Please see Bibliography of References for a list of abstracts, manuscripts and posters.

Other Studies

Thenar oxygen saturation (StO₂) measured non-invasively by near-infrared spectroscopy during weaning from mechanical ventilation. Preliminary results

Gruartmoner G, Mesquida J, Masip J, Martinez ML, Baigorri F, Artigas A. Int Care Med. 2009;35(Suppl 1):S206.

Aims: To determine whether changes in tissue oxygen saturation (StO₂) measured by near-infrared spectroscopy (NIRS) on the thenar eminence, and its changes derived from an ischemic challenge, can be used to predict success of weaning from mechanical ventilation.

Methods: Prospective clinical study, performed in a 26-bed medical-surgical intensive care unit, at a university-affiliated hospital. We recruited adult patients with acute respiratory failure receiving mechanical ventilation for at least 48 h, and considered ready to wean by their physicians. Patients underwent a 30 min spontaneous breathing trial (SBT). Continuous StO₂ was measured non-invasively on the thenar eminence. A transient arterial occlusion proximal to the StO₂ probe was performed twice (baseline, and at minute 30 of SBT). Demographic data, StO₂, gas exchange, ventilatory parameters and hemodynamic measurements were recorded just before starting the trial, and during the trial.

Results: Thirty patients were studied. Main variables measured are shown in Table 1. Five patients did not succeed the SBT. Twenty-three patients succeed the SBT, and were extubated. Two of these patients needed re-institution of MV within 24 h. Patients who failed the overall weaning trial (n = 7) showed a significant increase in their thenar StO₂ deoxygenation rate (DeOx) during the ischemic challenge at minute 30 of SBT as compared to patients who were successfully weaned (-25 ± 15 vs. -13 ± 3%/min, p 0.05). The ratio between the 30 min DeOx and the baseline DeOx (DeOx ratio) was also different between both groups of patients (1.8 ± 0.7 vs. 1.0 ± 0.3, p 0.009). The DeOx ratio showed an AUC 0.88 (p 0.01) for prediction of weaning success. A DeOx ratio cut-off value of 1.4 has a sensitivity 0.8, specificity 0.94, for predicting weaning success.

MEASUREMENTS AT BASELINE AND MINUTE 30

	Weaning success (n = 23)			Weaning failure (n = 7)
	Baseline	Minute 30		Baseline	Minute 30
MAP (mmHg)	82 ± 9	82 ± 15		81 ± 16	89 ± 23
RR (resp/min)	18 ± 3	23 ± 6		19 ± 2	29 ± 7
Vt (mL)	471 ± 8	470 ± 132		466 ± 60	335 ± 110
pH	7.46 ± 0.06	7.45 ± 0.08		7.46 ± 0.08	7.44 ± 0.03
pCO2 (mmHg)	34 ± 5	36 ± 7		36 ± 4	39 ± 4
StO2 (%)	81 ± 5	81 ± 6		76 ± 7	75 ± 8
DeOx (% per min)	-16 ± 12	-13 ± 3		-15 ± 7	-25 ±15*
DeOx ratio		1.04 ± 0.29			1.77 ± 0.69*

Conclusions: Weaning failure was associated with increased deoxygenation rate during an ischemic challenge after 30 min of SBT. Measurement of StO₂ and its changes during transient arterial occlusion might be helpful in predicting weaning outcome.