High Peak Airway Pressures Research Articles

Use of positive-pressure ventilation in dogs and cats: 41 cases (1990-1992)

Abstract Intermittent positive-pressure ventilation (ppv) is an invasive means of respiratory support that is indicated in animals with central and peripheral neuromuscular disease, as well as in those with primary disorders of the lung parenchyma. We reviewed the medical records of 34 dogs and 7 cats treated with ppv. The animals could be allotted to 2 groups; group 1 (21/41) had primary failure of ventilation attributable to neuromuscular disease or airway obstruction, and group 2 (20/41) had primary pulmonary parenchymal disease. Mean inspiratory time was 1.02 ± 0.2 seconds (range, 0.6 to 1.5 seconds). Mean inspiratory flow was 26.9 ± 18.5 L/min (range, 7 to 87 L/min), and was positively correlated with body weight (R = 0.57). Mean set respiratory rate was 19.6 ± 10 breaths/min (range, 5 to 60 breaths/min), with mean tidal volume of 15.5 ± 6.2 ml/kg of body weight. Positive end-expiratory pressure (peep) was required in 14 of 20 dogs in group 2. Mean peak airway pressure in group 1 was 21.6 ± 6.3 cm of H2O, whereas in group 2 it was 32.9 ± 12.5 cm of H2O. The higher peak airway pressure in group-2 dogs reflected poor lung compliance and the use of peep in dogs with parenchymal lung disease. Mean duration of ppv was 28.2 ± 29.4 hours (range, 2 to 137 hours). The overall survival rate was 39% (16/41). Factors that appeared to correlate with survival included age, with higher mortality in animals < 1 year old or > 11 years old (P < 0.01); body weight, with mortality highest in animals < 10 kg (P < 0.05); reason for ventilation, with survival in group 1 being 57%, and in group 2, 20%; and development of complications, with 28% of animals that developed major complications surviving, compared with 48% of those that did not develop major complications. Two major complications of ppv were documented: pneumothorax and pneumonia. Twelve of 41 animals developed pneumothorax and had been ventilated by use of peak airway pressures > 25 cm of H2O, or peep. An additional 6 animals developed subclinical pneumonia during treatment with ppv.

The laryngeal mask airway: Anesthetic gas leakage and fiberoptic control of positioning

Study Objective: To examine the anesthetic gas leakage and prelaryngeal position of the laryngeal mask airway (LMA). Design: Clinical trial evaluating LMA ventilation conditions. Setting: Lithotripsy room of a urology clinic at a university hospital. Patients: 100 adult ASA physical status I and II patients undergoing general anesthesia for kidney stone lithotripsy. Interventions: Anesthesia was induced with propofol 1.5 to 2.5 mglkg intravenously (IV) and fentanyl 1 to 1.5 μg/kg IV and maintained with isofurane plus nitrous oxide in oxygen. Measurements and Main Results: Waste anesthetic gas concentration, an indicator of mask tightness during intermittent positive-pressure ventilation, was measured using an infrared oxide analyzer. LMA position in relation to laryngeal skeleton was assessed using fiberoptic laryngoscopy. The LMA was found to be gastight in 62% of patients, with a peak airway pressure up to 25 cmH 2O. During peak airway pressure ventilation less than 10 cmH 2O and during spontaneous ventilation, waste anesthetic gas contamination in the anesthesiologist's breathing zone was within legal limits in every case. During peak airway pressure ventilation up to 30 cmH 2O, contamination was found within legal limits in 78% of all cases. Fiberoptic control showed a central position in 59% of cases, lateral deviations to the left or right in 29%, dorsal positions in 8%, and ventral positions in 4%. Incorrect ventral or dorsal positioning was related to forced reclining or forced f exion of the patient's head. There was no correlation between LMA position and tightness. The esophageal entrance was visible in 15 patients using high peak airway pressure greater than 25 CMH 2O. Conclusions: The LMA is a new airway management technique with good qualities of tightness and ventilation conditions. However, contraindications such as patients with a full stomach, intra-abdominal surgery, high peak airway pressure, prolonged operation, and an inexperienced anesthesiologist apply.

Histologic aspects of pulmonary barotrauma in critically ill patients with acute respiratory failure.

To describe histologically pulmonary barotrauma in mechanically ventilated patients with severe acute respiratory failure. Assessment of histologic pulmonary barotrauma. A 14-bed surgical intensive care unit (SICU) PATIENTS: The lungs of 30 young critically ill patients (mean age 34 +/- 10 years) were histologically examined in the immediate post-mortem period. None of them were suspected of pre-existing emphysema. Clinical events and ventilatory settings used during mechanical ventilation were compared with lung histology. Airspace enlargement, defined as the presence of either alveolar overdistension in aerated lung areas or intraparenchymal pseudocysts in nonaerated lung areas, was found in 26 of the 30 lungs examined (86%). Patients with severe airspace enlargement (2.6-40 mm internal diameter) had a significantly greater incidence of pneumothorax (8 versus 2, p < 0.05), were ventilated using higher peak airway pressures (56 +/- 18 cmH2O versus 44 +/- 10 cmH2O, p < 0.05) and tidal volumes (12 +/- 3 ml/kg versus 9 +/- 2 ml/kg, p < 0.05), were exposed significantly longer to toxic levels of oxygen (8.6 +/- 9.4 days versus 1.9 +/- 2 days at FIO2 > 0.6, p < 0.05) and lost more weight (6.3 +/- 9.2 kg versus 0.75 +/- 5.8 kg, p < 0.05) than patients with mild airspace enlargement (1-2.5 mm internal diameter). Underlying histologic lesions responsible for clinical lung barotrauma consist of pleural cysts, bronchiolar dilatation, alveolar overdistension and intraprenchymal pseudocysts. Mechanical ventilation appears to be an aggravating factor, particularly when high peak airway pressures and large tidal volumes are delivered by the ventilator.

A Survey on Manual Hyperinflation as a Physiotherapy Technique in Intensive Care Units

Summary There is minimal documented evidence about the commonly performed physiotherapy technique, manual hyperinflation (MH). This paper presents the findings of a literature review on MH and the analysis of a questionnaire sent in September 1991 to 176 senior respiratory physiotherapists working in NHS hospitals throughout Britain. The questionnaire aimed to ascertain the practice of MH by physiotherapists in an intensive care unit (ICU). Twelve questions were asked about technique, indications, benefits of treatment, and precautions, with particular regard to high peak airway pressures (PAP). It is recommended that a manometer (pressure measuring device) is included in the inflation circuit when performing MH to reduce the risk of barotrauma. Clearly, more research needs to be carried out to ascertain the effectiveness of MH as a technique.

Histopathologic Pulmonary Changes from Mechanical Ventilation at High Peak Airway Pressures

We investigated the histopathologic pulmonary changes induced by mechanical pulmonary ventilation (MV) with a high peak airway pressure and a large tidal volume in healthy baby pigs. Eleven animals were mechanically ventilated at a peak inspiratory pressure (PIP) of 40 cm H2O, a respiratory rate (RR) of 20 min-1, a positive end-expiratory pressure (PEEP) of 3 to 5 cm H2O, and an FIO2 of 0.4. High airway pressure MV was terminated in 22 +/- 11 h because of severe hypoxemia in the animals. Five of the baby pigs were killed for gross and light microscope studies. The pulmonary changes consisted of alveolar hemorrhage, alveolar neutrophil infiltration, alveolar macrophage and type II pneumocyte proliferation, interstitial congestion and thickening, interstitial lymphocyte infiltration, emphysematous change, and hyaline membrane formation. Those lesions were similar to that seen in the early stage of the adult respiratory distress syndrome (ARDS). The remaining six animals were treated for 3 to 6 days with conventional respiratory care with appropriate ventilator settings. Prominent organized alveolar exudate in addition to lesions was also found in the five animals. These findings were indistinguishable from the clinical late stage of ARDS. Six control animals were mechanically ventilated at a PIP of less than 18 cm H2O, a RR of 20 min-1, a PEEP of 3 to 5 cm H2O, and an FIO2 of 0.4 for 48 h. They showed no notable changes in lung functions and histopathologic findings. Aggressive MV with a high PIP is often applied to patients with respiratory distress to attain adequate pulmonary gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung Edema Caused by High Peak Inspiratory Pressures in Dogs: Role of Increased Microvascular Filtration Pressure and Permeability

Mechanical ventilation with high peak airway pressures (Paw) has been shown to induce pulmonary edema in animal experiments, but the relative contributions of transvascular filtration pressure and microvascular permeability are unclear. Therefore, we examined the effects of positive-pressure ventilation on two groups of open-chest dogs ventilated for 30 min with a peak Paw of 21.8 +/- 2.3 cm H2O (Low Paw) or 64.3 +/- 3.5 cm H2O (High Paw). No hemodynamic changes were observed in the Low Paw group during ventilation, but mean pulmonary artery pressure (Ppa) increased by 9.9 cm H2O, peak inspiratory Ppa by 24.6 cm H2O, and estimated mean microvascular pressure by 12.5 cm H2O during High Paw ventilation. During the same period, lung lymph flow increased by 435% in the High Paw and 35% in the Low Paw groups, and the terminal extravascular lung water/blood-free dry weight ratios were 5.65 +/- 0.27 and 4.43 +/- 0.13 g/g, respectively, for the two groups. Lung lymph protein clearances and minimal lymph/plasma ratios of total protein were significantly higher (p less than 0.05) after 2 h of increased left atrial pressure (PLA) in the High Paw group versus the Low Paw group, which indicates a significant increase in microvascular permeability. Lymph prostacyclin concentration in pulmonary lymph, measured as the stable metabolite 6-0-PGF1 alpha, was increased significantly by 70 to 150% from baseline (p less than 0.05) in both groups during the periods of increased Paw and increased PLA, but it was not significantly different between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimizing ventilatory settings using pulse oximetry in the transition between life and death

In the patient with catastrophic lung disease intra- and extrapulmonary factors interact to determine the O2-delivery to the peripheral lifethreathened organs. The therapeutic strategy will take into account both settings on the ventilator that are not harmful to the patient i.e. avoiding high peak airway pressures and high inspired oxygen fractions and circulatory support keeping the cardiac output adequate. Usually the arterial blood gases are frequently monitored as parameters determining optimal therapy. Recently pulse oximetry has been suggested as a noninvasive continuous monitoring method. It could be looked upon as an indicator and monitor of both ventilatory and circulatory optimality, because the parameter tells what “the sensor sees.” This might not be identical to the “true arterial saturation”, but it can be argued that this does not matter as long as the trend observed is useful in therapeutic decision making.In this study 25 patients with catastrophic lung disease i.e. a) panlobar alveolar infiltrates, b) a PaO2 >7.00 kPa with an FIO2 > 0.8 with 15 cm H2O PEEP and a cardiac index above 3.5 L/min/m2 and c) an effective compliance below 25 ml/cm H2O were studied and ventilatory and circulatory adjustments were made in order to reduce peak airway pressure to below 50 cm H2O and the FIO2 to below 0.6. Fourteen patients were randomised to monitoring with pulse oximetry and eleven to conventional arterial blood gas analysis. Using pulse oximetry the median time for optimization was 45 min with a range of 20–120, without pulse oximetry the median time was 95 min with range 60–240, p <0.05.It is concluded that pulse oximetry is a fast, reliable index of peripheral O2-delivery and can be regarded a “new parameter” in optimizing ventilatory strategy.

Severe impairment in lung function induced by high peak airway pressure during mechanical ventilation. An experimental study.

We explored the pulmonary effects of continuous mechanical ventilation (MV) at a peak inspiratory pressure of 50 cm H2O in healthy, paralyzed, and anesthetized adult sheep during a period of 48 h. The 9 control sheep (Group A) were ventilated with 40% oxygen at a tidal volume of about 10 ml/kg and a peak inspiratory pressure of 15 to 20 cm H2O. All these animals remained stable throughout the 48 h of MV with no change in lung function. The 7 sheep in Group B were ventilated with 40% oxygen using a pressure-controlled ventilator at 50 cm H2O peak inspiratory pressure, at a VT of 50 to 70 ml/kg. All sheep in Group B developed severe respiratory failure and died or were killed within 2 to 35 h, and showed parenchymal consolidation at autopsy. The 9 sheep in Group C were ventilated as in Group B, except that 3.8% CO2 was added to the inspired gases: the Group C animals deteriorated more slowly, with little change in PaO2 but with a severely reduced FRC, VT, total static lung compliance, and grossly abnormal lungs at autopsy. We conclude that in this model, mechanical ventilation at peak airway pressure of 50 cm H2O will lead to progressive impairment in pulmonary mechanics, lung function, acute respiratory failure, and alveolar cellular dysfunction, as demonstrated by highly abnormal minimal surface tension values of saline lung lavage fluid in both study groups.

Hypertension intracrânienne au cours de l'état de mal asthmatique

In three consecutive patients suffering from life-threatening asthma in a comatose state (mean age : 37 ±4 yr; Glasgow coma score : 3; bilateral mydriasis), intracranial pressure was monitored with an extradural transducer set-up a mean of 2 h after the onset of the coma. The aims were to detect intracranial hypertension and to improve its therapy. Basal therapy associated : 1) mechanical ventilation; 2) theophylline 1.5 g · 24 h −1, salbutamol 30 mg · 24 h −1, hydrocortisone 2 g · 24 h −1, pancuronium 0.5 mg · kg −1 · 24 h −1; 3) pentobarbitone 35 mg · kg −1 · 24 h −1, normohydration, normothermia and 30° head-up tilt. If the intracranial pressure rose above 15 mmHg, an i.v. bolus of pentobarbitone (5 mg · kg −1) was given if the barbiturate blood level was equal or below 100 μg · 1 −1. In case of failure, a dose of mannitol (20 mg) completed the therapy if blood therapy was equal or below 320 mosm · 1 −1. All patients developed intracranial hypertension (21, 53 and 23 mmHg, respectively). The intracranial hypertension followed the bronchospasm and disappeared with it. Hypoxaemia, hypercapnia and high peak airway pressures could explain the intracranial hypertension. All patients recovered without sequelae. This data should make us use with great care all treatments likely to increase the intracranial pressure during life-threatening asthma.

Successful Treatment of Experimental Neonatal Respiratory Failure Using Extracorporeal Membrane Lung Assist

A total of 44 preterm fetal lambs at great risk of developing respiratory failure were delivered by Cesarean section, and were then managed on conventional mechanical pulmonary ventilation. Fifteen animals initially fared well, and 14 of these were long term survivors. Twenty-nine other lambs showed a progressive deterioration in arterial blood gases within 30 minutes of delivery, of which 10 lambs were continued on mechanical pulmonary ventilation (20% survival), while the remaining 19 lambs were placed on an extracorporeal membrane lung respiratory assist (79% survival). Extracorporeal membrane lung bypass rapidly corrected arterial blood gas values, and permitted the use of high levels of CPAP instead of the continuation of mechanical pulmonary ventilation at high peak airway pressures. Improvement in lung function was gradual, and predictable. Early institution of extracorporeal respiratory assist using a membrane artificial lung rapidly corrected arterial blood gas values and significantly improved on neonate survival.

Improved Oxygenation and Lower Peak Airway Pressure in Severe Adult Respiratory Distress Syndrome: Treatment with Inverse Ratio Ventilation

Two patients with the adult respiratory distress syndrome (ARDS) were placed on pressure-controlled inverse-ratio ventilation (IRV) when their condition deteriorated despite optimal treatment with intermittent mandatory ventilation and positive end-expiratory pressure. In the first case, high peak airway pressure was reduced by 50 percent with the institution of IRV. In the second, refractory hypoxemia was eliminated by using an inspiratory-to-expiratory ratio of 4:1. These cases show that IRV may offer certain advantages in the treatment of severe ARDS.

Respiratory Distress Syndrome—New Therapeutic Approaches to a Complex Pathophysiology

In this review I have emphasized the complicated events that occur during the course of RDS. RDS is initiated by an inadequate pool size of functional surfactant within a structurally and functionally immature lung. Obstetric and delivery room management apparently can significantly influence surfactant function and, therefore, the incidence of RDS, possibly by affecting the permeability properties of the pulmonary vascular endothelium and alveolar epithelium. The course and severity of RDS will be further influenced by neonatal care and other occurrences such as the presence or absence of a PDA. Many details of the biochemical and physiologic events that result in RDS have not been defined, so we are currently unable to quantitatively understand how all the various factors interact during the course of RDS to give the characteristic clinical course of the disease. Variations in the magnitude and timing of these interactions will likely explain the variable manifestations of respiratory failure in the tiny infant. Within the context of the pathophysiology of RDS, surfactant replacement therapy and HFV represent two new and very different approaches to treatment. Initial clinical trials of surfactant replacement therapy in infants with RDS are encouraging, and experience with animal models indicates that such an approach will work. Replacement therapy also makes sense if one considers what is known about surfactant metabolism during RDS. However, no standard, tested, and safe preparation of surfactant is available. If past experience is any guide, it may not be easy to develop an acceptable product for general use. HFV offers an opportunity to ventilate infants with relatively high mean airway pressures but without the use of high peak airway pressures. Early clinical trials suggest the technique will benefit some infants, however no ventilators for HFV are available for clinical use. In light of the low mortality from respiratory failure in RDS and a morbidity from RDS resulting mostly from the other diseases of prematurity, these new therapeutic approaches need to be thoroughly tested and understood before general clinical use.

High-Frequency Jet Ventilation in Major Airway or Pulmonary Disruption

High-frequency jet ventilation is an experimental method of mechanical support, which achieves satisfactory alveolar ventilation and oxygenation at low peak-inspiratory pressures of 5 to 8 cm H 2O and low end-expiratory pressures of 3 to 5 cm H 2O. This characteristic was used to advantage in 23 patients with cancer, 12 of whom had tracheal or bronchial disruption complicated by pneumonia. Eight patients who could not be supported by conventional means were salvaged. Barotrauma complicated the very high peak airway pressures required to ventilate 8 of 11 patients with respiratory failure associated with diffuse interstitial pneumonia or pulmonary fibrosis. There were only 2 survivors despite temporary normalization of arterial blood gas values in 7 patients. Earlier use of high-frequency jet ventilation in patients with poor compliance may prevent pulmonary disruption in addition to deleterious hemodynamic and systemic effects of conventional high-pressure ventilation. Other applications under study include the role of jet ventilation in resection of the trachea or carina, and in major airway trauma.

Pneumothorax and pneumomediastinum during pediatric mechanical ventilation

The incidence of pulmonary barotrauma during mechanical ventilation in children beyond the neonatal age group was studied in two groups of patients. In the first group, 179 cases of pediatric mechanical ventilation for over 12 hours were retrospectively analyzed for the occurrence of pneumothorax and pneumomediastrinum. Eleven percent (6 of 57) of young infants (0--6 months) without hyaline membrane disease and 3% (4 of 122) of older infants and children (over 6 months) developed these complications. Pulmonary barotrauma in young infants occurred only after cardiothoracic surgery and involved the same site as the intraoperative repair in all cases. Pulmonary barotrauma in older infants and children occurred in patients with severe respiratory disease requiring high peak airway pressures, PEEP, and respiratory rates. In the second group, the incidence of pulmonary barotrauma during ventilation with PEEP greater than or equal to 15 cm H2O was analyzed in 14 patients including 4 patients from the previous group. Overall, 64% (9 of 14) of this group developed pulmonary barotrauma and 43% (6 of 14) developed pneumothorax. Of 9 patients receiving PEEP greater than or equal to 15 cm H2O for longer than 24 hours, 6 developed pulmonary barotrauma after the first 24 hours. The incidence of pneumothorax and pneumomediastinum in ventilated infants without hyaline membrane disease and children is comparable to adult series.

Diffuse interstitial pneumonia inimmunocompromised hosts

High-frequency jet ventilation is an experimental method of mechanical support, which achieves satisfactory alveolar ventilation and oxygenation at low peak-inspiratory pressures of 5 to 8 cm H2O and low end-expiratory pressures of 3 to 5 cm H2O. This characteristic was used to advantage in 23 patients with cancer, 12 of whom had tracheal or bronchial disruption complicated by pneumonia. Eight patients who could not be supported by conventional means were salvaged.Barotrauma complicated the very high peak airway pressures required to ventilate 8 of 11 patients with respiratory failure associated with diffuse interstitial pneumonia or pulmonary fibrosis. There were only 2 survivors despite temporary normalization of arterial blood gas values in 7 patients.Earlier use of high-frequency jet ventilation in patients with poor compliance may prevent pulmonary disruption in addition to deleterious hemodynamic and systemic effects of conventional high-pressure ventilation. Other applications under study include the role of jet ventilation in resection of the trachea or carina, and in major airway trauma.