CO2 ABSORBENTS

1. CO2 combines with water to form carbonic acid. CO2 absorbents are hydroxide salts which neutralise the carbonic acid.

2. Colour conversion of a pH indicator dye (e.g., ethyl violet from white to purple) by increasing hydrogen ion concentration signals absorbent exhaustion. Absorbent should be replaced when 50% to 70% has changed colour

3. CO2 absorbants absorb (this may contribute towards delayed induction and emergence) and degrade volatile agents

4. Soda Lime and Amsorb are the commonly used CO2 absorbents

5. Soda lime  consists of Ca(OH)2 [80%], NaOH, water and KOH. It is capable of absorbing up to 23 L of CO2 per 100 g of absorbent. Addition of silica decreases the danger of inhalation of NaOH dust and reduces the resistance to gas flow. The drier the soda lime, the more likely it will absorb and degrade volatile anesthetics.

6. Amsorb consists of Ca(OH)2, CaCl2, CaSO4 and polyvinylpyrrolidone to increase hardness. It is more inert towards volatile agents, so their degradation is less with Amsorb

7. The dry absorbents may break down the volatile anesthetics to carbon monoxide (CO) (e.g., sodium or potassium hydroxide). The formation of CO is highest with desflurane. Compound A is a byproduct of degradation of sevoflurane by absorbent.

Ⓜ️NEMO> CO-Des 'CODES' CoA-Sevo 'CAuSE'

Negative pressure pulmonary oedema (NPPO)

NPPO is associated with upper airway obstruction in a spontaneously breathing patient. 

It occurs in 0.05–0.1% of all general anaesthetic cases and laryngospasm has been reported as being the cause in 50% of cases.

The clinical course is most frequently observed on emergence from anaesthesia where incomplete recovery from general anaesthesia increases the likelihood of the development of laryngospasm, but it has also been reported after airway obstruction with a foreign body and blockage and biting of tracheal tubes, hanging, and strangulation. 

Pulmonary oedema is typically described as developing within 2 min of the obstruction.

Once the airway is occluded, the spontaneously breathing patient will continue to generate negative intrathoracic pressure which will increase substantially as respiratory distress develops.

There is an associated increase in sympathetic tone due to the stress of hypoxia and airway obstruction which increases SVR and elevates pulmonary artery pressure. 

This is further exacerbated by hypoxic pulmonary vasoconstriction. 

The combination of these processes creates a pressure gradient across the capillary–alveolar membrane which favours the movement of fluid into the lung parenchyma.

It is most common in younger patients, presumably because they are able to generate higher negative inspiratory pressures and, arguably, have a higher sympathetic tone and better cardiac function. 

The condition may resolve rapidly after definitive management of the airway obstruction, but in some cases, copious pulmonary oedema may form and it can be associated with pulmonary haemorrhage suggesting capillary membrane damage.

After recognition of the cause of obstruction, the treatment required ranges from relatively modest support such as brief periods of CPAP for 2 h to positive pressure ventilation over a period of 24 h.

Ref: Neurogenic pulmonary edema

Ronan O'Leary, 

Justin McKinlay 

Contin Educ Anaesth Crit Care Pain (2011) 11 (3): 87-92.

WHAT IS POYNTING EFFECT

This is an effect described with regards to the anesthetic gas ENTONOX

ENTONOX is a 50:50 mixture of gaseous oxygen and nitrous oxide

If the cylinder is stored below -6 degree (the pseudocritical temperature of ENTONOX) Celsius, the nitrous oxide component can separate as a liquid (lamination)

This can lead the delivery of uneven mixtures, too much oxygen at the beginning and too much N2O at the end of the cylinder life

Danger of lamination can be avoided by immersing the cylinder in water at 52 degree Celsius and inverting it 3 times, or by keeping it above a temperature of 10 degree Celsius for 2 hours before use.

Other methods are keeping the cylinder horizontal, at a temperature of 5 degrees or more for more than 24 hours OR by connecting a tube from the valve housing at the top to a point near the bottom which prevents the withdrawal of pure nitrous oxide

N.B. The critical temperature of a gas is the maximum temperature at which compression can cause liquefaction. Mixing gases may change their critical temperature. The Poynting effect produces a 50:50 mixture which reduces the crtical temperature of N20 (Critical temperature is 36.5 degree Celsius); so Entonox has a pseudocritical temperature of -6 degree Celsius

A FEW POINTS ABOUT A SHARED LUNG

🔸In the pregnant patient, the respiratory function deviates from the normal

🔸There is increased CO2 production by the mother and the foetus; but mostly you see a respiratory alkalosis. Why?

🔸This is because the stimuli from the raised pCO2 levels and that by the respiratory stimulant, progesterone,  sets the minute ventilation approximately 30% higher than the normal levels and this is more than what is needed to compensate for the increased CO2 production

🔸It is mainly the reduction in FRC (a reduction by 10-25% ; appears by 12th week ; is due to the reduced chest wall compliance ; lung compliance is normal ) which makes the patient more vulnerable to hypoxia.

🔸The alveolar diffusing capacity is reported to be normal during pregnancy

#SCAVENGING IN #ANESTHESIA

Scavenging refers to the method of extracting waste gases from the breathing system and venting them to an area where they will not be directly inhaled by staff or other patients.

Scavenging systems can be classified as open or closed.

Open refers to the basic system of extracting the gas from its point of entry into the theatre

Closed systems are more common and can be further subdivided into active and passive

No conservation of volatile agent is possible with either the active or the passive systems; conservation must occur within the anaesthetic breathing system itself, by the use of a circle system and low-flow anaesthesia.

The active and the passive both pass any waste gas to the atmosphere, polluting it to the same extent.

In the passive scavenging system an exhaust port collects the waste gases from the expiratory valve of the breathing system or from the ventilator and the gases pass through the transfer system (which consists of 30 mm low-resistance tubing) to the outside of the building, preferably above roof level.

If the theatre air is not recirculated, the waste gases can be piped to the exit port of the theatre ventilation system.

In the passive system, the gases are pushed to the atmosphere solely by the expiratory power of the patient

If the pathway to the atmosphere involves a vertical passage of gas, then the patient must overcome the atmospheric pressure required to push the gas over this distance; may be several floors of hospital! Means significant forces has to be overcome.

The use of gases with higher density, like nitrous oxide, adverse atmospheric conditions like high winds etc, will further increase the forces required to expel waste gases; this can even affect the cardiopulmonary status of the patient.

#anaesthesia , #TheLayMedicalMan , #EnviornmentalPollution , #MedicalProfessionalHealthHazard

Facebook page : Anesthesia Info from The Lay Medical Man

OSTEOGENESIS IMPERFECTA (OI) : POINTS OF ANESTHETIC RELEVANCE

🎲Bones and teeth are easy to break.The mandible is prone to fracture,but the facial bones are less so. Rib fractures have been reported. In the severest form, forced extension of the head during intubation carries a risk of vertebral fracture. Violent suxamethonium fasciculations can cause fractures.

🎲n the severe types of the disease,concern has been expressed that a blood pressure cuff may damage the humerus. Direct arterial monitoring has been suggested as an alternative

🎲Macrocephaly can be there. Airway problems may occur if the head is large, if there is macroglossia, or if the skeletal deformities are severe. If the head is large,a pillow placed under the chest may assist tracheal intubation.

🎲There is some evidence of hypermetabolism in this disease. Half of the patients have increased serum thyroxine levels. Hypermetabolic states, with hyperthermia, acidosis, sweating and cardiovascular instability, have been reported, but these are unrelated to Malignant Hyperthermia (MH).

🎲Surgery should be avoided in the pyrexial patient. Core temperature, oxygen saturation and ETCO2 should be monitored throughout surgery. Hyperthermia is reported to have responded to cooling alone.

🎲Platelet dysfunction may occur and produce a mild bleeding tendency, although the platelet count may be normal. But coagulopathies have been reported.

🎲Aortic and mitral valve insufficiency results from the defective connective tissue formation, but may be clinically inapparent. Sometimes cardiac surgery may be required

🎲Cranial developmental defects may cause brainstem compression, hydrocephalus, or vascular disruption. Softening of the basal portion of the occipital bone and upward movement of the cervical spine can combine to cause secondary basilar impression. Warning signs include cough, headache,vertigo, and trigeminal neuralgia.

🎲Those patients with kyphoscoliosis may have restrictive pulmonary defects. Sixty per cent have significant chest wall deformities. A thoracic scoliosis of more than 60 degrees will have severe effects on lung function, with a reduction in vital capacity to below 50%

🎲Although skeletal deformities and deranged coagulation may make regional anaesthesia technically difficult, successful and safe epidural anaesthesia has been reported in patients with OI.

Facebook page : Anesthesia Info from The Lay Medical Man

#anaesthesia , #TheLayMedicalMan , #Orthopedics , #OsteogenesisImperfecta , #fracture

INTRACRANIAL PRESSURE ( #ICP ) MEASUREMENT & HOW IT CAN GUIDE THERAPY❓

🔸ICP data can be used to

✔️predict outcome and evolution of intracranial pathology

✔️calculate and manage cerebral perfusion pressure (CPP) [without an ICP monitor, CPP is not known].

✔️direct management strategies, and

✔️limit the use of potentially deleterious therapies.

🔸Cerebral herniation is a pressure issue and an ICP monitor may allow early detection; it is preferable to avoid herniation than to treat it

🔸Information from an ICP monitor may provide useful information to guide patient care. For example, a patient with a worrisome-appearing CT scan who does not have intracranial hypertension may not require the same degree of treatment as a patient with a similar scan but elevated ICP.  Similarly, a patient with elevated ICP that is refractory to escalating management becomes an early candidate for “second tier” treatments or if very high, even withdrawal of care.

🔸ICP values have prognostic value and so it can guide management and discussions with the family about outcomes

🔸Even transient episodes of severely raised ICP and ischemia can be devastating to the traumatized brain, making it critical to accurately and continuously monitor ICP & CPP. Because insertion of intraparenchymal ICP monitors is safe, the ability to monitor CPP per se is a supportable argument for widespread ICP monitoring.

🔸Perhaps more important than a single ICP threshold may be a trend over time, ICP waveform analysis, or whether the ICP value is associated with other detrimental effects.

🔸When both ICP and brain oxygen are treated, the outcome may be better than if just ICP is treated after TBI

🔸The ICP waveform is a modified arterial pressure tracing

🔸 It has 3 peaks: P1, P2 & P3

🔸 P1 is a result of transmitted pressure from choroid plexus

🔸 The amplitude of P2 changes with brain compliance. If compliance is poor, amplitude will be high ( can even exceed that of P1) and vice versa

🔸P3 represents the dicrotic notch

🔸 Lundberg (A) or Plateau waves are steep rise of ICP to over 50 mm of Hg and lasting for 5-20 minutes; then it falls abruptly. Are always pathological and indicates significantly reduced compliance

🔸 Lundberg (B) waves are oscillations occurring every 1-2 minutes where ICP rises to over 20-30 mm of Hg from baseline in a crescendo manner. They are supposed to be result of altered cerebral (B)lood volume and altered tone of cerebral (B)lood vessels

🔸 Lundberg (C) waves are oscillations whose amplitude is less than that of B waves and are supposed to result because of interactions between cardiac and respiratory (C)ycles. They occur also in healthy individuals

METHODS OF MEASUREMENT OF ICP

➿ Intraventricular catheter - ventriculostomy represents the "gold standard" for pressure measurement

✔️Normally placed in the frontal horn of lateral ventricle

✔️Allows therapeutic CSF drainage

✔️Creates a pathway for infection

✔️In case of the Integra Neuroscience external drainage catheter, ICP readings are based on a fluid-filled transduction system that transmits changes in ICP through a saline-filled tube to a diaphragm on a strain gauge transducer. This monitor must be leveled with the foramen of Monro (approximately the level of the external auditory canal) after insertion and should be zero-balanced daily. The level of the drain can be adjusted to allow more or less CSF drainage.

 ➿Subdural bolt / Catheters

✔️ less invasive

✔️ Bolts commonly use fiberoptic technology that allows continuous ICP monitoring without CSF drainage. The fiberoptic type of catheter can be placed in the subdural space or in the brain parenchyma

✔️ Usually subdural space over frontal lobe of non-dominant hemisphere is selected

✔️ Prone to signal damping and calibration drift

✔️ Potential risk of infection

✔️ Doesn't require penetration of brain tissue

✔️Camino Post Craniotomy Subdural Pressure Monitor utilizes the craniotomy bur holes and flap as a point of entry. The monitor is zero-balanced and then tunneled under the scalp toward the craniotomy bur hole of choice and positioned in the subdural space. This monitor contains a microtransducer at the tip, which is similar to the OLM ICP monitor ( see below)

✔️Gaeltec ICT/B pressure sensor is intended to monitor ICP subdurally. It contains a balloon-covered pressure sensor that is activated when filled with air. This monitor is self–zero-balanced in vivo and is reusable.

➿Intracerebral transducer

✔️Parenchymal devices are easier to place, particularly when altered ventricular anatomy may limit ventricular catheter placement.

✔️However, intraparenchymal fiber-optic and electronic strain gauge systems are more expensive and cannot be recalibrated once in situ

✔️Inability to check zero calibration & drain CSF

✔️ Risk of infection

✔️Less reliable

✔️The Camino OLM ICP monitor measures ICP in the intraparenchymal tissue or subarachnoid space. It contains a transducer at the distal tip, thus measuring pressure without a fluid-filled system. The catheter is secured to the skull through an adjustable bolt, allowing placement at variable depths (up to 5 cm).

✔️The Codman Microsensor catheter can be used as an intraparenchymal or intraventricular monitor, depending on the depth of the catheter

✔️ Spiegelberg ICP monitors measure ICP through an air-pouch system attached to a pressure transducer connected to an electronic device. The probes differ, depending on where they rest (Epidural or Intraparenchymal)

🔸The incidence of infection ~ 2-7% with monitoring ≥ 5 days

🔸The risks are slightly greater with dural penetration

🔸The zero reference point of the transducer is usually taken as the external auditory meatus

🔸 Rather than the waveform type, the important factors appear to be the degree and duration of ICP elevation

🔸Two emerging non-invasive ICP monitoring methods include measuring the optic nerve sheath diameter  (ONSD) as seen on an ultrasound probe placed on the superolateral aspect of the orbit and the pulsatility index (PI) which is cal- culated from transcranial Doppler studies (TCD).

#NeuroAnesthesia , #anaesthesia , #TheLayMedicalMan , #NeuroCriticalCare , #CriticalCare , #NeuroICU

NORMAL SWALLOWING & DISORDERS OF SWALLOWING: For the #NeuroCriticalCare #Physician & #Anesthesiologist

👅Cranial nerves V,VII,IX,X,XI,XII contributes to swallowing

👅2 brain stem nuclei control swallowing: (1) Nucleus Tractus Solitarius(NTS) which is a pure sensory nucleus in the medulla (2) Nucleus Ambiguous (NA) which is a motor nucleus situated deep in the reticular formation in medulla
 
👅Sensory info sent via cranial nerves to NTS. Interneurons relay info to NA & surrounding reticular formation which sends efferent messages to cranial nerve pathways.

👅Muscles innervated by Trigeminal nerve helps in Mastication, jaw closure, upward movement of larynx, backward movement of tongue to soft palate, tensing and elevation of soft palate and posterior pharyngeal wall constriction

👅Muscles innervated by Facial nerve helps in mandibular depression and contributes to hyoid elevation

👅Glossopharyngeal nerve supplies Stylopharyngeus , contributes to palatoglossus - portion of middle pharyngeal constrictor Ⓜ️NEMO> “Glossy nerve helps Stylish Middle Class”

👅Vagus supplies muscles of soft palate (except Tensor Veli Palatini) - Superior, middle and inferior pharyngeal constrictors - Intrinsic muscles of larynx and muscles of esophagus Ⓜ️NEMO> “Vague nerve helps all classes”
 
👅Recurrent Laryngeal Nerve innervates Cricopharyngeus muscle.
 
👅Hypoglossal nerve innervates all intrinsic and some extrinsic muscles of tongue and geniohyoid ; hence responsible for all movements of the tongue
 
👅Aetiology of swallowing disorders: Stroke, Traumatic Brain Injury, Brain Tumor , Cerebral Palsy, Neuroleptic drug- induced Tardive dyskinesia , Surgery ( Generally damage to the pharyngeal plexus may occur with anterior cervical fusion. Injury of the seventh, tenth, and twelfth cranial nerves may occur with carotid endarterectomy, as these nerves are close to the carotid bifurcation), various forms of dementia, Movement disorders including Parkinsons disease, Multiple Sclerosis , Amyotrophic Lateral Sclerosis (ALS)
 
👅It has been suggested that recovery of swallowing in acute stroke patients may be rapid, warranting reassessment within 3 weeks of the initial swallowing evaluation
 
👅Abnormal volitional cough, abnormal gag,dysarthria,dysphonia, cough after swallow, voice change after swallow are indicators of risk of aspiration after acute stroke
 
👅But many of the neurologic disorders that affect swallowing are progressive; thus swallowing can be expected to decline as the disease worsens.
 
👅Dysarthria may correlate with dysphagia with bulbar Amyotrophic Lateral Sclerosis (ALS). Dysphagia increases as respiratory capacity decreases regardless of the form of ALS. Vital capacity should be consistently measured, as accurate and timely assessment of a clinically relevant decline in respiratory status is crucial for determining the timing of feeding tube placement
 
👅Pneumonia can be a frequent complication in patients with dysphagia owing to CNS disease
 
👅Although an abnormal gag reflex may be apparent in patients with dysphagia resulting from various neurologic disorders, it may be absent in healthy control subjects or it may be normal in patients with neurogenic dysphagia
 
👅The two imaging tools used to evaluate oropharyngeal dysphagia are Video Fluoroscopic Swallow Study (VSS- Gold Standard) and videoendoscopy. The Penetration-Aspiration Scale (PAS) provides an objective way during the VSS to measure the depth, response, and clearance of material entering the larynx and trachea.
 
👅They are also valuable in identifying and teaching maneuvers that may facilitate swallowing and prevent aspiration in a patient.
 
👅When significant aspiration cannot be prevented, alternatives to oral feeding such as percutaneous endoscopic gastrostomy (PEG) tube placement should be considered.
 
👅Patients with oropharyngeal dysphagia owing to CNS lesions are best managed by a team approach including a speech pathologist, neurologist, and gastroenterologist.
 
👅Swallowing therapy may include compensatory or rehabilitative strategies. Compensatory therapy does not change the physiology of the swallow; rather, bolus flow is redirected
 
👅Compensatory strategies consist of manipulation of posture, consistency of the liquid, and sensory input. Facilitatory postures that have been studied in the neurogenic population include chin tuck and head rotation to the weak side
 
👅Rehabilitative therapy includes muscular strengthening and range of motion exercises, thermal-tactile application, and swallowing maneuvers
 
👅Vocal fold medialization is the procedure generally performed to treat aspiration owing to an incompetent larynx
 
👅A tracheotomy may be performed for neurologic patients with chronic aspiration. Although it does not improve swallowing, it facilitates pulmonary toileting
 
👅Laryngotracheal separation is a more radical attempt to prevent chronic aspiration while allowing for oral intake. Although patients may return to oral diets, the ability to phonate is eliminated. If physiologic aspects of swallowing improve sufficiently, this procedure can be reversed, as the glottis is not affected.

#Swallowing , #Anesthesia , #TheLayMedicalMan , #CriticalCare , #Anatomy , #Physiology , #GastroEnterology

ICTAL BRADYCARDIA &ASYSTOLE: AN ENTITY ALL ANESTHESIOLOGISTS SHOULD KEEP IN MIND WHEN SEEING BRADYCARDIA IN A PATIENT WITH EPILEPSY

📌Ictal bradycardia/asystole is a poorly recognised cause of collapse late in the course of a typical complex partial seizure

📌It is important to identify ictal bradycardia as a potential harbinger of lethal rhythms, such as asystole, as this may be one important mechanism leading to sudden unexpected death in epilepsy (SUDEP)

📌Tachycardia is the most common rhythm abnormality occurring in 64–100% of temporal lobe seizures. Ictal bradycardia has been reported in less than 6% of patients with complex partial seizures

📌The ictal bradycardia syndrome occurs in mostly in patients with temporal lobe seizures.

📌It is believed that abnormal neuronal activity during a seizure can affect central autonomic regulatory centres in the brain leading to cardiac rhythm changes.

📌Ictal bradycardia/asystole may be unrecognised until documented during video-electroencephalograph (video EEG)–electrocardiogram (ECG) monitoring in those with refractory epilepsy, often in the context of pre-surgical evaluation

📌Other rhythm abnormalities which can occur are change in heart rate variability, ictal tachycardias and atrioventricular (AV) block

📌If sufficiently severe, the ictal-induced bradyarrhythmia temporarily impairs both cerebral perfusion and cortical function; the result has the dual effect of terminating the seizure, while at the same time triggering syncope with consequent loss of consciousness and postural tone. In essence, a complex partial seizure patient may manifest both seizure and syncope features during the same episode.

📌There are currently no guidelines on who should undergo further cardiovascular investigations ; dual chamber pacemaker implantation has been suggested as a treatment in the long term, for epilepsy patients who manifest this syndrome and suffer repeated falls; but there is not much mention in literature  both about diagnosis and about pharmacological and non pharmacological interventions to counter such episodes when presenting as an emergency situation in the perioperative scenario , especially when the patient is under anesthesia.

#Neurology , #NeuroCriticalCare , #Anesthesia , #LayMedicalMan , #CriticalCare , #Epilepsy , #Cardiology , #CardiacAnesthesia

Reference: Ictal bradycardia and atrioventricular block: a cardiac manifestation of epilepsy; Salman S. Allana  Hanna N. Ahmed  Keval Shah  Annie F. Kelly, Oxford Medical Case Reports, British Journal of Cardiology : Ictal Bradycardia and Asystole Associated with Intractable Epilepsy: A Case Series Elijah Chaila, Jaspreet Bhangu, Sandya Tirupathi, Norman Delanty; Ictal Asystole-Life-Threatening Vagal Storm or a Benign Seizure Self-Termination Mechanism? David G. Benditt, Gert van Dijk, Roland D. Thijs (Editorial:Circulation )

JNC 8 GUIDELINES FOR TREATMENT OF SYSTEMIC HYPERTENSION: A SUMMARY

(1)📌In the general population aged 60 years or more , initiate pharmacologic treatment to lower blood pressure (BP) at systolic blood pressure (SBP) ≥150 mm Hg or diastolic blood pressure (DBP) ≥ 90 mm Hg and treat to a goal SBP <150 mm Hg and goal DBP <90 mm Hg

(2)📌In the general population aged ≥60 years, if pharmacologic treatment for high BP results in lower achieved SBP (eg, <140 mm Hg) and treatment is well tolerated and without adverse effects on health or quality of life, treatment does not need to be adjusted.

(3)📌In the general population <60 years, initiate pharmacologic treatment

(a) to lower BP at DBP ≥90mmHg and treat to a goal DBP <90mmHg.

(b) to lower BP at SBP ≥140 mm Hg and treat to a goal SBP <140 mm Hg.

(4)📌In the population aged ≥18 years with (i) diabetes & (ii) chronic kidney disease (CKD), initiate pharmacologic treatment to lower BP at SBP ≥140 mmHg or DBP ≥90 mmHg and treat to goal SBP <140mmHg and goal DBP <90mmHg.

(5)📌In the general nonblack population, including those with diabetes, initial antihypertensive treatment should include a thiazide-type diuretic, calcium channel blocker (CCB), angiotensin-converting enzyme inhibitor
(ACEI), or angiotensin receptor blocker (ARB).

(6)📌In the general black population, including those with diabetes, initial antihypertensive treatment should include a thiazide-type diuretic or CCB.

(7)📌In the population aged 18 years with CKD, initial (or add-on) antihypertensive treatment should include an ACEI or ARB to improve kidney outcomes. This applies to all CKD patients with hypertension regardless of race
or diabetes status.

(8)📌If goal BP is not reached within a month of treatment, increase the dose of the initial drug or add a second drug from one of the classes : thiazide-type diuretic, CCB,ACEI, or ARB. The clinician should continue to assess BP and adjust the treatment regimen until goal BP is reached.

(9)📌If goal BP cannot be reached with 2 drugs, add and titrate a third drug from the list mentioned above (). Do not use an ACEI and an ARB together in the same patient.

(10)📌If goal BP cannot be reached using only the drugs mentioned above, because of a contraindication or the need to use more than 3 drugs to reach goal BP, antihypertensive drugs from other classes can be used.

#hypertension , #medicine , #TheLayMedicalMan , #jnc8 , #HTN , #anesthesia , #pharmacology , #BloodPressure ,#BP