Perioperative and Critical Care Flashcards
Respiratory failure
= PaO2 < 8kPa
Type 1 - Hypoxia with normal or low PaCO2
Type 2 - Hypoxia with hypercapnia (PaCO2 > 6kPa)
Causes of type 1 respiratory failure
- Ventilation/perfusion mismatch – pneumonia, pulmonary oedema, PE, asthma, emphysema, pulmonary fibrosis, ARDS
- Hypoventilation
- Abnormal perfusion
- Right -> left cardiac shunts
Management of type 1 respiratory failure
- Treat underlying cause
- Give oxygen by facemask (up to 60%)
- Assisted ventilation if still low O2 despite 60% O2
Causes of type 2 respiratory failure
- Pulmonary disease – COPD, asthma, pneumonia, end-stage pulmonary fibrosis, obstructive sleep apnoea
- Reduced respiratory drive – sedative drugs, CNS tumour or trauma
- Neuromuscular disease – poliomyelitis, myasthenia gravis, Guillain-Barre syndrome
- Thoracic wall disease – flail chest, kyphoscoliosis
Management of type 2 respiratory failure
- Treat underlying cause
- Controlled O2 therapy, starting at 24%, then recheck ABG and gradually increase as long as PaCO2 stays steady or lowers
- Consider assisted ventilation if rising hypercapnia and hypoxia
Indications for ABG
- Unexpected deterioration in ill patient
- Any acute exacerbation of chronic chest condition
- Any impaired consciousness or impaired respiratory effort
- Signs of CO2 retention (bounding pulse, drowsiness, flapping tremor, headache)
- Signs of hypoxia (cyanosis, confusion, visual hallucinations)
- To validate measurements from transcutaneous pulse oximetry
ABG interpretation
- pH acidosis or alkalosis?
- pCO2 high or low? does this fit with pH - if yes then respiratory problem
- HCO3 high or low? does this fit with pH - if yes then metabolic problem
- pO2 normal given FiO2?
- any compensation? partial or complete?
- anion gap, normal 10-18 = (Na+ + K+) - (Cl- + HCO3-)
Increased anion gap
Metabolic acidosis and increased anion gap
- due to increased production or reduced excretion of fixed/organic acids
- lactic acid (shock, infection, tissue ischaemia)
- urate (renal failure)
- ketones (DM, alcohol)
- drugs/toxins
Normal anion gap
Metabolic acidosis and normal anion gap
- due to loss of bicarbonate or ingestion of H+ ions
- renal tubular acidosis
- diarrhoea
- drugs
- addison’s disease
- pancreatic fistula
- ammonium chloride ingestion
Metabolic alkalosis
High pH, high HCO3-
- vomiting
- K+ depletion (diuretics)
- burns
- ingestion of base
Shock
= circulatory failure resulting in inadequate organ perfusion
= low BP, systolic <90 or MAP <65, and evidence of tissue hypoperfusion (mottled skin, low urine output, serum lactate >2, low GCS, pallor, cool peripheries, tachycardia, slow cap refill, tachypnoea, oliguria)
- BP = CO x SVR (so two causes of shock)
Shock - inadequate cardiac output
Hypovolaemia
- bleeding
- fluid loss (vomiting, burns, ‘third space loss’)
Pump failure (cardiogenic)
- cardiogenic shock (ACS, arrhythmias, aortic dissection, acute valve failure)
- secondary causes (PE, tension pneumothorax, cardiac tamponade)
Shock - peripheral circulatory failure
Sepsis (acute vasodilation from inflammatory cytokines - may be warm and vasodilated after fluid therapy, or cold and shut down before)
Anaphylaxis
Neurogenic (spinal cord injury, spinal anaesthesia)
Endocrine failure (Addison’s, hypothyroidism)
Drugs (anaesthetics, antihypertensives)
Management of shock
If BP unrecordable call cardiac arrest team.
Septic shock - abx, fluids (500ml boluses of crystalloids eg 0.9% saline), oxygen, critical care review
Anaphylaxis - secure airway, 100% O2 given, IM adrenaline every 5 mins, IV access for chloramphenamine and hydrocortisone
Cardiogenic - O2 titrate to normal, diamorphine IV, investigations and monitoring - correct arrhythmias/U+E abnormalities/acid-base disturbance, optimise filling pressure with either plasma expander or inotropic support
Hypovolaemic - raise legs, IV fluid bolus crystalloid, titrate to HR BP UO
Haemorrhagic - stop bleeding! 2L crystalloid, crossmatch blood, FFP with red cells
Sepsis
= life-threatening organ dysfunction caused by a dysregulated host response to infection
Moderate-high risk if…
- altered mental status
- raised resp rate
- low BP
- low urine output
- signs of infection
- rigors or temp <36
- impaired immunity
- recent surgery/trauma
- mottled/ashen/cyanotic skin, non-blanching rash
- -> sepsis 6!
Assessing fluid balance - underfilled
- tachycardia
- postural drop in bp (low bp is late sign)
- reduced cap refill
- reduced urine output
- cool peripheries
- dry mucous membranes
- reduced skin turgor
- sunken eyes
Assessing fluid balance - overfilled
- raised JVP
- pitting oedema of sacrum, ankles, legs/abdomen if severe
- tachypnoea
- bibasal crepitations
- pulmonary oedema on CXR
Fluid challenge
Rapid infusion of (200ml) fixed volume to see effect on SV, CVP / PAWP and correct hypovolaemia
0.9% saline as isotonic and same Na+ content as plasma
Crystalloids (saline, Hartmann’s, plasmolyte) also
Colloids (eg gelatin-based or blood) useful for resus but are expensive and not for maintenance
WHO analgesic ladder
- Paracetamol
- NSAID
- codeine
- morphine (IV/PO/PCA) -codeine
PCA review
Review daily by pain team or anaesthetist:
- pain score
- dosage history
- pump settings
- side effects
Nine survival variables pre-surgery
Age Sex Socioeconomic status Hx of IHD Hx of HF Hx of cerebrovascular disease Hx of peripheral arterial disease Hx of renal failure Aerobic fitness
Pre-op assessment
- systems review, especially CVS and resp, + endocrine, haem and neuro
- ANY possibility of pregnancy
- period of starvation, and assess reflux risk
- meds, ALLERGIES
- PMHx - for airway problems or spinal abnormalities if regional block
- past anaesthetic hx - airway, drug used, side effects
- FHx
- SHx - smoking (recent –> higher risk bronchospasm + more mucus), alcohol (tolerance to sedation, increase risk to patient, risk delirium tremens)
+ confirm reasons for surgery - informed consent and proposed site confirmed
ASA grading
1 – normal healthy patient
2 – mild systemic disease
3 – severe systemic disease
4 – severe systemic disease which is a constant threat to life
5 – moribund patient who is not expected to survive with or without the operation
6 – declared brain-dead, organs removed for donor purposes
Reflux
2 hours clear fluids - water has half life of 10-20 mins
6 hours solids (if normal peristalsis!)
- emptying rate is fastest for carbohydrates, then proteins, slowest for fats
- milk should be regarded as a solid (will thicken and congeal in the stomach)
- trauma and shock can cause delayed gastric emptying, so allow more time!
Pharmacological control of reflux
PPI - 90 mins pre anaesthesia
- lansoprazole, omeprazole
- inhibit H+/K+ ATPase on parietal cells, so preventing excretion of H+ and reducing gastric juice volume
H2 antagonist - 90 mins pre anaesthesia
- ranitidine
- competitively blocks histaminergic H2 receptors and inhibit acid secretion by gastric parietal cells
Antacid - immediately before
Prokinetic - 90 mins prior, unreliable
Risk factors for gastric reflux
Obesity Pregnancy Hiatus hernia Oesophageal stricture Drugs lowering LOS pressure eg anticholinergics, opioids, ethanol
Perioperative risk factors for thrombosis
Hypercoagulability - surgery, cancer, oestrogen therapy, puerperium Immobility Dehydration Poor CO Obstructed venous return Age >60 Previous DVT, PE, thrombophilia Recent CVS event Acute medical illness/infection Trauma
Virchow’s triad
For thrombosis:
Hypercoagulability
Vessel wall injury
Venous stasis
Diabetes control perioperatively
(all major surgery and critical illness affects glucose metabolism)
Stop all hypoglycaemics (metformin irrelevant)
Try not to stop insulin - eg maybe give half dose of long-acting insulin the night before, or treat with variable rate infusion - as risk of ketosis
Opioids
If giving IV boluses, always ensure availability of naloxone and bag-valve-mask
Avoid post-op in day cases
Morphine 0.1-0.2mg/kg in adults, much less in elderly, titrate against response. Slow onset, peak effect 10-15 mins IV, so give small doses regularly (eg 2mg/5mins)
Fentanyl rapid onset of action, so give eg morphine before effects wear off.
Adjuncts to improve quality of analgesia and reduce requirements - NSAIDs, COX2 inhibitors, paracetamol - usually diclofenac suppository (CONSENT FIRST)
Post-operative nausea and vomiting
25-30% after a GA
Caused by opioid anaesthesia, hypotension, dehydration, hypoxia, delayed return of GI function
Manage - ensure normal NEWS and hydration, adequate but not excessive analgesia, look for surgical cause, then give antiemetic (if one tried unsuccessful then try other class)
Anti-emetics
5HT3 antagonists
- effective, minimal side effects, can be given IV and rapid onset – good rescue remedy
- ondansetron is most commonly used (4mg IV)
Dexamethasone
- effective, long-half life, slow onset
- best for prophylaxis
H1 antagonists
- effective, but anticholinergic side effects, can cause tachyarrhythmias – give by slow IV and monitor ECG
- cyclizine 50mg IV
Dopamine (D2) antagonists
- slow onset of action, given IM
- prochlorperazine (metoclopramide ineffective)
Anaesthesia triad
ANALGESIA, hypnosis, muscle relaxation
Fentanyl
- Most common intraoperative opioid (synthetic) - better than morphine as rapid effects so reversible. Morphine only used after fentanyl induction.
- 100x more potent than morphine
Administration
- Bolus dose at induction of 1-3 micrograms/kg (before IV induction agent, also reduces laryngoscopy response)
- Repeated doses if above 15-30 mins surgery
Unwanted effects - Bradycardia - Hypotension - Respiratory depression \+ maybe PONV, urinary retention, constipation, itching
Can only discharge from recovery to ward when…
- Fully conscious, maintaining own airway
- Breathing and oxygenation satisfactory
- Stable CVS
- Pain and PONV adequately controlled
- Temperature within acceptable limits
- IV cannulae patent and flushed if necessary
- All surgical drains and catheters checked
May also need ward visit by anaesthetist - if ASA III-V, epidural or PCA running, central venous line in, complicated intraoperatively
Post-operative hypotension
Common in sick and elderly
- Hypovolaemia - elevate legs, give fluid, assess for bleeding, take FBC
- Arrhythmias - measure BP and perfusion, record ECG, correct electrolytes, treat
- Left ventricular failure - oxygen, fluid restrict, diuretics, inotropic support
- Septic shock - IV fluids, CVP monitoring, inotropic support, HDU/ICU, abx, look for surgical cause
Post-operative hypoxia causes
- Atelectasis
- Pain
- Chest infection
- Pulmonary oedema
- Aspiration
- Pneumothorax
- PE
- Pleural effusion
- ARDS
Indications for intubation rather than LMA
Patient factors
- severe reflux
- recently eaten (emergency surgery) -> rapid sequence induction
- obesity
Surgical factors
- long surgery (>2-4hrs)
- abdo/thoracic surgery where pressure on diaphragm
- positioning unusual (eg neuro, where sitting upright, or if need face down)
- if need to closely control ventilation and ensure no leak (eg neuro, where may need to increase CO2 to reduce bleeding in brain)
Local anaesthetics
Lidocaine – less toxicity, quickest (2% = 20mg/ml. 3mg/kg is max dose, or 7mg/kg with adrenaline)
Bupivicaine – more toxicity (heart – broad QRS tachycardia, brain – tingling, fits, death), longer lasting
Chirocaine (levobupivacaine) – less cardiac toxicity but longer lasting
Airway interventions
- 100% O2 by reservoir bag
- Chin lift/jaw thrust
- Guedel or nasopharyngeal airway
- Suction
Breathing interventions
- If RR = 0 – basic life support
- If RR<5 – consider naloxone
- If RR>25 – sit up, monitor SaO2, take ABG
- Early intubation to treat respiratory acidosis
Resp rate is the most sensitive sign of a critically ill patient!
Circulation interventions
- HR + BP
- Cap refill, peripheries
- Large bore IV access – FBC, coagulation screen, biochem screen, ABG + lactate, cultures
- 12 lead ECG
- Fluid challenge if shocked – 500ml Hartmann’s, Ringers lactate or colloid
Disability interventions
- If GCS<8 or non-response to voice o Recovery position o 100% O2 o Check airway patent o Blood glucose o Full neuro assessment
- Also red flag if sudden fall in level of consciousness
WHO surgical safety checklist
Sign in before start of anaesthesia
Time out before start of surgery
Sign out at end of surgery
- Correct patient
- Correct operation
- Correct site and side
- Check consent form
+ allergies, metalwork, when last ate/drank, medical records available, surgeon available and ready, blood glucose control if diabetic
