Table 1. Baseline characteristics of the study subjects.

Variable	HFNC success (n=23)	HFNC failure (n=29)	P
Age, years	58 [51–65]	56 [44–64]	0.52
Male sex	13 [57]	15 [52]	0.73
BMI, kg/m2	21.4 [20.7–23.5]	20.2 [18.9–22.9]	0.12
Underlying disease
Solid cancer	4 [17]	2 [7]	0.39
Hematologic malignancy	10 [44]	10 [35]	0.51
Connective tissue disease	3 [13]	7 [24]	0.48
Solid organ transplant	5 [22]	8 [28]	0.63
Steroid use	22 [96]	27 [93]	>0.99
Other immunosuppressant	6 [26]	13 [45]	0.16
Vital signs & laboratory data
Body temperature, °C	37.0 [36.7–38.0]	37.9 [37.2–38.5]	0.07
Mean arterial pressure, mmHg	81 [70–90]	77 [70–87]	0.63
Heart rate, beats/min	102 [93–116]	117 [109–122]	0.01
Breathing frequency, breaths/min	22 [21–24]	23 [21–24]	0.64
PaO2/FiO2	252 [199–317]	225 [167–276]	0.19
P(A-a)O2, mmHg	65 [48–140]	133 [65–226]	0.03
Serum bicarbonate, mEq/L	23.2 [20.4–27.0]	21.0 [17.6–23.0]	0.007
C-reactive protein, mg/dL	14.0 [4.5–17.1]	10.8 [6.2–18.5]	0.68
Lactate dehydrogenase, IU/L	356 [328–473]	600 [324–720]	0.16
Severity of illness
APACHE II score	15 [11–17]	17 [14–19]	0.07
SOFA score	3 [3–4]	4 [4–6]	0.002
Vasopressor use	2 [9]	16 [55]	<0.001
Co-infection
Bacteria/fungus	1 [4]	2 [7]	>0.99
Cytomegalovirus	0	7 [24]	0.01
Virus other than cytomegalovirus	4 [17]	7 [24]	0.74
Time from ARF to PCP treatment, hours	17 [6–30]	16 [5–34]	0.89

Data are presented as median (interquartile range) or number (percentage) of subjects. HFNC, high flow nasal cannula; BMI, body mass index; PaO₂, arterial partial pressure of oxygen; FiO₂, fraction of inspired oxygen; P(A-a)O₂, alveolar-arterial PO₂ difference; APACHE, Acute Physiology and Chronic Health Evaluation; SOFA, Sequential Organ Failure Assessment; ARF, acute respiratory failure; PCP, pneumocystis pneumonia.