Acute respiratory failure in the adult. 1

The Impact of the Society of Critical Care Medicine's Flagship Journal: Critical Care Medicine: Reflections of Critical Care Pioneers

On the 50th anniversary of the Society of Critical Care Medicine's journal Critical Care Medicine, critical care pioneers reflect on the importance of the journal to their careers and to the development of the field of adult and pediatric critical care.

Observational study to compare the effect of altitude on cardiopulmonary reserves of different individuals staying more than 6 weeks at 10,000 ft and 15,000 ft

Background

The variation in heights beyond high altitude has different effects on the cardiorespiratory profile of individuals because of variation in oxygen density with every thousand feet. This study was planned to analyze and compare the effects of difference in altitudes on cardiorespiratory profile from anesthesiologist's point of view.

Methods

A multicenter observational study was done involving two different groups of 600 patients at 10,000 ft (Group A) and 15,000 ft (Group B). Observation and comparison of oxygen saturation, 6-min walk test, and breath holding time was carried out.

Results

Fifty-five percent of subjects in Group A had oxygen saturation of more than 93% in comparison to 5.5% in Group B. This was statistically significant (P < 0.001). Two percent of subjects in Group A in comparison to 63.5% of Group B had oxygen saturation of less than 88% (P < 0.001). Percentage increase of more than 15% of heart rate was found to be statistically significant in all the age groups. Overall, 3.8% of individuals in Group A had breath holding time less than 15 s in comparison to 16.6% of individuals in Group B (P value < 0.001).

Conclusion

The study demonstrates that there is a significant fall in oxygen saturation, significant rise in the heart rate in 6-min walk test, and significant fall in the breath holding time in the group located at 15,000 ft. Heights beyond 10,000 ft should be restricted to life and limb saving surgeries, and logistics should be focused more on "scoop and run" than "stay and play" policy.

Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute respiratory illness characterised by bilateral chest radiographical opacities with severe hypoxaemia due to non-cardiogenic pulmonary oedema. The COVID-19 pandemic has caused an increase in ARDS and highlighted challenges associated with this syndrome, including its unacceptably high mortality and the lack of effective pharmacotherapy. In this Seminar, we summarise current knowledge regarding ARDS epidemiology and risk factors, differential diagnosis, and evidence-based clinical management of both mechanical ventilation and supportive care, and discuss areas of controversy and ongoing research. Although the Seminar focuses on ARDS due to any cause, we also consider commonalities and distinctions of COVID-19-associated ARDS compared with ARDS from other causes.

Development of a multi-patient ventilator circuit with validation in an ARDS porcine model

Purpose

The COVID-19 pandemic threatens our current ICU capabilities nationwide. As the number of COVID-19 positive patients across the nation continues to increase, the need for options to address ventilator shortages is inevitable. Multi-patient ventilation (MPV), in which more than one patient can use a single ventilator base unit, has been proposed as a potential solution to this problem. To our knowledge, this option has been discussed but remains untested in live patients with differing severity of lung pathology.

Methods

The objective of this study was to address ventilator shortages and patient stacking limitations by developing and validating a modified breathing circuit for two patients with differing lung compliances using simple, off-the-shelf components. A multi-patient ventilator circuit (MPVC) was simulated with a mathematical model and validated with four animal studies. Each animal study had two human-sized pigs: one healthy and one with lipopolysaccharide (LPS) induced ARDS. LPS was chosen because it lowers lung compliance similar to COVID-19. In a previous study, a control group of four pigs was given ARDS and placed on a single patient ventilation circuit (SPVC). The oxygenation of the MPVC ARDS animals was then compared to the oxygenation of the SPVC animals.

Results

Based on the comparisons, similar oxygenation and morbidity rates were observed between the MPVC ARDS animals and the SPVC animals.

Conclusion

As healthcare systems worldwide deal with inundated ICUs and hospitals from pandemics, they could potentially benefit from this approach by providing more patients with respiratory care.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00540-021-02948-2.

Perioperative Lung Protection: Clinical Implications

In the past, it was common practice to use a high tidal volume (VT) during intraoperative ventilation, because this reduced the need for high oxygen fractions to compensate for the ventilation-perfusion mismatches due to atelectasis in a time when it was uncommon to use positive end-expiratory pressure (PEEP) in the operating room. Convincing and increasing evidence for harm induced by ventilation with a high VT has emerged over recent decades, also in the operating room, and by now intraoperative ventilation with a low VT is a well-adopted approach. There is less certainty about the level of PEEP during intraoperative ventilation. Evidence for benefit and harm of higher PEEP during intraoperative ventilation is at least contradicting. While some PEEP may prevent lung injury through reduction of atelectasis, higher PEEP is undeniably associated with an increased risk of intraoperative hypotension that frequently requires administration of vasoactive drugs. The optimal level of inspired oxygen fraction (FIO2) during surgery is even more uncertain. The suggestion that hyperoxemia prevents against surgical site infections has not been confirmed in recent research. In addition, gas absorption-induced atelectasis and its association with adverse outcomes like postoperative pulmonary complications actually makes use of a high FIO2 less attractive. Based on the available evidence, we recommend the use of a low VT of 6-8 mL/kg predicted body weight in all surgery patients, and to restrict use of a high PEEP and high FIO2 during intraoperative ventilation to cases in which hypoxemia develops. Here, we prefer to first increase FIO2 before using high PEEP.

Factors for Predicting Noninvasive Ventilation Failure in Elderly Patients with Respiratory Failure

Noninvasive ventilation (NIV) is useful when managing critically ill patients. However, it is not easy to apply to elderly patients, particularly those with pneumonia, due to the possibility of NIV failure and the increased mortality caused by delayed intubation. In this prospective observational study, we explored whether NIV was appropriate for elderly patients with pneumonia, defined factors that independently predicted NIV failure, and built an optimal model for prediction of such failure. We evaluated 78 patients with a median age of 77 years. A low PaCO2 level, a high heart rate, and the presence of pneumonia were statistically significant independent predictors of NIV failure. The predictive power for NIV failure of Model III (pneumonia, PaCO2 level, and heart rate) was better than that of Model I (pneumonia alone). Considering the improvement in parameters, patients with successful NIV exhibited significantly improved heart rates, arterial pH and PaCO2 levels, and patients with NIV failure exhibited a significantly improved PaCO2 level only. In conclusion, NIV is reasonable to apply to elderly patients with pneumonia, but should be done with caution. For the early identification of NIV failure, the heart rate and arterial blood gas parameters should be monitored within 2 h after NIV commencement.

Partial pressure of arterial carbon dioxide and survival to hospital discharge among patients requiring acute mechanical ventilation: A cohort study

PURPOSE

To describe the prevalence of hypocapnia and hypercapnia during the earliest period of mechanical ventilation, and determine the association between PaCO2 and mortality.

MATERIALS AND METHODS

A cohort study using an emergency department registry of mechanically ventilated patients. PaCO2 was categorized: hypocapnia (<35mmHg), normocapnia (35-45mmHg), and hypercapnia (>45mmHg). The primary outcome was survival to hospital discharge.

RESULTS

A total of 1,491 patients were included. Hypocapnia occurred in 375 (25%) patients and hypercapnia in 569 (38%). Hypercapnia (85%) had higher survival rate compared to normocapnia (74%) and hypocapnia (66%), P<0.001. PaCO2 was an independent predictor of survival to hospital discharge [hypocapnia (aOR 0.65 (95% confidence interval [CI] 0.48-0.89), normocapnia (reference category), hypercapnia (aOR 1.83 (95% CI 1.32-2.54)]. Over ascending ranges of PaCO2, there was a linear trend of increasing survival up to a PaCO2 range of 66-75mmHg, which had the strongest survival association, aOR 3.18 (95% CI 1.35-7.50).

CONCLUSIONS

Hypocapnia and hypercapnia occurred frequently after initiation of mechanical ventilation. Higher PaCO2 levels were associated with increased survival. These data provide rationale for a trial examining the optimal PaCO2 in the critically ill.

Analytic Reviews : Initiating Mechanical Ventilation

Mechanical ventilation is a central facet of intensive care medicine. Technological progress has led to major advances in this field. Initiation of mechanical ventila tion remains standard; however, many options are now available to continue mechanical ventilation. These mechanical options include assist-control ventilation, intermittent mandatory ventilation, pressure support ventilation, positive end-expiratory pressure, and high- frequency ventilation. The sophistication of ventilators has also allowed more procedures to be performed dur ing mechanical ventilation, including bronchoscopy and transbronchial biopsy. Complications do occur during mechanical ventilation, but can be minimized by vigi lance and use of proper procedures. The recent increase in home care will lead to increased use of alternatives to conventional ventilatory modes. Finally, more well- designed studies are needed as newer techniques are promoted.

Extrapulmonary Causes of Respiratory Failure

The causes of respiratory failure can be divided into two main groups: extrapulmonary and pulmonary. Extrapulmonary causes of respiratory failure include conditions that exclusively or primarily cause respiratory failure by their effect on structures other than the lungs (i.e., the extrapulmonary compartment). To place the topic of extrapulmonary respiratory failure into perspective, we briefly review normal and abnormal gas exchange and then examine how one can use this information to suspect or confirm the diagnosis of an extrapulmonary cause of respiratory failure. We then review the individual causes of extrapulmonary respiratory failure. These have been divided into two main functional categories: (1) those that involve a decrease in normal force generation, and (2) those that involve an increase in resistance to (bulk flow) ventilation. We then briefly consider the treatment of these disorders from a respiratory point of view.

Neurologic Causes of Acute Respiratory Dysfunction

Many neurologic diseases can cause acute respiratory decompensation, therefore a familiarity with these diseases is critical for any clinician managing patients with respiratory dysfunction. In this article, we review the anatomy of the respiratory system, focusing on the neurologic control of respiration. We discuss general mechanisms by which diseases of the peripheral and central nervous systems can cause acute respiratory dysfunction, and review the neurologic diseases which can adversely affect respiration. Lastly, we discuss the diagnosis and general management of acute respiratory impairment due to neurologic disease.

Pediatric transport medicine and the dawn of the pediatric anesthesiology and critical care medicine subspecialty: an interview with pioneer Dr. Alvin Hackel

Dr. Alvin 'Al' Hackel (1932-) Professor Emeritus of Anesthesiology, Perioperative and Pain Medicine, and Pediatrics at the Stanford University School of Medicine, has been an influential pioneer in shaping the scope and practice of pediatric anesthesia. His leadership helped to formally define the subspecialty of pediatric anesthesiology ('who is a pediatric anesthesiologist?') and the importance of specialization and regionalization of expertise in both patient transport and perioperative care. His enduring impact on pediatric anesthesia and critical care practice was recognized in 2006 by the American Academy of Pediatrics when it bestowed upon him the profession's highest lifetime achievement award, the Robert M. Smith Award. Of his many contributions, Dr. Hackel identifies his early involvement in the development of pediatric transport medicine as well as the subspecialty of pediatric anesthesiology as his defining contribution. Based on a series of interviews held with Dr. Hackel between 2009 and 2014, this article reviews the early development of transportation medicine and the remarkable career of a pioneering pediatric anesthesiologist.

Hyperoxic acute lung injury

Prolonged breathing of very high F(IO(2)) (F(IO(2)) ≥ 0.9) uniformly causes severe hyperoxic acute lung injury (HALI) and, without a reduction of F(IO(2)), is usually fatal. The severity of HALI is directly proportional to P(O(2)) (particularly above 450 mm Hg, or an F(IO(2)) of 0.6) and exposure duration. Hyperoxia produces extraordinary amounts of reactive O(2) species that overwhelms natural anti-oxidant defenses and destroys cellular structures through several pathways. Genetic predisposition has been shown to play an important role in HALI among animals, and some genetics-based epidemiologic research suggests that this may be true for humans as well. Clinically, the risk of HALI likely occurs when F(IO(2)) exceeds 0.7, and may become problematic when F(IO(2)) exceeds 0.8 for an extended period of time. Both high-stretch mechanical ventilation and hyperoxia potentiate lung injury and may promote pulmonary infection. During the 1960s, confusion regarding the incidence and relevance of HALI largely reflected such issues as the primitive control of F(IO(2)), the absence of PEEP, and the fact that at the time both ALI and ventilator-induced lung injury were unknown. The advent of PEEP and precise control over F(IO(2)), as well as lung-protective ventilation, and other adjunctive therapies for severe hypoxemia, has greatly reduced the risk of HALI for the vast majority of patients requiring mechanical ventilation in the 21st century. However, a subset of patients with very severe ARDS requiring hyperoxic therapy is at substantial risk for developing HALI, therefore justifying the use of such adjunctive therapies.

Carbon dioxide dialysis will save the lung

Mechanical ventilation and ventilator-associated lung injury could be avoided by decreasing the ventilatory needs of the patient by extracorporeal carbon dioxide removal. The reasons for the increased ventilatory needs of the patients with acute respiratory distress syndrome are outlined, as well as some of the mechanisms of continuing damage. Extracorporeal gas exchange has been used mainly as a rescue procedure for severely hypoxic patients. Although this indication remains valid, we propose that extracorporeal carbon dioxide removal could control the ventilatory needs of the patient and allow the maintenance of spontaneous breathing while avoiding intubation and decreasing the concurrent sedation needs. A scenario is depicted whereby an efficient carbon dioxide removal device can maintain blood gas homeostasis of the patient with invasiveness comparable to hemodialysis. High carbon dioxide removal efficiency may be achieved by combinations of hemofiltration and metabolizable acid loads.

[Sedation an acute respiratory distress syndrome]

AIM

To assess the role of sedation and myorelaxant agents in acute respiratory distress syndrome (ARDS) and to propose an updated management according to recent literature. EXTRACTION OF DATA: From Medline and Cochrane database of English and French language articles. Keywords were: acute respiratory distress syndrome, acute lung injury, general anaesthetics, inhalation, intravenous anaesthetics and intensive care. Selection of original articles, reviews and expert reports. Case reports have been included.

TOPIC

ARDS is a clinical picture in which respiratory constraints are major because of hypoxemia. To insure correct haematosis, mechanical ventilation has to be considered. It constitutes, then, the most frequent indication of sedation in the intensive care unit. The objectives are to help the ventilation of lungs and to improve gas exchange, by controlling agitation, fight against ventilation and to reduce mechanical ventilation associated injuries. In this situation, use of myorelaxant agents is aimed at facilitating synchronization of the patient with his/her ventilator and serves to improve oxygenation during the early inflammatory phase of ARDS. Several mechanisms may enflame this improvement of oxygenation. One of the most probable effect on optimization is the possibility of optimize protective ventilation at the cares phase of ARDS and to reduce mechanical ventilation-associated injuries.

CONCLUSION

With regard to benefits and inconvenient, sedation is considered as a treatment of ARDS. Its goals are the well being of patient and his/her adaptation to ventilator, but also the prevention on mechanical ventilation associated injuries. Hence, most authors suggest using a deep sedation at the early phase of ARDS. In this contact, use of myorelaxant agent is an intersecting adjuvant if sedation is not enough. The benefit is terms of survival and outcome remains to show.

Respiratory Failure

Respiratory failure is defined as a failure in gas exchange due to an impaired respiratory system--either pump or lung failure, or both. The hallmark of respiratory failure is impairment in arterial blood gases. This review describes the mechanisms leading to respiratory failure, the indices that can be used to better describe gas exchange abnormalities and the physiologic and clinical consequences of these abnormalities. The possible causes of respiratory failure are then briefly mentioned and a quick reference to the clinical evaluation of such patients is made. Finally treatment options are briefly outlined for both acute and chronic respiratory failure.

Therapeutic effect of in vivo transfection of transcription factor decoy to NF-kappaB on septic lung in mice

Nuclear factor-kappaB (NF-kappaB) plays a key role in regulating expression of several genes involved in the pathophysiology of endotoxic shock. We investigated whether in vivo introduction of synthetic double-stranded DNA with high affinity for the NF-kappaB binding site could block expression of genes mediating pulmonary vascular permeation and thereby provide effective therapy for septic lung failure. Endotoxic shock was induced by an intravenous injection of 10 mg/kg Escherichia coli endotoxin in mice. We introduced NF-kappaB decoy oligodeoxynucleotide (ODN) in vivo 1 h after endotoxic shock by using a gene transfer kit. At 10 h, blood samples were collected for measurement of histamine and for blood-gas analysis. Gene and protein expression levels of target molecules were determined by means of Northern and Western blot analyses, respectively. The transpulmonary flux of (125)I-labeled albumin was used as an index of lung vascular permeability. Administration of endotoxin caused marked increases in plasma histamine and gene and protein expressions of histidine decarboxylase, histamine H(1) receptors, and inducible nitric oxide synthase in lung tissues. Elevated lung vascular permeability was also found. Blood-gas analysis showed concurrent decreases in arterial Po(2), Pco(2), and pH. All of these events induced by endotoxin were significantly inhibited by transfection of NF-kappaB decoy ODN but not by its mutated (scrambled) form (used as a control). Our results indicate for the first time the potential usefulness of NF-kappaB decoy ODN for gene therapy of endotoxic shock.

Geriatric pain management. The anesthesiologist's perspective

Geriatric patients have a unique physiology that makes their pain management problematic. This article reviews the issue of geriatric pain management from the perspective of the anesthesiologist. It looks at the main causes of geriatric chronic pain and emphasizes the different analgesic modalities available that can provide maximum relief and minimal potential side effects.

Sigh in acute respiratory distress syndrome

Mechanical ventilation with plateau pressure lower than 35 cm H2O and high positive end-expiratory pressure (PEEP) has been recommended as lung protective strategy. Ten patients with ARDS (five from pulmonary [p] and five from extrapulmonary [exp] origin), underwent 2 h of lung protective strategy, 1 h of lung protective strategy with three consecutive sighs/min at 45 cm H2O plateau pressure, and 1 h of lung protective strategy. Total minute ventilation, PEEP (14.0 +/- 2.2 cm H2O), inspiratory oxygen fraction, and mean airway pressure were kept constant. After 1 h of sigh we found that: (1) PaO2 increased (from 92.8 +/- 18.6 to 137.6 +/- 23.9 mm Hg, p < 0.01), venous admixture and PaCO2 decreased (from 38 +/- 12 to 28 +/- 14%, p < 0.01; and from 52.7 +/- 19.4 to 49.1 +/- 18.4 mm Hg, p < 0.05, respectively); (2) end-expiratory lung volume increased (from 1.49 +/- 0.58 to 1.91 +/- 0.67 L, p < 0.01), and was significantly correlated with the oxygenation (r = 0.82, p < 0.01) and lung elastance (r = 0.76, p < 0.01) improvement. Sigh was more effective in ARDSexp than in ARDSp. After 1 h of sigh interruption, all the physiologic variables returned to baseline. The derecruitment was correlated with PaCO2 (r = 0.86, p < 0.01). We conclude that: (1) lung protective strategy alone at the PEEP level used in this study may not provide full lung recruitment and best oxygenation; (2) application of sigh during lung protective strategy may improve recruitment and oxygenation.

Assessment of pulmonary function in the early phase of ARDS in pediatric patients

Scant data are available on lung function in acute respiratory distress syndrome (ARDS) in pediatric patients. We measured respiratory mechanics by single-breath occlusion and maximum expiratory flow-volume curves by forced deflation in ten critically ill infants with clinical ARDS. Ten mechanically ventilated infants without lung disease served as the control group. To assess the severity of the lung injury in the infants with ARDS, we modified an adult scoring system that calculates a score (from 0 to 4; > 2.5 indicates severe lung injury) based on the extent of chest radiographic changes, degree of hypoxemia, amount of positive end-expiratory pressure (PEEP), and total respiratory system compliance. The lung injury scores of our patients were in the range of 2.75 to 3.75. The lung injury scores of the control group were zero. The predominant alteration in lung function was restrictive, as characterized by a significant decrease in total respiratory system compliance (0.41 +/- 0.13 ml/cmH2O/kg versus 1.12 +/- 0.16 ml/cmH2O/kg of controls; P < 0.001) and forced vital capacity (21.5 +/- 6.5 ml/kg versus 59.2 +/- 6.3 ml/kg of controls; P < 0.001). Maximum expiratory flow rates at 10% forced vital capacity were significantly increased (23.6 +/- 20.1 ml/kg/sec versus 8.4 +/- 2.5 ml/kg/sec of controls; P < 0.05), confirming the absence of any significant obstructive abnormalities. The passive expiratory flow-volume curves were curvilinear and convex in shape, indicating inhomogeneous lung pathology. The inhomogeneous distribution of lung injury in ARDS restricts the validity of respiratory mechanics measurements that rely on a single-compartment model. However, the forced deflation technique allows accurate spirometric assessments of the severity of restrictive (and obstructive) lung function changes in intubated infants with severe ARDS. Such measurements can be incorporated into lung injury scoring systems to classify the severity of the disease process for the purpose of outcome evaluation and to evaluate the effect of therapeutic interventions.

Noninvasive positive-pressure ventilation in patients with acute respiratory failure

This article provides a systematic review of the literature on the application of noninvasive ventilation in various forms of hypercapnic and hypoxemic respiratory failures. A description of the underlying pathophysiology is followed by a review of physiologic data explaining the mechanisms of action of noninvasive ventilation. A critical review of clinical studies is presented with specific suggestions. The methodology of correctly implementing and monitoring noninvasive ventilation in patients with acute respiratory failure, critical to success, is detailed.

How does positive end-expiratory pressure decrease CO2 elimination from the lung?

Six chloralose-urethane anesthetized dogs (23 +/- 2 kg) underwent median thoracotomy (open pleural spaces) and constant mechanical ventilation with O2. We conducted measurements at baseline and during 25 min of ventilation with 3.3 cmH2O positive end-expiratory pressure (PEEP3) or 10.7 cmH2O PEEP (PEEP 11), including breath-by-breath values in the first 2 min after PEEP began. PEEP 11 immediately decreased pulmonary CO2 elimination per breath (VCO2,br, digital integration and multiplication of exhaled flow and FCO2) from 8.4 +/- 2.0 to 4.5 +/- 1.6 ml (P < 0.05) by significantly decreasing alveolar ventilation (VA) (29% increase in anatomical dead space (VDana) and generation of high VA/Q regions) and by decreasing alveolar PCO2 (PACO2) from 42.5 +/- 3.5 to 35.9 +/- 3.5 Torr (decreased CO2 transfer to the lung as electromagnetic aortic cardiac output (QT) decreased by 51%). The immediate dilution of alveolar gas and PACO2 by fresh gas as PEEP increased functional residual capacity by 1152 +/- 216 ml was offset by simultaneous decreased expiratory volume and, hence, CO2 accumulation. Compared to baseline, the 17% reduction in VCO2,br was sustained at 25 min after addition of PEEP 11 because VA remained depressed. Then, VCO2,br could only be restored to baseline if PACO2 sufficiently increased. However, CO2 transport was still in unsteady state at 25 min of PEEP. Peripheral tissue retention of CO2 and the significant increase in mixed venous PCO2 (PVCO2, 62.4 +/- 6.2 Torr) were not enough to normalize CO2 transfer to the lung and to sufficiently increase PACO2, especially during the continued depression in QT that occurred at higher PEEP. The sustained decrease in VCO2,br during PEEP was not mirrored by changes in end-tidal PCO2 (PETCO2).

A Prediction Rule For Mortality in the Medical Intensive Care Unit Based on Early Acute Organ-System Failure

We evaluated early acute organ-system failure (AOSF) as a predictor of mortality in medical intensive care unit (MICU) patients. Prospective data were obtained on 825 men admitted to a Veterans Administraion (VA) Medical Center MICU. Clinical criteria were used to diagnose the presence of 7 types of AOSF. Of the 2,364 AOSFs detected, 1,847 (78%) were “early” (i.e., detected within the first 48 hours of MICU stay). A random sample of 550 patients was selected for derivation of a prediction rule for MICU mortality based on age and number of early AOSFs. For each additional early AOSF, the adjusted odds of mortality increased by 3.3 (95% confidence interval: 2.7, 4.0; p < 0.0001). When applied to the cross-validation sample of 275 patients, this rule yielded a sensitivity of 77%, a specificity of 86%, and an overall correct classification rate of 82%. These results suggest that a simple rule based on number of AOSFs detected in the early portion of a patient's MICU stay may be a useful predictor of mortality.

Perianesthetic considerations for the elderly patient

The principles that guide the perianesthetic management of the elderly patient are the same as those used for all patients. What makes the care of this group challenging is not learning a new set of principles, but rather understanding the specific application of these guidelines to the unique traits of elderly patients. Only then is it possible to avoid complications that the elderly patient has very little margin of reserve to deal with.

Adult respiratory distress syndrome (ARDS): the basics

The term adult respiratory distress syndrome (ARDS) was first introduced by Ashbaugh and Petty more than two decades ago. Since then, our understanding of this clinicopathologic entity has increased significantly. However, little therapeutic progress has been achieved, and the mortality remains high. ARDS is characterized by diffuse pulmonary microvascular injury resulting in increased permeability and, thus, noncardiogenic pulmonary edema. Ventilation-perfusion lung studies have demonstrated that the predominant pathogenesis of hypoxemia in ARDS is related to intrapulmonary shunts. Common symptoms include dyspnea, tachypnea, dry cough, retrosternal discomfort, and moderate to severe respiratory distress. In most cases the diagnosis of ARDS is that of exclusion. The mainstay of therapy for this syndrome is the management of the underlying disorder causing it. To date, there are no specific pharmacologic interventions of proven value for the treatment of ARDS. Once the potentially treatable sources have been found and their therapy started, the main treatment for ARDS is supportive.

Survival following mechanical ventilation for acute respiratory failure in adult men

STUDY DESIGN

Survival following mechanical ventilation for acute respiratory failure has important implications for medical decision-making and allocation of expensive resources for critical care.

PROCEDURE

We reviewed a 5-year experience with mechanical ventilation in 383 men with acute respiratory failure and studied the impact of patient age, cause of acute respiratory failure, and duration of mechanical ventilation on survival. Survival rates were 66.6 percent to weaning, 61.1 percent to ICU discharge, 49.6 percent to hospital discharge, and 30.1 percent to 1 year after hospital discharge. When our data were combined with 10 previously reported series, mean survival rates were calculated to be 62 percent to ventilator weaning, 46 percent to ICU discharge, 43 percent to hospital discharge, and 30 percent to 1 year after discharge. Of 255 patients weaned from mechanical ventilation, 44 (17.3 percent) required an additional period of mechanical ventilation during the same hospitalization.

RESULTS

Age had a significant influence on survival to hospital discharge and on that to 1 year after hospital discharge, and the cause of acute respiratory failure had a significant influence on survival only to weaning. Survival was best in younger patients and those with COPD or postoperative respiratory failure and worst in patients resuscitated after cardiac or respiratory arrest. Increased duration of mechanical ventilation significantly reduced survival only to hospital discharge. Overall survival was significantly affected by age and cause of acute respiratory failure, but not by duration of mechanical ventilation.

CONCLUSION

We conclude that age, cause of acute respiratory failure, and duration of mechanical ventilation have specific influences on the generally poor outcome of mechanical ventilation for acute respiratory failure.

Effects of milrinone on lung water content in dogs with acute pulmonary hypertension

To evaluate the effects of milrinone (MIL) on hemodynamics and lung water content, we used 10 mongrel dogs with pulmonary hypertension (PH). To induce pulmonary hypertension, we administered two injections of glass beads stirred in saline to dogs. Mean pulmonary arterial pressure (PAP) and pulmonary vascular resistance significantly increased following induction. Milrinone, which inhibits cyclic AMP phosphodiesterase-(PDE) demonstrated pulmonary vasodilation, indicated a reduction in these two parameters. To clarify the drug mechanism, we measured lung water content as extravascular lung thermal volume (ETVL) using a thermo/sodium double-indicator dilution method. The induction of pulmonary hypertension produced a transient reduction in extravascular lung thermal volume. The parameter remained constant following milrinone administration, whereas the control showed a gradual increase. Of the 10 dogs, five were killed to measure gravimetrically the volume of lung water content as a comparison with extravascular lung thermal volume. We concluded that milrinone produced pulmonary vasodilation which induced a reduction in the transmural capillary pressure gradient according to Starling's hypothesis. This study suggests that the reduction in the transmural pressure gradient induced by milrinone may also prevent the re-elevation in extravascular lung thermal volume. Milrinone increases the cyclic AMP level in the endothelium and in the platelet which may affect either directly or indirectly the permeability of capillary endothelium.

Elevated pulmonary artery systolic storage volume associated with improved ventilation-to-perfusion ratios in acute respiratory failure

The possibility that an elevated pulmonary artery systolic storage volume (PASSV) correlates with improved overall ratios of ventilation-to-perfusion and hence benefits gas exchange in acute respiratory failure was examined. We examined this by assessing the correlation between PASSV and both the physiologic dead space to tidal volume ratio (VD/VT) and intrapulmonary shunt fraction (Qsp/Qt). The VD/VT and Qsp/Qt were used as an index of distribution of ventilation-to-perfusion as well as efficiency of pulmonary gas exchange. Twenty-eight patients suffering from acute respiratory failure were included. All required mechanical ventilation. PASSV was calculated from the pulmonary artery (PA) compliance and mean PA systolic distending pressure. Pulmonary arteriolar pressures were computed by Fourier analysis. PA compliance was derived from the PA time constant and the PA resistance. Storage volume fraction of stroke volume index (PASSV/SVI) was used to compare individual variations. There were inverse linear relationships between PASSV/SVI and VD/VT (r = 0.693, p less than 0.0001), and between PASSV/SVI and Qsp/Qt (r = 0.427, p = 0.012). Also, a direct correlation was found between VD/VT and PA time constant (r = 0.503, p = 0.002). The patients were divided into two groups based on PASSV/SVI to evaluate the effect of other hemodynamic data on PASSV. Comparison of the two groups revealed that VD/VT and Qsp/Qt were lower (p less than 0.0001, and p = 0.018, respectively), PA time constant was higher (p less than 0.001), and right ventricular stroke-work index was higher (p = 0.005) in the group with a high PASSV/SVI. There were no differences in other hemodynamic data between the two groups. These data suggest that an elevated PASSV may indeed benefit gas exchange in acute respiratory failure.

Mechanical ventilation

Among the many advances made in intensive care therapeutics in recent years, few have rivaled the impact of mechanical ventilators. Their expanded use affects all who practice in the critical care setting. This article reviews the physiologic basis for mechanical ventilation, how ventilators are classified, the various modes, and specific indications. A basic introduction is made into ventilator set up, weaning techniques, adjunctive drug therapy, and complications. The pharmacotherapy specialist who understands interactions between patients and ventilators, and the effects of mechanical ventilation on cardiopulmonary function will be best equipped to individualize drug therapy.

Fatal intrapulmonary arteriovenous shunting in cirrhosis--diagnosis by radionuclide lung perfusion scan

Intrapulmonary arteriovenous shunting is an important cause of hypoxaemia in patients with chronic liver disease. We describe an unusual case of a patient with haemochromatosis who died as a result of severe hypoxaemia which was due to this disorder. The shunt was demonstrated by radionuclide lung perfusion scanning.

Adult respiratory distress syndrome

The Adult Respiratory Distress Syndrome (ARDS) is a fulminant form of respiratory failure affecting many seriously ill patients. The early manifestations of ARDS are caused by increased permeability of the alveolo-capillary barrier leading to pulmonary edema, stiff lungs, and a large right-to-left intrapulmonary shunt. Polymorphonuclear leukocytes (PMNS) are involved in the pathogenesis of most ARDS, and multiple PMN mechanisms can effect pulmonary injury; interactions between PMN adherence, proteolytic enzyme release, and oxygen radical production are emphasized. ARDS therapy remains largely supportive and has had little impact on mortality. The complications of infection and multiorgan failure play important roles in determining ARDS outcome.

Correction of hemorrhagic shock-induced liver hypoxia with whole blood, Ringer's solution or with hetastarch

Liver oxygenation was studied with hemorrhagic hypotension and corrected using whole blood, a synthetic colloid (hydroxyethyl starch or hetastarch, HES; mol. wt. 120,000), or a crystalloid solution. Measurements were performed directly by recording pig liver tissue oxygen tension with an implanted silicone elastomer (Silastic) tube, and indirectly by calculating blood oxygen contributions. The direct method seems fairly reliable and accurately reflects different levels of bleeding and shock and their correction. Liver tissue oxygen tension (PlO2) may thus be used as an indicator of central organ response to shock management. PlO2 decreased during bleeding from 33.5 +/- 0.5 to 16.0 +/- 0.5 torr, and normalized rapidly after retransfusion. The baseline values were significantly exceeded after hetastarch infusion but were never reached with Ringer's solution. The correction of liver oxygen consumption was less complete after crystalloid infusion as well. On the other hand, the difference in liver oxygenation was less marked after crystalloid infusion and retransfusion, which restored perfusion to the baseline. The total amount of Ringer's solution needed to keep the animals hemodynamically stable during the 2-h follow-up period was four times higher than with hetastarch and some five times the blood volume shed. The cause of defective correction of liver oxygenation seems to be the poor response of liver blood flow to refilling in the Ringer group, in addition to apparent tissue edema after crystalloid infusion. According to our study, hemorrhagic hypotension related to liver oxygenation is more promptly and completely corrected with the colloid hydroxyethyl starch than with a crystalloid solution in the early phase of treatment.

Randomized double-blind, multicenter study of prostaglandin E1 in patients with the adult respiratory distress syndrome. Prostaglandin E1 Study Group

Prostaglandin E1 (PGE1) was compared to placebo in a 100-patient (50 PGE1, 50 placebo) randomized, double-blind, clinical trial to determine whether PGE1 therapy enhances survival of patients with adult respiratory distress syndrome (ARDS) when infused through a central line at 30 ng/kg/min continuously for seven days. At 30 days postinfusion, 30 PGE1 and 24 placebo patients had died. Total deaths judged to be related to the syndrome were 32 and 28 in the PGE1 and placebo groups respectively at six months. We conclude that PGE1 did not enhance survival in patients with established ARDS. PGE1 augmented the hyperdynamic circulation of these patients by reducing systemic and pulmonary vascular resistance, which resulted in a reduction of blood pressures and increased stroke volume, cardiac output, and heart rate. An improvement in oxygen availability and oxygen consumption was observed with PGE1 therapy. PGE1 was associated with an increased incidence of diarrhea (six patients in the PGE1 group vs one in the placebo group, p less than 0.05). Other adverse effects included hypotension (ten patients in the PGE1 group vs seven in the placebo group), fever (six patients in the PGE1 group vs three in the placebo group), and non-fatal dysrhythmias (ten in the PGE1 group vs five in the placebo group).

The influence of prostaglandin E1 on systemic and pulmonary haemodynamics after aortic surgery

The influence of a peroperative prostaglandin E1 (PGE1) infusion on systemic and pulmonary haemodynamics in a porcine model of aortic surgery was studied. Twenty-four pigs were randomised to PGE1 (100 ng/kg/min) or 0.9% Saline as placebo. Haemaccel was then infused to maintain a central venous pressure (CVP) of greater than 4 less than 6 mmHg and pulmonary artery wedge pressure (PAWP) of greater than 3 less than 5 mmHg. Standardised aortic surgery consisted of midline laparotomy, small bowel exteriorisation, 1.5 h aortic clamping and 1 h shock before resuscitation. Serial measurements of blood pressure (BP), cardiac output (CO), pulmonary vascular resistance (PVR), pulmonary shunt (A-V shunt), and arterial PO2 (PaO2) were recorded during and three days after surgery. Volume loading with Haemaccel prevented a significant fall in initial BP on PGE1 at 95.1 +/- 48 mmHg compared to 102 +/- 4.9 mmHg in control animals with similar CO in the two groups. Following release of the aortic clamp all animals became profoundly hypotensive with BP falling to 74.6 +/- 3.0 and 68.7 +/- 3.2 mmHg for PGE1 and placebo respectively, but CO was protected in those animals receiving PGE1 at 1.92 +/- 0.04 compared to 1.67 +/- 0.1 L/min/m2 on placebo and remained significantly higher following resuscitation and three days later (P less than 0.05). PGE1 also reduced the marked rise in pulmonary vascular resistance to 922 +/- 84 dynes-s/cm5/m2 during shock in control animals to only 555 +/- 30 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult respiratory distress syndrome: current concepts

Adult Respiratory Distress Syndrome (ARDS) is a common diagnosis in today's intensive care units, representing a final common pathway of lung response to a variety of disease states. Mortality rates remain excessively high, despite comprehensive monitoring and intensive treatment. The incidence, etiology, clinical features, pathology and pathophysiology of ARDS are reviewed, with special emphasis on current research regarding potentially injurious mediators and possible etiopathogenetic mechanisms. Current therapy is summarized, and new therapeutic modalities are assessed. It is hoped that increased knowledge and awareness of the various aspects of ARDS will lead to further understanding and better clinical results in patients with this syndrome.