Peri-operative management and anaesthesia for pyometra in a dog

Question 1

In animals with a pyometra, what kind of disturbances do they suffer from?

Answer 1

–Fluid deficits (PU/PD, V++)

–Pre-renal failure

–SIRS (systemic inflammatory response syndrome)

–Acid-base disturbances (can be acidotic as result of +++ hypovolaemia, or alkalotic due to V++ & Cl loss)

–Anaemia (chronic infection + blood loss into uterus)

–Diabetes

Question 2

Bonnie is presented to you during a busy Saturday morning surgery. She is a 6 year old female golden retriever with a history of lethargy, polydipsia and polyuria of 5-7 days duration. Her last season was approximately 6 weeks ago. The owners report a foul smelling discharge leaking from the dog’s vulva.

Clinical examination reveals a quiet, depressed dog. Subjectively the dog appears to be ‘dehydrated’, with tacky mucous membranes and a suggestion of prolonged skin tenting. The heart rate is 130 beats per minute, suggesting mild hypovolamia, and respiration rate is increased and is slightly laboured. CRT is 2 seconds. The dog is pyrexic. The abdomen is difficult to palpate due to extreme obesity. A scant amount of green pus is visible on the vet bed the dog is lying on. The dog weighs 43kg. The owner thinks the dog is drinking 2-3L per day roughly

Is this truly polydipsic?

Answer 2

• Even for a lean body weight (32kg) she is borderline PD
• PD= 100ml/kg/24hrs- she is not true PD
• Normal =2.15L

Question 3

Bonnie is presented to you during a busy Saturday morning surgery. She is a 6 year old female golden retriever with a history of lethargy, polydipsia and polyuria of 5-7 days duration. Her last season was approximately 6 weeks ago. The owners report a foul smelling discharge leaking from the dog’s vulva.

Clinical examination reveals a quiet, depressed dog. Subjectively the dog appears to be ‘dehydrated’, with tacky mucous membranes and a suggestion of prolonged skin tenting. The heart rate is 130 beats per minute, suggesting mild hypovolamia, and respiration rate is increased and is slightly laboured. CRT is 2 seconds. The dog is pyrexic. The abdomen is difficult to palpate due to extreme obesity. A scant amount of green pus is visible on the vet bed the dog is lying on. The dog weighs 43kg. The owner thinks the dog is drinking 2-3L per day roughly

Create a problem list for Bonnie

Answer 3

• Lethargic
• PUPD
• Foul smelling discharge from vulva
• Dehydration
• Tachycardic
• Tachypnoeic
• Mild hypovoaemia
• CRT 2 seconds
• Pyrexic
• Obese

Question 4

Bonnie is presented to you during a busy Saturday morning surgery. She is a 6 year old female golden retriever with a history of lethargy, polydipsia and polyuria of 5-7 days duration. Her last season was approximately 6 weeks ago. The owners report a foul smelling discharge leaking from the dog’s vulva.

Clinical examination reveals a quiet, depressed dog. Subjectively the dog appears to be ‘dehydrated’, with tacky mucous membranes and a suggestion of prolonged skin tenting. The heart rate is 130 beats per minute, suggesting mild hypovolamia, and respiration rate is increased and is slightly laboured. CRT is 2 seconds. The dog is pyrexic. The abdomen is difficult to palpate due to extreme obesity. A scant amount of green pus is visible on the vet bed the dog is lying on. The dog weighs 43kg. The owner thinks the dog is drinking 2-3L per day roughly

Give some differential diagnoses

Answer 4

• Pyometra
• Abdominal mass
• Diabetes mellitis
• Cushings
• Addissons
• Vaginitis
• Anaemia

Question 5

If PCV is increased and plasma proteins increase - what is your interpretation?

Answer 5

Fluid deficit

Question 6

If PCV is increased and plasma proteins is normal or decreased - what is your interpretation?

Answer 6

Splenic contraction

(pcythaemia, hypoproteinaemia

Question 7

If PCV is normal and plasma proteins is increased - what is your interpretation?

Answer 7

Normal hydration status with hyperproteinaemia

Anaemia and dehydration

Question 8

If PCV is decreased and plasma proteins is increased - what is your interpretation?

Answer 8

Anaemia and fluid deficits

Anaemia with hyperproteinaemia

Question 9

If PCV is decreased and plasma proteins is normal - what is your interpretation?

Answer 9

Non blood loss anaemia with normal hydration

Question 10

If PCV is normal and plasma proteins is normal - what is your interpretation?

Answer 10

Normal, Acute haemorrhage

Fluid deficits & anaemia & hypoproeinaemia

Question 11

If PCV is decreased and plasma proteins is decreased - what is your interpretation?

Answer 11

Blood loss, Anaemia and hypoproteinaemia

Overhydration

Question 12

Further tests confirm your suspicion of a pyometra. It is decided to perform a laparotomy in 3.5hrs time. You instruct the nurse to admit Bonnie and prepare her for surgery.

Why is medical management contraindicated?

Answer 12

Treatment of pyometra is prompt removal of the uterus and ovaries (ovariohysterectomy); in more stable patients medical treatment is possible using a variety of products where the aim is to end the luteal phase (since the condition is essentially ‘driven’ by progesterone) and to cause dilation of the cervix and to promote uterine contractions in an attempt to encourage drainage of pus from the uterus. The current state of Bonnie warrants a surgical approach as she is deteriorating rapidly, likely due to toxaemia

Question 13

With Bonnie:

IV access; where and what type of catheter? Is it warranted? The locum says she’s never seen a dog with pyometra put on fluids before. You insist on fluids, what type of fluids, and what rate prior to surgery?

Answer 13

• IV access essential for volume replacement and anaesthesia
• Consider a large bore OTN catheter
  
  • 18g OTN polyurethane based catheter (likely top be in situ for few days)
  • Proper preparation (septic, maybe diabetic patient?)
  • Administer an isotonic crystalloid
  • Patients with severe fluid deficits warrant a jugular catheter
• Fluid therapy
  
  • Isotonic (i.e. LRS or 0.9% NaCl)
• LRS has minimal K+
• Monitor potassium –will reduce

There is little justification for surgeryif volume correction and K+ have not been at least partially corrected

If anuric, must restore the urine output

Urinary catheter a good idea despite the risk of cystitis (++ contaminated vagina)

• Fluid rates:
  
  • 43 kg dog
  • 4 times maintenance is approximately 10ml/kg/hr
  • If fluid pump available set for 430 ml/hr

Question 14

What monitoring instructions prior to surgery do you give with Bonnie?

Answer 14

• Monitoring:
  
  • HR, RR, auscultate chest
  • Temp (core/extremities if possible)
  • CRT, mucous membrane colour
  • No reason why an ECG cant be put on, and if dog will tolerate a pulse oximeter that can be used too
  • CVP (would be nice to have but unlikely unless a central catheter placed)
  • Demeanour
  • Record these every 15 minutes on a chart to plot any improvements or deterioration

Question 15

If an infusion pump is not available it is often necessary to convert ml/kg/hr into drops/min

How can you do this with Bonnie if she weights 43kg?

Answer 15

• Drops/min = (ml/kg/hr) X (kg bodyweight) X (infusion set drops/ml)/60
• (10x45x20)/60=143
  
  • 143/60 (60 seconds per minute)
  • =2.4 drops
• Otherwise calculate drops per second
  
  • 430 x 20 = 8600 drops per hour (times by 20 because there are 20 drops per ml for a giving set)
  • 8600/60= 143 drops per minute
  • 143/60 = 2.4 drops/second or (2-3 drops/second)

Question 16

At midday you have 3 clients still to see, the nurse brings you in a coffee and says theatre is prepared for surgery, and she asks you what premed (if any?) would you like to have prepared and given to Bonnie. What do you suggest? (This practice has just about any drug you could want).

She also asks you if Bonnie needs some Metacam (meloxicam), what do you say?

Answer 16

• NSAIDs are contraindicated
  
  • Hypovolaemia
  • Maybe renal failure
• Avoid acepromazine in hypovolaemic patients , low dose ok if not too compromised
  
  • Because ACP causes vasodilation
• Dog can have an opioid (and should, METHADONE IS LICENSED FOR DOGS), and benzodiazepine if anxiolysis required
• Pre-oxygenate
• Any induction agent will be ok, use low doses and polypharmacy, remember propofol can cause profound vasodilation and apnoea
• Very sick patients, use opioid + BZD

Question 17

Induction of anaesthesia in Bonnie is smooth and more rapid than anticipated - why?

Answer 17

• Because she is so moribund
• Could induce without premed

Question 18

During the first 15 minutes blood pressure is less than optimum with 89/43, mean 58. You are busy scrubbing up, and are asked what the nurse should do to improve things. Again, this practice has access to all crystalloids, colloids (a tetrastarch), blood products and inotropes you could want.

What will you do?

Answer 18

• Intra operative low ABP
• Consider switching down inhalant
• Can supplement plane of anaesthesia with iv opioids (short acting), fentanyl SPC for dogs granted
• Give colloids (starch is my preference, not licensed, but > superior to gelatins)
  
  • Try a bolus, and see if it improves
  • If no colloid, can increase crystalloid rate
  • If no response to a colloid, (try an inotrope infusion e.g. dobutamine, or vasopressor e.g epinephrine/norepinephrine – > common in referral settings)
• Also consider autocaval compression, slight lateral tilt may help

Question 19

Respiratory rate is 5 breaths per minute, and ET CO2 is 58mmHg. What does this mean? What will you do? Consider IPPV and animal position and drugs.

Answer 19

• IPPV necessary if CO₂ going up
• Tilt slightly head up, weight taken off diaphragm
• Switch down inhalant (resp depression)
• Don’t give a respiratory stimulant because it increase myocardial oxygen demand
• The opioid, inhalant, induction agent and obesity will be causing the hypoventilation

Question 20

During surgery you exteriorise a large, friable, swollen uterus. At this point a tachycardia develops (HR 180) and the dog starts to pant. What do you say to the nurse? (no swearing allowed!). What are the common causes of tachycardia during anaesthesia?

Answer 20

• Sympathetic stimulation
• PaCO2, PaO2, pH abnormalities
• CNS disturbances
• Cardiac disease
• Drugs e.g. anticholinergics, NMBD etc (neuro muscular blockade drugs e.g. ketamine)

Question 21

Bonnie starts to pant during the surgery

Why is this happening?

Does it need treating - is output being compormised? is there a danger of VF?

Answer 21

Why is it happening?

• Check depth, CO₂, surgical stimuli etc

Does it need treating? Is output being compromised? Is there a danger of VF?

• Then consider opioid (e.g.fentanyl), lidocaine, propranolol, then procainamide, quinidine
• Cats propranolol, esmolol

Question 22

Towards the end of the procedure as you are closing the skin, you start to consider post operative analgesia, antibiotic cover and fluid therapy. Devise a plan. This practice has 24 hour nursing cover.

What do you want to use?

What do we want to avoid?

Answer 22

• Avoid NSAIDs until renal function improved and volume replaced
• Splash block, incisional bupivicaine
• Continue with opioids
• Can change from pure mu agonists to partial agonists/anatgonists
• Score the pain, reassess regularly
• TLC, feeding, bladder care
• Continue fluids post op, monitor

Question 23

Summarise the pathophysiological changes associated with pyometra and METABOLIC ACIDOSIS and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 23

A frequent finding which should resolve following restoration of tissue perfusion using fluid therapy; the use of bicarbonate is rarely if ever required.

Question 24

Summarise the pathophysiological changes associated with pyometra and HYPOKALAEMIA and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 24

Appropriate addition of potassium to the intravenous fluids is often required in these cases, refer to BSAVA Formulary. If not supplemented, hypokalaemia will get worse once fluid therapy has started due to enhanced renal excretion of potassium with increased urine output

Question 25

Summarise the pathophysiological changes associated with pyometra and RAISED AMYLASE AND LIPASE and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 25

These are not significant. Both are renally excreted and therefore increase in dehydration when renal excretion is compromised. The more specific test for pancreatitis (cPLI) is reassuringly normal

Question 26

Summarise the pathophysiological changes associated with pyometra and CHANGES IN LIVER ENZYMES and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 26

A number of complications may occur in patients with pyometra. Increased liver enzymes (secondary to sepsis/endotoxaemia or poor hepatic perfusion associated with hypovolaemia) are common but usually return to normal rapidly following removal of the uterus and restoration of fluid and electrolyte balance.

Question 27

Summarise the pathophysiological changes associated with pyometra and A NON-REGENERATIVE NORMOCHROMIC ANAEMIA and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 27

May also develop due to mild bone marrow suppression, blood loss at surgery and high volumes of fluid replacement therapy. Blood transfusion is rarely indicated, unless the packed cell volume (PCV) decreases below 20% and parameters such as HR, pulse

Question 28

Summarise the pathophysiological changes associated with pyometra and A LOW URINE SG and how these may affect the perioperative management of the case with respect to anaesthesia.

Answer 28

low urine SG would be more difficult to interpret because there are two possibilities: Endotoxaemia associated with E coli (pyometra) is having a reversible effect on the urine concentrating mechanism. This is one of the main reasons for polydipsia and polyuria in pyometra cases. In this case the azotaemia is still pre renal (due to dehydration) but the kidneys are unable to conserve water due to secondary effects of the endotoxaemia. This is reversible and therefore has no impact on a decision to operate.