RESPIRATORY FAILURE

Indications and practice of home invasive mechanical ventilation in children

BACKGROUND

Developments and technological advances in neonatal and pediatric intensive care units have led to a prolonged life expectancy of pediatric patients with chronic respiratory failure. Therefore, the number of hemodynamically stable pediatric patients with chronic respiratory failure who need mechanical ventilator assistance throughout the day has significantly increased.

AIMS

Numerous conditions, including parenchymal lung diseases, airway disorders, neuromotor disorders, or respiratory defects, can lead to chronic respiratory failure. For individuals who cannot tolerate non-invasive mechanical ventilation (NIMV), invasive mechanical ventilation (IMV) is the only suitable choice. Due to increasing need, mechanical ventilator technology is continuously evolving.

RESULTS

As a result of this process, home-type mechanical ventilators have been produced for patients requiring long-term IMV. Patients with chronic respiratory failure can be safely monitored at home with these ventilators.

DISCUSSION

Home follow-up of these patients has many benefits such as an increase in general quality of life and a positive contribution to their emotional and cognitive development.

CONCLUSION

In this compilation, indications for home-based IMV, features of home invasive mechanical ventilators (HMVs), patient monitoring, and the detailed advantages of using IMV at home will be elucidated.

Oxygen Therapy in COPD

Long-term oxygen therapy (LTOT) is a mainstay treatment for patients with severe resting hypoxemia secondary to chronic respiratory conditions including COPD. The evidence for LTOT is based on two trials that are now several decades old but have been insufficiently revisited. Therefore, many questions remain about precisely which patients experience the most benefit from LTOT, as well as how to define that benefit. Most studies have examined LTOT's effect on longevity rather than its impact on quality of life. In addition, many challenges exist in training both clinicians and patients on best practices for LTOT and associated equipment. Reimbursement policies have reduced the kinds of equipment available to the LTOT patient community, presenting additional challenges. This paper will review the current evidence for LTOT in COPD, the challenges involved with providing optimal therapy, and potential avenues of modernizing this essential intervention.

Changes in Oxygen Saturation During Fiberoptic Bronchoscopy: High-Flow Nasal Cannula versus Standard Oxygen Therapy

BACKGROUND

Hypoxemia is a relatively common complication in stable patients during fiberoptic bronchoscopy (FOB). To prevent this complication, high-flow nasal cannula (HFNC) has been described as an alternative to standard oxygen therapy. However, the advantages of HFNC over standard oxygen therapy in acute care patients receiving supplemental oxygen before FOB performed with an oral approach are unknown.

METHODS

We conducted an observational study that involved subjects with a presumptive diagnosis of pneumonia and a clinical indication for a bronchial aspirate sample. The type of oxygen support (standard oxygen therapy vs HFNC) was selected according to availability. The oxygen flow in the HFNC group was 60 L/min. In both groups, the FIO2 was set at 0.40. Hemodynamic, respiratory dynamics, and gas exchange data were collected at baseline, before, during, and 24 h after FOB.

RESULTS

Forty subjects were included, 20 in each group (HFNC and standard oxygen therapy). The study was performed on day 5 of hospitalization in the HFNC group and on day 4 in the standard oxygen therapy group (P = .10). No significant between-group differences in baseline characteristics were observed. HFNC vs standard oxygen therapy was associated with a smaller decrease in SpO2 levels during the procedure (94% vs 90%; P = .040, respectively) and with less variation between the last SpO2 measured before FOB and the lowest SpO2 during FOB (Δ SpO2 ): 2% versus 4.5% (P = .01, respectively).

CONCLUSIONS

In acute subjects who required oxygen support before FOB, the use of HFNC during FOB with an oral approach was associated with a smaller decrease in SpO2 and lower Δ SpO2 compared with standard oxygen therapy.

Oxygen-induced hypercapnia: physiological mechanisms and clinical implications

Oxygen is probably the most commonly prescribed drug in the emergency setting and is a life-saving modality as well. However, like any other drug, oxygen therapy may also lead to various adverse effects. Patients with chronic obstructive pulmonary disease (COPD) may develop hypercapnia during supplemental oxygen therapy, particularly if uncontrolled. The risk of hypercapnia is not restricted to COPD only; it has also been reported in patients with morbid obesity, asthma, cystic fibrosis, chest wall skeletal deformities, bronchiectasis, chest wall deformities, or neuromuscular disorders. However, the risk of hypercapnia should not be a deterrent to oxygen therapy in hypoxemic patients with chronic lung diseases, as hypoxemia may lead to life-threatening cardiovascular complications. Various mechanisms leading to the development of oxygen-induced hypercapnia are the abolition of ‘hypoxic drive’, loss of hypoxic vasoconstriction and absorption atelectasis leading to an increase in dead-space ventilation and Haldane effect. The international guideline recommends a target oxygen saturation of 88% to 92% in patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) and other chronic lung diseases at risk of hypercapnia.  Oxygen should be administered only when oxygen saturation is below 88%. We searched PubMed, EMBASE, and the CINAHL from inception to June 2022. We used the following search terms: “Hypercapnia”, “Oxygen therapy in COPD”, “Oxygen-associated hypercapnia”, “oxygen therapy”, and “Hypoxic drive”. All types of study are selected. This review will focus on the physiological mechanisms of oxygen-induced hypercapnia and its clinical implications.

Methods and Applications in Respiratory Physiology: Respiratory Mechanics, Drive and Muscle Function in Neuromuscular and Chest Wall Disorders

Individuals with neuromuscular and chest wall disorders experience respiratory muscle weakness, reduced lung volume and increases in respiratory elastance and resistance which lead to increase in work of breathing, impaired gas exchange and respiratory pump failure. Recently developed methods to assess respiratory muscle weakness, mechanics and movement supplement traditionally employed spirometry and methods to evaluate gas exchange. These include recording postural change in vital capacity, respiratory pressures (mouth and sniff), electromyography and ultrasound evaluation of diaphragmatic thickness and excursions. In this review, we highlight key aspects of the pathophysiology of these conditions as they impact the patient and describe measures to evaluate respiratory dysfunction. We discuss potential areas of physiologic investigation in the evaluation of respiratory aspects of these disorders.

Effects of patient-controlled analgesia with hydromorphone or sufentanil on postoperative pulmonary complications in patients undergoing thoracic surgery: a quasi-experimental study

Objective

To compare the analgesic effects of patient-controlled intravenous analgesia (PCA) with hydromorphone and sufentanil after thoracic surgery on postoperative pulmonary complications (PPCs).

Methods

A total of 142 patients who were scheduled for thoracic surgery were randomly allocated to receive PCA with hydromorphone (group A: experimental group): hydromorphone 0.2 mg/kg + dezocine 0.5 mg/kg + ramosetron 0.6 mg diluted with normal saline to 200 mL; or with sufentanil (group B: control group): sufentanil 3.0μg/kg + dezocine 0.5 mg/kg + ramosetron 0.6 mg diluted with normal saline to 200 mL. The parameters of intravenous analgesia pump were set as background dose 4 ml/h, PCA dose 1 mL, locking time 15 min. Pain NRS (numerical rating scale), Ramsay sedation score, nausea or vomiting score were evaluated at 0 h, 6 h, 12 h, 24 h, 48 h after operation. The cases of PPCs (atelectasis, pulmonary infection, respiratory failure), CRP (C-reaction protein) and inflammatory cells (white cell count and percentage of neutrophils) and blood gas analysis at 12 h after operation, length of ICU and postoperative stay were recorded for each patient.

Results

Data of 136 patients were analyzed. Compared with group B (4[IQR:2,2]), the pain NRS in group A (2[IQR:4,4]) was significantly lower at 6 h after operation (P = 0.000). The CRP in group A (69.79 ± 32.13 mg/L) were lower than group B (76.76 ± 43.42 mg/L) after operation, but the difference was not significant (P = 0.427). No difference of nausea or vomiting was found between group A (7.3%) and group B (5.8%) postoperatively (P = 0.999). The PPCs were happened in 11 patients in group A (16.2%) and 22 patients in group B (32.4%) and the difference between two groups was significant (P = 0.027). Seven patients in group A (10.3%) and eighteen patients in group B (26.5%) had clinical evidence of pneumonia and the difference between two groups was significant (P = 0.014). The length of ICU and postoperative stay in group A were 2.73 h and 1.82 days less than group B respectively but the differences were not significant (P = 0.234, P = 0.186 respectively).

Conclusion

Compared with sufentanil, hydromorphone may provide better postoperative analgesic effect with less pulmonary complications for patients undergoing thoracic surgery, and it may accelerate patients’ rehabilitation.

Trial registration

Randomized Controlled Trials ChiCTR1800014282c. Registered 3 January 2018.

Oxygen therapy in acute exacerbations of chronic obstructive pulmonary disease

Acute exacerbations of chronic obstructive pulmonary disease (COPD) are important events in the history of this debilitating lung condition. Associated health care utilization and morbidity are high, and many patients require supplemental oxygen or ventilatory support. The last 2 decades have seen a substantial increase in our understanding of the best way to manage the respiratory failure suffered by many patients during this high-risk period. This review article examines the evidence underlying supplemental oxygen therapy during exacerbations of COPD. We first discuss the epidemiology and pathophysiology of respiratory failure in COPD during exacerbations. The rationale and evidence underlying oxygen therapy, including the risks when administered inappropriately, are then discussed, along with further strategies for ventilatory support. We also review current recommendations for best practice, including methods for improving oxygen provision in the future.

Role of estimation of arterial blood gases in the management of stridor

AIM

We studied the epidemiology and etiology of stridor in our patients along with the role of arterial blood gas (ABG) analysis in their management. We also reviewed their prognostic indices and the clinical outcomes.

MATERIALS AND METHODS

It was a prospective study in a tertiary referral hospital in which 72 patients presenting with stridor, were independently evaluated by 3 different clinicians and clinically classified into mild, moderate and severe. Based on ABG values (pH, PO2, PCO2), we defined 3 groups of patients viz, those in respiratory failure, impending respiratory failure and those with no evidence of failure. Treatment was directed at the cause of stridor. Clinical outcomes were assessed and results classified as resolved, improved, stable and death.

RESULTS

Out of 72 patients, kappa coefficient of agreement between the 3 observers were found to be 0.014, indicating poor interobserver reliability for the working clinical classification. However, ABG analysis indicated otherwise, with 6 patients in respiratory failure, 19 progressing to impending failure. Hence we complied by the more objective ABG analysis in planning management. Laryngomalacia in children and hypopharyngeal malignancies in adults were found to be the most common causes of stridor in our study. As compared to other conditions, laryngomalacia in children had a poorer outcome (p = 0.001).

CONCLUSION

Early detection of impending respiratory failure was instrumental in achieving better clinical outcomes in our patients presenting with stridor. Thus we inferred that ABG analysis is a valuable tool in the effective management of stridor.

Hypercapnic respiratory failure: from the past to the future

The importance of non‐invasive ventilation

Adult Chiari malformation and sleep apnoea

Chiari malformation (CM) is primarily characterised by herniation of the cerebellar tonsils through the foramen magnum. Clinically, two main types of CM represent the vast majority of cases: type I (in adults) and type II (in infants). CM may result in neuronal impairment of the brainstem, upper spinal cord and cranial nerves. Part of the afferent and efferet systems and the central respiratory controlling system are located in the cranium-cervical transition and may be damaged in these pathologies, leading to respiratory disorders, such as respiratory failure and death. The ventilatory responses to exogenous and endogenous stimuli, such as responses to hypoxia and hypercapnia, are usually diminished, and apnea may be manifested and detected during sleep, allowing for the diagnosis. This study is a review of the relationship between sleep apnoea and adult CM.

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.

A prospective controlled study of sleep respiratory events in patients with craniovertebral junction malformation

Object. Craniovertebral junction malformation (CVJM) or Chiari malformation in adults, with or without syringomyelia and basilar invagination, produces neuronal dysfunction of the brainstem, cerebellum, cranial nerves, and upper spinal cord. The respiratory center and some of its afferent and efferent components can be altered in these diseases. The authors studied patients with and without CVJM to determine whether this physical feature contributed to sleep disturbances.

Methods. Respiratory manifestations during sleep were studied prospectively, by using whole-night polysomnography, in 32 symptomatic patients (CVJM group) and 16 healthy volunteers (control group). Patients with CVJM presented with more sleep disturbances (reports of snoring and apnea) than those in the control group. The apnea/hypopnea index values were higher in patients with CVJMs than in the control group (13 ± 15 compared with 3 ± 6; p = 0.007) and the rate of central sleep apneas was higher in the CVJM than in the control group (22 ± 30 compared with 4 ± 8%; p = 0.009). The apnea/hypopnea index was highest in the subgroup with basilar invagination than in the other subgroups. The central apneic episodes were more frequent in the patients with basilar invagination (35 ± 40%; p = 0.001) and in those with syringomyelia (17.6 ± 24.6%; p = 0.003) than in the control group (4 ± 8%). Patients with symptomatic CVJM, especially those with basilar invagination, presented with more sleep respiratory compromise than did those in the control group.

Conclusions. The incidence of sleep apnea/hypopnea syndrome is significantly higher in patients with CVJM.

Respiratory disturbances during sleep in syringomyelia and syringobulbia

OBJECTIVE

To determine the frequency and types of abnormalities of respiratory control during sleep in syringomyelia and syringobulbia and to provide a basis to predict patients at risk of sudden death.

METHODS

Thirty patients (15 male and 15 female; mean age 39.0 +/- 12.6 years) with communicating syringomyelia were divided into two groups: those with evidence of syringobulbia (17 patients) and those without compromise of the medulla or syringomyelia (13 patients). Patients were studied with pulmonary function studies and polysomnography. Respiratory center sensitivity to CO2 (rebreathing technique) was measured in 9 patients.

RESULTS

Severely affected patients had mild-to-moderate restriction and individual patients had bilateral diaphragmatic or vocal cord palsy, abnormal respiratory rhythm, prolonged inspiratory time, or an abnormal respiratory response to CO2. Very prolonged central, obstructive, and mixed sleep apneas with low O2 saturation values and a fixed heart rate were recorded in most patients with syringobulbia. Five patients developed severe respiratory complications and died during a follow-up period of 10 years. Respiratory abnormalities failed to correlate with syrinx size.

CONCLUSIONS

Severe abnormalities in respiratory rhythm generation during sleep occur in patients with syringobulbia. The respiratory disturbances are not due to muscle weakness and they are not correlated with the size of the cavity. The combination of dysphagia and dysphonia in patients with longstanding syringomyelia and syringobulbia predicted likelihood of respiratory disturbances during sleep.

Reversible hypercapnia in chronic obstructive pulmonary disease: a distinct pattern of respiratory failure with a favorable prognosis

PURPOSE

Hypercapnia is regarded as a poor prognostic indicator in chronic obstructive pulmonary disease (COPD), but many patients hospitalized with hypercapnia associated with an acute exacerbation of COPD revert to normocapnia during recovery. We wished to determine if this reversible hypercapnia represents a distinct pattern of respiratory failure in COPD, or simply a stage in the progression to chronic hypercapnia. We therefore compared the long-term clinical progression and survival of COPD patients with reversible hypercapnic respiratory failure (defined as type 2.1) to those with normocapnic (PaCO2 < 50 mm Hg; type 1) and also to those patients with chronic hypercapnic (PaCO2 > 50 mm Hg) respiratory failure (defined as type 2.2).

PATIENTS AND METHODS

We prospectively followed for 5 years a cohort of 85 patients who had been admitted as emergencies during a 1-year period to the respiratory unit of a University teaching hospital with an exacerbation of COPD complicated by respiratory failure (PaO2 < 60 mm Hg). The main long-term outcome measures were survival and blood gas changes.

RESULTS

Sixty-eight (80%) patients survived the initial admission, and 17 (27%) survived 5 years. PaCO2 rose substantially more during exacerbations in type 2.1 patients (mean 15.8 mm Hg), compared with type 2.2 (mean 6.8 mm Hg) and type 1 patients (mean 1.5 mm Hg). We analyzed 149 subsequent admissions among the survivors over the following 5 years. Type 2.1 patients had a better 5-year survival (28%) than type 2.2 (11% survival; P < 0.05), and similar to type 1 patients (33% 5-year survival). Only 24% of reversible hypercapnic patients developed chronic hypercapnia during long-term followup.

CONCLUSIONS

The data support reversible hypercapnia being a distinct manifestation of respiratory failure in COPD, with a similar prognosis to that of normocapnic respiratory failure.

Risk of sudden death during sleep in syringomyelia and syringobulbia

Clinical, respiratory, and polysomnographic findings in three patients with syringomyelia and syringobulbia who developed severe respiratory complications are described. Neurological examination showed evidence of IXth and Xth cranial nerve involvement with dysphagia and dysphonia, but there were no complaints of serious sleep difficulties. Two patients died during sleep and the other was resuscitated during a nap. All patients showed moderate restrictive ventilatory defects with reduced maximal buccal pressures and one also showed a low ventilatory response to CO2 rebreathing. Protracted central, obstructive, and mixed apnoeas and hypopnoeas were commonly observed during sleep. There were no changes in heart rate during these events. A combination of respiratory and cardiovascular mechanisms might have been responsible for the severe complications described.

Intraabdominal infection: pulmonary failure

Since its first description in 1967, the mortality of the adult respiratory distress syndrome (ARDS) has remained unchanged despite the increasing sophistication of supportive techniques. Few patients now die of refractory hypoxemia, the majority succumbing to the multiple systems organ failure syndrome, commonly due to sepsis. Sepsis is both the most common cause of ARDS, usually involving the abdomen, and the most frequent complication, usually affecting the lungs. ARDS is, thus, increasingly seen as the pulmonary component of multiple systems organ failure, triggered by the systemic response to sepsis. In critically ill patients, impairment of hepatic function and of the barrier function of the gut mucosa allows translocation of endotoxin derived from the aerobic Gram-negative bacteria within the gut. This releases mediators which are responsible for the activation of cellular and humoral cascades, resulting in the pathological changes seen in ARDS. This sequence of events underlines the importance of therapies directed at abnormal colonization of the gastrointestinal tract and elimination of the gut endotoxin pool. Selective decontamination of the digestive tract is attractive in that it attacks the problem from 2 sides: first, by eliminating colonization, it appears effective in preventing secondary infection and, second, it may also play a role in reducing the enteric endotoxin pool. Recent descriptions of pathological oxygen supply dependency in both ARDS and septic patients emphasize the similarity of pathophysiological abnormalities in the 2 conditions. Intensive supportive therapy to achieve adequate oxygen transport and aggressive investigation and surgical management of septic foci are the cornerstones of management of the established syndrome.

Malignant asthma presenting as right heart failure

Studies are reported of four patients (all lifetime non-smokers) who presented with right heart failure as a consequence of unrelieved asthmatic airways obstruction. These patients demonstrated severe airways obstruction with crackles on auscultation and hypercapnia. As shown here, such a presentation, without the usual pattern of dyspnoea and wheeze, tends to obscure the diagnosis and delays effective treatment. In three of the patients, treatment to relieve airways obstruction improved gas exchange, and the heart failure resolved. In the remaining patient, improvement was limited, and death ensued from respiratory failure. In patients who present with right heart failure, a relationship with airways obstruction and respiratory failure should be considered and assessed by objective tests. Delays in the effective treatment of these patients may result in the progression of their disease to a stage at which airways obstruction no longer responds to medical therapy.

Continuous positive airway pressure in bronchiolitis

Over five years 23 infants with evidence of respiratory insufficiency due to bronchiolitis were managed with continuous positive airway pressure (CPAP). This was applied through either a short nasal cannula (14 patients) or an endotracheal tube (nine patients). Clinical improvement was seen in all patients, and there were significant falls in mean respiratory and pulse rates and pressure of carbon dioxide (PCO2). Seven infants with PCO2 values exceeding 8.0 KPa (60.2 mm Hg) responded particularly well. CPAP is effective in bronchiolitis, and when applied by the nasal route it is relatively free from complications.

Respiratory failure revisited: acute exacerbations of chronic bronchitis between 1961-68 and 1970-76

Factors determining survival have been analysed retrospectively in 157 admissions of 135 patients with an acute exacerbation of chronic bronchitis and emphysema causing hypoxaemia and carbon dioxide retention. All were treated with controlled oxygen therapy. The death-rate increased with the age of the patient, but was not correlated with the age of the patient, but was not correlated with the severity of hypoxaemia on admission, when the patient was breathing air. The death-rate was significantly higher in those patients in whom arterial [H+] rose above 55 nmol/1 (pH = 7.26) during controlled oxygen therapy. The absence of a rise in the arterial PCO2 during controlled oxygen therapy was not necessarily indicative of a good prognosis, since 5 out of 18 patients showing this response subsequently died in that admission. Only 28% of the 111 patients who left hospital alive survived for five years.

Arterial hypoxia in acute pancreatitis

Severe arterial hypoxia while breathing ambient air (Pao2 less than 60 mm Hg) was recorded in 38 (45 per cent) of a group of 84 patients with acute pancreatitis when arterial blood gas monitoring was performed during the first week of illness. This contrasted with an incidence of 19 per cent severe hypoxia in a heterogeneous group of 68 patients with acute abdominal pain admitted as surgical emergencies. Clinical evidence of respiratory embarrassment was rarely present in either the patients with acute pancreatitis or the other patients. Arterial hypoxia was related to the prognosis in both groups. It is recommended that all patients with acute pancreatitis have routine arterial blood gas monitoring performed during the first 5 days of illness. Furthermore, all older patients (over 60 years) and younger patients with moderate hypoxia (Pao2 less than 70 mm Hg) should be given supplementary humidified oxygen. An awareness of occult respiratory insufficiency in surgical emergency admissions, and especially in acute pancreatitis, is of importance.

Acute effects of intermittent positive pressure breathing in patients with chronic obstructive lung disease

The immediate effects of intermittent positive pressure breathing (IPPB) on air were studied in seven patients (age 55-73 years) with advanced chronic obstructive lung disease (COLD) and with chronic respiratory insufficiency. Dynamic lung compliance was reduced by an average of 25% by IPPB, while inspiratory resistance increased by 40%. Distribution of inspired gas, as determined by nitrogen washout, became more even with IPPB. Respiratory frequency was not altered, whereas total ventilation increased by 25% during IPPB and PaCO2 was reduced. Oxygen uptake was reduced by 6%. PaO2 did not change during IPPB but had decreased by an average of 20% 10 minutes after IPPB and then slowly improved; PaCO2 did not change after IPPB. The pressures in the right atrium, pulmonary artery, and in pulmonary wedge position all increased approximately 2 mm Hg (approximately 2 cm H2O) with IPPB, while intrathoracic pressure rose on an average by 5 cm H2O, the transmural pressures thus being lowered during IPPB. The pulmonary vascular resistance was not significantly altered by IPPB, whereas the systemic vascular resistance rose 25%. Cardiac output was reduced approximately 20% and venous admixture almost 50%.

Studies on pulmonary function in patients during respiratory treatment. Diagnostic and prognostic evaluations

Twenty-nine patients, divided into three groups: 1) chronic obstructive pulmonary disease; 2) acute or chronic pulmonary disease with left heart failure; 3) respiratory insufficiency after peritonitis, pancreatitis, and/or sepsis, were studied during respirator treatment with regard to gas exchange, breathing mechanics and central circulation. The dead space ventilation was somewhat greater in group 1 than in the other groups. The alveolar-arterial oxygen tension difference was least in group 1, greater in group 2 and extremely high in group 3. Neither dynamic compliance of the thorax nor inspiratory resistance showed any significant differences between the groups. The cardiac output had the highest values in group 3. The venous admixture was generally small in group 1 and extremely large in group 3. The pulmonary artery pressures were highest in group 2. Three variables proved to be valuable when assessing the prognosis of a patient: a large venous admixture; a large alveolar-arterial oxygen tension difference, and a high pulmonary artery pressure indicated a less favourable prognosis.

Managing respiratory distress syndrome in adults

Respiratory distress syndrome in adults may be produced by any of a number of causes resulting in similar pathophysiologic changes and having identical therapeutic implications. The most important factors in treatment are early recognition and early institution of therapy.

Behaviour of commercially prepared I-125 fibrinogen in metabolic studies

In-vivo studies of fibrinogen metabolism were carried out using an I-120 labelled preparation of fibrinogen supplied commercially by the Radiochemical Centre, Amerhsham for use in the diagnosis of deep venous thrombosis. These studies show that the material is suitable for obtaining the main metabolic parameters of clinical interest, though degradation products may be present initially or appear during storage. If suitable corrections are applied the results agree well with those of other authors.