Principles of therapeutics and anaesthesia in of the neonate and pregnant animal Flashcards
What is the effect of increased Progesterone & metabolites during pregnancy on physiology?
Effect:
- Gastric emptying slower.
- Reduced epidural anaesthetic needs because progesterone is a positive allosteric modulators of GABBa receptors (ionotrophic receptors that are ion gated)- inhibitory NT. GABBA is involved in nociception and central sensitisation. Top down modulation of pain
- Progesterone also causes engorgement of epidural vessel enlargement reducing spinal CSF spaces- anaesthetic requirement is lower.
- Progesterone is immunomodulator in the gingiva
- Reduce peripheral vascular resistance so CVP stays the same.
- Renal plasma flow and GFR increase by 60% so creatinine and BUN are lower. So if normal or high can indicate renal function
Complications of this:
- Predisposes to gingivitis.
- Feel pain less- but they will still have nocioceptive stimuli so do not scimp on analgesia but it does mean can reduce anaesthesia
Preventative Action
- Cannot prevent progesterone metabolites unless terminating pregnancy
- Avoid drugs with nephrotoxic effects e.g. aminoglycosides and NSAIDs.
What is the effect of Heart Rate increases, CO increases, Blood volume increases during pregnancy on physiology?
Effect:
- CO increases (so HR increases)
- 30-50% increase in CO
- 40% increase in blood volume
Complication:
- Decreased blood flow to fetus
Preventative Action:
- Blood pressure monitoring
- IV fluid pre, intra and post operative
What is the effect of Plasma volume increases during pregnancy on physiology?
Effect:
- Increases > than RBC mass
- Relative anaemia throughout pregnancy which gets worse with the number of foetuses carries
Complication:
- Haemodilution and a decrease in Hb concentration
Preventative Action
- Intake of supplemented folic acid and iron.
- Colloids > crystalloids for fluid expansion.
What is the effect, complication and preventative action of PCV, TP & Hb decrease during pregnancy on physiology?
Effect:
- Hb and PCV decrease- Hb decreases because plasma volume increases
Complication:
- Haemodilution and a decrease in Hb concentration
Preventative action:
- Fluids if PCV is low. If PCV is really low can give packed red cells or whole blood transfusion but make sure you type before.
What is the effect, complication and preventative action for delay in compensatory mechanisms during hypovolaemia because you want to maintain ABP and CVP (both increase in labour) during pregnancy on physiology?
Effect:
- Not responsive to drugs we give to manipulate ABP.
- Physiological responses are slower
- Monitor during c- section for hypotension because this will reduce foetal blood perfusion
Complication:
- Continued hypoperfusion even with standard treatment. Less responsive to vasopressor or chromotrophic drugs.
Preventative action:
- Prophylactic treatment and immediate and aggressive treatment
What is the effect, complication and preventative action for Minute volume increases during pregnancy on physiology?
Effect:
- O2 demand increases
Complications:
- Hypoxaemia can be made worse
- If apnoea occurs hypoxaemia occurs rapidly
Preventative action:
- Pre –oxygenate, denitrogenates lungs so reserve is increased
What is the effect, complication and preventative action for O2 consumption increases during pregnancy on physiology?
Effect:
- O2 demand increases
Complications:
- Hypoxaemia can be made worse
- If apnoea occurs hypoxaemia occurs rapidly
Preventative action:
- Pre –oxygenate, denitrogenates lungs so reserve is increased
What is the effect, complication and preventative action pH & PaO2 normal during pregnancy on physiology?
Effect:
- none
Complications
- Renal compensation prevents alkalosis (early pregnancy alkalosis and late pregnancy acidosis)- hyperventilation causes alkalosis. Too much bicarbonate, nociception stress and hyperthermia.
Preventative action
- Maintain blood pressure to the kidneys and place on fluids if required
What is the effect, complication and preventative action the PaCO2 decreasing during pregnancy on physiology?
Effect:
- due to increased MV
Complications
- Alkalosis occurs due to oxygen demand
Preventative action:
- Increase deadspace
- Decrease respiratory rate
- Decrease tidal volume
What is the effect, complication and preventative action the total lung and vital capacity being normal FRC decreasing (FRC= functional residual capacity)
during pregnancy on physiology?
Effect:
- Cranial displacement of the diaphragm reduced total lung volume and FRC.
- Closer to alveolar closing capacity, atelectasis and intermediate size occurs.
- Airway closure more likely
Complications
- Desaturation occurs rapidly when apnoea occurs.
- Induction with inhaled anaesthetics and changes in depth occurs rapidly
Preventative action:
- Give big breaths during surgery
What is the effect, complication and preventative action of Gastric emptying time being delayed during pregnancy on physiology?
Effect:
- Increase likelihood of stomach ingesta.
Complications
- Vomiting and aspiration pneumonia
Preventative action
- Rapid induction technique and protection of the airway- hold the head.
- Feed little and often
What is the effect, complication and preventative action of intragastric pressure increased during pregnancy on physiology?
Effect
- Foetus presses up against abdominal contents increasing pressure in the stomach
Complication
- More likely to vomit
Preventative Action
- Rapid induction technique and protection of the airway- hold the head.
- Feed little and often
What is the effect, complication and preventative action of Oesophageal sphincter tone decreasing during pregnancy on physiology?
Effect:
- Regurgitation increases
Complication:
- Increase chance of aspiration pneumonia
Preventative action:
- Extubate when laryngeal function has returned- wait till they swallow
What is the effect, complication and preventative action of Gastrin levels increasing during pregnancy on physiology?
Effect
- Low pH of gastric fluid
Complication
- Stomach ulcers and gastric reflux causing oesophagitis
Preventative action
- Omeprazole prophylactically
What is the effect, complication and preventative action of Gastric motility is decreased during pregnancy on physiology?
Effect
- Due to small bowel and gall bladder reduced function.
- Progesterone induced effects.
Complication:
- Sedative effects- progesterone has a sedative effect.
- Medications per os have longer time to effect
Preventative action:
- Reversed by delivery because you reverse the hormonal influence .
What is the effect, complication and preventative action of BUN & creatinine decreasing during pregnancy on physiology?
Effect:
- GFR & RBF (renal blood flow) increased
Complications:
- Renally excreted drugs are excreted quicker.
- Acid base regulation is altered- decrease in bicarbonate threshold.
- Intermittent glucosuria makes testing for DM hard.
Preventative action:
- Don’t let GFR decrease
What is the effect, complication and preventative action of Epidural and CSF volume decreasing during pregnancy on physiology?
Effect:
- Due to progestone causing engorgement of epidural vessels in the epidural space.
Complications:
- Local anaesthetic spreads further in pregnant animals epidural space due to reduction in space.
- Overdose with injectables is possible
- Greater pressure in the epidural space means anaesthetics travel further
Preventative action
- Reduce drugs
- Monitor anaesthetic depth
What is the effect, complication and preventative action of a Large gravid uterus during pregnancy on physiology?
Effect
- Causes reduced lower oesophageal sphincter tone Causes increased pressure in the stomach.
- Puts pressure on the vena cava when positioned for anaesthesia
Complications:
- Potential reduction in CO/perfusion
- Potential reduce BF to fetus
Preventative action:
- Tilt off midline
What does the fetal circulation look like and where does it come from and drain to?
Featal circulation
- from descending aorta into the umbilical arteries into placenta where gas exhange with mother
- From it goes into umbilical vein
- then to ductus venosus
- into inferior VC
- Into cranial VC into RA shunts to LA then LV then all starts again.
This circulation bypasses the lungs some blood passes into the liver
How does drug administration effect the fetal circulation?
- A fixed dose of drug rapidly exposes foetus to high [drug] briefly
- A CRI or administration of an inhalant results in continuous transfer of the drug and can build up in the fetus to a dangerous level
How to choose durgs for a C section and things to consider?
- Commonest reason to anaesthetise a pregnant animal is for Caesarean section
- Choose drugs with a short duration of action
- Choose drugs with specific antagonists (if poss)
- Use the lowest possible dose (parturients need less 30-60%)
- Provide oxygen and intubate if GA
- Use local anaesthetics if possible to reduce MAC & provide analgesia
- Monitor ABP, administer fluids
What are the advantages and concerns of Anticholinergics?
Advantages:
Reduce salivation & inhibit vagal tone
Concerns:
Glycopyrrolate superior to atropine
What are the advantages and concerns of Benzodiazepines?
Adv
Muscle relaxation, flumazenil available to reverse effects
Concerns
Foetal depression, therefore avoid as can make the new born animals floppy and unresponsive
What are the advantages and concerns of Alpha 2 agonists?
Adv
- Sedation
Concerns
- Do not use as fetal perfusion reduced
What are the advantages and concerns of Pure mu opioids?
Adv
- Analgesia, naloxone available to reverese it (1-2 drops sub lingual foetus)
Concerns
- Resp depression & bradycardia
What are the advantages and concerns of Partial agonist/atagonist opioids? e.g buprenorphine
Adv
Analgesia, less resp depression cf pure mu opioids
Concerns
takes 60 minutes for effect so you may have done the c-section and her be waking up before she has felt the effects
What are the advantages and concerns of Phenothiazines?
Adv
- Ok at low doses
Concerns
- Reduced ability to metabolise
What are the advantages and concerns of Local anaesthetics?
Adv
- Safe, effective, best for survival
Concerns
- Hypotension with epidurals
What are the advantages and concerns of Barbiturates?
Advantages
- Short acting, higher Apgar scores in humans
Concerns
- Increased puppy mortality & less vigour
What are the advantages and concerns of Propofol?
Advantages
- Short acting, wait min 10 mins, can use with fentanyl & lidocaine
Concerns
- Do not use repeated doses or CRI
What are the advantages and concerns of ketamine?
Advantages
- Short acting, better maternal CVS stability
Concern
- Need BZD so rarely used
What are the advantages and concerns of Alfaxalone?
Advantages:
- Short acting, rapid clearance, better APGAR scores cf prop
Concern:
- Sleepy kittens with Saffan?
What are the advantages and concerns of Etomidate?
Advantages
- Short acting, use with fentanyl?
Concerns
- Not commonly available
What are the advantages and concerns of NSAIDs?
Advantage
- Analgesia & anti-inflammatory
Concerns
- Platelet aggregation, transfer to milk?
Discuss equine c section and which drugs are commonly avoided and tolerated?
- The aforementioned physiological changes also apply to the mare
- NO EBM to support the claim that any anaesthesia drugs cause foetal loss or damage (maybe detomidine better than xylazine…??)
- Many of the same considerations apply re colic surgery to the parturient mare
- Acepromazine often avoided, barbiturates usually avoided, ketamine/alpha 2 (could the xylazine be better for foal) well tolerated. Guaifenesin ok, low dose BZD ok too (curiously though we avoid in small animals)
- Need oxygen source for foal
- NOTE : induction drug doses are similar in a parturient mare to a non pregnant mare, as we don’t for example give the ketamine to effect, we will always give 2mg/kg or more
What is the pregnant mare postion for a c section?
- The pregnant mare should be tilted off the midline for the C section
- Once the foal has been delivered she can be repositioned.
- This approach will reduce the pressure of the gravid uterus on the vena cava. Blood pressure monitoring essential.
Discuss bovine c section LA blocks?
- Line block
- Inverted L
- Proximal & distal paravertebral
- Lumbosacral (small rums)
How is ABP effected in c section surgery?
- Gravid uterus presses on descending aorta
- Drugs you use may see decrease in respiratory rate
- A little head up tilt on the table will reduce pressure on diaphragm
Total lung capacity and vital capacity are compromised by?
Weight of gravid uterus when patient on back and can cause airway collapse.
Give a slightly bigger than physiological breath to prevent alveoli units closing down and preventing atelectasis
