Oxygen administration is frequently used in veterinary medicine to treat hypoxia. Conventional oxygen administration methods are readily available in most hospitals or clinics and don’t require specialized equipment or skills to administer to the patient. Conventional oxygen therapies include nasal cannula, oxygen cage, hood oxygen and flow-by/mask administration. With conventional oxygen therapy (COT), FIO₂ is limited to 30–75%, and no significant pressure support is provided. Moreover, increasing flow rate could lead to intolerance of the technique and lesion of nasal mucosa. In patients with severe hypoxemia (PaO₂ <60 mm Hg) who fail COT, more aggressive treatment is warranted. The purpose of this lecture is to describe pro and cons for indication and use of two advanced oxygen therapy techniques:

• High-flow oxygen therapy
• Noninvasive ventilation

High-Flow Oxygen Therapy

High-flow oxygen therapy (HOT) is a noninvasive respiratory support modality that provides a humidified and heated air-oxygen mixture to the patient via specific nasal prongs, at flow rates up to 2 L/kg/min. HOT is carried out using an air/oxygen blender, active humidifier, single heated tube, and specific nasal cannula. Those specific nasal cannulas should ideally be 50% or less the diameter of the nares.

Based on the actual literature, these settings could be recommended:

• Flow rate: 1 to 2 L/kg/min
• FiO₂: titrated to have an SpO₂ of 98–100%
• Temperature: a study comparing 31 and 37°C did not show any difference in HOT tolerance in healthy dogs. 31° should be preferred in hyperthermic patients.

HOT is considered to have several advantages:

• Good tolerance via administration of warm and humidified gas
• High delivered FIO₂
• Controllable delivered gas temperature
• Improve gas exchanges
• Provision of positive airway pressure at flow rate above 1 L/kg/min
• Reduction of work of breathing and respiratory rate
• Improvement of dyspnea score
• Ability to eat and drink under oxygen therapy
• Low level of sedation in the dog

Cons of HOT are:

• High associated costs (dedicated machine, high consumption of oxygen, high level of care)
• Some patients will need heavy sedation, especially in cats
• Development of gastric dilation has been described, but usually not clinically relevant
• Prong dislodgement
• Decrease positive pressure support with open-mouth breathing
• Oxygen toxicity
• No sufficient evidence to use HOT in hypercapnic patients
• Pneumothorax/pneumomediastinum: the risk of air-leak syndrome is considered very low, though persistence of a pre-existing pneumothorax that ceased upon discontinuation of HFNC has been reported

Noninvasive Ventilation

Noninvasive ventilation (NIV) is a ventilation mode in which intubation of the patient is not required. The most common NIV used is the continuous positive airway pressure (CPAP) ventilation applied by a face mask or by a helmet. The good adaptation to the muzzle and the sealing of the interface are the key points to maintain the required positive pressure during the respiratory cycle. In fact, the efficacy of the CPAP is related to the positive pressure inside the alveoli at the end of expiration, thus maintaining the alveoli open and recruiting the collapsed ones. The veterinary literature is mostly about the use of the helmet, while there are only two papers about the use of the face mask. An important aspect of the use of CPAP by face mask or helmet is the possible rebreathing of CO₂ due to an inadequate flow of gas (oxygen and/or air). For this reason, animals should not be left unattended during CPAP administration and the adequate inflation of the helmet should be always evaluated.

Based on the actual literature on the use of the helmet, these settings could be recommended:

• Flow rate: 8–10 L/min with the use of a Venturi valve which increases the flow to the helmet
• FiO₂: can be titrated adding an oxygen line to the helmet
• CPAP pressure: 3–7 cm H₂O depending on the patient

NIV CPAP is considered to have several advantages:

• Moderate to good tolerance
• High delivered FIO₂
• Improve gas exchanges
• Provision of a predetermined positive airway pressure
• Reduction of work of breathing and respiratory rate
• Improvement of dyspnoea score
• Low level of sedation in the dog

Cons of NIV CPAP are:

• High associated costs (disposable helmets, high consumption of oxygen, high level of care)
• Some patients will need heavy sedation, especially cats
• No immediate access to the airways of the patient in case of vomit
• The helmet needs to be removed for feeding and drinking

Conclusion

HOT and NIV CPAP are two useful techniques for improving oxygenation in critical patients. HOT should be taken into account in case of hypoxemia without ventilatory impairment, whilst NIV CPAP should be the first choice in case of hypoventilation. However, the tolerance of the patient towards a technique or another and the monitoring of the respiratory effects should be used to guide the clinician for the choice. Severe hypoventilation or respiratory fatigue should be treated with intubation and mechanical ventilation.

References

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