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Cough following general anaesthesia and abdominal surgery
Respirator), Medicine (1991) 85 (Supplement A), 13-16
Cough following general anaesthesia and abdominal surgery J. P. DILWORTH AND J. C. POUNSFORD*
Department of Medicine, Westminster Hospital, London SWI, and *Department of Care of the Elderly, Frenchay Hospital, Bristol, U.K.
Postoperative chest infection is a common complication of general surgery. We have assessed some of the risk factors implicated and reviewed the role of the cough reflex in the immediate postoperative period. Postoperative Chest Infection: The High Risk Patients Respiratory illness is a frequent cause of postoperative morbidity and mortality. In a series of 785 consecutive patients undergoing a variety of surgical procedures Wightman (1) reported 49 who developed pulmonary complications, including atelectasis (42%), acute or chronic bronchitis (38%), and pneumonia (18%). Abdominal operation, particularly emergency surgery for acute gastro-intestinal bleeding, had the highest complication rate. Cigarette smoking and preexisting chronic bronchitis were also significant risk factors. Males had a higher incidence of chest infection than did females, but when controlled for smoking habit, no sex difference was found. A study of a series of 520 patients undergoing elective thoracic and abdominal surgery (2) identified long operations, a history of smoking, and thoracic and upper abdominal surgery as being major risk factors for postoperative pneumonia, which occurred in nearly 20% of the patients. Other studies have identified chronic bronchitis and airways obstruction as major risk factors but the criteria used to diagnose infection are very variable. Instrumentation of the tracheobronchial tree and the anaesthetic agent may also have a significant effect. It has been suggested that increased bronchial secretion is an important risk factor for the development of postoperative infection and any impairment of airway clearance would therefore be a further complicating factor. The Importance of Cough in the Clearance of Bronchial Secretions Defence mechanisms of the lung are described in detail elsewhere (3) and include cough, mucociliary clearance, and phagocytosis by alveolar macrophages. 0954-6! 11/9l/0A00t 3+ 04 $03.00/0
The patency of the tracheobronchial tree is maintained primarily by a combination of mucociliary clearance and cough. The role of each has been demonstrated by radioaerosol techniques in normal subjects who show complete airway clearance by the mucociliary escalator (4). In the presence of excess secretions mucociliary clearance is impaired but cough, which enhances the removal of secretions from the large airways, compensates for this (4-7). To ensure adequate clearance of bronchial secretions, cough is likely to be of particular importance in the postoperative period in patients with chronic bronchitis. Cough will also be important in those who produce excess secretions during endotracheal intubation and general anaesthesia. Suppression of cough could lead to the accumulation of secretions and increase the risk of atelectesis and infection. The Suppression of Cough in the Perioperative Period There have been few studies examining cough in the immediate perioperative period. We have shown in a group of unselected patients undergoing elective upper abdominal surgery and general anaesthesia that the sensitivity of the cough reflex to inhaled irritants is decreased in the immediate postoperative period (8). Twenty-six patients were studied, and after the anaesthetic, analgesic and physiotherapy regimens had been standardized, the cough thresholds to inhaled capsaicin and citric acid were measured on the preoperative (baseline), and I st and 4th postoperative days. There was a marked fall in sensitivity to both irritants on the 1st postoperative day (P<0.01; Figs 1 and 2). On the 4th postoperative day cough threshold had returned towards baseline but remained high, the difference from baseline not quite achieving statistical significance (P=0.054 capsaicin; 0-058 citric acid; Figs 1 and 2). © t991 Bailli~reTindall
14
J. P. Dilworth and J. C. Pounsford
threshold between the preoperative and 1st postoperative day. Opiate administration is unlikely to account fully for these results as the change in cough threshold ~-'~ 96 was much greater than has been reported in other studies examining the effect of opiates on chemically48 induced cough (9-1 I). The difference between cough threshold on the preoperative and 4th postoperative 24 days, at which time no patient was receiving opiates, supports the hypothesis that additional factors are involved. The more lipid-soluble opiates (e.g. fentanyl and phenoperidone) given during a general anaesthetic could have had an effect at a relatively late stage postoperatively but no conclusive evidence for this was found. Halothane, chloroform and ether were not used in I-5 ~ our study, but animal data have shown variable effects I I I of these agents on nerve impulse production in airway -I 4-1 4-4 receptors which mediate the afferent limb of the cough Ooy from operotion reflex (11,12). At normal concentrations halothane Fig. I Cough threshold to inhaled capsaicin in the perio- increases slowly adapting pulmonary stretch receptor perative period. [ ( • ) cough assumed to occur at 192 x l0 7M; activity but at higher concentrations it is suppressed. ( - - ) cough assumed to occur at 24 x I0- ~M][from (8)]. C-fibre activity is increased at high concentrations and, although this could increase cough sensitivity, species variation does not enable conclusions to be drawn in man. The agents used in our study (enflurane and isoflurane) are short-acting and unlikely to have had an effect at the time cough measurements were made. Physiological changes in lung function, particularly reduction in lung volume; may alter airway receptor activity (13,14) but no data are available in man. Ali et aL (15) measured vital capacity at the time of upper -~ ~-o~abdominal surgery and found a fall of 32% in the immediate postoperative period returning to normal within 2 weeks of operation. Although lung function was not measured in our study, the inhalation technique involved a fixed 5-s inspiration (16); any reduc0.25 tion in lung volume would have reduced inspiratory flow rate and experimental evidence suggests this 0.125 lowers cough threshold (17), an opposite effect to that ! found. Pain from the abdominal incision will reduce -I +1 q-4 voluntary cough but the stimulus from inhaled irritants is strong and difficult to suppress. Doy from operotion A further explanation is hypoxaemia which is well Fig. 2 Cough threshold to inhaled citric acid in the periorecognized postoperatively (18). When severe it reduces perative period. [ ( • ) cough assumed to occur at 4.0 x I O- ~M] [from (8)], neural reflexes via the cough centre in the brain stem (19).
(0)
_---(°)I
!o.,[
Why is Cough Suppressed in the Postoperative Period A number of explanations for the decrease in cough sensitivity have been considered. Opiate analgesics suppress cough (9,10). In our study opiate doses were standarized and there was a correlation between timing of administration and the change in cough
Is the Suppression of Cough Postoperatively a Risk Factor for the Development of Postoperative Chest Infection? Theoretical reasons for cough suppression have already been discussed. Cough force measured by
Postoperative cough
intrapleural pressure monitoring in patients undergoing oesophageal surgery (20) was reduced in patients who developed chest infections but the differences did not achieve statistical significance. In our series five patients developed chest infection on the basis of purulent sputum, fever and/or radiographic change. Infection was apparent by the 2nd or 3rd postoperative day, but its development was not correlated with the sensitivity ofthe preoperative cough reflex. Four patients with infection had their cough threshold measured on the 1st postoperative day. The values were higher than those recorded preoperatively but were not significantly different from those recorded in patients with an uncomplicated postoperative course. On the 4th postoperative day two patients with chest infection underwent cough challenge and both had a persistently elevated threshold. The remaining patients had a threshold which had returned towards the base-line (preoperative) value. Interestingly, patients with viral upper respiratory tract infections have been reported to have a decrease in cough sensitivity (21), an effect opposite to that which we recorded in these patients. Effective cough depends upon an initial deep inspiration which will be impaired in patients with severe pain. Despite lack of experimental evidence that cough suppression affects the incidence of infection, clinical judgement suggests that cough suppression should be avoided in patients at risk because of increased retention of bronchial secretions (22).
15
Mucociliary function has also been shown to improve with fl2-adrenoceptor agonists. A balance between analgesia to assist effective coughing and sedation is difficult to achieve. Alternatives to opiate analgesia should be considered in patients where cough is thought to be necessary. Epidural anaesthesia diminishes the reduction in postoperative peak expiratory flow rate after caesarian section (28) and increases the force of cough after thoracic surgery (29).
Conclusion
Postoperative chest infection remains a common cause ofmorbidity in patients undergoing upper abdominal surgery, particularly those with excess bronchial secretions. Cough is required for the effective clearance of increased secretions from the tracheobronchial tree. Our studies have demonstrated a significant decrease in cough sensitivity after elective upper abdominal surgery. The aetiology of this has not been determined although opiate analgesia has some effect. There is no conclusive evidence that alteration in cough threshold or force increases the incidence of chest infection but there is evidence consistent with this hypothesis. Simple methods to improve the efficacy ofcough in the postoperative period already exist and should be considered in the high-risk patient. Further studies in this area are indicated.
References Alternatives to Coughing
Physiotherapy is invariably performed after upper abdominal surgery but there are few studies of its efficacy and there are doubts about its safety (23). Still less certain is the form it should take. Commonly used methods include turning to facilitate inflation of upper lung segments, deep breathing to increase ventilation and prevent atelectasis, and coughing and postural drainage to clear secretions (22,24). Turning and deep breathing will be indicated in most patients but encouragement to cough is probably only indicated in those patients with increased secretions, although Wollmer's data refute this (25). The forced expiration technique (26) avoids compression of the airways which occurs in cough and there is evidence to suggest that it is more effective on mucociliary clearance than is cough. Expectoration will be aided by adequate hydration and possibly by mucolytic agents. Bronchodilators will increase airway calibre in patients with reversible airways obstruction and may prevent bronchospasm which has been reported after physiotherapy (27).
I. Wightman JAK. A prospective survey of the incidence of postoperative pulmonary complications. Br J Surg 1968; 55: 85-91. 2. Garibaldi RA, Britt MR, Coleman ML, Reading JC, Pace NL. Risk factors for postoperative pneumbnia. Am J Med 1980;70: 677-680. 3. Cohen AB, Gold WM. Defence mechanisms of the lungs. Physiol Rev 1975;55: 325-350. 4. Pavia D, Agnew JE, Clarke SW. Cough and mucociliary clearance. Bull Eur Physiopathot Respir I986; 23 (Suppl I0): 41-45. 5. Puchelle E, Zahm JM, Girard F, Bertrand A, Polu JM, Aug F, Sandoul P. Mucociliary transport in vivo and in vitro. Relations to sputum properties in chronic bronchitis. Eur J Respir Dis 1982; 126:13 l-135. 6. Oldenburg FA, Dolovich MB, Montgomery JM, Newhouse MT. Effects ofpostural drainage, exercise and cough on mucus clearance in chronic bronchitis. Am Rev Respir Dis 1979; 120: 739-745. 7. Rossman CM, Waldes R, Sampson D, Newhouse MT. Effect of chest physiotherapy on the removal of mucus in patients with cystic fibrosis. Am Rev Respir Dis 1982;126: 131-135. 8. Dilworth JP, Pounsford JC, White ILl. Cough threshold after upper abdominal surgery. Thorax 1990;45: 207-209. 9. Empey DW, Laitenen LA, Young GA, Bye CE, Hughes DTD. Comparison of the antitussive effects of
16
J. P. Dilworth and J. C. Pounsford
codeine phosphate 20 mg, dextromethorphan 30 mg and noscapine 30mg using citric acid induced cough in normal subjects. Eur J Clin Pharmacol 1979; 16: 393-397. 10. Cox ID, Wallis PJW, Apps MCP, Hughes DTD, Empey DW, Osman RCA, Burke CA. An electromyographic method of objectively assessing cough intensity and use of the method to assess effects of codeine on the drugresponse curve to citric acid. Br J Clin Pharmacol 1984; lg: 377-382. I 1. Karlsson JA, Sant'Ambrogio G, WiddicombeJ.Afferent neural pathways in cough and reflex bronchoconstriction. J Appl Physio11989; 65: 1007-1023. 12. Coleridge HM, Coleridge JCG, Juck JC, Norman J. The effect of four volatile anaesthetic agents on the impulse activity of two types of pulmonary receptor. Br J Anaesth 1968; 40: 484-492. 13. Armstrong DJ, Luck JC. A comparative study of irritant and type J receptors in the cat. Respir Physiol 1974; 21: 47-60. 14. Coleridge HM, Coleridge JCG, Luck JG. Pulmonary afferent fibres of small diameter stimulated by capsaicin and by hyperinflation of lungs. J Physiol (Lond) 1965; 179: 248-263. 15. All J, Weisal RD, Layug AB, Kripke BJ, Hechman HB. Consequences of postoperative alterations in respiratory mechanics. Am J Surg 1974; 12,8: 376-382. 16. Pounsford JC, Birch M J, Saunders KB. Diurnal variation and adaptation of the cough response to inhaled citric acid in normal and asthmatic subjects. Thorax 1985; 49: 657-661. 17. Barros M J, Zammattio SJ, Rees PJ. Inspiratory flow rate and cough response to citric acid inhalations. Thorax 1989, 44: 860P (abstract). 18. Adelhoj B, Petring U, Larsen JC, Bigler DR, Anderson JB. Effect of subcutaneous salbutamol on postoperative pulmonary function in patients undergoing elective
cholecystectomy. Acta Anaesthesiol Scand 1985; 29: 722-725. 19. TatarM. Effect ofdenervation ofperipheralchemoreceptors on cough during hypoxia. Bull Eur Physiopathol Respir 1986; 23 (Suppl 10): 65 (abstract). 20. Sugimachi K, Ueo H, Natsuda Y, Kai H, lnokuchi K, Zaitsu A. Cough dynamics in oesophageal cancer: prevention of postoperative pulmonary complications. Br J Surg 1982; 69: 734-736. 21. Empey DW, Laitinen LA, Jacobs L, Gold WM, Nadel JA. Mechanisms of bronchial hyperreactivity in normal subjects after upper respiratory tract infection. Am Rev RespirDis 1976; 113: 131-130. 22. AI-JorfAS. Turn, cough and deep breath. Surg Gynaecol Obstet 1979; 149: 888-890. 23. Selsby DS. Chest physiotherapy--May be harmful in some patients. Br MedJ 1989; 29: 541-542. 24. May DB, Munt PW. Physiologic effects of chest percussion and postural drainage in patients with stable chronic bronchitis. Chest 1979; 75: 29-32. 25. Wollmer P, Ursing K, Midgren B, Eriksson L. Inefficiency of chest percussion in the therapy of chronic bronchitis. Eur J Respir Dis 1985; 66: 233-239. 26. Sutton PP, Parker RA, Wehler BA. Assessment of the forced expiration technique, postural drainage and directed cough in chest physiotherapy. Eur J Respir Dis 1983; 64: 62-68. 27. Campbell AH, O'Connell JM, Wilson F. The effect of chest physio-therapy on the FEVI in chronic bronchitis. MedJ Aust 1976; 1: 33-35. 28. Gamil M. Serial peak expiratory flow rates in mothers during caesarian section under extradural anaesthesia. BrJAnaesth 1989; 62: 415-418. 29. Yamazaki S, Ogawa J, Shohzu A, Yamazaki Y. Intrapleural cough pressure in patients after thoracotomy. J Thorac Cardiovasc Surg 1980; g0: 600-604.
Cough following general anaesthesia and abdominal surgery J. P. DILWORTH AND J. C. POUNSFORD*
Department of Medicine, Westminster Hospital, London SWI, and *Department of Care of the Elderly, Frenchay Hospital, Bristol, U.K.
Postoperative chest infection is a common complication of general surgery. We have assessed some of the risk factors implicated and reviewed the role of the cough reflex in the immediate postoperative period. Postoperative Chest Infection: The High Risk Patients Respiratory illness is a frequent cause of postoperative morbidity and mortality. In a series of 785 consecutive patients undergoing a variety of surgical procedures Wightman (1) reported 49 who developed pulmonary complications, including atelectasis (42%), acute or chronic bronchitis (38%), and pneumonia (18%). Abdominal operation, particularly emergency surgery for acute gastro-intestinal bleeding, had the highest complication rate. Cigarette smoking and preexisting chronic bronchitis were also significant risk factors. Males had a higher incidence of chest infection than did females, but when controlled for smoking habit, no sex difference was found. A study of a series of 520 patients undergoing elective thoracic and abdominal surgery (2) identified long operations, a history of smoking, and thoracic and upper abdominal surgery as being major risk factors for postoperative pneumonia, which occurred in nearly 20% of the patients. Other studies have identified chronic bronchitis and airways obstruction as major risk factors but the criteria used to diagnose infection are very variable. Instrumentation of the tracheobronchial tree and the anaesthetic agent may also have a significant effect. It has been suggested that increased bronchial secretion is an important risk factor for the development of postoperative infection and any impairment of airway clearance would therefore be a further complicating factor. The Importance of Cough in the Clearance of Bronchial Secretions Defence mechanisms of the lung are described in detail elsewhere (3) and include cough, mucociliary clearance, and phagocytosis by alveolar macrophages. 0954-6! 11/9l/0A00t 3+ 04 $03.00/0
The patency of the tracheobronchial tree is maintained primarily by a combination of mucociliary clearance and cough. The role of each has been demonstrated by radioaerosol techniques in normal subjects who show complete airway clearance by the mucociliary escalator (4). In the presence of excess secretions mucociliary clearance is impaired but cough, which enhances the removal of secretions from the large airways, compensates for this (4-7). To ensure adequate clearance of bronchial secretions, cough is likely to be of particular importance in the postoperative period in patients with chronic bronchitis. Cough will also be important in those who produce excess secretions during endotracheal intubation and general anaesthesia. Suppression of cough could lead to the accumulation of secretions and increase the risk of atelectesis and infection. The Suppression of Cough in the Perioperative Period There have been few studies examining cough in the immediate perioperative period. We have shown in a group of unselected patients undergoing elective upper abdominal surgery and general anaesthesia that the sensitivity of the cough reflex to inhaled irritants is decreased in the immediate postoperative period (8). Twenty-six patients were studied, and after the anaesthetic, analgesic and physiotherapy regimens had been standardized, the cough thresholds to inhaled capsaicin and citric acid were measured on the preoperative (baseline), and I st and 4th postoperative days. There was a marked fall in sensitivity to both irritants on the 1st postoperative day (P<0.01; Figs 1 and 2). On the 4th postoperative day cough threshold had returned towards baseline but remained high, the difference from baseline not quite achieving statistical significance (P=0.054 capsaicin; 0-058 citric acid; Figs 1 and 2). © t991 Bailli~reTindall
14
J. P. Dilworth and J. C. Pounsford
threshold between the preoperative and 1st postoperative day. Opiate administration is unlikely to account fully for these results as the change in cough threshold ~-'~ 96 was much greater than has been reported in other studies examining the effect of opiates on chemically48 induced cough (9-1 I). The difference between cough threshold on the preoperative and 4th postoperative 24 days, at which time no patient was receiving opiates, supports the hypothesis that additional factors are involved. The more lipid-soluble opiates (e.g. fentanyl and phenoperidone) given during a general anaesthetic could have had an effect at a relatively late stage postoperatively but no conclusive evidence for this was found. Halothane, chloroform and ether were not used in I-5 ~ our study, but animal data have shown variable effects I I I of these agents on nerve impulse production in airway -I 4-1 4-4 receptors which mediate the afferent limb of the cough Ooy from operotion reflex (11,12). At normal concentrations halothane Fig. I Cough threshold to inhaled capsaicin in the perio- increases slowly adapting pulmonary stretch receptor perative period. [ ( • ) cough assumed to occur at 192 x l0 7M; activity but at higher concentrations it is suppressed. ( - - ) cough assumed to occur at 24 x I0- ~M][from (8)]. C-fibre activity is increased at high concentrations and, although this could increase cough sensitivity, species variation does not enable conclusions to be drawn in man. The agents used in our study (enflurane and isoflurane) are short-acting and unlikely to have had an effect at the time cough measurements were made. Physiological changes in lung function, particularly reduction in lung volume; may alter airway receptor activity (13,14) but no data are available in man. Ali et aL (15) measured vital capacity at the time of upper -~ ~-o~abdominal surgery and found a fall of 32% in the immediate postoperative period returning to normal within 2 weeks of operation. Although lung function was not measured in our study, the inhalation technique involved a fixed 5-s inspiration (16); any reduc0.25 tion in lung volume would have reduced inspiratory flow rate and experimental evidence suggests this 0.125 lowers cough threshold (17), an opposite effect to that ! found. Pain from the abdominal incision will reduce -I +1 q-4 voluntary cough but the stimulus from inhaled irritants is strong and difficult to suppress. Doy from operotion A further explanation is hypoxaemia which is well Fig. 2 Cough threshold to inhaled citric acid in the periorecognized postoperatively (18). When severe it reduces perative period. [ ( • ) cough assumed to occur at 4.0 x I O- ~M] [from (8)], neural reflexes via the cough centre in the brain stem (19).
(0)
_---(°)I
!o.,[
Why is Cough Suppressed in the Postoperative Period A number of explanations for the decrease in cough sensitivity have been considered. Opiate analgesics suppress cough (9,10). In our study opiate doses were standarized and there was a correlation between timing of administration and the change in cough
Is the Suppression of Cough Postoperatively a Risk Factor for the Development of Postoperative Chest Infection? Theoretical reasons for cough suppression have already been discussed. Cough force measured by
Postoperative cough
intrapleural pressure monitoring in patients undergoing oesophageal surgery (20) was reduced in patients who developed chest infections but the differences did not achieve statistical significance. In our series five patients developed chest infection on the basis of purulent sputum, fever and/or radiographic change. Infection was apparent by the 2nd or 3rd postoperative day, but its development was not correlated with the sensitivity ofthe preoperative cough reflex. Four patients with infection had their cough threshold measured on the 1st postoperative day. The values were higher than those recorded preoperatively but were not significantly different from those recorded in patients with an uncomplicated postoperative course. On the 4th postoperative day two patients with chest infection underwent cough challenge and both had a persistently elevated threshold. The remaining patients had a threshold which had returned towards the base-line (preoperative) value. Interestingly, patients with viral upper respiratory tract infections have been reported to have a decrease in cough sensitivity (21), an effect opposite to that which we recorded in these patients. Effective cough depends upon an initial deep inspiration which will be impaired in patients with severe pain. Despite lack of experimental evidence that cough suppression affects the incidence of infection, clinical judgement suggests that cough suppression should be avoided in patients at risk because of increased retention of bronchial secretions (22).
15
Mucociliary function has also been shown to improve with fl2-adrenoceptor agonists. A balance between analgesia to assist effective coughing and sedation is difficult to achieve. Alternatives to opiate analgesia should be considered in patients where cough is thought to be necessary. Epidural anaesthesia diminishes the reduction in postoperative peak expiratory flow rate after caesarian section (28) and increases the force of cough after thoracic surgery (29).
Conclusion
Postoperative chest infection remains a common cause ofmorbidity in patients undergoing upper abdominal surgery, particularly those with excess bronchial secretions. Cough is required for the effective clearance of increased secretions from the tracheobronchial tree. Our studies have demonstrated a significant decrease in cough sensitivity after elective upper abdominal surgery. The aetiology of this has not been determined although opiate analgesia has some effect. There is no conclusive evidence that alteration in cough threshold or force increases the incidence of chest infection but there is evidence consistent with this hypothesis. Simple methods to improve the efficacy ofcough in the postoperative period already exist and should be considered in the high-risk patient. Further studies in this area are indicated.
References Alternatives to Coughing
Physiotherapy is invariably performed after upper abdominal surgery but there are few studies of its efficacy and there are doubts about its safety (23). Still less certain is the form it should take. Commonly used methods include turning to facilitate inflation of upper lung segments, deep breathing to increase ventilation and prevent atelectasis, and coughing and postural drainage to clear secretions (22,24). Turning and deep breathing will be indicated in most patients but encouragement to cough is probably only indicated in those patients with increased secretions, although Wollmer's data refute this (25). The forced expiration technique (26) avoids compression of the airways which occurs in cough and there is evidence to suggest that it is more effective on mucociliary clearance than is cough. Expectoration will be aided by adequate hydration and possibly by mucolytic agents. Bronchodilators will increase airway calibre in patients with reversible airways obstruction and may prevent bronchospasm which has been reported after physiotherapy (27).
I. Wightman JAK. A prospective survey of the incidence of postoperative pulmonary complications. Br J Surg 1968; 55: 85-91. 2. Garibaldi RA, Britt MR, Coleman ML, Reading JC, Pace NL. Risk factors for postoperative pneumbnia. Am J Med 1980;70: 677-680. 3. Cohen AB, Gold WM. Defence mechanisms of the lungs. Physiol Rev 1975;55: 325-350. 4. Pavia D, Agnew JE, Clarke SW. Cough and mucociliary clearance. Bull Eur Physiopathot Respir I986; 23 (Suppl I0): 41-45. 5. Puchelle E, Zahm JM, Girard F, Bertrand A, Polu JM, Aug F, Sandoul P. Mucociliary transport in vivo and in vitro. Relations to sputum properties in chronic bronchitis. Eur J Respir Dis 1982; 126:13 l-135. 6. Oldenburg FA, Dolovich MB, Montgomery JM, Newhouse MT. Effects ofpostural drainage, exercise and cough on mucus clearance in chronic bronchitis. Am Rev Respir Dis 1979; 120: 739-745. 7. Rossman CM, Waldes R, Sampson D, Newhouse MT. Effect of chest physiotherapy on the removal of mucus in patients with cystic fibrosis. Am Rev Respir Dis 1982;126: 131-135. 8. Dilworth JP, Pounsford JC, White ILl. Cough threshold after upper abdominal surgery. Thorax 1990;45: 207-209. 9. Empey DW, Laitenen LA, Young GA, Bye CE, Hughes DTD. Comparison of the antitussive effects of
16
J. P. Dilworth and J. C. Pounsford
codeine phosphate 20 mg, dextromethorphan 30 mg and noscapine 30mg using citric acid induced cough in normal subjects. Eur J Clin Pharmacol 1979; 16: 393-397. 10. Cox ID, Wallis PJW, Apps MCP, Hughes DTD, Empey DW, Osman RCA, Burke CA. An electromyographic method of objectively assessing cough intensity and use of the method to assess effects of codeine on the drugresponse curve to citric acid. Br J Clin Pharmacol 1984; lg: 377-382. I 1. Karlsson JA, Sant'Ambrogio G, WiddicombeJ.Afferent neural pathways in cough and reflex bronchoconstriction. J Appl Physio11989; 65: 1007-1023. 12. Coleridge HM, Coleridge JCG, Juck JC, Norman J. The effect of four volatile anaesthetic agents on the impulse activity of two types of pulmonary receptor. Br J Anaesth 1968; 40: 484-492. 13. Armstrong DJ, Luck JC. A comparative study of irritant and type J receptors in the cat. Respir Physiol 1974; 21: 47-60. 14. Coleridge HM, Coleridge JCG, Luck JG. Pulmonary afferent fibres of small diameter stimulated by capsaicin and by hyperinflation of lungs. J Physiol (Lond) 1965; 179: 248-263. 15. All J, Weisal RD, Layug AB, Kripke BJ, Hechman HB. Consequences of postoperative alterations in respiratory mechanics. Am J Surg 1974; 12,8: 376-382. 16. Pounsford JC, Birch M J, Saunders KB. Diurnal variation and adaptation of the cough response to inhaled citric acid in normal and asthmatic subjects. Thorax 1985; 49: 657-661. 17. Barros M J, Zammattio SJ, Rees PJ. Inspiratory flow rate and cough response to citric acid inhalations. Thorax 1989, 44: 860P (abstract). 18. Adelhoj B, Petring U, Larsen JC, Bigler DR, Anderson JB. Effect of subcutaneous salbutamol on postoperative pulmonary function in patients undergoing elective
cholecystectomy. Acta Anaesthesiol Scand 1985; 29: 722-725. 19. TatarM. Effect ofdenervation ofperipheralchemoreceptors on cough during hypoxia. Bull Eur Physiopathol Respir 1986; 23 (Suppl 10): 65 (abstract). 20. Sugimachi K, Ueo H, Natsuda Y, Kai H, lnokuchi K, Zaitsu A. Cough dynamics in oesophageal cancer: prevention of postoperative pulmonary complications. Br J Surg 1982; 69: 734-736. 21. Empey DW, Laitinen LA, Jacobs L, Gold WM, Nadel JA. Mechanisms of bronchial hyperreactivity in normal subjects after upper respiratory tract infection. Am Rev RespirDis 1976; 113: 131-130. 22. AI-JorfAS. Turn, cough and deep breath. Surg Gynaecol Obstet 1979; 149: 888-890. 23. Selsby DS. Chest physiotherapy--May be harmful in some patients. Br MedJ 1989; 29: 541-542. 24. May DB, Munt PW. Physiologic effects of chest percussion and postural drainage in patients with stable chronic bronchitis. Chest 1979; 75: 29-32. 25. Wollmer P, Ursing K, Midgren B, Eriksson L. Inefficiency of chest percussion in the therapy of chronic bronchitis. Eur J Respir Dis 1985; 66: 233-239. 26. Sutton PP, Parker RA, Wehler BA. Assessment of the forced expiration technique, postural drainage and directed cough in chest physiotherapy. Eur J Respir Dis 1983; 64: 62-68. 27. Campbell AH, O'Connell JM, Wilson F. The effect of chest physio-therapy on the FEVI in chronic bronchitis. MedJ Aust 1976; 1: 33-35. 28. Gamil M. Serial peak expiratory flow rates in mothers during caesarian section under extradural anaesthesia. BrJAnaesth 1989; 62: 415-418. 29. Yamazaki S, Ogawa J, Shohzu A, Yamazaki Y. Intrapleural cough pressure in patients after thoracotomy. J Thorac Cardiovasc Surg 1980; g0: 600-604.