Clinical Radiology (1992) 46, 218-220
Correspondence Letters are published at the discretion o f the Editor. Opinions expressed by correspondents are not necessarily those o f the Editor. Unduly long letters may be returned to the authors f o r shortening. Letters in response to a paper may be sent to the author o f the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. ReJbrenees should be given in the style specified in the Instruction to Authors at the front o f the Journal.
'PRE-OXYGENATION' FOR PATIENTS RECEIVING INTRAVENOUS SEDATION/ANALGESIA DURING RADIOLOGIC P R O C E D U R E S SIR We read with interest the technical report on 'Oxygen Saturation Monitoring During Sedation for Chemonueleolysis', by Newland et al. [1]. We agree with their conclusions that monitoring with pulse oximetry should be used in all patients receiving sedation for radiologic procedures, that supplementary oxygen (O2) should also be available, and that all radiologists be trained in management of the airway. Hypoxemia is avoidable. We routinely use supplemental oxygen in these patients, beginning 5 to 10 rain before intravenous (i.v.) sedation is given and continuing until the end of the procedure. Over the course of about 5 to 10 rain, supplemental 02 allows a partial replacement of the nitrogen contained in the functional residual capacity of the lung with a higher proportion of 02. This means that, if after sedation, an unexpected apnoeic episode or a transient period of bradypnea occurs the patient is much less likely to develop a reduction in their oxygen saturation. Usually, during apnoea or bradypnea hypoxia occurs before the CO2 concentration rises. With 'pre-oxygenation' the CO2 level rises, stimulating respiration, before the O2 saturation falls to dangerous levels. This phenomenon is well documented in the anaesthesia literature [2] and is widely used at the time of anaesthetic induction to avoid the potentially profound hypoxic events which may occur if an airway is difficult to secure. In the radiologic situation, patients may be elderly or have significant compromise o f one or more organ systems in addition to the one of procedural interest. They may have an unusual sensitivity to sedative agents (we use Diazemuls and Fentanyl) administered in standard doses. This problem is very diffficult to anticipate accurately. Theoretically, in some patients with chronic obstructive airways disease and Type II respiratory failure, administration of supplementary oxygen may be hazardous by eliminating the hypoxic drive. In our experience such patients are rarely encountered. We have found that 'Pre-Oxygenation' (either 40% by face mask or 2 to 41 per min by nasal prongs) combined with continuous pulse oximeter monitoring enables the radiologist to give adequate sedation and analgesia confidently and safely for most diagnostic and interventional procedures where this is required. We hope that your readers will find this information of some interest and consider incorporating this practice into their protocols. N. B U C K L E Y D. E. M A L O N E F. P. M c G R A T H
Departments o f Anaesthesia and Radiology McMaster University Main Street West Hamilton Ontario L 8 N 3Z5 Canada
References
1 Newland CJ, Spiers SPW, Finlay DBL. Technical Report: Oxygen saturation monitoring during sedation for chemonucleolysis. Clinical Radiology 1991;44:352-353. 2 Miller RD (ed.). Anesthesia, 3rd ed. Churchill Livingstone, 1990:1278.
tive arch DSA procedures performed for symptomatic cerebro-vascular disease at Charing Cross Hospital between 1987 and 1988 recorded six temporary neurological complications [2]. Five resolved within 6 h and the sixth resolved within 12 h. There were no long-term neurological complications in this series, but the short-term complication rate (2.5 %) was considerably higher than the zero rate found by Borgstein et al. [I]. An earlier study o f 230 arch and selective carotid arteriograms in patients with symptomatic cerebro-vascular disease [3] recorded five serious long-term neurological complications, an incidence of 2.2%, which is the figure quoted by Borgstein and his colleagues. We would like to point out that this technique was abandoned as soon as we obtained DSA equipment at Charing Cross Hospital and that we have been using arch flush injections with digital subtraction since that time. We felt that the higher incidence of neurological complications using the older technique was due to manipulating the catheter in the diseased carotid arteries and this is supported by the evidence o f Earnest et aL [4]. We were also interested to read that, although intra-arterial DSA produced better resolution than intravenous DSA, the latter provided adequate diagnostic information. This is unfortunately not true of our DSA equipment, and we are still using the arterial approach. The M R C European Carotid Surgery Trial [5] has shown that carotid surgery produces significant benefits in symptomatic patients with a stenosis greater than 70%. Dr Borgstein's paper showed that this degree of stenosis can be reliably diagnosed using the most modern DSA equipment and the intravenous technique. It seems to us that the best method of investigating these high risk patients is still open to question and depends upon the available equipment and expertise in individual institutions. M. E. PORTE J. MclVOR
References
1 Borgstein RL, Brown MM, Waterston J, Butler P, Thakkar CH, Wylie IG et al. Digital subtraction angiography (DSA) of the extracranial cerebral vessels: a direct comparison between intravenous and intra-arterial DSA. Clinical Radiology 1991 ;44:402-405. 2 Porte ME, Mclvor J, Cumings R. Neurological morbidity of aortic arch DSA in cerebro-vascular disease. Clinical Radiology 1990;42:367(Abstract). 3 McIvor J, Steiner TJ, Perkin GD, Greenhalgh RM, Clifford-Rose F. Neurological morbidity of arch and carotid arteriography for cerebrovascular disease. The influence of contrast medium and radiologist. British Journal o f Radiology 1987;60:117 122. 4 Earnest F, Forbes G, Sandok BA, Piepgras DG, Faust R J, Ilstrup D M et al. Complications o f cerebral angiography: prospective assessment of risk. American Journal ofRoentgenology 1984; 142:247253. 5 European Carotid Surgery Triallists Collaborative Group, M R C European Carotid Trial. Interim results for symptomatic patients with severe (70-90%) or with mild (0-29%) stenosis. Lancet 1991;337:1235-1243.
RETROSTERNAL
DIGITAL SUBTRACTION ANGIOGRAPHY (DSA) OF THE EXTRACRANIAL CEREBRAL VESSELS SIR- We were int~erested to read the paper by Borgstein [1] and his colleagues and were very impressed by the absence of neurological morbidity in 49 consecutive arch DSA examinations carried out on patients with symptoms o f cerebral ischaemia. A study of 233 consecu-
Chafing Cross Hospital Fulham Palace Road London W6 8 R F
GOITRE
MOBILITY
SIR - I read with interest the case report of spontaneous radiographic resolution of a retrosternal goitre [1], and in particular the inability to explain the goitre's change of position. I report a case of a 68-year-old lady referred for chest radiograph because of a prolonged productive cough. A retrosternal goitre was noted with features similar to those of the reported case. To evaluate the possibility of aspiration as a cause of her symptoms, a barium swallow
Correspondence Letters are published at the discretion o f the Editor. Opinions expressed by correspondents are not necessarily those o f the Editor. Unduly long letters may be returned to the authors f o r shortening. Letters in response to a paper may be sent to the author o f the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. ReJbrenees should be given in the style specified in the Instruction to Authors at the front o f the Journal.
'PRE-OXYGENATION' FOR PATIENTS RECEIVING INTRAVENOUS SEDATION/ANALGESIA DURING RADIOLOGIC P R O C E D U R E S SIR We read with interest the technical report on 'Oxygen Saturation Monitoring During Sedation for Chemonueleolysis', by Newland et al. [1]. We agree with their conclusions that monitoring with pulse oximetry should be used in all patients receiving sedation for radiologic procedures, that supplementary oxygen (O2) should also be available, and that all radiologists be trained in management of the airway. Hypoxemia is avoidable. We routinely use supplemental oxygen in these patients, beginning 5 to 10 rain before intravenous (i.v.) sedation is given and continuing until the end of the procedure. Over the course of about 5 to 10 rain, supplemental 02 allows a partial replacement of the nitrogen contained in the functional residual capacity of the lung with a higher proportion of 02. This means that, if after sedation, an unexpected apnoeic episode or a transient period of bradypnea occurs the patient is much less likely to develop a reduction in their oxygen saturation. Usually, during apnoea or bradypnea hypoxia occurs before the CO2 concentration rises. With 'pre-oxygenation' the CO2 level rises, stimulating respiration, before the O2 saturation falls to dangerous levels. This phenomenon is well documented in the anaesthesia literature [2] and is widely used at the time of anaesthetic induction to avoid the potentially profound hypoxic events which may occur if an airway is difficult to secure. In the radiologic situation, patients may be elderly or have significant compromise o f one or more organ systems in addition to the one of procedural interest. They may have an unusual sensitivity to sedative agents (we use Diazemuls and Fentanyl) administered in standard doses. This problem is very diffficult to anticipate accurately. Theoretically, in some patients with chronic obstructive airways disease and Type II respiratory failure, administration of supplementary oxygen may be hazardous by eliminating the hypoxic drive. In our experience such patients are rarely encountered. We have found that 'Pre-Oxygenation' (either 40% by face mask or 2 to 41 per min by nasal prongs) combined with continuous pulse oximeter monitoring enables the radiologist to give adequate sedation and analgesia confidently and safely for most diagnostic and interventional procedures where this is required. We hope that your readers will find this information of some interest and consider incorporating this practice into their protocols. N. B U C K L E Y D. E. M A L O N E F. P. M c G R A T H
Departments o f Anaesthesia and Radiology McMaster University Main Street West Hamilton Ontario L 8 N 3Z5 Canada
References
1 Newland CJ, Spiers SPW, Finlay DBL. Technical Report: Oxygen saturation monitoring during sedation for chemonucleolysis. Clinical Radiology 1991;44:352-353. 2 Miller RD (ed.). Anesthesia, 3rd ed. Churchill Livingstone, 1990:1278.
tive arch DSA procedures performed for symptomatic cerebro-vascular disease at Charing Cross Hospital between 1987 and 1988 recorded six temporary neurological complications [2]. Five resolved within 6 h and the sixth resolved within 12 h. There were no long-term neurological complications in this series, but the short-term complication rate (2.5 %) was considerably higher than the zero rate found by Borgstein et al. [I]. An earlier study o f 230 arch and selective carotid arteriograms in patients with symptomatic cerebro-vascular disease [3] recorded five serious long-term neurological complications, an incidence of 2.2%, which is the figure quoted by Borgstein and his colleagues. We would like to point out that this technique was abandoned as soon as we obtained DSA equipment at Charing Cross Hospital and that we have been using arch flush injections with digital subtraction since that time. We felt that the higher incidence of neurological complications using the older technique was due to manipulating the catheter in the diseased carotid arteries and this is supported by the evidence o f Earnest et aL [4]. We were also interested to read that, although intra-arterial DSA produced better resolution than intravenous DSA, the latter provided adequate diagnostic information. This is unfortunately not true of our DSA equipment, and we are still using the arterial approach. The M R C European Carotid Surgery Trial [5] has shown that carotid surgery produces significant benefits in symptomatic patients with a stenosis greater than 70%. Dr Borgstein's paper showed that this degree of stenosis can be reliably diagnosed using the most modern DSA equipment and the intravenous technique. It seems to us that the best method of investigating these high risk patients is still open to question and depends upon the available equipment and expertise in individual institutions. M. E. PORTE J. MclVOR
References
1 Borgstein RL, Brown MM, Waterston J, Butler P, Thakkar CH, Wylie IG et al. Digital subtraction angiography (DSA) of the extracranial cerebral vessels: a direct comparison between intravenous and intra-arterial DSA. Clinical Radiology 1991 ;44:402-405. 2 Porte ME, Mclvor J, Cumings R. Neurological morbidity of aortic arch DSA in cerebro-vascular disease. Clinical Radiology 1990;42:367(Abstract). 3 McIvor J, Steiner TJ, Perkin GD, Greenhalgh RM, Clifford-Rose F. Neurological morbidity of arch and carotid arteriography for cerebrovascular disease. The influence of contrast medium and radiologist. British Journal o f Radiology 1987;60:117 122. 4 Earnest F, Forbes G, Sandok BA, Piepgras DG, Faust R J, Ilstrup D M et al. Complications o f cerebral angiography: prospective assessment of risk. American Journal ofRoentgenology 1984; 142:247253. 5 European Carotid Surgery Triallists Collaborative Group, M R C European Carotid Trial. Interim results for symptomatic patients with severe (70-90%) or with mild (0-29%) stenosis. Lancet 1991;337:1235-1243.
RETROSTERNAL
DIGITAL SUBTRACTION ANGIOGRAPHY (DSA) OF THE EXTRACRANIAL CEREBRAL VESSELS SIR- We were int~erested to read the paper by Borgstein [1] and his colleagues and were very impressed by the absence of neurological morbidity in 49 consecutive arch DSA examinations carried out on patients with symptoms o f cerebral ischaemia. A study of 233 consecu-
Chafing Cross Hospital Fulham Palace Road London W6 8 R F
GOITRE
MOBILITY
SIR - I read with interest the case report of spontaneous radiographic resolution of a retrosternal goitre [1], and in particular the inability to explain the goitre's change of position. I report a case of a 68-year-old lady referred for chest radiograph because of a prolonged productive cough. A retrosternal goitre was noted with features similar to those of the reported case. To evaluate the possibility of aspiration as a cause of her symptoms, a barium swallow
![[Quantitative determination of cerebral perfusion using digital subtraction angiography (DSA)].](/assets/img/hold.png)
