HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT


delivered from a prolonged dystocia (120 minutes) with an APGAR score of 6 received a wide variety of fluid approaches ranging from none (with further close observation) to 500 mL to1Lof isotonic poly- ionic crystalloid fluids. In this situation—unless blood loss occurred or there was severe in utero sepsis—vascular volume resuscitation is not neces- sarily required initially. The APGAR score sug- gests a mildly to moderately asphyxiated foal, and additives suggested by respondents were aimed at early intervention for this. Supplements suggested to be added to the first bag included (in order of frequency mentioned): dextrose (1% to 5%), thia- mine (1 g/L), vitamin C, DMSO (1% to 2%), and 50%


MgSO4 (25 mL). Dextrose is aimed at providing energy support, thiamine supports normal intracel- lular energy metabolism, vitamin C and DMSO are provided as anti-oxidant treatment, and magnesium is thought to be neuroprotective. The second foal case, an obtunded, hypothermic minimally responsive 24-hour-old foal, represents a variety of conditions of the critically ill neonate ranging from severe sepsis to hypoxic ischemic dis- ease. Initial treatment of these foals is fairly uni- form and aimed at stabilization and intravascular volume resuscitation in addition to providing an en- ergy source. All respondents chose to administer isotonic polyionic crystalloid replacement fluids at bolus rates (20 mL/kg over 20 minutes, repeated as necessary), but the majority also recognized the need for almost immediate energy support. Energy support was supplied either as a piggyback CRI (4 mg/kg per minute, 250 mL/h 5% dextrose solu- tion to a 50-kg foal) or as a 1% additive to the first crystalloid bag followed by a CRI as described. I personally tend to include the first dose of any IV antimicrobial treatment in the first bag in addition to 1% dextrose while I begin preparing for dextrose CRI (5% dextrose at 250 mL/h initially will work for most foals) in these cases.


CNS Trauma


The 2-year-old Thoroughbred filly with a head injury from falling backward on its poll, with no epistaxis, represented a case of CNS trauma. This type of injury is not uncommon in practice and is probably seen most commonly in foals being halter-broken. The concern in these cases is the severity of injury, if there is basisphenoid injury, and if there is rectus capitis rupture or avulsion from the skull base. In this example, it was suggested that rectus capitis avulsion did not occur as a result of the absence of epistaxis. Coup–contra coup injuries also occur with these injuries, and fluid therapy is aimed at minimizing edema and further injury to the brain. Hypertonic saline is commonly recommended in the treatment of CNS injuries,8,9 particularly those in- volving the brain, and the respondents were appar- ently aware of this as hypertonic saline was the fluid of choice for the majority. A few chose not to ad- minister fluids immediately, whereas others opted


456 2013  Vol. 59  AAEP PROCEEDINGS for isotonic polyionic crystalloids or 0.9% saline.


Additives included thiamine. MgSO4 was also added to follow-up fluids at 20 mL 50% MgSO4/L for a maximum of 50 mg/kg.


Renal Injury


The anuric 10-year-old Arabian mare, badly tied up after an apparently energetic trail ride, represented a case of acute kidney injury associated with pig- ment (myoglobin) released from the body and depos- ited in the renal tubules. Initiation of diuresis is the first-order treatment in these cases. Respondents chose to treat this mare with isotonic polyionic crys- talloid replacement fluids as a bolus (generally 20 L), 0.9% saline, or hypertonic saline followed by isotonic polyionic crystalloid replacement fluids. Caution is required because continued administration of fluids to cases such as this without inducing urine produc- tion can be harmful and result in fluid overload with pulmonary edema. If an initial bolus does not re- sult in urine production, other methods of inducing diuresis should be attempted, such as furosemide, and fluid administration must be slowed down or stopped.


5. Conclusions


Hypertonic saline (1-L bags), isotonic polyionic crys- talloid fluids with a normal strong ion difference (1 L and 3- to 5-L bags) and 5% dextrose in water (1-L bags) appear to be the most commonly chosen IV fluids in this survey. Volumes that might be useful to have on hand for an initial IV fluid resuscitation in an ambulatory situation might include the following: Foals: 1 to 4 L isotonic polyionic crystalloid; 2 L


5% dextrose Adults: 2 L 7.5% hypertonic saline; 20 to 30 L isotonic polyionic crystalloid; hetastarch Commonly mentioned additives included thiamine, calcium (23% calcium gluconate), magnesium (50%


MgSO4), and polymyxin B, and all are easily carried in an ambulatory practice. If practical and within the client’s budget, hetastarch or a similar colloid may prove useful in some situations. The reader is cautioned that additional fluids


would be required for continued treatment of all cases listed above. Some specific fluid brands are listed in Table 1.


References and Footnotes


1. Lakritz J, Madigan J, Carlson GP. Hypovolemic hyponatre- mia and signs of neurologic disease associated with diarrhea in a foal. J Am Vet Med Assoc 1992;200:1114–1116.


2. Magdesian KG, Hirsh DC, Jang SS, et al. Characterization of Clostridium difficile isolates from foals with diarrhea: 28 cases (1993–1997). J Am Vet Med Assoc 2002;220:67–73.


3. Magdesian KG. Neonatal foal diarrhea. Vet Clin North Am Equine Pract 2005;21:295–312.


4. Hollis AR, Wilkins PA, Palmer JE, et al. Bacteremia in equine neonatal diarrhea: a retrospective study (1990– 2007). J Vet Intern Med 2008;22:1203–1209.


5. Pfennig CL, Slovis CM. Sodium disorders in the emergency


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