Respiratory Failure-When to Use HFNC and/or BiPAP Steven Podnos MD
Three Types of Respiratory Failure• Definition: Inadequate Gas Exchange• Three types:• Inability to Oxygenate• Inability to Ventilate• Inability to Protect Airway-never candidates for noninvasive ventilation!
Inability to Oxygenate• Implies that alveoli are not exchanging gases-usually hypoxemia. Can be V/Q mismatch or true shunt• Alveoli are filled with fluid-CHF, Non Cardiogenic Pulm Edema (ARDS), infected fluid (pneumonia)• Rx O2 to keep sat 90% or better• If unable to maintain sats with face mask/Nasal cannula- need HFNC, positive pressure like BiPAP or intubation• Usually increased work of breathing-patients may tire and develop hypercapnia (high pCO2)• Rx underlying condition: diurese CHF, supportive for ARDS, antibiotics for infection
Inability to Ventilate• Abnormalities in lung (or external) mechanics. Hallmark is hypercapnia. Elevated pCO2 displaces O2, but hypoxemia easy to treat. May be intrinsic to lung (COPD), or extrinsic (OD, neuromuscular disease)• Alveoli are “OK” in general• Common causes of type II (hypercapnic) respiratory failure• Chronic bronchitis and emphysema (COPD)• Severe asthma• Drug overdose• Poisonings• Myasthenia gravis• Polyneuropathy• Poliomyelitis• Primary muscle disorders• Porphyria• Cervical cordotomy• Head and cervical cord injury• Primary alveolar hypoventilation• Obesity hypoventilation syndrome• Pulmonary edema• Adult respiratory distress syndrome• Myxedema• Tetanus• (note overlap with failure to oxygenate)
Treatment of Respiratory Failure:• Airway• Oxygenation• Aerosol bronchodilators• Diuretics• Antibiotics• Supportive Rx for Hypercapnia is Positive Pressure Ventilation (external or with ETT)• Steroids for bronchospasm• DVT, GI bleed prophylaxis• O2 toxicity-including risk of worsening hypercapnia
Monitoring of Treatment• RR, HR• O2 sat• ABG mostly useful for pCO2, acid-base status• Mental Status
High Flow Nasal Cannula• In infants, high flow Nasal Cannula appears to have some positive pressure benefit and may be equivalent to Nasal CPAP in efficacy• In Adults, allows higher concentration of inspired oxygen than a traditional nasal cannula. Flows at 35L/min appear to provide low levels of positive pressure (CPAP), especially with a closed mouth.
HFNC or BiPAP in Adults• If the patient requires positive pressure ventilation, choose BiPAP.• If they patient primarily requires a high level of inspired oxygen (CHF, ARDS without fatigue), then HFNC may be adequate
Non Invasive Ventilation• Using positive pressure ventilation without an endotracheal tube• Used for Obstructive Sleep Apnea, Respiratory Support of various illnesses to prevent intubation
CPAP• Continuous Positive Airway Pressure-usually a set level pressure-same with inspiration and expiration. Note that Expiratory Pressure is the same thing as PEEP (Positive End Expiratory Pressure). Normal PEEP is zero!
BiPAP vs. CPAP• Individually set Inspiratory and Expiratory Pressures. Can also adjust timing of I/E• Indicated for difficulty with Oxygenation (EPAP/PEEP) and/or Respiratory muscle support (IPAP)• Contraindications: Risk of Aspiration, Agitation, Poor cough, lack of cooperation
Advantages of BiPAP• May reverse impending respiratory failure and avoid intubation• Reduced risk of nosocomial pneumonia• Buys time while reversing hypercapnia and cardiogenic pulmonary edeama
Disadvantages of BiPAP• Complications of noninvasive ventilation• Facial and nasal pressure injury and sores – Result of tight mask seals used to attain adequate inspiratory volumes – Minimize pressure by intermittent application of noninvasive ventilation – Schedule breaks (30-90 min) to minimize effects of mask pressure – Balance strap tension to minimize mask leaks without excessive mask pressures – Cover vulnerable areas (erythematous points of contact) with protective dressings• Gastric distension – Rarely a problem – Avoid by limiting peak inspiratory pressures to less than 25 cm water – Nasogastric tubes can be placed but can worsen leaks from the mask – Nasogastric tube also bypasses the lower esophageal sphincter and permits reflux• Dry mucous membranes and thick secretions – Seen in patients with extended use of noninvasive ventilation – Provide humidification for noninvasive ventilation devices – Provide daily oral care• Aspiration of gastric contents – Especially if emesis during noninvasive ventilation – Avoid noninvasive ventilation in patient with ongoing emesis or hematemesis• Complications of both noninvasive and invasive ventilation Barotrauma (significantly less risk with noninvasive ventilation)• Hypotension related to positive intrathoracic pressure (support with fluids)
BiPAP Settings• Typically begin with 10cm Inspiratory and 5cm Expiratory Pressures. Adjust as needed for support and hypoxemia.• Remember, EPAP = PEEP• PEEP paradoxically can help with both Shunt and Obstructive Disease