Inhalation Agents Part 3 Flashcards
What effects do inhaled agents have on MAP?
At equipotent doses all agents will have similar effects
- MAP decreases with increased concentration of Sevo, Iso and Des in a dose dependent manner
- SVR also decreases (vasodilation)
- Exceptions *
- Halothane decreases MAP by decreasing CO
- N2O has either no change or mildly increases MAP
How are halogenated agents dosed compared to N2O?
- N2O is based on flow (% x L/min)
- Halogenated agent based on MAC (% x MAC value)
How do halogenated agents effect HR?
Dose dependent and different for each agent
- Iso—> starting at .25 MAC, linear dose dependent increase in HR, especially with rapid increase in concentration
* Des—> ≥ 1 MAC- linear dose dependent increase in HR, especially with rapid increase in concentration
<1 MAC- min increase in HR
- Sevo—> no increase in HR until > 1.5 MAC
What is the rule of 24?
Total combined flow of Des x O2 flow if >24 will see tachycardia
- keep <24 to keep HR under control (have Des ~8 and flows ~3)
What type of patient must you be cautious with increasing agent slowly to prevent tachycardia?
Cardiac compromised
Is CI influenced by inhalation agents?
Minimally
- TEE shows Des to produce minor increase in EF compared to awake measurements
Rapidly increase the dose will rapidly increase HR with ________ and ________ when > _____MAC.
Iso and Des
1 MAC
Abrupt increase in HR is not observed with ______, ______, or _______ up to MAC 2.
Sevo, halo or enflurane
Do the newer agents predispose the heart to PVCs?
Not unless they are given in extremely high concentrations
—> halothane does d/t catecholamines and hypercarbia
How do the agents effect QT interval and what should be avoided?
Inhalation agents prolong QT interval
* avoid SEVO in patients with known congenital long QT syndrome (LQTS)
(Safe with beta blocker therapy)
How do inhalation agents effect CAD?
Data shows no difference between inhaled and IV opioid anesthetic
—> volatile anesthetics exert protective effect on the heart
- limit the area of myocardial injury and preserving function after exposure to ischemic insult
What is coronary steal?
ISO’s ability to dilate healthy coronary arteries and not stenotic arteries, thus stealing from diseased vessels
What is ischemic preconditioning?
Like inoculation or vaccination against ischemia
- protective mechanism present in all tissues
- exposure to brief episodes of ischemia confers protective effect on myocardium agains subsequent prolonged ischemic insult (reversible or irreversible)
What are the 2 periods of protection with ischemic preconditioning?
1st period: 1-2 hours after conditioning episode
2nd period: benefits reappear 24 hours later and can last as long as 3 days
What is the crucial event that confers protective activity with ischemia preconditioning?
Opening of mitochondrial ATP sensitive K+ channels
What effect do the agents have on chronic HTN?
BP will drop even lower with anesthesia
- vessels are always clamped down —> less blood volume- when gas vasodilates vessels are hypovolemia
—> IVF boluses help
What are the pulmonary effects of inhaled agents?
- increase in RR and decrease in tidal volume (minute ventilation preserved)
- as anesthesia deepens- gas exchange is less efficient (shallow breathing)
- PaCO2 increases proportionately to depth of anesthesia
- dose depended blunted response to hypercarbia
- apnea threshold increased- higher CO2 level needed to stimulate breathing
- hypoxic drive altered- O2 must be lower to stimulate breathing
How do the agents effect the chest wall?
Gas relaxes everything
- cephalad displacement of diaphragm
- inward displacement of rib cage from enhanced expiratory muscle activity—> decreases FRC
- atelactasis in dependent lung zones
- worse with spontaneous ventilation
- increasing PEEP can help
- limit HPV
- Bronchodilation: greatest effect when bronchoconstriction present
- will help with bronchospasm
What are the effects of pungency?
- Coughing- worse in asthma and smokers- use inhaler before (gas is irritating)
- breath holding
- laryngospasm
- arterial desaturation
- Des and Iso are pungent —> Des is the most pungent
(Non-pungent gases are Sevo, Halo, Nitrous Oxide)
What are the CNS effects of the agents?
- decrease CMRO2
- with normal CO2 levels- cerebral vasodilation with MAC > 0.6
≥1MAC vasodilation that increases flood flow -> be careful with increased ICP
How does N2O effect CNS differently?
- causes cerebral vasodilation
- increases CMRO2
- to counter these effects give opioids, barbs, or propofol. (Not ketamine—> bad for brains)
What happens to ICP with ≥1MAC of all agents?
Increases ICP
In head trauma keep gasses < 1 MAC
What happens to autoregulation of blood flow in the brain <1 MAC?
Impaired, worsens as MAC increases
How do the agents effect evoked potentials?
- depress amplitude and increase latency of SSEP in a dose dependent manner
- both of these are signs of nerve damage…..
- EPS abolished at 1 MAC
- or N2O + o.5 MAC
- even low concentrations (0.2-0.3) decrease reliability of MEPs
