has been solved by different surgeons by a variety of methods, all of which vary in their merits and disadvantages. The practice of clipping each suture with artery forceps and then threading these on large pins, though effective, tends to be somewhat cumbersome. Holding the sutures between the individual fingers of an assistant is satisfactory, provided sufficient spare hands are available. Coiled spring suture holders hold a large number of sutures, but the gaps in the coils are often too tight or too loose and they 0
The suture holder was made by Mr. R. Miles, senior technician at the Beaverbrook Respiratory Unit, The Children's Hospital, London.
CHEST, 66: 4, OCTOBER, 1974
have the further disadvantage of being fixed in position. The suture holder illustrated holds up to ten individual sutures in order, neatly grouped together. It consists of two stainless steel plates between which is sandwiched a 3 mm layer of synthetic rubber. One side of the suture holder is curved and is provided with ten slots, each of which ends in a round hole. To the other side of the suture holder is attached a flat rubber strip, which is fastened round an assistant's middle finger by means of nylon Velcro contact strips. Mter each suture has been sewn in place, it is passed into one of the slots where it is gripped by fine slits in the rubber until it passes into the hole at the base of each slit. It then runs freely. The loose ends of the sutures are collected together between the thumb and index finger of the hand to which the device is attached. Not only are the sutures held in order by this device, but their number is easily seen, and they can be moved at will by the assistant, and their direction and tension altered according to the needs of the surgeon. The suture holder is fully autoclavable and has already been used successfully in a number of cardiac procedures though presumably its use could be extended to other fields. ]. L. Mercer, M.D., London, England
Measurement of Tidal Volume To the Editor: The article in the February issue of Chest which examines the first attemt to remove a patient from respirator support, makes much mention of a lack of correlation between the change in tidal volume and frequency. The authors (Gilbert et al) make mention of using the spirometer in the expiratory line of the respirator to measure control values for tidal volume. There is, however, no mention of a correction of this volume to compensate for the respirator's compressable volume, which can account for as much as a 200 ml difference. COMMUNICATIONS TO THE EDITOR 463
The compressable volume refers to the volume of gas required to pressurize the respirator's internal volume and tubing during the inspiratory phase. This volume never reaches the patient to contribute to his ventilation. On expiration, this volume reexpands and is measured by the spirometer in the respirator's expiratory line. To correct for compressable volume the following formula is used: VT = spirometer volume - gauge pressure ( compressable volume in liters) For example: a patient being ventilated with a Bennett MA-l, requiring a pressure of 50 em H20 to deliver a 700 ml tidal volume (Bennett MA-l compressable volume is 3 liters) would actually receive a 550 ml tidal volume. I believe the aforementioned correction for tidal volume helps to explain the poor correlation between the change in tidal volume and frequency in the study. Donald MacLean, C.R.T.T. Inhalation Therapy, Presbyterian Hospital, New York City To the Editor: Mr. MacLean is quite correct in his statement about the necessity for taking into account the compressable volume of the respirator and tubing. This was taken into account in our work and the control values for tidal volume reported in table I and those used for calculating changes were corrected for this factor using the calculation that Mr. MacLean notes in his letter. I apologize for not having mentioned this correction in the methods section of this article. Robert Gilbert, M.D., Syracuse, New York
Fiberoptic Bronchoscopy for Detection of Early Lung Cancer To the Editor: Drs. Richardson et al (Early detection of lung cancer; Chest 64:741-46, 1973) voice enthusiasm for routine fiberoptic bronchoscopy as a means of detecting early lung cancer in high risk but asymptomatic patients over 40. I do not believe such enthusiasm is warranted, and the remainder of their article supports this view. Such a program would involve cytologic examination of collected bronchial washings and brushings on all patients. Elsewhere in the article one of the coauthors has indicated the considerable time and expense involved in this procedure and has concluded that routine screening by cytology would not be justified. Another co-author has outlined the inadequacies of screening procedures based on a sixmonth interval examination and states that much more frequent screening would be necessary. The authors make no statement as to how often the 464 COMMUNICATIONS TO THE EDITOR
asymptomatic patient should be screened and do not mention the expense to the patient. Is once a month bronchoscopy the answer to lung cancer? I think not! While the fiberoptic bronchoscope has undoubtedly increased the range and scope of bronchoscopy, I still believe that bronchoscopy is a procedure involving a slight risk, some discomfort, and considerable expense. As such, it should be done only on good clinical and laboratory indications. Unfortunately, much unnecessary bronchoscopy may result in an attempt to justify the existence of rapidly proliferating "bronchoscopists" and fiberoptic bronchoscopes. David G. Ashbaugh, M.D., F.C.C.P., Boise, Idaho To the Editor: Dr. Ashbaugh has misinterpreted our enthusiasm for investigation of the role of fiberoptic bronchoscopy in otherwise asymptomatic "high risk" patients. On re-reading the text it is easy to see how he could believe that we were advocating routine bronchoscopy as a solution to the problem of early lung cancer detection. It would be more accurate to say, however, that we feel that further research into the role of fiberoptic bronchoscopy in this problem is warranted. Such a study should be carried out only under controlled conditions such as those utilized in the early cancer detection part of the Mayo Lung Project where patients with positive sputum cytologies but negative chest x-ray films undergo complete fiberoptic bronchoscopy followed by selective segmental bronchial washings if no lesion is seen ( Fontana, Sanderson, Rosenow, personal communication). We agree entirely with Dr. Ashbaugh that bronchoscopy"... should be done only on good clinical and laboratory indications." The problem is that these indications are not yet clearly understood. Perhaps carefully done sputum cytology by the technique used at the Mayo Clinic will prove to be a satisfactory screening method for selecting patients for bronchoscopy. Perhaps, as we suggested, periodic fiberoptic bronchoscopy on high risk patients will prove to be a useful adjunct to early lung cancer detection. Because of the grim prognosis of carcinoma of the lung at the present time and the improved survival in patients whose diagnosis is made "early" in the course of their disease, we feel that any possible approach to improving early diagnosis should be fully investigated under controlled conditions. Robert H. Richardson, M.D.; Mitchell L. Rhodes, M.D.; Donald C. Zavala, M.D., and George N. Bedell, M.D., Pulmonary Disease Division, University of Iowa, Iowa City
CHEST, 66: 4, OCTOBER, 1974
1 Lyon LJ, Donoso E, Friedberg CK: Temporary control of ventricular arrhythmias by drug induced sinus tachycardia. Arch Int Med 123:436, 1969 2 Selzer A, Wray HW: Quinidine syncope. Paroxysmal ventricular fibrillation occurring during treatment of chronic atrial arrhythmias. Circulation 30:17, 1964
A New Suture Holder*
To the Editor: The large number of individual sutures needed in heart valve replacements has always presented the problem as to how they are best kept in order between being placed and tied. This has been solved by different surgeons by a variety of methods, all of which vary in their merits and disadvantages. The practice of clipping each suture with artery forceps and then threading these on large pins, though effective, tends to be somewhat cumbersome. Holding the sutures between the individual fingers of an assistant is satisfactory, provided sufficient spare hands are available. Coiled spring suture holders hold a large number of sutures, but the gaps in the coils are often too tight or too loose and they 0
The suture holder was made by Mr. R. Miles, senior technician at the Beaverbrook Respiratory Unit, The Children's Hospital, London.
CHEST, 66: 4, OCTOBER, 1974
have the further disadvantage of being fixed in position. The suture holder illustrated holds up to ten individual sutures in order, neatly grouped together. It consists of two stainless steel plates between which is sandwiched a 3 mm layer of synthetic rubber. One side of the suture holder is curved and is provided with ten slots, each of which ends in a round hole. To the other side of the suture holder is attached a flat rubber strip, which is fastened round an assistant's middle finger by means of nylon Velcro contact strips. Mter each suture has been sewn in place, it is passed into one of the slots where it is gripped by fine slits in the rubber until it passes into the hole at the base of each slit. It then runs freely. The loose ends of the sutures are collected together between the thumb and index finger of the hand to which the device is attached. Not only are the sutures held in order by this device, but their number is easily seen, and they can be moved at will by the assistant, and their direction and tension altered according to the needs of the surgeon. The suture holder is fully autoclavable and has already been used successfully in a number of cardiac procedures though presumably its use could be extended to other fields. ]. L. Mercer, M.D., London, England
Measurement of Tidal Volume To the Editor: The article in the February issue of Chest which examines the first attemt to remove a patient from respirator support, makes much mention of a lack of correlation between the change in tidal volume and frequency. The authors (Gilbert et al) make mention of using the spirometer in the expiratory line of the respirator to measure control values for tidal volume. There is, however, no mention of a correction of this volume to compensate for the respirator's compressable volume, which can account for as much as a 200 ml difference. COMMUNICATIONS TO THE EDITOR 463
The compressable volume refers to the volume of gas required to pressurize the respirator's internal volume and tubing during the inspiratory phase. This volume never reaches the patient to contribute to his ventilation. On expiration, this volume reexpands and is measured by the spirometer in the respirator's expiratory line. To correct for compressable volume the following formula is used: VT = spirometer volume - gauge pressure ( compressable volume in liters) For example: a patient being ventilated with a Bennett MA-l, requiring a pressure of 50 em H20 to deliver a 700 ml tidal volume (Bennett MA-l compressable volume is 3 liters) would actually receive a 550 ml tidal volume. I believe the aforementioned correction for tidal volume helps to explain the poor correlation between the change in tidal volume and frequency in the study. Donald MacLean, C.R.T.T. Inhalation Therapy, Presbyterian Hospital, New York City To the Editor: Mr. MacLean is quite correct in his statement about the necessity for taking into account the compressable volume of the respirator and tubing. This was taken into account in our work and the control values for tidal volume reported in table I and those used for calculating changes were corrected for this factor using the calculation that Mr. MacLean notes in his letter. I apologize for not having mentioned this correction in the methods section of this article. Robert Gilbert, M.D., Syracuse, New York
Fiberoptic Bronchoscopy for Detection of Early Lung Cancer To the Editor: Drs. Richardson et al (Early detection of lung cancer; Chest 64:741-46, 1973) voice enthusiasm for routine fiberoptic bronchoscopy as a means of detecting early lung cancer in high risk but asymptomatic patients over 40. I do not believe such enthusiasm is warranted, and the remainder of their article supports this view. Such a program would involve cytologic examination of collected bronchial washings and brushings on all patients. Elsewhere in the article one of the coauthors has indicated the considerable time and expense involved in this procedure and has concluded that routine screening by cytology would not be justified. Another co-author has outlined the inadequacies of screening procedures based on a sixmonth interval examination and states that much more frequent screening would be necessary. The authors make no statement as to how often the 464 COMMUNICATIONS TO THE EDITOR
asymptomatic patient should be screened and do not mention the expense to the patient. Is once a month bronchoscopy the answer to lung cancer? I think not! While the fiberoptic bronchoscope has undoubtedly increased the range and scope of bronchoscopy, I still believe that bronchoscopy is a procedure involving a slight risk, some discomfort, and considerable expense. As such, it should be done only on good clinical and laboratory indications. Unfortunately, much unnecessary bronchoscopy may result in an attempt to justify the existence of rapidly proliferating "bronchoscopists" and fiberoptic bronchoscopes. David G. Ashbaugh, M.D., F.C.C.P., Boise, Idaho To the Editor: Dr. Ashbaugh has misinterpreted our enthusiasm for investigation of the role of fiberoptic bronchoscopy in otherwise asymptomatic "high risk" patients. On re-reading the text it is easy to see how he could believe that we were advocating routine bronchoscopy as a solution to the problem of early lung cancer detection. It would be more accurate to say, however, that we feel that further research into the role of fiberoptic bronchoscopy in this problem is warranted. Such a study should be carried out only under controlled conditions such as those utilized in the early cancer detection part of the Mayo Lung Project where patients with positive sputum cytologies but negative chest x-ray films undergo complete fiberoptic bronchoscopy followed by selective segmental bronchial washings if no lesion is seen ( Fontana, Sanderson, Rosenow, personal communication). We agree entirely with Dr. Ashbaugh that bronchoscopy"... should be done only on good clinical and laboratory indications." The problem is that these indications are not yet clearly understood. Perhaps carefully done sputum cytology by the technique used at the Mayo Clinic will prove to be a satisfactory screening method for selecting patients for bronchoscopy. Perhaps, as we suggested, periodic fiberoptic bronchoscopy on high risk patients will prove to be a useful adjunct to early lung cancer detection. Because of the grim prognosis of carcinoma of the lung at the present time and the improved survival in patients whose diagnosis is made "early" in the course of their disease, we feel that any possible approach to improving early diagnosis should be fully investigated under controlled conditions. Robert H. Richardson, M.D.; Mitchell L. Rhodes, M.D.; Donald C. Zavala, M.D., and George N. Bedell, M.D., Pulmonary Disease Division, University of Iowa, Iowa City
CHEST, 66: 4, OCTOBER, 1974