5. On Bypass

E pur si muove!

(Galileo Galilei)

Lower temperature - lower UF


Perfusionist has to be like a respectable wife who knows and divines wishes of a surgeon. He should take surgeon for better and worse.

heparin was developed by cravens

Anticoagulation

гепарин имеет кинетику нулевого порядка:

100 ЕД/кг действуют 1 час

300 – 400  ЕД/кг действуют 2,5 часа

post-pump fibrinolysis

По сравнению с контрольной группой, как низкие (нагрузочная доза 1 млн КИЕ; общая доза > 2 млн КИЕ), так и высокие дозы (нагрузочная доза 2 млн КИЕ; общая доза > 4 млн КИЕ) апротинина увеличивали риск летального исхода в 1,58 и 2,07 раз соответственно, выявляя дозозависимый эффект.

Назначение апротинина связано с доказанно большим риском развития острой почечной недостаточности, требующей проведения гемодиализа, нарушений мозгового кровообращения и энцефалопатии, а также инфаркта миокарда и сердечной недостаточности в сравнении с другими антифибринолитиками (аминокапроновой и транексамовой кислотой). Ряд исследований выявил связь назначения апротинина и развития тромбоза сосудов малого круга, коронарных артерий.

Post-cardiopulmonary bypass mediastinal drainage correlates strongly with increased heparin concentration during cardiopulmonary bypass and protamine dose.

Heparin-induced thrombocytopenia is caused by heparin-related and platelet-activating antibodies.


As almost every people perfusionists have their own lists of fears. 
Fear close to the fear of vagina dentata - clamps that cut tubings

drifting temperature

VAVD> -80 mmHg destroys blood cells

RAP >15 kg

Kool-Aid


child is peeing Coca-Cola


Aprotinin lowers results of kaolin test


Pharmacological half life and clinical half life.


to pull air


Shinobi

team work

Occlusion must be set at the level of 1 mm/min for each roller head. That means that if you set occlusion at this level and go to have some coffee occlusion should be only 18 cm less

suction - shear stress. What is shear is not principal. The key word is stress.

Keeping the level you should count not mls, but seconds. Seconds needed for safe handling without any risk of losing the level.

Safety margin.

When clotting occurs, tubing often looks misted.

Retrograde autologous priming

When blood is flowing through vessels narrower than 2 mm in internal diameter, the apparent viscosity tends toward that of plasma.

Each HLM should have 6 large and 8 small tubing clamps and a large and a small gate clamp. Each HLM must have a hand crank available.

Occlusion of the arterial pump is set to be fully occlusive at 240mmHg.
Fully occlusive is defined here as a pressure fall of no more than 1mmHg/minute.

Start gas supply with V/Q=1 and F_iO₂=1.

test your cannula

aortic cannula - узкое место

пережатая артериальная магистраль на старте!

You have tubing, you have blood in, and you have a knob.

specific kidneys perfusion = 360 ml/min/100 g = 1100 ml/min = 22%

It is a useful habit always to hold a tubing clamp in your hand while on pump. At least, it may help you to develop your fine motor skill.

on beginning of bypass the amount of gas given is 60-70ml/kg and F_IO₂ 80%.

On cooling sweep and F_IO₂ should be lowered.

putting on the cross clamp

taking off the cross clamp

Ht > 23 is critical (DeFoe, 2001)

brisk urine flow


Since all records are anyway made on patient’s cellular level, comparing them with yours you may find out a regularity.

Pump manufacturers recommend setting roller pump occlusion such that the level of a 100 cm column of crystalloid drops 2.5 cm/min.

Sevo MAC on bypass is 1.5 times less.

Fahraeus-Lindquist effect is the effect of vessel diameter on blood flow. In very narrow vessels, blood behaves as if viscosity was reduced.

Normally, basal cardiac output is determined by oxygen consumption, which is approximately 250 mL/min. It is impractical to measure oxygen consumption during cardiac surgery; therefore, the generally accepted flow rate at 35° to 37°C and hematocrit of 25% is approximately 2.4 L/min m² in deeply anesthetized and muscle-relaxed patients.

Hemodilution reduces blood oxygen content from approximately 20 mL dL to 10 to 12 mL dL; consequently flow rate must increase over resting normal cardiac output or oxygen demand must decrease.

Five clamps may be enough. Anyway surgeons usually have much more clamps than you do, and it may come in handy.

Placing clamps on tubings you should consider that they always must be visible.

Hct prediction formula: (Ht x ОЦК) / (ОЦК + объем заполнения + инфузия до ИК).

In fixed diameter vessels with laminar flow, the linear relationship between flow and velocity is not affected by changes in temperature and Hct in clinical ranges. These results are explained by the Fahraeus-Lindquist effect.

Moderate hemodilution (Hct 22%) decreases blood viscosity by 30 – 50% at a low blood temperature whereas an increase in Hct increased blood viscosity. Blood viscosity increases when blood temperature decreases; however, the increase in viscosity is observed mostly at temperature below 15°C.

Fahraeus-Lindquist effect confirms that the apparent viscosity of whole blood varies with the Hct. Normally, plasma viscosity is 1.2 – 1.3 times that of water, whereas the blood viscosity is 2.4 times that of plasma.

Besides oxygen consumption there is also oxygen demand.

If hemoglobin level is less than 6 g/dl flow should be raised up to 3,3 l/m².

Use of roller pumps beyond 4 to 5 hours is associated with hemolysis, and for this reason roller pumps are inappropriate for mechanical assistance that may involve several days to weeks of support.

All centrifugal pumps work on the principle of generating a rotatory motion by virtue of moving blades, impellers, or concentric cones. These pumps can generally provide high flow rates with relatively modest increases in pressure.

As long as mean arterial pressure remains above 50 to 60 mm Hg (i.e., above the autoregulatory range), cerebral blood flow is preserved even if systemic flow is less than normal.

Systemic arterial blood pressure is a function of flow rate, blood viscosity (that is hematocrit), and vascular tone. Perfusion of the brain is normally protected by autoregulation, but autoregulation appears to be lost somewhere between 55 and 60 mm Hg during CPB at moderate hypothermia and a hematocrit of 24%.

In older patients, who may have vascular disease and/or hypertension, mean arterial blood pressure is generally maintained between 70 and 80 mm Hg at 37°C. Higher pressures are undesirable because collateral blood flow to the heart and lungs increases blood in the operative field.

If anesthesia is adequate, hypertension is preferably treated with nitroprusside instead of nitroglycerin, which predominately dilates veins.

During CPB oxygen consumption (VO2) equals pump flow rate times the difference in arterial (CaO2) and venous oxygen content (CvO2). For a given temperature, maintaining VO2 at 85% predicted maximum during CPB assures adequate oxygen delivery. Oxygen delivery (DO2) equals pump flow times CaO2 and should be above 250 mL/min/m2 during normothermic perfusion. Mixed venous oxygen saturation (SvO2) assesses the relationship between DO2 and VO2; values below 60% indicate inadequate oxygen delivery. Because of differences in regional vascular tone, higher SvO2 does not assure adequate oxygen delivery to all vascular beds.

A minimum V/Q 0.2 is needed when blood is circulated. V/Q less than 0.2 may result in inadequate gas exchange.


Hyperkalemia - 25 mg/kg CaCl2, adults - 0.5-1g.

In order to collect proper blood samples, withdraw at least 6 ml of blood.

Altered dose response to nitroglycerin, fentanyl, etc., due to varying degrees of absorption by synthetic materials.

Do not inject from luer ports leading to the cardiotomy filter. Drug could stagnate in the filter.

Sudden stop of the blood pump may cause gaseous emboli due to inertia force.

Systemic Pressures: 

Lower limits allowed for Pediatrics less then 2 years of age.

When the pediatric patient reaches 2 years old they have developed vascular tone comparable to that of an adult

At Cross Clamp: Magnesium: 50mg / Kg, Ca++: 10mg/Kg, Mannitol = 0.5 g/Kg

BLOOD FLOW RATE

0 – 3 кг ￫ 200 мл/кг

3 – 10 кг ￫ 150 мл/кг

10 – 15 кг ￫ 125 мл/кг

15 – 30 кг ￫ 100 мл/кг

30 – 55 кг ￫ 75 мл/кг

>55 кг ￫ 65 мл/кг

При ОСП > 2,2 л/мин только лишь увеличивается травма крови?

All roller pumps run anti-clockwise.

 

Antegrade Cerebral Perfusion

The axillary artery is sewed with an 8.0mm graft, the aortic cannula is placed to the graft. Normally when giving antagrade cerebral perfusion,we will control the pump flow rate according to the right radial arterial pressure.  The mean right radial artery pressure will around 50mmHg.Now we also use the infarred cerebral saturation monitor to detect the cerebral perfusion as well.

For antegrade cerebral perfusion, I think roller pump is better than centrifugal pump. For me, volume control is much more better than pressure control. Because you will actually  know how much you are delivering. Remember to observe the arterial line pressure as well.
Both the right radial artery pressure and arterial line pressure will give you a good indicator whether you are doing well or not.

We use antegrade cerebral perfusion for arch repairs. Since we use a 4:1 cardioplgia what we do is clamp the K+ solution line and open the blood bridge. We flush the line to remove any residual K+ and then, using a retrograde cardioplegia catheter to directly canulate the carotid(s,) we use the cardioplegia system to flow to the head giving only blood. The balloon self inflates and we flow as if we were giving to the coronary sinus, limiting flow to pressures of about 130mm of line pressure and 25-50mm of "cuff pressure" as messured in the catheter. You can still give additional plegia to the heart by Y'ing off to the heart and reinstituting the crystalloid K+ sol'n. Just flush out your K+ again before reperfusing the head. Safe and simple.

Q1.Any safety devices have to add at the heart lung machine during CPB? besides bubble sensor,low level sensor and monitor pre membrane pressure,etc.C an incorporate a Venous O2 saturation monitor, vent line with a one way valve, cp line pressure and auto cut off etc..

Don't  change pump occlusion on the run blindly.. Just inform the surgeon, cool down a bit, go offbypass and check the occlusion asap..reinitiate bypass..

Important Points / Tips