Anaesthesia, 1992, Volume 47, pages 196-198
Peripartum changes in gastric emptying
B. K . SANDHAR, R. H. ELLIOTT, I. W I N D R A M
AND
D. J. ROWBOTHAM
Summary Applied potential tomography was med to measure changes in gastric emptying during the peripartum period. Gastric emptying was measured sequentially in each of 10 healthy patients at 37-40 weeks gestation, 2-3 days postpartum and after the 6-week postnatal assessment (control). ‘dean ( S D ) times to 50% emptying were I5 ( 6 . 0 5 ) , I 1 ( 5 . 9 ) and 15 (5.5) min, respectively. There was no statistically signiJ!cant change in gastric emptying as a result of pregnancy in this group of women. Retrospective power analysis (assuming u = 0.05 and j = 0.20) shows the study design was adequate to detect a difference of 8 min.
Key words Gastrointestinal tract; gastric emptying. Measurement techniques; applied potential tomography. Obstetrics; gastric physiology.
Delayed gastric emptying may increase the risk of inhalation of gastric contents during anaesthesia. Various different methods have been used to measure gastric emptying in pregnant women and these have produced conflicting results. During pregnancy, X ray and scintigraphic techniques [ 1-31 are contraindicated and changes in pharmacokinetic parameters during pregnancy may affect solute absorption techniques such as paracetamol [4,5]. Ultrasound is a safe, reliable technique but requires skilled personnel and expensive equipment [6]. The purpose of this study was to follow the individual changes in gastric emptying during pregnancy using applied potential tomography (APT) and to compare this with the patient’s own control values obtained after the 6week postnatal assessment.
Methods Applied potential tomography
Applied potential tomography generates tomographic images of the resistivity of gastric contents using electrodes placed around the epigastrium. Following the ingestion of a test meal, changes in resistivity are measured. Sixteen
electrodes are placed around the abdomen at the level of the eighth costal cartilage (at the level of the gastric fundus or body). An alternating current (1 mA, 50 kHz) is passed between two opposite electrodes and the potential differences between the remaining pairs are measured. During the measurement cycle, each pair of electrodes act in sequence as drive electrodes and a total of 208 measurements are made in 100 ms. The effects of respiratory movements are removed by summating data from 150 cycles. Measurements are made before, and a t 1 min intervals after, the test meal. Data are stored on disc by a Nimbus R M computer and a cross-sectional image of the change in resistivity is produced incorporating changes in resistivity 4 cm above and below the plane of the electrodes. The area on the image representing the stomach is visible clearly and changes in resistivity with time within this area are calculated (Fig. I). Gastric secretion of hydrogen ions after ingestion of a test meal may affect resistivity measurement significantly. Therefore, it is necessary to administer a histamine type-2receptor antagonist prior to the measurement of gastric emptying with APT. Ranitidine was used in this study. The measurement of gastric emptying by APT has been shown to correlate very closely with scintigraphic techniques [7].
B.K. Sandhar, FCAnaes, R.H. Elliott, FCAnaes, Senior Registrars, I. Windram, SRN, Research Sister, D.J. Rowbotham, MD, MRCP, FCAnaes, FFARCSI, Senior Lecturer, Department of Anaesthesia, Leicester Royal Infirmary, Leicester LEI 5WW. Presented at the Anaesthetic Research Society meeting in Exeter, April 1991. Correspondence should be sent to D.J. Rowbotham please. Accepted 20 August 1991. 0003-2409/92/030 196+ 03 $03.00/0
@ 1992 The Association of Anaesthetists of G t Britain and Ireland
196
Peripartum changes in gastric emptying
197
I
37-40 weeks
2-3 days
Control
Fig. 3. Mean (SEM) times to 50% emptying (rnin). There were no significant differences.
plotted against time and the time to 50% emptying (T5,) recorded. Statistical analysis Fig. 1. Typical image of stomach contents produced by applied potential tomography in a patient in this study.
Study design
Results
The study was approved by the hospital Ethics Committee and written informed consent was obtained from each woman. Healthy pregnant women taking no medication and with no apparent obstetric complications were recruited. Gastric emptying was measured at 37-40 weeks gestation, 2-3 days postpartum and 6 weeks postpartum. If necessary, the latter measurement was delayed until breast feeding had ceased. At each measurement, the woman was fasted for 4 h and given ranitidine 150 mg orally 2 h before the study. The electrodes were placed around the upper abdomen and a reference value of resistivity was obtained. The woman was then given a drink of distilled water 400 ml and APT measurements were taken at 1 min intervals for 30 rnin during which the woman relaxed in the sitting position. Changes in the total resistivity of stomach contents were
30
r
i
0' 37-40 weeks pregnant
Data were tested for normality using the goodness of fit test and analysis was performed using analysis of variance for matched data.
2-3 days postpartum
Control
Fig. 2. Individual times to 50% emptying (rnin) in 10 patients.
Fourteen women were recruited to the study but four were later withdrawn because delivery was by Caesarean section. Mean (SD) age and weight of the women was 27.3 (0.5) years and 65.8 (9.4) kg. T,, values obtained for each woman are shown in Fig. 2. Mean (SD) T,, was 15 (6.1) min at 37-40 weeks, 11 (5.9) min at 2-3 days postpartum and 15 (5.5) rnin after the 6-week postnatal assessment (Fig. 3). There was no statistically significant change to T, and retrospective power-analysis (assuming ct = 0.05 and 3 / = 0.20) showed that the study was adequate to detect a difference of 8 min.
Discussion The results of the present study show no significant difference in gastric emptying during the three study periods. Data obtained a t 6 weeks postpartum represent the patients' own control value and it is interesting to note that in two patients, T, during pregnancy was twice the control value (Fig. 2). In both these patients, T, decreased within 3 days of delivery. Although gastric emptying during pregnancy was relatively delayed in these patients, it was still within the range of control values obtained for the group as a whole. The high incidence of inhalation of gastric contents during obstetric anaesthesia over the years has led to much interest in the effects of pregnancy on gastric emptying. Many different techniques have been used, and while some workers have shown delayed emptying during pregnancy, others have found no change. Some of the earlier studies using radiographic techniques failed to show a consistent effect. Hansen [I] demonstrated delayed emptying during pregnancy following a barium meal. However, no change was demonstrated by La Salvia and Steffen [2] using a thin barium meal and by Boyden and Rigler [3] using a fluoroscopic technique.
198
B.K. Sandhar et al.
Using simple dye dilution, Hunt and Murray [8] found no change in gastric emptying in pregnant women when compared with their own control values obtained 40 weeks after delivery. However, Davison and colleagues [9], using a double sampling dye dilution technique, found that emptying of water was delayed compared with nonpregnant controls. APT avoids the use of nasogastric tubes, which are uncomfortable and may affect gastric emptying. In the present study, the women were happy to return for repeat measurements and we had 100% compliance. Paracetamol absorption has been used during pregnancy to demonstrate delayed gastric emptying [S] or no change [ 101 compared with nonpregnant control groups. However, the altered pharmacokinetics of paracetamol during pregnancy [4] may render this technique inaccurate. Epigastric impedance [ 1 I] demonstrated no change in gastric emptying during pregnancy but gastric acid secretion was not blocked before the study and this may have affected the results since acid secretion alters gastric impedance. In that study, epigastric impedance was measured using a four electrode system and in 14 out of 68 patients, the area of the stomach was missed. The APT system used in our study utilises 16 electrodes and this enabled us to locate the stomach in all of the patients studied. APT is well tolerated and provides a useful method of assessing gastric emptying of liquid or solid meals in pregnant patients. The disadvantages of the APT technique is the need for HI-receptor blockade, but this is of little importance in this study as ranitidine is commonly administered to obstetric patients during labour. In summary, we have found APT to be an easy, reliable and well tolerated method of assessing gastric emptying in pregnant women. By using women as their own controls, we have shown that there is no consistent change in the rate of gastric emptying in the peripartum period.
References [I] HANSEN R. Zur Physiologie des Magens in der Schwangerschaft. Zentralblatt fur Gynakologie 1937; 61: 230614. [2] LA SALVIA LA, STEFFEN EA. Delayed gastric emptying time in labor. American Journal of Obstetrics and Gynecology 1950; 5 9 1075-81. [3] BOYDEN EA, RIGLERLG. Initial emptying time of stomach in prima gravidae as related to evacuation of biliary tract. Proceedings of the Society for Experimental Biology and Medicine 1944; 56: 200- I . [4] MINORS JO, ROBSON RA, BIRKETTDJ. Paracetamol metabolism in pregnancy. British Journal of Clinical Pharmacology 1986; 2 2 359-62. [5] SIMPSONKH, STAKFS AF, MILLERM. Pregnancy delays paracetamol absorption and gastric emptying in patients undergoing surgery. British Journal of Anaesthesia 1988; 60: 24-7. (61 BATEMAN DN, WHITTINGHAM TA. Measurement of gastric emptying by real-time ultrasound. Gut 1982; 2 3 524-7. YF, BIRDNC, BROWNBH, BARBER DC, [7] AVILLR, MANGNALL SEAGERAD, JOHNSONAG, READ NW. Applied potential tomography. A new non-invasive technique for measuring gastric emptying. Gastroenterology 1987; 92: 1019-26. [8] HUNTJN, MURRAYFA. Gastric function in pregnancy. Journal of Obstetrics and Gynaecology of the British Empire 1958; 65: 78-83. [9] DAVISON JS, DAVISON MC, HAYDM. Gastric emptying time in late pregnancy and labour. Journal of Obstetrics and Gynaecology of the British Commonwealth 1970: 77: 3 7 4 1 . [lo] MACFIEAG, MAGIDESAD, RICHMOND MN, REILLY CS. Gastric emptying in pregnancy. British Journal of Anaesthesia 1991; 67: 54-7. [Ill O'SULLIVAN GM, SUITON AJ, THOMPSONSA, CARRIELE, BULLINGHAM RE. Noninvasive measurement of gastric emptying in obstetric patients. Anesthesia and Analgesia 1987; 66:505-1 1.
Peripartum changes in gastric emptying
B. K . SANDHAR, R. H. ELLIOTT, I. W I N D R A M
AND
D. J. ROWBOTHAM
Summary Applied potential tomography was med to measure changes in gastric emptying during the peripartum period. Gastric emptying was measured sequentially in each of 10 healthy patients at 37-40 weeks gestation, 2-3 days postpartum and after the 6-week postnatal assessment (control). ‘dean ( S D ) times to 50% emptying were I5 ( 6 . 0 5 ) , I 1 ( 5 . 9 ) and 15 (5.5) min, respectively. There was no statistically signiJ!cant change in gastric emptying as a result of pregnancy in this group of women. Retrospective power analysis (assuming u = 0.05 and j = 0.20) shows the study design was adequate to detect a difference of 8 min.
Key words Gastrointestinal tract; gastric emptying. Measurement techniques; applied potential tomography. Obstetrics; gastric physiology.
Delayed gastric emptying may increase the risk of inhalation of gastric contents during anaesthesia. Various different methods have been used to measure gastric emptying in pregnant women and these have produced conflicting results. During pregnancy, X ray and scintigraphic techniques [ 1-31 are contraindicated and changes in pharmacokinetic parameters during pregnancy may affect solute absorption techniques such as paracetamol [4,5]. Ultrasound is a safe, reliable technique but requires skilled personnel and expensive equipment [6]. The purpose of this study was to follow the individual changes in gastric emptying during pregnancy using applied potential tomography (APT) and to compare this with the patient’s own control values obtained after the 6week postnatal assessment.
Methods Applied potential tomography
Applied potential tomography generates tomographic images of the resistivity of gastric contents using electrodes placed around the epigastrium. Following the ingestion of a test meal, changes in resistivity are measured. Sixteen
electrodes are placed around the abdomen at the level of the eighth costal cartilage (at the level of the gastric fundus or body). An alternating current (1 mA, 50 kHz) is passed between two opposite electrodes and the potential differences between the remaining pairs are measured. During the measurement cycle, each pair of electrodes act in sequence as drive electrodes and a total of 208 measurements are made in 100 ms. The effects of respiratory movements are removed by summating data from 150 cycles. Measurements are made before, and a t 1 min intervals after, the test meal. Data are stored on disc by a Nimbus R M computer and a cross-sectional image of the change in resistivity is produced incorporating changes in resistivity 4 cm above and below the plane of the electrodes. The area on the image representing the stomach is visible clearly and changes in resistivity with time within this area are calculated (Fig. I). Gastric secretion of hydrogen ions after ingestion of a test meal may affect resistivity measurement significantly. Therefore, it is necessary to administer a histamine type-2receptor antagonist prior to the measurement of gastric emptying with APT. Ranitidine was used in this study. The measurement of gastric emptying by APT has been shown to correlate very closely with scintigraphic techniques [7].
B.K. Sandhar, FCAnaes, R.H. Elliott, FCAnaes, Senior Registrars, I. Windram, SRN, Research Sister, D.J. Rowbotham, MD, MRCP, FCAnaes, FFARCSI, Senior Lecturer, Department of Anaesthesia, Leicester Royal Infirmary, Leicester LEI 5WW. Presented at the Anaesthetic Research Society meeting in Exeter, April 1991. Correspondence should be sent to D.J. Rowbotham please. Accepted 20 August 1991. 0003-2409/92/030 196+ 03 $03.00/0
@ 1992 The Association of Anaesthetists of G t Britain and Ireland
196
Peripartum changes in gastric emptying
197
I
37-40 weeks
2-3 days
Control
Fig. 3. Mean (SEM) times to 50% emptying (rnin). There were no significant differences.
plotted against time and the time to 50% emptying (T5,) recorded. Statistical analysis Fig. 1. Typical image of stomach contents produced by applied potential tomography in a patient in this study.
Study design
Results
The study was approved by the hospital Ethics Committee and written informed consent was obtained from each woman. Healthy pregnant women taking no medication and with no apparent obstetric complications were recruited. Gastric emptying was measured at 37-40 weeks gestation, 2-3 days postpartum and 6 weeks postpartum. If necessary, the latter measurement was delayed until breast feeding had ceased. At each measurement, the woman was fasted for 4 h and given ranitidine 150 mg orally 2 h before the study. The electrodes were placed around the upper abdomen and a reference value of resistivity was obtained. The woman was then given a drink of distilled water 400 ml and APT measurements were taken at 1 min intervals for 30 rnin during which the woman relaxed in the sitting position. Changes in the total resistivity of stomach contents were
30
r
i
0' 37-40 weeks pregnant
Data were tested for normality using the goodness of fit test and analysis was performed using analysis of variance for matched data.
2-3 days postpartum
Control
Fig. 2. Individual times to 50% emptying (rnin) in 10 patients.
Fourteen women were recruited to the study but four were later withdrawn because delivery was by Caesarean section. Mean (SD) age and weight of the women was 27.3 (0.5) years and 65.8 (9.4) kg. T,, values obtained for each woman are shown in Fig. 2. Mean (SD) T,, was 15 (6.1) min at 37-40 weeks, 11 (5.9) min at 2-3 days postpartum and 15 (5.5) rnin after the 6-week postnatal assessment (Fig. 3). There was no statistically significant change to T, and retrospective power-analysis (assuming ct = 0.05 and 3 / = 0.20) showed that the study was adequate to detect a difference of 8 min.
Discussion The results of the present study show no significant difference in gastric emptying during the three study periods. Data obtained a t 6 weeks postpartum represent the patients' own control value and it is interesting to note that in two patients, T, during pregnancy was twice the control value (Fig. 2). In both these patients, T, decreased within 3 days of delivery. Although gastric emptying during pregnancy was relatively delayed in these patients, it was still within the range of control values obtained for the group as a whole. The high incidence of inhalation of gastric contents during obstetric anaesthesia over the years has led to much interest in the effects of pregnancy on gastric emptying. Many different techniques have been used, and while some workers have shown delayed emptying during pregnancy, others have found no change. Some of the earlier studies using radiographic techniques failed to show a consistent effect. Hansen [I] demonstrated delayed emptying during pregnancy following a barium meal. However, no change was demonstrated by La Salvia and Steffen [2] using a thin barium meal and by Boyden and Rigler [3] using a fluoroscopic technique.
198
B.K. Sandhar et al.
Using simple dye dilution, Hunt and Murray [8] found no change in gastric emptying in pregnant women when compared with their own control values obtained 40 weeks after delivery. However, Davison and colleagues [9], using a double sampling dye dilution technique, found that emptying of water was delayed compared with nonpregnant controls. APT avoids the use of nasogastric tubes, which are uncomfortable and may affect gastric emptying. In the present study, the women were happy to return for repeat measurements and we had 100% compliance. Paracetamol absorption has been used during pregnancy to demonstrate delayed gastric emptying [S] or no change [ 101 compared with nonpregnant control groups. However, the altered pharmacokinetics of paracetamol during pregnancy [4] may render this technique inaccurate. Epigastric impedance [ 1 I] demonstrated no change in gastric emptying during pregnancy but gastric acid secretion was not blocked before the study and this may have affected the results since acid secretion alters gastric impedance. In that study, epigastric impedance was measured using a four electrode system and in 14 out of 68 patients, the area of the stomach was missed. The APT system used in our study utilises 16 electrodes and this enabled us to locate the stomach in all of the patients studied. APT is well tolerated and provides a useful method of assessing gastric emptying of liquid or solid meals in pregnant patients. The disadvantages of the APT technique is the need for HI-receptor blockade, but this is of little importance in this study as ranitidine is commonly administered to obstetric patients during labour. In summary, we have found APT to be an easy, reliable and well tolerated method of assessing gastric emptying in pregnant women. By using women as their own controls, we have shown that there is no consistent change in the rate of gastric emptying in the peripartum period.
References [I] HANSEN R. Zur Physiologie des Magens in der Schwangerschaft. Zentralblatt fur Gynakologie 1937; 61: 230614. [2] LA SALVIA LA, STEFFEN EA. Delayed gastric emptying time in labor. American Journal of Obstetrics and Gynecology 1950; 5 9 1075-81. [3] BOYDEN EA, RIGLERLG. Initial emptying time of stomach in prima gravidae as related to evacuation of biliary tract. Proceedings of the Society for Experimental Biology and Medicine 1944; 56: 200- I . [4] MINORS JO, ROBSON RA, BIRKETTDJ. Paracetamol metabolism in pregnancy. British Journal of Clinical Pharmacology 1986; 2 2 359-62. [5] SIMPSONKH, STAKFS AF, MILLERM. Pregnancy delays paracetamol absorption and gastric emptying in patients undergoing surgery. British Journal of Anaesthesia 1988; 60: 24-7. (61 BATEMAN DN, WHITTINGHAM TA. Measurement of gastric emptying by real-time ultrasound. Gut 1982; 2 3 524-7. YF, BIRDNC, BROWNBH, BARBER DC, [7] AVILLR, MANGNALL SEAGERAD, JOHNSONAG, READ NW. Applied potential tomography. A new non-invasive technique for measuring gastric emptying. Gastroenterology 1987; 92: 1019-26. [8] HUNTJN, MURRAYFA. Gastric function in pregnancy. Journal of Obstetrics and Gynaecology of the British Empire 1958; 65: 78-83. [9] DAVISON JS, DAVISON MC, HAYDM. Gastric emptying time in late pregnancy and labour. Journal of Obstetrics and Gynaecology of the British Commonwealth 1970: 77: 3 7 4 1 . [lo] MACFIEAG, MAGIDESAD, RICHMOND MN, REILLY CS. Gastric emptying in pregnancy. British Journal of Anaesthesia 1991; 67: 54-7. [Ill O'SULLIVAN GM, SUITON AJ, THOMPSONSA, CARRIELE, BULLINGHAM RE. Noninvasive measurement of gastric emptying in obstetric patients. Anesthesia and Analgesia 1987; 66:505-1 1.
