24 difficult to wean patients underwent three spontaneous breathing trials in random order, with PA catheter monitoring in place. T-piece spontaneous ventilation was compared with pressure support ventilation 7 cmH20 without PEEP, and with pressure support ventilation 7 cmH20 with 5 cmH20 PEEP. T-piece was associated with higher SBT failure rates and more patient effort, left ventricular failure, and smaller tidal volumes. The study suggests that in selected difficult-to-wean patients, clinical and physiological responses differ depending on the type of SBT used to ascertain whether or not a patient is ready for extubation. Of note, the authors did not extubate the patients who succeeded a PSV trial, because it has been shown that a spontaneous breathing trial using T-piece mimics the work of breathing performed after extubation, and an extubation failure is associated with high mortality.
Physiological comparison of three spontaneous breathing trials in difficult-to-wean patients
Intensive Care Med. 2010 Jul;36(7):1171-9
Category Archives: ICU
Stuff relevant to patients on ICU
Dexmedetomidine meta-analysis
Results from 24 studies on dexmedetomidine were assessed in a meta-analysis to determine the effect on ICU length of stay. The authors concluded that the limited evidence suggests that dexmedetomidine might reduce length of ICU stay in some critically ill patients, but the risk of bradycardia was significantly higher when both a loading dose and high maintenance doses (>0.7 μg/kg/h) were used.
Use of dexmedetomidine as a sedative and analgesic agent in critically ill adult patients: a meta-analysis.
Intensive Care Med. 2010 Jun;36(6):926-39
Mallampati assessment in ED airways
In a series of approximately 300 patients intubated in the ED, operators were unable to complete a Mallampati assessment in three quarters of them, citing lack of patient cooperation and critical illness as the main reasons. This is in keeping with work by Richard Levitan, lending further support to the lack of applicability of routine pre-operative airway assessment methods in critical care.
Feasibility of the preoperative Mallampati airway assessment in emergency department patients
J Emerg Med. 2010 Jun;38(5):677-8
British Thoracic Society pneumothorax guideline
The Britsh Thoracic Society has published its 2010 guidelines on the management of spontaneous pneumothorax. These are one of number of guidelines for the management of pleural disease.
Management of spontaneous pneumothorax: British Thoracic Society pleural disease guideline 2010
Thorax 2010;65(Suppl 2):ii18-ii31
All pleural disease guidelines
Saline can be used in place of US gel
A study comparing sterile saline as a conduction agent with ultrasound gel showed adequate visualization of anatomic structures for ultrasound-guided vascular access. The authors state that given sterile saline’s theoretical advantages over gel in terms of availability, cost, safety and ease of use in the procedural field, it should be considered as a viable alternative to gel as a conduction agent.
Use of sterile saline as a conduction agent for ultrasound visualization of central venous structures
Emerg Med Australas. 2010 Jun;22(3):232-5
Etomidate in RSI – systematic review
A systematic review of 20 included studies comparing a bolus dose of etomidate for rapid sequence induction with other induction agents resulted in the following conclusion:
“The available evidence suggests that etomidate suppresses adrenal function transiently without demonstrating a significant effect on mortality. However, no studies to date have been powered to detect a difference in hospital, ventilator, or ICU length of stay or in mortality”
The Effect of a Bolus Dose of Etomidate on Cortisol Levels, Mortality, and Health Services Utilization: A Systematic Review
Ann Emerg Med. 2010 Aug;56(2):105-13
Complex acid-base problems
Working out the expected compensatory response to an acid base disturbance often reveals a second acid-base problem that was otherwise hidden. I regularly use Winter’s formula when I see a metabolic acidosis, but I have trouble remembering the others, so here they are, from Harwood-Nuss’ Clinical Practice of Emergency Medicine (apologies if you ‘think’ in kilopascals):
Formulas Describing Expected Compensatory Response to Primary Acid–Base Disturbances
Simple Metabolic Acidosis
- Predicted decreased PCO2 mm Hg = 1.2 × Δ(HCO3-) mEq/L
- Predicted PCO2 mm Hg = 1.5(HCO3-) mEq/L + 8 ± 2
- Anticipated PCO2 approximates last two digits of arterial pH
Simple Metabolic Alkalosis
- Predicated increased Δ PCO2 mm Hg = 0.67 × Δ(HCO3-) mEq/L
Simple Acute Respiratory Acidosis
- Predicted decreased ΔpH units = 0.8 × Δ PCO2 mm Hg
- Predicted increased Δ(HCO3-) mEq/L = 0.1 × Δ PCO2 mm Hg
Simple Chronic Respiratory Acidosis
- Predicted decreased ΔpH units = 0.3 × Δ PCO2 mm Hg
- Predicted increased Δ(HCO3-) mEq/L = 0.35 × Δ PCO2 mm Hg
Simple Acute Respiratory Alkalosis
- Predicted increased ΔpH units = 0.8 × Δ PCO2 mm Hg
- Predicted decreased Δ(HCO3-) mEq/L = 0.2 × Δ PCO2 mm Hg
Simple Chronic Respiratory Alkalosis
- Predicted increased ΔpH units = 0.17 × Δ PCO2 mm Hg
- Predicted decreased Δ(HCO3-) mEq/L = 0.5 × Δ PCO2 mm Hg
Femoral SvO2 not so useful
Bloods sampled from both femoral vein and SVC-sited catheters in critically ill patients showed good correlation in lactate levels but the oxygen saturation was not so reliable, with >5% variation in more than 50% and >15% variation in some patients. The authors suggest one reason is that the femoral catheter tip usually sits in the iliac vein and samples blood prior to the mixing of blood returning from intra-abdominal organs. They advise caution in using SfvO2 to guide resuscitation when narrow end points are used, as this may lead to inappropriate vasoactive drug or blood component therapy.
Femoral-Based Central Venous Oxygen Saturation Is Not a Reliable Substitute for Subclavian/Internal Jugular-Based Central Venous Oxygen Saturation in Patients Who Are Critically Ill
Chest. 2010 Jul;138(1):76-83
ALI / ARDS strategies
A CME article in Critical Care Medicine summarises the literature on ARDS (including its limitations) and provides evidence based recommendations on what to do about severe hypoxaemia. They summarise:
For life-threatening hypoxaemia, initial management with a recruitment manoeuvre and/or high PEEP should be undertaken if plateau airway pressures and lack of barotrauma allow. If not, or if these are not effective, then proceed to the prone position or HFOV. If hypoxemia still persists, then consider the administration of inhaled NO. If NO fails, then glucocorticoids can then be administered. For elevated plateau airway pressures when tidal volumes are 4 mL/kg, consider prone positioning or HFOV. For life- threatening respiratory acidosis, consider the use of a buffer or continuous veno-venous hemofiltration. It is most important to assess for objective physiologic improvement in the appropriate time period for each intervention. If no benefit is evident, then the therapy should be discontinued to minimise harm and delay in the initiation of another therapy. If the patient continues to have life-threatening hypoxemia, acidosis, or elevated plateau airway pressures, then consider ECMO or extracorporeal carbon dioxide removal.
Therapeutic strategies for severe acute lung injury
Crit Care Med. 2010 Aug;38(8):1644-50
Less RSI desaturation with Roc
Some of my pre-hospital critical care colleagues in the UK exclusively use rocuronium in preference to suxamethonium for rapid sequence induction (RSI) of anaesthesia in critically ill patients. I couldn’t see a good reason to switch although now there’s some evidence that adds to the argument.
The muscle fasciculations caused by the depolarising effect of suxamethonium may increase oxygen consumption, which may shorten the apnoea time before desaturation. Non-depolarising neuromuscular blockers such as rocuronium should allow a longer apnoea time after RSI. In addition, drugs which reduce fasciculations (such as lidocaine and fentanyl) should delay the the onset of desaturation when given prior to suxamethonium.
These hypotheses were tested in a blinded, randomised controlled trial in 60 ASA-1 or -2 patients, who were scheduled for elective surgery under general anaesthesia. All patients received 2mg/kg propofol. One group was randomised to receive suxamethonium 1.5 mg/kg, a second group received rocuronium 1mg/kg plus lidocaine 1.5mg/kg and fentanyl 2mcg/kg, and a third group was given suxamethonium 1.5 mg/kg plus lidocaine 1.5mg/kg and fentanyl 2mcg/kg. The facemask was removed 50 seconds after the neuromuscular blocker was given and patients were intubated; the tube was then left open to air until desaturation to 95% occurred, which was timed.
Desaturation occurred significantly sooner in the suxamethonium-only group, followed by the sux/lido/fentanyl group, followed by the roc/lido/fentanyl group.
Of course these results are not necessarily directly applicable to the critically ill patient, and in this study there was no direct comparison between induction agent + rocuronium only and induction agent + suxamethonium only. Nevertheless the argument that suxamethonium-induced muscle fasciculations contribute to an avoidable increase in oxygen consumption is persuasive.
Effect of suxamethonium vs rocuronium on onset of oxygen desaturation during apnoea following rapid sequence induction
Anaesthesia. 2010 Apr;65(4):358-61