Risk prediction models for delirium in the intensive care unit after cardiac surgery: a systematic review and independent external validation.

Numerous risk prediction models are available for predicting delirium after cardiac surgery, but few have been directly compared with one another or been validated in an independent data set. We conducted a systematic review to identify validated risk prediction models of delirium (using the Confusion Assessment Method-Intensive Care Unit tool) after cardiac surgery and assessed the transportability of the risk prediction models on a prospective cohort of 600 consecutive patients undergoing cardiac surgery at a university hospital in Hong Kong from July 2013 to July 2015. The discrimination (c-statistic), calibration (GiViTI calibration belt), and clinical usefulness (decision curve analysis) of the risk prediction models were examined in a stepwise manner. Three published high-quality intensive care unit delirium risk prediction models (n=5939) were identified: Katznelson, the original PRE-DELIRIC, and the international recalibrated PRE-DELIRIC model. Delirium occurred in 83 patients (13.8%, 95% CI: 11.2-16.9%). After updating the intercept and regression coefficients in the Katznelson model, there was fair discrimination (0.62, 95% CI: 0.58-0.66) and good calibration. As the original PRE-DELIRIC model was already validated externally and recalibrated in six countries, we performed a logistic calibration on the recalibrated model and found acceptable discrimination (0.75, 95% CI: 0.72-0.79) and good calibration. Decision curve analysis demonstrated that the recalibrated PRE-DELIRIC risk model was marginally more clinically useful than the Katznelson model. Current models predict delirium risk in the intensive care unit after cardiac surgery with only fair to moderate accuracy and are insufficient for routine clinical use.

Local anaesthetic toxicity after bilateral thoracic paravertebral block in patients undergoing coronary artery bypass surgery.

We conducted a small pilot observational study of the effects of bilateral thoracic paravertebral block (BTPB) as an adjunct to perioperative analgesia in coronary artery bypass surgery patients. The initial ropivacaine dose prior to induction of general anaesthesia was 3 mg/kg, which was followed at the end of the surgery by infusion of ropivacaine 0.25% 0.1 ml/kg/hour on each side (e.g. total 35 mg/hour for a 70 kg person). The BTPB did not eliminate the need for supplemental opioids after CABG in the eight patients studied. Moreover, in spite of boluses that were within the manufacturer's recommendation for epidural and major nerve blocks, and an infusion rate that was only slightly higher than what appeared to be safe for epidural infusion, potentially toxic total plasma ropivacaine concentrations were common. We also could not exclude the possibility that the high ropivacaine concentrations were contributing to postoperative mental state changes in the postoperative period. Also, one patient developed local anaesthetic toxicity after the bilateral paravertebral dose. As a result, the study was terminated early after four days. The question of whether paravertebral block confers benefits in cardiac surgery remains unanswered. However, we believe that the bolus dosage and the injection rate we used for BTPB were both too high, and caution other clinicians against the use of these doses. Future studies on the use of BTPB in cardiac surgery patients should include reduced ropivacaine doses injected over longer periods.

Simulation of survivorship bias in observational studies on plasma to red blood cell ratios in massive transfusion for trauma.

BACKGROUND: Observational studies on injured patients requiring massive transfusion have found a survival advantage associated with use of equivalent number of units of fresh frozen plasma (FFP) and packed red blood cells (RBCs) compared with use of FFP based on conventional guidelines. However, a survivorship bias might have favoured the higher use of FFP because patients who died early never had the chance to receive sufficient FFP to match the number of RBC units transfused. METHODS: A Markov model using trauma data from local hospitals was constructed and various FFP transfusion scenarios were applied in Monte Carlo simulations in which the relative risk of death associated with exposure to high FFP transfusion was set at 1.00, so that the FFP : RBC ratio had no influence on mortality outcome. RESULTS: Simulation results showed that the relative risk associated with exposure to high FFP transfusion was less than 1.00 (0.33-0.56 based on programmed delays in achieving an FFP : RBC ratio of 1 : 1-2), thus demonstrating a survivorship bias in favour of FFP : RBC equal to or more than 1 : 1-2 in certain observational trauma studies. This bias was directly proportional to the delay in achieving a FFP : RBC ratio of 1 : 1-2 during resuscitation. CONCLUSION: Some observational studies comparing low and high FFP administration in injured patients requiring massive transfusion probably involve survivorship bias that inflates or creates a survival advantage in favour of a higher FFP : RBC ratio.

The dangers of trying to make ends meet: accidental intravenous administration of enteral feed.

We report a case of inadvertent intravenous administration of enteral feed, a very rare but potentially life-threatening complication of enteral feeding. Bacterial contamination of feed results in a severe septic response that requires broad-spectrum antibiotic cover and aggressive organ support. The failure of measures aimed at prevention of this complication must be investigated, and practice changed to ensure that further incidents are avoided.

Unusual neurological presentation of neuroblastoma.

Acute cerebellar ataxia and opsomyoclonus are presenting signs of occult neuroblastoma for a substantial proportion of paediatric patients. Cerebellar ataxia may be due to antibodies against the neuroblastoma cross-reacting with cerebellar tissue. This report is of a 26-month-old boy who presented with encephalitis-like features of ataxia, seizures, decreased consciousness, and involuntary movements. Magnetic resonance imaging of the brain and spine were normal 2 weeks after presentation. The child did not have the classical signs of opsoclonus or myoclonus at any stage of the disease but was found to have occult neuroblastoma. The late demyelinating changes seen on magnetic resonance imaging of the brain support an immunological basis for the paraneoplastic manifestations of occult neuroblastoma in this child. Occult neuroblastoma should be considered as one of the differential diagnoses for children presenting with persisting encephalitis-like features in the presence of normal neuroimaging findings.

Humidification in intensive care.

The normal physiological function of the upper respiratory tract is to filter and humidify inspired air. In intensive care units the upper respiratory tract is frequently bypassed. The importance of humidifying and warming the dry, cold, piped gas is well documented. The results of lack of adequate humidification include endotracheal tube obstruction, impairment of the mucociliary elevator and altered pulmonary function. Optimal levels of humidification are as yet undefined and useful clinical markers of adequate humidification are not available. As a result there is a bewildering array of humidification devices available at present, the most recent of which are heat and moisture exchangers with or without specific filtration properties. This article reviews available data on these humidification devices, and recommends an approach to their appropriate use, based on the probable physiological needs of individual patients.

Tension pneumoperitoneum aggravating respiratory failure. A case report.

A case of tension pneumoperitoneum secondary to barotrauma is reported. Any patient needing high pressures for ventilation and oxygenation is prone to this complication. The important respiratory and haemodynamic implications are discussed. It is suggested that drainage of a tension pneumoperitoneum is easy and safe and has major beneficial effects on the respiratory and cardiovascular systems.

Esmolol in a case of severe tetanus. Adequate haemodynamic control achieved despite markedly elevated catecholamine levels.

A patient with severe tetanus, who had a sympathetic crisis while sedated with 30 mg/h diazepam and 30 mg/h morphine, is described. Satisfactory control of the haemodynamic crisis was achieved with bolus doses of esmolol to a total of 180 mg. A disturbing finding was that although there was adequate control of the tachycardia and hypertension, arterial catecholamine levels remained markedly elevated. Adrenaline levels of 531 pg/ml (normal 10-110 pg/ml) and noradrenaline levels of 1,036 pg/ml (normal 100-500 pg/ml) were recorded when the patient had a systolic arterial pressure of 110 mmHg and a heart rate of 97/min. The implications of this finding are discussed.