1. Respiratory Failure CPAP/BIPAP

2. Respiratory Failure Definition Physiological Principles
Clinical Cases- how to approach respiratory failure at ward level
CPAP and BiPAP
Indications and Contra-indications
Take home message
We are not going to provide any great detail on invasive ventilation on ICU, instead this lecture concentrates on how to approach respiratory failure at ward level and as an FY1/2.
You will not be expected to know how to set/control an ICU ventilator.

3. Definition Type 1 Respiratory Failure Hypoxaemic pO2 < 8 kPa ON AIR
pCO2 < 6.0 kPa
Type 2 Respiratory Failure
Hypercapnic
pCO2 > 6.0 kPa
Respiratory failure is defined by lack of oxygen (PaO2 <8kPa), but is further classified into type 1 and type 2 respiratory failure by the presence of hypercapnia.

4. The oxygen cascade defines a stepwise reduction in partial pressure of oxygen between atmospheric concentration and the concentration at the effective site of oxygen utilisation- the mitochondrion.
Respiratory failure can occur due to problems at any of these steps, but is most commonly due to problems with Ventilation/Perfusion (V/Q) mismatch which describes the situation where an alveolus is perfused (ie receiving a supply of venous blood from the right heart), but not oxygenated (because the alveolus has malfunctioned, eg due to it being filled with fluid in pneumonia or cardiac failure). This blood remains unoxygenated, and then mixes with the oxygenated blood from other alveoli. If sufficient alveoli are affected, then the proportion of blood entering the left heart without being oxygenated can be enough to dilute the oxygenated blood and cause the blood entering the systemic circulation to be ‘hypoxic’.

5. Hypoxic or Type 1 Respiratory Failure
Normal or low Pco2
Causes of Hypoxia
Ventilation Perfusion Mismatch
Upper airway Obstruction
Low oxygen in inspired air
The clinical approach to respiratory failure consists of attempts to diagnose the underlying problem or cause, and initiation of treatment- aiming at both the cause (eg pneumonia), but also providing respiratory support to reverse the hypoxia.
Differentiating between type and type 2 respiratory failure is useful as it both helps to identify the cause, and to define the treatment in terms of oxygen therapy or other support.
Type 1 failure is ‘pure hypoxia’ and can be due to a number of problems not directly related to the lungs- eg upper airway obstruction. An “ABCDE’ approach can be useful to help exclude these rapidly reversible problems, however the mainstay of treatment is the provision of supplemental oxygen therapy.

6. Type 1 Respiratory Failure-Treatment
Treatment of the underlying cause
Treatment of the Hypoxia-
GIVE OXYGEN!
Usually in a de-escalation pattern- ie give more and reduce later when you have proven the patient does not need it, rather than starting low and working your way up.
If still hypoxic then….
This lecture is not about treatment of the underlying problem, however it is important that appropriate ‘disease specific’ therapy is commenced (eg antibiotics/nebulisers/diuretics etc).
Oxygen can be administered in a number of different ways depending on the requirements.
Nasal cannulae can deliver 2-4l/min of oxygen which results in an inspired oxygen concentration of 24-48%.
Face masks can deliver more- with the concentration depending on the oxygen flow rate- however the concentration received by the patient is not easy to determine as unless a specific ‘high flow generator’ is used, the patient will almost always entrain some air from outside the mask, which in turn will reduce the inspired oxygen concentration. Even non-rebreath/trauma masks with reservoir bags can only deliver about 60% oxygen.
High flow generators are available in critical care areas and some other wards, but they are not common on the general ward. These can produce flow rates in excess of 60l/min, which exceeds peak inspiratory flow and is sufficient to prevent entrainment of air during inspiration. These systems can deliver close to 100% oxygen.

7. Continuous Positive Airway Pressure
Oxygen delivered with positive pressure of between 4 and 25 cm H2O
Delivered via face mask/hood
CPAP might be considered as a step-up from oxygen delivery, and consists of a tightly fitting mask or hood that in addition to delivering a specific oxygen concentration (CPAP systems use high-flow generators), apply that oxygen at a defined pressure.

8. CPAP- Physiology Improves FRC Improves V/Q match
Decreases atelectasis
Decreased leakage of fluid into lungs
Splints airways open
Decreases work of breathing
Administering oxygen at a specific pressure has a number of beneficial effects, but primarily leads to an increase in functional residual capacity, which is the lung-volume where gas exchange occurs- essentially more lung becomes available for gas exchange.

9. CPAP indications Type 1 respiratory Failure Pulmonary Oedema
Fluid overload
Atelectasis
Chest infection
CPAP is a very effective therapy for type 1 respiratory failure, and should be considered when conventional face-mask oxygen or high-flow has failed.
There is no specific degree of hypoxia at which CPAP becomes indicated, and the transition to ‘higher’ forms of respiratory support remains a clinical decision based on response to initial therapy and the anticipated course of the pathological process the patient is suffering from. Much of this comes with experience, but the learning curve is short and most clinicans learn to recognise the patient who requires greater support very quickly.
As a rule of thumb, the patient who still has a PaO2 less than 8kPa despite maximal oxygen therapy in their given environment should be considered for escalation to HDU/ICU

10. Similar to breathing with your head stuck out of a moving car!!

11. Problems with CPAP Can expand pneumothoraces Can cause hypotension
Difficult to apply if there are facial injuries
CPAP is not a benign therapy and can cause problems. The most common of these is hypotension which occurs as a consequence of the increased intrathoracic pressure causing a decreased venous return and therefor decreased pre-load to the heart. This may respond to intravenous fluid therapy, but this may in itself be partially contra-indicated if there is felt to be any degree of pulmonary oedema.

12. Type 2 respiratory failure
Hypoxia with hypercapnia
Hypoventilation
Drug overdose
Weakness
Increased Dead Space
COPD
Type 2 respiratory failure presents a more complex problem. In addition to hypoxia, the patient is hypoventilating and is not generating sufficient alveolar gas flow to clear CO2.
This can be due to a number of causes- many of which are easily treated (eg opiate overdose, where a high PCO2 will usually rapidly reverse when the patient is given naloxone).
The most common causes of type 2 respiratory failure in clinical practice are however the spectrum of diseases that come under the umbrella of ‘COPD’. These conditions cause damage to the lungs which result in increased airway resistance (either through structural damage or increased secretions). The patient may be working very hard and looks like they are breathing heavily, however the increase in airway resistance means that the amount of air actually entering the alveoli is limited. Further, many alveoli are damaged and are inneffective at gas exchange. THe patient is making great efforts to get air into the alveolus, but nothing happens when it gets there.

13. Hypercapnoea in COPD
Combination of muscle fatigue and worsening lung mechanics
Increasing bronchial constriction, narrowing and oedema
Disordered central ventilatory drive
Result in High Pco2 and Low Po2
This initiates a cascade of problems which all lead to further deterioration. The hypoxia leads to further weakness, which in turn leads to less gas movement and further increases in CO2 levels. CO2 itself can cause sedation, and this in turn decreases respiratory effort

14. Hypercapnic Respiratory failure
Hypoxia still needs treating
However supplementary Oxygen can make it worse!!
Need extra support for the ventilatory pump
This is achieved by
BIPAP …
In addition to administration of oxygen, these patients may need ventilatory support to help increase their minute volume.
The initial approach to the patient with Type 2 respiratory failure is much the same as in Type 1. Make steps to identify the underlying cause and initiate treatment for this, administer oxygen in an attempt to reverse the underlying hypoxia.
In chronically hypoxic patients, the administration of oxygen remains contentious. This is based on the theory that chronic respiratory failure patients (usually those with severe COPD), have lost the normal reflex response to increased arterial CO2 levels, and as such rely on their hypoxia to trigger breathing. In this situation administering oxygen may lead to further hypoventilation and deterioration.
In practical terms these patients are probably quite rare, but they do exist, and caution should be taken when approaching a severe COPD patient. Most respiratory medicine departments will have protocolised approaches to oxygen therapy in COPD which consist of administration of controlled low concentration of oxygen and reassessment. However, in a true hypoxic emergency where the patient is rapidly deteriorating form hypoxia, then it may be necessary to administer oxygen in high concentrations in order to prevent death from hypoxia (which might be treatable), rather than worry about hypoventilation (which might not occur, and can be treated by intubation if you can keep the patient alive long enough for ICU to get there).

15. What is BIPAP? Biphasic Positive Airway Pressure –
CPAP but with additional pressure to support inspiration
Increases minute volume by increasing tidal volume

16. Machine and circuit

17. BIPAP Terms
EPAP-expiratory positive airway pressure, analogous to CPAP
IPAP-inspiratory positive airway pressure, the pressure given to support inspiration
These can vary from manufacturer to manufacturer, differnet brands of BiPAP/NIV machine can use wholly different terms.
IPAP and EPAP are common, and reflect the machines used in Leeds and most W. Yorks hospitals.

18. CPAP Vs. BIPAP CPAP EPAP/”CPAP” Augments tidal volume –improves PaCO2
Improvement in Oxygenation
IPAP
IPAP Te
BiPAP combines the benefits of CPAP, with additional inspiratory support that augments ventilation and minute volume and therefore helps CO2 clearance.
CPAP
EPAP/”CPAP”

19. When is BiPAP indicated?
Hypercapnoeic COPD exacerbations – not improved by controlled oxygen
Can prevent/reduce need for endotracheal intubation
Musculoskeletal conditions with respiratory failure (as long as airway is secure/patent)
Others – Obesity Hypoventilation Syndrome

20. BiPAP- Problems Mask intolerance Patient co-operation is crucial
Facial injury
Patient co-operation is crucial
Much as CPAP, plus a greater need for patient cooperation as ventilator synchrony with the patient is more difficult to achieve.

21. Case 1
A 65 yr old gentleman is admitted with SOB and chest pain. His ECG shows left bundle branch block ABGs on 15l non-rebreathe mask: pH PO2 10 kPa PCO kPa Bicarb 24.2
What do the blood gasses show?

22. Questions What is the diagnosis? Cardiogenic pulmonary oedema
What type of respiratory failure has he got?
Type 1 respiratory failure
How should he be managed?
Oxygen
CPAP
Medical treatment

23. Case 2 On 35% (Venturi) On air pH 7.30 pH 7.35 PCO2 10.2kPa
A 72 yr old Smoker admitted with worsening SOB and Cough with yellow sputum. At admission. ABG:
On 35% (Venturi)
pH 7.30
PCO kPa
Po kPa
HCO3 34mmol/l
On air
pH 7.35
pCO2 7.8 kPa
pO kPA
HCO3 32mmol/l
Compare the gasses above with case 1
what are the important differences?
On the second gas the patient has been given supplemental oxygen- has this helped?

24. Questions What is the diagnosis Exacerbation of COPD
What type of respiratory failure is it
Type 2
What is the treatment
Controlled oxygen (aim SpO %)
BiPAP
Medical management

25. Invasive Ventilation When all else has failed! Indications:
Respiratory failure that is refractory to other treatment
Respiratory failure with low conscious level
Tiring on other treatment
Airway compromise
Also used in other conditions (sepsis, trauma, head injury, post arrest etc)
Sometimes escalation through the treatment options described above is not possible. Intubation and invasive ventilation can become necessary in an emergency and there is sometimes no time to trial the intermediate steps.
Please note that Intubation and ventilation might be necessary for a variety of conditions wholly unrelated to the lungs. Not all ventilated patients have respiratory failure.

26. Problems with IPPV Requires endotracheal tube
Sedation (to almost anaesthetic levels)
Hypotension
Gastroparesis
Immobility
Vascular access
Risks of pneumonia
Limited to specialist areas (ICU)
Essentially IPPV necessitates a much larger package of care. The sedation used can generate a whole range of secondary complications that need more invasive treatment and can become life threatening in their own right.
It is also important to recognise that invasive ventilation can also fail and some patients can develop refractory hypoxia or hypercapnia despite such treatment. A range of options exist in terms of manipulation of the ventilator, prone position, advanced ventilation modes (eg high frequency oscillatory ventilation teat involves respiratory rates of >2Hz and has an active expiratory as well as inspiratory phase). In some cases, the degree of hypoxia may necessitate extracorporeal mechanical oxygenation with a machine.
All of these treatments are outside the scope fo this lecture, btu you should know that invasive ventilation is not a panacea for respiratory failure.

27. In a nut shell CPAP is for Type 1 failure BiPAP is for Type 2 failure
In terms of respiratory failure, IPPV is for when the above fails