Retrieval of an IV catheter fragment from the pulmonary artery 11 years after embolization

The use of a peripherally inserted central catheter (PICC) is occasionally complicated by intravascular fracture and central embolization of the catheter fragment. We present a patient in whom a PICC fragment was retrieved from the pulmonary artery 11 years after embolization following its incidental detection. Despite a history of IV drug abuse and mitral regurgitation, this patient remained asymptomatic and without complications. The catheter fragment was retrieved since the patient was believed to be at risk for endocarditis. This may be the longest duration reported of an embolized catheter fragment that was successfully removed. As the natural history of asymptomatic-retained central venous foreign bodies remains unclear, the decision to remove them should be individualized. In selected cases, these foreign bodies may be retrieved without complications even several years after embolization.

The physiologic effects of inverse ratio ventilation

STUDY OBJECTIVES

The efficacy of inverse ratio ventilation in ARDS is not clear. Furthermore, the mechanism responsible has not been determined. We designed an animal study to determine if inverse ratio ventilation improves gas exchange and by what mechanism.

DESIGN

Prospective randomized, controlled design was used.

SETTING

University of Missouri Pulmonary/Critical Care Animal Laboratory.

PARTICIPANTS

Nine dogs with oleic acid-induced lung injury as control animals to assess stability of the model, nine in the experimental model.

INTERVENTIONS

Conventional ventilation with full recruitment extrinsic positive end-expiratory pressure (PEEP) was compared with two other modes of ventilation. One was inverse ratio with extrinsic PEEP and the second was inverse ratio with intrinsic PEEP equal to full recruitment PEEP. Full recruitment levels of PEEP were defined by optimizing compliance, then increasing PEEP by 2.5 cm/H2O. Each type of ventilation was maintained for 45 min after the edema had stabilized. Comparison of lung injury over time requires stability of the model over time. Therefore, we also assessed the stability of the preparation over time by examining compliance, extravascular lung water, and venous admixture in nine control dogs with equivalent lung injury over the same time span.

MEASUREMENTS AND RESULTS

Mean airway pressure was increased by both types of inverse ratio ventilation, while compliance remained stable. Venous admixture was reduced (conv=0.32+/-0.12, inverse ratio with extrinsic PEEP=0.24+/-0.10, inverse ratio with intrinsic PEEP=0.28+/-0.11) with inverse ratio with extrinsic PEEP, but the improvement was less with inverse ratio with intrinsic PEEP, even though the mean airway pressure was higher.

CONCLUSIONS

We conclude that increasing mean airway pressure by prolongation of the inspiratory time improves gas exchange in our model of ARDS, but when mean airway pressure is increased further, allowing the development of intrinsic PEEP, the beneficial effects on gas exchange are less. Increasing mean airway pressure with intrinsic PEEP is not equivalent to other methods of increasing mean airway pressure.

A method to produce sedation in critically ill patients

OBJECTIVE

To evaluate a protocol based on continuous infusion of a benzodiazepine and morphine to produce apnea/decreased respiratory effort as an adjunct to complex mechanical ventilation in patients with respiratory failure.

DESIGN

Observational report of consecutive patients.

SETTING

University medical intensive care unit.

PATIENTS

Seventeen consecutive patients with acute respiratory failure requiring high levels of sedation and/or paralysis to facilitate mechanical ventilation were studied.

INTERVENTIONS

Patients were started on a continuous infusion of a benzodiazepine and morphine soon after mechanical ventilation was instituted. The dosages of the benzodiazepine and morphine were increased to the end point of diminished respiratory effort or apnea depending on the clinical status of the patient and ventilatory mode. This regimen was supplemented with single doses of neuromuscular blocking agents (NMBAs) only as the dosages of benzodiazepine/narcotic were being titrated. The benzodiazepine/narcotic agents were then gradually reduced as the patient's condition improved, often using an oral route of administration.

MEASUREMENTS AND RESULTS

The benzodiazepine/morphine combination produced apnea and diminished respiratory effort in patients requiring sedation from 2 to 50 days, including those with hemodynamic instability, hepatic dysfunction, renal dysfunction, and sepsis. The combination allowed the use of NMBAs to be minimized. There was no evidence of worsened hemodynamic instability as a result of the administration of these agents. The gastrointestinal tract could be used for nutrition in 8 of the 17 patients.

CONCLUSIONS

Continuous infusion of a benzodiazepine and morphine controlled the respiratory rate in patients with severe respiratory failure requiring complex mechanical ventilatory support.

Acute respiratory distress syndrome

OBJECTIVE

To review the pathophysiology, epidemiology, and therapy of patients with acute respiratory distress syndrome (ARDS).

DATA SOURCES

Articles pertaining to the pathophysiology, epidemiology, and supportive therapy of ARDS were chosen from a computerized literature search. Recent review articles addressing the specifics of treatment in an intensive care unit are cited rather than restating these specific aspects.

DATA EXTRACTION

Primary literature was chosen in reference to the pathophysiology, epidemiology, and supportive therapy of ARDS. Both human and animal studies were included. Review articles were cited regarding areas of ARDS supportive therapy rather than citing the primary literature.

STUDY SELECTION

Only peer-reviewed primary literature sources were chosen to describe the specifics of pathophysiology and epidemiology. When human data were unavailable, animal studies were cited. Recent review articles were cited for specifics on supportive therapy.

DATA SYNTHESIS

Consensus regarding the definition of ARDS and the difficulties of performing large controlled trials in patients with ARDS has made development of new modalities problematic. Understanding the underlying pathophysiology and risk factors for mortality are key to supportive therapy. Although many pharmacologic agents are being tested in patients with ARDS, attention to the aspects of supportive therapy is the only method to decrease mortality.

CONCLUSION

The mortality of ARDS continues to be 70%. Pharmacists can play an active role in the supportive therapy of patients with ARDS, which is currently the only way to impact mortality.

Nursing-based protocol for treatment of alcohol withdrawal in the intensive care unit

Inappropriate benzodiazepine dosing in patients exhibiting signs of alcohol withdrawal cause staff and patient safety problems. Our primary goal was to develop an alcohol withdrawal protocol based on objective measures, and then to coordinate benzodiazepine dosing with those measures and improve care of the patient withdrawing from alcohol. A secondary goal was to give the primary care nurse the flexibility to administer benzodiazepine doses as needed to improve patient and staff safety. We developed and implemented a modified version of a published withdrawal symptomatology scale; a corresponding scale was developed for benzodiazepine dosing by observing the usual lorazepam doses needed to control withdrawal symptoms. Both scales and care guidelines for the patient withdrawing from alcohol were organized in the form of preprinted orders. Since implementation of the alcohol withdrawal protocol, complaints regarding patient and staff safety have decreased. Other patient care units are beginning to use the protocol. A hospital-wide task force is developing patient care plans based on the protocol for all patients withdrawing from alcohol.

Nursing-based protocol for treatment of alcohol withdrawal in the intensive care unit

Inappropriate benzodiazepine dosing in patients exhibiting signs of alcohol withdrawal cause staff and patient safety problems. Our primary goal was to develop an alcohol withdrawal protocol based on objective measures, and then to coordinate benzodiazepine dosing with those measures and improve care of the patient withdrawing from alcohol. A secondary goal was to give the primary care nurse the flexibility to administer benzodiazepine doses as needed to improve patient and staff safety. We developed and implemented a modified version of a published withdrawal symptomatology scale; a corresponding scale was developed for benzodiazepine dosing by observing the usual lorazepam doses needed to control withdrawal symptoms. Both scales and care guidelines for the patient withdrawing from alcohol were organized in the form of preprinted orders. Since implementation of the alcohol withdrawal protocol, complaints regarding patient and staff safety have decreased. Other patient care units are beginning to use the protocol. A hospital-wide task force is developing patient care plans based on the protocol for all patients withdrawing from alcohol.

Accuracy of disposable blood pressure transducers used in the critical care setting

OBJECTIVES

To assess the initial accuracy, drift in calibration over several hours, and decline in accuracy over daily use of blood pressure transducers used in the critical care setting.

DESIGN

Prospective, criterion standard.

SETTING

Three critical care units in a university hospital.

SUBJECTS

Twenty-seven consecutively available high-pressure transducers were used to measure intra-arterial blood pressures, and 11 consecutively available low-pressure transducers were used to measure central venous and pulmonary arterial blood pressures.

INTERVENTIONS

High-pressure transducers were compared with a mercury column manometer, and low-pressure transducers were compared with a water column manometer at three pressure levels. Data were collected initially after installation of the pressure transducer, at 3 hrs, and at 6 hrs. Data collections were repeated on subsequent days.

MEASUREMENTS AND MAIN RESULTS

a) The majority of pressure transducers are accurate; b) there is no drift in the accuracy of pressure transducers over several hours; c) the accuracy of pressure transducers does not decline over subsequent days. Some transducers over-estimated standard pressures by 10 mm Hg and/or underestimated standard pressure by 17 mm Hg.

CONCLUSIONS

The majority of pressure transducers used in the critical care setting are accurate, although there are some transducers that may compromise patient care. Blood pressure transducers should be checked against a standard manometer upon installation, and daily during use.

Mechanism of respiratory arrest in an animal model of acute fatal bronchoconstriction

The cause of respiratory arrest in acute asthma is not known. By its nature, respiratory arrest is difficult to study clinically. The possible causes of respiratory arrest include cardiovascular dysfunction, respiratory muscle fatigue, and central respiratory failure. We used a dog model of respiratory arrest in acute bronchoconstriction that examined the effects of hypoxemia and intrinsic loading in an attempt to establish the mechanism. Our hypothesis was that, in a setting of hypoxemia and intrinsic loading similar to human fatal asthma, respiratory arrest is caused by a central respiratory failure, more specifically, failure of the central rhythm generator. We studied 18 dogs divided into 1) an intrinsically loaded group, 2) a hypoxemic group, and 3) both a loaded and a hypoxemic group. Intrinsic loading was induced with methacholine combined with selective beta 2-blockade, and the hypoxemia was controlled by varying inspired O2 fraction. Respiratory arrest occurred only in animals with both hypoxemia and intrinsic loading. We found no evidence of hemodynamic instability or respiratory muscle fatigue. Instead, there was an abrupt cessation of ventilation while the intensity of the central neural output was maintained. Our results are consistent with a failure of the central rhythm generator as the causal agent in respiratory arrest.

Hemodynamic effects of intravenous pyruvate in the intact, anesthetized dog

OBJECTIVES

There is evidence from human studies that pyruvate improves skeletal muscle endurance, and from isolated heart preparations that pyruvate is a positive inotrope. We examined the hemodynamic effects of intravenous pyruvate in an intact, anesthetized dog preparation in order to test its effects in an intact animal. Our hypothesis was that pyruvate is a positive inotrope in the intact dog.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal laboratory.

SUBJECTS

Ten mongrel dogs.

INTERVENTIONS

Two groups of animals were anesthetized with chloralose and urethane, mechanically ventilated, and hemodynamically monitored. The experimental group (n = 6) received an infusion of calcium pyruvate and sodium pyruvate, while the control group (n = 4) received an infusion of calcium chloride and sodium chloride.

MEASUREMENTS AND MAIN RESULTS

The intravenous infusion of calcium and sodium pyruvate resulted in increased cardiac output, left ventricular contractility, and mixed venous oxygen saturation values in the experimental group compared with the control group of four dogs. There were no significant detrimental effects except an increase in the mean serum calcium concentrations in both groups.

CONCLUSIONS

These data suggest that intravenous pyruvate may be a useful in vivo positive inotrope.

The effect of respiratory and lactic acidosis on diaphragm function

The relative effects of respiratory and metabolic acidosis on diaphragm function are not known. To determine these effects, we compared the effects of respiratory and lactic acidosis on the contractile properties of the diaphragm. We estimated diaphragmatic performance from the change in transdiaphragmatic pressure after supramaximal stimulation of the phrenic nerves in an open-chested, casted-abdomen dog. Similarly, we stimulated the gastrocnemius motor nerve and examined force production and relaxation rate to determine if there was a difference in the response of this skeletal muscle. There was a fall in diaphragm performance with respiratory acidosis (77.1 +/- 16.9 cm H2O versus 93.8 +/- 15.0 cm H2O baseline), but not with lactic acidosis (96.7 +/- 15.7 cm H2O versus 93.8 +/- 15.0 cm H2O baseline); and the gastrocnemius was unaffected by either acidosis. The changes with respiratory acidosis were similar to those seen with diaphragmatic fatigue and had similar relaxation rate changes, suggesting that intracellular pH may play a mechanistic role in respiratory muscle fatigue. In addition, the absence of a respiratory acidosis effect on a non-diaphragmatic skeletal muscle's function represents another physiologic difference between the diaphragm and other skeletal muscles.

The effect of hypopnea on low-pressure pulmonary edema

The effects of the mechanical factors involved in ventilation on pulmonary edema are only partially understood. To clarify the effect of ventilation on the adult respiratory distress syndrome (ARDS), we examined the effect of reducing rate and tidal volume on oleic acid-induced low-pressure pulmonary edema in dogs, hypothesizing that hypopnea would reduce lung edema. We placed the experimental animals on venous-venous extracorporeal membrane oxygenation (ECMO) for CO2 clearance and oxygenation 1 h after the injury. This allowed reduction of the ventilatory rate from 17.2 +/- 4.8 to 3.3 +/- 0.8 breaths/min and tidal volume from 20 to 16 ml/kg, effectively resting the injured lung. After 5 h of hypopnea there was no reduction in edema by gravimetric or extravascular thermal volume measurements. The ECMO-facilitated hypopnea reduced airway pressure and pulmonary artery pressure while improving arterial oxygen saturation but increased venous admixture. These results suggest that there may be a supportive role for ECMO-assisted hypopnea, but there was no direct beneficial effect of hypopnea on edema.

Adverse effects of large tidal volume and low PEEP in canine acid aspiration

When normal lungs are ventilated with large tidal volumes (VT) and end-inspired pressures (Pei), surfactant is depleted and pulmonary edema develops. Both effects are diminished by positive end-expiratory pressure (PEEP). We reasoned that ventilatory with large VT-low PEEP would similarly increase edema following acute lung injury. To test this hypothesis, we ventilated dogs 1 h after hydrochloric acid (HCl) induced pulmonary edema with a large VT (30 ml/kg) and low PEEP (3 cm H2O) (large VT-low PEEP) and compared their results with dogs ventilated with a smaller VT (15 ml/kg) and 12 cm H2O PEEP (small VT-high PEEP). The small VT was the smallest that maintained eucapnia in our preparation; the large VT was chosen to match Pei and end-inspired lung volume. Pulmonary capillary wedge transmural pressure (Ppwtm) was kept at 8 mm Hg in both groups. Five hours after injury, the median lung wet weight to body weight ratio (WW/BW) was 25 g/kg higher in the large VT-low PEEP group than in the small VT-high PEEP group (p less than 0.05). Venous admixture (Qva/Qt) was similarly greater in the large VT-low PEEP group (49.8 versus 23.5%) (p less than 0.05). We conclude that small VT-high PEEP is a better mode of ventilating acute lung injury than large VT-low PEEP because edema accumulation is less and venous admixture is less. These advantages did not result from differences in Pei, end-inspiratory lung volume, or preload (Ppwtm).(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilatory responses to inspiratory threshold loading in humans

Normal alveolar ventilation tends to be maintained during external mechanical loading. The precise manner by which this occurs is unclear but may involve intrinsic mechanisms related to the muscular pump, neural influences, and chemoreceptor control. Recent observations suggest that submaximal threshold loads may result in hyperventilation. In this study we explicitly examined the respiratory effects of sustained threshold loading in normal subjects. We found that sustained threshold loading resulted in hyperventilation associated with high P100's (mouth pressure 100 ms after the start of an occluded breath) and increased tidal volumes but with little effect on duty cycle or respiratory rate. In addition, this increased respiratory motor output was sustained for 30-60 s after the load was removed. At very high threshold loads, hyperventilation failed to occur, despite increased P100's. We conclude that threshold loading results in increased respiratory motor output and hyperventilation, a response that is different from that observed with either resistive or elastic loads, and that the failure to hyperventilate at the higher loads may be the result of mechanical limitation.

The mechanism of respiratory arrest in inspiratory loading and hypoxemia

Respiratory arrests occur in the clinical setting of respiratory failure, but the mechanism is unclear. We used a dog model with increased inspiratory resistance and hypoxemia to explore the cause. We hypothesized that respiratory muscle fatigue (RMF) played a role in these respiratory arrests, and that the combination of hypoxia and resistive loading would produce respiratory arrest by the mechanism of RMF. Our preparation had transdiaphragmatic pressures that were 40% of maximum (Pdimax = 46.3 +/- 10.0 cm H2O) and progressive hypoxia resulting in a final arterial PO2 of 38 +/- 9 mm Hg and a phrenic vein O2 content of 1.8 +/- 1.1 mg/dl. Instead of failure associated with carbon dioxide retention and RMF, we saw a rapid decrease in tidal volume and respiratory rate, leading to apnea over 30 to 60 s while the diaphragm still responded with significant pressure generation when externally stimulated. These results suggest that respiratory muscle fatigue may not be a major factor in respiratory arrests associated with inspiratory loading and hypoxia, but that suppression of central drive, induced by the combination of inspiratory loading and hypoxemia, may be important.