Pharmacology, devices, perioperative care and nutrition Flashcards
Smoking cessation
At least 3 weeks before surgery
Warfarin
Vitamin K antagonist
- Inhibits factors II, VII, IX, X
Reversal
- Vit K
- Prothrombinex 25u/kg
- FFP
- Time
- 3-5/7
Dabigatran
Direct Thrombin inhibitor
Half life 12-14 hours in normal renal function
Reversal
- Praxbind 5g in 2 doses
- Half life 47minutes
- but biphasic decay so some efficacy for 10 hours
- Half life 47minutes
Rivaroxiban
Direct factor Xa inhibitor
Half life 5-9 hours in normal renal function
- May be longer in older individuals (~12 hours)
Reversal
- Recombinant factor 10a
- Dialysis won’t work (high protein binding)
Pre operative cessation
- Recommend 48-72 hours cessation (the longer for high risk surgery)
Aspirin
Irreversible non selective COX inhibitor
Life of a platelet is 7 days
Reversal- Platelet transfusion (but never needed)
Clopidogrel
Antiplatelet agent
Irreversible inhibitor of P2Y12
Reversal: none specific
Ticagrelor
Antiplatelet agent
Reversible inhibitor of P2Y12
Reversal:
- specific antidote created, not available
- High protein binding in plasma
Unfractionated heparin
Activates antithrombin III
- Antithrombin III then inactivates thrombin and factor Xa
Half life- 1-2 hours
Reversal- Protamine
- 1mg per 100units received in the past 4 hours
Low molecular weight heparins
(Enoxaparin)
Antithromin III activator
higher ratio of inactivation of factor Xa (over thrombin) compared with unfractionated heparin
Partially reversible with protamine (the Xa effect is not reversed)
Half life (Enoxaparin)- 4.5 hours
Bowel prep before colorectal surgery
There is no strong evidence to support bowel prep in major colorectal surgery
additional considerations:
- Ease of laparoscopic approach
- loop ileostomy and leaving a laden colon
Thromboprophylaxis very high risk vs high risk surgeries
What is the recommended duration for anticoagulant thromboprophylaxis for each group
Very High- 28-35 days
- Hip or knee arthroplasty
- Major trauma
High- 5-10 days
- Major surgery >40 years
- Major surgery defined as any surgery >45 minutes OR any intrabdominal surgery
VTE in pregnancy and puerparium
Increased risk
Continue VTE for 4/52
Recommendations on the use of oestrogen preparations in the perioperative period
These increase the VTE risk
- OCP should be stopped pre op
- alternative methods of contraception should be advised
- HRT should be stopped for 6/52 at least
NSAIDS in anastomoses
Multiple studies with conflicting results
Effect is small if at all present
Effect on pain is also probably minimal
“my approach is a single dose of long acting NSAID given intraoperativey and then discontinued”
Post op NG tubes
Remove in theatre all but those for oesophageal surgery
Assessing perioperative risk:
Severity of surgery
NICE surgical severity grading
Grade 1
- Endoscopy
- Vasectomy
- dental
- Skin
Grade 2
- Heamorroidectomy
- Varicose veins
- Adenoidectomy
- Reduction of dislocated joint
Grade 3
- Amputation
- Mastectomy
- thyroidectomy
- Prostatectomy
Grade 4
- Colectomy
- Gastrectomy
- Renal transplant
- Hip replacement
Assessing perioperative risk:
NELA calculator
NELA calculator
- Age
- ASA
- Gender
- Cardiac
- Respiratory
- ECG
- SBP
- Pulse
- WCC
- Urea
- Creat
- Sodium
- Potassium
- GCS
- Operation type (major vs minor)
- Number of procedures
- anticipated blood loss
- peritoneal contamination
- malignancy
- Urgency
Assessing perioperative risk
what are the components of the possum score
Possum score
- Age
- Cardiac
- Respiratory
- ECG
- SBP
- Pulse
- Hb
- WCC
- Urea
- Creatinine
- Sodium
- Potassium
- GCS
- Operation type (minor, moderate, major, complex)
- Number of procedures
- EBL
- Peritoneal contamination
- Malignancy
- Urgency
Assessing perioperative risk
ASA
Initially five point system (later revised to six)
- Normal healthy patient
- Mild systemic illness
- Severe systemic illness
- Severe systemic illness that is a constant threat to life
- Moribund patient not expected to survive without the operation
- Brain dead, pertinent only in organ harvest
CPEX testing
Is the gold standard measure of cardiorespiratory function
Cardiopulmonary exercise testing (CPET) is a dynamic, non-invasive assessment of the cardiopulmonary system at rest and during exercise using a closed respiratory circuit, cardiac monitoring and a variable resistance exercycle
Outcome measures of Anaerobic threshhold, peak O2 consumtion and ventillatory efficiency for CO2 are associated with poor perioperative outcomes
- An anaerobic threshold (AT) of <11 oxygen.ml/min/kg is associated with an increased risk of perioperative mortality (18% vs <1%)
- “8 is shithouse, 10 is borderline”
Assessing frailty
Edminton frail scale
- Cognition
- Hospitalisation
- independance
- support
- meds
- nutrition
- mood
- continence
- performance of “stand up, walk three meters, turn around and come and sit back down”
Goal directed therapy
A principle of balanced resuscitation
Aim is to achieve adequate tissue perfusion without fluid overload of the extravascular compartment
- Basic parameters are restoration of normal blood pressure, pulse, mentation and urine output.
- these may not be possible to achieve so surrogate markers of tissue perfusion can be used
- Echo for estimation of central volume
- Base deficit
- Lactic acid consumes base creating a base deficit
- Lactate level
- Central venous SPO2
- these may not be possible to achieve so surrogate markers of tissue perfusion can be used
Trauma metabolic phases
Ebb
- Decreased resting energy expenditure
- Increased glycogenolysis
- Increased Gluconeogenesis
Flow
- Increased resting energy expenditure
- pyrexia
- increased muscle catabolism and wasting, loss of body nitrogen
- increased fat breakdown and decreased fat synthesis
- increased gluconeogenesis and impairment of glucose tolerance
What effects does sepsis have on the metabolism of protein, carbohydrate and lipid
Protein: high skeletal muscle breakdown and nitrogen loss
Carbohydrate: hyperglycaemia from increased gluconeogenesis and glycogenolysis
Lipid: decreased peripheral uptake causes hypertriglyceridaemia
Hypoglycaemia in sepsis
Conveys very poor prognosis, usually associated with mortality
Sepsis disrupts the inner membrane of hepatocyte mitochondria
- resultant marked decrease in aerobic metabolism of carbohydrate and fatty acids
- metabolism relies on anaerobic glucose metabolism.
- hypoglycaemia results from loss of glycogen reserves without adequate gluconeogenesis commencing- a late sign of hepatic dysfunction
Protein RDI
0.8g/kg/day
What are the three most improtant “non essential” amino acids in sepsis
Alanine
Glutamate
Aspartate
Metabolic energy by substrate
Fat- 39kJ/g
Glucose- 17.1kJ/g
Protein- 17.7kJ/g
Alcohol- 29.7 kJ/g
kcal per kJ conversion
- 2 kcal per kJ
- 24 kJ per kcal
What is the baseline resting metabolic expenditure?
what is the goal nutrition rate in critical illness
25-30kcal/kg/day
105-125kJ/kg/day
This is the goal rate of nutrition in critically unwell patients but should not be given in the first week as it may worsen outcomes.
8-10kcal/kg/day (34-42kJ/kg/day) is used for initial feeding in critically unwell patients
Additional metabolic energy requirements in disease states
Nutritional assessment
Historically divided into:
- Anthropometric
- BMI
- sub cut. fat thickness
- bioelectrical impedance
- Biochemical
- albumin
- urinary nitrogen losses
- Function
- immune competence
- low WCC
- muscle function
- grip strength
- immune competence
All combined maybe of some use in assessing perioperative risk but not reliable for nutrition assessment.
The MUST score is endorsed by the NHS for routine use in all hospital admissions
Refeeding syndrome
A syndrome of fluid and electrolyte shifts in refeeding, potentially fatal
Starvation depletes the normal concentration gradients across membranes
When energy is provided massive electrolyte shifts may occur
Most notably Potassium, phosphate, magnesium
What vitamin is crucial to provide prior to refeeding and why
Thiamine
Thiamine is an essential cofactor in oxydative phosphorylation of glucose, without thiamine glucose is metabolised to lactic acid
Wernicke-Korsakoff syndrome may occur if not replete before refeeding
Thymine vs Thiamine
Thymine is a DNA base.
Thiamine is a B vitamin (B1)
Effects on the intestine from lack of enteral feeding
Loss of height of vili
Loss of cellular proliferation
Mucosal atrophy
Translocation of bacteria and toxins
Lack of hormonal stimulation
Elemental diet
Used in patients with out normal capacity of enzymatic digestion
- short gut
- pancreatic insufficiency
Tranexamic acid
Synthetic lysine analogue
Antifibrinolytic
Apache II score
An ICU severity-of-disease classification system (Knaus et al., 1985)
Applied within 24 hours of admission of a patient to an intensive care unit (ICU): an integer score from 0 to 71
higher scores correspond to more severe disease and higher mortality
12 physiological parameters
- AaDO2 or PaO2 (depending on FiO2)
- Temperature (rectal)
- Mean arterial pressure
- pH arterial
- Heart rate
- Respiratory rate
- Sodium (serum)
- Potassium (serum)
- Creatinine
- Hematocrit
- White blood cell count
- Glasgow Coma Scale
Perioperative optimisation and specific considerations in cirrhosis
Local expertise
- Anaesthetic
- ICU
- Surgical
- Nursing
Varices
- Pre operative decompression with shunting
Transplantation
- Rescue transplantation should be discussed if MELD >15 in case decompensation occurs
Nutrition
Steps in a management plan for malignancy
Preoperative
- Complete assessment
- Stage
- Nutrition
- Fitness
- MDT
- Optimise
- Refer to other specialists
Operative
Post operative
- Psychosocial support
- Follow up
Clindamycin
Lincosamide antibiotic
Reversibly binds to 50S ribosomal subunits preventing peptide bond formation thus inhibiting bacterial protein synthesis
Important actions;
- Bacteriostatic or bacteriocidal depending on organism and concentration
- Suppresses toxin production
- Decreases penicillin binding protein production
- thereby increasing the ratio of beta lactam antibiotic to receptor
Important negatives
- Relatively high rates of C.diff
Suture choice:
Elective laparotomy, fascial closure
2-0 PDS on a CT-2 needle
Suture choice:
Handsewn bowel anastomosis
3-0 PDS on RB-1 or SH-2 needle
NTLC staple height:
Blue
Narrowest
1.5mm
NTLC staple height:
Gold
Medium:
1.8mm
NTLC staple height:
Green
Widest
2.0mm
Choice of stapler device:
Ileotransverse anastomosis
Ethicon NTLC 75 linear cutting:
Blue or Gold firing depending on tissue thickness
Ethicon TX60 linear non cutting:
Blue
Stapler choice: Division of rectum
Ethicon Contour.
Green load
Choice of stapler:
Stapled colorectal anastomosis
Ethicon ECS 29
(also available in 21,25,33mm)
Tachyphylaxis
Rapidly diminishing response to successive doses of a medication
- e.g somatostatin analogues (SSA) in carcinoid syndrome
What is PRRT
PRRT is the use of radiolabeled somatostatin analogues for the treatment of neuroendocrine tumours
- 2 agents are available, none in NZ
- Yttrium- 90 Dotatoc
- Lutetium-177 Dotatate
- Lutetium is FDA approved in the USA
- Several trials have shown survival advantage
- Continued use of octreotide before, during and after seems to be a standard part of that treatment.
Susceptibility is determided by somatostatin based imaging (PET or scintigraphy)
Serious side effects of antithyroid medications
Aplastic anaemia
Agranulocytosis
What antithyroid medication is used in pregnancy, why not the other one
Propylthiouracil is used in pregnancy
Carbimazole crosses the placenta and causes cretinism
How does carbimazole work
Carbimazole is converted to methimazole
Methimazole inhibits thyroid peroxidase
- prevents iodination of, and tyrosine coupling to, thyroglobulin
How should a patient with a genetic predisposition to cancer be followed up if there are no clear surveillance recommendations
Regular follow up with a primary care physician with an interest in genetic disorders and a low threshold for investigation of symptoms where they arise
How is weight adjusted for BMI in patients for nutritional goals of enteral and parenteral nutrition
BMI 18.5-30 should use current weight.
in obesity weight should be calculated as Ideal Body Weight (IBW) + 0.4x excess body weight
What is the role and rationale for protein provision in enteral and parenteral nutrition in critical illness
There is no evidence that early provision of protein improves outcomes.
Protein is provided in the hope that it may prevent muscle catabolism
carbohydrate is the dominant energy source in critical illness
- fat metabolism is impaired
How might haemostatic agents be grouped
what are examples of each
Passive Topical
- oxidised regenerated cellulose based
- SurgiCel
- SurgiCel fibrillar
- gelatin based
- Gelfoam
Active topical
- thrombin impregnated gelatin
- Floseal
- fibrin and thrombin sealants
- Tisseel
Systemic agents
- antifibrinolytic
- tranexamic acid
- activation of extrinsic pathway
- Novoseven (recombinant activated factor VII)
- use only in trials or in established factor VII deficiency
- possible use for reversal of rivaroxiban/apixaban
- use only in trials or in established factor VII deficiency
- Novoseven (recombinant activated factor VII)
Floseal
Gelatin matrix with thrombin impregnated
active topical haemostatic agent
mixed and prepared in the operating room
Tisseel
Active topical haemostatic sealant agent
pooled human plasma compound, stored frozen
contains thrombin, fibrin, antifibrinolytic agents, factor XIII
SurgicCel
passive topical haemostatic gauze
Oxidised regenerated cellulose product
promotes activation of the bodys normal coagulation cascade and a site for platelet adherence
SurgiCel Fibrillar
passive topical haemostatic fleece
oxidised regenerated cellulose product
promotes activation of the bodys normal coagulation cascade and a site for platelet adherence
PerClot
Topical passive haemostatic powder
absorbent plant starch
activation and concentration of platelets and coagulation factors
Bioglue
Two component surgical adhesive
Purified bovine serum albumin and glutaraldehyde
Basics of radiation safety
The portable x-ray machine is comprised of 2 components
- the columnator
- generates the x-rays
- the image intensifier
- receives the image
- patient should be positioned as close to the intensifier as possible
the dose of radiation received is subject to the inverse square law
- intensity = 1/distance2
- this applies to the patient and staff
As an operator
- always ensure PPE
- ensure all staff do the same
- wear a dosimeter
- wear x-ray eye protection
late complications of bariatric surgery
Anaemia
- B12 defiency due to no intrinsic factor
- Iron defiency due to high pH
Osteoporosis
- bypass of duodenum causes loss of calcium and vitamin D absorption
Weight loss
- inadequate weight gain and maintenance
Fogarty catheter sizes
The size of a fogarty catheter is measured by the inflated balloon in the french system
- in the range of these catheters the inflated balloon size in mm is approximately twice the french size
