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Gut mucosal ischaemia after cardiac surgery in patients with poor left ventricular function
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Gut mucosal ischaemia after cardiac surgery in patients with poor left ventricular function D.A. Friedlit, T. Wolfi, K. Skarvanl Department of Anaesthesia, University Hospital, Kantonsspital, 403 1 Baslex, Institute of Anaesthesiology, University Hospital, Inselspital, Bernet, Switzerland Introduction: Since we have become aware that gut ischaemia can cause translocation of endotosins and bacteria, generation of mediators and can adversely affect the outcome afker cardiac surgery (I), the gut perfusion during cardiac surgery and cardiopulmonary b_ypass (CPB) is of particular concern (2). During surgery and CPB mesenterial ischaemia may develop in response to hypotension, low pump flow, low 02-delivcly, elevated levels of endo- and esogenous catecholamines, angiotensin or vasopressin and/or hampered venous drainage (3). Recently, the monitoring of the pH of the gastric mucosa was reported to provide new insight into the adequacy of mesentcric oxygen supply (2). The purpose of lhis study was to describe changes of gastric mucosal pH (pHi) in patients with severely depressed haemodynamic function during open heart surgery. Methods: Afkcr the approval of the Ethical Committee and informed consent were obtained, 13 consecutive patients (6 female), 44-79 years old (mean 67) with ASA class III and IV (mean 3.15) and with a LV ejection fraction ~30% were studied. On the evening before surgery ranitidine as medication was started and continued until extubation. In all patients a 7.5-Fr fiberoptic thermodilution pulmonary artery (Opticath@) and radial artery catheters were inserted under local anaesthesia. Anaesthesia was induced and maintained with fentanyl, flunitrazepam and pancuronium and supplemented with isoflurane when needed. After endotracheal intubation a nasogastric tube incorporating a tonometric balloon (Tonomitor”) was inserted into the stomach. The pHi was calculated from the HendersonHasselbalch equation after determining pC0, of the saline in the balloon and bicarbonate in blood (4). Non-pulsatile hypothermic bypass (28-3O’C) was conducted in the standard fashion using a membrane oxygenator and pump flow of 1.8 l.min-‘.m-2. Cold crystalloid St. Thomas’ cardioplegia supplemented by continuous topical cooling was used for myocardial protection. The surgery involved myocardial revascularisation in 4 and valve rcplaccmcnt in 11 patients. Measurements: simultaneous measurements of heart rate, arterial, right atrial, wedge and pulmonary artery pressures, cardiac output, arterial and mised-venous 0, saturation, arterial blood gases, haemoglobin and temperature were performed as follows: 1) 30 minutes after induction, 2) before CPB, 3) during CPB (steady state), 4) at the end of operation, 5) 6-8 hours after operation and 6) after extubation of the trachea. The patients were separated in 2 groups (preop pHi Z7,34 and <7,34 respectively). Statistical analysis: Changes over time with repeatedmeasures analysis of variance, t-test for the comparison of the groups.
Results: All 13 patients were successfully separated from CPB. In 6 patients however a positive inotropic support and in one patient also IABP was needed. The patients were extubated within 8 to 21 hours (mean 14) after operation and discharged from hospital within 10 to 23 days (mean 14.7) with no complications. The majority of the patients (group 1, n=9) had a normal pHi before surgery (7.39-+0.024) and during CPB but showed a significant decrease in pHi at the end of operation, persisting till the end of the study. 4 patients (group 2) had an abnormally low pHi (7.3*0.035) already prior to surgery and eshibited a further marked decrease in pHi after the operation (Fig.). In contrast on CPB there was an increase in pHi indicating an improvement of mesenteric perfusion. There was no correlation between any of the haemodynamic and oxygenation parameters and the pHi throughout the study. GASTRIC
MUCOSAL
pHi
OVER
TIME
7.45
p
l
7.15
mean*SEM
%; ?!&I dk?!%g P8i3t piMn&i%; Discussion and Conclusion: We observed a consistent and prolonged decrease in pHi in patients with poor LV function after open heart surgery. The fall in pHi did not occurr before the end of operation and was particularly pronounced in a subgroup of patients who had a low pHi already before surgery. There were no changes in pHi during CPB. Patients exhibiting a marked decrease in pHi in the early postoperative period may be at risk of intestinal ischaemia and of its untowards sequelae. Further studies are warranted to confirm this hypothesis and to define the utility of pHi monitoring in cardiac surgery.
References: .. _..__-. (1) (2)
Fiddian-GreenRG. The predictive value of measurementsof pHi for complicationsafter cardiac swgely. Crit Care Med 15: I S356.1987 Landow L Gastric tonometry and venous oxylnetry in cardiac sureervontients.CritCare Med 19:1226-33.1991 Taylor KM. The role of angiotensinII d&g open-heartsurgery. Am Heari J 100:935-l2,1980 Fiddian-GreenRG. Tonometry: Theory end applications.Int Care World 9:60-65, 1992 I
(3) (4)
.
.
Gut mucosal ischaemia after cardiac surgery in patients with poor left ventricular function D.A. Friedlit, T. Wolfi, K. Skarvanl Department of Anaesthesia, University Hospital, Kantonsspital, 403 1 Baslex, Institute of Anaesthesiology, University Hospital, Inselspital, Bernet, Switzerland Introduction: Since we have become aware that gut ischaemia can cause translocation of endotosins and bacteria, generation of mediators and can adversely affect the outcome afker cardiac surgery (I), the gut perfusion during cardiac surgery and cardiopulmonary b_ypass (CPB) is of particular concern (2). During surgery and CPB mesenterial ischaemia may develop in response to hypotension, low pump flow, low 02-delivcly, elevated levels of endo- and esogenous catecholamines, angiotensin or vasopressin and/or hampered venous drainage (3). Recently, the monitoring of the pH of the gastric mucosa was reported to provide new insight into the adequacy of mesentcric oxygen supply (2). The purpose of lhis study was to describe changes of gastric mucosal pH (pHi) in patients with severely depressed haemodynamic function during open heart surgery. Methods: Afkcr the approval of the Ethical Committee and informed consent were obtained, 13 consecutive patients (6 female), 44-79 years old (mean 67) with ASA class III and IV (mean 3.15) and with a LV ejection fraction ~30% were studied. On the evening before surgery ranitidine as medication was started and continued until extubation. In all patients a 7.5-Fr fiberoptic thermodilution pulmonary artery (Opticath@) and radial artery catheters were inserted under local anaesthesia. Anaesthesia was induced and maintained with fentanyl, flunitrazepam and pancuronium and supplemented with isoflurane when needed. After endotracheal intubation a nasogastric tube incorporating a tonometric balloon (Tonomitor”) was inserted into the stomach. The pHi was calculated from the HendersonHasselbalch equation after determining pC0, of the saline in the balloon and bicarbonate in blood (4). Non-pulsatile hypothermic bypass (28-3O’C) was conducted in the standard fashion using a membrane oxygenator and pump flow of 1.8 l.min-‘.m-2. Cold crystalloid St. Thomas’ cardioplegia supplemented by continuous topical cooling was used for myocardial protection. The surgery involved myocardial revascularisation in 4 and valve rcplaccmcnt in 11 patients. Measurements: simultaneous measurements of heart rate, arterial, right atrial, wedge and pulmonary artery pressures, cardiac output, arterial and mised-venous 0, saturation, arterial blood gases, haemoglobin and temperature were performed as follows: 1) 30 minutes after induction, 2) before CPB, 3) during CPB (steady state), 4) at the end of operation, 5) 6-8 hours after operation and 6) after extubation of the trachea. The patients were separated in 2 groups (preop pHi Z7,34 and <7,34 respectively). Statistical analysis: Changes over time with repeatedmeasures analysis of variance, t-test for the comparison of the groups.
Results: All 13 patients were successfully separated from CPB. In 6 patients however a positive inotropic support and in one patient also IABP was needed. The patients were extubated within 8 to 21 hours (mean 14) after operation and discharged from hospital within 10 to 23 days (mean 14.7) with no complications. The majority of the patients (group 1, n=9) had a normal pHi before surgery (7.39-+0.024) and during CPB but showed a significant decrease in pHi at the end of operation, persisting till the end of the study. 4 patients (group 2) had an abnormally low pHi (7.3*0.035) already prior to surgery and eshibited a further marked decrease in pHi after the operation (Fig.). In contrast on CPB there was an increase in pHi indicating an improvement of mesenteric perfusion. There was no correlation between any of the haemodynamic and oxygenation parameters and the pHi throughout the study. GASTRIC
MUCOSAL
pHi
OVER
TIME
7.45
p
l
7.15
mean*SEM
%; ?!&I dk?!%g P8i3t piMn&i%; Discussion and Conclusion: We observed a consistent and prolonged decrease in pHi in patients with poor LV function after open heart surgery. The fall in pHi did not occurr before the end of operation and was particularly pronounced in a subgroup of patients who had a low pHi already before surgery. There were no changes in pHi during CPB. Patients exhibiting a marked decrease in pHi in the early postoperative period may be at risk of intestinal ischaemia and of its untowards sequelae. Further studies are warranted to confirm this hypothesis and to define the utility of pHi monitoring in cardiac surgery.
References: .. _..__-. (1) (2)
Fiddian-GreenRG. The predictive value of measurementsof pHi for complicationsafter cardiac swgely. Crit Care Med 15: I S356.1987 Landow L Gastric tonometry and venous oxylnetry in cardiac sureervontients.CritCare Med 19:1226-33.1991 Taylor KM. The role of angiotensinII d&g open-heartsurgery. Am Heari J 100:935-l2,1980 Fiddian-GreenRG. Tonometry: Theory end applications.Int Care World 9:60-65, 1992 I
(3) (4)
.
.