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Technical report: Oxygen saturation monitoring during sedation for chemonucleolysis
Clinical Radiology (1991) 44, 352-353
Technical Report: Oxygen Saturation Monitoring During Sedation for Chemonucleolysis C. J. N E W L A N D , S. P. W. SPIERS* and D. B. L. F I N L A Y
Department of Radiology and * Department of Anaesthesia, Leicester Royal Infirmary, Leicester Pulse oximetry is widely used during anaesthetic practice to monitor heart rate and oxygenation and has been recommended as a monitor when sedative techniques are used. We monitored 25 patients receiving sedation for chemonucleolysis and showed that 17 became hypoxaemic at some stage of the procedure, none of whom had clinically detectable signs of respiratory depression. We recommend that monitoring with pulse oximetry is used in all patients receiving sedation for radiological procedures and that all radiologists administering sedation be trained in airway management. Newland, C.J., Spiers, S.P.W. & Finlay, D.B.L. (1991). Clinical Radiology, 44, 352 353. Technical Report: Oxygen Saturation Monitoring During Sedation for Chemonucleolysis
Pulse oximeters are widely used in anaesthetic practice to monitor arterial oxygen saturation (SaO2) in patients during general anaesthesia and following intravenous sedation. Recent studies of sedative techniques used in patients undergoing endoscopic retrograde cholangiopancreatography (ERCP) (Griffin et al., 1990) and cardiac catheterization (Dodson et al., 1988) have shown that pulse oximeters demonstrated clinically undetected hypoxaemia in significant numbers of patients. Both reports speculated on the contribution of these episodes of hypoxaemia to myocardial ischaemia. Due to the discomfort and duration of the chemonucleolysis procedure, it is commonly carried out using some form of sedation and analgesia. In our department this consists of pethidine and diazemuls given intravenously to achieve the level of sedation required to carry out the procedure with minimal distress to the patient. Previous studies of the complications of chemonucleolysis have concentrated on the incidence of sensitivity reactions and neurological side-effects (Watts, 1977) without considering complications of the sedative technique used. In this study oxygen saturation was monitored by pulse 0ximetry in 25 sedated patients undergoing routine chemonucleolysis to determine the incidence of clinically undetected hypoxaemia.
P A T I E N T S AND M E T H O D S We studied 25 patients (14 male, 11 female, aged 19-59) receiving sedation for chemonucleolysis. Mean patient weight was 73.4 kg (s.d. 12.19). None had coexisting pulmonary disease. All were monitored continuously t h r o u g h o u t the procedure with a Datex Satlite pulse oximeter and Tekman chart recorder with the oximeter sensor on an index finger. The patients were placed in the prone position and baseline values of oxygen saturaifion were obtained over a 1 min period. Intravenous pethidine and diazemuls were then administered in incremental doses (pethidine 12.5 mg, diazemuls 2.5 rag) by the radiologist performing the Correspondence to: Dr C. J. Newland, Department of Radiology, Leicester Royal Infirmary, Leicester.
procedure (D.B.L.F.) to achieve an asleep but arousable patient; these were recorded by the observer (C.J.N.). Chemonucleolysis was then carried out in the standard way with the patient remaining in the prone position. The chart recordings were then analysed to determine the magnitude and duration of episodes of hypoxaemia, defined as oxygen desaturation to values of less than 9.0%. This corresponds to an arterial oxygen tension of 8kP, considered by most authorities to represent hypoxaemia.
RESULTS Baseline oxygen saturations demonstrated that no patient was hypoxaemic before the procedure (95 99%). Doses of sedative administered varied pethidine 37.5150 mg, diazemuls 5 35 mg. Average doses administered were 1.21 mg/kg (s.d. 0.34) of pethidine and 0.23 mg/kg (s.d. 0.09) of diazemuls. Seventeen of the 25 patients (68%) had between one and 25 episodes ofhypoxaemia lasting from 35 to 378 s, of whom eight had episodes lasting 30 s or more. There was no significant difference in the dose of pethidine or in the dose of diazemuls between the eight with episodes of hypoxaemia lasting greater than 30 s and the rest of the patients (Student's unpaired t-test). A trace from one of these patients is shown in Fig. 1. The lowest saturation recorded was 78%. The procedure lasted between 17 min and 40 min. At the end of the procedure only one patient remained -hypoxaemic. At no time was there clinical evidence of respiratory depression as defined by a respiratory rate less than 10, episodes of apnoea or episodes o f cyanosis.
DISCUSSION Hypoxaemia is common in sedated patients undergoing interventional procedures. An arterial oxygen saturation of 90% represents hypoxaemia and lies on the steep portion of the oxygen haemoglobin dissociation curve, where a small decrease in PaO2 will cause a large drop in the amount of oxygen carried. Episodes of desaturation to less than 90% occurred in 68% of our patients;
OXYGEN SATURATION MONITORING DURING SEDATION FOR CHEMONUCLEOLYSIS
hypoxaemic episodes were reported in 44% of patients undergoing ERCP (Griffin et al., 1990) and in 38% of those having cardiac catheterization (Dodson et al., 1988). The high incidence of hypoxaemic episodes in our study may be explained by the sedative-analgesic combination of drugs used and the position of the patient. Both drugs are known to cause respiratory depression and positioning the patient prone may cause abdominal compression which may result in ventilatory and circulatory embarrassment. Clinical signs of respiratory depression, with cyanosis or change in respiratory rate, can be difficult to detect especially when the view of the patient is obscured by radiographic machinery. Even when specifically sought, they are poor indicators of hypoxaemia. In the series of Griffin et aL (1990) only one of three patients with an oxygen saturation of less than 80% had cyanosis. In our study none had clinical signs of respiratory depression despite eight having episodes of desaturation lasting over 30 s. We feel that the high incidence of hypoxaemia, and the difficulty in detecting it clinically, indicate the need for adequate monitoring during radiological procedures in sedated patients. A pulse oximeter provides an easy, accurate (Taylor and Whitwam, 1986) and non-invasive means of monitoring pulse and oxygen saturation and is therefore ideal for use in a radiology department. Supplementary oxygen should also be available and we suggest that all radiologists be trained in management of the airway.
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REFERENCES -
Dodson, SR, Hensley, FA Jr, Martin, DE, Larach, DR & Morris, DL (1988). Continuous oxygen saturation monitoring during cardiac catheterisation in adults. Chest, 94, 28-31. Griffin, SM, Chung, SCS, Leung, JWC & Li, AKC (1990). Effect of intranasal oxygen on hypoxia and tachycardia during endoscopic cholangiopancreatography. British Medical Journal, 300, 83 84. Taylor, MB & Whitwam, JG (1986). The current status of pulse oximetry. Clinical value of continuous non-invasive saturation monitoring. Anaesthesia, 41,943-949 Watts, C (1977). Complications of chemonucleolysis for lumbar disc disease. Neurosurgery, 1, 2-5.
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Fig, 1
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Technical Report: Oxygen Saturation Monitoring During Sedation for Chemonucleolysis C. J. N E W L A N D , S. P. W. SPIERS* and D. B. L. F I N L A Y
Department of Radiology and * Department of Anaesthesia, Leicester Royal Infirmary, Leicester Pulse oximetry is widely used during anaesthetic practice to monitor heart rate and oxygenation and has been recommended as a monitor when sedative techniques are used. We monitored 25 patients receiving sedation for chemonucleolysis and showed that 17 became hypoxaemic at some stage of the procedure, none of whom had clinically detectable signs of respiratory depression. We recommend that monitoring with pulse oximetry is used in all patients receiving sedation for radiological procedures and that all radiologists administering sedation be trained in airway management. Newland, C.J., Spiers, S.P.W. & Finlay, D.B.L. (1991). Clinical Radiology, 44, 352 353. Technical Report: Oxygen Saturation Monitoring During Sedation for Chemonucleolysis
Pulse oximeters are widely used in anaesthetic practice to monitor arterial oxygen saturation (SaO2) in patients during general anaesthesia and following intravenous sedation. Recent studies of sedative techniques used in patients undergoing endoscopic retrograde cholangiopancreatography (ERCP) (Griffin et al., 1990) and cardiac catheterization (Dodson et al., 1988) have shown that pulse oximeters demonstrated clinically undetected hypoxaemia in significant numbers of patients. Both reports speculated on the contribution of these episodes of hypoxaemia to myocardial ischaemia. Due to the discomfort and duration of the chemonucleolysis procedure, it is commonly carried out using some form of sedation and analgesia. In our department this consists of pethidine and diazemuls given intravenously to achieve the level of sedation required to carry out the procedure with minimal distress to the patient. Previous studies of the complications of chemonucleolysis have concentrated on the incidence of sensitivity reactions and neurological side-effects (Watts, 1977) without considering complications of the sedative technique used. In this study oxygen saturation was monitored by pulse 0ximetry in 25 sedated patients undergoing routine chemonucleolysis to determine the incidence of clinically undetected hypoxaemia.
P A T I E N T S AND M E T H O D S We studied 25 patients (14 male, 11 female, aged 19-59) receiving sedation for chemonucleolysis. Mean patient weight was 73.4 kg (s.d. 12.19). None had coexisting pulmonary disease. All were monitored continuously t h r o u g h o u t the procedure with a Datex Satlite pulse oximeter and Tekman chart recorder with the oximeter sensor on an index finger. The patients were placed in the prone position and baseline values of oxygen saturaifion were obtained over a 1 min period. Intravenous pethidine and diazemuls were then administered in incremental doses (pethidine 12.5 mg, diazemuls 2.5 rag) by the radiologist performing the Correspondence to: Dr C. J. Newland, Department of Radiology, Leicester Royal Infirmary, Leicester.
procedure (D.B.L.F.) to achieve an asleep but arousable patient; these were recorded by the observer (C.J.N.). Chemonucleolysis was then carried out in the standard way with the patient remaining in the prone position. The chart recordings were then analysed to determine the magnitude and duration of episodes of hypoxaemia, defined as oxygen desaturation to values of less than 9.0%. This corresponds to an arterial oxygen tension of 8kP, considered by most authorities to represent hypoxaemia.
RESULTS Baseline oxygen saturations demonstrated that no patient was hypoxaemic before the procedure (95 99%). Doses of sedative administered varied pethidine 37.5150 mg, diazemuls 5 35 mg. Average doses administered were 1.21 mg/kg (s.d. 0.34) of pethidine and 0.23 mg/kg (s.d. 0.09) of diazemuls. Seventeen of the 25 patients (68%) had between one and 25 episodes ofhypoxaemia lasting from 35 to 378 s, of whom eight had episodes lasting 30 s or more. There was no significant difference in the dose of pethidine or in the dose of diazemuls between the eight with episodes of hypoxaemia lasting greater than 30 s and the rest of the patients (Student's unpaired t-test). A trace from one of these patients is shown in Fig. 1. The lowest saturation recorded was 78%. The procedure lasted between 17 min and 40 min. At the end of the procedure only one patient remained -hypoxaemic. At no time was there clinical evidence of respiratory depression as defined by a respiratory rate less than 10, episodes of apnoea or episodes o f cyanosis.
DISCUSSION Hypoxaemia is common in sedated patients undergoing interventional procedures. An arterial oxygen saturation of 90% represents hypoxaemia and lies on the steep portion of the oxygen haemoglobin dissociation curve, where a small decrease in PaO2 will cause a large drop in the amount of oxygen carried. Episodes of desaturation to less than 90% occurred in 68% of our patients;
OXYGEN SATURATION MONITORING DURING SEDATION FOR CHEMONUCLEOLYSIS
hypoxaemic episodes were reported in 44% of patients undergoing ERCP (Griffin et al., 1990) and in 38% of those having cardiac catheterization (Dodson et al., 1988). The high incidence of hypoxaemic episodes in our study may be explained by the sedative-analgesic combination of drugs used and the position of the patient. Both drugs are known to cause respiratory depression and positioning the patient prone may cause abdominal compression which may result in ventilatory and circulatory embarrassment. Clinical signs of respiratory depression, with cyanosis or change in respiratory rate, can be difficult to detect especially when the view of the patient is obscured by radiographic machinery. Even when specifically sought, they are poor indicators of hypoxaemia. In the series of Griffin et aL (1990) only one of three patients with an oxygen saturation of less than 80% had cyanosis. In our study none had clinical signs of respiratory depression despite eight having episodes of desaturation lasting over 30 s. We feel that the high incidence of hypoxaemia, and the difficulty in detecting it clinically, indicate the need for adequate monitoring during radiological procedures in sedated patients. A pulse oximeter provides an easy, accurate (Taylor and Whitwam, 1986) and non-invasive means of monitoring pulse and oxygen saturation and is therefore ideal for use in a radiology department. Supplementary oxygen should also be available and we suggest that all radiologists be trained in management of the airway.
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REFERENCES -
Dodson, SR, Hensley, FA Jr, Martin, DE, Larach, DR & Morris, DL (1988). Continuous oxygen saturation monitoring during cardiac catheterisation in adults. Chest, 94, 28-31. Griffin, SM, Chung, SCS, Leung, JWC & Li, AKC (1990). Effect of intranasal oxygen on hypoxia and tachycardia during endoscopic cholangiopancreatography. British Medical Journal, 300, 83 84. Taylor, MB & Whitwam, JG (1986). The current status of pulse oximetry. Clinical value of continuous non-invasive saturation monitoring. Anaesthesia, 41,943-949 Watts, C (1977). Complications of chemonucleolysis for lumbar disc disease. Neurosurgery, 1, 2-5.
IB-
12-
II
-
I0-
9-
8-
7-
6-
5-
4
-
B -
E-
l
353
-
I
60
I
I
70
OKygen
80
saturation'
Fig, 1
90
(% ~
"•1 I00