Makindo Medical Notes.com

Related Subjects: Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Fat embolism |Hyperventilation Syndrome |Acute Respiratory Distress Syndrome (ARDS) |Respiratory Failure |

It is quite possible for a patient with COPD to also have a PE. Patients may go from Type 1 to become Type 2 when they tire and hypoventilate or receive sedation. Intubation and ventilation treat both types.

About

• Respiratory failure (PaO₂ < 8 kPa) is a common medical emergency,
• Respiratory failure is a syndrome in which the respiratory system fails in one or both of its gas exchange functions: oxygenation and carbon dioxide elimination.
• It may be classified as either hypoxaemic with or without hypercapnia.
• Oximeters estimate arterial oxygen saturation are useful in assessment or monitoring.
• Oximeters tell us nothing about Carbon dioxide levels. For that we need an ABG.

Classification:

How much Oxygen should I give

• Normally Patients should have enough oxygen to achieve Sats 94-98%
• In COPD/T2 RF Patients should have enough oxygen to achieve Sats 88-92% and PO₂ > 7 Kpa
• Generally If O₂ sats > 98% then wean back on oxygen
• Generally If O₂ sats < 94% then consider increasing oxygen
• There are always exceptions to this e.g. In COVID we initially changed target to > 90% to conserve oxygen stocks. take advice if unsure.

Causes

• Type 1:Is the commonest form and usually due to alveolar fluid and similar pathologies. Often due to mismatch of ventilation and perfusion in the pulmonary alveolar bed.
  • Pulmonary oedema,
  • Pulmonary embolism
  • ARDS
  • Asthma
  • Pneumonia
  • High altitude
  • Upper airways obstruction
• Type 2: It is usually due to ventilatory weakness, sedation or diseases that impair ventilation Hypercapnia causes acidosis for which there is over days a corresponding rise in renal retention of bicarbonate.
  • Causes of Type 1 when tired, sedation, hypoventilation
  • CNS disease e.g. stroke, tumour
  • Exacerbation of COPD
  • Pneumonia
  • Neuromuscular weakness (Polio, GBS, MND, Spinal muscular atrophy)
  • Muscle weakness (Muscular dystrophy, Myotonic dystrophy, Pompe disease)
  • Flail chest, Rib#, Kyphoscoliosis
  • Obesity, sedation, hypercarbia, alcohol
  • Sputum and mucus plugs

Investigations

• Oxygen saturation probe: does not detect CO₂ levels.
• ABG: can tell pH, PO₂, PCO₂, HCO₃ and base excess
• ECG: STEMI, AF, S1Q3T3 PE, RV Changes of COPD
• CXR: may show COPD changes, pneumonia, pneumothorax but will not show PE
• CTPA: if T1RF and Wells score suggest possible PE

Management of Type 1 RF

• ABC, High flow oxygen unless suspected COPD - see below
• Make a diagnosis and manage cause
• Diuretics if fluid, Chest drain if PTX, Antibiotics if infection
• Bronchodilators/Steroids if Asthma/COPD
• Thrombolysis/Anticoagulation if PE
• May need CPAP or NIV depending on cause
• May need intubation or ventilation or ECMO

Management of Type 2 RF

• ABC, Controlled Oxygen therapy start with 24% venturi mask aim for PaO₂ > 7 kPa. The goal of treatment in acute on chronic type II respiratory failure is to achieve a PaO₂ (> 7.0 kPa or 52 mmHg) without increasing PaCO₂ and acidosis, while identifying and treating the precipitating condition.
• CO₂ retention is seen with warm dilated peripheries and the patient is sleep and has bounding pulses and may have a flapping tremor
• Often with COPD the patients have prolonged expiration phase and wheeze as well as inflated lungs and intercostal indrawing. lips are pursed to help keep collapsed small airways open
• if there is significant right heart failure then there will be signs of peripheral oedema, raised jugular venous pressure, hepatomegaly, ascites.
• Make a diagnosis and manage cause
• Frequent physiotherapy ± pharyngeal suction if mucus plugs or sputum to expectorate
• COPD+/- Pneumonia: Treat exacerbation if present.
• See other causes of Type 1 which may need addressed
• Noninvasive ventilation and if this fails to work then escalate to ITU
  • CPAP nasal or mask: Start at 5 cm H₂O
  • BiPAP Nasal or mask: Start at 10 cm H₂O inspiration/5 cm H₂O expiration
• May need intubation or ventilation: Initial ventilator settings:
  • FiO₂ 1.0
  • Tidal Volume- 6–10 ml/kg
  • RR 10 -12
  • PEEP- 5 cmH₂O
  • Pressure Support - 5 cmH₂O
• ECMO may be considered
• Drug-induced Hypoventilation: consider naloxone for opiates and flumazenil for benzodiazepines if drugs recently taken. May need Naloxone infusion.

Important scenarios to recognise

• Impending Respiratory arrest: HR> 120/min. RR >30. Low BP, Pale and sweaty, agitation, confusion. Rising PaCO₂ or fall in PaO₂. Needing higher FiO₂, rapid desaturation on disconnection from O₂
• Masks may be poorly tolerated leading to Hypoxia in confused patients. It might be best to see if Oxygen via nasal prongs at 1 or 2 L/min is more effective and continuous with less interruptions if it gives a satisfactory PaO₂.
• If a patient has normal PaO₂ on high flow oxygen this is abnormal as you would expect the patient to have a PaO₂ well above the normal range. These needs investigating as high FiO₂ can hide worsening pathology. Patients should have only enough oxygen to achieve Sats 94-98%.
• If a hypoxic asthmatic patient has an ABG with a normal paCO₂ (it should be low) this is a sign that they are tiring or worsening for some other reason and they need urgent ITU review
• A very low PaO₂ in a patient who looks completely well, is not short of breath and has normal O₂ saturations is likely a venous sample

References