Changes in regional blood flow and pCO2 gradients during isolated abdominal aortic blood flow reduction

Objective: pCO2 gradients are used for the assessment of splanchnic regional and local mucosal blood flow changes in experimental and clinical research. pCO2 gradients may not parallel blood flow changes because of concomitant changes in metabolism, hemoglobin, temperature, and the Haldane effect. Design and setting: A randomized, controlled animal experiment in a university experimental research laboratory. Interventions: An extracorporeal shunt with reservoir and roller pump was inserted between the proximal and the distal abdominal aorta in 16 pigs. In animals randomized to the low-flow group (n=8) splanchnic perfusion was reduced by running the roller pump. At baseline and after 45min of stable shunt flow superior mesenteric artery, celiac trunk, spleen artery, and portal vein blood flows and regional venous-arterial and jejunal and gastric mucosal-arterial pCO2 gradients were measured, and the respective regional O2 consumption rates (VO2) calculated. Measurements and results: In the low-flow group all regional blood flows and the associated VO2 decreased to roughly 50% of baseline values, and hemoglobin decreased from 7.3 (4.4-9.6) g/dl to 5.7 (4.1-8.9) g/dl. Decreasing regional blood flows were consistently associated with increasing regional and mucosal pCO2 gradients. Conclusions: During isolated reduction in abdominal aortic blood flow there is no preferential distribution to any splanchnic vascular bed and changes in regional pCO2 gradients reflect consistently the associated blood blow change

Change in stroke volume in response to fluid challenge: assessment using esophageal Doppler

Abstract.: Objective: To compare two methods of assessing a change in stroke volume in response to fluid challenge: esophageal Doppler and thermodilution with the pulmonary artery catheter. Design: Prospective study. Setting: Department of Intensive Care of a university medical center. Patients: 19 adult patients, intubated and sedated, with a pulmonary catheter and a clinical indication for a fluid challenge. Interventions: Two examiners independently assessed the effect of a fluid challenge on stroke volume and cardiac output with esophageal Doppler. Thermodilution performed by an independent clinician was used as the reference. Between-method variation and interobserver variability of the Doppler method were assessed. Measurements and results: There were no differences in stroke volume and cardiac output before volume challenge when measured with either of the two methods or by the two examiners using the esophageal Doppler. Despite a small bias between the methods and the two examiners using the esophageal Doppler (overall bias for cardiac output 0.3l/min), the precision was poor (1.8l/min). Conclusions: The esophageal Doppler method is a non-invasive alternative to the pulmonary artery catheter for the assessment of stroke volume in critically ill patients. Measurement of stroke volume response to fluid challenge using esophageal Doppler shows substantial interobserver variability. Despite the poor precision between methods and investigators, similar directional changes in stroke volume can be measure

Neurally adjusted ventilatory assist in patients with critical illness-associated polyneuromyopathy

Purpose: Diaphragmatic electrical activity (EAdi), reflecting respiratory drive, and its feedback control might be impaired in critical illness-associated polyneuromyopathy (CIPM). We aimed to evaluate whether titration and prolonged application of neurally adjusted ventilatory assist (NAVA), which delivers pressure (P aw) in proportion to EAdi, is feasible in CIPM patients. Methods: Peripheral and phrenic nerve electrophysiology studies were performed in 15 patients with clinically suspected CIPM and in 14 healthy volunteers. In patients, an adequate NAVA level (NAVAal) was titrated daily and was implemented for a maximum of 72h. Changes in tidal volume (V t) generation per unit of EAdi (V t/EAdi) were assessed daily during standardized tests of neuro-ventilatory efficiency (NVET). Results: In patients (median [range], 66 [44-80]years), peripheral electrophysiology studies confirmed CIPM. Phrenic nerve latency (PNL) was prolonged and diaphragm compound muscle action potential (CMAP) was reduced compared with healthy volunteers (p<0.05 for both). NAVAal could be titrated in all but two patients. During implementation of NAVAal for 61 (37-64)h, the EAdi amplitude was 9.0 (4.4-15.2)μV, and the V t was 6.5 (3.7-14.3)ml/kg predicted body weight. V t, respiratory rate, EAdi, PaCO2, and hemodynamic parameters remained unchanged, while PaO2/FiO2 increased from 238 (121-337) to 282 (150-440)mmHg (p=0.007) during NAVAal. V t/EAdi changed by −10 (−46; +31)% during the first NVET and by −0.1 (−26; +77)% during the last NVET (p=0.048). Conclusion: In most patients with CIPM, EAdi and its feedback control are sufficiently preserved to titrate and implement NAVA for up to 3days. Whether monitoring neuro-ventilatory efficiency helps inform the weaning process warrants further evaluatio

Subject–ventilator synchrony during neural versus pneumatically triggered non-invasive helmet ventilation

OBJECTIVE: Patient-ventilator synchrony during non-invasive pressure support ventilation with the helmet device is often compromised when conventional pneumatic triggering and cycling-off were used. A possible solution to this shortcoming is to replace the pneumatic triggering with neural triggering and cycling-off-using the diaphragm electrical activity (EA(di)). This signal is insensitive to leaks and to the compliance of the ventilator circuit. DESIGN: Randomized, single-blinded, experimental study. SETTING: University Hospital. PARTICIPANTS AND SUBJECTS: Seven healthy human volunteers. INTERVENTIONS: Pneumatic triggering and cycling-off were compared to neural triggering and cycling-off during NIV delivered with the helmet. MEASUREMENTS AND RESULTS: Triggering and cycling-off delays, wasted efforts, and breathing comfort were determined during restricted breathing efforts (<20% of voluntary maximum EA(di)) with various combinations of pressure support (PSV) (5, 10, 20 cm H(2)O) and respiratory rates (10, 20, 30 breath/min). During pneumatic triggering and cycling-off, the subject-ventilator synchrony was progressively more impaired with increasing respiratory rate and levels of PSV (p < 0.001). During neural triggering and cycling-off, effect of increasing respiratory rate and levels of PSV on subject-ventilator synchrony was minimal. Breathing comfort was higher during neural triggering than during pneumatic triggering (p < 0.001). CONCLUSIONS: The present study demonstrates in healthy subjects that subject-ventilator synchrony, trigger effort, and breathing comfort with a helmet interface are considerably less impaired during increasing levels of PSV and respiratory rates with neural triggering and cycling-off, compared to conventional pneumatic triggering and cycling-off

Cumulative lactate and hospital mortality in ICU patients

BACKGROUND: Both hyperlactatemia and persistence of hyperlactatemia have been associated with bad outcome. We compared lactate and lactate-derived variables in outcome prediction. METHODS: Retrospective observational study. Case records from 2,251 consecutive intensive care unit (ICU) patients admitted between 2001 and 2007 were analyzed. Baseline characteristics, all lactate measurements, and in-hospital mortality were recorded. The time integral of arterial blood lactate levels above the upper normal threshold of 2.2 mmol/L (lactate-time-integral), maximum lactate (max-lactate), and time-to-first-normalization were calculated. Survivors and nonsurvivors were compared and receiver operating characteristic (ROC) analysis were applied. RESULTS: A total of 20,755 lactate measurements were analyzed. Data are srpehown as median [interquartile range]. In nonsurvivors (n = 405) lactate-time-integral (192 [0–1881] min·mmol/L) and time-to-first normalization (44.0 [0–427] min) were higher than in hospital survivors (n = 1846; 0 [0–134] min·mmol/L and 0 [0–75] min, respectively; all p < 0.001). Normalization of lactate <6 hours after ICU admission revealed better survival compared with normalization of lactate >6 hours (mortality 16.6% vs. 24.4%; p < 0.001). AUC of ROC curves to predict in-hospital mortality was the largest for max-lactate, whereas it was not different among all other lactate derived variables (all p > 0.05). The area under the ROC curves for admission lactate and lactate-time-integral was not different (p = 0.36). CONCLUSIONS: Hyperlactatemia is associated with in-hospital mortality in a heterogeneous ICU population. In our patients, lactate peak values predicted in-hospital mortality equally well as lactate-time-integral of arterial blood lactate levels above the upper normal threshold

NEURAL CONTROL OF VENTILATION PREVENTS BOTH OVER-DISTENSION AND DE-RECRUITMENT OF EXPERIMENTALLY INJURED LUNGS.

BACKGROUND Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI). METHODS In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVAAL) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HLETT]) and after ALI (endotracheal tube [ALIETT] and during non-invasive ventilation [ALINIV]). Following titration, cNAVAAL was maintained for 5minutes. In 2 rabbits, procedures were repeated after vagotomy (ALIETT+VAG). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVAAL. RESULTS During ALIETT and ALINIV, normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HLETT; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALIETT, but not during ALINIV. During ALIETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment. CONCLUSIONS When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches

Tracheal tear and tension pneumothorax complicating bronchoscopy-guided percutaneous tracheostomy

Percutaneous dilatational tracheostomy (PDT) is a frequently conducted procedure in critically ill patients. Bronchoscopic guidance of PDT is generally recommended to minimize the risk of unintentional tracheal injury. We present a case of tracheal tear and tension pneumothorax, a rare but potentially life-threatening complication, during continuously bronchoscopy-guided PDT. Sealing the large tracheal air fistula with the cuff of an endotracheal tube helped bridge time to definitive surgical repair in our patient. Bronchoscopic guidance may minimize, but cannot completely eliminate, the risk of tracheal injury during PDT

An Unexpected Case of Black Mamba (Dendroaspis polylepis) Bite in Switzerland

Mambas (genus Dendroaspis) are among the most feared venomous African snakes. Without medical treatment, mamba bites are frequently fatal. First-aid treatment includes lymphatic retardation with the pressure immobilization technique. Medical management comprises continuous monitoring, securing patency of the airway, ensuring adequate ventilation, symptomatic measures, and administration of specific antivenin. We report an unusual case of a snake breeder bitten by a black mamba in Switzerland, report the clinical course, and review the lifesaving emergency management of mamba bites. This case highlights the importance of early antivenin administration and suggests that emergency and critical care physicians as well as first responders all around the world should be familiar with clinical toxinology of exotic snake bites as well as with the logistics to most rapidly make the specific antivenin available