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A Computer Analysis of Pulmonary Function in Surgical Patients
A Computer Analysis of Pulmonary Function in Surgical Patients William A. Neely, M.D., William T. Robinson, M.D., James D. Hardy, M.D., and William 0. Bobo, M.D. ABSTRACT A small analogue computer for studying the mechanics of ventilation in preoperative and postoperative patients has been designed. We found that more air was moved per minute and that respiratory rate was increased in the postoperative period. Most important was the finding that the increase in work per minute was proportionately greater than the amount of air moved. This finding implies an inherent decrease in efficiency with increased ventilation and airway obstruction or increased stiffness of the lungs postoperatively. There was a decrease in dynamic com liance but tidal volume remained unchanged during the postoperative perio8, emphasizing the importance of changes in compliance and work/ventilation ratio. In patients who developed respiratory difficulties postoperatively, a high work/ventilation ratio was noted preoperatively; these values rose to very high levels during the immediate postoperative period.
P
ulmonary failure is an important direct or contributing cause of death in surgical patients. On reviewing our surgical mortality figures over the past year, we have found that pulmonary failure is the cause of death in 25% of our patients and a contributing factor in an additional 25%. Review of the literature reveals that our statistics are not unique [5, 91. Phillips and Cope [7] reported that respiratory tract damage was the principal cause of death in burn patients. Gaensler [4]has stated that disorders of ventilation comprise about 95% of pulmonary function abnormalities. Blaisdell and associates [Z], reporting a series of patients with severe trauma, observed that of those patients who survived 24 hours, one-half later died of pulmonary complications. More and more patients are surviving early trauma and operation because better resuscitative techniques are available and fluid and blood replacement is emphasized. Now that blood gas measurements are readily available, pulmonary complications which would heretofore pass unnoticed are being observed in many patients [l, 3, 81. T o study the alterations in pulmonary function both in patients undergoing elective surgery and in severely injured patients, we have deg r o m the Department of Surgery, University of Mississippi School of Medicine, Jackson, Miss. Supported by National Institutes of Health Grant No. HE 09858. Presented at the Seventeenth Annual Meeting of the Southern Thoracic Surgical Association, Bermuda, Nov. 5-7. 1970. Address reprint requests to Dr. Neely. University of Mississippi Medical Center, Jackson, Miss. 39216.
VOL. 11, NO.
6,
JUNE,
1971
565
NEELY ET AL.
vised a small bedside analogue computer to measure the following variables: pulmonary power, pulmonary minute work, respiratory air flow, minute volume, intrapleural pressure, peak inspiratory flow, peak expiratory flow, mean tidal volume, total lung and airway resistance, pulmonary dynamic compliance, and work/ventilation ratio. These values can be read directly and are immediately available for evaluation and to aid in treatment. METHOD Since the method of study has been described elsewhere [61, it will be discussed only briefly. T h e respiratory flow signal and intrapleural pressure signal are amplified and fed through a multiplier that computes and displays an instantaneous product. This product is reduced in such a way that only the inspiratory half of the respiratory cycle is used in subsequent computations. Integration of the product (power) produces work, and integration of the flow signal produces volume. T h e integrating ampIifiers are reset to zero at oneminute intervals so that minute work and minute volume are displayed. Work/ ventilation ratio is obtained by dividing minute work by minute volume. Mean tidal volume is obtained by dividing minute ventilation by respiratory rate. Airway and lung tissue resistance is computed as minute work times 60 divided by minute volume. Dynamic compliance is computed as mean tidal volume divided by mean inspiratory pressure. Inspiratory pressure is read directly from the record.
PATIENT PREPARATION Immediately preoperatively and postoperatively a catheter-tipped esophageal balloon is passed to a point approximately 40 cm. distal to the external nares and is inflated with 10 to 15 cc. of air. T h e balloon is then moved up or down slightly to minimize cardiac pulsation. A mask with attached pneumotachygraph is placed over the patient’s face. The pressure recording is then adjusted using zero suppression so that the base line coincides with the beginning of inspiration. Postoperative studies are conducted in a like manner.
RESULTS The results in 21 patients studied in this manner are given in the Figure. There was always an increase in postoperative work except in those patients who had no preexisting cardiopulmonary disease. None of the groups in the Figure exhibited a greater preo erative work than the obese patients, but there was relatively little difference getween obese and nonobese groups postoperatively. The atients over 40 years of age had a greater increase in postoperative work than t.E ose less than 40. Minute ventilation changed noticeably in the groups that were over 40 years, male, nonobese, or had thoracotomy, preexisting cardiovascular disease, pulmonary complication, or longer duration of anesthesia. Alterations in respiratory rate generally paralleled those of minute volume. Work/ventilation ratio was increased in every group postoperatively. Preoperatively the obese group exhibited a higher ratio than the nonobese group; postoperatively the patients over 40 years and the obese group showed the greatest relative increase. The work/ventilation ratio also tended to be higher postoperatively in those patients with a history of preexisting cardiopulmonary disease. Surprisingly, the tidal volume did not change appreciably postoperatively. 566
THE ANNALS OF THORACIC SURGERY
w
M
z
C
4
?
2:
I
w
c
COMPLIANCE
(brePthr/nin.)
RATE
(joules/liter)
WORK/VENTILATION
MINUTE VOLUME
I
I
I
-
*
*
5.12
19.9
4
0.99
4
8
4
16.9 18.86 1728 1787 18.62 19.30
1.39-0.86
-
PRE-OP
*
7.76
5.58
4
4
5.40 4.52
DURATION OF ANESTH.
I
0.99
I
I
0.97 1.00 I
b
I 4
19.67 25.63 24.30 25.14 22.86
4
I
18.18 19.24 1714 18.93
1.13
I
0.77 0.65 0.60 0.66
6.96
706 6.57 -. 9.24 8.58 11.87 7.75 4
6.62
I
4
4
75.2 45.5 56.6 63.3-43.4
4
80.3 98.2 109.2
48.2
4
975
93.0 45.3 56.0
76.0
4
8
48.4 56.4 50.4
89.5 113.9 80.1
362.1 404.5 434.4 96.5 387.7 390.0 375.3 379.6 545.9 338.2
313.4 418.7 365.9 373.f 411.6 342.1 308.1 358.1 383.5 332.8 329.9 371.4 408.7349.2
21.63 25.20
4
1788
0.76 0.63 4 4 1.14 -0.86
9.33
4
708
*
I
6.85 10.56 8.30 12.38 8.07
+
5.34 3.50 4.97 4.77
I
PRE-EXISTING PULMONARY COMPLICATIONS
17.45 18.53
1.05
8
0.79
4
0.98 0.56 0.65
5.99 761
4
8.20 9.39 10.41
4
6.32 6.84 16.96 6.02 716 6.33 7.37
I
8.36 10.61
*
4.54
OPERATIVE PROCEDURE
11.48 8.33 10.81
4
6.87 3.54
1
oBESITy
POST-OP 26.0 21.5 24.79 21.29 2225 24.46 24.80
PRE-OP
PRE-OP
SEX
Mean preoperative and postoperative values of pulmonai y function in 21 surgical patients. Figures in parentheses in the column headings indicate the number of patients in each group. Statistical significance ( p < 0.05) within a group is indicated by a vertical arrow; statistical significance Cp < U.05) between groups is indicated by a horizontal arrozu.
I
AGE
1 I 1
NEELY E T AL. Compliance was decrensed postoperatively in every comparison except in the groups of patients who were female, obese, had no cardiopulmonary disease, liatl pulmonary complications, and whose anesthesia time was greater than four hours. Thoracotomy produced a higher postoperative compliance than that of patients who did not undergo thoracotomy. COMMENT
T h e data presented here have been divided as indicated in the Figure. T h e significant changes obtained between and within these arbitrary groups do not mean that these subdivisions are mutually exclusive and independent. For instance, the greater than 40 age group might also have experienced the longest operations, and the group might have been weighted with more patients having preexisting cardiopulmonary disease. An analysis of this type precludes absolute conclusions being drawn from the factors mentioned. Nevertheless, we believe that this analysis is useful in interpreting the data and in predicting postoperative problems. Operation, being a form of trauma, increases the work of respiration. Most of the changes that we demonstrated are predictable from the work of others and from clinical impressions. It is important to note, however, that the work/ventilation ratio is a measure of the efficiency of respiration. T h e values greater than 1 joule per liter in individual patients are definitely abnormal. T h e obese patients exhibited the highest work/ventilation ratio preoperatively and postoperatively. With the exception of those patients having long anesthesia times, the obese patients also exhibited the greatest increase in pulmonary work. Tidal volume did not change significantly between the preoperative and postoperative periods. If this holds true in subsequent studies, it will mean that expiratory rate is an excellent indicator of minute volume-and compliance and rate are the primary determinants of pulmonary work. Several inexplicable results became evident when the data were scrutinized more closely. Minute volume increased significantly in the nonobese patients, whereas the obese patients did not significantly increase their minute volume. One wonders if the obese patient may be incapable of generating a sustained increase in minute volume due to the high energy cost of the effort, as was illustrated in their increased workhentilation ratio. REFERENCES 1 . Able, F. L., Waldliausen, J. A., Daley, W. F., and Pearce, W. L. Pulmonary blood volume in hemorrhagic shock in the dog and primate. Amer. J . Physiol.
213:1072, 1967.
568
THE ANNALS OF THORACIC SURGERY
Pulmonary Function in Surgical Patients 2. Blaisdell, F. W.,Lim, R. C., Amberg, J. R., Choy, S. H., Hall, A. D., and Thomas, A. N. Pulmonary microembolism: A cause of morbidity and death after major vascular surgery. Arch. Surg. (Chicago) 93:776, 1966. 3. Borst, H. E., Berghund, E., Wittenburger, S. L., Mead, J., McGregor, M., and Collier, C. The effect of pulmonary vascular pressures on the mechanical properties of the lungs in anesthetized dogs. J. Clin. Invest. 36:1708, 1957. 4. Gaensler, E. A. Personal communication, 1969. 5. Jackson, T. M., and Lee, W. H., Jr. Major thermal burns: A mortality appraisal and review. Arch. Surg. (Chicago) 87:937, 1963. 6. Neely, W. A., Robinson, W. T., Holloman, G. H., Jr., and McMullan, M. H. An inexpensive bedside analogue computer for measuring respiratory work and certain other parameters. Surgery 69: 309, 1971. 7. Phillips, A. W., and Cope, 0. Burn therapy: 11. The revelation of respiratory tract damage as a principal killer of the burned patient. A n n . Surg. 155: 1, 1962. 8. Proctor, H. J., Moss, G. S., Homer, L. D., and Litt, B. D. Changes in lung compliance in experimental hemorrhagic shock and resuscitation. A n n . Surg. 169:82, 1969. 9. Taylor, F. W., and Gumbert, J. L. Cause of death from burns: Role of respiratory damage. Ann. Surg. 161:497, 1965.
NOTICE FROM THE SOUTHERN THORACIC SURGICAL ASSOCIATION The Eighteenth Annual Meeting of the Southern Thoracic Surgical Association will be held at the Holiday Inn Hotel in Tampa, Fla., November 4-6, 1971. Reservations may be made by writing to Mr. Adam Habler, Reservations Manager, P.O. Box 271, Tampa, Fla. 33601. Application for membership in the Southern Thoracic Surgical Association, on forms provided by the Association, should be sent directly to Frederick H. Taylor, M.D. (Chairman of the Membership Committee), 1012 Kings Dr., Charlotte, N.C. 28207, no later than September 1, 1971. Papers that are accepted for the program and are to be considered for b l i cation in T h e Annals should be submitted to the Editor by October 15, 1r 71 JAM= W. BROOKS, M.D. Secretary-Treasurer
VOL. 11, NO.
6,
JUNE,
1971
569
P
ulmonary failure is an important direct or contributing cause of death in surgical patients. On reviewing our surgical mortality figures over the past year, we have found that pulmonary failure is the cause of death in 25% of our patients and a contributing factor in an additional 25%. Review of the literature reveals that our statistics are not unique [5, 91. Phillips and Cope [7] reported that respiratory tract damage was the principal cause of death in burn patients. Gaensler [4]has stated that disorders of ventilation comprise about 95% of pulmonary function abnormalities. Blaisdell and associates [Z], reporting a series of patients with severe trauma, observed that of those patients who survived 24 hours, one-half later died of pulmonary complications. More and more patients are surviving early trauma and operation because better resuscitative techniques are available and fluid and blood replacement is emphasized. Now that blood gas measurements are readily available, pulmonary complications which would heretofore pass unnoticed are being observed in many patients [l, 3, 81. T o study the alterations in pulmonary function both in patients undergoing elective surgery and in severely injured patients, we have deg r o m the Department of Surgery, University of Mississippi School of Medicine, Jackson, Miss. Supported by National Institutes of Health Grant No. HE 09858. Presented at the Seventeenth Annual Meeting of the Southern Thoracic Surgical Association, Bermuda, Nov. 5-7. 1970. Address reprint requests to Dr. Neely. University of Mississippi Medical Center, Jackson, Miss. 39216.
VOL. 11, NO.
6,
JUNE,
1971
565
NEELY ET AL.
vised a small bedside analogue computer to measure the following variables: pulmonary power, pulmonary minute work, respiratory air flow, minute volume, intrapleural pressure, peak inspiratory flow, peak expiratory flow, mean tidal volume, total lung and airway resistance, pulmonary dynamic compliance, and work/ventilation ratio. These values can be read directly and are immediately available for evaluation and to aid in treatment. METHOD Since the method of study has been described elsewhere [61, it will be discussed only briefly. T h e respiratory flow signal and intrapleural pressure signal are amplified and fed through a multiplier that computes and displays an instantaneous product. This product is reduced in such a way that only the inspiratory half of the respiratory cycle is used in subsequent computations. Integration of the product (power) produces work, and integration of the flow signal produces volume. T h e integrating ampIifiers are reset to zero at oneminute intervals so that minute work and minute volume are displayed. Work/ ventilation ratio is obtained by dividing minute work by minute volume. Mean tidal volume is obtained by dividing minute ventilation by respiratory rate. Airway and lung tissue resistance is computed as minute work times 60 divided by minute volume. Dynamic compliance is computed as mean tidal volume divided by mean inspiratory pressure. Inspiratory pressure is read directly from the record.
PATIENT PREPARATION Immediately preoperatively and postoperatively a catheter-tipped esophageal balloon is passed to a point approximately 40 cm. distal to the external nares and is inflated with 10 to 15 cc. of air. T h e balloon is then moved up or down slightly to minimize cardiac pulsation. A mask with attached pneumotachygraph is placed over the patient’s face. The pressure recording is then adjusted using zero suppression so that the base line coincides with the beginning of inspiration. Postoperative studies are conducted in a like manner.
RESULTS The results in 21 patients studied in this manner are given in the Figure. There was always an increase in postoperative work except in those patients who had no preexisting cardiopulmonary disease. None of the groups in the Figure exhibited a greater preo erative work than the obese patients, but there was relatively little difference getween obese and nonobese groups postoperatively. The atients over 40 years of age had a greater increase in postoperative work than t.E ose less than 40. Minute ventilation changed noticeably in the groups that were over 40 years, male, nonobese, or had thoracotomy, preexisting cardiovascular disease, pulmonary complication, or longer duration of anesthesia. Alterations in respiratory rate generally paralleled those of minute volume. Work/ventilation ratio was increased in every group postoperatively. Preoperatively the obese group exhibited a higher ratio than the nonobese group; postoperatively the patients over 40 years and the obese group showed the greatest relative increase. The work/ventilation ratio also tended to be higher postoperatively in those patients with a history of preexisting cardiopulmonary disease. Surprisingly, the tidal volume did not change appreciably postoperatively. 566
THE ANNALS OF THORACIC SURGERY
w
M
z
C
4
?
2:
I
w
c
COMPLIANCE
(brePthr/nin.)
RATE
(joules/liter)
WORK/VENTILATION
MINUTE VOLUME
I
I
I
-
*
*
5.12
19.9
4
0.99
4
8
4
16.9 18.86 1728 1787 18.62 19.30
1.39-0.86
-
PRE-OP
*
7.76
5.58
4
4
5.40 4.52
DURATION OF ANESTH.
I
0.99
I
I
0.97 1.00 I
b
I 4
19.67 25.63 24.30 25.14 22.86
4
I
18.18 19.24 1714 18.93
1.13
I
0.77 0.65 0.60 0.66
6.96
706 6.57 -. 9.24 8.58 11.87 7.75 4
6.62
I
4
4
75.2 45.5 56.6 63.3-43.4
4
80.3 98.2 109.2
48.2
4
975
93.0 45.3 56.0
76.0
4
8
48.4 56.4 50.4
89.5 113.9 80.1
362.1 404.5 434.4 96.5 387.7 390.0 375.3 379.6 545.9 338.2
313.4 418.7 365.9 373.f 411.6 342.1 308.1 358.1 383.5 332.8 329.9 371.4 408.7349.2
21.63 25.20
4
1788
0.76 0.63 4 4 1.14 -0.86
9.33
4
708
*
I
6.85 10.56 8.30 12.38 8.07
+
5.34 3.50 4.97 4.77
I
PRE-EXISTING PULMONARY COMPLICATIONS
17.45 18.53
1.05
8
0.79
4
0.98 0.56 0.65
5.99 761
4
8.20 9.39 10.41
4
6.32 6.84 16.96 6.02 716 6.33 7.37
I
8.36 10.61
*
4.54
OPERATIVE PROCEDURE
11.48 8.33 10.81
4
6.87 3.54
1
oBESITy
POST-OP 26.0 21.5 24.79 21.29 2225 24.46 24.80
PRE-OP
PRE-OP
SEX
Mean preoperative and postoperative values of pulmonai y function in 21 surgical patients. Figures in parentheses in the column headings indicate the number of patients in each group. Statistical significance ( p < 0.05) within a group is indicated by a vertical arrow; statistical significance Cp < U.05) between groups is indicated by a horizontal arrozu.
I
AGE
1 I 1
NEELY E T AL. Compliance was decrensed postoperatively in every comparison except in the groups of patients who were female, obese, had no cardiopulmonary disease, liatl pulmonary complications, and whose anesthesia time was greater than four hours. Thoracotomy produced a higher postoperative compliance than that of patients who did not undergo thoracotomy. COMMENT
T h e data presented here have been divided as indicated in the Figure. T h e significant changes obtained between and within these arbitrary groups do not mean that these subdivisions are mutually exclusive and independent. For instance, the greater than 40 age group might also have experienced the longest operations, and the group might have been weighted with more patients having preexisting cardiopulmonary disease. An analysis of this type precludes absolute conclusions being drawn from the factors mentioned. Nevertheless, we believe that this analysis is useful in interpreting the data and in predicting postoperative problems. Operation, being a form of trauma, increases the work of respiration. Most of the changes that we demonstrated are predictable from the work of others and from clinical impressions. It is important to note, however, that the work/ventilation ratio is a measure of the efficiency of respiration. T h e values greater than 1 joule per liter in individual patients are definitely abnormal. T h e obese patients exhibited the highest work/ventilation ratio preoperatively and postoperatively. With the exception of those patients having long anesthesia times, the obese patients also exhibited the greatest increase in pulmonary work. Tidal volume did not change significantly between the preoperative and postoperative periods. If this holds true in subsequent studies, it will mean that expiratory rate is an excellent indicator of minute volume-and compliance and rate are the primary determinants of pulmonary work. Several inexplicable results became evident when the data were scrutinized more closely. Minute volume increased significantly in the nonobese patients, whereas the obese patients did not significantly increase their minute volume. One wonders if the obese patient may be incapable of generating a sustained increase in minute volume due to the high energy cost of the effort, as was illustrated in their increased workhentilation ratio. REFERENCES 1 . Able, F. L., Waldliausen, J. A., Daley, W. F., and Pearce, W. L. Pulmonary blood volume in hemorrhagic shock in the dog and primate. Amer. J . Physiol.
213:1072, 1967.
568
THE ANNALS OF THORACIC SURGERY
Pulmonary Function in Surgical Patients 2. Blaisdell, F. W.,Lim, R. C., Amberg, J. R., Choy, S. H., Hall, A. D., and Thomas, A. N. Pulmonary microembolism: A cause of morbidity and death after major vascular surgery. Arch. Surg. (Chicago) 93:776, 1966. 3. Borst, H. E., Berghund, E., Wittenburger, S. L., Mead, J., McGregor, M., and Collier, C. The effect of pulmonary vascular pressures on the mechanical properties of the lungs in anesthetized dogs. J. Clin. Invest. 36:1708, 1957. 4. Gaensler, E. A. Personal communication, 1969. 5. Jackson, T. M., and Lee, W. H., Jr. Major thermal burns: A mortality appraisal and review. Arch. Surg. (Chicago) 87:937, 1963. 6. Neely, W. A., Robinson, W. T., Holloman, G. H., Jr., and McMullan, M. H. An inexpensive bedside analogue computer for measuring respiratory work and certain other parameters. Surgery 69: 309, 1971. 7. Phillips, A. W., and Cope, 0. Burn therapy: 11. The revelation of respiratory tract damage as a principal killer of the burned patient. A n n . Surg. 155: 1, 1962. 8. Proctor, H. J., Moss, G. S., Homer, L. D., and Litt, B. D. Changes in lung compliance in experimental hemorrhagic shock and resuscitation. A n n . Surg. 169:82, 1969. 9. Taylor, F. W., and Gumbert, J. L. Cause of death from burns: Role of respiratory damage. Ann. Surg. 161:497, 1965.
NOTICE FROM THE SOUTHERN THORACIC SURGICAL ASSOCIATION The Eighteenth Annual Meeting of the Southern Thoracic Surgical Association will be held at the Holiday Inn Hotel in Tampa, Fla., November 4-6, 1971. Reservations may be made by writing to Mr. Adam Habler, Reservations Manager, P.O. Box 271, Tampa, Fla. 33601. Application for membership in the Southern Thoracic Surgical Association, on forms provided by the Association, should be sent directly to Frederick H. Taylor, M.D. (Chairman of the Membership Committee), 1012 Kings Dr., Charlotte, N.C. 28207, no later than September 1, 1971. Papers that are accepted for the program and are to be considered for b l i cation in T h e Annals should be submitted to the Editor by October 15, 1r 71 JAM= W. BROOKS, M.D. Secretary-Treasurer
VOL. 11, NO.
6,
JUNE,
1971
569