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Procedural Skills (SLO6)
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A 65 year old woman with known COPD presents to ED with worsening breathlessness and wheeze. Her observations on admission are: BP 135/87, HR 110, RR 24, SpO2 86% OA. Her ABG shows type II respiratory failure. She receives initial treatment with controlled oxygen therapy and bronchodilators but there is little improvement. Which of the following is an indication to start NIV in a patient with acute hypercapnic respiratory failure?
Answer:
Indications for NIV in acute hypercapnic respiratory failure (AHRF) as per BTS:- COPD (if persisting after bronchodilators and controlled oxygen therapy)
- pH < 7.35
- PCO2 > 6.5
- RR > 23
Non-Invasive Ventilation
Procedural Skills (SLO6)
Last Updated: 15th September 2022
Non-invasive ventilation (NIV) is the umbrella term used to describe the provision of ventilatory support through the patient's upper airway using a mask or similar device. NIV is principally indicated in patients with chronic obstructive pulmonary disease (COPD) with respiratory distress and hypercapnia, and in acute cardiogenic pulmonary oedema. NIV may also be used in patients who are not considered suitable for intubation. A ceiling of treatment, and whether escalation to intubation is indicated, must be defined at the outset. Do not use NIV as a substitute for intubation and invasive ventilation if the latter is more appropriate.
Patients treated with NIV should be managed in an environment with suitable monitoring, including continuous pulse oximetry, access to equipment for blood gas analysis, and immediate availability of resuscitation equipment. Staff should be fully trained and experienced in the use of NIV.
Indications
Indications for NIV in acute hypercapnic respiratory failure (AHRF) as per BTS:
- COPD (if persisting after bronchodilators and controlled oxygen therapy)
- pH < 7.35
- PCO2 > 6.5
- RR > 23
- Neuromuscular disease (NMD)
- Respiratory illness with RR > 20 if usual VC < 1L even if PCO2 < 6.5 OR
- pH < 7.35 and pCO2 > 6.5
Contraindications
The most important contraindication to the use of NIV is the need for immediate tracheal intubation and invasive ventilation. NIV is not indicated in asthma/pneumonia. Many of the factors previously considered as contraindications are relative or negated if tracheal intubation is considered inappropriate and NIV is to be used as the ceiling of treatment.
- Absolute contraindications as per BTS:
- Severe facial deformity
- Fixed obstruction of the upper airway
- Facial burns
- Relative contraindications as per BTS:
- pH < 7.15
- pH < 7.25 and additional adverse feature
- GCS < 8
- Confusion/agitation
- Cognitive impairment
- Further relative contraindications:
- Haemodynamically unstable patient (requiring inotropes/vasopressors, unless in ITU)
- Significant arrhythmia
- Untreated pneumothorax
- Vomiting
- Marked abdominal distension
- Copious respiratory secretions
Type of NIV
CPAP (Continuous Positive Airway Pressure):
- A constant positive pressure is applied throughout the respiratory cycle
- Indications
- Typically used for type I respiratory failure
- E.g. acute cardiogenic pulmonary oedema, obstructive sleep apnoea
- Procedure
- Start with a CPAP at 5 - 10 cmH2O
- Titrate FiO2 to achieve SpO2 of 94 - 98%
- If initial CPAP does not alleviate hypoxia, increase to maximum of 15 cmH2O as tolerated
- If CO2 level starts to increase consider BiPAP
BiPAP (Bi-level Positive Airway Pressure):
- Provides two levels of pressure support throughout the respiratory cycle: IPAP (Inspiratory) > (Expiratory) EPAP
- Indications
- Typically used for type II respiratory failure
- E.g. COPD, neuromuscular disease
- Procedure (as per BTS for AHRF)
- Pressure settings
- Start with initial EPAP 3 (or higher if OSA known/expected)
- Start with an initial IPAP 15 (20 if pH < 7.25) in COPD
- Titrate IPAP over 10 - 30 minutes to IPAP 20 -30 to achieve adequate augmentation of chest/abdo movement and slow RR (max IPAP 30 without expert review)
Increase EPAP if patient remains hypoxaemic (max EPAP 8 without expert review) - Start with an initial IPAP 10 (or 5 above usual setting) in NMD
- Backup rate
- Backup rate of 16-20.
- I:E ratio
- COPD: 1:2 to 1:3
- NMD: 1:1
- Inspiratory time
- COPD: 0.8 - 1.2 s
- NMD: 1.2 - 1.5 s
- Oxygenation
- Aim for 88-92% in all patients
- Pressure settings
Monitoring during NIV
- Observe the patient closely and assess: chest wall movement, coordination of respiratory effort with the ventilator, accessory muscle recruitment, respiratory rate, heart rate, oxygen saturations, patient comfort and mental state
- Clinical observations must be recorded every 15 minutes for the first hour and every 30 minutes during the next 4 hours
- Measure the arterial blood gas values after 1 hour of NIV therapy and after every subsequent change in settings
- Red flags in managing acute hypercapnic respiratory failure (AHRF) as per BTS:
- pH < 7.25 on optimal NIV
- RR persistent > 25
- New onset confusion or patient distress
- Actions if red flags identified:
- Check synchronisation, mask fit, exhalation port
- Give physiotherapy/bronchodilators, consider anxiolytic
- CONSIDER IMV
Indications for ICU referral
Indications for ICU referral in acute hypercapnic respiratory failure (AHRF) as per BTS:
- AHRF with impending respiratory arrest
- NIV failing to augment chest wall movement or reduce PCO2
- Inability to maintain SpO2 > 85-88% on NIV
- Need for IV sedation or adverse features indicating need for closer monitoring and/or possible difficult intubation
Complications
If patients are selected correctly, the majority of complications are relatively minor. Potential complications include:
- Hypotension (due to increased intrathoracic pressure reducing preload)
- Barotrauma (due to gas trapping and overinflation, pneumothorax is a rare complication)
- Gastric distension
- Pulmonary aspiration (vomiting or regurgitation into tight-fitting mask)
- Pressure necrosis of the bridge of the nose
- Discomfort from a tight-fitting mask
- Sinus or ear discomfort and nasal mucosal congestion or drying/ulceration
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
