CVC LINES and CVP
Central Venous Catheter and the Pressure Transducer
- Central Venous Catheter (CVC) connected to a pressure transducer*
- CVP blood pressure measurement
- venous blood sampling / ScvO2 (Central mixed venous oxygen saturation is the percentage of oxygen bound to hemoglobin in blood returning to the right side of the heart. This reflects the amount of oxygen “left over” after the tissues remove what they need)
Normal ScvO2 (from an internal jugular or subclavian vein) is > 70%
- deliver vasoactive drugs
- deliver chemotherapy drugs
- deliver total parental nutrition
- rapid fluid bolusing (studies have shown Intra-Osseous to be as quick for fluids in emergencies)
*CVCs also include Vascaths, Transvenous pacing catheters, Pulmonary Artery Caths and Peripherally Inserted Central Caths but not in the scope of this specific document
- fluctuations of vascular pressure cause a pulsation of the saline column
- wave forms differ depending on where the cannula is inserted
Calibrating (‘zeroing’) is as per Arterial Line
- ensure the transducer pressure tubing and flush solution (0.9% Saline) are correctly assembled and free of air bubbles
- place transducer at level of the right atrium / phlebostatic axis
- ‘off to patient, open to air (atmosphere)’
- press ‘zero’ -> sets atmospheric pressure as zero reference point
- whenever patient position is altered the transducer height should be altered
QUESTION – Again what is “zero”?
Central Venous Pressure
Reflects fluid preload to the heart
The central venous pressure (CVP) is the pressure measured in the central veins close to the heart. It indicates mean right atrial pressure and is frequently used as an estimate of right ventricular preload. The CVP does not measure blood volume directly, although it is often used to estimate this.
Normal central venous pressure is 2 – 8 mmHg (depending on the book you reference).
CVP is elevated by :
- over hydration which increases venous return
- heart failure or PA stenosis which limit venous outflow and lead to venous congestion
- positive pressure breathing
CVP decreases with:
- hypovolemic shock from haemorrhage etc
- fluid shift
- negative pressure breathing which occurs when the patient demonstrates intercostal retractions IE asthma
Image – https://www.skiptestCVC.com/waveforms+image
QUESTION – how many lumens can a CVC have?
So the CVP reflects fluid preload to the heart…
So what exactly is PRELOAD?
Preload is stretch. The amount of volume being returned to the right side of the heart from the systemic circulation. So this is negatively affected by decreased general fluid volume, low vascular tone, inflammatory response in sepsis, nitrates, sedation, diuretics etc and PEEP!
We increase preload by adding volume, increasing vascular tone, treating sepsis, lowering sedation etc.
While we are here;
the other measurement that CVP doesn’t reflect is AFTERLOAD
Afterload is squeeze. The amount of resistance the left side of the heart has to overcome in order to eject blood. In acute illness fluid volume boluses alone may not increase blood pressure. So this is positively (or some would say negatively) effected by drug mechanisms that cause arterial (and venous) constriction – vasopressors and inotropes.
These shrink the blood vessels to decrease the area in which the blood volume circulates.
Sometimes we want to reduce afterload, Hydralazine is a potent short acting arterial dilator and SNP (sodium nitroprusside) is another. Glycerine Trinitrate (GTN) is a great venous vasodilator.
The balance we aim for is to increase blood pressure / MAP while not making cardiac workload too high due to the added resistance to cardiac pumping.
ACCURACY AND MEASUREMENT ERRORS
Image – https://openi.nlm.nih.gov/detailedresult.php?img=PMC4152694_JOACP-30-430-g004&req=4
Conditions that must be met to ensure accuracy
- attached to distal lumen (lumen has closest outlet to Right Atrium)
- consistent patient positioning to view trend ie 30 degrees up (view previous position on chart)
- not rotated beyond 15% laterally (not on their side)
- lumen not blocked / clamped
- no air bubbles in tubing or transducer
- transducer is leveled and zeroed to desired point (ie. right atrium / phlebostatic axis)
- monitor calibrated accurately (zeroed)
- even femoral CVCs will display fluid pressure trends
Common sources of error
- bubbles in catheter-transducer system (lack of transfer of accurate pressure)
- lumen also being used for infusion (compliant tubing in system)
- transducer at incorrect / non – consistent position
- lumen blocked or partially blocked – kinked, clotted
Consistency of positioning
Measuring CVP relies on consistent positioning to mimic environmental influences for every CVP so please attempt to achieve similar positioning and always document patient position on the ICU chart.
The patent should be pretty much, but not always not laterally rotated but, on their back.
QUESTION – what is a CVP?
Passive leg raise (PLR)
By raising the patients legs above their heart the body returns approx 300mls back to the patients central circulation.
In combination with observation of haemodynamic and EtCO2 changes PLR mimics a fluid challenge.
However, no fluid is infused and the haemodynamic effects are rapidly reversible when the legs are dropped again. The procedure is repeated if a fluid bolus is indicated and given to see if a second bolus is required and so on.
Not suitable for patients with intra-abdominal hypertension, unreliable in profoundly hypovolaemic patients.
Central Venous Catheter care
Greatest risk to patient is system opening or dislodgement – AIR ENTRAINMENT (see complication lists below). These patients can mistakenly entrain deadly amounts of air through an open CVC site or lumen quickly and quietly.
CVCs are always sutured in, well dressed and kept on view at all times – not covered by blankets etc. They should have their weight supported to avoid accidental removal.
The insertion site should be observed closely every shift for signs of leakage, inflammation or infection. ALL INVASIVE LINES ARE CLEARLY LABELLED.
Image – Google image search 22/03/2018
CVC blood sampling is always a sterile technique. Aspiration sites are cleaned with alcohol wipes (and allowed to dry!) pre and post use.
Question – can you see the CVC?
Image – https://radiopaedia.org/images/7472288
- pressure bag (kept) inflated to 300mmHg
- 0.9% saline present in flush bag changed @ 0800 hrs 24hrly
- transducer at phlebostatic axis
- connected to distal lumen
- unpressurised lumens flushed 6/24
- lines changed / redressed 7/7 & PRN
REMOVAL OF LINE
- refer to current Procedural Guidelines
- medical order for removal
- educate patient as indicated
- gauze swab packet
- dressing pack
- 10mls 0.9% saline
- chlorhex fluid swab
- suture cutter
- occlusive dressing IE Opsite 3000 or similar
- rubbish bin
Lay patient flat – and they must remain so for at least 30 minutes post CVC removal.
Be prepared after removal to apply moderate pressure uninterrupted for 2-3 minutes minimum.
When haemostasis achieved apply gauze swab folded into quarters and secure with occlusive dressing.
Observe wound site at least 3 times 15 minutes apart post removal for bleeding and dressing security – reeducate patient if able to about ongoing observation re bleeding / dressing removal timing. If transferred to ward within 2 hours inform ward staff of risk of entrainment / haemorrhage.
Image – https://www.bardaccess.com/ clinical_training/ course_overviews.php
- pneumothorax (highest for Sub-Clavian Vein)
- failure to locate vein
- accidental arterial puncture
- guide wire / air embolus
- thoracic duct injury
- haemopericardium and tamponade
- catheter blockage
- chylothorax – a type of pleural effusion resulting from lymph formed in the digestive system called chyle accumulating in the pleural cavity due to either disruption or obstruction of the thoracic duct
- catheter knots
- infection (note no difference in the rate of catheter-related bloodstream infections between the Internal Jugular, Sub Clavian and Femoral sites – > 2.5 infections / 1000 catheter days)
- catheter fracture
- vascular erosion
- vessel stenosis
- osteomyelitis of clavicle
COMMON ICU CVC COMPLICATIONS
Daggy (non-adhered) or badly timed dressings dressings
If not airtight and well stuck they may as well not be there – it is your job to ensure quality for your patients safety, 7 daily dressing changes are the minimum expected after worldwide recommendations – take it down, closely observe the site for signs of infection and redress as above
Clean with saline and coat with a generic chorhex based fluid (IE Persist Plus) and allow to dry – then a generic occlusive dressing (IE Opsite 3000) some hospitals use antibacterial impregnated wafers around the actual insertion site
Badly timed line changes
Propofol, amiodorone, TPN and some other drugs all have recommended ‘short’ time change schedules – be aware
Always ensure they are tight and labeled start of shift and whenever adding a line, some CVCs can end up with numerous ‘piggybacks’ with 3 or 6 ways taps and in can get confusing and dangerous
Use “quick” line clips only when indicated
Answer to again what is zero? – this allows a common reference point for calibration as room atmospheric pressure should be around 760mmHg at sea level – this becomes ‘zero’
Answer to how many lumens can a CVC have? – peripheral CVCs called PICC (usually inserted into upper inner aspect of the arm and may have 1 – 3, a CVC as inserted into internal jugular, sub-clavian etc 1 – 5 lumens
Answer to what is a CVP? – measurement of the pressure in the vena cava adjacent to R) atrium (unless femoral access) used to determine central venous pressure, this reading may be helpful in indication of preload to heart
Answer to can you see the CVC?
Oh’s Intensive Care Manual 7th Edition 2014 by Andrew Bersten, Neil Soni