MEDICINE


ume for cytology (generally 0.5 mL minimum required), bacterial culture if indicated, Sarcocystis neurona and Neospora hughesii antibody detection, and additional diagnostics as indicated by the his- tory and clinical signs.


C1–C2 Spinal Fluid Collection


Fluid from the C1–C2 space occasionally drips spon- taneously from the needle. In two cases, negative pressure was encountered once in the subarachnoid space precluding gentle aspiration. In these cases the CSF dripped freely with the head below withers height and with patience, allowed enough volume to be collected for cytology and minimal additional testing (1.5 mL). Gentle aspiration is typically required to obtain the majority of the samples and routinely yields 5 mL or more with ease. Fluid is aspirated in 1 to 2 mL sequential aliquots as previ- ously described to reduce the amount of blood con- tamination associated with the first sample.5 It is ideal to use 3 to 5 mL Luer Slip syringes (avoid Luer Lock) and it is important to break the seal on the syringe prior to aspirating the sample to prevent exerting excessive pressure on the meninges. The stylet is replaced and the needle is withdrawn smoothly once an adequate sample volume is obtained. C1–C2 collection: typical yield, 5–8 mL.


Troubleshooting C1–C2 Spinal Needle Placement


If multiple attempts at needle placement occur, the needle track creates an artifact that obscures a clear image of the C1–C2 space and spinal cord. If this occurs, attempt the procedure from the other side following identical site preparation. If blood is ob- tained, it is likely that a vertebral vessel was inad- vertently punctured. In this case needle placement is likely too ventral. The procedure can be repeated with a new needle with care to ensure that the needle is placed in the dorsal C1–C2 space. If neg- ative pressure is encountered subsequent to switch- ing syringes (especially after easy aspiration of the previous 1 mL) the stylet is replaced and the needle is advanced an additional millimeter and should result in easy aspiration of the remaining sample. In this case, it is most likely that the original needle placement is just through the dura and becomes displaced from the subarachnoid space during the transition from one syringe to the next.


LS Space Procedure


The LS space is routinely located using anatomic landmarks (midline at the highest point of the hind- quarters, and or palpation of a depression between the cranial borders of the tuber sacrale, and or using an imaginary line drawn between the two caudal borders of the tuber coxae that intersects with mid- line).4 An approximately 15 cm  15 cm square is clipped to provide a sterile field for collection. After the initial aseptic preparation, the subcutaneous tis- sues and muscle is infiltrated with 5 mL of 2% lido-


480 2018  Vol. 64  AAEP PROCEEDINGS


caine with a 1.5-inch 22-gauge needle before final aseptic preparation. Midline can be difficult to dis- tinguish in some cases, the clinician can attempt to palpate the dorsal spinous process of L6 and use the tail to identify midline. The author often relies on a technician or ancillary person to stand well behind the horse (prior to initial needle puncture) to provide verbal direction on the location of midline. The most optimal horse position is for it to stand square with the hindlimbs slightly camped under. In some neurologic cases, this can be nearly impossible and the author appreciates the horse that will at least weight bear on both hind legs. The LS tap can be successful in the horse that is leaning or is not able to stand square with careful palpation and identification of midline. An 8-inch 18-gauge spi- nal needle is advanced perpendicular to the horse’s back in millimeter increments. Two hands are used to control the needle (one at the junction with the horse’s back and the other at the hub of the needle) to prevent the needle from deviating later- ally or in a cranial or caudal direction. When any change in resistance is encountered (sensation of a “pop”), the stylet is withdrawn and a 5-mL Luer Slip syringe that has had the seal broken is attached and used to check for the presence of spinal fluid. When negative pressure is encountered, the stylet is re- placed and the needle is advanced gradually. In most adult light-breed horses, 2 to 3 inches of needle remain out of the horse and the LS space is encoun- tered at a depth of 5 to 6 inches. A longer needle is sometimes required for draft breeds or heavily mus- cled horses. Some horses raise or swish their tail or drop their hindquarters perceivably when the nee- dle is just about to puncture the dura. These horses may or may not react explosively when the dura is punctured. However, many horses give no indication that you are approaching the space and they may or may not react when the needle enters the subarachnoid space.


LS Spinal Fluid Collection


Gentle aspiration is almost always required. A 5-mL Luer Slip syringe with the seal broken is pre- ferred to provide adequate pressure to promote CSF flow. Ensure a solid connection between the needle hub and syringe. Fluid flowed freely from one case. In some cases, the Queckenstedt’s maneuver (tran- siently raising the head and holding off both jugular veins) is instrumental in increasing intracranial pressure thus promoting CSF flow and enhancing collection volume. Fluid is aspirated in 1–2-mL ali- quots as described above. Typical yield, 5 mL.


Troubleshooting LS Spinal Needle Placement


If bone is encountered when the needle is at a depth of 3 to 4 inches, the needle is likely not in the proper location. Redirecting the needle is often unsuccess- ful. Reassessing the location of midline and select- ing a slightly different location is usually required. It is also important to ensure the needle remains


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212  |  Page 213  |  Page 214  |  Page 215  |  Page 216  |  Page 217  |  Page 218  |  Page 219  |  Page 220  |  Page 221  |  Page 222  |  Page 223  |  Page 224  |  Page 225  |  Page 226  |  Page 227  |  Page 228  |  Page 229  |  Page 230  |  Page 231  |  Page 232  |  Page 233  |  Page 234  |  Page 235  |  Page 236  |  Page 237  |  Page 238  |  Page 239  |  Page 240  |  Page 241  |  Page 242  |  Page 243  |  Page 244  |  Page 245  |  Page 246  |  Page 247  |  Page 248  |  Page 249  |  Page 250  |  Page 251  |  Page 252  |  Page 253  |  Page 254  |  Page 255  |  Page 256  |  Page 257  |  Page 258  |  Page 259  |  Page 260  |  Page 261  |  Page 262  |  Page 263  |  Page 264  |  Page 265  |  Page 266  |  Page 267  |  Page 268  |  Page 269  |  Page 270  |  Page 271  |  Page 272  |  Page 273  |  Page 274  |  Page 275  |  Page 276  |  Page 277  |  Page 278  |  Page 279  |  Page 280  |  Page 281  |  Page 282  |  Page 283  |  Page 284  |  Page 285  |  Page 286  |  Page 287  |  Page 288  |  Page 289  |  Page 290  |  Page 291  |  Page 292  |  Page 293  |  Page 294  |  Page 295  |  Page 296  |  Page 297  |  Page 298  |  Page 299  |  Page 300  |  Page 301  |  Page 302  |  Page 303  |  Page 304  |  Page 305  |  Page 306  |  Page 307  |  Page 308  |  Page 309  |  Page 310  |  Page 311  |  Page 312  |  Page 313  |  Page 314  |  Page 315  |  Page 316  |  Page 317  |  Page 318  |  Page 319  |  Page 320  |  Page 321  |  Page 322  |  Page 323  |  Page 324  |  Page 325  |  Page 326  |  Page 327  |  Page 328  |  Page 329  |  Page 330  |  Page 331  |  Page 332  |  Page 333  |  Page 334  |  Page 335  |  Page 336  |  Page 337  |  Page 338  |  Page 339  |  Page 340  |  Page 341  |  Page 342  |  Page 343  |  Page 344  |  Page 345  |  Page 346  |  Page 347  |  Page 348  |  Page 349  |  Page 350  |  Page 351  |  Page 352  |  Page 353  |  Page 354  |  Page 355  |  Page 356  |  Page 357  |  Page 358  |  Page 359  |  Page 360  |  Page 361  |  Page 362  |  Page 363  |  Page 364  |  Page 365  |  Page 366  |  Page 367  |  Page 368  |  Page 369  |  Page 370  |  Page 371  |  Page 372  |  Page 373  |  Page 374  |  Page 375  |  Page 376  |  Page 377  |  Page 378  |  Page 379  |  Page 380  |  Page 381  |  Page 382  |  Page 383  |  Page 384  |  Page 385  |  Page 386  |  Page 387  |  Page 388  |  Page 389  |  Page 390  |  Page 391  |  Page 392  |  Page 393  |  Page 394  |  Page 395  |  Page 396  |  Page 397  |  Page 398  |  Page 399  |  Page 400  |  Page 401  |  Page 402  |  Page 403  |  Page 404  |  Page 405  |  Page 406  |  Page 407  |  Page 408  |  Page 409  |  Page 410  |  Page 411  |  Page 412  |  Page 413  |  Page 414  |  Page 415  |  Page 416  |  Page 417  |  Page 418  |  Page 419  |  Page 420  |  Page 421  |  Page 422  |  Page 423  |  Page 424  |  Page 425  |  Page 426  |  Page 427  |  Page 428  |  Page 429  |  Page 430  |  Page 431  |  Page 432  |  Page 433  |  Page 434  |  Page 435  |  Page 436  |  Page 437  |  Page 438  |  Page 439  |  Page 440  |  Page 441  |  Page 442  |  Page 443  |  Page 444  |  Page 445  |  Page 446  |  Page 447  |  Page 448  |  Page 449  |  Page 450  |  Page 451  |  Page 452  |  Page 453  |  Page 454  |  Page 455  |  Page 456  |  Page 457  |  Page 458  |  Page 459  |  Page 460  |  Page 461  |  Page 462  |  Page 463  |  Page 464  |  Page 465  |  Page 466  |  Page 467  |  Page 468  |  Page 469  |  Page 470  |  Page 471  |  Page 472  |  Page 473  |  Page 474  |  Page 475  |  Page 476  |  Page 477  |  Page 478  |  Page 479  |  Page 480  |  Page 481  |  Page 482  |  Page 483  |  Page 484  |  Page 485  |  Page 486  |  Page 487  |  Page 488  |  Page 489  |  Page 490  |  Page 491  |  Page 492  |  Page 493  |  Page 494  |  Page 495  |  Page 496  |  Page 497  |  Page 498  |  Page 499  |  Page 500  |  Page 501  |  Page 502  |  Page 503  |  Page 504  |  Page 505  |  Page 506  |  Page 507  |  Page 508  |  Page 509  |  Page 510  |  Page 511  |  Page 512  |  Page 513  |  Page 514  |  Page 515  |  Page 516  |  Page 517  |  Page 518  |  Page 519  |  Page 520  |  Page 521  |  Page 522  |  Page 523  |  Page 524  |  Page 525  |  Page 526  |  Page 527  |  Page 528  |  Page 529  |  Page 530  |  Page 531  |  Page 532  |  Page 533  |  Page 534  |  Page 535  |  Page 536  |  Page 537  |  Page 538  |  Page 539  |  Page 540  |  Page 541  |  Page 542  |  Page 543  |  Page 544