High Flow Nasal Oxygen therapy in a young pregnant patient with hypoxemic respiratory failure due to H1N1 influenza viral infection

Pregnant women are at high risk of infection with the novel H1N1 influenza A virus. A 30-year-old pregnant woman at 35 weeks of gestation was admitted with acute onset fever, cough and shortness of breath with hypoxaemic respiratory failure. Laboratory investigations confirmed influenza A infection. This case report illustrates how High Flow Nasal Oxygen device gave good results in hypoxemic respiratory failure especially in the setting of possible unexpected infections and ventilator associated pneumonia.


Introduction
Pregnancy and postpartum period are considered increased risk factors for hospitalization, ICU admission, delayed recovery and death following H1N1 Influenza viral infection. World Health Organization says globally there is a decreasing trend in seasonal influenza. In tropical Asia, the trend is same. There are no recent data available from Sri Lanka, but cases of influenza continue to be reported from all areas of the country.
High Flow Nasal Oxygen device, a new respiratory therapeutic technique which provides warmed humidified high flow oxygen through a nasal cannula is used in patients with hypoxemic respiratory failure. The high flows (e.g. 50L) match with the patient's peak inspiratory flow rates.
In addition, it reduces anatomical dead space and creates a positive pressure in upper airways. Studies demonstrated that High Flow Nasal Device (HFND) provides better oxygenation when compared with conventional face masks and nasal cannulas. 1

Case Presentation
A 30yr old woman in her second pregnancy presented at 35weeks period of gestation with a 6day history of high grade fever, non-productive cough and shortness of breath to Base hospital, Mawanella, Sri Lanka. First pregnancy had been an emergency cesarean section due to foetal distress. She had been in good health throughout this pregnancy, gave no history of travels or exposure to anyone with probable influenza. She had no chronic medical issues and did not smoke. She was not vaccinated against influenza.
On admission, she was reported to have respiratory distress with peripheral oxygen saturation (SpO2) of 85%. She was transferred to intensive care unit (ICU) Teaching Hospital, Peradeniya. On arrival, she was conscious, rational with Glasgow coma scale of 15. She was febrile and tachypnoeic at 40breaths/minute. Chest examination revealed bibasal reduced breath sounds with rhonchi and coarse crepitations. SpO2 on air was 85%. Her HR was 127beats/minute and BP was 112/64mmHg. Abdominal examination revealed a single live fetus. Arterial blood gas analysis (ABG) showed pH: 7 This case report illustrates how non-invasive HFND gave good results in hypoxemic respiratory failure due to influenza H1N1 infection especially in the setting of possible unexpected infections and ventilator associated pneumonia. HFND has several physiological advantages over traditional oxygen therapy devices, including decreased nasopharyngeal resistance, washout of nasopharyngeal dead space, generation of positive pressure in the pharynx, increasing alveolar recruitment, humidification of airways, increased fraction of inspired oxygen and improved mucociliary clearance. 4.5 HFND was also associated with a higher partial pressure of arterial oxygen (PaO2) and lower respiratory rate. 5 HFND is most suitable in conditions of hypoxemic non hypercarbic situations. These patients usually need high fractional inspired oxygen concentration with high inspiratory flow rates. Traditional conventional devices like nasal prongs, face masks can only provide maximum flow rates up to 15L/minute and fractional inspired oxygen concentration not more than 40-55%. HFND can provide 100% humidified heated oxygen at a maximum flow rate of 60L/min. 6 It is better tolerated and more comfortable compared to traditional methods. 7 Although HFND is a supportive therapeutic technique, enhanced respiratory support with this novel device can save lives with very minimal complications.