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Arti cial colloids
· Examples: Voluven, volulyte, hetastarch, dextran, gelafusine
An Urban Experience
The two main ways we use intravenous  uid therapy is in the treatment of shock, in which  uids are administered as a bolus; or as a continuous infusion, in which it is used as maintenance therapy and for rehydration.
The de nition of shock is inadequate oxygen delivery resulting in anaerobic metabolism and mitochondrial dysfunction, eventually resulting in organ dysfunction. There are 4 different types of shock. 1) Hypovolaemic; 2) Obstructive; 3) Cardiogenic; and 4) Vasodilatory. The  rst three types of shock is categorised as “vasoconstrictive shock”, where peripheral vasoconstriction occurs in order to maintain perfusion. In vasodilatory shock vessels remain vasodilated as vasoconstriction is impaired. Table 1 describes common physical examination parameters of vasoconstrictive and vasodilatory shock, which severity worsens from mild, moderate, to decompensated shock.
Table 1. Clinical  ndings of Shock
Vasodilatory shock occurs due to systemic in ammatory response syndrome (SIRS), sepsis, anaphylaxis or general anaesthesia. Treatment involves addressing
the underlying cause; administering intravenous  uids; +/- vasopressors (noradrenaline or dopamine) if the patient remains hypotensive. During vasodilatory shock, capillaries are more permeable, and patients are often hypoalbuminaemic resulting in increased risk of  uid extravascation and  uid overload.
The aim of treating shock with intravenous  uid therapy is to rapidly  ll the intravascular space with intravenous  uids at doses which are described above. Intravenous  uids can be administered by various methods: Pressure bags are ideal in medium to large breed dogs, as it can deliver 1 litre of  uid within 8 minutes. If intravenous  uid is delivered too slowly, it can redistribute and will not treat shock. In small to medium sized dogs, a  uid pump can be used. In cats or small dogs prone to  uid overload you must be very careful about bolusing  uids. Safer methods to prevent  uid overload include drawing  uid up in a 50 mL syringe and delivering by hand; using a syringe driver; or using a paediatric burette (which can be used with or without a  uid pump).
· These are hyperosmolar solutions which increases oncotic pressure in the intravascular space. Unlike hypertonic saline, it doesn’t draw  uid in, but instead minimises redistribution of  uid into the interstitial space, hence helps maintain intravascular blood volume.
· Indications: severe hypoproteinaemia; large breed dogs; shock which is non-responsive to isotonic crystalloids
· Adverse effects/contraindications: Acute kidney injury, coagulopathy, increased risk of  uid overload
· Shock dose: Dogs 5 – 10 mL/kg; cats 2.5 – 5 mL/ kg delivered over 15 minutes IV. The maximum dose depends on the type of colloids.
Heart rate
↑ Cats ↓ or ↑
↑↑ Cats ↓ or ↑
↓ Cats ↓
Pulse quality
↓ or ↑ ↑ (vasodil)
↓↓ ↑ (vasodil)
↓↓↓ ↑ or ↓ (vasodil)
Mucus membrane colour
Pale pink Injected (vasodil)
Pale Injected (vasodil)
Very pale
Capillary re ll time (seconds)
1.5 – 2 < 1 (vasodil)
2 – 3 < 1 (vasodil)
Extremity/body temperature
↓ ↑ (vasodil)
↓↓ Cats ↓ body temp ↑ (vasodil)
↓ body temperature
Mild obtundation
Moderate obtundation
Hypovolaemic shock is the most common type of shock which occurs due to severe dehydration (> 8%), vomiting, diarrhoea, haemorrhage, third space loss of  uids, or polyuria. Treatment of hypovolaemic shock involves  uid resuscitation and correcting the underlying cause.
Obstructive shock is de ned by the obstruction of great vessels or the heart. This can occur due to gastric dilation and volvulus, pericardial effusion causing
cardiac tamponade, and pneumothorax. Treatment of obstructive shock involves very quickly relieving the obstruction. Gastric dilation and volvulus will also require  uid resuscitation, however use of  uid in pericardial tamponade may not be required and can be detrimental.
Cardiogenic shock occurs when there is inadequate circulation of blood due to poor left ventricular function. This can occur due to mitral valve disease, myocardial disease, or arrhythmias. This is the only type of shock
in which  uid therapy is contraindicated. Cardiogenic shock can be identi ed by obtaining a good history, auscultating the heart for murmurs or arrhythmias while palpating pulses for pulse de cits, performing an ECG, and/or performing a bedside echocardiogram to assess the left atrium to aortic ratio (LA:Ao) which is usually less than 1.3 – 1.5 and subjectively assessing the contractility of the heart.

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