46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
93
•
•
•
numbers look better but the volume of blood reaching vital organs is not
necessarily better (Fantoni et al. 2013).
Ephedrine: this drug has shown improved MAP by increasing both SVR and
cardiac index. This means that there is better blood pressure and more blood
volume reaching vital organs for perfusion. However, its mechanism of action
relies on the ability of the sympathetic system to respond, thus if the horse is
in severe shock, collapsed or there is a suspicion of decreased sympathetic
tone than the use of this drug is cautioned. The excellent improvement of
cardiovascular function was tested in healthy horses admitted for elective
procedures (Fantoni et al. 2013), its beneficial effects have not been tested in
colic horses yet.
Calcium: Useful to treat hypocalcaemia. Intraoperative blood gases may be
useful in determining the Ca2+. Best method is to spike 3 L isotonic crystalloid
bag to infuse over 20 to 40 minutes, as described for phenylephrine. Calcium
borogluconate 23% (spike bag with 5 to 10 mL per 100 kg). Calcium infusions
have proven to be an excellent positive inotropic agent during isoflurane
anaesthesia in horses (Snyder et al. 2013). Remember not to administer
blood products via the same intravenous port as fluids containing calcium.
Sudden bradycardia could indicate that the calcium infusion is being
administered too fast, or you are giving too much. To avoid this it is best to
start giving low doses and monitor response with regular blood gas analysis.
Sodium bicarbonate: Severe academia has negative inotropic effects and thus
may warrant correction if pH < 7.2. Sodium Bicarb required (mEq) = 0.3 x
BW (kg) x BE; give half this dose slowly and re-evaluate. Sodium Bicarb 8.4%
= 1.0 mEq/mL; Sodium Bicarb 4.2% = 0.5 mEq/mL (Boesch 2013, Snyder et al.
2013).
Monitoring success
Regular monitoring will ensure successful attempts and adjustments to the initial
perfusion plan (Tranquilli et al. 2007). The clinician should notice:
•
•
•
Improved mucous membrane colour and CRT: The mucous membrane
should return to a pink to pale pink colour. Excessively bleached gums may
indicate inadequate volume or excessive vasopressor treatment. Very
congested mucous membranes indicate not enough vasopressor treatment.
Improved direct blood pressure readings. Aim to achieve and maintain a
minimum MAP of 75 mmHg during the operation. The pulse pressure
(systolic – diastolic arterial blood pressure) should not exceed 40 to 50
mmHg; else this indicates that the heart is working too hard to maintain the
current MAP. Options to improve diastolic pressure are to increase vessel
tone (vasopressor) or volume (synthetic colloids and isotonic crystalloids).
Absence of pulse wave variation during IPPV. If there is pulse wave variation
during IPPV then this is an indicator of hypovolaemia. Relative hypovolaemia
may be responsive to vasopressor (endotoxemia, hypercapnia). Absolute
93