Effect of position on IAP

Effect of position on IAP

-HOB (head of bed increase IAP) significant when > 20-30 degree
หัวยิ่งสูงยิ่ง increase
-Trendelenberg decrease IAP
-ถ้าต้องการหัวสูง ก็ reverse trendelenberg ก็จะลด IAP ได้
-Prone significant increase ยกเว้น ใช้เตียงแบบ เปิดพุง
-Knee chest position increase abdominal pressure (เอาไว้เบ่งอึ)

Hypoxia and Hypoxemia

Hypoxemia
1.low FiO2
2.Hypoventilation
3.Shunt
4.V/Q
5.Diffusion defect
6. Low mixed venous

Hypoxia
1.Low oxygen delivery
-Anemic hypoxia
-Hypoxic hypoxia
-Stagnic hypoxia
2.Cytotoxic or Histotoxic

Resistance of the airways

Resistance of the airways describes the obstruction to airflow provided by the conducting airways, resulting largely from the larger airways (down to division 6-7), plus a contribution from tissue resistance resulting produced by friction as tissues of the lung slide over each other during respiration

Airway diameter depends on the level of the airway in the tracheobronchial tree, airway smooth muscle tone, traction on the air- way from surrounding lung tissue, and internal and external pressures on the airway.

Single breath Nitrogen in uneven ventilation

phase 3 = indicate uneven ventilation
phase 4 = closing volume

uneven ventilation มีสามแบบ
1. parallel
2. series
3. collateral

centriacinar emphysema => series pattern
-concentration inspire gas in most distal airway low
-เวลาดม 100 % oxygen เข้าไปน้อย มี Nitrogen ตรึม
-เวลาหายใจออก ก็ poorly ventilate , empty last ์
-Nitrogen ก็ค่อยๆออกมาช้าๆ ทำให้ กราฟ steep ขึ้น

Factor effect dead space

Pendulum effect

Pendulum effect มี 3 อันที่ mention ถึง

1. the pendulum is now towards the “low VT, rela- tively high PEEP and hypercapnia,” we have forgotten that more than 30 yr ago it was clearly shown that low VT leads to progressive lung atelectasis with consequent hypoxemia.The atelectasis occurring with time, in this case, was not likely due to compression (which is an immediate phenomenon), but rather to a progressive gas reabsorption caused by a regional gas uptake greater than supply. The lung collapse was, in fact, directly related to the degree of hypoventilation and could be prevented by large tidal volumes, even delivered intermittently. Several reports came to the same conclusion, including studies in patients with ARDS (18, 19).
Thus, in this study, we tested the following hypotheses: (1) that the current recommended ventilation, i.e., PEEP thought to be sufficient to keep the lung open at end-expiration and inspiratory plateau pressure equal or lower than 35 cm H2O maintain unresolved atelectasis; (2) that sighs should provide sufficient opening pressure to further recruit the lung and should provide sufficient volume to prevent new reabsorption atelectasis, which otherwise may develop if too low VT is used, despite a PEEP selected as currently recommended

2.In unilateral pneumothorax เป็น paradoxical movement of lung
เวลามี ลมรั่วในปอดข้างนึง เวลาหายใจเข้า ปอดข้างปกติจะมีลมที่หายใจเข้าท​างหลอดลมตามปกติ และ ลมจากปอดข้างที่มีรู (ลมจากภายนอก positive ดันไป) พอหายใจออกลมจากปอดปกติที่โต ไหลมาทางปอดข้างที่ลมรั่ว ที่แฟบ เกิดแบบนี้ไปมา ทำให้ไม่ได้รับลมใหม่ๆ เกิดเป็น deadspace

3.T pause ทําให้ alveoli โตค้าง ดันลมออกมาทาง pore of kohn and canal of lambert ไปยัง alveoli แฟบ
แต่ลมที่ไปไม่ใช่ลมใหม่ เป็นลมที่ผ่านการแลกเปลี่ยนมาบ้​างส่วน เลยเพิ่มoxygen ได้ไม่มาก

Hering–Breuer inflation reflex

Hering–Breuer inflation reflex,

named for Josef Breuer and Ewald Hering,is a reflex triggered to prevent over-inflation of the lungs. Pulmonary stretch receptors present in the smooth muscle of the airways respond to excessive stretching of the lung during large inspirations.

Once activated, they send action potentials through large myelinated fibers of the paired vagus nerves to the inspiratory area in the medulla and apneustic area of the pons.

In response, the inspiratory area is inhibited directly and the apneustic area is inhibited from activating the inspiratory area. This inhibits inspiration, allowing expiration to occur.

high tidal volume จะ reflex ให้ ลด RR

About the pressure

Pressures:
Airflow is due to changes in pressure in the thoracic cavity that are transmitted to the alveoli.
Three important pressures associated with breathing and airflow:
1. Pleural pressure (PPL): pressure in the pleural fluid between the lung and chest wall.
2. Alveolar pressure (PA): pressure inside the alveoli.
3. Transmural pressure (PTM): the pressure difference across the airway or across the lung wall.
-Transpulmonary pressure: alveolar pressure-pleural pressure. Keeps the lungs from collapsing. Is always positive during normal breathing.
-Transairway pressure: airway pressure-pleural pressure. Transairway pressure is important in keeping the airways open during expiration.
Inspiration:
PPL is negative during quiet breathing and becomes more negative during inspiration. This causes PA to drop with respect to atmospheric pressure (very little pressure needed, -1 mmHg)
Expiration:
PPL becomes less negative and PA becomes slightly positive (+1 mmHg)
During heavy breathing PA can go from -80 to 100 mmHg
Pneumothorax: hole in the thoracic cavity, PPL becomes 0, can no longer generate (-) pressures in the alveoli.

Magnetometers or inductance plethysmographic coils

Real-time tracing of esophageal pressure as a reflection of pleural pressure (Ppl) and abdominal pressure as a reflection of gastric pressure (Pga) in a patient with bilateral diaphragmatic paralysis. Decreased intrathoracic pressure (more negative Ppl) on inspiration (Insp) is associated with an abnormal decrease in gastric pressure (more negative Pga). At the same time, there is outward displacement of the rib cage (upward deflection of RC) with a paradoxical decrease in abdominal volume (downward deflection of AB).

สรุปกราฟ หายใจเข้า Pplเป็นลบ–>abn negative gastric pressure, rib cageยกเพราะaccessory m.,ท้องแฟบ

Rx
unilat–>diaphragm plicationถ้าจำเป็น = stabilized affected diaphragm–>affected lung better ventilation
bilat–>NIPPVถ้าsevere พวกอาการน้อยอย่าลืมทำpolys​om., ถ้าอาการไม่ดีขึ้นพิจารณาot​her NIV eg. negative pressure cuirassของอาจารย์ ยังหารูปไม่เจอ ดูเก่ามาก นำมาใช้แล้วลงchest journal1987
–>diaphragm pacing, แพง phrenic n.&muscleต้องปกติ ซึ่งมักเป็นพวกcord compression ซึ่งบางทีneed tracheos.อยู่แล้ว ไปใส่invasiv PPVเลยจะเหมาะกว่า

Work of breathing

หายใจที่ high VT ทำให้ compliance ลดลง เพิ่ม WOB

The hatched area plus the triangular area ABC represents pressure multiplied by volume and is the work of breathing. riangular area ABC is the work required to overcome elastic forces (CT), whereas the hatched area is the work required to overcome airflow or frictional resistances (R)

The total work of breathing has a minimum value at about 15 breaths/min under normal circumstances. For the same minute volume, minimum work is performed at higher frequencies with stiff (less compliant) lungs and at lower frequencies when the airflow resistance is increased.