Clinically relevant diaphragmatic dysfunction after cardiac operations

Imaging of the Diaphragm Following Cardiac Surgery: Focus on Ultrasonographic Assessment

Diaphragm dysfunction is a common complication following cardiac surgery. Its clinical impact is variable, ranging from the absence of symptoms to the acute respiratory failure. Post-operative diaphragm dysfunction may negatively affect patients' prognosis delaying the weaning from the mechanical ventilation (MV), extending the time of hospitalization and increasing mortality. Ultrasonography is a valid tool to evaluate diaphragmatic impairment in different settings, like the Intensive Care Unit, to predict successful weaning from the MV, and the Cardiovascular Rehabilitation Unit, to stratify patients in terms of risk of functional recovery failure. The aim of this review is to describe the pathophysiology of post-cardiac surgery diaphragm dysfunction, the techniques used for its diagnosis and the potential applications of diaphragm ultrasound.

Association between diaphragmatic dysfunction after adult cardiovascular surgery and prognosis of mechanical ventilation: a retrospective cohort study

BACKGROUND

Diaphragmatic dysfunction often occurs after adult cardiovascular surgery. The prognostic effect of diaphragmatic dysfunction on ventilatory management in patients after cardiovascular surgery is unknown. This study aimed to investigate the association between diaphragmatic dysfunction and prognosis of ventilatory management in adult postoperative cardiovascular surgery patients.

METHODS

This study was a single-center retrospective cohort study conducted at a tertiary care university hospital. This study included adult patients admitted to the intensive care unit under tracheal intubation after cardiovascular surgery. Spontaneous breathing trial was performed, and bilateral diaphragmatic motion was assessed using ultrasonography; diaphragmatic dysfunction was classified as normal, incomplete dysfunction, or complete dysfunction. The primary outcome was weaning off in mechanical ventilation. The duration of mechanical ventilation was defined as duration from the date of ICU admission to the date of weaning off in mechanical ventilation. The secondary outcomes were reintubation, death from all causes, improvement of diaphragm position assessed by chest radiographs. The subdistribution hazard ratio or hazard ratio (HR) with 95% confidence of intervals (CIs) were estimated by Fine-Gray models or Cox proportional hazard models adjusted for potential confounders.

RESULTS

Of 153 patients analyzed, 49 patients (32.0%) had diaphragmatic dysfunction. Diaphragmatic dysfunction consisted of incomplete dysfunction in 38 patients and complete dysfunction in 11 patients. Diaphragmatic dysfunction groups had longer duration of mechanical ventilation (68 h [interquartile range (IQR) 39-114] vs 23 h [15-67], adjusted subdistribution HR 0.63, 95% CIs 0.43-0.92). There was a higher rate of reintubation (12.2% vs 2.9%, univariate logistic regression analysis p = 0.034, unadjusted odds ratio = 4.70, 95% CIs 1.12-19.65), and a tendency to have higher death from all causes in the diaphragmatic dysfunction group during follow-up period (maximum 6.5 years) (18.4% vs 9.6%, adjusted HR 1.64, 95% CIs 0.59-4.53). The time to improvement of diaphragm position on chest radiograph was significantly longer in the diaphragmatic dysfunction group (14 days [IQR 6-29] vs 5 days [IQR 2-10], adjusted subdistribution HR 0.54, 95% CIs 0.38-0.77).

CONCLUSIONS

Diaphragmatic dysfunction after adult cardiovascular surgery was significantly associated with longer duration of mechanical ventilation and higher reintubation.

Persistent diaphragm dysfunction after cardiac surgery is associated with adverse respiratory outcomes: a prospective observational ultrasound study

BACKGROUND

Transient diaphragm dysfunction is common during the first week after cardiac surgery; however, the precise incidence, risk factors, and outcomes of persistent diaphragm dysfunction are not well described.

METHODS

In a single-centre prospective cohort study, we included all consecutive patients over 18 yr who underwent elective cardiac surgery. Diaphragm function was evaluated with ultrasound (M-mode) by recording the excursion of both hemidiaphragms at two different time points: preoperatively and after the seventh postoperative day in patients breathing without assistance. Significant diaphragm dysfunction after the seventh day of the index cardiac surgery was defined as a decrease in diaphragm excursion below the lower limit of normal: at rest, < 9 mm for women and < 10 mm for men; after a sniff test, < 16 mm for women and < 18 mm for men.

RESULTS

Overall, 122 patients were included in the analysis. The median [interquartile range (IQR)] age was 69 [59-74] years and 96/122 (79%) were men. Ten (8%) patients had diaphragm dysfunction after the seventh postoperative day. We did not identify risk factors for persistent diaphragm dysfunction. Persistent diaphragm dysfunction was associated with a longer median [IQR] duration of noninvasive (8 [0-34] vs 0 [0-0] hr; difference in medians, 8 hr; 95% confidence interval [CI], 0 to 22; P < 0.001) and invasive mechanical ventilation (5 [3-257] vs 3[2-4] hr; difference in medians, 2 hr; 95% CI, 0.5 to 41; P = 0.008); a higher reintubation rate (4/10, 40% vs 1/112, 0.9%; relative risk, 45; 95% CI, 7.1 to 278; P < 0.0001), a higher incidence of pneumonia (4/10 [40%] vs 7/112 [6%]; relative risk, 6; 95% CI, 2 to 16; P < 0.001), and longer median [IQR] length of stay in the intensive care unit (8 [5-29] vs 4 [2-6] days; difference in medians, 4 days; 95% CI, 2 to 12; P = 0.002).

CONCLUSION

The incidence of persistent diaphragm dysfunction was 8% in patients undergoing elective cardiac surgery and was associated with adverse respiratory outcomes.

STUDY REGISTRATION

ClinicalTrials.gov (NCT04276844); prospectively registered 19 February 2020.

Diaphragm Ultrasound in Cardiac Surgery: State of the Art

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

Speckle tracking ultrasonography as a new tool to assess diaphragmatic function: a feasibility study

A reliable method of measuring diaphragmatic function at the bedside is still lacking. Widely used two-dimensional (2D) ultrasonographic measurements, such as diaphragm excursion, diaphragm thickness, and fractional thickening (FT) have failed to show clear correlations with diaphragmatic function. A reason for this is that 2D ultrasonographic measurements, like FT, are merely able to measure the deformation of muscular diaphragmatic tissue in the transverse direction, while longitudinal measurements in the direction of contracting muscle fibres are not possible. Speckle tracking ultrasonography, which is widely used in cardiac imaging, overcomes this disadvantage and allows observations of movement in the direction of the contracting muscle fibres, approximating muscle deformation and the deformation velocity. Several studies have evaluated speckle tracking as a promising method to assess diaphragm contractility in healthy subjects. This technical note demonstrates the feasibility of speckle tracking ultrasonography of the diaphragm in a group of 20 patients after an aortocoronary bypass graft procedure. The results presented herein suggest that speckle tracking ultrasonography is able to depict alterations in diaphragmatic function after surgery better than 2D ultrasonographic measurements.

Diaphragm Dysfunction After Cardiac Surgery: Reappraisal

OBJECTIVES

The aim of this study was to re-investigate the incidence, risk factors, and outcomes of postoperative diaphragmatic dysfunction (DD) with actual cardiac surgery procedures.

DESIGN

Single-center, retrospective, observational study based on a prospectively collected database.

SETTING

Tertiary care cardiac surgery center.

PARTICIPANTS

Patients who underwent cardiac surgery between January 2016 and September 2019.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The DD group included patients with clinically perceptible diaphragmatic paralysis, which was confirmed by chest ultrasound (amplitude of the diaphragm movement in time-motion mode at rest, after a sniff test). The primary endpoint was the incidence of DD. Among 3,577 patients included, the authors found 272 cases of DD (7.6%). Individuals with DD had more arterial hypertension (64.3% v 52.6%; p < 0.0001), higher body mass index (BMI) (28 [25-30] kg/m²v 26 [24-29] kg/m²; p < 0.0002), and higher incidence of coronary bypass grafting (CABG) (58.8% v 46.6%; p = 0.0001). DD was associated with more postoperative pneumonia (23.9% v 8.7%; p < 0.0001), reintubation (8.8% v 2.9%; p < 0.0001), tracheotomy (3.3% v 0.3%; p < 0.0001), noninvasive ventilation (45.6% v 5.4%; p < 0.0001), duration of mechanical ventilation (five [four-11] hours v four [three-six] hours; p < 0.0001), and intensive care unit and hospital stays (14 [11-17] days v 13 [11-16] days; p < 0.0001). In multivariate analysis, DD was associated with CABG (odds ratio [OR] 1.9 [1.5-2.6]; p = 0.0001), arterial hypertension (OR 1.4 [1.1-1.9]; p = 0.008), and BMI (OR per point 1.04 [1.01-1.07] kg/m²; p = 0.003).

CONCLUSIONS

The incidence of symptomatic DD after cardiac surgery was 7.6%, leading to respiratory complications and increased ICU stay. CABG was the principal factor associated with DD.

Oesophageal pressure and respiratory muscle ultrasonographic measurements indicate inspiratory effort during pressure support ventilation

BACKGROUND

Bedside measures of patient effort are essential to properly titrate the level of pressure support ventilation. We investigated whether the tidal swing in oesophageal (ΔPes) and transdiaphragmatic pressure (ΔPdi), and ultrasonographic changes in diaphragm (TFdi) and parasternal intercostal (TFic) thickening are reliable estimates of respiratory effort. The effect of diaphragm dysfunction was also considered.

METHODS

Twenty-one critically ill patients were enrolled: age 73 (14) yr, BMI 27 (7) kg m^-2, and Pao₂/Fio₂ 33.3 (9.2) kPa. A three-level pressure support trial was performed: baseline, 25% (PS-medium), and 50% reduction (PS-low). We recorded the oesophageal and transdiaphragmatic pressure-time products (PTPs), work of breathing (WOB), and diaphragm and intercostal ultrasonography. Diaphragm dysfunction was defined by the Gilbert index.

RESULTS

Pressure support was 9.0 (1.6) cm H₂O at baseline, 6.7 (1.3) (PS-medium), and 4.4 (1.0) (PS-low). ΔPes was significantly associated with the oesophageal PTP (R²=0.868; P<0.001) and the WOB (R²=0.683; P<0.001). ΔPdi was significantly associated with the transdiaphragmatic PTP (R²=0.820; P<0.001). TFdi was only weakly correlated with the oesophageal PTP (R²=0.326; P<0.001), and the correlation improved after excluding patients with diaphragm dysfunction (R²=0.887; P<0.001). TFdi was higher and TFic lower in patients without diaphragm dysfunction: 33.6 (18.2)% vs 13.2 (9.2)% and 2.1 (1.7)% vs 12.7 (9.1)%; P<0.0001.

CONCLUSIONS

ΔPes and ΔPdi are adequate estimates of inspiratory effort. Diaphragm ultrasonography is a reliable indicator of inspiratory effort in the absence of diaphragm dysfunction. Additional measurement of parasternal intercostal thickening may discriminate a low inspiratory effort or a high effort in the presence of a dysfunctional diaphragm.

Early changes in diaphragmatic function evaluated using ultrasound in cardiac surgery patients: a cohort study

Little is known about the evolution of diaphragmatic function in the early post-cardiac surgery period. The main purpose of this work is to describe its evolution using ultrasound measurements of muscular excursion and thickening fraction (TF). Single-center prospective study of 79 consecutive uncomplicated elective cardiac surgery patients, using motion-mode during quiet unassisted breathing. Excursion and TF were measured sequentially for each patient [pre-operative (D1), 1 day (D2) and 5 days (D3) after surgery]. Pre-operative median for right and left hemidiaphragmatic excursions were 1.8 (IQR 1.6 to 2.1) cm and 1.7 (1.4 to 2.0) cm, respectively. Pre-operative median right and left thickening fractions were 28 (19 to 36) % and 33 (22 to 51) %, respectively. At D2, there was a reduction in both excursion (right: 1.5 (1.1 to 1.8) cm, p < 0.001, left: 1.5 (1.1 to 1.8), p = 0.003) and thickening fractions (right: 20 (15 to 34) %, p = 0.021, left: 24 (17 to 39) %, p = 0.002), followed by a return to pre-operative values at D3. A positive moderate correlation was found between excursion and thickening fraction (Spearman's rho 0.518 for right and 0.548 for left hemidiaphragm, p < 0.001). Interobserver reliability yielded a bias below 0.1 cm with limits of agreement (LOA) of ± 0.3 cm for excursion and - 2% with LOA of ± 21% for thickening fractions. After cardiac surgery, the evolution of diaphragmatic function is characterized by a transient impairment followed by a quick recovery. Although ultrasound diaphragmatic excursion and thickening fraction are correlated, excursion seems to be a more feasible and reproducible method in this population.

Diaphragm thickening in cardiac surgery: a perioperative prospective ultrasound study

Background

Diaphragm paresis is common after cardiac surgery and may delay the weaning from the ventilator. Our objective was to evaluate diaphragm thickening during weaning and secondly the muscle thickness as a marker of myotrauma.

Methods

Patients undergoing elective cardiac surgery were prospectively included. Ultrasonic index of right hemidiaphragm thickening fraction (TF) was measured as a surrogate criterion of work of breathing. A TF < 20% was defined as a low diaphragm thickening. Measurements of TF were performed during three periods to study diaphragm thickening evolution defined by the difference between two consecutive time line point: preoperative (D − 1), during a spontaneous breathing trial (SBT) in the intensive care unit and postoperative (D + 1). We studied three patterns of diaphragm thickness at end expiration evolution from D − 1 to D + 1: > 10% decrease, stability and > 10% increase. Demographical data, length of surgery, type of surgery, ICU length of stay (LOS) and extubation failure were collected.

Results

Of the 100 consecutively included patients, 75 patients had a low diaphragm thickening during SBT. Compared to TF values at D − 1 (36% ± 18), TF was reduced during SBT (17% ± 14) and D + 1 (12% ± 11) (P < 0.0001). Thickness and TF did not change according to the type of surgery or cooling method. TF at SBT was correlated to the length of surgery (both r = − 0.4; P < 0.0001). Diaphragm thickness as continuous variable did not change over time. Twenty-eight patients (42%) had a > 10% decrease thickness, 19 patients (29%) stability and 19 patients (28%) in > 10% increase, and this thickness evolution pattern was associated with: a longer LOS 3 days [2–5] versus 2 days [2–4] and 2 days [2], respectively (ANOVA P = 0.046), and diaphragm thickening evolution (ANOVA P = 0.02). Two patients experience extubation failure.

Conclusion

These findings indicate that diaphragm thickening is frequently decreased after elective cardiac surgery without impact on respiratory outcome, whereas an altered thickness pattern was associated with a longer length of stay in the ICU. Contractile activity influenced thickness evolution.

Trial registry number ClinicalTrial.gov ID NCT02208479

Electronic supplementary material

The online version of this article (10.1186/s13613-019-0521-z) contains supplementary material, which is available to authorized users.

Variable Definitions: Implications for the Prediction of Pulmonary Complications after Adult Cardiac Surgery

AIM

The aim of this paper was to review the implications that variable definitions have for the prediction of post-operative pulmonary complications after cardiac surgery.

METHOD

A review of the literature from 1980 to 2002. Selected studies demonstrated an original attempt to examine multivariate associations between pre, intra or post-operative antecedents and pulmonary outcomes in patients undergoing coronary artery bypass grafting (CABG). Reports that described the validation of established clinical prediction rules, testing interventions or research conducted in non-human cohorts were excluded from this review.

RESULTS

Consistently, variable factor and outcome definitions are combined for the development of multivariate prediction models that subsequently have limited clinical value. Despite being prevalent there are very few attempts to examine post-operative pulmonary complications (PPC) as endpoints in isolation. The trajectory of pulmonary dysfunction that precedes complications in the post-operative context is not clear. As such there is little knowledge of post-operative antecedents to PPC that are invariably excluded from model development.

CONCLUSION

Multivariate clinical prediction rules that incorporate antecedent patient and process factors from the continuum of cardiovascular care for specific pulmonary outcomes are recommended. Models such as these would be useful for practice, policy and quality improvement.

Controversies in Weaning from Mechanical Ventilation

Invasive mechanical ventilation can successfully support the patient with acute respiratory failure, but it is associated with considerable risks. Numerous complications of invasive mechanical ventilation have been identified, and these may contribute to increased mortality. Therefore after clinical improvement has occurred, considerable emphasis is placed on expeditiously freeing the patient from the ventilator. This process of getting a patient off mechanical ventilation has been variably termed weaning, liberation, or discontinuation (terms which may be used interchangeably), and can be further divided into “readiness testing” and “progressive withdrawal.” Over the last decade, new developments in our understanding of the process of weaning have provided investigators with the tools to address a number of key questions: How should readiness for weaning (and trials of spontaneous breathing) be determined? What is the role of weaning parameters in deciding when to initiate the weaning process? What is the best mode for conducting a spontaneous breathing trial and how should the patient be monitored? What are the mechanisms for weaning (and spontaneous breathing trial) failure? What is the best technique to facilitate progressive withdrawal? What other factors can facilitate liberation from mechanical ventilation? What are the risks of extubation failure and how can extubation outcome best be predicted? What is the role for protocols in facilitating weaning from mechanical ventilation?.

Use of Angle-Independent M-Mode Sonography for Assessment of Diaphragm Displacement

OBJECTIVES

Sonographic assessment of diaphragm displacement has conventionally been conducted with M-mode sonography via an anterior subcostal approach. This method is subject to measurement errors when diaphragm displacement is not in line with the M-mode plane. We aimed to compare measurements obtained by offline angle-independent (anatomic) M-mode sonography with conventional M-mode sonography.

METHODS

Fifty healthy adults were imaged with conventional and angle-independent M-mode sonography of the bilateral hemidiaphragms at 60% maximal inspiratory capacity using an inspiratory spirometer.

RESULTS

Left hemidiaphragm displacement was successfully imaged by conventional M-mode sonography in only 70% (n = 35), as lung expansion obscured imaging, whereas 92% (n = 46) were assessable by angle-independent M-mode sonography. All right hemidiaphragm displacement could be assessed. Conventional M-mode results were higher than angle-independent M-mode results on the right (mean ± SD, 4.9 ± 1.4 versus 4.6 ± 1.2 cm, respectively; P= .003) and left (5.4 ± 1.3 versus 4.6 ± 1.0 cm; P < .001). Displacement values were different for right versus left hemidiaphragms on conventional M-mode sonography (mean difference, 0.6 ± 0.2 cm; P = .005), with only mild agreement (R² = 0.35; P < .001). There was no laterality seen in the diaphragm displacement on angle-independent M-mode sonography (mean difference, 0.1 ± 0.1 cm; P = .47), with good agreement (R² = 0.76; P < .001).

CONCLUSIONS

Angle-independent M-mode sonography leads to better visualization and assessment of the left hemidiaphragm. It records lower displacement than conventional M-mode sonography in the bilateral diaphragms, likely because of fewer orientation and translation errors. Future study is indicated to assess the clinical utility of angle-independent M-mode sonography in a population with diaphragm dysfunction.

High thoracic anesthesia offers no major benefit over general anesthesia in on-pump cardiac surgery patients: a retrospective study

BACKGROUND

Thoracic epidural anesthesia (TEA) has been proposed to improve and facilitate early postoperative outcome in cardiac surgery. The aim of our study was to analyze early postoperative outcome data of patients undergoing cardiac surgery under general anesthesia (GA) with comparison to patients receiving combined TEA and GA.

METHODS

Medical records data from 288 patients who underwent elective on-pump cardiac surgery were retrieved and analyzed. Patients were divided into two study groups according to the type of anesthesia used: GA group (n = 141) and TEA group (n = 147). Early postoperative outcome data including quality of analgesia and major organ outcome parameters were compared between the study groups.

RESULTS

There was no major difference in early postoperative outcome data between the study groups, except for shorter time to extubation (6.0 ± 10.0 vs. 6.9 ± 8.8 h, respectively, P < 0.05) and hospital stay (10.7 ± 5.9 vs. 12.9 ± 8.8 days, respectively, P < 0.05) in TEA group compared to GA group. Also TEA group as compared to GA group had lower pain numeric rating scale scores (1 ± 1.1 vs. 1.4 ± 1.5 at 24 h, respectively, P < 0.05) and morphine requirements during the first 24 h after surgery (148.2 vs. 193 ± 85.4 μg/kg, respectively, P < 0.05).

CONCLUSION

Both anesthetic methods were equivalent in most postoperative outcome measures. Thoracic epidural analgesia provided superior pain relief, shorter time to extubation and earlier hospital discharge.

The Effects of Phrenic Nerve Degeneration by Axotomy and Crush on the Electrical Activities of Diaphragm Muscles of Rats

The aim of this study was to investigate the effect of axotomy and crush-related degeneration on the electrical activities of diaphragm muscle strips of experimental rats. In the present study, twenty-one male Wistar-albino rats were used and divided into three groups. The animals in the first group were not crushed or axotomized and served as controls. Phrenic nerves of the rats in the second and third groups were crushed or axotomized in the diaphragm muscle. Resting membrane potential (RMP) was decreased significantly in both crush and axotomy of diaphragm muscle strips of experimental rats (p < 0.05). Depolarization time (T DEP) and half-repolarization (1/2 RT) time were significantly prolonged in crush and axotomy rats (p < 0.05). Crushing or axotomizing the phrenic nerves may produce electrical activities in the diaphragm muscle of the rat by depolarization time and half-repolarization time prolonged in crush and axotomy rats.

Ultrasonography for Screening and Follow-Up of Diaphragmatic Dysfunction in the ICU

Purpose:

Reversibility and impact of diaphragmatic dysfunction (DD) are unknown. The principal aim was to describe diaphragmatic function as assessed by ultrasonography during weaning trials.

Materials and Methods:

The present study is a 6-month single-center prospective study. All patients under mechanical ventilation for more than 7 days and eligible for a spontaneous breathing trial (SBT) were enrolled prospectively.

Intervention:

Two blinded ultrasonographers evaluated each hemidiaphragm during SBT. Prevalence of DD among weaning failure and death and interobserver reproducibility have been evaluated.

Results:

The 34 included patients had a mean Simplified Acute Physiology Score version II of 55.7 ± 14 and a median intensive care unit (ICU) stay length of 17 days (13-30). Diaphragmatic dysfunction was found in 13 (38%) patients, on both sides in 8. Bilateral DD resolved before ICU discharge in 5 of the 7 reevaluated patients. No weaning failures were recorded. The ICU mortality was higher in patients with DD (37% vs 5%, P = .048). Mean interobserver agreement rate was 91%. Reproducibility was better with M-mode.

Conclusion:

The ICU-acquired DD usually improves before ICU discharge but might constitute a marker for greater disease severity. The present preliminary results require confirmation in a larger prospective multicenter study.

Improving ultrasonic measurement of diaphragmatic excursion after cardiac surgery using the anatomical M-mode: a randomized crossover study

PURPOSE

Motion-mode (MM) echography allows precise measurement of diaphragmatic excursion when the ultrasound beam is parallel to the diaphragmatic displacement. However, proper alignment is difficult to obtain in patients after cardiac surgery; thus, measurements might be inaccurate. A new imaging modality named the anatomical motion-mode (AMM) allows free placement of the cursor through the numerical image reconstruction and perfect alignment with the diaphragmatic motion. Our goal was to compare MM and AMM measurements of diaphragmatic excursion in cardiac surgical patients.

METHODS

Cardiac surgical patients were studied after extubation. The excursions of the right and left hemidiaphragms were measured by two operators, an expert and a trainee, using MM and AMM successively, according to a blinded, randomized, crossover sequence. Values were averaged over three consecutive respiratory cycles. The angle between the MM and AMM cursors was quantified for each measurement.

RESULTS

Fifty patients were studied. The mean (±SD) angle between the MM and AMM cursors was 37° ± 16°. The diaphragmatic excursion as measured by experts was 1.8 ± 0.7 cm using MM and 1.5 ± 0.5 cm using AMM (p < 0.001). Overall, the diaphragmatic excursion as estimated by MM was larger than the value obtained with AMM in 75 % of the measurements. Bland-Altman analysis showed tighter limits of agreement between experts and trainees with AMM [bias: 0.0 cm; 95 % confidence interval (CI): 0.8 cm] than with MM (bias: 0.0 cm; 95 % CI: 1.4 cm).

CONCLUSION

MM overestimates diaphragmatic excursion in comparison to AMM in cardiac surgical patients. Using MM may lead to a lack of recognition of diaphragmatic dysfunction.

Diaphragm ultrasonography to estimate the work of breathing during non-invasive ventilation

PURPOSE

Ultrasonography allows the direct observation of the diaphragm. Its thickness variation measured in the zone of apposition has been previously used to diagnose diaphragm paralysis. We assessed the feasibility and accuracy of this method to assess diaphragmatic function and its contribution to respiratory workload in critically ill patients under non-invasive ventilation.

METHODS

This was a preliminary physiological study in the intensive care unit of a university hospital. Twelve patients requiring planned non-invasive ventilation after extubation were studied while spontaneously breathing and during non-invasive ventilation at three levels of pressure support (5, 10 and 15 cmH(2)O). Diaphragm thickness was measured in the zone of apposition during tidal ventilation and the thickening fraction (TF) was calculated as (thickness at inspiration - thickness at expiration)/thickness at expiration. Diaphragmatic pressure-time product per breath (PTP(di)) was measured from oesophageal and gastric pressure recordings.

RESULTS

PTP(di) and TF both decreased as the level of pressure support increased. A significant correlation was found between PTP(di) and TF (ρ = 0.74, p < 0.001). The overall reproducibility of TF assessment was good but the coefficient of repeatability reached 18% for inter-observer reproducibility.

CONCLUSIONS

Ultrasonographic assessment of the diaphragm TF is a non-invasive method that may prove useful in evaluating diaphragmatic function and its contribution to respiratory workload in intensive care unit patients.

Identification of prolonged phrenic nerve conduction time in the ICU: magnetic versus electrical stimulation

PURPOSE

Retrospective study of prospectively collected data to assess the reliability of cervical magnetic stimulation (CMS) to detect prolonged phrenic nerve (PN) conduction time at the bedside. Because PN injuries may cause diaphragm dysfunction, their diagnosis is relevant in intensive care units (ICU). This is achieved by studying latency and amplitude of diaphragm response to PN stimulation. Electrical stimulation (ES) is the gold standard, but it is difficult to perform in the ICU. CMS is an easy noninvasive tool to assess PN integrity, but co-activates muscles that could contaminate surface chest electromyographic recordings.

METHODS

In a first set of 56 ICU patients with suspected PN injury, presence and latency of compound motor action potentials elicited by CMS and ES were compared. With ES as the reference method, CMS was evaluated as a test designed to indicate presence or absence of PN injury. In eight additional patients, intramuscular diaphragm recordings were compared with surface diaphragm recordings and with the electromyograms of possible contamination sources.

RESULTS

The sensitivity of CMS to diagnose abnormal PN conduction was 0.91, and specificity was 0.84, whereas positive and negative predictive values were 0.81 and 0.92, respectively. Passing-Bablok regression analysis suggested no differences between the two measures. The correlation between PN latency in response to CMS and ES was significant. The "diaphragm surface" and "needle" latencies were close, and were significantly different from those of possibly contaminating muscles. One hemidiaphragm showed likely signal contamination.

CONCLUSION

CMS provides an easy reliable tool to detect prolonged PN conduction time in the ICU.

Can lung volumes and capacities be used as an outcome measure for phrenic nerve recovery after cardiac surgeries?

Phrenic nerve is the main nerve drive to the diaphragm and its injury is a well-known complication following cardiac surgeries. It results in diaphragmatic dysfunction with reduction in lung volumes and capacities. This study aimed to evaluate the objectivity of lung volumes and capacities as an outcome measure for the prognosis of phrenic nerve recovery after cardiac surgeries. In this prospective experimental study, patients were recruited from Cardio-Thoracic Surgery Department, Educational-Hospital of College of Medicine, Cairo University. They were 11 patients with right phrenic nerve injury and 14 patients with left injury. On the basis of receiving low-level laser irradiation, they were divided into irradiated group and non-irradiated group. Measures of phrenic nerve latency, lung volumes and capacities were taken pre and post-operative and at 3-months follow up. After 3 months of low-level laser therapy, the irradiated group showed marked improvement in the phrenic nerve recovery. On the other hand, vital capacity and forced expiratory volume in the first second were the only lung capacity and volume that showed improvement consequent with the recovery of right phrenic nerve (P value <0.001 for both). Furthermore, forced vital capacity was the single lung capacity that showed significant statistical improvement in patients with recovered left phrenic nerve injury (P value <0.001). Study concluded that lung volumes and capacities cannot be used as an objective outcome measure for recovery of phrenic nerve injury after cardiac surgeries.

Helmet with specific settings versus facemask for noninvasive ventilation

OBJECTIVE

To compare the physiologic effects of noninvasive pressure-support ventilation (NPSV) delivered by a facemask, a helmet with the same settings, and a helmet with specific settings. Inspiratory muscle effort, gas exchange, patient-ventilator synchrony, and comfort were evaluated.

DESIGN

Prospective crossover study.

SETTING

A 13-bed medical intensive care unit in a university hospital.

PATIENTS

Eleven patients at risk for respiratory distress requiring early NPSV after extubation.

INTERVENTION

One hour after extubation, three 20-minute NPSV periods were delivered in a random order by facemask, helmet, and helmet with 50% increases in both pressure support and positive end-expiratory pressure and with the highest pressurization rate (95% max).

MEASUREMENTS AND MAIN RESULTS

Flow and airway, esophageal, and gastric pressure signals were measured under the three NPSV conditions and during spontaneous breathing. Compared with the facemask, the helmet with the same settings resulted in a greater inspiratory muscle effort, but this difference was abolished by the specific settings (pressure-time product in cm H2O.s.min, 63.8 [27.3-85.9], 81.8 [36.0-111.5], and 58.0 [25.4-79.5], respectively, p < 0.05, compared with 209.3 [29.8-239.6] during spontaneous breathing). Compared with the facemask, the helmet with the same settings worsened patient-ventilator synchrony, as indicated by longer triggering-on and cycling-off delays (0.14 [0.11-0.20] seconds vs. 0.32 [0.26-0.43] seconds, p < 0.05; and 0.20 [0.08-0.24] seconds vs. 0.27 [0.25-0.35] seconds, p < 0.01, respectively). The specific settings significantly improved the triggering-on delay compared with the helmet without specific settings (p < 0.01). Tolerance was the same with the three methods.

CONCLUSIONS

Our results suggest that increasing both the pressure-support level and positive end-expiratory pressure and using the highest pressurization rate may be advisable when providing NPSV via a helmet.

Ultrasonographic diagnostic criterion for severe diaphragmatic dysfunction after cardiac surgery

BACKGROUND

Severe diaphragmatic dysfunction can prolong mechanical ventilation after cardiac surgery. An ultrasonographic criterion for diagnosing severe diaphragmatic dysfunction defined by a reference technique such as transdiaphragmatic pressure measurements has never been determined.

METHODS

Twenty-eight patients requiring mechanical ventilation > 7 days postoperatively were studied. Esophageal and gastric pressures were measured to calculate transdiaphragmatic pressure during maximal inspiratory effort and the Gilbert index, which evaluates the diaphragm contribution to respiratory pressure swings during quiet ventilation. Ultrasonography allowed measuring right and left hemidiaphragmatic excursions during maximal inspiratory effort. Best E is the greatest positive value from either hemidiaphragm. Twenty cardiac surgery patients with uncomplicated postoperative course were also evaluated with ultrasonography preoperatively and postoperatively. Measurements were performed in semirecumbent position.

RESULTS

Transdiaphragmatic pressure during maximal inspiratory effort was below normal value in 27 of the 28 patients receiving prolonged mechanical ventilation (median, 39 cm H(2)O; interquartile range [IQR] 28 cm H(2)O). Eight patients had Gilbert indexes <or= 0 indicating severe diaphragmatic dysfunction. Best E was lower in patients with Gilbert index <or= 0 than > 0 (30 mm; IQR, 10 mm; vs 19 mm; IQR, 7 mm, respectively; p = 0.001). Best E < 25 mm had a positive likelihood ratio of 6.7 (95% confidence interval [CI], 2.4 to 19) and a negative likelihood ratio of 0 (95% CI, 0 to 1.1) for having a Gilbert index <or= 0. None of the patients with uncomplicated course had Best E < 25 mm either preoperatively or postoperatively.

CONCLUSIONS

Ultrasonographic-based determination of hemidiaphragm excursions in patients requiring prolonged mechanical ventilation after cardiac surgery may help identify those with and without severe diaphragmatic dysfunction as defined by the Gilbert index.

Right hemi-diaphragm paralysis following cardiac radiofrequency ablation

Diaphragm paralysis may occur after traumatic phrenic nerve injury. Here we report three patients in whom right hemi-diaphragmatic paralysis developed after cardiac radiofrequency ablation. We hypothesise that local focused thermal energy at the time of the ablation may have caused direct neuronal damage by axonal coagulation necrosis. The prognosis for this type of injury may be reasonably good; two of the three patients fully recovered diaphragm function by 1 year.

Topical Cooling for Myocardial Protection: The Results of a Prospective Randomized Study of the "Shallow Technique"

INTRODUCTION AND BACKGROUND

Respiratory distress following cardiac surgery is a troublesome complication. In several cases it is associated to cool-related phrenic nerve injury (PNI) after adoption of iced slush or hypothermic cardiopulmonary bypass. We compare two different strategies for myocardial protection: the "shallow technique" (ST) (dripping and prompt removal of cold saline solution from the epicardial surface) plus normothermic cardiopulmonary bypass, versus mild hypothermic cardiopulmonary bypass plus iced slush.

METHODS

Two hundred forty-nine patients undergoing elective cardiac surgery were randomly assigned to receive either ST (Group A) or iced slush (Group B). Occurrence of postoperative PNI (abnormal diaphragmatic movement plus alteration of nerve conduction) was evaluated. Multivariate analysis was performed for identification of factors associated to PNI. Patients had a 6-month follow-up.

RESULTS

PNI and failure of extubation occurred more frequently in Group B (p = 0.009 and p = 0.034, respectively), but there was no statistically significant difference in mean intensive care unit stay. Diabetes and the use of iced slush were independent predictors of phrenic dysfunction, while internal thoracic artery (ITA) harvest was a significant risk factor only among Group B patients. Abnormal diaphragmatic movement was persistent at 6 months only in 30% of Group B individuals who suffered this complication in the early postoperative.

CONCLUSIONS

ST likely reduces the incidence of postoperative PNI and might be protective mainly in the event of ITA harvest. It should be considered as a valuable tool for myocardial protection protocols.

Diaphragmatic paralysis after cardiac surgery in children: incidence, prognosis and surgical management

Diaphragmatic paralysis (DP) after cardiac surgery is an important complication especially in infants. We analyzed the incidence, clinical course, surgical management and follow up of the patients with DP, retrospectively. Between 1996 and 2005, 3,071 patients underwent cardiac surgery. Total number of patients with DP was 152 (4.9%). Out of 152 patients, 42 were surgically treated with transthoracic diaphragm plication (1.3%). The overall incidence of diaphragm paralysis was higher in correction of tetralogy of Fallot (31.5%), Blaloc-Taussig (B-T) shunt (11.1%) and VSD closure with pulmonary artery patch plasty (11.1). The incidence of DP which require plication was higher in B-T shunt (23.8%) arterial switch (19%) and correction of tetralogy of Fallot (11.9%). Mean and median age at the time of surgery were 17.8 +/- 3.6 and 6 months, respectively. Median time from cardiac surgery to surgical plication was 12 days. Indications for plication were repeated reintubations (n = 22), failure to wean from ventilator (n = 12), recurrent lung infections (n = 5) and persistent respiratory distress (n = 3). Mortality rate was 19.1%. Being under 1 year of age, pneumonia and plication 10 days after mechanical ventilation were associated with higher incidence mortality (P < 0.05). Phrenic nerve injury is a serious complication of cardiac surgery. It is more common after some special procedures. Spontaneous recovery is very rare. Being under 1 year of age, plication after 10 days from the surgery and pneumonia are major risk factors for mortality even in plicated patients. Transthoracic plication is helpful if performed early.

Assessment of diaphragmatic function with cervical magnetic stimulation in critically ill patients

The objective of this study was to evaluate a non-volitional measurement to assess diaphragmatic function in intubated and mechanically ventilated patients in a prospective pilot interventional clinical trial. The study was conducted in an 18-bed postoperative intensive care unit based at a university hospital. Patients were prospectively assigned to two groups. Group 1 consisted of eight patients with ventilator weaning failure. Group 2 consisted of eight intubated and ventilated patients who were studied shortly after major surgery and were successfully extubated there-after The twitch pressure response after cervical magnetic stimulation of the phrenic nerves was measured at the endotracheal tube at different PEEP levels. In group 2 the twitch transdiaphragmatic pressure, defined as the difference between twitch gastric and twitch oesophageal pressure was also evaluated. In group 1 the mean twitch pressure at the endotracheal tube on PEEP 0, 5 and 10 cmH2O was 5.2, 4.5 and 2.6 cmH2O: In group 2 this was significantly higher (15.1 cmH2O on PEEP 0 and 12.2 cmH2O on PEEP 5). A good correlation was found between twitch diaphragmatic pressure and twitch pressure at the endotracheal tube (r2 = 0.96) and between twitch oesophageal pressure and twitch pressure at the endotracheal tube (r2 = 0.98). Patients with weaning failure have significantly lower twitch pressure at the endotracheal tube suggesting diaphragmatic dysfunction. Twitch pressure at the endotracheal tube may be a useful parameter to screen for diaphragmatic dysfunction in intubated critically ill patients. Further studies are needed to confirm these preliminary findings.

Left hemidiaphragmatic mobility: assessment with ultrasonographic measurement of the craniocaudal displacement of the splenic hilum and the inferior pole of the spleen

OBJECTIVE

The purpose of this study was to evaluate the correlation between the radiographic and ultrasonographic measurements of craniocaudal displacement of the left hemidiaphragm.

METHODS

Forty-nine patients with clinical indications for interventional procedures prospectively underwent radiographic evaluation of left hemidiaphragmatic mobility and B-mode ultrasonographic measurement of craniocaudal displacement of the hilum and the inferior pole of the spleen. Ultrasonography was performed with a 3.5-MHz convex transducer in a left intercostal position under a longitudinal orientation. Statistical analyses were performed with linear regression, a paired Student t test, and Bland-Altman analyses.

RESULTS

The correlation between the craniocaudal splenic hilum displacement and radiographic measurements was found to be linear: hemidiaphragmatic mobility = 17.795 + 0.429 x splenic hilum displacement (SE for the regression coefficient = 0 .12; P = .0012), although the values obtained with both methods were statistically different (P < .05). The same results could be observed with the use of the inferior pole of the spleen: hemidiaphragmatic mobility = 9.5596 + 0.5455 x inferior polo displacement (SE for the regression coefficient = 0 .11; P < .0001). The mean difference between the values obtained by ultrasonography and by radiography was statistically significant (16.7 +/- 16.1 mm; P < .05 [hilum]; 18.9 +/- 14.2 mm; P < .05 [inferior pole]).

CONCLUSIONS

These results allow us to conclude that ultrasonography can be used as an alternative method for left hemidiaphragm mobility evaluation compared with radiography.

Static pressure volume curves and body posture in acute respiratory failure

OBJECTIVE

In acute respiratory distress syndrome the body posture effects on pressure-volume (PV) curves are still unclear. We examined the effects of prone position on inflation PV curves and their potential relationships with postural alterations in gas exchange.

DESIGN AND SETTING

Prospective study with patients serving as their own controls in a university-affiliated 30-bed intensive care unit.

PATIENTS AND PARTICIPANTS

Thirteen anesthetized, paralyzed, semirecumbent, mechanically ventilated patients with early/severe/diffuse ARDS.

INTERVENTIONS

Sequential body posture changes: preprone semirecumbent, prone, and postprone semirecumbent.

MEASUREMENTS AND RESULTS

In each posture hemodynamics, gas exchange, and lung volumes were determined before/during removal and after restoration of positive end-expiratory pressure (PEEP=10.2+/-0.6 cmH2O). At zero PEEP PV curves of respiratory system, lung, and chest wall were constructed. Prone position vs. preprone semirecumbent resulted in significantly reduced pressure at lower inflection point of lung PV curve (2.2+/-0.2 vs. 3.7+/-0.5 cmH2O) and increased volume at upper inflection point (0.87+/-0.03 vs. 0.69+/-0.05 l). Postural reduction in lower inflection point pressure of lung PV curve was the sole independent predictor of pronation-induced increases in PaO2/FIO2 (R2=0.76). PaO2/FIO2 increases were also significantly related with increases in functional residual capacity (R2=0.60).

CONCLUSIONS

In early/severe/diffuse ARDS prone position reduces lower inflection point pressure and increases upper inflection point UIP volume of the lung PV curve. Lower inflection point pressure reductions explain oxygenation improvements, which are also associated with a postural increase in functional residual capacity.

Physiologic effects of noninvasive ventilation during acute lung injury

A prospective, crossover, physiologic study was performed in 10 patients with acute lung injury to assess the respective short-term effects of noninvasive pressure-support ventilation and continuous positive airway pressure. We measured breathing pattern, neuromuscular drive, inspiratory muscle effort, arterial blood gases, and dyspnea while breathing with minimal support and the equipment for measurements, with two combinations of pressure-support ventilation above positive end-expiratory pressure (10-10 and 15-5 cm H2O), and with continuous positive airway pressure (10 cm H2O). Tidal volume was increased with pressure support, and not with continuous positive airway pressure. Neuromuscular drive and inspiratory muscle effort were lower with the two pressure-support ventilation levels than with other situations (p < 0.05). Dyspnea relief was significantly better with high-level pressure-support ventilation (15-5 cm H2O; p < 0.001). Oxygenation improved when 10 cm H2O positive end-expiratory pressure was applied, alone or in combination. We conclude that, in patients with acute lung injury (1) noninvasive pressure-support ventilation combined with positive end-expiratory pressure is needed to reduce inspiratory muscle effort; (2) continuous positive airway pressure, in this setting, improves oxygenation but fails to unload the respiratory muscles; and (3) pressure-support levels of 10 and 15 cm H2O provide similar unloading but differ in their effects on dyspnea.

Volume-guaranteed pressure-support ventilation facing acute changes in ventilatory demand

OBJECTIVE

To compare volume support ventilation (VSV) in which the pressure support level is continuously adjusted to deliver a preset tidal volume, with pressure support ventilation (PSV), in terms of patient behavior and ventilator response when ventilatory demand was increased by addition of dead space to the circuit.

DESIGN AND SETTING

Randomized cross-over study in an intensive care unit university hospital.

INTERVENTIONS

We assessed in ten patients being weaned off mechanical ventilation the effect of increasing the ventilatory demand by adding a heat-and-moisture exchanger to augment the dead space with a fixed level of PSV and VSV.

MEASUREMENTS AND RESULTS

Arterial blood gases, breathing pattern, and respiratory effort parameters at the end of each of the four steps. Adding dead space significantly increased minute ventilation and PaCO2 values with both PSV and VSV. Indexes of respiratory effort (pressure-time index of respiratory muscles and work of breathing) increased with both ventilatory modes after dead-space augmentation. This increase was 2.5-4 times with VSV than with PSV and induced overt respiratory distress in two patients. The assistance delivered during VSV decreased significantly after dead-space augmentation, from 15.0+/-6.5 to 9.1+/-4.8 cmH2O, whereas no change occurred with PSV.

CONCLUSIONS

With a fixed level of VSV, but not of PSV, an increase in ventilatory demand results in a decrease in the pressure support provided by the ventilator, opposite to the desired response. VSV may conceivably result in respiratory distress in clinical settings.

Postoperative Pulmonary Dysfunction in Adults After Cardiac Surgery With Cardiopulmonary Bypass: Clinical Significance and Implications for Practice

Postoperative pulmonary complications are the most frequent and significant contributor to morbidity, mortality, and costs associated with hospitalization. Interestingly, despite the prevalence of these complications in cardiac surgical patients, recognition, diagnosis, and management of this problem vary widely. In addition, little information is available on the continuum between routine postoperative pulmonary dysfunction and postoperative pulmonary complications. The course of events from pulmonary dysfunction associated with surgery to discharge from the hospital in cardiac patients is largely unexplored. In the absence of evidence-based practice guidelines for the care of cardiac surgical patients with postoperative pulmonary dysfunction, an understanding of the pathophysiological basis of the development of postoperative pulmonary complications is fundamental to enable clinicians to assess the value of current management interventions. Previous research on postoperative pulmonary dysfunction in adults undergoing cardiac surgery is reviewed, with an emphasis on the pathogenesis of this problem, implications for clinical nursing practice, and possibilities for future research.

Iatrogenic-induced dysfunction of the neuromuscular respiratory system

In the presence of respiratory symptoms that are associated with alveolar hypoventilation or a restrictive ventilatory defect and in the absence of parenchymal or pleural abnormalities on the chest radiograph, iatrogenic causes must be evoked, exactly as they are in the presence of interstitial lung disease. In most cases, the anamnestic and clinical contexts provide a strong diagnostic presumption. It is important to establish carefully the mechanism of the observed disorders, using the currently available arsenal of diagnostic tools for clinical and prognostic reasons and from a medicolegal standpoint. It is necessary to evaluate precisely the clinical repercussions of the respiratory neuromuscular abnormality to serve as a basis for follow-up and to discuss therapeutic options in certain cases (eg, nocturnal ventilation to correct nocturnal hypoventilation due to diaphragmatic dysfunction, diaphragm plication to alleviate dyspnea after complete phrenic nerve destruction, phrenic nerve pacing), again in the perspective of medicolegal actions.

Laparoscopic diaphragmatic plication: long-term results of a novel surgical technique for postoperative phrenic nerve palsy

BACKGROUND

Paralysis of the diaphragm is a severe complication of cardiothoracic surgery carrying significant morbidity and mortality. This study demonstrates a novel minimally invasive technique for treatment of phrenic nerve injuries presenting with symptomatic eventration of the diaphragm. It also presents long-term results of three patients treated with this operation.

METHODS

Chest x-ray proved eventration of the left diaphragm in all patients. Two patients required treatment due to prolonged respirator therapy/assisted ventilation for 4 weeks after cardiac surgery. One patient suffered from progressive dyspnea caused by increasing left-sided diaphragmatic elevation and underwent surgery 2 years after cardiac surgery. In all cases, a minimally invasive abdominal approach was chosen. During surgery the dome of the diaphragm was pulled down via three percutaneously inserted retention stitches. This resulted in two or three folds of the diaphragm located within the abdomen. These diaphragmatic folds were subsequently tightened using 12 to 15 unresorbable sutures with extracorporally prepared knots. Surgical as well as long-term follow-up results are presented of all patients and a review of the current literature is provided.

RESULTS

Mean operating time was 203 min; mean intraoperative blood loss was 130 ml. No major complications occurred during surgery or the postoperative period. At a median follow-up of 72 months no recurrence was observed.

CONCLUSIONS

Laparoscopic diaphragmatic plication provides excellent relief of symptoms caused by diaphragmatic paralysis. There is no perioperative morbidity, and hospital stay is short. The laparoscopic approach, therefore, is an attractive surgical alternative for the treatment of phrenic nerve palsy and should be considered in all suitable patients.

Helium/oxygen mixture reduces the work of breathing at the end of the weaning process in patients with severe chronic obstructive pulmonary disease

OBJECTIVE

To test the hypothesis that helium/oxygen mixture can reduce the work of breathing at the end of the weaning process in patients with chronic obstructive pulmonary disease.

DESIGN

Prospective, randomized, crossover study.

SETTING

Two medical intensive care units at two university tertiary care centers.

PATIENTS

Thirteen patients with chronic obstructive pulmonary disease evaluated just before and after extubation.

INTERVENTIONS

Helium/oxygen and air/oxygen mixtures were administered sequentially, for 20 mins each, in a randomized order, just before extubation. It was possible to repeat the study after extubation in five patients.

MEASUREMENTS AND MAIN RESULTS

Before extubation, the helium/oxygen mixture induced no significant variation in the breathing pattern. By contrast, it reduced the work of breathing from 1.442 +/- 0.718 J/L (mean +/- sd) to 1.133 +/- 0.500 J/L (p <.05). This reduction was explained mainly by a reduction in the resistive component of the work of breathing from 0.662 +/- 0.376 to 0.459 +/- 0.256 J/L (p <.01). We also observed a slight reduction in the intrinsic positive end-expiratory pressure from 2.9 +/- 2.1 cm H(2)O to 2.1 +/- 1.8 cm H(2)O (p <.05). Similar results were also observed after extubation in five patients in whom the repetition of the study was possible.

CONCLUSIONS

In spontaneously breathing intubated patients with chronic obstructive pulmonary disease recovering from an acute exacerbation, helium/oxygen mixture reduces the work of breathing as well as intrinsic positive end-expiratory pressure without modifying the breathing pattern.