To study about the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass

Автор: Reddy A.P., Sunitha R., Thangavel P., Ramkumar Dr.J., Miller S.G.

Статья в выпуске: 27, 2023 года.

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The study put forth the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass. The study was performed on 26 patients of either sex have age > 10 years and who underwent elective open-heart surgery from June 2017 - May 2018 in Sri Ramachandra Medical College & Research Institute. The patients with valvular heart diseases associated with other cardiac lesions like Intra cardiac shunts (ASD, VSD etc.) and Coronary artery disease (CABG) are excluded in the study. It examined the relationships among VO2, hemodynamics & DO2 during clinical perfusion, namely throughout moderately hypothermic CPB using a non-pulsatile roller pump while managing the alpha-stat acid-base with adults. The results revealed a linear relationship between VO2 and DO2, demonstrating that higher levels of delivery can perfuse and collect additional vascular beds throughout the CPB. Under bodily tissue perfusion, higher deliveries are advised to be avoided. The oxygen demand decreases by 7% for every 1OC decline in patient temperature.

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Heart disease, oxygen, patients, surgery

Короткий адрес: https://sciup.org/148326616

IDR: 148326616 | DOI: 10.18137/cardiometry.2023.27.200210

Текст научной статьи To study about the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass

Ashwanth P Reddy, R. Sunitha, Periyasamy Thangavel, J. Ram-kumar, S. George Miller. To study about the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass. Cardiometry; Issue No. 27; May 2023; p. 200-210; DOI: 10.18137/cardiometry.2023.27.200210; Available from:

Oxygen used by the body (VO2) is a standard metric of tissue perfusion adequacy throughout cardiopulmonary bypass (CPB)16 and a measure of metabolic activity15. Despite temperature’s impact on lowering metabolic activity during CPB, the research is divided on the key determinants of VO2 during CPB15,17. The relationships between ventilation (VO2) and oxygen delivery (DO2)16,18,19,20,21,22) and VO2 and hemodynamic variables during clinical CPB19,21,23 have been the subject of several investigations, both on animals and people, with varying results.

To study the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass.

Materials and methods

Criteria for inclusion

• Patients of either sex
• Patient age > 10 years
• Patients who underwent valvular heart surgeries

(including Redo valvular heart surgeries)

Exclusion criteria

• Patients with valvular heart diseases associated with other cardiac lesions like Intra cardiac shunts (ASD, VSD etc.)
• Coronary artery disease (CABG).

Data collection

Arterial * venous blood samples were collected: a) 10 mins. following initiation of CPB (mean tem perature of 32oC)

b) During hypothermia (mean temperature of 30^oC) c) During rewarming (mean temperature of 34^oC)

Anesthesia and Operative technique:

Anesthetic techniques are standardized for all patients. General anesthesia is induced with midazolam, fentanyl, whereas relaxation was achieved with vecuronium. Intravenous anesthesia is maintained by fentanyl throughout the operation. All our study patients undergo routine valvular heart surgeries through a median sternotomy and minimal invasive technique.

Heparin 400 IU/kg is given intravenously. Activated clotting duration being above 480 seconds triggers the initiation of cardiopulmonary bypass. Extracorporeal circulation is done with Sorin inspire adult membrane oxygenator, Sarns 8000 perfusion pump as well as a Spictra AF arterial line filter. Non-pulsatile perfusion is kept at a rate of flow of around 2.2 – 2.4 l/ m2 /min.

Patients are randomized by the perfusionist, using a computer-generated random number chart for addition of 10% mannitol to the priming solution. 1

liter Plasmalyte A solution, 3 mg /kg 20% mannitol as well as 10,000 IU heparin help prime the study group’s bypass circuit. 1-liter Plasmalyte A solution and 10,000 IU heparin help prime the control group’s bypass circuit.

Each patient is brought down until a nasopharyngeal temperature of around 28˚C. Following aortic cross-clamping, myocardial protection attained with intermittent antegrade cold blood cardioplegia (given at 08-10˚C). After rewarming, the aortic cross-clamp is released. Patients are rewarmed to around 37˚C. Heparinization is reversed by injecting protamine sulphate (1-1.3 mg per each 100 IU dose of heparin). Stable hemodynamics is used to wean patients off CPB. Patients are moved to the Cardiothoracic ICU following surgery.

Statistical Analysis:

Kolmogorov-Smirnov and Shapiro-Wilk tests

p-value < 0.05 is significant.

p-value > 0.05 is non-significant.

Discussion

Hypothermia is the temperature of the body being lower than 35oC or a state wherein a homeothermic mammal’s body temperature is below normal.

Nasopharyngeal temperature

Nasopharyngeal Temperature (ºC )	Cooling phase	Hypothermia	Rewarming phase
Mean	32.9615	30.5115	34.9846
Median	31.9000	30.3000	34.8500
Standard deviation	2.60938	2.30934	0.57667
Kolmogorov-Smirnova test (p-value)	0.011	0.000	0.133
Shapiro-Wilk test (p-value)	0.005	0.000	0.031

Cardiopulmonary bypass blood flow (CPB)

Cardiopulmonary bypass blood flow (CPB)	Cooling phase (Mean temperature of 32.9615^oC)	Hypothermia (Mean temperature of 30.5115^oC)	Rewarming phase (mean temperature of 34.9846^oC)
Mean	2.9077	2.8115	3.1115
Median	2.9500	2.8000	3.1000
Standard deviation	0.53361	0.37876	0.36696
Kolmogorov-Smirnova test (p-value)	0.200	0.192	0.200
Shapiro-Wilk test (p-value)	0.691	0.618	0.823

Mean arterial pressure (MAP)

Mean arterial pressure mmHg (MAP)	Cooling phase (Mean temperature of 32.9615^oC)	Hypothermia (mean temperature of 30.5115^oC)	Rewarming phase (mean temperature of 34.9846^oC)
Mean	45.0769	49.2308	54.3462
Median	43.5000	46.000	51.5000
Standard deviation	8.40439	11.19395	11.45406
Kolmogorov-Smirnova test (p-value)	0.2	0.013	0.196
Shapiro-Wilk test (p-value)	0.291	0.069	0.399

Oxygen delivery (DO2) and Oxygen consumption (VO2)

	Cooling phase (mean temperature of 32.9615^oC)		Hypothermia (mean temperature of 30.5115^oC)		Rewarming phase (mean temperature of 34.9846^oC)
	DO2(l/min)	VO2(l/min)	DO2(l/min)	VO2(l/min)	DO2(l/min)	VO2(l/min)
Mean	31357.28	4356.625	32300.3204	6904.912	35742.7075	8509.7171
Median	30337.89	4224.580	31911.4250	7180.2450	36710.300	8256.1150
standard deviation	7961.895	2503.319	5902.2588	2408.60283	5396.87619	2430.02405
Kolmogorov-Smirnova test (p-value)	0.200	0.200	0.200	0.200	0.141	0.200
Shapiro-Wilk test (p-value)	0.080	0.277	0.686	0.161	0.488	0.480

Peripheral arterial vascular resistance (mmHg)

Peripheral Arterial Vascular Resistance (mmHg)	Cooling phase (mean temperature of 32.9615^oC)	Hypothermia (Mean temperature of 30.5115^oC)	Rewarming phase (mean temperature of 34.9846^oC)
Mean	1000.4942	1006.2581	1068.7692
Median	937.2350	884.2650	995.2350
Standard deviation	586.10325	366.60336	431.82058
Kolmogorov-Smirnova test (p-value)	0.000	0.062	0.200
Shapiro-Wilk test (p-value)	0.000	0.351	0.737

Hemoglobin (Hb)

Hemoglobin Hb (g/dl)	Cooling phase (mean temperature of 32.9615^oC)	Hypothermia (Mean temperature of 30.5115^oC)	Rewarming phase (mean temperature of 34.9846^oC)
Mean	8.1577	8.7269	8.6577
Median	7.5500	8.6000	8.5500
Standard deviation	1.48086	1.37712	1.21398
Kolmogorov-Smirnova test (p-value)	0.022	0.200	0.200
Shapiro-Wilk test (p-value)	0.022	0.054	0.150

Fraction of inspired oxygen (FiO2 )

Fraction of Inspired Oxygen FiO₂ (%)	Cooling phase (Mean temperature of 32.9615^oC)	Hypothermia (Mean temperature of 30.5115^oC)	Rewarming phase (mean temperature of 34.9846^oC)
Mean	69.8077	59.0385	77.8846
Median	70.0000	60.0000	80.0000
Standard deviation	9.43194	7.12377	4.28324
Kolmogorov-Smirnova test (p-value)	0.023	0.042	0.000
Shapiro-Wilk test (p-value)	0.025	0.015	0.000

Sweep gas.

Sweep Gas (l/min)	Cooling phase (mean temperature of 32.9615^oc)	Hypothermia (Mean temperature of 30.5115^O)	Rewarming phase (mean temperature of 34.9846^oc)
Mean	2.3654	2.1154	2.5000
Median	2.5000	2.0000	2.5000
Standard deviation	0.50115	0.58835	0.44721
Kolmogorov-Smirnova test (p-value)	0.002	0.001	0.003
Shapiro-Wilk test (p-value)	0.029	0.60	0.001

Mean arterial pressure (MAP) and oxygen consumption (VO2)

Cooling phase (mean temperature of 32.9615oc) Hypothermia (mean temperature of 30.5115oc) Rewarming phase (mean temperature of 34.9846oc) MAP (mmHg) VO2 (l/min) MAP (mmHg) VO2 (l/min) MAP (mmHg) VO2 (l/min) Mean 45.0769 4356.62 49.2308 6904.912 54.3462 8509.7171 Median 43.5000 4224.580 46.000 7180.24 51.5000 8256.115 Standard deviation 8.40439 2503.319 11.19395 2408.60 11.45406 2430.024 Kolmogorov-Smirnova test (p-value) 0.2 0.200 0.013 0.200 0.196 0.200 Shapiro-Wilk test (p-value) 0.291 0.277 0.069 0.161 0.399 0.480 cardiopulmonary bypass blood flow (CPB) and oxygen consumption (VO2 )

	Cooling phase (Mean temperature of 32.9615^OC)		Hypothermia (Mean temperature of 30.5115^OC)		Rewarming phase (Mean temperature of 34.9846^OC)
	CPB BLOOD FLOW(l/min)	VO2(l/min)	CPB BLOOD FLOW(l/min)	VO2(l/min)	CPB BLOOD FLOW(l/min)	VO2(l/min)
Mean	2.9077	4356.62	2.8115	6904.912	3.1115	8509.7171
Median	2.9500	4224.580	2.8000	7180.24	3.1000	8256.115
Standard deviation	0.53361	2503.319	0.37876	2408.60	0.36696	2430.024
Kolmogorov-Smirnova test (p-value)	0.200	0.200	0.192	0.200	0.200	0.200
Shapiro-Wilk test (p-value)	0.691	0.277	0.618	0.161	0.823	0.480

CPB BLOOD FLOW ( l/min )

Arterial blood temperature

Arterial blood temperature (°C)	Cooling phase (Mean temperature of 32.9615^oc)	Hypothermia (Mean temperature of 30.5115^oc)	Rewarming phase (mean temperature of 34.9846^OC)
Mean	30.5962	31.8923	35.9115
Median	31.1000	32.0000	35.7000
Standard deviation	3.36711	2.98167	1.47141
Kolmogorov-Smirnova test (p-value)	0.200	0.200	0.007
Shapiro-Wilk test (p-value)	0.703	0.015	0.134

Venous blood temperature

Venous blood temperature (° C )	Cooling phase (Mean temperature of 32.9615^OC)	Hypothermia (Mean temperature of 30.5115^OC)	Rewarming phase (mean temperature of 34.9846^OC)
Mean	30.6885	31.5846	35.8115
Median	30.3500	32.1000	36.0000
standard deviation	2.83695	2.27977	0.89233
Kolmogorov-Smirnova test (p-value)	0.153	0.062	0.083
Shapiro-Wilk test (p-value)	0.134	0.425	0.164

Arteriovenous blood temperature difference

Arteriovenous blood temperature difference (°C)	Cooling phase (mean temperature of 32.9615^OC)	Hypothermia (Mean temperature of 30.5115^OC)	Rewarming phase (mean temperature of 34.9846^OC)
Mean	1.2423	1.3538	0.8181
Median	0.8000	0.9000	0.5000
Standard deviation	1.10097	0.96922	0.85763
Kolmogorov-Smirnova test (p-value)	0.083	0.002	0.000
Shapiro-Wilk test (p-value)	0.000	0.001	0.000

9000

8000

7000

6000

5000

4000

3000

2000

1000

CPB FLOW

VO2

4356,63

2,9077

Cooling phase

Hypothermia Rewarming phase

Arteriovenous Blood temperature difference

Physiology of hypothermia:

RATIONALE FOR THE USE OF HYPOTHERMIA:

• Hypothermia gives a degree of organ protection as well as safety margin throughout CPB.
• Hypothermia uses several mechanisms for its protective effect, one of which involves decreasing metabolic rate as well as oxygen consumption.
• Hypothermia aids in preserving stores of phosphates of high-energy & decreasing the release of excitatory neurotransmitters, which is vital in protecting the central nervous system.
• Hypothermia attenuates an excitotoxic cascade, which helps prevent the entry of calcium entry inside cells & restricts permeability of the membrane ^[10].

Our study aims to discover the relation between oxygen delivery and hemodynamics during cardiopulmonary bypass.

ABG parameters:

Includes venous oxygen content (Cvo2), Arterial oxygen content (Cao2), hemoglobin (Hb g/dl), Mixed venous oxygen saturation (Svo2) and venous oxygen content (Cvo2).

Applying cardiopulmonary bypass:

Acid–base control occurred after the regimen of alpha-stat. 1000-ml Plasmalyte solution as well as 150-ml Mannitol were used to prime the CPB circuit. Erythrocytes’ transfusion per CPB was studied at hematocrit <20%, combined with hypovolemia.

Statistical analysis for this study was done with the help of Kolmogorov-Smirnov, Shapiro- Wilk tests.

During the cooling phase (mean temperature of 32.9615OC) and hypothermic phase (mean temperature of 30.5115 OC) the cardiopulmonary bypass blood flow required was an average flow (mean of 2.9 l/min/ m2) whereas in rewarming phase (mean temperature of 34.9846OC) CPB blood flow requires a greater rate of blood flow (mean of 3.1 l/min/m2).

For every 10OC of temperature decrease in biologic systems, chemical processes’ rate of metabolism reduces with a factor of around two (Q10 factor)

The improvement I hypothermic CPB methods inspired the creation of devices that use heat-exchange for extracorporeal circuits which may rapidly heat (or cool) blood. During cooling, a huge temperature gradient might exist among the heat–exchanger unit & patient blood;

Mean arterial pressure at cooling phase (mean temperature of 32.9615 OC) and hypothermic phase (mean temperature of 30.5115OC) maintained at mean value of 49.2308mmHg. during rewarming phase (mean temperature of 34.9846OC) mean arterial pressure is of mean (54.3462mmHg) (i.e) increase in the cardiopulmonary bypass blood flow increases the mean arterial pressure simultaneously. Therefore, there is a linear relation between cardiopulmonary bypass rate of blood flow and the mean arterial pressure in all three phases (cooling, hypothermia and rewarming phase)

Oxygen delivery (DO2) refers to oxygen’s transfer rate from the lungs to the microcirculation and oxygen consumption (VO2) refers to oxygen’s removal rate from the blood for use by the tissues.

Oxygen content of venous and arterial blood was calculated, while cardiac output was measured during cardiac output monitor during each phase.

During cooling phase DO2 (mean 31357.28) and VO2 (mean 4356.625)

And hypothermia DO2 (mean 32300.3204) and VO2 (mean 6904.912)

And during rewarming phase DO2 (mean 35742.7075) and VO2 (mean 8509.717)

This study shows that DO2 (oxygen delivery) increases to keep up with the VO2 (oxygen consumption).

During rewarming phase (mean temperature of 34.9846OC) increase in CPB blood flow rate (mean 3.1115) increases both MAP (mean 54.3462) and PAVR (mean 1068.7692). Whereas, compared with cooling phase (mean temperature 32.9615OC) and hypothermia (mean temperature of 30.5115OC) minimal the CPB flow rate lower the MAP and PAVR (i.e) cooling phase (mean MAP- 45.0769, PAVR-1000.4942) and hypothermia (mean MAP-49.2308, PAVR- 1006.2581)

In hypothermic phase increase in Hb level, eventually it reduces the need of Fio2 and sweep gas but both Fio2 and sweep gas requires double the time during cooling and rewarming phase.

A direct linear relation was observed between oxygen consumption (VO2) and MAP, CPB blood flow rate only while rewarming. No relation was detected during cooling and hypothermia.

CONCLUSIONS

On commencement of cardiopulmonary bypass, a transient drop in the systemic pressure of blood is observed due to sudden decrease in blood viscosity resulting from hemodilution by the CPB priming solutions. As CPB continues there is a gradual increase in perfusion pressure due to increasing systemic vascular resistance.

Solubility of gases increases with decrease in patient temperature. The process of rewarming must be controlled to avoid overheating of blood, which may lead to microbubble formation due to reduced solubility of gases in blood as temperature increases, denaturing of proteins, cerebral injury.

Higher blood flow rate than the required can cause blood cell damage, impede the surgery by flooding the operative field, cause an excessive rise in central venous pressure.

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