Considerations for Specific Conditions: Life Stage/Pathologies Flashcards
What are the different risks for the different trimesters of pregnancy?
1st - embryotoxicity
2nd - placental separation - can lead to blood loss for mum and decreased or cessation of oxygen delivery to the foetus. 3rd - major physiological changes
Describe the changes associated with the CVS during pregnancy
CO and Blood volume increase to meet placenta needs. Plasma volume increases proportionally more so that red cell mass so results in a dilution anaemia.
Albumin concetrations decrease by dilution. Leads to greater free fractions of drugs in bloodstream, risk of overdose.
Cardiac reserve decreases and decrease in SVR. Vasodilation contributes to hypotension. Large belly can put pressure on vessels e.g. vena cava. Positioning is key.
Describe the changes associated with the respiratory system during pregnancy
Increase in minute volume, o2 consumption and metabolic o2 reuirements.
Decrease in functional residual capacity (FRC)- volume of gas left in lungs at end of a normal breath. More likely to destaturate/become hypoxaemic.
Supplement o2 before and after GA due to reduced FRC and increased metabolic oxygen requirement.
Describe the changes associated with the GI system during pregnancy
Uterus puts pressure on stomach, alters its position, changing the angle where the oesophagus enters the stomach making sphincter incompetent.
Progesterone decreases the tone of the oesophageal sphincter and slows digestion, food is in the stomach for longer.
Animal is prone to regurge - head up induction, sternal, secure ETT cuffed.
Describe the changes associated with the renal system during pregnancy
Increased CO, increasing renal blood flow. Increasing Glomerular filtration rate (GFR) - therefore concentrations of urea and creatnine therefore decrease because of this dilution.
What are our aims/concerns in non-pregnancy related surgeries on pregnant patients?
- Maintain oxygenation (pre-o2 and supplemetn in recovery. Measure spo2)
-Maintain co2 - want to prevent changes in SVR and acidaemia - Maintain BP systolic >90mmHg
- Avoid teratogenic drugs(that cause developmental malformations.
- Avoid drugs which will initiate labour (e.g. xylazine is an alpha 2 that is a know ecbolic drug - avoid!)
In short, what are our aims during a caesarean GA?
- Maintain placental oxygen delivery and blood flow until foetus deliveered.
- Use short-acting drugs or ones that do no cross placental barrier, reducing drugs that pass to foetus.
What properties affect whether a drug will be bale to cross the placental barrier?
- thickness of the tissue
- ionisation
- lipid solubility
- foetal concentration
- maternal concentration
- foetal metabolism
What are the pros and cons of using pre-meds in caesareans?
Pros:
- pre-emptive analgesia
- reduce induction/volatile agents, therefore reduce CVS and R depression
- smooth GA and avoid responses to Sx
- Smoother recovery
Cons:
- Mum already exhausted . doesnt require sedation
- drugs risk transferring to foetus
- cause respiratory, CV depression and lower Apgar score
What does an Apgar score assess? How?
Assesses the viability of foetuses at birth. Scores 1-3 for each parameter.
Measures HR <180, 180-220. >220.
Resp Effort <6bpm not crying, Mild crying 6-15bpm, crying >15bpm.
Reflex irritability - absence, grimace, vigorous
Motility - Flaccid, some flexion, active motions
MM colour Cyanotic, pale, pink
Score 7-10 no distress, 4-6 mod distress, 0-3 severe distress.
What drug is recomended by WSAVA for emergency C-sections
Fentanyl 3-5ug/kg
One off dose of NSAID at end of surgery also paracetemol in dogs. Use of local anaesthetics.
How much of a dose of opioids will be transferred into the milk?
1-2%
What can pain in a new mum cause?
Uterine vasoconstricyion, reduced blood flow and milk production.
Describe the considerations when preparing a caesarian for GA?
- if normotensive, start on maintenance IVFT.
- Clip and prep as much conscious to reduce GA time, sternal and lateral.
- Pre-o2 to maintain placental blood oxygencation and dam’s reduced FRC.
- Head-up induction as regurge prone
- Short-acting titratable drugs for induction
Describe the considerations when maintaining a caesarian under GA?
- intubated and on a low resistance breathing system.
- Cuffed ETT incase of regurge, use of IPPV.
- Low solubility volatile agents to ensure speedy recovery. MAC dcreased in pregnancy so may need less volatile agent percentage.
-Once in dorsal, uterus puts pressure on diaphragm, reducing FRC and ventilation and impeding venous return. Tilt animal slightly to left.
Describe the monitoring when doing a caesarian GA? and why is it important
Capnograph - important due to possibility of hypoventilation due to reduced tidal volume from uterus pressing on diaphragm.
Pulse ox - monitor close as reduced FRC, and to ensure good placental oxygenation.
BP - BP needs to be maintained to keep placental perfusion but can be reduced because of positioning and venous compression.
ECG - no specific risks
What is the difference between a paediatric patient and a neonate?
< 4 weeks old is neonate
4-12 weeks old is paediatric
Over 12 weeks, most things are well-developed so dont need to worry too much.
Describe the differences in a paediatric/ Neonatal patient’s Respiratory physiology
Limited reserve capacity (less FRC).
2-3 times increase in tissue o2 demand.
Higher RR.
Narrower trachea. Larger tongue proportionally than adults.
Neonatal animals have super compliant lungs so are pulled right in by chest wall movements so not much FRC.
Describe the differences in a paediatric/ Neonatal patient’s CVS
A foetus’ blood doesnt need to go through the lungs to pick up o2 as its supplied by maternal side. So instead it shunts blood from R to L heart without passing the lungs. By: The foramen ovale (which moves blood from the R atrium to the L atrium) and the ductus arteriosus (which moves blood from the pulmonary artery to the aorta).
When the neonatal animal takes its 1st breath, the oxygen casues vasdilation in the pulmonary vessels and makes PVR less than SVR causing blood to move from the R atrium into the pulmonary artery and the two now useless gaps in the heart close over in the first few days of life.
So if we have to GA a neonate that is less than a few days old we have to be careful not to increase PVR as it will revert to shunting blood except this time the mother doesnt oxygenate it and the neonate will become hypoxic.
Neonates are dependant on their HR to maintain CO (they cannot alter SV) so avoid bradycardia e.g. use of fentanyl, medetomidine and dexmedetomidine.
Describe the differences in a paediatric/ Neonatal patient’s hepatic physiology
Slower to metabolise drugs due to immature microsomal enzyme system until they are 8-12 weeks old.
Glycogen storage is low and not good at making new glucose so often hypoglycaemic. Tend to also have lower albumin levels.
Describe the differences in a paediatric/ Neonatal patient’s renal physiology
Neonates and paediatric patients total body water and extracellular fluid volume are higher so water requirements are higher.
Renal funciton is reduced so have poor ability to concentrate urine, poor ability to excrete a water load and poor acid/base regulation up until 6-8 weeks.
Describe the differences in a paediatric/ Neonatal patient’s thermoregulation
Born with little sc fat.
Poor thermoregulatory ability
Poor vasomotor tone
Super prone to hypothermia.
Worsened by pre-op starvation as metabolism generates heat.
High surface area to volume ratio so lose more heat.
Describe the differences in a paediatric/ Neonatal patient’s ability to deal with drugs
Seem resisitant to non-depolarising NMBAs but also have prolonged action. Start will small dose and titrate.
Renal and hepatic clearance of drugs is prolonged -base re-administration on pain scoring.
Due to higher extracellular water volume, water-soluble drugs such as ketamine may require higher doses.
Low albumin concentrations more pront to over dose.
Less sc fat for redistribution of drugs.
What specific considerations are there for GA’ing neonates/paediatric patients in addition to the underdevelopment of body systems?
Avoid prolonged starvation- promotes hypothermia and prone to hypoglycaemia.
<8 weeks or 2kgs starve for 1-2 hours.
Check for hypoglycaemia before induction.
Measure temperature and prevent hypothermia as best can.
Accurate weight and appropriate sized equipment.
How can we assess pain in a paediatric puppy or kitten?
- anthropomorphic approach
- pain assesmments designed for adults
- respose to palpation
- check for diminshed response of noted behaviour after administrtion of analgesic.
What considerations are there for selecting a pre-med for a pediatric patient?
- is pre-med necessary? Will reduce volumes of other drugs needed and pre-emptive analgesia.
- short acting drugs as clearance will be slower
- avoid drugs that cause bradycardia
-pthidine is a good choice as short acting full mu opoid. Can also use benzodiazepines to produce some sedation.
What considerations are there for inducing anaesthesia in a paediatric patient?
- IV access and pre-oxygenate (reduced FRC, increased MOD, intubation can be difficult due to large tongue and narrow trachea).
- Cut down ETTs so not excessive lengths.
What considerations are there for maintaining anaesthesia in a paediatric patient?
Inhalational is preferred to IV as less injectable drug to be metabolised.
A low solubility volatile agent such as sevo/iso will allow fast recovery.
Circuit - low drag, low resistance, low dead space. Chest wall is more compliant so will be less compression on venous return if IPPV needed.
IVFT indicated. Stiff myocardium less responsive to fluid loading. Monitor blood loss closely.
What considerations are there for recovery from anaesthesia in a paediatric patient?
- later extubation due to underdevelopment of gag reflex
- o2 supplementation esp if shivering
- food offered asap (check glucose intermittently under GA)
- Temperature monitored + warming
- IVFT until good intake
- Pain assessments.
The liver is a site of protein production, what can happen if this production is decreased? i.e. hypoproteinaemia
- Ascites (fluid in abdomen) which leads to compromised ventilation and reduced FRC.
- Peripheral Oedema (makes it hard to place IV)
- Lowered plasma oncotic pressure (this is a form of osmotic pressure induced by proteins, notably albumin, in the blood vessles plasma that draws water in from the interstitial space to the intravascular space).
- Affects drug - binding
What are the main functions of the liver
- Protein production
- Glucose homeostasis
- Erythopoietin production (hormone that stimulates RBC production)
- Involved in synthesis of blood coagulation factors
- Filtering out bacteria from the bloodstream.
- Biotransformation of drugs
If the liver is damaged what consequences may we see in a patient?
- lowered protein production - ascites, oedema, affects drug binding.
- Hypoglycaemia (then causes systemic neuronal damage and muscle weakness).
- Anaemia - due to blood loss due to clotting abbormalities, interferes with o2 carrying capacity and our ability to monitor mm colour (also jaundice does this).
- Hypocalcaemia secondary to reduced albumin (can cause muscle wekness - may need IPPV)
- Toxin build up and bacteraemia. Ammonia build up as liver isnt able to process it properly (AKA hepatic encephalopathy) - this affects the brain causing dull, depressed and seizures. Need thorough skin prep.
- Enlarged liver (hepatomegaly) can compress diaphragm and compromise ventilation and oxygenation (prone to hypoxia and hypercapnia).
- Some patients will concurrently get GI sigsns - v+, d+ etc.
- delayed recovery due to slower metabolism of drugs. Pain scoring instead of interval dosing.
What considerations are there for anaesthesia of a liver patient?
- liver already has poor oxygen delivery and perfusion - GA will make this worse.
- We aim for these 2 things: Providing adequate oxygenation and maintaining BP.
Propofol increases hepatic blood flow probably through significant vasodilation.
-Should use sgort-acting drugs with alternative route of metabolism/can be antagonised.
- Avoid benzodiazepines as have been linked to hepatic encephalopathy.
- Blood loss a worry in surgical repair of a shunt.
- If a shunt is ligated you may see drop in CVP as now have same volume going round the long way. This may compromise intestinal perfusion.
In recovery, we may see portal hypertension which can cause loss of blood circulation to abdominal organs. Animals may show signs of ascites, v+, d+, depression or respiratory distress. May even see seizures.
