Effectiveness of Transcutaneous Electrical Nerve Stimulation Following Cholecystectomy

Effectiveness of Transcutaneous Electrical Nerve Stimulation Following Cholecystectomy DOUGAL T SIM B S ~MCSP Unit Physiotherapist. Raigmore Hospital. Inverneab

Key words: TENS, cholecystectomy, post-operative analgesia, pulmonary

function.

Summary: A randomised study was undertaken to evaluate the effectiveness of transcutaneous electrical nerve stimulation (TENS) in relieving post-operative incisional pain. Thirty patients undergoing elective cholecystectomy through a right upper paramedian incision were randomly allocated to one of two groups, to receive different regimens of post-operdtive analgesia. Fifteen patients in one group received a conventional regimen of ondemand intramuscular papavereturn and 15 patients in the other group received TENS, supplemented by intramuscular papavereturn, if required. The effectiveness of TENS was evaluated by measuring both the analgesic and pulmonary effects on the first, second and fifth post-operative days. Pain was subjectively measured at rest, following deep breathing. and following coughing, using linear analogue pain scales. Pulmonary function was assessed by measuring FVC and FEV, with a Vitalograph spirometer. The study found no significant difference between the two groups o n comparing post-operative FEV, and FVC values, FEV,IFVC ratio. opiate analgesia requirements, post-operative pulmonary complications or mean number of days before either mobiliaation or hospital discharge. Analysis of subjective pain measurements revealed similar pain scores for both groups on all but the second post-operative day where a significant decrease (p < 0.05) was found for both rest pain and deep breathing pain scores for the TENS group. Patients within the TENS group also recorded significantly less pain following coughing on the fifth post-operative day. The degree of pain experienced by patients was found to influence the analgesic effect of TENS. The limited benefiu of TENS. following this particular surgical procedure. do not justify the additional cnst or time required for its implenientation. Biography: Mr Sim trained at the Queen‘s College.

Glasgnw, qualifying in 1980. As superintendent physiotherapist on the surgical unit. Stobhill General Hospital, Glasgow, he developed an interest and became actively involved in clinical research. In 1988 he began a part-time BSc(Hons) degree course at the Queen’s College, Glasgow. This article is based on his finalyear dissertation which was part requirement for a BSc(Hons) degree in health studies. He has recently taken up post as Unit physiotherapist. Raigmore Hospital, Inverness.

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POST-OPERATIVE pain resulting from an upper abdominal incision is regarded by many observers to be a major contributing factor of post-operative pulmonary dysfunction as patients are inhibited from coughing, taking deep breaths, mobilising themselves and co-operating w i th the physiotherapist. Following cholecystectomy, Crosbie and Sim (1986) reported that pulmonary function values of forced expiratory volume (FEV,) and forced vital capacity (FVC) were considerably reduced on the second and seventh post-operative days by as much as 5 5 % and 2 5 % respectively. Effective post-operative pain management is therefore essential, not only on humanitarian grounds but also to minimise the incidence and severity of pulmorlary complications. Additionally, the immediate post-operative narcotic analgesia regimen prescribed by the physician must endeavour t o avoid the risk of inducing pulmonary dysfunction and pulmonary complications. Many clinicians recognise t h a t t h e conventional intermittent administration of powerful analgesic narcotics, intramuscularly, provides unsatisfactory control of pain following abdominal surgery. This has been shown in many studies (Catling et a/, 1980; Fry, 1979, 1980; Tammisto and Tigerstedt, 1982). Although alternative methods of providing superior pain relief have been demonstrated intravenous infusion of papaveretum (Catling et a/, 1980); continuous subcutaneous pethidine (Davenport e t a / , 1985) and patient-operated on-demand techniques (Chakravarty et a/, 1979; Harmer et a/, 19831, the risk of inducing pulmonary depression and pulmonary complications is sometimes an undesirable consequence, especially where large doses of analgesics are administered. In recent years transcutaneous electrical nerve stimulation (TENS) has become a popular non-invasive treatment modality, used mainly in the management of chronic pain. The exact mechanism producing analgesia w i t h TENS remains obscure but it appears t o derive its effects through several mechanisms. According t o the gate-control theory of pain proposed by Melzack and Wall (19651, pain is transmitted primarily through small unmyelinated C fibres and such pain can be inhibited through stimulation of large myelinated A fibres. These large and small fibres from the periphery are thought to project into the ’gate’, which is formed in the cells of the substantia gelatinosa in the dorsal column of the spinal cord. The moderating function of the substantia gelatinosa is increased by large fibre stimulation and by small fibre stimulation and serves to inhibit the relay of afferent small fibre activity. These fibres have a low threshold to electrical stimulation (Tyler et a/, 1982). It is thought that electrical stimulation of the large myelinated A fibres causes ’closure of the gate’, so that the relay of painful peripheral stimuli along the small unmyelinated C fibres is inhibited. The recognition of pain in the substantia gelatinusa and hence the patient’s perception of pain is thus altered. There is also evidence that TENS can alter t h e conduction and amplitude of painful stimuli through the A delta fibres which are also thought t o transmit pain stimuli. This occurs in the peripheral nerve (Ignelzi et a / , 1976). TENS is also thought t o increase or stimulate the production of neuro endocrine substances, endorphins 715

and enkephalins. They modulate pain through their opioid activity (Goldstein, 1976). Endorphins are thought t o initiate a central descending inhibitory mechanism, resulting in a decreased perception of pain therefore producing an analgesic effect (Sjolund and Eriksson, 1978; Zimmerman, 1978). Modification of pain impulses is thought to occur at spinal cord, midbrain or thalamic levels. Current concepts that TENS does not depress pulmonary function, has no apparent effect on the sensorium apsrt from possible minor sedation and is non-toxic and simple in application, suggest an attractive alternative modality in the management of acute post-operative pain. Conflicting reports have appeared in recent medical literature concerning the effectiveness of TENS in acute post-operative pain management following upper abdominal surgery. Reuss e t a / (1988) reported no reduction in narcotic use or pulmonary complications following cholecystectomy through a right subcostal incision. Ali e t a / (1981) however, found a statistically significant reduction in narcotics administered and pulmonary complications following cholecystectomy through a midline incision. Cooperman et a/ (1977) also reported a reduction in narcotic use although the incisional approach was not specified. Chen era/ (1981) found no reduction in narcotic use or incidence of postoperative pulmonary complications in 2 5 patients who had undergone cholecystectomy, but no control group was evaluated. It has been shown that cholecystectomy via a right paramedian incision is more painful than through a right subcostal approach (Garcia-Valdecasas et a/, 1988). These studies evaluated the effectiveness of TENS in terms of reduced post-operative pulmonary complications and/or reduced analgesic narcotic administration. Other studies have employed post-operative pulmonary function values and/or subjective pain measurements, t o evaluate effectiveness. Jones et a/ (1990) reported a subjective improvement in pain relief following cholecystectomy, irrespective of electrode placement, but there was no standardisation of incisional approach. Ho e t a / (1987) also reported a subjective improvement in pain relief and an objective improvement in lung function measurements, following thoracotomy. Unfortunately, no control group was used, leading to ambiguity in their conclusions. Additionally, it is assumed that subjective pain measurements in both these studies were recorded with the patient at rest only. The present study was designed to evaluate the effectiveness of TENS following cholecystectomy, through a right upper paramedian incision, by measuring both the analgesic and pulmonary effects with pain subjectively measured following deep breathing and coughing as well as at rest. This procedure was compared with a control group, who received a conventional regimen of intermittent intramuscular pa paveretu m ,

Objectives of Study The aim of this study was t o investigate and evaluate the effectiveness of TENS in relation to pulmonary function and patients' subjective assessment of pain relief following cholecystectomy. Four objectives were established to satisfy this aim: 1. To measure and compare the values of FVC and FEV, in t w o groups of patients (experimental and control) pre- and post-cholecystectomy. 2. To measure subjectively and compare pain relief in the same t w o groups of patients at rest and immediately following deep breathing and coughing.

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3. To compare the opiate analgesia requirements of both groups post-operatively. 4. To observe and compare the average length of stay in hospital, the average number of post-operative days before mobilisation and any post-operative pulmonary complications, in both groups. Four null hypotheses were established before starting the study:

1. There is no significant difference in pulmonary function values FVC and FEV, between the t w o groups when compared on the first, second and fifth days following c holecystectomy. 2. There is no significant difference in FEV,/FVC ratio between the t w o groups when compared on the first, second and fifth days post-operatively.

3. There is no significant difference in subjective pain relief between the t w o groups when compared at rest, immediately following deep breathing, and after coughing, on the first, second and fifth days following cnolecystectomy. 4. There is no significant difference in the amounts of opiate analgesia administered t o both groups on the first and second days post-operatively.

Methods Subjects Thirty patients undergoing elective cholecystectomy at Stobhill General Hospital, Glasgow, were selected for this study. Pre-operatively they were allocated at random to one of t w o groups, to receive different regimens of post-operative analgesia. Group 1: Fifteen control patients who received a conventional o n - d e m a n d p o s t - o p e r a t i v e analgesic regimen of papaveretum, administered intramuscularly, at intervals (10-20 m g at four-hourly intervals as necessary). Group 2: Fifteen experimental patients fitted w i t h transcutaneous electrical nerve stimulators who reQeived supplementary intramuscular papaveretum, at interyals, if required. No patient w i t h a diagnosed history of respiratory disease, or thoracic deformity, or respiratory infection (pre-operatively), or cardiac pacemaker, was included in the study. Equipment TENS was provided using a dual channel Medaid unit (Par Medex Ltd, Hertfordshire), which uses an asymmetrical biphasic square pulse waveform w i t h a current amplitude of 0 - 5 milliamperes a t a frequency of 10-150 pulses per second with pulse duration of 50-3,000 microseconds. A spirometer (Vitalograph T M Ltd, Buckingham), was used to assess ventilatory capacity by measuring FVC and the FEV,. A Vitalograph chart record was used t o store the data. Linear pain analogue was used to measure pain relief subjectively. This consisted of an ungraduated vertical 10 cm straight line. A score of zero indicated no pain and a score of 10 indicated the worst pain ever experienced. The scores in between represented a subjective measurement of the severity of pain experienced by the patient. Patients were asked to mark the line according to their level of pain (Revill et a / , 1976). The TENS units and spirometer used in this study were calibrated and tested before, during and after the study bv the medical physics department of Stobhill General Hospital.

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Procedure

Data Analyses

The patients' consent was obtained on the day before surgery, at which time the regimen of post-operative analgesia was explained t o them including a short demonstration of TENS. To avoid bias this duty was undertaken by a clinician who was not involved in the study. All patients received narcotic premedication and a similar mode of anaesthesia consisting of thiopentone induction, intermittent positive pressure ventilation and maintenance of anaesthesia by a combination of inhalation agents supplemented by narcotics as required. All patients had a right upper paramedian muscle reflecting incision. After laparotomy all patients underwent operative cholangiogram and cholecystectomy. The TENS group were fitted in the recovery room, immediately post-operatively, with t w o sterile electrodes ( 4 6 m m x 255 m m ) one on either side of the incision and t w o non-sterile carbon rubber electrodes (46 m m x 9 5 mm) applied paravertebrally at the level of T,-T,,. TENS was then begun. As there is no acknowledged universal waveform which provides all patients with the optimal level of pain relief (Campe, 1978), patients were instructed pre-operatively simply t o alter the waveform to an intensity, frequency and pulse duration which provided them with most comfort. Additionally they were advised of the option of the intermittent or continuous mode of application. Patients using an intermittent regime were instructed t o apply stimulation for one hour. All patients were aware of the availability of intramuscular pa pave retum if pain persisted despite TENS. They were told pre-operatively t o request analgesics whenever they felt they were needed. This instruction was intended t o minimise the influence of any observerisupervisor bias. The control group received intramuscular papaveretum post-operatively. This was administered at a dosage dictated by the build of the patient and at a frequency dictated by the onset of pain and the availability of nursing staff. A detailed record was kept of all or any supplementary analgesic narcotics administered t o patients in both groups. Each analgesic regimen was used for 4 8 hours post-operatively and then substituted by oral non-opiate analgesia. The use of linear analogue pain scales and spirometer function was explained and demonstrated t o all patients on the day before surgery. Post-operatively, patients were requested to indicate their level of pain by marking the ungraduated scale at rest, immediately following a deep breath and immediately after coughing. A value to the nearest 1 m m was recorded for each test by measuring the distance from zero t o the patient's mark with a 10 cm ruler. Pain was subjectively assessed using this procedure, at the same time, on the first, second and fifth days following surgery. Spirometer tests were performed three times, with all patients in a standard position - high sitting. A rest period of t w o minutes between each breath was permitted. The maximum value obtained for each lung function parameter (FVC and FEV,) was recorded (Oldham and Cole, 1983). The ratio FEV,/FVC was expressed as a percentage. All spirometer tests were carried out by the same operator, at the same time, pre-operatively and on the first, second and fifth days following surgery. All patients underwent a familiarisation process, where several 'trial' tests were performed before the actual test was carried out. Data were stored on a Smart computer spreadsheet and database - (Innovative Software - lnformix Incorporated). Patient confidentiality was respected at all times.

Statistical arialyses of data' were undertaken on Minitab (Data Analyses Software). Since a normal distribution of data could not be assumed and both sample groups were fairly small, the Mann Whitney U test was considered most appropriate t o test each hypothesis. Since multiple Mann Whitney U tests were performed, a level of 0.05 divided by the number of tests was accepted as the level of significance (Howie, 1990).

-_

Results The t w o groups of patients included in the study were comparable in terms of age and sex. Group characteristics are shown in table 1. The results of each hypothesis tested was as follows: Hypothesis I - Comparison of Pulmonary Function Values The null hypothesis was not rejected. There was no significant difference (p > 0.05) found in either FEV, or FVC values between the t w o groups, when compared on the first, second or fifth days post-operatively. The median, mean, standard deviation and mean percentage values of pre- and post-operative forced expiratory volume in one second (FEV,) in litres, for both groups, is shown in table 2. The FEV, value was on average 3 3 % to 4 3 % of the preoperative values for both groups on the first post-operative day and 4 7 % - 5 5 % on the second day and had recovered by 7 7 % t o 8 0 % by the fifth post-operative day. The fall and rise of the FEV, values was almost identical for both groups. There was a significant difference (p < 0.05) found in FEV, values within each group, when pre-operative values Table 1: Analysis of study group characteristics

Mean age (years) Male:female ratio Number of patients with proven post-operative chest infection Mean number of post-operative days before mobilisation Mean number of post-operative days before discharge

Control group (n = 751

TENS group (n = 15)

51.8 (25-74) 2:13

47.0 (28-71) 1:14

2 2.13 (2-4) 7.13 (5-12)

1 2.13 (2-4)

6.2

(5-11)

Table 2: Forced expiratory volume in one second (FEV,) and forced vital capacity (FVC) in litres. Median, mean, standard deviation and mean percentage change from pre-operative value. P values were all non-significant Pre-operative values FEV, FVC

Post-operative values Day 1 Day 2 Day 5 cEV, FVC ( F W , FVC ( F f V , FVC I

I

Control group in= 15) Median Mean SD Mean I change

2.15 1.92 0.75

2.65 2.47 0.83

0.85 0.83 0.26

1.05 1.06 0.26

1.10

1.06 0.40

1.40 1.49 0.53

1.65 1.54 0.70

2.05 1.95 0.82

100.00 100.00 43.22 42.91 55.20 60.32 80.20 78.94 TENS group ln=151 Median 2.00 2.65 0.60 0.90 0.95 1.30 1.55 2.00 Mean 2.06 2.65 0.67 1.00 0.97 1.38 1.59 2.05 SD 0.47 0.61 0.44 0.60 0.27 0.30 0.37 0.37 Mean % change 100.00 100.00 32.52 37.73 47.08 52.07 77.18 77.35

-

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Hypothesis 3 - Comparison of Subjective Pain Relief Rest Pain: The null hypothesis was not rejected for rest pain on the first and fifth days post-operatively. A significant difference ( p > 0.05) was found between the t w o groups on the second post-operative day. The TENS group scored less severe rest pain than the control group. The postoperative median, standard deviation and mean linear analogue pain scores (mm) at rest for both groups are shown in table 3 and the mean values are expressed graphically in figure 3.

Pre op

1

- - - , ,

2

3

7

5

4

Post operative days Control group

TENS group

Fig 1: Pre- and post-operative mean values of forced expiratory volume in one second (FEV,) and forced vital capacity (FVC). For all values there was no significant difference at p

< 0 05

were compared on day one, day t w o and day five postoperative Iy. The pattern of change in mean FEV, values is illustrated graphically in figure 1. The median, mean, standard deviation and mean percentage values of pre- and post-operative FVC in litres, for both groups, is shown in table 2. The mean FVC values on the first post-operative day for both groups was 38% to 43% of the pre-operative FVC values, rising t o 52% t o 60% on the second day and recovering by 77% t o 79% by the fifth-operative day. Again, the fall and rise of the FVC values was almost identical for both groups. There was a significant difference found in FVC values within each group when pre-operative values were compared with values recorded on the first, second and fifth post-operative days. The pattern of change in mean FVC values is illustrated graphically in figure 1. Hypothesis 2 - Comparison of FEV,/FVC Ratio The null hypothesis was not rejected. There was no significant difference found between the t w o groups when compared on day one, t w o or five post-operatively. The pattern of change in mean percentage FEV,/FVC ratio for both groups is illustrated graphically in figure 2.

Deep Breathing Pain: The null hypothesis was not rejected on the first and fifth days post-operatively. There was, however, a significant difference found between the t w o groups on the second post-operative day. The TENS group scored considerably less pain following deep breathing than the control group. The post-operative median, standard deviation and mean linear analogue pain scores ( m m ) immediately following deep breathing for both groups are shown in table 3 and the mean values are expressed graphically in figure 3. Cough Pain: No significant difference was found on the first' and second post-operative days. There was, however, a Table 3:Linear analogue rest, deep breathing, and cough pain scores. Post-operative median, mean, standard deviation and range values (mm)

Rest

Day 1 Deep Cough breathing

Rest

Day 2 Deep Cough breathing

Control group In = 15) Median 30.00 45.00 69.00 32.00 41.00 Mean 37.07 48.60 75.13 31.07 38.67 SD 2.13 1.87 1.92 2.30 2.06 Range 20-84 30-92 51-100 0-77 7-63

TENS group (n = 15) Median 23.00 48.00 76.00 Mean 29.73 42.07 67.60 SD 2.46 2.75 2.09 Range 2-93 0-98 26-99 P value - control I/ TENS NS NS NS

10.00 15.53 1.41 0-45 0.05

Rest

Day 3 Deep Cough breathing

57.00 56.40 2.40 21-98

16.00 26.00 41.00 17.20 24.33 44.45 1.63 1.69 2.30 0-58 0-57 0-87

14.00 48.00 21.67 41.87 1.95 2.03 4-61 9-71

5.00 6.00j 10.00 10.13 14.46 21.67 1.16 1.79: 2.38 0-38 0-48 3-75

< 0.05

NS

NS

NS <0.05

SD=standard deviation. NS=non-significant

"1

After deep breathing

At rest

After coughing

1NS

901 NS

50

7

h 0.0465

2

Post-operative days @Control group

TENS group

Fig 2: Pre- and post-operative mean percentage values of FEV,/FVC ratio. For all values there w a s no significant difference a t p < 0.05

718

5

Post-operative days

- Control group i

TENS group

Fig 3: Post-operative mean linear analogue pain scores at rest, immediately following deep breathing, and after coughing

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significant difference found on the fifth post-operative day. The TENS group scored less severe pain immediately following coughing than the control group. The postoperative median, standard deviation and mean linear analogue pain scores ( m m ) immediately follow i n g cougkmg, for both graups are shown in table 3. The mean values are illustrated graphically in figure 3. The highest pain scores recorded for both groups at rest, following deep breathing and coughing were on the first day post-operatively. The severity of pain subsequently decreased with time. Both groups recorded higher pain scores following coughing than after deep breathing and higher pain scores following deep breathing than for quiet tidal breathing at rest.

Hypothesis 4 Comparison of Opiate Analgesia Requirements There were wide individual differences in analgesic narcotic doses and requirements within each group but statistically no significant difference was found between the t w o groups on either the first or second post-operative days. The null hypotheses was therefore not rejected. The post-operative median, standard deviation and mean values of opiate analgesia requirements (mg papaveretum) for both groups are shown in table 4. All patients within the TENS group required 15 t o 8 0 m g supplementary papaveretum on the first post-operative day (median 4 5 mg). Eight patients within this group required additional 15 to 8 0 mg papaveretum on the second post-operative day (median 15). The median value for analgesic narcotic requirements was identical for both groups on both post-operative days. Table 4: Opiate analgesia requirements (mg papaveretum) - postoperative median, mean, standard deviation and range values. P values were non-significant

Day 1

Day 2

Control group (n= 151 Median Mean Range

45.00 49.00 16.71 20-80

15.00 12.00 11.77 0-40

TENS group In = 151 Median Mean SD Range

45.00 46.67 19.88 15-80

15.00 18.00 24.84 0-80

SD

Additional Observations Three patients had proven chest infections, postoperatively, t w o were in the control group and one in the TENS group. There was no significant difference found between the t w o groups in terms of the mean number of days postoperatively before either mobilisation or hospital discharge. These findings are shown in table 1 - Group characteristics.

Discussion One of the main reasons for the great variety of postoperative analgesic regimens used is that they all attempt to produce adequate pain relief with minimal side effects, the main one being pulmonary dysfunction (Jones and Jordarl, 1987).

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Post-operative pulmonary dysfunction can be attributed t o pulmonary atelectasis and extra pulmonary depression. It manifests itself through pulmonary infection and hypoxia, complications which are not uncommon after abdominal surgery (Hansen e t a / , 1977; Morran and McArdle, 1980). Pulmonary infection predisposes to hypoxia and is associated with delay in post-operative mobilisation and delay in hospital discharge and in addition is a major contributing factor t o other morbid complications. Pulmonary dysfunction post-operatively is related t o patient, anaesthetic and surgical factors. In addition it is thought to be related t o post-operative pain and the opiate analgesia used to relieve it. Patient factors including age, male sex (King, 19831, obesity (Wightman, 19681, smoking and chronic pulmonary disease (Lancet, 1977) are all associated w i t h an increased risk. Anaesthetic factors including mechanical interference w i t h respiratory movements (Heneghan e t a/, 1984), accumulation of secretions, impairment of the cough reflex, bronchospasm, decreased ciliary activity and an increase in the viscosity and volume of bronchial secretions also contribute towards pulmonary dysfunction. Surgery itself, particularly upper abdominal surgery, contributes to pulmonary dysfunction by producing local irritation, inflammation and trauma to the abdominal musculature (Ford er a/, 19831, by inadvertently creating gaseous distension (Dubois er a/, 1966) and pneumoperitoneum (Bevan, 1961) and by producing pain. lncisional pain, worsened by tension on the affected muscles, has a number of effects. Fear of coughing and deep breathing will play a considerable part in the reduction of voluntary pulmonary capacity and may allow secretions t o accumulate. Pain may induce a tonic contraction of the abdominal muscles, causing an upward displacement of the diaphragm into the chest, thus compressing the lower lobes and further reducing pulmonary volume. This would result in a decreased diaphragmatic contribution to quiet tidal breathing (Munro et a/, 1977). Analgesia, apart from providing the desired post-operative pain relief, has also been shown to cause central depression of breathing (Catling et aY, 1980; Lancet, 19861, depression of the cough reflex and conscious level w i t h possible retention of secretions and aspiration of saliva and gastric contents (Hewelett and Branthwaite, 1975). In summary it is evident that post-operative pulmonary dysfunction and any resultant post-operative pulmonary complications are a result of either a restrictive or obstructive mechanism or a combination of both. In any event postoperative pain is considered a major contributing factor. Two different analgesic regimens were used in this study. These were an intermittent on-demand opiate analgesia the commonest method used in hospital practice - and TENS. The effectiveness of TENS was investigated in relation to some aspects of pulmonary function and subjective pain relief following cholecystectomy, and compared w i t h a conventional regimen of intermittent intramuscular papaveretum. From the results obtained and subsequent analysis of pulmonary function test data, there was no significant difference found in either FEV, or FVC when comparing the two post-operative analgesic regimens. However, it has been possible to identify certain trends, within each group, when post-operative pulmonary values were studied. The FEV, and FVC were decreased markedly on the first post-operative day. The FEV, value was reduced by 6 7 % - 5 7 % and the FVC value was reduced by 62%-57%. for both groups. This

71 3

was followed by a slow gradual recovery towards the preoperative values but neither FEV, nor FVC were fully restored by the fifth post-operative day. Indeed they were both 20%-23% below the pre-operative recorded values. This finding, that patients may be discharged from hospital w i t h an approximate 2 0 % reduction of their pre-operative value, is of interest. The implications of an initial postoperative reduction of 57%-62% in FVC, in a patient whose pre-operative capacity is assessed as being low may also be of considerable importance, when evaluating the benefits of both analgesic regimens. The variance of FEV, and FVC values with time, as seen in comparison of pre-operative and post-operative results, is consistent w i t h observations previously reported (Ali et a/, 1974; Hansen et a/, 1977; Latimer et a/, 1971). These results, therefore, were not entirely unexpected but they show that neither the opiate analgesic regimen used nor TENS, even in combination with supplementary papaveretum, make any significant difference in terms of mean percentage reduction or rate of recovery of these particular pulmonary values, following cholecystectomy. This would suggest that either the pain is not adequately controlled or that there are factors other than incisional pain that may be responsible for these reductions. The pattern of decrease in pulmonary function capacities, without significant alteration in FEV,/FVC ratio, indicates a restrictive pulmonary defect, with little or no obstructive component. The mechanism of this impairment is unclear, although pain is generally considered to be important. There may also be some dysfunction of the diaphragm, as this inhibition pattern has been reported in both quiet and forced pulmonary excursion and may persist until about the seventh post-operative day (Simmoneau et a/, 1983).

It should be recognised that the control of pain, per se, should not be expected t o result in the complete eradication of post-operative pulmonary dysfunction (Ali et a/, 1981). Adequate pain control, however, should facilitate improved co-operation with the physiotherapist. Patients should be less reluctant when requested t o take deep breaths and to cough. Early post-operative mobilisation, hospital discharge and minimal post-operative pulmonary complications are also desirable and expected benefits. Analysis of subjective linear analogue pain scores revealed individual significant differences within both groups in terms of rest pain, pain on deep breathing and coughing. Although the TENS group consistently recorded less pain for each measurement on the first, second and fifth days postoperatively, statistically, the overall impression was of similar pain scores for both analgesic regimens. A significant difference between the t w o groups was found on the second post-operative day, where both rest pain and deep breathing pain scores were found t o be less for the TENS group. Patients within the TENS group also recorded significantly less pain following coughing on the fifth post-operative day. Further detailed examination of subjective pain measurements revealed an interesting trend, where TENS was found to be significantly beneficial. Most benefit appeared to be derived when stimulation was applied at mean subjective pain scores between 31 m m and 3 9 mm. The control group recorded these scores at rest, and following deep breathing, on the second post-operative day. In contrast, the TENS group who received almost identical amounts of papaveretum, recorded scores between 16 m m and 2 2 m m at the same stage. Mean pain scores below and most certainly above this level of 31 m m to 3 9 m m showed no significant difference in analgesic effect between the t w o

720

groups. This fact was evident on the first post-operative day, especially following deep breathing and following coughing where the TENS group recorded mean pain scores of 4 2 m m and 6 8 mm, respectively. This trend was observed again on the second post-operative day, when the TENS group recorded a mean pain score of 43 mm following coughing. This would suggest that TENS even w i t h supplementary papaveretum is of no benefit or at least is subjectively no better than papaveretum alone in providing adequate pain relief, in the immediate post-operative stage, when pain is acutely severe and subjective pain measurements are concurrently high. This finding has obvious beneficial therapeutic implications when evaluating the m o s t appropriate time t o combine TENS w i t h papaveretum t o maximise its analgesic effect. No credible ex2lanation can be given as t o w h y the TENS group scored a less severe pain immediately after coughing on the fifth post-operative day. Both TENS and opiate analgesia were discontinued at this stage and no record was kept of the variable amounts of non-opiate analgesia administered to both groups. The fact that mean pain scores for the TENS group, immediately following coughing, on the first and second post-operative days were less than for the control group may have influenced this finding but the possibility that the TENS group may have received greater amounts of non-opiate analgesia cannot be ruled out. It was also apparent that maximal pain for both groups was experienced on the first post-operative day and subsequently decreased with time. This is similar to findings in other studies (Catling et a/, 1980; Rutter et al, 1980). The finding that coughing was associated w i t h more severe pain than either deep breathing or rest was expected. The consistent observation, that patients within both groups were unable t o cough or breathe deeply without significant pain during the first and second post-operative days, would suggest that this is the time when patients are most vulnerable t o the development of post-operative pulmonary complications. This is supported by the considerably r e T c e d post-operative pulmonary function values. These Were almost identically reduced in both groups during this immediate post-operative period. On comparing the post-operative opiate analgesic requirements of both groups, no significant difference in the amounts of papaveretum administered was found. It was also evident that TENS as a sole means of post-operative analgesia was inadequate on the first post-operative day. All patients within the TENS group required supplementary papaveretum at this stage and only seven patients managed to cope without it on the second post-operative day. There were wide individual variations in the dose and frequency of papaveretum adminstered to patients within both groups, which indicated wide individual differences in pain thresholds, but the median value of papaveretum for both groups on both the first and second post-operative days was identical. Although, as previously noted, Ali e t a / (1981) and Cooperman e t a/ (1977) described significant reductions in post-operative analgesic requirements, the results of this study did not concur. Despite the fact that both TENS and papaveretum were used in the attempt to achieve a pain-free state, patients within both groups indicated an appreciable amount of pain 3n their linear analogue scale in the immediate postzholecystectomy period. A greater, longer-lasting, reduction n pain would have led to a significant reduction in opiate malgesia being received by patients and might have led to 3 faster recovery of pulmonary function values for the pain-

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free group. This was not the case in this particular study. Theoretically, if TENS had facilitated more effective coughing and deep breathing, then earlier mobilisation and hospital discharge with a significant reduction in post-operative pu I mona r y com pl ica t ions might have been apparent . Unfortunately there was no significant difference found in either the mean number of days post-operatively before mobilisation or hospital discharge, nor in the post-operative pulmonary complications reported. Pain is a subjective interpretation of nociceptive input, therefore each patient will have a different appreciation of pain and pain threshold from comparable surgical stimuli. This will reflect in individual analgesic requirements varying considerably. The subjective interpretation of the patients' symptoms by the nurse administering the analgesics creates further variance (Baker e r a / , 1980). Until pain can be measured quantitatively, these individual variations will remain a problem in any pain research. The factors that influence the perception of pain are multiple and individual and include physical as well as psychological factors (Shealy, 1972). These factors are centrally modified by our previous experiences and ability t o understand the cause of pain and grasp its consequences. Briefing the patient pre-operatively on the potential value of TENS as a method of pain relief may improve end-results (Cooperman et a/, 1977). The findings of this study do not dispute entirely the analgesic effect of TENS but they do question its credibility as an effective means of post-operative analgesia, following this particular surgical procedure. Although the electrodes were conventionally applied para-incisionally and paravertebrally t o facilitate a maximal analgesic effect, and the pulse width, frequency and intensity were individually varied t o provide maximum comfort, the results were mainIy negative. These results may be explained by the fact that the potential benefits of TENS were not over-emphasised preoperatively. Also, bias was minimised while recording data and its effectiveness was evaluated against a control group, following cholecystectomy, through a right paramedian incision. These factors may account for the results found in this study and the conflicting reports previously documented in other studies. It was not the intention of this study t o discover the most beneficial frequency, dosage or duration of stimulation producing an analgesic effect, but in the light of these and other conflicting findings this seems the logical next step.

It is suggested that such results support the need for more emphasis t o be placed on supervising breathing exercises during the post-operative recovery period and for a more satisfactory immediate post-operative analgesic regimen. It was evident that neither regimen provided sufficient pain relief t o facilitate deep breathing or to allay the fear and inhibition of coughing. Severe incisional pain can prevent the mildest form of physiotherapy and the most co-operative patient from achieving optimum respiratory care. Satisfactory pain control, on the other hand, should allow the same patient to tolerate more vigorous physiotherapy, facilitate a faster recovery of pulmonary function values and allow more effective coughing. These benefits would help minimise the risk of post-operative pulmonary complications. Depression of pulmonary function of the magnitude recorded may be potentially hazardous t o patients. A heightened awareness of the scale of the problem will be of interest t o all concerned. On comparing the effectiveness of TENS in relation t o subjective pain relief, the overall impression was of similar pain scores at rest, following deep breathing and coughing. However, the finding that the TENS group recorded significantly less pain at rest and following deep breathing on the second post-operative day would lead t o the conclusion that the degree of pain experienced by a patient, following cholecystectomy, may influence the analgesic effect of TENS. When pain is moderately severe, TENS was found to be of limited benefit. This finding has obvious therapeutic implications when evaluating the most appropriate time to apply stimulation. TENS exacts an increased staff commitment and expense in the post-operative management of patients. In view of the lack of anticipated benefits, the finding that TENS patients required almost identical amounts of opiate analgesia and being aware of an increasingly cost conscious Health Service, one must conclude that following cholecystectomy through a right upper paramedian incisional approach, the limited benefits of TENS do not justify the additional cost or time.

Conclusion

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The findings of this study supported the first, second and fourth null hypotheses. The third null hypothesis was not supported entirely. Evaluating comparatively the effectiveness of TENS in relation t o pulmonary function, found no significant difference between the t w o post-operative analgesic regimens. The finding that FEV, and FVC values were considerably reduced in the immediate post-operative period was consistent w i t h previous reports. This reduction may be related t o pain but it was clearly unaffected by either analgesic regimen. No evidence of an obstructive pulmonary component was found and the depressed pulmonary function values were ascribed t o the restrictive effects of pain-related symptoms, including restriction of thoracic motion, inhibition of pulmonary excursion due t o abdominal muscle spasm, altered respiratory patterns and inhibition of the diaphragm.

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ACKNOWLEDGMENTS I wish to express my appreciation to all colleagues who helped me in carrying out this study. In particular I am extremely grateful to Dr Geoff Goats, The Queen's College, Glasgow; and Kate Howie, Stobhill General Hospital. Their help and advice was invaluable. I am also extremely grateful to the staff of the surgical unit and department of physiotherapy, Stobhill General Hospital, Glasgow,

who not only gave their support but also their encouragement.

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