Table 4—

Comparison in terms of arterial blood gases between patients with normal and abnormal traces

	Acute setting: ARF			At the start of long-term ventilation: CRF			At steady state: LTMV
	Normal	Abnormal	p-value	Normal	Abnormal	p-value	Normal	Abnormal	p-value
P_a,O₂	62±13	61.1±12	ns	68.2±12	64.4±11	ns	68.5±11	63.9±10	<0.03
Pa,_CO₂	63.2±12	70.3±14	<0.03	54.5±7	56.8±10	ns	42.9±6	46.5±9	ns (<0.07)
pH	7.33±0.04	7.31±0.06	ns	7.38±0.03	7.37±0.03	ns	7.41±0.02	7.39±0.03	<0.01
HCO₃^-							30.4±4.5	32.3±3.0	<0.02

Data are presented as mean±sd, unless otherwise stated. The values correspond to arterial blood gases performed before the start of the ventilation in the acute respiratory failure (ARF) and chronic respiratory failure (CRF) groups, and during the first hour in the morning following disconnection from the ventilator in the long-term mechanical ventilation (LTMV) group. As arterial carbon dioxide tension (P_a,CO₂) varies rapidly, lack of difference in terms of P_a,CO₂ between normal and abnormal traces in the LTMV group may be explained by the arterial blood gases sample timing. Note that the arterial oxygen tension (_P_a,O₂) difference between normal and abnormal traces in the LTMV group cannot be explained by a different prescription of oxygen (15 out of 53 patients in the abnormal group and nine out of 47 in the normal group; nonsignificant (ns)).