Electrical activity of the diaphragm during pressure support ventilation in acute respiratory failure

We compared crural diaphragm electrical activity (EAdi) with transdiaphragmatic pressure (Pdi) during varying levels of pressure support ventilation (PS) in 13 intubated patients. With changing PS, we found no evidence for changes in neuromechanical coupling of the diaphragm. From lowest to highest PS (2 cm H(2)O +/- 4 to 20 cm H(2)O +/- 7), tidal volume increased from 430 ml +/- 180 to 527 ml +/- 180 (p < 0.001). The inspiratory volume calculated during the period when EAdi increased to its peak did not change from 276 +/- 147 to 277 +/- 162 ml, p = 0.976. Respiratory rate decreased from 23.9 (+/- 7) to 21.3 (+/- 7) breaths/min (p = 0.015). EAdi and Pdi decreased proportionally by adding PS (r = 0.84 and r = 0.90, for mean and peak values, respectively). Mean and peak EAdi decreased (p < 0.001) by 33 +/- 21% (mean +/- SD) and 37 +/- 23% with the addition of 10 cm H(2)O of PS, similar to the decrease in the mean and peak Pdi (p < 0.001) observed (34 +/- 36 and 35 +/- 23%). We also found that ventilator assist continued during the diaphragm deactivation period, a phenomenon that was further exaggerated at higher PS levels. We conclude that EAdi is a valid measurement of neural drive to the diaphragm in acute respiratory failure.     

Ventilatory muscle support in respiratory failure with nasal positive pressure ventilation

Long-term intermittent mechanical ventilation results in improvements in ventilatory performance and clinical status between ventilation sessions in patients with chronic respiratory failure. The application of intermittent positive pressure ventilation through a nasal mask (NPPV) is a simple, noninvasive method for the provision of chronic intermittent ventilatory support. We investigated the effects of NPPV on inspiratory muscle activity in three normal subjects and nine patients with acute or chronic ventilatory failure due to restrictive (four subjects) or obstructive (five subjects) respiratory disorders. NPPV resulted in reductions of phasic diaphragm electromyogram amplitude to 6.7 +/- 0.7 percent (mean +/- SEM) of values obtained during spontaneous breathing in the normal subjects, 6.4 +/- 3.2 percent in the restrictive group, and 8.3 +/- 5.1 percent in the obstructive group. Simultaneous decreases in activity of accessory respiratory muscles were observed. The reductions in inspiratory muscle activity were confirmed by the finding of positive intrathoracic pressure swings on inspiration in all subjects. With NPPV, oxygen saturation and PCO2 remained stable or improved as compared with values obtained during spontaneous breathing. These results indicate that NPPV can noninvasively provide ventilatory support while reducing inspiratory muscle energy expenditure in acute and chronic respiratory failure of diverse etiology. Long-term assisted ventilation with NPPV may be useful in improving ventilatory performance by resting the inspiratory muscles.     

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation.

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.     

Noninvasive ventilation for acute respiratory failure.

Noninvasive ventilation (NIV) has emerged as a significant advance in the management of respiratory failure. There is now a wide body of prospective randomized-controlled trial data to support its use, particularly in the management of patients with acute or respiratory failure due to exacerbations of chronic obstructive pulmonary disease (COPD). Its successful application results in a more rapid resolution of the physiological derangements, reduces the need for intubation and, in larger studies, improves survival. A reduction in the number of infectious complications is a particular advantage. In patients with acute exacerbations of COPD there is evidence of benefit when NIV is introduced earlier in the course of the illness than would be the case for invasive ventilation and it should now be considered even with mild acidosis (pH<7.35) and tachypnoea (respiratory rate >23 breaths x min(-1)) after initial medical therapy. There is less clinical-trial data in patients with hypoxaemic respiratory failure, but again as with COPD those with less severe physiological disturbance are more likely to benefit. By contrast noninvasive continuous positive airways pressure, while being widely used has not been shown to reduce the need for intubation or to improve survival in patients with hypoxaemic respiratory failure, with the exception of acute cardiogenic pulmonary oedema. Noninvasive ventilation has been a real advance in the treatment of the critically ill. Most of the studies published to date, have excluded patients needing immediate intubation and it should be viewed as a complimentary technique rather than an alternative to invasive ventilation. It is best viewed as a means of preventing the need for endotracheal intubation and as a result should be introduced earlier than would be the case for invasive ventilation.     

Airway pressure release ventilation in severe acute respiratory failure

Airway pressure release ventilation (APRV), a new ventilatory support technique, was compared with conventional intermittent positive-pressure ventilation plus PEEP (CPPV) in 18 patients with severe acute respiratory failure. Patients were initially stabilized on CPPV and then switched to APRV. The APRV provided effective ventilatory support in 17 of 18 patients; APRV achieved similar levels of alveolar ventilation as CPPV (for APRV, mean PaCO2 = 45.0 +/- 6.2 mm Hg; vs for CPPV, mean PaCO2 = 43.3 +/- 5.7 mm Hg), with significantly lower mean maximum airway pressures (38.9 +/- 10.1 cm H2O vs 64.6 +/- 15.4 cm H2O; p = 0.0001) and mean VT (0.79 +/- 0.11 L vs 1.05 +/- 0.15 L; p = 0.0002). No significant differences in mean airway pressure, end-expiratory pressure, FIO2, ventilator rate, arterial blood gas levels, and hemodynamic function were noted between APRV and CPPV.     

Noninvasive proportional assist ventilation and pressure support ventilation during arm elevation in patients with chronic respiratory failure. A preliminary, physiologic study

BACKGROUND: It has been shown that upper limbs activity increases the respiratory workload in patients with chronic respiratory failure (CRF). The object of the present study was to investigate whether, in these patients: (i) noninvasive positive pressure ventilation (NPPV) could sustain the inspiratory muscles to meet the greater ventilatory demand during upper limbs activity with the arm elevation test (AE); (ii) proportional assist ventilation (PAV) might be superior to pressure support ventilation (PSV) during AE, because of its potential more adaptable response to sudden changes in the ventilatory pattern. METHODS: The study was performed in the pulmonary function laboratory of the Pulmonary Division in Verona General Hospital, Verona, Italy. We studied 8 male patients with CRF due to chronic obstructive pulmonary disease (COPD). Each patient received 2 treatment in random order with a crossover design: spontaneous breathing (SB), SB with AE, either PSV or PAV without and with AE, SB without and with AE, either PSV or PAV without and with AE. We measured: lung function tests, lung mechanics, ventilatory pattern and diaphragmatic effort (pressure time product, PTP(di)). RESULTS: (i) AE increases minute ventilation (+14%) and PTP(di) (+64%); (ii) ventilatory support, both with PSV and PAV unloads the diaphragm both at rest (PTP(di) -77% and -54%, respectively) and during arm elevation (PTP(di) -54% and -44%, respectively). CONCLUSIONS: PAV and PSV unloads the diaphragm in patients with CRF due to COPD both during SB and AE; PAV can be more efficient than PSV in assisting the diaphragm during AE in producing a greater level of minute ventilation for a similar rise in PTP(di) compared to PSV. Noninvasive ventilatory support should be considered in rehabilitation programs for training of upper limbs activity.     

Noninvasive determination of respiratory system mechanics during mechanical ventilation for acute respiratory failure

In 10 acutely ill patients mechanically ventilated for management of acute respiratory failure, respiratory system mechanics were determined with the interrupter technique as described recently (J Appl Physiol 1984; 56:681-690). Flow, volume, and tracheal pressure were measured throughout a series of brief expiratory interruptions. A plateau in tracheal pressure during interruption was observed in all patients, indicating respiratory muscle relaxation as well as equilibration between alveolar and tracheal pressure. Measurement of the plateau in postinterruption tracheal pressure, corresponding volume, and preceding flow enabled determination of the passive elastic and flow-resistive properties of the total respiratory system. In general, the volume-pressure relationship was linear over the expired volume examined and did not necessarily pass through the origin, indicating deviation of the end-expiratory lung volume during mechanical ventilation from the equilibrium position of the respiratory system. Elastance, or inverse slope of this relationship, averaged 16.88 +/- 1.90 (SE) cmH2O X 1(-1). The pressure-flow relationship of the respiratory system was curvilinear; resistance averaged 19.74 +/- 2.08 (SE) cmH2O X 1(-1) X s at a flow rate of 1.0 1 X s-1. In 6 patients the pressure-flow relationship was concave upward. An upward convexity, particularly towards end expiration, was present in the remaining patients. This was associated with characteristic "supramaximal" flow transients after expiratory interruptions, indicating the presence of dynamic airway compression and expiratory flow limitation. In conclusion, the interrupter technique enabled detailed examination of the passive elastic and flow-resistive properties of the total respiratory system in mechanically ventilated patients using simple, noninvasive equipment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Non-invasive pressure support ventilation in patients with respiratory failure due to severe acute cardiogenic pulmonary edema

BACKGROUND: Recent studies suggest the use of non-invasive pressure support ventilation (NIPSV) in patients with acute cardiogenic pulmonary edema (ACPE). However, it remains unclear whether all patients with ACPE benefit from NIPSV. OBJECTIVES: To investigate short-term effects of NIPSV on respiratory, hemodynamic and oxygenation parameters in patients with respiratory failure due to severe ACPE and to identify factors predicting the need for intubation and in-hospital mortality. METHODS: In a prospective, uncontrolled, open study, 28 patients admitted with signs and symptoms of severe respiratory distress due to ACPE were given NIPSV in addition to standardized pharmacological treatment. Physiological parameters were obtained before and after NIPSV, and intubation rate and in-hospital mortality were recorded. RESULTS: NIPSV increased arterial oxygenation from paO2 54.2 +/- 12.4 to 76.9 +/- 12.6 mm Hg (p = 0.0001) and decreased respiratory frequency from 40.1 +/- 8.2 to 22.4 +/- 4.9 breaths/min (p = 0.0001). Significant improvements were also noted for heart rate, blood pressure and the paO2/FiO2 ratio. Four patients (14%) required intubation despite NIPSV. Patients who required intubation had lower paCO2 levels (p = 0.0002), lower serum bicarbonate concentrations (p = 0.04) and lower systolic blood pressure (p = 0.045) than patients who were successfully treated with NIPSV. Eight patients (28.5%) died during hospitalization. In patients with a paCO2 < or =35 mm Hg on admission, the in-hospital mortality was 87%, but in patients with a paCO2 >35 mm Hg the in-hospital mortality was 6%. CONCLUSIONS: NIPSV improves oxygenation and alleviates respiratory distress in patients with respiratory failure due to severe ACPE. However, a subgroup of patients with hypocapnia on admission might have a poor prognosis, with a higher risk of intubation and in-hospital mortality.     

Noninvasive auto-titrating ventilation (AVAPS-AE) versus average volume-assured pressure support (AVAPS) ventilation in hypercapnic respiratory failure patients

Auto-titrating noninvasive ventilation (NIV) has been developed as a new mode applying variable expiratory-positive airway pressure (EPAP) in addition to variable inspiratory pressures (IPAP), both to deliver targeted tidal volume (VT) and to eliminate upper airway resistance. The purpose of this study is to evaluate whether NIV with auto-titrating mode will decrease more PaCO₂ within a shorter time compared to volume-assured mode in hypercapnic intensive care unit (ICU) patients. The hypercapnic respiratory failure patients treated with average volume assured pressure support- automated EPAP mode (group1) were compared with those treated with average volume-assured pressure support mode (group2). Two groups were matched with each other according to baseline diagnoses, demographic characteristics, arterial blood gas values, target VT settings and daily NIV usage times. Built-in software was used to gather the ventilatory parameters. Twenty-eight patients were included in group 1, and 22 in group 2. The decrease in PaCO₂ had been achieved within a shorter time period in group 1 (p?<?0.05). This response was more pronounced within the first 6 h (mean reduction in PaCO₂ was 7?±?7 mmHg in group 1 and 2?±?5 mmHg in group 2, p?=?0.025), and significantly greater reductions in PaCO₂ (18?±?11 mmHg in group 1 and 9?±?8 mmHg in group 2, p?=?0.008) and plasma HCO₃ levels (from 32 to 30 mEq and from 35 to 35 mEq, p?=?0.007) took place within first 4 days. While mean IPAP was similar in both groups, maximum EPAP, mean VT and leak were significantly higher in group 1 than in group 2 (p?<?0.05). Results of this preliminary study suggest that, this new auto-titrating NIV mode may provide additional benefit on volume-assured mode in decreasing PaCO₂ more efficiently and rapidly in hypercapnic ICU patients.     

Noninvasive mechanical ventilation in acute hypoxaemic respiratory failure.

In acute hypoxaemic respiratory failure (HRF), oxygenation, reduction in the work of breathing and in dyspnoea may be achieved by delivering noninvasive mechanical ventilation (NIMV). Several uncontrolled and 13 randomized controlled studies (RCS) were reviewed. Uncontrolled studies confirmed the feasibility and the possibility to improve arterial blood oxygenation with NIMV. The 13 RCS compared NIMV versus a conventional approach in a total of 720 patients with HRF. Endotracheal intubation was required in 186 of the 358 patients (median (95% confidence interval (CI)) 51%, (40-63%)) assigned to a conventional approach and in 107 of the 362 patients (29% (20-39%)) assigned to NIMV. Eleven of the 13 RCS found a reduction in the rate of endotracheal intubation with NIMV with an absolute risk reduction of 31% (30-33%). Ten of the 13 RCS found a reduction in the mortality rate which was 30% (19-40%) in the control group and 19% (13-26%) in the NIMV group. The mean absolute risk reduction was 15% (10-20%). In conclusion, noninvasive ventilation appears to be a useful method in avoiding endotracheal intubation and probably in reducing the morbidity of patients with hypoxaemic respiratory failure.     

无创正压通气治疗慢性阻塞性肺疾病急性呼吸衰竭

无创正压通气已经广泛用于慢性阻塞性肺疾病急性加重期的治疗,主要适应证包括呼吸增快、动脉氧分压下降、二氧化碳分压升高和呼吸性酸中毒,颜面部畸形、严重意识障碍、呼吸心跳停止以及血流动力学不稳定是其主要禁忌证。无创正压通气能够减轻呼吸肌负荷、减轻呼吸肌疲劳,具有降低患者病死率和气管插管率的作用。无创正压通气治疗时给予足够的压力支持和治疗时间是取得治疗效果的重要保证。     

Nasal positive pressure ventilation in patients with acute respiratory failure. Difficult and time-consuming procedure for nurses

Intubation and mechanical ventilation are well-established techniques in the management of patients with acute respiratory failure; however, there are situations in which these procedures cannot be used safely for various reasons. A recently described noninvasive technique, nasal positive-pressure ventilation (NPPV), has been developed for home ventilation of certain patients with chronic ventilatory insufficiency. We hypothesized that NPPV could be used in selected patients in whom intubation and mechanical ventilation were clearly indicated, but not immediately possible, or even contraindicated. Six patients were treated with NPPV during an episode of acute respiratory failure and enrolled in a prospective study. We found that NPPV was successful in avoiding intubation, but only in the three patients suffering from a restrictive pulmonary disorder, whereas the procedure was unsuccessful in patients with obstructive disorders. Moreover, in every patient, acute NPPV was very time-consuming for the nursing staff: in patients with restrictive disorders, a nurse had to monitor a patient submitted to NPPV during 41 +/- 9 percent of the duration of ventilation and during 91 +/- 9 percent of the NPPV time in patients with obstructive disorders. We conclude that acute NPPV may be attempted in selected patients with acute respiratory failure, predominantly patients with restrictive respiratory disorders, but that this procedure is very time-consuming for nurses.     

The role of noninvasive ventilation for acute respiratory failure

The use of NIV has been shown to facilitate discontinuing ventilatory dependence as well as provide support for adult patients with chronic lung disease without the need for endotracheal intubation. In fact, NIV has recently described as a potential support strategy following extubation failure. Therefore, using NIV as a bridge to liberation from mechanical ventilation may decrease many of the complications associated with long-term use of invasive airway devices as well complications from reinsertion of an artificial airway. Although firm data supporting the use of NIV in the adult population exists, the use of NIV in the pediatric population is based primarily on a series of case studies, retrospective chart reviews, and extrapolation from the adult data. The use of NIV for infants and children remains controversial. The important question to be asked is why there is a lack of randomized controlled trials on NIV in pediatrics? The answer lies somewhere between the lack of equipment designed specifically for pediatrics and the smaller number of patients available compared with adults. Data from the adult population may be more readily adapted to older children; however, it remains difficult to determine the criteria for noninvasive ventilatory use in infants and young children. In fact, this lack of data makes the formulation of firm selection guidelines for infants and children essentially impossible. However, for a select groups of pediatric patients with acute respiratory failure for whom an appropriate noninvasive device with interface is available, a trial of NIV may be seem reasonable to avoid the known negative effects of intubation and invasive mechanical ventilation.     

Effectiveness of noninvasive positive pressure ventilation in the treatment of acute respiratory failure in severe acute respiratory syndrome

OBJECTIVES: To study the effectiveness of noninvasive positive pressure ventilation (NIPPV) in the treatment of acute respiratory failure (ARF) in severe acute respiratory syndrome (SARS), and the associated infection risk. METHODS: All patients with the diagnosis of probable SARS admitted to a regional hospital in Hong Kong from March 9 to April 28, 2003, and who had SARS-related respiratory distress complications were recruited for NIPPV usage. The health status of all health-care workers working in the NIPPV wards was closely monitored, and consent was obtained to check serum for coronavirus serology. Patient outcomes and the risk of SARS transmission to health-care workers were assessed. RESULTS: NIPPV was applied to 20 patients (11 male patients) with ARF secondary to SARS. Mean age was 51.4 years, and mean acute physiology and chronic health evaluation II score was 5.35. Coronavirus serology was positive in 95% (19 of 20 patients). NIPPV was started 9.6 days (mean) from symptom onset, and mean duration of NIPPV usage was 84.3 h. Endotracheal intubation was avoided in 14 patients (70%), in whom the length of ICU stay was shorter (3.1 days vs 21.3 days, p < 0.001) and the chest radiography score within 24 h of NIPPV was lower (15.1 vs 22.5, p = 0.005) compared to intubated patients. Intubation avoidance was predicted by a marked reduction in respiratory rate (9.2 breaths/min) and supplemental oxygen requirement (3.1 L/min) within 24 h of NIPPV. Complications were few and reversible. There were no infections among the 105 health-care workers caring for the patients receiving NIPPV. CONCLUSIONS: NIPPV was effective in the treatment of ARF in the patients with SARS studied, and its use was safe for health-care workers.     

无创机械通气在食管癌切除术后急性呼吸衰竭患者中的疗效分析

目的：探讨无创机械通气(noninvasive positive pressure ventilation,NPPV)在食管癌切除术后急性呼吸衰竭(acute respiratory failure,ARF)患者中的疗效。方法回顾性分析了2009年6月至2014年6月我院重症医学科收治的食管癌切除术后发生 ARF 的患者,所有患者均首先行NPPV 治疗,根据患者是否最终需要气管插管行有创机械通气治疗,将患者分为 NPPV 成功组(A组)和 NPPV 失败组(B 组)。并记录患者的性别、年龄、入 ICU 时 APACHE Ⅱ评分、基础肺功能、手术方式、术中出血量、无创前和无创2 h 后的血气分析结果、使用 NPPV 的模式和压力支持水平、ICU 停留时间和28 d 死亡率。结果2009年6月至2014年6月我院共有912例患者行食管癌切除术,其中76例(8.3%)发生 ARF 纳入本研究。A 组66例(86.8%),B 组10例(13.2%)。2组性别分布、年龄、APACHE Ⅱ评分、FEV1%pred 和术中出血量差异无统计学意义(P 值均>0.05)。A 组行 NPPV 前氧合指数与 B 组比较差异无统计学意义[(162±35.7)mmHg vs (169±40.2)mmHg,t =1.760,P >0.05];但行 NPPV 2 h 后 A 组氧合指数显著高于 B 组[(246±25.4)mmHg vs (188±32.6)mmHg,t =3.210,P <0.05]。无创通气模式在2组间比较差异无统计学意义(χ2=0.451,P >0.05),但 A 组选择较高水平呼气末正压通气(8 cmH 2 O)的比例显著高于 B 组(χ2=16.348,P <0.05)。A 组患者平均 ICU 停留时间为(4.1±2.28)d,显著少于 B 组[(11.3±4.32)d,t =3.210,P =0.002]。无患者死亡。结论食管癌切除术后发生 ARF 的患者应该首选 NPPV 治疗,在治疗中需要选择较高水平的呼气末正压通气,可以改善患者的氧合水平,降低患者的插管率,缩短患者的 ICU 停留时间。同时在治疗过程中应该密切观察患者氧合指数的变化,避免插管时机的延误。     

Noninvasive ventilation for acute respiratory failure. Quite low time consumption for nurses.

Methods of noninvasive pressure support ventilation (NIPSV) are not always easy to apply in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD). The assistance time spent by nurses in relation to ventilatory time was prospectively studied, when NIPSV was used, in a sequential mode, in COPD patients with either acute exacerbations (58 patients, group I) or postextubation hypercapnic respiratory insufficiency (42 patients, group II) in a medical intensive care unit. During the first 24 h after enrolment, NIPSV was used for 6.7+/-3.2 h (mean+/-SD) in group I and 5.6+/-3.1 h in group II; the duration of NIPSV sessions and the nurse time consumption per session were respectively 47+/-12 and 11+/-7 min in group 1, and 46+/-12 and 11+/-6 min in group II. After the first 24 h of the study, the duration of NIPSV was 4.7+/-3.2 h x day(-1) in group I and 4.9+/-3.5 h x day(-1) in group II, and the nurse time consumption dropped significantly: the duration of NIPSV sessions and the nurse time consumption per session were respectively 44+/-10 and 7+/-4 min in group I, and 47+/-14 and 7+/-3 min in group II. Between the first 24 h and the subsequent period of 24 h, the nursing time dropped significantly (98 versus 59 min in group I (p<0.05), and 85 versus 52 min in group II (p<0.05)). There was no difference in the duration of NIPSV sessions, or in the overall assistance time per session, between the two groups of patients. In conclusion, the study seems to favour a quite low assistance time spent by nurses in relation to ventilatory time when noninvasive pressure support ventilation is used in chronic obstructive pulmonary disease patients with either acute exacerbations or postextubation hypercapnic respiratory insufficiency.