Physiology in Anaesthesia: Part 3 Flashcards
Aetiological factors in the development of retinopathy of prematurity
- prematurity
- hyperoxia
- hypocarbia
- vitamin E deficiency
- acidaemia
Preferred trimester for non-obstetric surgery in obstetric patients
second
What factors cause the increased in maternal intravascular fluid volume
- increased production of renin, angiotensin, and aldosterone
- promotion of sodium absorption and water retention
- progesterone circulation
Haematological changes in maternity
- increased intravascular fluid volume
- relative reduction in plasma protein concentration
- physiologic anaemia due to greater increase in plasma than RBC
- mild thrombocytopaenia
- mild leukocytosis
- increased fibrinogen and factor 7
- decreased factors 6, 8, and antithrombin 3
- decreased PT and PTT (20%)
What accounts for the large increase in cardiac output immediately after delivery
- autotransfusion after delivery
- reduced vascular capacitance from loss of placenta
- decreased lower extremity venous pressure from release of aortocaval compression
Do the following increase, decrease, or stay the same in pregnancy:
1. systemic blood pressure
2. central venous pressure
3. pulmonary capillary wedge pressure
4. venous capacitance
- decrease
- stay the same
- stay the same
- increase
Signs of aortocaval compression
nausea, vomiting
diaphoresis
dizziness
Cardiac auscultation in pregnancy
S1: accentuated, increased splitting
S3: common
S4: minority
EJS: 2/6
Acid-base changes in pregnancy
- PaCO2 reduced to 30mmHg
- Mild increase in arterial pH
- HCO3 reduced to 20-21 (increased renal excretion)
Lung volume changes in pregnancy
- FRC reduced 20%
- Equal reductions in RV and ERV
- Closing capacity unchanged
- Vital capacity not significantly changed
Reasons for increased risk of aspiration in pregnancy
- upward movement of oesophageal sphincter
- reduced oesophageal sphincter tone
- gastrin secreted by placenta stimulates gastric acid secretion
- gastric emptying unchanged unless in labour
- increased residual gastric volume
Why do pregnant women require smaller volumes of local anaesthetic for neuraxial blockade
- decreased size of epidural space
- decreased volume of CSF in subarachnoid space
- engorgement of epidural veins
- hormonal changes
Causes of decreased uterine perfusion pressure
- maternal hypotension
- hypovolaemia
- aortocaval compression
- anaesthesia
- increased uterine pressure
- hypocapnoea
- valsalva
- endogenous catecholamines, exogenous vasopressors
Why is foetal haemoglobin left shifted
HbF does not interact with 2,3-DPG
GA at which FHR monitoring is acceptable
25 weeks
Molecular weight below which drugs diffuse through placenta to foetus
1000 Daltons
Rate of diffusion of drugs to foetus depends on:
- maternal-foetal concentration gradients
- maternal protein binding
- molecular weight of drug
- lipid solubility
- degree of ionisation
What contributes to increased in size of the elderly heart
fibrosis and endothelial damage
lead to increased arterial stiffness
and decreased nitric-oxide induced vasodilation;
thus afterload is increased.
This causes concentric left ventricular hypertrophy.
Diseases in elderly associated with diastolic dysfunction
- systemic hypertension
- coronary artery disease
- cardiomyopathy
- aortic stenosis
- atrial fibrillation
- diabetes
- chronic kidney disease
In elderly, the following values are (increased/unchanged/decreased) compared to young adults:
1. systolic blood pressure
2. diastolic blood pressure
3. pulse pressure
4. left ventricular afterload
- increased
- decreased
- increased
- increased
What is age-related endothelial dysfunction
In the elderly, a decreased in the ability of the endothelium to dilate or contract blood vessels in response to physiologic and pharmacologic stimuli.
Changes to the heart’s conduction system in the elderly
- decreased proportion of pacemaker cells
- conductive tissue becomes infiltrated with fibrous and fatty tissue
Intrinsic ageing factors that influence the respiratory system
- decreased bronchiolar calibre
- decreased alveolar surface area
- increased lung collagen
- decreased lung elastin
- kyphoscoliosis
- increased thoracic cage rigidity
- decreased diaphragmatic strength
Extrinsic factors affecting the elderly lung
- pollution
- smoking
- general deconditioning
- coexisting disease
Functional consequences of respiratory ageing
- decreased lung elastic recoil
- increased lung compliance
- decreased oxygen diffusion capacity
- premature airway closure
- VQ mismatch
- increased A-a gradient - small airway closure and gas trapping
- decreased expiratory flow rates
What happens to lung volumes in the elderly (increase/decrease/no change)
Vital Capacity: decrease
Residual Volume: increase
Total lung capacity: no change
FRC: increased
Closing capacity: increased
How does smoking affect upper airway reflexes
- depletion of neuropeptide of airway sensory nerves
- inhibition of C-fibre transmission in the lower respiratory tract
What are morbidities associated with sleep disordered breathing
- systemic hypertension
- pulmonary hypertension
- dysrhythmias
- myocardial infarction
- stroke
- sudden death
- car accidents
- post-operative delirium
How is the functional capacity of the liver affected in old age
- protein synthesis diminished
- a1-acid glycoprotein increased
- plasma cholinesterase diminished
Factors associated with reduced resting core temperatures in the elderly
- neurologic disease
- diabetes
- low body weight
- lack of self-sufficiency
- consumption of less than two meals per day
- smoking
- alcohol consumption
Factors that predispose to GORD in the elderly
- sliding hiatal hernias
- shortened intra-abdominal segment of lower oesophageal sphincter
3.impaired clearance of refluxed acid - medications that reduce lower oesophageal sphincter pressure
- decreased oesophageal peristalsis
Medication that reduces lower oesophageal tone
anticholinergics
antidepressants
nitrates
calcium channel blockers
theophylline
Why do the elderly lose lean muscle mass
- decreased motor neurone innervation
- decreased physical activity
- decreased caloric intake
- endocrine shift towards catabolism
- decreased androgen production
- decreased protein consumption and synthesis
- raised inflammatory mediators
Perioperative consequences of having reduced lean muscle mass
- impaired mobilisation
- reduced cough efficiency
- reduced shivering thermogenesis
- altered drug disposition
- reduced functional reserve
- prolonged recovery and hospitalisation
Define post-operative delirium
Syndrome of fluctuating consciousness,
inattention, memory impairment, and perceptual abnormalities,
that typically occurs after a lucid interval of 1-3 days
after emergence from anaesthesia.
How is morphine metabolised
glucuronidation
What are the metabolites of morphine
morphine-3-glucuronide
morphine-6-glucuronide
