Tracheal gas insufflation apparatus. Performance of a novel phase-specific device.

Tracheal gas insufflation is a technique in which gas is injected intratracheally during positive pressure ventilation. The fresh gas rinses expired gas from the tracheal tube and anatomical dead space, aiding carbon dioxide elimination. This reduces ventilatory volume and pressure, helping to reduce ventilator-induced lung damage. Complications of tracheal gas insufflation include interference with ventilator function, tracheal damage and barotrauma. Expiratory washout is a variation of tracheal gas insufflation. We designed and constructed an original expiratory washout system and evaluated its safety and performance in lung and animal models. We found that expiratory limb and tracheal tube occlusion tests caused the device to disable itself at acceptable intratracheal pressures. We also demonstrated up to 31% reduction in tidal volume compared with conventional ventilation, supporting the possibility of using this device clinically to lessen volutrauma. We concluded that aspects of this design might alleviate many of the safety concerns of using tracheal gas insufflation.

The diagnosis of ventilator-associated pneumonia using non-bronchoscopic, non-directed lung lavages.

OBJECTIVES: (1)To assess the diagnostic utility of quantitative cultures of non-bronchoscopic lung lavage (NBL) in ventilator-associated pneumonia and evaluate the role of the Bacterial Index; (2) To assess the predictive value of NBL surveillance quantitative cultures in ventilated patients; (3) To evaluate the Clinical Pulmonary Infection Score (CPIS) system in ventilated patients. DESIGN: A prospective comparison of NBL with bronchoscopic bronchoalveolar lavage and protected specimen brush. SETTING: Three intensive care units in academic tertiary care centres. PATIENTS: 145 adults ventilated for 72 h, with and without clinical signs of pneumonia. INTERVENTIONS: Sampling of lower airway secretions by NBL, bronchoalveolar lavage and protected specimen brush. MAIN OUTCOME MEASURES: Diagnostic reliability of quantitative cultures, Bacterial Index and CPIS. RESULTS: 34 episodes of clinical ventilator-associated pneumonia were documented in 32 patients. 9 episodes were confirmed by concordant blood/pleural culture or post-mortem lung examination. Qualitative concordance of the predominant pathogen between sequential NBL: bronchoalveolar lavage and protected specimen brush was 83 %. Sensitivity and specificity of non-directed bronchial lavage at a threshold of 10(4) CFU/ml were 68 % and 70 % respectively (p = 0. 003) and were comparable with the bronchoscopic methods. However, the low positive predictive value of NBL indicates that quantitation in the absence of clinical signs is unlikely to be useful. Bacterial Index did not improve discriminatory power of quantitation compared with bacterial load of predominant organism. Mean CPIS for confirmed pneumonia cases was 8.4 +/- 1.01, significantly higher than for non-pneumonia observations (p = < 0.0001). CONCLUSION: NBL is a simple, safe, cheap, readily-available method of diagnosing ventilator-associated pneumonia with comparable diagnostic accuracy to bronchoscopic techniques. Quantitation of respiratory tract cultures can exclude pneumonia in patients with equivocal clinical signs. The diagnostic threshold should vary depending on the length of ventilation, likelihood of pneumonia and antibiotic administration. The Bacterial Index is a flawed mathematical device that has no contributory role in pneumonia diagnosis. The CPIS has some diagnostic role in selected cohorts of ventilated patients.

Blood volume determination by the carbon monoxide method using a new delivery system: accuracy in critically ill humans and precision in an animal model.

OBJECTIVE: To evaluate accuracy and repeatability of blood volume determinations made by the carbon monoxide method, using a ventilator-driven administration system. DESIGN: Prospective within-patient comparison, using simultaneous measurements by two methods to determine accuracy. Prospective laboratory investigation in animals to estimate repeatability. SUBJECTS: For accuracy: Nineteen ventilated critically ill patients in a university hospital intensive care unit. For repeatability: Six anesthetized, mechanically ventilated normovolemic pigs because this is impossible to perform in humans. INTERVENTIONS: In the accuracy study, a small mass of carbon monoxide was administered via a closed breathing system and arterial blood samples were taken from existing cannulas. In the repeatability study, an intramuscular sedative was given, followed by an inhalational anesthetic induction and mechanical ventilation via a tracheal tube. Left axillary artery and external jugular vein cannulas were sited. Anesthesia was maintained using an intravenous infusion. Five sequential circulating hemoglobin and blood volume estimations were made using the carbon monoxide method. MEASUREMENTS AND MAIN RESULTS: The small carboxyhemoglobin increase produced by uptake of a small, known mass of carbon monoxide was used to estimate the circulating blood volume. Simultaneous measurement, using 51Cr-labeled red blood cells, was performed. Twenty measurements were made in 19 patients. The bias (mean difference between blood volume measurements by the two methods) was 397 mL (5.53 mL x kg(-1)) +/-415 mL (+/-5.95 mL x kg(-1)); the limits of agreement (mean difference +/-2 SD) were -433 mL and 1227 mL (-6.36 mL x kg(-1) and 17.42 mL x kg(-1)). Therefore, 95% of expected differences will lie between these limits. The mean blood volume was 75.8 mL x kg(-1) in the animals. The coefficient of variation of repeated estimates was 9.49%. Mean circulating hemoglobin mass was 7.31 mmol with a coefficient of variation of 10.18%. The mean hemoglobin concentration, by co-oximetry, was 5.014 mmol x L(-1), coefficient of variation, 2.99%. CONCLUSION: This arrangement is a potential bedside method of estimating blood volume and circulating hemoglobin mass. We have rendered the technique more acceptable clinically by creating a ventilator-driven administration system.

Inhalation of nitric oxide in acute lung injury: results of a European multicentre study. The European Study Group of Inhaled Nitric Oxide.

OBJECTIVE: To determine whether inhalation of nitric oxide (INO) can increase the frequency of reversal of acute lung injury (ALI) in nitric oxide (NO) responders. DESIGN: Prospective, open, randomised, multicentre, parallel group phase III trial. SETTING: General ICUs in 43 university and regional hospitals in Europe. PATIENTS: Two hundred and sixty-eight adult patients with early ALI. INTERVENTIONS: NO responders were patients whose PaO(2) increased by more than 20 % when receiving 0, 2, 10 and 40 ppm of INO for 10 min within 96 h of study entry. Responders were randomly allocated to conventional treatment with or without INO. INO, 1-40 ppm, was given at the lowest effective dose for up to 30 days or until an end point was reached. The primary end point was reversal of ALI. Clinical outcome parameters and safety were assessed in all patients. RESULTS: Two hundred and sixty-eight patients were recruited, of which 180 were randomised NO responders. Frequency of reversal of ALI was no different in INO patients (61 %) and controls (54 %; p > 0.2). Development of severe respiratory failure was lower in the INO (2.2 % ) than controls (10.3 %; p < 0.05). The mortality at 30 days was 44 % for INO patients, 40 % for control patients (p > 0.2 vs INO) and 45 % in non-responders. CONCLUSIONS: Improvement of oxygenation by INO did not increase the frequency of reversal of ALI. Use of inhaled NO in early ALI did not alter mortality although it did reduce the frequency of severe respiratory failure in patients developing severe hypoxaemia.

Cerebral blood flow is proportional to cardiac index in patients with septic shock.

PURPOSE: In patients with septic shock, the cardiac index is often increased. Maldistribution of blood flow and regional hypoperfusion has been implicated as a key factor in the pathogenesis of organ dysfunction in these patients. We have investigated the relationship between cerebral blood flow and cardiac index in patients with septic shock. MATERIALS AND METHODS: We used Doppler ultrasound techniques to investigate limb and carotid blood flow in 15 patients with septic shock and 9 nonseptic controls. RESULTS: In the nonseptic control patients, common femoral and brachial blood flow were proportional to cardiac index (r=0.73 and 0.76; P=.038 and .017, respectively) reflecting a protective redistribution of flow to more vital organs. However, this relationship was absent in patients with septic shock (r=0.23 and 0.21). Furthermore, in the septic patients but not the nonseptic controls, cerebral blood flow was correlated with the cardiac index (r=0.66, P < .05 vs r=-0.36, NS in nonseptic controls). Carotid flow was independent of mean arterial pressure, PaCO2 and PaO2 in patients with septic shock. CONCLUSIONS: These data are consistent with a loss of autoregulation of cerebral blood flow and a change in the control of limb blood flow in humans with septic shock.

Splenic rupture following cardiopulmonary resuscitation.

Cardiopulmonary resuscitation has improved outcome from cardiac arrest. However complications may occur secondary to the resuscitation efforts. We present a case of intraabdominal haemorrhage, due to traumatic rupture of the spleen and discuss the problems of diagnosing intraabdominal haemorrhage in the post cardiac arrest patient, whose hypotension may be ascribed to myocardial dysfunction.

Peripheral gangrene associated with fulminating meningococcal septicaemia. Is early escharotomy indicated?

We present a case of a 3-month-old boy presenting with fulminating meningococcal septicaemia associated with extensive peripheral gangrene requiring amputation of three limbs. The surgical management options and the role of early fasciotomy are discussed.

Liver function and splanchnic ischemia in critically ill patients.

STUDY OBJECTIVE: To investigate the concept that splanchnic ischemia leads to hepatic dysfunction in the critically ill. DESIGN: Prospective study and analysis of patient data. SETTING: A general ICU in an inner-city London teaching hospital. PATIENTS: Twenty-seven consecutive critically ill patients with evidence of inadequate tissue perfusion requiring pulmonary artery catheterization and mechanical ventilation. MEASUREMENTS: In all patients, we measured the hepatic metabolism of lidocaine (lignocaine) to monoethylglycinexylidide (MEGX) and the clearance of indocyanine green (both dynamic, flow-dependent tests of hepatic function) over the first 3 days following admission to the ICU. These were compared with results of standard liver function tests and related to tonometric assessment of gastric intramucosal pH (pHim) and outcome. RESULTS: There were no significant differences in bilirubin, aspartate aminotransferase, alkaline phosphatase, and prothrombin levels, or in indocyanine green clearance between survivors and nonsurvivors. On day 3, the median MEGX level was higher in survivors than in nonsurvivors (16 vs 2.4 ng/mL, p < 0.001), and the median MEGX level in nonsurvivors fell over the 3 days (20.6 to 2.4 ng/mL, p < 0.002). MEGX levels were significantly correlated with pHim (Spearman rank correlation coefficient [Rs] = 0.69, p < 0.001) as were the changes in the two measurements over the 3 days (Rs = 0.46, p < 0.02). The MEGX formation test and gastric pHim were the most discriminatory with regard to death and survival. CONCLUSIONS: Our findings suggest that critically ill patients develop significant hepatic dysfunction that is associated with a poor outcome. This is likely to be due to a mismatch between hepatic metabolic demand and blood flow, and the MEGX formation test appears to be an extremely effective means of assessing liver function and flow in this group of patients.

Increasing splanchnic blood flow in the critically III.

STUDY OBJECTIVE: To assess the effect of low dose dopexamine and dopamine on splanchnic blood flow as measured by gastric intramucosal pH, hepatic metabolism of lidocaine (lignocaine) to monoethylglycinexy-lidide (MEGX), and plasma disappearance rate of indocyanine green (ICG). DESIGN: Single-blind randomization of patients with a gastric intramucosal acidosis to receive dopexamine (ten patients), dopamine (ten patients), or saline solution (five control patients) for 2 h. SETTING: All 25 patients were in the ICU of Guys' Hospital. PATIENTS: All patients met the criteria for the diagnosis of the systemic inflammatory response syndrome, were mechanically ventilated, and had pulmonary artery catheters placed. All had a low gastric intramucosal pH and had a median first 24-h acute physiology and chronic health evaluation (II) score of 22 (range, 7 to 40). MEASUREMENTS AND INTERVENTIONS: Baseline measurements of gastric intramucosal pH, MEGX formation from lidocaine, ICG plasma disappearance rate, heart rate, mean arterial pressure, pulmonary artery occlusion pressure, cardiac index, oxygen delivery index, oxygen uptake index, systemic vascular resistance, and arterial pH were taken. Dopexamine (1 mg.kg-1.min-1), dopamine (2.5 mg.kg-1.min-1), or 0.9% saline solution was then infused for 2 h, after which a repeated set of the measurements was taken. RESULTS: Dopexamine at a low dose had no effect on any of the systemic measurements. The median intramucosal pH rose from 7.23 to 7.35 (p < 0.005), the median ICG plasma disappearance rate from 7.6 to 11.3%.min-1 (p < 0.02), and the median MEGX concentration from 4 to 10.2 ng.mL-1 (p < 0.005). Dopamine had no effect on any of the measured variables. There were no changes in the control group. CONCLUSIONS: Low-dose dopexamine increases splanchnic blood flow as measured by gastric intramucosal pH, MEGX formation from lidocaine, and ICG clearance. The lack of any change in the systemic measurements suggests that these effects are the result of a selective vasodilatation of the splanchnic vessels. At the dose used in this study, dopamine had no effect on splanchnic blood flow. Dopexamine may be useful in the management of splanchnic ischemia in the critically ill.

Identification of futility in intensive care.

Rising costs of intensive care and the ability to prolong the life of critically ill patients creates a need to recognise early those patients who will die despite treatment. We used changes in a modified APACHE II score (organ failure score) to make daily predictions of individual outcome in 3600 patients. 137 patients were predicted to die and of these, 131 (95.6%) died within 90 days of discharge from hospital (sensitivity 23.4%, specificity 99.8%); a false-positive diagnosis rate of 4.4%. 2 of the 6 survivors have subsequently died but 4 are alive with good quality of life. Patients predicted to die stayed 1492 days in intensive care and incurred 16.7% of total intensive care expenditure and 46.4% of the cost of all patients that died. Median survival after a prediction to die was 2 days, accounting for 62% of intensive care patient days in this patient group, giving an effective intensive care cost per survivor of UK 129,651 pounds. If used prospectively, this algorithm has the potential to indicate the futility of continued intensive care but at the cost of 1 in 20 patients who would survive if intensive care were continued.

Protecting the gut and the liver in the critically ill: effects of dopexamine.

OBJECTIVE: To measure the clinical effects of dopexamine on systemic and splanchnic perfusion in critically ill patients. DESIGN: Prospective study. SETTING: General intensive care unit. PATIENTS: Ten patients with sepsis syndrome, acute respiratory failure, and at least one other organ system in failure. The median age of the patients was 62.5 yrs (range 29 to 78), and the median admission Acute Physiology and Chronic Health Evaluation (APACHE) II score was 24 points (range 14 to 38). INTERVENTIONS: Timed infusion of dopexamine to a maximum dose of 6 micrograms/kg/min. MEASUREMENTS AND MAIN RESULTS: Systemic hemodynamics and oxygen transport variables were obtained from measurements after arterial and pulmonary artery catheterization. Gastric intramucosal pH and hepatic blood flow/function measurements were made by tonometry and indocyanine green clearance, respectively. All measurements were made before dopexamine infusion, after 1 hr of dopexamine infusion, and again 1 hr after the infusion ended. Cardiac index increased with dopexamine from a baseline median of 4.0 L/min/m2 (range 1.2 to 5.5) to 4.8 L/min/m2 (range 1.5 to 8.03) (p < .01), and returned to its previous level 1 hr after the infusion ended (median 4.0 L/min/m2 [range 1.4 to 5.8], p < .01). During dopexamine infusion, gastric intramucosal pH improved significantly from a median baseline level of 7.21 (range 7.04 to 7.50) to 7.28 (range 7.13 to 7.46, p < .05). This improvement in gastric intramucosal pH was maintained (median 7.36 [range 7.13 to 7.46]) after the infusion ended. Indocyanine green half-life decreased but not significantly with dopexamine (medians before and during the infusion were 6.6 and 6.3 mins, respectively). Indocyanine green half-life increased significantly 1 hr after the infusion ended (median 7.4 mins [range 4.4 to 14.8], p < .05), and changes in cardiac index correlated with changes in indocyanine green half-life (Rs2 = 0.60, p < .001). Changes in gastric intramucosal pH were unrelated to all other measurements. CONCLUSIONS: Dopexamine improves gastric intramucosal pH, and thus, splanchnic oxygenation. This improvement in gastric intramucosal pH appears to be independent of dopexamine's systemic effects.

Assessment of splanchnic oxygenation by gastric tonometry in patients with acute circulatory failure.

OBJECTIVE: To investigate the importance of splanchnic ischemia in patients with acute circulatory failure by comparing gastric intramucosal pH as measured by tonometry with conventional methods of assessing adequacy of tissue oxygenation. DESIGN: Prospective cohort of patients with acute circulatory failure in first 24 hours after admission to the intensive care unit. SETTING: Two general intensive care units in London, England. PATIENTS: Consecutive sample of 83 patients of varying diagnostic categories that required pulmonary artery catheterization. MAIN OUTCOME MEASURES: Gastric intramucosal pH and hemodynamic, oxygen transport, and metabolic variables were measured on admission and at 12 hours and 24 hours after admission. Prediction of outcome (death or survival) by each measurement was assessed by sensitivity, specificity, and logistic regression analysis. RESULTS: Mean 24-hour Acute Physiology and Chronic Health Evaluation (APACHE II) score was 20.3. There were significant differences in mean gastric intramucosal pH between survivors and nonsurvivors on admission and at 24 hours, (7.40 vs 7.28, 7.40 vs 7.24, respectively; P < .001). Admission heart rate was higher (116 vs 101 beats per minute; P < .003) and mean arterial pressure lower (82 vs 97 mm Hg; P < .01) in nonsurvivors. There were no consistent differences in cardiac index, oxygen delivery, and oxygen uptake between survivors and nonsurvivors. Admission arterial pH was significantly lower (7.3 vs 7.36; P < .003), base excess more negative (-5.3 vs -1.9; P < .001), and lactate concentration higher (3.14 vs 1.91 mmol/L; P < .03) in nonsurvivors. Gastric intramucosal pH had a sensitivity of 88% for predicting death and a likelihood ratio of 2.32, higher than for any other variable. Only gastric intramucosal pH at 24 hours independently predicted outcome. CONCLUSIONS: Gastric intramucosal pH was the most reliable indicator of adequacy of tissue oxygenation in this group of patients. Inadequate regional blood flow as detected by a reduction in gastric intramucosal pH, but not by systemic measures, is an important contributor to morbidity and mortality in intensive care units.