Dimitris Georgopoulos

Bedside waveforms interpretation as a tool to identify patient-ventilator asynchronies

ObjectiveDuring assisted modes of ventilatory support the ventilatory output is the final expression of the interaction between the ventilator and the patient’s controller of breathing. This interaction may lead to patient-ventilator asynchrony, preventing the ventilator from achieving its goals, and may cause patient harm. Flow, volume, and airway pressure signals are significantly affected by patient-ventilator interaction and may serve as a tool to guide the physician to take the appropriate action to improve the synchrony between patient and ventilator. This review discusses the basic waveforms during assisted mechanical ventilation and how their interpretation may influence the management of ventilated patients. The discussion is limited on waveform eye interpretation of the signals without using any intervention which may interrupt the process of mechanical ventilation.DiscussionFlow, volume, and airway pressure may be used to (a) identify the mode of ventilator assistance, triggering delay, ineffective efforts, and autotriggering, (b) estimate qualitatively patient’s respiratory efforts, and (c) recognize delayed and premature opening of exhalation valve. These signals may also serve as a tool for gross estimation of respiratory system mechanics and monitor the effects of disease progression and various therapeutic interventions.ConclusionsFlow, volume, and airway pressure waveforms are valuable real-time tools in identifying various aspects of patient-ventilator interaction

Surgery and the respiratory muscles

Respiratory muscles are the only skeletal muscles vital to life. Surgical procedures can affect the respiratory muscles by a number of pathophysiological mechanisms including thoracoabdominal mechanics, reflexes, neuromechanical coupling, and loss of muscular integrity. Impairment of respiratory muscle function after surgery may lead to postoperative complications such as hypoventilation, hypoxia, atelectasis, and infections, some of which may be life threatening. In this paper we review surgery that impairs the function of the respiratory muscles—namely cardiac, thoracic, and upper abdominal surgery. Therapeutic interventions or protective measures for respiratory muscles during or after each type of surgery are also briefly addressed. Lung transplantation and lung volume reduction surgery are discussed, since both have been shown to improve the function of respiratory muscles, and possible pathophysiological mechanisms are reviewed. The preoperative assessment of respiratory muscle function is also considered. Furthermore, when postoperative pulmonary complications occur it is worth considering whether the cause could be dysfunction of the respiratory muscles and thus a proper assessment of their function is needed. The most important function of the respiratory muscles is breathing since they are the motor arm of the respiratory system. Breathing, a lifelong task, is borne mainly by the inspiratory muscles, especially the diaphragm. The other inspiratory muscles contribute little to quiet breathing but are recruited when higher levels of ventilation are required, such as in exercise and obstructive or restrictive lung disease. The expiratory muscles are not usually used during breathing except at high levels of ventilatory effort. A second function of the respiratory muscles is to perform explosive manoeuvres such as coughing and vomiting. The respiratory muscles also have a role as stabilisers of the thorax and abdomen since they take part in the formation of the thoracic and abdominal walls. Respiratory muscle function depends on the function of the respiratory centres, …

Proportional assist ventilation with load-adjustable gain factors in critically ill patients: comparison with pressure support.

ObjectivesIt is not known if proportional assist ventilation with load-adjustable gain factors (PAV+) may be used as a mode of support in critically ill patients. The aim of this study was to examine the effectiveness of sustained use of PAV+ in critically ill patients and compare it with pressure support ventilation (PS).Design and settingRandomized study in the intensive care unit of a university hospital.MethodsA total of 208 critically ill patients mechanically ventilated on controlled modes for at least 36 h and meeting certain criteria were randomized to receive either PS (n = 100) or PAV+ (n = 108). Specific written algorithms were used to adjust the ventilator settings in each mode. PAV+ or PS was continued for 48 h unless the patients met pre-defined criteria either for switching to controlled modes (failure criteria) or for breathing without ventilator assistance.ResultsFailure rate was significantly lower in PAV+ than that in PS (11.1 vs. 22.0%, P = 0.040, OR 0.443, 95% CI 0.206–0.952). The proportion of patients exhibiting major patient–ventilator dyssynchronies at least during one occasion and after adjusting the initial ventilator settings, was significantly lower in PAV+ than in PS (5.6 vs. 29.0%, P < 0.001, OR 0.1, 95% CI 0.06–0.4). The proportion of patients meeting criteria for unassisted breathing did not differ between modes.ConclusionsPAV+ may be used as a useful mode of support in critically ill patients. Compared to PS, PAV+ increases the probability of remaining on spontaneous breathing, while it considerably reduces the incidence of patient–ventilator asynchronies.

Buspirone Effect on Breathlessness and Exercise Performance in Patients with Chronic Obstructive Pulmonary Disease

Buspirone is an anxiolytic agent that appears to have no sedative effects. The aim of this study was to assess the effects of buspirone on breathlessness and exercise tolerance in patients with chronic airway obstruction. Sixteen patients, age 56.9 +/- 17.0; forced expiratory volume in 1 s (FEV1) 1.15 +/- 0.42 l; FEV1/forced vital capacity (FVC) 50.7 +/- 15.0%; PaCO2 42.2 +/- 5.5 mm Hg; and PaO2 57.6 +/- 10 mm Hg, underwent a 6-min walking test, an incremental cycle ergometer test, an incremental treadmill walking test with self-assessment of dyspnea on Borgs scale during exercise and an assessment of respiratory drive (P 0.1), timing [inspiration time (TI)/total breathing time (Ttot)], PaO2, PaCO2, FVC, FEV1, following oral administration for 14 days of placebo or buspirone (20 mg daily) in a double-blind, cross-over randomized way. We also used the symptom check list-90-R for the assessment of subjective complaints and symptomatic behavior. A significant improvement in anxiety, depression and obsessive symptoms and complaints was noted after buspirone treatment. The P 0.1, TI/Ttot, arterial blood gases and respiratory mechanics did not change after drug treatment. There was an improvement in exercise tolerance and in the sensation of dyspnea during the buspirone period. Thus, as given in this study, oral buspirone has therapeutic potential in the treatment of dyspnea in patients with chronic lung disease.

Effect of different levels of pressure support and proportional assist ventilation on breathing pattern, work of breathing and gas exchange in mechanically ventilated hypercapnic COPD patients with acute respiratory failure.

Background: Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified. Objectives: To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF). Methods: Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L1–L4) of support were applied. At each level, blood gases, flow, tidal volume (VT), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp – fv) were measured. Results: We found increases in ME with increasing levels of PSV but not with PAV. PO2 and VT increased whereas PCO2 decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO2 decreased and VT increased significantly only at L4 whereas PO2 increased from L1 to L4. Runaways were observed at L3 and L4 of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 ± 57 cm H2O/s·min in PSV and 194 ± 60 cm H2O/s·min in PAV. Conclusion: We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.

Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of end-inspiratory pause

The delivery of bronchodilators with a metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become widespread practice. However, the various ventilator settings that influence the efficacy of MDI are not well established. Application of an end-inspiratory pause (EIP) during drug delivery has been suggested as one of the factors that might increase the effectiveness of this therapy. To test this, the effect of EIP on the bronchodilation induced by beta2-agonists administered with MDI and a spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined. Twelve patients with COPD, mechanically ventilated on volume-controlled mode, were prospectively randomized to receive six puffs of salbutamol (100 microg x puff(-1)) either with or without EIP of 5 s duration. Salbutamol was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud-enhancer spacer. After a 6 h wash-out, patients were crossed over to receive salbutamol by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rmin) and maximum (Rmax) airflow resistance, the difference between Rmax and Rmin (deltaR), static end-inspiratory respiratory system compliance (Cst,rs) and cardiac frequency (fc) were measured before and at 15, 30 and 60 min after salbutamol administration. Salbutamol caused a significant decrease in dynamic and static airway pressures, Rmin and Rmax. These changes were not influenced by application of EIP and were evident at 15, 30 and 60 min after salbutamol. With and without EIP, Cst,rs,deltaR and fc did not change after salbutamol. In conclusion, salbutamol delivered with a metered-dose inhaler and a spacer device induced significant bronchodilation in mechanically ventilated patients with chronic obstructive pulmonary disease, the magnitude of which was not affected by an end-expiratory pause of 5 s. These results do not support the use of end-inspiratory pause when bronchodilators are administered in adequate doses during controlled mechanical ventilation.

Recombinant human erythropoietin therapy in critically ill patients: a dose-response study [ISRCTN48523317].

IntroductionThe aim of this study was to assess the efficacy of two dosing schedules of recombinant human erythropoietin (rHuEPO) in increasing haematocrit (Hct) and haemoglobin (Hb) and reducing exposure to allogeneic red blood cell (RBC) transfusion in critically ill patients.MethodThis was a prospective, randomized, multicentre trial. A total of 13 intensive care units participated, and a total of 148 patients who met eligibility criteria were enrolled. Patients were randomly assigned to receive intravenous iron saccharate alone (control group), intravenous iron saccharate and subcutaneous rHuEPO 40,000 units once per week (group A), or intravenous iron saccharate and subcutaneous rHuEPO 40,000 units three times per week (group B). rHuEPO was given for a minimum of 2 weeks or until discharge from the intensive care unit or death. The maximum duration of therapy was 3 weeks.ResultsThe cumulative number of RBC units transfused, the average numbers of RBC units transfused per patient and per transfused patient, the average volume of RBCs transfused per day, and the percentage of transfused patients were significantly higher in the control group than in groups A and B. No significant difference was observed between group A and B. The mean increases in Hct and Hb from baseline to final measurement were significantly greater in group B than in the control group. The mean increase in Hct was significantly greater in group B than in group A. The mean increase in Hct in group A was significantly greater than that in control individuals, whereas the mean increase in Hb did not differ significantly between the control group and group A.ConclusionAdministration of rHuEPO to critically ill patients significantly reduced the need for RBC transfusion. The magnitude of the reduction did not differ between the two dosing schedules, although there was a dose response for Hct and Hb to rHuEPO in these patients.

Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of tidal volume.

Objective: The delivery of bronchodilator drugs with metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become a widespread practice. However, the various ventilator settings that influence the efficacy of MDI are not well established. The tidal volume (VT) during drug delivery has been suggested as one of the factors that might increase the effectiveness of this therapy. To test this, the effect of two different VT on the bronchodilation induced by β2-agonists administered with MDI and a spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined.¶Methods: Nine patients with COPD, mechanically ventilated on volume-controlled mode, were prospectively randomised to receive six puffs of salbutamol (S, 100 μg/puff) either with a VT of 8 ml/kg (normal VT, 582 ± 85) or with a VT of 12 ml/kg (high VT, 912 ± 137). With both modes inspiratory flow was identical. S was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud enhancer spacer. After a ¶6-h washout, patients were crossed-over to receive S by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance, the difference between Rrs and Rint (ΔR), static end-inspiratory respiratory system compliance (Cst,rs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR) were measured before and at 15, 30 and 60 min after S.¶Results: S caused a significant decrease in dynamic and static airway pressures, PEEPi, Rint and Rrs. These changes were not influenced by VT and were evident at 15, 30 and 60 min after S. With normal and high VT, Cst,rs, ΔR and HR did not change after S.¶Conclusions: We conclude that S delivered with an MDI and a spacer device induces significant bronchodilation in mechanically ventilated patients with COPD, the magnitude of which is not affected by at least a 50 % increase in VT. These results do not support the VT manipulations when bronchodilators are administered in adequate doses during controlled mechanical ventilation.

Effects of breathing patterns on mechanically ventilated patients with chronic obstructive pulmonary disease and dynamic hyperinflation

AbstractObjectiveTo examine the circulatory and respiratory effects of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation (DH) during controlled mechanical ventilation.DesignProspective, controlled, randomized, non-blinded study.SettingRespiratory intensive care unit of a university hospital.PatientsNine patients with acute respiratory failure and DH due to acute exacerbations of COPD.InterventionsKeeping tidal volume and total breath duration (TTOT) constant, patients were ventilated at six different values of expiratory time (TE). TE changes were randomly induced by alterations of constant inspiratory flow