ASK Astro!
***DISCLAIMER*** As with all clinical generalizations, exceptions are common and sound clinical judgement is essential. Remember, even the best recipe cannot guarantee a good cookie!
Astro, when do I place a central line for neurosurgical cases?
That's a great question. Here are some general guidelines for when to consider placing a central venous catheter:
1. Medical or logistical indication: e.g. patient has poor cardiac function with reduced ejection fraction, difficult intravenous access, or will likely need vasopressor or hypertonic fluid administration in the OR/ICU
2. Location of surgery/surgical positioning: for example the level of the surgical site is above the right atrium or the intracranial abnormality lies near or under a venous sinus - this places the patient at increased risk for Venous Air Embolism (VAE). Remember a central line is not usually therapeutic for VAE but can be diagnostic and guide the surgeon's efforts to prevent further embolization. The appearance of air bubbles in the CVC line during continuous aspiration of blood from the distal CVC port can tell us if we are continuing to entrain air from the surgical site.
If VAE is of concern due to surgical position (30 degree or greater back elevation) or proximity of surgical site to venous sinus, placement of precordial doppler is the standard of care (see procedures tab for how to place)
3. Cooling: when employing hypothermia the peripheral vasculature clamps down and peripheral perfusion is greatly reduced, thus peripherally administered drugs will take much longer to get to the heart and may need large volume flushing to successfully deliver the drug. When we need rapid changes in blood pressure (e.g. for a vascular lesion) a central line is essential!
What if the surgeon doesn't want the patient to have a central line?
Check to see if there is a legitimate medical reason you overlooked and if not, politely assure the surgeon that in the opinion of your attending a central line is necessary for the intraoperative anesthetic management of the patient!
What if my patient has a port?
As long as the port works well (e.g. used successfully for induction and draws back well) you can utilize the port for your drips. Depending on the type of surgery and the potential for blood loss it is always prudent to obtain large bore peripheral access so that blood products can be given in an emergency.
Hey Astro! How do I know if the surgeon wants to do cooling?
That's a great question. Usually "mild hypothermia" or cooling to 33 degrees Celsius is employed in neurovascular surgery to reduce cerebral metabolic oxygen demand and inhibit apoptosis thereby protecting the brain from ischemic insult. Plan for cooling in large or complex aneurysms, and AVMs.
We no longer employee cooling for EC-IC Bypass/Moyamoya cases.
Consider cooling when there is the threat of interrupted or decreased blood flow to any portion of the brain. Always verify with the surgical team if cooling is indicated. Sometimes for small or superficial cavernous malformations cooling is unnecessary.
On that note...how do I cool?
What you'll need:
1. Up to two water blankets (one placed under the sheet of the bed and one on top of the patient) capable of cooling (down to 4 degrees Celsius) and warming (up to 42 degrees Celsius). If the patient is small, a bair hugger may be applied on top in lieu of a water blanket on top of the patient
2. Two temperature sources: esophageal temperature probe, bladder temperature (remember to ask the nurses for a temperature Foley)
3. Bladder irrigation tubing with luer lock to connect to the foley (ask your circulator)
How to do it:
1. After the patient is induced and the lines secured - set the cooling blankets to 4 deg Celsius. If you have a bair hugger on top of the patient leave it off until rewarming. Make sure to hook up two temperature monitoring sources (e.g. esophageal and bladder)
2. Turn on high flows equal to minute volume ~ typically 4 LPM of Nitrous/Oxygen (50%) or 4LPM Of Air/Oxygen (50%)
3. When the esophgeal temperature probe nears 34 degrees Celsius turn your blanket warmer UP to 30-32 degrees Celsius. This will usually cause a parodoxical decrease in esophgeal temperature to about 33 degrees Celsius. As the periphery begins to rewarm, cold blood from the extremities will begin to circulate towards the core, cooling the patient further. Waiting until the esophgeal temperature reads less than 34 can cause excessive cooling (Click here to review complications of hypothermia: https://www.openanesthesia.org/temperature/). Remember to turn your fresh gas flows down at this point to facilitate rewarming ~ 0.5 - 0.8 LPM (50% FiO2) depending on oxygen consumption.
4. When the attending surgeon begins working under the microscope and the critical portion of the surgery will soon be finished, full rewarming should begin. Both water blankets should be turned to 42 degrees Celsius. If you have one blanket warmer and one Bair Hugger, both should be turned on to 42 degrees Celsius.
Hi Astro, is my central line in the right place?
