British Journal of Anaesthesia 1992; 69: 346-348
EFFECT OF THE LARYNGEAL MASK AIRWAY ON LOWER OESOPHAGEAL SPHINCTER PRESSURE IN PATIENTS DURING GENERAL ANAESTHESIA P. G. RABEY, P. J. MURPHY, J. A. LANGTON, P. BARKER AND D. J. ROWBOTHAM
We have studied the tone of the lower oesophageal sphincter (LOS) in 40 adults undergoing routine body surface surgery and allocated randomly to receive anaesthesia either by face mask and Guedel airway or by laryngeal mask airway. In the laryngeal mask group there was a mean (SEM) decrease in barrier pressure (LOS minus gastric pressure) of 3.6 (1.4) cm H2O, compared with a mean increase of 2.2 (1.2) cm H2O in the face mask group (P < 0.005). KEY WORDS Equipment: laryngeal mask, face mask. Gastrointestinal tract: lower oesophageal sphincter.
Regurgitation and aspiration of gastric contents have been reported in association with the use of the laryngeal mask airway (LMA) [1-6]. Previous work using dye studies has shown that the incidence of regurgitation of gastric contents may be increased during general anaesthesia with spontaneous ventilation using the LMA, compared with a group anaesthetized via a face mask and Guedel airway [7]. The major barrier to oesophageal regurgitation of gastric contents is accepted generally to be the lower oesophageal sphincter (LOS). This study was designed to investigate the effect of LMA insertion on LOS pressure during anaesthesia. PATIENTS AND METHODS
Measurement of LOS pressure
LOS pressure was measured using a 3-mm diameter silastic orogastric probe containing subminiature strain-gauge pressure transducers (Gaeltec Ltd). These have advantages over larger diameter, water-perfused infusion manometers, causing less reflex activity and giving a more accurate reflection of the LOS pressure [8, 9]. The pressure signal was amplified and recorded onto a chart recorder (BTi Biox 2100). At designated times during the study (see below), the probe was passed through the mouth into the stomach and a period of 15 min was allowed for reflex peristalsis caused by insertion of the probe to subside. The probe was then withdrawn through the lower oesophagus using a hand-withdrawn, slow-
pull-through technique and a recording of the pressure was obtained. The barrier pressure was calculated as the difference between the intragastric pressure and the peak LOS pressure measured at the end of expiration. Such a technique has been shown to be reliable and not to miss significant pressure peaks [10]. Study design
After obtaining written informed consent and local Ethics Committee approval, we studied 40 patients (ASA I—II, aged 24-69 yr) undergoing body surface surgery. Patients were excluded if they were obese, taking drugs known to affect the LOS, or had a history of previous upper abdominal surgery, hiatus hernia, oesophageal reflux, peptic ulceration or diabetes mellitus. All patients were unpremedicated. Anaesthesia was induced with thiopentone 5 mg kg"1 and fentanyl 1 ug kg"1, and maintained with 1.5 % halothane and 67% nitrous oxide in oxygen, administered via a face mask and Guedel airway. Surgery was then allowed to commence. Ten minutes after induction of anaesthesia, the pressure probe was passed into the stomach. Fifteen minutes later, a baseline LOS pressure tracing was recorded using the technique described above. The probe was then re-introduced into the stomach. Patients were allocated randomly, before anaesthesia, for subsequent maintenance with either face mask and Guedel airway or LMA after baseline measurements had been made. The patients in the LMA group had a lubricated LMA of appropriate size sited by an experienced anaesthetist in the manner described by Brain [11]. The cuff was inflated with an appropriate volume of air (size 3, 20 ml; size 4, 30 ml). Patients in the face mask and Guedal airway group continued under anaesthesia as before. Both groups continued to breathe a constant inspired concentration of 1.5 % halothane and 66 % nitrous oxide in oxygen. After 15 min, a second recording of LOS barrier pressure was made in both groups. No difficulty was experienced in withP. G. RABEY, M.B., CH.B., F.R.C. ANAES.; P. J. MURPHY, M.B., CH.B., DJL, F.R.C.ANAES.; J. A . LANGTON, M J . , B J . , FJLC.ANAES.; P. BAKKEB, M.B., B.S., F.R.C.ANAES.; D . J. ROWBOTHAM, M.D., M.R-C.P. (UJC), FJLOANAES.; Department of Anaesthesia, University of
Leicester, Leicester Royal Infirmary, Leicester LEI 5WW. Accepted for Publication: May 11, 1992.
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
SUMMARY
LARYNGEAL MASK AIRWAY AND LOS PRESSURE TABLE I. Patient characteristics (mean (range)). No significant differences between groups Face mask group Number Age (yr) Sex(M:F) Weight (kg) Operation Inguinal herniorrhaphy Varicose veins Arthroscopy
LMA group
20 46.9 (25-69) 11:9 71(51-86) 7 8 5
20 44.3 (24-68) 11:9 68(49-81) 6 6 8
347
probe. There were no difficulties in inserting or placing the LMA. There was no significant difference in baseline measurements of LOS barrier pressures between the groups (table II). There was a mean increase in barrier pressure of 15.4 (SEM 7.1) % in the face mask group, compared with a 15.8 (7.4) % reduction in the LMA group (P < 0.005) (table II). LOS barrier pressure decreased considerably (by 10-15 cm H t O) in three patients (fig. 1). DISCUSSION
TABLE II. Effect of laryngeal mask insertion on lower oesophageal sphincter barrier pressure (mean (SEM)). *P < 0.05; **P < 0.01 compared with face mask group LOS barrier pressure (cm H,O) LMA group
18.0 (2.0) 20.2 (2.5) + 2.2(1.2)
17.7(2.0) 14.1 (1.7)* -3.6(1.4)**
10 987E 6 .5 to cD Q.
d Z 4 3 2 1 0 -20
-15
-10 10 Change in pressure (cm H2O)
15
20
FIG. 1. Change in lower oesophageal barrier pressure during anaesthesia with face mask ( 0 ) and laryngeal mask ( • ) •
drawing the LOS probe from behind the inflated LMA cuff, and no additional manipulation of the LMA was required. All pressure recordings were coded, and interpreted by an independent bunded observer. The LOS barrier pressure for each tracing was calculated using the method described above. Data were tested for normality using the Kolmogorov-Smirnov goodness of fit test, and analysed using Student's paired t test. RESULTS
The groups were comparable in age, sex, weight and type of surgery (table I). Two patients were withdrawn from the study because of difficulty in passing the oesophageal
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
Baseline Final Change
Face mask group
We have demonstrated that the LOS barrier pressure is reduced during general anaesthesia in some patients after insertion of an LMA when compared with a group anaesthetized via a face mask and Guedel airway. The barrier pressure might have been affected by differences between the groups in the depth of anaesthesia. However, anaesthesia was standardized in each group and there were no differences in type of surgery. All patients had a clear airway throughout, and it is therefore unlikely that LMA insertion resulted in significant improvement of the airway such that the uptake of anaesthetic agent and depth of anaesthesia would be altered. Likewise, any differences caused by the effect of surgical stimulation would be expected to be the same in each group, as the numbers having each operation were similar, and all operations were performed by one of only two surgeons. The patients who demonstrated large decreases in LOS barrier pressure were not in any identifiable subgroup of patients. Some of the drugs used in this study are known to decrease the LOS pressure, including thiopentone [12] and halothane [13]. No data for fentanyl are available, but other opioids are known to decrease the LOS pressure [9]. The effect of nitrous oxide on the LOS is less clear, as 67 % nitrous oxide in oxygen has been reported to reduce the LOS pressure [13], but 50% has been reported not to affect it [14]. In any case, our study design ensured that there was no difference between the groups in exposure to any of these drugs. We observed an increase in the LOS barrier pressure in the control face mask group during the study period. This may reflect a return towards preinduction values as the plasma concentrations of drugs used to induce anaesthesia decreased as a result of redistribution and metabolism. This effect was presumably concealed in the LMA group patients by the reduction in LOS barrier pressure caused by the LMA. No previous investigations have been made into the effect of the method of airway maintainance or of the LMA on the LOS barrier pressure. Therefore we cannot make any comparisons between our data -and those of others. Other investigators have shown that normal individuals exhibit a large variation in LOS barrier pressures, and that there is considerable overlap in barrier pressures of normal subjects and those with reflux. A correlation exists between reflux and barrier pressure [15], and although it is not possible to define a barrier pressure below which
348
In conclusion, this study has demonstrated that a decrease in LOS barrier pressure may occur when an LMA is used for airway management during anaesthesia with spontaneous ventilation. This may provide a possible explanation for the increased incidence of regurgitation of gastric contents that has been shown to occur when a LMA is used compared with a face mask [7]. Further work is necessary to establish the precise nature of this effect and its clinical significance. REFERENCES 1. Cyana AM, Macleod DM. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167.
2. Campbell JR. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167. 3. Criswell J, John R. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167. 4. Griffen RM, Hatcher IS. Aspiration pneumonia and the laryngeal mask airway. Anaesthesia 1990; 45: 1039-1040. 5. Koehi N. Aspiration and the laryngeal mask airway. Anaesthesia 1991; 46: 419. 6. Brain AIJ. The laryngeal mask and the oesophagus. Anaesthesia 1991; 46: 701-702. 7. Barker P, Langton JA, Murphy PJ, Rowbotham DJ. Regurgitation of gastric contents during general anaesthesia using the laryngeal mask airway. British Journal of Anaesthesia 1992; 69: 314-315. 8. Weihrauch TR, Janisch HD. Esophageal manometry— Methods and value in science and clinical practice. Zeitschrift fir Gastroenterologie 1990; 28: 584-588. 9. Cotton BR, Smith G. The lower oesophageal sphincter and anaesthesia. British Journal of Anaesthesia 1984; 56: 37-46. 10. Welch RW, Drake ST. Normal lower esophageal sphincter pressure: A comparison of rapid vs. slow pull-through techniques. Gastroenterology 1980; 78: 1446-1451. 11. Brain AIJ. The Intavent Laryngeal Mask Instruction Manual. Henly-on-Thames: Intavent International SA, 1990; 43-53. 12. Smith G, Dalling R, Williams TIR. Gastro-oesophageal pressure gradient changes induced by induction of anaesthesia and suxamethonium. British Journal of Anaesthesia 1978; 50: 1137-1143. 13. Senhati GH, Frey R, Star EG. The action of inhalation anaesthetics upon the lower oesophageal sphincter. Acta Anaesthesiologica Belgica 1980; 31: 91-98. 14. Brock-Utne JG, Downing JW. The effect of 50% nitrous oxide on lower oesophageal sphincter tone. Anaesthesia 1983; 38:383-385. 15. Haddad JK. Relation of gastroesophageal reflux to yield sphincter pressures. Gastroenterology 1970; 58: 175. 16. Ingelfinger FJ. Esophageal motility. Physiological Reviews 1958; 38: 533-584. 17. Mittal RK. Current concepts of the antireflux barrier. Gastroenterology Clinics of North America 1990; 19: 501-516.
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
reflux will occur, a reduction in barrier pressure would be expected to increase the risk of gastric reflux. The mechanism of the observed reduction in LOS barrier pressure after LMA insertion is unknown. Events occurring proximally in the alimentary canal are known to have consequences distally. The presence of a bolus in the pharynx provokes a swallowing reflex in the awake human, and this is known to be associated with a marked but transient reduction in LOS pressure [16]. We did not observe any patient swallowing during this study, and the timing of measurements make it unlikely that this mechanism caused the reduction in LOS pressure. In contrast, sustained distension of the oesophagus by balloon induces prolonged relaxation of the LOS [17], and it may be that distension of the pharynx by the inflated LMA cuff similarly reduces the LOS barrier pressure.
BRITISH JOURNAL OF ANAESTHESIA
EFFECT OF THE LARYNGEAL MASK AIRWAY ON LOWER OESOPHAGEAL SPHINCTER PRESSURE IN PATIENTS DURING GENERAL ANAESTHESIA P. G. RABEY, P. J. MURPHY, J. A. LANGTON, P. BARKER AND D. J. ROWBOTHAM
We have studied the tone of the lower oesophageal sphincter (LOS) in 40 adults undergoing routine body surface surgery and allocated randomly to receive anaesthesia either by face mask and Guedel airway or by laryngeal mask airway. In the laryngeal mask group there was a mean (SEM) decrease in barrier pressure (LOS minus gastric pressure) of 3.6 (1.4) cm H2O, compared with a mean increase of 2.2 (1.2) cm H2O in the face mask group (P < 0.005). KEY WORDS Equipment: laryngeal mask, face mask. Gastrointestinal tract: lower oesophageal sphincter.
Regurgitation and aspiration of gastric contents have been reported in association with the use of the laryngeal mask airway (LMA) [1-6]. Previous work using dye studies has shown that the incidence of regurgitation of gastric contents may be increased during general anaesthesia with spontaneous ventilation using the LMA, compared with a group anaesthetized via a face mask and Guedel airway [7]. The major barrier to oesophageal regurgitation of gastric contents is accepted generally to be the lower oesophageal sphincter (LOS). This study was designed to investigate the effect of LMA insertion on LOS pressure during anaesthesia. PATIENTS AND METHODS
Measurement of LOS pressure
LOS pressure was measured using a 3-mm diameter silastic orogastric probe containing subminiature strain-gauge pressure transducers (Gaeltec Ltd). These have advantages over larger diameter, water-perfused infusion manometers, causing less reflex activity and giving a more accurate reflection of the LOS pressure [8, 9]. The pressure signal was amplified and recorded onto a chart recorder (BTi Biox 2100). At designated times during the study (see below), the probe was passed through the mouth into the stomach and a period of 15 min was allowed for reflex peristalsis caused by insertion of the probe to subside. The probe was then withdrawn through the lower oesophagus using a hand-withdrawn, slow-
pull-through technique and a recording of the pressure was obtained. The barrier pressure was calculated as the difference between the intragastric pressure and the peak LOS pressure measured at the end of expiration. Such a technique has been shown to be reliable and not to miss significant pressure peaks [10]. Study design
After obtaining written informed consent and local Ethics Committee approval, we studied 40 patients (ASA I—II, aged 24-69 yr) undergoing body surface surgery. Patients were excluded if they were obese, taking drugs known to affect the LOS, or had a history of previous upper abdominal surgery, hiatus hernia, oesophageal reflux, peptic ulceration or diabetes mellitus. All patients were unpremedicated. Anaesthesia was induced with thiopentone 5 mg kg"1 and fentanyl 1 ug kg"1, and maintained with 1.5 % halothane and 67% nitrous oxide in oxygen, administered via a face mask and Guedel airway. Surgery was then allowed to commence. Ten minutes after induction of anaesthesia, the pressure probe was passed into the stomach. Fifteen minutes later, a baseline LOS pressure tracing was recorded using the technique described above. The probe was then re-introduced into the stomach. Patients were allocated randomly, before anaesthesia, for subsequent maintenance with either face mask and Guedel airway or LMA after baseline measurements had been made. The patients in the LMA group had a lubricated LMA of appropriate size sited by an experienced anaesthetist in the manner described by Brain [11]. The cuff was inflated with an appropriate volume of air (size 3, 20 ml; size 4, 30 ml). Patients in the face mask and Guedal airway group continued under anaesthesia as before. Both groups continued to breathe a constant inspired concentration of 1.5 % halothane and 66 % nitrous oxide in oxygen. After 15 min, a second recording of LOS barrier pressure was made in both groups. No difficulty was experienced in withP. G. RABEY, M.B., CH.B., F.R.C. ANAES.; P. J. MURPHY, M.B., CH.B., DJL, F.R.C.ANAES.; J. A . LANGTON, M J . , B J . , FJLC.ANAES.; P. BAKKEB, M.B., B.S., F.R.C.ANAES.; D . J. ROWBOTHAM, M.D., M.R-C.P. (UJC), FJLOANAES.; Department of Anaesthesia, University of
Leicester, Leicester Royal Infirmary, Leicester LEI 5WW. Accepted for Publication: May 11, 1992.
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
SUMMARY
LARYNGEAL MASK AIRWAY AND LOS PRESSURE TABLE I. Patient characteristics (mean (range)). No significant differences between groups Face mask group Number Age (yr) Sex(M:F) Weight (kg) Operation Inguinal herniorrhaphy Varicose veins Arthroscopy
LMA group
20 46.9 (25-69) 11:9 71(51-86) 7 8 5
20 44.3 (24-68) 11:9 68(49-81) 6 6 8
347
probe. There were no difficulties in inserting or placing the LMA. There was no significant difference in baseline measurements of LOS barrier pressures between the groups (table II). There was a mean increase in barrier pressure of 15.4 (SEM 7.1) % in the face mask group, compared with a 15.8 (7.4) % reduction in the LMA group (P < 0.005) (table II). LOS barrier pressure decreased considerably (by 10-15 cm H t O) in three patients (fig. 1). DISCUSSION
TABLE II. Effect of laryngeal mask insertion on lower oesophageal sphincter barrier pressure (mean (SEM)). *P < 0.05; **P < 0.01 compared with face mask group LOS barrier pressure (cm H,O) LMA group
18.0 (2.0) 20.2 (2.5) + 2.2(1.2)
17.7(2.0) 14.1 (1.7)* -3.6(1.4)**
10 987E 6 .5 to cD Q.
d Z 4 3 2 1 0 -20
-15
-10 10 Change in pressure (cm H2O)
15
20
FIG. 1. Change in lower oesophageal barrier pressure during anaesthesia with face mask ( 0 ) and laryngeal mask ( • ) •
drawing the LOS probe from behind the inflated LMA cuff, and no additional manipulation of the LMA was required. All pressure recordings were coded, and interpreted by an independent bunded observer. The LOS barrier pressure for each tracing was calculated using the method described above. Data were tested for normality using the Kolmogorov-Smirnov goodness of fit test, and analysed using Student's paired t test. RESULTS
The groups were comparable in age, sex, weight and type of surgery (table I). Two patients were withdrawn from the study because of difficulty in passing the oesophageal
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
Baseline Final Change
Face mask group
We have demonstrated that the LOS barrier pressure is reduced during general anaesthesia in some patients after insertion of an LMA when compared with a group anaesthetized via a face mask and Guedel airway. The barrier pressure might have been affected by differences between the groups in the depth of anaesthesia. However, anaesthesia was standardized in each group and there were no differences in type of surgery. All patients had a clear airway throughout, and it is therefore unlikely that LMA insertion resulted in significant improvement of the airway such that the uptake of anaesthetic agent and depth of anaesthesia would be altered. Likewise, any differences caused by the effect of surgical stimulation would be expected to be the same in each group, as the numbers having each operation were similar, and all operations were performed by one of only two surgeons. The patients who demonstrated large decreases in LOS barrier pressure were not in any identifiable subgroup of patients. Some of the drugs used in this study are known to decrease the LOS pressure, including thiopentone [12] and halothane [13]. No data for fentanyl are available, but other opioids are known to decrease the LOS pressure [9]. The effect of nitrous oxide on the LOS is less clear, as 67 % nitrous oxide in oxygen has been reported to reduce the LOS pressure [13], but 50% has been reported not to affect it [14]. In any case, our study design ensured that there was no difference between the groups in exposure to any of these drugs. We observed an increase in the LOS barrier pressure in the control face mask group during the study period. This may reflect a return towards preinduction values as the plasma concentrations of drugs used to induce anaesthesia decreased as a result of redistribution and metabolism. This effect was presumably concealed in the LMA group patients by the reduction in LOS barrier pressure caused by the LMA. No previous investigations have been made into the effect of the method of airway maintainance or of the LMA on the LOS barrier pressure. Therefore we cannot make any comparisons between our data -and those of others. Other investigators have shown that normal individuals exhibit a large variation in LOS barrier pressures, and that there is considerable overlap in barrier pressures of normal subjects and those with reflux. A correlation exists between reflux and barrier pressure [15], and although it is not possible to define a barrier pressure below which
348
In conclusion, this study has demonstrated that a decrease in LOS barrier pressure may occur when an LMA is used for airway management during anaesthesia with spontaneous ventilation. This may provide a possible explanation for the increased incidence of regurgitation of gastric contents that has been shown to occur when a LMA is used compared with a face mask [7]. Further work is necessary to establish the precise nature of this effect and its clinical significance. REFERENCES 1. Cyana AM, Macleod DM. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167.
2. Campbell JR. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167. 3. Criswell J, John R. The laryngeal mask: Cautionary tales. Anaesthesia 1990; 45: 167. 4. Griffen RM, Hatcher IS. Aspiration pneumonia and the laryngeal mask airway. Anaesthesia 1990; 45: 1039-1040. 5. Koehi N. Aspiration and the laryngeal mask airway. Anaesthesia 1991; 46: 419. 6. Brain AIJ. The laryngeal mask and the oesophagus. Anaesthesia 1991; 46: 701-702. 7. Barker P, Langton JA, Murphy PJ, Rowbotham DJ. Regurgitation of gastric contents during general anaesthesia using the laryngeal mask airway. British Journal of Anaesthesia 1992; 69: 314-315. 8. Weihrauch TR, Janisch HD. Esophageal manometry— Methods and value in science and clinical practice. Zeitschrift fir Gastroenterologie 1990; 28: 584-588. 9. Cotton BR, Smith G. The lower oesophageal sphincter and anaesthesia. British Journal of Anaesthesia 1984; 56: 37-46. 10. Welch RW, Drake ST. Normal lower esophageal sphincter pressure: A comparison of rapid vs. slow pull-through techniques. Gastroenterology 1980; 78: 1446-1451. 11. Brain AIJ. The Intavent Laryngeal Mask Instruction Manual. Henly-on-Thames: Intavent International SA, 1990; 43-53. 12. Smith G, Dalling R, Williams TIR. Gastro-oesophageal pressure gradient changes induced by induction of anaesthesia and suxamethonium. British Journal of Anaesthesia 1978; 50: 1137-1143. 13. Senhati GH, Frey R, Star EG. The action of inhalation anaesthetics upon the lower oesophageal sphincter. Acta Anaesthesiologica Belgica 1980; 31: 91-98. 14. Brock-Utne JG, Downing JW. The effect of 50% nitrous oxide on lower oesophageal sphincter tone. Anaesthesia 1983; 38:383-385. 15. Haddad JK. Relation of gastroesophageal reflux to yield sphincter pressures. Gastroenterology 1970; 58: 175. 16. Ingelfinger FJ. Esophageal motility. Physiological Reviews 1958; 38: 533-584. 17. Mittal RK. Current concepts of the antireflux barrier. Gastroenterology Clinics of North America 1990; 19: 501-516.
Downloaded from http://bja.oxfordjournals.org/ at New York University on June 30, 2015
reflux will occur, a reduction in barrier pressure would be expected to increase the risk of gastric reflux. The mechanism of the observed reduction in LOS barrier pressure after LMA insertion is unknown. Events occurring proximally in the alimentary canal are known to have consequences distally. The presence of a bolus in the pharynx provokes a swallowing reflex in the awake human, and this is known to be associated with a marked but transient reduction in LOS pressure [16]. We did not observe any patient swallowing during this study, and the timing of measurements make it unlikely that this mechanism caused the reduction in LOS pressure. In contrast, sustained distension of the oesophagus by balloon induces prolonged relaxation of the LOS [17], and it may be that distension of the pharynx by the inflated LMA cuff similarly reduces the LOS barrier pressure.
BRITISH JOURNAL OF ANAESTHESIA
