RESPIRATORY SYSTEM CHANGES IN NEONATE AND ADULT

Anatomical differences in the airway and the differences in respiratory physiology between a neonate and an adult

Neonate

Adult

Anatomical Changes: They have a larger head and tongue Narrow nasal passages Cephalad Larynx Large Epiglottis Short Trachea and Neck Narrowest part of airways is the cricoid cartilage Ribs are pliable and horinzontal,diaphragmatic muscles are weaker and abdomen protuberant so the respiratory rate is increased to compensate for less efficient ventilation. Small airways and limited number of alveoli reduces their lung compliance Alveolar maturation is not complete So the work of breathing is increased and respiratory muscles fatigue easily Tidal volume and dead space are per kilogram of body weight and are constant in all age groups Physiological Changes Chest wall collapse during inspiration and relatively low residual volume at expiration There is reduction in Functional Residual Capacity which limits oxygen reserves during periods of apnoea and predisposes neonates to hypoxemia and atelactasis Relatively higher rate of oxygen consumption Ventilation is not hypoxia and hypercapnia driven on the contrary the reduce ventilation

Anatomical Changes Propotionate smaller head and tongue Broader nasal passages Caudad Larynx Smaller Epiglottis Relatively elongated neck and trachea Narrowest part of the airway is the glottis Ribs are more more curved with stronger muscles making ventilation more efficient Airways better developed Physiological Changes Increased compliance of chest wall and better residual volume increase the functional residual capacity which gives a better oxygen reserve Ventialtion is hypoxia and hypercapnia driven ,partial pressure of oxygen and carbon dioxide is a feedback to respiratory centres in brain

weaning criteria from ventilator

Principles involved in weaning a patient from ventilatory support in an ICU

Weaning procedures are usually started only after the underlying disease process that necessitated mechanical ventilation has significantly improved or is resolved. The patient should also have an adequate gas exchange , appropriate neurological and muscular status, and stable cardiovascular function.

Weaning indices are objective criteria that are used to predict the readiness of patients to maintain spontaneous ventilation.

The rapid shallow breathing index (f/V_T, where 'f' is the respiratory rate and 'V_T' is the tidal volume measured during the first minute of a T-piece trial) is superior to conventional parameters in predicting the outcome of weaning while arterial blood gases and respiratory rate.

The intact airway reflexes and a cooperative patient are mandatory prior to completion of the weaning process unless the patient has a cuffed tracheostomy tube.

Mechanical Criteria for weaning/extubation

Criteria                                                                                measurement

Inspiratory pressure                                                         <-25cmH2O

Tidal Volume                                                                       >5ml/kg

Vital Capacity                                                                      >10ml/Kg

Minute Ventilation                                                             <10ml

Rapid Shallow Breathing Index                                          <100

With the patient breathing spontaneously

Adequate oxygenation should be maintained that is the arterial haemoglobin saturation of >90% at FiO2 of 0.4-0.5 with less than 5cm of H2O of PEEP

                              RSBI  =  f(breaths/min) /VT(L)

   Patients with RSBI of 100 or less can be successfully extubated

The most common techniques to wean a patient from the ventilator include SIMV, PRESSURE SUPPORT VENTILATION, low levels of CPAP, spontaneous breathing short periods on T-piece.

Hyponatraemia

What are the symptoms and signs of hyponatraemia? Calculate the sodium deficit in a 70 Kg adult male with serum sodium of 122mmol/L. How will you replace the deficit?

Hyponatremia is a plasma sodium concentration less than 135 mEq/L.

S/S of hyponatraemia:

·        Nausea/vomiting

·        Visual disturbances

·        Depressed levels of consciousness

·        Agitation,confusion,coma

·        Muscle cramps,weakness and myoclonus

·        Coma and death

Sodium deficit in a 70kg male with serum sodium of 122mmol/L

Na+ deficit = TBW*(140-122)

TBW is approximately 60% of body weight in males(TBW is total body water)

Na+ deficit = 70*0.6*(135-122)=756 mEq/L

Replacement of the deficit:

The optimal rate of correction seems to be 0.6 to 1 mmol/L/hr until the sodium concentration is 125 mEq/L; correction then proceeds at a slower rate.
 One half the deficit can be administered over the first 8 hours, and the next half can be administered over 1 to 3 days if symptoms remit. Sodium concentration should be monitored every 1 to 2 hours during rapid correction.
Menstruanting female patients are at greater risk for developing significant neurologic sequelae after hyponatremia., Estrogens seem to alter the function of Na⁺/K⁺-ATPase in the rat brain, which could alter the brain's compensatory mechanisms for hyponatremia.
Management of hyponatremia involves elimination of the underlying condition when possible (e.g., stop TURP syndrome as soon as possible).

The use of normal saline (308 mOsm/L) alone may worsen the hyponatremia, depending on the patient's serum and urine osmolality  Severe coma or seizures can be managed with one or more approaches, including 3% hypertonic saline (513 mEq/L), fluid restriction, or furosemide