#anaesthetics #tables see also: [[ARDSnet ventilator settings]], [[Peri-intubation collapse]], [[Airway|Intubation]] > [!references]- > - [Dunn - Ventilation](x-devonthink-item://39F048C1-ECE6-41AC-841A-6FD53FC32F9F) > - [Dunn - Ventilation in special circumstances](x-devonthink-item://73C66D50-5D35-4744-BE63-5E36BA71F4F8) > - [Rosen - Ventilation in special circumstances](x-devonthink-item://75CFF8C0-7DFA-43BD-B20E-0E5FEE1C280D?page=7&start=1738&length=30&search=Special%20Clinical%20Circumstances) > - [Deranged physiology -- ventilation strategies for ARDS](https://derangedphysiology.com/main/required-reading/respiratory-medicine-and-ventilation/chapter%20512/ventilation-strategies-ards) > - [Deranged Physiology -- trials and guidelines mechanical ventilation](https://derangedphysiology.com/main/required-reading/respiratory-medicine-and-ventilation/Chapter%20001/trials-and-guidelines-respiratory-medicine-and-mechanical-ventilation) > - [WikiEM Mechanical ventilation](https://wikem.org/wiki/Mechanical_ventilation_(main)) > - [Deranged physiology - Intrinsic PEEP and dynamic hyperinflation](https://derangedphysiology.com/main/required-reading/mechanical-ventilation/Chapter-610/intrinsic-peep-and-dynamic-hyperinflation) > - [Wilcox - placing pt on ventilator](x-devonthink-item://210CF8FD-EE20-4A01-B41B-BCB51BF84B2E?page=54) | modality | indications | TV | RR | PEEP | Aims | | ------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------ | --------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------- | | [[ARDSnet ventilator settings\|ARDSnet]]<br>(Lung protective ventilation) | - [[ARDS]] | 4-6mL/kg PBW<br>- start at 6-8mL/kg and titrate down | - match to patient (<35) | - start 15-20<br>- ween PEEP and FiO2 to obtain targets<br>- if PPlateau >30, reduce TV by 1mL/kg to as low as 4mL/kg | - lung protective ventilation <br>- oxygenation 88-95% and wean PEEP and FiO2 to obtain target<br>- plateau pressure ≤ 30<br>- pH 7.3-7.35<br>- I:E ≤ 1 | | Permissive hypercaponea | - [[Asthma]]<br>- [[COPD]]<br>- [[pneumothorax#Bronchopleural fistula\|broncho-pleural fistula]]<br> | 6mL/kg PBW<br>MV 5-8 L/min<br>- flow rate 100L/min | - 6-10 breaths/min | (controversial)<br><5 cm H2O<br><br>plateau <30<br>peaks as low as possible as well | - low I:E ration ≥ 1:5<br>- sedation and paralysis<br>- C/I in raised ICP, severe ↓ contractility | | Normal | | 6-8 mL/kg IBW (usually ~7mL/kg ok); COPD patients may need higher TV to prevent dynamic hyperinflation | 12-20 breaths/min<br><br>normal MV is 4-5 L/min, but titrate setting to pathology | minimum PEEP 5 | inspiratory flow rate ~ 60L/min | # manoeuvres ## inspiratory pause Inspiratory Pause to Assess Pplat (*plateau pressure*) Plateau pressure (Pplat): Pressure felt by the lungs, determined by Vt and lung compliance; *Goal Pplat < 30 in ARDS* ![[Pasted image 20250104234444.png]] > high peak, high plateau - means problem is in the lungs > - mainstem intubation - check CXR or POCUS > - atelectasis > - pulm oedema > - ARDS > - pnemothorax ![[Pasted image 20250104234157.png]] > an increase in the gradient between the peak and plateau pressures (eg ↑ peak pressure; low plateau) indicates high airway resistance: > - kinked endotracheal tube - unkink it > - mucous plugging - suction > - bronchospasm - bronchodilators > - tube too narrow ## expiratory pause Expiratory Pause to Assess *autoPEEP* autoPEEP: Hyperinflation as a result of incomplete emptying before next breath; Risk of ↓BPs /PEA ![[Pasted image 20241004203231.png]] expiratory hold showing increased pressure due to auto PEEP # approach to high pressures see also: [[Peri-intubation collapse#troubleshooting post-intubation hypoxia or hypotension]] causes: - ETT blocked/kinked -- suction - kinking of circuit or tubing - patient/ventilator dysnchrony - [[pneumothorax]] - ETT in mainstem bronchus - oesophageal intubation - auto PEEP / breath stacking - bronchospasm (asthma, [[Anaphylaxis]], LVF, aspiration) **management:** - check ETT - check circuit - check patinet for dyssynchrony, bronchospasm, PTx, RM bronchus intubation - if no abnormal findings, reduce TV by 1mL/kg - ensure adequate sedation and add NM paralysis to improve chest wall compliance # patient positioning - head of bed elevation > 30 deg - lateral decubitus for severe unilateral lung disease - Good lung *DOWN* generally to improve [[VQ mismatch and its discontents|V/Q]] matching - good lung up for these exceptions: massive haemoptysis (prevent blood aspirating into good lung), large abscess, unilateral emphysema (prevent hyperinflation) # Dynamic hyperinflation and auto-PEEP 3 determinants of dynamic hyperinflation: 1. volume inspired 2. time for expiration (depends on rate and inspiratory time) 3. severity of the air-flow obstruction ![[Pasted image 20250104230626.png]] gas flow trace demonstrating failure of expiratory flow to return to baseline, indicating gas trapping. ![[Pasted image 20250104232534.png]] in **Dynamic hyperinflation** patients are breathing at near their total lung capacity. gas is trapped in the lungs by the arrival of the next breath, and lungs are unable to return their normal passisve relaxation volume (FRC) *Note* intrinsic PEEP is not synonymous with dynamic hyperinflation or breath stacking; but high intrinsic PEEP can lead to dynamic hyperinflation. Indeed, some degree of intrinsic PEEP is adaptive to help overcome extrinsic PEEP necessary for mechanical ventilation. > management: > - treat reversible factors (bronchospasm, secretions) > - prolong expiratory time (decrease I:E ration, decrease RR, increase inspiratory flow) > - decrease tidal volume > - set exogenous PEEP to 2/3 intrinsic PEEP (some use zero PEEP) > - if in doubt and dynamic hyperinflation suspected, disconnect ETT from circuit to allow spontaneous exhalation, then reconnect the ventilator **Minute ventilation** is the most important determinant of dynamic hyperinflation. for a given minute ventilation, the extent of dynamic hyperinflation is similar regardless of the specific combination of respiratory rate and tidal volume. Chart below shows the effect of minute ventilation (Ve) and inspiratory flow rate (VI) on dynamic hyperinflation during mechanical ventilation for severe asthma. VEE: volume at end expiration. VEI: volume at end inspiration. VT: tidal volume. ![[Pasted image 20250104232351.png]] --- # Mechanical ventilation overview see also: [Deranged physiology - practical differences between pressure and volume controlled ventilation](https://derangedphysiology.com/main/cicm-primary-exam/respiratory-system/Chapter-542/practical-differences-between-pressure-and-volume-controlled-ventilation) ## Pressure control vs volume control ![[Pasted image 20241224175416.png]] *Volume control* delivers pre-selected TV at constant flow rate, and the peak airway pressure is determined by the mechanical properties of resistance and elastance of lungs and chest wall. *Pressure control* has desired inflation pressure selected (eg 15 cmH2O) to achieve target tidal volume, and a decelerating inspiratory flow rate provides high flows at onset to obtain desired inflation pressure quickly. since there is no airflow at the end of inspiration, the end-inspiratory airway pressure is equivalent to the alveolar pressure > multiple systematic reviews and meta-analyses have shown no significant difference btwn VCV and PCV in terms of mortality, length of mechanical ventilation, oxygenation, and haemodynamic stability. however, there are some potential benefits of PCV in specific situations: better distribution of gas flow in pts with acute lung injury, and potentially lower peak airway pressures. | mode | Advantages | Disadvantages | | -------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Volume Control | - maintain constant TV despite Δ in mechanical properties of lungs<br>- especially useful for limiting TV during lung protective ventilation<br>- initial flow rate lower than in pressure-controlled modes → avoids a high resistance-related early pressure peak<br>- better for [[traumatic brain injury\|TBI]] where tight PaCO2 control necessary <br>- if airway resistance fluctuates significantly (eg status asthmaticus), can maintain reliable minute volme | constant inspiratory flow rate creates two potential disadvantages:<br>- duration of inspiration is short → can lead to uneven alveolar filling<br>- the maximum inspiratory flow is limited when flow is constant; ∴ the inspiratory flow rate can be inadequate for pts with ↑ ventilatory demands.<br>- recruitment may be poorer in lung units with poor compliance<br><br>mean airway pressure lower; may be worse in pts with severe hypoxia. Also, in presence of a leak, mean airway pressure may be unstable. | | Pressure Control | - reduced patient-ventilator dyssynchrony<br>- ↑ mean airway pressure → improves oxygenation<br>- ↑ duration of alveolar recruitment<br>- protective against barotrauma <br>- better for one-lung ventilation | - change in TV with changes in airway resistance or lung elastance → can lead to alveolar over-distension and ventilator-induced lung injury from volutrauma<br>- a high early inspiratory flow may breach the pressure limit if airway resistance is high | | PRVC <br>(pressure-regulated volume control) | constant tidal volume (like volume control) but limits end-inspiratory airway pressures (like PC)<br>- ventilator monitors lung compliance and uses lowest airway pressure needed to give TV<br>- sustained lung unit recruitment<br>- pressure minimised<br>- guaranteed minute volume | - pts with high ventilatory drive may not receive the needed inspiratory flow rate, leading to ventilator asynchrony<br>- mean airway pressure will be somewhat variable | **Pressure control:** ![[Pasted image 20250105011108.png]] **Volume control:** ![[Pasted image 20250105011423.png]] ## Tidal volume chart **Females:** | Height (ft/in) | 4 mL/kg PBW | 6 mL/kg PBW | 8 mL/kg PBW | |-------------|-------------|-------------|-------------| | 5' 0 | 182 | 273 | 364 | | 5' 1 | 191 | 287 | 382 | | 5' 2 | 200 | 301 | 401 | | 5' 3 | 210 | 314 | 419 | | 5' 4 | 219 | 328 | 438 | | 5' 5 | 228 | 342 | 456 | | 5' 6 | 237 | 356 | 474 | | 5' 7 | 246 | 370 | 493 | | 5' 8 | 256 | 383 | 511 | | 5' 9 | 265 | 397 | 530 | | 5' 10 | 274 | 411 | 548 | | 5' 11 | 283 | 425 | 566 | | 6' 0 | 292 | 439 | 585 | | 6' 1 | 302 | 452 | 603 | | 6' 2 | 311 | 466 | 622 | | 6' 3 | 320 | 480 | 640 | | 6' 4 | 329 | 494 | 658 | | 6' 5 | 338 | 508 | 677 | | 6' 6 | 348 | 521 | 695 | | 6' 7 | 357 | 535 | 714 | | 6' 8 | 366 | 549 | 732 | | 6' 9 | 375 | 563 | 750 | | 6' 10 | 384 | 577 | 769 | | 6' 11 | 394 | 590 | 787 | | 7' 0 | 403 | 604 | 806 | **Males:** | Height (ft/in) | 4 mL/kg PBW | 6 mL/kg PBW | 8 mL/kg PBW | |-------------|-------------|-------------|-------------| | 5' 0 | 200 | 300 | 400 | | 5' 1 | 209 | 314 | 418 | | 5' 2 | 218 | 328 | 437 | | 5' 3 | 228 | 341 | 455 | | 5' 4 | 237 | 355 | 474 | | 5' 5 | 246 | 369 | 492 | | 5' 6 | 255 | 383 | 510 | | 5' 7 | 264 | 397 | 529 | | 5' 8 | 274 | 410 | 547 | | 5' 9 | 283 | 424 | 566 | | 5' 10 | 292 | 438 | 584 | | 5' 11 | 301 | 452 | 602 | | 6' 0 | 310 | 466 | 621 | | 6' 1 | 320 | 479 | 639 | | 6' 2 | 329 | 493 | 658 | | 6' 3 | 338 | 507 | 676 | | 6' 4 | 347 | 521 | 694 | | 6' 5 | 356 | 535 | 713 | | 6' 6 | 366 | 548 | 731 | | 6' 7 | 375 | 562 | 750 | | 6' 8 | 384 | 576 | 768 | | 6' 9 | 393 | 590 | 786 | | 6' 10 | 402 | 604 | 805 | | 6' 11 | 412 | 617 | 823 | | 7' 0 | 421 | 631 | 842 |