What is oxygen flux? b) Draw oxygen haemoglobin dissociation curve ,enumerate the factors producing leftward and rightward shift

Oxygen Flux: The amount of oxygen leaving the left ventricle per minute in the arterial blood has been termed as the "Oxygen Flux"
 O2 Flux = Q  ([Hb] * SatHb * 1.34 ml/g) + (Pa O2 * 0.03ml/L)
Q = cardiac output
                               
                                                                                                                             
At pH 7.4 the Po2 which is then oxygen tension at which the haemoglobin is 50% saturated is  26.6mm of Hg , which is reduced when the curve shifts to left and Po2 is increased when the curve  shifts to right

1) pH(Bohr Effect)-A fall in pH which may either be respiratory or metabolic causes the curve to shift to the right and lowers the O2 affinity which displaces O2 from haemoglobin and makes more O2 available to tissues.
A rise in pH causes a leftward shift in the oxygen-haemoglobin dissociation curve which increases the haemoglobin  affinity for oxygen while reducing its availability to tissues.
2) 2,3 Diphosphoglycerate(2,3 DPG) is a by -product of glycolysis (the Rapoport-luerbering shunt) and accumulates during anaerobic metabolism.
A rise in 2,3 DPG is associated with a rightward shift in the oxyhaemoglobin dissociation curve and a reduction in haemoglobin affinity of oxygen which delivers more oxygen to tissues
A low concentration of 2,3 DPG is associated with a leftward shift of the curve.
3) Temperature-A fall in temperature shifts the curve to the left while a rise in temperature shifts the curve to right and reduced affinity of haemoglobin to oxygen thus facilitates more oxygen delivery to tissues.

Enumerate various methods for pain relief in labour and elaborate Technique, advantages and disadvantages of any one of them

                          Various methods of pain relief during labour are
                              |                                                                  |
Nonpharmacological                                                       Pharmacological

1. Childbirth Education                                               Systemic medication
2. Hydrotherapy                                                           Opiods like meperidine,fentanyl
3. Aromatherapy                                                         Sedative-Tranquiliser like barbiturate
4. Audiotherapy and massage                                     Phenothiazines and benzodiazepine
5. Psychoprophylasix                                                  Inhalational Analgesia like
6. Trancutaneous electrical nerve stimulation             Entonox 50 : 50 N₂O/O₂ mixture
7.                                                                                  Desflurane (0.2%), enflurane, and                                                                                                      isoflurane (0.2% to 0.25%)

In addition to the above pharmacological and nonpharmacogical methods there are certain regional techniques like

1. Epidural Analgesia
2. Spinal Analgesia
3. Combined Spinal-Epidural Analgesia
4. Continuous Epidural Infusion
5. Patient-Controlled Epidural Analgesia
6. Paracervical and Pudendal Blocks
7. Lumbar Sympathetic Blocks

EPIDURAL ANALGESIA

Advantages: 

• Effective pain relief and attenuation of adverse physiological response to pain 
• Reduction in maternal catecholamine levels
• Increased maternal intervillous blood flow
• Improved uteroplacental blood flow
• Can be converted into continuous epidural and patient controlled epidural analgesia
• The epidural catheter can be used to provide anesthesia in inadvertent ceaserian section and post operative analgesia of the same

DISADVANTAGES

• Hypotension
• Unintentional intravascular injection
• Unintentional intrathecal injection
• Post puncture dural headache
• Maternal fever

TECHNIQUE

Assess all patients before placement of a regional block with history, clinical examination, and evaluating the airway.Informed consent is obtained, and the patient explained the procedure and the potential complications of the technique. 

A full check of emergency equipment ,immediate availability of resuscitative drugs and an intravenous infusion  started, and appropriate maternal and fetal monitoring should be in place before starting the procedure.
Epidural technique requires placement of the needle tip into the ligamentum flavum for the loss-of-resistance and hanging-drop methods.

With a lumbar approach  Touhy 18G needle is used and  the depth from skin to the ligamentum flavum commonly approaches 4 cm, the midline, which requires needle control if unintentional dural puncture is to be prevented.The loss-of-resistance technique involves inserting the needle to the ligamentum flavum and then attaching a 3- to 5-mL glass syringe filled with 2 mL of saline and a small (0.25-mL) air bubble.  When the epidural space is entered, the pressure applied to the syringe plunger allows the solution to flow without resistance into the epidural space.
epidural catheters should be inserted only 2 to 3 cm into the epidural space for surgical or obstetric patients needing rapid onset of analgesia. Threading more catheter may increase the likelihood of catheter malposition but in obstetric patients the catheter can be inserted between 4 and 6 cm to optimize efficacy and prevent unintentional movement of the catheter during prolonged labor analgesia. Multiport (three lateral ports) or single–end-hole (uniport or distal port) catheters are available.  Despite an adequately positioned catheter during first use of a local anesthetic, each subsequent injection should be preceded by aspiration and an epidural test dose because catheter migration into vessels and the subarachnoid or subdural space does occur.

Long-acting amides such as bupivacaine or ropivacaine are most frequently used because they produce excellent sensory analgesia while sparing motor function, particularly at low concentrations (<0.1%). Analgesia for the first stage of labor may be achieved with 5 to 10 mL of bupivacaine or ropivacaine (0.125%) combined with fentanyl (50 to 100 µg) or sufentanil (5 to 10 µg).    

                                                                                         

Criteria for Discharge after day care surgery

All patients must be evaluated prior to discharge from PACU and discharge criteria are established depending whether the patient is going to ICU, regular ward, outpatient department or directly to home
Mandatory stay in PACU for specified time is not required,patient are observed for their ability to protect airways with no respiratory depression and mental function is clear.

Evaluation of the patient in PACU for discharge is under the following guidelines

 Patients should be alert and oriented or mental status returned to baseline.
   2.     A minimum mandatory stay is not required.
   3.     Vital signs should be stable and within acceptable limits.
   4.     Discharge should occur after patients have met specified criteria.
   5.     Use of scoring systems may assist in documentation of fitness for discharge.
   6.     The requirement to urinate before discharge and drink and retain clear liquids should not be part of a routine discharge protocol although they may be appropriate for selected patients.
   7.     Outpatients should be discharged to a responsible adult who will accompany them home.
   8.     Outpatients should be provided with written instructions regarding postprocedure diet, medications, activities, and a phone number to call in case of emergency.

Two Most Commonly Used Postanesthesia Care Unit Discharge Criteria Systems

MODIFIED  ALDRETE SCORING SYSTEM POSTANESTHETIC DISCHARGE SCORING SYSTEM Respiration Vital signs 2 = Able to take deep breath and cough 2 = BP + pulse within 20% preop baseline 1 = Dyspnea/shallow breathing 1 = BP + pulse within 20–40% preop baseline 0 = Apnea 0 = BP + pulse >40% preop baseline O2 saturation Activity 2 = Maintains Spo2 >92% on room air 2 = Steady gait, no dizziness or meets preop level 1 = Needs O2 inhalation to maintain O2 saturation >90% 1 = Requires assistance 0 = O2 saturation <90% even with supplemental oxygen 0 = Unable to ambulate Consciousness Nausea and vomiting 2 = Fully awake 2 = Minimal/treated with PO medication 1 = Arousable on calling 1 = Moderate/treated with parenteral medication 0 = Not responding 0 = Severe/continues despite treatment Circulation Pain 2 = BP ± 20 mm Hg preop Controlled with oral analgesics and acceptable to patient: 1 = BP ± 20–50 mm Hg preop 2 = Yes 0 = BP ± 50 mm Hg preop 1 = No Activity Surgical bleeding 2 = Able to move four extremities voluntary or on command 2 = Minimal/no dressing changes 1 = Able to move two extremities 1 = Moderate/up to two dressing changes required 0 = Unable to move extremities 0 = Severe/more than three dressing changes required Score ≥9 for discharge Score ≥9 for discharge BP, blood pressure; PO, oral. Controlling post operative pain,controlling nausea and vomiting and re-establishing normothermia. Patients in majority meet the above criteria within 60 minutes and in addition to the above pateint receiving regional anesthesia should show signs of proprioception,sympathetic,bladder resolution and motor blockade Day care cases should be further evaluated for home readiness and complete psychomotor recovery. All out patients shouls be discharged home in the company of a responsible adult and with written post operative notes and emergency help details and perform routine follow up.

Preoperative assessment and risk stratification in a patient of cirrhosis of liver

Preoperative assessment
Clinical History

1. History of weight loss,malaise,dyspepsia,jaundice,heavy alcohol intake,hematemesis,easy bruising,pedal edema,dyspnoea,easy fatigue,
2. Previous surgeries and its association with jaundice,drug intake(acetaminophen,rifampicin,phenytoin,),blood transfusion,
3. Physical examination: Palmar erythema, Dupytrens contracture,spider naevi,peripheral edema, bruising,gynaecomastia muscle wasting,glossitis,hepatomegaly,parotid swelling,encephalopathy,features of portal hypertension like ascitis,spenomegaly and caput medusae.
4. Investigations: A full blood count to detect anemia,thrombocytopenia,Prothrombin time is a indicator of hepatocellular function,Base line renal function,Liver function test,Electrocardiography and echocardiography if risk factors of left ventricular dysfunction,cardiomyopathy,Chest radiography and lung fuction test to deliniate any restrictive or obstructive pulmonary disease

Risk Stratification

Preoperative evaluation of patients with liver disease should focus on extent of liver dysfunction and effect on other organ 

Viral hepatitis is a risk to theatre personnel and patients should be screened for Hepatitis B and C

Modified Child-Turcotte-Pugh Scoring System

Parameters	Modified Child-Turcotte-Pugh Score *
	1	2	3
Albumin (g/dL)	>3.5	1.8-3.5	<2.8
Prothrombin time
Seconds prolonged	<4	4-6	>6
International normalized ratio	<1.7	1.7-2.3	>2.3
Bilirubin (mg/dL) †	<2	2-3	>3
Ascites	Absent	Slight-moderate	Tense
Encephalopathy	None	Grade I-II	Grade III-IV

Points are added to make a total scoring -score of 5-6 is considerd Child's class A and is associated with low operative mortality risk(>5%) , a Score of 7-9 is Child's class B and is associated with moderate risk(25%) and a total score of 10-15 is Child's class C and carries high risk (>50%)

Other indicators of poor prognosis include malnutrition,emergency surgery,sepsis and blood loss.

Predicting perioperative risk of cirrhosis and other forms of acute and chronic liver disease is enhanced by the incorporation of the Model for End-stage Liver Disease (MELD) score Although the MELD score was introduced as a tool to better prioritize organ allocation for orthotopic liver transplantation, studies suggest the superiority of MELD to CPT in predicting both intermediate and long-term survival for patients with cirrhosis, acute alcoholic hepatitis, and other forms of chronic liver disease.MELD score is based on patients serum bilirubin,creatinine and international normalised ratio(INR) for prothrombin time and is calculated with a validated predictive equation (3.8x ln bilirubin value)+(11.2x ln INR) +(9.6xln creatinine value,where ln is the natutal logarithm. The maximum MELD score is 40 ,a MELD score of at least 8 predicts good outcome after TIPS and > 18 predicts poor outcome but since its implementation  MELD is expanded to predict mortality and morbidity in other procedures

other scoring systems to evaluate are Glasgow coma score if patient has hepatic encephalopathy

Anaesthetic management of Tonsillectomy in pediatric patients

Indication for tonsillectomy
* chronic or acute recurrent tonsillitis
* peritonsillar abscess formation
* obstructive tonsillar hyperplasia
Pathophysiology of recurrent acute tonsillitis
Tonsillar hyperplasia ~> chronic airway obstruction ~>sleep apnoea~> hypoxia and CO2 retention
                                                                                                         |                              
                                                Increased airway pressure and pulmonary vasoconstriction
                                                                                                        |
                  Pulmonary artery hypertension and right heart failure~> cor pulmonale
Preoperative Evaluation

1. H/o frequent infections
2. Current use of antibiotics and antihistamines 
3. H/o sleep apnoe

Physical examination

• Presence of audible respirations / mouth breathing/ nasal quality of speech
• Facies - elongated face, retrognathic mandible and high arched palate
• Chest retractions
• Airway- evaluation of tonsillar size,presence of wheeze or rales,inspiratory stridor
• Investigations- haematocrit, coagulation parameters,chest radiograph,electrocardiograph last 2 required if recent pneumonia and bronchitis 

Anaesthetic management

Premedication

* Sedative premedication is avoided in view of maintaining airway latency

* antisialogogue is used to minimise secretions

Induction

 1)  Volatile anaesthetic induction with mask ( parental presence in anxious unpremeditated child)

 2).  Tracheal induction with deep inhalation / aided with short acting muscle relaxants( supraglottic region is packed with gauze and cuffed endotracheal tube to prevent pharyngeal blood to seep into trachea

Monitors 

1) Precordial stethoscope

2) Electrocardiograph 

2) Automated blood pressure

3) Pulse oximetry

4) end tidal CO2

Emergence

Should be rapid and child should be alert to maintain airway prior to shifting to recovery

Complications 

1) Emesis. Maybe due to irritant blood in the stomach or due to airway stimulation caused by inflammation and edge a of surgery,treated with ondansetron 0.1 mg to 0.15mg with or without dexamethasone

2) Post operative haemorrhage. 75% of post operative haemorrhage is in the first 6 hours of surgery and the next 25% is the next 24 hours

Treatment is by pharyngeal packing and electro cautery,sometimes patients are returned to OR for reexploration

In the above scenario patient is considered full stomach, intubated with rapid sequence 

Meticulous fluid management with strict blood pressure monitoring

Post operative pain is managed with acetaminophen and corticosteroids to reduce inflammation and edema

   

Describe the mechanism by which IABP augments coronary perfusion. What are the indications and contra indications for the use of IABP?

Intra-aortic balloon pumps are an important adjunct to temporary support of the failing myocardium,it's counter pulsation mechanism of action augments the cardiac output by reducing the after load stress of the left ventricle and increasing the coronary artery perfusion during diastole.

Mechanism of action

IABP are placed per cutaneous into the descending aorta and has a balloon tip which is placed 3-5 cm distal to the left subclavian artery and is inflated with 30-50ml of helium.

The device is triggered to inflate shortly after the aortic valve closure and deflate just prior to ventricular contraction,the timing of the inflation and deflation are so adjusted to allow maximal diastolic coronary perfusion and maximal ventricular systolic unloading.As the IABP is timed with the cardiac cycle hence a regular rhythm is desirable for its proper functioning and any tachyarrhythmias should be controlled.

The timing is best monitored with the arterial pressure trace and daily chest radiograph are taken to see the position of the balloon tip as proximal migration of the tip into the left common carotid or the subclavian artery can cause damage or dissection while distal migration can lead to obstruction and possible embolisation  of the mesenteric or the  renal arteries.

Indications of IABP 

1) Severe cardiac pump failure following cardiopulmonary bypass and inability to wean.

2)Refractory angina after maximal medical treatment

3)Treatment of complications of myocardial infarction in patients being prepared for revascularization either with surgery or angioplasty

4)To support patients after cardiac transplantation

Contraindications of IABP

1) Severe aortic regurgitation

2)Mobile atheroma of the descending aorta

3)Aortic dissection

4)Dynamic left ventricle outflow tract obstruction

assessment of autonomic neuropathy in diabetic mellitus

What is the significance of autonomic neuropathy in diabetes mellitus ?how can it be assessed?

Autonomic neuropathy is associated with hemodynamic lability  particularly in change in position and initiation of mechanical ventilation. Diabetic patients with autonomic neuropathy are at increased risk for intraoperative hypotension and perioperative cardiorespiratory arrest. There may be an exaggerated pressor response to tracheal intubation. Autonomic neuropathy predisposes to intraoperative hypothermia.

Diabetic patients may have delayed gastric emptying as a result of diabetic autonomic neuropathy, and therefore an increased risk of pulmonary aspiration of gastric contents.

Assessment of autonomic neuropathy :

Cardiovascular

·        Resting tachycardia

·        Exercise intolerance

·        Orthostatic hypotension

·        Silent myocardial ischaemia

Gastrointestinal

·        Oesophageal  dysphagia

·        Gastroparesis

·        Constipation

·        Diarhoea

·        Faecal incontinence

Genitourinary

·        Neurogenic bladder

·        Erectile dysfunction

·        Retrograde ejaculation

·        Female sexual dysfunction

Metabolic

·        Hypoglycaemic unawareness

Sudomotor

·        Anhidrosis

·        Heat intolerance

·        Gustatory sweating

·        Dry skin

Pupillary

·        Pupillomotor function impairment

·        Argyll-robertson pupil

Tests for diabetic autonomic neuropathy

·        Early stage: abnormality of heart rate response during deep breathing alone

·        Intermediate: an abnormality of valsalva response

·        Late stage: the presence of postural hypotension

Prethoracotomy assessment and optimisation

How would you evaluate and prepare a patient with chronic bronchiectasis scheduled for pneumonectomy? Briefly enumerate the postoperative complications.

Prethoracotomy assessment involves all of the factors of a complete anesthetic assessment: past history, allergies, medications, upper airway.

The concurrent illness in the thoracic surgical patient is bronchi ecstasies  which causes the dominant clinical feature of impairment of expiratory airflow.Assessment of the severity of Bronchiectasis is  on the basis of the FEV1% of predicted values. The American Thoracic Society currently categorizes stage I as greater than 50% predicted ,stage II as 35% 50%, and stage III as less than 35%. Stage I patients should not have significant dyspnea, hypoxemia, or hypercarbia, and other causes should be considered if these are present.

Respiratory Drive

Many stage II or III patients have an elevated Paco2 at rest and this CO2 retention is due to to an inability to maintain the increased work of respiration (WResp) required to keep the Paco2 normal in patients with mechanically inefficient pulmonary function .

Right Ventricular Dysfunction

Right ventricular (RV) dysfunction occurs in a majority of patients,the dysfunctional right ventricle is poorly tolerant of sudden increases in afterload, such as the change from spontaneous to controlled ventilation.RV function becomes critical in maintaining cardiac output as the pulmonary artery pressure rises. The RV ejection fraction does not increase with exercise in COPD patients as it does in normal patients. Chronic recurrent hypoxemia is the cause of the RV dysfunction and the subsequent progression to cor pulmonale.

Cor pulmonale is to be ruled out in patients with an FEV1 less than 1 L more so in patients with a FEV1 less than 0.6 L. The only therapy that has been shown to improve long-term survival and decrease right-sided heart strain in is oxygen. Patient who have resting Pao2 less than 55 mm Hg should receive supplemental home oxygen; this includes those who desaturate to less than 44 mm Hg with usual exercise. The goal of supplemental oxygen is to maintain a Pao2 of 60 to 65 mm Hg.

Preoperative Therapy for Bronchiectasis

There are four treatable complications of bronciectasis  that are to be  treated prior to surgery. These are atelectasis, bronchospasm, respiratory tract infections, and pulmonary edema . 

A comprehensive program of pulmonary rehabilitation involving physiotherapy, exercise, nutrition, and education can improve functional capacity for patients with severe Bronchiectasis.

Among the different modalities available (e.g., cough and deep breathing, incentive spirometry, PEEP, continuous positive airway pressure [CPAP]), there is no clearly proven superior method.

All COPD patients should receive maximal bronchodilator therapy as guided by their symptoms. Only 20% to 25% of COPD patients will respond to corticosteroids. In a patient who is poorly controlled on sympathomimetic and anticholinergic bronchodilators, a trial of corticosteroids may be beneficial.

Smoking

Pulmonary complications are decreased in thoracic surgical patients who cease smoking for more than 4 weeks before surgery. Carboxyhemoglobin concentrations decrease if smoking is stopped more than 12 hours.It is extremely important for patients to avoid smoking postoperatively. Smoking leads to a prolonged period of tissue hypoxemia. Wound tissue oxygen tension correlates with wound healing and resistance to infection. 

Assessment of Respiratory Function

The best assessment of respiratory function comes from a detailed history of the patient's quality of life. All pulmonary resection patients should have baseline simple spirometry preoperatively.Objective measures of pulmonary function are required to guide anesthetic management .

Respiratory Mechanics

Many tests of respiratory mechanics and volumes show correlation with post-thoracotomy outcome: forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), maximal voluntary ventilation (MVV), residual volume/total lung capacity ratio (RV/TLC), and . It is useful to express these as a percent of predicted volumes corrected for age, sex, and height (e.g., FEV1%). Of these the most valid single test for post-thoracotomy respiratory complications is the predicted postoperative FEV1 (ppoFEV1%),which is calculated as follow

ppo FEV1%= preoperative FEV1%mutiplied with [1-%functional tissue removed/100]

Patients with a ppoFEV1 greater than 40% are at low risk for postresection respiratory complications. 

Lung Parenchymal Function

Lung parenchymal function indicates the ability of the lung to exchange oxygen and carbon dioxide between the pulmonary vascular bed and the alveoli. Traditionally, arterial blood gas data such as Pao2 less than 60 mm Hg or Paco2 greater than 45 mm Hg have been used as cutoff values for pulmonary resection.

The most useful test of the gas exchange capacity of the lung is the diffusing capacity for carbon monoxide (DLco). The DLco correlates with the total functioning surface area of the alveolar-capillary interface. This simple noninvasive test, which is included with spirometry and plethysmography by most pulmonary function laboratories, is a useful predictor of perioperative mortality but not long-term survival.The corrected DLco can be used to calculate a postresection (ppo) value using the same calculation as for the FEV1 . A ppoDLco less than 40% predicted correlates with both increased respiratory and cardiac complications.

Cardiopulmonary Interaction

The final and perhaps most important assessment of respiratory function is an assessment of the cardiopulmonary interaction. Formal laboratory exercise testing is currently the “gold standard” for assessment of cardiopulmonary function,and the maximal oxygen consumption (Vo2max) is the most useful predictor of post-thoracotomy outcome. The risk of morbidity and mortality is unacceptably high if the preoperative Vo2max is less than 15 mL/kg/min.Few patients with a Vo2max greater than 20 mL/kg/min have respiratory complications (for comparison, the highest Vo2max recorded is 85 mL/kg/min.

Stair climbing is done at the patient's own pace but without stopping and is usually documented as a certain number of flights. There is no exact definition for a “flight,” but 20 steps at 6 in/step is a frequent value. The ability to climb five flights correlates with a Vo2max greater than 20 mL/kg/min, and climbing two flights corresponds to a Vo2max of 12 mL/kg/min. A patient unable to climb two flights is at extremely high risk.

A 6MWT distance of less than 2000 ft (610 m) correlates to a Vo2max less than 15 mL/kg/min and also correlates with a fall in oximetry (Spo2) during exercise. Patients with a decrease of Spo2 greater than 4% during exercise predicts an increased morbidity and mortality.

Ventilation-Perfusion Scintigraphy

Prediction of postresection pulmonary function can be further refined by assessment of the preoperative contribution of the lung or lobe to be resected using ventilation-perfusion    lung scanning. If the lung region to be resected is nonfunctioning or minimally functioning, the prediction of postoperative function can be modified accordingly. This is particularly useful in pneumonectomy patients,and    scanning should be considered for any pneumonectomy patient who has a preoperative FEV1 and/or DLco less lthan 80%

lung mechanics, parenchymal function, and cardiopulmonary interaction—should be made for each patient. These three aspects of pulmonary function form the “three-legged stool” that is the foundation of prethoracotomy respiratory assessment 

Post operative complications

Cardiac complications represent the second most common cause of perioperative morbidity and mortality in the thoracic surgical population.

Arrhythmia

Dysrhythmias are a common complication of pulmonary resection surgery, and the incidence is 30% to 50% of patients in the first week postoperatively when Holter monitoring is used.  of these arrhythmias, 60% to 70% are atrial fibrillation. Several factors correlate with an increased incidence of arrhythmias: extent of lung resection (pneumonectomy, 60%, versus lobectomy, 40%, versus nonresection thoracotomy, 30%) intrapericardial dissection, intraoperative blood loss, and age of the patient

Ischemia

Because the majority of pulmonary resection patients have a smoking history, they already have one risk factor for coronary artery disease. Elective pulmonary resection surgery is regarded as an “intermediate risk” procedure in terms of perioperative cardiac ischemia.The overall documented incidence of post-thoracotomy ischemia is 5% and peaks on days 2 to 3 postoperatively. 

Renal Dysfunction

Renal dysfunction after pulmonary resection surgery is seen in patients who developed a significant elevation of serum creatinine concentration in the post-thoracotomy period, compared with 0% (0/99) in those who did not show any renal dysfunction. The factors, which were associated with an increased risk of renal impairment, were history of previous renal impairment, diuretic therapy, pneumonectomy, postoperative infection, and blood transfusion. Nonsteroidal anti-inflammatory drugs (NSAIDs) were not associated with renal impairment

Venous Air Embolism

How will you diagnose and manage a case of VAE during Spine Surgery?

Detection of Venous Air Embolism

The monitors employed for the detection of VAE  are the combination of a precordial Doppler and expired CO2 monitoring and are the current standard of care. Doppler placement in a left or right parasternal location between the second and third or third and fourth ribs has a very high detection rate for gas embolization,and when good heart tones are obtained, maneuvers to confirm adequate placement seem to be unnecessary. TEE is more sensitive than precordial Doppler to VAE  and offers the advantage of identifying right-to-left shunting of air.  Its safety during prolonged use (especially with pronounced neck flexion) is not well established, however. Expired nitrogen analysis is theoretically attractive. The expired nitrogen concentrations involved in anything less than catastrophic VAE are very small, however, and push the available instrumentation to the limits of its sensitivity

Management of an Acute Air Embolic Event

Prevent further air entry    Notify surgeon (flood or pack surgical field)    Jugular compression    Lower the head Treat intravascular Air    Aspirate right heart catheter    Discontinue N2O    Fio2: 1.0    Pressors/inotropes    Chest compression

Right Heart Catheter

All patients who undergo sitting posterior fossa procedures are given  a right heart catheter. Although catastrophic, life-threatening VAE is relatively uncommon, a catheter that permits immediate evacuation of an air-filled heart is for resuscitation.

An example of a procedure for which the right heart catheter is usually omitted is microvascular decompression of the fifth cranial nerve for tic douloureux or the seventh cranial nerve for hemifacial spasm. The essentially horizontal semilateral position and the very limited retromastoid craniectomy these procedures require have resulted in a very low incidence of Doppler-detectable VAE. .

Positioning of the heart catheter-multi-orificed catheter is located with the tip 2 cm below the superior vena caval–atrial junction, and a single-orificed catheter should be located with the tip 3 cm above the superior vena caval–atrial junction. Although these small distinctions in location may be relevant for optimal recovery of small volumes of air when cardiac output is well maintained, for the recovery of massive volumes of air in the face of cardiovascular collapse, anywhere in the right atrium should suffice. Right heart placement can be confirmed by (1) x-ray, (2) pull back from the right ventricle while monitoring intravascular pressure, or (3) intravascular electrocardiogram (ECG)

Techniques for Reducing the Incidence of Venous Air Embolism

 PEEP has been advocated in the past as a means of reducing the incidence of VAE or of responding to an acute VAE event to prevent further air entry however  even 10 cm of PEEP would be unlikely to result in positive venous pressures in cerebral venous structures, which may be 25 cm above the heart. The ineffectiveness of PEEPand the relative superiority of jugular venous compression in increasing cerebral venous pressures have been confirmed by several investigations.

The release of a Valsalva maneuver promotes paradoxical embolism. In addition, the impairment of systemic venous return caused by the sudden application of substantial PEEP may be undesirable in the face of the cardiovascular dysfunction already caused by the VAE event.

It has been associated that a patient who has sustained a hemodynamically significant VAE should be placed in a lateral position with the right side up. The rationale is that air would remain in the right atrium, where it would notcontribute to an air lock in the right ventricle, and where it would remain amenable to recovery via a right atrial catheter. The first difficulty is that this repositioning is all but impossible with a patient in a pin head holder.and also it failed to identify any hemodynamic benefit

.

Anesthetic management of Pheochromocytoma

Discuss the pre-anesthetic preparation, anaesthetic goals and intra-operative management of a 30yr old female patient with diagnosis of pheochromocytoma scheduled for excision of adrenal tumour?

Pre-anesthetic preparation

Investigations

Routine laboratory are the complete blood cell count( elevated hematocrit consistent with a reduced intravascular volume and hemoconcentration)., ECG( Left ventricular hypertrophy and nonspecific T-wave changes are two of the more common ECG findings..Chest radiography may reveal cardiomegaly,

 Standardized imaging methods such as computed tomography and magnetic resonance imaging are used in the noninvasive localization of these tumors.

Ultrasound and magnetic resonance imaging are especially useful in pregnant patients.

¹³¹I-Metaiodobenzylguanidine scintigraphy is also effective in localizing recurrent or extra-adrenal masses.

 Biochemical determination of free catecholamine concentration and catecholamine metabolites in the urine is the most common screening test used to establish the diagnosis of pheochromocytoma. Urinary vanillylmandelic acid and unconjugated norepinephrine and epinephrine levels are measured in a 24-hour urine collection and are expressed as a function of the creatinine clearance. Excess production of catecholamines is diagnostic for pheochromocytoma

To rule out familial association, as this tumour is sometimes part of the pluriglandular-neoplastic syndrome known as multiple endocrine adenoma type IIa or type IIb and is manifested as an autosomal dominant trait. Type IIa consists of medullary carcinoma of the thyroid, parathyroid adenoma or hyperplasia, and pheochromocytoma. What used to be called type IIb is now often called pheochromocytoma in association with phakomatoses such as von Recklinghausen's neurofibromatosis and von Hippel-Lindau disease with cerebellar hemangioblastoma.

A reduction in mortality associated with resection of pheochromocytoma (from 40% to 60% to the current 0% to 6%) occurred when α-adrenergic receptor blockade was introduced as preoperative and preprocedure preparatory therapy for such patients.
Adrenergic receptor blockade with prazosin or phenoxybenzamine restores plasma volume by counteracting the vasoconstrictive effects of high levels of catecholamines. This re-expansion of fluid volume is often followed by a decrease in hematocrit. Phenoxybenzamine, is initially  given in doses of 20 to 30 mg/70 kg orally because of variable sensitivity once or twice a day. And increased 60 to 250 mg/day depending on requirement. The efficacy of therapy is judged by the reduction in symptoms (especially sweating) and stabilization of BP.
 For patients who have carbohydrate intolerance because of inhibition of insulin release mediated by α-adrenergic receptor stimulation, α-adrenergic receptor blockade may reduce fasting blood sugar levels. For patients who exhibit ST-T changes on the ECG, long-term preoperative and preprocedure α-adrenergic receptor blockade (1 to 6 months) is tried,,adrenergic receptor blockade with propranololis used for patients who have persistent arrhythmias or tachycardia e. β-Adrenergic receptor blockade should not be used without concomitant α-adrenergic receptor blockade lest the vasoconstrictive effects of the latter go unopposed and thereby increase the risk for dangerous hypertension.
The optimal duration of preoperative therapy with phenoxybenzamine can vary from 10 to 14 days, as judged by the time needed to stabilize BP and ameliorate symptoms. Some recommend using the following criteria:

1.         No in hospital BP more than 160/90 mm of hg should be present 48hrs before surgery.

	2.	Orthostatic hypotension should be present, but BP on standing should not be lower than 80/45 mm Hg.
	3.	The ECG should be free of ST-T changes that are not permanent.
	4.	No more than one premature ventricular contraction (PVC) should occur every 5 minutes

Anesthetic goals

1.       Good preoperative optimization with controlled vitals.

2.      Maitaining a deep level of anesthesia intraoperatively

3.      Strict and meticulous monitoring.

4.      Managing hypertensive and hypotensive episode crisis promptly

5.      .Meticulous fluid management.

Anesthetic Management

Although there is no clear advantage to one anesthetic technique over another, drugs that are known to liberate histamine are avoided.

Because of the potential for ventricular irritability, halothane is not administered

Monitoring is done with Pulse-oximetry,ECG,non-invasive blood pressure capnography and if required invasive monitoring.

 A potent sedative-hypnotic, in combination with an opioid analgesic, is used for induction.

 It is extremely important to achieve an adequate depth of anesthesia before proceeding with laryngoscopy to minimize the sympathetic nervous system response to this maneuver.

Maintenance is provided with an opioid analgesic and a potent inhalation agent. Manipulation of the tumor may produce marked elevations in blood pressure. Acute hypertensive crises are treated with intravenous infusions of nitroprusside or phentolamine or any vasodilator. Phen-tolamine is a short-acting α-adrenergic antagonist that may be given as an intravenous bolus (2 to 5 mg) or by continuous infusion.

Tachydysrhythmia is controlled with intravenous boluses of propranolol (1-mg increments) or by a continuous infusion of the ultrashort-acting selective β₁-adrenergic antagonist esmolol. The disadvantage of long-acting beta-blockers may be persistence of bradycardia and hypotension after the tumor is removed..

 Magnesium sulfate given as an infusion with intermittent boluses has successfully controlled blood pressure Nicardipine, nitroglycerin, diltiazem, fenoldopam, and prostaglandin E₁ can all been used.

The reduction in blood pressure that may occur after ligation of the tumor's venous supply which  can be dangerously abrupt and should be anticipated through close communication with the surgical team. Restitution of any intravascular fluid deficit is the initial therapy in this situation. After replenishment of the intravascular volume, if the patient remains hypotensive, phenylephrine is administered.

After surgery, catecholamine levels return to normal over several days. Postoperatively,  meticulous monitoring for  hypertension is done  for 1 to 3 days but it may take 10 days to become normotensive.

Anaesthetic management of tracheosophageal fistula

Discuss the peri-operative problems and anaesthetic management of a two day old child scheduled to undergo TEF repair?

TEF is a fistulous communication between the trachea and esophagus, occurring due to defective embryogenesis. This communication is close to the carina and clinically presents at birth. It is usually associated with an atresia of the esophagus, which ends as a blind upper pouch in the neck or upper thorax, the distance between the upper and lower esophagus is variable.

 ANOMALIES ASSOCIATED WITH TEF    
Vertebral.                      Scoliosis and other vertebral defects
Anorectal.                       Imperforate anus,malrotation and duodenal atresia
Cardiac.                          ASD,VSD,PDA,TOF,right sided aortic arch
Renal.                             Renal agenesis ,dysplasia, polycystic kidneys,horseshoe kidney
Limb.                              Radial  anomalies ,polydactyle    

PATHOPHYSIOLOGY
The two main problems in the newborn with TEF are
1. Aspiration pneumonitis –saliva, oral secretions and oral feeds pool in the blind upper
pouch and overflow into the trachea. Gastric secretions enter the lungs through the fistula.
Bag and mask ventilation in the newborn with TEF is avoided because this causes air to enter the stomach via the fistula, causing distention of the stomach, which hinders ventilation by tenting the diaphragm. Further distension, especially in a ventilated infant, may cause rupture of stomach and Pneumoperitoneum. This situation dictates early gastrostomy to provide a vent for the gases.
2. Dehydration – In the fetus the first sign of esophageal atresia may be Polyhydramnios in the mother.Atresia of the esophagus leads to an inability to swallow amniotic fluid leading to dehydration in the fetus and Polyhydramnios in the mother
 PREOPERATIVE STABILIZATION

Keep nil oral
Head up position – to prevent regurgitation of stomach contents
suction catheter – a slow suction applied to the upper pouch.This makes sure there is no pooling of saliva overflowing into the trachea.
IV access. IV fluids to correct dehydration and avoid hypoglycemia- isotonic solution like NS may be given correct dehydration . 5% Dextrose with 1/4th Normal saline to prevent hypoglycemia.
Correction of acid base abnormalities.
Antibiotics –Inj. Ampicillin/ gentamicin
Inj. Vit.K 1mg IV/IM. (0.5mg if wt< 1500g)
ECHO – to find out associated cardiac anomaly and to look for right sided aortic arch. Evaluation of other anomalies – Chest and abdominal xray.,Renal ultrasound.
Optimisation of Respiratory status.This may range from simple oxygen supplementation to CPAP mask to more invasive methods.If pneumonia is severe infant may need intubation and ventilation in NICU in which case Endotracheal tube is positioned in such a way as to not ventilate the fistula and minimal pressure settings are used. In such babies gastric inflation must be monitored as it can impede ventilation as already explained.
a preop rigid Bronchoscopy usually just before surgery to define site of entry of distal TEF as well as to assess the degree of tracheomalacia. 
Anaesthetic Management
The major anesthetic issues include (1) evaluation for aspiration pneumonia; (2) overdistention of the stomach from entry of air directly into the stomach through the fistula; (3) inability to ventilate the child because of the large size of the fistula; (4) problems associated with other anomalies, particularly a patent ductus arteriosus (shunting) and other forms of congenital heart disease; and (5) the need for postoperative intensive care.
Generally, an “awake sedated” intubation is performed with administration of 0.5 to 1 µg/kg offentanyl and 25 to 50 µg/kg of midazolam and topicalize the tongue, larynx, and vocal cords with no more than 5 mg/kg of lidocaine (1.0%).
The endotracheal tube is intentionally passed into the right main bronchus and then slowly withdrawn until breath sounds are heard on the left. Often this technique ensures that the tip of the endotracheal tube is placed beyond the origin of the fistula, thus avoiding massive distention of the stomach.
Care must be taken to avoid rupturing the stomach, so spontaneous and gently assisted ventilation may be appropriate until the fistula is ligated or a gastrostomy is completed. A change in the distance of insertion of the endotracheal tube of as little as 1 to 2 mm may determine whether the anesthesiologist is ventilating both lungs, one lung, or the fistula. Therefore, because a change in oxygen saturation may be the first indication that all is not well, the pulse oximeter is one of the most useful monitors in managing these children. A preductal and postductal location (two pulse oximeters) will diagnose intracardiac shunting. Taping the stethoscope to the left side of the chest in the axilla also decreases the possibility of unrecognized endobronchial intubation. Some surgeons prefer that the infant remain intubated postoperatively, whereas others prefer an attempt at extubation; it should be noted that approximately 30% will require reintubation for clearing of secretions.
Intraoperative temperature maintenance
Postoperative pain may be managed with a caudal catheter threaded up to the thoracic level and either intermittent bupivacaine (1 to 2 mL of 0.125% with epinephrine 1 : 200,000) administered every 6 to 8 hours or a continuous infusion of chloroprocaine (1.5%) with fentanyl (0.4 µg/mL) infused at 0.3 to 0.8 mL/kg/hr. Note that such management may be undertaken only with the full support of a pediatric pain service.