Peri-operative care Flashcards
Definition of acute respiratory distress syndrome
Acute lung injury characterised by severe hypoxaemia in the absence of cardiogenic cause.
Criteria:
Acute onset within 7 days
PaO2:FiO2 ratio <300mmHg
Bilateral infiltrates on CXR
Alveolar oedema not explained by fluid overload or cardiogenic cause
Causes of acute respiratory distress syndrome
Direct causes: pneumonia, smoke, aspiration, fat embolus
Indirect causes: sepsis, acute pancreatitis, polytrauma
Pathophysiology of acute respiratory distress syndrome
Injury to the lung -> inflam -> breakdown of alveolar-capillary barrier -> fluid infiltration and pulm oedema -> impaired ventilation and gas exchange -> hypoxia.
Damage to type II alveolar cells -> reduced surfactant production -> reduced lung compliance which worsens ventilation
Clinical features of acute respiratory distress syndrome
Worsening dyspnoea, hypoxia, tachycardia, tachypnoea, inspiratory crackles on auscultation
Investigations for acute respiratory distress syndrome
Routine bloods (FBC, U+E, amylase, CRP)
Blood cultures
ABG
CXR (diffuse bilateral infiltrates similar to that of pulm oedema)
Management of acute respiratory distress syndrome
Supportive treatment with ventilation (most require ITU support, CPAP, etc)
Focused treatment of underlying cause
Circulatory support (inotropes, vasodilators)
What is post-op atelectasis ?
Partial collapse of the small airways. Typically occurs <24hrs post-op
Pathophysiology of atelectasis
Combination of airway compression, alveolar gas resorption intra-operatively and impairment of surfactant production
Atelectasis causes reduced airway expansion and subsequent accumulation of pulmonary secretions -> predisposes the patient to hypoxia, reduced lung compliance, pulm infection and acute respiratory failure
Risk factors for atelactisis
Age, smoking, general anaesthesia, duration of surgery, pre-existing lung/neuromuscular disease, porlonged bed rest, poor post-op pain control (= shallow breathing)
Clinical features of atelectasis
Varying degree of respiratory compromise
Tachypnoea
Reduced O2 sats
Investigations for atelectasis
Typically a clinical diagnosis (= new resp symptoms <24hrs post-op)
CXR may reveal small areas of airway collapse
CT may be done is CXR unhelpful (rare)
Management and prevention of atelectasis
Deep breathing exercises
Chest physiotherapy
Analgesia
Prevention = chest physiotherapy post-op
Post-op pneumonia (hospital acquired pnuemonia) aetiology
reduced mobility/bedridden -> inability to fully ventilate lungs -> accumulation of secretions -> infection
Hospital environment flora different to what patient is used to (E coli, S aureus, S pneumonia, Pseudomonas)
Surgical patients often have multiple comorbidities, compromising their immune system
Patients may require ITU intubation and ventilation which is a major risk factor
Risk factors for post-op pneumonia
Age, smoking, known respiratory disease or recent viral illness, poor mobility, mechanical ventilation, immunosuppression, underlying comorbidities
Differential diagnoses for pneumonia
Acute heart failure, acute coronary syndrome, PE, Asthma/COPD exacerbation, pleural effusion, empyema, anxiety
Investigations for pneumonia
Routine bloods (FBC, U+E, CRP), blood cultures, ABG (if sats are very low), sputum sample if cough is productive, CXR (consolidation with air bronchograms)
Management of post-op pneumonia
O2 (aim for 94%+, or 88-92% if CO2 retainers)
Manage any sepsis
Empirical antibiotics until sensitivities return (first-line co-amoxiclav or doxycycline, if severe/septic use tazocin, if MRSA use vancomycin)
Complications of pneumonia
Pleural effusion
Empyema
Respiratory failure
Sepsis
Risk factors for aspiration pneumonia in surgical patients
reduced GCS, iatrogenic interventions (eg. NG misplacement), prolonged vomiting without NG, underlying neuro condition, oesophageal stricture/fistula, post-abdo surgery
Virchow’s triad
Abnormality of blood flow (stasis) - immobility
Abnormality of blood components (hypercoagulability) - smoking, sepsis, malignancy, inherited disorder
Abnormality of vessel wall (endothelial damage) - atheroma, inflammation, direct trauma
Risk factors of VTE
Age, previous VTE, smoking, pregnancy, current active malignancy, COCP/HRT, immobility >3 days, recent surgery, inherited thrombophilia (factor V leiden, antiphospholipid syndrome), obesity
Management of VTE
DOAC first line - Factor Xa inhibitors (apixaban, rivaroxaban) or direct thrombin inhibitors (dabigatran). Dabigatran needs 5 days of LMWH before starting DOAC.
Some patients require warfarin instead of DOAC (needs LMWH until INR target is reached)
LMWH alone is recommended in cancer-associated VTE
Anticoagulation required for 3 months if provoked VTE. May require lifelong if proximal/persistent/high risk
Mechanical vs pharmacological thromboprophylaxis
Mechanical: Intermittent pneumatic compression (used in theatre), TED stockings (contraindicated in peripheral arterial disease, peripheral oedema, local skin conditions)
Pharmacological: LMWH (if eGFR<30 consider unfractionated heparin)
DVT clinical features
unilateral leg pain, swelling, erythema, warmth
Low grade pyrexia
Pitting oedema
Tenderness or prominent superficial veins
65% asymptomatic
Investigations for DVT
DVT Well’s score should be calculated
Score <= 1: DVT unlikely. Do D-Dimer to exclude.
Score >1: DVT likely. Do USS doppler to confirm.
Well’s Score
Clinical signs Heart rate >100 Recent surgery/immobilisation Previous PE/DVT Haemoptysis Malignancy Alternative diagnosis less likely than PE/DVT
PE clinical features
Sudden onset dyspnoea Pleuritic chest pain Cough Haemoptysis (rare) Tachycardia Tachypnoea Pyrexia Raised JVP (rare) Pleural rub/ pleural effusion (rare) Remember to examine for DVT
Investigations for PE
Calculate PE Well’s score
Score <=4: PE unlikely, D-dimer to exclude
Score >4: PE likely, CTPA to confirm (V/Q scan if poor renal function)
CXR to exclude other pathology
ECG to exclude MI
ECG changes for PE
RBBB RV strain (Inverted T waves V1-V4) Rare S1Q3T3 (deep S wave lead 1, pathological Q wave lead 3, inverted T wave lead 3)
Surgical causes of hyperkalaemia
Post-op AKI
Repeated blood transfusions
Drugs (K+ sparing diuretics, ACE-I, ARB), excessive K+ treatment, dehydration, pre-existing conditions (addison’s)
Clinical features of hyperkalaemia
Asymptomatic, paraesthesia, muscle weakness, N+V, arrhythmias
Investigations of hyperkalaemia
Routine bloods (U+E, calcium and phosphate, magnesium), VBG (immediate K+ levels)< ECG, catheterisation (fluid balance), review obs/fluid status/medications
ECG changes with hyperkalaemia
Tall tented T waves, flattened P waves, QRS lengthening, heart block, BBB, axial deviation, sine wave, VF/asystole
Management of hyperkalaemia
Regular bloods and ECG monitoring
Alert senior +/- HDU support
Myocardium stabilisation (10ml 10% calcium gluconate) if ECG changes present or if mod/severe. Continuous cardiac monitoring required during calcium gluconate treatment.
Variable rate insulin with dextrose infusion (200ml 20% dectrose with insulin over 30 mins) to drive K+ intracellularly.
Salbutamol nebs to drive K+ intracellularly.
Oral calcium resonium to drive K+ into the bowel and out of the body.
Haemodialysis to drive K+ out of the body
Causes of hypokalaemia
Excess loss:
GI - vomiting, diarrhoea, distulae, laxative abuse
Urinary - diuretics, excess mineralocorticoid (Conn’s, cushing’s), hypomagnesaemia, polyuria, renal tubular acidosis
Skin - burns, excess sweating
Inadequate intake - malnutrition, inadequate IV K+
Intracellular shifts:
Alkalosis (H+ shifts out of cell to buffer pH and K+ shifts into cell to buffer electrical charge across membrane)
Excessive insulin (increased NaKATPase shifts K+ into cell)
Excessive beta agonists (salbutamol) increase NaKATPase
Clinical features of hypokalaemia
Asymptomatic
Muscle weakness, paraesthesia, ileus/pseudo-obstruction, hypotonia, hyporeflexia, hcramps, tetanus, resp failure, arrhythmia
ECG changes in hypokalaemia
Cardiac hyperexcitability (re-entrant loops) Elongated PR interval T wave flattening/inversion Prominent U wave ST depression VT/VF
Investigations of hypokalaemia
ECG
Bloods (FBC, U+E, calcium and phosphate, magnesium)
VBG
Management of hypokalaemia
Treatment of underlying cause
If mild without ECG changes give oral Sando-K
If mod-severe with ongoing losses or unable to take oral give IV K+ replacement
IV K+ can normally be given at max 10mmol/hr, if aggressive replacement required consider central line
Regular bloods should occur during K+ replacement
Causes of hypernatraemia
Hypovolaemic - diuretics (loop), dehydration (diarrhoea, vomiting, burns, sweating), acute tubular necrosis, hyperosmolar hyperglycaemic state
Euvolaemic - diabetes insipidus
Hypervolaemic - excess hypertonic saline administration, steroid excess (conns, cushings)
Clinical features of hypernatraemia
Asymptomatic
Excessive thirst (due to thirst response, plus rise in Na+ drives fluid extracellularly)
Weakness
Lethargy
Confusion
If >180 –> ataxia, tremor, coma, seizure
Investigations for hypernatraemia
Bloods (glucose, U+Es)
ABG/VBG
Urine osmolality (hypertonic urine indicates vomiting/burns/diarrhoea, isotonic urine indicates diuretics, hypotonic urine indicates diabetes insipidus)
ADH levels and CT head may be needed to assess pituitary
Diabetes insipidus
-what is it, two different types, clinical features, investigations
Excessive excretion of dilute urine and increased thirst response
Cranial DI - impaired ADH secretion from posterior pituitary (post-pituitary surgery, or post-head injury)
Nephrogenic DI - impaired response to ADH
Clinical features - polyuria and compensatory polydipsia
Investigations - water deprivation test (pt deprived of fluids for 8 hours, urine osmolality checked, then desmopressin given, then urine osmolality checked again)
Management of hypernatraemia
Replace fluid deficit (enteral fluid replacement preferred, but if not possible 5% dextrose is preferred IV)
Correct serum sodium (dont correct too rapidly due to risk of cerebral oedema)
Manage underlying cause
Causes of hypo-osmotic hyponatraemia
Hypovolaemic - vomiting, diarrhoea, diuretic
Euvolaemic - acute fluid overload, SIADH
Hypervolaemic - CCF, liver failure, acute tubular necrosis
What are the complications post-op of hyponatraemia
hyponatraemia causes low plasma osmolality resulting in fluid shifting intracellulary -> cellular swelling/oedema
Tissue oedema impairs healing of wounds/anastamoses
Can also cause cerebral oedema and raised ICP
Why is hyponatraemia common post-op?
As part of the stress response, the hypothalamus and posterior pituitary produce cortisol and ADH –> increased free water resorption in excess of sodium –> hyponatraemia
Surgical patients also receive a lot of IV fluids, if the fluids are mostly dextrose there will be a dilutional effect on the sodium conc
Clinical features of hyponatraemia
Asymptomatic
Malaise, headache, confusion, LOC, seizures
Central pontine myelinolysis
Central pontine myelinolysis
In chronic hyponatraemic patients if there is a rapid sodium correction there will be a large change in extracellular osmolarity -> causes damage to myelin sheaths of the nerves to the brainstem -> confusion, balance problems, pseudobulbar palsy, quadriplegia
Diagnosed via MRI head. No cure.
Management of hyponatraemia
Fluid balance (fluid monitoring +/- catheterisation) IV fluids (0.9% saline) preferred over enteral replacement Monitor renal function and electrolyte levels regularly Urine osmolality and sodium conc may be required.
Dont increase sodium levels too rapidly due to risk of central pontine myelinolysis
Risk factors for hypoglycaemia
Overdose of insulin/hypoglycaemics
Diabetes mellitus
Post-gastrectomy/gastric bypass (lack of ghrelin which usually suppresses insulin)
Alcohol excess (reduced liver function -> reduced gluconeogenesis)
Renal dialysis (reduced clearance of insulin, reduced gluconeogensis, increased insulin sensitivity)
Beta blockers (inhibition of hepatic gluconeogenesis)
Decompensated liver disease (reduced gluconeogenesis)
Adrenal insufficiency/Addisons (low adrenaline/cortisol -> increased sensitivity to insulin)
Clinical features of hypoglycaemia
Sweating, tingling lips/extremeties, tremor, dizziness, slurred speech, confusion, tachycardia, tachypnoea, focal neurology/reduced conciousness
Management of hypoglycaemia
If conscious give 10g glucogel PO, then complex carbs and regular monitoring of BMs
If unconscious give IV glucose 100ml 20% over 5-15 mins. If unable to gain IV access give IM glucagon
Whats the pathophysiology of haemolytic disease of the newborn
RhD- female becomes exposed to RhD antigens (previous RhD+ pregnancy or previous blood transfusion) and creates anti-D antibodies. Female then becomes pregnant with RhD+ foetus. Mum’s anti-D antibodies cross the placenta and attack the foetus RBCs causing foetal anaemia
ABO blood grouping universal donor
O-
doesnt have any A/B/rhesus antigens on the RBC surface so nothing for the recipient to attack
ABO blood grouping universal recipient
AB+
Has all of the A, B and rhesus antigens in their circulation already so wont create any antibodies against the donor blood
Indications for CMV neg blood products
Pregnant women, intra-uterine transfusions, neonates (<28 days)
Because of risk of congenital cytomegalovirus
Indications for irradiated blood products
(treated with X-Rays to prevent remaining WBCs from dividing, reduces risk of GVHD).
Hodgkins lymphoma, intra-uterine transfusion, recent stem cell transplant, on chemo, if receiving blood from first/second degree fam members
Procedure for blood transfusion
3 points of identification
Gain consent
Label the bottles (handwrite) at bedside
Complete transfusion request form at bedside
Prescribe each unit individually
Specific observations before transfusion, at 15 mins, at 1 hours, at completion
Transfuse with green or grey cannula
Packed red cells
- indications
- duration of administration
- how much it increases Hb by
Indications: acute blood loss, chronic anaemia (if symptomatic, if Hb<70 or <80 if cardiovascular disease)
Administered over 2-4 hours. Must be complete within 4 hours of coming out of store
1 unit increases Hb by 10
Platelets
- Indications
- Duration of administration
- How much it increases platelets by
Indicated in haemorrhagic shock in a trauma patient, profound thrombocytopaenia (<10), bleeding with thrombocytopaenia (<30), or if pre-operative platelet level <50
Administered over 30 minutes
1 adult therapeutic dose should increase platelets by 20-40
Fresh frozen plasma
- what does it contain
- indications
- duration of administration
consists mostly of clotting factors
indicated in DIC, and haemorrhage secondary to liver disease, all massive haemorrhage (usually after 2nd RBCs)
Administered over 30min
Cryoprecipitate
- what does it contain
- indications
- duration of administration
Mostly contains fibrinogen, von willebrand factor, factor VIII and fibronectin
Indicated in DIC with low fibrinogen (<1g/L), vvWF disease, or massive haemorrhage
Administer stat
Fluid and electrolyte daily requirements for an adult
25ml/kg/day water
1mmol/kg/day sodium
1mmol/kg/day potassium
50g/day glucose
Hierarchy of feeding
insufficient calories -> oral nutritional supplements (ONS)
insufficient calories orally/dysfunctional swallow -> NG
Blocked/ dysfunctional oesophagus -> gastrostomy (PEG/RIG)
Stomach inaccessible/ outflow obstruction -> jejunostomy
Jejunum inaccessible/ intestinal failure -> parenteral nutrition
Peri-op nutrition advice
Reduce NBM time (6hrs for food and drink, 2 hours for clear fluid), pre-op loading, minimise drains and NG, rapid reintroduction of feeding post-op
Drugs to stop before surgery
(CHOW)
Clopidogrel 7 days before
Hypoglycaemics
Oral contraceptive pill/HRT 4 weeks before
Warfarin 5 days before and switch to LMWH
Ramipril stop 24 hours before (?)
Drugs to alter
Switch SC insulin to VRIII
Increase steroids and consider switching to IV
Drugs to start
LMWH
TED stockings
Antibiotic prophylaxis for orthopaedic, vascular and GI surgery