Table 4.

Relationship Between Center Volume and Length of Mechanical Ventilation After Cardiac Surgery

Center Volume	Unadjusted		Adjusted
	HR (95% CI)	P Value	HR (95% CI)	P Value
Volume as a continuous variablea	0.93 (0.89–0.97)	0.001	0.99 (0.93–1.06)	0.81
Volume as a categorical variable
<175	1.16 (1.10–1.23)	<0.001	1.26 (1.16–1.37)	<0.001
175–275	1.14 (1.08–1.21)	<0.001	1.19 (1.11–1.28)	<0.001
≥275	Ref		Ref
STS‐EACTS risk categories 1–3
Volume as a continuous variablea	0.96 (0.91–1.01)	0.15	1.02 (0.94–1.10)	0.64
Volume as a categorical variable
<175	1.17 (1.09–1.26)	<0.001	1.25 (1.13–1.38)	<0.001
175–275	1.21 (1.13–1.31)	<0.001	1.21 (1.11–1.32)	<0.001
≥275	Ref		Ref
STS‐EACTS risk categories 4–5
Volume as a continuous variablea	1.00 (0.92–1.08)	0.95	0.86 (0.76–0.97)	0.011
Volume as a categorical variable
<175	1.00 (0.91–1.10)	0.99	1.46 (1.25–1.70)	<0.001
175–275	0.98 (0.89–1.08)	0.73	1.16 (1.03–1.30)	0.018
≥275	Ref		Ref

Abbreviations: CI, confidence interval; OR, odds ratio; Ref, reference; STS‐EACTS, Society of Thoracic Surgeons–European Association for Cardiothoracic Surgery.

^aVolume as a continuous variable depicts comparison of high center volume vs low center volume.