Know Your A-Lines (Part 2)

Once you understand the basic functions of the components of your arterial line set-up and know how to position it properly the next level of mastery involves spotting other errors and optimizing them.
If you notice that your pulse pressure is very wide your patient may be severely volume depleted, they may have profound aortic insufficiency, or your arterial line may be lying to you.  Alternatively, a very narrow pulse pressure can relay cardiac tamponade or an error in measurement.  Here’s how, why, and how to fix it.
Why:
The fluid pressure wave the is transmitted to the arterial catheter and hydraulic tubing to displace the transducer and register as a blood pressure has a frequency which is expressed in cycles per unit time (beats per minute) and an amplitude of energy is expressed per beat until the wave reflects against the transducer.  At certain lengths the wave is reflected back upon itself such the peaks and troughs of the waves (heartbeats) align exactly.  This causes the amplitudes to be additive.  The shortest distance that provokes this is described as the first harmonic and can be determined by the inverse of the wave’s frequency. As the wave travels along your tubing it expresses force against the wall of the tubing and expends energy.  This causes the wave to “wind down” and is termed dampening.  The analogy to describe this process is dropping a ball onto the ground: each time the ball bounces it expends more energy and each bounce is smaller until it comes to rest.  How long it takes the ball to come to rest depends on the “hardness” of the ground, and this is termed the dampening constant.  In your arterial line set-up this hardness constant is derived from the elasticity of the patient’s vasculature and of the IV tubing and stopcock system you use to conduct the pressure wave.
 A figure demonstrating sign waves and harmonics.
How:
If the system is underdampened, harmonic waves develop and generate a blood pressure with a falsely extreme amplitudes (higher systolic and lower diastolic pressures than the patient is experiencing).  Underdampending can be caused by excessively long and stiff IV tubing.  You can detect underdampending on your waveform by looking for beats with a very rapid upstroke and a sharp, peaked appearance on your monitor.  If the system is overdampened then excess friction leads the pressure wave to expend its energy early and promotes falsely narrow pulse pressures.  Overdampending can be caused by bubbles within the tubing, kinks within the catheter, blood clots on or within the catheter, low volumes of fluid within the flush system, low pressure applied to the pressure bag.  The good news is that the MAP (described by the midpoint in the sine wave of the heartbeat) is unchanged by these artifacts.  However your systolic and diastolic blood pressures still yield clinical data and having gone through the trouble of placing an invasive monitoring system, you want them to be accurate.
The fix:
You can test to determine if your system is overdampened or underdampened by performing a square flush test.  Do this by opening the continuous flus hvalve to create a square wave and observing the subsequent oscillations.  If the system returns to baseline after one or two oscillations then the dampening of the system has been optimized.  If there are more than one or two oscillations then the system is underdampened.  If there are no oscillations then the system is overdampened.
Tubing should be exactly 4 feet to promote the correct length.  Longer lengths of tubing can promote harmonics.
Use dedicate arterial pressure tubing when possible to maintain the appropriate compliance (“hardness”) of the walls of the system.  Avoid large diameter tubing as this will lead to overdampening.
Remove air bubbles by flushing the line (flush to air rather than to the patient) or by aspirating them.
Tighten all connections.
Remove any excessive stopcocks.
Cheatham ML. Hemodynamic Monitoring: Principles to Practice.  http://www.surgicalcriticalcare.net/Lectures/PDF/hemodynamic%20monitoring%20principles%20to%20practice.pdf.  Updated 1/13/2009.  Accessed 5/2/2016.
Nickson C.  Life in the Fast Lane.  http://lifeinthefastlane.com/ccc/arterial-line/. Updated 6/14/2015.  Accessed 5/3/2016.

What do YOU carry – privat equipment of an Austrian Anaesthesiologist and Emergency Physician

IMG_2706

Years ago I carried an emergency backpack with me. It was a present, looked really professional and cool  but it was so huge that there was nearly no space for additional luggage in my car trunk when the backpack was placed there. It was stuffed with a lot of pricy tools as a pulsoxymeter, a laryngoscope, ET-tubes, larynx-tubes, O2-tank, Ambu-bag (Mark V), Samsplints, and so on.

After a while two things happened: first of all I became Dad of my first child (a daughter – today I´m the proud dad of four great kids). Belive me, I didnt even start arguing with my wife about the importance of an emergency backpack which was so big that there was not enough space to carry our baby buggy. Not talking about the missing space for any additional luggage. The second thing was that I realized that it was a lot of really booring work to keep track of the f***ing expiration dates of over 100 items. Last but not least storing drugs in a car at temperatures from -15°C in the Winter to 40°C and more in the summer isn´t the best idea too.

So I decidet to make a radical cut and removed my emergency-equpiment from my car. I didn´t carry anything more than the little first aid box which is required by law in Austria this times. I did so for eight years till my second child (a son) broke his arm really bad at a birthdayparty at the hous of a good friend in the countryside. The good thing: Ursula (my friend) is a veterinarian, the bad thing: I sedated my son with veterinary Ketamine (250ml bottle) and had to use a i.v. line usually used for horses. Dont worry – it worked well.

After that I realized that there was a need for carrying emergency-equipment beyond the little first aid box (has to be carried in any car in austria – required by law) with me.

I reflected upon it dozends of times and developed my personal emergency-equipment to carry with me. It had to be small and versatile. I wanted only items in it which I could use without the need of monitoring devices. And it had to be small enough to carry it with me in my backbag, shoulder bag, diaper bag and so on.

Here it is:

A simple click box. I own 3 identical ones. One placed in my car, one in my everyday shoulder bag and one at home. This makes it easy to replace the drugs regularly (usually one unit contains 5 vials – very near to the amount you need to stock up three sets) and keeping track of the expiration dates. The vials are placed in foam-material which I bought at the local hardware store and cutted in shape.

IMG_2707 IMG_2708 IMG_2709 IMG_2710

Content:

Drugs:

  • 2 10ml vials saline 0.9%
  • 1 3ml vial Midazolam 5mg/ml
  • 1 5ml vial Flumazenil 0.1mg/ml
  • 1 4ml vial Ondansetron 2mg/ml
  • 1 2ml vial S-Ketamine 25mg/ml
  • 1 1ml vial Epinephrine 1mg/ml
  • 1 1ml vial Ephedrin 50mg/ml
  • 1 2ml vial Nalbuphin 10mg/ml
  • 1 4ml vial Dimetinden 1mg/ml
  • 1 2ml vial Sugammadex (a leftover – removed after taking the pictures)

So I can treat anaphylaxis, asthma, perform a procedural sedation, provide analgesia, prevent nausea and vomiting (I always apply Ondansetron before using S-Ketamine or opioids in emergency situations) in a very safe manner.

other devices:

  • tourniquet
  • 2 5ml syringes
  • 1 iv line 20G (flow rate 61 ml/min)
  • 1 iv line 18G (flow rate 100 ml/min)
  • 1 back check valve (with luer lock for the iv lines)
  • 1 Canulla Fixation Dressing (Curagard SP – this one keeps iv lines better in place than other ones I know. Very adhesiv, really smart design – omega shaped)
  • 4 band-aids (as you know, in real life there is nearly nothing requested more often from a physician than a band-aid)

I´ve used this box a lot of times till today. One life could definitly be safed with this minimalist equipment. I was able to treat an severe anaphylactic reaction after a wasp sting in a public swimming bath two years ago. Applying half of the epinephrin 1 minute after the sting intramuscularly and the rest in little boluses iv   kept the women alive till the helicopter arrived. Having two iv lines placed before the veins collapsed simplyfied the further management.

What do you think? Any further suggestions? What can be made better? I´d love to read your comments.

Yours Kostja

___________

Kostja Steiner is Anesthesiologist, Intensive Care Doc and Emergency Physician in Graz, Austria

 

PAC conference – Hopper and Piper on “No Place Like Home”

We have teamed up with APLS to share the videos from their Paediatric Acute Care Conferences. These videos have never been open access before, so if you weren’t able to attend the conferences, then now’s your chance to catch up.

The PAC Conference is run each year by APLS and consists of presentations on a range of topics relevant to paediatric acute and critical care.

Susie Piper has been the Director of Paediatrics and Child Health for the Illawarra Shoalhaven Local Health District since 2012. She graduated from UNSW in 1990 and trained as a paediatrician at the Sydney Children’s Hospital and the Children’s Hospital at Westmead over the next ten years, including a six month stint in Tanzania during the Rwandan refugee crisis. With an interest in ambulatory care and ‘hospital in the home’, Dr Piper worked at Wyong Hospital and Campbelltown Hospital prior to coming to Illawarra, where she helped to establish a Paediatric Assessment Unit that aimed to treat kids locally and avoid hospital admission if possible. Dr Piper is hoping to establish similar models of care in Illawarra, particularly at Shellharbour Hospital.

Sandy Hopper is a dual-qualified Emergency Physician and Emergency Paediatrician, working at the Emergency Department of the Royal Children’s Hospital in Melbourne. He holds special interests in adolescent emergency medicine, mental health, observational and short stay medicine, and medical education.

In this talk they discuss managing acute illness in children without hospital admission.

Sandy Hopper and Susie Piper discuss ways of blurring the boundaries between in and outpatient care.  They talk about why we admit kids to hospital, explore alternative options to admission and describe two examples of programs aimed at minimising kids time in hospital.

ECG of the Week – 2nd May 2016 – Interpretation

This ECG is from a 76 yr old male who presented to his GP with exertional dysponea. Past medical history of hypertension.



Click to enlarge

Rate:
  • Atrial rate 84 bpm
  • Ventricular rate 42 bpm
Rhythm:
  • Regular atrial activity
  • Regular ventricular activity
  • 2:1 Pattern
Axis:
  • Normal (-33 deg)
Intervals:
  • PR - Normal (~200ms) - when conducted
  • QRS - Normal (100ms)
  • QT - 450ms
Segments:

  • Nil significant changes

Additional:

  • Relatively large T waves in leads II, aVF, V3 when compared with QRS voltage
Interpretation:

  • 2:1 AV Block
What happened ?

The patient was admitted under the cardiology team, nil reversible causes were identified. During monitoring the patient had runs of Mobitz II 2nd Degree AV block and underwent an uneventful pacemaker insertion.

References / Further Reading

Life in the Fast Lane

Textbook
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.