Effect of FiO2 in the measurement of VO2 and VCO2 using the E-COXV metabolic monitor. / Efecto de la FiO2 sobre la medición del VO2 y la VCO2 con el monitor metabólico E-COVX.

OBJECTIVE: We evaluated the effect of changes in FiO2 on the bias and accuracy of the determination of oxygen consumption (V˙O2) and carbon dioxide production (V˙CO2) using the E-COVX monitor in patients with mechanical ventilation. DESIGN: Descriptive of concordance. SETTING: Intensive Care Unit. PATIENTS OR PARTICIPANTS: Patients with mechanical ventilation. INTERVENTIONS: We measured V˙O2 and V˙CO2 using the E-COVX monitor. Values recorded were the average in 5min. Two groups of 30 patients. We analyzed: 1) the reproducibility in the measurement of V˙O2 and V˙CO2 at FiO2 0.4, and 2) the effect of the changes in FiO2 on the measurement of V˙O2 and V˙CO2. Statistical analysis was performed using Bland and Altman test. VARIABLES OF MAIN INTEREST: Bias and accuracy. RESULTS: 1) FiO2 0.4 reproducibility: The bias in the measurement of V˙O2 and V˙CO2 was 1.6 and 2.1mL/min, respectively, and accuracy was 9.7 to -8.3% and 7.2 to -5.2%, respectively, and 2) effect of FiO2 on V˙O2: The bias of V˙O2 measured at FiO2 0.4 and 0.6 was -4.0mL/min and FiO2 0.4 and 0.8 was 5.2mL/min. Accuracy between FiO2 0.4 and 0.6 was 11.9 to -14.1%, and between FiO2 0.4 and 0.8 was 43.9 to -39.7%. CONCLUSIONS: The E-COVX monitor evaluates V˙O2 and V˙CO2 in critical patients with mechanical ventilation with a clinically acceptable accuracy until FiO2 0.6.

Enteral nutrition volume is not correlated with lower respiratory tract infection in patients on mechanical ventilation.

OBJECTIVE: To evaluate the effect of enteral nutrition volume, gastrointestinal function and the type of acid suppressive drug upon the incidence of lower respiratory tract infections in critically ill patients on mechanical ventilation (MV). DESIGN: A retrospective secondary analysis was carried out. SETTING: The Intensive Care Unit of a University Hospital. PATIENTS OR PARTICIPANTS: Patients≥18-years-old expected to need MV for more than four days, and receiving enteral nutrition by nasogastric tube within 24h of starting MV. INTERVENTIONS: We correlated enteral nutrition volume administered during the first 10 days, gastrointestinal function and the type of acid suppressive therapy with the episodes of lower respiratory tract infection up until day 28. Cox proportional hazards ratios in univariate and adjusted multivariate models were used. Statistical significance was considered for p<0.05. MAIN VARIABLES OF INTEREST: Lower respiratory tract infection episodes. RESULTS: Sixty-six out of 185 patients (35.7%) had infection; 27 patients had ventilator-associated pneumonia; and 39 presented ventilator-associated tracheobronchitis. Uninfected and infected groups were similar in terms of enteral nutrition volume (54±12 and 54±9mL/h; p=0.94) and caloric intake (19.4±4.9 and 19.6±5.2kcal/kg/d; p=0.81). The Cox proportional hazards model showed neurological indication of MV to be the only independent variable related to infection (p=0.001). Enteral nutrition volume, the type of acid suppressive therapy, and the use of prokinetic agents were not significantly correlated to infection. CONCLUSIONS: Enteral nutrition volume and caloric intake, gastrointestinal dysfunction and the type of acid suppressive therapy used were not associated to lower respiratory tract infection in patients on MV.

Respiratory CO2 response in acute cervical spinal cord injury (CO2 response in spinal cord injury).

STUDY DESIGN: Retrospective study. OBJECTIVES: The objective of this study was to compare the CO2 response of acute tetraplegic cervical spinal cord injury (SCI) patients undergoing mechanical ventilation with a control group of critically ill patients ready for weaning of mechanical ventilation and successfully extubated. SETTING: This study was conducted at the intensive care unit of a University Hospital in Mallorca, Spain. METHODS: CO2 response was studied in 12 acute tetraplegic cervical SCI patients at the C4-C7 level and 22 control patients. The control group patients were consecutively selected from a database of patients with mechanical ventilation and who were successfully extubated after a CO2 response test. To increase the CO2 , we used the method of re-inhalation of expired air, and we evaluated the hypercapnic ventilatory response, the change in minute ventilation induced by the increase of partial pressure of arterial carbon dioxide (PaCO2 ), which measures the whole respiratory system (metabolic control, neuromuscular or ventilatory apparatus), and the hypercapnic drive response, the change in the airway occlusion pressure at 100 ms induced by the increase in PaCO2, which measures the chemosensitivity of the respiratory center. RESULTS: Cervical SCI patients were younger than the control group patients (26±7 and 62±12 years, respectively; P<0.001). Mean values of the hypercapnic ventilatory response in cervical SCI and control groups were 0.52±0.31 and 0.64±0.33 l min(-1) per mm Hg (P=0.40), respectively, and the hypercapnic drive response was 0.24±0.16 and 0.48±0.23 cm H2O per mm Hg (P=0.001), respectively. CONCLUSION: Acute tetraplegic cervical SCI patients had reduced hypercapnic drive response that may contribute to the difficult weaning, without reduction in hypercapnic ventilatory response.

Respiratory CO2 response depends on plasma bicarbonate concentration in mechanically ventilated patients.

OBJECTIVE: There is controversy about the effects of high plasma bicarbonate concentration ([HCO3(-)]) and the CO2 response test. We analyzed the relationship between [HCO3(-)] and the variation in hydrogen ion concentration (pH) for a given change in PaCO2, and its effects upon CO2 response. DESIGN: A retrospective study was carried out. SETTING: Two intensive care units. PATIENTS: Subjects with and without chronic obstructive pulmonary disease (COPD), at the beginning of weaning from mechanical ventilation. INTERVENTIONS: The CO2 response was evaluated by the re-inhalation of expired air method, measuring the hypercapnic ventilatory response (ΔVE/ΔPaCO2) and hypercapnic drive response (ΔP01/ΔPaCO2), where VE is minute volume and P0.1 is airway occlusion pressure 0.1s after the initiation of inspiration. MAIN OUTCOME MEASURES: [HCO3(-)] and CO2 response. RESULTS: A total of 120 patients in the non-COPD group and 48 in the COPD group were studied. COPD patients had higher mean [HCO3(-)] than non-COPD patients (33.2 ± 5.4 vs. 25.7 ± 3.7 mmol/l, p<0.001). In both non-COPD and COPD patients we observed a significant inverse linear relationship between [HCO3(-)] and pH change per mmHg of PaCO2 (p<0.001), ΔVE/ΔPaCO2 (p<0.001) and ΔP0.1/ΔPaCO2 (p<0.001). CONCLUSIONS: There is an inverse linear relationship between [HCO3(-)] and the variation of pH for a given change in PaCO2 and the CO2 response.

Correlation between brain interstitial and total serum cortisol levels in traumatic brain injury. A preliminary study.

INTRODUCTION: Brain cortisol availability has never been evaluated in patients with traumatic brain injury (TBI). Cerebral microdialysis is a well-established technique for monitoring brain metabolism in neurocritically ill patients, which may be used to measure interstitial cortisol. The objective of this preliminary study was to measure brain interstitial cortisol and its correlation with total serum cortisol in patients with TBI. METHODS: We prospectively studied 6 patients with severe TBI admitted to the Intensive Care Unit of our tertiary University Hospital in which multimodal neuromonitoring including cerebral microdialysis with a high cut-off of 100 k-Da and 20-mm long membrane was used. Serum and brain interstitial cortisol microdialysis samples were obtained every 8 h and analyzed afterwards. RESULTS: Linear regression analysis of total serum cortisol and brain interstitial cortisol in the whole population showed a moderate correlation (R2=0.538, p<0.001, no.=118). However, intra-individual correlation showed a great variability, with correlation coefficients ranging from a R2=0.091 to R2=0.680. CONCLUSION: Our prospective and preliminary study showed a moderate correlation of brain interstitial cortisol and total serum cortisol values in patients with diffuse TBI. However, intra-individual analysis showed a great variability. These results suggest that total serum cortisol may not reflect brain cortisol availability in half of TBI patients.

Effect of the route of nutrition and L-alanyl-L-glutamine supplementation in amino acids' concentration in trauma patients.

PURPOSE: Our purpose was to assess the amino acids' (AAs) profile in trauma patients and to assess the effect of the route of nutrition and the exogenous ALA-GLN dipeptide supplementation on plasma AAs' concentration. METHODS: This is a secondary analysis of a previous randomized controlled trial. On day 1 and day 6 after trauma, plasma concentration of 25 AAs was measured using reverse phase high-performance liquid chromatography. Results were analyzed in relation to the route of nutrition and supplementation of ALA-GLN dipeptide. Differences between plasma AAs' concentrations at day 1 and day 6 were evaluated using the Student's t test or Mann-Whitney-Wilcoxon test. One-way ANOVA and the Kruskal-Wallis test were used to compare groups. A two-sided p value less than 0.05 was considered statistically significant. RESULTS: Ninety-eight patients were analyzed. Mean plasma concentrations at day 1 were close to the lower normal level for most AAs. At day 6 we found an increase in the eight essential AAs' concentrations and in 9 out of 17 measured non-essential AAs. At day 6 we found no differences in plasma concentrations for the sum of all AAs (p = .72), glutamine (p = .31) and arginine (p = .23) distributed by the route of nutrition. Administration of ALA-GLN dipeptide increased the plasma concentration of alanine (p = .004), glutamine (p < .001) and citrulline (p = .006). CONCLUSIONS: We found an early depletion of plasma AAs' concentration which partially recovered at day 6, which was unaffected by the route of nutrition. ALA-GLN dipeptide supplementation produced a small increase in plasma levels of glutamine and citrulline.

Effect of barbiturate coma on adrenal response in patients with traumatic brain injury.

INTRODUCTION: Barbiturate coma is the second tier measure recommended by guidelines to treat post-traumatic refractory intracranial pressure. Systemic hypotension is its most important side effect. Recent evidence suggests that low-dose corticosteroid therapy may be used in a subset of patients with traumatic brain injury (TBI) to avoid hypotension. We evaluated adrenal function in TBI patients undergoing barbiturate coma, as treatment of their refractory intracranial hypertension. MATERIALS AND METHODS: We prospectively studied 40 patients with moderate to severe TBI. Group A (17 patients) were treated with barbiturate coma. Group B (23 patients) presented intracranial hypertension controlled with first tier measures, and acted as a control. Adrenal function was evaluated by using the high-dose corticotropin stimulation test within 24 h after brain injury and after barbiturate coma induction. RESULTS: Within 24 h after TBI, adrenal function was similar in both groups. Once barbiturate coma was induced, patients in group A treated with barbiturate coma presented a higher incidence of adrenal insufficiency compared with the control group B (53% vs 22%, p=0.03). Patients treated with barbiturates, who developed adrenal impairment, required higher doses of norepinephrine to maintain cerebral perfusion pressure than patients treated with barbiturates without adrenal impairment (1.07+/-1.04 microg/kg/min vs 0.31+/-0.32 mug/kg/min, p=0.03). CONCLUSIONS: Patients with TBI treated with barbiturate coma are at higher risk of developing adrenal insufficiency. This subset of patients presented higher requirements of vasoactive support to avoid hypotension. In these patients corticosteroid therapy may have potential therapeutic implications to treat hemodynamic instability.

Normal values of functional residual capacity in the sitting and supine positions.

The measurement of functional residual capacity (FRC) has assumed new importance in the diagnosis of acute respiratory failure. However few reference values exist for FRC in supine positions for both sexes. We measured the FRC in 100 healthy subjects with the helium dilution closed circuit method in the sitting and supine positions. There were 50 women aged 20 to 63 years and 50 men aged 22 to 65 years. Fifty five subjects were smokers (25 women and 30 men) but no significant differences were found between FRC of smokers and nonsmokers. The FRC always decreased when the subject changed from the sitting to supine position. In this study, the correlation coefficients between FRC and height were statistically significant for both sexes, the influence of age and weight on FRC being negligible. Our results provide useful reference values for FRC in the supine position.

The accuracy of the Biox 3700 pulse oximeter in patients receiving vasoactive therapy.

The accuracy of pulse oximetry for the prediction of oxygen saturation of arterial blood in patients with shock has been hardly studied. This study was undertaken to determine if O2 arterial saturation estimated by the Biox 3700 pulse oximeter (SpO2) with an ear probe could reliably substitute for the measurements of O2 saturation (HbO2) with an IL-282 Co-Oximeter in samples of arterial blood obtained from 24 caucasian patients. All patients were mechanically ventilated and needed vasoactive drugs (dopamine and/or dobutamine). Of 24 patients 13 had shock: cardiogenic (n = 6) and septic (n = 7). The mean difference between HbO2 and SpO2 was 2.49% +/- 4.24, with a 95% confidence interval of 0.7% to 4.3% (p = 0.009). There were clinically important differences between both methods since in 9 of 24 patients (37%) SpO2 values were at least 4% lower or greater than HbO2. This disagreement was also apparent in patients with (6/13, 46%) or without shock (3/11, 27%). To conclude, pulse oximetry is not always a sufficiently reliable method to predict HbO2 in patients with or without shock treated with vasoactive drugs.

Validation of a new closed circuit indirect calorimetry method compared with the open Douglas bag method.

New equipment designed for the routine measurement of oxygen uptake (VO2) using a closed circuit method has been validated by comparing it with a standard Douglas bag method. The equipment (The Caloric Measurement Unit, CMU) has been tested in 10 critically ill patients during mechanical ventilation (MV) and in 10 spontaneously breathing healthy subjects. Determinations of VO2 and of the resting energy expenditure (REE) were measured in duplicate with the standard method and once with the CMU. Six additional patients receiving MV were studied with the CMU to evaluate the reproducibility and the effect of FIO2 = 1 vs FIO2 = 0.43 on VO2 measurements. Considering the whole group of 10 patients and 10 subjects, the mean difference of VO2 between both methods was -2 +/- 21 ml/min (95% confidence interval, -11.8 to 7.8 ml/min, p = 0.6) standard deviation. Both methods had a similar reproducibility and the mean difference of VO2 measured at the two different FIO2 with the CMU was -3.2 +/- 11 ml/min (95% confidence interval, -14.7 to 8.4 ml/min, p = 0.5). No statistically significant difference was found between derived REE values obtained from either method. These data show a good correlation between the two methods suggesting that CMU may be used in place of the standard method with the same accuracy in measurement of VO2 even at FIO2 = 1.

Measurement of functional residual capacity during mechanical ventilation. Comparison of a computerized open nitrogen washout method with a closed helium dilution method.

The functional residual capacity of patients treated with mechanical ventilation was measured with two methods: the closed helium dilution method and the open nitrogen washout method with a computerized system. Measurements of FRC were made with and without PEEP. The results obtained did not show significant differences between the methods. Additionally we checked the accuracy of the open nitrogen washout method to measure FRC of patients and healthy subjects breathing high concentrations of oxygen which was the same as breathing air. Both methods were equally reliable and safe when measuring the FRC of patients on mechanical ventilation but the nitrogen method was easier and quicker.

The effect of lateral positions on gas exchange in patients with unilateral lung disease during mechanical ventilation.

Positional changes have long been known to have a gravitational effect on the distribution of pulmonary blood flow. The effect of body position, supine, right and left lateral decubitus, on gas exchange were evaluated in 10 patients with predominantly unilateral lung disease. All patients were treated with mechanical ventilation and PEEP. Arterial blood gases, measured after 15 min in each of the three positions, showed that lying on the side of the "normal" lung resulted in a higher arterial pO2 (mean: 144 mmHg) than lying on that of the "damaged" lung (mean: 86 mmHg). The delta AapO2 values were 334 to 391 mmHg. Both differences were statistically significant (p less than 0.005). No significant changes mean arterial carbon dioxide tensions were noted.

Diagnosis of nosocomial pneumonia in mechanically ventilated patients by the blind protected telescoping catheter.

OBJECTIVES: To demonstrate that blind insertion of the protected telescoping catheter (PTC-NB) through the orotracheal tube can provide reliable pulmonary samples for the diagnosis of nosocomial pneumonia (NP) in ventilated patients. DESIGN: We performed a random comparison between the protected telescoping catheter introduced through a bronchofiberscope (PTC-B) and the PTC-NB to diagnose NP. SETTING: A general intensive care unit of a University Hospital. PATIENTS: 40 consecutive patients on mechanical ventilation and with suspicion of NP. The diagnosis of NP was suspected by clinical and chest X-ray findings. MEASUREMENTS AND RESULTS: NP was confirmed microbiologically in 26 (65%) patients and maintained in 8 patients by clinical and radiological criteria. PTC-NB confirmed the microbiological diagnosis of PN in 21 (80%) patients. The use of antibiotics prior taking respiratory samples reduced the sensitivity of PTC-NB and PTC-B from 100-74% and from 94-70% (p = 0.001). Both techniques agreed in 24 of 33 (73%) patients but such agreement was better when PN was on the right lung. Two patients developed a self-limiting hemoptysis after the PTC-B procedure. CONCLUSIONS: PTC-NB is as sensitive as specific as PTC-B for diagnosing PN in mechanically ventilated patients, being a much easier technique to use.

Metabolic rate in severe head trauma.

BACKGROUND: The metabolic rate of patients suffering severe head trauma (HT) is not well defined, and large variations of resting energy expenditure (REE) have been reported, suggesting an important nonuniformity of REE distribution in HT patients. The purpose of this clinical study was to assess the metabolic rate in mechanically ventilated patients suffering from severe isolated HT, or HT associated with other injuries, in the absence of gross motor activity. METHODS: Eighty HT patients undergoing mechanical ventilation were studied between 48 and 72 hours after injury. Three groups of patients were studied in the following clinical settings: (group A) isolated HT, not receiving morphine (n = 34); (group B) isolated HT, receiving an intravenous perfusion of morphine (n = 26) to control gross motor activity; and (group C) HT associated with other serious injuries, receiving intravenous morphine (n = 20) to induce sedation and analgesia. REE was measured with the open-Douglas-bag method. RESULTS: No significant differences among the three groups were found in the metabolic rate expressed as the percentage of measured REE from predicted REE and REE expressed in terms of body weight. The mean percent measured REE was 123 +/- 16, and REE expressed in terms of body weight was 30 +/- 5 kcal/kg per day. Severe hypermetabolism was diagnosed if mean percent measured REE was greater than 130 and was present in 25 of 80 (31%) patients. CONCLUSIONS: Severe HT treated with or without morphine was characterized by a moderate state of hypermetabolism after the first days of trauma, but an important proportion of HT patients showed considerably elevated metabolic rates.

Gastroesophageal reflux in intubated patients receiving enteral nutrition: effect of supine and semirecumbent positions.

The incidence of gastroesophageal reflux (GER) in critically ill patients as well as the effect of a nasogastric tube (NGT) and body position as risk factors for GER were determined. Seventy patients with orotracheal intubation receiving enteral nutrition through a NGT for more than 48 hours were prospectively studied with two randomly assigned body positions: supine or semirecumbent. Detection of GER was achieved by scintigraphy after labeling gastric contents with 500 microCi of technetium-99m sulfur colloid administered through the NGT. In 50 patients scintigraphy was performed after subjects had remained in the randomized position for 2 hours with the NGT pinched. Twenty additional patients were studied after the NGT had been removed. In 50 patients with NGT, GER was present in 74% (37 of 50) and was higher in the supine position (81%, 21 of 26) than in the semirecumbent position (67%, 16 of 24), but this difference was not statistically significant (p = .26). In 20 patients without NGT, the incidence of GER was 35% (7 of 20) and it was also higher in the supine (50%, 6 of 12) than in the semirecumbent position (12%, 1 of 8, p = .16). There was a statistically significant difference between GER in patients with and without NGT (74% vs 35%, p = .0002). These data show that there is a high incidence of GER in patients with orotracheal intubation and NGT. The presence of a NGT is a risk factor for GER. Semirecumbency does not prevent GER, but there is less incidence than in the supine position.

Incidence of gastroesophageal reflux and aspiration in mechanically ventilated patients using small-bore nasogastric tubes.

BACKGROUND: Use of a large-bore nasogastric tube (NGT) and patient position are considered key factors in promoting gastroesophageal reflux (GER) and pulmonary aspiration in critically ill patients. The objective of this study was to determine the incidence of GER and pulmonary aspiration of gastric contents in mechanically ventilated (MV) patients using small-bore NGTs. METHODS: We studied 30 patients on mechanical ventilation for acute respiratory failure who tolerated enteral nutrition through a small-bore NGT. Patients were randomly assigned to a group with (n = 16) or without (n = 14) a small-bore NGT and were maintained in a semirecumbent position during the study. GER and aspiration of gastric contents were assessed by a radioisotopic technique. Scans were done 24 hours after technetium-99m administration (n = 30). In 9 patients a dynamic scintigraphy was performed immediately after colloid administration, and samples of blood and tracheal and oropharyngeal secretions were obtained basally, 30 minutes, and 24 hours after technetium administration and analyzed for radioactivity using a gamma counter. RESULTS: Both groups were similar in age, underlying diagnosis, number of days of mechanical ventilation at the day of study, and mortality. There were no GER reaching the oropharynx and aspiration of gastric contents in both groups. CONCLUSIONS: GER and aspiration of gastric contents were not detected in MV patients using small-bore NGTs and may be a simple measure to prevent ventilator-associated pneumonia.