A lung model to demonstrate dynamic gas trapping and intrinsic positive end-expiratory pressure at realistic ventilation settings.

Intrinsic positive end-expiratory pressure (PEEP) and gas trapping are recognised hazards during ventilation of patients with airflow obstruction. Demonstration of these phenomena on conventional lung models using realistic ventilation settings is difficult. We describe an Intrinsic PEEP Model that is able to demonstrate dynamic gas trapping and intrinsic PEEP at realistic ventilation settings, and demonstrate its ability to develop intrinsic PEEP in a timeframe useful for teaching. The model uses a Heimlich valve to permit a lower resistance on inspiration than expiration. The model was tested using a series of typical ventilation settings which, when applied in a clinical setting on patients with airflow obstruction issues, would result in prolonged low expiratory flow and the development of intrinsic PEEP of 10 to 20 cmH2O, and ultimately significant gas trapping. The IPM can be used to demonstrate this effect and the ventilator adjustments required to minimise these problems.

Bench performance of ventilators during simulated paediatric ventilation.

This study compares the accuracy and capabilities of various ventilators using a paediatric acute respiratory distress syndrome lung model. Various compliance settings and respiratory rate settings were used. The study was done in three parts: tidal volume and FiO2 accuracy; pressure control accuracy and positive end-expiratory pressure (PEEP) accuracy. The parameters set on the ventilator were compared with either or both of the measured parameters by the test lung and the ventilator. The results revealed that none of the ventilators could consistently deliver tidal volumes within 1 ml/kg of the set tidal volume, and the discrepancy between the delivered volume and the volume measured by the ventilator varied greatly. The target tidal volume was 8 ml/kg, but delivered tidal volumes ranged from 3.6-11.4 ml/kg and the volumes measured by the ventilator ranged from 4.1-20.6 ml/kg. All the ventilators maintained pressure within 20% of the set pressure, except one ventilator which delivered pressures of up to 27% higher than the set pressure. Two ventilators maintained PEEP within 10% of the prescribed PEEP. The majority of the readings were also within 10%. However, three ventilators delivered, at times, PEEPs over 20% higher. In conclusion, as lung compliance decreases, especially in paediatric patients, some ventilators perform better than others. This study highlights situations where ventilators may not be able to deliver, nor adequately measure, set tidal volumes, pressure, PEEP or FiO2.

Tongue swelling complicating management of a ventilated patient with acute respiratory distress syndrome secondary to novel influenza A (H1N1).

The recently emerged novel influenza A H1N1 virus continues to spread globally. The use of oseltamivir for treatment and prophylaxis of infection is recommended and its use has climbed steeply although there is little data available on its benefit in critically unwell patients with H1N1 influenza. A rare side-effect of oseltamivir treatment reported in post-marketing surveillance is tongue and lip swelling/angioedema. This case report describes the management of a critically ill ventilated patient with severe acute respiratory distress syndrome who developed clinically significant tongue and lip swelling during treatment with oseltamivir.

Can learning to sustain life be BASIC? Teaching for the initial management of the critically ill in Australia and New Zealand.

Commonly in Australia and New Zealand, initial intensive care support of critically ill patients is by non-intensive care trained medical and nursing staff Basic Assessment and Support in Intensive Care (BASIC) is an internationally run short course to assist practitioners to gain knowledge and skills to manage the early hours of critical illness. The aim of this study was to assess the performance and acceptance of the BASIC course as conducted in an Australian metropolitan teaching hospital and a major regional centre in New Zealand. Performance on pre- and post-course multiple choice examinations and the overall course assessment by all participants attending between 2005 and 2009 was analysed. Of 796 participants, 338 (42%) were in Australia and 458 (58%) in New Zealand. Compared to New Zealand, Australian non-intensive care consultants and junior medical staff attended more commonly at 9% vs 4% and 62% vs 42% respectively, while nurses more frequently attended in New Zealand (47% compared to 12%, P < 0.001). The pre-course open book examination result averaged 79% (95% confidence interval 78 to 80) and the post-course closed book examination was 64% (95% confidence interval 63 to 65). The post-course examination score was predicted by pre-course examination score (beta = 0.22, 95% confidence interval 0.17 to 0.27), nursing occupation, (beta = -3.96, 95% confidence interval -5.03 to -2.90) and the availability of a scenario-based simulation module (beta = 0.22, 95% confidence interval 0.17 to 0.27, R2 = 0.38, P < 0.001). Participants generally found they had learned a great deal from the program and that the course material was of an appropriate level. The BASIC course was found to be a positive learning experience for health care practitioners inexperienced in the management of the critically ill.

Sedation and delirium in the intensive care unit: an Australian and New Zealand perspective.

A survey was conducted to determine sedation and delirium practices in Australian and New Zealand intensive care units. The survey was in two parts, comprising an online survey of reported sedation and delirium management (unit survey) and a collection of de-identified data about each patient in a unit at a given time on a specified day (patient snapshot survey). All intensive care units throughout Australia and New Zealand were invited by email to participate in the survey. Twenty-three predominantly metropolitan, level III Australian and New Zealand intensive care units treating adult patients participated. Written sedation policies were in place in 48% of units, while an additional 44% of units reported having informal sedation policies. Seventy percent of units routinely used a sedation scale. In contrast, only 9% of units routinely used a delirium scale. Continuous intravenous infusion is the primary means of patient sedation (74% of units). While 30% of units reported routinely interrupting sedation, only 10% of sedated patients in the snapshot survey had had their sedation interrupted in the preceding 12 hours. Oversedation appears to be common (46% of patients with completed sedation scales). Use of neuromuscular blockade is low (10%) compared to other published studies. Midazolam and propofol were the most frequently used sedatives. The proportion of patients developing delirium was 21% of assessable patients. Failed and self-extubation rates were low: 3.2% and 0.5% respectively. In Australian and New Zealand intensive care units, routine use of sedation scales is common but not universal, while routine delirium assessment is rare. The use of a sedation protocol is valuable and should be encouraged.

Fatal vitamin C-associated acute renal failure.

Although daily ingestion of high-dose vitamin C is generally regarded as largely innocuous, fatal nephrotoxicity can occur in some rare circumstances. We report a case where the patient, who chose to forgo any advanced conventional medical intervention (dialysis and mechanical ventilation), had failed to disclose his use of high-dose vitamin C and subsequently died. Intra-renal oxalate crystal deposition was demonstrated at autopsy. Directed enquiry with the family then revealed his high-dose vitamin C usage. Even though fully-informed discussion was limited by incomplete prospective disclosure, it remains the prerogative of any competent patient to decline any treatment, including those that may be considered life-saving.

Resuscitation of critically ill patients based on the results of gastric tonometry: a prospective, randomized, controlled trial.

OBJECTIVE: To determine whether additional therapy aimed at correcting low gastric intramucosal pH (pHi) improves outcome in conventionally resuscitated, critically ill patients. DESIGN: Prospective, randomized, controlled study. SETTING: General intensive care unit (ICU) of a university teaching hospital. PATIENTS: A total of 210 adult patients, with a median Acute Physiology and Chronic Health Evaluation II score of 24 (range, 8-51). INTERVENTIONS: All patients were resuscitated according to standard guidelines. After resuscitation, those patients in the intervention group with a pHi of <7.35 were treated with additional colloid and then dobutamine (5 microg/kg/min then 10 microg/kg min) until 24 hrs after enrollment. MEASUREMENTS AND MAIN RESULTS: There were no significant differences (p > .05) in ICU mortality (39.6% in the control group vs. 38.5% in the intervention group), hospital mortality (45.3% in the control group vs. 42.3% in the intervention group), and 30-day mortality (43.7% in the control group vs. 40.2 in the intervention group); survival curves; median modified maximal multiorgan dysfunction score (10 points in the control group vs. 13 points in the intervention group); median modified duration of ICU stay (12 days in the control group vs. 11.5 days in the intervention group); or median modified duration of hospital stay (60 days in the control group vs. 42 days in the intervention group). A subgroup analysis of those patients with gastric mucosal pH of > or =7.35 at admission revealed no difference in ICU mortality (10.3% in the control group vs. 14.8% in the intervention group), hospital mortality (13.8% in the control group vs. 29.6% in the intervention group), or 30-day mortality (10.3% in the control group vs. 26.9% in the intervention group). CONCLUSIONS: The routine use of treatment titrated against pHi in the management of critically ill patients cannot be supported. Failure to improve outcome may be caused by an inability to produce a clinically significant change in pHi or because pHi is simply a marker of disease rather than a factor in the pathogenesis of multiorgan failure.

Oxygen delivery, oxygen consumption, and gastric intramucosal pH are not improved by a computer-controlled, closed-loop, vecuronium infusion in severe sepsis and septic shock.

OBJECTIVE: To investigate the influence of the neuromuscular blocking agent vecuronium on oxygen delivery (DO2), oxygen consumption (VO2), oxygen extraction ratio, and gastric intramucosal pH in heavily sedated patients with severe sepsis or septic shock. DESIGN: Prospective, randomized, placebo-controlled, cross-over trial. SETTING: University hospital intensive care unit. PATIENTS: Eighteen mechanically ventilated patients with severe sepsis or septic shock. INTERVENTIONS: All patients were heavily sedated. After baseline measurement, a computer-controlled, closed-loop infusion of either vecuronium or saline was initiated and further measurements were made at 40 and 60 mins. The procedure was repeated with the alternative agent after return of neuromuscular function. MEASUREMENTS AND MAIN RESULTS: DO2, VO2, intramucosal pH were monitored using pulmonary artery catheters, a gas exchange monitor, and gastric tonometers. Changes from baseline were compared (paired t-test, p = .05). The vecuronium closed-loop infusion achieved T1 between 5% and 15% at 40 mins. There was a significant difference in the changes from baseline for static respiratory compliance in the vecuronium closed-loop infusion group compared with the saline closed-loop infusion group. There was no significant difference in the change from baseline for systemic or pulmonary vascular resistance, DO2, VO2, oxygen extraction ratio, or intramucosal pH. CONCLUSIONS: In these patients, vecuronium infusion achieved the targeted level of paralysis and improved respiratory compliance but did not alter intramucosal pH, VO2, DO2, or oxygen extraction ratios. With deep sedation, neuromuscular blockade in severe sepsis/septic shock does not significantly influence oxygen flux and should be abandoned as a routine method of improving tissue oxygenation in these patients.

Comparison of intrathoracic and intra-abdominal measurements of central venous pressure.

BACKGROUND: Complications can arise from standard intrathoracic central venous pressure (CVP) measurements in critically ill, mechanically ventilated patients. We have assessed the feasibility of catheterisation by the femoral route to measure CVP in the abdomen (ACVP). We compared measurements by the standard jugular or subclavian route (TCVP) with simultaneous ACVP measurements by the femoral route. METHODS: Between June, 1994 and May, 1995, we recruited 20 critically ill adult patients with various disorders; all patients already had a TCVP line in situ. We placed a femoral catheter in the inferior vena cava close to the right atrium under electrocardiographic guidance. The catheter position was confirmed (and corrected if necessary) by chest radiography. CVP was measured from both sites hourly for 6 h. Positive end-expiratory pressure, mean airway pressure, and intra-abdominal pressure were recorded simultaneously. FINDINGS: One patient was excluded because radiography showed that the catheter position was incorrect. For 133 paired measurements of ACVP and TCVP in the remaining 19 patients, the mean difference was 0.45 mm Hg (SD 0.89: 95% Cl 0.30-0.60); the limits of agreement were -1.33 to 2.23 mm Hg (-1.63 to 2.53). We found a small tendency for the difference between ACVP and TCVP to increase as positive end-expiratory pressure and mean airway pressure increased; the difference was statistically, but not clinically, significant. INTERPRETATION: Our study showed that for clinical purposes CVP can be measured by a femoral catheter placed in the abdominal inferior vena cava near the right atrium. This approach can replace standard TCVP measurements in critically ill, mechanically ventilated patients.

Fatal acute hepatorenal failure following potassium permanganate ingestion.

Potassium permanganate (KMnO4), a powerful oxidizing agent, is readily available without prescription. Tissue contact produces coagulation necrosis and the lethal consequences of oral ingestion are well described, with most deaths because of airway oedema and obstruction or circulatory collapse. Whilst systemic toxicity is reported, its mechanism is unclear. We describe a case of suicidal ingestion of KMnO4 followed by acute hepatorenal toxicity resulting in the death of the patient. The clinical course bore close resemblance to that of severe paracetamol overdose. We discuss the pathogenesis of the systemic toxicity of KMnO4 and postulate that it is due to oxidative injury from free radicals generated by the absorbed permanganate ion. We recommend that N-acetyl cysteine be given within the first few hours to all patients with potassium permanganate poisoning.

A comparison of the haemodynamic effects of intrathecal meperidine, meperidine-bupivacaine mixture and hyperbaric bupivacaine.

PURPOSE: To study the haemodynamic effects of intrathecal meperidine, administered either alone or mixed with bupivacaine. METHODS: We studied 42 Chinese patients, aged 59-87 yr, scheduled for transurethral bladder or prostate surgery, randomized into three equals groups, that received either meperidine 0.8 mg.kg-1, meperidine 0.4 mg.kg-1 plus 1.5 ml of 0.5% heavy bupivacaine or 3 ml of heavy bupivacaine 0.5%. Non-invasive systolic (SAP) and mean (MAP) arterial pressures, central venous pressure and cardiac index, stroke index and heart rate (HR) measured by the BoMed NCCOM3-R7S bioimpedance device, were recorded over the first 25 min. Systemic vascular resistance index (SVRI) was derived. Onset of sensory and motor block was also measured. Decreases in MAP of 25% were treated with colloid and metaraminol. RESULTS: The onset of block was slower in the meperidine group (P < 0.05). Decreases in SAP, MAP and SVRI (all; P < 0.001) occurred within five minutes in all three groups. The HR was increased in the bupivacaine group (P = 0.03), but bradycardias treated with atropine occurred in six patients receiving meperidine and four patients receiving the mixture. Six patients receiving meperidine and two patients receiving the mixture required general anaesthesia for inadequate block. The incidence of nausea and vomiting was higher in the patients receiving meperidine (P < 0.05). No other complications were encountered. CONCLUSIONS: Intrathecal meperidine used alone or mixed with bupivacaine has no intra-operative advantage over heavy bupivacaine 0.5%.

Accuracy of the tonometric function of recycled gastric tonometer catheters.

We investigated the accuracy of recycled gastric tonometer catheters, using a prospective laboratory model, within the Intensive Care Unit of a University teaching hospital. Ten used tonometer catheters and three new catheters were exposed to known constant PCO2 levels between 23-65 torr (3.06-8.66 kPa) in a gas mixing chamber, at a temperature of 35.5-38 degrees C and a relative humidity > 95%. The tonometer balloons were primed with normal saline, and after a 30-minute equilibration time, the saline was sampled for PCO2 measurements. Steady-state PCO2 (PCO2(SS)) and gastric mucosal pH (pHi) values were derived using a correction factor and the Henderson-Hasselbalch equation. There was no difference in the mean or distribution of PCO2(SS) values between recycled and new catheters. The PCO2(SS) values of recycled catheters were within the 95% confidence limits of those of new catheters. Individual catheter values did not differ significantly from each other (ANOVA P = 0.05). Using an arterial HCO3- value of 21 mmol/l, the calculated pHi values of used catheters varied < 1.5% of the mean pHi of new catheters. The tonometric performance of recycled gastric tonometer catheters was similar to that of new catheters when tested in vitro.

Paediatric acute renal failure. A report on 2 cases successfully managed with continuous venovenous haemodiafiltration.

In critically ill patients continuous venovenous haemodiafiltration (CVVHD) is a method of renal replacement therapy gaining popularity. The advantage of CVVHD over intermittent haemodialysis and peritoneal dialysis lies in the accurate control of ultrafiltration and of solute clearance. Two paediatric patients with acute renal failure treated successfully with CVVHD are described. The role of CVVHD in renal supportive therapy in South African paediatric intensive care units is discussed.

Continuous venovenous haemodiafiltration--an audit demonstrating control of electrolytes with haemodynamic stability in the critically ill.

OBJECTIVE: Renal replacement therapy has evolved significantly in the last 15 years, resulting in a large diversity of techniques with differing attributes. Theoretical advantages of the continuous over intermittent techniques in critically ill patients include haemodynamic stability and a reduction in disequilibrium syndrome. Limited clinical evidence supports this, but a clear reduction in mortality or morbidity has yet to be shown. The technique of renal replacement therapy in the Intensive Care Unit at Baragwanath Hospital was recently revised and a retrospective study of the haemodynamic and electrolyte changes associated with implementing continuous venovenous haemodiafiltration (CVVHD) was carried out. METHOD: A retrospective analysis of demographic data, haemodynamic and physiological parameters in 10 consecutive patients receiving CVVHD during a 10-week period was conducted. Patients' systolic (SBP), and mean (MAP) arterial blood pressures, heart rates (HR), and central venous pressures (CVP) during the first 36 hours after the implementation of CVVHD were reviewed. Serum creatinine, urea and potassium values were also collated. Other organ system failures and outcomes were noted. RESULTS: HR decreased by 6.1% (SD 1.5) and average MAP rose (12.1%; SD 7.8) as did SBP (12.4%; SD 6.3), compared with the values immediately before CVVHD: CVP was unchanged. Control of hyperkalaemia was effected in all cases. Serum urea and creatinine levels were well controlled, and clearances were closely related to the dialysate flow. Although the mortality rate was high, it was lower than predicted. No deaths were directly attributable to acute renal failure or complications of CVVHD: CONCLUSION: In the critically ill, CVVHD provides excellent serum urea and creatinine clearance and control of electrolytes without further compromise of haemodynamics. The low associated morbidity, the ease of implementation and the efficacy of the technique may make CVVHD the technique of choice for ARF in the intensive care unit.