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Comparison of effect of narcotic and epidural analgesia on postoperative respiratory function
Comparison of Effect of Narcotic and Epidural Analgesia on Postoperative Respiratory Function Lance Miller, MD, FRCS (C), Montreal, Quebec, Canada Morris Gertel, MD, FRCP (C), Montreal, Quebec, Canada Gordon S. Fox, MD, FRCP (C), Montreal, Quebec, Canada Lloyd D. MacLean, MD, FRCS (C), Montreal, Quebec, Canada
Spence and Smith [I] and Muneyuki et al [2] have demonstrated that 24 hours after upper abdominal surgery patients have higher oxygen tensions when postoperative pain relief is managed by continuous epidural rather than narcotic analgesia. However, these investigators have not shown early differences in the measured mechanics of ventilation despite their findings regarding differences in oxygen tension. Therefore, a prospective study of postoperative respiratory function was undertaken in twenty randomly selected patients older than thirty years of age admitted to hospital for elective cholecystectomy. Ventilatory function was measured for the first 24 hours after surgery using simple tests. A single method of anesthesia was used for all subjects. Postoperative pain relief was achieved with intramuscular meperidine in half the patients and the remainder received intermittent doses of epidural lidocaine. Met hod None of the patients had significant cardiovascular or respiratory disease as evaluated by history, electrocardiogram, and chest radiography. Before the study was begun, a Wright peak flow meter was calibrated against flow as determined by flow through a bobbin type rotameter. A graph was plotted so that the actual flow could be calculated from the obFrom Departments of Surgery and Anaesthesia. Royal Victoria Hospital, and McGill University, Montreal, Quebec. Canada. This work was supported by a grant from the Medical Research Council of Canada. Reprint requests should be addressed to Lloyd D. Maclean, MD, Surgeon-in-Chief, Royal Victoria Hospital, 667 Pine Avenue, Montreal, Quebec, Canada.
Vofuma 131, March 1976
served flow. Our particular flow meter gave values consistently below actual peak flow when plotted at high and low flows on the graph. Vital capacity was measured with a previously calibrated Wright respirometer attached to a close-fitting face mask. Preoperative assessment was made 24 hours before surgery. With the patient in the supine position three recordings of expiratory peak flow and vital capacity were performed. An average value of the three recordings was then calculated and used as the preoperative value. Postoperative pain relief was achieved with epidural injections of lidocaine and in group II patients with intramuscular meperidine. Respiratory function was assessed by measuring expiratory peak flow, vital capacity, and arterial blood gases. These tests were used because they are simple and easily and rapidly performed at bedside. Immediately on return to the recovery room, the patients were given 28 per cent oxygen by Campbell mask. An arterial blood gas sample was taken 10 to 15 minutes after admission to the recovery room. An arterial blood gas sample was taken during the third to fourth postoperative hour at which time the patient’s pain had been relieved by either meperidine or an epidural injection of lidocaine. After this, the Campbell mask was removed and the means of three measurements of expiratory peak flow and vital capacity were recorded and expressed as a percentage of the preoperative value. All the measurements were repeated the following morning, the only difference in technic being that all the patients were breathing room air. Respiratory function and blood gas samples were all taken by the same investigator (JLM); anesthetics were administered and epidural catheters were inserted by one of two anesthetists (MG and GSF). All blood gas
291
Miller et al
analyses were performed on an Instrumentation tory model 113 blood gas system. Significance sults was determined by Student t test.
Laboraof the re-
charge of the recovery room. Group I patients remained in the recovery room until after the study period. Group II patients returned to the ward after the usual period in the recovery room.
Anesthesia and Analgesia Technic All patients were premeditated with 100 mg pentobarbitone, 0.4 mg atropine sulfate, and 50 to 75 mg meperidine intramuscularly one hour before scheduled operation. In all group I patients an epidural catheter was inserted at a convenient intervertebral space between the twelfth thoracic and third lumbar interspace prior to induction of general anesthesia. Anesthesia was induced with a “sleep dose” of thiopentone. Tracheal intubation was facilitated by the use of 60 to 100 mg succinylcholine intravenously. Anesthesia was maintained in all patients with nitrous oxide, oxygen, intravenous meperidine, and d-tubocurarine as required for muscle relaxation. At the and of the operation, curarisation was reversed with 1.2 mg atropine and 2.5 mg prostigmine intravenously. Postoperatively, epidural analgesia was initiated and maintained in group I patients with 1 or 2 per cent lidoCaine with l/200,000 epinephrine given in hourly doses throughout the study period. Postoperative analgesia in
TABLE
I
Preoperative in Groups
Status of Patients I and II Per
Group
Mean Age (vr)
Age Range (vr)
Mean Height (inches)
I II
49* 11 55 * 12
33to68 35 to 74
64.9?3 64.5 i 3
Note:
TABLE
f = standard
II
Preoperative
Group I II
78 396i 387 * 93
Note:
TABLE
ers
15 ? 35
30 30
Respiratory
310 275
Duration
Assessment
I and II
Range (L/min)
? = standard
I II
(pounds)
deviation.
of Groups Mean Expiratory Peak Flow Rate (L/ min)
Mean Weight
Cent Smok-
141.4* 150.8
to 573 to 530
Mean Vital Capacity (L) 2.25 1.90
+ 0.7 f 0.7
Range (L) 1.37 1.18
* 3.4 * 2.4
deviation.
of Operations
and Narcotic
Dose
Mean Operative Time (min)
Range (min)
(mg)
Range (mg)
II
104*44 128 f 54
55 to 195 65 to 245
67 * 21 75 * 26
40 to 120 40 to 120
Note:
+ = standard
deviation.
Group
I
292
group II patients was achieved with intramuscular meperidine in doses judged adequate by the anesthetist in
Mean Dose Meperidine
Results Both groups were comparable in age, height, weight, and smoking habits as shown in Table I. In group I there were six females and four males and in group II there were seven females and three males. Preoperatively there were no significant differences in expiratory peak flow and vital capacity between the two groups. (Table II.) Table III demonstrates that there was no significant difference between the two groups as to the duration of operation or the amount of meperidine received intraoperatively. The operative time was considered as the interval between induction of anesthesia and the time the patient left the operating room. Although the patients were admitted for elective cholecystectomy, some did undergo additional operative procedures, which as noted in Table III made no significant difference between the two groups with reference to the operative time or the amo’unt of narcotic required. The operative procedures for group I include: cholecystectomy (4 patients); cholecystectomy and operative cholangiogram (3); cholecystectomy with common bile duct exploration (1); cholecystectomy with right inguinal herniorrhaphy (1); and cholecystectomy with incidental appendectomy and umbilical herniorrhaphy (1). The operative procedures for group II include: cholecystectomy (7 patients); cholecystectomy with common bile duct exploration (2); and cholecystectomy and Nissen fundoplication (1). Arterial oxygen tension (PaOs), per cent oxygen saturation, and carbon dioxide tension (PaCOs) were comparable in both groups during the immediate postoperative period and 3 to 4 hours after surgery. However, on the morning after surgery, patients in group I had significantly higher arterial oxygen tensions (p
The American Journal of Surgery
Postoperative
difference in vital capacity. There was no difference between the groups in expiratory peak flow rate at 3 to 4 hours postoperatively, nor on the following morning. The postoperative analgesia requirement for group I were 958 f 481 mg (SD) lidocaine (mean number of doses, 12.8 i 7.3 [SD]) and for group II, 167 f 99 mg (SD) meperidine (mean number of doses, 2.7 f 1.3 [SD]). The final assessment in the postoperative period, comparing complications and length of hospital stay, showed the mean duration of hospital stay to be 9.2 f 1.8 days (SD) for group I and 11.2 f 5.4 days (SD) for group II. The mean number of days in hospital included the day of operation and the day of discharge. One patient in the narcotic group (group II) who had cholecystectomy and common bile duct exploration remained in hospital for twentysix days postoperatively but was awaiting placement in a convalescent home during the latter part of his hospitalization. One patient in each group had pulmonary complications: a suspected, unproved, untreated pulmonary embolus in one patient in the epidural group and atelectasis with a small pleural effusion in one patient in the narcotic group. Five patients in group I and one in group II required a urinary catheter. There is no significant difference between the length of hospital stay in the two groups. TABLE IV
Respiratory
Function
Comments
Expiratory peak flow has been shown to be a good measure of ventilatory function [3]. Shortly after surgery, both groups of patients had similar ventilatory measurements. There was no statistical difference in expiratory peak flow in 4 hours after return to the recovery room and after the establishment of postoperative analgesia. The significant difference in vital capacity indicates that those patients with epidural analgesia were capable of taking a deep inspiration on command or at will. However, the difference in ability to deep breathe had no appreciable effect on oxygen tension at that time. Twenty-four ‘hours after surgery, group I patients had expiratory peak flow and vital capacity measurements that were closer to preoperative levels than were group II measurements; however, although no significant difference existed between the two groups, the epidural group had greater arterial oxygen tensions and lower carbon dioxide tensions than did the narcotic group. The lower carbon dioxide tension implies greater minute alveolar ventilation in group I. The differences in oxygen saturation are of importance since the oxygen tension falls on the steep part of the oxygen hemoglobin dissociation curve. These differences
Postoperative Blood Gas Analyses
Per Cent Oxygen Saturation
Pa02 (mm Hg)
Group I
Group II
Group I
Time
Group I I
PaC02 (mm Hg) Group I
Group I I
Immediately postoperatively
128.9
5 57.4
154.4
f 78.0
97.4 ? 0
96.6 f 0.7
40.1
? 4.2
40.7
+ 3.3
3 to4 hr postoperatively 24 hr postoperatively
133.4
f 65.9
136.5
2 62.3
97.8 * 0.32
97.4 * 0.5
37.4
+ 4.5
40.3
+ 4.3
i 16
95.0 t 0.67t
90.8
33.4
k 3.0$
36.4
k 3.1
Note: *p < i p < z p <
80.2
+ 0.9
-
t = standard 0.01. 0.001. 0.04.
TABLE V
63.3
f 13.6”
deviation.
Changes in Expiratory Peak Flow and Vital Capacity Expiratory Peak Flow (per cent of control) Group I
Internal 3 to 4 hr postoperatively 1st postoperative day ______ Note: + = standard
Volume 131. March 1976
48.3
? 13.4
48 i 10.4
Group II
Group I
k 20.1
49.9
r 15.2
(NS) 42.1 ? 10.2
45.6
2 14.0
43.6
(NS) deviation;
Vital Capacity (per cent of control) Group II 36.5 + 12.6 (p = < 0.05) 42.1 ?- 20.2 (NS)
NS = not significant.
293
Miller et al
in oxygen saturation occurred in patients who had no preoperative respiratory disease. We did not compare the alveolar-arterial oxygen difference between the groups as this would provide no more useful comparison than arterial oxygen tensions. Since mixed venous blood was not obtained, a comparison of total shunt was not calculated because we could not assume comparable arteriovenous differences in oxygen content in the two groups. The patients in group II were at a disadvantage early in the initial recovery period due to their inability to inspire deeply and to open previously closed alveoli. This could have hastened the onset of atelectasis which resulted in decreased ventilation/perfusion ratios and decreased arterial oxygen tensions. Epidural analgesia allowed group I patients to breathe deeply or sigh and theoretically minimized the chance of atelectasis. Narcotics are known to decrease the frequency of sighing [4]. These findings are in agreement with those of Spence and Smith [I] who studied a group of patients very similar to ours. They demonstrated the onset of ventilation/perfusion abnormalities as early as 45 minutes after the administration of a narcotic analgesic for pain after cholecystectomy. Twenty-four hours after surgery, the measured mechanics of ventilation were impaired in both groups to a similar degree, but arterial oxygen tensions were superior after epidural analgesia. Spence and Smith [1] did not measure ventilation in the early postoperative period. Our findings demonstrate that 24 hours after surgery, simple tests of respiratory function will not help to identify those patients who might have arterial oxygen desaturation. Patients in group I who maintained an adequate vital capacity in the early postoperative period had higher arterial oxygen saturation the day after surgery. Expiratory peak flow was of no value in predicting changes in arterial oxygen tension. The changes in expiratory peak flow, vital capacity, and blood gases could possibly be more pronounced in the elderly or in patients with preexisting lung disease. Evidence for this might be obtained by another study of older patients
294
with higher closing volumes [5], or a study of patients with diffuse pulmonary disease. An obvious disadvantage of this technic, which might be more troublesome in the elderly, is urinary retention. Summary randomized comparison was A prospective, made of the value of meperidine versus epidural analgesia when used for the relief of pain after cholecystectomy in twenty patients without cardiopulmonary disease. Respiratory function was assessed the day before surgery and at 3 to 4 hours and 24 hours after operation by the bedside measurement of expiratory peak flow, vital capacity, and arterial blood gases. The two groups of patients were comparable as to age, height, weight, smoking habits, preoperative peak flow, vital capacity, and duration of operation. The arterial oxygen tension and oxygen saturation were significantly greater and carbon dioxide tension lower in the epidural analgesia group 24 hours after operation. At this time peak flow rates and vital capacity were not different. However, at 3 to 4 hours postoperatively, vital capacity was significantly greater in the epidural anesthesia group. This might account for the differences in arterial blood gases the following day. These findings suggest that epidural analgesia is valuable in the early postoperative period after upper abdominal surgery. References 1. Spence AA, Smith G: Postoperative analgesia and lung function: a comparison of morphine with extradural block. Br J Anaesth 43: 144. 1971. 2. Muneyuki M. Veda Y, Urabe N. Takeshita H. lnamoto A: Postoperative pain relief and respiratory function in man: comparison between intermittent intravenous injections of meperidine and continuous lumbar epidural analgesia. Anesthesiology 29: 304, 1966. 3. Wright, BM, McKerron CB: Maximum forced expiratory flow rate as a measure of ventilatory capacity. Br Med J 21: 1041,1959. 4. Egbert LD, Bendixen HH: Effect of morphine on breathing pattern; possible factor in atelectasis. JAMA 168: 485, 1964. 5. Anthonisen NR, Danson J, Robertson PC, Ross WRD: Airway closure as a function of age. Resp Physiol8: 58, 1969.
The Amdcan
Journal of Surgery
Spence and Smith [I] and Muneyuki et al [2] have demonstrated that 24 hours after upper abdominal surgery patients have higher oxygen tensions when postoperative pain relief is managed by continuous epidural rather than narcotic analgesia. However, these investigators have not shown early differences in the measured mechanics of ventilation despite their findings regarding differences in oxygen tension. Therefore, a prospective study of postoperative respiratory function was undertaken in twenty randomly selected patients older than thirty years of age admitted to hospital for elective cholecystectomy. Ventilatory function was measured for the first 24 hours after surgery using simple tests. A single method of anesthesia was used for all subjects. Postoperative pain relief was achieved with intramuscular meperidine in half the patients and the remainder received intermittent doses of epidural lidocaine. Met hod None of the patients had significant cardiovascular or respiratory disease as evaluated by history, electrocardiogram, and chest radiography. Before the study was begun, a Wright peak flow meter was calibrated against flow as determined by flow through a bobbin type rotameter. A graph was plotted so that the actual flow could be calculated from the obFrom Departments of Surgery and Anaesthesia. Royal Victoria Hospital, and McGill University, Montreal, Quebec. Canada. This work was supported by a grant from the Medical Research Council of Canada. Reprint requests should be addressed to Lloyd D. Maclean, MD, Surgeon-in-Chief, Royal Victoria Hospital, 667 Pine Avenue, Montreal, Quebec, Canada.
Vofuma 131, March 1976
served flow. Our particular flow meter gave values consistently below actual peak flow when plotted at high and low flows on the graph. Vital capacity was measured with a previously calibrated Wright respirometer attached to a close-fitting face mask. Preoperative assessment was made 24 hours before surgery. With the patient in the supine position three recordings of expiratory peak flow and vital capacity were performed. An average value of the three recordings was then calculated and used as the preoperative value. Postoperative pain relief was achieved with epidural injections of lidocaine and in group II patients with intramuscular meperidine. Respiratory function was assessed by measuring expiratory peak flow, vital capacity, and arterial blood gases. These tests were used because they are simple and easily and rapidly performed at bedside. Immediately on return to the recovery room, the patients were given 28 per cent oxygen by Campbell mask. An arterial blood gas sample was taken 10 to 15 minutes after admission to the recovery room. An arterial blood gas sample was taken during the third to fourth postoperative hour at which time the patient’s pain had been relieved by either meperidine or an epidural injection of lidocaine. After this, the Campbell mask was removed and the means of three measurements of expiratory peak flow and vital capacity were recorded and expressed as a percentage of the preoperative value. All the measurements were repeated the following morning, the only difference in technic being that all the patients were breathing room air. Respiratory function and blood gas samples were all taken by the same investigator (JLM); anesthetics were administered and epidural catheters were inserted by one of two anesthetists (MG and GSF). All blood gas
291
Miller et al
analyses were performed on an Instrumentation tory model 113 blood gas system. Significance sults was determined by Student t test.
Laboraof the re-
charge of the recovery room. Group I patients remained in the recovery room until after the study period. Group II patients returned to the ward after the usual period in the recovery room.
Anesthesia and Analgesia Technic All patients were premeditated with 100 mg pentobarbitone, 0.4 mg atropine sulfate, and 50 to 75 mg meperidine intramuscularly one hour before scheduled operation. In all group I patients an epidural catheter was inserted at a convenient intervertebral space between the twelfth thoracic and third lumbar interspace prior to induction of general anesthesia. Anesthesia was induced with a “sleep dose” of thiopentone. Tracheal intubation was facilitated by the use of 60 to 100 mg succinylcholine intravenously. Anesthesia was maintained in all patients with nitrous oxide, oxygen, intravenous meperidine, and d-tubocurarine as required for muscle relaxation. At the and of the operation, curarisation was reversed with 1.2 mg atropine and 2.5 mg prostigmine intravenously. Postoperatively, epidural analgesia was initiated and maintained in group I patients with 1 or 2 per cent lidoCaine with l/200,000 epinephrine given in hourly doses throughout the study period. Postoperative analgesia in
TABLE
I
Preoperative in Groups
Status of Patients I and II Per
Group
Mean Age (vr)
Age Range (vr)
Mean Height (inches)
I II
49* 11 55 * 12
33to68 35 to 74
64.9?3 64.5 i 3
Note:
TABLE
f = standard
II
Preoperative
Group I II
78 396i 387 * 93
Note:
TABLE
ers
15 ? 35
30 30
Respiratory
310 275
Duration
Assessment
I and II
Range (L/min)
? = standard
I II
(pounds)
deviation.
of Groups Mean Expiratory Peak Flow Rate (L/ min)
Mean Weight
Cent Smok-
141.4* 150.8
to 573 to 530
Mean Vital Capacity (L) 2.25 1.90
+ 0.7 f 0.7
Range (L) 1.37 1.18
* 3.4 * 2.4
deviation.
of Operations
and Narcotic
Dose
Mean Operative Time (min)
Range (min)
(mg)
Range (mg)
II
104*44 128 f 54
55 to 195 65 to 245
67 * 21 75 * 26
40 to 120 40 to 120
Note:
+ = standard
deviation.
Group
I
292
group II patients was achieved with intramuscular meperidine in doses judged adequate by the anesthetist in
Mean Dose Meperidine
Results Both groups were comparable in age, height, weight, and smoking habits as shown in Table I. In group I there were six females and four males and in group II there were seven females and three males. Preoperatively there were no significant differences in expiratory peak flow and vital capacity between the two groups. (Table II.) Table III demonstrates that there was no significant difference between the two groups as to the duration of operation or the amount of meperidine received intraoperatively. The operative time was considered as the interval between induction of anesthesia and the time the patient left the operating room. Although the patients were admitted for elective cholecystectomy, some did undergo additional operative procedures, which as noted in Table III made no significant difference between the two groups with reference to the operative time or the amo’unt of narcotic required. The operative procedures for group I include: cholecystectomy (4 patients); cholecystectomy and operative cholangiogram (3); cholecystectomy with common bile duct exploration (1); cholecystectomy with right inguinal herniorrhaphy (1); and cholecystectomy with incidental appendectomy and umbilical herniorrhaphy (1). The operative procedures for group II include: cholecystectomy (7 patients); cholecystectomy with common bile duct exploration (2); and cholecystectomy and Nissen fundoplication (1). Arterial oxygen tension (PaOs), per cent oxygen saturation, and carbon dioxide tension (PaCOs) were comparable in both groups during the immediate postoperative period and 3 to 4 hours after surgery. However, on the morning after surgery, patients in group I had significantly higher arterial oxygen tensions (p
The American Journal of Surgery
Postoperative
difference in vital capacity. There was no difference between the groups in expiratory peak flow rate at 3 to 4 hours postoperatively, nor on the following morning. The postoperative analgesia requirement for group I were 958 f 481 mg (SD) lidocaine (mean number of doses, 12.8 i 7.3 [SD]) and for group II, 167 f 99 mg (SD) meperidine (mean number of doses, 2.7 f 1.3 [SD]). The final assessment in the postoperative period, comparing complications and length of hospital stay, showed the mean duration of hospital stay to be 9.2 f 1.8 days (SD) for group I and 11.2 f 5.4 days (SD) for group II. The mean number of days in hospital included the day of operation and the day of discharge. One patient in the narcotic group (group II) who had cholecystectomy and common bile duct exploration remained in hospital for twentysix days postoperatively but was awaiting placement in a convalescent home during the latter part of his hospitalization. One patient in each group had pulmonary complications: a suspected, unproved, untreated pulmonary embolus in one patient in the epidural group and atelectasis with a small pleural effusion in one patient in the narcotic group. Five patients in group I and one in group II required a urinary catheter. There is no significant difference between the length of hospital stay in the two groups. TABLE IV
Respiratory
Function
Comments
Expiratory peak flow has been shown to be a good measure of ventilatory function [3]. Shortly after surgery, both groups of patients had similar ventilatory measurements. There was no statistical difference in expiratory peak flow in 4 hours after return to the recovery room and after the establishment of postoperative analgesia. The significant difference in vital capacity indicates that those patients with epidural analgesia were capable of taking a deep inspiration on command or at will. However, the difference in ability to deep breathe had no appreciable effect on oxygen tension at that time. Twenty-four ‘hours after surgery, group I patients had expiratory peak flow and vital capacity measurements that were closer to preoperative levels than were group II measurements; however, although no significant difference existed between the two groups, the epidural group had greater arterial oxygen tensions and lower carbon dioxide tensions than did the narcotic group. The lower carbon dioxide tension implies greater minute alveolar ventilation in group I. The differences in oxygen saturation are of importance since the oxygen tension falls on the steep part of the oxygen hemoglobin dissociation curve. These differences
Postoperative Blood Gas Analyses
Per Cent Oxygen Saturation
Pa02 (mm Hg)
Group I
Group II
Group I
Time
Group I I
PaC02 (mm Hg) Group I
Group I I
Immediately postoperatively
128.9
5 57.4
154.4
f 78.0
97.4 ? 0
96.6 f 0.7
40.1
? 4.2
40.7
+ 3.3
3 to4 hr postoperatively 24 hr postoperatively
133.4
f 65.9
136.5
2 62.3
97.8 * 0.32
97.4 * 0.5
37.4
+ 4.5
40.3
+ 4.3
i 16
95.0 t 0.67t
90.8
33.4
k 3.0$
36.4
k 3.1
Note: *p < i p < z p <
80.2
+ 0.9
-
t = standard 0.01. 0.001. 0.04.
TABLE V
63.3
f 13.6”
deviation.
Changes in Expiratory Peak Flow and Vital Capacity Expiratory Peak Flow (per cent of control) Group I
Internal 3 to 4 hr postoperatively 1st postoperative day ______ Note: + = standard
Volume 131. March 1976
48.3
? 13.4
48 i 10.4
Group II
Group I
k 20.1
49.9
r 15.2
(NS) 42.1 ? 10.2
45.6
2 14.0
43.6
(NS) deviation;
Vital Capacity (per cent of control) Group II 36.5 + 12.6 (p = < 0.05) 42.1 ?- 20.2 (NS)
NS = not significant.
293
Miller et al
in oxygen saturation occurred in patients who had no preoperative respiratory disease. We did not compare the alveolar-arterial oxygen difference between the groups as this would provide no more useful comparison than arterial oxygen tensions. Since mixed venous blood was not obtained, a comparison of total shunt was not calculated because we could not assume comparable arteriovenous differences in oxygen content in the two groups. The patients in group II were at a disadvantage early in the initial recovery period due to their inability to inspire deeply and to open previously closed alveoli. This could have hastened the onset of atelectasis which resulted in decreased ventilation/perfusion ratios and decreased arterial oxygen tensions. Epidural analgesia allowed group I patients to breathe deeply or sigh and theoretically minimized the chance of atelectasis. Narcotics are known to decrease the frequency of sighing [4]. These findings are in agreement with those of Spence and Smith [I] who studied a group of patients very similar to ours. They demonstrated the onset of ventilation/perfusion abnormalities as early as 45 minutes after the administration of a narcotic analgesic for pain after cholecystectomy. Twenty-four hours after surgery, the measured mechanics of ventilation were impaired in both groups to a similar degree, but arterial oxygen tensions were superior after epidural analgesia. Spence and Smith [1] did not measure ventilation in the early postoperative period. Our findings demonstrate that 24 hours after surgery, simple tests of respiratory function will not help to identify those patients who might have arterial oxygen desaturation. Patients in group I who maintained an adequate vital capacity in the early postoperative period had higher arterial oxygen saturation the day after surgery. Expiratory peak flow was of no value in predicting changes in arterial oxygen tension. The changes in expiratory peak flow, vital capacity, and blood gases could possibly be more pronounced in the elderly or in patients with preexisting lung disease. Evidence for this might be obtained by another study of older patients
294
with higher closing volumes [5], or a study of patients with diffuse pulmonary disease. An obvious disadvantage of this technic, which might be more troublesome in the elderly, is urinary retention. Summary randomized comparison was A prospective, made of the value of meperidine versus epidural analgesia when used for the relief of pain after cholecystectomy in twenty patients without cardiopulmonary disease. Respiratory function was assessed the day before surgery and at 3 to 4 hours and 24 hours after operation by the bedside measurement of expiratory peak flow, vital capacity, and arterial blood gases. The two groups of patients were comparable as to age, height, weight, smoking habits, preoperative peak flow, vital capacity, and duration of operation. The arterial oxygen tension and oxygen saturation were significantly greater and carbon dioxide tension lower in the epidural analgesia group 24 hours after operation. At this time peak flow rates and vital capacity were not different. However, at 3 to 4 hours postoperatively, vital capacity was significantly greater in the epidural anesthesia group. This might account for the differences in arterial blood gases the following day. These findings suggest that epidural analgesia is valuable in the early postoperative period after upper abdominal surgery. References 1. Spence AA, Smith G: Postoperative analgesia and lung function: a comparison of morphine with extradural block. Br J Anaesth 43: 144. 1971. 2. Muneyuki M. Veda Y, Urabe N. Takeshita H. lnamoto A: Postoperative pain relief and respiratory function in man: comparison between intermittent intravenous injections of meperidine and continuous lumbar epidural analgesia. Anesthesiology 29: 304, 1966. 3. Wright, BM, McKerron CB: Maximum forced expiratory flow rate as a measure of ventilatory capacity. Br Med J 21: 1041,1959. 4. Egbert LD, Bendixen HH: Effect of morphine on breathing pattern; possible factor in atelectasis. JAMA 168: 485, 1964. 5. Anthonisen NR, Danson J, Robertson PC, Ross WRD: Airway closure as a function of age. Resp Physiol8: 58, 1969.
The Amdcan
Journal of Surgery