Fluid therapy

Canine Haemoabdomen - Part 2

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Part 2 of the two-part mini-series on canine haemoabdomen based loosely around:

Herold LV, Devey J, Kirby R, Rudloff E. Clinical evaluation and management of hemoperitoneum in dogs. J Vet Emerg Crit Care 2008. 18(1):40-53.

“This clinical review combines a search of the veterinary literature with the clinical experience of the authors to provide a resource for the emergency management of hemoperitoneum in dogs.”

See Part 1 HERE.

1. Maintaining Oxygen-Carrying Capacity

Bleeding – peritoneal or otherwise – involves loss of all blood components including red cells with their oxygen-carrying haemoglobin
Majority of blood oxygen content is haemoglobin-bound; much smaller proportion dissolved in plasma (the two components are inter-related)
Oxygen supplementation plus improving effective circulation by volume resuscitation will help to improve tissue oxygen delivery to a variable extent; but replacing oxygen-carrying capacity – i.e. haemoglobin – is the major factor. 
Haemoglobin is replenished either by transfusing red blood cells and/or by using a haemoglobin-based oxygen-carrying solution (HBOC) – Oxyglobin®
Red cell transfusions: packed/stored or fresh, just red cells or whole blood, allogenic or autologous

“Once volume resuscitation has been initiated, and hemoperitoneum diagnosed, transfusion therapy can be considered to optimize oxygen-carrying capacity.”

Decision to transfuse is multifactorial depending on e.g.

  • Manual PCV/haematocrit – individual and trend
  • Signs suggesting anaemia has become clinically significant
  • Whether red cell loss is on-going and how soon likely to stop/be stopped
  • Cause
  • Etc.

Not all dogs with haemoabdomen will meet transfusion criteria but certainly a number will.

In some cases improving oxygen-carrying capacity will be life-saving; in others it will be (very) helpful but not absolutely necessary for survival.

Transfusing patients with active haemorrhage will inevitably result in loss of some of the transfused product into the peritoneal cavity with only transient benefit on systemic oxygen-carrying capacity. Is this the best short-term use of the product?
Does it make more sense in some cases to withhold red cell transfusion until active bleeding has been stopped?

2. Arresting On-going Haemorrhage

DEPENDS ON CAUSE

Vitamin K anticoagulant rodenticide: replenish clotting factors with plasma
Angiostrongylosis: coagulopathy is complex, multifactorial, poorly understood; plasma may help but may not resolve coagulopathy.

MALIGNANT TUMOUR RUPTURE most common; haemangiosarcoma most common – especially splenic rupture

Timing of surgery (after exclusion of detectable lung metastases of course!) in these cases?

Depends on individual patient, practice circumstances, timing of day etc.

Many cases can be stabilised with volume resuscitation +/- red cell transfusion, monitored closely and have diagnostic imaging +/- surgery with less urgency and more stable for general anaesthesia – e.g. next day if patient presents in the evening. But some will not be stabilised, continue to bleed, dump resuscitation fluids into their abdomen…and need surgery with greater urgency.

Alternative approach is to start volume resuscitation, exclude detectable lung metastases, and operate with emergency approach. Until the bleeding lesion is removed on-going haemorrhage will not be stopped and the patient will not be definitively stabilised?

Especially if your ability to give a red cell transfusion is very limited maybe you don’t want to risk the patient continuing to bleed?

And indeed are you set up in a way that makes it easy or practical to monitor the patient closely for an extended period of time before surgery?

Spectrum of cases and multiple considerations. What is your most common approach? Let me know.

3. Autologous Transfusion (Cell Salvage)

Blood transfusion products and options may be (severely) limited. Can we harvest blood lost into peritoneal cavity and give it back to the patient?

Benefits e.g.

  • Readily available source of transfusion
  • Likely to be cheaper to client
  • Avoids compatibility issues of using allogenic red cells
  • Avoids potential risks associated with storage of red cells
“Autotransfusion is an effective method for rapidly providing red blood cells and intravascular volume when imminent death precludes the preparation of allogenic transfusion or when other blood products are not available.”

More people would be in favour than not as long as strict asepsis and rational technique is used and of course even more so if the perception is that the patient would die without it.

Blood aspirated from abdominal cavity can be processed using automated cell salvage machine (e.g. Cell Saver® 5+ Autologous Blood Recovery System) to separate out red cells, or administered without processing/separation. Either way strict asepsis is essential.

“Intra-abdominal blood is collected aseptically by aspirating into a sterile syringe with paracentesis or by suctioning into a sterile container at the time of surgery…Abdominal blood associated with chronic hemorrhage can usually be collected and infused without anticoagulant because the blood is defibrinated when it comes in contact with the peritoneal surface…However, when hemorrhage is acute and rapid there may be insufficient time for defibrination and anti-coagulation of abdominal blood is necessary before autotransfusion (7 mL of citrate–phosphate dextrose adenine should be added to each 50 mL of abdominal blood collected)…The blood should be administered through a blood administration set or in-line blood filter.”

Is Cell Salvage Contraindicated With Suspected Haemangiosarcoma?

Does aspirating and transfusing abdominal haemorrhage containing haemangiosarcoma cells disseminate cancer systemically? No worthwhile veterinary evidence; small amount of human evidence with other cancer types.
Canine haemangiosarcoma is reported to have metastasised in virtually all patients at the time of diagnosis; if cell salvage is deemed life-saving, should it be done regardless?

“Reported contraindications for autologous transfusion of abdominal blood include the presence of septic peritonitis and the presence of ruptured neoplastic abdominal masses due to the potential for systemic disease dissemination. Desmond et al. reviewed the risk of neoplastic dissemination associated with salvage and autotransfusion of intra-abdominal blood during oncologic surgery in humans. No increase in tumor recurrence or decrease in survival rate was reported. The use of leukocyte depletion filters over the standard red blood cell transfusion filters has been recommended to reduce risk of tumor dissemination by autotransfusion in humans. Leukocyte depletion filters are not readily available in most veterinary practices and may be costly to utilize. There are no studies of metastatic risk with autotransfusion in veterinary patients.”

Cite references from 1990's – nothing more recent?

4. Abdominal Counterpressure (Abdominal pressure bandage)

Intention: apply external pressure to increase intra-abdominal pressure and thereby tamponade bleeding. Realistically intra-abdominal pressure is only likely to be increased sufficiently to exceed venous pressure and reduce venous haemorrhage. Therefore excessively tight bandages do not necessarily offer any greater advantage and are likely to be associated with greater complications.

Contraindications:

  • Pelvic or femoral fractures
  • Respiratory distress due to pneumothorax or pleural effusion
  • Diaphragmatic rupture
  • Head trauma

Repeated abdominal free fluid scanning (potentially use of ‘abdominal fluid score’) increasingly used to monitor disease progression, including on-going blood loss – cannot be done with abdominal pressure bandage in place.

May significantly increase discomfort in post-operative patients, those with abdominal trauma etc.

Place abdominal bandage starting caudally approximately at level of pubis and move cranially up to xiphoid stopping before caudal rib margin.
Removed once patient has remained stable for a reasonable period ideally trying to minimise how long the bandage is in place to reduce potential complications.
Abrupt removal can potentially cause life-threatening hypotension due to rapid redistribution of blood or haemorrhage from vessels where tamponade was previously achieved.
Removal should commence at cranial end (i.e. in opposite direction to how bandage was placed); stagger by cutting a small section every 15-30 minutes.
Monitor patient closely throughout for deterioration.

Do abdominal pressure bandages do anything? Do they actually work?

No published good quality clinical evidence on this.
In absence of contraindications, decision at this time is opinion- rather than evidence-based

Authors write:

“it is often enough to reduce or even stop hemorrhage from vascular defects. In addition the application of abdominal counterpressure also may produce a tamponade effect on bleeding abdominal organs and vessels, reduce the size of peritoneal space and reduce hemorrhage volume.”

…but cite human medicine paper from 1979 as evidence – nothing more recent in people? Nothing more recent in dogs and cats??
[Pelligra R, Sandberg EC. Control of intractable abdominal bleeding by external counterpressure. J Am Med Assoc 1979. 241(7):708–713.]

Authors also write:

“In a study of dogs with experimentally produced hemoperitoneum, application of an abdominal bandage to provide counterpressure improved survival.”

…But cite experimental canine paper from 1986 with tiny sample size (5 dogs versus 3 dogs). Is this really reliable evidence of a clinically significant effect?
That’s great, right? Well, if you look at the reference that is cited it is an experimental paper from 1986 using 5 dogs in one group and 3 dogs in the other and a mechanism of haemorrhage that is not what we deal with clinically. So we must ask whether this is even evidence of a level that we should be paying attention to. Maybe.
[McAnulty JF, Smith GK. Circumferential external counterpressure by abdominal wrapping and its effect on simulated intra-abdominal hemorrhage. Vet Surg 1986. 15 (3):270–274.]

“No clinical evaluations of external counterpressure have been reported in veterinary patients…In the experience of the authors, when hemoperitoneum and ongoing hemorrhage prevents patient stabilization, and no contraindications exist, the application of counterpressure may correct hypotension and reduce or eliminate the need for immediate surgical intervention to control hemorrhage in dogs.”

Decision to use abdominal counterpressure depends on e.g.

  • You, your opinion and anecdotal experience
  • Individual patient and particular circumstances

Do you routinely use an abdominal pressure bandage?
If you don’t routinely do this, would you consider it in certain cases?
And if so, in what types of cases?

If you would like a copy of the main review article on which these episodes are loosely based then use the Contact form on the website, Tweet @VetEmCC or message me via the Veterinary ECC Small Talk Facebook page.

Papers that informed this episode:

Herold LV, Devey J, Kirby R, Rudloff E. Clinical evaluation and management of hemoperitoneum in dogs. J Vet Emerg Crit Care 2008. 18(1):40-53.

Desmond MJ, Thomas MJG, Gillon J, et al. Perioperative red cell salvage. Transfusion 1996. 36:644–651.

Edelman MJ, Potter P, Mahaffey KG, et al. The potential for reintroduction of tumor cells during intraoperative blood salvage: reduction of risk with use of RC-400 leukocyte depletion filter. Urology 1996. 47:179–181.

Hirst C, Adamantos S. Autologous blood transfusion following red blood cell salvage for the management of blood loss in 3 dogs with hemoperitoneum. J Vet Emerg Crit Care 2012. 22(3):355-360.

Kellett-Gregory LM, Seth M, Adamantos S, Chan D. Autologous canine red blood cell transfusion using cell salvage devices. J Vet Emerg Crit Care 2013. 23(1):82-86.

Kisielewicz C, Self IA. Canine and feline blood transfusions: controversies and recent advances in administration practices. Vet Anaesth Analg 2014. 41(3):233-242.

McAnulty JF, Smith GK. Circumferential external counterpressure by abdominal wrapping and its effect on simulated intra-abdominal hemorrhage. Vet Surg 1986. 15 (3):270–274.

Pelligra R, Sandberg EC. Control of intractable abdominal bleeding by external counterpressure. J Am Med Assoc 1979. 241(7):708–713.

Valbonesi M, Bruni R, Lercari G, et al. Autopharesis and intraoperative blood salvage in oncologic surgery. Transfus Sci 1999. 21:129–139.

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015 Canine Haemoabdomen - Part 1

Some Things To Know...

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Recent (April 2015) Facebook post (Veterinary ECC Small Talk page, ER Vet Tech Rounds group):

“When You Hear About A 'Collapsed Dog' What Are The Top Three Differentials That Come To Mind?”

Approximately 150 responses
Haemoabdomen in particular due to splenic rupture mentioned by approximately 80% of respondents

Episode loosely based around:

Herold LV, Devey J, Kirby R, Rudloff E. Clinical evaluation and management of hemoperitoneum in dogs. J Vet Emerg Crit Care 2008. 18(1):40-53.

“This clinical review combines a search of the veterinary literature with the clinical experience of the authors to provide a resource for the emergency management of hemoperitoneum in dogs.”

1. Causes:

Traumatic vs. non-traumatic

NON-TRAUMATIC cases of clinically significant canine haemoabdomen most common – especially rupture of intra-abdominal tumours – especially haemangiosarcoma lesions

Other non-traumatic causes:

  • Haematoma rupture
  • Systemic coagulopathy due to e.g. vitamin K antagonist anticoagulant rodenticides, Angiostrongylus vasorum (canine lungworm)
  • Gastric dilation-volvulus (GDV)
  • Liver torsion
  • Splenic torsion
  • Etc.
“Don’t assume that every dog with a non-traumatic haemoabdomen has a tumour and in particular please don’t go chopping open dogs that have a primary systemic coagulopathy!”

Obviously some dogs will have a secondary consumptive coagulopathy that needs to be managed along with the primary problem.

Clinically significant TRAUMATIC haemoabdomen relatively rare?
Focused abdominal ultrasonography (A-FAST) may reveal small clinically insignificant bleeds more commonly?

2. Canine abdominal haemangiosarcoma:

A dog with a non-traumatic haemoabdomen:

  • What is the probability that this individual dog has a bleeding structural mass lesion as the cause?
  • What is the probability that that bleeding lesion is a tumour rather than a haematoma?
  • If it is a tumour, what is the probability that it is haemangiosarcoma?

Sweeping superficial summary of some papers listed below – papers not been critiqued for quality/reliability:
Malignant neoplasia most common cause of non-traumatic haemoabdomen in dogs occurring in approximately 65-85% of cases
Of those approximately 60-75% are haemangiosarcoma lesions

3. History, Clinical Signs and Physical Examination:

Will depend to an extent on:

  • Cause
  • Single/multiple bleeding episodes
  • Severity of current bleeding episode

Not all cases are collapsed

 “At least 40 mL/kg of peritoneal fluid is required to detect a fluid wave, making abdominal distension an insensitive indicator of early or slow forming free abdominal fluid.”

Radiography more sensitive, ultrasonography even more sensitive
40 ml/kg cut-off: is a universal cut-off rational across breeds, standing vs. recumbent, all palpators? Evidence for this figure??

“Four objectives must be met during resuscitation efforts: (1) to re-establish and maintain effective circulating volume, (2) to diagnose hemoperitoneum and identify database abnormalities, (3) to maintain oxygen-carrying capacity, and (4) to arrest ongoing hemorrhage. The actions to achieve these goals are often undertaken simultaneously depending on the severity of clinical signs. When clinical signs indicating decompensatory shock are present, immediate resuscitation will preclude definitive diagnostic evaluation; however, a rapid assessment of the packed cell volume (PCV), total solids (TS), and abdominocentesis results can be evaluated to confirm a diagnosis of hemoperitoneum.”

Make sure to provide analgesia as needed.

4. Re-establish and maintain effective circulating volume:

How best to resuscitate haemorrhagic hypovolaemia?
Overly aggressive crystalloid resuscitation harmful; rapid increases in intravascular hydrostatic pressure may blow off clots and promote further/on-going bleeding
We can’t leave the patient in a shocked state and on the flipside we don’t want to exacerbate the haemorrhage. So what do you do?

Careful conservative titrated resuscitation; end-point is adequate but not necessarily normal systemic perfusion
Stop resuscitation when end-point reached and continue to monitor closely
Assess and resuscitate perfusion using physical examination parameters – supplemented by blood pressure and lactate if available

‘Hypotensive resuscitation’:

Resuscitate systemic blood pressure to a low-normal end-point (e.g. mean arterial blood pressure (MAP) 60 mmHg; Doppler systolic 80-90 mmHg)
But:
Do not use blood pressure in isolation; systemic blood pressure is a proxy for but not the same thing as systemic perfusion
Ensure non-invasive blood pressure measurements are repeatable/reliable/

See podcast episode 009 for discussion of resuscitation fluids and crystalloids versus colloids

Haemoglobin-based oxygen-carrying solutions provide both oxygen-carrying capacity and colloidal support:

  • Oxyglobin® only one currently available; not in all countries
  • Potentially very expensive resuscitation strategy

‘Haemostatic resuscitation’:

Not mentioned in review article
Replace lost whole blood with comparable blood products – packed red blood cells, plasma, platelets
Increasingly adopted and researched in human medicine; also use of specific clotting factors/clotting factor combinations and antifibrinolytics especially tranexamic acid.
Minimises harm from not replacing like-for-like, also dilutional coagulopathy etc.

Very unrealistic in vast majority of veterinary practice environments? Adequate and timely access to blood components? Financially affordable strategy for pet carers?

5. Diagnosing haemoabdomen:

Venous manual packed cell volume (PCV) and plasma total solids (TS):

May suggest acute haemorrhage – does not localise to abdominal cavity

Both red blood cells and protein are lost from the circulation in haemorrhage and therefore PCV and TS do not change initially:

  • Remember that PCV is a percentage and TS a concentration, i.e. neither is a measure of absolute quantity.
  • In the first few minutes following haemorrhage, the absolute number of red blood cells and plasma protein molecules will be reduced but PCV and TS are unchanged.
  • Fluid then moves from the interstitial compartment into the bloodstream diluting the remaining red cells and protein and causing a decrease in the measured PCV and TS.
    • It takes a while for fluid shift and therefore dilution to occur although it is not possible to be too precise about the exact length of time in clinical patients.
    • In dogs the spleen contracts in response to haemorrhage and expels a large amount of stored red blood cells into the circulation; therefore PCV may remain in the normal range for a while despite low TS, i.e. with blood loss, TS is usually expected to fall first followed by PCV in dogs.
    • The response of the spleen in cats is either much less substantial or in fact non-existent depending on which reference one consults.
  • As yet more time passes PCV will also fall depending on whether haemorrhage is on-going, the severity of any on-going haemorrhage, and any treatment instituted.

Evaluate for systemic coagulopathy

 “Resuscitation efforts should not be delayed while awaiting laboratory results.”

…and I couldn’t agree with that more.

Identify free peritoneal fluid – ultrasonography best way to do this
Aspirate – including potentially with ultrasound guidance – and analyse
Blood lost into the abdomen (and other cavities) often has an echogenic appearance

When analysed the fluid will:

  • Be grossly sanguineous but non-clotting
  • Have a PCV that is similar to (could be lower, same or higher than) the patient’s circulating PCV
  • Have red blood cells, possible occasional erythrophagocytosis, and typically no platelets on cytology
    • Note: although cytology is not required to diagnosis haemoabdomen, it should always be performed to exclude the presence of a concurrent septic process which would then make surgery an emergency following stabilisation.

Beware of over-interpreting fluid aspirated from any body cavity as being consistent with haemorrhage purely based on gross appearance. It is not unusual for fluid to grossly appear consistent with bleeding only for PCV measurement to then be inconsistent – grossly sanguineous fluid can for example have a PCV of less than 5-10%.

“Repeated paracentesis during stabilization and hospitalization provides information to monitor the progression of intra-abdominal bleeding. An increasing trend in the abdominal PCV that parallels a decreasing trend in the peripheral PCV indicates ongoing or active hemorrhage.”

Note that intravenous resuscitation with red cell-free fluids – including plasma – may affect both venous and effusion PCV and hence laboratory evaluation.

Part 2 includes maintaining oxygen-carrying capacity, arresting haemorrhage, possible use of abdominal counterpressure etc.

Papers that informed this episode:

Aronsohn MG, Dubiel B, Roberts B, Powers BE. Prognosis for acute nontraumatic hemoperitoneum in the dog: a retrospective analysis of 60 cases (2003-2006). J Am Anim Hosp Assoc 2009. 45(2):72-77.

Hammond TN, Pesillo-Crosby SA. Prevalence of hemangiosarcoma in anemic dogs with a splenic mass and hemoperitoneum requiring a transfusion: 71 cases (2003-2005). J Am Vet Med Assoc 2008. 232(4):553-8.

Herold LV, Devey J, Kirby R, Rudloff E. Clinical evaluation and management of hemoperitoneum in dogs. J Vet Emerg Crit Care 2008. 18(1):40-53.

Lux CN, Culp WTN, Mayhew PD, et al. Perioperative outcome in dogs with hemoperitoneum: 83 cases (2005–2010). J Am Vet Med Assoc 2013. 242(10):1385-1391.

Pintar J, Breitschwerdt EB, Hardie EM, Spaulding KA. Acute nontraumatic hemoabdomen in the dog: a retrospective analysis of 39 cases (1987-2001). J Am Anim Hosp Assoc 2003. 39(6):518-522. 

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007 Listeners' Questions on Fluid Therapy

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For online training material on Parenteral Fluid Therapy and Hypovolaemia, Shock and Dehydration, CLICK HERE.

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004 Fluid Choice in Tomcat Urethral Obstruction (Blocked Cats)

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Not all blocked cats are hypoperfused on presentation but those that are should be resuscitated with fluid therapy given as boluses to restore perfusion with the approach being tailored to the individual patient. This should be done BEFORE you consider sedating or indeed anaesthetising to attempt catheterisation.

Will I rupture the bladder?

“If I give blocked cats lots of fluid therapy while their bladder is obstructed, won’t I rupture the bladder?"

NO! The risk is very very very small and has to be weighed up against the undoubted benefit of fluid resuscitation in these cases. 

Why won't I rupture the bladder?

For the kidney to make urine it needs to have an adequate blood supply. The blood supply to the kidneys of a blocked cat in shock will be moderately or even severely compromised and this means that the impetus to make urine will be significantly decreased. At the same time as the bladder is obstructed and under high pressure this pressure is transmitted via the ureters to the kidneys; this back pressure on the kidneys will also act to oppose urine production. So on the one hand there is little forward impetus to make urine and on the other hand there is back pressure not to make urine; hence blocked cats in shock are unlikely to be making much urine at all. Obviously as you perform intravenous fluid resuscitation and the blood supply to the kidneys increases you will promote the formation of urine but you will also be going on to deal with the obstruction very soon and so this is not a concern.

** FOR AN IN-DEPTH PRESENTATION AND COURSE NOTES ON THE MANAGEMENT OF BLOCKED CATS PLEASE SEE HERE. **

Does it matter which fluid we choose for the initial resuscitation phase?

A replacement isotonic crystalloid is used. Typical choice is between Hartmann’s (buffered lactated Ringer’s solution, compound sodium lactate) and  0.9% sodium chloride ('normal' saline).

Blocked cats have:

  • Hyperkalaemia: clinically significant life-threatening hyperkalaemia is not uncommon in the more severe cases
  • Acidaemia due to metabolic acidosis: typically less of a concern but can have significant adverse physiological consequences and can be life-threatening if sufficiently severe

0.9% sodium chloride:

Potassium-free; blocked cats are hyperkalaemic so why would you want to give them more potassium?

But...promotes hyperchloraemic acidosis and can exacerbate existing acidaemia.

Hartmann's solution:

Contains 5 mmol/l potassium - as do Normosol-R and Plasmalyte 148; this is nevertheless lower than clinically significant hyperkalaemia and use will decrease potassium concentration through dilution.

But...solution that promotes alkalosis, alkalinising solution; may help resolve metabolic acidosis.

(Also contains small amount of calcium which is no bad thing given that these cats are often hypocalcaemic.)

Bottom line: choice of fluid between these two types has not thus far been shown to be clinically significant....

Drobatz KJ, Cole SG. The influence of crystalloid type on acid-base and electrolyte status of cats with urethral obstruction. J Vet Emerg Crit Care 2008. 18(4):355-361.

Prospective randomised non-blinded study

Cats that presented to the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania with urethral obstruction between September 2000 and November 2004 were eligible for inclusion.

Inclusion criteria:

  • Baseline blood pH and potassium measured initially
  • At least one subsequent measurement of these parameters within the following 12 hours

Urethral obstruction diagnosed based on compatible clinical signs + large, firm, non-expressible urinary bladder

Exclusion criteria:

  • Owners elected to not pursue treatment and elected euthanasia
  • Baseline blood pH and potassium as well as one subsequent measurement of those variables within 12 hours of admission not obtained

Coin-flip randomisation to receive either Normosol-R or 0.9% sodium chloride.

Blood samples collected before any therapy for analysis of blood pH, bicarbonate, pCO2, base excess, sodium, chloride, potassium, ionised calcium, ionised magnesium, and glucose.
Biochemical analysis of serum urea nitrogen (SUN), serum creatinine, and serum phosphorus performed on some cats.

Further therapy and monitoring at discretion of attending clinician; non-blinded

Results:

  • 68 cats: 39 Normosol-R, 29 0.9% sodium chloride
  • Very similar comparable groups including with respect to initial pH and potassium concentrations
  • While there were no statistically significant differences between groups at baseline, cats in the Normosol- R group had a significantly higher blood bicarbonate concentration at 12 hours and significantly higher blood pH at 6 hours and 12 hours.
  • There were no statistically significant differences in blood potassium concentration or the amount of fluid administered between groups at any time.
  • In comparison with the absolute values, the increase in blood pH from baseline was significantly greater in the Normosol-R group than the 0.9% sodium chloride group at 6 hours and 12 hours following admission and this difference also approached significance at 2 hours.
  • Blood potassium levels declined steadily in both groups and no statistically significant differences were found in the rate of decline from baseline between groups.
  • Cats in the 0.9% sodium chloride group had a significantly higher blood sodium concentration at 2 hours and 6 hours, as well as a significantly higher blood chloride concentration at 6 hours and 12 hours. The increase in blood chloride from baseline was significantly higher in the 0.9% sodium chloride group than in the Normosol-R group at 2 hours, 6 hours, and 12 hours.

Use of Normosol-R was associated with a greater increase from baseline in blood pH and bicarbonate values than was the use of 0.9% sodium chloride.

Although Normosol-R contains 5mmol/l of potassium, the absolute value and rate of decline in blood potassium levels were nearly identical between the groups in this study.

Authors say: “While statistically significant, the differences identified between groups in the present study may not have been clinically significant in this patient population. From both prior research and widespread clinical experience, it is clear that both balanced isotonic crystalloid solutions and 0.9% sodium chloride are acceptable fluid choices for the treatment of most cases of urethral obstruction in cats. However, possi-ble implications of the current study pertain to severely affected cats with profound metabolic acidosis. In these cases, any acidifying effect of 0.9% sodium chloride could be deleterious, as severe metabolic acidosis impairs cardiovascular function, compounding the untoward effects of hyperkalemia and hypocalcemia. The use of a balanced isotonic crystalloid would achieve similar results in the treatment of per-fusion abnormalities and hyperkalemia, along with more rapid improvement in acid–base status.”

Study limitations:

  • Not blinded
  • Treatment not standardised across groups
  • No mention of power calculation with respect to sample sizes needed to show significant different between the groups
  • As always...larger sample size if possible!

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