Editing Breathing

Respiratory failure occurs when there is inadequate pulmonary gas exchange such that blood and carbon dioxide cannot be maintained at normal levels.

* PaO2 < 8kPa is the point on the oxygen-haemoglobin dissociation curve below which rapid desaturation occurs
* Type 1 RF: hypoxia with normal or reduced carbon dioxide
* Type 2 RF: hypoxia with hypercarbia (may have a chronic element - check if bicarbonate is high)
* Commonest cause of decreased LoC in the surgical patient


== '''Classify causes of respiratory failure:''' ==

* '''Acute fall in functional residual capacity without pulmonary vascular dysfunction'''
** Failure of chest mechanics after trauma or other processes that render the lungs stiff and non-compliant
** Acute post-op atelectasis, sputum retention, pneumonia or depression of respiration caused by analgaesic, sedative or neuromuscular blocking drugs
** Frailty and malnutrition contribute
* '''Acute fall in FRC, with pulmonary vascular dysfunction'''
** Left ventricular failure
** Fluid overload
** Pulmonary hypertension
** PE
** Neurogenic pulmonary oedema
** ARDS
* '''Airflow obstruction'''
** COPD
** Asthma
** Others

== Presentation: ==

* Dyspnoea, tachypnoea, apnoea
* Unable to speak in complete sentences
* Using accessory muscles of respiration
* Centrally cyanosed
* Sweating and tachycardic
* Decreased LoC

== '''Initial assessment/management:''' ==

* '''High flow oxygen'''
** Don't worry about depressing hypoxic drive to breathe
**
* '''Apply pulse oximeter'''
** Delay of around 20seconds between actual and displayed values
** Sats >94% is equivalent to 8kPa oxygen
** Impeded by:
*** Factors blocking skin
*** Arrhythmias
*** Profound anaemia
*** SaO2 < 70%
*** Movement
*** Peripheral vasoconstriction
*** Diathermy
*** Bright lights
* '''Chart review'''
* '''Hx and systematic examination'''
** Look, listen, feel - as per 'ABCD' section
* '''Available results'''
** ABG
** ECG
** Bloods
** CXR
** Pre-op RFTs
*** Peak expiratory flow
*** Vital capacity
*** FEV1

== '''Other management factors:''' ==

* Chest PT
* Incentive spirometry
* Nebulised saline, and change inhalers to nebs
* Adequate analgaesia
* Bring CPAP
* HDU vs ICU
* Art line etc
* Humidified oxygen
** Whenever oxygen by mask for >24 hours is required
** High sputum load

== '''Other investigations''' ==

* CTPA
* Sputum sample
* Blood cultures
* COVID/viral PCRs

== '''High-flow nasal oxygen''' ==

* Can deliver up to 100% oxygen with high flows and high humidity
* Good for patients with a high sputum load or those who cannot clear secretions
* Pressure equivalent to 5cm H2O delivered, which can help with WoB
* Generally well-tolerated
* Mainly used for type 1 respiratory failure

== '''CPAP''' ==

* High-flow oxygen supplied through a tight-fitting mask, incorporating expiratory valves, which maintains a set airway pressure from 2.5 to 10cmH20. 
* Airway pressure is prevented from dropping below the set value, leading to recruitment of underventilated alveolae, increased FRC, decreased intrapulmonary shunt and work of breathing, and may improve oxygenation
* Most useful in type 1 resp failure
* Can be used after major surgery to reduce the risk of respiratory complications
* Must be co-operative and in control of airway
* Be careful after upper GI surgery due to risk of involuntary air swallowing and gastric distension
* Can be connected to tracheostomy
* Failing to tolerate CPAP:
** Refractory hypoxaemia
** Increased respiratory rate
** Progressively smaller tidal volumes
** CO2 retention
** Agitation -> obtundation

== '''NIV (BIPAP - bilevel positive airway pressure)''' ==

* Useful in type 2 resp failure to prevent or treat CO2 retention
* High pressure during inspiration (about 20cm H2O), lower pressure during expiration (5cm H2O)
* The pressure difference generates gas flow into the lungs during inspiration
* Not appropriate if CV unstable, decreased GCS, severe metabolic acidosis, low RR, unco-operative
* NGT usually required to reduce gastric distension
* '''If CO2 doesn't improve within 30 mins, it probably won't work'''
* Generally requires critical care support
* Failing to tolerate:
** Refractory hypoxaemia
** Increased RR
** Progressively smaller tidal volumes with worsening CO2 retention

== '''Ventilation''' ==

*
* Allows control of all factors to suit patient's needs, including oxygen 100% and adjustment of RR, TV and frequency
* SIMV - synchronised intermittent mandatory ventilation
** Preserves some of the patient's respiratory muscle activity by synchronising ventilation around the patient's own respiratory effort
* PEEP
** High PEEP causes decreased venous return and a fall in CO, which may be very severe if the patient is hypovolaemic
** High PEEP can cause barotrauma
** High PEEP plus high oxygen can promote the toxic effects of oxygen - generally don't go above 80% with high PEEP
* Highest level of respiratory support is basically PCIRV (pressure-controlled inverse ratio ventilation), FiO2 > 0.8, PEEP>10cm H2O, and permissive hypercarbia. The only other things to do from here are to increase FiO2 to 100% and pronate the patient. After that you will need to put them on cardiopulmonary bypass.
* '''Weaning'''
** Requires:
*** Original cause of resp failure has been treated
*** Sedative drugs low enough not to depress respiration
*** FiO2<0.4 is sufficient maintain PaO2
*** No hypercarbia
*** Minimal sputum
*** Nutritional status is normal and electrolytes
*** Diaphragm and intercostals are working
*** The patient is reasonably co-operative

== Atelectasis ==

* Absence of gas from all or part of a lung
* Reduced breathing -> retention of secretions -> distal collapse
* Risk factors:
** Elderly
** Obese
** Smokers
** Lung disease
* Prevent:
** Pre-op breathing exercises
** Intra-op humidification
** Ensuring good tidal volumes
** Avoid unnecessarily high FiO2
* Presentation
** Cough
** SOB
** CP
** Pleural effusion
** Can develop into cyanosis/tachycardia
** Inflammatory markers will generally be normal - if raised, suspect transformation into pneumonia
* Treat
** Deep breathing
** Coughing
** Analgaesia
** Incentive spirometer
** Mobilisation
** High-flow nasal oxygen

== Pneumonia ==

* Parenchymal or alveolar inflammation and abnormal alveolar filling with fluid
* Severity:
** CURB65 - three or more factors = ICU
** Confusion
** Urea>7
** RR>=30
** SBP <90 or DBP < 60
** Age >=65

[[Category:Critical care]]