Intro to Hypoxic pulmonary vasoconstriction Arun Shetty
Hypoxic pulmonary vasoconstriction, a seldom heard phenomenon but very effective physiologic property which helps lungs utilise ventilation to the maximum
Intro to Hypoxic pulmonary vasoconstriction Arun Shetty
Hypoxic pulmonary vasoconstriction, a seldom heard phenomenon but very effective physiologic property which helps lungs utilise ventilation to the maximum
Anesthetic consideration in smokers,alcoholics and addictsAftab Hussain
Anaesthetic consideration in smokers alcoholic and drug addicts. As an anaesthesiologist we must be aware with the problems associated with their management and interaction with anaesthetics.
Neuromuscular monitoring, also known as train of four monitoring, is a technique used during recovery from the application of general anesthesia to objectively determine how well a patient's muscles are able to function. It involves the application of electrical stimulation to nerves and recording of muscle response using, for example, an acceleromyograph. Neuromuscular monitoring is typically used when neuromuscular-blocking drugs have been part of the general anesthesia and the doctor wishes to avoid postoperative residual curarization (PORC) in the patient, that is, the residual paralysis of muscles stemming from these drugs.
Anesthetic consideration in smokers,alcoholics and addictsAftab Hussain
Anaesthetic consideration in smokers alcoholic and drug addicts. As an anaesthesiologist we must be aware with the problems associated with their management and interaction with anaesthetics.
Neuromuscular monitoring, also known as train of four monitoring, is a technique used during recovery from the application of general anesthesia to objectively determine how well a patient's muscles are able to function. It involves the application of electrical stimulation to nerves and recording of muscle response using, for example, an acceleromyograph. Neuromuscular monitoring is typically used when neuromuscular-blocking drugs have been part of the general anesthesia and the doctor wishes to avoid postoperative residual curarization (PORC) in the patient, that is, the residual paralysis of muscles stemming from these drugs.
Outline the various factors affecting airway resistance and correlate it to changes in pulmonary ventilation.
Describe the metabolism of surfactant, discuss its significance and relate its deficiency to clinical conditions.
Define compliance of the lung and chest wall, illustrate and discuss the compliance curve and describe the effect of surfactant on it.
Discuss work of breathing and relate it to clinical conditions.
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
ASA GUIDELINE
NYSORA Guideline
2 Case Reports of Gastric Ultrasound
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Pulmonary Thromboembolism - etilogy, types, medical- Surgical and nursing man...VarunMahajani
Disruption of blood supply to lung alveoli due to blockage of one or more pulmonary blood vessels is called as Pulmonary thromboembolism. In this presentation we will discuss its causes, types and its management in depth.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
263778731218 Abortion Clinic /Pills In Harare ,sisternakatoto
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Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
2. Respiratory function and
importance to anesthesia
CELLULAR RESPIRATION
The principal function of the lungs is to allow gas exchange
between blood and inspired air.
Types :
Aerobic Respiration
Anaerobic respiration
3. 1) Aerobic respiration
Nearly all human cells derive energy aerobically (i.e. by using
O2).
Carbohydrates, fats and proteins are metabolized to two carbon
fragments (acetyl-CoA) that enter the citric acid cycle within
mitrochondria.
Acetycl-CoA is metabolized to CO2- energy is derived and stored
in nicotinamide adenine dinucleotide (NDA), flavin adenine
dinucleotide (FAD), and guanosine triphosphate (GTP).
Energy is subsequently transferred to adenosine triphosphate
(ATP) through a process called oxidative phosphorylation.
4. 2) Anaerobic respiration
In the absence of O-2, ATP can be produced only from the
conversion of glucose to pyruvate to lactic acid.
When O2 tension is restored to normal, lactate is reconverted to
pyruvate and aerobic metabolism is resumed.
Effects of anesthesia on Cell metabolism
General anesthesia typically reduces both oxygen consumption
and CO2 production by about 15%.
The greater reductions are in cerebral and cardiac O 2
consumption.
5. MUSCLES OF RESPIRATION
I) Inspiratory muscles
A) During normal breathing
1) Diaphragm
Contraction of diaphragm cause base of thoracic cavity to
descent 1.5 to 7 cm in deep inspiration.
Responsible for 75% of the change in intrathoracic volume
during quiet inspiration.
2) External intercostals muscles
6. B) During forced inspiration
Also other accessory muscles like sternocleidomastoid, scalene and
pectoralis major muscle play role.
II) Expiratory muscles
A) During normal breathing – Expiration is passive process occur
due to elastic recoil of lung.
B) During forced expiration - abdominal muscles and internal
intercostals muscle play role.
7. Mechanism of ventilation
The movement of lungs are determined by impedance of the
respiratory system which can be divided into the –
1) Elastic resistance of tissue and gas liquid interface
It governs lung volume and the associated pressure under static
condition.
2) Non elastic resistance to gas flow
It relates to frictional resistance to airflow and tissue deformation.
8. 1) Elastic resistance
The lung and the chest wall are elastic structure. In between lung
and chest wall, a thin layer of fluid is present by which lung slide
easily on the chest wall but resist being pulled away from it.
Due to elastic recoil of the chest wall, chest wall has a tendency to
expand outward and lungs has tendency to collapse due to elastic
recoil of lung.
At the end of quiet expiration, the elastic recoil of the chest wall is
just balanced by the elastic recoil of lung.
If the chest wall is opened, the lung collapse and if the lung lose
their elasticity, the chest wall expands and become borrow shaped.
The recoil property of chest wall due to structure component that
resist deformation and probably include chest wall muscle tone. The
elastic recoil of the lung is due to their high content of elastin fibre
and the surface tension forces acting at the airfluid interface in
alveoli.
9. Surface tension forces
Surface tension forces tend to reduce the area of interface and
favour alveolar collapse.
According to Laplace law
Pressure =
2T
R
=
2×surface tension
Radius
So alveolar collapse is directly proportional to surface tension but
inversely proportional to alveolar size. Collapse is more likely
when surface tension increases or alveolar size decrease.
10. The surface tension of the alveoli is reduced by the surfactant
which is secreted by type II pneumocyte .
Ability of surfactant to lower surface tension is directly
proportional to its concentration with in alveolus.
In smaller alveoli
Surfactant are
more concentrate
↓ ↓ surface tension
Prevent collapse
In larger alveoli
Surfactant are less
concentrated
Relative ↑ in
surface tension
Prevent overdistens of alveoli
11. Compliance of respiratory system
Elastic recoil is usually measured in terms of compliance which is
defined as the change in volume divided by change in
transpulmonary pressure.
Compliance of lung =
Change in lung volume
Change in transpulmonary pressure
Transpulmonary pressure – The pressure needed to keep the
lung inflated at a certain volume, i.e pleural minus alveolar
pressure ,is known as transpulmonary pressure.
Normal lung compliance is 0.2-0.3L/cm of H2O (2-3 L/k Pa)
12. Pressure volume relationships of lung
• It is typical of an elastic structure.
•
pleural pressure is lower in upper regions.
• Regional transpulmonary pressure is thus higher for apical lung units than for basal ones in an
upright subject.
• The consequences will be that lower lung regions expand more for a given increase in
transpulmonary pressure than the upper units do.
• Thus ventilation goes preferably to the lower lung regions.
Compliance is critically dependent on the lung volume at which it is
measured.
13. Change in pressure volume curve in different disease
Right shift
Fibrotic lung disease
Idiopathic fibrosis
Alveolar proteinosis
Granulomatous diseases like sarcoidosis
Interstitial and alveolar edema
Left shift
Emphysema (loss of elastic tissue)
Chronic bronchitis
Asthma
14. Examples of pressure volume curves of the lung in health and lung disease. The much
flatter slope of the curve in fibrotic lung disease which reflects a considerable increase in
pressure variation and respiratory work. Parallel shift in the pressure volume curve of an
asthmatic and bronchitic patient, which shows that compliance need not change in these
diseases, although lung volume may have increased. Finally note the sleep slope of the
curve of an emphysematous patient. This indicates loss of elastic tissue and might even
suggest reduced respiratory work.
15. Compliance of chest wall
Compliance of chest wall =
Change in chest volume
Change in transthoracic pressure
* Transthoracic pressure equals atmospheric pressure minus
intrapleural pressure.
Normal value 0.2 L/cm H2O
Compliance of chest wall reduce : Obesity
Condition causing generalized edema
Joint disorder like amkylosing spondylitis.
16. Lung volumes
These are important parameter in respiratory physiology and
clinical practice. Lung capacities are clinically useful measurement
that represent a combination of two or more volumes.
Measurement
Definition
Average adult value
Male
Female
Tidal volume (V-T)
Volume of air that is expired and
inspired during normal breath
500 ml
500ml
Inspiratory reserve volume (IRV)
Maximum additional volume that
can be inspired above tidal volume
3300ml
1900ml
Expiratory reserve volume (ERV) Maximum volume that can be
expired below tidal volume
1000ml
700ml
Residual volume (RV)
Volume remaining after maximal
exhalation
1200ml
1100ml
Total lung capacity (TLC)
RV+ERV+VT + IRV
6000ml
4200ml
2200ml
1800ml
Functional
(FRC)
residual
capacity RV+ERV
17. Diagram showing respiratory excursions during normal breathing and
during maximal inspiration and maximal expiration
18. Functional residual capacity (ERV+RV)
FRC determined by the balance between the inward elastic recoil
of the lungs, and the outward recoil of the thoracic cage.
FRC decreases with paralysis and anaesthesia.
Other factor effect the FRC:
o Body size (increases of about 32-51 ml/cm of height)
o Gender (10% less in women of same height)
o Posture (supine posture decreases FRC by 0.5-1.0 litre in an
adult)
o Lung pathology.
19. Measuring FRC – 3 main approaches
1) Nitrogen washout
2) Helium wash-in
3) Body plethysmography
Closing volume (CV)
Small airway lacking cartilaginous support depend on radial
traction caused by the elastic recoil of surrounding tissue to
keep them open.
The volume above RV at which airways begin to close
during expiration is called closing volume.
20. Closing capacity (CC)
Sum of RV and closing volume is called closing capacity.
Airway closure is normal physiological phenomenon and is the
effect of increasing pleural pressure during expiration.
When pleural pressure became “positive”, it will exceed the
pressure inside the airway which is just or nearly atmospheric
at a low flow rate.
Higher pressure outside than inside will comprises the airway
and may close it.
21. There is a vertical pleural pressure gradient with a difference of approximately 7.5cm H 2O between the
upper most and lowermost regions, Causes a transpulmonary pressure gradient with higher pressure inside
the airway and alveolus in the upper part and higher pressure outside the alveolus and airway in the lower
part, This results in closure of the airways in lower part.
22. In young subjects airway closure may not occurs until they
have expired to RV.
With increasing age of 65 to 70 years, airway closure may
occurs above FRC.
This means that in elderly subjects, dependent regions are
intermittently closed during the breath, it is the major
explanation of why arterial oxygenation decreases with age.
In supine position FRC is reduced where as CC is not affected
by body position, so closure of airways may occur above FRC
even in young subjects.
In 70 years old subjects, in supine position, the airways may be
continuously closed if CC exceeds FRC plus VT.
23. Airway closure occurs at higher lung volumes in patients with
–
i. Obstructive lung disease
ii. Secretions, edema of the airway wall
iii. Increase bronchial muscle tone.
Vital capacity (VC)
It is the maximal volume of air which can be expelled from
lungs by forcefull effort following a maximal inspiration in
addition to body habits.
VC is also dependent on respiratory muscle strength, and
chest lung compliance.
Normal VC is ~60-70ml/kg.
24. II) Non elastic resistance
Normal total airway resistance is about 0.5-2cm H2O
Resistance is mainly contributed by medium sized bronchi.
Resistance in larger airway is low because of their larger
diameter, whereas resistance is smaller airway is also low
because of their large total cross sectional area.
The most important cause of increased airway resistance include
bronchospasm, secretions and mucosal oedema as well as volume
related and flow related airway collapse.
A) Volume related airway collapse
At low volume airway resistance become inversely proportional
to lung volume.
Increasing lung volume upto normal with positive end expiratory
pressure (PEEP) can reduce airway resistance.
25. B) Flow related airway collapse
During forced exhalation, reversal of normal transmural airway
pressure can cause collapse of these airway (dynamic airway
compression).
This is because of if generation of a positive pleual pressure
and if large pressure drop across intrathoracic airway.
The point along the airway where dynamic compression occurs
is called the equal pressure point. This equal pressure point
move towards smaller airway as lung volume decreases.
Emphysema and asthma predisposes patient to dynamic airway
compression. Emphsema destroys the elastic tissues that
normally support smller airway.
26. Forced vital capacity
Measuring vital capacity as an exhalation that is as hard and as
rapid as possible provides important information about airway
resistance.
The ratio of the forced expiratory volume is 1s (FEV1) to the
total forced vital capacity (FVC) is proportionate to the degree
of airway obstruction.
Normally, FEV1/FVC >80%
Forced mid expiratory flow (FEV25-75%) is effort independent
and a more reliable measurement of obstruction.
27. Work of breathing
Component that make up the work of breathing during quiet
inspiration are :I)
Non elastic work
a.
Viscous resistance (7%)
b.
Airway resistance (28%)
II) Elastic work (65%)
28. VENTILATION PERFUSION RELATIONSHIP
Ventilation
Ventilation is usually measured as the sum of all exhaled gas
volumes in 1 min (minute ventilation, or V). if VT is constant.
Minute ventilation = respiratory rate × tidal volume
For the average adult at rest, minute ventilation is about 5L/min.
Some of the inspiratory gas remain in the airway and not take part
in alveolar gas exchange,is known as Dead space,
Dead space may be –
Apparatus dead space
Anatomical dead space
Alveolar dead space
29. Anatomical dead space – related to the volume of conducing
passage.
Alveolar dead space – related to alveoli that are well ventilated
but poorly perfused.
Physiological dead space – sum of anatomical dead space and
alveolar dead space
In upright position – dead space is normally about 150ml for
most adult (~2ml/kg)
Dead space is approximately 30% of VT.
VD
VT
=
PACO2- PECO2
PACO2
PACO2= alveolar CO2 tension.
PECO2= mixed expired CO2 tension.
=
0.3
31. Distribution of ventilation
Alveolar ventilation is unevently distributed in the lungs.
Right lung receives more ventilation than the left one (53%
versus 47%), and lower (dependent) areas of both lungs tend to
be better ventilated than do not the upper areas because of a
gravitationally induced gradient in intrapleural pressure.
Pleural pressure increase by 0.3cmH2O/cm vertical distance.
Because of a higher transpulmonary pressure, alveoli in upper
lung areas are near maximally inflated and relatively
noncompliant, and they undergo little expansion during
inspiration.
In contrast, the smaller alveoli in dependent areas have a lower
transpulmonary pressure, are more compliant, and undergo
greater expansion during inspiration.
32. Pulmonary perfusion
Approximately 5L/min of blood flowing through the lungs,
only about 70-100mL at any one time is within the pulmonary
capillaries undergoing gas exchange.
Small increases in pulmonary blood volume normally occur
during cardiac systole and with each normal (spontaneous)
inspiration.
A shift in posture from supine to erect decreases pulmonary
blood volume (upto 27%).
Changes in systemic capacitance also influence pulmonary
blood volume: systemic venoconstriction shift blood from the
systemic to the pulmonary circulation, whereas vasodilation
causes a pulmonary to systemic redistribution.
Hypoxia is a powerful stimulus for pulmonary vasoconstriction.
33. Distribution of pulmonary perfusion
Pulmonary pressure increases down the lung by 1cm H2O/cm
distance.
This cause pressure difference between apex to base of 11 to
15mmHg.
34. Distance
Blood flow
Vertical distribution of blood flow in the
lung
Zone I :
Alveolar pressur > vascular pressure
No perfusion
Zone II :
Pulmonary arterial pressure >alveolar
pressure whcih in trun exceeds venous
pressure.
Increase blood flow
Zone III:
Both arterial and venous pressure exceed
alveolar pressure, so perfusion pressure is
arterial minus venous pressure.
Zone IV:
In the bottom of lung decrease in blood flow
because of increase in interstitial pressure
comprising extraalveolar vessels..
35. Causes of Hypoxemia and Hypercapnia
Hypoventilation
Shunting of deoxygenated blood past the lung
Ventilation/perfusion mismatched.
Diffusion impairment (grossly abnormal lungs)
Hypoventilation
Defined as ventilation that results in a PaCO2 above 45mmHg.
Present when minute ventilation is high if the metabolic demand
or dead space increases.
36. Ventilation/perfusion mismatched
At rest, both ventilation and perfusion increase down the lung.
Perfusion increases more than ventilation.
The difference between upper most and lowermost 5cm
segment being 3 times for ventilation and 10 times for
perfusion.
V/Q ratio :
At apex = 5.0
At middle = 1.0
At bottom = 0.5
37. Shunts
Shunting denotes the process whereby desaturated, mixed venous
blood from the right heart returns to the left heart without being
resaturated with O2 in the lungs.
The overall effect of shunting decrease (dilute) arterial O 2
content ; this type of shunt is referred to as right to left.
Intrapumonary shunts are often classified as absolute or relative.
Absolute shunt refers to anatomic shunts and lung units where
V/Q is zero. A relative shunt is an area of the lung with a low but
finite V/Q ratio.
38. In normal person, the amount of shunt is 2-3% (due to venous
blood flow from bronchi entering the pulmonary vein, as well as
coronary venous blood entering the left ventricle via thebesian
vein).
Pathological shunt –
o Obstructive lung disease
o Vascular disorders
o Atelectasis
o Consodilation
39. TRANSPORT OF GASES
I)Oxygen transport
Most oxygen is carried in the blood as oxyhemoglobins.
Hb carrying about 1.39ml of O2 per gram of Hb.
41. Right shift
• Increase CO2 concentriction
• Increase temperature
• Increase 2-3 DPG (diphosphoglycerate) concentration
• Increase pH (acidosis)
• Decrease PO2
• Anaemia
Left shift
• Fetal blood
• Decrease pH (alkalosis)
• Decrease temperature
• Decrease 2-3 DPG
42. II) CO2 Transport
This is carried in three forms :• Dissolved
• As bicarbonate
• As carbamino compounds, especially carbamino haemoglobin
43. Respiratory function during anaesthesia
Lung volume and respiratory mechanics during
anesthesia
Lung volume
FRC is reduced by 0.8 to 1.01 by changing body position from
upright to supine, and there is another 0.4-0.5L decrease when
anesthesia has been induced.
End expiratory lung volume is thus reduced from approximately
3.5 to 2L, the latter being close or equal to RV.
Anesthesia per se causes a fall in FRC despite maintenance of
spontaneous breathing.
44. Compliance and resistance of the respiratory system
Resistance of the total respiratory system and the lungs during
anesthesia increase during both spontaneous breathing and
mechanical ventilation.
Atelectasis and airway closure during anesthesia
Atelectasis
Atelectasis appears in approximately 90% of all patients, who
are anesthetized. It is seen during spontaneous breathing and
after muscle paralysis and whether intravenous or inhaled
anesthetics are used.
15-20% of the lung is regularly collapsed at the base of the lung
during uneventful anesthesia.
45. After thoracic surgery and cardiopulmonary bypass, more than
50% of the lung can be collapsed even several hours after surgery.
The amount of atelectasis decreases toward the apex, which is
mostly spared.
There is a weak correlation between the size of the atelectasis and
body weight or body mass index (BMI).
Obese patients showing larger atelectasis areas than lean ones do.
The atelectasis is independent of age, with children and young
people showing as much atelectasis as elderly patients.
Patients with COPD showed less or even no atelectasis during the
45 minutes of anesthesia.
The mechanism that prevents the lung from collapse is not clear but
may be airway closure occurring before alveolar collapse takes
place, or it may be an altered balance between the chest wall and
the lung that counters a decrease in lung dimensions.
46. Cranial shift of the diaphragm
and a decrease in transverse
diameter
of
the
thorax
contribute to lowered functional
residual capacity (FRC) during
anesthesia.
Decreased ventilated volume
(atelectasis and airway closure)
is a possible cause of reduced
lung compliance.
Decreased airway dimensions
by the lowered FRC should
contribute to increased airway
resistance (Raw).
47. Prevention of atelectasis during anesthesia
Several interventions can help prevent atelectasis or even reopen
collapsed tissue.
The application of 10cm H2O PEEP has been tested in several
studies and will consistently reopen collapsed lung tissue.
The persistence of shunt may be explained by a redistribution of
blood flow toward more dependent parts of the lungs when
intrathoracic pressure is increased by PEEP.
Under such circumstances, any persisting aatelectasis in the
bottom of the lung receives a larger share of the pulmonary blood
flow than without PEEP.
48. Increased intrathoracic pressure will impede venous return and
decrease cardiac output. This results in a lower venous oxygen
tension for a given oxygen uptake and reduces arterial oxygen
tension.
Second the lung recollapses rapidly after discontinuation of
PEEP. Within 1 minute after cessation of PEEP the collapse is as
large as it was before the application of PEEP.
Maintenance of muscle tone
Use of an anesthetic that allows maintenance of respiratory
muscle tone will prevent atelectasis from forming.
Ketamine does not impair muscle tone and does not cause
collapse.
Another technique used in an attempt to restore respiratory
muscle tone in pacing of the diaphragm by applying phrenic
nerve stimulation, which did reduce the atelectatic area.
49. Recruitment maneuvers
The use of sigh maneuver or a double VT has been advocated to
reopen any collapsed lung tissue.
For complete reopening of all collapsed lung tissue,an inflation
pressure of 40cm H2o is required.such a large inflation
corresponds to a maximum spontaneous inspiration, called VC
maneuver
Minimizing gas resorption
Ventilation of the lungs with pure oxygen after a VC maneuver
that had reopened previously collapsed lung tissue resulted in
rapid reappearance of the atelectasis.
If one the other hand, 40% O2 in nitrogen is used for ventilation
of the lungs, atelectasis reappears slowly and 40 minutes after the
50. Breathing of 100% O2 just for a few minutes before
and during commencement of anesthesia, increases
the safety margin in the event of difficult intubation
of the airway with prolonged apnea.
51. Avoidance of the preoxygenation procedure (ventilation with
30% O2) eliminated atelectasis formation during induction and
subsequent anesthesia.
Preoxygenation can also be provided without producing
atelectasis if undertaken with continuously increased airway
pressure, as with continuous positive airway pressure (CPAP).
Postanesthetic oxygenation (100% O2) 10 minutes before
termination of anesthesia together with a VC maneuver at the end
of anesthesia.
This is most likely the effect of first reopening collapsed tissue
and then under the influence of 100% O2 derecruiting previously
opened lung tissue.
A VC maneuver followed a lower O2 concentration, 40% kept the
lung open after recruitment until the end of anesthesia.
52. Airway Closure
Intermittent closure of airways can be expected to reduce the
ventilation of dependent lung regions.
Such lung regions may then become “low VA/Q” units if
perfusion is maintained or not reduced to the same extent as
ventilation.
Because anesthesia causes a reduction in FRC of 0.4-0.5L, it may
be anticipated that airway closure will become more prominent
in an anesthetized subjects.
A simple three compartment lung model can be constructed to
explain the impaired oxygenation during anesthesia.
53. Three compartment model
of
the
lung
in
an
anesthetized subject.
Upper part of the lung, the alveoli
and airways are open (Zone A).
Middle and lower parts of the lung,
the airways are intermittently closed
and impede ventilation (Zone B).
The bottom of lung, the alveoli have
collapsed (atelectasis, Zone C).
54. Distribution of ventilation and blood flow during
anesthesia
Distribution of ventilation
Ventilation was shown to be distributed mainly to the upper lung
regions, and there was a successive decrease down the lower half
of the lung.
PEEP increases dependent lung ventilation in anesthetized
subjects in the lateral position.
More even distribution between the upper and lower lung regions
have also been made in supine anesthetized humans after previous
inflation if the lungs, similar to PEEP.
Thus, restrotation of overall FRC toward or beyond the awake
level returns gas distribution toward the awake pattern.
55. Distribution of lung blood flow
PEEP causes a redistribution of blood flow toward dependent lung
regions.
Forcing blood volume downward to the dorsal side of the lungs
may increase fractional blood flow an atelectatic region.
56. Ventilation perfusion matching during anesthesia
Dead space, shunt,
relationships
and
ventilation
perfusion
Both CO2 elimination and oxygenation of blood are impaired in
patients during anesthesia.
The impended CO2 elimination can be attributed to increased
dead space ventilation.
Anatomic dead space is unchanged, indicating that the “alveolar”
dead space must have increased during anesthesia.
The impaired CO2 elimination is most easily corrected by
increasing the ventilation.
57. The impairment is arterial oxygenation during anesthesia is
generally considered to be more severe at higher ages, obesity
worsens the oxygenation of blood and smokers show more
impairment in gas exchange than nonsmokers do.
Effects of anesthetics on respiratory drive
Spontaneous ventilation is frequently reduced during anesthesia.
Thus inhaled anesthetics, as well as barbiturates for intravenous
use, reduce sensitivity to CO2.
Anesthesia also reduces the response to hypoxia. Attenuation of
the hypoxic response may be attributed to an effect on the carotid
body chemoreceptors.
58. Factors that influence respiratory function during
anesthesia
Spontaneous breathing
During spontaneous breathing, the lower, dependent portion of
the diaphragm moved the most, whereas with muscle paralysis,
the upper, nondependent part showed the largest displacement.
Increased oxygen fraction
When FIO2 was increased to 0.5 an increase in shunt of 3% to
4% was noticed.
Thus a certain dependence on FIO2 appears to exist, explained
by attenuation of the HPV response with increasing FIO2 or
further development of atelectasis and shunt in lung units with
59. Body position
Because FRC is dramatically reduced by the combined effect of
the supine position and anesthesia, it might be advantageous to
choose a more upright position in an anesthetized subject to
preserve FRC.
Age
Arterial oxygenation is further impeded with increasing age of
the patient.
There appears to be increasing VA/Q mismatch with age, with
enhanced perfusion of low VA/Q regions both in awake subjects
and when they are subsequently anesthetized.
Major cause of impaired gas exchange during anesthesia at ages
younger than 50 years is shunt, whereas at higher ages
60. Obesity
Obesity worsens the oxygenation of blood.
A major explanation appears to be a markedly reduced FRC,
which promotes airway closure to a greater extent than in a
normal subject.
Pre-existing lung disease
Smokers and patients with lung disease have more severe
impairment of gas exchange in the awake state than healthy
subjects do and this difference also persists during anesthesia.
61. Regional anesthesia
Ventilatory effects of regional anesthesia depend on the type
and extension of motor blockade.
With extensive blocks that include all the thoracic and lumbar
segments, inspiratory capacity is reduced by 20% and
expiratory reserve volume approaches zero. Diaphragmatic
function however, is often spared.
Editor's Notes
Breathing of 100% O2 just for a few minutes before and during commencement of anesthesia, increases the safety margin in the event of difficult intubation of the airway with prolonged apnea. However there turned out to be a price for it.