Arterial oxygen tensions in mechanically ventilated ICU patients and mortality: a retrospective, multicentre, observational cohort study.

BACKGROUND: Supplemental oxygen therapy is commonly required for respiratory failure requiring mechanical ventilation in the ICU. However, hyperoxaemia may be injurious and may increase mortality. We evaluated the relationship amongst the degree of hyperoxaemia and changes in fraction of inspired oxygen (Fio2) in response to hyperoxaemia, as well as associations with mortality in mechanically ventilated ICU patients. METHODS: We retrospectively identified all invasively mechanically ventilated patients admitted to five ICUs, and retrieved all oxygen tension (Pao2) and Fio2 data. We assessed the time between arterial blood gas (ABG) samples, proportions of patients with hyperoxaemia, and changes in Fio2 when hyperoxaemia was present. The primary outcome was the association between Pao2 (assessed by mechanically ventilated exposure-time-divided area under the curve [AUC]) and mortality (in-ICU and post-ICU discharge) using a multistate illness-death model with transition intensities estimated by Cox proportional hazards models. RESULTS: We assessed 177 769 ABG analyses obtained from 4998 patients between January 2012 and June 2016. The median time between ABGs was 3 h (inter-quartile range: 2-4 h); the median Pao2 was 11.3 kPa (9.8-13.6 kPa), and Fio2 was 0.40 (0.35-0.50). Hyperoxaemia (Pao2 >13.7 kPa) was present in 23.9% of the ABGs, and hyperoxaemia seemed to be disregarded when Fio2 was <0.40, as >50% of these Fio2 values were not subsequently reduced. AUC Pao2 >16.0 kPa was associated with increased ICU mortality (adjusted hazard ratio: 1.75; 95% confidence interval: 1.28-2.40). CONCLUSIONS: In mechanically ventilated ICU patients, hyperoxaemia was common. Although oxygen supplementation was often reduced when hyperoxaemia was observed, several patients remained hyperoxaemic. Hyperoxaemia was associated with increased ICU mortality in these patients.

Long-term mortality and health-related quality of life of lower versus higher oxygenation targets in ICU patients with severe hypoxaemia.

PURPOSE: We assessed outcomes after 1 year of lower versus higher oxygenation targets in intensive care unit (ICU) patients with severe hypoxaemia. METHODS: Pre-planned analyses evaluating 1-year mortality and health-related quality-of-life (HRQoL) outcomes in the previously published Handling Oxygenation Targets in the ICU trial which randomised 2928 adults with acute hypoxaemia to targets of arterial oxygen of 8 kPa or 12 kPa throughout the ICU stay up to 90 days. One-year all-cause mortality was assessed in the intention-to-treat population. HRQoL was assessed using EuroQol 5 dimensions 5 levels (EQ-5D-5L) questionnaire and EQ visual analogue scale score (EQ-VAS), and analyses were conducted in both survivors only and the intention-to-treat population with assignment of the worst scores to deceased patients. RESULTS: We obtained 1-year vital status for 2887/2928 (98.6%), and HRQoL for 2600/2928 (88.8%) of the trial population. One year after randomisation, 707/1442 patients (49%) in the lower oxygenation group vs. 704/1445 (48.7%) in the higher oxygenation group had died (adjusted risk ratio 1.00; 95% confidence interval 0.93-1.08, p = 0.92). In total, 1189/1476 (80.4%) 1-year survivors participated in HRQoL interviews: median EQ-VAS scores were 65 (interquartile range 50-80) in the lower oxygenation group versus 67 (50-80) in the higher oxygenation group (p = 0.98). None of the five EQ-5D-5L dimensions differed between groups. CONCLUSION: Among adult ICU patients with severe hypoxaemia, a lower oxygenation target (8 kPa) did not improve survival or HRQoL at 1 year as compared to a higher oxygenation target (12 kPa).

Localized muscle pain causes prolonged recovery after fatiguing isometric contractions.

The purpose of this study was to investigate the force and electromyographic (EMG) signal recorded from the muscles immediately after a sustained fatiguing contraction with or without muscle pain. Ten subjects performed sustained dorsi- and plantarflexions at two contraction levels (50 and 80% of maximum voluntary contraction) until exhaustion with or without muscle pain induced by injection of 6% hypertonic saline in one of the torque producing muscles. The muscle pain intensity was scored on a visual analogue scale (VAS, 0-10 cm). The root mean square (RMS) of the surface EMG signal from plantarflexors and dorsiflexors were estimated during maximum voluntary contractions (MVC) and ramp contractions before and after the fatiguing task at 0, 5, 10 and 15 min during the recovery phase. VAS scores immediately after the contractions with hypertonic saline (on average 3.2 +/- 1.1 cm) progressively decreased during recovery and no pain was experienced 15 min after the contraction. After the painful contraction the RMS-EMG during MVC was on average decreased (23.4 +/- 7.4%) compared to the non-painful condition both in muscles where pain was previously induced and in non-painful synergists. During recovery, the slope of the torque-EMG curve during ramp contraction was significantly decreased (28.4 +/- 8.1%) after the painful contraction compared to the control contraction both for the muscle previously exposed to pain and also the other active synergists. The decreased EMG during recovery after painful contractions compared with control was not accompanied by significant reductions in force during MVC indicating a change in the strategy for motor unit recruitment. This study shows that localized muscle pain inhibits muscle activation and increases the effects of fatigue on EMG recovery curves both for painful and non-painful synergists probably by a central effect. These effects can modify the normal patterns of synergistic activation and can also generate overload problems in muscle pain patients if compensatory motor control strategies are applied.

The influence of muscle pain and fatigue on the activity of synergistic muscles of the leg.

The purpose of this study was to investigate the effect of experimentally induced muscle pain on the motor-control strategies of synergistic muscles during submaximal fatiguing isometric contractions. The root mean square (RMS) and median frequency (MF) of the surface electromyographic (EMG) signal from synergistic plantarflexors and dorsiflexors were assessed to exhaustion. Ten subjects performed sustained dorsiflexions and plantarflexions at two contraction levels, 50% and 80% of maximum voluntary contraction, with or without muscle pain, induced by injection of 6% hypertonic saline in one synergist. In the painful contractions, the RMS of the EMG signal was decreased compared to the control condition in the initial phase of the contraction, in the muscles where pain was induced as well as in the nonpainful synergists. Moreover, the EMG signal MF decreased faster during muscle pain than in the control condition. The endurance time was shorter during muscle pain, and some of the nonpainful synergists showed increased compensatory activity at the end of the contractions to maintain the target force. The decreased EMG activation during pain was coupled with significantly decreased torque levels during the painful condition that would partly explain the results. However, the ratio between force and EMG amplitude was decreased for both the painful and nonpainful synergists, so other mechanisms might explain the present findings. This study shows that localized muscle pain can reorganize the EMG activity of synergists where no pain is present. These findings may have implications for the understanding of manifestations seen in relation to painful musculoskeletal disorders.