Spontaneous Breathing Patients Research Articles

Profile of reintubated patients submitted to daily weaning screen and spontaneous breathing trial in a general ICU

Mechanical ventilation (MV) weaning is the transition of artificial ventilation to spontaneous breathing of patients intubated for more than 24 hours. Reintubation may occur, even if the weaning process has been well conducted, in 13 to 19% of the extubated patients. Daily weaning screen and spontaneous breathing trial are widely used to evaluate patients ready to be weaned, although a reintubation risk may occur [1]. The objective of this study was to verify the profile of patients that failed the weaning process and needed to be reintubated.

Reliability of pressure measurements via balloon catheters is high: an evaluation of six esophageal catheters

Reliable measurement of esophageal pressure is a prerequisite for analysis of respiratory system mechanics in spontaneous breathing patients. For that purpose, various types of balloon catheters exist that differ in material, size and shape. In physical models we studied the quality of pressure measurement via six different balloon catheters, three of them containing a second balloon for measurement of gastric pressure.

Evaluation of techniques for estimating the power spectral density of RR-intervals under paced respiration conditions

Heart rate variability (HRV) analysis is increasingly used in anaesthesia and intensive care monitoring of spontaneous breathing and mechanical ventilated patients. In the frequency domain, different estimation methods of the power spectral density (PSD) of RR-intervals lead to different results. Therefore, we investigated the PSD estimates of fast Fourier transform (FFT), autoregressive modeling (AR) and Lomb-Scargle periodogram (LSP) for 25 young healthy subjects subjected to metronomic breathing. The optimum method for determination of HRV spectral parameters under paced respiration was identified by evaluating the relative error (RE) and the root mean square relative error (RMSRE) for each breathing frequency (BF) and spectral estimation method. Additionally, the sympathovagal balance was investigated by calculating the low frequency/high frequency (LF/HF) ratio. Above 7 breaths per minute, all methods showed a significant increase in LF/HF ratio with increasing BF. On average, the RMSRE of FFT was lower than for LSP and AR. Therefore, under paced respiration conditions, estimating RR-interval PSD using FFT is recommend.

EComment. Ambulatory veno-venous extracorporeal membrane oxygenation

We read with great interest the article by Nosotti et al. [1]. The authors presented their experience with the use of veno-venous extracorporeal membrane oxygenation (ECMO) in 11 patients with severe end-stage lung failure awaiting lung transplantation. Seven patients were awake, while 4 patients required invasive mechanical ventilation. The authors describe significant improvements in the 1-year survival rate in non-sedated patients. In addition, the authors found a tendency to shorter duration of mechanical ventilation, intensive care unit stay and overall in-hospital stay for spontaneous breathing patients on ECMO after lung transplantation. Although we applaud the efforts of Nosotti et al. and recognize the value of ECMO in non-intubated patients to overcome the drawbacks of long-term mechanical ventilation, we believe that the use of the currently available dual-lumen Avalon Elite cannula (Avalon Laboratories, LLC, Los Angeles, CA, USA) offers many advantages in awake, spontaneously breathing patients and should be the preferred approach for patients with acute respiratory failure, and for those being considered for a bridge-to-lung transplantation [2, 3]. Traditional veno-venous ECMO uses a two-cannula technique that requires bed rest and, in most circumstances, necessitates the patient to remain sedated and mechanically ventilated. The Avalon Elite cannula is the first Food and Drug Administration-approved device for single-site veno-venous ECMO in adults. The catheter is usually inserted into the right jugular vein and has 2 lumens; one lumen drains deoxygenated blood from the superior and inferior vena cava, and the other lumen returns oxygenated blood to the right atrium. Due to its unique design, this single-site cannula avoids recirculation of blood and increases the efficacy of ECMO. Additional advantages include not only the possibility to extubate the patient but also to permit ambulation. By allowing the patient to ambulate and to participate in physical therapy, the risk of ventilator-associated pneumonia and deconditioning is significantly decreased [4]. To further reduce the inconvenience of the cannula for awake patients, Shafii et al. described an alternative site to implant the Avalon Elite cannula [5]. Through the left subclavian vein and under fluoroscopic guidance, the cannula can be securely introduced and positioned. The subclavian access was shown to be more comfortable for patient ambulation and easier for nursing care. In patients requiring prolonged support and specifically for those bridged to lung transplant, veno-venous ECMO with single site cannulation can be an excellent alternative to current cannulation strategies. Conflict of interest: none declared

Flexible fiberoptic bronchoscopy and remifentanil target-controlled infusion in ICU: a preliminary study

Flexible fiberoptic bronchoscopy (FFB) is a major diagnostic tool commonly used in intensive care unit (ICU). However, it generates discomfort and pain and can worsen respiratory and/or hemodynamic condition of critically ill patients. Remifentanil is an ultrashort-acting opioid drug that has been shown to provide effective sedation for painful procedures in spontaneous breathing patients. The aim of this study is to evaluate the safety and efficacy of sedation with remifentanil target-controlled infusion (Remi-TCI) in patients with spontaneous ventilation undergoing FFB in ICU. Monocentric prospective study. All patients received Remi-TCI with initial effect-site target concentration of 2 ng/mL, progressively titrated according to their comfort and sedation. Respiratory and hemodynamic parameters were assessed before, during, and after the procedure, as well as comfort, level of sedation, FFB conditions, and recovery patterns. Global Remi-TCI data and potential complications of the procedure were also recorded. Fourteen patients were included. FFB was successful in all patients with good conditions (sedation, global comfort, and cough). No severe hemodynamic or respiratory complications occurred during procedure. Maximum target concentration and total dose of remifentanil were 2.5 ng/mL (2-4 ng/mL) and 1.4 μg/kg (0.7-2.4 μg/kg), respectively, over 10 min. Patients reported low level of pain and good satisfaction with the procedure. FFB under sedation with Remi-TCI seems to be safe and effective in critically ill patients with spontaneous ventilation. Such results could be the first step towards wider use of Remi-TCI in patients experiencing awkward and/or painful procedures in this setting.

Partial ventilatory support modalities in acute lung injury and acute respiratory distress syndrome-a systematic review.

PurposeThe efficacy of partial ventilatory support modes that allow spontaneous breathing in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is unclear. The objective of this scoping review was to assess the effects of partial ventilatory support on mortality, duration of mechanical ventilation, and both hospital and intensive care unit (ICU) lengths of stay (LOS) for patients with ALI and ARDS; the secondary objective was to describe physiologic effects on hemodynamics, respiratory system and other organ function.MethodsMEDLINE (1966–2009), Cochrane, and EmBase (1980–2009) databases were searched using common ventilator modes as keywords and reference lists from retrieved manuscripts hand searched for additional studies. Two researchers independently reviewed and graded the studies using a modified Oxford Centre for Evidence-Based Medicine grading system. Studies in adult ALI/ARDS patients were included for primary objectives and pre-clinical studies for supporting evidence.ResultsTwo randomized controlled trials (RCTs) were identified, in addition to six prospective cohort studies, one retrospective cohort study, one case control study, 41 clinical physiologic studies and 28 pre-clinical studies. No study was powered to assess mortality, one RCT showed shorter ICU length of stay, and the other demonstrated more ventilator free days. Beneficial effects of preserved spontaneous breathing were mainly physiological effects demonstrated as improvement of gas exchange, hemodynamics and non-pulmonary organ perfusion and function.ConclusionsThe use of partial ventilatory support modalities is often feasible in patients with ALI/ARDS, and may be associated with short-term physiological benefits without appreciable impact on clinically important outcomes.

Administration of propofol for sedation of non-mechanically ventilated patients in non-critical care areas by anesthesia providers and non-anesthesia trained healthcare providers: a systematic review.

The use of propofol as a sedative in various outpatient settings is controversial. At the heart of this controversy is the use of propofol by non-anesthesia trained healthcare providers. To synthesize the best available evidence on the administration of propofol for sedation by anesthesia and non-anesthesia providers in spontaneous breathing patients in non-critical care settings. This review considered non-anesthesia trained and anesthesia trained healthcare providers administering propofol as the agent for sedation in patients of all ages who were not mechanically ventilated and were undergoing procedures for gastrointestinal endoscopy, cardiac catheterization, and procedural sedation for emergency room and radiology procedures.This review included studies where propofol was the sole sedative agent used by non-anesthesia trained, and formally trained anesthesia healthcare providers.This review considered as outcomes procedure time, return to baseline functioning, postoperative recovery time, mean amount of propofol administered, patient satisfaction, incidence of adverse hemodynamic and respiratory events, unplanned admission to hospital, and death.This review considered randomized controlled trials, cohort studies, case-control studies, and case series/report studies. The search strategy aimed to find both published and unpublished studies in English language beginning with the commercial use of propofol in 1989 through 2011. Search was performed across: CINAHL, MEDLINE, Nursing@Ovid, EMBASE, Elsevier Science Direct, Mednar, and Proquest. Studies were critically appraised by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute. Data was extracted using the standardized data extraction tool from the Joanna Briggs Institute. Due to the heterogeneous nature of the interventions and outcome measurements, a meta-analysis was not possible; results are presented in a narrative summary. 9 studies were included in the review: 1 randomized controlled trial, 2 cohort studies, and 6 descriptive studies. In seven of the studies, non-anesthesia providers administered propofol, while two studies had anesthesia providers providing propofol sedation. Five studies reported procedure time. None of the studies reported a return to baseline functioning. Four studies reported postoperative recovery time. One study reported mean propofol dosage according to the two phases of the study, while another study in addition to reporting total and mean propofol dosages, differentiated propofol dosage according to ASA classification. Six of the studies reported average or mean propofol dosage, with one study also reporting the propofol induction dosage. Reporting of adverse hemodynamic and respiratory events varied in the studies. None of the studies reported unplanned admission to the hospital or death. The evidence suggests that anesthesia healthcare providers have the experience and training to safely administer propofol in non-critical care settings involving procedures in non-mechanically ventilated patients. The evidence also suggests that non-anesthesia trained healthcare providers can safely administer propofol sedation in low-risk patients who are not mechanically ventilated if they have received specialized training in the use of propofol sedation, are experienced in its administration, and follow a defined dosage protocol. The administration of propofol sedation by anesthesia providers can be safely administered in patients of all risk categories and depth of sedation.The administration of propofol sedation by non-anesthesia providers can be safely administered to low risk patients for moderate sedation providing the non-anesthesia provider is specially trained and experienced in the administration of propofol sedation while using a defined dosage protocol. Randomized controlled trials are needed to examine the propofol sedation by non-anesthesia healthcare providers in spontaneous breathing patients in non-critical care settings. The type of training required for safe administration of propofol in the outpatient settings should be explored.

Procedural Aspects and Physiologic Mechanisms of the Deep Inspiratory Maneuver

Sir, we have read the paper by S. Preau et al. “Hemodynamic changes during a deep inspiration maneuver predict fluid responsiveness in spontaneously breathing patients” with great interest. Based on the fundamental ideas of dynamic hemodynamic monitoring, inducing cardiac preload variations and monitoring corresponding pulse pressure variations [1], the paper presents a novel technique of varying cardiac preload in spontaneously breathing (SB) patients that does not necessitate specialised equipment apart from routine clinical monitoring. The paper is indeed relevant because it is, to our knowledge, the first to present the feasibility of a deep breathing method (deep inspiratory maneuver, DIM) for inducing preload changes. For the purpose of better understanding the presented technique, we wish to pose the following questions for the authors. Concerning compliance and applicability in terms of intention-to-treat: it is not clear which proportion of SB patients with acute circulatory failure was able to comply with the DIM. Can compliance be expected to be as high as 87% (26 of 30) for this generally defined patient group? Concerning the calculations: DIM-induced changes are defined by the authors as. DIM-induced changes = (maximal value during DIM − minimal value during quiet SB prior to DIM)/((maximal value during DIM − minimal value during quiet SB prior to DIM)/2). How large was the time window when estimating the minimal value during quiet SB prior to DIM? Did the time window vary or was it fixed? The maximal value during DIM was found in either phase 2 or phase 4 of the DIM. In which phase was the maximal value typically found? Were the maximal values during the two phases generally of the same magnitude? Instructing the patients to perform the DIM: this is important should the technique be validated by other study groups and in turn gain widespread use. Did the authors in any way evaluate if the slow continuous inspiration strain was associated with a more or less constant inspiratory flow or was most air generally inspired in the first phase of inspiration, perhaps amplifying maximal value during DIM phase 2? How were instructions given on inspiratory flow rate? Did you make any instructions to the patients (directly or indirectly) what tidal volume should be during DIM? Did they inspire to, for example, maximal or convenient lung volume? Concerning the physiological mechanisms: did you experience any patients with significant heart rate variability (HRV)? The respiratory part of HRV (with its subsequent varying passive filling time of the ventricles) could be another mechanism inducing preload variations and as such it could confound results obtained with the DIM technique. On the other hand, HRV is known to be significantly reduced during sepsis [2]. We also have a few comments and suggestions to the proposed physiological mechanisms. The decrease in left ventricular stroke volume during DIM phase 1 is suggested to be induced by increasing ventricular afterload. However, we think that another and perhaps more important mechanism is the reduced intrathoracic pressure reducing left ventricular preload during the initial phase of inspiration—until the increasing right ventricular stroke volume with the delay of pulmonary transit time again increases left ventricular preload substantially. In line with this suggestion, but as a “reversed mechanism,” we also believe that the increasing intrathoracic pressure during passive expiration (DIM phase 4) contributes somewhat to the increasing left ventricular (preload and) stroke volume in DIM phase 4 in addition to the suggested overall increase in intrathoracic blood volume. As a last comment, we would like to suggest that the DIM phases 2 and 4 could potentially disclose right ventricular failure: a large maximal value during DIM phase 2 relies on biventricular preload responsiveness whereas a large value in DIM phase 4 relies mostly, if not fully, on left ventricular preload responsiveness. Even though the authors did not encounter any cases of preload unresponsiveness associated with high ΔPPdim (specificity was 100%) low phase 2 values associated with high phase 4 values could theoretically disclose right ventricular failure—even when taking interventricular dependence into account.

Hemodynamic Changes during a Deep Inspiration Maneuver Predict Fluid Responsiveness in Spontaneously Breathing Patients

Objective. We hypothesized that the hemodynamic response to a deep inspiration maneuver (DIM) indicates fluid responsiveness in spontaneously breathing (SB) patients. Design. Prospective study. Setting. ICU of a general hospital. Patients. Consecutive nonintubated patients without mechanical ventilation, considered for volume expansion (VE). Intervention. We assessed hemodynamic status at baseline and after VE. Measurements and Main Results. We measured radial pulse pressure (PP) using an arterial catheter and peak velocity of femoral artery flow (VF) using continuous Doppler. Changes in PP and VF induced by a DIM (ΔPPdim and ΔVFdim) were calculated in 23 patients. ΔPPdim and ΔVFdim ≥12% predicted responders to VE with sensitivity of 90% and specificity of 100%. Conclusions. In a restricted population of SB patients with severe sepsis or acute pancreatitis, ΔPPdim and ΔVFdim are accurate indices for predicting fluid responsiveness. These results should be confirmed in a larger population before validating their use in current practice.

La stimulation phrénique implantée

The implanted phrenic nerve stimulation is a technique restoring the spontaneous breathing in patients with a failing respiratory command, which leads to a dependency on mechanical ventilation. This technique may particularly involve quadriplegic patients with a high-level spinal cord injury and patients with congenital central hypoventilation syndrome. The electrophysiological diaphragm investigations allow a better patient selection, assessing in one hand a definite problem with central respiratory command and on the other hand the integrity of phrenic nerves. To date, two different phrenic stimulation techniques are available in France: the quadripolar intra-thoracic stimulation and the bipolar intra-diaphragmatic stimulation. Both techniques allow patients to be weaned off their mechanical ventilator, improving dramatically their quality of life. In fact, one of the systems (phrenic intra-diaphragmatic stimulation) was granted reimbursement in France in 2009 and is now on the social security list of reimbursed products. In the future, the phrenic intra-diaphragmatic stimulation may find its place in the intensive care unit with temporal use following surgeries leading to specific respiratory complications as well as diaphragmatic atrophy induced by prolonged mechanical ventilation.

Changes in Airway and Respiratory Tissue Mechanics After Cardiac Surgery

Because of the critical importance of the first postoperative week in the development of respiratory complications after cardiac surgery, the mechanical properties of the respiratory system in this period were followed up systematically. The input impedance of the respiratory system (Zrs) was measured during spontaneous breathing in patients (n=35) undergoing cardiac surgery on the day before surgery to establish the baseline, and for six days thereafter. The airway resistance was inferred from the average of the resistive component of Zrs, while the changes in respiratory elastance were assessed from the imaginary part of Zrs by model fitting. An assessment was made of the impact on the postoperative changes of factors characteristic of the patients (gender, age, smoking, and obesity) or the surgery duration and the need or not for a cardiopulmonary bypass. Airway resistance increased immediately after extubation (peak rise on day 1, evening: 48+/-10%) and subsequently gradually decreased to the initial level, the recovery proving prolonged in obese patients. Postoperative elevation in elastance peaked later (day 2, evening: 83+/-14%), lasted longer, and was affected by both cardiopulmonary bypass (p<0.05) and obesity (p<0.005). These findings demonstrate the need for particular attention in the postoperative management of patients after cardiac surgery in order to reduce the immediate airway symptoms, and to take steps to maintain the lungs open during the critical postoperative days 2 and 3, especially in obese patients and (or) if the surgery involves the use of cardiopulmonary bypass.

Partitioning of exhaled NO in ventilated patients undergoing cardiac surgery

The change in exhaled NO after cardio-pulmonary bypass remains controversial. The aims were to determine whether exhaled NO sources (alveolar or bronchial) are modified after bypass, and whether mechanical ventilation (MV) settings during bypass modify exhaled NO changes. Thirty-two patients were divided into three groups: without MV during bypass and positive end-expiratory pressure (PEEP) (n=12), dead space MV without PEEP (n=10) and dead space MV with PEEP (n=10). Alveolar NO concentration and bronchial NO flux were calculated before and 1h after surgery using a two-compartment model of NO exchange developed in spontaneous breathing patients. Whereas a significant decrease in bronchial NO was found after bypass in the two groups without PEEP during bypass, this decrease was not observed in patients with dead space ventilation with PEEP. Alveolar NO was not significantly modified whatever the ventilation settings. In conclusion, the impairment of bronchial NO seemed related to airway closure since dead space mechanical ventilation with PEEP prevented its decrease.

On-line monitoring of lung mechanics during spontaneous breathing: a physiological study

Monitoring the mechanics of breathing in patients with advanced chronic obstructive lung diseases prior to lung transplantation is useful to characterize changes in the mechanical properties of the lungs. On-line methods of monitoring immediately process the data for clinical decisions. However, the few available methods are so far limited to monitor respiratory mechanics in ventilator-dependent patients. We investigated whether on-line monitoring of the lung mechanics, including intrinsic PEEP, was feasible in spontaneously breathing patients. In 9 stable patients with chronic obstructive pulmonary disease (COPD) and 11 with cystic fibrosis (CF) undergoing the procedure for the lung transplantation waiting list, we applied 2 methods of on-line monitoring (modified recursive least squares, RLS and modified multiple linear regression methods, SLS) of intrinsic PEEP (P(0)), dynamic lung elastance (E(Ldyn)) and inspiratory resistance (R(Linsp)), and compared them with an off-line graphical analysis (GA), our reference technique. In CF patients, there was no difference between methods, while in COPD, the median values of E(Ldyn) and R(Linsp) were significantly different between GA/SLS and GA/RLS, respectively (Dunn's, p<0.05). However, the correlation was very high for all comparisons, particularly for E(Ldyn) (R>0.98) and R(Linsp) (R>0.93). Moreover, Bland-Altman plots showed that the mean differences were consistently low and the intervals of agreement reasonable. Our study suggests that on-line methods are reliable for monitoring lung mechanics in spontaneous breathing patients with severe lung diseases and could help clinicians in their decision-making process.

Spectral analysis of respiratory-related hemodynamic variables in simulated hypovolemia: a study in healthy volunteers with spontaneous breathing using a paced breathing activity

BackgroundA dynamic preload index such as stroke volume variation (SVV) is not as reliable in spontaneous breathing (SB) patients as in mechanically ventilated patients. This study examined the hypothesis that spectral analysis of hemodynamic variables during paced breathing (PB) activity may be a feasible index of volume changes and fluid responsiveness, despite insufficient respiratory changes in the preload index during SB activity.MethodsBlood pressure and stroke volume (SV) were measured in 16 subjects undergoing PB (15 breaths/min), using a Finometer device and the Modelflow method. Respiratory systolic pressure variation (SPV) and SVV were measured and respiratory frequency (RF, 0.2-0.3 Hz) of power spectra of SPV (SPVRF) and SVV (SVVRF) were computed using fast Fourier transformation. Progressive hypovolemia was simulated with lower body negative pressure (LBNP). Volume challenges were produced by infusion of normal saline and subsequent release of LBNP to baseline. Fluid responsiveness, defined as a >20% increase in SV, was assessed by the area under the curve (AUC) of receiver operating characteristic curves.ResultsGraded hypovolemia caused a significant increase in SPVRF and a decrease in SVVRF. During volume expansion, SPVRF decreased and SVVRF rose significantly. Fluid responsiveness was better predicted with SVVRF (AUC 0.75) than with SPVRF, SPV, or SVV. SVVRF before volume challenge was significantly correlated with volume expansion-induced changes in SV (r = -0.64).ConclusionsThese results suggest that RF spectral analysis of dynamic preload variables may enable the detection of volume change and fluid responsiveness in SB hypovolemic patients performing PB activity.

Advantage of spontaneous breathing in patients with respiratory failure

The fact that different modalities of mechanical ventilation are associated with a number of serious side effects and risks and can influence the clinical outcome of patients, the various modes of mechanical ventilation have, over the past ten years, been the subject of a wide variety of scientific studies. Many of these modalities are designed for partial ventilatory support, which might reflect the complexity of the issue of patient’s ventilator interactions when spontaneous breathing activity is present, compared to controlled mechanical ventilation. Spontaneous breathing modes during mechanical ventilation may integrate intrinsic feedback mechanisms that should help prevent ventilator- induced lung injury and improve synchrony between the ventilator and the patient’s demand. The improvements in pulmonary gas exchange, systemic blood flow, and oxygen supply to the tissue that have been observed when spontaneous breathing has been maintained during mechanical ventilation are reflected in the clinical improvement in the patient’ s condition. It is the aim of this article to review the effects of preserved spontaneous breathing activity during mechanical ventilation in patients with acute respiratory failure.

Global end-diastolic volume and global end-diastolic volume index are age dependent in awake, spontaneous-breathing patients after elective craniotomy

Estimation of cardiac preload is an important prerequisite for adequate volume resuscitation. The global end-diastolic volume (GEDV) and the global end-diastolic volume index (GEDVI) are surrogate parameters for preload and have been hypothesized to be age dependent [1]. The current study was performed to assess the influence of age on the preload parameters GEDV and GEDVI prospectively.

Preoperative Alterations in Correlation Properties and Complexity of R–R Interval Dynamics Predict the Risk of Atrial Fibrillation after Coronary Artery Bypass Grafting in Patients with Preserved Left Ventricular Function

We evaluated whether there are constant preoperative alterations in nonlinear R-R interval dynamics that associate with the risk of postoperative atrial fibrillation in patients with preserved left ventricular function. We analyzed mean normal-to-normal R-R intervals, short-term scaling exponent of detrended fluctuation analysis (DFA alpha(1)), approximate entropy and entropy of symbolic dynamics (SymDyn En) from 10-minute ECG recordings during rest, paced breathing, and passive tilt performed 1 day before surgery in 67 elective coronary artery bypass grafting patients. Nineteen patients developed postoperative atrial fibrillation. The preoperative DFA alpha(1) was constantly lower in patients developing postoperative atrial fibrillation than in patients remaining in sinus rhythm (P = 0.016); during spontaneous breathing, the DFA alpha(1) was 0.93 +/- 0.33 in patients with atrial fibrillation and 1.13 +/- 0.24 in patients with sinus rhythm. The entropy of symbolic dynamics was higher during the spontaneous breathing in patients with atrial fibrillation than in patients with sinus rhythm (4.72 +/- 0.51 vs 4.36 +/- 0.51, P = 0.012). Higher short-term scaling exponent of detrended fluctuation analysis during the spontaneous breathing period reduced the risk of postoperative atrial fibrillation (OR 0.31 for an interquartile increase in DFA alpha(1), 95% CI 0.13-0.78), while higher entropy of symbolic dynamics increased it (OR 3.16 for an interquartile increase in SymDyn En, 95% CI 1.23-8.10), independently of age and clinical risk factors. The preoperatively altered nonlinear R-R interval dynamics were independent predictors of postoperative atrial fibrillation and might become a useful tool for the risk assessment of atrial fibrillation.

Variations in Pulse Oximetry Plethysmographic Waveform Amplitude and Hemodynamic Assessment Induced by Passive Leg Raising in Spontaneously Breathing Adult Volunteers

Background: In hemodynamically unstable patients with spontaneous breathing activity, predicting volume responsivenss is a difficult challenge. Our objective was to test whether the respiratory changes in pulse oxymetry plethysmographic waveform amplitude (POP) and in stroke volume (ΔSV) could predict fluid responsiveness to passive leg raising (PLR) in normal volunteers. Methods: We investigated 25 normal volunteers. We assessed hemodynamic status (HR, SBP, MAP, CI and SVI) and calculated the respiratory variation in pulse oximetry plethysmographic waveform amplitude at supine and after PLR. We attached a pulse oximeter of 25 spontaneously breathing volunteers as several time points: after 1 min and 5 min in supine position and during PLR at 60. Heart rate, non-invasive blood pressures (mean arterial pressure, systolic blood pressure), maximal POP (POPmax), minimal POP (POPmin) and ΔPOP defined as (POPmax− POPmin)/[(POPmax+POPmin)/2] were recorded using monitor. Results: Comparing to supine and PLR, systolic blood pressure and mean arterial pressure were not different, but the change in cardiac index, stroke volume and respiratory variation in POP were significant different. In response group (≥10% in ΔCI), the change in cardiac index, stroke volume and respiratory variation in POP were significant greater. Conclusions: PLR induces a significant decrement of variation in POP amplitude among spontaneouely breathing volunteers. We suppose that the changes in stroke volume and the respiratory variation in pulse oximetry plethysmographic waveform amplitude induced by PLR predict fluid responsiveness in spontaneous breathing patients.

End-expiratory lung volume during mechanical ventilation: a comparison with reference values and the effect of positive end-expiratory pressure in intensive care unit patients with different lung conditions.

IntroductionFunctional residual capacity (FRC) reference values are obtained from spontaneous breathing patients, and are measured in the sitting or standing position. During mechanical ventilation FRC is determined by the level of positive end-expiratory pressure (PEEP), and it is therefore better to speak of end-expiratory lung volume. Application of higher levels of PEEP leads to increased end-expiratory lung volume as a result of recruitment or further distention of already ventilated alveoli. The aim of this study was to measure end-expiratory lung volume in mechanically ventilated intensive care unit (ICU) patients with different types of lung pathology at different PEEP levels, and to compare them with predicted sitting FRC values, arterial oxygenation, and compliance values.MethodsEnd-expiratory lung volume measurements were performed at PEEP levels reduced sequentially (15, 10 and then 5 cmH2O) in 45 mechanically ventilated patients divided into three groups according to pulmonary condition: normal lungs (group N), primary lung disorder (group P), and secondary lung disorder (group S).ResultsIn all three groups, end-expiratory lung volume decreased significantly (P < 0.001) while PEEP decreased from 15 to 5 cmH2O, whereas the ratio of arterial oxygen tension to inspired oxygen fraction did not change. At 5 cmH2O PEEP, end-expiratory lung volume was 31, 20, and 17 ml/kg predicted body weight in groups N, P, and S, respectively. These measured values were only 66%, 42%, and 34% of the predicted sitting FRC. A correlation between change in end-expiratory lung volume and change in dynamic compliance was found in group S (P < 0.001; R2 = 0.52), but not in the other groups.ConclusionsEnd-expiratory lung volume measured at 5 cmH2O PEEP was markedly lower than predicted sitting FRC values in all groups. Only in patients with secondary lung disorders were PEEP-induced changes in end-expiratory lung volume the result of derecruitment. In combination with compliance, end-expiratory lung volume can provide additional information to optimize the ventilator settings.

Can dynamic indicators help the prediction of fluid responsiveness in spontaneously breathing critically ill patients?

To investigate whether the respiratory changes in arterial pulse (DeltaPP) and in systolic pressure (DeltaSP) could predict fluid responsiveness in spontaneously breathing (SB) patients. Because changes in intrathoracic pressure during spontaneous breathing (SB) might be insufficient to modify loading conditions of the ventricles, performances of indicators were also assessed during a forced respiratory maneuver. Prospective interventional study. A 34-bed university hospital medico-surgical ICU. Thirty-two SB patients with clinical signs of hemodynamic instability. A 500-ml volume expansion (VE). Cardiac index, assessed using transthoracic echocardiography, increased by at least 15% after VE in 19 patients (responders). At baseline, only dynamic indicators were higher in responders than in nonresponders (13+/-5% vs. 7+/-3%, p=0.003 for DeltaPP and 10+/-4% vs. 6+/-2%, p=0.002 for DeltaSP). Moreover, they significantly decreased after VE (11+/-5% to 6+/-4%, p<0.001 for DeltaPP and 8+/-4% to 6+/-3%, p<0.001 for DeltaSP). DeltaPP and DeltaSP areas under the ROC curve were high (0.81+/-0.08 and 0.82+/-0.08; p=0.888, respectively). A DeltaPP>or=12% predicted fluid responsiveness with high specificity (92%) but poor sensitivity (63%). The forced respiratory maneuver reproducing a dyspneic state decreased the predictive power. Due to their lack of sensitivity and their dependence to respiratory status, DeltaPP and DeltaSP are clearly less reliable to predict fluid responsiveness during SB than in mechanically ventilated patients. However, when their baseline value is high without acute right ventricular dysfunction in a participating patient, a positive response to fluid is likely.