- Email: [email protected]
Distinguishing cerebrospinal fluid from saline used to identify the extradural space
British Journal of Anaesthesia 1996; 77: 784–785 SHORT COMMUNICATIONS
Distinguishing cerebrospinal fluid from saline used to identify the extradural space
B. A. Z. EL-BEHESY, D. JAMES, K. F. KOH, N. HIRSCH AND S. M. YENTIS
Summary Because of the potential seriousness of unrecognized dural puncture during the performance of extradural analgesia and the widespread use of normal saline for the “loss of resistance” technique, it is important to differentiate between cerebrospinal fluid (CSF) and saline dripping from the extradural needle. During insertion of lumbar drains in 10 neurosurgical patients, we first identified the extradural space using saline for loss of resistance. Temperature (using the back of the gloved hand), pH, glucose and protein (using urine testing sticks) were tested by a blinded observer for ability to distinguish saline aspirated from the extradural space from CSF aspirated on establishing the dural puncture. Temperature, glucose and protein were independently 100% accurate in distinguishing saline from CSF. One saline sample had a pH value greater than 7 compared with nine CSF samples. We conclude that simple bedside testing for temperature, glucose, protein and pH accurately distinguished between CSF and saline used to identify the extradural space. (Br. J. Anaesth. 1996; 77: 784–785) Key words Anaesthetic techniques, extradural. Spinal cord, extradural space.
Cerebrospinal
fluid.
Accidental dural puncture is a recognized complication of extradural anaesthesia.1 It is important to recognize this immediately, as subsequent injection of local anaesthetic intended for the extradural space may produce unexpectedly extensive blocks.2 Although dural puncture is indicated usually by free flow of cerebrospinal fluid (CSF) through the extradural needle, this may not always be the case, and CSF may drip only slowly from the needle hub.3 If saline is used to identify the extradural space, using a “loss of resistance” technique, the anaesthetist may be uncertain if any clear fluid dripping from the needle is saline or CSF. Properties of CSF which have been used to identify it include temperature, glucose and protein content, pH and the absence of turbidity on mixing with thiopentone; however, these tests have been compared in relation to distinguishing CSF from local anaesthetic, for example after extradural anaesthesia.4 In addition,
the effect of injecting saline into the extradural space on the properties mentioned above has not been determined. As most dural punctures occur during placement of the extradural needle,1 and saline is used more widely for loss of resistance than local anaesthetic solutions,1 it would be more relevant clinically to compare these methods of distinguishing CSF from saline aspirated from the extradural space through the needle.
Methods and results After obtaining medical Ethics Committee approval and informed consent, we studied patients undergoing neurosurgery that required insertion of a lumbar drain as part of the procedure (or as the actual procedure). General anaesthesia was induced according to the individual anaesthetist’s preference (except in two patients who had insertion of lumbar drains only during local anaesthesia). The patient was then turned to the left lateral position and the extradural space identified with a 14-gauge lumbar drain needle using loss of resistance to saline. On identifying the extradural space, 10 ml of saline were injected in the space and 0.2–1.0 ml was aspirated into a 2-ml syringe. If none of the saline could be aspirated, another 5 ml of saline were injected and if still none could be aspirated the patient was excluded from the study. After aspirating saline, the needle was advanced through the dura and a similar volume of CSF was aspirated in another 2-ml syringe. Passage of the subarachnoid drain and further management continued as standard practice. The syringes were labelled as A or B according to randomly assigned instructions, and handed to a second investigator who was unaware of the allocation. The blinded investigator then immediately tested the temperature of a drop of the contents of each syringe on the back of his gloved hand to decide if it felt “warm” or “cold”. Both fluids then were tested for glucose,
BASEL A. Z. EL-BEHESY, MB, BCH, FRCA, DAVID JAMES, MB, BS, FRCA, K. F. KOH, MMED (ANAES), NICHOLAS HIRSCH, MB, BS, FRCA, Department of Anaesthesia, The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG. STEVE M. YENTIS, BSC, MB, BS, MD, FRCA, Magill Department of Anaesthetics, Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH. Accepted for publication: August 8, 1996. Correspondence to S.M.Y.
Identifying the extradural space
785
Table 1 Results of stick testing of saline and cerebrospinal fluid (CSF) samples obtained through the Tuohy needle Patient No. 1 2 3 4 5 6 7 8 9 10
Saline
CSF
Glucose
Protein
pH
Temp.
Glucose
Protein
pH
Temp.
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
5 5 7 7 7 7.5 6.5 5 5 6
Cold Cold Cold Cold Cold Cold Cold Cold Cold Cold
+ + + + + + Trace Trace Trace Trace
++ + ++ + + ++ ++ ++ + ++
8 8 8.5 7.5 7.5 5 8.5 8.5 8 8
Warm Warm Warm Warm Warm Warm Warm Warm Warm Warm
protein and pH using urinary testing sticks. Data were analysed using Fisher’s exact test. Eighteen patients were recruited into the study. Eight were excluded because it was impossible to aspirate sufficient saline after an additional 5 ml of saline. The remaining 10 comprised six females and four males, mean age 45 (range 25–63) yr. The neurosurgical procedures carried out included five trans-sphenoidal hypophysectomies, two lumbar drain insertions, one transoral odontoidectomy, one transoral C1 biopsy and one excision of cervical neurofibroma. The results of temperature and stick testing are shown in table 1. None of the saline samples tested positive for glucose or protein or was warm to the touch, compared with all 10 of the CSF samples (P:0.0001, two-tailed Fisher’s exact test). One saline sample had a pH value 97, compared with nine CSF samples (P:0.0001, two-tailed Fisher’s exact test). There were no incidences of bloody tap.
Comment Anaesthetists have used different techniques for distinguishing saline from CSF during identification of the extradural space using saline for the loss of resistance test. Observation of free flow of CSF alone has been shown to be unreliable.3 In this study, despite its small size, we have demonstrated that subjective testing for temperature of the fluid and simple bedside objective testing using urinary testing sticks can reliably distinguish CSF from saline, even when obtained from the extradural space. Although dural puncture in our study was produced with a 14-gauge needle, there is no reason to suppose the results would be different if a 16-gauge needle had been used. Although saline normally does not contain glucose or protein, a positive test may theoretically result from blood contamination or CSF diffusion to the extradural space.5 Our study showed that even on injection of saline into the extradural space it still tested negative for both. Earlier studies that tested for glucose to differentiate CSF from local anaes-
thetic injected previously into the extradural space showed that positive testing for glucose did not necessarily imply that the tested fluid was CSF.4 5 The consistent result of glucose testing in our study may represent different properties of local anaesthetic solutions and saline, or because saline was aspirated immediately after injection, thus not providing sufficient time for contamination with glucose from the extradural space or vessels. Alternatively, injection of 10 ml of saline into the extradural space may have diluted any contamination with glucose or protein. However, of interest is the fact that even after injection of this volume and an additional 5 ml, eight patients had to be excluded because insufficient volume of saline could be aspirated. We have no explanation for the variation in saline pH values obtained; the same manufacturers’ products (both saline and testing strips) were used in all cases. It is possible that for estimation of pH using testing strips, subjective judgement as to which of the manufacturer’s supplied colour bands best matches the sample’s indicator colour is less reliable than with the other tests. Finally, it is important to emphasize that this study showed that testing for only temperature, glucose, protein and pH were useful at the time of identifying the extradural space with the needle. The use of aspiration testing and the test dose of local anaesthetic after insertion of the catheter are still mandatory.
References 1. Stride PC, Cooper GM. Dural taps revisited. Anaesthesia 1993; 48: 247–255. 2. Morgan B. Unexpectedly extensive conduction blocks in obstetric extradural analgesia. Anaesthesia 1990; 45: 148–152. 3. Holloway TE, Telford RJ. Observations on deliberate dural puncture with a Tuohy needle: depth measurements. Anaesthesia 1991; 46: 722–724. 4. Tessler MJ, Wiesel S, Wahba RM, Quance DR. A comparison of simple identification tests to distinguish cerebrospinal fluid from local anaesthetic solution. Anaesthesia 1994; 49: 821–822. 5. Waters JH, Ramanathan S, Chuba JV. Glucose in extradural catheter aspirate. Anesthesia and Analgesia 1993; 76: 546–548.
Distinguishing cerebrospinal fluid from saline used to identify the extradural space
B. A. Z. EL-BEHESY, D. JAMES, K. F. KOH, N. HIRSCH AND S. M. YENTIS
Summary Because of the potential seriousness of unrecognized dural puncture during the performance of extradural analgesia and the widespread use of normal saline for the “loss of resistance” technique, it is important to differentiate between cerebrospinal fluid (CSF) and saline dripping from the extradural needle. During insertion of lumbar drains in 10 neurosurgical patients, we first identified the extradural space using saline for loss of resistance. Temperature (using the back of the gloved hand), pH, glucose and protein (using urine testing sticks) were tested by a blinded observer for ability to distinguish saline aspirated from the extradural space from CSF aspirated on establishing the dural puncture. Temperature, glucose and protein were independently 100% accurate in distinguishing saline from CSF. One saline sample had a pH value greater than 7 compared with nine CSF samples. We conclude that simple bedside testing for temperature, glucose, protein and pH accurately distinguished between CSF and saline used to identify the extradural space. (Br. J. Anaesth. 1996; 77: 784–785) Key words Anaesthetic techniques, extradural. Spinal cord, extradural space.
Cerebrospinal
fluid.
Accidental dural puncture is a recognized complication of extradural anaesthesia.1 It is important to recognize this immediately, as subsequent injection of local anaesthetic intended for the extradural space may produce unexpectedly extensive blocks.2 Although dural puncture is indicated usually by free flow of cerebrospinal fluid (CSF) through the extradural needle, this may not always be the case, and CSF may drip only slowly from the needle hub.3 If saline is used to identify the extradural space, using a “loss of resistance” technique, the anaesthetist may be uncertain if any clear fluid dripping from the needle is saline or CSF. Properties of CSF which have been used to identify it include temperature, glucose and protein content, pH and the absence of turbidity on mixing with thiopentone; however, these tests have been compared in relation to distinguishing CSF from local anaesthetic, for example after extradural anaesthesia.4 In addition,
the effect of injecting saline into the extradural space on the properties mentioned above has not been determined. As most dural punctures occur during placement of the extradural needle,1 and saline is used more widely for loss of resistance than local anaesthetic solutions,1 it would be more relevant clinically to compare these methods of distinguishing CSF from saline aspirated from the extradural space through the needle.
Methods and results After obtaining medical Ethics Committee approval and informed consent, we studied patients undergoing neurosurgery that required insertion of a lumbar drain as part of the procedure (or as the actual procedure). General anaesthesia was induced according to the individual anaesthetist’s preference (except in two patients who had insertion of lumbar drains only during local anaesthesia). The patient was then turned to the left lateral position and the extradural space identified with a 14-gauge lumbar drain needle using loss of resistance to saline. On identifying the extradural space, 10 ml of saline were injected in the space and 0.2–1.0 ml was aspirated into a 2-ml syringe. If none of the saline could be aspirated, another 5 ml of saline were injected and if still none could be aspirated the patient was excluded from the study. After aspirating saline, the needle was advanced through the dura and a similar volume of CSF was aspirated in another 2-ml syringe. Passage of the subarachnoid drain and further management continued as standard practice. The syringes were labelled as A or B according to randomly assigned instructions, and handed to a second investigator who was unaware of the allocation. The blinded investigator then immediately tested the temperature of a drop of the contents of each syringe on the back of his gloved hand to decide if it felt “warm” or “cold”. Both fluids then were tested for glucose,
BASEL A. Z. EL-BEHESY, MB, BCH, FRCA, DAVID JAMES, MB, BS, FRCA, K. F. KOH, MMED (ANAES), NICHOLAS HIRSCH, MB, BS, FRCA, Department of Anaesthesia, The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG. STEVE M. YENTIS, BSC, MB, BS, MD, FRCA, Magill Department of Anaesthetics, Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH. Accepted for publication: August 8, 1996. Correspondence to S.M.Y.
Identifying the extradural space
785
Table 1 Results of stick testing of saline and cerebrospinal fluid (CSF) samples obtained through the Tuohy needle Patient No. 1 2 3 4 5 6 7 8 9 10
Saline
CSF
Glucose
Protein
pH
Temp.
Glucose
Protein
pH
Temp.
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
5 5 7 7 7 7.5 6.5 5 5 6
Cold Cold Cold Cold Cold Cold Cold Cold Cold Cold
+ + + + + + Trace Trace Trace Trace
++ + ++ + + ++ ++ ++ + ++
8 8 8.5 7.5 7.5 5 8.5 8.5 8 8
Warm Warm Warm Warm Warm Warm Warm Warm Warm Warm
protein and pH using urinary testing sticks. Data were analysed using Fisher’s exact test. Eighteen patients were recruited into the study. Eight were excluded because it was impossible to aspirate sufficient saline after an additional 5 ml of saline. The remaining 10 comprised six females and four males, mean age 45 (range 25–63) yr. The neurosurgical procedures carried out included five trans-sphenoidal hypophysectomies, two lumbar drain insertions, one transoral odontoidectomy, one transoral C1 biopsy and one excision of cervical neurofibroma. The results of temperature and stick testing are shown in table 1. None of the saline samples tested positive for glucose or protein or was warm to the touch, compared with all 10 of the CSF samples (P:0.0001, two-tailed Fisher’s exact test). One saline sample had a pH value 97, compared with nine CSF samples (P:0.0001, two-tailed Fisher’s exact test). There were no incidences of bloody tap.
Comment Anaesthetists have used different techniques for distinguishing saline from CSF during identification of the extradural space using saline for the loss of resistance test. Observation of free flow of CSF alone has been shown to be unreliable.3 In this study, despite its small size, we have demonstrated that subjective testing for temperature of the fluid and simple bedside objective testing using urinary testing sticks can reliably distinguish CSF from saline, even when obtained from the extradural space. Although dural puncture in our study was produced with a 14-gauge needle, there is no reason to suppose the results would be different if a 16-gauge needle had been used. Although saline normally does not contain glucose or protein, a positive test may theoretically result from blood contamination or CSF diffusion to the extradural space.5 Our study showed that even on injection of saline into the extradural space it still tested negative for both. Earlier studies that tested for glucose to differentiate CSF from local anaes-
thetic injected previously into the extradural space showed that positive testing for glucose did not necessarily imply that the tested fluid was CSF.4 5 The consistent result of glucose testing in our study may represent different properties of local anaesthetic solutions and saline, or because saline was aspirated immediately after injection, thus not providing sufficient time for contamination with glucose from the extradural space or vessels. Alternatively, injection of 10 ml of saline into the extradural space may have diluted any contamination with glucose or protein. However, of interest is the fact that even after injection of this volume and an additional 5 ml, eight patients had to be excluded because insufficient volume of saline could be aspirated. We have no explanation for the variation in saline pH values obtained; the same manufacturers’ products (both saline and testing strips) were used in all cases. It is possible that for estimation of pH using testing strips, subjective judgement as to which of the manufacturer’s supplied colour bands best matches the sample’s indicator colour is less reliable than with the other tests. Finally, it is important to emphasize that this study showed that testing for only temperature, glucose, protein and pH were useful at the time of identifying the extradural space with the needle. The use of aspiration testing and the test dose of local anaesthetic after insertion of the catheter are still mandatory.
References 1. Stride PC, Cooper GM. Dural taps revisited. Anaesthesia 1993; 48: 247–255. 2. Morgan B. Unexpectedly extensive conduction blocks in obstetric extradural analgesia. Anaesthesia 1990; 45: 148–152. 3. Holloway TE, Telford RJ. Observations on deliberate dural puncture with a Tuohy needle: depth measurements. Anaesthesia 1991; 46: 722–724. 4. Tessler MJ, Wiesel S, Wahba RM, Quance DR. A comparison of simple identification tests to distinguish cerebrospinal fluid from local anaesthetic solution. Anaesthesia 1994; 49: 821–822. 5. Waters JH, Ramanathan S, Chuba JV. Glucose in extradural catheter aspirate. Anesthesia and Analgesia 1993; 76: 546–548.