Hiccup-like Contractions in Mechanically Ventilated Patients: Individualized Treatment Guided by Transpulmonary Pressure.

Hiccups-like contractions, including hiccups, respiratory myoclonus, and diaphragmatic tremor, refer to involuntary, spasmodic, and inspiratory muscle contractions. They have been repeatedly described in mechanically ventilated patients, especially those with central nervous damage. Nevertheless, their effects on patient-ventilator interaction are largely unknown, and even more overlooked is their contribution to lung and diaphragm injury. We describe, for the first time, how the management of hiccup-like contractions was individualized based on esophageal and transpulmonary pressure measurements in three mechanically ventilated patients. The necessity or not of intervention was determined by the effects of these contractions on arterial blood gases, patient-ventilator synchrony, and lung stress. In addition, esophageal pressure permitted the titration of ventilator settings in a patient with hypoxemia and atelectasis secondary to hiccups and in whom sedatives failed to eliminate the contractions and muscle relaxants were contraindicated. This report highlights the importance of esophageal pressure monitoring in the clinical decision making of hiccup-like contractions in mechanically ventilated patients.

Airway pressure morphology and respiratory muscle activity during end-inspiratory occlusions in pressure support ventilation.

BACKGROUND: The driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined. METHODS: Retrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a "passive-like" decrease followed by plateau, a pattern with "clear plateau," and an "irregular rise" pattern, which included all cases of late or continuous increase, with or without plateau. RESULTS: Data from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmH2O, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively. CONCLUSIONS: The pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.

Validation of a Proposed Algorithm for Assistance Titration During Proportional Assist Ventilation With Load-Adjustable Gain Factors.

BACKGROUND: The present study aimed to validate a recently proposed algorithm for assistance titration during proportional assist ventilation with load-adjustable gain factors, based on a noninvasive estimation of maximum inspiratory pressure (peak Pmus) and inspiratory effort (pressure-time product [PTP] peak Pmus). METHODS: Retrospective analysis of the recordings obtained from 26 subjects ventilated on proportional assist ventilation with load-adjustable gain factors under different conditions, each considered as an experimental case. The estimated inspiratory output (peak Pmus) and effort (PTP-peak Pmus) were compared with the actual-determined by the measurement of transdiaphragmatic pressure- and the derived PTP. Validation of the algorithm was performed by assessing the accuracy of peak Pmus in predicting the actual inspiratory muscle effort and indicating the appropriate level of assist. RESULTS: In the 63 experimental cases analyzed, a limited agreement was observed between the estimated and the actual inspiratory muscle pressure (-11 to 10 cm H2O) and effort (-82 to 125 cm H2O × s/min). The sensitivity and specificity of peak Pmus to predict the range of the actual inspiratory effort was 81.2% and 58.1%, respectively. In 49% of experimental cases, the level of assist indicated by the algorithm differed from that indicated by the transdiaphragmatic pressure and PTP. CONCLUSIONS: The proposed algorithm had limited accuracy in estimating inspiratory muscle effort and with indicating the appropriate level of assist.

Molecular response of the human diaphragm on different modes of mechanical ventilation.

BACKGROUND: The mechanical stress that the human diaphragm is exposed to during mechanical ventilation affects a variety of processes, including signal transduction, gene expression, and angiogenesis. OBJECTIVES: The study aim was to assess the change in the production of major angiogenic regulators [vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF2), and transforming growth factor beta 1 (TGFB1)] on the human diaphragm before and after contraction/relaxation cycles during mechanical ventilation. METHODS: This observational study investigates the diaphragmatic mRNA expression of VEGF, FGF2, and TGFB1 in surgical patients receiving general anesthesia with controlled mechanical ventilation (CMV) with muscle relaxation (group A, n = 13), CMV without muscle relaxation (group B, n = 10), and pressure support of spontaneous breathing (group C, n = 9). Diaphragmatic samples were obtained from each patient at two time points: 30 min after the induction of anesthesia (t1) and 90 min after the first specimen collection (t2). RESULTS: No significant changes in the mRNA expression of VEGF, FGF2, and TGFB1 were documented in groups A and C between time points t1 and t2. In contrast, in group B, the mRNA levels of the above angiogenic factors were increased in time point t2 compared to t1, a finding which was statistically significant (pVEGF = 0.003, pFGF2 = 0.028, pTGFB1 = 0.001). CONCLUSIONS: These findings suggest that the molecular response of the human diaphragm before and after application of diverse modes of mechanical ventilation is different. Angiogenesis via the expression of VEGF, FGF2, and TGFB1 was only promoted in CMV without muscle relaxation, and this may have important clinical implications.

Determinants of weaning success in patients with prolonged mechanical ventilation.

INTRODUCTION: Physiological determinants of weaning success and failure are usually studied in ventilator-supported patients, comparing those who failed a trial of spontaneous breathing with those who tolerated such a trial and were successfully extubated. A major limitation of these studies was that the two groups may be not comparable concerning the severity of the underlying disease and the presence of comorbidities. In this physiological study, we assessed the determinants of weaning success in patients acting as their own control, once they are eventually liberated from the ventilator. METHODS: In 30 stable tracheotomised ventilator-dependent patients admitted to a weaning center inside a respiratory intensive care unit, we recorded the breathing pattern, respiratory mechanics, inspiratory muscle function, and tension-time index of diaphragm (TTdi = Pdisw/Pdimax [that is, tidal transdiaphragmatic pressure over maximum transdiaphragmatic pressure] x Ti/Ttot [that is, the inspiratory time over the total breath duration]) at the time of weaning failure (T0). The measurements were repeated in all the patients (T1) either during a successful weaning trial (successful weaning [SW] group, n = 16) or 5 weeks later, in the case of repeated weaning failure (failed weaning [FW] group, n = 14). RESULTS: Compared to T0, in the FW group at T1, significant differences were observed only for a reduction in spontaneous breathing frequency and in TTdi (0.21 +/- 0.122 versus 0.14 +/- 0.054, P = 0.008). SW patients showed a significant increase in Pdimax (34.9 +/- 18.9 cm H2O versus 43.0 +/- 20.0, P = 0.02) and decrease in Pdisw/Pdimax (36.0% +/- 15.8% versus 23.1% +/- 7.9%, P = 0.004). CONCLUSIONS: The recovery of an inadequate inspiratory muscle force could be the major determinant of 'late' weaning success, since this allows the patients to breathe far below the diaphragm fatigue threshold.

Daily interruption of sedative infusions in an adult medical-surgical intensive care unit: randomized controlled trial.

AIM: This article is a report of a study conducted to determine if a nursing-implemented protocol of daily interruption of sedative infusions vs. sedation as directed by the intensive care unit team would decrease duration of mechanical ventilation. BACKGROUND: Continuous rather than intermittent infusion of sedative and analgesic agents leads to greater stability in sedation level, but has been correlated with prolongation of mechanical ventilation and hospitalization of critical care patients. Daily interruption of sedative infusions in mechanically ventilated patients has reduced the duration of mechanical ventilation and length of stay in intensive care. METHOD: A randomized controlled trial was carried out from November 2004 to March 2006 with 97 patients receiving mechanical ventilation and continuous infusion of sedative drugs in an intensive care unit in Greece. The primary outcome measure was the duration of mechanical ventilation. Secondary outcomes were length of intensive care unit stay, length of hospital stay, overall mortality, total doses of sedative and analgesic medicines and Ramsay scores and duration of cessation of sedative infusions per day. RESULTS: The median duration of mechanical ventilation was 8.7 days vs. 7.7 days (P = 0.7). Length of intensive care unit stay (median: 14 vs. 12, P = 0.5) and in the hospital (median: 31 vs. 21, P = 0.1) was similar between the intervention and control groups. The absence of statistically significant differences in these variables remained when patients with brain injury were examined separately. CONCLUSION: The nursing-implemented protocol of daily interruption of sedative infusions was neither beneficial nor harmful compared with usual practice, which has as its primary target the earliest possible awakening of patients.

Physiological responses during a T-piece weaning trial with a deflated tube.

RATIONALE: T-piece trials and spontaneous breathing trials through the tracheostomy tube are often used as weaning techniques. They are usually performed with the cuff inflated, which may increase the inspiratory load and/or influence the tidal volume generated by the patient. We assessed diaphragmatic effort during T-piece trials with or without cuff inflation. SETTINGS: Respiratory intensive care unit METHODS: We measured breathing pattern, transdiaphragmatic pressure (Pdi), the pressure-time product of the diaphragm, per minute (PTPdi/min) and per breath (PTPdi/b), and lung mechanics (lung compliance and resistance) in 13 tracheotomized patients ready for a weaning trial. V(T) was recorded with respiratory inductive plethysmography (RIP-V(T)) or pneumotachography PT-V(T)). Patients completed two T-piece trials of 30[Symbol: see text]min each with or without the cuff inflated. RESULTS: RIP-V(T) and PT-V(T) values were similar with the cuff inflated, but PT-V(T) significantly underestimated RIP-V(T) when the cuff was deflated, and therefore the RIP-V(T) was chosen as the reference method. The RIP-V(T) was significantly greater and the Pdi and PTPdi/min significantly lower when the cuff was deflated than when it was inflated. The efficiency of the diaphragm, calculated by the ratio of PTPdi/b over RIP-V(T), was also improved, while no changes were observed in lung mechanics. CONCLUSIONS: Diaphragmatic effort is significantly lower during a T-piece trial with a deflated cuff than when the cuff is inflated, while RIP-V(T) is higher, so that the diaphragm's efficiency in generating tidal volume is also improved.