Canadian Respiratory Journal

Research Article

Predictors of Helmet CPAP Failure in COVID-19 Pneumonia: A Prospective, Multicenter, and Observational Cohort Study

Table 1

Clinical characteristics at admission and after CPAP positioning and predictors of CPAP failure


Characteristics (n = 354)	All CPAP patients (n = 354)	CPAP success (n = 218)	CPAP failure (n = 136)	value^a

Age (years)	64 (56–73)	62 (54–71)	69 (60–76)	<0.001
Males, n (%)	260 (73.4)	164 (75.2)	96 (70.6)	0.336
Hypertension, n (%)	164 (46.3)	98 (45)	66 (48.5)	0.512
Diabetes mellitus, n (%)	80 (22.6)	45 (20.6)	35 (25.7)	0.275
Ischemic heart disease, n (%)	56 (15.8)	21 (9.6)	35 (25.7)	<0.001
COPD, n (%)	25 (7.1)	10 (4.6)	15 (11)	0.021
DNI, n (%)	51 (14.4)	19 (8.7)	32 (23.5)	<0.001
In-hospital treatment (n = 272)
Systemic corticosteroids, n (%)	190 (69.9)	107 (69.0)	83 (70.9)	0.734
Tocilizumab, n (%)	45 (12.7)	25 (11.5)	20 (9.2)	0.682
LMWH, prophylactic, n (%)	103 (37.9)	67 (43.2)	36 (30.8)	0.067
LMWH, therapeutic, n (%)	156 (57.4)	84 (54.2)	72 (61.5)	0.084
Outcomes (n = 354)
Time to CPAP start, days	2 (1–4)	2 (1–4)	1 (0–3)	0.086
CPAP duration, days	6 (3–9)	6 (4–10)	4 (3–8)	<0.001
Hospital length of stay, days	16 (11–25)	18 (13–26)	11 (6–20)	<0.001
Admitted to ICU, n (%)	97 (27.4)	0	97 (71.3)	N.A.
Received NIV after CPAP failure in ICU, n (%)	20 (20.6)	0	20 (20.6)	N.A.
ETI, n (%)	71 (20.1)	0	71 (52.2)	N.A.
ETI after NIV, n (%)	20 (100)	0	20 (100)	N.A.
ETI not moved to ICU, n (%)	7 (2.0)	0	7 (5.1)	N.A.
In-hospital mortality, n (%)	96 (27.1)	0	96 (70.6)	N.A.
ICU mortality, n (%)	64 (66.0)	0	65 (66.0)	N.A.
Mortality after positioning NIV, n (%)	12 (60.0)	0	12 (60.0)	N.A.
Mortality among DNI, n (%)	32 (9.0)	0	32 (23.5)	N.A.
Clinical variables at admission
White blood cells (×10⁶/L)	7.37 (5.50–10.11)	7.06 (5.4–9.6)	8.5 (5.7–11.6)	0.019
Platelets (×10⁶/L)	214 (165–298)	221 (172–303)	201 (148–284)	0.052
D-dimer (µg/L FEU)	854 (489–1425)	709 (425–1199)	1084 (642–2456)	<0.001
CRP (mg/L)	34 (12–114)	31 (11–92)	39 (15–143)	0.039
Body temperature (°C)	37.1 (36.4–38)	37 (36.4–37.8)	37.4 (36.5–38)	0.067
CPAP parameters
PEEP (cmH₂O)	10 (7.5–10)	10 (7.5–10)	10 (8–12)	0.002
FiO₂ (%)	60 (50–60)	60 (50–60)	60 (60–70)	<0.001
Respiratory and clinical parameters before CPAP positioning (T0)
pH	7.47 (7.45–7.50)	7.47 (7.45–7.50)	7.48 (7.45–7.51)	0.808
PaCO₂ (mmHg)	33 (29–37)	33 (30–37)	32 (29–35)	0.058
PaO₂/FiO₂ (mmHg)	161 (100–252)	194 (122–273)	110 (68–181)	<0.001
A-a O₂ gradient (mmHg)	239 (61–432)	179 (56–315)	326 (96–604)	<0.001
Respiratory rate (bpm)	27 (23–30)	25 (22–30)	28 (24–34)	<0.001
Glasgow coma scale	15 (15–15)	15 (15–15)	15 (15–15)	0.001
ROX index (%/bpm)	8 (4.4–14.8)	9.5 (5.9–15.9)	5.4 (3.3–11.1)	<0.001
mROX index (mmHg/bpm)	6.1 (3.6–9.7)	7.3 (4.8–11.1)	4.3 (2.3–6.5)	<0.001
HACOR score	4.0 (0–6.0)	2 (0–5.0)	6 (3.0–6.3)	<0.001
Respiratory and clinical parameters 1 hour after CPAP positioning (T1)
pH	7.46 (7.44–7.49)	7.46 (7.44–7.49)	7.47 (7.43–7.49)	0.812
PaCO₂ (mmHg)	36 (33–40)	37 (34–40)	35 (31–39)	0.004
PaO₂/FiO₂ (mmHg)	188 (126–251)	207 (161–265)	132 (108–220)	<0.001
A-a O₂ gradient (mmHg)	254 (196–308)	230 (183–279)	302.6 (234–330)	<0.001
Respiratory rate (bpm)	24 (20–28)	24 (20–28)	26 (22–30)	<0.001
Glasgow coma scale	15 (15–15)	15 (15–15)	15 (15–15)	0.011
ROX index (%/bpm)	6.9 (5.6–8.5)	7.6 (6.2–9.2)	6.2 (4.7–7.7)	<0.001
mROX index (mmHg/bpm)	7.6 (5.1–10.9)	8.8 (6.7–12.1)	5.8 (3.8–8.9)	<0.001
HACOR score	2 (0–5)	1 (0–3)	5 (2–6)	<0.001

Data are presented as medians (interquartile range), unless otherwise stated. DNI, “do-not-intubate” order; A-a O₂ gradient, alveolar-arterial oxygen gradient; bpm, breaths per minute; CI, confidence interval; CPAP, continuous positive airway pressure; CRP, C-reactive protein (upper limit of normal = 10 mg/L); FEU, fibrinogen equivalent units; GCS, Glasgow coma scale; PaO_2, arterial partial pressure of oxygen; PaCO_2, arterial partial pressure of carbon dioxide; ROX index, SpO₂/FiO₂/respiratory rate; mROX index, modified ROX index (PaO₂/FiO₂/respiratory rate); HACOR, heart rate, acidosis (pH), consciousness (Glasgow coma scale: GCS), oxygenation, and respiratory rate; AUROC, area under the receiver operating characteristic curve. ^aComparison between CPAP success and CPAP failure. denotes seven (3.2%) patients in the success group vs. 16 (11.8%) patients in the failure group had a GSC <15. denotes eight (3.7%) patients in the success group vs. 15 (11%) patients in the failure group had a GSC <15. denotes among patients admitted to ICU.