Tidal Volume (TV)- Volume of gas inspired or expired in each breath during normal quiet respiration. It is 400-500 ml ie 10ml/kg

Inspiratory Reserve Volume ( IRV)- It is the maximum volume of gas which a person can inhale from end inspiratory position. It is 2400 to 2600 ml.

Inspiratory Capacity ( IC)- It is the maximum volume which can be inhaled from end expiratory position ie, IRV + TV. It is 2500 + 500= 3000 ml or 3 L

Expiratory Reserve Volume- Maximum volume of gas that can be expired after normal expiration. It is 1200 to 1500 ml.

Vital Capacity- Maximum volume of gas that can be exhaled after maximum inhalation ie, it is IRV+TV+ ERV. Its value is 4200 to 4500 ml ( 75-80 ml/kg).

Functional Expiratory Volume ( FEV)- It is vital capacity per time. FEV1 is VC in 1^st sec.

Residual Volume- It is the volume of gas still present in lungs after maximal expiration. It is 1200-1500 ml.

Maximum breathing capacity- Maximum volume of air that can be breathed/minute. It is 120-170 litre/min ( normally it can be measured for 15 sec and expressed as litre/min)

Minute Volume- It is tidal volume X Respiratory rate. It is 500 X 12= 6000 ml/min

Total Lung volume- IRV+TV+ERV+RV = 5500 to 6000ml

Functional Residual Capacity( FRC)- It is the volume of gas in lungs after end expiration. It is ERV + RV. It is 2400-2600 ml. During anaesthesia FRC decreases by 15-20%.

DEAD SPACE: It is the volume of the respiratory tract that does not participate in gas exchange. It is approximately 300 ml in normal lungs.

a.ANATOMIC DEAD SPACE: Volume of the conducting airways, approximately 150 ml

b.PHYSIOLOGIC DEAD SPACE: The volume of the lung that does not participate in gas exchange.In normal lungs, is equal to the anatomic dead space (150 ml). May increase in several lung diseases.

Reference- Short Text book of Anesthesia- A. Yadav, Web.

Level of Block

Spinal Anaesthesia also called Subarachnoid block or Intrathecal Block.

Operations

Indications:

1. Abdominal & vaginal hysterectomies
2. Laparoscopy Assisted Vaginal Hysterectomies (LAVH) combined with general anaesthesia
3. Caesarean sections
4. Hernia (inguinal or epigastric)
5. Piles fistulae & fissures
6. orthopaedic surgeries on the pelvis, femur, tibia and the ankle
7. nephrectomy
8. cholecystectomies
9. trauma surgery on the lower limbs, especially if the patient is full-stomach
10. Open tubectomies
11. Trans-urethral resection of prostate

Position- Lateral, Sitting or Prone.

Approach- Midline, Paramedian or Lumbosacral ( Taylor- 1 cm medial, 1 cm lateral to Posterior Superior Iliac Spine)

Space- L3-L4 or L4-l5

Site of action- Spinal Nerves and dorsal ganglia minimally on Spinal cord.

Drugs used-

Local Anaesthetics-

1. Xylocaine 5% in 7.5% Dextrose ( Hyperbaric 1.03333 spg)

2.Bupivacaine 0.5% in 8% dextrose

3. Tetracaine 1% in 5 D

4. Procaine 10% in 5D

Opioids

Ketamine

Needle Used- Duracutting- Quincke-Babcock and Greene  and Duraseparating -pencil tip point end ( Whitcre, Sporte and Pitkin)

Factors Affecting Block-

Volume, Baricity,Position of patient,Intra-abdominal pressure, Spinal curvature and factors like age,obesity and height

Complications

• * Spinal shock.
• * Cauda equina injury.
• * Cardiac arrest.
• * Hypothermia.
• * Broken needle.
• * Bleeding resulting in hematoma, with or without subsequent neurological sequelae due to compression of the spinal nerves
• * Infection: immediate within six hours of the spinl anaesthetic manifesting as meningism or meningitis or late, at the site of injection, in the form of pus discharge, due to improper sterilization of the LP set.
• * PDPH:post dural puncture head ache or post spinal head ache

Post-op: Urine Retention

Source : Youtube Video

Mechanical ventilation of lungs is carried out by intubating the patient by nasal or oral route or through tracheostomy and connecting endotracheal or tracheostomy tube to ventilator.

A boy on mechanical Ventilator

INDICATIONS:

1. On the basis of blood gas analysis
   • pO2<50mmHg in room air or pO2<60mmHg on FIO2 >.5
   • pH< 7.25(acute respiratory failure)
   • pCO2 >50mmHg
   • pO2/FIO2< 250mmHg
   • p(A-a)O2 gradient> 350mmHg on 100% oxygen
2. On the basis of pulmonary function
   • respiratory rate >35/min
   • vital capacity<15ml/kg
   • dead space volume>0.6
   • peak negative pressure -20cmH2O
   • tidal volume <5ml/kg
3. Other
   • excessive fatigue of respiratory muscles
   • loss of protective airway reflexes which makes patient vulnerable for aspiration
   • inability to cough adequately

TYPES OF VENTILATORS

• TIMED CYCLED- these cycle to expiration once a predetermined time is elapsed since inspiration. Tidal volume is determined by set inspiratory flow and inspiratory time. These are used in operation theatres and in neonates.
• PRESSURE CYCLED- these cycle to expiration once predetermined pressure is reached. So if there is leak in circuit the predetermined pressure will not be reached and patient will remain in inspiration. Conversely if airway pressure is high there will be premature end of inspiration and patient can be hypoventilated so these ventilators are no more used
• VOLUME CYCLED- inspiration is terminated when a preset tidal volume is delievered. So theoretically the patient can not be hypoventilated even if lung compliance changes but actually this is not the case, a portion of tidal volume
  (120-150ml) is lost in the ventilator breathing circuit and if patient’s pulmonary compliance is decreased the delievered tidal volume can further be decreased. So all these consideration should be kept in mind while setting the tidal volume and accurate tidal volume reaching the patient can only be calculated by putting spirometer at the endotracheal tube. These ventilators are most commonly used in ICUs.

SETTINGS OF VENTILATOR:

Typical ventilator settings are-

Tidal volume-10ml/kg

Frequency-  10-12breaths/ min

I:E- 1:2

Inspiratory flow rate-  60-80 litres/min

Positive end expiratory pressure(PEEP)- 3-5 cm of H2O

Trigger sensitivity (for assist mode)–1 to -2 cm H2O

FIO2- 0.5

Ventilator Machine

MODES OF VENTILATION:

1. Controlled mode ventilation (CMV)/ intermittent positive pressure ventilation(IPPV) : in this mode patient’s own effort is nil. Only ventilator is delievering the preset tidal volume at preset frequency.
2. Assist controlled ventilation: in assist control mode assist means the ventilator supplementation of patient initiated breath ( which itself does not have adequate tidal volume) and control means back up rate which is set up by clinician. So if patient’s spontaneous breath rate exceeds backup rate, no control breaths will be delievered and ventilator will purely behave in assist mode.
3. Synchronized intermittent mandatory ventilation (SIMV): in this mode ventilator will deliever only between patient’s efforts or to coincide with the beginning of spontaneous effort i.e. synchronizing with the patient spontaneous respiration.
4. Positive end expiratory pressure (PEEP): positive pressure is given at the end of expiration to prevent the alveoli to collapse and small airways to close, so that more time is available for gaseous exchange.
5. Inverse ratio ventilation(IRV): ratio of inspiration to expiration is reversed(2:1). Prolonged inspiration will maintain positive pressure. So more or less it acts like PEEP. It is said to be better then PEEP and there is even distribution of ventilation.
6. Pressure support ventilation: if a patient is on spontaneous respiration with adequate frequency but not adequate tidal volume, this mode is helpful in increasing the tidal volume.
7. High frequency ventilation: this mode is applicable in conditions in which adequate tidal volume is maintained by high frequency
8. Biphasic positive pressure ventilation(BIPAP): this is newer mode and is variation of pressure controlled ventilation and differs from conventional pressure controlled mode that spontaneous breathing is always possible
9. Airway pressure release ventilation(APRV): applied to a patient on CPAP where there is periodic release of CPAP to decrease the incidence of barotrauma and hypotension.

COMPLICATIONS OF MECHANICAL VENTILATION

1. 1. pulmonary barotraumas:

• incidence- 7 to 10%
• pneumothorax
• pneumomediastinum
• bronchopleural fistula
• pneumopericardium
• pneumoperitoneum
• air embolism

1. 2. infection:

• pulmonary- due to prolonged intubation and frequent suction
• urinary- due to prolonged catheterization
• wound infection
• intravenous catheter related

1. 3. complications due to prolonged intubation

• airway edema
• sore throat
• laryngeal ulcer and granuloma
• laryngeal web
• tracheal stenosis
• tracheal fibrosis

1. 4. GIT:

• Stress ulcers
• Paralytic ileus

1. 5. cardiovascular:

• right ventricular strain or even right ventricular failure

1. 6. nosocomial infection
2. liver and kidney dysfunction due to decreased cardiac output
3. neuromuscular weakness- if muscle relaxants are used for longer periods
4. ciliary activity- it is impaired if non humified oxygen is used.

10. oxygen toxicity- if higher concentration is used

11. psychological- depression and emotional trauma

12. due to prolonged bed rest-

• DVT and thromboembolism
• Bed sores

13. financial burden

WEANING FROM VENTILATOR:

It means discontinuing the ventilatory support.

Arbitrary guidelines for weaning are:

1. pO2>60mmHg or O2 saturation >90% on FIO2<50% and PEEP<5 mmHg
2. pCO2 <50mmHg
3. respiratory rate <20/min
4. vital capacity>15ml/kg
5. Vd\Vt<0.6
6. tidal volume > 5ml/kg
7. minute ventilation<10litres/min
8. inspiratory pressure<-30cmH2O
9. arterial pH is normal
10. normal haemoglobin
11. norma cardiac status at the time of weaning eg at the time of weaning patient should not have tachycardia, hypertension
12. normal electrolytes
13. adequate nutritional status

METHOD OF WEANING:

From control mode ventilation patient is shifted to SIMV and then keep on decreasing the rate of breath delievered by ventilator gradually till it becomes 1 to 2 breaths/min. if the tidal volume is not sufficient then pressure supported ventilation may be instituted. The pressure support is decreased gradually till the patient achieves adequate tidal volume. Once the patient’s frequency and tidal volume is adequate then ventilator can be disconnected and T tube is attached to endotracheal tube. If patient is able to maintain normal pulmonary and cardiac function and shows normal blood gas analysis for more than 2 hrs, extubation can be attempted.

– By Dr. Anjali Subedi