High-altitude–related disorders—part ii: prevention, special populations, and chronic medical conditions

This second section of a 2-part review on high-altitude-related disorders focuses on strategies for prevention of high-altitude illness, identification of populations at increased risk for high-altitude illness, and effects of high altitude on selected chronic medical conditions. Practical aspects of advising and educating patients traveling to high altitude will be discussed, with special reference to pregnant women, infants and young children, healthy elders, and chronic medical conditions that may place persons at greater risk for high-altitude illness. The special concerns of pre-verbal children will be covered relative to the risks of high altitude for those too young to voice symptoms of illness and, thus, at-risk for potential serious consequences caused by delay in diagnosis and treatment.

High-altitude-related disorders—part I: pathophysiology, differential diagnosis, and treatment

As increasing numbers of people choose to sojourn or retire to the mountains, high-altitude illness is becoming a pathological phenomenon about which healthcare providers should have greater awareness. Hypoxia is the primary cause of high-altitude illness, but other stressors on the sympathetic nervous system, such as cold and exertion, also contribute to disease development and progression. Although variable across persons, symptoms of high-altitude disorders usually occur at altitudes over 7000 feet, and typically in 1 of 3 forms: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), or high-altitude pulmonary edema (HAPE). Major symptoms include nausea, poor sleep, headache, lassitude, cough, dyspnea on exertion and at rest, ataxia, and mental status changes. As a rule, illness occurring at high altitude should be attributed to the altitude until proven otherwise. Treatment is best accomplished by descent and by oxygen or pharmacologic intervention if necessary. Under no circumstances should a person with worsening symptoms of high-altitude illness delay descent. As will be discussed in part II of this article, gradual ascent and subsequent acclimatization to altitude is the most effective prevention, though acetazolamide (Diamox) may be a useful prophylactic measure in some.

Pattern and predictors of early rejection after lung transplantation

BACKGROUND

Most lung transplant recipients experience improvement in their underlying pulmonary condition but are faced with the threat of allograft rejection, the primary determinant of long-term survival. Several studies examined predictors of rejection, but few focused on the early period after transplantation.

OBJECTIVES

To describe the pattern and predictors of early rejection during the first year after transplantation to guide the development of interventions to facilitate earlier detection and treatment of rejection.

METHODS

Data for donor, recipient, and posttransplant variables were retrieved retrospectively for 250 recipients of single or double lung transplants.

RESULTS

Most recipients (85%) had at least 1 episode of acute rejection; 33% had a single episode; 23% had recurrent rejection; 3% had persistent rejection; 13% had refractory rejection; and 14% had clinicopathological evidence of chronic rejection. Serious rejection (refractory acute rejection or chronic rejection) developed in 27% of recipients. Compared with other recipients, recipients who had serious rejection had more episodes of acute rejection (P = .004), and the first acute episodes occurred sooner after transplantation (P = .01) and were of a higher grade (P = .002).

CONCLUSIONS

Recipients who experienced higher grades for their first episode of acute rejection (P = .03) and higher cumulative rejection scores (P = .004) were significantly more likely than other recipients to have serious rejection during the first year after transplantation.

Pattern and Predictors of Early Rejection After Lung Transplantation

• Background Most lung transplant recipients experience improvement in their underlying pulmonary condition but are faced with the threat of allograft rejection, the primary determinant of long-term survival. Several studies examined predictors of rejection, but few focused on the early period after transplantation.

• Objectives To describe the pattern and predictors of early rejection during the first year after transplantation to guide the development of interventions to facilitate earlier detection and treatment of rejection.

• Methods Data for donor, recipient, and posttransplant variables were retrieved retrospectively for 250 recipients of single or double lung transplants.

• Results Most recipients (85%) had at least 1 episode of acute rejection; 33% had a single episode; 23% had recurrent rejection; 3% had persistent rejection; 13% had refractory rejection; and 14% had clinicopathological evidence of chronic rejection. Serious rejection (refractory acute rejection or chronic rejection) developed in 27% of recipients. Compared with other recipients, recipients who had serious rejection had more episodes of acute rejection (P = .004), and the first acute episodes occurred sooner after transplantation (P = .01) and were of a higher grade (P = .002).

• Conclusions Recipients who experienced higher grades for their first episode of acute rejection (P=.03) and higher cumulative rejection scores (P = .004) were significantly more likely than other recipients to have serious rejection during the first year after transplantation.

Management of patients in the intensive care unit: comparison via work sampling analysis of an acute care nurse practitioner and physicians in training

BACKGROUND

Little is known about aspects of practice that differ between acute care nurse practitioners and physicians that might affect patients' outcomes.

OBJECTIVE

To determine if time spent in work activities differs between an acute care nurse practitioner and physicians in training (pulmonary/critical care fellows) managing patients' care in a step-down medical intensive care unit.

METHODS

Work sampling techniques were used to collect data when the nurse practitioner had 6 months' or less experience in the role (T1), after the nurse practitioner had 12 months' experience in the role (T2), and when physicians in training provided care on a rotational schedule (nurse practitioner not present, T3). These data were used to estimate the time spent in direct management of patients, coordination of care, and nonunit activities.

RESULTS

Results for T1 and T2 were similar. When T2 and T3 were compared, the nurse practitioner and the physicians in training spent approximately half their time in activities directly related to management of patients (40% vs 44%, not significantly different). The nurse practitioner spent more time in activities related to coordination of care (45% vs 18%; P < .001) and less time in nonunit activities (15% vs 37%; P < .001).

CONCLUSION

The nurse practitioner and the physicians in training spent a similar proportion of time performing required tasks. Because of training requirements, physicians spent more time than the nurse practitioner in nonunit activities. Conversely, the nurse practitioner spent more time interacting with patients and patients' families and collaborating with health team members.

Management of Patients in the Intensive Care Unit: Comparison Via Work Sampling Analysis of an Acute Care Nurse Practitioner and Physicians in Training

• Background Little is known about aspects of practice that differ between acute care nurse practitioners and physicians that might affect patients’ outcomes.

• Objective To determine if time spent in work activities differs between an acute care nurse practitioner and physicians in training (pulmonary/critical care fellows) managing patients’ care in a step-down medical intensive care unit.

• Methods Work sampling techniques were used to collect data when the nurse practitioner had 6 months’ or less experience in the role (T1), after the nurse practitioner had 12 months’ experience in the role (T2), and when physicians in training provided care on a rotational schedule (nurse practitioner not present, T3). These data were used to estimate the time spent in direct management of patients, coordination of care, and nonunit activities.

• Results Results for T1 and T2 were similar. When T2 and T3 were compared, the nurse practitioner and the physicians in training spent approximately half their time in activities directly related to management of patients (40% vs 44%, not significantly different). The nurse practitioner spent more time in activities related to coordination of care (45% vs 18%; P &lt; .001) and less time in nonunit activities (15% vs 37%; P &lt; .001).

• Conclusion The nurse practitioner and the physicians in training spent a similar proportion of time performing required tasks. Because of training requirements, physicians spent more time than the nurse practitioner in nonunit activities. Conversely, the nurse practitioner spent more time interacting with patients and patients’ families and collaborating with health team members.

Developmental stages of sleep from birth to adolescence, common childhood sleep disorders: overview and nursing implications

Sleep is an important physiological process with profound impact on the body. Sleep undergoes normal developmental changes and common sleep problems are seen in general pediatric practice. This article discusses normal developmental changes related to sleep, common sleep disorders experienced by children and how nurses can assist parents in coping with these changes and disorders.

Effect of Tracheal Gas Insufflation During Weaning From Prolonged Mechanical Ventilation: A Preliminary Study

• Background Tracheal gas insufflation reduces inspired tidal volume and minute ventilation in spontaneously breathing patients and may facilitate weaning from mechanical ventilation.

• Objective To determine if tracheal gas insufflation can reduce ventilatory demand during weaning trials in patients who require prolonged mechanical ventilation.

• Methods A reduction in ventilatory demand was defined as a relative decrease in tidal volume, minute ventilation, and mean inspiratory flow during trials with tracheal gas insufflation compared with the values during trials without this therapy. A total of 14 subjects underwent T-piece trials with and without insufflation (flow rate 6 L/min) on 2 consecutive days; the order of insufflation was randomized. Tidal volume, minute ventilation, and mean inspiratory flow were measured at baseline (without insufflation) and 2 hours later.

• Results Differences in ventilatory demand were not significant when comparisons were made for condition (tracheal gas insufflation vs no flow) or time (baseline vs 2 hours) for the total group (P = .48). Subjects were classified post hoc as responders (n = 9) or nonresponders (n = 5). Comparisons between responders and nonresponders indicated a significant (P = .02) 3-way multivariate interaction for group (responder vs nonresponder), condition (tracheal gas insufflation vs no flow), and time (baseline vs 2 hours) for ventilatory demand variables.

• Conclusion Tracheal gas insufflation can reduce ventilatory demand during weaning trials in some patients who require mechanical ventilation.

Effect of tracheal gas insufflation during weaning from prolonged mechanical ventilation: a preliminary study

BACKGROUND

Tracheal gas insufflation reduces inspired tidal volume and minute ventilation in spontaneously breathing patients and may facilitate weaning from mechanical ventilation.

OBJECTIVE

To determine if tracheal gas insufflation can reduce ventilatory demand during weaning trials in patients who require prolonged mechanical ventilation.

METHODS

A reduction in ventilatory demand was defined as a relative decrease in tidal volume, minute ventilation, and mean inspiratory flow during trials with tracheal gas insufflation compared with the values during trials without this therapy. A total of 14 subjects underwent T-piece trials with and without insufflation (flow rate 6 L/min) on 2 consecutive days; the order of insufflation was randomized. Tidal volume, minute ventilation, and mean inspiratory flow were measured at baseline (without insufflation) and 2 hours later.

RESULTS

Differences in ventilatory demand were not significant when comparisons were made for condition (tracheal gas insufflation vs no flow) or time (baseline vs 2 hours) for the total group (P = .48). Subjects were classified post hoc as responders (n = 9) or nonresponders (n = 5). Comparisons between responders and nonresponders indicated a significant (P = .02) 3-way multivariate interaction for group (responder vs nonresponder), condition (tracheal gas insufflation vs no flow), and time (baseline vs 2 hours) for ventilatory demand variables.

CONCLUSION

Tracheal gas insufflation can reduce ventilatory demand during weaning trials in some patients who require mechanical ventilation.

Early discharge following abdominal aortic aneurysm repair: Impact on patients and caregivers

Although early discharge is common place, little is known about its impact after abdominal aortic aneurysm (AAA) surgery. We sought to prospectively describe patient outcomes and caregiving experience after early discharge following elective AAA repair using a standard or endovascular grafting system (EGS) procedure. Fifty-one patients (Standard, n=25; EGS, n=26) completed questionnaires on symptoms and health-related quality of life (HRQoL) while hospitalized and 1, 4, and 8 weeks after discharge. Data were also obtained from caregivers. HRQoL decreased at Week 1 in both groups but returned to near baseline by Week 8. Standard AAA patients experienced more symptoms and activity limitations, but these were concentrated in Week 1. Most caregivers were positive about caregiving and required no additional resources. Findings suggest that most patients who undergo early discharge following elective AAA surgery experience few problems. Those problems that occur concentrate in the week following discharge, suggesting the need for closer monitoring at this time.

Exercise maintenance following pulmonary rehabilitation: effect of distractive stimuli

STUDY OBJECTIVE

To determine if distractive auditory stimuli (DAS) in the form of music would promote adherence to a walking regimen following completion of a pulmonary rehabilitation program (PRP) and, thereby, maintenance of gains achieved during the program.

DESIGN

Experimental, randomized, two-group design with testing at baseline, 4 weeks, and 8 weeks.

SETTING

Outpatient.

PATIENTS

Twenty-four patients (4 men and 20 women) with moderate-to-severe COPD (FEV(1) 41.3 +/- 13% predicted [mean +/- SD]).

INTERVENTION

Experimental group subjects (n = 12) were instructed to walk at their own pace for 20 to 45 min, two to five times a week, using DAS with a portable audiocassette player. The control group (n = 12) received the same instructions, but no DAS.

MEASUREMENTS AND RESULTS

Primary outcome measures were perceived dyspnea during activities of daily living (ADL) and 6-min walk (6MW) distance. Secondary outcome measures were anxiety, depressive symptoms, health-related quality of life (QoL), global QoL, and breathlessness and fatigue at completion of the 6MW. In addition, all subjects recorded the distance and time walked using self-report (pedometers and daily logs). There was a significant decrease in perceived dyspnea during ADL (p = 0.0004) and a significant increase in 6MW distance (p = 0.0004) over time in the DAS group compared to the control group. DAS subjects increased 6MW distance 445 +/- 264 feet (mean +/- SD) from baseline to 8 weeks, whereas control subjects decreased 6MW distance to 169 +/- 154 feet. No significant differences were noted for the remaining variables. The cumulative distance walked by the DAS group was 19.1 +/- 16.7 miles compared to 15.4 +/- 8.0 miles for the control group, a 24% difference (p = 0.49). Despite this difference, self-report exercise log data were similar for the two groups.

CONCLUSION

Subjects who used DAS while walking had improved functional performance and decreased perceptions of dyspnea, whereas control subjects could not maintain post-PRP gains. DAS is a simple, cost-effective strategy that may have the potential to augment the effectiveness of post-PRP maintenance training.

Resource Utilization Related to Atrial Fibrillation After Coronary Artery Bypass Grafting

• Background Studies of resource utilization by patients with new-onset atrial fibrillation after coronary artery bypass grafting have addressed only length of stay and bed charges.

• Objective To compare resource utilization between patients with new-onset atrial fibrillation and patients without atrial fibrillation after isolated coronary artery bypass grafting.

• Methods Retrospective review of clinical and administrative electronic databases for 720 subjects who underwent isolated coronary artery bypass grafting with cardiopulmonary bypass in 25 months at one medical center. The prevalence of atrial fibrillation was determined, and resource utilization in various hospital cost centers was compared between subjects with and without atrial fibrillation.

• Results The prevalence of new-onset atrial fibrillation was 33.1%. Compared with subjects without atrial fibrillation, subjects with atrial fibrillation had a longer stay (5.8 ± 2.4 vs 4.4 ± 1.2 days, P&lt; .001), more days receiving mechanical ventilation (P=.002) and oxygen therapy (P&lt; .001), and higher rates of readmission to the intensive care unit (4.6% vs 0.2%, P&lt; .001). Subjects with atrial fibrillation also had more laboratory tests (P&lt; .001) and more days receiving cardiac drugs, heparin, diuretics, and electrolytes. Subjects with atrial fibrillation had higher total postoperative charges ($57261 ± $17 101 vs $50 905 ± $10 062, P = .001), a mean difference of $6356. The mean differences were greatest for bed charges ($1642), laboratory charges ($1215), pharmacy ($989), and respiratory care ($582).

• Conclusions The economic impact of atrial fibrillation after coronary artery bypass grafting has been underestimated.

Resource utilization related to atrial fibrillation after coronary artery bypass grafting

BACKGROUND

Studies of resource utilization by patients with new-onset atrialfibrillation after coronary artery bypass grafting have addressed only length of stay and bed charges.

OBJECTIVE

To compare resource utilization between patients with new-onset atrial fibrillation and patients without atrialfibrillation after isolated coronary artery bypass grafting.

METHODS

Retrospective review of clinical and administrative electronic databases for 720 subjects who underwent isolated coronary artery bypass grafting with cardiopulmonary bypass in 25 months at one medical center The prevalence of atrial fibrillation was determined, and resource utilization in various hospital cost centers was compared between subjects with and without atrialfibrillation.

RESULTS

The prevalence of new-onset atrial fibrillation was 33.1%. Compared with subjects without atrialfibrillation, subjects with atrialfibrillation had a longer stay (5.8 +/- 2.4 vs. 4.4+/-1.2 days, P<.001), more days receiving mechanical ventilation (P =.002) and oxygen therapy (P<.001), and higher rates of readmission to the intensive care unit (4.6% vs. 0.2%, P<.001). Subjects with atrial fibrillation also had more laboratory tests (P<.001) and more days receiving cardiac drugs, heparin, diuretics, and electrolytes. Subjects with atrialfibrillation had higher total postoperative charges ($57261 +/- $17101 vs. $50905 +/- $10062, P = .001), a mean difference of $6356. The mean differences were greatest for bed charges ($1642), laboratory charges ($1215), pharmacy ($989), and respiratory care ($582).

CONCLUSION

The economic impact of atrialfibrillation after coronary artery bypass grafting has been underestimated.

Predictors and impact of atrial fibrillation after isolated coronary artery bypass grafting

OBJECTIVE

Although an extensive number of studies have attempted to identify predictors of new-onset atrial fibrillation (AFIB) after coronary artery bypass grafting (CABG), a strong predictive model does not exist. Prior studies have included patients recruited from multiple centers with variant AFIB prevalence rates and those who underwent CABG in combination with other surgical procedures. Also, most studies have focused on pre- and perioperative characteristics, with less attention given to the initial postoperative period. The purpose of this study was to comprehensively examine pre-, peri-, and postoperative characteristics that might predict new-onset AFIB in a large sample of patients undergoing isolated CABG in a single medical center, utilizing data readily available to clinicians in electronic data repositories. In addition, length of stay and selected postoperative complications and disposition were compared in patients with AFIB and no AFIB.

DESIGN

Retrospective, comparative survey.

SETTING

University-affiliated tertiary care hospital.

PATIENTS

Patients with new-onset AFIB who underwent isolated standard CABG or minimally invasive direct vision coronary artery bypass were identified from an electronic clinical data repository.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The prevalence of AFIB in the total sample (n = 814) was 31.9%. Predictors of AFIB included age (p =.0004), number of vessels bypassed (p =.013), vessel location (diagonal [p <.003] or posterior descending artery [p <.001]), and net fluid balance on the operative day (p =.015). Forward stepwise regression analysis produced a model that correctly predicted AFIB in only 24% of cases, with age (14%) and body surface area (9%) providing the most prediction. The incidence of embolic stroke was higher in AFIB (n = 8) vs. no AFIB (n = 4) patients, but stroke preceded AFIB onset in seven of eight cases. Subjects with AFIB had a longer stay (p =.0004), more intensive care unit readmissions (p =.0004), and required more assistance at hospital discharge (p =.017).

CONCLUSIONS

Despite attempts to examine comprehensively predictors of new-onset AFIB, we were unable to identify a robust predictive model. Our findings, in combination with prior work, imply that it may not be feasible to predict the development of new-onset AFIB after CABG using data readily available to the bedside clinician. In this sample, stroke was uncommon and, when it occurred, preceded AFIB in all but one case. As anticipated, AFIB increased length of stay, and patients with this complication required more assistance at discharge.

Effect of Positioning on Oxygenation in Single-Lung Transplant Recipients

• Background Many benefits and adverse effects of positioning are related to changes in ventilation and perfusion. A number of unique factors related to the allograft make the effects of positioning difficult to determine in single-lung transplant recipients.

• Objectives To determine the effect of 3 body positions (supine, lateral with allograft lung down, and lateral with native lung down) on oxygenation and blood flow in single-lung transplant recipients in the 24 hours immediately after surgery.

• Methods A quasi-experimental repeated-measures design with stratified assignment to 1 of 3 different sequencing patterns for turning group was used to study 15 transplant recipients, 9 with emphysema and 6 with fibrosis. Oxygenation, ventilation, and blood flow measures (heart rate, blood pressure) were assessed after each turn. The effect of ischemic reperfusion injury was also explored.

• Results The oxygenation, ventilation, and blood flow variables did not differ significantly across group, diagnosis, or time. Oxygenation variables measured when the allograft lung was dependent did not differ significantly from such measurements obtained when the native lung was dependent.

• Conclusions No single position maximizes oxygenation in the immediate postoperative period in single-lung transplant recipients. Although a single standard protocol for positioning cannot be supported, the study does support the idea that transplant recipients can be safely turned in the immediate postoperative period without compromising oxygenation or hemodynamic status.

Effect of positioning on oxygenation in single-lung transplant recipients

BACKGROUND

Many benefits and adverse effects of positioning are related to changes in ventilation and perfusion. A number of unique factors related to the allograft make the effects of positioning difficult to determine in single-lung transplant recipients.

OBJECTIVES

To determine the effect of 3 body positions (supine, lateral with allograft lung down, and lateral with native lung down) on oxygenation and blood flow in single-lung transplant recipients in the 24 hours immediately after surgery.

METHODS

A quasi-experimental repeated-measures design with stratified assignment to 1 of 3 different sequencing patterns for turning group was used to study 15 transplant recipients, 9 with emphysema and 6 with fibrosis. Oxygenation, ventilation, and blood flow measures (heart rate, blood pressure) were assessed after each turn. The effect of ischemic reperfusion injury was also explored.

RESULTS

The oxygenation, ventilation, and bloodflow variables did not differ significantly across group, diagnosis, or time. Oxygenation variables measured when the allograft lung was dependent did not differ significantly from such measurements obtained when the native lung was dependent.

CONCLUSIONS

No single position maximizes oxygenation in the immediate postoperative period in single-lung transplant recipients. Although a single standard protocol for positioning cannot be supported, the study does support the idea that transplant recipients can be safely turned in the immediate postoperative period without compromising oxygenation or hemodynamic status.

Effects of continuous, expiratory, reverse, and bi-directional tracheal gas insufflation in conjunction with a flow relief valve on delivered tidal volume, total positive end-expiratory pressure, and carbon dioxide elimination: a bench study

INTRODUCTION

Tracheal gas insufflation (TGI) can increase total positive end-expiratory pressure (total-PEEP) when flow is delivered in a forward direction, necessitating adjustments to maintain total-PEEP constant. When TGI is delivered throughout the respiratory cycle, additional adjustments are needed to maintain tidal volume (V(T)) constant.

OBJECTIVE

Determine if bi-directional TGI (bi-TGI) (simultaneous flows toward the lungs and upper airway) in combination with a flow relief valve eliminates the increase in total-PEEP and maintains a constant V(T), thus simplifying TGI administration.

METHODS

Using an artificial lung model and pressure control ventilation, we studied the effect of TGI at 10 L/min on inspired V(T), total-PEEP, and CO(2) elimination during 6 conditions: (1) control (no TGI, no catheter in the airway), (2) baseline (catheter in the airway but no TGI), (3) continuous TGI, (4) expiratory TGI, (5) reverse TGI, and (6) bi-TGI. Each condition was studied under 3 inspiration-expiration ratios (1:1, 1:2, and 2:1). A preset flow relief valve was inserted into the ventilator circuit during all TGI conditions with continuous flow.

SETTING

University research laboratory.

RESULTS

CO(2) elimination efficiency was similar under all conditions. Total-PEEP increased with continuous TGI and expiratory TGI, decreased during reverse TGI, and was unchanged during bi-TGI. With the flow relief valve in place, and no adjustment in mechanical ventilation, the change in minute ventilation ranged from 0% to 10%, with the least change during bi-TGI (0-5%). During bi-TGI, gas flow was equivalent in both directions during dynamic conditions and the flow relief valve consistently removed gas at 10 L/min under various pressures.

CONCLUSIONS

Our data from an artificial lung model support that continuous bi-TGI minimizes the change in total-PEEP seen during other TGI modalities. The flow relief valve compensated for the extra gas volume delivered by the TGI catheter, thereby eliminating the need to make ventilator adjustments. Used in combination with a flow relief valve, bi-TGI appears to offer unique advantages by providing a simpler method to deliver TGI. Further testing is indicated to determine if similar benefits occur in the clinical setting.

Atrial fibrillation: prevalence after minimally invasive direct and standard coronary artery bypass

BACKGROUND

This study identified and compared the prevalence of new-onset atrial fibrillation (AFIB) following standard coronary artery bypass grafting (SCABG) with cardiopulmonary bypass (CPB) and minimally invasive direct vision coronary artery bypass grafting (MIDCAB) without CPB. A further comparison was made between AFIB prevalence in SCABG and MIDCAB subjects with two or fewer bypasses.

METHODS

This is a retrospective, comparative survey. Patients with new-onset AFIB who underwent SCABG or MIDCAB alone were identified electronically using a triangulated method (International Classification of Diseases, 9th revision, Clinical Modification [ICD-9 CM] code; clinical database word search; and pharmacy database drug search).

RESULTS

The total sample (n = 814; 94 MIDCAB, 720 SCABG) exhibited a trend toward lower AFIB prevalence in MIDCAB (23.4%) versus SCABG (33.1%) subjects (p = 0.059). AFIB prevalence in the SCABG subset with two or less vessel bypasses (n = 98; n = 18 single vessel, n = 80 double vessels) and MIDCAB subjects (n = 94; n = 90 single vessels, n = 4 double vessels) was almost identical (SCABG subset 24.5% versus MIDCAB 23.4%, p = 0.860). Slightly more than half (56.9%) of new-onset AFIB subjects were identified by ICD-9 CM codes, with the remainder by word search (37.7%) or procainamide query (5.4%).

CONCLUSIONS

In this sample, the number of vessels bypassed seemed to have a greater influence on AFIB prevalence than the application of CPB or the surgical approach. Retrospective identification of AFIB cases by ICD-9 CM code grossly underestimated AFIB prevalence.

Monitoring and humidification during tracheal gas insufflation

In order to use tracheal gas insufflation (TGI) in a safe and effective manner, it is important to understand potential interactions between TGI and the mechanical ventilator that may impact upon gas delivery and carbon dioxide (CO2) elimination. Furthermore, potentially serious complications secondary to insufflation of cool, dry gas directly into the airway and the possibility of tube occlusion must be considered during use of this adjunct modality to mechanical ventilation. Regardless of the delivery modality (continuous TGI, expiratory TGI, reverse TGI, or bidirectional TGI), conventional respiratory monitoring is required. However, TGI with mechanical ventilation can alter tidal volume and peak inspiratory pressure and can lead to the development of intrinsic positive end-expiratory pressure. Therefore, depending on the gas delivery technique used, it is important to carefully monitor these ventilatory parameters for TGI-induced changes and understand the potential need for adjustments to ventilator settings to facilitate therapy and avoid problems. Optimally, gas insufflated by the TGI catheter should be conditioned by addition of heat and humidity to prevent mucus plug formation and potential damage to the tracheal mucosa. Finally, patients must be closely monitored for increases in peak inspiratory pressure from obstruction of the tracheal tube and should have the TGI catheter removed and inspected every 8-12 hours to assess for plugs.

Rejection after organ transplantation: a historical review

Progress toward understanding the biochemical basis of human individuality spans centuries, but tissue rejection remains the primary clinical challenge of organ transplantation. This article highlights the chronology of scientific discoveries made in the quest to overcome the rejection associated with transplantation. The purposes of this review are to raise clinicians' awareness of the advances in surgery, genetics, immunology, and immunosuppression that have contributed to the current knowledge of tissue rejection and to indicate potential new directions in this challenging field.

Rejection after organ transplantation: a historical review

Progress toward understanding the biochemical basis of human individuality spans centuries, but tissue rejection remains the primary clinical challenge of organ transplantation. This article highlights the chronology of scientific discoveries made in the quest to overcome the rejection associated with transplantation. The purposes of this review are to raise clinicians' awareness of the advances in surgery, genetics, immunology, and immunosuppression that have contributed to the current knowledge of tissue rejection and to indicate potential new directions in this challenging field.

Auto-positive end-expiratory pressure during tracheal gas insufflation: testing a hypothetical model

OBJECTIVE

The major benefit of tracheal gas insufflation (TGI) is an increase in CO2 elimination efficiency by removal of CO2 from the anatomical deadspace. In conjunction with mechanical ventilation, TGI may also alter variables that affect CO2 elimination, such as minute ventilation and peak airway pressure (peak Paw) and cause the development of auto-positive end-expiratory pressure (auto-PEEP). We tested the hypothesis that TGI-induced auto-PEEP alters ventilatory variables. We predicted that TGI-induced auto-PEEP offsets the beneficial effects of TGI on CO2 elimination and that keeping total PEEP (ventilator PEEP + auto-PEEP) constant enhances the CO2 elimination efficiency afforded by TGI.

DESIGN

Prospective study of two series of patients with acute respiratory distress syndrome receiving mechanical ventilation.

SETTING

Intensive care units at a university medical center.

PATIENTS

Each series consisted of eight sequential hypercapnic patients.

INTERVENTIONS

In series 1, we examined the effect of continuous TGI at 0 and 10 L/min on PaCO2, without compensating for the development of auto-PEEP. In series 2, we examined this same effect of continuous TGI while reducing ventilator PEEP to keep total PEEP constant. TGI-induced auto-PEEP was calculated based on dynamic compliance measurements during zero TGI flow conditions (deltaV/deltaP) after averaging the two baseline values for peak Paw and tidal volume and assuming compliance did not change between the zero TGI and TGI flow conditions (deltaVTGI/deltaPTGI).

MEASUREMENTS AND MAIN RESULTS

In series 1, total PEEP increased from 13.2 +/- 3.2 cm H2O to 17.8 +/- 3.5 cm H2O without compensation for auto-PEEP (p = .01). PaCO2 decreased (p = .03) from 56.2 +/- 10.6 mm Hg (zero TGI) to 52.9 +/- 9.3 mm Hg (TGI at 10 L/min), a 6% decrement. In series 2, total PEEP was unchanged (p = NS). PaCO2 decreased (p = .03) from 59.5 +/- 10.4 mm Hg (zero TGI) to 52.2 +/- 8.3 mm Hg (TGI at 10 L/min), a 12% decrement. There was no significant change in PaO2; there were no untoward hemodynamic effects in either series.

CONCLUSIONS

These data are consistent with the hypothesis that mechanical ventilation + TGI causes an increase in auto-PEEP that can blunt CO2 elimination. In addition to the ventilator modifications necessary to keep ventilatory variables constant when TGI is used, it is also necessary to reduce ventilator PEEP to keep total PEEP constant and further enhance CO2 elimination efficiency.