IVC collapse depends on breathing pattern

A high degree of sonographically-visualised collapse of the inferior vena cava (IVC) during inspiration suggests a volume-responsive cardiac output. This inspiratory collapse is said to be due to a fall in intra-thoracic pressure. However, the IVC traverses the abdominal compartment and is therefore under the influences of hepatic weight, intra-abdominal pressure, and venous return of pooled splanchnic and lower extremity blood.

Diaphragmatic descent, which increases intra-abdominal pressure, may contribute to the respiratory change in IVC diameter. This was borne out in a volunteer study in which diaphragmatic breathing was compared with chest wall breathing. With diaphragmatic breathing there was a trend for a larger IVC collapse index (median 0.80, range 0.48–1.00 vs. 0.57, range 0.13–1.00, P = 0.053). The authors state:
These findings suggest that during inspiration the IVC, in addition to responding to falling intra-thoracic pressure, may also be compressed with diaphragmatic descent and have implications regarding the use of IVC diameters to estimate the central venous pressure without knowing the manner of breathing, intra-abdominal pressure, or magnitude of diaphragmatic excursion.”

The take home message for me is that there is probably a more complex mechanism of IVC behaviour during respiration than is often taught, and that breathing pattern and abdominal issues may influence the IVC diameter and degree of collapse seen on ultrasound. This might not however negate the correlation between a high degree of collapse and fluid-responsiveness, which is what I’m looking for in my patients with shock or hypotension.

Incidentally the first author of this study is Bruce Kimura, a pioneer of focused echo in the emergency setting and author of a fantastic little book all about the parasternal long axis approach, which seems to be impossible to source on the web at the moment.

AIMS: Although the inspiratory ‘collapse’ of the inferior vena cava (IVC) has been used to signify normal central venous pressure, the effect of the manner of breathing IVC size is incompletely understood. As intra-abdominal pressure rises during descent of the diaphragm, we hypothesized that inspiration through diaphragmatic excursion may have a compressive effect on the IVC.

METHODS AND RESULTS: We measured minimal and maximal intrahepatic IVC diameter on echocardiography and popliteal venous return by spectral Doppler during isovolemic inspiratory efforts in 19 healthy non-obese volunteers who were instructed to inhale using either diaphragmatic or chest wall expansion. During inspiration, the maximal diaphragmatic excursion and popliteal vein flow were compared between breathing methods. The IVC ‘collapsibility index,’ IVCCI, was calculated as (IVC(max)-IVC(min))/IVC(max). The difference in diaphragmatic excursion between diaphragmatic and chest wall breaths in each subject was correlated with the corresponding change in IVCCI. Diaphragmatic breathing resulted in more diaphragmatic excursion than chest wall breathing (median 3.4 cm, range 1.7-5.8 vs. 2.2 cm, range 1.0-5.2, P= 0.0003), and was universally associated with decreased popliteal venous return (19/19 vs. 9/19 subjects, P< 0.004). The difference in diaphragmatic excursion correlated with the difference in IVCCI (Spearman’s rho = 0.53, P= 0.024).

CONCLUSION: During inspiration of equivalent tidal volumes, the reduction in IVC diameter and lower extremity venous return was related to diaphragmatic excursion, suggesting that the IVC may be compressed through descent of the diaphragm.

The effect of breathing manner on inferior vena caval diameter
Eur J Echocardiogr. 2011 Feb;12(2):120-3

Alfentanil for Procedural Sedation

An evaluation of single-agent alfentanil for procedural sedation in the ED has been published by the team at Hennepin County Medical Centre. A short-acting opioid, alfentanil induces 7 to 9 minutes of pain relief after a single bolus of 10 mcg/kg, a duration of action similar to that of propofol. It produces analgesia and sedation but not amnesia. In this study of 148 adult patients, alfentanil doses and the use of supplemental oxygen were at treating physician discretion. it appeared to be effective for ED procedural sedation but displayed a rate of airway or respiratory events leading to an intervention similar to that of previous reports of deeper sedation with propofol. The authors state ‘Despite very high rates of procedural pain and recall, subjects remained highly satisfied.’

STUDY OBJECTIVE: We administer alfentanil sedation for minor procedures in the emergency department (ED), and our primary objective is to assess the incidence of airway and respiratory adverse events leading to an intervention. Our secondary goals are to assess for other adverse events, the depth and duration of sedation, the incidence of subclinical respiratory depression, and patient perceptions of the quality of the sedation.

METHODS: In this observational study of adults receiving alfentanil for ED procedures, we recorded the incidence of airway or respiratory adverse events leading to an intervention (increase/addition of supplemental oxygen, bag-valve-mask ventilation, airway repositioning, or stimulation to induce breathing). Secondary goals were assessed with monitoring (including capnography), the Observer’s Assessment of Alertness/Sedation (OAA/S) scale, and postprocedure patient visual analog scale ratings of pain, recall, and satisfaction.

RESULTS: Airway or respiratory events leading to intervention were observed in 39% of the 148 subjects (supplemental oxygen 18%, bag-valve mask 3%, airway repositioning 2%, stimulation 18%); none were clinically significant. The median OAA/S nadir was 4 (interquartile range 3 to 5). Median patient ratings were positive (pain 26 mm, recall 98, satisfaction 100 mm).

CONCLUSION: Alfentanil appears effective for ED procedural sedation but displays a rate of airway or respiratory events leading to an intervention similar to that of previous reports of deeper sedation with propofol.

Alfentanil for Procedural Sedation in the Emergency Department
Ann Emerg Med. 2011 Feb;57(2):117-21

EMS makes a difference

A Position Statement of the National Emergency Medical Services Advisory Council summarises the substantial evidence base documenting improved patient outcomes resulting from prehospital interventions and emergency medical services (EMS) systems. The fully referenced document is available in free full text .

The document concludes with this summary:

  • EMS makes a difference by producing clinically meaningful reductions in time to definitive treatment and improved health outcomes for patients with STEMI. Trained EMS providers are proficient in the capture and interpretation of 12-lead ECGs, can andshould make or participate in triage decisions to bypass closer hospitals in favor of to PCI-capable facilities, when clinically indicated. Efforts should continue to educate the public to call 9-1-1 at the first sign of a heart attack.

  • EMS makes a difference by decreasing the times to CPR and defibrillation, defined as the two critical factors for surviving cardiac arrest.

  • EMS makes a difference and is a critical component of effective stroke care. EMS must advocate for quality, standardized stroke protocols, performance improvement systems and training, and expedient transport of stroke patients to specialty care centers. EMS systems must partner with their dispatch agencies to ensure the use of quality Emergency Medical Dispatch protocols that provide proper stroke care instructions and activate appropriate resources. Efforts should continue to educate the public to call 9-1-1 at the first sign of a stroke.

  • EMS makes a difference by improving survival and neurological function for patients with respiratory emergencies. Proper prehospital care decreases the need for intubations and the number of required hospital admissions and improves cerebral performance in patients with respiratory distress. The addition of CPAP to the EMS tool kit provides immediate and longer-term benefits and further reduces hospitalization rates and healthcare costs.

  • EMS makes a difference by allowing EMS providers to use diagnostic tools such as blood glucometry, pulse oximetry, and 12-lead ECGs to efficiently evaluate patients and determine whether more advanced evaluation is necessary.

  • EMS makes a difference by treating many diabetic patients at home without the need for transport; thereby improving patient satisfaction and decreasing healthcare costs.

  • EMS makes a difference by accurately identifying patients experiencing out-of-hospital cardiac arrest who have no realistic chance of survival and determining whether transport to a hospital is warranted, thus reducing transports, decreasing hospital and patient costs, and increasing the availability of EMS resources.

  • EMS makes a difference with its expanding role in the healthcare system. EMS has the potential to provide improved patient outcomes and more customer satisfying primary care while offering clinically appropriate alternatives to hospital transport in addition to standard 9-1-1 responses. In a fully integrated healthcare system, EMS will provide preventive services, acute care, and overall community health.

  • EMS makes a difference in trauma care by providing rapid assessment, early notification to trauma centers, and rapid triage and transport to trauma centers, when appropriate. EMS will continue to be the community’s safety net.

  • EMS makes a difference with pediatric shock patients when shock is recognized and treated aggressively. The healthcare system must advocate for a systems approach to pediatrics similar to trauma, STEMI, and stroke systems of care and standardized training for all healthcare providers.

 

EMS Makes a Difference: Improved clinical outcomes and downstream healthcare savings
free full text

In V.Fib and talking to you!

Some patients with severe refractory heart failure are kept alive thanks to implantable pumps such as the left ventricular assist device (LVAD). Many emergency physicians are likely to be unfamiliar with these but could encounter patients who have them. One particular peculiarity is that latter generation devices maintain non-pulsatile flow and provide or assist cardiac output independent of cardiac rhythm. In extreme situations patients can have life-sustaining cardiac outputs without palpable pulses or even audible heart sounds.

Click on image for Wikipedia article

A great example of how weird this can get is provided by a case of a 66 year male with an LVAD (HeartMate II (Thoratec Corporation)) who presented due to spontaneous discharge of his internal cardioverter-defibrillator (ICD). He was alert but had no pulses, and no detectable blood pressure using both a manual sphygmomanometer and an automated non-invasive blood pressure device. His 12 lead showed ventricular fibrillation. An invasive blood pressure showed a mean arterial pressure (mAP) of 80 mmHg. Several hours later his VF was successfully terminated and his mAP remained 80 mmHg

Some interesting points made by the authors include:

  • CPR was unnecessary in this guy but in cases of severe RV dysfunction it might need to be done to provide flow into the LV.
  • A danger of CPR in patients with an LVAD is the risk of damage to the device or ventricular rupture

LVAD use is significantly increasing so we can expect to encounter more episodes of previously impossible presentations to our emergency departments.

ABSTRACT
Optimal medical treatment, cardiac resynchronization, and the use of an implantable cardioverter defibrillator are established therapies of severe congestive heart failure. In refractory cases, left ventricular assist devices are more and more used not only as bridging to cardiac transplantation but also as destination therapy. Ventricular arrhythmias may represent a life-threatening condition and often result in clinical deterioration in patients with congestive heart failure. We report a case of asymptomatic sustained ventricular fibrillation with preserved hemodynamics caused by a nonpulsatile left ventricular assist device. Consecutive adequate but unsuccessful discharges of the implantable cardioverter defibrillator were the only sign of the usually fatal arrhythmia, prompting the patient to consult emergency services. Electrolyte supplementation and initiation of therapy with amiodarone followed by external defibrillation resulted in successful restoration of a stable cardiac rhythm after 3.5 hours.

Asymptomatic Sustained Ventricular Fibrillation in a Patient With Left Ventricular Assist Device
Ann Emerg Med. 2011 Jan;57(1):25-8.

TIA workup renders ABCD2 unhelpful

ABCD2 is recommended to stratify the risk of stroke in patients presenting to the ED with TIA symptoms. In some centres this is used to differentiate those that need to be admitted for further evaluation and treatment from those that can be followed up in the outpatient setting. A recent study showed that if a detailed work up was done in the ED on all TIA patients (followed by appropriate intervention), the ABCD2 score did not predict adverse outcomes, which were lower in this cohort than in the original ABCD2 cohort.

STUDY OBJECTIVE: We study the incremental value of the ABCD2 score in predicting short-term risk of ischemic stroke after thorough emergency department (ED) evaluation of transient ischemic attack.

METHODS: This was a prospective observational study of consecutive patients presenting to the ED with a transient ischemic attack. Patients underwent a full ED evaluation, including central nervous system and carotid artery imaging, after which ABCD2 scores and risk category were assigned. We evaluated correlations between risk categories and occurrence of subsequent ischemic stroke at 7 and 90 days.

RESULTS: The cohort consisted of 637 patients (47% women; mean age 73 years; SD 13 years). There were 15 strokes within 90 days after the index transient ischemic attack. At 7 days, the rate of stroke according to ABCD2 category in our cohort was 1.1% in the low-risk group, 0.3% in the intermediate-risk group, and 2.7% in the high-risk group. At 90 days, the rate of stroke in our ED cohort was 2.1% in the low-risk group, 2.1% in the intermediate-risk group, and 3.6% in the high-risk group. There was no relationship between ABCD2 score at presentation and subsequent stroke after transient ischemic attack at 7 or 90 days.

CONCLUSION: The ABCD2 score did not add incremental value beyond an ED evaluation that includes central nervous system and carotid artery imaging in the ability to risk-stratify patients with transient ischemic attack in our cohort. Practice approaches that include brain and carotid artery imaging do not benefit by the incremental addition of the ABCD2 score. In this population of transient ischemic attack patients, selected by emergency physicians for a rapid ED-based outpatient protocol that included early carotid imaging and treatment when appropriate, the rate of stroke was independent of ABCD2 stratification.

An Assessment of the Incremental Value of the ABCD2 Score in the Emergency Department Evaluation of Transient Ischemic Attack
Ann Emerg Med. 2011 Jan;57(1):46-51

Midazolam smoothens adult ketamine sedation

In adults undergoing procedural sedation with ketamine, 0.03 mg/kg IV midazolam reduced recovery agitation compared with placebo.

You don’t need this. Just give the midazolam.

STUDY OBJECTIVE: We assess whether midazolam reduces recovery agitation after ketamine administration in adult emergency department (ED) patients and also compared the incidence of adverse events (recovery agitation, respiratory, and nausea/vomiting) by the intravenous (IV) versus intramuscular (IM) route.

METHODS: This prospective, double-blind, placebo-controlled, 2×2 factorial trial randomized consecutive ED patients aged 18 to 50 years to 4 groups: receiving either 0.03 mg/kg IV midazolam or placebo, and with ketamine administered either 1.5 mg/kg IV or 4 mg/kg IM. Adverse events and sedation characteristics were recorded.

RESULTS: Of the 182 subjects, recovery agitation was less common in the midazolam cohorts (8% versus 25%; difference 17%; 95% confidence interval [CI] 6% to 28%; number needed to treat 6). When IV versus IM routes were compared, the incidences of adverse events were similar (recovery agitation 13% versus 17%, difference 4%, 95% CI -8% to 16%; respiratory events 0% versus 0%, difference 0%, 95% CI -2% to 2%; nausea/vomiting 28% versus 34%, difference 6%, 95% CI -8% to 20%).

CONCLUSION: Coadministered midazolam significantly reduces the incidence of recovery agitation after ketamine procedural sedation and analgesia in ED adults (number needed to treat 6). Adverse events occur at similar frequency by the IV or IM routes.

Ketamine with and without midazolam for emergency department sedation in adults: a randomized controlled trial
Ann Emerg Med. 2011 Feb;57(2):109-114

Pre-hospital RSI and single use blades

Single-use metal laryngoscope blades were compared in a randomised trial in the pre-hospital setting by French SAMU physicians. First-pass intubation success (defined as one advancement of the tube in the direction of the glottis during direct laryngoscopy) was similar between conventional and disposable metal blades.

A French doctor (not involved in the study)

STUDY OBJECTIVE: Emergency tracheal intubation is reported to be more difficult with single-use plastic than with reusable metal laryngoscope blades in both inhospital and out-of-hospital settings. Single-use metal blades have been developed but have not been compared with conventional metal blades. This controlled trial compares the efficacy and safety of single-use metal blades with reusable metal blades in out-of-hospital emergency tracheal intubation.

METHODS: This randomized controlled trial was carried out in France with out-of-hospital emergency medical units (Services de Médecine d’Urgence et de Réanimation). This was a multicenter prospective noninferiority randomized controlled trial in adult out-of-hospital patients requiring emergency tracheal intubation. Patients were randomly assigned to either single-use or reusable metal laryngoscope blades and intubated by a senior physician or a nurse anesthetist. The primary outcome was first-pass intubation success. Secondary outcomes were incidence of difficult intubation, need for alternate airway devices, and early intubation-related complications (esophageal intubation, mainstem intubation, vomiting, pulmonary aspiration, dental trauma, bronchospasm or laryngospasm, ventricular tachycardia, arterial desaturation, hypotension, or cardiac arrest).

RESULTS: The study included 817 patients, including 409 intubated with single-use blades and 408 with a reusable blade. First-pass intubation success was similar in both groups: 292 (71.4%) for single-use blades, 290 (71.1%) for reusable blades. The 95% confidence interval (CI) for the difference in treatments (0.3%; 95% CI -5.9% to 6.5%) did not include the prespecified inferiority margin of -7%. There was no difference in rate of difficult intubation (difference 3%; 95% CI -7% to 2%), need for alternate airway (difference 4%; 95% CI -8% to 1%), or early complication rate (difference 3%; 95% CI -3% to 8%).

CONCLUSION: First-pass out-of-hospital tracheal intubation success with single-use metal laryngoscopy blades was noninferior to first-pass success with reusable metal laryngoscope blades.

Out-of-Hospital Tracheal Intubation With Single-Use Versus Reusable Metal Laryngoscope Blades: A Multicenter Randomized Controlled Trial
Ann Emerg Med. 2011 Mar;57(3):225-31

Delayed door-to-balloon even with helicopters

For a whole bunch of reasons, patients with ST-elevation myocardial infarction who undergo interhospital transfer for primary percutaneous coronary intervention may not meet the required 90 minute door-to-balloon time. In a new study of patients transferred by helicopter, only 3% of STEMI patients transferred for reperfusion met the 90-minute goal. Should this result in an increase in the use of fibrinolysis at non–percutaneous coronary intervention hospitals?

Opportunity for gratuitous helicopter shot never knowingly declined

STUDY OBJECTIVE: Early reperfusion portends better outcomes for ST-segment elevation myocardial infarction (STEMI) patients. This investigation estimates the proportions of STEMI patients transported by a hospital-based helicopter emergency medical services (EMS) system who meet the goals of 90-minute door-to-balloon time for percutaneous coronary intervention or 30-minute door-to-needle time for fibrinolysis.

METHODS: This was a multicenter, retrospective chart review of STEMI patients flown by a hospital-based helicopter service in 2007. Included patients were transferred from an emergency department (ED) to a cardiac catheterization laboratory for primary or rescue percutaneous coronary intervention. Out-of-hospital, ED, and inpatient records were reviewed to determine door-to-balloon time and door-to-needle time. Data were abstracted with a priori definitions and criteria.

RESULTS: There were 179 subjects from 16 referring and 6 receiving hospitals. Mean age was 58 years, 68% were men, and 86% were white. One hundred forty subjects were transferred for primary percutaneous coronary intervention, of whom 29 had no intervention during catheterization. For subjects with intervention, door-to-balloon time exceeded 90 minutes in 107 of 111 cases (97%). Median door-to-balloon time was 131 minutes (interquartile range 114 to 158 minutes). Thirty-nine subjects (21%) received fibrinolytics before transfer, and 19 of 39 (49%) received fibrinolytics within 30 minutes. Median door-to-needle time was 31 minutes (interquartile range 23 to 45 minutes).

CONCLUSION: In this study, STEMI patients presenting to non-percutaneous coronary intervention facilities who are transferred to a percutaneous coronary intervention-capable hospital by helicopter EMS do not commonly receive fibrinolysis and rarely achieve percutaneous coronary intervention within 90 minutes. In similar settings, primary fibrinolysis should be considered while strategies to reduce the time required for subsequent interventional care are explored.

Reperfusion Is Delayed Beyond Guideline Recommendations in Patients Requiring Interhospital Helicopter Transfer for Treatment of ST-segment Elevation Myocardial Infarction.
Ann Emerg Med. 2011 Mar;57(3):213-220

H1N1 or CAP?

A scoring system composed of clinical, radiological, and laboratory variables purports to distinguish H1N1 influenza virus infection from community acquired pneumonia1. An accompanying editorial2 suggests that while further validation is required, the most useful application of the score might be in those with a score of 0 or 1 (out of 5), in whom the the high negative predictive value might safely avoid inpatient isolation and neuraminidase inhibitor treatment in the under-65s.

Background Early identification of patients with H1N1 influenza-related pneumonia is desirable for the early instigation of antiviral agents. A study was undertaken to investigate whether adults admitted to hospital with H1N1 influenza-related pneumonia could be distinguished clinically from patients with non-H1N1 community-acquired pneumonia (CAP).

Methods Between May 2009 and January 2010, clinical and epidemiological data of patients with confirmed H1N1 influenza infection admitted to 75 hospitals in the UK were collected by the Influenza Clinical Information Network (FLU-CIN). Adults with H1N1 influenza-related pneumonia were identified and compared with a prospective study cohort of adults with CAP hospitalised between September 2008 and June 2010, excluding those admitted during the period of the pandemic.

Results Of 1046 adults with confirmed H1N1 influenza infection in the FLU-CIN cohort, 254 (25%) had H1N1 influenza-related pneumonia on admission to hospital. In-hospital mortality of these patients was 11.4% compared with 14.0% in patients with inter-pandemic CAP (n=648). A multivariate logistic regression model was generated by assigning one point for each of five clinical criteria: age ≤65 years, mental orientation, temperature ≥38°C, leucocyte count ≤12×10(9)/l and bilateral radiographic consolidation. A score of 4 or 5 predicted H1N1 influenza-related pneumonia with a positive likelihood ratio of 9.0. A score of 0 or 1 had a positive likelihood ratio of 75.7 for excluding it.

Conclusion There are substantial clinical differences between H1N1 influenza-related pneumonia and inter-pandemic CAP. A model based on five simple clinical criteria enables the early identification of adults admitted with H1N1 influenza-related pneumonia.

1. Clinical and laboratory features distinguishing pandemic H1N1 influenza-related pneumonia from interpandemic community-acquired pneumonia in adults
Thorax. 2011 March; 66(3): 247–252 Free Full Text

2. Predicting the unpredictable: is it possible clinically to separate H1N1 from non-H1N1 community-acquired pneumonia?
Thorax. 2011 Mar;66(3):187-8