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A SIMPLE METHOD FOR CONTINUOUS MONITORING OF DIRECT MEAN ARTERIAL PRESSURE
Brit. J. Anaesth. (1967), 39, 986
A SIMPLE METHOD FOR CONTINUOUS MONITORING OF DIRECT MEAN ARTERIAL PRESSURE BY S. SlVAPRAGASAM AND J. W. SANDISON
University College Hospital of the West Indies, Mono, Jamaica, West Indies SUMMARY
Several methods of measurement of direct arterial pressure which do not require transducers and amplifiers have been described. The benefits of a simple and reliable method of continuous uninterrupted observation of arterial pressure are obvious to all who have had to rely on conventional sphygmomanometry during major surgery. If authors are agreed that for this purpose direct cannulation of an artery is necessary, there is no widespread agreement regarding the manometers used to link up with the cannula. Various types have been employed. Pneumatic manometers based on compression of an air column present problems of calibration and fragmentation (Blackburn, 1966; Fink, 1963; Hale, 1964). Others have depended on aneroid manometers (Aarons, 1965; Mallard, Payne and Peachey, 1963; Severinghaus, 1957) which are insensitive at low pressures and introduce difficulties of sterilization. Any non-flushing system is limited in time by damping and inevitable blockage of the cannula (De Bono, 1963). A method is described here using a simple mercury manometer to measure continuously the mean arterial blood pressure. DESCRIPTION
Apparatus required. (1) The manometer consists of a glass reservoir (volume approximately 5 ml) which merges
at its lower end into a J-tube. Two tapered side limbs open into the upper surface of the reservoir, one of these limbs being wider than the other. It may be easily reproduced by any glass blower. The manometer is attached to a metal back plate equipped with a scale calibrated in mm, the zero of which coincides with the middle of the glass reservoir. The back plate clips on to a drip stand. (2) A pressure infuser unit (Fenwall BD4). This consists of a pouch with a sealed bladder in one wall, which when inflated pneumatically squeezes an inserted plastic infuser pack, at a pressure indicated by a simple gauge. It was designed for rapid intravenous infusion. (3) A 500-ml plastic pack containing a suitable infusion solution such as normal saline or Hartmann's. These can be obtained commercially. (4) A drip set and a length of extension tubing. The drip set must have a rubber injection site near the distal end. Assembling the apparatus. The simple components of this apparatus can be assembled in less than 5 minutes. Sterile mercury is syringed into the reservoir until the level in the reservoir and the J-tube reach the zero mark. The position of the back plate is adjusted so that the zero mark is at heart level. The plastic pack containing the infusion fluid is inserted into the pressure infuser and the drip set connected
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
Several methods of measuring direct arterial pressure without electronic equipment have been described in the past, none of which is truly satisfactory. A method is described using simple components, including a pressurized infusion system and a mercury manometer. This system is easily set up and readily autodaved. The inertia cf the system is high but it is claimed that the apparatus provides a reliable continuous measurement of mean arterial pressure. The slow continuous flush prevents blockage of the arterial cannula, and the extent and significance of any errors caused by this flush rate are discussed. This has been used in fifty patients both in the operating theatre and in the Recovery and Intensive Therapy Units. It has proved to be a satisfactory method and no serious complications have occurred.
CONTINUOUS MONITORING OF DIRECT MEAN ARTERIAL PRESSURE from the plastic pack to the reservoir. This is achieved by first discarding the plastic nylon adapter at the distal end of the drip tubing and then slipping the rubber sleeve (normally used for injection) over the wider of the two tapered side limbs of the reservoir.
987
The percutaneous arterial cannulation of the radial or brachial artery is performed by using a paediatric scalp vein set gauge 23 (Baxter R35) in children. In adults either a Cournand arterial needle or a flexible nylon catheter (Portex intravenous Cannula FG4) is inserted, the latter by a modified Seldinger technique.
Suspending hook< Plastic pack-
Bellows Metal back plate calibrated in mm
Extension tubing to narrow limb t_
Clamp A
Rubber sleeve to wide limb Glass reservoir (I.D. about 25 mm)
Mercury column
FIG.
1
The extension drip tubing fits directly on to the narrower side limb and the infusion fluid is run into the reservoir, air being easily displaced from the system. The fluid is compressed to well above expected systolic pressure and the extension tubing is then connected to the artery. Clamp A (fig. 1) is adjusted to allow a slow constant flush rate of approximately 5 drops/minute (20 ml hour) and the mean arterial pressure is read. The mercury, the manometer and the scale can be repeatedly autoclaved, and if used with fresh disposable drip and extension tubing there are no problems regarding sterility. Care must be taken during preparation and autoclaving to avoid fracturing the glassware.
With this apparatus, the mean arterial pressure is indicated continuously on the manometer and no interruption of monitoring is required for flushing purpose. Providing that flushing is carefully maintained there is little likelihood of blood gaining entrance to the cannula with subsequent blockage. A fall in blood pressure followed by a sharp rise would allow flowback of blood into the system at a rate greater than the flush rate but within the next few minutes the blood will be reflushed into the artery. The flush rate, of course, can be momentarily increased. Similarly witti a large cannula in the artery there may be some mixing of blood and flushing solution due to the wide fluctuations of the mercury meniscus but these may be damped by partially applying clamp B (fig. 1). It has not been found necessary to add heparin to the flushing fluid except in cases where monitoring has been continued for many hours outside of theatre. In these circumstances 10 mg (1000 units) is added to 500 ml of flushing solution. The magnitude of error in the mean arterial pressure estimation that occurs due to the continuous flush is small and depends on the flush rate and the size and patency of the cannula. Using a small needle, the 23-gauge scalp vein needle, with a flush rate of 5 drops/min, an increase of 8-10 mm Hg is obtained in excess of the reading taken with no flushing. However, with an 18-gauge arterial needle or an FG4 catheter no appreciable difference in the reading occurred at the recommended flush rate. Another possible source of error is a change in the zero level of mercury in the reservoir due to the fluctuations of mercury in the long limb of the J-tube. But as the cross-sectional area of the former is at least 100 times greater than that of the latter, this is not a significant factor (Burton, 1965). The fluctua-
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
COMMENT
BRITISH JOURNAL OF ANAESTHESIA
988
CLINICAL EXPERIENCE
This method has been found to be simple and most reliable. The apparatus is inexpensive when compared with electronic monitoring devices. It has been used in fifty patients, not only in the operating theatre but in the recovery and intensive therapy wards. The youngest patient so monitored was 3 years of age and the longest period of monitoring was 52 hours. Like other methods of direct arterial pressure monitoring, it is particularly applicable when estimation of blood pressure by conventional methods is either difficult or unreliable as in the presence of severe vasoconstriction and low cardiac output states, or where very frequent readings are required over a short period of time. One further advantage is that it provides an excellent pulse monitor. The dangers of this method are those associated with arterial cannulation and infusion. The amount of fluid introduced into the arterial system is low and no signs of arterial spasm or ischaemic changes have been observed. This type of pressurized system allows no possibility of air embolism. We have experienced no serious complications.
De Bono, E. F. (1963). A simple method for intraarterial pressure measurement. Lancet, 1, 1142. Fink, B. R. (1963). Pneumatic monitor for arterial blood pressure. Anesthesiology, 24, 872. Hale, D. E. (1964). Arterial and venous pressure readings during open-heart surgery. Cleveland Clin. Quart., 35, 45. Mallard, T. R., Payne, T. P., and Peachey, C. J. (1963). Continuous monitoring of blood pressure by intra-arterial catheterization of the radial artery using a watch type manometer. J. Physiol. (Lond)., 167, 10P. Severinghaus, J. (1957). Aneroid manometer for arterial blood pressure. Anesthesiology, 81, 906. UNE METHODE SIMPLE POUR SUIVRE CONTINUELLEMENT LA PRESSION ARTERIELLE DIRECTE SOMMAIRE
Jusqu'a present plusieurs m^thodes pour mesurer sans equipement ilectronique la pression arterielle directe ont 6te decrites, mais aucune ne donne reellement satisfaction. On decrit une mithode simple, comprenant un systeme pressurisi d'infusion et un manometre au mercure. Ce systeme se construit facilement et il peut etre autoclavi sans difficult^. L'inertie du systeme est elevee mais on croit que l'appareil permet de mesurer continuellement et avec exactitude la pression arterielle moyenne. Le flux continu lent empcche l'obstruction de la canule arterielle, et on discute l'£tendue et la signification des erreurs, qui seraient causees par ce flux. La m6thode a £t£ employee chez 50 patients, aussi bien en salle d'operation que dans la salle de soins postopiratoires intensifs. Elle s'est ave>6e comme satisfaisante et il n'y a pas eu de complications serieuses. BIN EINFACHES VERFAHREN ZUR FORTLAUFENDEN DIREKTEN KONTROLLE DES ARTERIELLEN MITTELDRUCKS ZUSAMMENFASSUNG
In der Vergangenheit wurden mehrere nicht-elektronische Verfahren zur direkten Kontrolle des arteriellen Blutdrucks angegeben. Keines von ihnen befriedigt. Es wird eine Methode mit einfachen Hilfsmitteln—u.a. mit einem Druckinfusionssystem und Quecksilbennanometer—angegeben. Dieses System lafit sich lcicht zusammensetzen und autoklaviieren. Trotz hoher Tragheit des Systems soil sich der arterielle Mitteldruck verlafllich fortlaufend messen REFERENCES lassen. Durch eine kontinuierliche Durcnspulung wird Aarons, B. J. (1965). Simple apparatus for the simul- die Injectionsnadel frei gehalten. Ausmafl und taneous monitoring of central venous and mean Bedeurung von Mefifehlern durch diese Spiilung werden besprochen. D?s System wurde bei 50 arterial pressures in the ward. Thorax, 20, 382. Blackburn, J. P. (1966). A disposable monitor for Patienten im Operationssaal, auf der Operativ- und Intensiy-Station erprobt. Die Ergebnisse waren arterial blood pressure. Anaesthesia, 21, 109. Burton, A. C. (1965). Physiology and Biophysics of the bcfriedigend, emstliche Komplikationen wurden nicht beobachtet. Circulation. Chicago: Year Book.
Printed In Great Britain by John Sberratt & Son Ltd.. Park Road, Altrincham
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
tions in the mercury column may again be reduced by compressing the extension tubing. The inertia of this system is high and no claim is made that systolic and diastolic pressures can be followed. It does, however, provide a reasonably accurate measurement of a true mean pressure or area pressure and with a larger arterial cannula in situ the readings have consistently fallen within 5 mm of the calculated mean pressure (systolic+2xdiastolic)/3. The errors have little clinical significance when, as is usual, the changes in a series of readings are being followed.
A SIMPLE METHOD FOR CONTINUOUS MONITORING OF DIRECT MEAN ARTERIAL PRESSURE BY S. SlVAPRAGASAM AND J. W. SANDISON
University College Hospital of the West Indies, Mono, Jamaica, West Indies SUMMARY
Several methods of measurement of direct arterial pressure which do not require transducers and amplifiers have been described. The benefits of a simple and reliable method of continuous uninterrupted observation of arterial pressure are obvious to all who have had to rely on conventional sphygmomanometry during major surgery. If authors are agreed that for this purpose direct cannulation of an artery is necessary, there is no widespread agreement regarding the manometers used to link up with the cannula. Various types have been employed. Pneumatic manometers based on compression of an air column present problems of calibration and fragmentation (Blackburn, 1966; Fink, 1963; Hale, 1964). Others have depended on aneroid manometers (Aarons, 1965; Mallard, Payne and Peachey, 1963; Severinghaus, 1957) which are insensitive at low pressures and introduce difficulties of sterilization. Any non-flushing system is limited in time by damping and inevitable blockage of the cannula (De Bono, 1963). A method is described here using a simple mercury manometer to measure continuously the mean arterial blood pressure. DESCRIPTION
Apparatus required. (1) The manometer consists of a glass reservoir (volume approximately 5 ml) which merges
at its lower end into a J-tube. Two tapered side limbs open into the upper surface of the reservoir, one of these limbs being wider than the other. It may be easily reproduced by any glass blower. The manometer is attached to a metal back plate equipped with a scale calibrated in mm, the zero of which coincides with the middle of the glass reservoir. The back plate clips on to a drip stand. (2) A pressure infuser unit (Fenwall BD4). This consists of a pouch with a sealed bladder in one wall, which when inflated pneumatically squeezes an inserted plastic infuser pack, at a pressure indicated by a simple gauge. It was designed for rapid intravenous infusion. (3) A 500-ml plastic pack containing a suitable infusion solution such as normal saline or Hartmann's. These can be obtained commercially. (4) A drip set and a length of extension tubing. The drip set must have a rubber injection site near the distal end. Assembling the apparatus. The simple components of this apparatus can be assembled in less than 5 minutes. Sterile mercury is syringed into the reservoir until the level in the reservoir and the J-tube reach the zero mark. The position of the back plate is adjusted so that the zero mark is at heart level. The plastic pack containing the infusion fluid is inserted into the pressure infuser and the drip set connected
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
Several methods of measuring direct arterial pressure without electronic equipment have been described in the past, none of which is truly satisfactory. A method is described using simple components, including a pressurized infusion system and a mercury manometer. This system is easily set up and readily autodaved. The inertia cf the system is high but it is claimed that the apparatus provides a reliable continuous measurement of mean arterial pressure. The slow continuous flush prevents blockage of the arterial cannula, and the extent and significance of any errors caused by this flush rate are discussed. This has been used in fifty patients both in the operating theatre and in the Recovery and Intensive Therapy Units. It has proved to be a satisfactory method and no serious complications have occurred.
CONTINUOUS MONITORING OF DIRECT MEAN ARTERIAL PRESSURE from the plastic pack to the reservoir. This is achieved by first discarding the plastic nylon adapter at the distal end of the drip tubing and then slipping the rubber sleeve (normally used for injection) over the wider of the two tapered side limbs of the reservoir.
987
The percutaneous arterial cannulation of the radial or brachial artery is performed by using a paediatric scalp vein set gauge 23 (Baxter R35) in children. In adults either a Cournand arterial needle or a flexible nylon catheter (Portex intravenous Cannula FG4) is inserted, the latter by a modified Seldinger technique.
Suspending hook< Plastic pack-
Bellows Metal back plate calibrated in mm
Extension tubing to narrow limb t_
Clamp A
Rubber sleeve to wide limb Glass reservoir (I.D. about 25 mm)
Mercury column
FIG.
1
The extension drip tubing fits directly on to the narrower side limb and the infusion fluid is run into the reservoir, air being easily displaced from the system. The fluid is compressed to well above expected systolic pressure and the extension tubing is then connected to the artery. Clamp A (fig. 1) is adjusted to allow a slow constant flush rate of approximately 5 drops/minute (20 ml hour) and the mean arterial pressure is read. The mercury, the manometer and the scale can be repeatedly autoclaved, and if used with fresh disposable drip and extension tubing there are no problems regarding sterility. Care must be taken during preparation and autoclaving to avoid fracturing the glassware.
With this apparatus, the mean arterial pressure is indicated continuously on the manometer and no interruption of monitoring is required for flushing purpose. Providing that flushing is carefully maintained there is little likelihood of blood gaining entrance to the cannula with subsequent blockage. A fall in blood pressure followed by a sharp rise would allow flowback of blood into the system at a rate greater than the flush rate but within the next few minutes the blood will be reflushed into the artery. The flush rate, of course, can be momentarily increased. Similarly witti a large cannula in the artery there may be some mixing of blood and flushing solution due to the wide fluctuations of the mercury meniscus but these may be damped by partially applying clamp B (fig. 1). It has not been found necessary to add heparin to the flushing fluid except in cases where monitoring has been continued for many hours outside of theatre. In these circumstances 10 mg (1000 units) is added to 500 ml of flushing solution. The magnitude of error in the mean arterial pressure estimation that occurs due to the continuous flush is small and depends on the flush rate and the size and patency of the cannula. Using a small needle, the 23-gauge scalp vein needle, with a flush rate of 5 drops/min, an increase of 8-10 mm Hg is obtained in excess of the reading taken with no flushing. However, with an 18-gauge arterial needle or an FG4 catheter no appreciable difference in the reading occurred at the recommended flush rate. Another possible source of error is a change in the zero level of mercury in the reservoir due to the fluctuations of mercury in the long limb of the J-tube. But as the cross-sectional area of the former is at least 100 times greater than that of the latter, this is not a significant factor (Burton, 1965). The fluctua-
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
COMMENT
BRITISH JOURNAL OF ANAESTHESIA
988
CLINICAL EXPERIENCE
This method has been found to be simple and most reliable. The apparatus is inexpensive when compared with electronic monitoring devices. It has been used in fifty patients, not only in the operating theatre but in the recovery and intensive therapy wards. The youngest patient so monitored was 3 years of age and the longest period of monitoring was 52 hours. Like other methods of direct arterial pressure monitoring, it is particularly applicable when estimation of blood pressure by conventional methods is either difficult or unreliable as in the presence of severe vasoconstriction and low cardiac output states, or where very frequent readings are required over a short period of time. One further advantage is that it provides an excellent pulse monitor. The dangers of this method are those associated with arterial cannulation and infusion. The amount of fluid introduced into the arterial system is low and no signs of arterial spasm or ischaemic changes have been observed. This type of pressurized system allows no possibility of air embolism. We have experienced no serious complications.
De Bono, E. F. (1963). A simple method for intraarterial pressure measurement. Lancet, 1, 1142. Fink, B. R. (1963). Pneumatic monitor for arterial blood pressure. Anesthesiology, 24, 872. Hale, D. E. (1964). Arterial and venous pressure readings during open-heart surgery. Cleveland Clin. Quart., 35, 45. Mallard, T. R., Payne, T. P., and Peachey, C. J. (1963). Continuous monitoring of blood pressure by intra-arterial catheterization of the radial artery using a watch type manometer. J. Physiol. (Lond)., 167, 10P. Severinghaus, J. (1957). Aneroid manometer for arterial blood pressure. Anesthesiology, 81, 906. UNE METHODE SIMPLE POUR SUIVRE CONTINUELLEMENT LA PRESSION ARTERIELLE DIRECTE SOMMAIRE
Jusqu'a present plusieurs m^thodes pour mesurer sans equipement ilectronique la pression arterielle directe ont 6te decrites, mais aucune ne donne reellement satisfaction. On decrit une mithode simple, comprenant un systeme pressurisi d'infusion et un manometre au mercure. Ce systeme se construit facilement et il peut etre autoclavi sans difficult^. L'inertie du systeme est elevee mais on croit que l'appareil permet de mesurer continuellement et avec exactitude la pression arterielle moyenne. Le flux continu lent empcche l'obstruction de la canule arterielle, et on discute l'£tendue et la signification des erreurs, qui seraient causees par ce flux. La m6thode a £t£ employee chez 50 patients, aussi bien en salle d'operation que dans la salle de soins postopiratoires intensifs. Elle s'est ave>6e comme satisfaisante et il n'y a pas eu de complications serieuses. BIN EINFACHES VERFAHREN ZUR FORTLAUFENDEN DIREKTEN KONTROLLE DES ARTERIELLEN MITTELDRUCKS ZUSAMMENFASSUNG
In der Vergangenheit wurden mehrere nicht-elektronische Verfahren zur direkten Kontrolle des arteriellen Blutdrucks angegeben. Keines von ihnen befriedigt. Es wird eine Methode mit einfachen Hilfsmitteln—u.a. mit einem Druckinfusionssystem und Quecksilbennanometer—angegeben. Dieses System lafit sich lcicht zusammensetzen und autoklaviieren. Trotz hoher Tragheit des Systems soil sich der arterielle Mitteldruck verlafllich fortlaufend messen REFERENCES lassen. Durch eine kontinuierliche Durcnspulung wird Aarons, B. J. (1965). Simple apparatus for the simul- die Injectionsnadel frei gehalten. Ausmafl und taneous monitoring of central venous and mean Bedeurung von Mefifehlern durch diese Spiilung werden besprochen. D?s System wurde bei 50 arterial pressures in the ward. Thorax, 20, 382. Blackburn, J. P. (1966). A disposable monitor for Patienten im Operationssaal, auf der Operativ- und Intensiy-Station erprobt. Die Ergebnisse waren arterial blood pressure. Anaesthesia, 21, 109. Burton, A. C. (1965). Physiology and Biophysics of the bcfriedigend, emstliche Komplikationen wurden nicht beobachtet. Circulation. Chicago: Year Book.
Printed In Great Britain by John Sberratt & Son Ltd.. Park Road, Altrincham
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 24, 2015
tions in the mercury column may again be reduced by compressing the extension tubing. The inertia of this system is high and no claim is made that systolic and diastolic pressures can be followed. It does, however, provide a reasonably accurate measurement of a true mean pressure or area pressure and with a larger arterial cannula in situ the readings have consistently fallen within 5 mm of the calculated mean pressure (systolic+2xdiastolic)/3. The errors have little clinical significance when, as is usual, the changes in a series of readings are being followed.