Non-Equilibrium Method for the Non-Invasive Estimation of Arterial PCO2

Background: Under conditions of pulmonary ventilation/perfusion mismatch, end-tidal PCO2 (ETPCO2) may severely underestimate arterial PCO2 (PaCO2). Objective: We aimed to develop a method for the accurate non-invasive estimation of PaCO2 from ETPCO2. Methods/Patients: The fact that ETPCO2 is a mixture of PCO2 from both the ventilated and perfused alveoli, and the ventilated but unperfused ones (‘alveolar deadspace’), was brought into mathematical terms. Using the model, by inspiring two gases with different CO2 content and determining the corresponding ETPCO2 values, the PCO2 of the ventilated and perfused alveoli (truePCO2) may be calculated as an estimate of PaCO2. The model was applied on 12 ventilated patients aged 53 to 78 yrs. Estimates of PaCO2 were compared to the results of invasive determination. Results: Conventional ETPCO2 and PaCO2 differed on average by 22 percent (95% confidence interval, 18 to 26). Depending on the difference between the two inspiratory PCO2 levels used, the unsigned error of the model-based estimate typically was 5 percent (95% confidence interval, 3.5 to 7) or better. Conclusion: We provide a non-invasive method for the accurate estimation of PaCO2 and suggest its implementation into ventilators for the close monitoring of pulmonary treatment response.


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Effects of Permissive Hypercapnia on Pulmonary Mechanics and Hemodynamics during Mechanical Ventilation in Severe Acute Respirat

Objectives: To evaluate effects of permissive hypercapnia (PHC) on pulmonary mechanics and hemodynamics in patients with severe acute respiratory distress syndrome (ARDS). Methods: We observed the influence of different tidal volume (VT) on pulmonary mechanics and hemodynamics in 10 patients with severe ARDS. Results: PHC was induced by decreasing VT from 10 - 12 ml/kg (routine VT) to 6 - 8 ml/kg (small VT). Arterial oxygen pressure and saturation remained unchanged, but pulmonary venous admixture was increased (p < 0.05). Airway plateau pressure and mean pressure were also decreased markedly. C20/C, which reflects lung overdistention, was increased significantly. Mean arterial pressure, central venous pressure, pulmonary arterial pressure were not changed, while systemic vascular resistance index was decreased markedly (p < 0.05). Cardiac index (CI) and oxygen delivery (DO2) were increased (p < 0.05), while oxygen consumption remained unchanged. Conclusions: PHC, which was induced by small VT, might prevent lung overdistention and led to an increase in CI and DO2.


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A Prior Brain Microinjury Attenuates Hypermetabolism Induced by Brain Ischemia-Reperfusion in the Mouse

We have previously shown that a prior brain microinjury improves survival of mice following brain ischemia, though the precise mechanism remains to be determined. The purpose of the present study was to examine the modulatory effects of the brain microinjury on postischemic brain metabolism. Sixty-eight DDY mice were divided into four groups: sham-operated non-ischemia, sham-operated ischemia, brain-injured non-ischemia, and brain-injured ischemia groups. Brain microinjury was induced by vertically inserting a 25-gauge needle into the brain at selected four sites. Seven days after the injury or sham-operation, animals in two ischemia groups were subjected to brain ischemia (60 min occlusion of bilateral carotid arteries). Using 2-[14C] deoxyglucose method, relative metabolic activity of brain regions was measured seven days after brain microinjury or sham operation in two non-ischemia groups and seven days after brain ischemia in the other two ischemia groups. There were no significant differences in relative metabolic activity of any brain region measured when compared between sham-operated and brain-injured animals without ischemia. In mice with sham operation, metabolic activity after ischemia was significantly higher in 8 of 22 brain regions examined that that measured without ischemia (p < .05). In mice with brain microinjury, metabolic activity remained unchanged following brain ischemia in any brain region examined except in the mammilary complex. The minor brain injury it self did not affect regional brain metabolism but attenuated postischemic increase in metabolic activity, suggesting that the ability of an antecedent brain microtrauma to attenuate postischemic hypermetabolism is involved in protection from subsequent ischemic-reperfusion injury.


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Procalcitonin May be a Better Predictor of Interleukin-6 than Conventional Inflammatory Markers

Objective: To determine the correlation and predictive accuracy of conventional inflammatory variables (body temperature, leukocyte count, neutrophil percentage, absolute neutrophil count [ANC], C-reactive protein [CRP]) and a new inflammatory marker, procalcitonin (PCT), with elevated levels of interleukin-6 (IL-6) in septic patients. Materials and Methods: Fifty-one patients were enrolled in the study. Systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, and septic shock were diagnosed according to ACCP/SCCM criteria. Serum concentrations of PCT, IL-6 and CRP were determined within 24 hours after the clinical onset of sepsis or SIRS. Leukocyte count, neutrophil percentage, and ANC, as well as maximal body temperature were also recorded. Results: Among all investigated variables, PCT most significantly correlated with serum IL-6 levels. Based on area under the receiver operating characteristics curve, PCT exhibited the highest predictive capability (0.685 for IL-6 ¡Ý 500 pg/mL, and 0.858 for IL-6 ¡Ý 1000 pg/mL), body temperature (0.662 and 0.792, respectively) and CRP (0.625 and 0.727, respectively) offered moderate predictive accuracy, while leukocyte count, neutrophil percentage and ANC carried the lowest predictive capability. Sensitivity, specificity, positive and negative predictive values all followed the same pattern. Conclusion: Compared with conventional inflammatory variables, PCT may reflect more reliably the elevated IL-6 levels.


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Does Pulse Pressure Variation Correlate with Conventional Measures of Preload?

Objective: Systolic pressure variation (SPV) and pulse pressure variation (PPV) are sensitive and specific predictors of cardiovascular response to fluid challenge, with PPV being slightly more accurate. SPV does not correlate well with conventional measure of preload such as pulmonary artery occlusion pressure (PPAO), central venous pressure (CVP) or echocardiographic measures such as end-diastolic area (EDA), especially in patients with decreased left ventricular (LV) function. Because PPV is a more sensitive and specific predictor of preload responsiveness, we questioned whether PPV would correlate with conventional measures of preload. Design: Prospective repeat measures series. Setting: University teaching hospital cardiac operating theatre. Patients: Eight anesthetized cardiac surgery patients before and after cardiopulmonary bypass. Interventions: Positive pressure ventilation with tidal volumes of 8-10 ml/kg. Measurements: PPAO, CVP, arterial pressure and 2-dimensional LV mid-axis cross-sectional areas with transesophageal echocardiography were measured both before and after bypass during a brief apneic period followed by a mechanical breath. All measures were performed with the chest closed. Main Results: Using linear regression modeling, neither SPV nor PPV correlated with PPAO, CVP or EDA. This suggests that preload responsiveness and estimates of LV end-diastolic volume reflect different physiologic concepts.


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The Addition of Trickle Feeds Reduces the Complications Associated with Parenteral Nutrition

Background: “Trickle feeds” are frequently added to patients receiving parenteral nutrition on the assumption that providing small volumes of enteral nutrition reduces the complications associated with parenteral nutrition. This hypothesis, however, has not been tested. Objective: The aim of this study was to compare the incidence of ventilator-associated pneumonia and the Standardized Mortality Ratio in critically ill ICU patients receiving parenteral nutrition alone as compared to parenteral nutrition together with trickle feeds. Design: This was a non-randomized cohort study. The incidence of ventilator-associated pneumonia and the Standardized Mortality Ration was compared in critically ill ICU patients with an acute abdominal processes who had received at least 3 days of parenteral nutrition or parenteral nutrition together with trickle feeds. The diagnoses of pneumonia was made by protected specimen bruch sampling. Results: Thirty two patients received parenteral nutrition alone and 34 parenteral nutrition together with trickle feeds. The patients receiving trickle feeds had a loweer incidence of confirmed bacterial pneumonia (8 vs 28%; p=0.05) and a trend towards a lower hospital mortality. The Standardized Mortality Ratio was 1.4 in the patients receiving parenteral nutrition alone and 0.85 in patients receiving trickle feeds together with parenteral nutrition; a 44% reduction in mortality. Conclusion: This study suggests that the addition of “trickle” feeds to parenteral nutrition reduces infective complications and may reduce hospital mortality.


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Assessement of Change in Body Water By Multiple Frequency Bioelectrical Impedance in Patients Undergoing Cardiopulmonary Bypass

Objective: To evaluate the relationship between changes in body bioelectrical impedance (BI) at 1, 50, 100 kHz and fluid balance, as an index of body water changes, in patients undergoing cardiopulmonary bypass.
Design: Descriptive, correlative.
Setting: Intensive Care Unit of a cardiac center Patients: Twenty male patients, before and after elective coronary artery bypass graft surgery with cardiopulmonary bypass.
Interventions: None.
Measurements: Whole body bioelectrical impedance using multiple frequency bioelectrical impedance (Dietosystem, Italy) at multiple frequencies (1, 50, 100 kHz) was conducted preoperatively and three times during the 24 hour postoperative period. The volume of body water compartment was calculated using Guricci’s formula. The calculated fluid balances uncorrected for insensible water losses were measured from fluid intake and output.
Findings: In 24 hours after surgery calculated total body water (TBW), extracellular water (ECW), and intracellular water (ICW) increased by 16.0%, 20.7%, and 13.0%, respectively, but the values were within desirable ranges. There was no correlation between TBW changes measured by MFBIA and calculated fluid balance.
Conclusions: The current study indicates that changes of body water compartment occur during 24 hours after CABG. Calculated ICW increases within 24 hours after CABG.


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Pro- and Anti-Infl ammatory Balance of Septic Patients is Associated with Severity and Outcome

Purpose: To study infl ammatory profile in patients with sepsis, severe sepsis and septic shock with regards to organ dysfunction and outcome, and to identify a pattern associated with more catastrophic course of illness, organ failure and risk of death. Material and methods: Twenty-nine consecutive patients with sepsis admitted to a medical Intensive Care Unit of a tertiary university hospital (November 2002-December 2003). Plasmatic levels of interleukin-6 (IL-6) and interleukin-10 (IL- 10) as pro-infl ammatory and anti-infl ammatory markers were measured at baseline, 12, 24 and 48 hours of evolution. Results: There is a positive association between higher levels of IL-6 and severity of the septic process, organ dysfunctions and risk of death, statistically signifi cant at anytime (at baseline, 12, 24 and 48 hours, p <0.05). Higher IL-6/IL-10 ratios associate signifi cantly with risk of death at 24 hours (RR=1.45 if higher or equal to the median). Conclusions: Plasmatic biomarkers measurement during the initial phase of sepsis may help to individualize therapy. An evaluation at 24 h based on IL-6/IL-10 ratio may anticipate a more aggressive infl ammatory profi le. These patients would specially benefi t from immunomodulating therapies to improve survival.


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Use and Understanding of Therapeutic Hypothermia in Developing Countries

Purpose: The use of therapeutic hypothermia (TH) has increased in the treatment of comatose victims of cardiac arrest, traumatic brain injury, refractory dysrhythmias, neonatal encephalopathy and asphyxia, near-drowning and hemorrhagic shock. The purpose of this study was to ascertain the level of understanding of TH use for comatose victims of cardiac arrest among healthcare providers in two developing countries. Methods: A 22-question survey was administered to physicians, nurses, and other health professionals who attended two large emergency medicine and critical care meetings in Indonesia and Mexico. The questionnaire included socio-demographic characteristics of the respondents. Specifi c questions regarding TH awareness and its use were included, as well as questions examining familiarity with the current recommendations from International Liaison Committee on Resuscitation (ILCOR) Results: Two hundred and sixty-six surveys were collected from the two countries. Of all respondents, 15.54% had used TH: 37.8% were nurses and 31.58% physicians (ñ =0.012). TH was used most frequently administered in the coronary care unit and the emergency department (55% and 45%, ñ =0.005). Eight percent of all respondents had TH protocols established at their institutions, mostly by nursing personnel (80% ñ =0.009). Practitioners reported they were not familiar with the ILCOR guidelines (97% of the respondents from Mexico and 87% of the respondents from Indonesia (ñ =0.009)). Among those using TH, active rewarming was used by 71% of respondents queried in Indonesia as compared with 38% of respondents surveyed in Mexico (ñ =0.001). Conclusions: TH appears underutilized in our sample of practitioners from two developing countries. Clinicians in these countries are not familiar with ILCOR TH guidelines. Therapeutic hypothermia is certainly practical in most clinical settings and programs aimed at educating practitioners about TH are needed in developing countries to improve neurological outcome in comatose victims of cardiac arrest.


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