Respiratory system mechanics in sedated, paralyzed, morbidly obese patients

The duration of intra-abdominal hypertension strongly predicts outcomes for the critically ill surgical patients: a prospective observational study

INTRODUCTION

Intra-abdominal hypertension (IAH) is associated with morbidity and mortality in critically ill patients. The present study analyzed the clinical significance of IAH in surgical patients with severe sepsis.

METHODS

This was a prospective study carried out in the surgical intensive care unit (SICU). Intra-abdominal pressure (IAP) was measured three times a day via a urinary catheter filled with 25 mL of saline. IAH was defined as an IAP ≥ 12 mmHg, and the peak IAP was recorded as the IAP for the day. Data were analyzed in terms of IAH development and the IAH duration.

RESULTS

Of the 46 patients enrolled in the study, 42 developed IAH while in the SICU. The development of IAH aggravated the clinical outcomes; such as longer SICU stay, requirement of ventilator support, and delayed initiation of enteral feeding (EF). The IAH duration showed a significant correlation with pulmonary, renal, and cardiovascular function, and enteral feeding. The IAH duration was an independent predictor of 60-day mortality (odds ratio: 1.196; p = 0.014).

CONCLUSIONS

The duration of IAH is a more important prognostic factor than the development of IAH; thus every effort should be made to reduce the IAH duration in critically ill patients.

TRIAL REGISTRATION

NCT01784458.

[Non-invasive mechanical ventilation in postoperative patients. A clinical review]

Non-invasive ventilation (NIV) is a method of ventilatory support that is increasing in importance day by day in the management of postoperative respiratory failure. Its role in the prevention and treatment of atelectasis is particularly important in the in the period after thoracic and abdominal surgeries. Similarly, in the transplanted patient, NIV can shorten the time of invasive mechanical ventilation, reducing the risk of infectious complications in these high-risk patients. It has been performed A systematic review of the literature has been performed, including examining the technical, clinical experiences and recommendations concerning the application of NIV in the postoperative period.

Sleep-Disordered Breathing in Patients with Polycystic Liver and Kidney Disease Referred for Transcatheter Arterial Embolization

BACKGROUND AND OBJECTIVES

Sleep-disordered breathing (SDB) is prevalent among patients with CKD, but its prevalence among patients with symptomatic autosomal dominant polycystic kidney disease (ADPKD) and its association with total liver and kidney volume remain unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study examined the association between height-adjusted total liver and kidney volume (htTLKV) and SDB in a cross-sectional study of 304 adult patients with symptomatic ADPKD who were hospitalized at Toranomon Hospital for transcatheter arterial embolization and who underwent pulse oximetry between April 2008 and November 2013. SDB was defined as having a 3% oxygen desaturation index of ≥15 events per hour of sleep. Logistic regression was performed with sex-specific quartiles of htTLKV as the main predictor, using patient data and comorbidities as covariates.

RESULTS

Overall (54.6% women, mean age 56.2±9.4 years, 83.5% on hemodialysis), 177 of 304 patients (58.2%) had SDB. SDB was strongly associated with htTLKV quartiles, demonstrating that odds ratios (ORs) and 95% confidence intervals (95% CIs) for SDB were 1.63 (0.76 to 3.48), 2.35 (1.09 to 5.06), and 4.61 (1.98 to 10.7) for htTLKV quartiles 2-4 (P for trend, P=0.003), respectively. Older age (OR, 1.81 per 10 years; 95% CI, 1.29 to 2.55), male sex (OR, 3.87; 95% CI, 1.96 to 7.66), receiving hemodialysis (OR, 3.46; 95% CI, 1.62 to 12.1), and higher body mass index (≥25 kg/m(2)) (OR, 3.03; 95% CI, 1.08 to 8.52) were also associated with SDB.

CONCLUSIONS

In this highly selected population of patients with symptomatic ADPKD referred for transcatheter arterial embolization, SDB was highly prevalent and independently associated with higher htTLKV.

Intraoperative positive end-expiratory pressure evaluation using the intratidal compliance-volume profile

BACKGROUND

Lung-protective mechanical ventilation during general surgery including the application of PEEP can reduce postoperative pulmonary complications. In a prospective clinical observation study, we evaluated volume-dependent respiratory system compliance in adult patients undergoing ear-nose-throat surgery with ventilation settings chosen empirically by the attending anaesthetist.

METHODS

In 40 patients, we measured the respiratory variables during intraoperative mechanical ventilation. All measurements were subdivided into 5 min intervals. Dynamic compliance (CRS) and the intratidal volume-dependent CRS curve was calculated for each interval and classified into one of the six specific compliance profiles indicating intratidal recruitment/derecruitment, overdistension or all. We retrospectively compared the occurrences of the respective compliance profiles at PEEP levels of 5 cm H2O and at higher levels.

RESULTS

The attending anaesthetists set the PEEP level initially to 5 cm H2O in 29 patients (83%), to 7 cm H2O in 5 patients (14%), and to 8 cm H2O in 2 patients (6%). Across all measurements the mean CRS was 61 (11) ml cm H2O(-1) (40-86 ml cm H2O(-1)) and decreased continuously during the procedure. At PEEP of 5 cm H2O the compliance profile indicating strong intratidal recruitment/derecruitment occurred more often (18.6%) compared with higher PEEP levels (5.5%, P<0.01). Overdistension was practically never observed.

CONCLUSIONS

In most patients, a PEEP of 5 cm H2O during intraoperative mechanical ventilation is too low to prevent intratidal recruitment/derecruitment. The analysis of the intratidal compliance profile provides the rationale to individually titrate a PEEP level that stabilizes the alveolar recruitment status of the lung during intraoperative mechanical ventilation.

TRIAL REGISTRATION NUMBER

DRKS00004286.

Measurement of esophageal pressure at bedside: pros and cons

PURPOSE OF REVIEW

Esophageal pressure measurement well estimates pleural pressure. The interpretation of absolute values is often debated for various reasons, but the changes in pressure measured are considered very accurate provided that a number of precautions are taken. The information provided by these measurements is unique in nature and has an enormous potential to influence management. It allows to study the exact influence of the chest wall and to determine the real lung distending pressure. It is also the only way to quantify respiratory muscle activity and the work of breathing.

RECENT FINDINGS

The application of esophageal pressure monitoring potentially covers a large field, especially for what concerns mechanical ventilation. This goes from the acute phase of the acute respiratory distress syndrome (ARDS) to weaning and patient-ventilator interactions. During ARDS, recent findings indicate that this measurement may help titrating the level of positive end-expiratory pressure or to determine the well tolerated upper limit of airway pressure.

SUMMARY

Application of esophageal pressure monitoring is limited by technical issues, the need for background physiological knowledge and the fact that very few studies have assessed a direct influence of this measurement on patients' outcome. The technique is underused in everyday practice.

Brazilian recommendations of mechanical ventilation 2013. Part 2

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumologia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Effect of intra-abdominal pressure on respiratory mechanics

INTRODUCTION

There has been an exponentially increasing interest in intra-abdominal hypertension (IAH). The intra-abdominal pressure (IAP) markedly affects the function of the respiratory system.

METHODS

This review will focus on the available literature from the past few years. A Medline and Pubmed search was performed in order to find an answer to the question "What is the impact of increased IAP on respiratory function in the critically ill?".

RESULTS

In particular, increased IAP increases chest wall elastance (or decreases compliance) and promotes cranial shift of the diaphragm, with consequent reduction in lung volume and atelectasis formation. Compression of the lung parenchyma also triggers pulmonary infection. During general anaesthesia, in normal subjects, IAP does not affect the chest wall mechanics, but plays a relevant role in the caudal-cranial displacement of the abdominal content, the diaphragm and consequent changes in lung mechanics and function. In obese patients, the increased IAP is the major determinant of the reduction in lung volume, atelectasis formation and alterations in chest wall mechanics. In ARDS patients the measurement of IAP and chest wall mechanics is important for a better interpretation of respiratory mechanics, hemodynamics and appropriate setting of the ventilator. Furthermore, increased IAP promotes lung oedema, ventilator induced lung injury and reduced lymphatic flow in normal and diseased lungs.

CONCLUSION

Increased IAP markedly affects respiratory function in such a way that it has an impact on daily clinical practise.

Determinants of noninvasive ventilation success or failure in morbidly obese patients in acute respiratory failure

PURPOSE

Acute respiratory failure (ARF) is a common life-threatening complication in morbidly obese patients with obesity hypoventilation syndrome (OHS). We aimed to identify the determinants of noninvasive ventilation (NIV) success or failure for this indication.

METHODS

We prospectively included 76 consecutive patients with BMI>40 kg/m2 diagnosed with OHS and treated by NIV for ARF in a 15-bed ICU of a tertiary hospital.

RESULTS

NIV failed to reverse ARF in only 13 patients. Factors associated with NIV failure included pneumonia (n = 12/13, 92% vs n = 9/63, 14%; p<0.0001), high SOFA (10 vs 5; p<0.0001) and SAPS2 score (63 vs 39; p<0.0001) at admission. These patients often experienced poor outcome despite early resort to endotracheal intubation (in-hospital mortality, 92.3% vs 17.5%; p<0.001). The only factor significantly associated with successful response to NIV was idiopathic decompensation of OHS (n = 30, 48% vs n = 0, 0%; p = 0.001). In the NIV success group (n = 63), 33 patients (53%) experienced a delayed response to NIV (with persistent hypercapnic acidosis during the first 6 hours).

CONCLUSIONS

Multiple organ failure and pneumonia were the main factors associated with NIV failure and death in morbidly obese patients in hypoxemic ARF. On the opposite, NIV was constantly successful and could be safely pushed further in case of severe hypercapnic acute respiratory decompensation of OHS.

Observational study of the effect of obesity on lung volumes

BACKGROUND

Severe obesity causes respiratory morbidity and mortality. The impact of obesity on the mechanics of breathing is not fully understood.

PATIENTS AND METHODS

We undertook a comprehensive observational study of lung volumes and elasticity in nine obese and nine normal weight subjects, seated and supine, during spontaneous breathing. Seated and supine total lung capacity (TLC) and subdivisions were measured by multibreath helium dilution method. Using balloon catheters, oesophageal (Poes) and gastric (Pgas) pressures were recorded. Transpulmonary pressure (PL) was calculated as mouth pressure (Pmouth)-Poes, and complete expiratory PL volume curves were measured.

RESULTS

The obese group had a body mass index (BMI) of 46.8 (17.2) kg/m(2), and the normal group had a BMI of 23.2 (1.6) kg/m(2) (p=0.001). Obese and normals were matched for age (p=0.233), gender (p=0.637) and height (p=0.094). The obese were more restricted than the normals (TLC 88.6 (16.9) vs 104.4 (12.3) %predicted, p=0.033; FEV1/FVC 79.6 (7.3) vs 82.5 (4.2) %, p=0.325), had dramatically reduced expiratory reserve volume (ERV 0.4 (0.4) vs 1.7 (0.6) L, p<0.001) and end-tidal functional residual capacity (FRC) was smaller (37.5 (6.9) vs 46.9 (4.6) %TLC, p=0.004) when seated, but was similar when supine (39.4 (7.7) vs 41.5 (4.3) %TLC, p=0.477). Gastric pressures at FRC were significantly elevated in the obese (seated 19.1 (4.7) vs 12.1 (6.2) cm H2O, p=0.015; supine 14.3 (5.7) vs 7.1 (2.6) cm H2O, p=0.003), as were end-expiratory oesophageal pressures at FRC (seated 5.2 (6.9) vs -2.0 (3.5) cm H2O, p=0.013; supine 14.0 (8.0) vs 5.4 (3.1) cm H2O, p=0.008). BMI correlated with end-expiratory gastric (seated R(2)=0.43, supine R(2)=0.66, p<0.01) and oesophageal pressures (seated R(2)=0.51, supine R(2)=0.62, p<0.01).

CONCLUSIONS

Obese subjects have markedly increased gastric and oesophageal pressures, both when upright and supine, causing dramatically reduced FRC and ERV, which increases work of breathing.

Respiratory function during anesthesia: effects on gas exchange

Anaesthesia causes a respiratory impairment, whether the patient is breathing spontaneously or is ventilated mechanically. This impairment impedes the matching of alveolar ventilation and perfusion and thus the oxygenation of arterial blood. A triggering factor is loss of muscle tone that causes a fall in the resting lung volume, functional residual capacity. This fall promotes airway closure and gas adsorption, leading eventually to alveolar collapse, that is, atelectasis. The higher the oxygen concentration, the faster will the gas be adsorbed and the aleveoli collapse. Preoxygenation is a major cause of atelectasis and continuing use of high oxygen concentration maintains or increases the lung collapse, that typically is 10% or more of the lung tissue. It can exceed 25% to 40%. Perfusion of the atelectasis causes shunt and cyclic airway closure causes regions with low ventilation/perfusion ratios, that add to impaired oxygenation. Ventilation with positive end-expiratory pressure reduces the atelectasis but oxygenation need not improve, because of shift of blood flow down the lung to any remaining atelectatic tissue. Inflation of the lung to an airway pressure of 40 cmH2O recruits almost all collapsed lung and the lung remains open if ventilation is with moderate oxygen concentration (< 40%) but recollapses within a few minutes if ventilation is with 100% oxygen. Severe obesity increases the lung collapse and obstructive lung disease and one-lung anesthesia increase the mismatch of ventilation and perfusion. CO2 pneumoperitoneum increases atelectasis formation but not shunt, likely explained by enhanced hypoxic pulmonary vasoconstriction by CO2. Atelectasis may persist in the postoperative period and contribute to pneumonia.

Corrected end-tidal P(CO(2)) accurately estimates Pa(CO(2)) at rest and during exercise in morbidly obese adults

BACKGROUND

Obesity affects lung function and gas exchange and imposes mechanical ventilatory limitations during exercise that could disrupt the predictability of Pa(CO(2)) from end-tidal P(CO(2)) (P(ETCO(2))), an important clinical tool for assessing gas exchange efficiency during exercise testing. Pa(CO(2)) has been estimated during exercise with good accuracy in normal-weight individuals by using a correction equation developed by Jones and colleagues (P(JCO(2)) = 5.5 + 0.9 x P(ETCO(2)) – 2.1 x tidal volume). The purpose of this project was to determine the accuracy of Pa(CO(2)) estimations from P(ETCO(2)) and P(JCO(2)) values at rest and at submaximal and peak exercise in morbidly obese adults.

METHODS

Pa(CO(2)) and P(ETCO(2)) values from 37 obese adults (22 women, 15 men; age, 39 ± 9 y; BMI, 49 ± 7; [mean ± SD]) were evaluated. Subjects underwent ramped cardiopulmonary exercise testing to volitional exhaustion. P(ETCO(2)) was determined from expired gases simultaneously with temperature-corrected arterial blood gases (radial arterial catheter) at rest, every minute during exercise, and at peak exercise. Data were analyzed using paired t tests.

RESULTS

P(ETCO(2)) was not significantly different from Pa(CO(2)) at rest (P(ETCO(2)) = 37 ± 3 mm Hg vs Pa(CO(2)) = 38 ± 3 mm Hg, P = .14). However, during exercise, P(ETCO(2)) was significantly higher than Pa(CO(2)) (submaximal: 42 ± 4 vs 40 ± 3, P < .001; peak: 40 ± 4 vs 37 ± 4, P < .001, respectively). Jones’ equation successfully corrected P(ETCO(2)), such that P(JCO(2)) was not significantly different from Pa(CO(2)) (submax: P(JCO(2)) = 40 ± 3, P = .650; peak: 37 ± 4, P = .065).

CONCLUSION

P(JCO(2)) provides a better estimate of Pa(CO(2)) than P(ETCO(2)) during submaximal exercise and at peak exercise, whereas at rest both yield reasonable estimates in morbidly obese individuals. Clinicians and physiologists can obtain accurate estimations of Pa(CO(2)) in morbidly obese individuals by using P(JCO(2)).

Clinical consequences of altered chemoreflex control

Control of ventilation dictates various breathing patterns. The respiratory control system consists of a central pattern generator and several feedback mechanisms that act to maintain ventilation at optimal levels. The concept of loop gain has been employed to describe its stability and variability. Synthesizing all interactions under a general model that could account for every behavior has been challenging. Recent insight into the importance of these feedback systems may unveil therapeutic strategies for common ventilatory disturbances. In this review we will address the major mechanisms that have been proposed as mediators of some of the breathing patterns in health and disease that have raised controversies and discussion on ventilatory control over the years.

Supine position related obstructive sleep apnea in adults: pathogenesis and treatment

The most striking feature of obstructive respiratory events is that they are at their most severe and frequent in the supine sleeping position: indeed, more than half of all obstructive sleep apnea (OSA) patients can be classified as supine related OSA. Existing evidence points to supine related OSA being attributable to unfavorable airway geometry, reduced lung volume, and an inability of airway dilator muscles to adequately compensate as the airway collapses. The role of arousal threshold and ventilatory control instability in the supine position has however yet to be defined. Crucially, few physiological studies have examined patients in the lateral and supine positions, so there is little information to elucidate how breathing stability is affected by sleep posture. The mechanisms of supine related OSA can be overcome by the use of continuous positive airway pressure. There are conflicting data on the utility of oral appliances, while the effectiveness of weight loss and nasal expiratory resistance remains unclear. Avoidance of the supine posture is efficacious, but long term compliance data and well powered randomized controlled trials are lacking. The treatment of supine related OSA remains largely ignored in major clinical guidelines. Supine OSA is the dominant phenotype of the OSA syndrome. This review explains why the supine position so favors upper airway collapse and presents the available data on the management of patients with supine related OSA.

Obesity in anesthesia and intensive care

Obesity is a global epidemic increasingly affecting management of anesthesia as well as intensive care medicine. Possible improvements in therapy require consideration of the specific pathophysiology of the obese, their concomitant diseases, and the complications associated with morbid obesity. Systematic assessment of perioperative risk factors is essential for an appropriate management. Paradoxically, overweight and moderately obese patients undergoing surgery have a lower risk when compared to patients with normal weight. The highest mortality and morbidity rates in this setting are reported for underweight and morbidly obese patients. The better chance of survival when compared to normal-weight individuals in the perioperative setting has been described the obesity paradox. In particular, the commitment of all involved physicians to improve all aspects of care will reduce the perioperative risk in obese patients. Physiological and pharmacological characteristics of the obese should also be considered. Furthermore, adequate technical equipment and practical skills of all members of the anesthesia team significantly contribute to risk reduction and therapeutic success in obese patients.

The semi-seated position slightly reduces the effort to breathe during difficult weaning

PURPOSE

The influence of posture on breathing effort in patients with difficult weaning is unknown. We hypothesized that posture could modulate the breathing effort in difficult-to-wean patients.

METHODS

A prospective, crossover, physiologic study was performed in 24 intubated patients breathing with pressure support who had already failed a spontaneous breathing trial or an extubation episode. Their median duration of mechanical ventilation before measurements was 25 days. Breathing pattern, occlusion pressure (P (0.1)), intrinsic PEEP (PEEP(i)), and inspiratory muscle effort evaluated by the pressure-time product of the respiratory muscles and the work of breathing were measured during three postures: the seated position in bed (90°LD), simulating the position in a chair, the semi-seated (45°), and the supine (0°) positions consecutively applied in a random order. A comfort score was obtained in 17 cooperative patients. The influence of position on chest wall compliance was measured in another group of 11 sedated patients.

RESULTS

The 45° position was associated with the lowest levels of effort (p ≤ 0.01) and occlusion pressure (p < 0.05), and tended to be more often comfortable. Respiratory effort was the lowest at 45° in 18/24 patients. PEEP(i) and PEEP(i)-related work were slightly higher in the supine position (p ≤ 0.01), whereas respiratory effort, heart rate, and P (0.1) values were increased in the seated position (p < 0.05).

CONCLUSION

A 45° position helps to unload the respiratory muscles, moderately reduces PEEP(i), and is often considered as comfortable. The semi-seated position may help the weaning process in ventilator-dependent patients.

Positive pressure for obesity hypoventilation syndrome

Obesity is increasing world-wide; obesity hypoventilation syndrome (OHS), formerly Pickwickian syndrome, has increased in parallel. Despite its prevalence, OHS has not been studied well, but there is abundant evidence that it is tightly linked with sleep-disordered breathing, most commonly obstructive sleep apnea. This article reviews the pathophysiology of OHS as well as the literature regarding the benefits of treating this disorder with positive airway pressure. We also emphasize that while positive pressure treatments may temporize cardiopulmonary disease progression, simultaneous pursuit of weight reduction is central to long-term management of this condition.

Airway tube exchanger techniques in morbidly obese patients

Morbidly obese patients may present a challenge during airway management. When airway tube exchange is required, it can even be more challenging than the primary intubation. With the increasing prevalence of morbid obesity over the years, there will be increasing numbers of these patients presenting for surgical procedures, including ones that require endotracheal tube exchanges. It is therefore important for anesthesiologists to be familiar with options and limitations of the airway tube exchanger techniques.

Experience of severe desaturation during anesthetic induction period in an obese adult patient with Prader-Willi syndrome -A case report-

Prader-Willi syndrome is characterized by infantile hypotonia, childhood-onset obesity, short stature, mental retardation, hyperphagia, hypogonadism. After infantile hypotonia phase, patient is prone to morbid obesity due to hyperphagia. Complications associated with morbid obesity are recognized as the main risk factors for death the lifespan of patients with Prader-Willi syndrome. We experienced desaturation and bronchospasm during arteriovenous fistula surgery in an obese adult with Prader-Willi syndrome.

Oxygen delivery through high-flow nasal cannulae increase end-expiratory lung volume and reduce respiratory rate in post-cardiac surgical patients

BACKGROUND

High-flow nasal cannulae (HFNCs) create positive oropharyngeal airway pressure, but it is unclear how their use affects lung volume. Electrical impedance tomography allows the assessment of changes in lung volume by measuring changes in lung impedance. Primary objectives were to investigate the effects of HFNC on airway pressure (P(aw)) and end-expiratory lung volume (EELV) and to identify any correlation between the two. Secondary objectives were to investigate the effects of HFNC on respiratory rate, dyspnoea, tidal volume, and oxygenation; and the interaction between BMI and EELV.

METHODS

Twenty patients prescribed HFNC post-cardiac surgery were investigated. Impedance measures, P(aw), ratio, respiratory rate, and modified Borg scores were recorded first on low-flow oxygen and then on HFNC.

RESULTS

A strong and significant correlation existed between P(aw) and end-expiratory lung impedance (EELI) (r=0.7, P<0.001). Compared with low-flow oxygen, HFNC significantly increased EELI by 25.6% [95% confidence interval (CI) 24.3, 26.9] and P(aw) by 3.0 cm H(2)O (95% CI 2.4, 3.7). Respiratory rate reduced by 3.4 bpm (95% CI 1.7, 5.2) with HFNC use, tidal impedance variation increased by 10.5% (95% CI 6.1, 18.3), and ratio improved by 30.6 mm Hg (95% CI 17.9, 43.3). A trend towards HFNC improving subjective dyspnoea scoring (P=0.023) was found. Increases in EELI were significantly influenced by BMI, with larger increases associated with higher BMIs (P<0.001).

CONCLUSIONS

This study suggests that HFNCs reduce respiratory rate and improve oxygenation by increasing both EELV and tidal volume and are most beneficial in patients with higher BMIs.

Effect of PEEP on regional ventilation during laparoscopic surgery monitored by electrical impedance tomography

BACKGROUND

Anesthesia per se and pneumoperitoneum during laparoscopic surgery lead to atelectasis and impairment of oxygenation. We hypothesized that a ventilation with positive end-expiratory pressure (PEEP) during general anesthesia and laparoscopic surgery leads to a more homogeneous ventilation distribution as determined by electrical impedance tomography (EIT). Furthermore, we supposed that PEEP ventilation in lung-healthy patients would improve the parameters of oxygenation and respiratory compliance.

METHODS

Thirty-two patients scheduled to undergo laparoscopic cholecystectomy were randomly assigned to be ventilated with ZEEP (0 cmH(2)O) or with PEEP (10 cmH(2)O) and a subsequent recruitment maneuver. Differences in regional ventilation were analyzed by the EIT-based center-of-ventilation index (COV), which quantifies the distribution of ventilation and indicates ventilation shifts.

RESULTS

Higher amount of ventilation was examined in the dorsal parts of the lungs in the PEEP group. Throughout the application of PEEP, a lower shift of ventilation was found, whereas after the induction of anesthesia, a remarkable ventral shift of ventilation in ZEEP-ventilated patients (COV: ZEEP, 40.6 ± 2.4%; PEEP, 46.5 ± 3.5%; P<0.001) was observed. Compared with the PEEP group, ZEEP caused a ventral misalignment of ventilation during pneumoperitoneum (COV: ZEEP, 41.6 ± 2.4%; PEEP, 44 ± 2.7%; P=0.013). Throughout the study, there were significant differences in the parameters of oxygenation and respiratory compliance with improved values in PEEP-ventilated patients.

CONCLUSION

The effect of anesthesia, pneumoperitoneum, and different PEEP levels can be evaluated by EIT-based COV monitoring. An initial recruitment maneuver and a PEEP of 10 cmH(2)O preserved homogeneous regional ventilation during laparoscopic surgery in most, but not all, patients and improved oxygenation and respiratory compliance.

Should mechanical ventilation be guided by esophageal pressure measurements?

PURPOSE OF REVIEW

Despite the well recognized role of mechanical ventilation in lung injury, appropriate surrogate markers to guide titration of ventilator settings remain elusive. One would like to strike a balance between protecting aerated units from overdistension while recruiting unstable units, thereby reducing tissue damage associated with their cyclic recruitment and derecruitment. To do so requires some estimate of the topographical distribution of parenchymal stress and strain.

RECENT FINDINGS

Recent studies have highlighted the importance of chest wall recoil and its effect on pleural pressure (Ppl) in determining lung stress. Although esophageal pressure (Pes) has traditionally been used to measure the average Ppl in normal upright patients, in recumbent acute lung injury/acute respiratory distress syndrome patients Pes-based estimates of Ppl are subject to untestable assumptions. Nevertheless, Pes measurements in recumbent patients with injured lungs strongly suggest that Ppl over dependent parts of the lung can exceed airway pressure by substantial amounts. Moreover, results of a pilot study in which Pes was used to titrate positive end-expiratory pressure (PEEP) suggest clinical benefit.

SUMMARY

Notwithstanding its theoretical limitations, esophageal manometry has shown promise in PEEP titration and deserves further evaluation in a larger trial on patients with injured lungs.

A randomised trial comparing sufentanil versus remifentanil for laparoscopic gastroplasty in the morbidly obese patient

BACKGROUND AND OBJECTIVE

This prospective, randomised double-blind study compared the effects of target control infusion (TCI) of sufentanil and remifentanil on the quality of recovery and post-operative pain control in morbidly obese patients undergoing laparoscopic gastroplasty.

METHODS

Following institutional Ethics Committee approval and written informed consent, 100 morbidly obese patients were randomised to receive either TCI sufentanil (0.3 ng ml⁻¹; S-group; N = 50) or TCI remifentanil (3 ng ml⁻¹; R-group; N = 50) in combination with desflurane (O₂/air mixture: FiO₂, 50%). Quality of recovery was estimated by means of the modified Aldrete score and by the ability to perform psychomotor tests with the same competence post-operatively as pre-operatively. Post-operative pain was evaluated by the quantity of piritramide needed to achieve a visual analogue scale (VAS) less than 3. Statistical analysis was performed using an unpaired Student's t-test, Mann-Whitney U-test and χ² test, as appropriate.

RESULTS

Patient and surgical characteristics were similar among groups. In the R-group, time to extubation was significantly shorter, but VAS significantly higher than that in the S-group (P < 0.01). Quality of recovery and duration of post-anaesthesia care unit stay were comparable between groups (S-group: 119 ± 27 min and R-group: 119 ± 35 min). Piritramide consumption during the first 4 post-operative hours was higher in the R-group than in the S-group [S-group (median, range): 11.5 mg, 5.5-16.0; R-group: 18.0 mg, 14-22, P < 0.01], but not later on.

CONCLUSION

In the conditions of the present study, although TCI sufentanil resulted in slower awakening than TCI remifentanil, it was associated with a better quality of recovery.

Intensive care in the obese

Nearly 20% of all patients admitted to an intensive-care unit are obese. Their excess weight puts them at risk for several problems and complications during their intensive-care unit stay. Especially, pulmonary problems need particular attention, and comprehensive knowledge of the specific pathophysiologic changes of the respiratory system is important. Lung protective ventilation strategies, supplemented by lung-recruiting manoeuvres, may be feasible in critically ill obese patients with lung injury. Careful positioning of the obese is essential to optimise ventilation and facilitate weaning from mechanical ventilation. Optimal hypocaloric nutrition with a high proportion of proteins is advised to control hyperglycaemia. Because mortality in obese patients is similar to or lower than in non-obese ones, it is conceivable that obesity has a protective effect in the critically ill.

Sedation considerations for the nonintubated obese patient in critical care

Sedation of the obese critical care patient presents unique challenges that include altered respiratory function and a predisposition to respiratory suppression and airway obstruction. Sedative drugs have pronounced effects on obese patients. Knowledge of the anatomic and physiologic changes associated with obesity, airway management, and sedation agents better prepares one to care for these patients safely and effectively.

Non-invasive ventilation in postoperative patients: a systematic review

BACKGROUND

Postoperative pulmonary complications, generally defined as any pulmonary abnormality occurring in the postoperative period, are still a significant issue in clinical practice increasing hospital length of stay, morbidity and mortality. Non-invasive ventilation (NIV), primarily applied in cardiogenic pulmonary edema, decompensated COPD and hypoxemic pulmonary failure, is nowadays also used in perioperative settings.

OBJECTIVE

Investigate the application and results of preventive and therapeutic NIV in postsurgical patients.

DESIGN

A systematic review.

DATA SOURCES

Medical literature databases were searched for articles about "clinical trials," "randomized controlled trials" and "meta-analyses." The keywords "cardiac surgery," "thoracic surgery," "lung surgery," "abdominal surgery," "solid organ transplantation," "thoraco-abdominal surgery" and "bariatric surgery" were combined with any of these: "non-invasive positive pressure ventilation," "continuous positive airway pressure," "bilevel ventilation," "postoperative complications," "postoperative care," "respiratory care," "acute respiratory failure," "acute lung injury" and "acute respiratory distress syndrome."

RESULTS

Twenty-nine articles (N=2,279 patients) met the inclusion criteria. Nine studies evaluated NIV in post-abdominal surgery, three in thoracic surgery, eight in cardiac surgery, three in thoraco-abdominal surgery, four in bariatric surgery and two in post solid organ transplantation used both for prophylactic and therapeutic purposes. NIV improved arterial blood gases in 15 of the 22 prophylactic and in 4 of the 7 therapeutic studies, respectively. NIV reduced the intubation rate in 11 of the 29 studies and improved outcome in only 1.

CONCLUSIONS

Despite these limited data and the necessity of new randomized trials, NIV could be considered as a prophylactic and therapeutic tool to improve gas exchange in postoperative patients.

A comparison of desflurane versus propofol: the effects on early postoperative lung function in overweight patients

BACKGROUND

In this study, we evaluated the influence of propofol versus desflurane anesthesia in overweight patients on postoperative lung function and pulse oximetry values.

METHODS

We prospectively studied 134 patients with body mass indices of 25 to 35 kg/m(2) undergoing minor peripheral surgery lasting 40 to 120 minutes. Patients were randomly assigned to receive propofol (total IV anesthesia) or desflurane anesthesia via a tracheal tube targeting bispectral index values of 40 to 60. Premedication, adjuvant drug usage, and ventilation were standardized. We measured oxyhemoglobin saturation and lung function preoperatively (baseline), and at 10 minutes, 0.5 hour, 2 hours, and 24 hours after tracheal extubation. All values were measured with the patient supine, in a 30° head-up position. Changes from preoperative baseline values were first analyzed for the impact of body mass index and type of anesthesia using univariate methods, followed by linear regression and multivariate analysis of variance.

RESULTS

Within the first 2 hours after surgery, the propofol group displayed lower oxyhemoglobin saturation (at 2 hours, mean ± SD, 93.8% ± 2.0% vs 94.6% ± 2.1%; P < 0.007) and lung function (forced vital capacity, forced expiratory volume exhaled in 1 second [FEV(1)], peak expiratory flow, midexpiratory flow [MEF], forced inspiratory vital capacity, and peak inspiratory flow; between 11% and 20% larger reduction from baseline in the propofol group, all P < 0.001) compared with the desflurane group. Even 24 hours after surgery, FEV(1), peak expiratory flow, MEF, forced inspiratory vital capacity, and peak inspiratory flow were reduced more in the propofol group (all P < 0.01). At 2 hours after extubation, increasing obesity was associated with decreasing FEV(1) and MEF in patients anesthetized with propofol but not desflurane (P < 0.01).

CONCLUSION

We conclude that, for superficial surgical procedures of up to 120 minutes, maintenance of anesthesia with propofol impairs early postoperative lung function and pulse oximetry values more than with desflurane. Furthermore, increasing obesity decreases pulmonary function at 2 hours after propofol anesthesia but not after desflurane anesthesia.

The LMA CTrach™ in morbidly obese and lean patients undergoing gynecological procedures: a comparative study

PURPOSE

The tracheas of obese patients may be more difficult to intubate than those of normal-weight patients. The aim of this study was to compare the airway management quality in morbidly obese and lean patients with use of the LMA CTrach.

METHODS

After Ethics Committee approval, 60 adult patients (30 morbidly obese patients with body mass index >40 kg/m² and 30 lean patients with body mass index <30 kg/m²) scheduled to undergo gynecological surgery were enrolled in this prospective study. The induction of anesthesia was standardized using propofol, fentanyl, and rocuronium. Ventilation and intubation success rates, time taken to achieve successful ventilation, and intubation through the CTrach and airway complications were recorded.

RESULTS

The CTrach was successfully inserted and adequate ventilation through the CTrach was achieved in 59 patients (98%). Only 1 patient in the lean group was not able to ventilate through the CTrach. We were successful in endotracheal intubation, either under vision or blind, in 56 patients (93%). We were able to view the larynx in 51 patients (85%). Total intubation time was significantly longer in morbidly obese patients, 69 (311) s, than in lean patients, 33 (107) s [median (range)] (P < 0.001).

CONCLUSIONS

We concluded that the time to intubate the trachea in obese patients was significantly longer than in lean patients when the LMA CTrach was used.

Difficulties in managing the surgical patient who is morbidly obese

Managing patients who are morbidly obese in the intensive care unit is associated with a variety of problems uncommonly experienced with the those who are not morbidly obese. Clinicians experience a myriad of unique problems and circumstances, from the need for special beds and lifts to unusual and unknown volumes of distribution resulting in unclear drug dosing. This review examines several issues including sedation, invasive monitoring, venous thromboembolism prophylaxis, surgical infections, nutritional support, and other complications that may be of particular importance to the critically ill patient who is morbidly obese. In many cases, care is altered based on the complicating issues surrounding morbid obesity. In other cases, the presence of obesity suggests no alterations in our routine critical care delivery. A comprehensive review of the literature is undertaken, data are critically considered, and overall opinion is rendered based on the available peer-reviewed literature. In many cases, data are not available that address the specific patient population in question, so related papers (like gastric bypass data) are considered. Many issues do not have definitive answers based on randomized controlled trials, and much is left to treating clinician opinion and local practice patterns. Where good data exist, however, one should consider carefully and individually deviation from the evidence-based approach.

[The role of respiratory physiotherapy in the lung function of obese patients undergoing bariatric surgery. A review]

INTRODUCTION

Obesity, considered a new worldwide epidemic, is characterised by excess adipose tissue and contributes to a series of chronic diseases and increased mortality. Obesity associated to surgical procedure in these patients makes respiratory physiotherapy a must to recover lung function and prevent postoperative pulmonary complications.

AIMS

To assess the effects of respiratory physiotherapy on the lung function of obese patients undergoing weight loss surgery.

MATERIAL AND METHODS

We conducted a literature review October 2008-June 2009 of data which had been published over the last thirty years and which was available on the Medline, Pubmed ans Scielo databases.

CONCLUSION

Pre- and postoperative respiratory physiotherapy is vital for patients undergoing weight loss surgery irrespective of technique used, as it can prevent pulmonary complications inherent in the surgical procedure and aid lung function recovery.

Perioperative management of obese patients

Obesity is a metabolic disease that is on the increase all over the world. Up to 35% of the population in North America and 15-20% in Europe can be considered obese. Since these patients are characterised by several systemic physiopathological alterations, the perioperative management may present some problems, mainly related to their respiratory system. Body mass is an important determinant of respiratory function before and during anaesthesia not only in morbidly but also in moderately obese patients. These can manifest as (a) reduced lung volume with increased atelectasis; (b)derangements in respiratory system, lung and chest wall compliance and increased resistance; and (c) moderate to severe hypoxaemia. These physiological alterations are more marked in obese patients with hypercapnic syndrome or obstructive sleep apnoea syndrome. The suggested perioperative ventilation management includes (a) awake and/or facilitated endotracheal intubation by using a video-laryngoscope; (b) tidal volume of 6-10 ml kg(-1) ideal body weight, increasing respiratory rate to maintain physiological PaCO2, while avoiding intrinsic positive end-expiratory pressure (PEEPi); and (c) a recruitment manoeuvre (35-55 cmH2O for 6 s) followed by the application of an end-expiratory pressure (PEEP) of 10 cmH2O. The recruitment manoeuvre should always be performed only when a volemic and haemodynamic stabilisation is reached after induction of anaesthesia. In the postoperative period, beach chair position, aggressive physiotherapy, noninvasive respiratory support and short-term recovery in intermediate critical care units with care of fluid management and pain may be useful to reduce pulmonary complications.

A deep breath bronchoconstricts obese asthmatics

BACKGROUND

Asthma is characterized by the loss of a deep breath (DB)-induced bronchodilation and bronchoprotection. Obesity causes lung restriction and increases airway resistance, which may further worsen the capacity of a DB to induce bronchodilation; however, whether increasing BMI impairs the bronchodilatory response to a DB in asthmatics is unknown.

METHODS

The population consisted of 99 subjects, 87 with moderate to severe persistent asthma and 12 obese control subjects. Using transfer impedance we derived airway resistance (Raw). Participants breathed for 1 minute and took a slow DB followed by passive exhalation to functional residual capacity (FRC) and tidal breathing for another minute.

RESULTS

After a DB, obese asthmatics had the largest percent increase in Raw (median 9.8% interquartile range [IQR] 3.1-15.1), compared with overweight (6.5% IQR -1.3, 12.1) and lean (0.7% IQR -3, 7.9) asthmatics and obese controls (2.5% IQR -.6, 11) (p for trend = 0.008). The association between the percent increase in Raw after a DB and BMI as a continuous variable was significant (p = 0.02).

CONCLUSIONS

In obese, moderate to severe and poorly controlled asthmatics, a DB results in increased Raw. This phenomenon was not observed in leaner asthmatics of similar severity or in obese control subjects.

Xenon anesthesia improves respiratory gas exchanges in morbidly obese patients

Background. Xenon-in-oxygen is a high density gas mixture and may improve PaO2/FiO2 ratio in morbidly obese patients uniforming distribution of ventilation during anesthesia. Methods. We compared xenon versus sevoflurane anesthesia in twenty adult morbidly obese patients (BMI > 35) candidate for roux-en-Y laparoscopic gastric bypass and assessed PaO2/FiO2 ratio at baseline, at 15 min from induction of anaesthesia and every 60 min during surgery. Differences in intraoperative and postoperative data including heart rate, systolic and diastolic pressure, oxygen saturation, plateau pressure, eyes opening and extubation time, Aldrete score on arrival to the PACU were compared by the Mann-Whitney test and were considered as secondary aims. Moreover the occurrence of side effects and postoperative analgesic demand were assessed. Results. In xenon group PaO2-FiO2 ratio was significantly higher after 60 min and 120 min from induction of anesthesia; heart rate and overall remifentanil consumption were lower; the eyes opening time and the extubation time were shorter; morphine consumption at 72 hours was lower; postoperative nausea was more common. Conclusions. Xenon anesthesia improved PaO2/FiO2 ratio and maintained its distinctive rapid recovery times and cardiovascular stability. A reduction of opioid consumption during and after surgery and an increased incidence of PONV were also observed in xenon group.

Awake endotracheal intubation and prone patient self-positioning: anesthetic and positioning considerations during percutaneous nephrolithotomy in obese patients

BACKGROUND AND PURPOSE

Obesity is associated with adverse outcomes with certain urologic procedures and may make patient positioning more difficult. We describe our technique of awake intubation and prone patient self-positioning before percutaneous nephrolithotomy (PCNL), and review the literature regarding prone positioning in obese patients and the impact of obesity on PCNL.

METHODS

Patient preparation begins with detailed preoperative counseling regarding the procedure. Premedication with a sedative and antisialagogue is followed by airway topicalization to suppress gag reflex and pain. Fiberoptic bronchoscope intubation is then carried out. The patient then positions himself/herself comfortably before induction of general anesthesia.

RESULTS

We have successfully performed awake intubation and patient prone self-positioning followed by PCNL, most recently in a 58-year-old (body mass index 51.3 kg/m(2)) man with a history of gastric bypass, diabetes mellitus, and hypertension, without added morbidity. Adverse effect on patient cardiopulmonary dynamics can be minimized in the prone position.

CONCLUSIONS

The technique of awake intubation with prone patient self-positioning can be helpful for positioning morbidly obese patients before PCNL and has been safe and effective in properly selected patients. Efficacy of PCNL should not be impacted by obesity or prone positioning and morbidity minimized provided that surgical and anesthesia teams understand and safeguard against potential complications.

Pressure-dependent stress relaxation in acute respiratory distress syndrome and healthy lungs: an investigation based on a viscoelastic model

Introduction

Limiting the energy transfer between ventilator and lung is crucial for ventilatory strategy in acute respiratory distress syndrome (ARDS). Part of the energy is transmitted to the viscoelastic tissue components where it is stored or dissipates. In mechanically ventilated patients, viscoelasticity can be investigated by analyzing pulmonary stress relaxation. While stress relaxation processes of the lung have been intensively investigated, non-linear interrelations have not been systematically analyzed, and such analyses have been limited to small volume or pressure ranges. In this study, stress relaxation of mechanically ventilated lungs was investigated, focusing on non-linear dependence on pressure. The range of inspiratory capacity was analyzed up to a plateau pressure of 45 cmH₂O.

Methods

Twenty ARDS patients and eleven patients with normal lungs under mechanical ventilation were included. Rapid flow interruptions were repetitively applied using an automated super-syringe maneuver. Viscoelastic resistance, compliance and time constant were determined by multiple regression analysis using a lumped parameter model. This same viscoelastic model was used to investigate the frequency dependence of the respiratory system's impedance.

Results

The viscoelastic time constant was independent of pressure, and it did not differ between normal and ARDS lungs. In contrast, viscoelastic resistance increased non-linearly with pressure (normal: 8.4 (7.4-11.9) [median (lower - upper quartile)] to 35.2 (25.6-39.5) cmH₂O·sec/L; ARDS: 11.9 (9.2-22.1) to 73.5 (56.8-98.7)cmH₂O·sec/L), and viscoelastic compliance decreased non-linearly with pressure (normal: 130.1(116.9-151.3) to 37.4(34.7-46.3) mL/cmH₂O; ARDS: 125.8(80.0-211.0) to 17.1(13.8-24.7)mL/cmH₂O). The pulmonary impedance increased with pressure and decreased with respiratory frequency.

Conclusions

Viscoelastic compliance and resistance are highly non-linear with respect to pressure and differ considerably between ARDS and normal lungs. None of these characteristics can be observed for the viscoelastic time constant. From our analysis of viscoelastic properties we cautiously conclude that the energy transfer from the respirator to the lung can be reduced by application of low inspiratory plateau pressures and high respiratory frequencies. This we consider to be potentially lung protective.

Clinical review: Ventilatory strategies for obstetric, brain-injured and obese patients

The ventilatory management of patients with acute respiratory failure is supported by good evidence, aiming to reduce lung injury by pressure limitation and reducing the duration of ventilatory support by regular assessment for discontinuation. Certain patient groups, however, due to their altered physiology or disease-specific complications, may require some variation in usual ventilatory management. The present manuscript reviews the ventilatory management in three special populations, namely the patient with brain injury, the pregnant patient and the morbidly obese patient.

[Atelectasis in general anesthesia and alveolar recruitment strategies]

Atelectasis occurs in most patients during general anesthesia and is the main cause of hypoxemia. The objective of this review is to examine the causes and diagnosis of atelectasis and the different strategies for reducing or preventing this complication and improving oxygenation. Pulmonary atelectasis is mainly caused by 3 factors: compression, gas absorption, and lack of surfactant. Compression and gas absorption are, however, the 2 most commonly implicated factors. Lung collapse is accentuated if pure oxygen is inhaled during induction or if the patient is morbidly obese. Laparoscopic, thoracic, and upper abdominal interventions also carry risk of lung collapse. Various techniques may be used to prevent atelectasis or to reopen collapsed lung tissue. These include using positive end-expiratory pressure or a high tidal volume-thus providing a higher airway pressure (vital capacity maneuver)-or both in combination. Alveolar recruitment strategies have been tried in bariatric surgery, single-lung ventilation, laparoscopy, and adult respiratory distress syndrome. Their application has reduced or prevented atelectasis, thereby reducing postoperative pulmonary complications.

Alveolar recruitment and arterial desflurane concentration during bariatric surgery

BACKGROUND

We investigated whether reversal of intraoperative atelectasis with the lung recruitment maneuver (RM) affects desflurane arterial concentrations during bariatric surgery.

METHODS

After anesthetic induction and maintenance with propofol, patients were randomized to receive alveolar RM at intervals (RM group) or not (controls). Desflurane 6% was initiated, and rate of increase of alveolar desflurane concentration (ratio of end-expiratory to inspiratory concentrations, F(A)/F(I)) and desflurane blood concentrations were measured in both groups. Blood and end-tidal desflurane concentrations were also measured after the discontinuation of anesthesia.

RESULTS

The RM group had higher intraoperative Pao(2)/Fio(2) compared with the control group (both, P < 0.001). During induction, the rate of increase in blood desflurane concentrations was rapid in both groups. At comparable mechanical ventilation settings, median times to achieve 0.5 mM (approximately 3%) were 2.1 and 1.59 min (P = 0.09) in the control and RM group, respectively. The times to achieve 0.7 mM (approximately 4.2%) desflurane were 15.9 and 9.3 min in the control and RM group, respectively (P = 0.08). Desflurane blood concentrations tended to be higher during the first 30 min after induction in the RM group (P = 0.066). During maintenance or emergence, the blood desflurane concentrations were not different between control and RM groups. Consequently, the time to eye opening did not differ between groups.

CONCLUSION

Although the RM during bariatric surgery represents an effective method for improving intraoperative oxygenation, it does not significantly affect the desflurane blood concentrations during anesthesia or its elimination during emergence.