mechanical vent master study

beginning of semester

life functions (in order)

ventilation (breath sounds, VT, PaCO2), oxygenation (PaO2, color), circulation (pulse), perfusion (BP, temp, urine)

negative

natural environment of pressure (+, -)

airway resistance

(PIP - plateau) / flow (L/sec)

normal Raw

.5-2.5cmH2O/L/sec

less than 15cmH2O

acceptable Raw for mechanical ventilation

increase flow

decreases resistance, increases pressure

compliance

volume change per unit of pressure change, how easy it is to distend then return to original shape

normal compliance value

120mL/cmH2O

mv compliance value

50-150mL/cwp

dynamic compliance

Vt / (PIP-PEEP)

static compliance

Vt / (Pplat - PEEP)

increased resistance on graph

the difference between PIP and plateau will appear large

increased compliance

can get air in but cant get air out, no recoil on the lungs, COPD

decreased compliance

lungs are less stretchy and are stiff, pulmonary fibrosis, ARDS

PIP and Plat increase

increased compliance, concern for lung injury (volutrauma, barotrauma) disease process may be worsening

just PIP or just Pplat increasing

if just one is increasing it could be caused by a patient coughing, increased secretions, biting the tube etc.

deadspace

ventilation without perfusion, 30% is normal (150mL), increases CO2, end tidal gradient drops

Vd/Vt

total deadspace (physiologic / tidal volume) (PaCO2-PECO2) / PaCO2

shunt

perfusion without ventilation, opposite of deadspace (R-L deox blood bypasses lungs to L heart, L-R hole causes leakage of O2 blood in deox)

V/Q classic equation

Qs/Qt = (CCO2 - CaO2) / (CCO2 - CvO2)

clinical shunt equation

(A-aDO2/20) + 5 = % (A= alveolar, a= arterial)

normal physiological shunt

3-5%

alveolar air equation

PAO2 = (760 - 47)FiO2 - (PaCO2 / .8)

alveolar arterial oxygen difference

A-aDO2, normal is 5-15

a/A ratio

arterial alveolar oxygen ratio, normal is >74%, significant if <60%

I:E ratio

(I time/I time) : (E time/I time)

total cycle time

60sec / rate (bpm) → units in seconds

I time

Vt / flow (mL / sec)

E time

TCT - I time

albumin

3.5-5, protein storage, hard to get off ventilator if abnormal

plateau pressure

best indicator of alveolar pressure

trigger

starts breath, can be triggered by time (RR), pressure (pt effort/assist creates pressure drop) or flow (pt effort/assist drops flow)

limit

keeps the breath open on the vent flow (reaches certain point), pressure (lung protective, holds open) does not end breath

cycle

ends the breath, volume, pressure, time (breath stops after preset time), flow (PSV)

mandatory/control breaths

machine triggers and cycles breaths (starts and stops)

assisted breaths

patient triggers breath, machine cycles / ends them

spontaneous breaths

patient triggers and cycles breaths

volume limited SIMV w/ PSV

breathing spontaneously, patient works respiratory muscles, machine delivers set breath number with fixed pressure or VT, between mandatory breaths pt breathes on their own, pressure support added to overcome ETT resistance and make independent breaths easier, gradual weaning & synchrony

pressure regulated volume control

delivers a target tidal volume (VC) using the lowest possible pressure by adjusting inspiratory pressure breath to breath (if exhaled volume is too low, machine increases pressure next breath slowly and vice versa, limits peak pressures, adapts to compliance and resistance changes)

VC / A/C

volume assist/control, delivered a set tidal volume with each mandatory breath (or pt triggered)

PC A/C

pressure assist/control, delivers a set inspiratory pressure above PEEP for each breath, VT varies with compliance and resistance

PSV

pressure support ventilation, augments spontaneous breaths with a set pressure above PEEP, pt controls rate and timing, used for SBT and weaning

tidal volume

initial setting 4-8mL/kg (4-6 for ARDS, lung protective, 5-7 COPD/air trapping, 6-8 status athmaticus), target pplat <30, <28 protective

PBW

males- 50kg + 2.3kg X (height in inches - 60), women is 45.5 insead of 50

PEEP

initial 5cmH2O for refractory hypoxemia (post resus, smoke inhalation, ARDS) increase based on FiO2 requirement, PEEP tolerance and cardiovascular response

flow rate

maximum flow delivered by the vent during inspiration, air hunger is usually a peak flow issue, typically go w/ default setting unless flow hungry

I:E ratio

typically 1:2 to 1:4, longer E time for patients with air trapping/auto-PEEP

increased E time

can be achieved by increasing flow rate, increasing E time, decreasing I time or I time %, decreasing frequency, decreasing tidal volume

peak inspiratory pressure

set based off of plateau number (from insp hold) when switching from VC → PC, start from the plat (this is their safe zone where alveoli are not overdistending)

low VT

100mL lower than expired tidal volume, detect and alert leaks or disconnect

low inspiratory pressure alarm

10-15cmH2O below observed PIP, detect and alert leaks or disconnect

high inspiratory pressure alarm

10-15cmH2O above observed PIP, detect and alert conditions due to increase in resistance or decrease in compliance (water in circuit, secretions, ET kinking, tension pneumo, coughing)

apnea alarm

15-20sec time delay, detects and alert apnea or circuit disconnection

high frequency alarm

10/min over observed total frequency, detect and alert patient distress or improper or improper sensitivity setting

high and low FiO2

high 5-10% over analyzed, low 5-10% below analyzed

safe pressure limits

PIP <50cmH2O, Pplat <30cmH2O, MAP <30cmH2O, PEEP <10cmH2O

hemodynamic compromise (from vent)

PPV → increased intrathoracic pressure, decreased venous return (preload) → decreased CO2 → decreased BP

high peak low plat (physiology)

mucus plus, bronchospasm, ET tube block, biting

high peak high plat

ARDS, pulmonary edema, pneumothorax, ETT migration to single bronchus, effusion

barotrauma

injury from excessive airway pressures (high PIP/plat) causes pneumothorax / mediastinum, subq emphysema

atelectrauma

cyclic recruitment and derecruitment of unstable alveoli causes collapse

volutrauma

over distension of alveoli from large tidal volumes even at low pressures

permissive hypercapnia

changing the vent settings to allow for hypercapnia in order to avoid barotrauma / promote lung protective strategy

desired VT, ventilation and frequency

(known PaCO x known X (other variable)) / desired PaCO2

mean airway pressure

½ (PIP - PEEP) x (Itime/TCT) + PEEP, higher = better oxygenation but more pressure risks

double triggering

decrease I time, increase flow, PC mode

auto-PEEP triggering

air trapping, decrease RR, increase flow, set PEEP

reverse triggering

sedation is too deep, decrease then reassess

premature cycling

cycle % too high in PSV, decrease cycle off %

high pressure alarm

increased Raw, decreased compliance, biting/kinking

low pressure alarm

inccreased compliance, leak, circuit disconnect

high Ve alarm

patient over breathing → pain, anxiety, metabolic acidosis

low Ve alarm

patient not receiving adequate minute ventilation → increased PaCO2

expiratory hold

measures auto-PEEP

mechanical vent indications

>50mmHg PaCO2 with pH <7.25, COPD >50mmHg with pH <7.2, drug overdose, flail chest, neuromuscular disease

impending ventilatory failure

VE >10L/min, VC <10mL/kg, NF/MIP >-20, RR >35bpm, VC >10mL/kg

refractory hypoxemia

respiratory failure, PaO2 <60torr despite FiO2 >60%