Acute respiratory failure in the adult. 2

Curiosity, Opportunity, and Luck: Were the 1970s Different?

Control of Breathing Using an Extracorporeal Membrane Lung. By T Kolobow, L Gattinoni, TA Tomlinson, JE Pierce. Anesthesiology 1977; 46:138-41. Reprinted with permission. Body Position Changes Redistribute Lung Computed-Tomographic Density in Patients with Acute Respiratory Failure. By L Gattinoni, P Pelosi, G Vitale, A Pesenti, L D'Andrea, D Mascheroni. Anesthesiology 1991; 74:15-23. Reprinted with permission. Dr. Gattinoni's scientific career was primarily driven by curiosity. His generation was not formally trained, but he was part of a community of young and enthusiastic colleagues who were forging a new discipline: intensive care medicine. The most significant opportunity of Dr. Gattinoni's career was becoming the research fellow of a visionary genius, Dr. Theodor Kolobow, who focused on extracorporeal carbon dioxide removal after the failure of the first trial on extracorporeal membrane oxygenation. CO2 removal, by allowing control over the intensity of mechanical ventilation, opened the path to "lung rest" to prevent ventilator-induced lung injury. A unique opportunity for research was the spontaneous birth of a network of scientists who became friends in the European Group of Research in Intensive Care Medicine. In this environment, it was possible to develop core concepts such as the "baby lung" and to understand the mechanisms underlying computed tomography-density redistribution in the prone position. Physiology guided us in the 1970s, and understanding mechanisms remains of paramount importance today.

The future of mechanical ventilation: lessons from the present and the past

The adverse effects of mechanical ventilation in acute respiratory distress syndrome (ARDS) arise from two main causes: unphysiological increases of transpulmonary pressure and unphysiological increases/decreases of pleural pressure during positive or negative pressure ventilation. The transpulmonary pressure-related side effects primarily account for ventilator-induced lung injury (VILI) while the pleural pressure-related side effects primarily account for hemodynamic alterations. The changes of transpulmonary pressure and pleural pressure resulting from a given applied driving pressure depend on the relative elastances of the lung and chest wall. The term ‘volutrauma’ should refer to excessive strain, while ‘barotrauma’ should refer to excessive stress. Strains exceeding 1.5, corresponding to a stress above ~20 cmH₂O in humans, are severely damaging in experimental animals. Apart from high tidal volumes and high transpulmonary pressures, the respiratory rate and inspiratory flow may also play roles in the genesis of VILI. We do not know which fraction of mortality is attributable to VILI with ventilation comparable to that reported in recent clinical practice surveys (tidal volume ~7.5 ml/kg, positive end-expiratory pressure (PEEP) ~8 cmH₂O, rate ~20 bpm, associated mortality ~35%). Therefore, a more complete and individually personalized understanding of ARDS lung mechanics and its interaction with the ventilator is needed to improve future care. Knowledge of functional lung size would allow the quantitative estimation of strain. The determination of lung inhomogeneity/stress raisers would help assess local stresses; the measurement of lung recruitability would guide PEEP selection to optimize lung size and homogeneity. Finding a safety threshold for mechanical power, normalized to functional lung volume and tissue heterogeneity, may help precisely define the safety limits of ventilating the individual in question. When a mechanical ventilation set cannot be found to avoid an excessive risk of VILI, alternative methods (such as the artificial lung) should be considered.

The Necessity of Chest Physical Therapy for Thoracoscopic Oesophagectomy

Radical surgery for thoracic oesophageal cancer is highly invasive and often leads to respiratory complications; thoracoscopic surgery is a less-invasive alternative. We examined the need for chest physical therapy (CPT) after thoracoscopic oesophagectomy. Thirty-six consecutive patients, randomly selected for either thoracotomy or thoracoscopic surgery, were included in a randomized clinical trial and received CPT under the same protocol. During short-term post-operative follow-up, both groups showed a marked reduction in respiratory function and responded to CPT to the same extent, although 2 weeks after surgery some parameters of respiratory function were significantly higher in the thoracoscopy group. Thoracoscopic surgery has been reported to be less invasive than standard thoracotomy, but our results suggest that the procedure is also invasive with respect to respiratory function and that CPT should be performed before and after thoracoscopic surgery.

A review of leukofiltration in cardiac surgery: the time course of reperfusion injury may facilitate study design of anti-inflammatory effects

The systemic inflammatory response syndrome (SIRS) is a well-recognized phenomenon attending cardiopulmonary bypass (CPB) surgery. SIRS leads to costly complications and several strategies intended to ameliorate the symptoms have been studied, including leukocyte reduction using filtration. Although the body of work suggests that leukoreduction attenuates SIRS, discrepancies remain within the literature. The recent literature is reviewed, highlighting the areas where concordance is lacking. Investigations into many promising device-related technologies are often deterred by the high costs of clinical trials. Adding to costs is the fact that clinical end points generally require large sample sizes. An understanding, however, of the pathogenesis of reperfusion injury can guide the investigator to choose physiologic response measures that correlate well with clinical outcome, but feature low inherent variability, allowing for clinical trials with smaller sample sizes. With this goal in mind, a model for the pathogenesis of reperfusion injury is described. Using a model of reperfusion injury as underpinnings for the design of prospective pilot studies, we show that salvaged blood reinfused following CPB elicits time-dependent effects on pulmonary function as predicted by the model. Data are illustrative of principles that could expand the scope of clinical investigations designed to validate the use of physiologic response measures as correlates of clinical outcome. Such investigations would target surrogate markers of clinical outcome, measured at clinically relevant times. Once validated, these surrogate markers would, thereafter, become economical screening tools for clinical studies of device-related or pharmacological anti- inflammatory interventions.

Safety of withdrawing inhaled nitric oxide therapy in persistent pulmonary hypertension of the newborn

OBJECTIVE

Because of case reports describing hypoxemia on withdrawal of inhaled nitric oxide (I-NO), we prospectively examined this safety issue in newborns with persistent pulmonary hypertension who were classified as treatment successes or failures during a course of I-NO therapy.

METHODS

Randomized, placebo-controlled, double-masked, dose-response clinical trial at 25 tertiary centers from April 1994 to June 1996. Change in oxygenation and outcome (death and/or extracorporeal membrane oxygenation) during or immediately after withdrawing I-NO were the principal endpoints. Patients (n = 155) were term infants, <3 days old at study entry with echocardiographic evidence of persistent pulmonary hypertension of the newborn. Exclusion criteria included previous surfactant treatment, high-frequency ventilation, or lung hypoplasia. Withdrawal from treatment gas (0, 5, 20, or 80 ppm) started once treatment success or failure criteria were met. Withdrawal of treatment gas occurred at 20% decrements at <4 hours between steps.

RESULTS

The patient profile was similar for placebo and I-NO groups. Treatment started at an oxygenation index (OI) of 25 +/- 10 (mean +/- SD) at 26 +/- 18 hours after birth. For infants classified as treatment successes (mean duration of therapy = 88 hours, OI <10), decreases in the arterial partial pressure of oxygen (PaO(2)) were observed only at the final step of withdrawal. On cessation from 1, 4, and 16 ppm, patients receiving I-NO demonstrated a dose-related reduction in PaO(2) (-11 +/- 23, -28 +/- 24, and -50 +/- 48 mm Hg, respectively). For infants classified as treatment failures (mean duration of therapy = 10 hours), no change in OI occurred for the placebo group (-13 +/- 36%, OI of 31 +/- 11 after the withdrawal process); however a 42 +/- 101% increase in OI to 46 +/- 21 occurred for the pooled nitric oxide doses. One death was possibly related to withdrawal of I-NO.

CONCLUSION

For infants classified as treatment successes, a dose response between the I-NO dose and decrease in PaO(2) after discontinuing I-NO was found. A reduction in I-NO to 1 ppm before discontinuation of the drug seems to minimize the decrease in PaO(2) seen. For infants failing treatment, discontinuation of I-NO could pose a life-threatening reduction in oxygenation should extracorporeal membrane oxygenation not be readily available or I-NO cannot be continued on transport.

When to ventilate

Within the setting of trauma, there are many indications for intubation and ventilation, but the ultimate aims are always the same. These are to ensure airway patency and security, provide an acceptable level of arterial oxygenation at the lowest possible inspired oxygen concentration, control arterial carbon dioxide tension and optimize pulmonary and systemic blood flow.

The clinical situation, developing trends, and the experience of the individual concerned will all influence the decision to intubate and ventilate the patient who has suffered trauma. This paper considers the ‘rule-of-thumb’ indications for intubation in the emergency room and discusses the factors which may influence their interpretation.

The impact of prostanoids on pulmonary gas exchange during abdominal surgery with mesenteric traction

We investigated the effect of intravenous (iv) ibuprofen on prostanoid release and on pulmonary gas exchange after abdominal mesenteric traction (MT) during either abdominal aortic surgery or pancreas resection. In a prospective, randomized, double-blind study, 400 mg ibuprofen (pancreas n = 13, aorta n = 13) or a placebo (pancreas n = 13, aorta n = 13) was administered iv before skin incision. MT was applied uniformly. The prostanoid plasma concentrations, venous admixture (Q(va)/Q(t)), and PaO2/FIO2 ratio were determined at baseline (before MT) and 5, 15, 45, and 90 min after MT. Patients who underwent aortic surgery were older and exhibited a lower preoperative PaO2 than those who underwent pancreas resection. Placebo-treated patients revealed a 30-fold peak increase in 6-keto-prostaglandin F1alpha (stable metabolite of prostacyclin) levels after intentional MT during aortic as well as pancreatic operations. This response was accompanied by an increase in Q(va)/Q(t) (ibuprofen: pancreas 7% +/- 1%, aorta 14% +/- 2%; placebo: pancreas 16% +/- 3%, aorta 26% +/- 3%/15 min after MT [mean +/- SEM, P < 0.05, placebo vs ibuprofen]), which resulted in decreased PaO2/ FIO2 ratio only in the aortic surgery patients (ibuprofen: 310 +/- 19; placebo: 237 +/- 24 15 min after MT, [mean +/- SEM, P < 0.05]). The authors conclude that ibuprofen-pretreated patients demonstrated almost constant prostanoid levels without changes in pulmonary gas exchange after MT.

Estimation of condensed pulmonary parenchyma from gas exchange parameters in patients with multiple trauma and blunt chest trauma

Pulmonary gas exchange in correlation with condensed lung volume was prospectively studied in 10 patients with multiple injuries and blunt chest trauma. The purpose was to find nomograms that allow the estimation of the extent of pulmonary density from gas exchange parameters. The condensed lung volume was determined planimetrically from serial transverse sections of chest computed tomographic scans. There was no correlation between condensed lung volume and mean pulmonary artery pressure, pulmonary vascular resistance, systemic vascular resistance, or cardiac index and a week negative correlation to the oxygenation index (PaO2/FIO2) (r2 = 0.46) and to the total static lung compliance (r2 = 0.29). A strong correlation between pulmonary density and intrapulmonary shunt fraction (Qs/Qt) (r2 = 0.95) as well as alveoloarterial PO2 difference (P[A-a]O2) (r2 = 0.86) was evident. By using linear regression equations (linear regression line with 95% confidence interval), nomograms were calculated. The extent of pulmonary density can easily be obtained from these nomograms by measuring Qs/Qt or P(A-a)O2. The presented nomograms may be helpful in monitoring the effect of treatment in patients with blunt chest trauma.

Refractory hypoxemia due to intrapulmonary shunting associated with bronchioloalveolar carcinoma

Bronchioloalveolar carcinoma caused severe refractory hypoxemia due to intrapulmonary shunting in a patient. Preoperative evaluation by occlusion of the pulmonary lobar artery supplying the tumor showed normalization of the arterial oxygen saturation. Resection of the involved lobe corrected the intrapulmonary shunting, and the patient required no further supplemental oxygen. However, with recurrence of the tumor over the next 6 months the patient became progressively more hypoxemic and died.

Assessment of respiratory distress in the asthmatic child: when should we be concerned?

The physician caring for the acutely ill asthmatic child has a wide variety of signs and systems to assist in assessment. An assessment of the severity of the disease should be based on the medical history, and signs and symptoms due to hypoxia on various target organs. Laboratory evaluation, while helpful, has limited applicability in the young child but should be used as an adjunct to clinical assessment where necessary. Based on the history, physical examination, and laboratory assessment (when appropriate), acute asthma symptoms should be categorized as mild, moderate, or severe. Treatment then can be tailored to disease severity.

Adrenergic vasopressor agents and mechanical ventilation for the treatment of experimental septic shock

OBJECTIVE

Vasopressor agents and mechanical ventilation are routine interventions for the treatment of sepsis complicated by hypotension. It was our hypothesis that such treatment singly or in combination increases the duration of survival.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Thirty male Sprague-Dawley rats anesthetized with intraperitoneal injection of pentobarbital.

INTERVENTIONS

Peritonitis was induced by cecal ligation and spillage of cecal contents into the abdominal cavity. The first phase of this study was performed on 15 spontaneously breathing Sprague-Dawley rats that were randomized to three groups of five animals each. One group received treatment with dopamine. The second group received norepinephrine. The third group received only the diluent as a placebo. Concentrations of the vasopressor agents were increased such that mean arterial pressure was maintained at approximately 80% of baseline values; the volumes infused were kept constant. For the second phase of this study, the grouping of animals and the techniques of study were identical, except that rats were mechanically ventilated.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure was best maintained with norepinephrine. However, no statistically significant differences in duration of survival, cardiac index, arterial blood lactate concentration, or arterial and venous PCO2 and PO2 values were identified between groups. With mechanical ventilation, survival was prolonged (p < .01). Survival was increased from an average of 291 mins to 342 mins with dopamine, from 257 mins to 352 mins in placebo controls, and from 280 mins to 329 mins with norepinephrine. Again, no significant differences in hemodynamic and blood gas measurements, or in the duration of survival between vasopressor-treated and control animals were documented.

CONCLUSIONS

No benefit or detriment was demonstrated when vasopressor agents were administered to sustain arterial pressure in the course of experimental peritonitis in this murine model of septic shock. This finding contrasted with highly significant prolongation of survival when animals were mechanically ventilated. There was no evidence that routine vasopressor therapy, under these controlled experimental conditions in rats, improved duration of survival.

Initiation of mechanical ventilation in the emergency department

Mechanical ventilation is frequently initiated by emergency physicians. Further, the physician on duty in the emergency department is frequently responsible for evaluating ventilated patients who decompensate in the intensive care unit when other physicians are not present in the hospital. A bewildering array of features on new mechanical ventilators has made their appropriate and effective use increasingly complex. Knowledge of the pathophysiology of acute respiratory failure and changes in lung physiology during positive pressure ventilation will aid the emergency physician in choosing an appropriate ventilator modality and initial settings to maximally benefit patients with respiratory insufficiency due to various causes. An appreciation of the adverse effects of mechanical ventilation and problems commonly encountered in patients on ventilators will prepare the emergency physician to rapidly assess and effectively manage the patient who deteriorates in this setting.

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.

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.

[Multiple trauma: definition, shock, multiple organ failure]

Multiple organ failure (MOF) following major trauma occurs in response to perfusion deficits, a persistent inflammatory focus, or a persistent focus of dead and/or injured tissue. Several pathophysiologic aspects are considered relevant to current clinical practice. Their application in settings of trauma and surgical sepsis reduces overall mortality and incidence of multiple organ failure. With regard to the pathophysiologic background (I) microcirculatory resuscitation, (II) source control, and (III) metabolic support appear to be important therapeutic principles. (I) Microcirculatory Resuscitation: Since time is a critical factor in damage control, resuscitation and restoration of microvascular perfusion needs to occur as soon as possible if multiple system organ failure is to be avoided during the later time course. (II) Source control: The best treatment for multiorgan failure appears to be prevention. With early, aggressive control or removal of risk factors for multiple organ failure, namely early surgical intervention for control of hemorrhage, control of potential septic sources, decompression, and early fracture stabilization reductions in the incidence and mortality of MOF have been observed. Metabolic support: Malnutrition appears to be an important cofactor in morbidity and mortality. (III) Metabolic support needs to be started early and prior to the phenomenon of nitrogen retention during the hypermetabolic state of multiple organ failure.

Variable apparatus deadspace

A variable apparatus deadspace was used to maintain normocapnia during artificial ventilation of the lungs in anaesthetised adults. End-tidal carbon dioxide tension could be varied, if the need arose, within the range 4.0-5.2 kPa in both open and circle breathing systems when a fixed tidal volume of 12 ml.kg-1 and minute volume ventilation of 120 ml.kg-1.min-1 were employed.

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)

Assessment of the efficiency of pulmonary oxygenation. The choice of oxygenation index

Oxygen-derived indices are often used as alternatives to determination of venous admixture (Qva/Qt) when a pulmonary arterial catheter is not in use, but the question of which more accurately indicates the efficiency of oxygenation is controversial. The theoretical relationships between six measures of oxygenation (PaO2, SaO2, P(A-a)O2, PaO2/FIO2, P(A-a)O2/PaO2, PaO2/PAO2) and venous admixture were analyzed with special reference to the influence of the concentration of inspired oxygen (FIO2). In addition, the predictability of Qva/Qt was evaluated on the basis of 100 authentic sets of arterial and mixed venous blood gas data. Of the above six indices, PaO2/FIO2 was most accurate (r = 0.88), but was far from independent of the FIO2 used. However, a direct Estimate of Venous Admixture (EVA) - based on arterial blood analysis and with C(a-v)O2 assigned a value of 50 ml.l-1 - predicted Qva/Qt still better (r = 0.95). It is concluded that when mixed venous blood gas data are lacking, EVA is the preferable measure of oxygenation.

Intrapulmonary haematoma complicating mechanical ventilation in patients with chronic obstructive pulmonary disease

Intrapulmonary haematomas occurred during mechanical ventilation of two patients with advanced chronic obstructive pulmonary disease and bullous dystrophy. In both cases, the haematomas were revealed by blood-stained aspirates, a fall in haemoglobin level, and the appearance of radiological opacities. Haematoma occurrence in the area of a bulla which recently has rapidly increased in size, suggests that the haematoma is due to the rupture of stretched vessels embedded in the wall of the bulla.

The artificial ventilation of acute spinal cord damaged patients: a retrospective study of forty-four patients

The case histories of the 44 ventilated spinal cord damaged patients who have been treated at the Mersey Regional Spinal Injuries Centre prior to 1985 were reviewed. Complications of ventilation were commoner in patients whose ventilation was initiated prior to transfer to the specialised centre. Inappropriate early management before or during transfer to the spinal injuries centre led to the need for ventilation in several cases. Spinal cord damaged patients should be transferred to a specialised comprehensive centre as soon as possible after injury so that the requirement for ventilation can be minimised, the incidence of cardiac and respiratory arrest reduced, optimal methods of ventilation and weaning employed and global emotional and educational support provided from the outset for the patient and his family.

Respiratory function during pressure support ventilation

Pressure support ventilation (PSV) is a pressure assist form of mechanical ventilatory support that augments the patient's spontaneous inspiratory efforts with a clinician selected level of positive airway pressure. To understand the effects of PSV on respiratory function, experiments were performed on 15 stable patients requiring synchronized intermittent mandatory ventilation (SIMV), as well as on a mechanical model simulating these patients' ventilatory systems. In the clinical study, gas exchange, airway pressures, blood pressure and heart rate were measured while SIMV was replaced by enough PSV to approximate the baseline SIMV tidal volume (VT). Measurements were repeated while this PSV level was then reduced in three 5 cm H2O steps every 10 to 15 minutes. It was found that PSV was a reasonable form of mechanical ventilatory support in patients with spontaneous ventilatory drives. It improves patient comfort, reduces the patient's ventilatory work, and provides a more balanced pressure and volume change form of muscle work to the patient. The clinical significance of these properties during the weaning process remain to be determined.

Perfluorochemicals and hyperbaric oxygen in radiation therapy

It has been postulated that tumors contain hypoxic cells of decreased radiation sensitivity, which limit curability with radiation therapy. Hyperbaric oxygen has been used in an attempt to improve tumor oxygenation. The nature of the oxygen concentration-radiation sensitivity relationship (oxygen increases the slope of the radiation cell survival curve) suggests that a small number of hypoxic cells, as few as one in one million, would limit tumor curability. Oxygen moves by diffusion from the capillary into the tumor. An increase in partial pressure in the capillary will increase the effective diffusion distance. To improve tissue oxygenation effectively the partial pressure of oxygen in blood must be significantly increased throughout the length of the capillary, in particular at the venous end. Theoretical considerations indicate that hyperbaric oxygen as presently used in radiation therapy, 3 ATA, would lead to only marginal improvement. PartO2 may be as much as 0.8 atm below that of the inspired gas; this plus the consumption of oxygen along the length of the capillary lead to predictions of values for PEnd CapO2 of less than twice normal. Such considerations explain the rather limited success of hyperbaric oxygen with radiation therapy. Thus it is unnecessary to postulate an absence of hypoxic cells to explain this clinical observation. In the presence of perfluorocarbon micelles the non-hemoglobin-bound oxygen carrying capacity of blood is significantly increased. Theoretical considerations predict that the difference between PartO2 and PO2 of the inspired gas should be decreased. Furthermore, the nonhemoglobin-bound oxygen carrying capacity should be adequate to satisfy tissue consumption requirements without unloading hemoglobin, thereby avoiding the "PO2 buffering effect of hemoglobin" and permitting a significant increase in PO2 throughout the capillary length. This effect has been demonstrated using a rodent tumor model.

Blood volume following diuresis induced by furosemide

Changes in blood volume were investigated following intravenous injection of a single dose of furosemide in 21 patients with pulmonary edema. In a subset of 10 patients in whom the blood urea nitrogen level was 11.4 +/- 2.2 mg/dl and the serum creatinine level was 1.3 +/- 0.1 mg/dl and in whom total urine output exceeded 1 liter over a four- to six-hour interval ("diuretic" group), no significant change in plasma or total blood volume was observed, nor were there any significant changes in hematocrit. In a "nondiuretic" group of 11 patients who had moderately decreased renal function (blood urea nitrogen level 59.3 +/- 13.0 mg/dl and serum creatinine level 2.3 +/- 0.3 mg/dl) and in whom total urine output was less than 1 liter over the four- to six-hour interval, there was a significant increase in blood volume with a concomitant decrease in hematocrit and hemoglobin levels. Furosemide-induced diuresis therefore did not deplete intravascular volume. To the contrary, actions of furosemide that were independent of its diuretic action were associated with an expansion of plasma volume in the absence of diuresis. This may be related to the venous capacitance effects of furosemide with lowering of venous resistance and, therefore, lowering of the capillary hydrostatic pressure. In addition, there was an increase in colloid osmotic pressure. Both mechanisms increase the effective oncotic pressure gradient, which favors reabsorption of extravascular (edema) fluid. It is concluded that intravascular volume was therefore replenished at a rate equal to or in excess of the volume removed by diuresis.

Bedside evaluation of respiratory distress

Observations made at the time of the first trial of independent ventilation in 112 episodes of mechanical ventilatory support led to identification of a group of indicators, each of which, when present, was significantly associated (p less than 0.05) with a need for continued mechanical ventilation and/or with death. Six of these were potentially suitable for use in a format for clinical assessment of the risk of respiratory failure: pulse over 120 or under 70 beats per minute, respiratory rate of over 30, palpable scalene muscle recruitment in inspiration, palpable abdominal tensing in expiration, presence of irregular irregularity of respiratory rhythm with apneic pauses of varying duration, and coma or any condition preventing a patient from responding appropriately to commands aimed at producing ventilatory movements like those needed for vital capacity testing. When none of the six signs was present, there was a 90 percent chance of a favorable outcome. With one or two indicators positive, more than 50 percent of the subjects required further ventilatory support or died. There were no favorable outcomes when three or more of the signs were present together.

Pathophysiology of bacteremia

Despite the frequency and importance of both nosocomial and "community-acquired" bacteremia, definitive information concerning crucial pathophysiologic events in human bacteremia remains sparse. An extensive variety of clinical manifestations, such as fever, rigors, shock, altered circulatory dynamics, cutaneous manifestations changes in the coagulation, complement, and other mediator systems, and effects on the lungs, heart, kidney, liver, and other end organs, have been described, but it is difficult to determine the relative frequency of these events in bacteremia caused by different species. The extensive number of bacterial species capable of producing bacteremia and variations in the type of presentation, such as acute, asymptomatic, and chronic, even when bacteremia is produced by the same species, undoubtedly contribute to this difficulty and suggest that a variety of pathophysiologic mechanisms occur in various bacteremias. In contrast, the relative frequency of various manifestations and some pathophysiologic mechanisms have been better delineated in Gram-negative bacteremia. The development of bacteremia enhances the lethality of most types of localized infection and several studies have demonstrated a relation between the magnitude of bacteremia and the outcome of the disease. Among various pathophysiologic alterations, mechanisms involved in the production of fever have been delineated most clearly. Fever appears to reflect a "common pathway" with almost all infectious agents and results from release of endogenous pyrogen from phagocytic cells. Endogenous pyrogen regulates the thermostatic setting of the body through its effect on the anterior hypothalamus. Endogenous pyrogen seems identical with Interleukin 1 and exerts a variety of other biologic activities. An extensive number of bacterial components have been proposed as "effectors" and an equally large number of endogenous substances proposed as "mediators" of the pathophysiologic events in bacteremia. The importance of many of these effectors and mediators has been postulated largely on the basis of in vitro and animal studies. The lack of critical clinical studies hampers extrapolation of these experimental studies to human bacteremia. The development of more effective therapy for the complications of bacteremia, such as shock, will continue to be hampered until the mechanisms involved in the production of those pathophysiologic events that are crucial determinants of outcome have been delineated more precisely in human disease.

Adult-type respiratory distress syndrome in children. Experience with seven cases

Adult respiratory distress syndrome (ARDS) is not well recognized in children. We report seven individuals, ranging in age from 1.5 to 16 years. The clinical picture of ARDS reached a peak in 72 hours from admission and was associated with a 28.5 per cent death rate (2/7). In no case was an organism isolated, either from bronchial washings via a flexible bronchoscope or from open lung biopsy specimen. ARDS is characterized by severe damage to the alveolar-capillary unit and probably inadequate production of lung surfactant, resulting in severe hypoxia, hypoxemia, intrapulmonary shunting, and marked decline in pulmonary compliance. The prognosis remains poor in the pediatric age group. The pathophysiology of this entity is outlined, with guidance for monitoring and therapy.

Non-linear model of the mechanics of breathing applied to the use and design of ventilators

Respiratory treatment involves clinical problems which are often related to the pulmonary and circulatory condition of the patient. Choice of a proper respirator and its adequate use are very important for overcoming a good deal of the clinical problems which may arise. A good automatic ventilator should, under all circumstances, be capable of assuring a suitable gas exchange at the pulmonary level with as little alteration as possible to the physiological functions of the body. In this paper a non-linear model of the mechanics of breathing is used to examine: (1) the effects of four theoretical inspiratory flow patterns in intermittent positive pressure ventilation (IPPV); (2) the differences obtained with respect to IPPV when we use a positive end-expiratory pressure (PEEP) or a negative pressure in the expiratory phase (IPNPV); (3) the performances of four automatic ventilators at present on the market and commonly used in departments of anaesthesia and intensive care. The results obtained by simulation of the respiratory system indicate that, in practice, an ideal ventilator neither exists nor can be designed. The manner of using the ventilator leads to different results, more so than the theoretical inspiratory flow pattern or the type of ventilator used. The tables and graphs shown in the paper help to utilize the ventilator in such a way as to optimize the parameters which, each time, are considered the most important.

Optimum PEEP selection using a desk top computer

Considering the problem of the selection of an optimum end-expiratory pressure level in mechanically ventilated intensive care patients suffering from acute respiratory insufficiency a procedure is presented for the display of the physiological response to various end-expiratory pressures using an HP 9845 desk top computer. The response is generated as an interpolated curve using natural cubic spline functions. The method was applied in 15 intensive care patients. For any patient a proposed best level of end-expiratory pressure is obtained; moreover, the display allows an insight into the occurring physiological changes. This is completed by an estimation of the extent of the beneficial effect in individual cases.

Treatment of postoperative respiratory distress syndrome

We have studied 45 patients with postoperative adult respiratory distress syndrome (ARDS) who were treated by mechanical ventilation during the last four years. This period was divided into two periods, and the mortality and progress after treatment were analysed. The overall, mortality was 56%. In the first period this rate was as high as 76%, while in the second period this rate improved to 43%. This improvement in the second period was thought to have resulted from aggressive cardiorespiratory treatment and the diminution of infection. According to the course of ARDS after treatment, four types could be classified. Type 1 showed rapid improvement in respiratory function. Type 2 showed gradual improvement. Type 3 showed relapse of respiratory failure. Type 4 resisted mechanical ventilation. Patients of types 3 and 4 had extremely poor prognoses. Stricter management to avoid infection, specific treatment of multiple organ failure (which was seen frequently) seemed advantageous. High frequency positive pressure ventilation (HFPPV) may have some role in improving the respiratory function of the patients with ARDS.

The effect of smoke inhalation on pulmonary surfactant

This paper details efforts to define the primary pathophysiology of acute smoke inhalation without the variables of infection, burns, or fluid resuscitation. A standard dose of smoke (wood and kerosene) was delivered at 37 C to mongrel dogs. The parameters studied included blood gases, carboxyhemoglobin, pulmonary and systemic hemodynamics, respiratory mechanics, surface tension area curves as an indication of surfactant activity, and in vivo photomicroscopy. The FiO2 of the smoke was 17 volumes per cent; the carbon monoxide 17,000 ppm. Immediately following smoke exposure, dense, nonsegmental atelectasis developed. Hemodynamic changes were insignificant, but the PaO2 fell to 49 mmHg; the right to left shunt rose from 5 to 41%. Surfactant reduction was significant: enough to cause an increase in the minimum surface tension from 7 to 22 dynes/cm. This surfactant loss may explain the atelectasis seen and the marked instability of subpleural alveolar walls. The data collected are consistent and support the acute inactivation of surfactant as one of the primary pathophysiologic events in smoke inhalation. The clinical correlation is good; surfactant loss may explain why victims of smoke inhalation are so vulnerable to fluid administration if they have thermal burns as well effectiveness of medical devices.

Gas exchange, pulmonary mechanics and haemodynamics in adult respiratory distress syndrome: experimental results in Lewe miniature pigs

Adult respiratory distress syndrome (ARDS) is a common medical emergency in respiratory care complicating a great variety of traumas and diseases. An animal model from Lewe miniature pigs has been developed to study the ARDS under standardized conditions; it is based on aspiration pneumonitis, a disorder often observed in ARDS, injuring the lung alveolar surfactant system. The experimental study was conducted under neuroleptanalgesia. ARDS was produced by intratracheal application of hydrochloric acid (0.2 mol/l) in an amount of 1.0 ml/kg body wt. The animals were ventilated automatically by a standardized ventilatory pattern in IPP mode. In all animals the time course of oxygenation ratio (Pa,O2/F1O2), arterial CO2 tension (Pa,CO2), ratio of alveolo--arterial oxygen tension difference to inspired oxygen fraction (Aa,DO2/F1O2), oxygen exchange ratio ((AaDO2/Pa,O2), lung compliance (CL), inspiratory airway resistance (RrsI), dead space ratio VD/VT), pulmonary artery pressure (PAP) and systemic blood pressure were studied. Changes in quasi-static volume--pressure curves, percentage change in lung water content and gross pathological finding were used to integrate the findings into a system of pathophysiological changes in ARDS. The animal group to which hydrochloric acid was administered shows severe pulmonary distress leading to death within 3.5--7.5 h. No significant changes in the measured parameters could be observed in the control group over a 14 h period. The results suggest that aspiration pneumonitis in Lewe miniature pigs is very suitable to investigate various problems in pathogenesis of ARDS. The model provides reproducible results which correlate very well with findings in different ARDS states. The models serves both to compare clinical states and to search for newer therapeutic manoeuvres.