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406 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

Case study
Mr Smith was a 51-year-old man admitted to ICU with septic shock decreased over the next two days, enabling weaning of the FiO 2 to
due to gangrene in his groin. His comorbidities included insulin- 0.35 whilst PEEP remained at 15 cmH 2 O. PEEP was then decreased
dependent diabetes, hypertension and obesity; his admission by 2.5 cmH 2 O twice a day during which time his PaO 2 and SpO 2
weight was 140 kg. Prior to ICU admission, he received 8 L of fluid remained stable.
resuscitation, but remained oliguric and required 25 mcg/min nor- On day 6, his PEEP was down to 7.5 cmH 2 O and CXR was much
adrenaline to maintain a MAP ≥65 mmHg.
improved. Sedation was halved during the morning multidisci-
On admission to ICU, his arterial blood gas was: pH 7.24, PaCO 2 plinary round however he continued to require high dose opiates
−
37 mmHg, PaO 2 79 mmHg, SpO 2 95%, HCO 3 15.6 mmol/L. He was for his wound pain. During the next few hours, his spontaneous
ventilated with SIMV-VC, FiO 2 0.7, PEEP 5 cmH 2O, f 14, V T 600 mL, rate increased and the mandatory breath rate was decreased to 8.
with PIP of 38 cmH 2 O, a spontaneous rate of 8 and V T of 300 mL. At 1700h he became agitated and intolerant of mandatory ventila-
His supine CXR showed small lung fields and diffuse bilateral infil- tor breaths. Rather than increase the sedation, the ventilator mode
trates suggestive of fluid overload. He required large doses of was changed to PSV (PS 15 cmH 2 O/PEEP 7.5 cmH 2 O) which was
sedation to tolerate SIMV and frequently reached the set peak well tolerated. His gas exchange remained stable overnight, and
inspiratory pressure limit. Mr Smith’s head-of-bed was raised as far the following morning sedation was turned off and analgesia
as his groin wound would allow (about 20 degrees) and the whole decreased.
bed tilted to further raise his head. Subsequently, PEEP was
increased to 10 cmH 2 O; and FiO 2 decreased to 0.5 and he was Over the next few days his limb and cough strength gradually
switched to PSV (PS 14, PEEP 10 cmH 2 O). This was well tolerated improved. His mobility was limited due to the groin wound and
and sedation was decreased. RRT, so he was changed to intermittent RRT to facilitate periods of
mobilisation. On day 10 Mr Smith’s ventilator settings were FiO 2
On day 2, during hyperbaric oxygen therapy and despite heavy 0.35, PS 12, PEEP 7.5 cmH 2 O, his spontaneous rate was 18 and V T
sedation, Mr Smith developed agitation, ventilator dyssynchrony 600. His CXR was much improved, gas exchange was good and he
and desaturation (PaO 2 60 mmHg, SpO 2 86% on FiO 2 1). Tracheal could cough spontaneously with minimal sputum. He remained on
suction yielded thin white sputum, but no improvement to oxy- intermittent RRT, but had a normal pH. He was cooperative and had
genation. PEEP was increased to 15 cmH 2O and muscle relaxants reasonable limb strength. He was extubated during the morning
administered. The ventilator mode was changed from SIMV-VC to multidisciplinary round. His gas exchange was good whilst awake,
SIMV-PC resulting in reduced mean airway pressures and improved but he ‘snored’ and had transient drops in SpO 2/PaO 2 and elevated
oxygenation. PaCO 2 when asleep and therefore required NIV overnight.
Mr Smith’s metabolic acidosis continued with deteriorating On day 13 Mr Smith was discharged to the respiratory ward where
renal function and worsening CXR. Renal replacement therapy he could have nocturnal CPAP, and was subsequently diagnosed as
(RRT) was commenced on day 3. His cumulative fluid balance having sleep apnoea.

Research vignette

Blackwood B, Alderdice F, Burns K, Cardwell C, Lavery G, O’Halloran Review methods
P. Use of weaning protocols for reducing duration of mechanical We included randomised and quasi-randomised controlled trials of
ventilation in critically ill adult patients: Cochrane systematic weaning from mechanical ventilation with and without protocols
review and meta-analysis. British Medical Journal 2011; 342: c7237. in critically ill adults.
Abstract Data selection
Objective Three authors independently assessed trial quality and extracted
To investigate the effects of weaning protocols on the total dura- data. A priori subgroup and sensitivity analyses were performed.
tion of mechanical ventilation, mortality, adverse events, quality of We contacted study authors for additional information.
life, weaning duration, and length of stay in the intensive care unit
and hospital. Results
Eleven trials that included 1971 patients met the inclusion criteria.
Design Compared with usual care, the geometric mean duration of
Systematic review.
mechanical ventilation in the weaning protocol group was reduced
Data sources by 25% (95% confidence interval 9% to 39%, P = 0.006; 10 trials);
Cochrane Central Register of Controlled Trials, Medline, Embase, the duration of weaning was reduced by 78% (31% to 93%,
CINAHL, LILACS, ISI Web of Science, ISI Conference Proceedings, P = 0.009; six trials); and stay in the intensive care unit length
Cambridge Scientific Abstracts, and reference lists of articles. We by 10% (2% to 19%, P = 0.02; eight trials). There was significant
did not apply language restrictions. heterogeneity among studies for total duration of mechanical