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© 1999 International Anesthesia Research Society
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Introduction |
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Continuous spinal anesthesia seemed destined to have a bright future in orthopedic, abdominal, urological, obstetrical, gynecological, and vascular procedures (1–7). Unfortunately, in 1991, Rigler et al. (8) advanced the suspicion that microcatheters could be the cause of "cauda equina syndrome" (perineal sensory loss and changes in sphincter functions), which developed in four patients after continuous spinal anesthesia (one of these four cases, however, occurred with a macrocatheter) and suggested that this complication occurred because of maldistribution of large volumes of a hypertonic anesthetic solution around cauda equina roots (i.e., 5% hyperbaric lidocaine solution, even if not all of the cases reported by Rigler et al. involved hyperbaric lidocaine). Using a transparent spinal canal model, Lambert and Hurley (9) confirmed this hypothesis experimentally.
Considering this hypothesis, and after seven more cases of neurological deficits had been reported, the Food and Drug Administration ordered the suspension of the use of microcatheters in the United States on May 29, 1992 (10). This suspension was also enforced in Canada, but not in Europe, where the thought prevailed that using weaker hypertonic solutions (i.e., 2% lidocaine plain solution, 0.5% bupivacaine plain, or hyperbaric solution) would reduce the cytotoxicity of anesthetic solutions (11,12).
Other potential causes of neurological complications may, however, derive from septic or aseptic contamination of microcatheters due to involuntary or faulty maneuvers during their insertion. The aim of the present work was to simulate such faulty maneuvers and to study, by electron microscopy, the results of the contamination to evaluate the potential danger.
We also studied the tips of microcatheters used clinically to check for the presence of traces of possible involuntary contamination.
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Methods |
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Two types of microcatheters were studied. The first was the Co-Span 28-gauge nylon microcatheter (Kendall Healthcare, Mansfield, MA). This is the only catheter we routinely used in clinical practice during the last 8 yr, because of its soft tip and the easy insertion and extraction of the stylet. The second was the Micro Spinal 28-gauge polyamide microcatheter (TFX/Rush Inc., Duluth, GA), which we did not use in clinical practice because it is more difficult to insert and because the fixed stylet makes the tip potentially painful and dangerous. Samples of powdered gloves and of microcatheter tips, aseptically removed, were examined by using scanning electron microscopy. Samples of four powdered gloves were examined on the external surface, and four other samples (of the same gloves) were examined on the internal surface. The microcatheter samples were divided into five groups. Five sterile Co-Span 28-gauge catheters and five sterile Micro-Spinal 28-gauge catheters were examined to detect any differences in structure (Group 1). Five sterile microcatheters of each type were touched on the tip with powdered sterile gloves (Group 2). Five sterile microcatheters of each type were passed through a 22-gauge needle with a Quincke point after being touched on the tip with powdered sterile gloves (Group 3). Five sterile microcatheters of each type were touched on the tip with powdered sterile gloves that had previously touched a patient’s skin disinfected with povidone-iodine (Group 4). Ten Co-Span 28-gauge microcatheters were removed from an equal number of patients at the end of an operation (hip arthroplasty) after the microcatheters had been in the subarachnoid space for 75–100 min (Group 5).
In Groups 2–4, the tips of the microcatheters were held for 5 s between the thumb and index finger of the gloved hand. In each group, the samples of tips (2.5-cm distal segment of microcatheters) were aseptically cut and immediately placed in a sterile test tube. The tips were then cut for observation at the electron microscope by using sterile tweezers and scissors.
Samples of powdered gloves and catheter tips from Groups 1–3 were not fixed because we needed to observe the surface of the tips. Samples from Groups 4 and 5 were taken sterilely and fixed for 2 h in a mixture of glutaraldehyde at 4% and 0.1 M Na cacodylate buffered at pH 7.4 at ambient temperature, then postfixed in 1% osmium tetroxide for 1.5 h. Dehydration was effected with a serial ethanol concentration (50–100°), and samples were dried with a critical point dryer. The tips were fixed with silver paint on aluminum stubs and covered with a gold layer (degree of purity 99.9%) with a sputter coater. The observation was made at a scanning electron microscope operating at 20 kV.
With the electron microscope, it is possible to obtain information other than the mere morphology of the sample. In fact, the interaction between the electron beam and the sample generates a range of signals that can be used to obtain information on the composition of the sample. In energy-dispersive spectrometry analysis, the signal used is radiograph emission. Therefore, in addition to the groups considered, we studied (by using energy-dispersive spectrometry) three Co-Span microcatheters whose tips had been touched with powdered gloves and passed through a 22-gauge spinal needle to exactly identify the type of impurities present on the surface, in case traces of other substances were present (e.g., magnesium silicate, a component of talcum powder, or iron from the needle).
Co-Span microcatheters were inserted with sterile technique by the midline or paramedian route with the patient in the lateral position. The 22-gauge needle insertion site was usually L3-4. For insertion, the catheter was always held 10 cm from the tip. The lumbar and lower thoracic areas were prepared with 10% povidone-iodine solution. The anesthetist wore a hat, mask, and sterile powdered gloves, but no sterile gown was worn and the operator’s hands had not been washed. After placement (3 cm into the subarachnoid space) of the microcatheter, 15–20 mg of hyperbaric 0.5% bupivacaine was injected, and a sterile gauze pad bathed with povidone-iodine solution was applied to prevent moisture and bending of the catheter, which was taped onto the patient’s back and shoulder. The microcatheters remained in place until spinal analgesia (0.3–0.4 mg of morphine) was administered through the filter (0.2 mm) with an appropriate small syringe. The microcatheters were always withdrawn by the anesthetist when the patients were still in the lateral position, without further application of disinfectant solution.
Informed consent was obtained from patients in Group 5, and the study was approved by the ethics committee of our hospital.
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Results |
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TopIntroductionMethodsResultsDiscussionReferences |
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Observation of the internal surface of the powdered sterile gloves showed the presence of numerous starch grains of various diameters in direct contact with the latex (Fig. 1A), whereas observation of the external surface revealed the a uniform carpet of grains of calcium carbonate on which rare starch grains were seen (Fig. 1B).
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Comparison of the two types of microcatheters (Group 1) showed that the surface of the Co-Span catheters, made of pressed nylon resin, is irregular and granulous (Fig. 1D), whereas the surface of Micro-Spinal catheters, made of polyamide, is smooth and has regular grooves, some of which are very deep (Fig. 1, C and E). On both, however, the smooth and the granulous microcatheter surfaces can easily retain granules of calcium carbonate when touched with powdered gloves (Group 2) (Fig. 1, E and F). Traces of povidone-iodine (Fig. 2, C and E) were also observed, and traces of both substances (providone-iodine and granules of calcium carbonate) were sometimes found (Group 4) (Fig. 2D). In one case, a starch grain was found on the surface of a catheter (Fig. 2F). We did not observe bacterial contamination on microcatheter tips from Groups 1–4. Semiquantitative energy-dispersive spectrometry microanalysis confirmed that all particles on the catheters contained calcium (Fig. 3).
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Study of the conformation of the microcatheter tips (Group 1) demonstrated that the orifice of the tip of Micro-Spinal catheters is less regular than that of the Co-Span catheters (Fig. 4, A, C, D, and E). The tips of the latter are truncated (with an angle of 90°) (Fig. 4A) or cut at an angle of 45° (Fig. 4E), according to the lot examined. In one case, the lumen of the tip of a new Co-Span catheter seemed to be obstructed by extraneous matter, probably residue from the manufacturing process (Fig. 4F).
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The external surface of microcatheters touched with powdered gloves is partially cleaned by its passage through the lumen of the spinal needle (Group 3) (Fig. 2, A and B), but this is not true of the tip, which can retain more contaminating powder (Fig. 4, A and B). On the distal segment of all the Co-Span microcatheters recovered at the end of surgery, a proteic precipitate, red blood cells, and, in three cases, macrophages were seen (Group 5) (Fig. 5, A–D). Macrophages were noted on the tip of three catheters that had remained in the subarachnoid space for 80, 95, and 100 min. In one case, after a total hip prosthesis operation that lasted 90 min, numerous cocci surrounded by leukocytes were also observed (Fig. 5, E and F).
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Discussion |
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TopIntroductionMethodsResultsDiscussionReferences |
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The starting point of our research was the work of Green at al. (13), who investigated the contamination of epidural catheters during normal handling with starch-powdered gloves. We demonstrated the ease of contamination of the distal segment of microcatheters with powder from gloves (calcium carbonate) and disinfectant (povidone-iodine solution) when the tip is held between the thumb and index finger. This is true for both catheters made of pressed nylon resin and those made of polyamide, although the surface of the latter is smoother and seems to retain a smaller quantity of powder.
Passage through the lumen of the spinal needle partially cleans the external surface of the catheter, but not the tip, with the result that any impurities present can enter into the subarachnoid space. Calcium carbonate is an inert salt, only slightly hydrosoluble, and it is considered incapable of inducing aseptic inflammatory reactions. On the contrary, talcum, still used as powder for gloves, can induce an aseptic inflammatory reaction (meningismus) in the subarachnoid space (13). However, the packets of gloves we used bear the instruction "after donning, remove powder by standard aseptic method." Our research shows that, although very rarely (one reported case), the surface of a microcatheter can be contaminated by starch grains, which can induce an aseptic inflammatory reaction (14) in the peridural space (13) and, probably, in the subarachnoid space. Microcatheters also can easily be contaminated with povidone-iodine solution when touched with gloves stained with this solution. It does not seem that povidone-iodine solution can induce meningeal reactions if the patient is not allergic to iodine.
It was surprising that, in the case of septic contamination, the microcatheter was inserted with the normal precautions by an experienced anesthetist. The surprise arises from the fact that the catheter had not been exposed for long to the ambient air and that its insertion presented no difficulties. We can only hypothesize that the catheter had inadvertently touched a nonsterile zone or that the gloves had been contaminated in the same manner, or that there was unnoticed damage to the gloves. (The anesthetist’s hands had not been washed with a disinfectant solution.) It is also possible that the septic contamination of the microcatheter occurred during its passage through the tip of the spinal needle (Quincke point), when it could have been contaminated by cutaneous bacterial flora (generally staphylococcus) of the insertion site, if not sufficiently disinfected.
We do not believe that the catheter was contaminated originally, because cocci have never been found on samples. Furthermore, bacteriological studies of catheters’ culture have always yielded negative results. However, we did not observe signs or symptoms of central nervous system infection. This is likely because: 1) there was an intense leukocytic reaction that circumscribed the contaminated zone; 2) the local anesthetic used (15 mg of hyperbaric 0.5% bupivacaine) has marked antibacterial properties (15–16); and 3) the patient was treated, as routinely happens, with cephalothin (4 g IV on the day of surgery and 2 g IV daily for five days thereafter) to prevent surgical wound infection.
Although cephalothin does not reach high levels in cerebrospinal fluid (CSF), it probably exercises a bacteriostatic effect in the CSF, especially if the bacterial load is small. It has, however, been shown that septic contamination of an intrathecal catheter does not necessarily involve infection of the central nervous system (17).
The constant presence of red cells, found on the tips of microcatheters recovered from patients, is certainly due to the minimal bleeding produced in the subcutaneous transit during recovery. In no case were there traces of blood in the CSF aspirated to confirm the correct positioning of the microcatheter in the subarachnoid space. We believe, instead, that the presence of macrophages and proteic precipitates may represent a reaction that occurred while the distal section of the microcatheter was in the subarachnoid space. In fact, the time that elapsed between recovery of the microcatheters and fixing in the mixture of glutaraldehyde and Na cacodylate was less than two minutes, a time too brief for complex vital reactions to take place.
The fact that the catheter tip is rapidly covered by a proteic precipitate indicates the fate that probably awaits a microcatheter fragment that breaks off during recovery: it probably remains encapsulated and isolated and stays inactive in the subarachnoid space for an indefinite period of time (18).
In conclusion, from this research, no mechanisms to explain the cauda equina syndrome associated with the use of microcatheters emerge, other than maldistribution of large doses of local anesthetic in the subarachnoid space. Nevertheless, the images obtained by the scanning electron microscopy show that the surfaces of the tips of microcatheters, if touched by mistake, can easily be contaminated by powder from gloves and by disinfectants. The adhesion of these particles is facilitated by the irregularity of the surfaces of nylon microcatheters. This contamination, however, should have no consequences if the impurities have no capacity to provoke chemical irritation (for example, talcum powder and alcohol) or allergies (e.g., allergenic complex latex proteins-starch particles carried by calcium carbonate) (19). Bacterial contamination of microcatheters may also occur even when the anesthesiologist believes that he or she has operated under sterile conditions. Fortunately, in most cases, septic contamination is without consequences (17). It is, however, recommended that anesthetists, besides following the suggestions of Rigler et al. (8), wash their hands and forearms before donning sterile gloves and that they do not touch the tips of microcatheters.
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Acknowledgments |
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This work was supported by a research fund assigned to FR, and by a fund of Centro Grandi Strumenti (CGS) of the University of Pavia, Italy.
We thank Mr. A. Rizzi of Centro Nazionale Ricerche of Milan, Mr A. Fantuzzi of Direzione Salute Ambientale of the Pirelli Company, and Dr. G. Moscato of the Maugeri Foundation of Pavia, for their technical explanations.
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References |
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Hurley RJ, Lambert DH. Continuous spinal anesthesia with a microcatheter technique: preliminary experience. Anesth Analg 1990;70:97–102.
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Webster J, Barnard M, Carli F. Metabolic response to colonic surgery: extradural vs. continuous spinal. Br J Anaesth 1991;67:467–9.
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Kestin IG, Madden AP, Mulvein JT, et al. Comparison of incremental spinal anaesthesia using a 32-gauge catheter with extradural anaesthesia for elective caesarean section. Br J Anaesth 1991;66:232–6.
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Guinard JP, Chiolero R, Mavrocordatos P, et al. Prolonged intrathecal fentanyl analgesia via 32-gauge catheters after thoracotomy. Anesth Analg 1993;77:936–41.
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Rigler ML, Drasner K, Krejcie TC, et al. Cauda equina syndrome after continuous spinal anesthesia. Anesth Analg 1991;72:275–81.
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Lambert DH, Hurley RJ. Cauda equina syndrome and continuous spinal anesthesia. Anesth Analg 1991;72:817–9.
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Green MA, Lam Y, Moss F. Starch, gloves and extradural catheters. Br J Anaesth 1995;75:768–7.
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Beezhold D, Beck WC. Surgical glove powders bind latex antigens. Arch Surg 1992;127:1354–7.
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