PHARMACOKINETICPHARMACOKINETICS OF S OF

INHALATIONAL INHALATIONAL AGENTS RELAVANT AGENTS RELAVANT TO ANAESTHEISTTO ANAESTHEIST

BYBY

Dr.NARASIMHA REDDY M.D,D.A,Dr.NARASIMHA REDDY M.D,D.A,

PROFESSOR AND HOD,PROFESSOR AND HOD,

DEPT OF ANAESTHESIOLOGY,DEPT OF ANAESTHESIOLOGY,

KURNOOL MEDICAL COLLEGE,KURNOOL MEDICAL COLLEGE,

KURNOOL.KURNOOL.

PARMACOKINETICS contdPARMACOKINETICS contd

• INTRODUCTIONINTRODUCTION

• HISTORYHISTORY

• PHARMACOKINETICSPHARMACOKINETICS

INTRODUCTIONINTRODUCTION

History started with History started with

inhalational anaesthetic agents.inhalational anaesthetic agents.

↓↓

Modern equipment Modern equipment

↓↓

Electronic gadgetsElectronic gadgets

HISTORYHISTORY

In 1951 – Seymour Kety In 1951 – Seymour Kety

In 1963 – Concept of MAC by Merkel and In 1963 – Concept of MAC by Merkel and

Eger.Eger.

In 1974 – Redefinition by Eger.In 1974 – Redefinition by Eger.

Other people who contributedOther people who contributed

Severinghaus, Mapleson and Epstein.Severinghaus, Mapleson and Epstein.

DEFINITIONSDEFINITIONS

Pharmacokinetics: what the body is Pharmacokinetics: what the body is doing to the drug.doing to the drug.

Pharmacodynamics: what the drug is Pharmacodynamics: what the drug is doing to the body.doing to the body.

Def. of some symbols:Def. of some symbols:

PPDD – Delivered partial pressure – Delivered partial pressure (tension)(tension)

FFDD – Delivered concentraion (fraction) – Delivered concentraion (fraction)

PPI I – Inspired partial pressure – Inspired partial pressure

PPAA – Alveolar partial pressure – Alveolar partial pressure

FFAA – Alveolar concentration – Alveolar concentration

PPaa – Arterial blood partial pressure – Arterial blood partial pressure

PPCNSCNS – Brain partial pressure – Brain partial pressure

PARMACOKINETICS contdPARMACOKINETICS contd

Anaesthetist manipulates concentration of Anaesthetist manipulates concentration of anaesthetic agent in the brain indirectly.anaesthetic agent in the brain indirectly.

A series of partial pressure gradients exists A series of partial pressure gradients exists from the anaesthetic machine to brain from the anaesthetic machine to brain tissue.tissue.

Partial pressure of anaesthetic agent in the Partial pressure of anaesthetic agent in the alveoli determines the partial pressure of alveoli determines the partial pressure of anaesthetic agent in the brain.anaesthetic agent in the brain.

PARMACOKINETICS contdPARMACOKINETICS contd

The factors involved for difference in tension The factors involved for difference in tension are:are:

1)1) VentilationVentilation2)2) UptakeUptake3)3) ConcentrationConcentration The factors which influence the input of The factors which influence the input of

anaesthetic agents – INFLOW FACTORSanaesthetic agents – INFLOW FACTORS

The factors which influence the loss of The factors which influence the loss of anaesthetic agents from alveoli- anaesthetic agents from alveoli- OUTFLOW FACTORSOUTFLOW FACTORS..

INFLOW FACTORSINFLOW FACTORS

1)1) Flow rate of carrier gas.Flow rate of carrier gas.

2)2) Conc. delivered by vaporizer.Conc. delivered by vaporizer.

3)3) Breathing systems.Breathing systems.

a) Non rebreathing VS rebreathing.a) Non rebreathing VS rebreathing.

b) Total volume of the system.b) Total volume of the system.

c) Arrangement of components. c) Arrangement of components.

d) Agent solubility in components.d) Agent solubility in components.

INFLOW FACTORS INFLOW FACTORS CONTD.CONTD.4)4) Effective alveolar ventilation Effective alveolar ventilation

Tidal volume Tidal volume

sponta vs sponta vs controlledcontrolled

Breath rateBreath rate

Dead spaceDead space

FRCFRC

5)5) Conc. Effect and Second gas effect. Conc. Effect and Second gas effect.

FLOW RATE OF FLOW RATE OF GAS/VAPORIZERSGAS/VAPORIZERSFLOW RATE OF CARRIER GASFLOW RATE OF CARRIER GAS::Precision flow meters which can deliver Precision flow meters which can deliver

100ml – 10lt/min 100ml – 10lt/min Fine needle valvesFine needle valvesFlow meters are specific for each gas.Flow meters are specific for each gas.VAPORIZERSVAPORIZERS::Compensated for back pressure and Compensated for back pressure and

barometric pressure.barometric pressure.The outflow depends on saturated The outflow depends on saturated

vapour pressure and carrier gas vapour pressure and carrier gas splitting ratio.splitting ratio.

FLOW FROM COMMON GAS FLOW FROM COMMON GAS OUTLETOUTLET

Factors which influence the conc. Of Factors which influence the conc. Of anae. agent delivered from anae. agent delivered from common gas outlet:common gas outlet:

a)a) Total gas flow rate (vol/time)Total gas flow rate (vol/time)

b)b) Conc of anaesthetic agent (vol/cent)Conc of anaesthetic agent (vol/cent)

TENSION OF ANA. AGENT IN TENSION OF ANA. AGENT IN THE INSPIRED GASTHE INSPIRED GASCorrugated rubber tubingCorrugated rubber tubing 1) Non- rebreathing1) Non- rebreathing 2) Partial rebreathing2) Partial rebreathing 3) Total rebreathing3) Total rebreathingIn rebreathing the gas mixtures may be In rebreathing the gas mixtures may be

diluted by residual gases in the system.diluted by residual gases in the system.Vol. of circle system is 4-5lts. Reservoir bag Vol. of circle system is 4-5lts. Reservoir bag

2lts.2lts.To wash out this vol. at 5lts/min may take 5-To wash out this vol. at 5lts/min may take 5-

6minutes.6minutes.The arrangement of components in the circle The arrangement of components in the circle

system is designed to give highest conc. system is designed to give highest conc. Of the anaesthetic agent and oxygen.Of the anaesthetic agent and oxygen.

TENSION OF ANAE. AGENT IN TENSION OF ANAE. AGENT IN ALVEOLAR GASALVEOLAR GAS

Depends on 2 factors:Depends on 2 factors:1)1) Conc. Of anae. AgentConc. Of anae. Agent2)2) Alveolar ventilationAlveolar ventilation If ventilation is controlled or assisted the conc. Of anae. If ventilation is controlled or assisted the conc. Of anae.

agent raises rapidly. Denitrogneation enhances this agent raises rapidly. Denitrogneation enhances this effect.effect.

Alveolar ventilation is a function of Alveolar ventilation is a function of a) tidal vol.a) tidal vol. b) dead spaceb) dead space c) ventilatory ratec) ventilatory rateThe tidal vol. and ventilatory rate can be manipulated by The tidal vol. and ventilatory rate can be manipulated by

assist or controlled ventilation. assist or controlled ventilation. The dead space is increased by certain drugs and position.The dead space is increased by certain drugs and position.

FRCFRC

FRC is less in supine position, abd FRC is less in supine position, abd distension, pregnancy and obesity. distension, pregnancy and obesity.

↓ ↓ FRC → FRC → Induction and recovery. Induction and recovery. ↓ ↓ FRC →FRC → Hypoxia at a faster rate Hypoxia at a faster rate

“ “ Of the steps between delivered and Of the steps between delivered and brain anae. Partial pressure none is brain anae. Partial pressure none is more pivotal than that between the more pivotal than that between the inspired conc. and alvoelar gases”.inspired conc. and alvoelar gases”.

CONCENTRATION EFFECTCONCENTRATION EFFECTwhen a high conc of an anaesthetic agent is when a high conc of an anaesthetic agent is

administered in the inspired gases a very large administered in the inspired gases a very large conc gradient between the alveoli and blood conc gradient between the alveoli and blood exists especially if partial denitrogenation is done, exists especially if partial denitrogenation is done, regardless of the solubility of the anaesthetic regardless of the solubility of the anaesthetic agent. agent.

Nitrous oxide is less soluble but 30 times more Nitrous oxide is less soluble but 30 times more soluble than nitrogen. soluble than nitrogen.

The total volume of nitrous oxide absorbed into the The total volume of nitrous oxide absorbed into the body over 1-2.5hrs after anaesthesia can be up to body over 1-2.5hrs after anaesthesia can be up to 30lts, 5-6lts being absorbed in the first 30lts, 5-6lts being absorbed in the first 10minutes. 10minutes.

““The rate of raise of FA/F1 ration is The rate of raise of FA/F1 ration is determined by Fi and alveolar ventilation”determined by Fi and alveolar ventilation”

CONCENTRATING EFFECT CONCENTRATING EFFECT

As half of NAs half of N22O is removed from the O is removed from the lung the conc of second gas lung the conc of second gas increases from 1-1.7 although the increases from 1-1.7 although the absolute volume does not change. absolute volume does not change. The relative conc increases because The relative conc increases because of the reduction in total lung volume.of the reduction in total lung volume.

SECOND GAS EFFECT SECOND GAS EFFECT The second gas effect has two components The second gas effect has two components • one concentrating effect and one concentrating effect and • Second one is – if lung is not allowed to Second one is – if lung is not allowed to

collapse but is replenished with gas collapse but is replenished with gas containing same conc then more of second containing same conc then more of second gas is brought in to the lung. According to gas is brought in to the lung. According to Epstein the increased inspiratory ventilation Epstein the increased inspiratory ventilation is the second part of second gas effect. The is the second part of second gas effect. The imp. of conc. vs increased inspired ventilation imp. of conc. vs increased inspired ventilation to the second gas effect depends on the to the second gas effect depends on the solubility of the second gas. If solubility is solubility of the second gas. If solubility is more the explanation lies in increased more the explanation lies in increased ventilation and if solubility is less the ventilation and if solubility is less the concentrating effect is imp. concentrating effect is imp.

OUTFLOW FACTORSOUTFLOW FACTORSThe gradient in the anaesthetic agent pps The gradient in the anaesthetic agent pps

from the alveoli to the CNS can be divided from the alveoli to the CNS can be divided into two steps: into two steps:

1)from the tension of anaesthetic agent in 1)from the tension of anaesthetic agent in the alveolar gas to tension of anaesthetic the alveolar gas to tension of anaesthetic agent in the arterial blood.agent in the arterial blood.

2) from the tension of anaesthetic agent in 2) from the tension of anaesthetic agent in the arterial blood to the tension in the CNS.the arterial blood to the tension in the CNS.

““The partial pressure of the anaesthetic The partial pressure of the anaesthetic agent in the alveoli governs the PP of agent in the alveoli governs the PP of the anaesthetic in the body tissues the anaesthetic in the body tissues including Brain.”including Brain.”

MACMAC• Def: conc of an agent in the alveoli at 1 atm that Def: conc of an agent in the alveoli at 1 atm that

prevents skeletal muscle movement in 50% of prevents skeletal muscle movement in 50% of patients in response to supramaximal stimulus. patients in response to supramaximal stimulus.

It is used as an index to measure the potency and It is used as an index to measure the potency and relate the potency of other agents. relate the potency of other agents.

MAC 1 corresponds to ED55. MAC 1 corresponds to ED55. MAC usually expressed as vol % and it does not MAC usually expressed as vol % and it does not

change with altitude. Usually 1.3 to 1.5 times MAC change with altitude. Usually 1.3 to 1.5 times MAC is necessary for operations and this is equal to is necessary for operations and this is equal to ED95. ED95.

• MAC bar: is the alveolar conc required to “block MAC bar: is the alveolar conc required to “block autonomic reflexes”. It is 1.5-2times the MAC. autonomic reflexes”. It is 1.5-2times the MAC.

• MAC awake: It is return of consciousness MAC 0.5.MAC awake: It is return of consciousness MAC 0.5.• MAC 0.2 is patient responding to commands. MAC 0.2 is patient responding to commands. ““MAC is a concentration but anaesthetic MAC is a concentration but anaesthetic

effect is produced by partial pressures”.effect is produced by partial pressures”.

MAC contdMAC contd

Factors that raise the MAC: Factors that raise the MAC:

1) Hyperthermia1) Hyperthermia

2) Ch. Alcohol abuse.2) Ch. Alcohol abuse.

3) Abuse of CNS depressants.3) Abuse of CNS depressants.

4) Cocaine and amphetamines 4) Cocaine and amphetamines

MAC contdMAC contdFactors that decrease MAC:Factors that decrease MAC:1) Old age1) Old age2) Hypothermia2) Hypothermia3) Pregnancy3) Pregnancy4) Hypotension4) Hypotension5) Lithium5) Lithium6) α-2 adrenergic agonists6) α-2 adrenergic agonists7) Lidocaine7) Lidocaine8) Opioids8) Opioids9) Benzodiazepines9) Benzodiazepines10) Barbiturates10) Barbiturates11) Calcium channel blockers11) Calcium channel blockers12) N12) N22O.O.

TEN. OF ANAE. ARTERIAL TEN. OF ANAE. ARTERIAL BLOODBLOODThe uptake of anaesthetic agent from The uptake of anaesthetic agent from

the alveoli which has the effect of the alveoli which has the effect of lowering the agent is a product of lowering the agent is a product of three factors:three factors:

1) Solubility of the agent in the blood 1) Solubility of the agent in the blood (blood/ gas par coefficient)(blood/ gas par coefficient)

2) Pul blood flow2) Pul blood flow

3) Alveolar to mixed venous PP 3) Alveolar to mixed venous PP difference difference

SOLUBILITY OF THE AGENTSOLUBILITY OF THE AGENT

• A partition coefficient expresses the A partition coefficient expresses the ratio of the solubilities of an agent in ratio of the solubilities of an agent in each 2 phases i.e such as blood and each 2 phases i.e such as blood and gas.(table).gas.(table).

• According to blood gas par. coefficients According to blood gas par. coefficients the inhaled anaesthetics can be the inhaled anaesthetics can be grouped as:grouped as:

1) poorly soluble anaesthetics 1) poorly soluble anaesthetics 2) moderately soluble anaesthetics.2) moderately soluble anaesthetics.

EQUILIBRIUMEQUILIBRIUM

• Def: condition where no difference in partial Def: condition where no difference in partial pressures of agent exists between two pressures of agent exists between two phases such as gas phase in alveoli and the phases such as gas phase in alveoli and the dissolved phase in blood.dissolved phase in blood.

• Expressed in conc. and not as partial Expressed in conc. and not as partial pressures.pressures.

• The larger the blood/gas par coefficient the The larger the blood/gas par coefficient the more soluble the agent in the blood and more soluble the agent in the blood and larger the uptake by the blood and reduction larger the uptake by the blood and reduction in partial pressure in the alveoli(PA) and in partial pressure in the alveoli(PA) and consequent reduction in Pa and Pcns.consequent reduction in Pa and Pcns.

OVER PRESSURE EFFECTOVER PRESSURE EFFECT• More soluble the agent higher conc More soluble the agent higher conc

required during induction than required during induction than normally required for maintenance. normally required for maintenance.

• Poorly soluble agents demonstrate a Poorly soluble agents demonstrate a more rapid raise of FA/FI during more rapid raise of FA/FI during induction and reach equilibrium at a induction and reach equilibrium at a faster rate and changes in ventilation faster rate and changes in ventilation have little effect.have little effect.

“ “When partial pressures are at When partial pressures are at equilibrium between two phases equilibrium between two phases concentration may be dissimilarconcentration may be dissimilar””

PULMONARY BLOOD FLOW PULMONARY BLOOD FLOW

• Increase in cardiac output slows down the Increase in cardiac output slows down the raise of alveolar conc even though the raise of alveolar conc even though the equilibrium is attained faster in between equilibrium is attained faster in between tissue compartments tissue compartments

• Effect of increase in cardiac output on FA/FI Effect of increase in cardiac output on FA/FI ratio is more pronounced with soluble ratio is more pronounced with soluble agents. Decrease in co with soluble agents agents. Decrease in co with soluble agents can cause high FA/FI ratio and sudden can cause high FA/FI ratio and sudden increase in PP in CNS. This is further increase in PP in CNS. This is further complicated by increase in alveolar complicated by increase in alveolar ventilation. Profound depression of CVS and ventilation. Profound depression of CVS and CNS can occur. CNS can occur.

ALVEOLAR TO MIXED VENOUS ALVEOLAR TO MIXED VENOUS PP PP DIFFERENCE DIFFERENCE

• Highest during induction and gradually comes Highest during induction and gradually comes down. down.

• Reflects the total tissue uptake of anaesthetic Reflects the total tissue uptake of anaesthetic agent over time . agent over time .

• tissue saturation with anaesthetic agent tissue saturation with anaesthetic agent →→ gradual raise in PP and FA/FI ratio also gradual raise in PP and FA/FI ratio also increases. PA/PI approaches equilibrium and increases. PA/PI approaches equilibrium and concomitantly Pa/PA also reaches equilibriumconcomitantly Pa/PA also reaches equilibrium

“ “ Increased pul blood flow and increased Increased pul blood flow and increased

blood solubility have more pronounced blood solubility have more pronounced

effects with more soluble agents”effects with more soluble agents”

VENTILATION/PERFUSIONVENTILATION/PERFUSION MISMATCH MISMATCH • In rt to lt shunts a portion of the pul. blood In rt to lt shunts a portion of the pul. blood

flow will not come in contact with inspired flow will not come in contact with inspired gas producing a great gradient between gas producing a great gradient between alveolar to arterial anaesthetic agent. alveolar to arterial anaesthetic agent.

• The gradient depends on the size of the The gradient depends on the size of the shunt.shunt.

• The partial pressure (Pa ) is less and so the The partial pressure (Pa ) is less and so the Pcns. Pcns.

• In VA/VQ abnormalities the anaesthetic In VA/VQ abnormalities the anaesthetic effect with poorly soluble agents is delayed effect with poorly soluble agents is delayed than the more soluble agents than the more soluble agents

FRCFRC • In obese patients ERV and FRC are In obese patients ERV and FRC are

reduced, more so in supine position reduced, more so in supine position nearly to closing volumes producing nearly to closing volumes producing true rt to left shunt. true rt to left shunt.

• Smaller FRC theoretically must Smaller FRC theoretically must produce faster equilibration between produce faster equilibration between PI, PA and pa but because of collapse PI, PA and pa but because of collapse of alveoli and shunting there is a of alveoli and shunting there is a delay in uptake of anaesthetic agent delay in uptake of anaesthetic agent so that Pa/PA ratio is reduced and so so that Pa/PA ratio is reduced and so induction is delayed.induction is delayed.

TENSION OF ANAESTHETIC TENSION OF ANAESTHETIC AGENTS IN CNS:(PCNS )AGENTS IN CNS:(PCNS )

• several characteristics of the body tissues several characteristics of the body tissues regulate the amount of anaesthetic agent regulate the amount of anaesthetic agent reached from the blood :reached from the blood :

1) Solubility in particular tissue and 1) Solubility in particular tissue and

2) Blood flow through the tissue2) Blood flow through the tissue

3) Volume of the tissue3) Volume of the tissue

4) Gradient between arterial to tissue 4) Gradient between arterial to tissue concs.concs.

Tissues are categorized according to Tissues are categorized according to perfusion and solubility perfusion and solubility characteristics into 4 groups:characteristics into 4 groups:

1) Vessel rich group (VRG)1) Vessel rich group (VRG)

2) Muscle group (MG)2) Muscle group (MG)

3) Vessel poor group (VPG)3) Vessel poor group (VPG)

4) Fat group (FG).4) Fat group (FG).

1) VRG: Brain, heart, kidney, liver and endocrine glands.1) VRG: Brain, heart, kidney, liver and endocrine glands. Mass is < 10% of body wt but they receive 75% Mass is < 10% of body wt but they receive 75% of CO. of CO. Perfusion ratio is 70ml/100ml of tissue/min. Perfusion ratio is 70ml/100ml of tissue/min. Takes large amount of anaesthetic while induction. Takes large amount of anaesthetic while induction. Equilibration with arterial pp of anaesthetic is> Equilibration with arterial pp of anaesthetic is> 90% complete with in 8 mts.90% complete with in 8 mts. 2) MG: After 8minutes the tissue uptake of anaesthetic 2) MG: After 8minutes the tissue uptake of anaesthetic agent is mainly by muscle and skin. agent is mainly by muscle and skin. MG is 50% of body wt and receives 20% of CO. MG is 50% of body wt and receives 20% of CO. Perfusion rate is 3ml/100gm/min.Perfusion rate is 3ml/100gm/min. Takes longer time to get equilibrium may be 3-Takes longer time to get equilibrium may be 3- 4hrs. 4hrs.

3) FG: Acts as final large reservoir of 3) FG: Acts as final large reservoir of anaesthetic anaesthetic

agent. agent.

Affinity is 25-75 times> affinity of blood. Affinity is 25-75 times> affinity of blood.

FG 20% of body wt and receives 6% of FG 20% of body wt and receives 6% of

COP.COP.

Perfusion ratio of 3ml/100ml/min. Perfusion ratio of 3ml/100ml/min.

Equilibration may not occur in clinical Equilibration may not occur in clinical

anesthesia.anesthesia.

Distribution to CNS Distribution to CNS • various areas of brain and spinal cord play an various areas of brain and spinal cord play an

important role in getting equilibrium with important role in getting equilibrium with anaesthetic agent and by which end result anaesthetic agent and by which end result occurs, like loss of consciousness movement, occurs, like loss of consciousness movement, analgesia, depression and blockade of autonomic analgesia, depression and blockade of autonomic reflexes and relaxation. reflexes and relaxation.

• Since brain tissue is highly perfused and raise of Since brain tissue is highly perfused and raise of tension of anaesethic agent is rapid and uptake tension of anaesethic agent is rapid and uptake ceases with in a short period, the raise is more ceases with in a short period, the raise is more with poorly soluble agents but depends on with poorly soluble agents but depends on pressure gradient between agent, PA, Pcns and pressure gradient between agent, PA, Pcns and CBF. CBF.

““Tissue uptake of anaesthetic is governed Tissue uptake of anaesthetic is governed by tissue solubility, perfusion, tissue size by tissue solubility, perfusion, tissue size and tissue saturation”and tissue saturation”..

RECOVERY FROM RECOVERY FROM ANAESTHESIA ANAESTHESIA Nearly all the factors that govern the rate at Nearly all the factors that govern the rate at

which the alveolar conc raises in induction which the alveolar conc raises in induction apply to recovery. apply to recovery.

The immediate decline of the anaesthetic level The immediate decline of the anaesthetic level is rapid because of the wash out of the FRC. is rapid because of the wash out of the FRC.

As the ventilation removes the anaesthetic As the ventilation removes the anaesthetic from the alveoli more and more anaesthetic from the alveoli more and more anaesthetic gets washed into the alveoli from the gets washed into the alveoli from the tissues. This depends on the venous alveolar tissues. This depends on the venous alveolar anesthetic gradient which will be higher for anesthetic gradient which will be higher for more soluble agents. So the fall in alveolar more soluble agents. So the fall in alveolar levels will be slow when compared to less levels will be slow when compared to less soluble agents. soluble agents.

DIFFERENCES BETWEEN DIFFERENCES BETWEEN INDUCTION AND RECOVERY INDUCTION AND RECOVERY

Mainly two:Mainly two:1) There is no such counterpart for an 1) There is no such counterpart for an

overpressure effect and the elimination overpressure effect and the elimination of anaesthetic depends on the return of anaesthetic depends on the return of the agent from the tissues.of the agent from the tissues.

2) Since all tissues do not have the same 2) Since all tissues do not have the same PP at recovery and although the vessel PP at recovery and although the vessel rich group may be getting depleted of rich group may be getting depleted of its anesthetic content, fat may still its anesthetic content, fat may still take up anaesthetic agent in the blood. take up anaesthetic agent in the blood.

DIFFUSION HYPOXIA DIFFUSION HYPOXIA Patient if allowed to breath room air on Patient if allowed to breath room air on

discontinuation of anaesthesia with nitrous oxide discontinuation of anaesthesia with nitrous oxide hypoxia can occur. hypoxia can occur.

On recovery from anaesthesia large volumes of On recovery from anaesthesia large volumes of nitrous oxide flood the alveoli; this dilutes the gases nitrous oxide flood the alveoli; this dilutes the gases inside the alveoli including oxygen.inside the alveoli including oxygen.

As large volumes of nitrous oxide is washed out it As large volumes of nitrous oxide is washed out it takes carbon dioxide also suppressing the takes carbon dioxide also suppressing the respiratory stimulation. respiratory stimulation.

Hence diffusion hypoxia is due to dilution of alveolar Hence diffusion hypoxia is due to dilution of alveolar gases and respiratory depression.gases and respiratory depression.

This problem exists for the first 5-10min during This problem exists for the first 5-10min during recovery and this is more important in a pt with recovery and this is more important in a pt with existing respiratory disease.existing respiratory disease.

This can be managed by discontinuing of nitrous This can be managed by discontinuing of nitrous oxide few minutes before and giving 100% oxygen oxide few minutes before and giving 100% oxygen for some time.for some time.